Preparation And Characterization Of Antimicrobial Antifouling Organic Ultrafiltration Membrane

Over the past years, a membrane filtration process has been widely used in water purification and wastewater treatment, and receives considerable attention due to its many advantages. However, the inherent hydrophobic property often causes severe organic fouling and bio- fouling, which influe nces the ultrafiltration efficiency, shortens membrane life and restricts the app lications of po lymer ultrafiltration membranes. Therefore, it is necessary to improve hydrophilic and antibacterial properties of po lymer membranes. In this work, we attempt to study and prepare novel or ganic ultrafiltration membranes with antibacterial and antifouling properties. In this paper, three kind of MWNTs based antibacterial agent were synthesized. MWNTs were firstly oxidized by strongly oxidizing agent and then further mod ified to be antibacterial agents. The antibacterial agents were applied to improve the hydraulic permeation, rejection performance and antibacterial property of po lymer membranes.Firstly, multi-walled carbo n nanotubes grafted with（3-chloro-2-hydroxypropyl）-（5,5-dimethylhydantoinyl-1- ylmethyl）-dimethylammoniu m chloride（MWNTs-g-CDDAC） were doped in a PVDF spinning solution to prepare a kind o f novel PVDF/MWNTs-g-CDDAC hollow fiber ultrafiltration membrane with antibacterial and antifouling properties. The MWNTs-g-CDDAC were synthesized and characterized by FTIR, XPS and TGA. With the addition of MWNTs- g-CDDAC in the dopes, the sponge- like structure was suppressed and the finger- like macrovoids grow wider for the PVDF/MWNTs-g-CDDAC hollow fi ber membranes. The surface hydrop hilicity and antifouling ability of the membranes were evidently improved by introducing MWNTs- g-CDDAC onto the membranes. The pure water permeability gradua lly increased with the loading of MWNTs-g-CDDAC in the hybrid membranes, and the highest value of 94.7 L·m^-2·bar^-1·h^-1 was obtained with 0.5 wt% MWNTs-g-CDDAC add ition in the dope. The permeation flux recovery ratio increased with the add ition of MWN Ts-g-CDDAC, and M-75（0.75 wt% MWNTs-g-CDDAC loading in dope） exhibited the highest permeation flux recovery ratio value of 90.6% after two ultrafiltration-cleaning cycles for a BSA aqueous solution. The fabricated PVDF/MWN Ts-g-CDDAC membranes had favorable antibacterial efficacy, and M-75 showed the utmost sterilization ratios of 92.7% and 95.2% against E. coli and S. aureus, respectively.Secondly, multiwalled carbo n nanot ube s grafted with sulfaguanidine（MWNTs-g-SG） were doped in a PVDF dope solution to prepare flat sheet PVDF/MWNTs- g-SG ultrafiltration membrane with antibacterial and antifouling properties by means of non-solve nt induced phase separation（NIPs）. The MWNTs-g-SG were synthesized and characterized by FTIR, TGA, Zetasizer and elemental analyzer. Compared to the first work, the introduce of MWNTs-g-SG led to similar conclusions in the second work. Due to the casting solution contained 3.0wt% PVP and PVP as hydrophilic organic compounds could accelerate the phase separation process in the phase separation process, the sub- layer structure of po lymer membrane was not fully developed and the macrovoids structure was highly developed. The pure water permeability gradually increaseed with the loading of MWNTs-g-SG in the hybrid membranes, and the highest value of 172.3 L·m^-2·bar^-1·h^-1 was obtained with 0.60wt% MWNTs-g-SG addition in the dope. The permeation flux recovery ratio increased with the add ition of MWNTs- g-SG, M-3 exhibited the highest permeation flux recovery ratio value of 88.4% after two ultrafiltration-cleaning cycles for a BSA aqueous solution. The fabricated PVDF/MWNTs- g-SG membranes had favorable antibacterial efficacy, and M-4 showed the utmost sterilization ratios of 95.8% and 96.7% aga inst E. coli and S. aureus, respectively.Finally, multi- walled carbo n nanotubes were first mod ified by Fenton reage nt and then grafted with polyhexamethylene biguanide hydrochloride（MWNTs-g-PHMB）. Using MWN Ts-g-PHMB as the additives to prepare a kind of novel PES/MWNTs- g-PHMB ultrafiltration membrane with antibacterial and antifouling properties. The MWNTs- g-PHMB were synthesized and characterized by FTIR and Zetasizer. The effect of MWNTs-g-PHMB content on PES/MWN Ts-g-PHMB membrane morphology, hydrophilicity, permeability, anti-pollution and antibacterial properties were investigated. The results showed that with the addition of MWN Ts-g-PHMB in the dopes, the sponge-like structure was supp ressed and the finger- like macrovoids were developed. The introduce of MWNTs-g-PHMB not only can signi ficant ly enhance the PES membrane surface hydrophilic, surface roughness and protein adsorption properties, but also improve the flux and antifouling ability.When the MWNTs-g-PHMB added amount reached to 0.50wt%, the largest water flux of 90.0 L·m^-2·bar^-1.h^-1 for PM-50. After two flux decay and regeneration, The permeation flux recovery ratio was still maintain more than 90.0%. Antibacterial test indicated that PES/MWN Ts-g-PHMB hybrid membranes had excellent antibacterial properties. When the amount of MWNTs- g-PHMB in the dopes reached and/or exceeds 0.25wt%, the antibacterial rate of E. coli and S. aureus exceeded 99.0%.