Improved photocatalytic production of hydrogen peroxide over graphitic carbon nitride doped with potassium salts

Hydrogen peroxide (H₂O₂) has long been recognized as an important green cleaning chemical. Due to its narrow bandgap and nitrogen-rich structure, graphitic carbon nitride (g-C₃N₅) is considered a promising photocatalyst for H₂O₂ generation. However, the limited visible light harvesting capacity and weak charge separation ability of bulk g-C₃N₅ limit its photocatalytic activity. Herein, to address the low photogenerated carrier mobility of g-C₃N₅, we successfully synthesized a series of K-ion-doped g-C₃N₅ (KCN) by co-calcination of 3-amino-1,2,4-triazole with potassium salt. The effects of different potassium salts (potassium oxalate-K₂C₂O₄, potassium nitrate-KNO₃, and potassium hydroxide-KOH) and different additions on the photocatalytic ability of g-C₃N₅ were compared and systematically analyzed. The results showed that the KCN sample synthesized with KOH as dopant exhibits the highest H₂O₂ yield up to 1546.7 µmol L^-1h^-1, seven times more than that of pure g-C₃N₅. The excellent photocatalytic H₂O₂ evolution efficiency is confirmed by DFT calculations to be mainly attributed to the rational design of g-C₃N₅, which produces more pronounced cyano groups under high-temperature calcination and alkaline environment while promoting the formation of N vacancies. This design effectively promotes the separation of electron-hole pairs and the optimization of carrier transport capacity, and as a result, KOH doping exhibits better photocatalytic performance. The current work provides a more favorable modification strategy for future solar energy conversion.