Controllable construction of polymer/inorganic interface for poly(vinyl alcohol)/graphitic carbon nitride hybrid pervaporation membranes

Abstract

Highly water-selective hybrid pervaporation membranes with excellent water/ethanol separation performance and superior water channels were fabricated by incorporating graphitic carbon nitride (g-C3N4), activated g-C3N4 (O-g-C3N4) and polydopamine modified g-C3N4 (PDA@O-g-C3N4) nanosheets into poly(vinyl alcohol) (PVA) matrix. The nonselective polymer/inorganic interface channels between PVA and g-C3N4, O-g-C3N4 and PDA@O-g-C3N4 in hybrid membranes were controllable constructed through hydrogen bonds, rigid and flexible chemical bonds, respectively. The membrane performances were tested in the pervaporation (PV) process for the dehydration of 90 wt% ethanol/water mixtures at 75 °C. The results revealed that with the increase of binding force among polymer/inorganic interface, from hydrogen bonds (CPVA-g-C3N4), to rigid (CPVA-O-g-C3N4) and flexible chemical bonds (CPVA-PDA@O-g-C3N4), the total flux decreased from 4634 to 2328 g/(m2h) and the separation factor increased from 32.4 to 57.9. It is implied that the nonselective polymer/inorganic interface channels were controlled successfully. Meanwhile, compared with the pure cross-linked PVA (CPVA) membrane (total flux 2325 g/(m2h) and separation factor 18.7), incorporation of g-C3N4, O-g-C3N4 and PDA@O-g-C3N4 could all lead to an increase of surface hydrophilicity of the CPVA membranes along with an increase in membrane tortuosity and membrane water-selective channels that was favorable to the selective permeation of water molecules. Namely, these new hybrid membranes can break the “trade-off effect” effectively. Moreover, due to the ordered alignment of g-C3N4, O-g-C3N4 and PDA@O-g-C3N4 nanosheets and the strong interfacial interactions among these nanosheets, succinic acid (Sa) and the PVA matrix, the hybrid composite membranes showed both high swelling resistance and mechanical stability.