Enhancing water flux of thin-film nanocomposite (TFN) membrane by incorporation of bimodal silica nanoparticles

Modern reverse osmosis (RO)/nanofiltration (NF) membranes are primarily made of thin-film composites (TFC) fabricated through interfacial polymerization of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) on a polysulfone (PSF) supporting membrane. In this study, two types of bimodal silica nanoparticles (similar to 80 nm) with different internal pore structures were synthesized and incorporated into the polyamide (PA) thin-film layer during interfacial polymerization at concentrations varying from 0 to 0.1 wt%. The as-prepared membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, and their performances were evaluated in terms of the water permeability and salt rejection. The results showed the water permeability increased with increasing BSN concentrations, reaching a maximum of 53.5 L m(-2) h(-1) at a bimodal silica nanoparticle (BSN) concentration of 0.5 wt% (pressure at 300 psi, NaCl concentration: 2000 ppm). This represented a flux increase of approximately 40%, while a near constant salt rejection of 95% was maintained. The study demonstrated that the internal micro-mesoporous structures of bimodal silica nanoparticles contributed significantly to the membrane performance, which is consistent with previous studies with relatively uniform internal pores.