Formation Of Oxidized Active Chlorine On Porous Electrode And Its Removal Of 2,4-Dichlorophenol

Electrochemical oxidation?EO?is a kind of wastewater treatment technology that can efficiently degrade refractory organics,has no secondary pollution,and is easy to control.It has attracted much attention in the field of industrial wastewater treatment.The high efficiency of electrochemical oxidation comes from the formation of oxidizing substances?for example,OH?.Since Cl^-is ubiquitous in various types of wastewater,it also generates chlorine oxide active substances during EO process such as Cl₂,HClO,ClO^-,etc.The electrochemical oxidation of pollutants occurs in the solution on the surface of the electrode.Due to the effect of spatial confinement,the microphysical field on the electrode surface?especially the porous electrode?tends to form a microenvironment,which is very different from the main body of the solution.Most studies to date have tended to focus on the bulk of the solution,without considering the impact of this microenvironment.Therefore,it is necessary to explore the similarities and differences between the electrode surface and the solution body and the impact on the degradation of pollutants.In this paper,porous sub-stoichiometric titanium oxide electrode is used as the anode to characterize the similarities and differences between the surface of the electrode and the main solution,and explore the generation of active chlorine species on the surface of the electrode and the main solution of the solution during the electrochemical oxidation process,and further apply it to 2,4-dichlorophenol?2,4-DCP?wastewater treatment,and explored the feasibility of the hydrogen produced by the recovery system in the reaction to compensate for energy consumption.The porous sub-stoichiometric titanium oxide anode has been characterized.Its surface resembles a sponge,the pore size is mostly large pores,and the impedance is low.The main crystal phase is Ti₄O₇ and there is a small amount of Ti₅O₉.Taking pH as an example,the difference in the properties of the anode surface and the main body of the solution was analyzed.When Na₂SO₄,NaClO₄,and NaCl were used as electrolytes,the anode surface was acidic?pH value is about 3?,and the distance between the anode and cathod was not obvious to the anode surface pH influences.Due to the influence of the electrochemical reaction rate,the pH of the anode surface stabilizes faster when the current density is high,and the current density has little effect on the stabilization time of the solution body pH.The higher the NaCl concentration in the electrolyte,the higher the pH value of the solution body,which is caused by the generation of NaOH in the electrolysis.The formation rules of total active chlorine species?represented by total residual chlorine?,Cl₂,HClO,and ClO^- on the anode surface and solution body were explored.On the anode surface,when the current density does not exceed 5 mA/cm²,after increasing the current density due to OH reacts withCl^-,and the production of HClO and residual chlorine increases rapidly.The increase in current density promotes the formation of Cl₂ at low current density.The linear relationship between the amount of Cl₂ and the initialCl^- concentration in the experiment proves that theCl^- concentration at high current density restricts the growth of Cl₂.The amount of HClO on the anode surface did not change significantly when theCl^-concentration was higher than 0.2 mol/L.On the one hand,it caused more Cl· to produce Cl₂.On the other hand,it also strengthened the side reaction between HClO and Cl·.In the main body of the solution,ClO^- is the form of most chlorine active substances?the ratio is higher than 99.9%?,the highest is 2483.9 ?mol/L,which is mainly caused by the diffusion and conversion of the anode HClO.The electrochemical behavior of 2,4-DCP on the surface of porous substoichiometric titanium oxide anode was explored.The direct oxidation reaction of 2,4-DCP was limited by both diffusion and adsorption,mainly by diffusion.The effects of current density andCl^-concentration on 2,4-DCP are comprehensively analyzed.Compared with the case withoutCl^-addition,the addition of 0.1mlo/L Cl^- makes the removal rate of 2,4-DCP at each current density Increase: 25.92% at 1 mA/cm²,7.61% and 6.07% at 5 and 10 mA/cm²,respectively,due to the degradation of 2,4-DCP by ClO^-.As theCl^-concentration increases,the removal rate of 2,4-DCP increases because of the increased ClO -concentration.A closed bipolar electrode is used to recover the hydrogen evolved during the oxidation of 2,4-DCP to compensate for energy consumption.The purity of the recovered hydrogen can reach 98%,which can make up for 20-30% of the electricity consumed by EO.