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2006-Synthesis of Titanium Dioxide (TiO2) Nanomaterials

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									                   Copyright © 2006 American Scientific Publishers                                                                                            Journal of
                   All rights reserved                                                                                                  Nanoscience and Nanotechnology
                   Printed in the United States of America                                                                                       Vol. 6, 906–925, 2006




           Synthesis of Titanium Dioxide (TiO2) Nanomaterials
                                                                        Xiaobo Chen∗ and Samuel S. Mao
                                       Environmental Energy Technology Division, Lawrence Berkeley National Laboratory
                                  and Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA

                    Titanium dioxide (TiO2 ) is a promising material for many emerging applications. Even more promis-
                    ing are the benefits offered by the material when its length scale is reduced to the nanometer range.
                    Nanomaterials usually exhibit unique properties resulting from either the extremely large surface
                    area-to-volume ratio or the quantum confinement effect of energy carriers. In this article we present
                    an overview of recent progress in the synthesis of TiO2 nanomaterials. The topics include synthe-
                    sis of TiO2 nanoparticles, nanorods, nanowires, nanotubes, and mesoporous/nanoporous materials
                    using different preparation approaches such as sol–gel, sol, hydrothermal, solvothermal, and vapor
                                                        Delivered by Ingenta to:
                    deposition. The applications of TiO2 nanomaterials are also briefly summarized.
                                                                                   University of Houston
                    Keywords: Titanium dioxide, Nanomaterials, Nanoparticles, Nanorods, Nanowires, Nanotubes,
                                                    IP : 129.7.158.43
                                               Mesoporous/Nanoporous Materials.
                                                             Wed, 23 Aug 2006                               21:22:10

CONTENTS                                                                                                   The past decade has witnessed an exponential growth of
                                                                                                        activities in TiO2 nanomaterials research, driven by both
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   906
2. Synthesis of TiO2 Nanomaterials . . . . . . . . . . . . . . . . . . . . . . . .                907
                                                                                                        the excitement of scientific discoveries at the nanometer
   2.1. Synthesis of TiO2 Nanoparticles . . . . . . . . . . . . . . . . . . . .                   907   scale and the potential of economic impact resulted from
   2.2. Synthesis of TiO2 Nanorods . . . . . . . . . . . . . . . . . . . . . . . .                911   photovoltaic and photocatalytic applications, for instance.
   2.3. Synthesis of TiO2 Nanowires . . . . . . . . . . . . . . . . . . . . . . .                 914   New physical and chemical properties usually emerge as
   2.4. Synthesis of TiO2 Nanotubes . . . . . . . . . . . . . . . . . . . . . . .                 916   the length scale of a material is reduced to nanome-
   2.5. Synthesis of TiO2 Mesoporous/Nanoporous Materials . . . .                                 918
3. Applications of TiO2 Nanomaterials . . . . . . . . . . . . . . . . . . . . .                   919
                                                                                                        ters. These properties may vary with material’s size or
4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    919   shape,8–33 which can result from the confinement of elec-
   Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .         920   tronic motion to a length scale that is comparable to or
   References and Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .           920   smaller than that characterizing the electronic motion in
                                                                                                        a conventional bulk material (called the electron Bohr
1. INTRODUCTION                                                                                         radius, which is usually a few nanometers), or alternatively
                                                                                                        from the dramatically increased surface, as the size of a
Titanium dioxide (TiO2 ), occasionally called titanium                                                  nanomaterial decreases. The large surface area brought
white or titanium pigment, is truly the white of the 20th                                               about by the small particle size is beneficial to most TiO2 -
century. Although discovered in 1821, it was not until 1916                                             based devices, as it promotes the reaction or interaction
the Titanium Pigment Corporation of Niagara Falls, New                                                  between the devices and other media in contact with the
York and the Titan Co., AS of Norway began commer-                                                      surface.9 10 16
cial production of TiO2 as white pigment. Other than its                                                   Unlike many nanomaterials such as II–VI, III–V type
widely publicized use as a pigment, TiO2 is also a good                                                 semiconductor,8 9 29 33–36 the synthesis of well-controlled
photocatalyst as well as a component of oxygen sensors                                                  TiO2 nanomaterials has not become mature until very
and antimicrobial coating materials. Enormous research                                                  recently. In this review, we attempt to trace down the
effort dedicated to the study of the properties and applica-                                            recent progress in the synthesis of TiO2 nanomaterials in
tions of TiO2 under light illumination has been fascinated                                              the form of nanoparticles, nanorods, nanotubes, nanowires,
with the discovery of photocatalytic splitting of water                                                 and mesoporous/nanoporous materials. Although we try to
on a TiO2 electrode in 1972 (Fujishima and Honda).1–3                                                   offer an objective and complete account of the subject,
Since then, TiO2 has been exploited for photovoltaics,                                                  our attempt may be incomplete due to rapid growth of
photocatalysis, photochromics, electrochromics, and vari-                                               the technology as well as the limitation of our knowledge.
ous types of sensors.4–7                                                                                We realize that it is virtually impossible to list all the
                                                                                                        important contributions in a review article like this one,
  ∗
      Author to whom correspondence should be addressed.                                                and we would like to apologize for not mentioning

906                 J. Nanosci. Nanotechnol. 2006, Vol. 6, No. 4                                             1533-4880/2006/6/906/020            doi:10.1166/jnn.2006.160
Chen and Mao                                                             Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

contributions which other researchers might consider to       Alcoxolation:
be crucial. Although the properties37–40 and chemical
modifications/sensitization41–49 of TiO2 nanomaterials are
not reviewed here, the applications46 50–53 of TiO2 nano-
materials are briefly summarized. We note here that there
                                                              Oxolation:
are also many other reviews which give alternative assess-
ments of the field.3 7 54–60


2. SYNTHESIS OF TIO2 NANOMATERIALS
                                                              Olation:
2.1. Synthesis of TiO2 Nanoparticles

2.1.1. Synthesis of TiO2 Nanoparticles by
       Sol–Gel Method

Sol–gel method is perhaps the most widely applied
approach to prepare TiO2 nanoparticles.61–81 Sol–gel
method is based on hydrolysis of an alkoxide or halide
precursor with subsequent condensation to the inorganic
                                             Delivered
framework. The formation of TiO2 from titanium (IV) by Ingenta to: of water used during the gelation procedure
                                                            The amount
                                              University Houston
alkoxide proceeds via an acid-catalyzed hydrolysis step ofdetermines the contribution of each reaction. The structure
followed by condensation:16 62 82–95             IP : 129.7.158.43final gel depends on the relative contribution of
                                                            of the
                                           Wed, 23 Aug 2006 21:22:10
                                                            alcoxolation, oxolation, and olation. For low concentration
                         H+
 (RO)3 −Ti−O−R +H2 O −→ (RO)3 −Ti−O−H+R −OH                 of water, hydrolysis rates are low and excess titanium
                                                            alkoxide in the solvent favors the development of Ti–O–
 2(RO)3 −Ti−O−H −→ (RO)3 −Ti−O−Ti− OR 3 +H2 O
                                                            Ti chains through alcoxolation. Because each Ti is coor-
Sometimes, with alcoholic permutation reaction              dinated with four O atoms, the development of Ti–O–
                                                            Ti chains results in three-dimensional polymeric skele-
    Ti(OR)3 + xR (OH) ←→ Ti(OR)3−x (OR )x + xROH            tons with close packing. For a medium amount of water,
                                                            high hydrolysis rates favor the formation of Ti(OH)4 and
The hydrolysis and condensation reactions are competitive   reduce the relative contribution of alcoxolation. The first-
with alcoxolation, oxolation, and olation as analyzed by    order particles are loosely packed due to the presence of
Bessekhouad et al.71                                        a large quantity of Ti–OH and insufficient development

                             Dr. Xiaobo Chen is a research engineer of University of California at Berkeley and a
                             visiting scientist of Lawrence Berkeley National Laboratory. He obtained his Ph.D. degree
                             from Case Western Reserve University, an M.S. degree from Chinese Academy of Sci-
                             ences, and two B.S. degrees (Chemistry and Economics) from Peking University. Dr. Chen
                             is specialized in the development of semiconductor nanomaterials for photocatalysis, pho-
                             tovoltaics, and phototherapy applications. He has written about 20 scientific papers in the
                             field of nanomaterial.




                             Dr. Samuel S. Mao is a career staff scientist of Lawrence Berkeley National Laboratory and
                             an adjunct faculty of the University of California at Berkeley. He obtained his Ph.D. degree
                             in Engineering from the University of California at Berkeley in 2000. His current research
                             involves the development of nanostructured materials and devices, as well as ultrafast laser
                             technologies. Dr. Mao is the team leader of multi-million dollar high throughput materials
                             discovery program supported by the U.S. Department of Energy. He has contributed over
                             50 technical publications and delivered invited lectures at many scientific conferences and
                             universities. He is the associate editor of International Journal of Nanotechnology.



J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                              907
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                      Chen and Mao

of three-dimensional polymeric skeletons. For high con-
centration of water, the large excess of water favors the
formation of Ti(OH)4 O+ H2 by the coordination of water to
Ti(OH)4 . This reactive Ti–HO+ –Ti species can contribute
to the development of polymeric Ti–O–Ti chains through
the olation reaction. Thus, a three-dimensionally devel-
oped gel skeleton again yields closely packed first-order
particles. The formed Ti–O+ H–H species are very reactive
and quickly condense on other Ti–OH with production of
water or alcohol to yield Ti–O–Ti chains.71
   Oskam et al.62 reported their study on the growth kinet-
ics of TiO2 nanoparticles synthesized from aqueous solu-
tion using TTIP as precursor. They found that the average
particle radius increased linearly with time, in agreement
with the Lifshitz-Slyozov-Wagner model for coarsening.
The rate constant for coarsening increased with tempera-
ture due to the temperature dependence of the viscosity
of the solution and the equilibrium solubility of TiO2 . At
longer times and higher temperatures, secondary particles
                                                 Delivered by Ingenta to:
were formed by epitaxial self-assembly of primary parti-
                                                  University of Houston
cles, where the number of primary particles per secondary       Fig. 1. Effects of sodium oleate and sodium stearate on the shape of
                                                     IP : 129.7.158.43
particle increased with time.
                                               Wed, 23 Aug 2006uniform anatasecompound at initial pH in a solution of 0 (10stan-
   Sugimoto et al. performed a thorough study on the
                                                                the
                                                                      21:22:10 TiO2 particles formed 10.5 under otherwise M)
                                                                Ti(IV)-TEOA (1:2)
formation of TiO2 nanoparticles by tuning the reaction          dard conditions. Reprinted with permission from [63], T. Sugimoto et al.,
              63–65                                   4+        J. Coll. Interf. Sci. 259, 53 (2003). © 2003, Elsevier.
parameters.         Typically, a stock solution of Ti was
prepared by mixing TTIP with triethanolamine (TEOA) at          process, low temperature synthesis method was developed
a molar ratio of [TTIP]:[TEOA] = 1:2, followed by addi-         which involved prolonged heating time below 100 C for
tion of doubly water to make an aqueous stock solution          the as prepared gel.68 81 Alternatively, continuous reaction
of 0.50 M Ti4+ . Then, 10 ml of the stock solution was          method,69 semi-continuous reaction method80 and two-
mixed with the same volume of the solution of a shape           stage mixed method were employed to achieve the high
controller. The final solution was aged at 100 C for 24 h,       crystallinity and dispersity of TiO2 nanoparticles.
and then aged at 140 C for 3 days. HClO4 or NaOH solu-
tion was added to tune the pH of the solution. They found       2.1.2. Synthesis of TiO2 Nanoparticles by
that TEOA changed the morphology of TiO2 nanoparticles                   Micelle and Inverse Micelle
from cuboidal to ellipsoidal at pH above 11. Diethylen-
etriamine (DETA) also modified the particle shape to             Micelles are formed as aggregates of surfactant molecules
ellipsoidal above pH 9.5 and the aspect ratio of TiO2 nano-     when the surfactant concentration exceeds the critical
particles was much higher than that with TEOA. Second-          micelle concentration (cmc) in water. In normal micelles,
ary amines, such as diethylamine, and tertiary amines, such     the hydrophobic hydrocarbon chains of the surfactants
as trimethylamine and triethylamine, acted as a complex-        are oriented toward the interior of the micelle, and the
ing agent of Ti(IV) ions to promote the growth of ellip-        hydrophilic groups of the surfactants are in contact with
soidal particles of a low aspect ratio, rather than a shape     the surrounding aqueous medium. Above the cmc, the
controller to produce ellipsoids of a high aspect ratio.        physical state of the surfactant molecules changes dra-
Sodium oleate and sodium stearate were found to mod-            matically, and additional surfactant exists as aggregates
ify the particle shape from round-cornered cubes to sharp-      or micelles. The bulk properties of the surfactant change
edged cubes.63 The particle size of the anatase TiO2 was        around the cmc, such as osmotic pressure, turbidity,
increased from ca. 5 to 30 nm with pH increasing from           solubilization, surface tension, conductivity, and self-
0.6 to 12 by aging the Ti(OH)4 gel at 140 C for 72 h.64         diffusion. On the other hand, reverse micelles are formed
Figure 1 shows the representative TEM of TiO2 nanopar-          in nonaqueous medium where the hydrophilic head-
ticles from their study.                                        groups are directed toward the core of the micelles while
   Single-phase nanocrystalline anatase powders with            the hydrophobic groups are directed outward. In the case
average particle sizes between 7 and 50 nm were syn-            of reverse micelles, there is no obvious cmc because the
thesized by heating amorphous titania in air by Zhang           number of aggregates is usually small and they are not
et al.72 73 96–98 Large quantities of single phase solids can   sensitive to the surfactant concentration.
be produced via this method. To avoid the agglomeration             Micelle and inverse micelle are widely employed to
of the TiO2 nanoparticles during the crystallization            synthesize TiO2 nanoparticles aiming to overcome the

908                                                                                     J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                          Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials




