Preparation And Performances Of Anti-Biofouling Aromatic Polyamide Composite Reverse Osmosis Membranes

As one of the most energy-efficient desalination methods,reverse osmosis?RO?membrane technology has been widely used in the filed of water treatment such as water purification,seawater and brackish water desalination.However,RO membranes are prone to severe biofouling,which leads to the irreversible decrease of membrane performance,and hence increases the cost and application difficulty of RO membrane separation process.As a result,the application of RO separation technology will be seriously restricted.To solve this problem,we prepared novel anti-biofouling RO membraes without the sacrifice of permselectivity.A green approach was developed to in situ immobilize silver nanoparticles?AgNPs?onto the commercial polyamide RO membrane?virgin membrane?surface to enhance its anti-biofouling property.Fisrt,an ultrathin precursor layer of tannic acid–ferric ion–polyethylenimine?TA-Fe-PEI?complex was deposited onto the RO membrane surface,which was fabricated by the covalent and coordinative cross-linking of ferric chloride?FeCl₃?,tannic acid?TA?,and polyethyleneimine?PEI?.Then,AgNPs were in situ formed on the membrane surface to obtain the TA-Fe-PEI/Ag-modified membrane via the reduction of silver ammonia aqueous solution?Ag?NH₃?₂OH?by TA.Compared with the virgin membrane,the water flux and salt rejection of TA-Fe-PEI/Ag-modified membrane increased.Besides,the anti-biofouling test showed that after contacting with Escherichia coli and Bacillus subtilis,TA-Fe-PEI/Ag-modified membrane showed mortalities of 100%.Static immersion experiment demonstrated that AgNPs were stably immobilized on the membrane surface.The second interfacial polymerization reaction method was developed to graft biguanidine cationic polymer onto the polyamide RO membrane?virgin membrane?surface to enhance its anti-biofouling property.First,Biguanidine functionalized polyvinylamine?PVAm G?with PVAm as the polymeric matrix and biguanidine groups as the anti-bacterial functional groups was prepared via the chemical reaction of polyvinylamine?PVAm?and dicyandiamide.Then,the nacent RO membrane was prepared by first interfacial polymerization of m-phenylenediamine?MPD?and trimesoyl chloride?TMC?.After that,the PVAmG-modified membrane was prepared by grafting PVAmG onto the nacent membrane surface via the second interfacial polymerization reaction of amine groups in PVAmG and acyl chloride groups on nacent membrane surface.The water flux and salt rejection of PVAm G-modified membrane were nearly the same as those of the unmodified membrane.Besides,the anti-biofouling test showed that after contacting with Escherichia coli and Bacillus subtilis,PVAmG-modified membrane showed mortalities of 99.9%.