Synthesis and characterisation of Co2+-incorporated ZnO nanoparticles prepared through a sol-gel method

•ZnO nanoparticles were synthesized by the sol gel method with no capping agent.•Effects of lower doping amount of Co2+ on size of ZnO were investigated.•The optical properties shifts to visible region of Co2+ doped ZnO were observed.•Finding of good potential properties for photocatalytic degradation of Congo red.

The properties of ZnO nanoparticles were modified by doping them with cobalt ions (Co2+) in various compositions through a sol-gel route. The Co2+-doped ZnO nanoparticles were characterised using X-ray diffraction (XRD), UV/Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and zeta potential measurements. A hexagonal wurtzite-phase structure of Co2+-doped ZnO was observed, with a slight decrease in particle size as the Co2+ doping concentration increased. Absorption by Co2+-doped ZnO was found to shift to longer wavelengths, towards the visible region, which was also confirmed by photoluminescence analysis. The band gap of the Co2+-doped ZnO samples decreased from 3.19 to 2.66 eV as the content of dopant Co2+ increased from 0.0 to 1.0 wt.%. The zeta potential results showed slight effects of Co2+ doping compared with undoped ZnO, indicating that Co2+ doping influences the optical properties and morphology of pure ZnO nanoparticles. The photocatalytic activity of the Co2+-doped ZnO samples was evaluated for the removal of Congo red dye from aqueous solution under solar radiation. The Co2+-doped ZnO samples showed higher effective removal of the dye using the optimal doping of 0.50 wt.%, which produced higher efficiency (about 96%, compared with 80% for pure ZnO).

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