Colloidal TiO2 Nanocrystals with Engineered Defectivity and Optical Properties

Abstract

Partially reduced forms of titanium dioxide (sometimes called “black” titania) have attracted widespread interest as promising photocatalysts of oxidation due to their absorption in the visible. The main approaches to produce it rely on postprocessing at high temperatures (up to 800 °C) and high pressures (up to 40 bar) or on highly reactive precursors (e.g., TiH2), and yield powders with poorly controlled sizes, shapes, defect concentrations and distributions. We describe an approach for the one-step synthesis of TiO2 colloidal nanocrystals at atmospheric pressure and temperatures as low as 280°C. The temperature of reaction allows to control the density of oxygen vacancies by nearly two orders of magnitude independently of their size, shape, or colloidal stability. This synthetic pathway appears to produce vacancies that are homogeneously distributed in the nanocrystals, rather than being concentrated in an amorphous shell. As a result the defects are protected from oxidation and result in stable optical properties in oxidizing environments.