Effect of oxygen and WO3 additive on anatase-to-rutile phase transformation in TiO2 nanoparticles

Phase transformation of TiO2 powder (P25) and pure anatase (PA) was investigated under pure oxygen as well as vacuum from 500 to 1,000 °C. The rutile percentage calculated based on the XRD data was used to estimate the phase transformation process. It was found that the vacuum suppressed the phase transformation of P25 relative to pure oxygen atmosphere. A model was proposed to explain the effect of oxygen on the phase transformation of TiO2. Furthermore, P25 samples showed lower phase transformation temperature (between 600 and 800 °C) compared with PA (over 1,000 °C). The existed rutile phase in P25 was regarded as a transformation inducer due to an interface between anatase and rutile phases since the nucleation activation energy on the interface is lower than that on the surface. And this interface effect is also adopted to explain the role of additive WO3, which retarded the phase transformation of P25 but promoted the phase transformation of PA.