Study On Preparation And Anti-fouling Properties Of PAN Mixed Matrix Membranes Modified By Micro/nano Particles

Nowadays,worldwide water pollution is becoming more and more serious.Membrane technology,with ultra-separation and purification abilities,is one of the most efficient methods to solve the pollution problem and water shortage.Among various membrane technologies,ultrafiltration has the great advantages of energy saving,high efficiency,and low driving force.It can effectively separate macromolecular organic matters,colloidal particles and proteins.For ultrafiltration,our research mainly focused on separation of mixed matrix membranes(MMMs)with polyacrylonitrile(PAN)as raw polymer.In order to solve the membrane fouling,physical blending method was employed for the membrane modification.During the fabrication,Nano-inorganic particles,namely Halloysite nanotubes(HNTs),Attapulgite Clay(ATPC)and Serpentine miner(SRPM),were introduced as three kinds of micro-carriers.Dextrorotary amino acid(D-amino acid),which can naturally inhibit the growth of bacteria and microorganisms,was adhered to the surfaces of the three carriers by using the adhesion of polydopamine.The prepared composites(micro-inorganic particles/polydopamine/D-amino acid)were blended with PAN to further synthesize PAN-based MMMs.As a result,PAN MMMs with strong anti-biofouling property were developed.With the help of XRD,TEM/SEM,FTIR,XPS,AFM,contact angle device and other instruments,the micro-morphology,chemical structure and hydrophilic properties of the MMMs were studied.The physical and chemical indexes for evaluation of the MMMs’performances,such as pure water flux,BSA rejection and circulating anti-pollution of the membrane were measured.At beginning,HNTs were used as the carrier and were modified with one of the D-amino acids(D-leucine).The effects of the amount of the composite additive(HDD(L))prepared by adding D-leucine in the PAN MMMs were investigated and compared with the pure PAN ultrafiltration membrane.The results indicated that with the increase of the HDD(L)amounts,the performances of the PAN MMMs showed a trend of rising first and then declining after the HDD(L)amount over 5 wt%.From original PAN membrane to the 5 wt%PAN MMMs,the pure water flux soared from 489.65 L/(m~2·h)to 1334.21 L/(m~2·h),increased by 172%,the rejection rate of bovine serum albumin(BSA)increased from 80.90%to 100%,and the flux recovery rate after three times antifouling-cycles rose from 43.31%to 72.78%.Furthermore,influences of three kinds of D-amino acids on the structures and properties of PAN MMMs were investigated.It was found that powder modified with D-leucine had more uniform distribution of particle size and better dispersion due to its neutral charge.The performance of the prepared D-leucine MMM was better than those of D-Tyrosine MMM and D-Tryptophan MMM.It also showed excellent anti-biofouling ability in the experimental studies of anti-Escherichia coli(E.coli).Besides above-mentioned approach,ATPC and SRPM were used as two carriers,respectively.Composites(ADD and SDD)were fabricated based on the adhesive force between the D-leucine and the carrier.The effects of the additives(ADD and SDD)on the structures and properties of the PAN MMMs were also investigated.The results showed that the influence of the amount of the two additives on the PAN MMMs were similar to that of HDD(L),which reached the optimum at 5 wt%in the measured range.For the membrane with 5 wt%ADD,the pure water flux raised up to 186%,the BSA rejection rate reached 100%,and the flux recovery rate increased to 52.75%.For the membrane with 5 wt%SDD,the pure water flux raised up to 181%,the BSA rejection rate reached 100%,and the flux recovery rate increased to 50.38%.Both of them also showed excellent anti-biofouling abilities in the anti-E.coli experiments.Finally,the longevity,stability,selectivity and reproducibility of the three best PAN MMMs(i.e.the membrane with 5 wt%HDD(L),the membrane with 5 wt%ADD(L)and the membrane with 5 wt%SDD(L))were tested with standard BSA solution for 300 hours to explore their potential application.The long-time study showed that after 300 hours of protein filtration,all three BSA rejection rates were over89.7%,much higher than 80.9%of the pure PAN membrane.The surface resistance to E.coli also remained at a comparable level after 300 hours.The PAN MMMs hold great promise for industrial trends of environmental protection.