Bridging the permeability-selectivity gap: optimizing TFC membranes with graphene oxide, ZIF-8 MOF, and carbon nanotubes using Box-Behnken design, transport modeling, and CFD validation.

A novel thin-film composite (TFC) polyamide reverse osmosis membrane incorporating graphene oxide (GO), zeolitic imidazolate framework-8 (ZIF-8), and carboxylated carbon nanotubes (CNT-COOH) was fabricated by interfacial polymerization for brackish water desalination. Functionalized nanomaterials (0.05 wt% GO, 0.03 wt% ZIF-8, and 0.02 wt% CNT-COOH) were dispersed in the aqueous m-phenylenediamine phase before reaction with trimesoyl chloride. SEM, TEM, AFM, FTIR, and XPS analyses confirmed successful nanomaterial incorporation, increased hydrophilicity, lower roughness, and a more negative surface charge compared with conventional TFC membranes. Under the common benchmark conditions (10 bar, 10 000 ppm NaCl, 25 °C), the TFC-GO/MOF/CNT membrane achieved pure water permeability of 8.2 L m-2 h-1 bar-1 and NaCl rejection of 99.4%. The verified 18-run Box-Behnken model (12 edge runs plus six center-point replicates) identified a multiresponse optimum near 15.7 bar, 2000 mg per L NaCl, and 33 °C, with predicted flux of 91.20 L m-2 h-1 and rejection of 98.37%; the nearest experimental run (16 bar, 2000 mg L-1, 30 °C) yielded 91.19 L m-2 h-1 and 98.372% rejection. Five transport models fitted the experimental data with R 2 > 0.992. The membrane also showed excellent antifouling performance, with 95.8% flux recovery after BSA fouling, and 30-day stability with 2.1% flux decline. These results demonstrate that GO/MOF/CNT incorporation improves TFC membrane permeability, selectivity, and durability.