Preparation of hollow TiO₂ spheres of the desired polymorphs by layer-by-layer assembly of a water-soluble titanium complex and hydrothermal treatment

A facile approach, based on the polyelectrolyte-mediated electrostatic adsorption of a water-soluble titanium complex on colloid templates and hydrothermal treatment, is presented for the formation of hollow TiO₂ spheres of the desired polymorphs. The core-shell particles were formed by the alternate deposition of titanium-glycolate complex 1 and positively charged polyelectrolyte, poly(allylamine hydrochloride) (PAH) on spherical polystyrene (PS) templates by utilizing electrostatic interactions for shell formation. Hollow spheres formed with the polyionic complex of 1 and PAH were obtained by removal of the PS templates. Formation of the polyionic complex affected the crystallization of TiO₂ from 1 by hydrothermal treatment. Hollow spheres of brookite and anatase were obtained by hydrothermal treatment at pH 4 and 10, respectively. The approach presented here can be exploited for the fabrication of novel advanced titania-based materials with desired structures and polymorphs. Hollow titania spheres with anatase and brookite phases were selectively fabricated by hydrothermal treatment of hollow capsules formed by a polyionic water-soluble Ti complex and a cationic polyelectrolyte.