Photocatalytic Degradation Of Bisphenol A By Carbon-based Material Modified MIL-101(Fe) Coupled With Visible Light Activated Sodium Persulfate

Bisphenol A（BPA）is widely distributed in water environment,but the treatment effect of conventional methods is limited because of its good water stability.The combination of photocatalysis and persulfate advanced oxidation technology is a new treatment technology for efficient treatment of refractory organic compounds.Traditional Fenton-like catalysts still have some problems,such as slow conversion rate of Fe（III）and Fe（II）,limited light absorption capacity and so on.Metal-organic framework material（MOFs）has attracted wide attention as a heterogeneous Fenton catalyst because of its large number of unsaturated metal sites and high specific surface area.The development of MOFs-based heterogeneous Fenton catalysts with fast Fe（III）/Fe（II）cycle conversion rate is of great practical significance for the removal of refractory organic pollutants in the environment.In this study,carbon nitride（g-C₃N₄）and carbon quantum dots（CQDs）were modified respectively,and then two kinds of MIL-101（Fe）composites modified by nano-carbon materials were prepared by solvothermal method,and their catalytic activity and reaction mechanism for degradation of organic pollutants were studied.The main conclusions are as follows:Bulk g-C₃N₄was stripped into nano-flake CN by ultrasound-assisted liquid phase stripping method,and CN/MIL-101（Fe）composites with high catalytic activity were synthesized by solvothermal method.CN/MIL-101（Fe）composites are used to activate PS under visible light to produce SO₄·^-accelerate the degradation of BPA.The removal rate of BPA by CN/MIL-101（Fe）/PS/vis system can reach 95.9%within60 min,and its degradation rate is 4.4 times and 3.2 times higher than that of CN/PS/vis and MIL-101（Fe）/PS/vis system,respectively.Under certain conditions,the catalytic degradation effect of CN/MIL-101（Fe）/PS/vis system increased with the decrease of pollutant concentration,the increase of catalyst dosage,the increase of PS dosage and the decrease of initial p H.The contribution of the main active substances produced by CN/MIL-101（Fe）/PS/vis system in the process of BPA catalytic degradation to the degradation of target pollutants is in the following order:h⁺>·O₂^->SO₄·^->·OH.N,S:CQD_Swere encapsulated in the framework of MIL-101（Fe）by two-step hydrothermal method.Compared with MIL-101（Fe）,N,S:CQD_S/MIL-101（Fe）composites broadened the absorption range of visible light.The degradation rate of N,S:CQD_S/MIL-101（Fe）/PS/vis system can reach 100%in 60 minutes,its degradation rate is 3.6 times that of MIL-101（Fe）/PS/vis system.The optimal process parameters of N,S:CQD_S/MIL-101（Fe）/PS/vis system are as follows:the initial concentration of BPA is 20 mg/L,the dosage of catalyst is 40 mg/L,and the dosage of PS is 3 mmol/L.By means of free radical capture experiment,transient fluorescence and photoelectricity test,it was revealed that there is synergism of photocatalysis and heterogeneous Fenton like in N,S:CQD_S/MIL-101（Fe）/PS/vis system.The introduction of N,S:CQD_Senhances the absorption ability of visible light,produces more electron hole pairs,and more photogenerated electrons act on the metal center of MIL-101（Fe）to promote the Fe（III）/Fe（II）cycle and realize the continuous activation of PS.In addition,N,S:CQD_S/MIL-101（Fe）/PS/vis system showed good stability and catalytic activity,and the construction of composites effectively inhibited the loss of iron ions.