Size-Dependent Anatase to Rutile Phase Transformation and Particle Growth

Abstract

Phase transformation and particle growth are fundamental processes that govern final particle size and morphology, as well as phase composition. At the nanoscale, these processes can be significantly affected by initial particle size. Rates of anatase growth and its transformation to rutile increase with decreasing initial size under hydrothermal conditions at pH 1 and pH 3. Overall, rates are slower at the higher pH. At pH 1, the data fit well to a kinetic model developed based on a dissolution–precipitation mechanism. However, at pH 3, it deviates substantially from the model, indicating that the transformation occurs via a different mechanism or a mixture of dissolution–precipitation and another mechanism, which likely involves aggregation. Finally, the compactness of the aggregates affects the processes significantly. That is, densely aggregated particles show higher transformation and growth rates, compared to loosely aggregated ones.