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Synthesis - PowerPoint

VIEWS: 267 PAGES: 50

									 Chemical Synthesis of
Nanostructured Materials
Length scale
Nano-synthesis Technology
World market
Research
Top-down versus Bottom-up
      Bottom-up Process - What to control




                           +
• Colloidally stable nanoparticles
• Reproducible
• Adaptable surface properties
• Easy + cheap
•(Biocompatible or biodegradable systems)
Colloids
Colloids


 To some the word `colloidal' conjures up visions of things indefinite in
 shape, indefinite in chemical composition and physical properties, fickle
 in chemical deportment, things infilterable and generally unmanageable.
                                                            Hedges, 1931



Application                        Involved Principles
• Pharmaceutics, cosmetics, • Formation and stabilization of
inks, paints, foods, foams, end-use products
chemicals
• Photographic      products, • Formation of colloids for use in
ceramics, paper coatings, subsequent manufacturing
catalysts, magnetic media     processes
• Pumping     of      slurries, • Handling properties of colloids,
coating technology, filtration rheology, sintering
• Water purification, fining of • Destruction of unwanted
wines and beer                  colloidal systems
  Nucleation & Growth


Typical precipitation reaction:




Reactant 1 + Reactant 2              T, t
                                                         Product + By-product
                                   Stabilizer


  Nucleation                                       Agglomeration
  (critical size)              Primary particles
                                                                        Particles
                                                Growth

                    Crystallites
     Clusters
Colloidal stability
Colloidal stability
Surface potential
      DLVO Theory


• The scientists Derjaguin, Verwey, Landau and Overbeek developed a theory
in the 1940s which dealt with the stability of colloidal systems.
• DVLO theory suggests that the stability of a particle in solution is dependent
upon its total potential energy function VT.
• This theory recognizes that VT is the balance of several competing
contributions:
          VT = VA + VR + VS
• VS is the potential energy due to the solvent, it usually only makes a marginal
contribution to the total potential energy over the last few nanometers of
separation. Much more important is the balance between VA and VR, these are
the attractive and repulsive contributions. They potentially are much larger and
operate over a much larger distance.
.
VA = -A/(12 π D2)
where A is the Hamaker constant and D is the particle separation.

VR = 2 π ε a ζ2 exp(-κD)
where a is the particle radius, π is the solvent permeability, κ is a function of
the ionic composition and ζ is the zeta potential.
  DLVO Theory


                                 DVLO theory suggests that the stability of
                                 a colloidal system is determined by the
                                 sum of these van der Waals attractive (VA)
                                 and electrical double layer repulsive (VR)
                                 forces that exist between particles as they
                                 approach each other due to the Brownian
                                 motion they are undergoing.


This theory proposes that an energy barrier resulting from the repulsive force
prevents two particles approaching one another and adhering together.

Therefore if the particles have a
sufficiently  high     repulsion,    the
dispersion will resist flocculation and
the colloidal system will be stable.
However if a repulsion mechanism
does not exist then flocculation or
coagulation will eventually take place.
    DLVO Theory


Therefore to maintain the stability of the colloidal system, the repulsive
forces must be dominant. How can colloidal stability be achieved? There
are two fundamental mechanisms that affect dispersion stability:
• Steric repulsion - this involves polymers added to the system adsorbing
onto the particle surface and preventing the particle surfaces coming into
close contact. If enough polymer adsorbs, the thickness of the coating is
sufficient to keep particles separated by steric repulsions between the
polymer layers, and at those separations the van der Waals forces are too
weak to cause the particles to adhere.
• Electrostatic or charge stabilization - this is the effect on particle
interaction due to the distribution of charged species in the system.



 Electrostatic stabilization     Introduction of spatial constraints

   +               + + ++
 + ++             +
+                  + + ++
 + + ++
Control of Particle size
Dispersant effect - (Steric force)
      Methods for Nanosynthesis



 1) Physical methods: Carbon arc, Laser ablation, Vapour trapping….

