The Preparation Of SS/ZnO/PbO₂ Array Electrode Material And Its Electrocatalytic Degradation Of Phenol

Due to the strong toxicity and nonbiodegradability,effective degradation of phenol has become a major problem in the organic wastewater field.Electrocatalytic oxidation technology is gradually becoming the main force in the field due to the advantages of strong degradation ability,wide practical range and environmental protection.As the core of the electrocatalytic oxidation,the electrocatalytic activity of the electrode directly determines the efficiency of electrocatalytic oxidation.At present,the most widely used anode is the metal oxide coated electrode,and the Pb O₂electrode has been widely employed to the field of electrocatalysis due to its metal-like conductivity and stability.However,Pb O₂ electrodes also have many problems such as small electrochemical active surface area,low electrocatalytic activity and mechanical strength,and short service life.To overcome these problems and promote the industrialization of electrocatalytic oxidation technology,it is crucial to improve the performance of Pb O₂ electrodes.Based on the problems,a series of Pb O₂ electrodes（SS/Zn O/Pb O₂ electrodes）were constructed on a stainless steel-based Zn O film,and its electrocatalytic degradation performance of phenol and related basic theory were systematically studied.First,the vertical deposition technology is used to prepare polystyrene（PS）microsphere templates on the stainless steel;then put the PS templates in Zn（NO₃）₂solution to construct the SS/Zn O film by the cathodic reduction of nitrate ions and synergy of zinc ions;Finally,the SS/Zn O/Pb O₂ array electrodes were prepared by anodic electrodeposition on the SS/Zn O film.Combined with the scanning electron microscopy（SEM）,X-ray diffraction（XRD）and linear scanning voltammetry（LSV）and other characterization methods,the effects of various preparation conditions on the structure morphology and electrochemical performance of the Pb O₂ electrodes were studied by the single factor experiments,and the best preparation process was determined.The best preparation process of the SS/Zn O templates are as follows:the current density of 5m A·cm^-2,the deposition time of 15min,the Zn（NO₃）₂ solution of0.1mol·L^-1,the temperature of 65℃and the stirring speed of 200r·min^-1.The preparation process of the SS/Zn O/Pb O₂ electrodes are as follows:the current density of 5m A·cm^-2,the deposition time of 25min,the Pb（NO₃）₂ solution of 190g·L^-1,the temperature of 65℃and the stirring speed of 200r·min^-1.Using physical and electrochemical methods,the structural morphology,phase composition and electrocatalytic activity of the SS/Zn O/Pb O₂ electrodes and traditional Pb O₂ electrodes were mainly investigated.SEM results showed that the Pb O₂ active layer possesses a regular petal-like array structure,the size of single clustered Pb O₂ particles is approximately 0.5μm,and the clustered Pb O₂ is composed of numerous small-sized Pb O₂ grains.XRD results showed that the Zn O and the Pb O₂active layer are composed of Zn O andβ-Pb O₂,respectively.Electrochemical tests results showed that the SS/Zn O/Pb O₂ electrodes possess a larger electrochemical active surface area,and the active surface area(q _T*=0.0522C·cm^-2)is approximately2.6 times that of the traditional Pb O₂ electrodes(q _T*=0.0203C·cm^-2).Morevoer,The electrodes have a large exchange current density(i⁰=6.213×10^-5m A·cm^-2)and small oxygen evolution potential（1.480V）,oxygen evolution activation energy(E_a=31.334k J·mol^-1)and charge transfer resistance(R_ct=14.190Ω·cm²).The stability and service life of the SS/Zn O/Pb O₂ electrodes have been significantly improved.Cyclic voltammetry（CV）and other methods were employed to investigate the degradation behavior of phenol on the SS/Zn O/Pb O₂ electrode surface.Additionally,the factors affecting the removal rate were investigated to determine the best process parameters of phenol degrdation process.Degradation behavior studies showed that phenol degradation process is controlled by the adsorption process.The oxidation method of phenol on the Pb O₂ electrode surface is mainly the direct oxidation.The phenol degradation follows the quasi-first-order reaction kinetics.The reaction rate constant is significantly higher than that of the traditional Pb O₂ electrodes.The optimal degradation process of phenol determined by the single factor investigation is as follows:the concentration of phenol solution is 100mg·L^-1,the concentration of Na₂SO₄ solution is 0.1mol·L^-1,the degradation temperature is 25℃,and the p H of the degradation solution is 7.0 and the degradation current density is 30m A·cm^-2.To further improve the electrocatalytic activity and stability of the SS/Zn O/Pb O₂electrode,PEG and Co（II）were employed to modify the SS/Zn O/Pb O₂ electrode.The morphology and element composition of the SS/Zn O/PEG-Co（II）-Pb O₂ electrodes were studied in combination with SEM and X-ray electron spectroscopy（XPS）.LSV and EIS methods were used to characterize the electrocatalytic activity and stability of the composite electrode.Combined with the degradation of phenol,the adsorption of phenol on the electrodes and the control steps in the degradation process were studied.The half-life method was employed to determine the reaction order,the half-life and the reaction rate constant of phenol degradation.Finally,the high-performance liquid chromatography（HPLC）was used to investigate the possible degradation pathway of phenol on the electrode surface.SEM results showed that a large number of Pb O₂grains possessed spherical structure are constructed on the surface of the modified SS/Zn O/PEG-Co（II）-Pb O₂ electrode.The size of single Pb O₂ is approximately 0.4μm.The bonding between the grains is closer and the cracks are significantly reduced.XRD results showed that the composite electrode surface is still composed ofβ-Pb O₂and XPS results showed that the electrode surface contains four elements（Pb,O,C and Co）.Electrochemical tests results showed that the modified electrodes also show some obvious advantages in the oxygen evolution potential,the oxygen evolution activation energy,the charge transfer resistance and the exchange current density.Phenol(C₀=100mg·L^-1)degradation experiments results showed that the modified electrodes possess the shortest half-life(t_1/2=66.2min)and the largest reaction rate constant(k=0.00917min^-1)and degradation rate（RE=91.1%）.The reaction order is1.031.HPLC results indicated that the possible degradation pathway of phenol is as follows:under the attack of hydroxyl radical（?OH）,phenol is first decomposed into o-diphenol and p-diphenol,and further converted into benzoquinone.And then the ring of benzoquinone is broken and converted into small molecular acids（maleic acid and fumaric acid）,which are further converted into oxalic acid,and finally mineralized into CO₂ and H₂O.