Fabrication of Predominantly Mn~(4+)-Doped TiO_2 Nanoparticles under Equilibrium Conditions and Their Application as Visible-Light Photocatalyts

摘要

The chemical state of a transition-metal dopant in TiO_2 can intrinsically determine the performance of the doped material in applications such as photocatalysis and photovoltaics. In this study, manganese-doped TiO_2 is fabricated by a near-equilibrium process, in which the TiO_2 precursor powder precipitates from a hydrothermally obtained transparent mother solution. The doping level and subsequent thermal treatment influence the morphology and crystallization of the TiO_2 samples. FTIR spectroscopy and X-ray photoelectron spectroscopy analyses indicate that the manganese dopant is substitutionally incorporated by replacing Ti~(4+) cations. The absorption band edge can be gradually shifted to 1.8eV by increasing the nominal manganese content to 10 at%. Manganese atoms doped into the titanium lattice are associated with the dominant 4+ valence oxidation state, which introduces two curved, intermediate bands within the band gap and results in a significant enhancement in photoabsorption and the quantity of photogenerated hydroxyl radicals. Additionally, the high photocatalytic performance of manganese-doped TiO_2 is also attributed to the low oxygen content, owing to the equilibrium fabrication conditions. This work provides an important strategy to control the chemical and defect states of dopants by using an equilibrium fabrication process.