Magnetically separable Ni0.6Fe2.4O4 nanoparticles as an effective adsorbent for dye removal: Synthesis and study on the kinetic and thermodynamic behaviors for dye adsorption

Abstract

Abstract Magnetically separable Ni0.6Fe2.4O4 nanoparticles were successfully synthesized by a two-step method incorporating a micro-emulsion synthetic process and following calcination of the precursor. The as-prepared samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray energy dispersive spectroscopy (EDS), which indicate that the obtained sample is cubic phase Ni0.6Fe2.4O4 nanoparticles with spinel structure. The BET tests show that the specific surface area of the Ni0.6Fe2.4O4 nanoparticles is 113.95 m2 g−1 with uniform pore size distribution at about 5.86 nm in diameter. The as-obtained sample exhibits ferromagnetic behavior at room temperature, making it magnetically separable in the solution. The as-prepared porous Ni0.6Fe2.4O4 nanoparticles showed excellent adsorption capacity and rapid adsorption rate for Congo red (CR) dye in aqueous solution. The maximum adsorption capacity of CR was 72.73 mg g−1 and 92.04% of the dye can be removed within the initial 9 min of contact time. The effects of contact time, initial pH and temperature on CR adsorption were systematically investigated. To understand the adsorption behavior of CR onto the Ni0.6Fe2.4O4 nanoparticles, the adsorption data were analyzed using the pseudo-first-order model, pseudo-second-order model, intra-particle diffusion, and the Boyd model. And the results indicate that the adsorption kinetics can be described using the pseudo-second-order model. During the adsorption process, film diffusion is the rate-determine step for the adsorption of CR. The equilibrium data can be fitted linearly according to the Langmuir model. Thermodynamic analyses show that the adsorption process is exothermic and spontaneous. The adsorption of CR onto the Ni0.6Fe2.4O4 nanoparticles is a physisorption process, during which electrostatic adsorption was the main driving force.