The Enhanced Mechanism And Efficiency Of Photoelectrocatalytic System For 4-chlorophenol Degradation

Photoelectrocatalysis represents a new type of advanced oxidation technology,which can degrade most kinds of refractory organic contaminants.It has the advantages of simple operation,controllable reaction and no secondary pollution.Compared with the electrochemical oxidation,there is no special difference except for electrode materials that need to be driven by solar irradiation.Both of them are able to carry out wastewater treatment under mild controlled conditions.However,the advantages of anti-electrode fouling and low energy consumption in the process of photoelectrocatalysis make this strategy more promising in practical application.In this paper,electrode fouling was in situ characterization in the process of electrochemical oxidation,aiming at gaining insight into its mechanism and influencing factors.In addition,the photoelectrocatalytic systems composed of electrolytic cell and galvanic cell were used to water purification.The pollutant degradation could be enhanced by photoelectrode modification and peroxymonosulfate introduction as electron acceptor.Based on the above,the researches were as follows.Electrode fouling is a problem that commonly occurs during electro-oxidation water purification.This study focused on identifying the fouling behavior of Pt electrode associated with the formation of polymeric layer during electro-oxidation of phenol.The in situ electrochemical measurements and non-destructive observation of the electrode morphology were reported.The results demonstrated that the electrode fouling was highly dependent on thermodynamic process of electrode that was controlled by anode potential.At anode potential lower than 1.0 V vs SHE,the direct electro-oxidation caused the electrode fouling by the formation of polymeric film.The fouling layer decreased the electrochemically active surface area from 8.38 cm² to 1.57 cm²,indicated by the formation of polymeric film with thickness of 2.3?m,increase in mass growing at a rate of 3.26?g cm^-2 min^-1.In comparison,at anode potential higher than 2.7 V vs SHE,the anions could exert a major influence to the behavior of electrode fouling.The presence of chloride was shown to mitigate the fouling of electrode significantly through preventing the formation of polymeric film by active chlorine produced from anodic oxidation of chloride.Since chloride is the most abundant anionic species existing in both natural and engineered water system,this study not only offers a deep insight into the mechanism of electrode fouling,but also suggests strategies for anti-fouling in the presence of chloride in electro-oxidation process.To solve the electrode fouling during the electro-oxidaiton of phenlic pollutants under low potential,the photoelectrocatalysis(PEC)is proposed.This paper investigated the anti-electrode fouling effect and modified photoelectrode for wastewater treatment in PEC system.We created an efficient PEC system with oxygen-deficient WO_3-x nanoplate array film serving as photoanode through surface reduction method.WO_3-xphotoanode would be fouled in electrochemical oxidation(EO),while this phenomenon could be avoided in PEC.Oxygen vacancy had a slight impact to catalytic activity of photoanode,but exhibited an enhanced performance when anodic polarization was imposed.Both WO₃ and WO_3-x electrodes showed an insignificant removal of 4-chlorophenol(4-CP)and dechlorination under individual photocatalytic condition.When anodic polarization was applied at 1.2 V vs SHE,85.5%removal of 4-CP and 48.0%dechlorination efficiency could be obtained for WO_3-x photoanode,accounting for the values being 32.7%and 25.8%higher than that for WO₃ photoanode.The improved PEC performance of WO_3-xphotoanode under low potential bias should result from faster interfacial charge transfer,mitigation of electron-hole recombination,and production of higher amount of hydroxyl radical.Therefore,it can be more effective for the degradation of phenolic organic pollutants.In view of the fact that PEC system still needs external power source to drive the reaction,we have built a galvanic cell system driven by solar.This study reported the development of complete solar-driven dual-photoelectrode fuel cell(PFC)based on WO₃photoanode and Cu₂O photocathode with peroxymonosulfate(PMS)serving as cathodic electron acceptor.As indicated by photoelectrochemical measurements,the PMS was able to improve thermodynamic properties of photocathode,achieving an increased open circuit potential from 0.42 V to 0.65 V.Under simulated sunlight irradiation,the maximum power density of 0.12 m W cm^-2 could be obtained at current density of 0.34m A cm^-2,which was 8.57 times of that produced by PFC without PMS(0.014 m W cm^-2).Correspondingly,adding PMS(1.0 m M)increased overall removal efficiency of 4-CP from 39.8%to 96.8%,accounting for the first-order kinetic constant(k=0.056 min^-1)being 6.67 times of that in the absence of PMS(k=0.0084 min^-1).Radical quenching and ESR results suggested the contribution of free radicals(·OH and SO₄^·-)and non-radical pathway associated with direct activation of PMS by Cu₂O photocathode.FTIR analysis confirmed the strong non-radical interaction between Cu₂O photocathode and PMS,resulting in 4-CP removal via activation of PMS by surface complex on Cu₂O.The proof-in-concept complete solar-driven dual-photoelectrode fuel cell may offer an effective manner to realize water purification and power generation,making wastewater treatment more economical and more sustainable.