Fig. 2. (A) TEM image of TiO2 nanoparticles. Reprinted with permis-
sion from [99], K. D. Kim et al., Coll. Surf. A 254, 99 (2005). © 2005,
Elsevier. (B) TEM image of TiO2 nanoparticles. Reprinted with permis-
sion from [100], G. L. Li and G. H. Wang, Nanostruct. Mater. 11, 663      Fig. 3. TEM image of TiO2 nanoparticles. Reprinted with permission
(1999). © 1999, Elsevier.                                                 from [101], J. Lin et al., J. Am. Chem. Soc. 124, 11514 (2002). © 2002,
                                                                          American Chemical Society.
shortcomings of the sol–gel method, i.e., aiming at better
size and shape distribution controls.99–107 Kim et al.99 con-  methacrylate) (PDMAEMA-b-PFOMA). They found that
ducted Taguchi method, a statistical experimental design       the size of TiO2 nanoparticles prepared in the presence of
method, to optimize experimental conditions for the prepa-     reverse micelles increased as the molar ratio of water to
                                                Delivered
ration of TiO2 nanoparticles using microemulsion-mediated by Ingenta to:
                                                               surfactant headgroup as well as the precursor-to-surfactant
                                                 University Houston
method. The values of H2 O/surfactant, H2 O/TEOT, ammo- ofratio increased.
                                                    IP : 129.7.158.43 nanoparticle prepared in the above micelle and
nia concentration, feed rate, and reaction temperature            The TiO2
                                              Wed, 23 Aug 2006 21:22:10 normally has amorphous structure, and the
were chosen as significant parameters to optimize parti-        reverse micelle
cle size and particle size distribution. Consequently, amor-   heating process which tends to improve their crystalline
phous TiO2 nanoparticles with particle size in the range       structure normally leads to crystal growth and agglom-
of 10–20 nm have been synthesized, and converted to            eration. Lin et al.101 found that the crystalline structure
anatase phase at 600 C and to the stable rutile phase          of TiO2 nanoparticles initially synthesized by controlled
at 900 C. Li et al.100 developed nanometer-sized tita-         hydrolysis of titanium alkoxide in reverse micelles in a
nia particles by chemical reactions between TiCl4 solution     hydrocarbon solvent could be improved upon annealing
and ammonia in reversed microemulsion systems. Cyclo-          in situ in the presence of the micelles at temperatures
hexane and a mixture of poly(oxyethylene)5 nonyle phe-         considerably lower than those required for the traditional
nol ether and poly(oxyethylene)9 nonyle phenol ether with      calcination treatment in the solid state. They also found
weight ratio 1:1 were used as oil phase and nonionic sur-      that the crystalline TiO2 nanoparticles still maintained the
factant, respectively. The as-produced TiO2 nanoparticles      same physical parameters and remained in a stable sus-
were amorphous and transformed into anatase heated at          pension. This method allowed the preparation of mono-
temperature from 200 to 750 C and into rutile at tempera-      dispersed crystalline TiO2 nanoparticles as they were
tures higher than 750 C accompanied with agglomeration         initially produced in the microemulsion. Figure 3 shows
and growth. Figure 2 shows the typical TiO2 nanoparticles      the representative TEM image of TiO2 nanoparticles from
from Refs. [99] and [100].                                     Ref. [101].
   Zhang et al.102 found shuttle-like crystalline TiO2
nanoparticles could be synthesized by hydrolysis of tita-      2.1.3. Synthesis of TiO2 Nanoparticles by Sol Method
nium tetrabutoxide in the presence of acids in NP-5 (Igepal
CO-520)-cyclohexane reverse micelle at room tempera-           To overcome many of the problems for aqueous systems,
ture. They found that the reaction conditions had sig-         nonhydrolytic sol–gel processes have been developed to
nificant effects on the crystal structure, morphology, and      obtain high quality TiO2 nanoparticles by various groups
particle size of the products and the acidity, the type        in nonhydrous solution.108–110 Nonhydrolytic sol–gel pro-
of acid used, and the microenvironment of the reverse          cesses usually apply the reaction of titanium chloride with
micelles were the key factors affecting the formation of       a variety of different oxygen donor molecules, e.g., a metal
rutile at room temperature. Prolonged reaction time and        alkoxide or an organic ether.111–115 The formation of the
increased [H2 O]/[NP-5] and [H2 O]/[Ti(OC4 H9 4 ] ratios       Ti–O–Ti bridges results from the condensation between
led to agglomeration of the particles. Lim et al.104           Ti–Cl and Ti–OR. The alkoxide functions can be provided
prepared TiO2 nanoparticles by controlled hydrolysis           by titanium alkoxides or can be formed in situ by reaction
of TTIP in reverse micelles formed in CO2 with                 of the titanium chloride with alcohols or ethers. For exam-
the surfactants ammonium carboxylate perfluoropolyether         ple, in the method used by Niederberger and Stucky,110
             −    +
(PFPECOO NH4 ) (Mw = 587) and poly(dimethyl amino              TiCl4 was slowly added to anhydrous benzyl alcohol under
ethyl methacrylate-block-1H, 1H, 2H, 2H-perfluorooctyl          vigorous stirring at room temperature. The reaction vessel

J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                                   909
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                                Chen and Mao




Fig. 4. (A) TEM image of TiO2 nanoparticles derived from reaction of       Fig. 5. TEM images of TiO2 nanoparticles prepared by hydrothermal
TiCl4 and TTTP in TOPO/heptadecane at 300 C. (B) A high-resolution         method. Reprinted with permission from [118], J. Yang et al., Mater. Sci.
TEM image of a single particle. Reprinted with permission from [116],      Eng. C 15, 183 (2001). © 2001, Elsevier.
T. J. Trentler et al., J. Am. Chem. Soc. 121, 1613 (1999). © 1999, Amer-
ican Chemical Society.
                                                                Chae et al.126 reported their study on TiO2 nanoparticles
was kept at 40–150 C for 1–21 days. After centrifuge,
                                                             by hydrothermal reaction of titanium alkoxide stabilized
the precipitate was thoroughly washed with ethanol and
                                                             in acidic ethanol/water solution. They found the sizes of
THF, and calcinated at 450 C for 5 h. In the method
                                                             particles could be controlled to the range of 7–25 nm by
by Trentler and Colvin,116 titanium halide was mixed with
distilled trioctylphosphine oxide (TOPO) in heptadecane      adjusting the concentration of Ti precursor and the com-
                                                             position
and heated to 300 C under dry nitrogen gas. A metal by Ingenta of the solvent system. The TiO2 samples syn-
                                               Delivered               to:
                                                             thesized under this acidic ethanol/water environment were
alkoxide was then rapidly injected into the hot solution. of Houston
                                                University mainly primary particles in anatase phase without sec-
Reactions were completed within 5 min. The reaction :pre-
                                                   IP 129.7.158.43
                                                             ondary structure.
cipitates were isolated by centrifugation and subsequently 2006 21:22:10 Typically, 1.5–15 mmol TTIP was added
                                            Wed, 23 Aug dropwise to 150 mL of mixed ethanol and water solution
washed with acetone. Figure 4 shows typical TEM images
for the TiO2 nanocrystals developed by Trentler et al.,116   at pH 0.7 with nitric acid. After several hours of stirring,
where well-dispersed and crystallized nanoparticles were     the clear solution was reacted at 240 C for 4 h in a
obtained directly from the reaction without annealing step   hydrothermal bomb. Crystallized TiO2 nanoparticles were
as using sol–gel or micelle methods.                         obtained as a colloidal suspension. Representative TEM
                                                             images of TiO2 nanoparticles are shown in Figure 6. As
2.1.4. Synthesis of TiO2 Nanoparticles by                    shown, well-dispersed and crystallized TiO2 nanoparticles
        Hydrothermal Method                                  can be directly obtained using hydrothermal method.

Hydrothermal synthesis is a method that is widely used for
the production of (ultra) small powders and particles espe-
cially in the ceramics industry. It is normally conducted in
steel pressure vessels called autoclaves with/without Teflon
linen with the reaction of aqueous solutions under con-
trolled temperature and/or pressure. The temperature can
be elevated above the boiling point of the water, reach-
ing the pressure of vapor saturation. The internal pressure
developed is controlled by the temperature and the amount
of solution added to the autoclave. TiO2 nanoparticles
have been developed with hydrothermal method by various
groups.117–126 In the study by Yang et al.,118 TiO2 precipi-
tates were obtained by adding 0.5 M isopropanol solution
of the titanium butoxide dropwise into the deionised water
([H2 O]/[Ti] = 150). The white precipitates were peptized
at 70 C for 1 h by adding peptizer tetraalkylammonium
hydroxides, and were filled in Teflon containers after filtra-
tion and treated at 240 C for 2 h. The as-obtained powders
were washed with deionised water, absolute ethanol, and
then dried at 60 C. They found that under the same con-
centration of peptizer, particle size decreased by increas-                Fig. 6. TEM images of 7-nm-sized TiO2 nanoparticles (a) prepared
                                                                           from 0.10 M TTIP in 4:1 ethanol/water with a high-resolution TEM
ing the carbon chain length and that the morphology of
                                                                           image (d), (b) 15-nm particles prepared from 0.04 M TTIP in 1:2
the particles was also greatly influenced by the peptizers                  ethanol/water, (c) 25-nm particles prepared from 0.02 M TTIP in 1:8
and their concentrations. Typical TEM images of the TiO2                   ethanol/water. Reprinted with permission from [126], S. Y. Chae et al.,
nanoparticles are shown in Figure 5.                                       Chem. Mater. 15, 3326 (2003). © 2003, American Chemical Society.

910                                                                                           J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                           Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

2.1.5. Synthesis of TiO2 Nanoparticles by                                  spray     pyrolysis,144   laser-induced             pyrolysis,145   146

       Solvothermal Method                                                 ultrasonic-assisted hydrolysis.147 148
Solvothermal method is very similar to hydrothermal
                                                              2.2. Synthesis of TiO2 Nanorods
method except that the solvent used here is non-aqueous.
Solvothermal method takes the advantages of both sol and      2.2.1. Synthesis of TiO2 Nanorods by
hydrothermal methods in the control of size, shape distri-           Direct Oxidation of Titanium
butions, and the high crystallinity of TiO2 nanoparticles in
the reaction. Solvothermal method has been employed to        Crystalline TiO2 nanorods can be obtained by direct oxi-
synthesize TiO2 nanoparticles by Kim and co-workers.     127  dation of titanium metal plate with hydrogen peroxide as
In a typical procedure, TTIP is used as precursor and         widely explored by Wu and co-workers.149–154 Typically,
anhydrous toluene is used as solvent. Different amounts       Ti plate was pickled in a 2 M HF solution at ambient tem-
of TTIP were mixed with toluene at the weight ratio of        perature and ultrasonically cleaned in deionized water. The
1–3:10 in a glove box with argon atmosphere. The mix-         plate was then soaked in a 50 ml 30 wt% H2 O2 solution
ture was vigorously stirred with a magnetic stirrer for 3 h   and kept at 353 K in an oven for 72 h. Subsequently, the
and transferred into a stainless steel autoclave with teflon   Ti plate was taken out and washed gently with deionized
liner kept at 250 C for 3 h without stirring. After cool-     water and dried in air. Figures 8(a) and (b) show a low
ing gradually to room temperature, the precipitates were      magnification and high magnification SEM images of TiO2
separated with centrifugal separator and then dried. The      nanorods prepared with this method.149 The formation of
                                                              crystalline titania was thought through a dissolution pre-
authors found that as the composition of TTIPDelivered by Ingenta to:
                                                in the solu-
                                                                                     154
tion increased, the average particle size of TiO2 powders ofcipitation mechanism, either deposited on the Ti surface
                                                 University Houston
                                                              through
tended to increase in the range of weight ratio of IP : 129.7.158.43 an inhomogeneous nucleation and growth pro-
                                                    1–3:10.
                                              TiO2 23 not     cess, or precipitated in the solution through a homogenous
At 1/20 and 2/5, pale crystalline phase of Wed, was Aug 2006 21:22:10
produced. Figure 7 shows the typical TEM images.127

2.1.6. Synthesis of TiO2 Nanoparticles by
       Chemical Vapor Deposition
Seifried et al. reported their study on the fabrication of
TiO2 nanoparticles by chemical vapor deposition.128 They
found that thick crystalline titania films with grain sizes
below 30 nm as well as nanocrystalline titania particles
with sizes below 10 nm could be prepared by pyrolysis
of TTIP in a mixed helium/oxygen atmosphere, using
liquid precursor delivery. Ayllon et al.129 reported their
plasma enhanced chemical vapor deposition study of TiO2
nanoparticles, where the amorphous nanoparticles deposi-
ted on the cold areas of the reactor at temperatures not
higher than 90 C were well crystallized with a relatively
high surface area after annealed at high temperatures.
   Besides the above methods, other approaches were
also used to prepare TiO2 nanoparticles. These methods
include electrostatic spray hydrolysis,130 diffusion flame
pyrolysis,131–136 thermal plasma pyrolysis,137–143 ultrasonic




                                                                           Fig. 8. SEM morphology of the Ti plate surface after soaking in the
Fig. 7. TEM micrographs and electron diffraction patterns of the prod-     30 wt% H2 O2 solution at 353 K for 72 h. (a) Low magnification, (b) high
ucts prepared from the solution at: (A) 1:10, (B) 2:10, and (C) 3:10.      magnification image showing rod-like morphology. Reprinted with per-
Reprinted with permission from [127], C.-S. Kim et al., J. Cryst. Growth   mission from [149], J. M. Wu, J. Cryst. Growth 269, 347 (2004). © 2004,
254, 405 (2003). © 2003, Elsevier.                                         Elesevier.

J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                                    911
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                              Chen and Mao




