One-step synthesis of monodisperse TiO₂ nanopowder and a transparent, colloidally stable dispersion with high photocatalytic activity

TiO₂ is a widely studied semiconductor photocatalyst; however, the synthesis and high-yield isolation of monodisperse TiO₂ nanopowders capable of forming transparent and colloidally stable dispersions remain challenging. Herein, a facile one-step solvothermal method is reported for synthesizing ∼10 nm monodisperse TiO₂ nanoparticles with a yield exceeding 98% via treatment of a TiCl₄ solution in a methylene chloride/t-butanol mixture at 100 °C. Unlike commonly used commercial TiO₂ nanoparticles (e.g., Evonik P25, also known as Degussa P25), the resulting nanoparticles exhibit excellent colloidal stability in water for over 20 weeks without agglomeration, with a zeta potential of approximately 40 mV. The dispersion demonstrates high optical transparency in the visible range, with transmittance exceeding 93% at wavelengths of 500 nm and above. The isolated TiO₂ nanopowder shows high photocatalytic activity for hydrogen production from an aqueous methanol solution, achieving an apparent quantum efficiency of 51.64%. The synthesized TiO₂ exhibits strong potential for solution-processed applications and coatings, where a colloidally stable aqueous dispersion is desirable.