Chapter 3-2: Synthesis of metal nanoparticles and films 3.2.1 Introduction 3.2.2 Theory: nucleation-seed-nanocrystals 3.2.3 Chemical reduction method: (synthesis of Au and bi-metallic nanoparticles) 3.2.4 Sonochemical 3.2.5 Hydrothermal 3.2.6 Electrochemical reduction 3.2.7 Thermolysis and Photolysis 3.2.8 Chemical Vapor Deposition 3.2.9 Physical Vapor Deposition (Vacuum evaporation)Keyword: ReductionExamples of metal particles from chemical reduction in aqueous solutionsCTAB = cetyltrimethylammonium bromide (C16H31)(CH3)3NBr SDS = sodium dodecyl sulfate CH3(CH2)11OSO3NaExamples of metal particles from chemical reduction in non-aqueous solutionsHDAEx. Preparation of Au Ex. Preparation of Au nanoparticlesnanoparticles by a by a chemical reduction routechemical reduction routeAu3+SaltReducing agentCapping agentAu nanoparticles?Type of capping agent/stabilizers: e.g. CTAB?Concentration of the reactants?pH value of the solution?Duration of heat treatmentParameters Affecting Particle Growth/ Shape/ StructureParameters Affecting Particle Growth/ Shape/ StructureCTAB = cetyltrimethylammonium bromide (C16H31)(CH3)3NBr SDS = sodium dodecyl sulfate CH3(CH2)11OSO3NaAu Au nanoparticlesnanoparticles prepared in the presence of a prepared in the presence of a surfactant (CTAB)surfactant (CTAB)CTAB = cetyltrimethylammonium bromideJ. Phys. Chem. B. 2001, 105, 4065Templating method (A4)纳纳纳纳Reverse Micelles (Reverse Micelles (反胶束法反胶束法反胶束法反胶束法) )Water-in-oil dropletsWater pool w = H2O surfactantParticle size is controlled by the size of the water droplets in which synthesis takes placeRw= 3VaqH2Osurfactant = head polar group area Vaq= volume of waterConsider that: R = 3V/AV = volume , R = radius, A = surface area纳纳DendrimerDendrimer- -TemplatedTemplated NanoclusterNanocluster SynthesisSynthesisStructure of poly(amidoamine) dendrimer (PAMAM)Generation 2 PAMAM Dendrimer聚酰胺胺DendrimerDendrimer- -TemplatedTemplated NanoclusterNanocluster SynthesisSynthesisPAMAM 1 x 10-6mol+CuAc2 1 x 10-5molHydrazine 1 x 10-4molCu NanoclsutersFormation of Cu nanoclusters can be monitored by UV-vis spectrophotometryReaction is pH dependent: Presumably H+ions compete with Cu2+ions for the tertiary amine sitesPioneered in 1998, by Donald A. Tomalia (Michigan Molecular Institute Richard M. Crooks (TAMU)J. Am. Chem. Soc. 1998, 120, 4877 J. Am. Chem. Soc 1998, 120, 7355t1t2t3t4=21hDendrimerDendrimer- -TemplatedTemplated NanoclusterNanocluster SynthesisSynthesisBimetallic NanoparticleCore-Shell (by successive reduction)Mixed Alloy (by co-reduction)M1M1M2+M2+ ReductantM1M1+ ReductantM1+ M2+ ReductantToshima, N.; Yonezawa, T. New Journal of Chemistry 1998, 1179-1201.However, there are complicated situations:e.g. in Au-Pd system: a) Au followed by Pd ? monometallic Au + Pd; b) Pd followed by Au ? Pd-Au but not core-shell; c) co-reduction of Au and Pd ? AuPd (core-shell); d) large Pd core followed by Au ? PdAu (core-shell)Sacrificial hydrogen protective strategy for the preparation of bimetallic nanoparticles with a Pd shell-Pt core structure.Y. Wang, N. Toshima, J. Phys. Chem. B, 1997, 101, 5301.Synthesis of FePt alloy nanoparticleSynthesis of Silver NanowiresAgNO3+HO(CH2)2OHPVP:Ag=1:1160-180 oCCH2CH() NOnPtCl2(PVP)(聚乙烯基吡咯烷酮)AgNO3 +PtCl2Mechanism: Chemistry versus ArtPtCl2(CH2OH)2 Pt seedsAgNO3PVPPVP ?GrowthVarious Stages of Wire Growth10 min20 min40 min60 minSilver Nanowires with 40 nmXRDEx.) Au nanorods synthesized by seed-mediated chemical reductionAu nanorods synthesized by seed-mediated chemical reductionFrom 3.5-4 nm spherical seeds can grow out to 20-30 nm wide and up to 600 nm long nanorods, and no more.Structure-directing agentAu nanorods synthesized by seed-mediated chemical reduction: aspect ratio (L/w)Dependence of gold nanorod aspect ratio on the tail length of the cationic surfactant CnTAB (all alkyltrimethylammonium bromides).111111100110Two factors to determine L/w: 1) seed size; 2) tail length.Au nanorods synthesized by seed-mediated chemical reduction“Zipping model”: the formation of the bilayer of CnTAB (squiggles) on the nanorod (black rectangle) surface may assist nanorod formation as more gold ion (black dots) is introduced.The preferential binding is based on sterics - the Au atom spacing on the side faces is more comparable to the size of the CTA+headgroup than the close- packed 111 face of gold, which is at the ends of the nanorods. (CCH note: Could also be due to energy reason.)Planar density of atoms of FCC structure111: 0.907100: 0.785110: 0.555Au nanorods synthesized by seed-mediated chemical reductionMechanism of surfactant-directed metal nanorod growth: The single crystalline seed particles have facets that are differentially blocked by surfactant (or an initial halide layer that then electrostatically attracts the cationic surfactant). Subsequent addition of metal ions and weak reducing agent lead to metallic growth at the exposed