Cobalt ferrite nanoparticles via a template-free hydrothermal route as an efficient nano-adsorbent for potential textile dye removal

Abstract

We have reported herein the preparation of a pure cobalt ferrite (CoFe₂O₄) nanostructure, as an efficient nano-adsorbent, via a template-free hydrothermal and post thermal conversion route. We prepared micro-spherical particles of a cobalt carbonate/iron carbonate (CoCO₃/FeCO₃) composite precursor using the hydrothermal reaction of cobalt sulfate, iron sulfate, ascorbic acid, and ammonium carbonate at 140 °C for 3 h. Various parameters influencing the hydrothermal reaction have been studied. Thermal decomposition of the carbonate composite precursors prepared using different Co²⁺ : Fe²⁺ molar ratios generated various impure products. However, the CoCO₃/FeCO₃ composite precursor synthesized employing a 0.4Co²⁺ : 0.6Fe²⁺ molar ratio produced a pure spinel CoFe₂O₄ nanostructure with an average crystallite size of 9.5–21.6 nm on calcination in the temperature range of 400–600 °C for 2 h. The products were identified using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), high resolution transmission electron microscopy (HR-TEM), nitrogen physical adsorption (BET), zeta potential and thermal analysis. The as-prepared spinel CoFe₂O₄ product showed a high adsorption capacity (91.7 mg g⁻¹) toward Reactive Red 195 (RR195) dye in 20 min. The adsorption results fitted well the pseudo-second-order kinetics and could be well described by the Langmuir isotherm model. The RR195 dye adsorption was spontaneous, exothermic, and a physisorption process, implied from the calculated thermodynamic constants: ΔG⁰ (from −0.022 to −0.711 kJ mol⁻¹), and ΔH⁰ (−7.55 kJ mol⁻¹). It is concluded that the suggested CoFe₂O₄ nanostructure can be employed as an efficient nano-adsorbent for the removal of RR195 textile dye from aqueous solutions.