Fig. 9. (a) Low and (b) high magnification SEM image of large-scale
nanorod arrays prepared by oxidizing titanium with acetone at 850 C
for 90 min. Reprinted with permission from [155], X. Peng and A. Chen,
J. Mater. Chem. 14, 2542 (2004). © 2004, The Royal Society of            Fig. 10. TEM overview of TiO2 nanorods prepared at 100 C with
Chemistry.                                                               OLEA 35 g, TTIP 5 mmol, TMAO 2 M 5 mL: (a) low and (b) high
                                                                         magnification. Reprinted with permission from [161], P. D. Cozzoli et al.,
nucleation and growth process. The crystalline phase of                  J. Am. Chem. Soc. 125, 14539 (2003). © 2003, American Chemical
                                                                         Society.
titania can be controlled by the addition of inorganic salts
of NaX (X = F− , Cl− , and SO2− ). The anions instead of
                                 4                            Cozzoli and co-worker156–161 reported the growth of high
cations in the solution was thought to play a role. The       aspect ratio anatase TiO2 nanorods by controlled hydrol-
addition of F− and SO2− helped the formation of pure
                          4                                   ysis of TTIP in oleic acid (OLEA) as surfactant at 80–
anatase; while the addition of Cl− favored the formation      100 C for 6–12 h. Typically,161 35 g of OLEA was dried
                                               Delivered by Ingenta to:
of rutile. The anions were supposed to affect the precip-
                                                 University ofat 120 C for 1 h, after which it was cooled to 80–100 C
itation rate and hence the resultant crystal phases of the
                                                               Houston
                                                              under nitrogen flow. 1–10 mmol of TTIP was added and
                                                   IP : 129.7.158.43
TiO2 nanorods. Worth to mention is the green chemistry
                                             Wed, 23 Aug stirred for 5 min. A 0.5–5 mL of a 0.1–2 M aqueous
in this method with very low residual pollutant produced 2006 21:22:10
                                                              base solution [trimethylamino-Noxide dihydrate or anhy-
in the mass production of self-assembled TiO2 nanorods.       drous (TMAO), trimethylamine (TMA), tetramethylammo-
However, the TiO2 nanorods produced so far with this          nium hydroxide (TMAH), tetrabutylammonium hydroxide
method is larger than 50 nm. Optimal conditions need to       (TBAH), triethylamine (TEA), or tributylamine (TBA)]
be explored to prepare smaller nanorods with diameter less    was rapidly injected. When water-insoluble bases (TEA
than 5 nm.                                                    and TBA) were employed as the catalysts, they were added
   Aligned TiO2 nanorods arrays can be obtained by oxi-       to the TTIP/OLEA mixture before water injection. The
dizing titanium substrate using acetone as the oxygen         solution was kept at 80–100 C and stirred over 6–12 h.
source at 850 C for 90 min as demonstrated by Peng            The remaining water content was removed under vac-
and Chen.155 These authors found that the oxygen source       uum and an excess of ethanol (or methanol) was added
played an important role in the final product’s structure.     to precipitate OLEA-coated TiO2 nanorods. Typical TEM
Pure oxygen yielded crystal grain films, argon with a low      images of the TiO2 nanorods are shown in Figure 10. In
concentration of oxygen produced random nanofibers gro-        this reaction, the hydrolysis of a titanium alkoxide was
wing from the ledges of the TiO2 grains, whereas highly       manipulated by the chemical modification of the titanium
dense and well-aligned TiO2 nanorod arrays were formed        precursor with the carboxylic acid (which also behaved
with acetone as the oxygen source. The authors attributed     as stabilizing solvent), and the use of suitable catalysts
these remarkable differences to the competition of the        (tertiary amines or quaternary ammonium hydroxides) to
oxygen and titanium diffusion involved in the titanium        promote fast (in 4–6 h) crystallization in mild conditions.
oxidation process. With pure oxygen, oxygen diffusion         The growth of TiO2 nanorods were mainly attributed to a
dominated because of the high oxygen concentration, thus      kinetically overdriven growth mechanism.
oxidation occurred at the Ti metal and titanium oxide inter-
face, forming large polycrystalline TiO2 grains. When ace-    2.2.3. Synthesis of TiO2 Nanorods by
tone was used as the oxygen source, Ti cations diffused to            Sol–Gel Template Method
the oxide surface first, and then reacted with the adsorbed
acetone species to form aligned TiO2 nanorod arrays. The      Anodic alumina membranes (AAMs) have been employed
representative results are shown in Figures 9(a) and (b).     as a template for the preparation of TiO2 nanorods as
                                                              reported by Miao and co-workers.162 163 TiO2 nanorods can
2.2.2. Synthesis of TiO2 Nanorods by Sol Method               be obtained by dip coating porous AAMs into boiled TiO2
                                                              sol followed by drying process and heat treatment. Typ-
An exciting finding in the preparation of TiO2 nanorods is     ically, TiO2 sol solution was prepared by mixing TTIP
the successful application of the sol method as explored      (2.84 g) dissolved in ethanol (4.7 g) with a solution con-
by various researchers recently,156–161 which allows the      taining 0.54 g water, 1 g acetyl acetone, and 4.7 g ethanol
preparation of highly crystallized TiO2 nanorods with high    and stirred gently for 20 min. After boiled in ethanol at
aspect ratios and small diameters in the range <5 nm.         78 C for 10 min, AAM was immersed into the above

912                                                                                         J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                         Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

                                                                         2.2.5. Synthesis of TiO2 Nanorods by
                                                                                Solvothermal Method
                                                                         Narrow-dispersed TiO2 nanorods were developed with a
                                                                         surfactant-aided solvothermal method by Kim and co-
                                                                         workers.170 Typically, TTIP was dissolved in anhydrous
                                                                         toluene with oleic acid as surfactant and stirred for 24 h
                                                                         and then kept at 250 C for 20 h in an autoclave without
                                                                         stirring. After cooling gradually to room temperature, ace-
                                                                         tone was added to yield the precipitate, which was sep-
                                                                         arated with centrifugal separator and dried in vacuum.
Fig. 11. Low-magnification TEM image of anatase nanorods (A) and
a single nanorod (B). Reprinted with permission from [162], L. Miao      When sufficient amount of TTIP or surfactant was added in
et al., Appl. Surf. Sci. 238, 175 (2004). © 2004, Elsevier.              the solution, long dumbbell-shaped nanorods were formed,
                                                                         due to the oriented growth along [001] axis. The authors
TiO2 sol solution at 80 C for 10 min, then dried in air                  found that the concentration of rods increased as concen-
and calcined at 400 C for 10 h. The AAM template                         tration of titanium precursor in the solution increases, at
can be removed by dissolving AAM in 10 wt% H3 PO4                        fixed precursor to surfactant weight ratio of 1:3. Anatase
aqueous solution. The crystalline phase of TiO2 nanorods                 nanorods were obtained from the solution with precursor-
can be controlled by the calcination temperature. Anatase                to-surfactant weight ratio of more than 1:3 for precursor-
nanorods can be obtained at low temperature while rutile
                                                          Delivered by Ingenta to:
                                                                         to-solvent weight ratio of 1:10, or from the solution with
nanorods can be obtained at high temperature. The size
                                                                          Houston
                                                            University ofprecursor-to-solvent weight ratio of more than 1:5 for
of these TiO2 nanorods is controlled by the pore size of
                                                              IP : 129.7.158.43
                                                                         precursor-to-surfactant weight ratio of 1:3. The diameter
the AAM template, typically ranging from 100–300 nm
                                                      Wed, 23 Aug 2006 21:22:10these nanorods could be tuned by the pre-
                                                                         and length of
in diameter and several microns in length. AAM template                  cursor to surfactant or solvent weight ratios. Typically,
with small pore sizes is necessary to fabricate smaller TiO2             the diameter and length of these nanorods were about
nanorods. Typical TEM for these TiO2 nanorods are shown                  3–5 nm and 18–25 nm, respectively. Figure 13 shows the
in Figure 11.                                                            TEM micrographs and electron diffraction patterns of the
                                                                         nanorods prepared from the solution at the weight ratio of
                                                                         precursor:solvent:surfactant = (a) 1:5:3 and (b) 1:10:5.
2.2.4. Synthesis of TiO2 Nanorods by
         Hydrothermal Method
                                                                         2.2.6. Synthesis of TiO2 Nanorods by
Figure 12 shows the SEM images of TiO2 nanorods film                              Chemical Vapor Deposition
with hydrothermal method by Jiang and co-workers.164
                                                                         TiO2 nanorods have been grown on a WC-Co substrate by
These TiO2 nanorods were prepared by hydrothermal treat-
                                                                         metalorganic chemical vapor deposition (MOCVD) using
ment of a 0.15 M titanium trichloride aqueous solution
                                                                         TTIP as the precursor by Pradhan and co-workers.171
supersaturated with NaCl at 160 C for 2 h. Alterna-
                                                                         The diameter and length of these nanorods were about
tively, Gao and co-workers165–169 treated dilute TiCl4 solu-             50–100 nm and 0.5–2 m, respectively. The authors also
tion at 333 to 423 K for 12 h in the presence of acid or
inorganic salts and successfully obtained TiO2 nanorods.
The morphology of the resulting nanorods can be tuned
by adding different surfactant168 or changing the solvent
compositions.166




                                                                         Fig. 13. TEM micrographs and electron diffraction patterns of
Fig. 12. (a) Low-magnification FE-SEM image of a TiO2 nanorod film         the products prepared from the solutions at the weight ratio of
deposited on a glass wafer, (b) morphology of a single papilla at high   precursor:solvent:surfactant = (a) 1:5:3 and (b) 1:10:5. Reprinted with
magnification. Reprinted with permission from [164], X. Feng et al.,      permission from [170], C.-S. Kim et al., J. Cryst. Growth 257, 309
Angew. Chem. Int. Ed. 44, 5115 (2005). © 2005, Wiley-VCH.                (2003). © 2003, Elsevier.

J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                                  913
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                        Chen and Mao




                                                                   Fig. 15. Cross-section SEM photograph of TiO2 nanowires electrode-
                                                                   posited in AAM pores. Reprinted with permission from [174], S. Liu
                                                                   and K. Huang, Solar Energy Mater. Solar Cells 85, 125 (2004). © 2004,
                                                                   Elsevier.

Fig. 14. (A–C) 45 -tilted SEM images of TiO2 nanorods grown at         obtained by heating the deposited       template at 500 C for
                                                      Delivered
630 C, 560 C, and 535 C, respectively. Reprinted with permission by Ingenta to:
                                                                       4 h. A representative SEM image         of the TiO2 nanowires
from [172], J. J. Wu and C. C. Yu, J. Phys. Chem. B 108, University of Houston Figure 15.174
                                                         3377 (2004).  is shown in
© 2004, American Chemical Society.                          IP : 129.7.158.43
                                              Wed, 23 Aug 2006 21:22:10
found that nanorod grew at approximately 500 C, while              2.3.2. Synthesis of TiO2 Nanowires by Sol–Gel
mostly nanoparticles were deposited at 600 C and a thin                   Electrophoresis Template Method
film was formed at 400 C. The presence of Co was
                                                                   Ordered TiO2 nanowire arrays have been successfully fab-
considered to act to catalyze the formation of the TiO2
                                                                   ricated into the nanochannels of a porous anodic alumina
nanorods, and the presence of NH3 resulted in thinner and
                                                                   membrane by sol–gel electrophoretic deposition of TiO2
longer TiO2 nanorods.
                                                                   colloidal suspensions.175 Typically TTIP was dissolved in
   Wu and Yu developed a template- and catalyst-free
                                                                   ethanol and stirred for 30 min at room temperature. Then
MOCVD method to prepare aligned TiO2 nanorods.172
                                                                   glacial acetic acid mixed with deionized water and ethanol
Figures 14(A)–(C) show TiO2 nanorods grown on fused
                                                                   was added. The pH is adjusted to 2–3 with a small amount
silica substrates using this method. Typically, the precur-
                                                                   of nitrate acid. For the electrophoretic deposition, a plati-
sor, titanium acetylacetonate Ti(C10 H14 O5 , was placed on
                                                                   num sheet is used as the anode, and an AAM with a Au
a Pyrex glass container and loaded into the low-temperature
zone of the furnace which was controlled at 200–230 C              substrate attached to a Cu foil is used as the cathode. TiO2
to vaporize the solid reactant. The vapor was carried by a         sol is deposited at a voltage of 2–5 V using a dc power
1000-sccm N2 /O2 flow into the high-temperature zone of             supply and annealed at 500 C for 24 h. Isolated TiO2
the furnace in which substrates were located. TiO2 nano-           nanowires were obtained by dissolving in the AAM in
structures were grown directly on bare fused silica or             5 wt% NaOH solution at 30 C for 20 min and then lightly
silicon substrates at a temperature of 500–700 C. Single-          washed several times with distilled water. Figure 16 shows
crystalline rutile and anatase TiO2 nanorods were formed
at 630 C and 560 C under a pressure of 5 Torr, respec-
tively; while walls of anatase TiO2 composed of aligned
nanorods were formed at 535 C under 3.6 Torr (Fig. 14C).

2.3. Synthesis of TiO2 Nanowires

2.3.1. Synthesis of TiO2 Nanowires by
       Electrodeposition in Template
In this method, AAM is employed as template,
TiO2 nanowires are electrodeposited into the pores of
AAM.173 174 Typically, the electrodeposition is carried out
                                                                   Fig. 16. (A) SEM image of the fabricated TiO2 nanowires. (B) TEM of
in 0.2 M TiCl3 solution with pH = 2. Titanium or its               one of the TiO2 nanowires; the inset shows the SAED results taken from
compound is deposited into the pores of AAM by pulsed              it. Reprinted with permission from [175], Y. Lin et al., J. Phys. Condens.
electrodeposition approach. Pure anatase TiO2 can be               Mater. 15, 2917 (2003). © 2003, Institute of Physics Publishing.

914                                                                                   J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                            Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials




Fig. 17. (A) SEM image of TiO2 nanowires and (B) SEM image of a
single nanowire. The inset shows a [010] SAED recorded perpendicular
to the long axis of the wire. Reprinted with permission from [179], Y. X.
Zhang et al., Chem. Phys. Lett. 365, 300 (2002). © 2002, Elsevier.

a SEM image of the fabricated TiO2 nanowires and TEM
of one of the TiO2 nanowires.175

2.3.3. Synthesis of TiO2 Nanowires by
       Hydrothermal Method
                                                         Delivered by Ingenta to:
Hydrothermal method is a common method employed to of Houston
                                                 University
prepare TiO2 nanowires by different groups.176–179 In a:typ-
                                                    IP 129.7.158.43 (a) TEM images of the synthesized bamboo-shaped Ag-doped
                                                             Fig. 18.
                                              placed into a
ical procedure, TiO2 white powders were Wed, 23 Aug 20062 21:22:10 TEM image of a nanowire heterojunction. The inset
                                                             TiO nanowires, (b)
Teflon-lined autoclave containing 10–15 M NaOH aqueous        is the ED pattern from area A. (c) High-resolution TEM image of a
                                                             nanowire heterojunction from the selected area in the knot. The Ag
solution and maintained at 150–200 C for 24–72 h with-       phase is marked by black arrows. Reprinted with permission from [180],
out stirring. TiO2 nanowires were obtained after the cooled  B. Wen et al., Inorg. Chem. 44, 6503 (2005). © 2005, American Chemi-
sample was washed with dilute HCl aqueous solution, dist-    cal Society.
illed deionized water and absolute ethanol. Figure 17 shows
a typical SEM image of TiO2 nanowires and SEM image          deposition.183–185 Typically, pure Ti metal powder was
of a single nanowire prepared by Zhang and co-workers.179    loaded as the titanium source. Then, the temperature was
                                                             increased to 850 C under the protection of an argon gas
2.3.4. Synthesis of TiO2 Nanowires by                        flow and held for 3 h. The distance between the substrate
        Solvothermal Method                                  and source was kept at ∼0.5 mm.185 A typical SEM image
                                                             of TiO2 nanowires is shown in Figure 19.185 Alternatively,
The preparation of TiO2 nanowires by solvothermal
                                                             a layer of Ti nanopowders can be deposited on the sub-
method is very similar to hydrothermal method.180–182
                                                             strate before the growth of TiO2 nanowires,183 184 and Au
Typically, 0.5 g TiO2 powder was mixed with aqueous
                                                             can also be employed as the catalyst.183
10 M NaOH and absolute ethanol with a volume ratio
of 1:1. The mixed solution was kept in an autoclave at
170–200 C for 24 h and then cooled to room temperature
naturally. The sample was then washed several times with
dilute HCl aqueous solution and deionized water until the
pH value of the washing solution reached about 7, fol-
lowed by drying the sample at 60 C for 12 h in air.181 In a
revised procedure, titanium butoxide was used as precursor
and AgNO3 as catalyst, bamboo-shaped Ag-doped TiO2
nanowires were developed as shown in Figure 18.180 The
authors found that Ag phase only existed in heterojunc-
tion between the single-crystalline TiO2 nanowires through
electron diffraction and high resolution TEM studies at the
heterojunction of the bamboo-shaped TiO2 nanowires.180

2.3.5. Synthesis of TiO2 Nanowires by
       Physical Vapor Deposition
                                                                            Fig. 19. SEM image of the TiO2 nanowire arrays prepared by PVD
TiO2 nanowire arrays can also fabricated by a simple                        method. Reprinted with permission from [185], B. Xiang et al., J. Phys.
physical vapor deposition (PVD) method or thermal                           D Appl. Phys. 38, 1152 (2005). © 2005, Institute of Physics Publishing.