 2) Chemical methods


                                 T, p, t
  Reactant 1 + Reactant 2                        Product + …




Sonochemistry                    Hydrothermal           Sol-gel
                                   methods              methods
                Microwave
                                                                  Wet chemical co-
                synthesis
                                                                   precipitation

                                           Microencapsulation
Sol-gel process
Advantage & Disadvantage
Application
          Powder Technology Laboratory

          Applications: InkJet Media - ILFORD




Polymer

          Support

            time




                          Nanoporous
                                        Support
                                         time
Monodisperse SiO2 Particles
Monodisperse SiO2 Particles from MTMS
Monodisperse SiO2 Particles from TEOS
Solvothermal Synthesis
Solvothermal Synthesis
Solvothermal Synthesis - Tungsten Oxide
  Sonochemistry

 Chemistry enhanced /assisted by ultrasound
 Effect: Acoustic cavitation
 Frequencies: 20kHz - 10MHz
 Main event: Creation, growth, collapse of a bubble that is formed in the liquid


 The stage leading to the growth of
 the     bubble    occurs   through
 diffusion of solute vapour into the
 volume of the bubble, which
 eventually collapses



Chemistry e.g. for Chalcogenides (S2-, Se2-, Te2-):

MeCl2 + S/Se/Te                   Product
Solvent: EtOH/Ethylendiamine
     Sonochemistry

   Role of ultrasonic radiation:
        a) Dissociation of chalcogens and formation of E2-
        b) Prevention of aggregation


  Application:
  a) Deposition of nanoparticles on ceramic and polymeric surfaces
  b) Insertion of nanomaterials into mesoporous materials
  c) Formation of protein-micro- and nanospheres
                               Fig. 2. SEM images detailing various
                               stages of t-Se wire growth: (a)
                               Spherical colloids of a-Se synthesized
                               by reducing selenious acid with
                               hydrazine. (b) Colloidal particles
                               recovered from an ethanol dispersion
                               right after sonication (for 30 s). Note
                               that these particles have undergone a
                               morphological change (c) A sample
                               obtained at the initial stage of wire
                               growth (d) The final product, in which
Ultrasonics Sonochemistry 11   all a-Se colloids have already been
(2004) 47ff                    transformed into t-Se nanowires with a
                               uniform diameter.
  Microwave-assisted synthesis

Role of microwave radiation:
Direct and very fast heating of the sample by microwave radiation induces
uniform reactions, can improve the yield, and possibly enables different
kinetic pathways of synthesis

Example: Synthesis of acicular magnetite
 Wet chemical synthesis: Acicular goethite (a-FeO(OH)) as starting
  material is transformed to hematite (acicular, a-Fe2O3), which is heated
  carefully under hydrogen to yield the product
 Microwave synthesis: Decomposition of Fe2+/Fe3+ aqueous solutions with
  concurrent dissociation of urea in a microwave field




   Materials Research Bulletin 33/11
   (1998) 1571
Reduction in solution
Reduction in solution
Reduction in solution - How to control the particles
Reduction in solution - How to control the particles


Seed-mediated growth
Reduction in solution - Seed-mediated growth
Reduction in solution - Seed-mediated growth
   Template synthesis


Surfactant: Surfactants = surface active agents


Materials, which have a special propensity to locate (ie adsorb) at interfaces, or
which form colloidal aggregates in solution at very low molar concentrations


Micelles: Micelles are the simplest of all amphiphilic self-organizing structures.




                      Spherical
                      micelle                                  Bicontinuous structure



                     Cylindrical micelle
                                                               Vesicles
      Template synthesis


  1. Gold particles in micelles

                                            Hydrophylic             Hydrophobic tail
Amphiphilic molecules spontaneously         head group
self-organize into various structures.
                                                Amphiphilic molecule


                                             Synthesis: A-B diblock copolymer is used for
                                             micelle formation
                                             Polymer:Poly(styrene-block-2-vinyl-pyridine)
                                             Idea: An inorganic compound such as HAuCl4
                                             is bound selectively to the Polyvinylpyridine
                                             block of the polymer and thus solubilized within
                                             the core of the micelle. Afterwards, the
                                             compound is transformed by chemical reaction
                                             to the metal.


                                    J. P. Spatz, A. Roescher, M. Möller Adv. Mater. 8/4 (1996)
     Template synthesis


Hosts:




1-D tunnel hosts      2-D layered hosts      3-D framework hosts
(Zeolites, Lipid      (Oxide-, halide-,      (Carbon sieves, Zeolites,
bilayer vesicles,     chalcogenide layers,   Polymers, cages,
Inorganic tunnels)    clays, graphite)       buckyball comlexes)


 Materials: inorganic, organic or metallorganic
 Insulators, semiconductors, metalls or supraconductors.
 Sizes: 5-10.000 Å (channels), 3-50 Å (interlamellar spaces),
         10.000 Å (cavity diameters)
                                                        J. Mater. Chem. 7/7 (1997) 1089ff.
    Template synthesis

