Thin-film nanocomposite (TFN) membranes enjoy advantages over the traditional membranes for water purification purposes. TFN membranes are fabricated primarily through interfacial polymerization: diamines are reacted with acyl chlorides. Nanoparticles are added either to aqueous or organic solutions. A polyamide layer forms at the interface of two immiscible phases. In this present study, silica nanoparticles were dispersed in water or n-hexane medium. Scanning electron microscopy-energy dispersive X-ray spectroscopy revealed that dispersing the nanoparticles in n-hexane led to the embedment of more silica in the polyamide layer. A cross-flow nanofiltration setup was used to evaluate the membrane performance, with pure water and different feed salt solutions as feed. The results demonstrated that dispersing the nanoparticles in water led to the formation of a defective polyamide layer. However, dispersion in n-hexane resulted in a TFN membrane with a high separation performance. Moreover, the membrane exhibited stability for 62 h.