Visible light assisted photocatalytic performance of Ni and Th co-doped ZnO nanoparticles for the degradation of methylene blue dye

Nickel (Ni) and thorium (Th) co-doped zinc oxide (ZnO) nanoparticles were prepared by the co-precipitation method. The synthesized nanoparticles were characterized using UV-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron spectroscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) techniques. The photocatalytic activity of the prepared catalysts was evaluated by the degradation of methylene blue (MB) dye under visible light irradiation. XRD and SEM results revealed that Ni-Th-ZnO has a hexagonal and rods like morphology with an average crystallite size of 30nm. Ni-Th-ZnO possesses excellent photocatalytic activity for the degradation of MB when compared to that of Ni-ZnO, Th-ZnO, ZnO and TiO₂. The photocatalytic activity of Ni-Th-ZnO is obviously affected by the reaction parameters. The maximum MB degradation (93% with 70% COD removal) was achieved with Ni-Th-ZnO concentration of 0.375g/L, initial MB concentration of 1.5μM, pH 10 and irradiation time of 180min. A possible photocatalytic mechanism has also been proposed. Moreover, the photocatalyst could be reused for four times without remarkable loss of its activity.