Nucleopore Membranes

Compounds: Polypyrrole and Poly(3-methylthiophene)
•Synthesis: Nanoporous nucleopore membrane is used as template during
 synthesis
•Nucleopore polycarbonate membrane filter, containing linear cylindrical pores
 of equivalent pore diamter covering the range 300 Å to 10.000 Å.
•Monomer solution is separated by the polymerization agent (ferric salt) by a
 this membrane
     Chemical co-precipitation

Synthesis of Colloidal Platinum Nanoparticles


Synthesis: K2PtCl4 is reduced by H2 in the presence of sodium-polyacrylate in
an argon atmosphere at room temperature to give colloidal platinum.
Parameters: pH, ratio of initial metal salt and capping material, concentrations




        20nm                      20nm




 Different reaction conditions yield different particles:
 cubic and tetrahedral


                                                             SCIENCE 272 (1996) 1924ff.
          Biosynthesis

1. Protein based recognition system

1.1 antibody ↔ hapten group interaction
 hapten group: low molecular weight organic compound which binds specifically to
 antibodies




                         +




      =                       H
                                  N     NO2
O2N          N
                                  O2N
                                              hapten group = dinitrophenyl group
                                                       H
                 H
           NO2                                          N            NO2

                                                         O2 N
          DNP-DNP antigen connector                               Adv. Mater. 1999,11, 449-452
      Biosynthesis

1.2 biotin ↔ streptavidin interaction


                                                                                   Biotin
4X                +

                                                                                   Streptavidin



1.3 latest development: de novo protein linker
sequences of 12 amino acids that directly recognize distinct surfaces of semiconductor
materials, thereby avoiding the necessity of previous chemical functionalization of the
particles

1 μm lines of GaAs                                   same pattern
separated by 4 μm lines of                           exposed to TMR
SiO2 spacing were                                    and the peptide
exposed to tetramethyl
rhodamine (TMR) without
the peptide
                                                                       Nature 2000, 405, 665-668
      Biosynthesis            2. DNA-based nanoparticle aggregation



 can be synthesized by automated methods
 short double helices show great mechanical rigidity,
  so they can serve as rod spacer between two
  tethered functional components on both ends
 nature provides highly specific biomolecular reagents
  to process DNA materials



             +
                                   Linking
                                  DNA strand
Two sorts of nanoparticles
  functionalized with two
 different oligonucleotides



8 and 31 nm gold particles
functionalized with two
different oligonucleotides
                                                          J. Am. Chem. Soc. 1998, 120, 12674-75
leading to satellite structure
by linkage with a
bifunctional DNA strand
           Biosynthesis

     3. Biomimetic systems

     Analogously to biomolecule-based oligomerization of nanoparticles,
     reversible abiotic recognition systems can be applied




                                                                                 +   +




                                                             +       +
                                                                                         Host/guest interaction
            ≡                    O   O                           ≡                       between
                             O           O

                       O
                                                                                         dibenzylammonium and
                             O           O       H                           H
HS
                   O             O   O
                                                     +
                                                     N
                                                                             +
                                                                             N           the dibenzo-24-crown-8
                                                         H               H
                                                                                         group
undecylthiol functionalized with a
dibenzo-24-crown-8 group                     bis-dibenzylammonium
                                             dication                                J. Am. Chem. Soc. 2000, 122, 6252-57
       Biosynthesis

4. Biotemplating

Examples for templates
• bacterial cell surface proteins
• nano- and micrometer – sized nucleic acid compounds
• hollow biomolecular compartments like viruses
                                                                                 S-Layer

S-Layers                                                                          TEM Grid
Multiple copies of a single
polypeptide, which spontaneously                                                  gold coating
forms highly regular nanoporous
superlattices of varying symmetry


                                          Electron irradiation

                                                                          gold nanoparticles




                                                                 Supramol. Sci. 1998, 5, 15-19
       Biosynthesis

5. Magnetotactic Bacteria

Examples for templates
• Magnetotactic bacteria are a heterogeneous group of procaryotes
• They orient and migrate along geomagnetic field lines
• Migration based on intracellular magnetic structure, so-called magnetosomes
• Magnetosomes: membrane-bound magnetite particles




                                                             J.Molec.Microbiol.Biotechnol. (1999) 1(1) 79.
Biosynthesis

								
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