Hosted by: Mark S. Hybertsen

TiO2 is an important technological material with widespread applications in photocatalysis, photovoltaics, and self-cleaning surfaces. Behavior of the photoexcited electrons, particularly near its surfaces, as well as the surface structure of the material itself are two crucial constituents of its scientifically interesting properties. In this work, we focus on the excess and photoexcited electrons in anatase, the TiO2 polymorph most relevant to photocatalysis and solar energy conversion. Our results provide a bridge between the surface science experiments under vacuum conditions and the observations of crystal-face-dependent photocatalysis on anatase and support the idea that optimization of the ratio between different anatase facets can help enhance the photocatalytic activity of this material. Furthermore, we use a combined first principles and classical approach to study the reduction of anatase under H2 atmosphere. Experiments done in a similar setup yields a black TiO2 powder which shows a superior photocatalytic efficiency. This material is characterized to have an amorphous TiO2-x shell covering the anatase core. However, a detailed structural understanding of the material and the origins of its superior activity remains a mystery to date. We identify the main pathways of TiO2 reduction by H2 and explore the initial stages of surface amorphization in a spherical nanoparticle.