High-Performance mild annealed CNT/GO-PVA composite membrane for brackish water treatment

Two-dimensional (2D) graphene oxide (GO)-based materials with tunable physicochemical properties have enormous potential for developing next-generation desalination membranes. Nevertheless, weak interlamellar interactions result in poor selectivity towards small ions, limiting the wide applicability of GO membranes. Controlling the swelling of the GO membrane while maintaining high permeability and selectivity is a significant scientific and technological challenge. To address the issues above, we used one-dimensional (ID) carbon nanotubes (CNT) as a nano-spacer and polyvinyl alcohol (PVA) as an adhesive. Synergistic ionic complexation between 1D-CNT, 2D-GO, and PVA was studied using various analytical techniques. The intercalation of CNT between GO nanosheets and the cross-linking of CNT/GO-PVA significantly improved the separation performance. Pressure-assisted filtration was used to coat the CNT/GO-PVA on hydrophilic mixed cellulose esters (MCE) support with pore size 0.22 µm to obtain a highly ordered laminated structure. Five minutes of mild annealing at 80 °C narrowed the laminar channels of the GO nanosheets by transforming the oxygen-containing functional groups. In a dead-end filtration unit, the CNT₅/GO₁₅-PVA_0.5 composite membrane exhibits a high rejection of 94.2% to sodium sulphate (Na₂SO₄) and 85.86% to sodium chloride (NaCl), accompanied by a high permeate rate of 14.2–13.45 LMH at 5 bar operating pressure. The salt rejection studies were evaluated for continuous operation for 72 h for all membranes. Due to the synergistic effect of CNT, GO, and PVA, prepared membranes demonstrated the potential for practical water separation applications with desired permeability and selectivity.