Anatase TiO2 hollow nanosheets: dual roles of F−, formation mechanism, and thermal stability

Abstract

Anatase TiO₂ hollow nanosheets with a width of 550 nm, a thickness of 100 nm, and a hole diameter of 350 nm were hydrothermally fabricated in an aqueous solution containing NH₄VO₃, HF, and HCl at an appropriate composition. Structural analyses on the products obtained at different intervals during the synthesis revealed that the formation of the anatase TiO₂ hollow nanosheets consisted of three steps: oriented assembly of square-like NH₄TiOF₃ nanoparticles, topochemical conversion of NH₄TiOF₃ to anatase TiO₂, and selective etching by F⁻ on the flat nanosheets. The fluorine anion was involved in the formation of NH₄TiOF₃ as the key intermediate, it directed the construction of the nanosheet, and participated in the etching process to generate the hollow structure. The resultant anatase TiO₂ hollow nanosheets exhibited a rather high thermal stability, maintaining the anatase crystallite structure and the hollow shape up to 1073 K.