Metatitanic Acid Pseudomorphs after Titanyl Sulfates: Nanostructured Sorbents and Precursors for Crystalline Titania with Desired Particle Size and Shape

Abstract

A new preparation method for the synthesis of TiO2 microrods in aqueous media starting with solid hydrated titanyl sulfate crystals with defined morphology is presented. The method is based on the extraction of sulfate ions from the crystals and their replacement with hydroxyl groups in aqueous ammonia solution leaving the Ti–O framework intact. The particle size and morphology of the starting hydrated titanyl sulfate is closely preserved in the pseudomorphs of amorphous metatitanic acid including such details like the layered structure of the original hydrated titanyl sulfate crystals. When annealed up to 1200 °C, the rod-like morphology of particles is retained, while the phase composition changes to anatase/rutile. The rod-like particles of metatitanic acid possess excellent sorption properties toward radionuclides. The mechanism of pseudomorph formation is discussed based on the structures of the precursors, including the hitherto unknown structure of titanyl sulfate dihydrate determined by electron diffraction tomography.