Preparation Of Manganese Dioxide-based Nanocomposite And Its Catalytic Degradation Performance Of Sulfadiazine

In recent years,Li-ion batteries have been widely used in electric vehicles and other electronic devices due to their light weight,good performance and high safety,but a large number of spent Li-ion batteries need to be properly disposed.In addition,environmental pollution caused by the massive use and discharge of antibiotics has attracted people's attention.Sulfadiazine has been detected in the outlet water of sewage plants,that shows it is difficult to completely degrade sulfadiazine by the traditional process.Advanced oxidation processes can effectively remove antibiotics,but it also has some shortcomings,such as small pH range,high iron leaching amount and catalyst consumption.Therefore,it is particularly important to develop a material with high catalytic activity and good stability.In this work,the cathode material of spent Li-ion battery was used as the precursor to synthesize MnO₂ of different crystalline forms and its zero-valent iron composite material(MnO₂-Fe(0))by acid leaching and hydrothermal method,respectively.MnO₂ in different crystalline forms and MnO₂-Fe(0)were explored to activated separately peroxymonosulfate(PMS)and H₂O₂ to degrade sulfadiazine(SDZ)in water,and the characteristics and mechanism of each method were analyzed.The specific content and discussion were as follows:(1)MnO₂ was recovered from the spent Li-ion batteries by acid leaching and hydrothermal methods,and the catalyst was characterized by XRD,SEM,XPS and BET techniques.In addition,the activation effect of catalysts prepared by two methods was compared,and the results reflected that MnO₂ prepared by hydrothermal method had better catalytic activity.Under the optimal conditions that SDZ concentration was 10mg/L,pH was 6,the catalyst dosage was 0.2 g/L,and PMS was 1 m M,the removal rate of SDZ was 95.2%within 120 min.The single-factor degradation processes were analyzed to conform to the pseudo first-order kinetic model.The catalyst was recycled for 5 times,and the result showed that the activity of catalyst was relatively stable.The free radical trapping experiment and electron paramagnetic resonance spectrometer(EPR)showed that sulfate radical was the main active free radical in the system,and hydroxyl radical also contributed a small part.(2)MnO₂-Fe(0)was synthesized by a simple hydrothermal method,and a series of characterization methods were used to study the properties of the materials,such as TEM,PL,DRS,EIS and CV.The effects of pH value,H₂O₂ concentration,SDZ concentration,the iron content and addition of catalyst on degrading SDZ by photo-Fenton reaction were studied.The results showed that SDZ concentration was significantly reduced under the combined action of light and H₂O₂,and the removal rate reached 98.6%within 60 min.The different single-factor experiments were followed the pseudo first-order kinetic model.The stability and mineralization rate of the composite material were also studied.The intermediates of SDZ degradation were analyzed by HPLC-MS,and four degradation pathways were preliminarily simulated.The results showed that the detachment of functional groups was the main degradation mode of SDZ.Using radical trapping experiments and EPR characterization,it was analyzed that hydroxyl radical played a major role in this system.Loading zero-valent iron made MnO₂ had more active sites and better catalytic performance.