Co-Mn-Fe complex oxide catalysts from layered double hydroxides for decomposition of methylene blue: Role of Mn

Composite Co-Mn-Fe oxide catalysts were prepared by thermal decomposition of layered double hydroxide (LDH) or hydrotalcite-like precursors. A series of catalysts at different Mn/Fe ratios were obtained and characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) spectrometry, UV-vis diffuse reflectance spectroscopy and BET surface area analysis. The catalysts were tested for methylene blue (MB) dye decomposition under visible light illumination with and without the assistance of NaHSO3. When visible light illumination was used on the catalyst in the presence of NaHSO3, the degradation efficiency was greatly enhanced. All the Mn-containing samples showed much higher capability to degrade MB than that of MnO2 under the same conditions. The [0]CoMnFe-LDO sample which did not contain any Mn showed lower degrading ability than MnO2. In addition to determining the role of Mn and the Mn/Fe ratio of the complex oxide catalysts on the decomposition of MB, the stability and reusability of these complex oxide catalysts were also tested and found to be good.