This research article describes the synthesis of cobalt-oxide nanoparticles by simple precipitation technique and their environmental application. The prepared Co₃O₄ nanoparticles were characterised by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, selected area diffraction, and energy-dispersive X-ray spectroscopy, along with elemental mapping analysis. The characterisation images revealed that as-synthesised nanomaterial had a hexagonal sheet-like morphology with average particle size 10–20 nm and was crystalline in nature. The nano-adsorbent displayed its efficiency in methyl orange adsorption from aqueous solution. Several adsorption factors such as pH, initial concentration, time, and temperature were examined, and isotherm, kinetic, and thermodynamic data were observed. The adsorption rate was fast and followed a pseudo–second-order kinetic model. The adsorption isotherm could be suited with both Langmuir and Freundlich isotherms. The adsorption process turned out to be spontaneous and exothermic. The effects of the various factors for methyl orange removal were analysed using the Box–Behnken design. A second-order quadratic model was used to project the response. Analysis of variance analysed the significance of the factors and their interactions. Three-dimensional response surface plots were used to determine the interactive effects of the independent factors on methyl orange adsorption capacity. The successful regeneration of Co₃O₄ nanoparticles suggested their usefulness in wastewater treatment and various other industrial settings. The reusability and efficient adsorptive capacity of nano-adsorbent for environmental management represent the importance of this work.