High charge transfer response of g-C3N4/Ag/AgCl/BiVO4 microstructure for the selective photocatalytic reduction of CO2 to CH4 under alkali activation

This study revealed the fabrication of a flower-shaped g-C3N4/Ag/AgCl/BiVO4 (CAB) microstructure and its application for the selective photocatalytic conversion of CO2 to CH4. The morphology of CAB revealed flower-shaped microstructures with size ranging from 3 to 5 mu m. The photoelectrochemically optimized CAB-1 microstructure, containing AgNO3 = 3 g L-1 and g-C3N4 = 0.025 g, showed the highest photocurrent density (17.4 mA cm(-2)) at a low applied potential which is several folds larger than bare g-C3N4 and BiVO4. After activating the CO2 adsorption on the CAB-1 surface with 0.2 M NaOH, the achieved rate of photocatalytic CH4 formation was similar to 205 mu mol h(-1) g(-1) with 100% selectivity. The mechanistic study, comprising Mott-Schottky measurements and isotope labeling experiment, revealed that the selective CO2 reduction takes place by concerted proton-coupled electron transfer mechanism. The Ag/AgCl acted as an electron-hole mediator after BiVO4 forms a Schottky barrier with Ag, and AgCl provided a polarization effect. (C) 2018 Elsevier Inc. All rights reserved.