Effect of hexagonal-boron nitride nanosheets (h-BNNSs) on the structural morphology and performance of polyvinylidene fluoride (PVDF) membranes for water-oil separation

Hexagonal-boron nitride nanosheets/polyvinylidene fluoride (h-BNNSs/PVDF) composite membranes were successfully fabricated through a facile one-step phase inversion process. The amount of h-BNNSs incorporated into the PVDF membranes was varied within the mass percent range of 0–3 %, and the influence of the membranes' structural properties on water-oil separation was investigated. Surface roughness and wettability analyses (water contact angle data) showed that the membranes are hydrophilic, and the average surface roughness measurements reveal that the presence of h-BNNSs enhances the wettability of the composite membranes. In addition, h-BNNSs in composite membranes increased the total porosity which favoured enhanced membrane separation flux. Scanning electron microscopy investigations revealed flat surfaces with porous structures, sponge-like morphology and granular-like porous structures. The performance of the composite membranes for water-oil separation revealed that the addition of h-BNNSs to the membrane polymeric matrix resulted in enhanced selectivity towards water with the highest flux of 384.96 L/m2h, and selectivity efficiency of 99.60 % for a 3 % h-BNNSs/PVDF composite membrane, with no transmembrane pressure applied. The preference for water as a filtrate is attributed to the superior water permeation properties of the h-BNNSs and PVDF interaction. Water permeability was due to the presence of positively charged B atoms which pull the oxygen atoms in the water molecules. The improvement in fluxes of the investigated membranes, upon the addition of h-BNNSs makes them excellent candidates for water-oil emulsion separations.