(217dn) Template-Free Synthesis of TiO2 Microcages With Improved Photocatalytic Activity

Hollow titanium dioxide (TiO₂) materials have received considerable attention in the past few decades because of its unique properties and many promising applications in environmental and energy areas. To date, various strategies have been developed for the preparation of hollow TiO₂ structures. However, most of the resultant hollow structures by these strategies are spherical.

Herein, we report a template-free and room-temperature synthesis of polyhedral TiO₂ microcages  by using (NH₄)₂TiF₆ and NaOH as the reactants and the self-assembling agarose gel as the matrix. The resultant microcages have the edge sizes of 1.40 ± 0.33 μm, and their shells are about 48 nm in thickness with mesopores about 3.8 nm in size. The intermediate, TiOF₂ crystals, may act an important role during the formation of this kind of polyhedral TiO₂ microcages. The mesopores may be formed through removing the agarose gel fibers embedded in the shell. TiO₂ microcage is further analyzed by the selective area electron diffraction (SAED) and high resolution TEM (HRTEM). This result confirms that the shell of TiO₂ microcages consists of anatase TiO₂ nanoparticles. All the TiO₂ microcage samples exhibit superior photocatalytic activity than Degussa P25 for the decoloration rate of methyl orange (MO) under artificial solar light irradiation. Moreover, the degradation rates of MO by different TiO₂ microcage catalysts calcined at different temperatures (400, 500, 600 ^oC) are compared. It indicates that TiO₂ microcage annealed at 600 ^oC displays the biggest degradation rate in all TiO₂microcage samples, which can be attributed to the best crystallinity.

This study may provide a novel and facile approach for the template-free and green synthesis of hollow structure materials.