Bandgap engineered g-C₃N₄ and its graphene composites for stable photoreduction of CO₂ to methanol

Carbon nitride (g-C₃N₄) is a two-dimensional material with several advantages over other photocatalysts, such as metal-free, biocompatible, chemically and thermally stable, to name a few. However, it usually suffers from low charge carrier mobility, high recombination rate, low electrical conductivity, and, more importantly, low absorption in the visible range. To address the multiple shortcomings, a simple and cost-effective copolymerization strategy was developed to synthesize g-C₃N₄ by selecting the appropriate precursors and optimizing the synthesis parameters, which resulted in lowering the bandgap from 2.80 eV to as narrow as 2.40 eV. To further improve the charge separation and conductivity, g-C₃N₄ and reduced graphene oxide (rGO) based composites were synthesized. The obtained composite catalysts were studied for photocatalytic CO₂ reduction. It is important to note that g-C₃N₄/rGO composites resulted in the selective photoreduction of CO₂ to methanol as the only liquid product with evolution rates of ∼114 μmol g⁻¹ h⁻¹ along with H₂ (68 μmol g⁻¹ h⁻¹) under scavenger free conditions and exhibited robust stability.