Direct measurement and modeling of spontaneous charge migration across anatase–brookite nanoheterojunctions

Nanocomposites are at the heart of the present nanotechnology revolution in several strategic fields, including Green Chemistry, sensors and pollutant remediation. The promising and extensively examined nanotitania photocatalysts have performances hampered by the rapid recombination of photogenerated charge carriers. To better understand these materials, here we generalize the 2D-heterojunctions physics to 3D patchworks of intimately associated anatase and brookite mixed crystallites, i.e. multi-phase polymorphs, MPPs. The synthesized composite material is fully characterized experimentally and by simulations. We demonstrate that the anatase–brookite interphase behaves as a ground-state nano-diode containing an almost ideal nanocapacitor, associated with a net migration of electrons from anatase to brookite. Implications of the direct observation of a polarized interphase on the understanding of nanotitania photocatalysts at the atomic scale are discussed.