Investigation of hot electron behaviors in plasmonic AgAu@TiO2 nanostructures
Date of Issue2018
School of Materials Science and Engineering
Exploiting plasmonic metal nanostructure is of great importance to achieve highly efficient light-matter interactions. Anisotropic plasmonic metal nanoparticles display excellent optical characteristics from UV, throughout the visible light region to the NIR region of the solar spectrum, which allows high-efficiency conversion of solar energy into chemical energy. Under surface plasmon resonance (SPR) excitation, energetic hot carriers can be generated via dephasing of free electrons oscillation. However, efforts are still needed for better understanding the plasmonic induced hot electrons. In this thesis, several metal/semiconductor hybrid nanostructures based on AgAu core-shell nanoprisms and titanium dioxide were successfully synthesized, photocatalysis efficiencies based on hydrogen generation under visible light were evaluated aim to discover the generation and transfer process of plasmon generated hot electrons. To achieve this goal, the following works have been done. First, for the first time, a Janus nanostructure composed of AgAu nanoprism and titanium dioxide nanosphere was reported. The hybrid nanostructure experience enhanced photocatalytic activity for hydrogen evolution reaction (HER) compare with the conventional metal@semiconductor core-shell nanostructure. The three-phase interphase connecting AgAu nanoprisms, TiO2 nanosphere and environment close the gap between hot electron generation location and photocatalytic reaction site. Moreover, the interface experience largely enhanced electric field along the plasmonic AgAu nanoprisms edges. The site-selective Au nanoparticles photodeposition further confirmed the photocatalysis reaction site on the AgAu/TiO2 Janus nanostructure. Second, facet-selective gold nanoparticles deposition onto AgAu@TiO2 nanoprisms was achieved. Plasmonic metal nanostructures can enhance the local electric field around the nanoparticles under plasmon excitation, the distribution of electric field is closely related to the morphology of the anisotropic nanostructure. To evaluate the relationship between electric field enhancement and hot electron generation distribution, photodeposition of gold nanoparticles on AgAu@TiO2 nanoprisms were performed under irradiation of visible i Abstract light covering their localized surface plasmon resonance wavelength. Gold nanoparticles were preferentially loaded at the tips and started growing along the side of AgAu@TiO2 nanoprisms with the increasing amount of gold precursor. The deposition site of gold nanoparticles intuitionally represent the hot carriers’ distribution and corresponding the electric field enhancement of an anisotropic nanostructure. Third, silver nanoprisms were synthesized and coated by a thin layer of gold; the Ag@Au core-shell nanoprisms were employed as plasmonic templates. Titanium dioxide shell with different thickness was further coated onto the AgAu nanoprisms, the direct contact of TiO2 and AgAu nanoprisms improved the hot electron lifetime by plasmon-mediated electron transfer process. TiO2 shell works as an electron filter, and the photocatalytic efficiency decrease as TiO2 shell become thicker, which is caused by the increased travel distance of hot electrons. Photocatalytic efficiencies of the hybrid nanostructures under visible light can be enhanced by loading platinum nanoparticles as co-catalyst to reduce the charge carrier recombination. However the photocatalytic efficiency increase then decrease with increase TiO2 shell thickness, the close gap between plasmonic AgAu core and Pt nanoparticles is conducive to hot electron transfer, but the plasmon coupling between AgAu nanoprisms and Pt nanoparticles lead to damping of local E-field and further affect the hot carrier generation and recombination.
DRNTU::Engineering::Computer science and engineering