Preparation of water-dispersible TiO₂ nanoparticles from titanium tetrachloride using urea hydrogen peroxide as an oxygen donor

TiO₂ nanoparticles were prepared from titanium tetrachloride (TiCl₄) in CH₂Cl₂ at 80 °C for 30 h, 42 h and 70 h using urea hydrogen peroxide (UHP) as an oxygen donor with a TiCl ₄: UHP molar ratio of 1 : 2. The XRD patterns and Raman spectroscopy results showed that the products consisted of anatase TiO₂. IR and solid-state ¹³C NMR with cross polarization and magic angle spinning techniques revealed the presence of urea. TEM observation revealed that the products prepared by the reactions for 30 and 42 h consisted of water-dispersible spheroid nanoparticles with a long axis of ~5 nm, while an aggregation of nanoparticles was evident upon reaction for 70 h. Thermogravimetry, inductively-coupled plasma emission spectrometry and CHN analysis showed that the amount of urea increases in the following order: TiO₂-42h, TiO₂-70h, TiO₂-30h. The photocatalytic activity of the products dispersible in water (TiO ₂-30h and TiO₂-42h) was estimated based on the degradation behaviour of methylene blue, and TiO₂-42h showed higher photocatalytic activity than TiO₂-30h. It is proposed that TiCl ₄ was directly oxidized by UHP to form anatase TiO₂ in the early stage of the process.