Multi-scale modeling of titanium dioxide: Controlling shape with surface chemistry

An important aspect in the use of titanium dioxide at the nanoscale for advanced photochemical applications is the controlled manipulation of the size, phase and morphology of the nanoparticles in solution. Solution pH is often used to alter such properties at the nanoscale. We have used a multi-scale thermodynamic model to investigate the effects of pH on the shape and phase stability of titanium dioxide nanoparticles. As input for the model, surface energies and surface tension of low index stoichiometric surfaces of anatase and rutile under hydrogen rich and hydrogen poor conditions have been calculated using density functional theory. Our results show how the anatase phase is stabilized in acidic solution while the rutile phase is stabilized in alkaline solution, and that pH may also be used to induce structural and phase transitions.