Tailored Graphene Oxide Incorporated PES/CA Mixed-Matrix Loose Nanofiltration Membranes for Water Softening and...

Achieving a simultaneous enhancement of permeability and selectivity remains a central challenge in nanofiltration membrane design. Here, we report the fabrication of high-performance polyether sulfone-cellulose acetate (PES/CA) mixed-matrix membranes via phase inversion, employing polyvinylpyrrolidone (PVP) as a pore-forming agent and graphene oxide (GO) as a hydrophilic nanofiller to precisely tailor membrane structure and transport behavior. Systematic characterization using SEM, FTIR, and physicochemical analyses reveals that PVP induces the formation of interconnected finger-like channels and macrovoids, whereas GO incorporation significantly enhances surface hydrophilicity and interfacial compatibility within the polymer matrix. An optimal GO loading of 1.5 wt.% enables uniform dispersion, maximizing wettability and transport efficiency; in contrast, higher loading (2 wt.%) leads to nanosheet agglomeration, reduced hydrophilicity, and restricted permeation pathways. The synergistic interplay between PVP-induced porosity and GO-enhanced surface functionality results in a finely tuned membrane architecture that alleviates the conventional permeability-selectivity trade-off. The optimized membrane exhibits a stable pure water flux of 95 L m^-2 h^-1, coupled with improved salt rejection efficiencies of 46% (NaCl), 75% (MgCl₂), and 59% (Na₂SO₄), significantly outperforming pristine PES/CA membranes. These findings demonstrate a scalable and effective strategy for designing loose nanofiltration membranes, offering promising potential for energy-efficient water softening and divalent salt removal from brackish water.