J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                                     915
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                             Chen and Mao

2.3.6. Synthesis of TiO2 Nanowires from                                  particles to form nanosheets; (ii) the exfoliation accom-
       Layered Titanate Particles                                        panied by splitting to form brush-like nanosheets; and
                                                                         (iii) the split of nanosheets to form wire structures.186
In the development of TiO2 nanowires, the unconventional
method developed by Wei and co-workers based on lay-
                                                                 2.4. Synthesis of TiO2 Nanotubes
ered titanate particles is worth to mention.186 Typically,
0.15 g layered material Na2 Ti3 O7 was dispersed into a          2.4.1. Synthesis of TiO2 Nanotubes by
15 ml 0.05–0.1 M HCl solution, and kept at 140–170 C                    Direct Anodic Oxidation of Titanium
for 3–7 days in an autoclave. The product was filtered,
washed with H2 O, and finally dried at 60 C for 4 h.              Preparation of TiO2 nanotubes by anodic oxidation of
Figure 20 shows a representative TEM image of the TiO2           titanium foil was extensively studied by Grimes and
nanowires from Na2 Ti3 O7 and the proposed formation             co-workers187–198 and other groups.199–203 Typically, tita-
mechanism.186 In Na2 Ti3 O7 , Na+ cations reside between         nia nanotube was prepared by anodizing a titanium sheet
shared [TiO6 ] octahedral layers, which are held by the          in a 0.5% hydrogen fluoride electrolyte solution under an
                                            +
strong static interaction between the Na cations and the         anodization voltage of 10–20 V for 10–30 min.142 A plat-
[TiO6 ] unit. Under hydrothermal conditions, this static         inum counter-electrode was used. The as-prepared amor-
                                                                 phous nanotubes were then annealed at 500 C for 6 h in
interaction was weakened because the interlayer distance
                                         +                       oxygen resulting in crystallized titania. The authors found
was enlarged as the result of larger H3 O molecule gradu-
                                                                 that the nanotube architecture was stable up to approxi-
ally replacing Na+ cations in the interlayer space of [TiO6 ] by Ingenta to:
                                                 Delivered       mately 580 C, above which oxidation and grain growth
                                                  Ti3 O7 par-
sheets. As a result, the layered compound Na2University of Houston
                                                                 in the titanium support disrupted the overlying nanotube
                                                     7 sheet-
ticles are gradually exfoliated. Numerous H2 Ti3 OIP : 129.7.158.43
                                                                 array. Figure 21 shows the SEM images of TiO2 nanotubes
shaped products were formed when Na+ in Wed,323 was 2006 21:22:10
                                               Na2 Ti O7 Aug
                                                                 prepared using a 20 V anodization voltage and 500 C
exchanged by H+ in the dilute HCl solution. An intrinsic
                                                                 annealization for 6 h in oxygen.195 The TiO2 nanotubes
tension exists since the nanosheet does not have inversion       were crystallized in the anatase phase at a temperature of
symmetry, i.e., the layer is asymmetric. In order to release     about 280 C and transformed completely to rutile at about
the strong stress and lower the total energy, the nanosheets     620 C in dry environments and 570 C in humid argon. At
are split, resulting in the formation of nanowires. There are    higher temperature, crystallization of the titanium support
three steps in the formation of TiO2 nanowire from lay-          caused the nanotube architecture to collapse and densify.196
ered H2 Ti3 O7 : (i) the exfoliation from layered Na2 Ti3 O7
                                                                         2.4.2. Synthesis of TiO2 Nanotubes by
                                                                                Sol–Gel Template Method
                                                                         AAM204–207 and other organic compounds208 209 was
                                                                         employed as templates to prepare TiO2 nanotubes by var-
                                                                         ious groups. Lee and co-worker205 reported their study of
                                                                         TiO2 nanotubes by sol–gel template method. TTIP solu-
                                                                         tion was obtained by mixing TTIP with 2-propanol and
                                                                         2,4-pentanedione in the molar ratio of 1:20:1 at room tem-
                                                                         perature. The AAM template membrane was dipped into
                                                                         this solution for 1 min. After removal from the solution,
                                                                         the membrane was vacuumed until the entire volume of
                                                                         the solution was pulled through the membrane. The mem-
                                                                         brane was hydrolyzed over a solution of 0.15 M HCl for




Fig. 20. (a) TEM images of TiO2 nanowires and (b) the proposed for-      Fig. 21. SEM images of TiO2 nanotubes prepared using a 20 V anodiza-
mation mechanism of TiO2 nanowires from the layered Na2 Ti3 O7 parti-    tion voltage and 500 C annealization for 6 h in oxygen. (a) Top view;
cles by a soft chemical process. Reprinted with permission from [186],   (b) vertical cross-sectional view. Reprinted with permission from [195],
M. Wei et al., Chem. Phys. Lett. 400, 231 (2004). © 2004, Elsevier.      O. K. Varghese et al., Adv. Mater. 15, 624 (2003). © 2003, Wiley VCH.

916                                                                                        J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                         Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

                                                                      material is treated with NaOH aqueous solution, Ti–O–Na
                                                                      and Ti–OH bonds are formed after some of the Ti–O–Ti
                                                                      bonds are broken. The Ti–O–Na and Ti–OH bonds are
                                                                      believed to react with acid and water to form new Ti–
                                                                      O–Ti bonds when the material is treated with HCl aque-
                                                                      ous solution and distilled water. The titania nanotubes are
                                                                      formed in the stage of the acid treatment following the
                                                                      alkali treatment. The Ti–OH bond may form a sheet, which
                                                                      is contained in the tube structure. The Ti–O–Ti bonds or
                                                                      Ti–O–H–O–Ti hydrogen bonds are generated through the
Fig. 22. (a) SEM images of the TiO2 tubules prepared in the alu-      dehydration of Ti–OH bonds by HCl aqueous solution,
mina membrane with 200-nm-diameter pores. (b) TEM images of TiO2
tubules prepared in the alumina membrane with 200-nm-diameter pores.
                                                                      the bond distance from one Ti to the next Ti on the sur-
Reprinted with permission from [205], S. Lee et al., Chem. Mater. 16, face decreases, resulting in the folding of the sheets. Dur-
4292 (2004). © 2004, American Chemical Society.                       ing this process, a slight, residual electrostatic repulsion
                                                                      due to Ti–O–Na bonds may lead to connection between
24 h, air-dried for 60 min at room temperature, and then              the ends of the sheets and thus the completion of a tube
placed in a furnace at 673 K for 2 h. After the AAM                   structure.211
template membrane was dissolved by immersing the mem-                    Figure 24 shows high resolution TEM images of
brane into 6 M NaOH solution for several minutes, pure                TiO2 nanotubes developed by Du and co-workers.214 The
                                                       Delivered                to:
TiO2 nanotubes were obtained. Figure 22 shows SEM and by Ingentafound that the above mechanism by Kasuga et al.
TEM images of TiO2 nanotubes prepared using the sol–gel University ofauthors
                                                                       Houston
template method.
                                                                      did not
                                                           IP : 129.7.158.43 apply to their case, since the nanotubes were
                                                    Wed, 23 Aug 2006 21:22:10 the treatment of TiO2 in NaOH aqueous
                                                                      formed during
                                                                      solution.
2.4.3. Synthesis of TiO2 Nanotubes by                                    Wang and co-workers223 suggested that the formation
        Hydrothermal Method                                           mechanism of TiO2 nanotubes followed a 3D → 2D → 1D
                                                                      model. This model stated that the raw TiO2 was first trans-
Hydrothermal has been a very common method used to                    formed into lamellar structures and then bent and rolled
prepare TiO2 nanotubes since it was developed by Kasuga               to form nanotubes. They suggested that two-dimensional
and co-workers210 211 and modified by other groups.212–226             lamellar TiO2 was essential to the formation of TiO2 nano-
In a typical synthesis process, TiO2 powders were placed              tubes. Yao and coworkers224 further suggested that TiO2
into 2.5–20 M NaOH aqueous solution and held for 20 h                 nanotubes were formed by rolling up the single-layer TiO2
at 20, 60, or 110 C in an autoclave. The treated pow-
ders were washed with dilute HCl aqueous solution and
distilled water, then separated from the washing solu-
tion by centrifugation. Figure 23 shows typical TEM
images of TiO2 nanotubes.210 The following TiO2 nanotube
formation process has been proposed. When the raw TiO2




                                                                         Fig. 24. Plane-view HRTEM images of titanium oxide nanotubes
                                                                         (a) before and (b) after HCl washing, and (c) a cross-sectional view of a
Fig. 23. TEM image of TiO2 nanotube. Reprinted with permission           nanotube before washing. Reprinted with permission from [214], G. H.
from [210], T. Kasuga et al., Langmuir 14, 3160 (1998). © 1998, Ameri-   Du et al., Appl. Phys. Lett. 79, 3702 (2001). © 2001, American Institute
can Chemical Society.                                                    of Physics.

J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                                   917
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                                         Chen and Mao




                                                                                 Fig. 26. A schematic drawing illustrating the formation process of the
                                                                                 TiO2 nanotubes. NaOH initially disturbs the crystalline structure (a) of
                                                                                 raw anatase TiO2 crystals (b). The free octahedral reassemble to link
                                                                                 together by sharing edges with the formation of hydroxy bridges between
                                                                                 the Ti ions resulting in a zig-zag structure (c), leading to growth along the
                                                               Delivered by Ingenta to: of the anatase phase. Lateral growth occurs in the
                                                                                 [100] direction
                                                                University [001] direction
Fig. 25. (a) HRTEM images of TiO2 nanotubes. Right inset is the elec- of Houston leading to the formation of two-dimensional crystalline
                                                                                 sheets (d).
                                                                    IP : 129.7.158.43 To saturate dangling bonds and reduce the surface to vol-
tron diffraction pattern taken by focusing the electron beam on a single
                                                            Wed, 23 Aug ume 21:22:10
tube. Left inset is the enlarged picture of the tube wall. (b) Cross-sectional 2006 ratio the crystalline sheets roll-up, lowering the total energy, result
view of TiO2 nanotubes. Reprinted with permission from [224], B. D.              in (e) anatase TiO2 nanotubes. Reprinted with permission from [228],
Yao et al., Appl. Phys. Lett. 82, 281 (2003). © 2003, American Institute         W. Wang et al., J. Mater. Res. 19, 417 (2004). © 2004, Materials Research
of Physics.                                                                      Society.


sheets with a rolling-up vector of [001], attracting other                       2.5. Synthesis of TiO2
sheets to surround the tubes from their HRTEM study as                                Mesoporous/Nanoporous Materials
shown in Figure 25. In the study carried out by Bavykin
and co-workers,227 they suggested that the mechanism of                          Mesoporous/nanoporous TiO2 has been well studied in
nanotube formation involves the wrapping of multilay-                            the past decade.229–252 In the method developed by Stucky
ered nanosheets rather than scrolling or wrapping of single                      group229–246 and adopted by others,236 240 243 248 249 252
layer nanosheets followed by crystallization of successive                       amphiphilic poly(alkylene oxide) block copolymers were
layers. They suggested that the driving force for curving                        used as structure-directing agents in non-aqueous solutions
of the sheets arose from asymmetry due to, e.g., preferen-                       for organizing the network-forming metal-oxide spe-
tial doping of the sheets with sodium or hydrogen (e.g.,                         cies. In a typical synthesis process, 1 g of poly (alky-
hydrogen deficient H2 Ti3 O7 ) together with unsymmetrical                        lene oxide) block copolymer Pluronic P-123 [HO(CH2
surface forces due to locally high surface energy during                         CH2 O)20 (CH2 CH(CH3 O)70 (CH2 CH2 O)20 H,        designated
the crystallisation/dissolution.227                                              EO20 PO70 EO20 ] or Pluronic F-127 [HO(CH2 CH2 O)106
   Wang and co-workers228 suggested a mechanism by                               (CH2 CH(CH3 O)70 (CH2 CH2 O)106 H, designated EO106 PO70
which the anatase TiO2 nanotubes grow as illustrated in                          EO106 ], was dissolved in 10 g of ethanol (EtOH). 0.01 mol
Figure 26. The crystalline structure of raw anatase TiO2                         of TiCl4 precursor was added with vigorous stirring for
crystals is disturbed during the reaction with NaOH, where                       1/2 h. The resulting sol solution was gelled in an open
the Ti–O–Ti bonding between the basic building blocks                            Petri dish at 40 C in air for 1–7 days. The as-made bulk
of the anatase phase, the octahedra, may be broken. The                          sample was then calcined at 400 C for 5 h in air to
free octahedra reassemble by sharing edges between the                           remove the surfactant species.245
Ti ions with the formation of hydroxy bridges, forming                              Other surfactants have also been employed to direct the
a zig-zag structure. This leads to the growth along the                          formation of mesoporous TiO2 . Tetradecyl phosphate (a
[100] direction of the anatase phase. The formation of oxo                       14-carbon chain) was used as the surfactant in forming
bridges between the Ti centers (Ti–O–Ti bonds) in the                            hexagonal mesoporous TiO2 material by Antonelli and
[001] direction leads to lateral growth, and eventually the                      Ying,253 and dodecyl phosphate was used by Putnam and
formation of two-dimensional crystalline sheets. To sat-                         co-workers.241 Cetyltrimethylammonium bromide (CTAB),
urate these dangling bonds from the surface and lower                            a cationic surfactant was also proved to be an effective sur-
the total energy, the sheets roll-up. Local variation in the                     factant for developing mesoporous TiO2 ,232 233 239 as well
solution temperature can also assist the tendency for the                        as the recently reported Gemini surfactant237 and dodecy-
tubes to roll up.                                                                lamine, a neutral surfactant.244 Carbon nanotubes250 and

