Safranin-O dye removal by synthesized copper oxide nanoparticles: Isotherms, kinetics, and thermodynamics

Copper oxide nanoparticles (CuONPs) were synthesized by a photo-irradiation chemical method and investigated for the removal of Safranin-O dye from aqueous solution. The prepared nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD confirmed the formation of crystalline monoclinic CuO, while TEM showed nearly spherical to hemispherical particles with an average size of 38.58 ± 20.08 nm. The adsorption behavior of Safranin-O on CuONPs was studied under different experimental conditions, including initial dye concentration, contact time, pH, and temperature. The adsorption capacity increased with pH, reaching a maximum at pH 11, while equilibrium was attained after 60 min. The maximum adsorption capacity was 4.3236 mg/g at 298 K. Equilibrium data were analyzed using the Langmuir and the Freundlich isotherm models, and the Freundlich model provided the better fit, suggesting adsorption on a heterogeneous surface. Kinetic data were examined using pseudo-first-order and pseudo-second-order models, and the pseudo-second-order model showed better agreement with the experimental results among the tested linear models. Thermodynamic analysis showed that the adsorption process was exothermic, with ΔH = −17.86 kJ/mol and ΔS = −84.83 J/mol.K, while the positive ΔG values indicated that the process was thermodynamically non-spontaneous under the studied conditions. These findings show that CuONPs can be used as an adsorbent for the removal of Safranin-O from aqueous media under suitable operating conditions. • CuO NPs are good adsorbent surface due to high surface to volume ratio. • Reusability of CuO NPs makes it efficient for adsorption applications. • The interaction between CuO NPs and safranin occurs mainly through electrostatic attraction, hydrogen bonds, and ᴨ-ᴨ interaction.