چكيده به لاتين
In this study, a positively charged thin film nanocomposite nanofiltration membrane was fabricated and its performance was evaluated in desalination process to achieve a highly permeable and selective membrane with anti-fouling properties. To this purpose, preparation conditions were optimized and then pure polymer ultrafiltration membranes and mixed matrix were fabricated by incorporation of acid treated-multiwalled carbon nanotubes (MWCNTs-COOH) or graphene oxide (GO) into polyacrylonitrile (PAN) matrix. Results showed that pure water permeation and water flux recovery for MWCNTs-COOH/ PAN membrane with optimal loading of functionalized carbon nanotubes (0.6 % w/w), were 315.15 LMH and 88/84%, that indicated an improvement of 65% and 29%, respectively, compared with the pure PAN membrane. Moreover, for GO /PAN matrix membrane, under the optimal loading of graphene oxide (1.5% wt), pure water permeation and water flux recovery were 393.46 LMH/bar and 91%, respectively, which indicated 103% and 32% improvement in comparison to the corresponding values of the pure PAN membrane, respectively. In the next step, effective parameters in surface coating by polyethylene amine were optimized to fabricate a thin film composite nanofiltration membrane. At obtained optimal conditions, first, the surface of the fabricated pure ultrafiltration membranes in previous step was contacted with a solution of polyethylene amine (concentration= 2000 ppm and pH=10) for 40 minutes, then cross-linked with a 0.5% glutaraldehyde aqueous solution for 30 minutes at 60 °C. For 500 ppm feed from MgCl2, the permeation of pure water and salt retention for optimum membrane obtained 7 LMH/bar and 88.6%, respectively. Thin film nanocomposite nanofiltration membranes were fabricated by coating (optimized in the previous step) on the surface of optimized MWCNTs-COOH/ PAN and GO/ PAN mixed matrix membranes. The permeability and rejection of the fabricated thin film nanocomposite nanofiltration membranes substrated on MWCNTs-COOH / PAN Was 9/7 LMH/ bar and 90%, respectively. Also, the permeability and rejection of the fabricated thin film nanocomposite nanofiltration membranes substrated on GO / PAN was 11.48 LMH/ bar and 86%, respectively. Considering the results, in nanofiltration membranes containing MWCNTs-COOH and GO as membrane substrate, compared to pure polymeric substrated nanofiltration membranes, not only the permeability was improved by 38% and 64%, respectively, but also the inverse relationship between permeability and rejection was overcome. Regarding salts rejection, membranes follow the order R (MgCl2)>R (MgSO4)>R (NaCl)>R (Na2SO4) which confirms positively charge nature of the membranes, that indicating domination of Donnan exclusion mechanism.