918                                                                                                  J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                          Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

mesoporous SBA-15234 have also been employed as the                  odor emission sources such as sewage and municipal solid
skeleton to prepare mesoporous TiO2 .                                wastes, can be effectively decomposed by TiO2 nanomate-
   Liu et al.235 and Zhang et al.251 developed a template-           rials under UV irradiation.275 TiO2 photocatalyst can also
free method to synthesize mesoporous TiO2 . In the report            be used to kill bacteria, as carried out with E. coli
by Liu et al.,235 24.0 g of titanium (IV) n-butoxide ethanol         suspensions.372 373 The strong oxidizing power of illumi-
solution (weight ratio of 1:7) was prehydrolyzed in the              nated TiO2 can be used to kill tumor cells in cancer
presence of 0.32 mL of 0.28 M HNO3 aqueous solu-                     treatment.311–316
tion (TBT:HNO3 ∼ 100:1) at room temperature for 3 h.                    Fogging of the surface of mirrors and glass occurs
0.32 mL of deionized water was added to the prehy-                   when humid air condenses, with the formation of many
drolyzed solution and stirred for an additional 2 h. The sol         small water droplets, which scatter light. Various glass
solution in a closed vessel was kept at room temperature             products, i.e., mirrors and eyeglasses, can now be imparted
without stirring to gel and age. After aging for 14 days,            with antifogging functions with TiO2 nanomaterials having
the gel was dried at room temperature, ground into a fine             superhydrophilic or superhydrophobic surface.374–377 Stain-
powder, washed thoroughly with water and ethanol, and                proofing, self-cleaning properties can now be bestowed on
dried to produce the as-prepared porous TiO2 . Upon calci-           many different types of surface by means of the superhy-
nation at 450 C for 4 h under air, crystallized mesoporous           drophilic and/or superhydrophobic effect.356–365 For exam-
TiO2 material was obtained.235                                       ple, an oil smear on a plastic utensil can be spontaneously
                                                                     released from the surface when it is simply soaked in
                                                                     water. Self-cleaning window glass has been developed, as
                                                    Delivered by Ingenta to:
3. APPLICATIONS OF
    TIO2 NANOMATERIALS                                University ofwell as TiO2 -containing, self-cleaning paint.
                                                                      Houston
                                                                        TiO2
                                                          IP : 129.7.158.43nanomaterials have been widely used as photocat-
                                                  Wed, nano-
Besides the research on the synthesis of TiO223 Aug 2006 21:22:10    alytic electrodes for solar energy applications. When sen-
materials,254–267 the application of TiO2 nanomaterials has          sitized with organic dyes or inorganic narrow band gap
been another hot research area in the past decades. The              semiconductors, TiO2 can absorb light into the visible light
various application areas of TiO2 nanomaterials can be cat-          region and convert solar energy into electrical energy in
egorized into four types according to the based properties           solar cell applications.339–344 For example, overall solar to
of TiO2 nanomaterials as summarized in Table I.                      current conversion efficiencies of 10.6% have been reached
   TiO2 nanomaterial normally has electronic band gap                by the group led by Michael Gratzel at Swiss Federal
larger than 3.0 eV, and high absorption in the UV region.            Institute of Technology with the so-called dye-sensitized-
Its optical properties allow it to be a good candidate               solar-cell (DSSC) technology.343 TiO2 nanomaterials have
for UV protection applications.268–273 Besides that, TiO2            been widely studied for water-splitting and hydrogen pro-
nanomaterial is very stable, non-toxic and cheap. It has             duction due to its suitable electronic band structure with
shown very high photocatalytic activity against various              the redox potential of water.317–338 Using TiO2 nanomate-
pollutant and has been regarded as the most promis-                  rials as active photoelectrode materials for the production
ing and widely used nanomaterials as environment-benign              of electricity and/or hydrogen is one of the most important
photocatalyst for the decomposition of various aqueous               research areas for future clean energy applications, i.e.,
and gas pollutants.    274–310
                               For example, Me mercaptan             when facing the world-wide oil crisis.
(CH3 SH), a representative odorous pollutant from various               Another application of TiO2 nanomaterials when sen-
                                                                     sitized with dyes or metal nanoparticles is to build pho-
Table I. Examples of the Applications of TiO2 nanomaterials.
                                                                     tochromic devices.345–355 378 TiO2 nanomaterials have also
                                                                     been used as sensor for various gases and humility.366−371
Property            Applications

Optical             UV-protections: sunglasses, window268–273
Photocatalytic      Photocatalyst for environmental protections: decom-     4. SUMMARY
                       position of organic/inorganic pollutant in the air
                       and water, for out- and in-door air and water        Over the past decade, a variety of different approaches have
                       purification;274–310                                  been developed to prepare TiO2 nanomaterials, including
                    As photocatalyst for self-sterilizing materials for     sol–gel, sol, hydrothermal, solvothermal, and vapor depo-
                       hospital and indoor wall application;                sition. These methods have yielded TiO2 nanomaterials of
                    As photocatalyst for cancer therapy;311–316
                                                                            diverse morphology, e.g., nanorods, nanotubes, and nano-
                    As photocatalyst for water-splitting and hydrogen
                       production;317–338                                   particles of different size. TiO2 nanomaterials have shown
                    As active electrode for dye-sensitized solar cell and   promise for the applications ranging from photocatalysis
                       photochromic applications.339–355                    and photovoltaics to sensors. Successful preparation of
Superhydrophilic/   Self-cleaning and anti-fogging materials                mono-dispersed TiO2 nanomaterials is the very first step
superhydrophobic      for building, window, and mirrors.356–365
Electric            Sensors for gases and humility.366–371
                                                                            towards the realization of the many benefits offered by the
                                                                            materials at the nanometer scale.
J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                           919
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                             Chen and Mao

Acknowledgment: This research has been supported by                        40. S. H. Szczepankiewicz, J. A. Moss, and M. R. Hoffmann, J. Phys.
the U.S. Department of Energy.                                                 Chem. B 106, 2922 (2002).
                                                                           41. X. Q. Chen, J. Y. Yang, and J. S. Zhang, J. Central South Univ.
                                                                               Tech. 11, 161 (2004).
References and Notes                                                       42. X. Chen and C. Burda, J. Phys. Chem. B 108, 15446 (2004).
                                                                           43. X. Chen, Y. Lou, A. C. S. Samia, C. Burda, and J. L. Gole, Adv.
  1. A. Fujishima and K. Honda, Nature 37, 238 (1972).                         Funct. Mater. 15, 41 (2005).
  2. A. Fujishima, T. N. Rao, and D. A. Tryk, J. Photochem. Photobiol.     44. O. Diwald, T. L. Thompson, T. Zubkov, E. Goralski, S. D. Walck,
     C: Photochem. Rev. 1, 1 (2000).                                           and J. T. Yates, Jr., J. Phys. Chem. B 108, 6004 (2004).
  3. D. A. Tryk, A. Fujishima, and K. Honda, Electrochimica Acta 45,       45. F. Gracia, J. P. Holgado, A. Caballero, and A. R. Gonzalez-Elipe,
     2363 (2000).                                                              J. Phys. Chem. B 108, 17466 (2004).
  4. M. Grätzel, Nature 414, 338 (2001).                                   46. K. Tennakone, P. K. M. Bandaranayake, P. V. V. Jayaweera,
  5. A. Hagfeldt and M. Grätzel, Chem. Rev. 95, 49 (1995).                     A. Konno, and G. R. R. A. Kumara, Phys. E 14, 190 (2002).
  6. A. L. Linsebigler, G. Lu, and J. T. Yates, Jr., Chem. Rev. 95, 735    47. E. Palomares, J. N. Clifford, S. A. Haque, T. Lutz, and J. R.
     (1995).                                                                   Durrant, J. Am. Chem. Soc. 125, 475 (2003).
  7. A. Millis and S. L. Hunte, J. Photochem. Photobiol. A: Chem. 108,     48. Y. Diamant, S. G. Chen, O. Melamed, and A. Zaban, J. Phys.
     1 (1997).                                                                 Chem. B 107, 1977 (2003).
  8. A. P. Alivisatos, J. Phys. Chem. 100, 13226 (1996).                   49. D. Cahen, G. Hodes, M. Graetzel, J. F. Guillemoles, and I. Riess,
  9. C. Burda, X. Chen, R. Narayanan, and M. A. El-Sayed, Chem. Rev.           J. Phys. Chem. B 104, 2053 (2000).
     105, 1025 (2005).                                                     50. T. Ohno, Water Sci. Technol. 49, 159 (2004).
 10. X. Chen, Y. Lou, S. Dayal, X. Qiu, R. Krolicki, C. Burda, C. Zhao,    51. T. Ohno, T. Mitsui, and M. Matsumura, Chem. Lett. 32, 364 (2003).
     and J. Becker, J. Nanosci. Nanotechnol. 5, 1408 (2005).               52. A. Kay and M. Graetzel, Chem. Mater. 14, 2930 (2002).
                                                           M. C. Munoz,
 11. L. Chico, W. Jaskolski, M. P. Lopez-Sancho, and Delivered by Ingenta to:
                                                                           53. K. Kalyanasundaram and M. Gratzel, Coord. Chem. Rev. 177, 347
     Int. J. Nanotechnol. 2, 103 (2005).
                                                                               (1998).
                                                            University of Houston
 12. J. Guo, Int. J. Nanotechnol. 1, 193 (2004).
                                                                           54. J. B.
                                                               IP : 129.7.158.43 Asbury, E. Hao, Y. Wang, H. N. Ghosh, and T. Lian, J. Phys.
 13. C. Ma, D. Moore, Y. Ding, J. Li, and Z. L. Wang, Int. J. Nanotech-
                                                                               Chem. B 105, 4545 (2001).
     nol. 1, 431 (2004).                              Wed, 23 Aug 2006 21:22:10 R. Amal, G. Low, and S. McEvoy, J. Nanoparticle
                                                                           55. D. Beydoun,
 14. S. S. Mao, Int. J. Nanotechnol. 1, 42 (2004).
                                                                               Res. 1, 439 (1999).
 15. K. Niesz, M. Grass, and G. A. Somorjai, Nano Lett. 5, 2238 (2005).
                                                                           56. A. J. Frank, N. Kopidakis, and J. van de Lagemaat, Coord. Chem.
 16. G. A. Somorjai and Y. G. Borodko, Catal. Lett. 76, 1 (2001).
                                                                               Rev. 248, 1165 (2004).
 17. V. F. Puntes, N. G. Bastus, I. Pagonabarraga, O. Iglesias,
                                                                           57. A. Hagfeldt and M. Grätzel, Chem. Rev. 95, 49 (1995).
     A. Labarta, and X. Batlle, Int. J. Nanotechnol. 2, 62 (2005).
                                                                           58. M. R. Hoffmann, S. T. Martin, W. Choi, and D. W. Bahnemann,
 18. A. Stashans, Int. J. Nanotechnol. 1, 399 (2004).
                                                                               Chem. Rev. 95, 69 (1995).
 19. L. Vayssieres, A. Hagfeldt, and S. E. Lindquist, Pure Appl. Chem.
                                                                           59. A. L. Linsebigler, G. Lu, and J. T. Yates, Jr., Chem. Rev. 95, 735
     72, 47 (2000).
                                                                               (1995).
 20. L. Vayssieres, Adv. Mater. 15, 464 (2003).
                                                                           60. O. K. Varghese and C. A. Grimes, J. Nanosci. Nanotechnol. 3, 277
 21. L. Vayssieres and M. Graetzel, Angew. Chem. Int. Ed. 43, 3666
                                                                               (2003).
     (2004).
 22. L. Vayssieres, Chem. Sens. 20, 324 (2004).                            61. P. Liu, J. Bandara, Y. Lin, D. Elgin, L. F. Allard, and Y. P. Sun,
 23. L. Vayssieres, Int. J. Nanotechnol. 1, 1 (2004).                          Langmuir 18, 10398 (2002).
 24. L. Vayssieres, C. Sathe, S. M. Butorin, D. K. Shuh, J. Nordgren,      62. G. Oskam, A. Nellore, R. L. Penn, and P. C. Searson, J. Phys.
     and J. Guo, Adv. Mater. 17, 2320 (2005).                                  Chem. B 107, 1734 (2003).
 25. Z. L. Wang and Z. Pan, Adv. Mater. 14, 1029 (2002).                   63. T. Sugimoto, X. Zhou, and A. Muramatsu, J. Coll. Interf. Sci. 259,
 26. Z. L. Wang, Adv. Mater. 15, 432 (2003).                                   53 (2003).
 27. C. Xu and X. Sun, Int. J. Nanotechnol. 1, 452 (2004).                 64. T. Sugimoto, X. Zhou, and A. Muramatsu, J. Coll. Interf. Sci. 259,
 28. Y. Zhang, R. E. Russo, and S. S. Mao, Appl. Phys. Lett. 87,               43 (2003).
     133115/1 (2005).                                                      65. T. Sugimoto and X. Zhou, J. Coll. Interf. Sci. 252, 347 (2002).
 29. A. J. Nozik, Inorg. Chem. 44, 6893 (2005).                            66. T. Sugimoto, X. Zhou, and A. Muramatsu, J. Coll. Interf. Sci. 252,
 30. J. M. Nedeljkovic, O. I. Micic, S. P. Ahrenkiel, A. Miedaner, and         339 (2002).
     A. J. Nozik, J. Am. Chem. Soc. 126, 2632 (2004).                      67. T. Sugimoto, K. Okada, and H. Itoh, J. Coll. Interf. Sci. 193, 140
 31. J. L. Blackburn, D. C. Selmarten, and A. J. Nozik, J. Phys. Chem. B       (1997).
     107, 14154 (2003).                                                    68. N. Uekawa, J. Kajiwara, K. Kakegawa, and Y. Sasaki, J. Coll.
 32. W. Chen, Z. Wang, Z. Lin, and L. Lin, J. Appl. Phys. 82, 3111             Interf. Sci. 250, 285 (2002).
     (1997).                                                               69. K. D. Kim and H. T. Kim, Coll. Surf. A 207, 263 (2002).
 33. C. B. Murray, C. R. Kagan, and M. G. Bawendi, Annu. Rev. Mater.       70. K. D. Kim and H. T. Kim, Powder Technol. 119, 164 (2001).
     Sci. 30, 545 (2000).                                                  71. Y. Bessekhouad, D. Robert, and J. V. Weber, J. Photochem. Photo-
 34. X. Chen, Y. Lou, A. C. Samia, and C. Burda, Nano Lett. 3, 799             biol. A: Chem. 157, 47 (2003).
     (2003).                                                               72. H. Zhang and J. F. Banfield, Chem. Mater. 14, 4145 (2002).
 35. X. Chen, Y. Lou, and C. Burda, Int. J. Nanotechnol. 1, 105 (2004).    73. H. Zhang, M. Finnegan, and J. F. Banfield, Nano Lett. 1, 81 (2001).
 36. X. Chen, A. C. Samia, Y. Lou, and C. Burda, J. Am. Chem. Soc.         74. S. V. Manorama, K. M. Reddy, C. V. G. Reddy, S. Narayanan, P. R.
     127, 4372 (2005).                                                         Raja, and P. R. Chatterji, J. Phys. Chem. Solids 63, 135 (2001).
 37. M. Anpo, Pure Appl. Chem. 72, 1265 (2000).                            75. K. M. Reddy, C. V. G. Reddy, and S. V. Manorama, J. Solid State
 38. T. Berger, M. Sterrer, O. Diwald, E. Knoezinger, D. Panayotov,            Chem. 158, 180 (2001).
     T. L. Thompson, and J. T. Yates, Jr., J. Phys. Chem. B 109, 6061      76. A. Pottier, S. Cassaignon, C. Chaneac, F. Villain, E. Tronc, and
     (2005).                                                                   J. P. Jolivet, J. Mater. Chem. 13, 877 (2003).
 39. D. W. Bahnemann, M. Hilgendorff, and R. Memming, J. Phys.             77. J. H. Lee and Y. S. Yang, J. Europ. Ceram. Soc. 25, 3573 (2005).
     Chem. B 101, 4265 (1997).                                             78. J. H. Lee and Y. S. Yang, Mater. Chem. Phys. 93, 237 (2005).

