Hydrothermal Syntheses of Colloidal Carbon Spheres from Cyclodextrins

Abstract

Colloidal carbon spheres have been prepared from aqueous α-, β-, and γ-cyclodextrin (CD) solutions in closed systems under hydrothermal conditions at 160 °C. Both liquid and solid-state 13C NMR spectra taken for samples at different reaction times have been used to monitor the dehydration and carbonization pathways. CD slowly hydrolyzes to glucose and forms 5-hydroxymethyl furfural (HMF) followed by carbonization into colloidal carbon spheres. The isolated carbon spheres are 70−150 nm in diameter, exhibit a core−shell structure, and are comprised of a condensed core (C═C) peppered with resident chemical functionalities including carboxylate and hydroxyl groups. Evidence from 13C solid-state NMR and FT-IR spectra reveal that the evolving carbon spheres show a gradual increase in the amount of aromatic carbon as a function of reaction time and that the carbon spheres generated from γ-CD contain significantly higher aromatic carbon than those derived from α- and β-CD.