Synthesis of uniform anatase TiO₂ nanoparticles by gel-sol method: 1. Solution chemistry of Ti(OH)_n^(4-n)+ complexes

The mole fractions of hydroxo complexes of titanium(IV) ion in an aqueous solution with 0.10 mol dm^-3 NaClO₄ at 25°C have been determined as a function of pH by a newly developed analytical procedure based on UV spectrophotometry, using a metastable homogeneous solution of 1.25 × 10^-4 mol dm^-3 in total concentration of Ti(IV). Also, the total concentration of the hydroxo complexes in equilibrium with Ti(OH)₄ solid, or the solubility of Ti(OH)₄ solid in an inhomogeneous system, has been obtained by ICP measurement for the solution phase. A combination of these data yielded the absolute concentration of each complex species in equilibrium with Ti(OH)₄ solid. Finally, Ti(OH)₃⁺ complex has been assigned to the precursor for the formation of anatase TiO₂ nanoparticles transformed from Ti(OH)₄ gel from a comparison between the above equilibrium data and a kinetic study on the formation rate of the anatase TiO₂ particles in the gel-sol system.