Study On Preparation And Characterization Of PbO₂ Anode Based On Porous Titanium And Its Application In Electro-catalytic Degradation Of Musk Pollution In Aqueous Solution

In recent years,electrochemical oxidation technology as an advanced oxidation treatment for organic pollutant wastewater has attracted increasing attention due to its easily operation,low energy consumption and environmental compatibility.The research hotspot of the literatures mainly focuses on the study of excellent electrode materials,electrochemical degradation mechanism,the synergistic effect of electrochemical oxidation technology and other degradation technology.However,the development of electrodes with high electrochemical activity and stability is one of the key factors affecting the efficiency of electrochemical oxidation,mainly due to that the performance of the electrode material directly determines the electrochemical oxidation effect and the current energy consumption and other indicators.Due to its low cost,good conductivity,high oxygen over-potential and better electrochemical stability,Ti/Pb O₂ electrode has been widely used in electro-synthesis,electrolysis and more recently wastewater treatment process.In order to further improve the performance of Pb O₂ electrode,a great deal of effort is being spent on some new methods,such as the adding of new intermediate layer between the titanium substrate and oxidation layer,doping metal or non-metallic ions into the oxide layer,and using new preparation technologies.However,the above methods still has inevitable limitations,and little effort has been spent on the research of improvement for titanium substrate.This work focuses on the investigation the preparation and characterization of an improved Ti/SnO₂-Sb₂O₃/Pb O₂ based on porous titanium substrate compared with planar titanium substrate.The preparation parameters of porous Ti/SnO₂-Sb₂O₃/Pb O₂ electrode were systematically optimized and modified.In addition,this paper investigates the electrochemical degradation of Musk ketone（MK）in aqueous solution with porous Ti/ SnO₂-Sb₂O₃/Pb O₂ electrode.The main research contents and results were summarized as follows:The porous Ti/SnO₂-Sb₂O₃/Pb O₂ electrode was successfully prepared on a porous titanium substrate by thermal decomposition and electro-deposition method respectively.Characterization experiments including scanning electron microscopy（SEM）,X-ray diffraction（XRD）,linear sweep voltammograms（LSV）,cyclic voltammertry（CV）,electrochemical impedance spectroscopy（EIS）,accelerated life time test and degradation experiment of methylene blue trihydrate were performed to determine the effect of the different Ti substrate.Compared with planar Ti substrate,the results show that the porous Ti substrate decreased the grain size of lead dioxide.The surface structure of porous Ti V substrate and porous Ti/SnO₂-Sb₂O₃ can improve interlayer coating structure effectively and favors the formation of Pb O₂ during electro-deposition.The porous Ti/SnO₂-Sb₂O₃/Pb O₂ had higher oxygen evolution over-potential,higher active surface area and higher electrochemical activity.Besides,the life of porous Ti/ SnO₂-Sb₂O₃/Pb O₂（214 h）was 3.69 times as much as that of planar Ti/SnO₂-Sb₂O₃/Pb O₂ electrode（58 h）.Due to its highest over-potential and large active surface area,the porous Ti/SnO₂-Sb₂O₃/Pb O₂ electrode showed the best degradation performance in the simulated wastewater treatment.The degradation rate constant of Methylene blue trihydrate on the porous Ti substrate lead dioxide（0.03868 min-1）was 1.52 times that on planar Ti substrate lead dioxide（0.02542 min-1）.In summary,porous titanium substrates are importance for the performance improvement of electrodes.On the basis of the above experiment,the influence of preparation parameters on the surface structure and crystal characteristics of porous Pb O₂ electrode was systematically investigated by SEM,XRD and LSV in detail,including Sn/Sb,number of firing,electrodeposition time,current density and deposition temperature.The optimal preparation parameters of porous Ti/SnO₂-Sb₂O₃/Pb O₂ electrode were determined as follow: Sn/Sb（Molar ratio）9:1,sintered 12 times,electro-deposition time 30 min,electrodeposition temperature of 65 °C,current density of 30 m A cm-2.In addition,the novel porous Ti/SnO₂-Sb₂O₃/Pb O₂ prepared has high removal efficiency for MK and has the characteristics of reusability and safety and the degradation of MK fitted to the pseudo-first-order kinetics.In order to further study the characteristics of electrochemical degradation of MK,the main influencing factors,including electrolyte concentrations,current densities,initial p H and initial MK concentrations were evaluated.The degradation efficiency of 50 mg L-1 of MK achieved 99.13% after 120 min electrolysis under the optimal condition with a 0.06 mol L-1 Na2SO4 at a current density of 40 m A·cm-2 with the neutral solution environment of p H=7,respectively.The corresponding half-life time（t1/2）was 19.68 min.In order to further study the degradation pathway of MK,the intermediate products of MK was analyzed by GC-MS,the mainly six metabolites were detected including 2,2-Dimethylpropanoic acid,Malonamide,（S）-2-Hydroxypropanoic acid,acetic acid and formic acid were detected.The degradation mechanism was proposed by cyclic voltammograms tests and a possible degradation pathway including ring open,hydroxyl radical oxidation,hydrogen reduction reaction and mineralization was proposed based on the analysis of intermediates.In order to further improve the performance of porous Ti/ SnO₂-Sb₂O₃/Pb O₂ electrode,A novel Bi-CNT co-doped Pb O₂ electrode with porous titanium as substrate（porous Ti/ SnO₂-Sb₂O₃/Bi-CNT-Pb O₂）was successfully prepared by electrochemical deposition method.The microstructure and electrochemical properties of modified electrodes were characterized by scanning electron microscopy（SEM）,energy-dispersive spectroscopy（EDS）,X-ray diffraction（XRD）,linear sweep voltammetry（LSV）,cyclic voltammetry（CV）and electrochemical active surface area respectively.The results of EDS showed that CNT or Bi can be successfully doped into the Pb O₂ films.Bi and CNT codoped caused a visible change on the morphology characteristics of Pb O₂ films because of the formation of small crystal grain size,which can provide higher specific surface area.The crystalline grain diameters were calculated roughly which indicates that the Bi-CNTPb O₂ electrode has the smallest grain size according to Debye-Sherrer formula.The linear polarization curves show that porous Ti/SnO₂-Sb₂O₃/Bi-CNT-Pb O₂ exhibited the highest oxygen evolution over-potential of 1.87 V（vs.SCE）,which was higher than other modified electrodes,including Bi-Pb O₂（1.84 V）,CNT-Pb O₂（1.79 V）and Pb O₂（1.78 V）.At the same time,the voltammetric charge quantity indicated that the total electrochemical surface area of modified electrodes decreased in the order of Bi-CNT-Pb O₂,Bi-Pb O₂,CNTPb O₂ and pure Pb O₂,demonstrating that the porous Ti/SnO₂-Sb₂O₃/Bi-CNT-Pb O₂ had larger electrochemical active surface area.Lastly,GCE and SCE of modified electrodes were determined according to the degradation experiment of Methyl orange.Clearly,the Bi-CNT-Pb O₂ electrode had the highest current efficiency（62.3%）and the highest removal efficiency（84.8%）compared with the other electrodes.