Thin film nanocomposite membrane incorporated with silver-carbon nanotube hybrid for desalination

Abstract

Addressing water scarcity is an essential of the sustainable development’s goal. One potential solution for new water resource is desalination. Forward osmosis (FO) desalination, utilizing the concept of osmotic pressure difference between high and low salinity streams across semipermeable membrane is of interest in the membrane research community in recent years. Nevertheless, practical application of FO desalination has been limited by the unsatisfactorily membrane performance to simultaneously offer high permeability and excellent anti-fouling properties. Hence, the overall goal of this study was the development of high-performance thin film nanocomposite (TFN) membrane with consistent water flux, high salt rejection and good biofouling resistance. Hybrid nanofiller, silver-functionalized carbon nanotubes, Ag-fCNTs synthesized via hydrothermal method was blended with PES dope solution and TFN membranes were fabricated by varying nanofiller loading (0.1, 0.3 and 0.5 wt%) using phase inversion followed by interfacial polymerization technique. Different characterizations such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and transmission electron microscope (TEM) confirmed the successful formation of Ag-fCNTs. The effects of Ag-fCNTs on the membrane properties and physical characteristics such as, chemical functionality, morphologies, surface roughness and surface hydrophilicity were analyzed. The resultant TFN membranes exhibited enhanced hydrophilicity, porosity and surface roughness, which in turn improved the overall membrane performance. Evaluation using dead-end reverse osmosis revealed that TFN membranes enhanced the water permeability without trade-off in salt rejection and the structural parameter (S) was reduced, indicating the suppression of internal concentration polarization. Furthermore, FO performance significantly improved e.g., the water flux of the optimum blending ratio, TFN0.3 achieved 27.99 l/m²h in pressure retarded osmosis (PRO) mode by using 2.0 M NaCl/RO water as the draw/feed solution, while the specific salt flux was acceptable at 0.15 g/m²h. However, antibacterial assessment and antibiofouling filtration experiments of pristine TFC and TFN membranes against the Gram-negative bacteria, E. coli demonstrated no noticeable antibacterial activity. This could be related to the small amount of Ag nanoparticles used (1:5 ratio) for Ag-fCNTs hybridization. Despite showing poor anti-biofouling properties, the promising water flux and salt rejection improvement implied the potential of the newly developed TFN for practical FO desalination application.