Fe-MOFs For Photo-fenton Degradation Of Tri (2-Chloroisopropyl) Phosphate And Its Disturbance On E.coli Metabolism

Organophosphate flame retardants（OPFRs）as a substitute for brominated flame retardants,had been widely used and released into the environment,becoming an emerging contaminant.Tris（2-chloroisopropyl）phosphate（TCPP）had attracted a lot of attention among numerous OPFRs because of its large yield,wide application,persistence,bioaccumulation,and biological toxicity and high-water solubility.Therefore,TCPP was selected as the target contaminant in this work and heterogeneous photo-Fenton reaction system（Fe-MOFs+H₂O₂+Vis）catalyzed by Fe-based metal-organic frameworks（Fe-MOFs）was constructed.The degradation efficiency of TCPP in the system was explored.Based on Density Functional Theory（DFT）calculation and high resolution tandem mass spectrometer,the degradation products and pathways of TCPP were identified and analyzed.The reaction mechanism and transformation regulation of TCPP degradation in Fe-MOFs+H₂O₂+Vis system was profoundly revealed.The detoxification mechanism of TCPP was systematically explained by toxicity prediction and metabolomics technology.Based on metabolomics technology,the metabolic pathway disturbance of Fe-MOFs to the model organism（Escherichia coli（E.coli））was preliminarily recognized at the molecular level.The main conclusions of this study were as follows:（1）MIL-88 was prepared and used as heterogeneous photo-Fenton catalyst for TCPP degradation in polluted water,and the heterogeneous photo-Fenton reaction mechanism and performance were investigated.The results indicated that the surface Fe^Ⅲ of MIL-88 obtained photogenerated electrons and was reduced to Fe^Ⅱbecause of the excitation of Fe-O clusters in MIL-88 under visible light irradiation.Then the formed Fe^Ⅱ reacted with the coordinated H₂O₂on the metal sites to generate·OH and Fe^Ⅲ,resulting in Fe^Ⅲ/Fe^Ⅱ cycle.Radical quenching experiments and electron paramagnetic resonance（EPR）confirmed that·OH produced by heterogeneous photo-Fenton catalytic process dominated TCPP degradation.Compared with traditional iron-based catalysts（such as Fe₂O₃ and Fe₃O₄）,MIL-88 exhibited better catalytic activity and the degradation efficiency of TCPP reached approximately 95%（60 min）.TCPP could be degraded at neutral p H in this system and the applicable p H range was broader than that of Fenton system.MIL-88 possessed excellent stability in the catalytic process,and the dissolution of iron was less than 2 mg/L.It could still maintain high catalytic activity after three cycle experiments.（2）In order to enhance the migration of photo-generated electrons and thus accelerate the surface Fe^Ⅲ/Fe^Ⅱ cycle of catalyst,amino functionalized metal organic frameworks（MIL-88B-NH₂）was successfully prepared.It was used as a heterogeneous photo-Fenton catalyst to degrade TCPP in water.The mechanism of amino groups（NH₂）enhancing the light absorption of the catalyst and the oxidation ability of heterogeneous photo-Fenton reaction was clarified.The results showed that the degradation efficiency of TCPP in MIL-88B-NH₂+H₂O₂+Vis system reached almost 100%,which was significantly higher than in MIL-88B+H₂O₂+Vis system（approximately 73%）.NH₂ group exhibited an"antenna"effect,which could enhance the light absorption of MIL-88B-NH₂ and simultaneously promoted the generation and migration of photogenerated electrons.Under the irradiation of visible light,both Fe-O clusters and organic ligands（2-Aminoterephthalic Acid,H₂-ATA）of MIL-88B-NH₂ could produce photogenerated electrons.The formed double excitation pathways would promote the transfer of photogenerated electrons to Fe^Ⅲ on the material surface and accelerate the transformation from Fe^Ⅲto Fe^Ⅱ,so as to improve the decomposition efficiency of H₂O₂,generate sufficient·OH in the system and simultaneously boost the Fe^Ⅲ/Fe^Ⅱ cycle,leading to the increase of the degradation efficiency of TCPP.The iron dissolution amount of MIL-88B-NH₂was significantly lower than that of MIL-88B,and the iron dissolution amount after three cycle experiments was lower than the environmental safety value,which effectively avoided secondary pollution.In addition,the coexisting anions had no obvious effect on the degradation efficiency of TCPP,but humic acid（HA）might induce“light shielding effect”which had a great impact on TCPP degradation.