Enhanced removal of methylene blue dye by bimetallic nano-sized MOF-5s

Metal-organic framework 5 (MOF-5) and bimetallic MOF-5s (Co/Zn and Ni/Zn) were prepared via a simple solvothermal method. Samples were characterized by various techniques such as powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectroscopy (DRS), inductively coupled plasma (ICP) and elemental analysis (EA). Photocatalytic decolorization of methylene blue (MB) dye in the aqueous solutions was examined under UV and visible light irradiation. The degradation of MB solutions was calculated by changes in the UV–Vis absorbencies of the aqueous solutions at λmax = 664 nm. The influence of various parameters such as the catalyst loading, dye concentration, initial pH of the dye solution and adding electron acceptors (H2O2, tert-Butyl hydroperoxide (TBHP), KBrO3, KIO4 and (NH4)2S2O8) on the degradation reaction was studied. Moreover, metal doping can improve the photocatalytic activity of MOF-5 due to the synergistic effect, narrow band gap and so on. The results show that Co/Zn-MOF-5 photocatalyst exhibited better photocatalytic activity than Ni/Zn-MOF-5 and raw MOF-5 for MB decolorization under UV and visible light irradiation. Furthermore, adding different electron acceptors, except TBHP, enhanced the photocatalytic performance of photocatalysts with a different rate. Also, kinetic studies revealed that the reactions follow pseudo-first-order. Additionally, bimetallic MOF-5s did not show obvious activity reduction in MB decolorization during five recycling usages.