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Influence of oxidation process on the adsorption capacity of activated carbons from lignocellulosic precursors

Mourão, P.A.M., Laginhas, C., Custódio, F., Nabais, J.M.V., Carrott, P.J.M., Carrott, M.M.L. Ribeiro
Fuel processing technology 2011 v.92 no.2 pp. 241-246
Fourier transform infrared spectroscopy, activated carbon, adsorption, almonds, carbon dioxide, chemical composition, hulls, lignocellulose, nitric acid, nitrogen, oxidation, p-nitrophenol, phenol, shoots, sorption isotherms, surface area, temperature, vines
A set of activated carbon materials non-oxidised and oxidised, were successfully prepared from two different lignocellulosic precursors, almond shell and vine shoot, by physical activation with carbon dioxide and posterior oxidation with nitric acid. All samples were characterised in relation to their structural properties and chemical composition, by different techniques, namely nitrogen adsorption at 77K, elemental analysis (C, H, N, O and S), point of zero charge (PZC) and FTIR. A judicious choice was made to obtain carbon materials with similar structural properties (apparent BET surface area ∼850–950m²g⁻ ¹, micropore volume ∼0.4cm³g⁻ ¹, mean pore width ∼1.2nm and external surface area ∼14–26m²g⁻ ¹). After their characterisation, these microporous activated carbons were also tested for the adsorption of phenolic compounds (p-nitrophenol and phenol) in the liquid phase at room temperature. The performance in liquid phase was correlated with their structural and chemical properties. The oxidation had a major impact at a chemical level but only a moderate modification of the porous structure of the samples. The Langmuir and Freundlich equations were applied to the experimental adsorption isotherms of phenolic compounds with good agreement for the different estimated parameters.