Cu-doped g-CN catalyst with stable Cu and Cu for enhanced amoxicillin degradation by heterogeneous electro-Fenton process at neutral pH.

The development of new heterogeneous Cu-based solid catalysts for hydroxyl radical (∙OH) generation plays a crucial role in degradation of pollutants at neutral pH circumstance. In this work, a Cu-doped graphitic carbon nitride (g-CN) complex was synthesized in one-step pyrolysis process using copper chloride dihydrate and dicyandiamide as precursors. The results reveal that after Cu doping, the bulk structure of g-CN was destroyed with fragmentary morphology formation. Besides, Cu and Cu were successfully embedded in g-CN sheet. Moreover, amoxicillin (AMX) removal by heterogeneous electro-Fenton process was performed to evaluate the catalytic activity of the Cu-doped g-CN. 99.1% AMX removal efficiency was obtained after 60 min electrolysis under neutral pH condition when the current density was 12 mA cm and the catalyst dosage was 0.3 g L. Both Cu and Cu were stably retained in the Cu-doped g-CN catalyst and AMX removal efficiency reached 91.1%, even after 5 cycles, manifesting the remarkable stability of Cu-doped g-CN. Also, Cu-doped g-CN possessed excellent catalytic activities for AMX removal in various waterbodies. According to the catalytic mechanism analysis, the ∙OH was proved to be the primary reactive species for AMX removal in heterogeneous electro-Fenton process. Based on the identification of sixteen different intermediate products, the possible degradation pathways were proposed. This work provides a simple method to synthesize a Cu-based solid catalyst containing stable Cu and Cu  for degradation of pollutants in wastewater.