Facile Synthesis of Thin Film Cobalt-doped Zinc Oxide Nanorods Photoanode for Efficient Methylene Blue Degradation

ZnO nanorod thin films doped with cobalt were successfully synthesized on Indium Thin Oxide (ITO) glass substrates using the chemical bath deposition method to assess their characteristics and methylene blue degradation capabilities. ZnO nanorod thin films doped with cobalt were successfully synthesized on Indium ThinOxide (ITO) glass substrates using the chemical bath deposition method to evaluate their characteristics and methylene blue degradation capabilities. This study compared undoped and Co-doped ZnO on ITO glass substrates for photoelectrocatalytic (PEC) applications. XRD analysis confirmed that all samples exhibited a crystalline hexagonal wurtzite structure, with no additional phases detected in films with 5 % Co doping. The formation of nanorod structures in both undoped and Co-doped ZnO was revealed by SEM images where the presence of Co in the doped ZnO was confirmed through EDX analysis  UV-DRS analysis indicated changes in band gap values with the addition of 5 % Co doping, decreasing from 3.09 to 3.07 eV for the ZnO/ITO and Co-ZnO/ITO photoanode. Evaluation of the PEC performance of the photoanodes toward methylene blue in an aqueous solution showed that Co doping enhanced the PEC efficiency of the ZnO/ITO photoanode. The decolourization efficiency of methylene blue reached 93.72 % using Co-ZnO/ITO, which is higher than that of ZnO/ITO at 86.84 %. Furthermore, the kinetic study showed that Co-ZnO/ITO photoanode follows a first-order reaction kinetics model with a reaction rate constant of 0.0085 min−1. The result of our study suggests the potential of Co-ZnO/ITO photoanode in addressing dyecontamination issues effectively. HIGHLIGHTS Co-doped ZnO thin films synthesized via chemical bath deposition method. Hexagonal structure retained; band gap reduced from 3.09 to 3.07 eV. Co-doped ZnO showed 93.72 % methylene blue degradation vs. 86.84 % for ZnO. First-order kinetics with a rate constant of 0.0085 min⁻¹ for Co-ZnO/ITO. Co-ZnO/ITO thin films show promise for dye-contaminated water treatment. GRAPHICAL ABSTRACT