Developing carbon-metal nanohybrids for the simultaneous removal of heavy metals and radionuclides from contaminated water

Maamoun, I.*; Tanaka, Kazuya  ; Dohi, Terumi   ; Kanno, Futoshi*; Tsubaki, Shuntaro*; Iguram, Noriyuki*

The co-occurrence of high contamination levels of heavy metals and radionuclides in (waste) water causes major consequences on health and ecosystems, producing short- and long-term harmful effects. Meanwhile, most of the conventional adsorbents/materials do not efficiently provide simultaneous removal of heavy metals and radionuclides. Iron (Fe) nanoparticles have been widely used in water treatment applications, due to their unique sorption abilities and the involvement of different mechanisms for contaminants removal. Correspondingly, combining Fe nanoparticles with other transition metals, such as zirconium (Zr), results in enhanced reaction rates and faster electron transfer, suggesting bi-metallic Fe/Zr as a good candidate for the simultaneous removal of heavy metals and radionuclides from contaminated water. In this work, carbon-metal nanohybrids were developed by supporting bi-metallic Fe/Zr nanoparticles on graphitic carbon, and their potential was investigated for the simultaneous removal of chromium, arsenic, and uranium from aqueous solutions. The graphitic carbon was prepared considering two approaches; the first approach is the hydrothermal carbonization of citric acid in the presence of potassium nitrate (KNO). The second approach was the graphitization of detonated nano-diamonds via annealing at 900C. The nanohybrids were synthesized by the addition of the as-prepared graphitic carbon to the Fe/Zr precursor(s) followed by the chemical reduction using borohydride (BH) reductant while mixing at 30C. The synthesized nanohybrids were characterized using different techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Microwave irradiation (2.45 GHz) was used for the post-treatment of the spent nanohybrids to achieve high recyclability over several consecutive removal experiments.