UV light-induced oxygen doping in graphitic carbon nitride with suppressed deep trapping for enhancement in CO_(2) photoreduction activity

摘要

While photoreduction of CO_(2) to CH 4 is an effective means of producing value-added fuels,common pho-tocatalysts have poor activity and low selectivity in photocatalytic CO_(2)-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 CO_(2) adsorption energy and improves the CO_(2)-to-CH 4 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.