Development of High-flux and Anti-fouling Polyamide Thin-film Nanocomposite RO/PRO Membrane through Coating and Embedding of TiO2 Nanomaterials

Abstract

In this dissertation, development of high performance and fouling resistant PA TFC membrane was implemented by coating and embedding of TiO2 nanomaterial for RO and PRO applications. Firstly, the surface of PA TFC membrane was coated with TiO2 nanoparticles (TNPs) via a sol-gel-derived spray coating method. The optimum TiO2 nanoparticle coating layer, which is dense and durable without blocking the pore or surface, was formed by base-catalyzed (ammonium hydroxide) TiO2 sol-gel-derived spray coating. Through this optimized coating condition, the active and support layer of a commercial TFC was coated with TiO2 nanoparticles (TNPs) for RO and PRO application, respectively. This TNP coating imparted hydrophilic properties and a negative charge to the membrane surface. These modified surface properties reduced the interaction force between humic acid and membrane surface and resulted in the enhancement of fouling resistance in RO and PRO process. The less favorable foulant-membrane interaction of the TNP-coated membrane was confirmed by a lower interaction force between a humic acid-tethered AFM tip and the membrane surface. A TNP coating of support layer increased water flux and reduced reverse salt flux in PRO process, while water flux and salt rejection were maintained when the proper amounts of TiO2 sol was coated in RO process. Secondly, TiO2 nanomaterials embedded polyamide thin-film nanocomposite membrane was fabricated for enhancement of water flux and fouling resistance. In addition, the effect of structure and surface property of nanomaterial on water flux was evaluated by comparison of TiO2 nanotube (TNT) and TiO2 nanoparticle (TNP) embedded PA TFN membrane. The TFN RO membranes containing TNT or TNP exhibited similarly high hydrophilicities and enhanced water permeability compared with a conventional RO membrane. Although TNP TFN RO membrane has similar surface hydrophilicity with TNT TFN RO membrane when the same amount of TNP and TNT are embedded, the TNT TFN RO membranes had better water permeability than the TNP TFN RO membranes. Compared with non-porous TNP, nanochannels of TNT provided additional enhanced water permeability by serving as water transport passageways. From these results, it is expected that the addition of TiO2 nanomaterials in PA TFC membrane can enhance the performance and fouling resistance in RO and PRO process.