Visible light-driven enhanced CO2 reduction by water over Cu modified S-doped g-C3N4

Abstract

We synthesized Cu modified S-doped g-C₃N₄ thin sheets using calcination followed by a wet-impregnation method. Herein, the photocatalytic performance of the as-synthesized sheets was systematically studied for gas-phase CO₂ reduction using water at room temperature under visible light illumination. The optimum photocatalyst, 2% Cu-SCN, illustrated the best production rates of CO and CH₄, approximately 3 and 7 times higher, respectively, than those of pristine g-C₃N₄. Stability testing also revealed the prolonged lifetime of 2% Cu-SCN. Characterization results confirmed that Cu existed in Cu⁰, Cu⁺, and Cu²⁺ oxidation states. Also, Cu was efficient at extending the absorption wavelength range and reducing recombination events, partially owing to surface plasmon resonance effects. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies suggested that COO⁻ and HCHO are the active intermediates for CO formation. Moreover, bicarbonate species had a higher absorbance value on the Cu-modified sheets, and could be an intermediate for CH₄ production. The findings revealed that Cu⁰/Cu⁺ played a pivotal role in increasing methane selectivity. The present work thus successfully demonstrated the synergistic use of both a metal and non-metal on a host photocatalyst to be a promising strategy for efficient CO₂ reduction.