Colorful TiO2-x microspheres cooperating with titanium Schiff base complex for efficient visible light photocatalysts

As a promising photocatalyst, the large band gap of TiO2 imposes restriction on its light absorption in the visible region, making it less application in industrial fields. Herein, we design a facile solvothermal method to fabricate colorful defective TiO2-x microspheres with controllable morphological and porous structure, large specific surface area and tunable band gap on the basis of the Schiff base reaction between acetylacetone and ethylenediamine which produce bis(acetylacetone)ethylenediamine (acacen). The acacen, as a tetradentate Schiff-base ligand, has four binding sites which can stabilize titanium centers to produce titanium Schiff base complexes. The color of TiO2-x-Ti(acacen)y complexes changes from yellowish to brown and red with the variation of the acacen ligand, and the corresponding bandgap narrows from 3.25 eV to 2.16 eV as a result of the newly formed Ti3+ and oxygen vacancies (Vo) in the TiO2 lattice. In addition, red TiO2-x microspheres cooperating with titanium Schiff base complex demonstrate high photocatalytic efficiency in methylene blue under visible light as well as hydroxyl radical generation in contrast to yellowish TiO2 microspheres, revealing the significance of this strategy for morphological and bandgap manipulation in defective TiO2-x nanomaterials for high-performance photocatalysis.