Photo-induced reduction of CO2 to CO with hydrogen over plasmonic Ag-NPs/TiO2 NWs core/shell hetero-junction under UV and visible light

Abstract

Graphical abstract: Ag-NPs-promoted TiO2 nanowires (TiO2 NWs) core/shell hetero-junction with plasmonic properties for selective CO production in photo-induced CO2-hydrogen system has been investigated. Ag-NPs were photo-deposited over the TiO2 NWs and characterized by XRD, TEM, N2-adsorption-desorption, XPS, UV-vis and PL spectroscopy. Ag-NPs in metal-state were successfully coated on the TiO2 NWs surface, producing core-shell hetero-junction. Ag-NPs coated over TiO2 NWs exhibited strong absorption of visible light due to localized surface plasmon resonance (LSPR) excitation, trapped electrons and hindered charges recombination rate. The synergistic effect of Ag-NPs coated over TiO2 NWs for CO2 conversion was evaluated in a gas-phase system under UV and visible light irradiation. The plasmonic Ag-NPs/TiO2 NWs demonstrated excellent photoactivity in the reduction of CO2 into CO, CH4 and CH3OH under visible light irradiation. The results show that 3wt.% Ag-NPs-loaded TiO2 NWs was found to be the most active, giving the highest CO evolution of 983μmole-g-catal.−1h−1 at selectivity 98%. This amount of CO produced was 23 times more than the TiO2 NWs and 109 times larger than the yield of CO produced over the pure TiO2. More importantly, the quantum yield was substantially enhanced for CO evolution. The LSPR excitation and synergic effect of Ag-NPs which can effectively accelerate the charge separation was proposed to be responsible for the enhancement of photocatalytic activity. The photo-stability of Ag-NPs/TiO2 NWs evidenced in cyclic runs for selective CO production under visible light, yet photoactivity declined over the irradiation time under UV-light. The reaction mechanism to describe the reaction pathways is also presented.