Highly water-selective hybrid membrane by incorporating g-C3N4 nanosheets into polymer matrix

• Ultrathin and nanoporous g-C3N4 nanosheets were synthesized.
• g-C3N4 nanosheets were filled in alginate to fabricate hybrid membranes.
• Ordered transport channels and sieving effect were rendered by g-C3N4 nanosheets.
• Hybrid membranes showed high water permeability and separation selectivity.

In this study, highly water-selective hybrid membranes with superior water/ethanol separation performance were fabricated by incorporating g-C3N4 nanosheets (CNs) into sodium alginate (SA) matrix. CNs were synthesized by thermal oxidation “etching” and ultrasound exfoliation methods, and their ultrathin and nanoporous structures were characterized by atomic force microscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and X-ray diffraction. Due to the strong interfacial interactions between CNs and SA chains, the hybrid membranes exhibited higher mechanical strength and swelling resistance. Particularly, the horizontally aligned lamellar structure of CNs within hybrid membranes could render ordered channels for water transport, whereas the nanoporous structure of CNs could render additional sieving effect. Moreover, the intervention of CNs on polymer chain packing could render decreased crystallinity. Accordingly, the hybrid membranes exhibited excellent water permeability and selectivity for water/ethanol mixture separation. Especially, for the membrane containing 3 wt% CNs, the permeation flux could reach 2469 g/m2 h while the separation factor was as high as 1653 under 76 °C and 10 wt% feed water concentration. Meanwhile, the hybrid membranes showed good long-term stability. This study could be extended to fabricate a variety of CNs-incorporated membranes for diverse liquid mixture or gas mixture separations.

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