Abstract

EFFECT OF COBALT DOPING ON THE STRUCTURAL, OPTICAL, AND PHOTOCATALYTIC PROPERTIES OF ZNO FOR METHYLENE BLUE DEGRADATION

*Rajendra K. Pawar

Abstract

The uncontrolled discharge of synthetic dyes into aquatic environments poses a significant environmental and health hazard, with methylene blue (MB) being one of the most persistent pollutants. In this study, pure zinc oxide (ZnO) and cobalt-doped ZnO (Co–ZnO1 and Co–ZnO2) nanoparticles were synthesized via a co-precipitation method to evaluate the effect of cobalt incorporation on structural, optical, morphological, and photocatalytic properties. X-ray diffraction (XRD) confirmed the presence of ZnO and cobalt oxide phases with average crystallite sizes of 35.72 nm (ZnO), 36.22 nm (Co–ZnO1), and 45.27 nm (Co–ZnO2). UV–Vis absorption spectra revealed bandgap modifications, with Co doping inducing blue shifts and bandgap broadening (Eg = 3.28 eV for ZnO, 3.96 eV for Co–ZnO1, and 3.47 eV for Co–ZnO2). FT-IR analysis validated Zn–O lattice vibrations and Co incorporation, while FE-SEM and EDS confirmed morphology changes and successful cobalt substitution. Photocatalyti studies demonstrated efficient degradation of MB under visible-light irradiation, with maximum performance observed for undoped ZnO (86.33% degradation at 140 min), followed by Co–ZnO2 (76.22%) and Co–ZnO1 (66.11%). The reduced performance of doped samples was attributed to dopant-induced aggregation, charge recombination, and surface morphology alterations, although Co–ZnO2 retained moderate activity due to an improved balance between dopant level and bandgap tuning. These findings highlight the complex interplay between dopant concentration, crystallite size, and surface morphology in tailoring ZnO-based photocatalysts for dye degradation.

Keywords: Zinc oxide; Cobalt doping; Photocatalysis; Methylene blue degradation; Co-precipitation.