Diazanyl and SnO2 bi-activated g-C3N4 for enhanced photocatalytic CO2 reduction

Abstract

Considering the non-ideal performance of g-C₃N₄ on photocatalytic CO₂ reduction, diazanyl and SnO₂ bi-activated g-C₃N₄ (SnO₂/HyUCN) was synthesized by changing the surface amino group into diazanyl and in situ depositing SnO₂ nanoparticles via two-step redox reactions. The presence of SnO₂ and diazanyl was proved by X-ray photoelectron spectroscopy (XPS) and Ag⁺ oxidation methods, respectively. For comparison, de-diazanyl g-C₃N₄ (SnO₂/UCN) was also prepared. SnO₂/HyUCN showed the highest photocatalytic CO₂ reduction performance, and its CO generating rate reached 21.5 μmol g⁻¹ h⁻¹, which was 6 and 4.1 times that of pristine g-C₃N₄ (UCN) and SnO₂/UCN, respectively. CO₂ adsorption–desorption test and CO₂ adsorption energy comparison based on DFT calculations revealed the enhanced CO₂ adsorption of SnO₂/HyUCN. The time-resolved photoluminescence (PL), surface photovoltage spectrum (SPV) and electrochemical tests revealed the suppressed recombination of photogenerated electron–hole pairs for SnO₂/HyUCN. Furthermore, the photocatalytic mechanism was discussed at the molecular level by the in situ Fourier transform infrared (FT-IR) spectroscopy.