Co(II) Removal from Aqueous Solution by Birhodanine-Functionalized Magnetite Nanoparticles: Kinetic and Thermodynamic Studies

The present work explains the synthesis of [(E)-5-(3-(3-(trimethoxysilyl)propyl)-4-oxo-2-thioxothiazolidin-5-ylidene)-3-phenethyl-2-thioxothiazolidin-4-one] (TMOS-BIRD) to silylate magnetite nanoparticles (MNPs), and removal of Co(II) ions. The prepared NPs were characterized by FTIR analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). Based on thermogravimetric analysis (TGA), the birhodanine content of the prepared nano-particles (NPs) was obtained as 48 mg g-1. The capability of MNP@BIRD for removal of Co(II) cations was shown investigated under the optimal conditions of contact time, pH, adsorbent dosage and initial Co(II) concentration. The results declared that the adsorption kinetics obeys pseudo-first-order kinetics while fitting of the adsorption data into the Langmuir isotherm outlined the maximum adsorption capacity of 6.02 mg g-1. The value was in accordance the experimental value (Qe.exp = 5.36 mg g-1). Thermodynamic investigations unraveled the spontaneous nature of the adsorption process (ΔG = -5.37 kJ mol-1, at 25±1°C). The positive ΔH and ΔS values (ΔH = 30.81 kJ mol-1, ΔS = 123.55 J mol-1.K-1) revealed the endothermic nature of the adsorption process while randomness at the solid/liquid interface is increased during. In addition, the MNP@BIRD Nps were regenerated by simple washing with an aqueous 0.1 M HCl solution. The study of the reusability of the prepared magnetic sorbent revealed that MNP@BIRD NPs can be reused several times without any significant decrease in its extraction efficiency. These findings suggest that the silylated NPs are stable and reusable, and they can be applied to removal of Co(II) cations in water treatment processes.