Modulating the support layer for the fabrication of high flux nanofiltration membrane and its application in desalination and micropollutants’ rejection

Nanofiltration (NF) membranes have a great potential for rejecting salts and contaminants from various water sources. Nonetheless, the persistent trade-off relationship between flux and rejection remains a significant obstacle in membrane-based filtration. Herein, high flux NF membranes were developed by dissolving a series of hydrophobic diamines (2-chloro-4,6-diamino-1,3,5-triazine (DA1), benzoguanamine (DA2), and acetoguanamine (DA3)) in polysulfone (PSF) support layer prior to phase inversion process. The resulting solutions were cast over polyether terephthalate (PET) via phase inversion method, while the active layer was developed through interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC). The structural and surface properties of both modified and unmodified polysulfone supports, as well as the impact of diamine modification on the formation of active polyamide (PA) layer were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), atomic force microscope (AFM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), water contact angle (WCA), and zeta-potential. These analyses revealed the fabrication of NF membranes with unique polyamide active layers. Cross-flow filtration tests were conducted to evaluate water flux at varying pressures, leading to the selection of an optimal operational pressure of 15 bar. Subsequently, the control and modified membranes were tested for rejection of various salts and pharmaceutical drugs solutions, and the analysis was conducted using a total dissolved solids (TDS) meter and high-performance liquid chromatography with diode array detection (HPLC-DAD) system respectively. Optimization of the hydrophobic diamine concentration in the polysulfone solution revealed that a 0.1 wt% inclusion yielded the best results. The control membrane presented a flux of 25.8 L m⁻².h⁻¹, while the addition of DA1, DA3 and DA2 not only maintained comparable or enhanced rejection of salts and pharmaceuticals drugs but also increased the flux to 30 L m⁻².h⁻¹, 63.8 L m⁻².h⁻¹ and 95.4 L m⁻².h⁻¹ respectively at 15 bar of feed pressure. This study presents a simple and effective approach for enhancing the permeate flux of nanofiltration membranes.