920                                                                                          J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                             Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

 79. I. N. Kuznetsova, V. Blaskov, I. Stambolova, L. Znaidi, and          120. J. Yang, S. Mei, and J. M. F. Ferreira, J. Am. Ceram. Soc. 84, 1696
     A. Kanaev, Mater. Lett. 59, 3820 (2005).                                  (2001).
 80. L. Znaidi, R. Seraphimova, J. F. Bocquet, C. Colbeau-Justin, and     121. J. Yang, S. Mei, and J. M. F. Ferreira, J. Mater. Res. 17, 2197
     C. Pommier, Mater. Res. Bull. 36, 811 (2001).                             (2002).
 81. Y. Li, T. J. White, and S. H. Lim, J. Solid State Chem. 177, 1372    122. J. Yang, S. Mei, and J. M. F. Ferreira, J. Europ. Ceram. Soc. 24,
     (2004).                                                                   335 (2003).
 82. M. A. Anderson, M. J. Gieselmann, and Q. Xu, J. Membr. Sci. 39,      123. J. Yang, S. Mei, and J. M. F. Ferreira, J. Coll. Interf. Sci. 260, 82
     243 (1988).                                                               (2003).
 83. E. A. Barringer and H. K. Bowen, Langmuir 1, 420 (1985).             124. J. Yang, S. Mei, and J. M. F. Ferreira, Mater. Sci. Forum 455–456,
 84. E. A. Barringer and H. K. Bowen, Langmuir 1, 414 (1985).                  556 (2004).
 85. C. Kormann, D. W. Bahnemann, and M. R. Hoffmann, J. Phys.            125. M. Andersson, L. Oesterlund, S. Ljungstroem, and A. Palmqvist,
     Chem. 92, 5196 (1988).                                                    J. Phys. Chem. B 106, 10674 (2002).
 86. J. Livage, M. Henry, and C. Sanchez, Prog. Solid State Chem. 18,     126. S. Y. Chae, M. K. Park, S. K. Lee, T. Y. Kim, S. K. Kim, and W. I.
     259 (1988).                                                               Lee, Chem. Mater. 15, 3326 (2003).
 87. B. O’Regan and M. Graetzel, Nature 353, 737 (1991).                  127. C. S. Kim, B. K. Moon, J. H. Park, S. T. Chung, and S. M. Son,
 88. T. Sugimoto, Adv. Coll. Interf. Sci. 28, 65 (1987).                       J. Cryst. Growth 254, 405 (2003).
 89. J. H. Jean and T. A. Ring, Langmuir 2, 251 (1986).                   128. S. Seifried, M. Winterer, and H. Hahn, Chem. Vapor Depos. 6, 239
 90. J. L. Look and C. F. Zukoski, J. Am. Ceram. Soc. 78, 21 (1995).           (2000).
 91. J. L. Look and C. F. Zukoski, J. Am. Ceram. Soc. 75, 1587 (1992).    129. J. A. Ayllon, A. Figueras, S. Garelik, L. Spirkova, J. Durand, and
 92. D. Vorkapic and T. Matsoukas, J. Am. Ceram. Soc. 81, 2815 (1998).         L. Cot, J. Mater. Sci. Lett. 18, 1319 (1999).
 93. D. Vorkapic and T. Matsoukas, J. Coll. Interf. Sci. 214, 283 (1999). 130. D. G. Park and J. M. Burlitch, Chem. Mater. 4, 500 (1992).
 94. R. L. Penn and J. F. Banfield, Geoch. Et Cosmoch. Acta 63, 1549       131. H. D. Jang and S. K. Kim, Mater. Res. Bull. 36, 627 (2001).
     (1999).                                              Delivered by Ingenta to: T. Kodas, T. Pluym, and Y. Xiong, Aerosol Sci. Technol.
                                                                          132. A. Gurav,
 95. C. J. Barbe, F. Arendse, P. Comte, M. Jirousek, F. Lenzmann,              19, 411
                                                           University of Houston (1993).
     V. Shklover, and M. Gratzel, J. Am. Ceram. Soc. 80, 3157 (1997).     133. S. Vemury, S. E. Pratsinis, and L. Kibbey, J. Mater. Res. 12, 1031
                                                               IP : 129.7.158.43
 96. H. Zhang and J. F. Banfield, J. Mater. Chem. 8, 2073 (1998).               (1997).
                                                       Wed, (2000).
 97. H. Zhang and J. F. Banfield, J. Phys. Chem. B 104, 348123 Aug 2006 21:22:10Flame Synthesis of Nanoparticles: Effect of Charging
                                                                          134. S. Vemury,
 98. H. Zhang and J. F. Banfield, Chem. Mater. 17, 3421 (2005).
                                                                               (Titanium Chloride), Dissertation, University of Cincinnati, Cincin-
 99. K. D. Kim, S. H. Kim, and H. T. Kim, Coll. Surf. A 254, 99 (2005).
                                                                               nati, OH, USA (1996).
100. G. L. Li and G. H. Wang, Nanostruc. Mater. 11, 663 (1999).
                                                                          135. S. E. Pratsinis, S. Vemury, and W. Zhu, Polym. Mater. Sci. Eng. 73,
101. J. Lin, Y. Lin, P. Liu, M. J. Meziani, L. F. Allard, and Y. P. Sun,
                                                                               31 (1995).
     J. Am. Chem. Soc. 124, 11514 (2002).
                                                                          136. S. Vemury and S. E. Pratsinis, Appl. Phys. Lett. 66, 3275 (1995).
102. D. Zhang, L. Qi, J. Ma, and H. Cheng, J. Mater. Chem. 12, 3677
                                                                          137. X. H. Wang, J. G. Li, H. Kamiyama, M. Katada, N. Ohashi,
     (2002).
                                                                               Y. Moriyoshi, and T. Ishigaki, J. Am. Chem. Soc. 127, 10982
103. K. T. Lim, H. S. Hwang, S. S. Hong, C. Park, W. Ryoo, and K. P.
                                                                               (2005).
     Johnston, Studies Surf. Sci. Catal. 153, 569 (2004).
                                                                          138. S. M. Oh, J. G. Li, and T. Ishigaki, J. Mater. Res. 20, 529 (2005).
104. K. T. Lim, H. S. Hwang, W. Ryoo, and K. P. Johnston, Langmuir
                                                                          139. T. Ishigaki, S. M. Oh, and D. W. Park, Transact. Mater. Res. Soc.
     20, 2466 (2004).
                                                                               Jpn. 29, 3415 (2004).
105. Y. Li, N. H. Lee, D. S. Hwang, J. S. Song, E. G. Lee, and S. J.
                                                                          140. Y. L. Li and T. Ishigaki, J. Phys. Chem. B 108, 15536 (2004).
     Kim, Langmuir 20, 10838 (2004).
106. J. C. Yu, H. Y. Tang, J. Yu, H. C. Chan, L. Zhang, Y. Xie, H. Wang,  141. S. M. Oh and T. Ishigaki, Thin Solid Films 457, 186 (2004).
     and S. P. Wong, J. Photochem. Photobiol. A: Chem. 153, 211           142. S. M. Oh, S. S. Kim, J. E. Lee, T. Ishigaki, and D. W. Park, Thin
     (2002).                                                                   Solid Films 435, 252 (2003).
107. S. S. Hong, M. S. Lee, S. S. Park, and G. D. Lee, Catal. Today 87,   143. Y. L. Li and T. Ishigaki, Thin Solid Films 407, 79 (2002).
     99 (2003).                                                           144. J. M. Nedeljkovic, Z. V. Saponjic, Z. Rakocevic, V. Jokanovic, and
108. J. Tang, Y. Wu, E. W. McFarland, and G. D. Stucky, Chem.                  D. P. Uskokovic, Nanostruc. Mater. 9, 125 (1997).
     Commun. 1670 (2004).                                                 145. M. Scepanovic, Z. D. Dohcevic-Mitrovic, I. Hinic, M. Grujic-
109. H. Parala, A. Devi, R. Bhakta, and R. A. Fischer, J. Mater. Chem.         Brojcin, G. Stanisic, and Z. V. Popovic, Mater. Sci. Forum 494, 265
     12, 1625 (2002).                                                          (2005).
110. M. Niederberger, M. H. Bartl, and G. D. Stucky, J. Am. Chem. Soc.    146. M. Grujic-Brojcin, M. J. Scepanovic, Z. D. Dohcevic-Mitrovic,
     124, 13642 (2002).                                                        I. Hinic, B. Matovic, G. Stanisic, and Z. V. Popovic, J. Phys. D:
111. V. Lafond, P. H. Mutin, and A. Vioux, Chem. Mater. 16, 5380               Appl. Phys. 38, 1415 (2005).
     (2004).                                                              147. C. W. Oh, G. D. Lee, S. S. Park, C. S. Ju, and S. S. Hong, Korean
112. P. Arnal, R. J. P. Corriu, D. Leclercq, P. H. Mutin, and A. Vioux,        J. Chem. Eng. 22, 547 (2005).
     Chem. Mater. 9, 694 (1997).                                          148. C. W. Oh, G. D. L. Seong, S. Park, C. S. Ju, and S. S. Hong, React.
113. P. Arnal, R. J. P. Corriu, D. Leclercq, P. H. Mutin, and A. Vioux,        Kinet. Catal. Lett. 85, 261 (2005).
     J. Mater. Chem. 6, 1925 (1996).                                      149. J. M. Wu, J. Cryst. Growth 269, 347 (2004).
114. J. N. Hay and H. M. Raval, Chem. Mater. 13, 3396 (2001).             150. J. M. Wu, T. W. Zhang, Y. W. Zeng, S. Hayakawa, K. Tsuru, and
115. J. N. Hay and H. M. Raval, J. Sol–Gel Sci. Technol. 13, 109 (1998).       A. Osaka, Langmuir 21, 6995 (2005).
116. T. J. Trentler, T. E. Denler, J. F. Bertone, A. Agrawal, and V. L.   151. J. M. Wu and T. W. Zhang, J. Photochem. Photobiol. A: Chem.
     Colvin, J. Am. Chem. Soc. 121, 1613 (1999).                               162, 171 (2004).
117. F. Cot, A. Larbot, G. Nabias, and L. Cot, J. Europ. Ceram. Soc.      152. J. M. Wu, S. Hayakawa, K. Tsuru, and A. Osaka, Scripta Mater.
     18, 2175 (1998).                                                          46, 705 (2002).
118. J. Yang, S. Mei, and J. M. F. Ferreira, Mater. Sci. Eng. C 15, 183   153. J. M. Wu, S. Hayakawa, K. Tsuru, and A. Osaka, Cryst. Growth
     (2001).                                                                   Design 2, 147 (2002).
119. J. Yang, S. Mei, and J. M. F. Ferreira, J. Am. Ceram. Soc. 83, 1361  154. J. M. Wu, S. Hayakawa, K. Tsuru, and A. Osaka, Scripta Mater.
     (2000).                                                                   46, 101 (2002).

J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                                     921
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                            Chen and Mao

