A water-dispersible, carboxylate-rich carbonaceous solid: synthesis, heavy metal uptake and EPR study
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Thermal oxidation of Na-cholate hydrate at 300 °C in air results in a carbonaceous solid (SC-30) nanomaterial bearing a steroid interior and a significant fraction of carboxylate sites. Electron Paramagnetic Resonance spectroscopy reveals that SC-30 bears a significant concentration of stable C-based radicals located at the interior of the steroid carbonaceous matrix. H-binding, determined by potentiometric acid–base titrations show that the SC-30 contains three types of H-binding sites. One type with pKa = 4.2 corresponds to surfacial metal-binding COOH groups. A second type of sites with pKa = 6.2 corresponds to COOH buried at the interior of the SC-30 carbon matrix, which are inactive in metal binding. A third type with pKa = 8.5—is also inactive in metal binding—originates from aggregated stacked-states like those observed for cholate in solution. The surfacial COO− carboxylate groups, confer the solid hydrophilic character, therefore it can be easily dispersed in water at high concentrations providing clear aqueous colloids. pH-edge metal uptake experiments and Surface Complexation Modelling show that SC-30 is an efficient heavy metal adsorbent in aqueous solution for Pb2+ and Cu2+ ions at pH 5–8. A structural/functional model is discussed based on the heterogeneous character of the SC-30 material.
KeywordsElectron Paramagnetic Resonance Electron Paramagnetic Resonance Spectrum Radical Site Electron Paramagnetic Resonance Study Electron Paramagnetic Resonance Data
This study has been supported by the Operational Program Research and Development for Innovations-European Social Fund (CZ.1.05/2.1.00/03.0058). The authors thank Dr. Safarova (Palacky University) for technical assistance in TEM measurements.
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