Photocatalytic degradation of organic dye via atomic layer deposited TiO2 on ceramic membranes in single-pass flow-through operation

Photocatalytic membranes operating under flow-through conditions are promising for continuous single-pass water treatment, while factors influencing pollutant removal require further understanding. In this work, anodized aluminium oxide membranes with pore sizes of 20 nm and 200 nm were coated with a titanium dioxide (TiO2) photocatalyst via atomic layer deposition. The impact of operational parameters on the photocatalytic efficiency of these membranes was examined. The convective flow through the coated membrane pores enhanced the accessibility of the model pollutant methylene blue (MB) resulting in effective mass transfer and, hence, significant photodegradation. The MB removal increased up to 50% with increasing coating thickness (up to 6 nm) and ultraviolet (UV, 365 nm) light intensity (2 mW/cm2). Above these values, the degradation was no longer limited by these parameters. The high degradation achieved below the UV content of terrestrial sunlight signifies the applicability of TiO2. Experiments demonstrate that the convective MB molar flux, under low membrane flux or low MB concentration, limits the reaction rate, but results in a high removal (up to 80%). Thus, a continuous process in photocatalysis coupled with membrane filtration exhibits significant potential for treating polluted water.