Effect of Different Metal Doping of ZnO Nanoparticles on Photocatalytic Degradation of Dye Wastewater

Undoped ZnO and metal-doped ZnO (ZnO:M) nanoparticles (NPs), with M [Formula: see text] Ca, V and Al, have been synthesized, with the same metal content ([Formula: see text]%), by the sol–gel method. The M-doping effects on the ZnO NPs properties are studied by a variety of techniques, including XRD, TEM and UV–Vis spectroscopy. XRD analysis confirmed that the synthesized samples were crystalline with a hexagonal wurtzite phase. X-ray peak broadening analysis was used to estimate crystallite sizes, which range from 22[Formula: see text]nm to 34[Formula: see text]nm, and microstrain values varying between [Formula: see text] and [Formula: see text]. TEM images show the hexagonal shape and the nanometric size of pure ZnO and ZnO:M NPs. Compared with undoped ZnO NPs band gap energy (3.20[Formula: see text]eV), a small redshift was obtained for Ca- (3.11[Formula: see text]eV), V- (3.18[Formula: see text]eV) and Al-doped (3.17[Formula: see text]eV) ZnO NPs. Visible-light-driven photocatalytic properties of M-doped ZnO NPs have been monitored through photodegradation of methylene blue (MB), and the results are compared with the pure ZnO and commercial P25. The metal doping hindered photocatalytic decolorization under visible light irradiation, which obeyed pseudo-first-order kinetics model. In this research, Ca-doped ZnO has shown the highest photocatalytic activity of ∼98% within 150[Formula: see text]min when compared with the other M-doped ZnO samples and the reference photocatalyst P25, while ZnO:Al NPs demonstrated the lowest photocatalytic activity among the dopants. The enhancement of photocatalytic activity of M-doped ZnO samples is mainly due to their smaller particle size and capability for reducing the electron–hole pair recombination. Ca-doped ZnO NPs, which exhibit the highest photocatalytic efficiency, could be used as a promising material for application in dye wastewater treatment processes.