Preparation Of PbO₂ Anode Material Modified By Halloysite Nanotubes And Study On Degradation Of Methylene Blu

In the process of treating organic wastewater with electrocatalytic oxidation technology,electrode materials,as the core of the treatment method,are mainly used to transfer current and catalyze the degradation of pollutants.Therefore,the performance of anode materials directly affects the degradation efficiency of pollutants.PbO₂electrode is considered as an excellent metal oxide anode for electrocatalytic oxidation because of its high oxygen evolution overpotential,low cost and good chemical stability.However,it has defects such as small catalytically active surface area,coarse grains,and short service life.Therefore,the development of modified PbO₂ anodes with good electrocatalytic activity as well as stability has become a research hotspot.In this paper,chitosan（CTS）modified Halloysite nanotubes（HNTs）were used for doping modification of electrodeposited PbO₂ electrode,and HNTs-CTS-PbO₂composite anode material was prepared in nitrate system.The surface properties of doped nanoparticles and the optimum preparation conditions of composite anode materials were studied.The physical and electrochemical properties of traditional PbO₂electrode,HNTs-PbO₂ electrode and HNTs-CTS-PbO₂ electrode were analyzed.The composite electrode was used for the degradation of methylene blue（MB）dye wastewater,the comprehensive performance of the degradation of MB was investigated,and the possible degradation mechanism of MB on the composite electrode was discussed.The main work completed and conclusions obtained are as follows:（1）Scanning Electron Microscope（SEM）showed that HNTs had tubular structure before and after modification,and FTIR Spectrometer（FT-IR）results showed that CTS were successfully modified on HNTs.Compared with the unmodified HNTs,the modified HNTs-CTS showed a smaller particle size（0.71μm）and a larger Zeta potential（11.86 m V）in the plating solution,showing better dispersion.The electrode morphology was investigated by SEM,the deposition amount of nanoparticles was investigated by Energy Dispersive X-ray Spectrometers（EDS）and the oxygen evolution activity of the electrode was analyzed by Linear Sweep Voltammetry（LSV）.Finally,the preparation conditions of HNTs-CTS-PbO₂ electrode were determined as follows:The dosage of HNTs-CTS was 4 g·L^-1,the deposition current density was 10m A·cm^-2,the concentration of sodium dodecyl benzene sulfonate（SDBS）was 0.06g·L^-1,the deposition temperature was 40℃,and the deposition time was 50min.The composite electrode prepared under these conditions has more uniform and compact surface morphology,more deposition amount of nanoparticles and better ability to inhibit oxygen precipitation.（2）SEM shows that PbO₂,HNTs-PbO₂ and HNTs-CTS-PbO₂ electrodes are typical pyramid structures,and HNTs-PbO₂ and HNTs-CTS-PbO₂ electrodes have finer apparent grain size than traditional PbO₂electrodes.X-ray diffraction（XRD）results show that the surface of the coating is composed ofβ-PbO₂,and the minimum grain size（22.71 nm）can be obtained by Scherrer’s formula,indicating that the modified electrode has more catalytic active sites.EDS and X-ray Photoelectron Spectroscopy（XPS）showed that HNTs-CTS were successfully deposited into the composite electrode coating.Electrochemical characterization showed that HNTs-CTS-PbO₂electrode had higher oxygen evolution overpotential（1.643 V）,larger electrochemical reactive surface area(2.51 C·cm^-2)and lower charge transfer resistance（0.3819Ω·cm²）.The accelerated life test results show that the HNTs-CTS-PbO₂ electrode has the longest electrolytic life（47h）,indicating that the electrocatalytic activity and stability of the modified composite electrode are improved.The analysis of electrode failure mechanism shows that the corrosion of electrolyte itself and the impact of reactive oxygen species gradually destroy the electrode coating and eventually lead to electrode failure.（3）HNTs-CTS-PbO₂ electrode was used for degradation of MB dye wastewater.The optimal degradation parameters of MB on HNTs-CTS-PbO₂ electrode were determined by single factor experiment:The initial concentration of degradation solution was 100 mg·L^-1,the applied current density was 30 m A·cm^-2,the supporting electrolyte anhydrous Na₂SO₄ concentration was 0.25 mol·L^-1,the initial p H value was7,and the degradation temperature was 25℃.The degradation of MB on HNTs-CTS-PbO₂ electrode follows the quasi-first-order reaction kinetics,and is mainly caused by indirect oxidative degradation caused by hydroxyl radicals.The electrochemical catalytic oxidation capacity of traditional PbO₂,HNTs-PbO₂ and HNTs-CTS-PbO₂ electrodes for MB was evaluated.The results showed that HNTs-CTS-PbO₂ electrode had high decolorization rate（99.52%）,high TOC removal rate（65.67%）and high MCE（28.46%）for MB,and the modified composite anode also had excellent degradation stability during the degradation process.In addition,the hydroxyl radical（·OH）generation capacity of different anode materials was analyzed,and the results showed that HNTs-CTS-PbO₂ electrode had stronger ability to generate active substances.The degradation mechanism of MB on HNTs-CTS-PbO₂ electrode shows that MB molecules are mainly under the action of reactive oxide hydroxyl radicals,firstly,the C-N bond is broken,making MB demethylation or aromatic ring cleavage,and then the hydroxyl radicals attack the unstable double bonds in aromatic heterocycles,generating amines,sulfonic acids and phenolic compounds containing single aromatic rings,and finally mineralized into CO₂,H₂O and other inorganic small molecules.