Improvement of the separation and antibiological fouling performance using layer-by-layer self-assembled nanofiltration membranes

A novel surface-modified nanofiltration (NF) membrane was prepared by layer-by-layer (LbL) self-assembly of positively charged polyethylenimine (PEI) and glutaraldehyde (GA) and negatively charged carboxymethyl chitosan (NO-CMC) alternately on the polyethersulfone (PES) membrane surfaces. The alteration aimed at improving the membrane separation performance, which was investigated in the study. In order to enhance antibiological fouling performance of the NF membrane, the silver nanoparticles (AgNPs) were coated on the modified membrane in two different modes. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), zeta potential measurement, and water contact angle measurements were employed to characterize the formed membrane surface chemical composition and morphology. The rejection of different single nonheavy metal salts, yielded from the modified membrane, followed the order of MgCl2 > MgSO4 > CaCl2 > Na2CO3 > NaCl > Na2SO4. Additionally, the rejection of single heavy metal salts Cr3+, Cu2+, Cd2+, Ni2+ was 88.95%, 84.04%, 82.69% and 83.47%, respectively, whereas the rejection of Cr3+, Cu2+, Cd2+, Ni2+ increased to 91.77%, 90.70%, 89.74% and 87.22%, respectively, in the mixed salt solution. Moreover, the rejection of Cu2+ and Cd2+ increased to 96.12% and 94.38% after adjusting pH. As a result of loading the AgNPs on the modified membrane with a suitable mode, the antibiological fouling ability of the membrane was immensely improved by AgNPs. Graphic abstract