Preparation Of Modified PbO₂ Electrocatalyst For Purification Of Organic Contaminants In Coal Gasification Wastewater

Due to its prestigious advantages of easy preparation,high oxygen evolution overpotential（OEP）,metal-like conductivity and stability,PbO₂ electrode has been widely employed for electrocatalytic degradation of organic pollutants.However,the pure PbO₂ electrode suffers from small electrochemically active surface area,low catalytic activity,low electrochemical stability and short service life,which limits its practical application.Therefore,in order to resolve such issues and promote the industrialization of electrochemical oxidation technology,it is of great significance to improve the electrocatalytic performance of the PbO₂ electrode.Based on the above problems,a series of modified PbO₂ electrodes were prepared on the titanium substrate and their electrocatalytic degradation performance towards organic pollutants as well as the potential degradation mechanism were systematically investigated.First,the Sn O₂-Sb₂O₃ intermediate layer was coated by thermal deposition method;then the PbO₂ active layer was obtained by electrodeposition method;finally the co-electrodeposition method was used to prepare Eu/PbO₂ and Eu/GO/PbO₂electrodes.Firstly,from the perspective of metal element doping,europium（Eu）,a rare earth metal,was selected to modify PbO₂ electrode,and the Eu/PbO₂ electrode was fabricated by co-electrodeposition for degradation of hydroquinone.It was shown that the doping of Eu induced the formation of smaller PbO₂particle size and more compact microstructure,which effectively improved the electrocatalytic activity and stability of Eu/PbO₂ electrode.Besides,the optimal degradation conditions of hydroquinone by single-factor investigation were obtained as followed:the initial concentration of hydroquinone was 50 mg L^-1,the concentration of Na₂SO₄ electrolyte was 0.1 mol L^-1,the p H value was 6.0,and the current density was 30 m A cm^-2.Combined with LC-MS test results,the possible degradation pathway of hydroquinone were elucidated as follows:under the attack of·OH,the para-hydroxyl groups first broke to form benzoquinone,and then the ring of benzoquinone was opened to generate small molecular fatty acids,which are further transformed into oxalic acid,and finally completely mineralized to CO₂ and H₂O.In order to further enhance the catalytic activity of Eu/PbO₂ electrode,graphene oxide（GO）was selected to modify it from the perspective of increasing the specific surface area,and it was used for the degradation of hydroquinone and the purification of coal gasification wastewater.As compared to pure PbO₂ electrode,the introduction of GO can provide more electrochemically active sites,which enables the Eu/GO/PbO₂electrode to have a higher oxygen evolution overpotential（2.64 V）,thus improving its electrocatalytic activity.The operating conditions are optimized and when GO concentration was 5 mg L^-1,the initial concentration of hydroquinone was 50 mg L^-1,the concentration of Na₂SO₄ electrolyte was 0.1 mol L^-1,the p H value was 7.0,and the current density was 30 m A cm^-2,the hydroquinone removal ratio was 96.55%.The results of mineralization current efficiency（MCE）and energy consumption（EC）evaluation showed that the CE values of pure PbO₂ electrode,GO/PbO₂ electrode,Eu/PbO₂ electrode and Eu/GO/PbO₂ electrode were 0.17,0.113,0.122 and 0.095(k Wh（g TOC）^-1),respectively,and in comparison,the Eu/GO/PbO₂ electrode still maintained the highest current efficiency（2.53%）after 180 min degradation.In-depth analysis of the degradation mechanism was carried out using LC-MS technique to track and identify the intermediates in the degradation process.More significantly,the simulated degradation experiments of coal gasification wastewater showed that the Eu/GO/PbO₂ electrode could achieve a TOC removal ratio of 41%and simultaneously maintain a superior electrochemical stability.