Fe-C Derived From MOFs For Microelectrolysis-fenton Like Degradation Of Dyestuff Wastewater

In recent years,with the continuous development of industrialization,water pollution has become increasingly serious.Dye is an indispensable industrial raw material,which leads to the most prominent pollution problem of dye wastewater to the environment.Zero-valent iron activated carbon（Fe-C）internal micro-electrolysis（IME）is a wastewater treatment technology developed in 1970s,which has been widely used in various industrial wastewater treatment at present.However,the traditional IME process suffers from some problems,such as narrow operating p H range,easy passivation of catalyst,insufficient oxidation ability and so on.Therefore,we put forward the problems of insufficient oxidation capacity and narrow p H range of micro-electrolysis-Fenton-like system for improving oxidation.In addition,the metal-organic framework（MOFs）with frame structure was used as the matrix,and nano-composite materials were obtained by calcination under nitrogen protection,which were used for micro-electrolysis and Fenton-like catalytic degradation of simulated dye wastewater rhodamine B（Rh B）.In this work,we synthesized cobalt/iron-porous graphitic carbon（Co/Fe@PC）,copper/iron@nitrogen-doped porous graphitic carbon（Cu/Fe@PCN）,zinc/iron@nitrogen-doped porous graphitic carbon（Zn/Fe@PCN）three catalysts were used to catalyze the micro-electrolysis-like Fenton degradation of Rh B,and their catalytic performance was evaluated,and the catalytic mechanism was discussed.The main research contents and results are as follows:（1）Co/Fe co-doped porous graphite carbon（Co/Fe@PC）nanocomposites were successfully prepared by one-step pyrolysis with Co/Fe-MOF,in which the Co Fe nanoparticles were uniformly coated on porous graphite carbon derived from MOF.It was used to microelectrolysis-Fenton degrade rhodamine B through the main active substance·OH.The color and TOC removal rate of 100 mg/L rhodamine B reached99.41%and 64.6%,respectively,for 30 min.Rhodamine B was degraded into small molecular organic acids,alcohols and lipids by N-demethylation and chromophore cleavage,until it was finally degraded into CO₂ and H₂O,and no new colored organics were produced in the degradation process.The degradation process follows the first-order reaction kinetics,and its rate constant is much higher than that of the previous similar studies.The excellent catalytic performance of Co/Fe@PC catalyst is attributed to the coupling effect of micro-electrolysis and Fenton reaction,and the acceleration of cobalt on electron transport and Fe²⁺reduction.Co⁰/Fe⁰ undergoes galvanic corrosion to generate Co²⁺/Fe²⁺and H₂O₂,and then these products undergo Fenton reaction to generate Co³⁺/Fe³⁺and?OH,thus forming a circulating system of Co³⁺/Fe³⁺and Co²⁺/Fe²⁺,enhancing the activation of H₂O₂ and ensuring the efficient degradation of Rh B.（2）Nitrogen doped Cu/Fe@PC（Cu/Fe@PCN）nanocomposite with core-shell structure was successfully prepared by one-step pyrolysis with g-C₃N₄ doped Cu/Fe-MOF.It was used as catalyst to active peroxymonosulfate（PMS）to degrade rhodamine B.The degradation of rhodamine B was a microelectrolysis-Fenton-like degradation process dominated by adsorption and PMS activation with non-free radical singlet oxygen（¹O₂）.It was mainly realized by cracking,ring opening and mineralization of chromophore group.Within 30 min,the degradation efficiency of 50 mg/L Rh B reached100%,and the rate constant reached 0.5307 min^-1.The excellent performance of Cu/Fe@PCN catalyst was attributed to the synergistic effect of Cu and Fe.The doping of Cu not only accelerated the electron transmission and promoted the effective reduction of Fe²⁺,but also formed a circulating system of Fe²⁺/Fe³⁺and Cu⁺/Cu²⁺,which ensured the efficient catalytic activity of the catalyst.This study provides some insights for pollutants degradation by microelectrolysis-Fenton-like system.（3）Using g-C₃N₄ as nitrogen source,the catalyst Zn/Fe@PCN was successfully prepared by carbonizing the mixture of g-C₃N₄ and Zn/Fe-MOF by one-step pyrolysis,and it was applied to the degradation of Rh B.It was found that the degradation of Rh B was a microelectrolysis-Fenton-like degradation process which mainly absorbed and activated PS.Within 30 min,the degradation rate of 50 mg/L Rh B was 95.92%and the reaction rate constant was 0.6453 min^-1.This is due to the synergistic effect of Zn and Fe.The addition of Zn and N not only promotes the transfer of electrons,but also the existence of Zn accelerates the effective reduction of Fe²⁺,which guarantees the high activity of the catalyst.In addition,repeated experiments show that the catalyst has good stability.（4）Among the three systems of Co/Fe@PC/H₂O₂,Cu/Fe@PCN/PMS and Zn/Fe@PCN/PS,the Cu/Fe@PCN/PMS system has the best effect.