The stability of polymeric membranes in a TiO2 photocatalysis process

The coupling of photocatalysis with membrane separation has emerged as a promising water treatment process. This study focuses on the selection of polymeric membranes for the photocatalytic-membrane process. Ten membranes were evaluated under ultraviolet (UV) and TiO2 photocatalysis conditions. Membrane stability was characterized by changes in pure water flux (PWF), release of total organic carbon (TOC) and scanning electron microscope (SEM) morphology analysis. The results revealed that polytetrafluoroethylene (PTFE), hydrophobic polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) membranes showed the greatest stability. However, in a study of the oxidative stability of membranes, it was found that the PAN membrane is not suitable to be exposed to 10 days of 200 mM H2O2/UV conditions. Tests with cross-flow filtration conditions to prevent titanium dioxide (TiO2) cake formation were carried out. It was shown that during the non-cake situation, TiO2 deposition was minimized at appropriate pH values and this reduced membrane deterioration. Deposition of cakes with various thicknesses of TiO2 affected the stability of the membranes to different extents. In general, the thicker the cake layer, the less the damage done by the photocatalytic reaction on the membrane. Chemical changes on the membrane surface after the TiO2 cake studies were characterized using attenuated total reflection-Fourier transform infrared (ATR-FTIR). The results obtained using powdered activated carbon (PAC) as a separating layer showed that close contact between the TiO2 and the membranes was the main mechanism for the detrimental effect of TiO2 on polymeric membrane exposed to UV light.