（3）Co doping MIL-88B（MIL-88B（Fe,Co））was successfully synthesized and used as heterogeneous photo-Fenton catalyst for TCPP degradation.The unique role of Co in elevating the photo-Fenton performance of the catalyst was revealed.The degradation efficiency of TCPP in MIL-88B（Fe,Co）+H₂O₂+Vis system could reach 99.3%.In comparison with MIL-88B,the surface area MIL-88B（Fe,Co）increased significantly,implying the more catalytic active sites on the surface of the catalyst,which was beneficial for coordinating with H₂O₂ in solution.Additionally,Co doping also formed double active sites（Fe,Co）in MIL-88B（Fe,Co）.The improvement of these properties contributed to elevating the photo-Fenton catalytic activity of the catalyst.The system also showed degradation ability for tris（2-chloroethyl）phosphate（TCEP）and triphenyl phosphate（TPHP）.The effects of the interaction of solution p H,catalyst dosage and H₂O₂ concentration on TCPP degradation were investigated by response surface methodology（RSM）.The result presented that p H might play an important role in the efficient degradation of TCPP in MIL-88B（Fe,Co）+H₂O₂+Vis system.（4）The degradation intermediates of TCPP in Fe-MOFs+H₂O₂+Vis system were identified by DFT calculation and high resolution tandem mass spectrometer（HRMS）,including C₆H₁₃Cl₂O₄P（m/z 251.000）,C₃H₈Cl O₄P（m/z 174.992）,C₉H₁₇Cl₂O₅P（m/z 307.026）,C₉H₁₆Cl₃O₅P（m/z 340.987）,C₉H₁₇Cl₂O₆P（m/z 323.021）,C₉H₁₈Cl₃O₅P（m/z 343.003）,C₆H₁₂Cl O₆P（m/z 247.013）,C₆H₁₃Cl₂O₅P（m/z 266.992）and C₃H₈Cl O₅P（m/z 190.987）.The conversion pathways mainly included hydroxylation,dechlorination,carboxylation and oxidation.The toxicity prediction of intermediates showed that TCPP was effectively detoxified via the treatment of Fe-MOFs+H₂O₂+Vis system.The results of metabolomics indicated that TCPP and its degradation products interfered with the metabolic activities of E.coli,but some metabolites related to energy metabolism were up-regulated under the stress of TCPP degradation products,which further confirmed that the stress degree of TCPP degradation products on E.coli was alleviated.（5）Based on metabolomics technology,the disturbance of MIL-88,MIL-88B-NH₂ and MIL-88B（Fe,Co）on the metabolic activities of E.coli was also recognized.The results demonstrated that they had a certain disturbance on the metabolic activities of E.coli.53,59and 63 differential metabolites were screened respectively,and 40 common differentially expressed metabolites were found,indicating that the metabolic activities of E.coli were similar at a certain extent under the stress of three catalysts.Aminoacyl-t RNAs biosynthesis,citric acid cycle（TCA cycle）,arginine biosynthesis,glyoxylic acid and dicarboxylic acid metabolism,alanine,aspartic acid and glutamate metabolism were highly enriched.In this work,the heterogeneous photo-Fenton system catalyzed by Fe-MOFs was constructed,which realized the efficient degradation goal of TCPP.The mechanism of heterogeneous photo-Fenton reaction catalyzed by Fe-MOFs was clarified,and the transformation regulation and detoxification mechanism of TCPP in heterogeneous photo-Fenton system catalyzed by Fe-MOFs were also illustrated.The observations of this work would provide practical reference and theoretical basis for the treatment of refractory organic pollutants,and better guide the design,preparation and application of catalytic materials.