Preparation of polyamide thin film nanocomposite membranes containing silica nanoparticles via an in-situ polymerization of SiCl4 in organic solution

Thin film nanocomposite (TFN) membranes with improved permeability is important in the energy-efficient reverse osmosis membrane processes. In this paper, we demonstrate a facile method for the formation of polyamide/silica TFN membranes by an in-situ interfacial polymerization of aqueous amine and acid chloride/silicon tetrachloride (SiCl4) solutions. Water permeability is greatly enhanced with minimal loss in NaCl rejection. Polyamide/silica TFN membranes with 0.04% w/v SiCl4 exhibit a pure water permeability up to 9.7 L m−2 h−1 bar−1, which is 2.02 times more than that of the pristine thin film composite (TFC) membranes, while high rejection to NaCl (96.5%) is maintained. TEM tomograms confirm the existence of silica nanoparticles (NPs) in the thin PA film. More permeable voids are created in the cross-section of TFN membranes. Outer voids are buried underneath the PA protuberances and overhanging crumples. Inner voids and silica NPs are both encapsulated by polyamide. Top surfaces become more hydrophilic and negatively charged. With the optimal amount of SiCl4 loading, the formation of non-selective voids around the particles is minimized. Covalent and hydrogen bonds are formed between SiCl4 and PA polymers. These polyamide/silica nanocomposite membranes outperform many other TFN membranes in water permeability and salt rejection.