Effects Of Cathode Materials On Degradation Of Tetracycline By Electro-activated Persulfate

In recent years,the serious harm caused by tetracycline pollutants into the environment has been widely concerned,and strict control of tetracycline emissions has become a social consensus.Tetracycline hydrochloride（TCH）,as a typical representative of tetracycline,is widely used in medical and animal husbandry industries.Conventional wastewater treatment processes are difficult to effectively degrade TCH.Therefore,it is particularly necessary to try to take some new technologies to effectively treat TCH.Advanced oxidation technology based on electro-activated persulfate（PDS）is considered to be one of the ideal methods for the degradation of TCH due to its strong oxidizing ability and green environmental protection.The process of electro-activated persulfate occurs at the cathode,so the influence of cathode material on the activation efficiency is criticalIn the experiment,three conventional electrodes of nickel foam（NF）,copper and graphite were used as cathodes to study the effect and mechanism of cathodic activation of PDS on TCH degradation.The mechanism of cathodic activation of PDS was explored by quenching experiments and electrochemical characterization.The effects of operating conditions on TCH degradation were investigated by single factor experiments.On this basis,Pt@MOF（Fe）/NF material was prepared by hydrothermal method by loading Pt and Fe-based MOF on the surface of nickel foam as cathode activated PDS,and its improvement effect on the degradation of TCH by electroactivated PDS was investigated.The performance and mechanism of activated PDS were studied by characterization and analysis of self-made cathode.The main research contents and results are as follows:（1）In the cathode activated PDS system,the degradation rate of TCH is much higher than the addition of PDS oxidation alone and direct electrolysis reduction.It indicated that during the electrolysis process,PDS and cathode had synergistic effect and produced active substances with strong oxidizability,and the degradation process of TCH conformed to pseudo-second-order kinetics in the PDS system activated by different cathodes.By investigating the operating conditions,the optimum degradation conditions were determined as follows:current density 20 m A/cm²,initial PDS concentration 5 mmol/L,initial p H=7.After 120 min of degradation under the optimal conditions,the degradation rate of TCH in Pt@MOF（Fe）/NF cathode system reached 71.4%,while the degradation rates of TCH in graphite,Cu and NF cathode systems were 56.7%,52.0%and 44.5%,respectively,indicating that cathode material was one of the important factors affecting the degradation of TCH by electro-activated PDS,and the degradation rate of TCH was significantly improved by modifying the material.（2）The quenching experiments showed that the main active substances in the four cathode-activated PDS systems were sulfate radical(SO₄^-·)and hydroxyl radical（·OH）,and·OH was the main active substance.H*quenching experiment and CV curve proved that when PDS was activated at the cathode,H*did not play a role,and PDS was mainly directly activated by electrons on the electrode surface.The electrochemical impedance spectroscopy（EIS）curves showed that the difference of charge transfer ability of the four cathodes was one of the main reasons for the different degradation efficiency of TCH by cathode activation PDS.（3）Through the characterization and analysis of Pt@MOF（Fe）/NF material,the reason for its high activation performance was revealed:SEM electron microscopy confirmed that cluster-packed structures with different sizes were grown on the surface of NF,which increased the active sites of the reaction,and was beneficial for PDS to obtain electrons for activation.FT-IR characterization detected the functional groups of the self-made materials,indicating the metal O bond formed by terephthalic acid and Fe³⁺,confirming the formation of Fe-MOF.EDS results show that the proportion of Fe,Ni,Pt in the material,and found that the elements grow uniformly on the surface of NF,which is beneficial to prevent the aggregation of Pt elements,thereby improving the stability and catalytic ability of the material.The sharp and narrow peaks in the XRD results indicate that the structure of the load has good crystallinity.In addition,it also indicates that Fe-MOF is loaded on the NF surface,which can combine the active centers of the two and show good catalytic performance.XPS further analyzed the valence state of each element on the surface of the material.The results showed that Pt element transformed from ionic state to elemental state,which improved the catalytic ability,and Fe element also existed in Fe³⁺state.On the one hand,the valence state of Fe³⁺can change,which can accelerate the transfer of electrons to Pt.In addition,Fe³⁺can also be used as a catalyst to promote the activation of PDS.（4）The UV-Vis spectra of TCH showed that the characteristic functional groups of TCH were attacked and destroyed by active substances such as SO₄^-·and·OH in the system during the degradation process,resulting in intermediate products with similar structure of TCH,which could be further mineralized to CO₂ and H₂O.Finally,it is confirmed that the degradation rate of TCH in the system without cell separation is better than that in the system with cell separation,indicating that the cathode and anode have a synergistic effect in the process of electrochemical activation of PDS,and the active substances produced on the anode also contribute to the degradation of TCH.