Asymmetric TiO2 hybrid photocatalytic ceramic membrane with porosity gradient: Effect of structure directing agent on the resulting membranes architecture and performances

Asymmetric TiO2 hybrid photocatalytic ceramic membranes with porosity gradient have been fabricated via acid-catalyzed sol–gel method. Different structure directing agents (SDAs) i.e. Pluronic P-123, Triton X-100, Tween 20 and Tween 80 were incorporated in the preparation of TiO2 sol to obtain a porous multilayered TiO2 coated on the alumina ceramic support. Six different SDA-modified membrane specimens were fabricated. Four of which were coated with the TiO2 sols prepared using only one type of SDA. The remaining two specimens were fabricated via multilayer coating of different TiO2 sols prepared using different types of SDAs. Physico-chemical and morphological properties of different TiO2 layers were thoroughly investigated. The membrane M1 which had the most porous TiO2 sub-layers showed a high pure water permeability of 155Lm−2h−1bar−1. The membrane showed a relatively high Rhodamine B (RhB) removal of 2997mgm−2 over 8h treatment duration in the batch photoreactor, second only to the Pluronic-based TiO2 membrane (specific RhB removal of 3050mgm−2). All membrane specimens exhibited good performances while operated in the flow-through photocatalytic membrane reactor. Over 91% of RhB removal capability was retained after 4 treatment cycles. All membranes also showed self-cleaning property by retaining >90% of initial flux after 4 treatment cycles. The flexibility of optimizing membrane performances by fine-tuning the porosity gradient configuration of the photocatalytic layer has also been demonstrated.