Vortex-Fluidic-Mediated Fabrication of Polysulfone Ultrafiltration Membranes Incorporating Graphene Oxide

Polysulfone (PSF) ultrafiltration membranes were fabricated using a continuous flow micro-mixing process under high shear in a vortex fluidic device (VFD), followed by phase inversion of the cast solution. This involved investigating the effect of PSF concentrations (10, 15, and 20%) and rotational speed of the VFD for continuous mixing at 30 °C on the membranes' properties. These were compared with variants fabricated using conventional batch mixing in relation to structural, morphological, thermal, and mechanical properties, in addition to aspects of hydrophilicity and filtration performance. Graphene oxide (GO) was then incorporated into these membranes using both techniques in order to enhance their properties. The required mixing time for VFD processing was significantly shorter relative to conventional mixing, being reduced from >24 to <4 h. Scanning electron microscopy established that for microfluidic mixing, the PSF membranes possessed a more finger-like cross-section for a 10% PSF concentration, with a more sponge-like structure at higher concentrations. Moreover, the higher the rotational speed of the VFD, the higher the resulting porosity and permeability, with optimal levels of 84.3 ± 2.4% and 106 ± 4.3 LMH/bar, respectively, at 7k rpm. This brought about a 22% increase in porosity and permeability relative to the control experiment using conventional mixing. Compared to pristine PSF membranes, incorporating 1 wt % of GO using VFD processing increased the permeability of the membranes from 97.26 ± 3.3 to 123 ± 3.9 LMH/bar, with the NaCl rejection from 18.53 ± 1.3 to 34.3 ± 1.7% and bovine serum albumin rejection from 53.83 ± 2.00 to 74.2 ± 2.1%, respectively.