Characterization of carbon nano-onions for heavy metal ion remediation

Carbonaceous nanomaterials, such as fullerene C₆₀, carbon nanotubes, and their functionalized derivatives have been demonstrated to possess high sorption capacity for organic and heavy metal contaminants, indicating a potential for remediation application. The actual application of these nanomaterials, however, is often hindered by the high cost of materials and the limited understanding of their mobility in porous media. In this work, carbon nano-onions (CNOs), a relatively new addition to the carbonaceous nanomaterials, were synthesized in a cost-effective way using a laser-assisted combustion synthesis process, and carefully characterized for their potential remediation application. Surface oxidized CNOs possessed 10 times higher sorption capacity than C₆₀ for heavy metal ion contaminants including Pb²⁺, Cu²⁺, Cd²⁺, Ni²⁺, and Zn²⁺. CNOs aqueous suspension can be very stable in NaCl solution at ionic strength up to 30 mM and CaCl₂ solution at ionic strength up to 4 mM CaCl₂ when pH ranged from 5 to 9, which are consistent with environmentally relevant conditions. Interactions of CNOs with iron oxide and silica surfaces under favorable condition were found to be electrostatic in origin. Mobility of CNOs in quartz sands was controlled by electrolyte type and concentration. Approximately 4.4, 25.1, and 92.5 % of injected CNO mass were retained in the sand column in ultrapure water, 1 mM NaCl, and 1 mM CaCl₂ solutions, respectively.