Performance And Mechanism Of PTCDA/MIL-88(Fe) Composite For 2,4-Dichlorophenoxyacetic Acid Elimination

As industrialization deepens,a large amount of untreated or non-compliant wastewater containing new pollutants is discharged into the water environment of the earth,causing serious water pollution problems.The new pollutants widely concerned both domestically and internationally mainly include persistent organic pollutants controlled by international conventions,endocrine disruptors,antibiotics and so on.Pesticides are typical persistent organic pollutants,and residual pesticides may cause pollution to soil,atmosphere,and groundwater.2,4-Dichlorophenoxyacetic acid（2,4-D）and its corresponding salt belong to phenoxy carboxylic acid herbicides,which can persist in the environmental water for a long time,posing a huge threat to ecological environment and human health.Photocatalytic activation,corresponding to advanced oxidation technology,has the advantages of simple operation and utilization of solar energy activation,making the development of efficient and recyclable novel photocatalytic activation agents become a research hotspot in water environment restoration.Metal-organic framework materials（MOFs）introduce materials with special properties such as oxidized graphene and perylene-3,4,9,10-tetracarboxylic dianhydride（PTCDA）during the synthesis process,which can obtain MOF composites with excellent catalytic performance.In this research,a ball milling method was used to prepare a PTCDA/MIL-88A（Fe）composites,which consists of the environmentally friendly metal-organic framework material MIL-88A（Fe）and the narrow bandgap semiconductor material PTCDA.The performance of composites photocatalysis in activating hydrogen peroxide（H₂O₂）and peroxymonosulfate（PMS）for the degradation of the organic pollutant2,4-D has been investigated,as well as the effects of different influencing factors and the reusability and stability of the material.The specific research contents and results of this paper are as follows:1.MIL-88A（Fe）was obtained via room-temperature preparation method.PTCDA/MIL-88A（Fe）composites（PTx My）were prepared by using a ball milling method to construct heterojunctions between different proportions of PTCDA and MIL-88A（Fe）.The composition and properties of the materials were characterized by powder X-ray diffraction（PXRD）,Fourier transform infrared spectroscopy（FTIR）,ultraviolet-visible diffuse reflectance spectroscopy（UV-Vis）,scanning electron microscopy（SEM）,high-resolution transmission electron microscopy（HRTEM）,and X-ray photoelectron spectroscopy（XPS）,which confirmed the successful composites formation of PTCDA and MIL-88A（Fe）.The introduction of PTCDA broadened the light absorption range of the composites,reduced the bandgap width,and laid the foundation for subsequent photocatalytic activation experiments.2.The photocatalysis-activated H₂O₂ degradation performance toward 2,4-D was investigated over different ratios of PTx My composites under visible light irradiation.The optimal ratio of PT25M175 was selected for exploring the influencing factors,including p H values（5,6,7,8,and 9）,initial concentration,H₂O₂ dosage,and co-ions（such as ions in tap water and lake water）on the photocatalysis-activated H₂O₂ degradation of 2,4-D.Results showed that the introduction of PTCDA into the composites enabled the rapid adsorption of 2,4-D onto the surface of the PT25M175 composite,which was subsequently degraded by advanced oxidation processes.The synergistic effect of adsorption and photocatalysis-activated H₂O₂ not only accelerated the oxidation efficiency of 2,4-D but also achieved the recycling of material.The five-cycle experimental results demonstrated that PT25M175,as a photo-Fenton material,possesses both repeatability and stability.Additionally,the photocatalysis-activated H₂O₂ by PT25M175 composite also exhibited universality in the degradation of emerging organic contains（EOCs）,suggesting its potential for the removal of various EOCs.Active species capture experiments and ESR spectra confirmed the presence of ·OH,O2·-and 1O2 as the active species in the reaction system.Toxicity Estimation Software and plant growth toxicity experiments demonstrated the harmlessness of the reaction system to the ecological environment.3.The photocatalysis-activated PMS degradation performance toward the organic pollutant 2,4-D was investigated over PTx My under visible light.The effects of different p H values（2,4,6,8,and 10）,initial concentration,and inorganic anions on the degradation of organic pollutant 2,4-D were investigated.The cyclic experiment results also showed that the PT25M175 composite had excellent repeatability and stability in the photocatalysis-activated PMS system.Additionally,the PT25M175/PMS/Vis system exhibited excellent performance in removing EOCs and showed the universality.Active species capture experiments and ESR spectra confirmed the presence of ·OH,O2·-,1O2 and SO4·-in photocatalysis-activated PMS degradation of 2,4-D,and their respective contribution rates were estimated.The concentrations of each radical in the reaction system were determined through radical quantification experiments.Ecotoxicological assessments through plant growth toxicity experiments demonstrated the harmlessness of the reaction system to the ecological environment.4.The experimental results of photocatalytic activation AOP to efficiently degrade the organic pollutant 2,4-D demonstrated the potential application of multifunctional MOF and metal-free organic compound PTCDA-based composites in future water treatment.The Z-scheme heterojunction mechanism of PTCDA/MIL-88A（Fe）composites for the degradation of 2,4-D by photocatalysis-activated H₂O₂ and PMS were proposed through electrochemical experiments,electron spin resonance（ESR）testing,X-ray photoelectron spectroscopy（XPS）testing,platinum nanoparticle deposition experiments and density functional theory（DFT）calculations.It was confirmed PTCDA/MIL-88A（Fe）composites exhibit a faster rate of charge carrier separation than individual MIL-88A（Fe）and PTCDA.The introduction of PTCDA was found to suppress the recombination of photoinduced electron-hole pairs on PT25M175 composite by photoluminescence spectroscopy testing.Possible degradation pathways for 2,4-D were proposed based on DFT calculations and LC-MS.