Preparation Of Fe-Based MOF Materials And Their Degradation By Adsorption Of Disinfection By-Products

The disinfection of drinking water is essential for preventing waterborne epidemics and protecting public health.Chlorination is the most common and cost-effective method used in China.However,disinfection by-products（DBPs）are formed as a result of the reaction between the disinfectant and natural organic matter in the water.Some of these DBPs have been found to be hazardous to human health,including being genotoxic,carcinogenic,and toxic to reproductive development.To remove these organic pollutants,adsorption and photocatalysis are important techniques.Metal-organic frameworks（MOF）have attracted attention as adsorbent and catalytic materials due to their crystalline properties,high specific surface area,and abundant pore channels and functional groups.In this study,we investigated Fe-based MOF that are water-stable,structurally rich,and environmentally friendly.We also modified their structure to improve their stability and recyclability.Our research focused on the MOF’s ability to adsorb and degrade highly toxic disinfection by-products and their precursors.The main findings of our study are presented below.（1）NH₂-MIL-53（Fe）metal-organic framework materials were synthesized by the solvothermal method.The morphological adjustment of the MOF crystals was achieved by changing the synthesis conditions.The NH₂-MIL-53（Fe）material with high specific surface area(130.3 m²g^-1),clear grain morphology and high crystallinity was prepared at 140℃&8 h.The green material was used as an adsorbent for the adsorption of 2,6-dichlorobenzoquinone（2,6-DCBQ）,a highly toxic disinfection by-product of halogenated benzoquinones.The adsorption performance of 2,6-DCBQ was also characterized by the determination of its content using ultra performance liquid chromatography with ultraviolet detector（UPLC-TUV）.The effects of temperature,pH and mass concentration of 2,6-DCBQ on its adsorption were also investigated.The adsorption of NH₂-MIL-53（Fe）material at 20℃,pH=7,and 20 mg L^-12,6-DCBQ for 120 min achieved more than 95%adsorption of2,6-DCBQ in water,and the maximum adsorption amount reached 790 mg g^-1,and the adsorption process was in accordance with the quasi-first-order kinetic law.After five cycles of experiments,the adsorption rate of NH₂-MIL-53（Fe）on 2,6-DCBQ in water still reached more than 80%.（2）In order to achieve efficient recovery of NH₂-MIL-53（Fe）,Fe₃O₄@SiO₂@PDA@NH₂-MIL-53（Fe）（FSPN）magnetic composites were synthesized by a layer-by-layer self-assembly method to achieve stable and sufficient loading of NH₂-MIL-53（Fe）by using the abundant active sites on the surface of PDA.the magnetic effect of Fe₃O₄ and can realize the rapid magnetic separation of the material.This green material was applied to adsorb highly toxic 2,6-dichloro-1,4-benzoquinone（2,6-DCBQ）and its precursors bisphenol A（BPA）and phenol.the maximum adsorption capacities of FSPN magnetic material for 2,6-DCBQ,BPA and phenol were 109.3 mg g^-1,82.4 mg g^-1and 64.8 mg g^-1,respectively.The FSPN magnetic material showed good adsorption performance and stability for all three target compounds over a wide pH and temperature range,and was easily recoverable.The adsorption process can be well fitted with a quasi-level kinetic model and Freundlich adsorption isotherm,which indicates that the adsorption process is more inclined to physical adsorption and is consistent with a multilayer adsorption process.Combined with the material characterization and adsorption performance,it is hypothesized that the main mechanism of adsorption of disinfection by-products by magnetic materials is the use ofπ-πinteractions,hydrogen bonding and pore adsorption.After five cycles,the adsorption rates of the synthesized FSPN magnetic materials were still above 80%for the three target species.（3）Polyethylene terephthalate（PET）is a commonly used polymer material with the advantages of structural stability and high mechanical strength.PET@PDA@NH₂-MIL-53（Fe）（PNM）composites were prepared by in situ growth of NH₂-MIL-53（Fe）on the surface of waste PET by surface etching and solvothermal method.The material exhibited some photocatalytic activity for disinfection by-products and their precursors under Xe lamp simulated sunlight.To enhance the photocatalytic activity,the photo-Fenton system formed by PNM and trace H₂O₂achieved 99%degradation of 2,6-dichloro-1,4-benzoquinone（2,6-DCBQ）in 30 min,and more than 98%and95%degradation of phenol and bisphenol A（BPA）in 60 min,indicating a synergistic effect between PNM and H₂O₂.Combined with the photoelectric properties of the materials and radical trapping experiments,it can be known that hydroxyl radicals（·OH）and holes（h⁺）play a major role in the degradation process.The intermediate degradation products were resolved using UPLC-QTOF and GC-MS,and the possible degradation pathways of DBPs were speculated.The toxicity of the intermediate products was evaluated by Toxtree software,and the degradation products were found to be significantly less carcinogenic,teratogenic and mutagenic,demonstrating the feasibility of the degradation process.the PNM photocatalyst exhibited excellent structural stability and recyclability,maintaining an efficient degradation rate after 5 cycles,and the degradation rate could still reach over95%at 60 min.This study realized the reuse of waste PET and provided a new direction to explore the development and application of green photocatalytic materials.