Efficient photocatalytic CO2 and Cr(VI) reduction on carbon spheres/g-C3N4 composites with enriched nitrogen vacancies

Abstract

In this study, carbon spheres (CS)/g-C₃N₄ composite materials were fabricated by a hydrothermal method, and the characterizations have confirmed the successful anchoring of CS onto the surface of g-C₃N₄, constructing enriched nitrogen vacancies during the synthesis process. The photocatalytic CO₂ reduction activity of g-C₃N₄ is enhanced by all of these advantageous factors. The significant enhancement can be attributed to the tight interfacial interaction between CS and g-C₃N₄, which endows with the photocatalyst a larger specific surface area, higher light utilization efficiency and stronger capability for photoinduced charges separation. Furthermore, the presence of nitrogen vacancies further accelerates the separation and migration efficiency of photogenerated charges, provides additional active sites to promote the adsorption and activation of CO₂ molecules, thereby effectively boosting the photocatalytic activity for CO₂ reduction. The CO₂ conversion rate on CS/g-C₃N₄ composite materials is higher than that on the reference g-C₃N₄. The apparent quantum yield (AQY) is also superior to that of the reference g-C₃N₄ under three different monochromatic light irradiations. The stability of the catalyst was verified through cycling experiments, indicating promising potential practical industrial application. The CO₂ reduction mechanism and transformation pathways were elucidated using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The photocatalytic reduction rate constant of Cr(VI) by 50CS/CN is 2.9 times higher than that by CN. This study introduces a facile approach for synthesizing g-C₃N₄-based photocatalytic materials, providing an interesting strategy to boost photocatalytic activity of g-C₃N₄ for photocatalytic CO₂ and Cr(VI) reduction.