Hydrothermal synthesis of aqueous nano-TiO2 sols

A poorly crystalline nano-anatase precursor with the crystallite sizes of about 3.5 nm was prepared via reprecipitation of nano-anatase at pH = 7.0 from a highly transparent sol obtained by acidic peptization of hydrous titania precipitates, hydrolysed product of titanium isopropoxide. The weakly agglomerated nano-anatase precursor has been used for preparing well crystalline nano-TiO2 sols by hydrothermal treatment at pH = 9.5 using a weak base, NH4OH. The crystallite size gradually grew with increasing temperature and reached 7.6 nm (X-ray) at 175 degrees C after 4 h of hydrothermal treatment. The sizes of particles were mostly in the range 5-15 nm. The hydroxyl content in the nano-TiO2 decreased with increasing hydrothermal temperature of treatment and supported a gradual growth of nano-TiO2 as evident from the X-ray and TEM.