155. X. Peng and A. Chen, J. Mater. Chem. 14, 2542 (2004).              193. G. K. Mor, K. Shankar, M. Paulose, O. K. Varghese, and C. A.
156. P. D. Cozzoli, M. L. Curri, and A. Agostiano, Chem. Commun.             Grimes, Nano Lett. 5, 191 (2005).
     3186 (2005).                                                       194. C. Ruan, M. Paulose, O. K. Varghese, G. K. Mor, and C. A. Grimes,
157. P. D. Cozzoli, E. Fanizza, M. L. Curri, D. Laub, and A. Agostiano,      J. Phys. Chem. B 109, 15754 (2005).
     Chem. Commun. 942 (2005).                                          195. O. K. Varghese, D. Gong, M. Paulose, K. G. Ong, E. C. Dickey,
158. P. D. Cozzoli, E. Fanizza, R. Comparelli, M. L. Curri,                  and C. A. Grimes, Adv. Mater. 15, 624 (2003).
     A. Agostiano, and D. Laub, J. Phys. Chem. B 108, 9623 (2004).      196. O. K. Varghese, D. Gong, M. Paulose, C. A. Grimes, and E. C.
159. P. D. Cozzoli, R. Comparelli, E. Fanizza, M. L. Curri,                  Dickey, J. Mater. Res. 18, 156 (2003).
     A. Agostiano, and D. Laub, J. Am. Chem. Soc. 126, 3868 (2004).     197. O. K. Varghese, D. Gong, W. R. Dreschel, K. G. Ong, and C. A.
160. P. D. Cozzoli, R. Comparelli, E. Fanizza, M. L. Curri, and              Grimes, Sens. Actuators B: Chem. B94, 27 (2003).
     A. Agostiano, Mater. Sci. Eng. C 23, 707 (2003).                   198. O. K. Varghese, D. Gong, M. Paulose, K. G. Ong, and C. A.
161. P. D. Cozzoli, A. Kornowski, and H. Weller, J. Am. Chem. Soc.           Grimes, Sens. Actuators B: Chem. B93, 338 (2003).
     125, 14539 (2003).                                                 199. J. M. Macak, H. Tsuchiya, and P. Schmuki, Angew. Chem. Int. Ed.
162. L. Miao, S. Tanemura, S. Toh, K. Kaneko, and M. Tanemura, Appl.         44, 2100 (2005).
     Surf. Sci. 238, 175 (2004).                                        200. V. M. Prida, M. Hernandez-Velez, M. Cervera, K. Pirota, R. Sanz,
163. L. Miao, S. Tanemura, S. Toh, K. Kaneko, and M. Tanemura,               D. Navas, A. Asenjo, P. Aranda, E. Ruiz-Hitzky, F. Batallan,
     J. Cryst. Growth 264, 246 (2004).                                       M. Vazquez, B. Hernando, A. Menendez, N. Bordel, and R. Pereiro,
164. X. Feng, J. Zhai, and L. Jiang, Angew. Chem. Int. Ed. 44, 5115          J. Magn. Magn. Mater. 294, e69 (2005).
     (2005).                                                            201. X. Quan, S. Yang, X. Ruan, and H. Zhao, Environ. Sci. Technol.
165. Q. Zhang and L. Gao, Langmuir 19, 967 (2002).                           39, 3770 (2005).
166. S. Yang and L. Gao, Chem. Lett. 34, 1044 (2005).                   202. H. Tsuchiya, J. M. Macak, L. Taveira, E. Balaur, A. Ghicov,
167. S. Yang and L. Gao, Chem. Lett. 34, 972 (2005).                         K. Sirotna, and P. Schmuki, Electrochem. Commun. 7, 576 (2005).
168. S. Yang and L. Gao, Chem. Lett. 34, 964 (2005). Delivered by Ingenta to: Wang, R. Chen, and L. Li, Solid State Commun. 134,
                                                                        203. J. Zhao, X.
169. Q. Huang and L. Gao, Chem. Lett. 32, 638 (2003). University of Houston  705 (2005).
170. C. S. Kim, B. K. Moon, J. H. Park, B. C. Choi, and H. J.: Seo,     204. Y. Chen,
                                                              IP 129.7.158.43 J. C. Crittenden, S. Hackney, L. Sutter, and D. W. Hand,
     J. Cryst. Growth 257, 309 (2003).                                       Environ. Sci.
                                                      Wed, 23 Aug 2006 21:22:10 Technol.Y.39, 1201 (2005). 16, 4292 (2004).
171. S. K. Pradhan, P. J. Reucroft, F. Yang, and A. Dozier, J. Cryst.   205. S. Lee, C. Jeon, and     Park, Chem. Mater.
     Growth 256, 83 (2003).                                             206. S. M. Liu, L. M. Gan, L. H. Liu, W. D. Zhang, and H. C. Zeng,
172. J. J. Wu and C. C. Yu, J. Phys. Chem. B 108, 3377 (2004).               Chem. Mater. 14, 1391 (2002).
173. Y. Lei, L. D. Zhang, and J. C. Fan, Chem. Phys. Lett. 338, 231     207. M. S. Sander, M. J. Cote, W. Gu, B. M. Kile, and C. P. Tripp, Adv.
     (2001).                                                                 Mater. 16, 2052 (2004).
174. S. Liu and K. Huang, Solar Energy Mater. Solar Cells 85, 125       208. J. H. Jung, H. Kobayashi, K. J. C. van Bommel, S. Shinkai, and
     (2004).                                                                 T. Shimizu, Chem. Mater. 14, 1445 (2002).
175. Y. Lin, G. S. Wu, X. Y. Yuan, T. Xie, and L. D. Zhang, J. Phys.    209. J. H. Jung, T. Shimizu, and S. Shinkai, J. Mater. Chem. 15, 3979
     Condens. Mater. 15, 2917 (2003).                                        (2005).
176. A. R. Armstrong, G. Armstrong, J. Canales, R. García, and P. G.    210. T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, and K. Niihara,
     Bruce, Adv. Mater. 7, 862 (2005).                                       Langmuir 14, 3160 (1998).
177. A. R. Armstrong, G. Armstrong, J. Canales, R. García, and P. G.    211. T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, and K. Niihara,
     Bruce, Angew. Chem. Int. Ed. 43, 2286 (2004).                           Adv. Mater. 11, 1307 (1999).
178. R. Yoshida, Y. Suzuki, and S. Yoshikawa, J. Solid State Chem. 178, 212. D. V. Bavykin, E. V. Milsom, F. Marken, D. H. Kim, D. H. Marsh,
     2179 (2005).                                                            D. J. Riley, F. C. Walsh, K. H. El-Abiary, and A. A. Lapkin, Elec-
179. Y. X. Zhang, G. H. Li, Y. X. Jin, Y. Zhang, J. Zhang, and L. D.         trochem. Commun. 7, 1050 (2005).
     Zhang, Chem. Phys. Lett. 365, 300 (2002).                          213. S. H. Chien, Y. C. Liou, and M. C. Kuo, Synthetic Metals 152, 333
180. B. Wen, C. Liu, and Y. Liu, Inorg. Chem. 44, 6503 (2005).               (2005).
181. B. Wen, C. Liu, and Y. Liu, New J. Chem. 29, 969 (2005).           214. G. H. Du, Q. Chen, R. C. Che, Z. Y. Yuan, and L. M. Peng, Appl.
182. B. Wen, C. Liu, and Y. Liu, J. Phys. Chem. B 109, 12372 (2005).         Phys. Lett. 79, 3702 (2001).
183. J. M. Wu, H. C. Shih, and W. T. Wu, Chem. Phys. Lett. 413, 490     215. G. Gundiah, S. Mukhopadhyay, U. G. Tumkurkar, A. Govindaraj,
     (2005).                                                                 U. Maitra, and C. N. R. Rao, J. Mater. Chem. 13, 2118 (2003).
184. J. M. Wu, H. C. Shih, W. T. Wu, Y. K. Tseng, and I. C. Chen,       216. A. Kukovecz, M. Hodos, Z. Konya, and I. Kiricsi, Chem. Phys.
     J. Cryst. Growth 281, 384 (2005).                                       Lett. 411, 445 (2005).
185. B. Xiang, Y. Zhang, Z. Wang, X. H. Luo, Y. W. Zhu, H. Z. Zhang,    217. Y. Lan, X. Gao, H. Zhu, Z. Zheng, T. Yan, F. Wu, S. P. Ringer, and
     and D. P. Yu, J. Phys. D Appl. Phys. 38, 1152 (2005).                   D. Song, Adv. Funct. Mater. 15, 1310 (2005).
186. M. Wei, Y. Konishi, H. Zhou, H. Sugihara, and H. Arakawa, Chem.    218. S. H. Lim, J. Luo, Z. Zhong, W. Ji, and J. Lin, Inorg. Chem. 44,
     Phys. Lett. 400, 231 (2004).                                            4124 (2005).
187. D. Gong, C. A. Grimes, O. K. Varghese, W. Hu, R. S. Singh,         219. R. Ma, K. Fukuda, T. Sasaki, M. Osada, and Y. Bando, J. Phys.
     Z. Chen, and E. C. Dickey, J. Mater. Res. 16, 3331 (2001).              Chem. B 109, 6210 (2005).
188. G. K. Mor, O. K. Varghese, M. Paulose, and C. A. Grimes, Sens.     220. L. Qian, Z. L. Du, S. Y. Yang, and Z. S. Jin, J. Mol. Struct. 749,
     Lett. 1, 42 (2003).                                                     103 (2005).
189. G. K. Mor, O. K. Varghese, M. Paulose, N. Mukherjee, and C. A.     221. D. S. Seo, J. K. Lee, and H. Kim, J. Cryst. Growth 229, 428 (2001).
     Grimes, J. Mater. Res. 18, 2588 (2003).                            222. Z. R. Tian, J. A. Voigt, J. Liu, B. McKenzie, and H. Xu, J. Am.
190. G. K. Mor, K. Shankar, O. K. Varghese, and C. A. Grimes, J. Mater.      Chem. Soc. 125, 12384 (2003).
     Res. 19, 2989 (2004).                                              223. Y. Q. Wang, G. Q. Hu, X. F. Duan, H. L. Sun, and Q. K. Xue,
191. G. K. Mor, M. A. Carvalho, O. K. Varghese, M. V. Pishko, and            Chem. Phys. Lett. 365, 427 (2002).
     C. A. Grimes, J. Mater. Res. 19, 628 (2004).                       224. B. D. Yao, Y. F. Chan, X. Y. Zhang, W. F. Zhang, Z. Y. Yang, and
192. G. K. Mor, O. K. Varghese, M. Paulose, and C. A. Grimes, Adv.           N. Wang, Appl. Phys. Lett. 82, 281 (2003).
     Funct. Mater. 15, 1291 (2005).                                     225. Z. Y. Yuan and B. L. Su, Coll. Surf. A 241, 173 (2004).

922                                                                                         J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                             Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

226. M. Wang, D. J. Guo, and H. L. Li, J. Solid State Chem. 178, 1996      261. J. Kim, O. Wilhelm, and S. E. Pratsinis, J. Nanosci. Nanotechnol.
     (2005).                                                                    4, 226 (2004).
227. D. V. Bavykin, V. N. Parmon, A. A. Lapkin, and F. C. Walsh,           262. N. L. V. Carreno, R. C. Lima, L. E. B. Soledade, E. Longo, E. R.
     J. Mater. Chem. 14, 3370 (2004).                                           Leite, A. Barison, A. G. Ferreira, A. Valentini, and L. F. D. Probst,
228. W. Wang, O. K. Varghese, M. Paulose, C. A. Grimes, Q. Wang,                J. Nanosci. Nanotechnol. 3, 516 (2003).
     and E. C. Dickey, J. Mater. Res. 19, 417 (2004).                      263. H. Ding, M. K. Ram, and C. Nicolini, J. Nanosci. Nanotechnol.
229. M. H. Bartl, S. P. Puls, J. Tang, H. C. Lichtenegger, and G. D.            1, 207 (2001).
     Stucky, Angew. Chem. Int. Ed. 43, 3037 (2004).                        264. K. G. Ong, O. K. Varghese, G. K. Mor, and C. A. Grimes,
230. M. H. Bartl, S. W. Boettcher, E. L. Hu, and G. D. Stucky, J. Am.           J. Nanosci. Nanotechnol. 5, 1801 (2005).
     Chem. Soc. 126, 10826 (2004).                                         265. O. K. Varghese, M. Paulose, K. Shankar, G. K. Mor, and C. A.
231. M. H. Bartl, S. W. Boettcher, K. L. Frindell, and G. D. Stucky,            Grimes, J. Nanosci. Nanotechnol. 5, 1158 (2005).
     Acc. Chem. Res. 38, 263 (2005).                                       266. A. Kumbhar and G. Chumanov, J. Nanosci. Nanotechnol. 4, 299
232. E. Beyers, P. Cool, and E. F. Vansant, J. Phys. Chem. B 109, 10081         (2004).
     (2005).                                                               267. M. R. Kim, S. J. Ahn, and D.-J. Jang, J. Nanosci. Nanotechnol. 6,
233. S. Cabrera, J. El Haskouri, A. Beltran-Porter, D. Beltran-Porter,          180 (2006).
     M. D. Marcos, and P. Amoros, Solid State Sci. 2, 513 (2000).          268. A. P. Popov, A. V. Priezzhev, J. Lademann, and R. Myllylae,
234. H. Ding, H. Sun, and Y. Shan, J. Photochem. Photobiol. A: Chem.            J. Phys. D: Appl. Phys. 38, 2564 (2005).
     169, 101 (2004).                                                      269. B. Mahltig, H. Boettcher, K. Rauch, U. Dieckmann, R. Nitsche,
235. C. Liu, L. Fu, and J. Economy, J. Mater. Chem. 14, 1187 (2004).            and T. Fritz, Thin Solid Films 485, 108 (2005).
236. H. Luo, C. Wang, and Y. Yan, Chem. Mater. 15, 3841 (2003).            270. D. K. Hwang, J. H. Moon, Y. G. Shul, K. T. Jung, D. H. Kim, and
237. Y. Y. Lyu, S. H. Yi, J. K. Shon, S. Chang, L. S. Pu, S. Y. Lee, J. E.      D. W. Lee, J. Sol–Gel Sci. Technol. 26, 783 (2003).
     Yie, K. Char, G. D. Stucky, and J. M. Kim, J. Am. Chem. Soc. 126,     271. K. K. Gupta, V. S. Tripathi, H. Ram, and H. Raj, Colourage 49, 35
     2310 (2004).                                         Delivered by Ingenta to:
                                                                                (2002).
238. T. A. Ostomel and G. D. Stucky, Chem. Commun. 1016 (2004).             Houston
                                                           University of272. J. W. Kim, J. W. Shim, J. H. Bae, S. H. Han, H. K. Kim, I. S.
239. T. Peng, D. Zhao, K. Dai, W. Shi, and K. Hirao, J. Phys. Chem. B
                                                               IP : 129.7.158.43 H. H. Kang, and K. D. Suh, Coll. Polym. Sci. 280, 584
                                                                                Chang,
     109, 4947 (2005).                                                          (2002).
                                                                    Aug
                                                      Wed, 23 E. L. 2006 21:22:10
240. M. D. Perez, E. Otal, S. A. Bilmes, G. J. A. A. Soler-Illia,
                                                                           273. Y. Zhang, L. Zhang, C. Mo, Y. Li, L. Yao, and W. Cai, J. Mater.
     Crepaldi, D. Grosso, and C. Sanchez, Langmuir 20, 6879 (2004).
                                                                                Sci. Technol. 16, 277 (2000).
241. R. L. Putnam, N. Nakagawa, K. M. McGrath, N. Yao, I. A. Aksay,
                                                                           274. K. K. Akurati, A. Vital, R. Hany, B. Bommer, T. Graule, and
     S. M. Gruner, and A. Navrotsky, Chem. Mater. 9, 2690 (1997).
                                                                                M. Winterer, Int. J. Photoenergy 7, 153 (2005).
242. Y. Saito, S. Kambe, T. Kitamura, Y. Wada, and S. Yanagida, Solar
                                                                           275. Y. Liu, X. Chen, J. Li, and C. Burda, Chemosphere 61, 11 (2005).
     Energy Mater. Solar Cells 83, 1 (2004).
                                                                           276. L. C.-K. Liau, H. Chang, T. C.-K. Yang, and C. L. Huang, J. Chem.
243. X. Wang, J. C. Yu, H. Y. Yip, L. Wu, P. K. Wong, and S. Y. Lai,
                                                                                Eng. Jpn. 38, 813 (2005).
     Chem.—A Europ. J. 11, 2997 (2005).
                                                                           277. J. F. Fu, M. Ji, and D. N. An, J. Environ. Sci. 17, 942 (2005).
244. Y. Wang, S. Zhang, and X. Wu, Nanotechnology 15, 1162 (2004).
                                                                           278. S. Mohanty, N. N. Rao, P. Khare, and S. N. Kaul, Water Res. 39,
245. P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka, and G. D.
                                                                                5064 (2005).
     Stucky, Nature 396, 152 (1998).
                                                                           279. R. S. Sonawane and M. K. Dongare, J. Mol. Catal. A: Chem. 243,
246. P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka, and G. D.
                                                                                68 (2006).
     Stucky, Chem. Mater. 11, 2813 (1999).
                                                                           280. S. Rengaraj and X. Z. Li, J. Mol. Catal. A: Chem. 243, 60 (2006).
247. D. K. Yi and Y. Kim, Nano Lett. 3, 207 (2003).
248. J. C. Yu, L. Zhang, and J. Yu, Chem. Mater. 14, 4647 (2002).          281. N. M. Mahmoodi, M. Arami, N. Y. Limaee, and N. S. Tabrizi,
249. J. C. Yu, X. Wang, L. Wu, W. Ho, L. Zhang, and G. Zhou, Adv.               J. Coll. Interf. Sci. 295, 159 (2006).
     Funct. Mater. 14, 1178 (2004).                                        282. D. Fabbri, A. B. Prevot, and E. Pramauro, Appl. Catal. B: Environ.
250. Y. Yu, J. C. Yu, J. G. Yu, Y. C. Kwok, Y. K. Che, J. C. Zhao,              62, 21 (2006).
     L. Ding, W. K. Ge, and P. K. Wong, Appl. Catal. A 289, 186 (2005).    283. F. Bosc, D. Edwards, N. Keller, V. Keller, and A. Ayral, Thin Solid
251. Y. Zhang, G. Li, Y. Wu, Y. Luo, and L. Zhang, J. Phys. Chem. B             Films 495, 272 (2006).
     109, 5478 (2005).                                                     284. L. Li, Q. Y. Wu, Y. H. Guo, and C. W. Hu, Micropor. Mesopor.
252. M. Zukalova, A. Zukal, L. Kavan, M. K. Nazeeruddin, P. Liska,              Mater. 87, 1 (2005).
     and M. Graetzel, Nano Lett. 5, 1789 (2005).                           285. S. Mozia, M. Tomaszewska, and A. W. Morawski, Desalination
253. D. M. Antonelli and J. Y. Ying, Angew. Chem. Int. Ed. 34, 2014             185, 449 (2005).
     (1995).                                                               286. R. Thiruvenkatachari, T. O. Kwon, and I. S. Moon, Separat. Sci.
254. D. S. Kommireddy, A. A. Patel, T. G. Shutava, D. K. Mills, and             Technol. 40, 2871 (2005).
     Y. M. Lvov, J. Nanosci. Nanotechnol. 5, 1081 (2005).                  287. J. R. Parga, S. S. Shukla, and D. L. Cocke, Res. J. Chem. Environ.
255. J. Zhang, Z. Liu, B. Han, J. Li, Z. Li, and G. Yang, J. Nanosci.           9, 60 (2005).
     Nanotechnol. 5, 945 (2005).                                           288. D. Chatterjee and S. Dasgupta, J. Photochem. Photobiol. C:
256. P. Sujaridworakun, D. Pongkao, A. Ahniyaz, Y. Yamakawa,                    Photochem. Rev. 6, 186 (2005).
     T. Watanabe, and M. Yoshimura, J. Nanosci. Nanotechnol. 5, 875        289. M. Canle Lopez, M. I. Fernandez, S. Rodriguez, J. A. Santaballa,
     (2005).                                                                    S. Steenken, and E. Vulliet, Chem. Phys. Chem. 6, 2064 (2005).
257. U. C. Bandugula, L. M. Clayton, J. P. Harmon, and A. Kumar,           290. P. Raja, J. Bandara, P. Giordano, and J. Kiwi, Industr. Engin. Chem.
     J. Nanosci. Nanotechnol. 5, 814 (2005).                                    Res. 44, 8959 (2005).
258. M. A. Barakat, G. Hayes, and S. I. Shah, J. Nanosci. Nanotechnol.     291. J. Yang, C. Chen, H. Ji, W. Ma, and J. Zhao, J. Phys. Chem. B 109,
     5, 759 (2005).                                                             21900 (2005).
259. O. K. Varghese, G. K. Mor, C. A. Grimes, M. Paulose, and              292. M. A. Rahman and M. Muneer, Desalination 181, 161 (2005).
     N. Mukherjee, J. Nanosci. Nanotechnol. 4, 733 (2004).                 293. C. Sahoo, A. K. Gupta, and A. Pal, Desalination 181, 91 (2005).
260. I. Kartini, P. Meredith, X. S. Zhao, J. C. D. Da Costa, and G. Q.     294. S. Y. Yang, Y. X. Chen, L. P. Lou, and X. N. Wu, J. Environ. Sci.
     Lu, J. Nanosci. Nanotechnol. 4, 270 (2004).                                17, 761 (2005).

