In this article, cobalt oxide (Co₃O₄) nanoparticles were prepared using chemical synthesis (CS-Co₃O₄ NPs) and green synthesis (GS-Co₃O₄ NPs) processes, respectively, from nitrate precursor and Moringa oleifera seed (MOS) extract. The cubic structure of the prepared Co₃O₄ NPs with spherical morphology was confirmed. The optical properties were performed for CS and GS-Co₃O₄ NPs, and their bandgap energies were found to be 3.17 and 3.20 eV, respectively. The BET-specific surface area was measured as 97 m² g⁻¹ (CS-Co₃O₄ NPs) and 128 m² g⁻¹ (GS-Co₃O₄ NPs). The GS-Co₃O₄ NPs have improved optical absorption characteristics and thermal stability compared to the CS-Co₃O₄ NPs samples. The Co₃O₄ NPs were utilized as catalysts to degrade the cationic-methylene blue (MB) dye and the anionic-methyl orange (MO) dye under UV and sunlight irradiation. The degradation of MB and MO dyes with nanocatalysis was characterized using UV–visible spectroscopy and a pseudo-first-order kinetics model. These results suggested that the degradation of MB and MO dyes under sunlight irradiation shows better efficiency. Thus, GS-Co₃O₄ NPs have excellent optical properties, their photocatalytic performance toward MB and MO dye degradation is highly influenced, with an efficiency nearly reaching 100%.