Tuning the Permeability–Selectivity Balance of Polyamide Nanofiltration Membranes with Functionalized MoS2 Nanosheets and Hyperbranched Polyester

<jats:p>Thin-film composite nanofiltration membranes are constrained by a permeability-selectivity trade-off, as increasing free volume can accelerate water transport while compromising solute rejection. Here, molybdenum disulfide (MoS2) nanosheets were chemically exfoliated and functionalized with hydroxyl, amino, carboxyl, or dihydroxyl ligands, and subsequently incorporated into piperazine-trimesoyl chloride polyamide selective layers by interfacial polymerization. Hyperbranched polyester (HPE) was evaluated independently and then combined with the best-performing functionalized nanosheets. At 150 ppm, carboxylated MoS2 delivered a water permeance of 43.50 L m-2 h-1 bar-1 with 94.81% Na2SO4 rejection. HPE further enhanced membrane hydrophilicity and water permeance while maintaining high sulfate rejection within an appropriate concentration window. Co-incorporation of 150 ppm carboxylated MoS2 and 0.4% (w/v) HPE produced the best overall permeability-selectivity balance, reaching 58.60 L m-2 h-1 bar-1 while retaining &gt;90% Na2SO4 rejection. Spectroscopic and microscopic analyses verified the incorporation of both modifiers and revealed increasingly hydrophilic and nodular polyamide surfaces. Molecular dynamics simulations further showed that MoS2/HPE interlayer spacings of 6–9 Å preserved ion rejection above 90%, whereas expansion toward 12 Å promoted water transport at the expense of ion exclusion. These results demonstrate that functional-group chemistry and HPE loading act as coupled design parameters for regulating interfacial compatibility, hydrophilicity, free volume, and nanoscale transport pathways in polyamide nanofiltration layers.</jats:p>