Light Treatment of Silica-Coated Gold Nanorods to Have Enhanced Catalytic Performances and Structures

Abstract

The optical, structural, and catalytic properties of silica-coated gold nanorod structures treated by light have been investigated using the time-dependent and static UV-Vis absorption spectroscopy and electron microscopy. Chapter 1 describes the enhanced catalytic performances of light-treated mesoporous silica-coated gold nanorods via the reduction of 4-nitrophenol in the presence of sodium borohydride. The light treatment of mesoporous silica-coated gold nanorods prior to catalytic experiments improves the catalytic activity of the nanocatalyst extensively without deteriorating the encapsulation effect of mesoporous silica that enhances the stability and reusability of the nanocatalyst by preventing the aggregation and dissolution of gold nanorods. Irradiation increases the catalytic rate constant largely with reducing the activation energy and the induction time of the catalytic reaction substantially

surface atom restructuring induced by photothermal annealing during irradiation has rendered the metallic surface to adsorb reactants easily and to facilitate rapid electron relays from BH4- to 4-nitrophenol, lowering the kinetic barrier of the catalytic reaction considerably. Chapter 2 presents laser-induced welding of linearly assembled gold nanostructures to fabricate silica-coated gold nanowire structures using the nanosecond laser. Self-assembled chains of end-to-end linked gold nanorods can be fabricated in isopropanol solution in the absence of linker molecules. End-to-end assembled gold nanorods could be directly encapsulated with silica in mixture solution of IPA and aqueous colloids of gold nanorods. In order for the assembly to have electrical ohmic contact, the assemblies of gold nanorods are irradiated by nanosecond laser and welded to have nanoconjunction, producing gold nanowire structures. The thermalized photon energy of surface-plasmon excitation of coupled gold nanochains has induced gold nanorods to electrically weld together within silica shells, generating silica-coated gold nanowires.