The Synergistic Mechanism And Performance Of Electro-Generated·OH And Interface Joule Heating Effect For Pollutants Degradation

The demand for treatment of refractory industrial wastewater is increasing,however,traditional treatment methods cannot satisfy the upgrading standards and reducing emissions.The electrochemical oxidation method employs“clean”electrons to drive organic pollutants degradation.It has the advantages of high efficiency,environmental friendliness and easy automation,which has attracted much attention in the field of decentralized water treatment.However,due to the extremely great reactivity and short half-life of electro-generated·OH,it only exists within sub-micron boundary layer near the anode.Therefore,under the action of microphysical fields at the anodic interface,·OH electro-formation,reactivity,mass transfer,and mediated-oxidation within the boundary layer become complicated.As such,aming to enhanced the efficiency of·OH-mediated indirect electrooxidation,the study focused on the effective identification of transient·OH and its role in indirect mediated-oxidation for pollutants degradation under the action of interfacial microphysical fields.The main research contents and results are as follows:Aiming at the current insufficient evidence for electron spin resonance(ESR)spectroscopy of electro-generated·OH,based on the principle of kinetic selectivity,an in-situ spin trapping method for effective electro-generated·OH identification was established.Combining electrochemical tests,density functional theory calculations and high-resolution time-of-flight mass spectrometry analysis,it was found that the rational reason why ESR-spectrum for·OH was rarely reported in the electro-oxidation system was as follows.DMPO and DMPO-OH adducts underwent side reactions of direct oxidation,dehydrogenation and polymerization within the highly oxidizing anodic boundary layer,resulting in losing spin-trapping ability for DMPO and accelerating the formation of interferencial signals(?G⁰=-805.72kJmol^-1;2.38 V vs SHE).By eliminating the possibility of false positive detection,and adjusting key spin-trapping parameters based on the kinetic selection theory,a reliable method based on in-situ spin trapping to identify electro-generated·OH was proposed with selectively inhibited generation kinetics of interferencial signal.Meanwhile,this study evaluated the dependence of·OH formation on the electrolysis time(?10 min),current densities(3.3-20.8mA cm^-2),anode potential(1.8-4 V vs SHE)and anode material.In response to the general assuming in the literature that electro-oxidation of pollutants occurs at constant room temperature,the anodic“Interfacial Joule Heating”(IJH)effect during electro-oxidation was discovered and verified by infrared thermal imaging,thermocouple measurement and numerical simulation.By characterizing the temporal and spatial distribution characteristics of the temperature field between the anodic interface and the bulk solution,it was found that the anodic interfacial temperature continued to rise to 70.2?at 10mAcm^-2,which is 2.1-fold of the bulk solution temperature.Consideing IJH effect,real-time correction was implemented for key parameters of mass transfer-reaction model,it was revealed theoretically and experimentally that with coupled temperature-electron-velocity-concentration fileds at anode interface,the IJH phenomenon enhanced the mass transfer(2.59 folds)and effective reaction kinetics(58%),expanded the thickness of the boundary layer(25%).To this end,IJH effect on indirect electrooxidation for pollutants degradation exihibited an activation energy-dependent characteristic.Compared with the constant interfacial temperature setted at room temperature,the percentage of activated molecules and electrooxidation kinetics of pollutants can be increased by 0.44-2.51 times and 1.57-2.28 times respectively.Based on the IJH effect,it was preliminarily verified that the low-temperature wastewater is locally heated within the sub-micron boundary layer to ensure feasibility of electro-oxidation pollutants efficiently.The results showed that compared with the significant inhibition of Fenton oxidation at low temperature,the interfacial temperature was increased from 8.1?to 38.7? at 20mAcm^-2with IJH effect,resulting in slight difference between the electro-oxidation kinetics of pollutants at room-temperature and low-temperature.The probe molecular compounds tests indicated that increasing the interfacial temperature helps to prompt charge transfer kinetics,electroactive area,reactivity and utilization of electro-generated·OH,which elucidated the positive correlation between interfacial temperature and the kinetics for direct oxidation via DET route and indirect·OH-mediated oxidation.These results offered the reasonable explainations for inhibited kinetics of direct oxidation and pollutants electooxidation(2mAcm^-2)at the low temperature.Combined with the results of electro-oxidation experiments and numerical simulation,it suggested that a kinetic compensation for the interfacial mass transfer-reaction process assisted by IJH effect even at low temperatures,where IJH effect could enhance the mass-transfer by 73%,promot·OH reactivity and the percentage of activated molecules by 44.8-172.77%,increase kinetic rate by 53.1-178.3% within the boundary layer rate.This offers compensation for the interfical mass transfer-reaction process.Additionally,it is also revealed that at low temperature,the enhancement of the electro-oxidation efficiency for pollutants depended on the activation energy with IJH effect.Thus,this research provided proof-of-concept to develop an IJH effect-based electrochemical manner for wastewater treatment at low-temperature,with strengthened the reactivity and utilization of crucial·OH within the anodic boundary layer.