In-situ coating TiO2 surface by plant-inspired tannic acid for fabrication of thin film nanocomposite nanofiltration membranes toward enhanced separation and antibacterial performance

A major issue hindering development of thin film nanocomposite (TFN) nanofiltration (NF) membrane is the interfacial defects induced by nanomaterial aggregation in top layer. Although various nanomaterials surface modification strategies have been developed to eliminate the interfacial defects, they usually involve extra modification steps and complex post-treatments. Inspired by the substrate-independent coating ability of tannic acid (TA) and the fact that the phenolic hydroxyl groups in TA can react with acyl chloride group in trimesoyl chloride, a TA coating solution containing TiO2 nanoparticles was used as an aqueous phase of interfacial polymerization to prepare interfacial modified TFN NF membranes in this study. Surface modification of TiO2 nanoparticles and interfacial polymerization can be carried out in a single step without any extra pre-modification step. It was found that the TA coating on TiO2 nanoparticles surface could decrease TiO2 aggregations and enhance interfacial compatibility between TiO2 and polyester matrix. The TFN NF membrane prepared at a TiO2 loading of 0.020 wt% exhibited a pure water flux of 28.8 L m-2 h−1 (284% higher than that of the controlled TFC membrane), and possessed enhanced NaCl and Na2SO4 rejections of 57.9% and 94.6%, respectively, breaking through the trade-off between permeability and selectivity.