Complex doping chemistry owing to Mn incorporation in nanocrystalline anatase TiO2 powders

Abstract

Mn-doped TiO₂ powders with a wide range of nominal doping levels were fabricated using a one-step hydrothermal method followed by 400 °C annealing. Anatase powders with a uniform size distribution below 10 nm were obtained. The maximum solubility of Mn in the TiO₂ lattice was around 30%, beyond which the Mn₃O₄ compound appeared as a secondary phase. The optical absorption edges for Mn-doped anatase TiO₂ were red-shifted effectively through increasing Mn content. Alloying chemistry and associated elemental valences were elaborated through combining X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and theoretical simulation in the framework of density functional theory (DFT). The results showed that the Mn species exhibited mixed valence states of 3+ and 4+ in anatase TiO₂, with the latter being the key to remarkable photocatalytic performance.