Manipulating the separation performance of nanofiltration membranes by coating thickness of organic phase during interfacial polymerization

The construction of an efficient magnesium-lithium separation thin film composite membrane with dual aqueous-phase monomers (PIP and MPD)

A series of thin film composite (TFC) membranes was prepared with piperazine (PIP) and m-phenylenediamine (MPD) in different ratios, and the magnesium-lithium separation performance of TFC membranes in salt-lake brine with the magnesium-lithium ratio of 28 were systematically compared. The prepared TFC membranes exhibited high rejection of magnesium ions and negative rejection of lithium ions with high water flux, enabling high magnesium-lithium separation efficiency. The characterisation using FTIR spectroscopy, XPS, zeta potential measurements, and SEM techniques indicated that the composition and surface morphology of the membrane prepared with dual aqueous monomers were found to be different from those prepared with single aqueous monomers under the similar conditions. The interfacial polymerization process of different monomers and the structure-performance mechanism of TFC membranes were further discussed.

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^-2·h^-1·bar^-1 under a pressure of 0.4 MPa. Additionally, the NF membrane shows excellent selectivity toward inorganic salts, with a rejection order of MgCl₂ > CaCl₂ > MgSO₄ > Na₂SO₄ > NaCl. Under optimal conditions, the membrane was able to reject up to 94.33% of 1,000 mg/L of MgCl₂ 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.