Flux and salt rejection enhancement of polyvinyl(alcohol) reverse osmosis membranes using nano-zeolite

Zeolite based membranes have been extensively studied over the past decade for enhanced reverse osmosis (RO) performances. In this study, poly vinyl alcohol (PVA)-networked cellulose (NC) membranes incorporated with nano zeolite-Y were prepared through a facile slip casting approach using various nano zeolite-Y loadings from 0.05 to 1.0 wt%. The nano zeolite was prepared through a unique ball milling process. Membrane hydrophilicity was seen to increase with increase in zeolite loading, while improved tensile strength (8.7 MPa) and tensile modulus (67 MPa) were obtained on small zeolite additions of 0.05 wt%. No prominent peak shifts were observed in differential scanning calorimeter (DSC) testifying to the thermal stability of the membranes. Membranes were tested for RO using 25,000 mg/L NaCl solution. Optimum RO performance was achieved for 0.5 wt% nano zeolite registering a salt rejection (R_s) of 99.52% with a flux increase of 34.2% compared to the bare PVA-NC membranes. Thus, addition of nano-Y to the polymer matrix provides preferential water pathways which facilitate water flow through the membrane. In addition, the irregular crystal morphology of the nano-Y, the size exclusion principle and the ion exchange mechanism provided a high salt rejection for the PVA-NC-nano Y membranes.