Synthesis of CuZnAl layered double hydroxide and degradation of oxytetracycline in water by activated peroxymonosulfate

YAN Xu; LI Xuguang; SONG Wen; ZHU Baocun

doi:10.13732/j.issn.1008-5548.2025.02.005

Abstract：Objective Layered double hydroxide(LDH)is a widely available and cost-effective material known for its unique structure,large specific surface area,controllable interlayer ion exchange,and stability.LDH is capable of activating peroxymonosulfate(PMS)in advanced oxidation processes,offering advantages such as high efficiency,abundant surface hydroxyl groups,and a range of active species.In this study,CuZnAl-LDH was synthesized using the co-precipitation method.The structure and prop-erties of CuZnAl-LDH were characterized using scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM),X-ray diffraction(XRD),and Fourier-transform infrared(FTIR)spectroscopy.The synthesis of CuZnAl-LDH was explored leveraging the favorable attributes of LDHs,such as robust catalytic activity,customizable struc-ture,simple synthesis process,excellent dispersibility,and potential application in advanced oxidation processes.Further-more,the effectiveness of activated PMS in degrading recalcitrant pollutants in water was investigated,highlighting the potential of CuZnAl-LDH as a catalyst in advanced oxidation applications. Methods The CuZnAl-LDH-x(x=1,2,…,5)was prepared by the co-precipitation method using CuCl2·2H2O,ZnCl2 and AlCl3·6H2O at various molar ratios of Cu,Zn,and Al elements.The obtained powder was characterized by SEM,FTIR and XRD.The degradation experiments in CuZnAl-LDH-PMS system were conducted using OTC as a typical antibiotic in water.The experi-mental conditions,including the molar ratio of Cu,Zn,and Al elements,catalyst and PMS dosage,solution pH,and environ-mental factors such as inorganic anions and humic acid,were optimized.The mechanisms were also investigated by a quenching experiment and electron paramagnetic resonance(EPR)spectroscopy,and high performance liquid chromatography-mass spec-trometry(HPLC-MS)was used to determine the degradation products of OTC in CuZnAl-LDH-1-PMS system.With distilled water as a control,tap water,Yellow River water,a city landscape lake water,and a campus landscape lake water were selected as water samples to conduct OTC degradation experiment. Results and Discussion The synthesized CuZnAl-LDH exhibited a dense hexagonal layered structure with XRD peaks,typical LDH structure.Among the CuZnAl-LDH-x-PMS systems,the composition with a molar ratio of Cu,Zn,and Al elements at 5∶1∶2 demonstrated the highest efficiency in degrading OTC.Under optimized conditions(initial pH of 6,CuZnAl-LDH-1 dos-age of 20 mg/L,and PMS concentration of 1 mmol/L),the removal ratio of 10 mg/L OTC reached 96.25％after 40 min.The CuZnAl-LDH-l-PMS catalytic system exhibited robust resistance to interference from environmental factors such as pH,inor-ganic anion and humic acid.The quenching experiment and EPR test showed that the degradation of OTC in CuZnAl-LDH-1-PMS system occurred via free radical pathway(·OH,SO4-·,·O2-)and non-free radical pathway(1O2),with·OH identified as the primary active radical species.A total of 10 intermediates were detected,leading to two degradation pathways for OTC.Compared with distilled water,the degradation rates of OTC in tap water,Yellow River water,a city landscape lake water,and a campus landscape lake water decreased slightly. Conclusion CuZnAl-LDH-x was synthesized via a simple co-precipitation method and characterized by its typical layered struc-ture,resembling hydrotalcite,and its properties.The CuZnAl-LDH-PMS system efficiently activates PMS to degrade OTC,achieving a maximum degradation rate.The CuZnAl-LDH-PMS catalytic system exhibited robust resistance to interference from factors like pH,inorganic anions(Cl-,HCO3-,NO3-,SO42-),and humic acid(HA),with minimal impact on OTC degradation rates.Bursting and EPR experiments revealed that OTC degradation by the CuZnAl-LDH-PMS system involved both free radical pathways(·OH,SO4-·,·O2-)and non-free radical pathways(1O2),with·OH identified as the primary active radical species.In actual water samples such as tap water,Yellow River water,a city and a campus landscape lake water,OTC degradation rates ranged from 74％to 95％,indicating the practical application potential of the CuZnAl-LDH-PMS catalytic system.