Hot-water desalination using thermally stable thin film nanocomposite membranes reinforced with graphitic carbon nitride nanosheets (gC3N4)

There is a growing need for thermally stable membranes in water treatment, as most commercial membranes exhibit poor performance at elevated temperatures. This study explores the incorporation of hexametaphosphate-modified graphitic carbon nitride (HMP-gC 3 N 4 ) nanosheets into the polyamide selective layer of thin-film nanocomposite (TFN) membranes to enhance thermal stability, water permeability, salt rejection, and fouling resistance. The unique physicochemical properties of HMP-gC 3 N 4 , particularly its hydrophilicity and thermal and chemical robustness, significantly improved membrane performance. Various chemical and microscopy characterizations confirmed the successful integration of HMP-gC 3 N 4 nanosheets within the polyamide matrix. Filtration tests demonstrated that HMP-gC 3 N 4 TFN membranes exhibited higher water flux, superior organic and biofouling resistance, and enhanced thermal stability, while maintaining high salt rejection, compared to neat thin-film composite (TFC) membranes. The TFN membranes also demonstrated strong antibacterial activity against E. coli , further enhancing biofouling resistance. Molecular dynamics (MD) simulations revealed that the inclusion of rigid gC 3 N 4 nanosheets significantly enhanced the molecular packing and reduced fractional free volume in the PA layer, thereby improving thermal resistance. After five days of cyclic operation at 75 °C, the TFN membrane maintained a high NaCl rejection rate of 98.2%, confirming its excellent durability. These findings highlight the potential of gC 3 N 4 nanosheets as a promising nanofiller for next-generation high-temperature desalination membranes, offering improved durability, efficiency, and longevity under harsh operational conditions. • Phosphate-gC 3 N 4 TFNs boost RO flux while sustaining ≥98% NaCl rejection. • Membranes retain performance through five 75 °C heating–cooling cycles. • MD simulation shows T g rise to 190 °C and lower FFV, improving thermal stability. • Hydrophilic, antibacterial surfaces mitigate SA/BSA/ E. coli fouling; FRR to 97%. • Thin, dense PA layer from nanosheet dispersion lowers mass transfer resistance.