A thin film nanocomposite (TFN) membrane containing oleic acid modified silica nanoparticles was synthesized via interfacial polymerization on polysulfone (PSf) asymmetric membrane for the removal of pesticides from water. m-Phenylenediamine (MPD) with trimesoyl chloride (TMC) was polymerized to prepare a polyamide layer. SiO2 nanoparticles (∼15 nm) were successfully modified by oleic acid (OA) and incorporated into a TMC solution at concentrations ranging from 0 to 0.3 w/v%. The prepared TFN membranes were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopy, and contact angle measurements. It was found that the use of modified silica nanoparticles as an additive can decrease membrane pore size, surface roughness, and contact angle. Rejection and permeate flux measurements were carried out for three triazines including atrazine, propazine, and prometryn. The effects of molecular weight and size, hydrophobicity, and dipole moment of triazines on the rejection were investigated. The results revealed that the addition of modified SiO2 in TMC solution up to 0.17 w/v% (S2 membrane sample) increased the permeate flux and showed the best rejection among the all prepared membranes. Prometryn with the largest molecular size had the highest rejection and its rejection remained unchanged at 99%. For all membrane cases, the lowest rejection (84.4–90.2%) was obtained for propazine due to its higher dipole moment. Also, the highest rejection occurred at the pressure of 10 bar and the feed concentration of 10 ppm.

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