| In this study,tubular carbon membrane with both conductivity and filtration was used as cathode to construct an electro-Fenton reactor.The effect of the filtration flux of the carbon membrane on the performance of the electro-Fenton system for methyl orange(MO)degradation was investigated,and the underlying mechanism was discussed.The tubular carbon membrane was used as cathode to construct a filtered electro-Fenton reactor,and its operating conditions were optimized.The filtration flux significantly affected the MO degradation.When the flux was increased from 0 to 100 L/(m2·h),the MO removal was markedly increased by 31.3%from 64.1%and TOC removal was increased by 33.4%from 33.0%.This showed that the filtration behavior improve the treatment efficiency of the reactor.When the current density was increased from 1 to 4 mA·cm-2,the MO removal increased from 72.3%to 95.3%and TOC removal increased from 16.2%to 66.4%.When the current density continued to increase to 6 mA·cm-2,the MO and TOC removal did not increase significantly,but the mineralization current efficiency decreased markedly from 138.4%to 98.2%.In addition,the initial pH and Fe2+ dosage were also studied,when the initial pH value increased from 1 to 7,the MO degradation increased first and then decreased;Fe2+dosage increased from 0 to 0.8 mmol/L,and the MO degradation also increased first and then decreased.Under the conditions of 100 L/(m2·h),4 mA·cm-2,initial pH=3,and 0.2 mmol/L Fe2+ dosage,the removal of methyl orange and TOC can reach 95.3%and 66.4%,respectively.The degradation kinetics constant was 0.03856 min-1 based on first order reaction,and the instantaneous current efficiency was 40.1%.The reason for the improvement of the MO degradation induced by filtration behavior of the carbon membrane cathode was analyzed,found that flux could effectively enhance the production of hydrogen peroxide and promote the regeneration of Fe2+ to reduce the dosage of reagents.The increase of flux from 0 to 100 L/(m2·h)significantly enhanced the production of hydrogen peroxide by 7.08 mg/L(71.1%)from 9.9 to 17.1 mg/L.The results showed that the filtration behavior increased the active sites of two-electron reduction of oxygen,significantly enhanced the production of hydrogen peroxide.When the filtration flux increased from 0 to 150 L/(m2·h)the concentration of Fe2+ in reactor increased from 3.7 mg/L to 6.7 mg/L at the stable stage,and the Fe2+ proportion among the total iron in the effluent increased accordingly from 34.8%to 66.1%.Through material balance calculation,it was found that Fe remained less on the surface of carbon membrane.When the flux was 100 L/(m2·h)and 0.2 mmol/L Fe2(SO4)3 was added,the MO removal was 90.7%similar to that of Fe2+,which was 38.5%higher than 0 L/(m2·h).The results indicated that the filtration operation can promote the reduction of Fe3+and effectively maintain a high concentration of Fe2+ in the reactor.SEM and EDS analysis of the used carbon membrane indicated that the filtration operation accelerated the transfer of Fe to the cathode and Fe increased with the increase of flux.The characteristic peaks of Fe were not detected.by X-ray photoelectron spectroscopy(XPS).A series of electrochemical tests were carried out on the electrodes.CV and LSV analysis showed that the filtration operation converted the mass transfer from by diffusion to by convective,which greatly improved the electron transfer efficiency.The maximum response current increased from 57.7 to 69.2 mA.EIS analysis showed that the increase of flux could effectively reduce the internal resistance of the cathode,:firom 1.65 ?(0 L/(m2·h))to 1.33 ?(150 L/(m2·h))and improved the electrochemical performance of the electo-Fenton system. |
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