Synthesis of Ordered Multivalent Mn-TiO2 Nanospheres with Tunable Size: A High Performance Visible-Light Photocatalyst

A facile and reproducible method has been developed for the synthesis of ordered anatase Mn-TiO2 nanospheres with controllable sizes in the range 200-300 nm by simply varying the amount of manganese(II) chloride added. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM) measurements, and it was found that the manganese exists in multivalent forms (Mn4+/Mn3+) and substitutes for some of the Ti4+ in the anatase TiO2 lattice. The presence of Mn significantly influences the morphology and high-temperature stability of TiO2, and extends its light absorption range. Surface photovoltage and photocurrent measurements revealed that an electronic interaction between the Mn and TiO2 was present, in which Mn served as an electron acceptor and effectively inhibited the charge recombination in TiO2; this is thought to be responsible for the highly efficient photocatalytic activity of the material in the degradation of rhodamine B (RhB) under visible-light irradiation (lambda > 420 nm).