Ag/Ag2WO4 plasmonic catalyst for photocatalytic reduction of CO2 under visible light

Abstract

The conversion of CO2 into organic compounds is a promising method to mitigate global warming and assist in sustaining energy resources. A series of plasmonic photocatalysts, comprised of Ag supported on Ag2WO4(Ag/Ag2WO4) with different crystalline phases, are fabricated by a facile ion-exchange method and subsequent reduction with hydrazine hydrate. The catalysts are characterized using X-ray diffraction (XRD) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), UV-Vis absorption spectroscopy, and Brunauer-Emmett-Teller analyses. Compared with Ag2WO4, the Ag/Ag2WO4 exhibits a markedly improved quantum yield (QY), energy returned on energy invested (EROEI), and turnover number (TON) for CO2 reduction to CH4 under visible-light irradiation. Among Ag/α-Ag2WO4, Ag/β-Ag2WO4, and Ag/γ-Ag2WO4 catalysts, the highest activity for CO2 photoreduction to CH4 is obtained for Ag/β-Ag2WO4 with an actual molar composition of 4% Ag and 96% Ag2WO4. Correspondingly the QY, EROEI, TON, and pseudo first-order rate constant are 0.145%, 0.067%, 9.61, and 1.96×10-6 min-1, respectively. Moreover, the plasmonic Ag/Ag2WO4 photocatalysts are stable after repeated reaction cycles under visible-light irradiation. It is proposed that the localized surface plasma resonance effect of surfacedeposited Ag contributed to the enhanced activities and stabilities of the Ag/Ag2WO4 photocatalysts.