Enhancing desalination performance of thin film composite membrane through layer by layer assembly of oppositely charged titania nanosheet

Reverse osmosis (RO) is a mature desalination technology that provides an effective solution to solve global water scarcity issues. In this study, thin film nanocomposite (TFN) membrane for RO desalination was fabricated by depositing positively charged titania nanosheet (pTNS) and negatively charged titania nanosheet (nTNS) on the surface of polyamide (PA) layer through layer by layer (LbL) assembly. The pTNS was synthesized through solid-state calcination and acid ion-exchange. Though the additional step of exfoliation, single sheet nTNS with improved hydrophilicity property was obtained. The hydration layer created on the surface of TNS-PA could hinder the direct contact of salt ions with the surface of TFN membrane, hence significantly enhance the water permeability and salt rejection. The membrane surface hydrophilicity was improved and surface roughness was decreased with the increasing number of bilayers. However, the excessive pTNS/nTNS bilayer coating has imposed additional hydraulic resistance hence resulted in the reduction of water permeability. The highest water permeability of 0.8 L·m−2·h−1·bar−1 (60% improvement) was achieved with the 2 bilayers of TNS-PA TFN as compared to the pristine PA membrane. The sodium chloride (NaCl) rejection was 98.45% which was also higher than pristine membrane with rejection of 96.65%.