Advanced ceramics in radical filtration: TiO2 layer thickness effect on the photocatalytic membrane performance

Membranes with advanced oxidation processes (AOPs) are a promising combination to separate and degrade organic pollutants in a single system. In this work, we describe the fabrication and characteristics of nine membranes with different TiO2 top layer thicknesses (from 0.26 to 21.9 mu m), giving attention to the critical catalyst thickness and the formation of defects. We also report the optimum photocatalyst thickness for our single-layer membranes (similar to 2.74 mu m), after which more titanium dioxide does not improve the degradation. However, an increase in degradation for membranes with multiple TiO2 layers was still possible. These results and the comparisons with the literature suggested that the optimal catalyst thickness is closely related to the material morphology. We obtained a maximum degradation at the lower filtration rate (1.6 L m-2 h-1) of 72% with a single layer membrane of 3.4 mu m and 82% with a membrane with six layers of 21.9 mu m. Furthermore, a 1D mass transport and reaction model that describes the coating thickness effect was developed and fitted with the experimental data. Other parameters are also discussed, such as light penetration limitations, surface area, and surface reaction rate constant. These results and analysis provide a better understanding of the fabrication and optimization of photocatalytic membranes.