Effects of montmorillonite on phase transition and size of TiO2 nanoparticles in TiO2/montmorillonite nanocomposites

Abstract

Nanostructured TiO2/montmorillonite (TiO2/Mt) materials have many applications in a variety of fields such as plastic degradation, photocatalysis, antibacterial agent development and water purification. In order to homogeneously disperse TiO2 nanoparticles within the interlayer space of montmorillonite, an in-situ interlayer reaction method was developed to prepare nanostructured TiO2/Mt materials. Briefly, cetyl trimethylammonium (CTA+) was first intercalated into the interlayer of the montmorillonite structure. Then tetrabutyl orthotitanate (TBOT) was introduced into the interlayer space of the CTA+/montmorillonite (CTA+/Mt) nanocomposites by solvation. TBOT in the nanocomposites underwent in-situ hydrolysis, de-hydroxylation and annealed at different temperatures. During annealing, CTA+ was burnt off and TiO2 formed in the interlayer space of montmorillonite. The average crystal size of TiO2 in TiO2/Mt was compared with that of both the pure TiO2 nanoparticles and the mixture of pure TiO2 and montmorillonite. The intermediate and final products were characterized by X-ray diffraction, FT-Raman spectroscopy and transmission electron microscopy. The results showed that the phase-change temperature for transformation of TiO2 nanoparticles in TiO2/Mt nanocomposites from anatase to rutile phase was higher than that for pure TiO2 nanoparticles and the mixture of pure TiO2 and montmorillonite. Pure TiO2 nanoparticles were all converted to rutile when the annealing temperature was increased to over 800°C. However, the anatase-TiO2 still existed in TiO2/Mt, even though the annealing temperature reached a much higher temperature of 1200°C. In addition, at the same annealing temperature, the average crystal size of TiO2 in TiO2/Mt nanocomposites was smaller than that of either the pure TiO2 or the mixture of pure TiO2 and montmorillonite.