| Treatment of Nitrogenous Heteraromatic Compounds(NHCs)which exhibit biological toxicity and biorefractory property using traditional electrochemical oxidation technology still has shortcomings,such as its low catalytic efficiency and low current efficiency caused by mass transfer limitation.In this study,we prepared three-dimensional macroporous Pb O2 and Ru O2(3D-Pb O2 and 3D-Ru O2)electrodes to improve the catalytic efficiency,and then compared the oxidation performance of these two electrodes using flutriafol as target pollutant;established a reactive electrochemical membrane system by applying the 3D-Pb O2 as anode in an electrochemical filtration reactor to improve the mass transfer in the electrochemical reaction;finally,deep insight into the kinetics and mechanisms of electrochemical oxidation of flutriafol using Pb O2 electrode was obtained by quantum chemistry calculations combined with experimental methods.The main idea could be interpreted as following:Polystyrene sphere(PS)was used as hard template to prepare Pb O2 and Ru O2 active layer on a porous Ti substrate by templated electro-deposition method and the obtained active layer possess a complete 3D porous structure.FESEM results show that Pb O2 and Ru O2 active layer comprises multilayer ordered,closed-packed,interconnected spherical cavities.Nitrogen adsorption/desorption analysis was used to investigate the characteristic of porous structure of the Pb O2 and Ru O2 active layer,and the result showed that introduction of PS templates can significantly improve the BET surface area and amount of micro-and mesopores in the active layer.LSV,CV and EIS was used to study the electrochemical performance of Pb O2 and Ru O2electrodes,and the result showed that electroactive sites and electrochemical porosity of Pb O2and Ru O2 electrode were significantly enhanced compared with electrodes prepared by traditional methods.Then,we compared the degradation performance of Pb O2 and Ru O2electrodes using NHCs exemplified by flutriafol.Under the same experimental conditions,the flutriafol removal on Pb O2 electrode was 33.1%,which is 1.97 times higher than that on Ru O2electrode,indicating that Pb O2 electrode is more suitable for treatment of flutriafol wastewater.In order to amplify the advantage of the structure of 3D-Pb O2 electrode and enhance the removal efficiency of flutriafol,we designed an electrochemical filtration reactor to improve the mass transfer and established an electrochemical membrane system using Pb O2 as anode.CA result showed that the limited current density of 3D-Pb O2 membrane system was 4.12m A·cm-2,which is 2.1 times higher than that of traditional electrochemical system,indicating that electrochemical filtration reactor can significantly enhance the mass transfer efficiency in electrochemical reaction.The mechanism of enhanced removal of flutriafol by 3D-Pb O2membrane system was deeply investigated,and the result showed that high electrochemical effective surface area of 3D-Pb O2 anode can increase·OH production.On the other hand,the novel porous structure of 3D-Pb O2 can shorten the diffusion path of contaminants to electrode surface and thus enhance the mass transfer.The thickness of diffusion layer on the electrode surface is reduced from 360?m to less than 500 nm,significantly improving the utilization of·OH,and then effectively enhancing flutriafol removal and current efficiency.Effects of key operating parameters,such as current density,flow rate on flutriafol removal in 3D-Pb O2membrane system were systematically studied.The result showed that under the optimal conditions,flutriafol removal efficiency on 3D-Pb O2 membrane system was 73.8%.Compared with traditional system,the removal efficiency was increased by 3.1 times,and the current efficiency was improved by 4.9 times.Electrochemical technology was usually used in pre-treatment stage to decrease toxicity and increase biodegradability of wastewater,but electrochemical degradation of flutriafol may generate intermediates that are more toxic.Because it is hard to separate and analyze intermediates forming during the electrochemical oxidation using experimental methods,in this study,quantum chemistry calculations were used to analyze the reaction energy barrier of degradation reaction from every reactive sites of reactants,revealing the degradation pathway and mechanism that are more likely to occur by comparing the potential energy surface profile of different pathways.The results demonstrated that hydrogen absorption reaction on saturated aliphatic hydrocarbon,addition reaction on unsaturated aliphatic hydrocarbon and aromatic ring,and direct transfer of single electron are the main ways for·OH to degrade flutriafol,generating intermediates including radical IM2,IM10,4-FP,2-FP,muconic acid and maleic acid.The key intermediates of degradation of flutriafol were identified and quantitatively analyzed by the experimental methods,which confirmed the reliability of the predicted reaction pathway,indicating that quantum chemical calculation is a powerful tool to predict the reaction pathway of organic compounds.Finally,the electrocatalysis experiments of practical wastewater containing flutriafol showed that at 5 m A·cm-2,the energy consumption was only 0.055 kwh·g-1 TOC when 30%of TOC was removed,and the toxicity of the wastewater was significantly reduced,the value of LC50,48h was increased from 15%to 42%,demonstrating the excellent development prospect of 3D-Pb O2 membrane system for the application of tailwater advanced treatment. |
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