Positively charged nano-CuO/N-doped pomegranate peel biochar for efficient degradation of chloroquine phosphate and phosphorus recovery

Regulating the surface charge of biochar is crucial for its catalytic performance and adsorption capability. Here, Cu 2+ and melamine (Me) modified pomegranate peel powder (Cu-Me-PP) was prepared by coordination self-assembly method using waste pomegranate peel as the raw material. Then, nano-CuO and N-graphite doped biochar (CuO-N-PC) with positively charged surfaces were successfully prepared by pyrolysis of Cu-Me-PP and valence state regulation. The CuO-N-PC-300/ peroxymonosulfate (PMS) system could completely degrade the chloroquine phosphate (CQ) antibiotic within 30 min. Moreover, the effects of catalyst dosage, PMS dosage, solution pH, CQ concentration, and coexisting ions on the degradation efficiency of CQ were studied. It was found that CuO-N-PC-300 could not only catalyze the degradation of CQ but also remove 86.8 % of the phosphorus in the solution via electrostatic adsorption. Zeta potential analyses and molecular electrostatic potential calculations revealed that the electrostatic adsorption between the positively charged biochar and PO 4 3− were the key factors for the recovery of phosphorus. Electrochemical analyses, quenching experiments, electron paramagnetic resonance (EPR) tests, and DFT calculations were employed to explore the potential activation mechanism of PMS. Both interfacial electron transfer and the Cu 2+ /Cu + redox reaction were important pathways for activating PMS, generating a large number of •OH and 1 O 2 during the degradation of CQ. Finally, two degradation pathways of CQ were proposed based on LC-MS analysis, and the ecological toxicity was evaluated. This work provided an efficient method for the activation of PMS and the recovery of phosphorus by constructing positively charged nano-CuO sites on the surface of biochar.