UV light-induced oxygen doping in graphitic carbon nitride with suppressed deep trapping for enhancement in CO2 photoreduction activity

While photoreduction of CO2 to CH4 is an effective means of producing value-added fuels, common pho-tocatalysts have poor activity and low selectivity in photocatalytic CO2-reduction processes. Even though creating defects is an effective photocatalyst fabrication route to improve photocatalytic activity, there are some challenges with the facile photocatalyst synthesis method. In this work, an O element is in-troduced into a graphitic carbon nitride (CN) skeleton through a precursory ultraviolet light irradiation pretreatment to increase the visible light absorption and enhance the carrier density of this modified non-metal CN photocatalyst; the charge transfer dynamics thereof are also studied through electrochem-ical tests, photoluminescence spectroscopy, and nanosecond transient absorption. We verify that the op-timized sample exhibits lower charge recombination and a suppressed 84 ns electron-trapping lifetime, compared to the 103 ns electron-trapping lifetime of the CN counterpart, and thereby contributes to ro-bust detrapping and a fast transfer of active electrons. Through density functional theory calculations, we find that the improved light absorption and increased electron density are ascribed to O-element doping, which enhances the CO2 adsorption energy and improves the CO2-to-CH4 photoreduction activity; it be-comes 17 times higher than that of the bare CN, and the selectivity is 3.8 times higher than that of CN. Moreover, the optimized sample demonstrates excellent cyclic stability in a 24-hour cycle test. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.