Hierarchical macrochanneled layered titanates with "house-of- cards"-type titanate nanosheets and their superior photocatalytic activity

Novel three-dimensional (3D) hierarchical macroporous-mesoporous layered titanates were synthesized by self-assembly of interconnected "house-of-cards"-type nanosheets with a facile template-free solvothermal method in presence of hydrazine. Prolonging the time of solvothermal treatment led to the enlargement in size and thickness of the titanate nanosheets in the materials. When the solvothermal temperature was increased, diamond-shaped nanoparticles without macrochannels were formed. Stability of the unique 3D architectures in the materials was attained by post-thermal treatment of the materials in temperatures ranging between 500 and 900°C. During the post-thermal treatment, a gradual transformation from flake-like titanates with porous structures to anatase/rutile crystalline particles was also observed. Such changes in the hierarchical morphology significantly altered the porosity, crystallinity, and optical and photoelectrochemical properties of the layered titanate materials. Owing to their hierarchical 3D porous structures, large surface area and appropriate band gap energy, these novel layered titanate materials exhibited higher adsorption capacity and more efficient photodegradation catalytic activity towards organic contaminants in wastewater compared with the commercially available P25 TiO ₂ (Degussa/Evonik) and many other previously reported hierarchical TiO₂ materials.