Removal of methylene blue from wastewater under a low power irradiation source by Zn, Mn co-doped TiO2 photocatalysts

Abstract

In present study, a series of Zn, Mn co-doped titania (TiO₂) photocatalysts with varying dopant concentrations (0.0, 1.0 and 2.0 at%) were synthesized via the sol–gel process. The co-doped photocatalysts were characterized using XRD, XPS, SEM, TEM, Raman, FTIR and UV-vis DRS techniques, where methylene blue was used as a probe environmental pollutant. The photocatalytic performances of the synthesized photocatalysts were evaluated under very low (∼2 W) UV and visible power irradiation sources. Analysis of X-ray diffraction patterns suggests the multiphase structure of the photocatalyst, while XPS results demonstrate that in co-doped TiO₂, the oxidation state of doped Zn metal ions is 2 (Zn²⁺), while Mn is in +2 and +3 (Mn^2+/Mn³⁺) state. The optical study results reveal a red shift in the co-doped samples, where with an increase in co-dopant concentration, the band gap is reduced. The highest photocatalytic degradation of MB is obtained with 1.0 at% Zn, Mn co-doped TiO₂, which is due to enhancement of light absorbance in the UV region caused by the additional impurity energy levels introduced in the bad-gap of TiO₂ by the co-dopants. The as-synthesized 1.0 at% Zn, Mn co-doped TiO₂ provides a very high degradation efficiency (66.6 W⁻¹ min⁻¹) and thus may be practically used in the dye removal process efficiently.