On the modeling of heavy metals and rare earth elements adsorption on colloidal carbon-based nanoparticles

Acid-base and metal ions adsorptive properties of colloidal carbon-based nanostructured materials, bearing a variable number of oxygen-containing functional groups at the surface, were investigated and modeled. Hydrophilic carbonaceous nanoparticles (HNPs) with uniform dimensions and a good grade of dispersion in water, were obtained through the oxidation of a carbon black with nitric acid, at a temperature of 100 °C, for different reaction times (2-24 h). The acid-base properties of the functional groups were evaluated in water suspension by potentiometry and infrared spectroscopy. By means of X-ray fluorescence, infrared spectroscopy and differential pulse voltammetry the interaction properties of HNPs with Cd, Zn, Pb and selected Ln ions have also been investigated. The experimental data, collected in the 2.0-7.0 pH range, suggest that the adsorption of metal ions on HNPs is controlled by chemical adsorption involving the strong complexation of metal ions with the carboxylic groups on the surface of HNPs. Particularly, the high complexation of Ln ions opens the exploitation of HNPs in solid phase extraction for preconcentration, separation and determination of rare earth elements and actinides.