Study On The Removal Of Triclosan By Metal-organic Frameworks And Its Functional Fiber Membrane

Triclosan?TCS?is a multi-purpose biocide and belongs to typical pharmaceuticals and personal care products.TCS has become one of the most frequently detected compounds in the environment.Increasing attention has been given to explore efficient technology for the treatment of TCS.Metal-organic frameworks?MOFs?is a new kind of porous material,which is composed of metal atoms or metal clusters and organic ligands.It has the characteristics of large specific surface area,open channels,uniform pore size and adjustable structure.Based on these unique characteristics of MOFs,the removal of TCS from water was investigated by MOFs and polyacrylonitrile?PAN?/MOF nonafiber membranes as well as laccase immobilized PAN/MOF nanofiber membranes.The mechanisms of adsorption of TCS by MOF and degradation of TCS by laccase were also studied.The purpose was to explore the application of MOFs and its composites for TCS treatment.The main contents and results are as follows:1.The microporous structure MIL-53?Al?and mesoporous structure meso-MIL-53?Al?were synthesized by hydrothermal method,and the adsorption behavior of TCS on different pore structure MIL-53?Al?s was studied by sequencing batch experiment.The results showed that the two kinds of MOFs with different pore structures had good adsorption properties for TCS under the conditions of wide pH range?4⁹?,high ionic strength?0¹00 mM?and coexistence of different impurities.The adsorption capacity of the two kinds of MOFs on TCS was much higher than that of the traditional activated carbon.The adsorption capacity of meso-MIL-53?Al?(488 mg g^-1)was higher than that of the MIL-53?Al?(447 mg L^-1),the adsorption rate of the former for 1 mg L^-1 TCS was 4.4 times higher than that of the latter,suggesting that the mesoporous structure was favorable for TCS migration on the adsorbent.Results also showed that more than 60%surface area of the two kinds of MOFs maintained after repeated use for three times,which indicated that MIL-53?Al?s were good TCS adsorbents.2.To understand adsorption mechanism of organic compounds on MOF,the adsorption and co-adsorption behaviors of phenol?Phen?,catechol?Cate?,pyrogallol?Pyro?,naphthol?Naph?,bisphenol A?BPA?,TCS and biphenyl?Biph?onto MIL-53?Al?were investigated.Results showed that the order of adsorption capacity of seven compounds on MIL-53?Al?is Biph>TCS>Naph>BPA>Pyro>Cate?Phen,indicating that adsorption is affected by the number of benzene ring and hydroxyl on the benzene ring.Freundlich model?FM?parameter K_f for Biph,TCS,Naph,BPA,and Phen on MOF had a significant linear relationship with their logK_ow values,indicating hydrophobic interactions also plays an important role in adsorption of aromatic organic compounds on MIL-53?Al?.In the binary mixtures with TCS as the main adsorbate,the presence of Phen and Naph increased the number of adsorption sites of TCS on MIL-53?Al?,promoting the adsorption of TCS,while the presence of BPA and Biph decreased the number of adsorption sites of TCS on MIL-53?Al?,inhibiting the adsorption of TCS.It was observed that the competitive intensity of the four co-existing organic compounds to TCS on MIL-53?Al?increased with the increase logK_ow values of the compounds.In the binary mixtures of BPA and Naph with similar logK_ow values,both of BPA and Naph reduced each other's saturated adsorption capacity on MIL-53?Al?.The competitive strength of BPA to Naph was greater than Naph to BPA and the degree of overlap of energy site distribution was higher for BPA to Naph than Naph to BPA as well.3.Porous PAN/MIL-53?Al??P-PAN/MIL-53?Al??nanofiber membrane with high availability was prepared by using polyethylene oxide as polymer template.Both P-PAN/MIL-53?Al?and as-synthesized PAN/MIL-53?Al?nanofiber menbranes with loading of 50%MIL-53?Al?were used for adsorptive removal of TCS.Results showed that P-PAN/MIL-53?Al?had better TCS adsorption performance than the as-synthesized one.The second-order kinetic constants and initial adsorption rate h resulted from P-PAN/MIL-53?Al?nanofibers were significantly higher than that of PAN/MIL-53?Al?at different initial concentrations of TCS,while the removal half-life of TCS resulted from P-PAN/MIL-53?Al?was significantly lower than that of PAN/MIL-53?Al?.The better adsorption performance of TCS onto P-PAN/MIL-53?Al?nanofibers can be ascribed to the higher porosity.P-PAN/MIL-53?Al?nanofiber membrane could be effectively regenerated in weak alkaline?pH 9?methanol aqueous solution,and the adsorption capacity of TCS onto P-PAN/MIL-53?Al?nanofiber membrane had little change after being reused for three times.4.Laccase was immobilized on the surface of PAN/MIL-53?Al?nanofiber membranes through amidination reaction and successfully applied to remove TCS from water.Results showed that the pH and temperature adaptability,operation stability and storage stability of the laccase was improved by immobilized on the surface of the PAN/MIL-53?Al?nanofiber membranes.The removal rate of TCS by laccase immobilized on PAN/MIL-53?Al?nanofibers was higher than that by pure PAN immobilized enzyme and free enzyme,indicating that the adsorption of TCS by PAN/MIL-53?Al?nanofibers and the degradation of TCS by the immobilized laccase on the surface of the PAN/MIL-53?Al?nanofibers had synergistic effect.The optimal pH value of TCS removal by laccase immobilized PAN/MIL-53?Al?nanofibers was about 5.0,and the optimal temperature was 45?.Humic acid?HA?can inhibit the removal TCS by immobilized laccase nanofibers.5.The transformation kinetics,products and pathways of TCS by laccase were studied systematically.The effect of HA on the transformation process of TCS by laccase was also emphasized.Results showed that the transformation of TCS by laccase was in accordance with the first-order kinetic model.The transformation products of TCS by laccase mainly included dimer,trimer and tetramer of TCS and a small amount of 2,4-dichlorophenol?2,4-DCP?.HA inhibited the transformation rate of TCS by laccase through participating in the enzymatic reaction,competing with TCS for laccase.The identification and quantification of byproducts of TCS indicated that HA could inhibit TCS self-coupling pathways by cross-linking and couple with TCS self-coupling products through C-O-C,C-N-C and C-C bond,thereby significantly reducing the relative content of TCS self-coupling products such as dimer,trimer,tetramer of TCS.In addition,HA could induce laccase further oxidating phenoxy radicals produced by one-electron oxidized of TCS,producing quinone structure products,which could be further oxidized to form 2-hydroquinone and 2,4-DCP.