Chemical oxidation of mesoporous carbon foams for lead ion adsorption

Acid treated mesoporous carbon foams, with surface areas (SBET) as high as 2207 m2 g−1, were synthesised by the carbonisation of fructose over ZnCl2 templates and tested as adsorbents of Pb(II) ions from aqueous solutions. Whilst the oxidising acid treatment disrupted the morphology of the foams, it also led to a proliferation of oxide moieties on the surface of the material which acted as binding sites for Pb(II) ions. Characterisation of the oxidised surfaces by IR spectroscopy and measurement of the zero point charge (pHpzc) showed that the number of acidic surface sites increased with increasing acid concentration and temperature. The oxidised carbon foams were tested for their efficiency at removing Pb(II) ions from aqueous solutions, using batch adsorption techniques. The concentration dependence of Pb(II) ion uptake by the mesoporous carbon adsorbents could be fitted to Langmuir, Freundlich and Dubinin–Kaganer–Radushkevich (DKR) isotherms, from which the maximum adsorption capacity (Qm) and the energy of adsorption (Ea) was derived. Ea values obtained for the mesoporous carbon adsorbents were associated with weak adsorption (<8 kJ mol−1), ion exchange adsorption (8–16 kJ mol−1) and chelation (>16 kJ mol−1) depending on the surface oxidation conditions used.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of mesoporous carbon foams with surface areas in excess of 2000 m2 g−1. ► Oxidation of carbon surface using HNO3 varying molar strengths and temperatures. ► Creates profusion of oxygenated surface functionalities. ► Triggers a collapse in pore structure and surface areas of mesoporous carbon foams. ► Maximum Pb(II) uptake of 188 mg g−1 using 10 M HNO3 at 105 °C treatments..