Controlled synthesis of TiO₂ nanorod arrays immobilized on ceramic membranes with enhanced photocatalytic performance

In this work, TiO₂ nanorod arrays (NRAs) were synthesized directly on flat sheet Al₂O₃ ceramic membrane (CM) substrates by a two-step hydrothermal method. The effects of the addition of anions and cations and the preparation parameters in the second step on the morphology and size of TiO₂ were investigated in detail, and the photocatalytic activities of the as-synthesized TiO₂-loaded ceramic membranes were investigated by the degradation of methylene blue (MB) under UV light. The results highlighted that the growth of TiO₂ on the CM strongly depended on the synthesis conditions. The anions of Cl^- and Br^- were favorable for the further growth of TiO₂ nanorods, while the anions of SO₄^2- and PO₄^3- with larger ionic radius and higher charge number could retard the growth of TiO₂ nanorods. The SO₄^2- and PO₄^3- could accelerate the formation of nanospheres or nanosheets, respectively. The cation like Na⁺, K⁺, Mg²⁺ and Ca²⁺ had no obvious impact on the formation of TiO₂ NRAs. TiO₂ nanorods exhibited the highest photocatalytic activity, as about 2.2 and 1.9 times larger than those of TiO₂ nanosheets and TiO₂ nanospheres, respectively. More importantly, the as-synthesized TiO₂ NRAs-loaded ceramic membrane could be easily reused and exhibited better photocatalytic stability. These findings would aid the development of TiO₂ photocatalytic materials with high performance.