Explication of polydopamine modified g-C3N4 as effective additive in PVDF nanocomposite membrane fabrication for enhanced ultrafiltration and self-cleaning performance

Nanocomposite membranes (NCMs) incorporated with nanomaterials have recently received increasing attention, but the preparation of high-performance membranes is still challenging due to the hydrophilicity and self-aggregation of the nanoparticles. In this study, graphite carbon nitride containing nitrogen defects was modified using dopamine (PDA@DCN) for effective alleviation of the agglomeration of nanoparticles resulting in a uniform casting solution. A non-solvent-induced phase separation method was adapted to prepare PVDF NCMs by using PDA@DCN as an effective additive. Superior permeability and selectivity were exhibited by the PDA0.25 @DCN/PVDF2 membrane (where a DA concentration of 0.25 g/100 mL was used in PDA@DCN preparation and 2% PVP was added during the membrane preparation) with the pure water flux of 390 L/(m2·h) and Bovine serum albumin (BSA) rejection of 95.9%. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that the improvement of the flux recovery rate of PDA0.25 @DCN/PVDF2 was due to the decreased attractive interaction for fouling. Ternary phase diagram and viscosity experiments confirmed that the addition of PDA0.25 @DCN accelerated phase inversion rate (as evident from thermodynamics and kinetics) and increased the porosity with smaller average surface pore size, which is expected to have good permeability and selectivity as an ultrafiltration membrane. Moreover, an excellent self-cleaning performance was demonstrated by PDA0.25 @DCN/PVDF2, with a flux recovery rate of 84.5%, simply under visible light irradiation, which indicates its potential for environment-friendly practical application.