Modified MWNTs To Prepare PVDF Membranes With Antibacterial And Easy Cleaning Properties

In recent years,ultrafiltration technology has been widely used as an effective approach for applications in drinking water treatment and waste water drainage and reuse treatment and membrane bioreactor.However,due to the inherent hydrophobic property,PVDF membrane fouling?including biofouling and organic fouling?decreases the ultrafiltration efficiency and shortens membrane life.Therefore,membrane surfaces with both superior antibacterial and self-cleaning properties are the most attractive owing to their long-standing diverse functions.In this work,we attempt to study and fabricate different kinds of antibacterial and anti-fouling PVDF membranes.In brief,three different kinds of antibacterial agent were used to modify MWNTs.After the modification,MWNTs was added into casting solution to prepare PVDF hybrid ultrafiltration membranes.Following,the hydrophilcity,permeability,anti-fouling and antibacterial abilities were studied.Firstly,rough MWNTs were oxidized to O-MWNTs.Following,N-halamin epoxide and siloxane were grafted onto the O-MWNTs?N-Si-MWNTs?to fabricate PVDF hybrid membranes by using a non-solvent induced phase separation method?NIPS?.The membrane morphology was observed under a field emission scanning electron microscopy.The results demonstrated that the PVDF hybrid membranes had an asymmetrical structure,and their hydraulic permeability was evidently enhanced with the addition of modified MWNTs.When compared with the primitive PVDF membrane,the hybrid membranes presented improved surface hydrophilicity.After three ultrafiltration–regeneration cycles with bovine serum albumin as model biofoulant and pure water as detergent,the PVDF hybrid membranes exhibited a high flux recovery ratio?FRR?.Furthermore,when compared with other membranes,the membrane containing N-Si-MWNTs displayed the highest FRR value of above 96.5%after the entire fouling and cleaning experiment.The fabricated PVDF/N-Si-MWNTs hybrid membranes had excellent antibacterial efficacy,presenting maximum antibacterial efficacy of 98.0%and 95.6%against Staphylococcus aureus and Escherichia coli,respectively.Secondly,2-Dimethylaminoethyl chloride hydrochloride?DCH?used as quaternary ammonium precursor was grafted onto MWNTs by epichlorohydrin.The obtained N⁺-MWNTs was used as additive to prepare PVDF hybrid ultrafiltration membranes.Field emission scanning electron microscopy?FESEM?was used to observe the morphology.The results demonstrated that the surface roughness and hydrophilicity of PVDF/N⁺-MWNTs hybrid membrane were obviously improved.Besides,in the ultrafiltration-regeneration cycles with bovine serum albumin as model biofoulant,the pure water permeation was improved from 110.5 L.M^-2.h^-1.bar^-1 to197.4 L.M^-2.h^-1.bar^-1.Especially in the third cycle,the flux recovery ratio?FRR?was evidently improved.The prepared PVDF/N⁺-MWNTs hybrid membranes had excellent antibacterial efficacy against Escherichia coli and Staphylococcus aureus.Especially after three cycles,the antibacterial ratio remains high.Finally,biological polyphenols gallogen?extracted from pomegranate bark?was used to modify MWNTs.The obtained R-MWNTs were added into casting solution to prepare PVDF hybrid membranes.With different additive amount,the morphology and properties were studied.The results show that the hydrophilicity and mechanical property were enhanced with the increase of MWNTs.Besides,in the ultrafiltration of BSA solution,the permeation property was significantly changed.The pure water permeation was improved from 110.3 L.M^-2.h^-1.bar^-11 to 256.8 L.M^-2.h^-1.bar^-1.For inherent antibacterial property,the PVDF/R-MWNTs membrane with gallogen possessed outstanding antibacterial efficiency.When the added amount of R-MWNTs reached to 0.6 wt%,the antibacterial efficiency against Escherichia coli and Staphylococcus aureus was 90.2%and 90.1%,respectively.