Combining phthalimide innate of a positive-charge nanofiltration membrane for high selectivity and rejection for bivalent cations.

A positively charged nanofiltration (NF) membrane is known to have exceptional separation performance for bivalent cations in aqueous solutions. In this study, a new NF activity layer was created using interfacial polymerization (IP) on a polysulfone (PSF) ultrafiltration substrate membrane. The aqueous phase combines the two monomers of polyethyleneimine (PEI) and phthalimide, while successfully producing a highly efficient and accurate NF membrane. The conditions of the NF membrane were studied and further optimized. The aqueous phase crosslinking process enhances the polymer interaction, resulting in an excellent pure water flux of 7.09 L·m·h·bar under a pressure of 0.4 MPa. Additionally, the NF membrane shows excellent selectivity toward inorganic salts, with a rejection order of MgCl > CaCl > MgSO > NaSO > NaCl. Under optimal conditions, the membrane was able to reject up to 94.33% of 1,000 mg/L of MgCl solution at an ambient temperature. Further to assess the antifouling properties of the membrane with bovine serum albumin (BSA), the flux recovery ratio (FRR) was calculated to be 81.64% after 6 h of filtration. This paper presents an efficient and straightforward approach to customize a positively charged NF membrane. We achieve this by introducing phthalimide, which enhances the membrane's stability and rejection performance.