Lecture 4 Nanoscopic Particles: synthesis, properties & applications

Transcription

1 Lecture 4 Nanoscopic Particles: synthesis, properties & applications 20 nm

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8 Optical properties: size matters CdSe/ZnS Core-Shell nanoparticles have size-dependent optical properties. ZnS CdSe 2.3 nm 4.2 nm 4.8 nm 5.5 nm Larger Band Gap Smaller Band Gap

9 Optical properties: Shape & Composition Matters 200 nm 100 nm 100 nm 100 nm 100 nm A B C D E Ag Prisms ~100 nm Au Spheres ~100 nm Au Spheres ~50 nm Ag Spheres ~90 nm Ag Spheres ~40 nm

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12 Band structure of solid state materials

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16 (Doped semiconductors)

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25 TOP: tri-n-octylphosphine For CdSe, the TOP/TOPO combination is extremely successful, where TOP binds preferentially to the Se and TOPO binds to Cd. tri-n-octylphosphine oxide (TOPO)

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40 Nanoscopic Metal Particles: synthesis, properties & applications

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49 SPR of Metal Nanoparticles: The Influence of Direction of Measure C. Noguez, J. Phys. Chem. C 2007, 111, M. B. Cortie, X. Xu, M. J. Ford, Phys. Chem. Chem. Phys. 2006, 8, 3520.

50 Synthesis of colloidal metal nanoparticle Key issues 1. Can we synthesize monodisperse nanoparticles? 2. Can we control the size of the particle? 3. Can we obtain the desired crystal structure? 4. Can we control the shape of the particle? 5. Can we align the nanoparticles on substrates?

51 Method I: Salt reduction method

52 Synthesis of Nanoparticles with well-defined size and shape Light, citrate, ascorbic acid Hydrazine, DMF, NaBH 4, amine Reductant Metal Salts CTAB, CTAC PVP, AOT, amine HAuCl 4 AgNO 3 K 2 PdCl 4 K 2 PtCl 4 Surfactants

53 Control of Particle Morphology Metal precursors reduction kinetics Reaction parameter control Regulation of lowindex planes growth Metal precursor Reductant Surfactant/stabilizer Solvent Temperature Foreign ion ph rate via selective adsorption

54 Noble Metal Nanocrystal Au Rhombic Dodecahedron Au Octahedron Au Icosahedron Au Plate Chem. Commun., 2009, Pd Cube Pd Flower Chem. Commun., 2008, Chem. Phys. Lett., 2009, 468, J. Phys. Chem. C, 2007, 111, Chem. Phys. Lett., 2006, 432, J. Am. Chem. Soc., 2009, 113, Nano Lett., 2009, 9, Au Cube Au Cuboctahedron Pd Multipodal Cube U-Shaped Pd Cube Pt Flower Chem. Commun., 2010, 46, Bimetallic Nanocrystals Ag-Au Alloy Nanoprisms Chem. Lett., 2007, 36, Flower-Shaped Porous Au-Pd Alloy Nanoparticles J. Phys. Chem. C, 2008, 112, Au-Pd Core-Shell Octahedron J. Am. Chem. Soc., 2009, 131, Au-Pt Core-Shell NPs Angew. Chem. Int. Ed., 2010, 49,

55 Protective agents: necessary to prevent agglomeration Type I: uses electrostatic stabilization Uses the Coulombic repulsion between particles due to the electrical double layer formed by ions adsorbed at the particle surface and the corresponding counter ions: e.g. gold sols prepared by the reduction of [AuCl 4 ] - with sodium citrate (C 6 H 5 Na 3 O 7 )

56 Type II: uses steric stabilization 1. Uses the coordination of bulky organic molecules (e.g. polymers, phosphates, amines, thioethers, THF, long-chain alcohols, surfactants, etc.) 2. Lipophilic* (hydrophilic) protective agents give colloids soluble in organic (water) media *lipophilic : fat-loving, tend to dissolve in fat-like (e.g. hydrocarbon) solvents

57 Reverse micelles technique Reverse micelles (water-inoil droplets stabilized by a monolayer of surfactant) serve as nanoscale reactors TEM images of 9 nm Co nanoparticles

58 Borohydride Reduction Methods for Monolayer-Protected Metal Nanoparticles Thiol 1 2 NaBH 4 (aq) Metal salt solution 3 Work-up 1-Phase Thiol 2 3 NaBH 4 (aq) Organic solvent (toluene, benzene) 4 Metal salt (aq) Work-up 1 Phase transfer 2-Phase

59 Hydrogen Reduction Method used for electrostatically stabilized metal sols and polymer-stabilized hydrosols of Pd, Pt, Rh & Ir Moiseev s giant palladium cluster: Pd 561 L 60 (OAc) 180 (L=phenanthroline, bipyridine) Finke-type Ir 0 nanocluster P 2 W 15 Nb 3 O and Bu 4 N + stabilized Ir 0 300

