Bi₂₄O₃₁Br_xCl_10-x Solid Solution Enhances Photo-assisted PMS Activation By NiCo₂O₄ For Tetracycline Degradation

In recent years,persulfate（PMS）has attracted great attention due to its strong oxidation ability.Bimetallic catalyst has a good catalytic effect in the activation of PMS,because there is interaction between the two metals,which shows a synergistic effect in the process of activation of PMS,making bimetallic compounds have more advantages than single metal in the process of activation of PMS.Although pure bimetallic compounds can activate PMS,there are still some problems in the process of activation.For example,simple bimetallic compounds in the process of synthesis may occur particle aggregation,which makes the number of active sites of bimetallic compounds decrease in the reaction process,and then affect the degradation efficiency.Therefore,UV photolysis,transition metals,high temperature pyrolysis and photocatalysis are usually introduced to assist in the activation of organic pollutants degraded by PMS.Among them,photocatalysis is an ideal method to assist activation of PMS due to its high efficiency,no secondary pollution and low energy consumption.The results show that PMS is a good photocatalyst for photocatalysis.Therefore,the combination of bismuth oxyhalide solid solution photocatalysis technology and bimetallic persulfate activation technology is a promising strategy for wastewater treatment in the future.In this study,based on the successful preparation of NiCo₂O₄/Bi₂₄O₃₁Br₁₀photocatalyst,NiCo₂O₄/Bi₂₄O₃₁Br_xCl_10-x photocatalyst was synthesized through the introduction of solid solution to further enhance the efficiency of photo activated PMS degradation of TCH.The synthetic materials were characterized by various means.The effects of pH,the amount of catalyst,the concentration of tetracycline,the amount of PMS and different anions and cations on the photocatalytic activity of PMS were investigated.The detailed mechanism of degradation of tetracycline antibiotics based on solid solution NiCo₂O₄/Bi₂₄O₃₁Br_xCl_10-x was discussed through free radical capture and ESR test,（1）The results of material analysis showed that NiCo₂O₄/Bi₂₄O₃₁Br₁₀ and NiCo₂O₄/Bi₂₄O₃₁Br_xCl_10-x materials were successfully synthesized by hydrothermal method and high temperature calcination method,and the synthesized materials were characterized by XRD.The results showed that the synthesized materials had high purity.（2）NiCo₂O₄/Bi₂₄O₃₁Br₁₀ and NiCo₂O₄/Bi₂₄O₃₁Br_xCl_10-x have strong photocatalytic activity for degradation of TCH.NiCo₂O₄/Bi₂₄O₃₁Br₁₀ successfully degraded 90.8%tetracycline in 18 minutes.This is mainly because the electrons generated by Bi₂₄O₃₁Br₁₀can promote the rapid conversion of Co²⁺/Co³⁺and Ni²⁺/Ni³⁺and the formation of free radicals.NiCo₂O₄/Bi₂₄O₃₁Br_xCl_10-x can degrade 85.3%tetracycline in 4 minutes,and the degradation rate constant is about 3 times that of NiCo₂O₄/Bi₂₄O₃₁Br₁₀.The main reason is that the introduction of solid solution further improves the light response range of the material and improves the electron hole separation efficiency.（3）The results showed that the concentration of PMS,the amount of catalyst,the pH value and the concentration of tetracycline had significant effects on the degradation efficiency.Cation and anion have little effect on the degradation process.Cycle experiments showed that NiCo₂O₄/Bi₂₄O₃₁Br₁₀and NiCo₂O₄/Bi₂₄O₃₁Br_xCl_10-x catalysts had good stability.（4）The possible intermediates in the degradation process of tetracycline were analyzed by liquid chromatography mass spectrometry.It was confirmed that SO₄^·-/h⁺/HO·/¹O₂ was the main free radical.In this study,a stable and efficient PMS photocatalyst for wastewater treatment was developed.