Ionic liquid-assisted synthesis of P- and F-co-doped porous CN for boosting CO2 photoreduction

Abstract

Graphitic carbon nitride (CN), a promising photocatalyst for CO₂ reduction, suffers from inefficient light harvesting and sluggish charge separation dynamics, which severely restricts its application. Ionic liquids (ILs) have been used for the assisted preparation of photocatalysts, thus effectively altering their geometric and electronic properties. Herein, the 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF₆) IL was introduced as a modifier to successfully construct a P- and F-co-doped porous CN catalyst via simple calcination of the IL and urea without any organic solvents and templates. The optimized catalyst exhibited an enhanced photocatalytic activity for CO₂ reduction via gas–solid mode under visible light irradiation, achieving CO and CH₄ evolution rates of 39.9 and 2.63 μmol g⁻¹ h⁻¹ (CO selectivity of 94%), which were 7.8 and 4.8 times higher than those of pristine CN, respectively. PFCN also demonstrated excellent reusability and stability. Comprehensive characterization revealed that the strategy of doping of P and F atoms significantly enlarged the surface area, improved CO₂ adsorption, broadened visible-light harvesting, and accelerated charge transfer and separation efficiency. This work highlights the potential of ILs as multifunctional agents for designing high-performance doped CN photocatalysts.