Study on the fabrication and investigation of the structural, optical and photocatalytic properties of Co2+, Ni2+ co-doped ZnO nanomaterials

Abstract

In this study, Co2+, Ni2+ co-doped ZnO nanomaterials (Co,Ni-ZnO NMs) were successfully fabricated by hydrothermal method at low temperature at 90oC for 12 hours. Co2+ and Ni2+ ions were doped into the ZnO nanomaterials at ratios of 1 mol% and 2 mol%, respectively (calculated compared to the number of moles of Zn2+). The methods used to study on the structure and properties of materials such as XRD, SEM/ EDX and UV-vis spectra. The results showed that the fabricated materials were in the form of wurtzite single-phase and nanometer structure. The optical band gap energy (Eg) of Co, Ni-ZnO NMs was determined based on to the Kubelka–Munk equation and achieved a the value of 3.17 eV. The Eg of undoped ZnO was about of 3.34 eV. Reducing this optical gap energy of the material is desirable in research on semiconductor materials with the aim to improve the applicability of materials that are responsive under irradiation of light shifted to visible region. Besides, the results also showed that the ZnO nanomaterials co-doped with Co2+ and Ni2+ achieved a photocatalytic efficiency for degradation of the methylene blue (MB) dye solution in the visible light regions. Thus, ZnO material co-doped with Co2+ and Ni2+ ions has achieved superiority in optical applications stimulated by visible light (undoped ZnO material only achieves optical applications in the ultraviolet light region). The rate constant for the MB dye photocatalytic decomposition reaction had been determined according to the Langmuir Hinshelwood (L-H) kinetic model. This decomposition rate constant of the fabricated samples all complied with the first-order kinetic model with a high R2 correlation coefficient (achieved above of 0.92). The rate constant of the Co,Ni-ZnO NMs sample was approximately 17.8 times larger than that of the undoped ZnO sample (achieved 0.006204 and 0.0003471 min-1, respectively).