The Study On The Hydrothermally-assisted Electrocatalytic Oxidation Of Phenol-containing Wastewater Under Mild Conditions

At present,water environment pollution caused by untreated wastewater or substandard wastewater discharged from different industries is pretty serious in our country.Industrial wastewaters often contain high concentrations of organic pollutants.Typical representatives of these organic pollutants are phenol and its derivatives.Phenol has an adverse effect on the human health and high toxicity to aquatic organisms.Therefore,it is of great necessity to develop efficient treatment technologies for phenol-containing wastewater.Hydrothermally-assisted electrocatalytic oxidation technology is the technology of electrochemical oxidation under hydrothermal conditions,it is a new technology by combining hydrothermal oxidation technology and electrocatalytic oxidation technology.The hydrothermal conditions can enhance the treatment efficiency of electrocatalytic oxidation technology by lowering the dielectric constant of electrolyte solutions and improving the mass transfer of organic pollutants.In addition,the foul of electrode can be well avoided and the yield of active radicals was enhanced in hydrothermal environment,which can lead to more effective degradation of pollutants.In this paper,the hydrothermal electrocatalytic oxidation system with Mn₂O₃/Graphite felt（GF）anode was developed to treat phenol-containing wastewater,and the reaction mechanism of the system was also discussed.Firstly,the suitable electrode material for the hydrothermal electrocatalytic oxidation system of phenol was screened.Fe-Co-Nickel doped nickel foam electrode,Ti/Mn O₂electrode and Mn₂O₃/GF electrode were prepared.The efficiencies of phenol removal in hydrothermal electrocatalytic oxidation systems with these three electrodes as anodes were compared.Besides,the shedding of catalyst active component from the anode surface was observed to evaluate the stability of the anode.The results showed that Mn₂O₃/GF anode had the best catalytic activity,and the catalyst on the electrode surface did not fall off obviously.The morphology,elemental valence,crystal structure and thermal stability of the electrode were characterized by SEM,XRD,XPS and TG.Secondly,the influence of reaction conditions on phenol removal was studied and optimized.The effects of reaction temperature,initial solution p H,current density and electrolyte concentration on the removal efficiency of phenol were investigated.The results exhibited that the highest phenol removal efficiency was observed when the reaction temperature was 60℃,initial solution p H was 5,current intensity was 120 m A and electrolyte solution was 50 mmol/L sodium sulfate solution.The removal efficiencies of phenol and TOC under optimized conditions were 91.7%and 72.3%,respectively,while the removal efficiencies of phenol and TOC in conventional electrocatalytic oxidation system（room temperature）were only56.9%and 46.5%.After five consecutive experiments,the removal efficiency of phenol was still more than 80%,indicating that Mn₂O₃/GF electrode had high stability.Finally,the reaction mechanism of the Mn₂O₃/GF hydrothermal electrocatalytic oxidation system was discussed.The results of radical quenching experiments and hydroxyl radical capture experiments showed that hydroxyl radical played a major role in the oxidation of phenol,while superoxide radical played a minor role.In addition,more hydroxyl radicals were produced under hydrothermal conditions,which was an important reason for more efficient degradation of phenol.On the basis of the degradation products of phenol detected by GC-MS,the possible degradation pathway of phenol was deduced.