Preparation Of Antibacterial Ultrafiltration Membranes And Their Antibiofouling Performance

Ultra-filtration(UF) technologies have been widely applied to water treatment, however, few present ultra-filtration membranes have antimicrobial activity. As the microbe adsorbed and reproducing on the membrane surface, the biofouling may be developing and the breeding microbes squint towards pervading into the filtrated water. In this paper, a few antimicrobial nano materials, such as nano-Ag(n-Ag), Ag embedded nano-TiO2(Ag-n-TiO2), and single-walled carbon nanotubes (SWCNTs)were mixed with PVC,which is one of the inexpensive materials. Then the mixture were prepared into membranes by phase inversion process respectively.We proposed the technique of the antibacterial membranes'synthesis and studied the characteristic of these original membranes unprecedented.With the scanning electron microscope(SEM), we could check the membranes' micro-structure characterization, it was found that all the membranes'surface was dotted with tiny uniform pores. The upper surface was the dense epidermis while the lower surface with holes, there was a very thin skin layer supported by a thick porous layer composed of pores and macrovoids. It exhibited that the membrane cross-section structure was a typical non-symmetrical structure, there was no significantly change on the membranes'structures. It proved that the nano materials could be dispersed in the polymeric matrix fully with the magnetic force agitation and sonication. N-Ag, Ag-n-TiO2, and SWCNTs all ameliorate the hydrophility of membranes, as their contents were 2%,2%,1% in the membranes, it showed that the contact angle decreased 17.16%,15.95％,15.54% accordingly, respectively. It maybe because the nano materials had large specific surface area, when they were added into the membranes, the membranes'apparent activation energy was increased, and then the hydrophility enhanced.E.coli was used as the model microbe to investigate the antibacterial activity of membranes before and after their modification by adding the nano materials. The n-Ag/PVC membranes and the Ag-n-TiO2/PVC membranes displayed obvious antibacterial activity and could grow an inhibition zone on the solidified agar media. With the plant counts, we also found the number of E.coli in n-Ag/PVC membranes'filtrate and Ag-n-TiO2/PVC membranes'filtrate were less than the control membranes. As the nano materials'contents were 2%,2% in the membranes, the bacterial trapping rate increased 22% and 24% respectively, moreover, biofilm development on the modified membranes'surface was harder than the control membranes, the antibacterial activity could last for a long time. With the mechanism analysise, we thought that the metal ions were stripping from the membranes and made a puncture of the microbe cell or bated the activities of enzyme.Taken n-Ag and Ag-n-TiO2 ions'figure into account, the round ions are apt to depolymerize from the membranes and weaken the membranes'antibacterial activity. In this paper, we were mixed PVC with SWCNTs and prepared UF membranes similarly as an further study, differently, there was no inhibition zone came out on the SWCNTs/PVC membranes towards the E.coli on solidified agar media. We also undertook the filtrate trial and found that as SWCNTs content from 0% to 1.5%, the bacterial trapping rate was not related to SWCNTs quantity. However, in aqueous solution, the dissociatived SWCNTs showed an extreme anti-bacterial activity while they touched the bacteria cell directly, as the contents were 0.5g/L, 1g/L,2g/L in the water solution, the E.coli was killed off after 8 hours, 987.09‰,991.34‰,996.78‰, respectively.With the mechanism analysise, puncture is the imaginable reason that made the bacteria death, when the SWCNTs were mixed with PVC and compounded into membranes, the puncture action would be restrained. One of the imaginabale reasons about the water-dissociatived SWCNTs'anti-bacterial performance to E.coli is they touched the bacteria cell and pierced the cell directly, another likely cause is the extreme adsorbability of SWCNTs, with which the SWCNTs could adsorb E.coli noto them and then slow the cell metabolism so as to restrain the activity of E.coli or even make it die.