Effect of holmium doping on the structure and photocatalytic behavior of TiO-based nanosheets.

A series of holmium-doped TiO2-based nanosheet (Ho-TNS) photocatalysts with different Ho/Ti molar ratios were prepared via a simple hydrothermal method. The photocatalysts were characterized by field-emission scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction (XRD), Raman Spectroscopy, X-ray photoemission spectroscopy, nitrogen adsorption-desorption isotherm measurement, ultraviolet-visible light diffuse reflectance spectra (DRS), and fluorescence spectra (FL). The TEM images of Ho-TNS exhibit clearly sheet-like structures and existence of the (201) plane of H2Ti3O7. The increased (101) peak intensity in XRD spectrum and the enhanced Eg mode (141 cm-1) in Raman spectrum indicate that Ho doping has obvious influence on the formation and structure of Ho-TNS, which can be explained by the formation of Ho-O-Ti bonds. With the doping ratio (Ho/Ti molar ratio) increasing from 0 to 2.0 %, the absorption edge shifts to a longer wavelength, and the band-gap of photocatalysts reduces from 3.18 to 3.07 eV. The decline of FL intensity implies that the photocatalysts with higher Ho content have higher electron-hole separation efficiency. However, after Ho doping, the surface structure of specimens is significantly altered, which will lead to the specific surface areas and adsorption capacity decrease. Under the combined effect of the variables, the photocatalyst with a doping ratio of 1.0 % reaches the best photoactivity, which is 1.90-fold and 12.38-fold higher compared with undoped TNS and P25 under visible light, respectively. The high photoactivity of the prepared Ho-TNS indicates that it may be useful for dealing with wastewater. [ABSTRACT FROM AUTHOR]