Study On Potentiometric Regulation Strategies For Enhancing E-fenton Efficiency

With the development of the application of plastic products,the endocrine disruptors in the waste are more and more concerned with the potential adverse effect of the public health.In recent years,due to the low cost and high efficiency advantage of the EF technology in the field of wastewater treatment research,it has become an important research object in the AOPs technology.During the EF process,the content of the H₂O₂ produced by the electrocatalysis of the cathode generally determines the amount of the oxide species,·OH,required to degrade the organic contaminants,thus determining the efficiency of the EF operation,Therefore,setting the 2e^-ORR favorable potential for EF degradation has become a recognized method of operation.However,since?1?the concentration of dissolved oxygen in the electrolyte is low?2?2e^-ORR is the electrode process of the multi-electron participation,the potential for 2e^-ORR in the general case is much higher than the optimum FRR potential.A single higher potential is used to control the degradation process of EF,although a considerable H₂O₂electrocatalytic yield may be available,but this means of operation does not seem to give full play to the maximum degradation potential of EF since the FRR is suppressed at higher potential.However,if a lower constant potential operation EF is apply,while that cathode has a more suitable Fe²⁺condition,the EF efficiency will eventually be reduced due to an insufficient output of H₂O₂.Therefore,it is of great significance to solve the contradiction between 2e^-ORR and FRR electrode process,so as to release the potential of degradation efficiency.And finally,the purpose of improving the EF efficiency and reducing the energy consumption is achieved.?1?Preparation of nitrogen-doped biomass carbon-cathode of water hyacinth and application in DMPIn this study,a novel nitrogen-doped biochar oxygen reduction reaction cathode-water hyacinth carbon,was prepared by ZnCl₂ molten salt carbonization without additional nitrogen source,which displayed a high performance in EF process.The BET result shows that water hyacinth carbon achieved a much larger specific surface area(829 m²·g^-1)than non-melt salt carbonized one(323 m²·g^-1).Furthermore,characterization by XPS and EIS shows that both pyridinic-N?43.24%?and graphitic-N?56.75%?existed in water hyacinth carbon and Warburg constant was only 0.051.Because of a high H₂O₂ producing yield 1.7 mmol·L^-1 and corresponding current efficiency 81.2±2.5%in molten salt carbonized water hyacinth biochar,a high kinetic constant 0.318 min^-1 in DMP degradation was achieved,which was 4 times higher than graphite powder(0.076 min^-1).The TOC removal achieved 86.8%in 30 min and the corresponding energy consumption reached a low level 60.15 kW·h·kgTOC^-1.?2?Design of bi-potential-EF and its application in degradation of DMPDuring EF process,it is considered that the best degradation effect can be obtained when H₂O₂ generation yield is the highest.Thus,the optimal potential of H₂O₂generation is frequently applied in EF degradation.However,not only the 2e^-ORR but the FRR also affects EF efficiency.In this work,ACF was used as cathode and applied during EF process.The highest H₂O₂ generation yield was found at-0.5 V while the optimal potential for FRR was found at-0.1 V,which proved that the EF efficiency was suppressed when-0.5 V was applied as degradation potential,because under this potential,Fe²⁺could not effectively reduced back to Fe²⁺.The EF degradation efficiency was also restrained at-0.1 V due to the low H₂O₂ generation rate.A novel strategy Dual-potential-EF was presented in this work to resolve the contradiction between 2e^-ORR and FRR.By periodically applying the optimum potential of 2e^-ORR and FRR,the EF system can have a sufficient amount of H₂O₂ generation yield at the same time with a good Fe³⁺reduction capability.EPR detection indicated that more hydroxyl radicals were produced during the Dual-potential process compared with the one achieved by constant potential-0.5 V.An outstanding DMP mineralization rate of94.0%was achieved within 30 min and corresponding energy consumption was 0.762×10⁴ kJ·kgTOC^-1 while the constant potential method reached 73.4%at-0.5 V and corresponding energy consumption was 1.54×10⁴ kJ·kgTOC^-1.?3?Design of FRR-EF and its application in degradation of DMPIn general,the H₂O₂ generation can only be occurred at relative high overpotential because of the lack of dissolved oxygen in electrolyte and the multi-electron transfer step during electrode process.However,H2O2 generation potential is frequently applied in EF degradation process.In this work,the disadvantages of using high overpotential for EF degradation was found.The ORR and HER occurred at high overpotential would consume much proton,which cause alkalized on the surface of cathode.The Fe³⁺precipitated as FeOOH on cathode surface instead of being reduced back to Fe²⁺,leading to the loss of Fenton's reagent.Besides,the precipitation of Fe not only increased R_ct of cathode,but also weaken the mass transfer efficiency on electrode according to EIS test,which led to the reduction of electrode life.Thus,GDE device was applied to ensure a novel H₂O₂ generation rate at low potential.And more critically,the optimal potential for FRR rather than for 2e^-ORR was applied during EF degradation,which achieved a better degradation efficiency.At the same time,this strategy saved energy consumption,also prolonged the service life of cathode.