Enhanced interfacial interaction between polysulfone and polyamide layers via chloromethylation and amination: Improving permeability of nanofiltration membranes for water treatment applications

Controlling the physicochemical properties of the support layer provides an effective strategy to enhance the separation performance of thin-film composite (TFC) nanofiltration (NF) membranes. In this study, three TFC membranes were fabricated via interfacial polymerization (IP) of piperazine (PIP) and trimesoyl chloride (TMC) on chemically tailored polysulfone (PSF)-based supports. Chloromethylated polysulfone (CMPSF) was synthesized by chloromethylation of PSF using paraformaldehyde, chlorotrimethylsilane, and tin(IV) chloride, followed by phase-inversion casting onto polyethylene terephthalate (PET) backing material. Prior to IP, one CMPSF support was used as a control, while the other two were functionalized with PIP or 1,2-bis(3-aminopropylamino)ethane (TA) for surface amination and subsequent participation in polyamide (PA) layer formation. X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle, and zeta potential analyses confirmed successful support functionalization and PA layer formation, with the modified supports exhibiting enhanced hydrophilicity and reduced PA crosslinking. At 15 bar, the PIP-CMPSF-PA and TA-CMPSF-PA membranes achieved water fluxes of 52.5 and 53.3 LMH, respectively, compared with 36.7 LMH for CMPSF-PA, corresponding to increases of 30.1% and 31.1%. The increased permeability was achieved while maintaining comparable salt rejection, although rejection of low-molecular-weight pharmaceuticals decreased after support functionalization, while high-molecular-weight compounds remained highly rejected. The new membranes also exhibited similar BSA-induced flux decline, with reductions of 9.3-11.6% during 360 min of filtration, together with stable water flux and MgSO 4 rejection during a 40 h short-term laboratory testing. These findings demonstrate that support functionalization can regulate PA layer formation and enhance water permeability while maintaining separation performance.