Magnetic hollow carbon nanospheres for removal of chromium ions

Abstract

Magnetically functionalized carbon materials as adsorbents have shown outstanding adsorption capacity for Cr(VI) removal. Here, magnetic hollow carbon nanospheres (MHCSs) have been fabricated by simply changing the pyrolysis temperature from 600 to 850 °C of the polymer counterparts, which were denoted as MHCS-n, where n is 600, 700, or 850 °C. The MHCS composite displayed spherical morphology with a hollow air core and crack-free carbon shell structure, which was homogenously and controllably loaded with nanosized (ca. 10 nm) Fe-based nanoparticles (ca. 8.9 wt%). In principle, the hollow structure would allow more exposed adsorption sites to adsorbate than a solid structure. When evaluated as an absorbent for Cr(VI) ion removal, such highly engineered MHCSs exhibited excellent adsorption capacity. The maximum adsorption capacity of Cr(VI) per weight of adsorbent was 200 mg g⁻¹, which was much higher than those of other carbon-based adsorbents reported in literature. The extraordinary adsorption capacity of MHCS-700 may be attributed to two factors: (i) the large specific surface area would provide abundant functional groups, (ii) the developed graphitic structures provide electrostatic interactions between π electrons and Cr species. Furthermore, magnetic iron-based nanoparticles allowed fast separation of the MHCSs from liquid suspension. Thus, the MHCSs may serve as an ideal candidate for chromium removal in water treatment.