Preparation And Application Of A Multifunctional Membrane Based On Polydopamine Coatings

Biocatalytic membrane which could combine mass transfer with biochemical reaction and improve enzymatic catalysis efficiency,is promising in biochemical engineering.However,due to the lack of efficient enzyme immobilization technologies,biocatalytic membrane suffers from low enzyme loading,low activity and low stability,which limits its further application.Aiming at these problems,this thesis focused on the construction and optimization of a multifunctional membrane based on polydopamine(PDA)coatings,and also investigated its application in water purification.The main research contents and results were summarized as follows:(1)Based on mussel-inspired chemistry and biological membrane properties,a multifunctional membrane was firstly proposed and prepared by applying 'reverse filtration'of a laccase solution and subsequent 'dopamine coating' on a nanofiltration(NF)membrane support,which was applied on bis-phenol A(BPA)removal.The BPA removal efficiency of NF270 multifunctional membrane was 84.3±7.3%when initial BPA concentration was 10 mg·L-1,outperforming the conventional Fenton treatment(55%).The super performance of the multifunctional membrane was due to a combination of separation(reducing the enzymatic burden),adsorption(enriching the substrate concentration as well as prolonging the residence time)and finally,catalysis(oxidizing the pollutants and breaking the'adsorption saturation limits'),and the synergistic effect enhanced the micro-pollutant removal efficiency.(2)To further improve the performance of the multifunctional membrane(i.e.enzyme loading,activity and stability),three multifunctional membranes were prepared by 'reverse filtration' of laccase and subsequently different coating strategies:single dopamine(DA)coating,DA/polyethyleneimine(PEI)co-depostion,and DA/Cu2+ co-deposition on NF270 membrane support.Compared with the single DA coating,two co-deposition methods not only accelerated the process of DA self-polymerization,improving its uniformity and stability,but also exhibited much better performances in terms of enzyme loading,activity and permeability as well as the stability of immobilized enzyme.The sandwich structure(skin layer-laccase-support/coating layer)of these biocatalytic membranes endowed their both sides with catalytic ability,which was used to construct a bifacial enzymatic membrane reactor(EMR)for highly efficient micro-pollutant removal(taking BPA as an example),and it was highest for the EMR with the DA/Cu2+ coated membrane.Besides,the stability of the bifacial EMR could be well maintained by in situ product removal,which was achieved by pressure-driven convective mass transfer.This work clearly confirmed the benefits of the mussel-inspired co-deposition for biocatalytic membrane fabrication,and demonstrated the potential to achieve a high and stable micro-pollutant removal by manipulating the enzyme loading,location and activity as well as substrate/product mass transfer of the biocatalytic membrane.In summary,this thesis not only proposes a novel strategy for biocatalytic membrane preparation and a new concept of multifunctional membrane,but also solves some application problems,such as the low removal efficiency of micro-pollutant by the traditional membrane filtration and the low operation stability of biocatalytic membrane.Moreover,this work provides a new methodology for the preparation and application of biocatalytic membrane,and the obtained multifunctional membrane and bifacial EMR are promising in tertiary wastewater treatment or household water purifier.