Synergistic effect in plasmonic Au/Ag alloy NPs co-coated TiO2 NWs toward visible-light enhanced CO2 photoreduction to fuels

Abstract

Plasmonic Au/Ag alloy NPs supported on TiO2 nanowires (TiO2 NWs) have been designed and synthesized through a facile hydrothermal and photo-deposition method. The samples were characterized by XRD, FE-SEM, TEM, N2-adsorption-desorption, XPS, Raman, UV–vis and PL spectroscopy. Bimetallic Au/Ag NPs were presented over the TiO2 NWs as an alloy, thus exhibited strong absorption of visible light due to the localized surface plasmon resonance (LSPR) excitation. The synergistic effect in plasmonic Au/Ag alloy NPs for selective photocatalytic CO2 reduction with H2 to CO and hydrocarbons under visible light irradiation was investigated. The present design of plasmonic Au/Ag NPs co-decorated TiO2 NWs leads to remarkably enhanced photoactivity of CO2 reduction to CO. The CO evolution rate as a main product over the Au-Ag alloy NPs coated TiO2 NWs was 1813 μmole-g-catal.−1 h−1 at selectivity 98%. This amount was approximately 1.72 time larger comparing to Au-NPs/TiO2 NWs, 1.84 fold more than the Ag-NPs/TiO2 NWs, 72.52 fold than the TiO2 NWs and 201 fold more than the amount of CO produced over the bare TiO2-NPs. This great enhancement can be attributed to synergistic effects in Au/Ag-NPs, enhanced visible light absorption due to Au-Ag alloy formation and improved charge separation in LSPR-excited TiO2 NWs. In addition, turnover productivity is introduced to investigate the effect of operating parameters on the performance of photocatalysts. The plasmonic reaction mechanism of Au-Ag NPs in conjunction with LSPR excitation and charge transport to understand the reaction pathway is described.