Effect of cobalt doping on optical, magnetic and photocatalytic properties of ZnO nanoparticles

Cobalt doped ZnO nanoparticles (Zn1-xCoxO(0.00 <= x <= 0.1)) was synthesized by a two-step co-precipitation method using oxalic acid and ammonium hydroxide. The effect of Co doping on the crystallite structure, optical, magnetic and photocatalytic properties of ZnO was investigated. The X-ray powder diffraction (XRD) patterns confirmed that all Zn1-xCoxO samples exhibited hexagonal wurtzite structure. Further, the lattice parameters revealed an increasing trend in doped samples which indicated the incorporation of Co ions into the ZnO lattice. The X-ray photoelectron spectroscopic (XPS) survey suggested that Co ion incorporated into the ZnO lattice with a Co2+ oxidization state. The scanning electron micrograph (SEM) showed that the average size decreased with increasing doping concentration. Photoluminescence (PL) showed blue emission peak at 475 nm, green emission peak at 545 nm and yellow emission peak at 580 nm, respectively. UV-vis spectral illustrated the substitution of Co2+ in ZnO leaded to band gap narrowing. Vibrating sample magnetometer (VSM) demonstrated doped samples exhibited ferromagnetism behavior at room temperature. The Zn0.96Co0.04O sample showed enhancement in the photocatalytic degradation efficiency of methylene blue as compared to the pure ZnO. However, increasing doping concentrations of Co leaded to a decrease of photocatalytic efficiency.