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.

Key words: Photolysis, Carbon dioxide reduction, Methane, Silver tungstate, Localized surface plasma resonance