Submicron-sized anatase, Ti[O.sub.2] with high photocatalytic activity, and [O.sub.2] nanocrystals formed via hydrothermal technique

The compositional dependence of the crystalline phase and properties of precipitates ([Ti.sub.x][Sn.sub.1-x][O.sub.2]) in the Ti[O.sub.2]-Sn[O.sub.2] system, which were hydrothermally formed at 100-200°C from the precursor solutions of Ti[C.sub.l4] and Sn[Cl.sub.4] under weakly basic conditions in the presence of tetramethylammonium hydroxide (TMAH) was investigated. Rutile-type (Ti, Sn)[O.sub.2] solid solutions with nanosized crystallite were directly formed at 180°C in the composition range of x = 0-0.8. Nanoparticles with anatase crystallite around 10 nm as a main crystalline phase of precipitates that were formed in the compositions x = 0.9 and 1.0 showed similar photocatalytic activity. As the hydrothermal treatment temperature rose from 100 to 200°C, the crystallite size of rutile solid solution, [Ti.sub.0.5] [Sn.sub.0.5][O.sub.2], increased from 2.5 to 8.0 nm. The optical band gap of the samples changed in the range of 2.93-3.25 eV depending on their composition in the system. At the composition of x = 1.0, submicron-sized anatase-type pure Ti[O.sub.2] particles (sizes of cuboid sides are around 100-120 nm) with pretty high crystallinity and superior photocatalytic activity were formed from the aqueous solution of Ti[Cl.sub.4] under basic hydrothermal condition at 180°C in the presence of TMAH with concentration as 1.3 times high as the condition in the case of the nano-sized anatase.