Highly photoactive 2D titanium dioxide nanostructures prepared from lyophilized aqueous colloids of peroxo-polytitanic acid

Abstract

Reaction of hydrogen peroxide with suspensions of thoroughly washed precipitates obtained by neutralization of aqueous solution of titanyl sulfate with aqueous ammonia leads to transparent yellow liquids. In this way prepared colloid solution is a two phase system in which, beyond the water phase, also a liquid hydrated peroxo-polytitanic acid component is present. Freeze drying of this colloid liquid provides a foamy material consisting of thin foils of peroxo-polytitanic acid containing small but not negligible amount of chemically bound ammonia. These foams annealed at temperature above ∼200°C lose water, ammonia and excess of oxygen providing foamy amorphous oxide. At higher temperatures above ∼280°C the amorphous material crystallizes to anatase which transforms at temperatures >850°C to rutile. The size and shape of the initial leaflets forming the foam is preserved up to ∼900°C. Slit shaped porosity is formed during annealing. We observed that the annealed material is highly photoactive, probably owing to highly anisotropic shape of anatase aggregates and their perfect crystallinity.