J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                                      923
Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials                                                                               Chen and Mao

295. J. Wang, F. Y. Wen, Z. H. Zhang, X. D. Zhang, Z. J. Pan, L. Zhang,    330. J. H. Park, S. Kim, and A. J. Bard, Nano Lett. 6, 24 (2006).
     L. Wang, L. Xu, P. L. Kang, and P. Zhang, J. Environ. Sci. 17, 727    331. J. H. Park and A. J. Bard, Electrochem. Solid-State Lett. 8, G371
     (2005).                                                                    (2005).
296. F. Akbal, Environ. Prog. 24, 317 (2005).                              332. M. Pujadas and P. Salvador, J. Electrochem. Soc. 136, 716 (1989).
297. T. Tanimura, A. Yoshida, and S. Yamazaki, Appl. Catal. B: Environ.    333. P. Salvador, New J. Chem. 12, 35 (1988).
     61, 346 (2005).                                                       334. A. Schwarz, K. J. Hartig, and N. Getoff, Adv. Hydrog. Energy 5,
298. L. Lhomme, S. Brosillon, D. Wolbert, and J. Dussaud, Appl.                 643 (1986).
     Catal. B: Environ. 61, 227 (2005).                                    335. D. Tafalla and P. Salvador, J. Electroanal. Chem. Interf.
299. C. W. Oh, G. D. Lee, S. S. Park, C. S. Ju, and S. S. Hong, Korean          Electrochem. 270, 285 (1989).
     J. Chem. Eng. 22, 547 (2005).                                         336. S. Takabayashi, R. Nakamura, and Y. Nakato, J. Photochem.
300. L. Canle, J. A. Santaballa, and E. Vulliet, J. Photochem. Photo-           Photobiol. A: Chem. 166, 107 (2004).
     biol. A: Chem. 175, 192 (2005).                                       337. A. Yamakata, T. A. Ishibashi, and H. Onishi, Int. J. Photoenergy
301. L. Li, W. Zhu, L. Chen, P. Zhang, and Z. Chen, J. Photochem.               5, 7 (2003).
     Photobiol. A: Chem. 175, 172 (2005).                                  338. A. Yamakata, T. A. Ishibashi, and H. Onishi, J. Mol. Catal. A:
302. S. X. Li, F. Y. Zheng, X. L. Liu, F. Wu, N. S. Deng, and J. H.             Chem. 199, 85 (2003).
     Yang, Chemosphere 61, 589 (2005).                                     339. M. Graetzel and R. F. Howe, J. Phys. Chem. 94, 2566 (1990).
303. W. Zhang, X. X. Wang, and X. Z. Fu, Chin. Chem. Lett. 16, 1275        340. C. G. Granqvist, Adv. Mater. 15, 1789 (2003).
     (2005).                                                               341. M. Gratzel, J. Sol–Gel Sci. Technol. 22, 7 (2001).
304. F. Thevenet, O. Guaitella, J. M. Herrmann, A. Rousseau, and           342. M. Gratzel, J. Photochem. Photobiol. C: Photochem. Rev. 4, 145
     C. Guillard, Appl. Catal. B: Environ. 61, 58 (2005).                       (2003).
305. K. Demeestere, J. Dewulf, T. Ohno, P. H. Salgado, and H. Van          343. M. Gratzel, J. Photochem. Photobiol. A: Chem. 164, 3 (2004).
     Langenhove, Appl. Catal. B: Environ. 61, 140 (2005).                  344. M. Gratzel, MRS Bull. 30, 23 (2005).
                                                         Delivered         345. M. Biancardo, R. Argazzi, and C. A. Bignozzi, Inorg. Chem. 44,
306. J. Zhu, J. Zhang, F. Chen, K. Iino, and M. Anpo, Topics Catal. 35, by Ingenta to:
     261 (2005).                                                                9619 (2005).
                                                                            Houston
                                                           University of346. K. Kawahara, K. Suzuki, Y. Ohko, and T. Tatsuma, Phys. Chem.
                                                              G. : 129.7.158.43
307. V. Augugliaro, S. Coluccia, E. Garcia-Lopez, V. Loddo, IPMarci,
     G. Martra, L. Palmisano, and M. Schiavello, Topics Catal. 35, 237          Chem. Phys. 7, 3851 (2005).
     (2005).
                                                     Wed, 23 Aug 2006 21:22:10and H. Shen, Acta Metall. Sinica 18, 275 (2005).
                                                                           347. M. J. Chen
                                                                           348. J. Okumu, C. Dahmen, A. N. Sprafke, M. Luysberg, G. von
308. H. Hidaka, N. Watanabe, and S. Horikoshi, Trends in Air Pollut.
                                                                                Plessen, and M. Wuttig, J. Appl. Phys. 97, 094305/1 (2005).
     Res. 157 (2005).
                                                                           349. N. Freestone, Chem. Indust. 27 (2005).
309. V. Augugliaro, E. Garcia-Lopez, V. Loddo, S. Malato-Rodriguez,
                                                                           350. K. Naoi, Y. Ohko, and T. Tatsuma, Chem. Commun. 1288 (2005).
     I. Maldonado, G. Marci, R. Molinari, and L. Palmisano, Solar
                                                                           351. R. G. Palgrave and I. P. Parkin, J. Mater. Chem. 14, 2864 (2004).
     Energy 79, 402 (2005).
                                                                           352. T. He, Y. Ma, Y. Cao, H. Liu, W. Yang, and J. Yao, J. Coll. Interf.
310. N. M. Mahmoodi, M. Arami, N. Y. Limaee, and N. S. Tabrizi,
                                                                                Sci. 279, 117 (2004).
     Chem. Eng. J. 112, 191 (2005).
                                                                           353. K. Iuchi, Y. Ohko, T. Tatsuma, and A. Fujishima, Chem. Mater. 16,
311. R. Cai, K. Hashimoto, Y. Kubota, and A. Fujishima, Chem. Lett.
                                                                                1165 (2004).
     427 (1992).
                                                                           354. K. Naoi, Y. Ohko, and T. Tatsuma, J. Am. Chem. Soc. 126, 3664
312. H. Sakai, R. Baba, K. Hashimoto, Y. Kubota, and A. Fujishima,
                                                                                (2004).
     Chem. Lett. 185 (1995).
                                                                           355. Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and
313. A. P. Zhang and Y. P. Sun, World J. Gastroenterol. 10, 3191 (2004).
                                                                                A. Fujishima, Nature Mater. 2, 29 (2003).
314. S. Ivankovic, M. Gotic, M. Jurin, and S. Music, J. Sol–Gel Sci.       356. K. T. Meilert, D. Laub, and J. Kiwi, J. Mol. Catal. A: Chem. 237,
     Technol. 27, 225 (2003).                                                   101 (2005).
315. D. M. Blake, P. C. Maness, Z. Huang, E. J. Wolfrum, J. Huang,         357. A. Bozzi, T. Yuranova, and J. Kiwi, J. Photochem. Photobiol. A:
     and W. A. Jacoby, Separat. Purif. Meth. 28, 1 (1999).                      Chem. 172, 27 (2005).
316. N. P. Huang, M. H. Xu, C. W. Yuan, and R. R. Yu, J. Photochem.        358. X. T. Zhang, O. Sato, M. Taguchi, Y. Einaga, T. Murakami, and
     Photobiol. A: Chem. 108, 229 (1997).                                       A. Fujishima, Chem. Mater. 17, 696 (2005).
317. R. Abe, K. Sayama, K. Domen, and H. Arakawa, Chem. Phys. Lett.        359. K. Guan, Surf. Coat. Technol. 191, 155 (2005).
     344, 339 (2001).                                                      360. E. D. Sam, M. Urgen, F. Z. Tepehan, and V. Gunay, Key Eng.
318. R. Abe, K. Sayama, and H. Sugihara, J. Phys. Chem. B 109, 16052            Mater. 264–268, 407 (2004).
     (2005).                                                               361. L. Cassar, MRS Bull. 29, 328 (2004).
319. R. Abe, K. Sayama, and H. Arakawa, Chem. Phys. Lett. 371, 360         362. S. Smith, Chem. Rev. (United Kingdom) 12, 31 (2002).
     (2003).                                                               363. A. Fujishima, T. N. Rao, and D. A. Tryk, Int. Glass Rev. 128
320. A. Galinska and J. Walendziewski, Energy Fuels 19, 1143 (2005).            (2002).
321. K. J. Hartig and N. Getoff, Adv. Hydrog. Energy 4, 1085 (1984).       364. Y. Ohko, S. Saitoh, T. Tatsuma, and A. Fujishima, J. Electrochem.
322. S. U. M. Khan, M. Al-Shahry, and W. B. Ingler, Jr., Science 297,           Soc. 148, B24 (2001).
     2243 (2002).                                                          365. A. Nakajima, K. Hashimoto, T. Watanabe, K. Takai, G. Yamauchi,
323. S. U. M. Khan and J. Akikusa, J. Electrochem. Soc. 145, 89 (1998).         and A. Fujishima, Langmuir 16, 7044 (2000).
324. J. Kiwi, Chem. Phys. Lett. 83, 594 (1981).                            366. H. Tokudome, Y. Yamada, S. Sonezaki, H. Ishikawa, M. Bekki,
325. A. Kudo, Catal. Surveys from Asia 7, 31 (2003).                            K. Kanehira, and M. Miyauchi, Appl. Phys. Lett. 87, 213901/1
326. Y. Matsumoto, U. Unal, N. Tanaka, A. Kudo, and H. Kato, J. Solid           (2005).
     State Chem. 177, 4205 (2004).                                         367. W. P. Tai, Nanomaterials 115 (2005).
327. M. Matsuoka, M. Kitano, M. Takeuchi, M. Anpo, and J. M.               368. A. M. Ruiz, A. Cornet, and J. R. Morante, Sens. Actuators B: Chem.
     Thomas, Topics Catal. 35, 305 (2005).                                      B111–B112, 7 (2005).
328. M. Matsuoka, M. Kitano, M. Takeuchi, M. Anpo, and J. M.               369. B. C. Yadav, R. K. Shukla, and L. M. Bali, Indian J. Pure Appl.
     Thomas, Mater. Sci. Forum 486–487, 81 (2005).                              Phys. 43, 51 (2005).
329. G. K. Mor, O. K. Varghese, M. Paulose, K. Shankar, and C. A.          370. H. Miyazaki, T. Hyodo, Y. Shimizu, and M. Egashira, Sens.
     Grimes, Mater. Res. Soc. Sympos. Proc. 836, 29 (2005).                     Actuators B: Chem. B108, 467 (2005).

924                                                                                           J. Nanosci. Nanotechnol. 6, 906–925, 2006
Chen and Mao                                                                        Synthesis of Titanium Dioxide (TiO2 ) Nanomaterials

371. S. H. Si, Y. S. Fung, and D. R. Zhu, Sens. Actuators B: Chem.      375. Y. Takata, S. Hidaka, M. Masuda, and T. Ito, Int. J. Energy Res.
     B108, 165 (2005).                                                       27, 111 (2003).
372. Y. Kikuchi, K. Sunada, T. Iyoda, K. Hashimoto, and A. Fujishima,   376. Z. Z. Gu, A. Fujishima, and O. Sato, Angew. Chem. Int. Ed. 41,
     J. Photochem. Photobiol. A: Chem. 106, 51 (1997).                       2067 (2002).
373. K. Sunada, Y. Kikuchi, K. Hashimoto, and A. Fujishima, Environ.    377. Y. Takata, S. Hidaka, J. M. Cao, K. Tanaka, M. Masuda, T. Ito,
     Sci. Technol. 32, 726 (1998).                                           T. Watanabe, and M. Shimohigoshi, Therm. Sci. Eng. 8, 33 (2000).
374. L. Sirghi, T. Aoki, and Y. Hatanaka, Surf. Rev. Lett. 10, 345      378. K. Kawahara, K. Suzuki, Y. Ohko, and T. Tatsuma, Phys. Chem.
     (2003).                                                                 Chem. Phys. 7, 3851 (2005).


                                                                    Received: 31 August 2005. Revised/Accepted: 5 January 2006.




                                                    Delivered by Ingenta to:
                                                     University of Houston
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                                                   Wed, 23 Aug 2006 21:22:10




J. Nanosci. Nanotechnol. 6, 906–925, 2006                                                                                               925

								
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