Feasibility of brackish water and landfill leachate treatment by GO/MoS2-PVA composite membranes

Two-dimensional (2D) based layered materials with tunable chemical functionalities and surface charge properties have emerged for on-demand applications including membrane technology. However, the process control, time and energy-efficient production of non-swelling graphene oxide (GO) with retaining physicochemical properties are still challenging. In this work, we have fabricated highly ordered GO membrane on cellulose acetate supporting membrane filters of 1.2 μm pore size using molybdenum disulphide (MoS2) as a nano-spacer and polyvinyl alcohol (PVA) as an adhesive for the first time with limited swelling. The fabricated membranes were used for NaCl rejection and removal of toxic heavy metal ions, and the radioactive element from landfill leachate water. The introduction of hydrophilic PVA, thickness control using a various amount of nanospacer and graphene oxide played a vital role in the transport mechanism, permeability, and selectivity index. The composition of PVA and MoS2 in the coating solution was optimized to tune the d-spacing of graphene oxide layers. The newly developed composite membranes have 89% rejection rate to NaCl and 3.96 L/m2h water flux at low operating pressures of 5 bar. Also, the prepared membranes have a high rejection of multivalent metal ions in landfill leachate. 86.5% to 99.8% rejection rate of multivalent metal ions in landfill leachate was observed for the M3 (GO (10): MoS2 (10): PVA (0.5)) membrane. The excellent rejection performance is ascribed to the combined impact of size exclusion, ion adsorption, electrostatic interaction and Gibbs-Donnan exclusion mechanism. The excellent stability and high rejection rate even after 216 h of operation make the fabricated membranes promising for use in practical water separation applications.