Synthesis of novel surface-modified hematite nanoparticles for the removal of cobalt-60 radiocations from aqueous solution

In this study, novel surface-modified hematite nanoparticles (α-Fe2O3 NPs) were prepared at 250 °C using iron(III) chloride hexahydrate (FeCl3·6H2O) and oleic acid (C18H34O2) as raw materials for the removal of cobalt-60 radiocations from aqueous solutions by hydrothermal method. α-Fe2O3 NPs were characterized by X-ray diffraction, Fourier transform infrared (FT-IR), scanning electron microscope, transmission electron microscopy and Brunauer–Emmett–Teller. According to the results, the average diameter and length of the synthesized α-Fe2O3 nanorods varied in the range of 30–60 and 400–700 nm, respectively, when the specific surface area was 31.29 m2/g. In batch experiments, the effect of some variables such as pH (2–10), adsorbent weight (0.5, 1, 1.5, 2.5, 3.75 and 5 mg in 25 mL solution), initial concentration of cobalt-60 radiocations (1, 10, 25, 50, 75 and 100 mg/L), temperature (25, 30, 35, 40 and 45 °C) and contact time (1, 2, 3, 4, 5 and 6 h) was investigated at 120 rpm. The optimized condition for cobalt-60 adsorption onto α-Fe2O3 NPs was obtained in pH 6.5, initial radiocation concentration of 1 mg/L, contact time of 2 h and nano-α-Fe2O3 sorbent concentration of 20 mg/L. On the other hand, the results indicated that adsorption of cobalt-60 onto the synthesized nano-α-Fe2O3 well fitted the Ho model as linear pseudo-second-order kinetics. In contrast, analysis of equilibrium data showed that the Redlich–Peterson isotherm model was suitable for describing cobalt-60 adsorption onto α-Fe2O3 NPs and the maximum uptake capacity was about 142.86 mg/g at 25 ± 1 °C according to Langmuir isotherm results. Meanwhile, the actual maximum adsorption capacity was about 99 mg/g. Therefore, it can be concluded that the synthesized novel surface-modified α-Fe2O3 NPs is an environment-friendly and a promising adsorbent for the removal of cobalt-60 radiocations from aqueous solutions.