Bisulfite assisted photocatalytic degradation of methylene blue by Ni-Fe-Mn oxide from MnO₄ intercalated LDH

A novel composite of Ni-Fe-Mn ternary metal oxide (Mn-LDO) was synthesized by MnO₄ ⁻ intercalation into NiFe-LDH and calcination to improve photocatalytic efficiency. The conventional Ni-Fe binary metal oxide (C-LDO) prepared from Ni-Fe-LDH was also employed for comparison. Bisulfite was added to the above oxides in order to improve the photocatalytic degradation during the reaction. The as-synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), Brunauer, Emmett, and Teller (BET), UV–Vis diffuse reflectance spectroscopy and X-ray photoelectron spectra(XPS). Photocatalytic activities of these catalysts were evaluated for methylene blue (MB) degradation under the visible light with and without the assistance of NaHSO₃. The results indicated that Mn-LDO showed superior photocatalytic decomposition capability of MB than that of C-LDO. Moreover, Mn-LDO showed much higher photocatalytic degradation efficiency of MB in the presence of NaHSO₃ than only the single Mn-LDO degradation system. The stability and recyclability of the catalyst were also investigated.