Template-free synthesis of TiO2 microcages in agarose gels with improved photocatalytic activity

Abstract

A template-free synthesis of TiO2 microcages by using (NH4)2TiF6 and NaOH as the reactants and the agarose gel as the reaction medium is developed. The resultant TiO2 microcages possess a pseudo-cubic morphology with the edge size of 1–2 μm and the shell thickness around 48 nm. It is found that the shell of TiO2 microcages consists of anatase TiO2 nanoparticles about 15 nm in diameter, and possesses the mesopores about 3.8 nm in size. A proposed formation mechanism suggests that pseudo-cubic Na5Ti3F14 microcages firstly generate in agarose gels due to the incomplete hydrolysis of TiF6 2− and the inhibited diffusion effect of gels, and then transform into anatase TiO2 without changing the morphology as the agarose gels are removed in hot water about 90 °C. These TiO2 microcage samples exhibit higher photocatalytic activity than Degussa P25 for the degradation of methyl orange under artificial solar light irradiation, which can be attributed to their well-preserved hollow structure with mesopores. This study may devote a novel and facile approach for the template-free synthesis of hollow structure functional materials.