Enhanced photocatalytic CO2 reduction via S atom-promoted carbon nitride complexed with imidazolium-based ionic liquids: Achieving superior selectivity

The utilization of carbon nitride (C 3 N 4 ) in photocatalytic CO 2 reduction faces obstacles due to significant charge recombination of photogenerated electron-hole pairs, limited light-harvesting capability, and a constrained surface area. In this study, S-C 3 N 4 /IL composites were synthesized by molecular docking of ionic liquids (IL) through S atoms in layered carbon nitride under environmental conditions by simple self-assembly technology to achieve efficient photocatalytic CO 2 reduction. Contrasted with pristine C 3 N 4 (1.1 μmol g -1 h −1 ), S-C 3 N 4 /IL demonstrated over a 300-fold increase in the rate of CO 2 reduction to CO (310 µmol g -1 h −1 ), achieving an approximate 100 % selectivity. Moreover, the possible reaction mechanism was proposed by in-situ infrared and DFT calculations. The remarkable photocatalytic efficacy of S-C 3 N 4 /IL can be ascribed to multiple factors: 1) augmented visible light absorption range and enhanced interfacial compatibility due to sulfur doping, fostering improved interaction between the amphiphilic ionic liquid and the hydrophobic C 3 N 4 ; 2) suppressed char + ge recombination, facilitating increased generation of abundant free radicals; 3) the Coulombic interaction between the IL’s anionic and cationic components with the formed electron-hole pairs, thereby impeding their recombination. Besides, ultraviolet photoelectron spectroscopy, fluorescence lifetime support these results. DFT calculation suggests S doping also plays a critical role in reducing free energy of *COOH formation. In addition, 13 C isotope experiment confirms the carbon source of CO from CO 2 . This proposition paves the way for enhancing the photocatalytic prowess of carbon nitride in CO 2 reduction.