Study On Preparation And Application Of Graphene Oxide Based Nanocomposites Incorporated Polyamide Membranes

The lack of fresh water poses a serious threat to the human society with economic development and population bloom.The membrane separation technology has attracted widespread attention in seawater desalination due to its simple operation and low energy input.Especially,the development of reverse osmosis(RO)and forward osmosis(FO)membranes has promoted the membrane technology for desalination.Thin film composite(TFC)membranes prepared by interfacial polymerization are considered to be the state-of-the-art products with excellent performance,good flexibility,and low preparation cost in the field of RO and FO.However,the trade-off between permeability and rejection as well as membrane fouling,especially severe biofouling remain major obstacle to TFC membrane application.Therefore,novel nanocomposites and membrane preparation methods need to be explored to overcome these limitations.Base on the optimization of TFC membrane structure and polyamide(PA)layer inherent characteristics,novel high-performance RO membrane and sandwich FO membrane were fabricated by taking advantages of the graphene oxide-based nanocomposites in this work.The main research findings are as follows:Firstly,a new multifunctional nanocomposite of GOQD/AP was synthesized by loading bactericidal material-silver phosphate(AP)on graphene oxide quantum dots(GOQD)with an ultra-small size and unique zero-dimensional structure.Then GOQD/AP was introduced into the PA layer via interfacial polymerization to prepare thin film nanocomposite(TFN)RO membrane.The effect of GOQD/AP contents on the membrane separation performance was investigated at 16 bar using 2000 mg/L NaCl feed solution.Results showed that the addition of 50 mg/L GOQD/AP could break membrane "trade-off" to some extent and the water flux of TFN-GOQD/AP50 membrane was 39.6 L·m-2·h-1(LMH),which was 1.5-fold higher than that of the pristine TFC membrane.Meanwhile,the salt rejection(98.4%)was maintained at a slightly higher level than the TFC membrane(98.3%).The antibacterial property evaluation of TFN-GOQD/AP50 membrane was performed with E.coli and a sterilization rate of 99.9%was reached.In addition,TFN-GOQD/AP50 membrane exhibited a slow release rate and a low total release content of Ag+under dynamic soaking conditions for 30 days.Moreover,the incorporation of GOQD/AP improved the membrane fouling resistance against bovine serum albumin(BSA)and humic acid(HA)and the resultant TFN-GOQD/AP50 membrane possessed a lower total fouling ratio and a higher flux recovery ratio during a fouling test of 21 h.Additionally,GOQD/Ag nanocomposite was fabricated by combining GOQD and highly effective germicidal material of silver(Ag).Then a novel triple-layered TFN(t-TFN)FO membrane was developed by preparing a PA active layer doped with different contents of GOQD/Ag via interfacial polymerization on a carbon nanotube(CNT)interlayer,which was deposited on the surface of porous substrate by vacuum filtration.The optimal t-TFN-GOQD/Ag0,1 membrane exhibited approximately 7.9-fold enhancement in water flux of 65.8 LMH compared to pristine TFC(p-TFC)membrane without a CNT interlayer and the reverse salt flux was less than 1.5 g·m-2·h-1(gMH)using 1 mol/L NaCl as draw solution and deionized water as feed solution under PA layer facing draw solution(AL-DS)mode,which showed that the presence of CNT interlayer and GOQD/Ag could effectively alleviate the internal concentration polarization and improve perm-selectivity of membrane.Meanwhile,the antibacterial activity was assessed using gram-negative E.coli and gram-positive S.aureus as ical strains by incubating with the membrane for 2 h,and the t-TFN-GOQD/Ag0.1 membrane presented strong inhibition rate of 99.8%to E.coli and 97.3%to S.aureus.In addition,long-term release behavior of Ag+in the PA layer and fouling resistance of membrane to HA and BSA were also investigated.The results showed that the effective combination of GOQD and Ag endowed the t-TFN membrane a lasting bactericidal potential and enhanced antifouling property.In summary,two novel membranes of RO and FO with high perm-selectivity,strong antibacterial activity and improved antifouling ability were designed via the addition of graphene oxide-based multifunctional nanocomposites to regulate molecular and structural characteristics of PA layer.Both of these TFN membranes can overcome the shortcomings of conventional TFC membranes and provide a new idea to develop advanced nanocomposite membranes.