Preparation, characterization, and kinetic and thermodynamic studies of mixed-phase TiO2 nanoparticles prepared by detonation method

• The mixed-phase TiO2 nanoparticles, consisting of anatase (34.8 wt%, ca. 9.4 nm) and rutile were prepared by detonation method.
• In contrast to normal transformation from anatase to rutile, a small quantity of rutile particles may transform to anatase phase.
• Transformation kinetics of the detonation-prepared TiO2 sample is modeled.
• Thermal treatment may be employed to control the particle size and phase content of detonation-prepared TiO2 nanoparticles.

Although detonation method has been reported to prepare TiO2 nanoparticles, phase transformation and crystal growth of detonation-prepared TiO2 nanoparticles have not been explored extensively. In this study, mixed-phase TiO2 nanoparticles, consisting of anatase (34.8 wt%, ∼9.4 nm) and rutile (65.2 wt%, ∼18.2 nm), were prepared by the detonation method. The phase transformation in the TiO2 sample at different annealing temperatures was modeled to understand the transformation behaviors. Thermal treatment experiments of the detonation-prepared TiO2 nanoparticles indicated that the initial process involved an anatase-to-rutile transformation. The TiO2 grains coarsened drastically after thermal treatment at 600 °C for 1 h. In contrast to a normal transformation, the anatase-to-rutile transformation was followed by conversion of rutile to anatase in large crystals. Moreover, smaller TiO2 particles could gain more kinetic energy and combine rapidly with the increase in temperature, forming larger particles. Anatase was transformed completely to rutile after thermal treatment at 720 °C for 3.5 h. The transformation temperature from anatase to rutile of the detonation-prepared TiO2 nanoparticles was approximately 80 °C lower than that of TiO2 prepared by conventional methods. Therefore, thermal treatment may be employed to control the particle size and phase content of detonation-prepared TiO2 nanoparticles.