Photocatalysts in Polysulfone Membrane for the Removal of Humic Acid: The Effects of PVP and PVA on Membrane Morphology, Separation Performance and Catalytic Hindrance

Photocatalytic membranes exhibit great potential for water treatment since they combine the filtration and photo degradation in a single unit. Although blending photocatalytic nanoparticles into polymeric thin film remains the simplest method to prepare the photocatalytic membrane, the entrapped photocatalyst showed less catalytic activity due to the agglomeration and shielding effects in the polymer matrix. In this work, PVP (polyvinyl pyrrolidone) and PVA (poly(vinyl alcohol)) were used to stabilize the photocatalytic nanoparticles (TiO2, Mn-TiO2 and ZnO) in the polysulfone (PSf) membrane. Most importantly, these additives affect the formation of finger-like pores which influence the separation performance and also the hindrance of photocatalytic activities. The surface hydrophilicity of PSf/PVP/TiO2 and PSf/PVP/Mn-TiO2 membranes increased by 12.25° and 16.67°, respectively after adding photocatalysts. On the other hand, the PSf membrane with PVP and ZnO nanoparticles exhibited improvement in water permeability, about 7 times higher than the neat membrane. The PSf/PVP/ZnO membrane even offered higher rejection of humic acid (HA) than the PSf/PVP/TiO2 and PSf/PVP/Mn-TiO2 membranes. In the photo degradation test, ZnO only showed a reduction of 5.41% in its photo activity when it was blended into the PSf membrane with PVP. When PVA was used in the preparation of the PSf/PVA/ZnO membrane, the permeability improvement was greatly reduced compared to the PSf/PVP/ZnO membrane. PVA also resulted in a great hindrance to the photocatalytic activity of ZnO in the PSf membrane, more than 37%.