Synthesis of Hierarchical Flower-like AlOOH and TiO₂/AlOOH Superstructures and their Enhanced Photocatalytic Properties

Hierarchical flower-like boehmite superstructures (HFBS) composed of intermeshed nanoflakes were synthesized by hydrothermal treatment from as-formed aluminum hydroxide microspheres, which were prepared by adding aluminum spheres into a sodium metaaluminate solution. A two-step mechanism for the formation of HFBS is proposed, which involves initial formation of Al(OH) 3 microspheres followed by their transformation to AlOOH. The as-prepared HFBS superstructures can be easily transformed into γ-Al 2 O 3 superstructures without morphology change by calcination at 500 °C for 2 h. Furthermore, the TiO 2 nanoparticles can homogeneously deposited on the surface of HFBS by the vapor-thermal method. The TiO 2 nanoparticles coated on HFBS showed higher photocatalytic activity for photocatalytic decolorization of rhodamine B (RhB) aqueous solution than Degussa P25 (P25) and TiO 2 powders prepared at the same experimental conditions. A significant enhancement of the photocatalytic activity can be related to several factors, including hierarchical porous structure, high dispersion of TiO 2 particles, and the increased light-harvesting abilities. Moreover, TiO 2 -coated HFBS can settle naturally within 5 min, which is beneficial for separation and recycling, considering their future applications in wastewater treatment.