Dioxygen atom co-doping g-C3N4 for boosted photoreduction activity of CO2 and mechanistic investigation

Abstract

Visible-light photocatalytic reduction of carbon dioxide with the help of photocatalysts has become an important means to mitigate the greenhouse effect. In this paper, co-doped graphitic carbon nitride (g-C₃N₄) with different doping concentrations of dioxygen atoms was prepared by thermal condensation, and dioxygen atom co-doped g-C₃N₄ (OICN-0.5) with the optimal doping concentration was successfully found, with CO and CH₄ yields and total electron consumption 8.36 and 7.96 times those of the raw semiconductor material. By doping with oxygen atoms, the bandgap width of carbon nitride changed from 2.77 eV to 2.66 eV, and its VB and CB also changed from +1.41 eV and −1.36 eV to +1.39 eV and −1.27 eV, respectively. Doping with oxygen atoms not only introduces new impurity energy levels and adjusts the energy band structure, but also further acts as a high-electronegativity center to regulate the space charge distribution and enhances the off-domain large π-bond conjugation system, thus facilitating electron transport between the g-C₃N₄ lamellae. The gas flow generated by ammonium oxalate pyrolysis during the synthesis process also caused the edges of the lamellar structure of g-C₃N₄ to curl to increase the interlamellar communication, reduce the carrier transport distance, and expose more active sites. Thus the final changes in internal properties and external structure result in a seven-fold increase in the efficiency of photocatalytic reduction of carbon dioxide.