Enhanced photocatalytic activity of hierarchical structure TiO2 hollow spheres with reactive (001) facets for the removal of toxic heavy metal Cr(vi)

Abstract

Hierarchical structure TiO₂ hollow spheres composed of nanometer-sized building blocks, nanoflakes with exposed anatase (001) facets, have been synthesized with a high yield through a facile fluoride-mediated hydrothermal route. The average diameter of the resultant TiO₂ hollow spheres is ∼1 μm, and the width of well-crystallized anatase phase nanoflakes is ∼50 nm. Nitrogen adsorption–desorption measurement revealed that the products have a high specific surface area of 26 m² g⁻¹ and abundant mesoporous structure. The TiO₂ hollow spheres were used to photocatalytically degrade Cr(VI) in solution. The results indicate an enhanced photocatalytic activity compared to other TiO₂ structures, owing to the high specific surface area and abundant mesoporous properties of the TiO₂ hollow spheres. Besides, the presence of the reactive (001) facets also contributed to the enhanced activity; it was found that the (001) facets are more effective in the adsorption of Cr(VI) than the commonly exposed (101) facets. Furthermore, the surface fluorination of TiO₂ hollow spheres was found to have a negative role in the photocatalytic removal of Cr(VI). The TiO₂ hollow spheres not only can remove Cr(VI) from wastewater; they also can reduce the adsorbed toxic Cr(VI) to Cr(III), further forming oxides or hydroxides. In addition, the TiO₂ hollow sphere photocatalysts with micron-scale size showed high durability in the cyclic tests.