Construction of In-modified CN-based photocatalyst with In‒N chemical bond for efficient photoreduction of CO2

Abstract

Graphitic carbon nitride (g-C₃N₄), as an efficient photocatalytic material, has garnered significant attention in CO₂ reduction. However, its practical application is hindered by the high recombination rate of photogenerated charge carriers and insufficient product selectivity. In this study, an indium (In)-modified polymeric carbon nitride (In-PCN) catalyst was successfully synthesized via calcination of MIL-68(In) precursor with urea, aiming to systematically investigate its regulatory mechanism in photocatalytic CO₂ reduction. Experimental characterizations revealed that trace amounts of In were uniformly incorporated into the PCN framework through In‒N bonds, preserving its layered porous structure while significantly enhancing charge carrier separation efficiency and reducing interfacial charge transfer resistance. Under visible-light irradiation, the In-PCN exhibited a CO production rate of 19.37 μmol g⁻¹ h⁻¹ with 91.5% selectivity, representing a 2.2-fold enhancement compared to pristine PCN, and maintained stable activity over 16 h of cyclic operation. In situ Fourier transform infrared (in-FTIR) spectroscopy and density functional theory (DFT) calculations demonstrated that In sites stabilize the critical intermediate *COOH (ΔG decreased from +2.02 eV to +1.03 eV) and optimize electron transfer pathways, thereby significantly lowering the activation energy barrier for CO₂ reduction. Furthermore, the incorporation of In suppresses the generation of H₂ and increases the reduction efficiency of CO₂ by preventing the dissociation of H₂O molecules on the catalyst surface. Band structure analysis further revealed that In doping reconstructs the electronic distribution of PCN, enhancing surface charge density to promote CO₂ adsorption and selective reduction. This work provides theoretical insights and experimental validation for the rational design of metal-modified PCN catalysts with a chemical coordination environment, advancing their application in efficient and selective photocatalytic CO₂ conversion.