Synthesis of Nanocrystalline TiO₂ and Reduced Titanium Oxides via Rapid and Exothermic Metathesis Reactions

Nanocrystalline titanium dioxide is conventionally produced by aqueous precipitation reactions, followed by annealing post-treatment, which can also cause structural conversions from the photocatalytically active anatase to rutile phases. Solvent-free exothermic solid-state metathesis (SSM) reactions have shown wide utility in the synthesis of binary solids. This paper describes the application and chemical flexibility of the SSM method for the synthesis of TiO 2 from TiCl 3 and Na 2 O 2 . The use of an insulating crucible and addition of a NaCl heat sink to this rapid and exothermic SSM led to improved product crystallinity and increases in anatase to rutile TiO 2 phase content. Small particle size products were synthesized at high salt dilution levels. The photocatalytic activity of SSM synthesized TiO 2 powders containing some anatase TiO 2 were comparable to a commercial TiO 2 standard, even though the SSM powders had 30−50% lower surface areas. By changing the Na 2 O 2 reagent to a more oxygen deficient one, Na 2 O, reduced titanium phases, primarily Ti 2 O 3, were synthesized along with Na−Ti−O structures.