Improving visible light-driven CO₂ conversion to high calorific fuels over sustainable highly crystalline and holey sulphur doped graphitic carbon nitrides

The effectiveness of CO₂ reduction through g-C₃N₄ (CN) is considerably hindered by poor visible light absorption and the high rate of recombination of electron-hole (e⁻/h⁺) pairs. An effective method for increasing CO₂ photoreduction efficiency is to incorporate non-metal components into the CN to modify its electronic properties and enhance its performance. This research presents the findings of our inquiry into sulfur-doped graphitic carbon nitrides (S–CN) for CO₂ reduction through visible light. The XPS study reveals that the substitution of nitrogen atoms in the heptazine ring by sulfur (S) doping significantly influences the electronic configuration of CN, while the UV–visible absorbance spectra reveals that the CN band gap value 2.64 eV has reduced to 2.50 eV after S doping. Therefore, S–CN exhibits exceptional visible-light absorption, separation and migration of photoexcited e⁻/h⁺, corroborated by photoluminescence and transient photocurrent response experiments. Besides, S–CN demonstrated remarkable CO₂ reduction capabilities without any cocatalyst or sacrificial agent, achieving CO/CH₄ formation rates of 25/3 μmolg⁻¹h⁻¹, outperforming traditional CN. Our research highlights the relevance of impeding the e⁻/h⁺ recombination process to boost solar energy conversion output, suggesting potential for productive solar fuel generation using g-C₃N₄.