The efficient degradation of high concentration phenol by Nitrogen-doped perovskite La2CuO4 via catalytic wet air oxidation: Experimental study and DFT calculation

Herein, N-doped perovskite La2CuO4 (LCO) (N-LCO(M)) was fabricated by sol-gel rapid calcination method using melamine (M) as N source/ligand, and applied for the catalytic wet air oxidation (CWAO) to degrade highconcentration phenol-containing simulated wastewater. The experimental results exhibited that N-LCO(M) illustrated enhanced phenol degradation efficiency. Thereinto, 87.9% COD degradation efficiency was achieved in simulated wastewater containing 8000 mg/L phenol, while for undoped LCO prepared with citric acid (CA) as ligand (LCO(CA)) was only 43.8%. The systematic characterizations and density functional theory (DFT) calculations were utilized to verify the above results. The results revealed that N doping favored the formation of more oxygen vacancies (*) and facilitated the charge transfer between Cu and O. More oxygen vacancies (*) reinforced the ability of N-LCO(M) to adsorb O2 to form reactive oxygen species (O*), and meanwhile, the charge transfer between Cu and O was manifested as the redox cycle of the catalytic active metal Cu2+/Cu1+. The redox cycle also promoted the formation of O2  & BULL; and HO & BULL;, making the more exhaustive degradation of phenol. This successfully proved that N doping was core to improving the activity and stability of N-LCO(M). Moreover, a possible mechanism of phenol degradation was proposed based on the experimental results and DFT calculations. Eventually, the toxicity of the intermediate products was further evaluated by quantitative structure-activity relationship (QSAR) analysis, showing the significantly reduced toxicity of the intermediate products. Overall, the proposed CWAO technique is a green and promising wastewater treatment method.

Automated summary

In this study, N-doped perovskite La2CuO4 (N-LCO(M)) was synthesized using the sol-gel rapid calcination method with melamine as the N source/ligand, and applied for the catalytic wet air oxidation (CWAO) of high-concentration phenol-containing simulated wastewater. The results showed that N-LCO(M) exhibited enhanced phenol degradation efficiency, with a COD degradation efficiency of 87.9% achieved in simulated wastewater containing 8000 mg/L phenol, compared to only 43.8% for undoped LCO prepared with citric acid as the ligand (LCO(CA)). Systematic characterizations and density functional theory (DFT) calculations verified that N doping favored the formation of more oxygen vacancies and facilitated charge transfer, thus enhancing the adsorption of O2 and promoting the redox cycle of Cu2+/Cu1+, leading to the more exhaustive degradation of phenol. The proposed CWAO technique was proven to be a green and promising wastewater treatment method, with the toxicity of the intermediate products significantly reduced.