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61 Method II: Electrochemical synthesis 1. Oxidative dissolution of M bulk anode 2. Migration of M n+ to the cathode 3. Reductive formation of zerovalent metal atoms at the cathode 4. Nucleation and growth of metal particles 5. Arrest of the growth process and stabilization by protecting agents 6. Precipitation of the nanoparticles

62 Advantage: 1. Can avoid by-products resulting from chemical reducing agents 2. Allows for size-selective particle formation by adjusting the current density applied, the distance between the electrodes, the rxn time and T, & the polarity of the solvent: e.g. monodisperse Pd 0 (1-6nm), NR 4+ -stabilized Ni 0 3. Bimetallic nanocolloids (Pd/Ni,Fe/Co, Fe/Ni) accessible if 2 M bulk anodes used

63 Modified electrolysis cell for the preparation of layered bimetallic Pt/Pd nanocolloids A preformed (Oct) 4 NBrstabilized Pt colloid electrolized with Pd anode

64 Method III: Laser Ablation Metal colloids: pure without any effect of ion, stabilizer, etc. Roughened metal plates: can be used repeatedly Laser ablation setup for preparing metal colloids and roughened metal plates. Metal colloids Metal plates

65 Absorbance (AU) nm Au-Ag Alloy Nanoparticles from Laser Ablation of Au-Ag Bulk Alloy TEM 1064 nm UV-Vis Ag Ag 3 Au 1 Ag 2 Au 2 Ag 1 Au 3 Au R= Mol. frac. Au 20 nm Wavelength ( nm )

66 Method IV: Microwave- Assisted Synthesis Angew. Chem. Int. Ed. 2011, 50,

67 Miscellaneous Methods Microemulsion Surfactants Membranes Polyelectrolytes Seeding Growth Photochemistry Sonochemistry Radiolysis Thermolysis SPM h h h Photochemistry Seeding Growth

68 Seed-Mediated Growth of Nanorods and Nanowires

69 Applications of nanoparticles Catalysis Sensors Organic or Biosynthesis Nonlinear Optics Quantum Electronics Optoelectronic Devices Single Molecule Detection Solar and Fuel Cell Battery Biominerallization

70 Applications of nanoparticles Catalysts 1. Catalysts for homogeneous rxns: lipophilic or hydrophilic metal colloids (dissolved in the form of organosols or hydrosols) can serve as catalysts in organic and aqueous solutions: e.g. aq. solutions of Moiseev s giant Pd colloids catalyze oxidative acetoxylation rxns 2. Catalysts for heterogeneous rxns

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72 Egg-shell type catalysts 1. Active metal particles as a thin layer (<250nm) on the surface: applied in the hydrogenation of C-C double bonds, organic carbonyl groups & unsaturated C-N bonds 2. Size & composition of the metal particles can be controlled independently of the support

73 AFM image of a sulfobetaine-12 stabilized Pt hydrosol (3nm) adsorbed on highly oriented pyrolytic graphite (HOPG) after dipping (left) and after additional washing (right)

74 Cortex catalysis An active metal forms an extremely fine shell less than 10nm thick on the support (e.g. Al 2 O 3 )

75 Functionalization of nanoporous alumina membranes and immobilization of metal colloids on the pore walls TEM image of a one-dimensional Au 55 cluster wire in a nanoporous alumina membrane

76 Absorbance Catalytic Reduction of Nitro Compounds with Silver Nanoparticle NO 2 OH 0.8 E(Ag + ) V E(Ag ) n - - E ED(BH 4 ) e-relay NH 2 OH E (4NP) EA E(Ag ) bulk V (4AP) SuccessiveUV-visible spectra (1 min time interval) of 4-nitrophenol(4NP) Time / min Absorbance vs time plot of the reduction of 4-nitrophenol (4NP)

77 Fuel Cells for Portable Electronic Devices anode cathode e - catalysts Fuel H + O 2 CO 2 membrane H 2 O Most common fuel; Methanol (Direct Methanol Fuel Cell, DMFC)

78 Shape-Dependent Catalytic Activity of Nanoparticles A. R. Tao, S. Habas, P. Yang, Small 2008, 4, 310. N. Tian, Z.-Y. Zhou, S.-G. Sun, Y. Ding, Z. L. Wang, Science 2007, 316, 732.

79 Applications of nanoparticles Sensors Ex: Nanoparticle-Based DNA Detection Schemes Colorimetric Absorbance ( Scanometric ) A G C T Science 2000, 289, Science 1997, 277, Conductivity Light Scattering (d=50 nm) (d=100 nm) Science, 2002, 295, mm J. Am. Chem. Soc., 2001, 123, Science, 2001, 294, 1901.

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81 Alignments of Nanoparticles Au 55 monolayers with a hexagonal (a) and a cubic (b) structure 200 nm DNA-directed Nanoparticle Assembly

82 Applications of nanoparticles Biomineralization Experimental scheme O - O MBA capped Au nanoparticle S Au Ca 2+ CO 2 CaCO 3 crystallization Without nanoparticles