Synthesis of brookite TiO2 nanoparticles by thermolysis of TiCl4 in strongly acidic aqueous media

Nanometric particles of titania, brookite and rutile polymorphs were synthesised by thermolysis of TiCl4 in concentrated HCl solutions. The Cl∶Ti molar ratio seems to be the key factor in determining the crystalline phases and their relative proportions as well as the particle size and a large proportion of brookite can be obtained under specific conditions. The complex Ti(OH)2(Cl)2(OH2)2 seems to be the precursor of the brookite phase. The presence of chloride ions is also necessary to stabilise brookite in suspension. Depending on the acidity and the ageing conditions, different morphologies of brookite nanoparticles are obtained, namely spheroidal particles or platelets. Stable sols of pure brookite are obtained by peptization of the solid phase.