Abstract

New types of Cu-doped spherical-shaped activated carbons were prepared by pyrolysis at 700 °C of chitosan hydrogels impregnated with KOH at ratios (m_KOH/m_chitosan) ranging from 22.5% to 135%. At KOH impregnation ratio lower than 63%, the precursor Cu doping allowed obtaining bead-shaped activated carbons (diameter ~ 2 mm) and the highest specific surface areas (1145 m² g⁻¹). The absence of copper doping yielded to activated carbon powders whatever the KOH impregnation ratio. As increasing the impregnation ratio higher than 63%, the materials porosity type turns from exclusively microporous to both microporous and mesoporous. The microporous volume, determined by N₂ adsorption at 77 K and CO₂ adsorption at 273 K, attains a maximum (about 0.5 cm³ g⁻¹) for a 63% impregnation ratio. Scanning Electron Microscopy (SEM) images show a multi-scale porosity for a KOH impregnation ratio higher than 45%. Nanoparticles of Cu and CuO were identified by SEM and Transmission Electron Microscopy in the ACs beads prepared from copper-doped chitosan. Whatever the composition, the beads are formed of N-enriched carbons showing mainly pyridinic and pyrrolic groups evidenced by XPS.