CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 40 (2014) 6747–6757 Asymmetric TiO 2 hybrid photocatalytic ceramic membrane with porosity gradient: Effect of structure directing agent on the resulting membranes architecture and performances Ronn Goei a,b , Teik-Thye Lim a,b,n a School of Civil and Environmental Engineering, Nanyang Technological University, Block N1, 50 Nanyang Avenue, Singapore 639798, Singapore b Nanyang Environment & Water Research Institute (NEWRI), Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore Received 6 November 2013; received in revised form 23 November 2013; accepted 29 November 2013 Available online 12 December 2013 Abstract Asymmetric TiO 2 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 TiO 2 sol to obtain a porous multilayered TiO 2 coated on the alumina ceramic support. Six different SDA-modified membrane specimens were fabricated. Four of which were coated with the TiO 2 sols prepared using only one type of SDA. The remaining two specimens were fabricated via multilayer coating of different TiO 2 sols prepared using different types of SDAs. Physico-chemical and morphological properties of different TiO 2 layers were thoroughly investigated. The membrane M1 which had the most porous TiO 2 sub-layers showed a high pure water permeability of 155 L m À2 h À1 bar À1 . The membrane showed a relatively high Rhodamine B (RhB) removal of 2997 mg m À2 over 8 h treatment duration in the batch photoreactor, second only to the Pluronic-based TiO 2 membrane (specific RhB removal of 3050 mg m À2 ). 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 490% 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. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Titanium dioxide (TiO 2 ); Structure directing agent (SDA); Photocatalytic membrane reactor (PMR); Asymmetric membrane; Ceramic membrane 1. Introduction Ceramic membranes possess many sterling characteristics as compared to the polymeric membranes such as its excellent chemical, physical, and biological stabilities, its relative high permeability with self-cleaning property, and its resistance to the UV irradiation [1–4]. Furthermore, ceramic materials are resistant to many cleaning agents such as acid, chlorine, and solvents. Ceramic materials also can be sterilized at higher temperature and exhibit a relatively longer life-span when compared with the polymeric materials. Since the pioneering work of Anderson et al. [1], synergistic coupling of ceramic membrane filtration and UV-assisted photocatalytic degradation has been receiving much attention [5–9]. The use of powder photocatalysts posses some inher- ence disadvantages such as particle aggregation, difficult application in the continuous reactor, and the need of catalyst recovery at the end of the treatment. Thus, by immobilizing photocatalyst into a membrane support, we can overcome the above-mentioned disadvantages. This synergistic coupling provides an avenue for the complete degradation of many recalcitrant pollutants, unlike the conventional membrane processes that only separate the pollutants without degrading www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.11.137 n Corresponding author at: School of Civil and Environmental Engineering, Nanyang Technological University, Block N1, 50 Nanyang Avenue, Singapore 639798, Singapore. Tel.: þ65 6790 6933; fax: þ 65 6791 0676. E-mail address: cttlim@ntu.edu.sg (T.-T. Lim).