Comparative DCMD performance of hydrophobic-hydrophilic dual-layer hollow fibre PVDF membranes incorporated with different concentrations of carbon-based nanoparticles

High wetting resistance and high permeate flux are crucial for membrane distillation (MD) to achieve a high performance. To achieve both of these qualities, this work focused on the fabrication of co-extruded dual-layer hollow fibre polyvinylidene fluoride nanocomposite membranes with hydrophobicity gradients. The nanocomposite membranes were incorporated with hydrophobised carbon-based nanoparticles, i.e. multi-walled carbon nanotube (MWCNT) and graphene nanoplatelet (GNP). The effect of different concentrations of nanoparticles (0, 1 and 2 wt%) on the properties and MD performance of the membranes were investigated. The outer layers of the nanocomposites membranes were more hydrophobic than the neat membrane, and the membrane containing 2 wt% of hydrophobised GNP exhibited the highest contact angle of 111.1°. All the inner layers of the membranes were found to be hydrophilic with contact angle of about 60°, thus proving that hydrophobicity gradients were achieved in the membranes. All the membranes had pore sizes and porosities around 0.1 μm and 21.8–42.9% respectively, which are suitable to be used in MD. The surface roughness and wetting resistance of all the nanocomposite membranes, especially the ones with GNP, were higher than the neat membrane and the values increased with increasing concentration of nanoparticles. These membrane characteristics had effects on the direct contact MD (DCMD) performance where all the nanocomposite membranes showed better flux than the neat membrane. The membrane incorporated with 2 wt% of hydrophobised GNP achieved the highest flux of 8.27 kg/(m2h). All the membranes achieved salt rejections of more than 99.9%.