Tailored Graphene Oxide Incorporated PES/CA Mixed‐Matrix Loose Nanofiltration Membranes for Water Softening and Divalent Salt Removal

ABSTRACT 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% (MgCl 2 ), and 59% (Na 2 SO 4 ), 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.