Synergizing interstitial K and substitutional O by dual-doping on carbon nitride for efficient CO2 photoreduction

Abstract

Photocatalytic CO2 reduction is a promising tactic to fix surplus CO2 and generate high-value products. Non-metallic graphitic carbon nitride (CN) is a robust and inexpensive photocatalyst for CO2 reduction, yet its efficiency remains limited by poor light absorption, sluggish charge kinetics, and low surface area. Here, we report K and O dual-doped CN (K/O-CN) synthesized by facile molten salt calcination for efficient CO2 photoreduction. Distinctive from CN, K/O-CN owned regular nanorod structure and introduced cyano terminal groups, due to the reconstruction of C-N bond by interstitial K doping and substitutional doping of O within CN matrix. K/O-CN displayed a CO production rate of 4.5 ± 0.2 μmol g−1h−1, which was 7.5 times as much as pristine CN and surpassed the performance of O-CN or K-CN. The enhanced CO2 reduction of K/O-CN was derived from its enlarged surface area and pore volume, magnified CO2 adsorption capacity, and narrowed band gap with better visible light absorption. The dual-doping of K and O accelerated the charge separation and reinforced reduction potential with a more negative conduction band. DFT calculation reveals that dual-doping impeded charge recombination by increasing spatial distance between photoinduced electrons and holes and caused a kinetic preference for CO desorption.