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

Rather, Rayees Ahmad, Khan, Musharib, Lo, Irene M.C.
Journal of catalysis 2018 v.366 pp. 28-36
adsorption, carbon dioxide, carbon nitride, electric current, electron transfer, isotope labeling, methane, methane production, microstructure, photocatalysis, silver, silver chloride, silver nitrate, sodium hydroxide
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 µm. 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 ∼205 µmol 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.