Efficacy And Mechanism Of CuO_x/γ-Al₂O₃-Catalyzed Heterogeneous Fenton Degradation Of Cephalexin In Water

As antibiotics are more and more widely used in China,the water pollution issues caused by them are becoming more and more serious.Loaded heterogeneous Fenton is one of the most researched advanced oxidation techniques for the efficient removal of antibiotics from water.In this study,Cu O_x/γ-Al₂O₃heterogeneous catalysts were prepared by evaporation-induced self-assembly.The performance of the heterogeneous catalysts for the degradation of cephalexin and the stability of the catalysts were investigated.The adsorption of cephalexin on the catalyst surface was studied by DFT calculations,and the catalytic degradation mechanism of cephalexin was investigated by experimental and DFT calculations.The results of the study were obtained as follows.1.Cu O_x/γ-Al₂O₃heterogeneous catalysts were prepared by evaporation-induced self-assembly and were able to effectively degrade cephalexin.The prepared catalysts were characterized by XRD,SEM and BET,which showed that the prepared catalysts had a good mesoporous structure and the Cu oxides were uniformly dispersed on the surface of theγ-Al₂O₃material,as well as the system catalysts were obtained by optimizing the usage conditions.When the catalyst dosage was 0.2 g·L^-1and the concentration of H₂O₂was 0.02 mol·L^-1,the catalyst was able to achieve 97.04%degradation of the initial concentration at 20 mg·L^-1cephalexin within 30 min.,the degradation rate remained at 83%after 5 repeated uses,indicating the material had good stability.2.The adsorption configurations of cephalexin on the surfaces of the three metal oxides were calculated by the DFT method,and the corresponding electron density maps and Mulliken charge layouts were calculated.On the surface ofγ-Al₂O₃（110）,the most stable adsorption configuration was found when O₁₈of cephalexin adsorbed with the Al atoms on the surface ofγ-Al₂O₃and H₃₇adsorbed with the O atoms on the surface of the material.In contrast,the adsorption of cephalosporin on both Cu O and Cu₂O crystal surfaces was hydrogen-bonded adsorption with relatively weak stability,indicating that the Cu O_x/γ-Al₂O₃material adsorbs cephalosporin mainly through the larger surface area ofγ-Al₂O₃.3.The mechanism of catalyst degradation of cephalexin was investigated experimentally and computationally.Firstly,it was demonstrated by ESR analysis,quenching experiments and XPS analysis that the catalyst degraded the contaminants mainly through the·OH radicals generated by Cu⁺and Cu²⁺activated H₂O₂.The reaction energy barrier calculation for Cu⁺and Cu²⁺activated H₂O₂demonstrated that Cu⁺had a lower reaction energy barrier than Cu²⁺.Afterwards,the degradation pathway of the contaminant was verified by LC-MS,and a major degradation pathway was derived from the intensity of the obtained liquid mass peaks.By calculating the simplified Fukui function of cephalexin,the most reactive site of the contaminant was C₁₂.It was easily attacked by hydroxyl radicals first,which matched the obtained degradation pathway.After that,afterwards the energy barrier of the major reaction pathway was calculated by transition state search Calculations were then performed.