A facile synthesis approach for GO-ZnO/PES ultrafiltration mixed matrix photocatalytic membranes for dye removal in water: Leveraging the synergy between photocatalysis and membrane filtration

Photocatalytic membranes offer a unique opportunity of exploiting the combined benefits of membrane filtration and photocatalytic degradation, however, striking a practical balance between the two processes remains a challenging prospect. In this work, we explored the filtration and simulated solar light-mediated photocatalytic performance of polyethersulfone (PES) ultrafiltration membranes embedded with graphene oxide-zinc oxide (GO-ZnO) nanocomposite photocatalyst. A novel and simple double casting phase inversion method was used to fabricate the GO-ZnO/PES mixed matrix photocatalytic membranes with varying GO-ZnO loadings. Polyvinylpyrrolidone (PVP) was used as a pore-forming agent to minimize the pore blocking effect of high concentrations of GO-ZnO nanocomposite. The membranes were characterized for surface morphology and functionality, pore size, water uptake, and solute rejection properties using various techniques including scanning electron microscopy, atomic force microscopy, Raman spectroscopy, contact angle measurements, streaming potential analysis and cross-flow filtration. The incorporation of GO-ZnO improved the hydrophilicity of the membranes and the addition of PVP augmented the pure water flux of the PVP membranes compared to the PES membranes. Meanwhile, both PES and PVP membranes displayed poor overall salt rejection, which improved with increase in the GO-ZnO concentration. The rejection of carbamazepine and brilliant black (BB) followed a similar trend, with the highest rejection (carbamazepine ≈ 80%) and BB (≈ 70%) attained at 1% GO-ZnO. Furthermore, the PVP membrane with 1% GO-ZnO showed the highest photocatalytic degradation of BB, and the degradation kinetics were nearly 25 times higher than those recorded over the PVP membrane without nanoparticles. Overall, this work demonstrated that membrane filtration and photocatalytic properties can be improved by tailoring the membrane synthesis method to ensure high photocatalyst loading while retaining high flux, rejection, and photocatalytic capability.