Two series of carbons were prepared from Agave americana fibres (A) mixed with

The effect of heteroatoms on hydrogen adsorption properties of activated and hybrid carbon materials is critically described. For that purpose, olive stones were activated chemically with KOH, and subsequently washed or not, and oxidised with ozone or not. Olive stones were also activated physically with CO 2 . A series of activated carbons prepared by chemical activation of sucrose was also investigated for comparison. As a result, many activated carbons with different pore-size distributions, surface areas, average micropore widths, oxygen contents and amounts of mineral matter could be compared. All were thoroughly characterised by adsorption of N 2 , CO 2 and H 2 O, elemental analysis, XPS, thermogravimetry, and adsorption of H 2 at different pressures. Many correlations between textural parameters, composition and adsorption properties could be evidenced, and were critically discussed. We show that the hydrogen uptake at 77 K is controlled by the following parameters, listed by decreasing order of importance: specific surface area, average micropore size, surface chemistry and shape of the pore size distribution. At room temperature (i.e., at 298 K), the adsorbed hydrogen uptake was in the range of 0.19 to 0.42 wt. %; the presence of large amounts of alkali metals can further improve the hydrogen adsorption properties, but surface chemistry still has a major influence, especially through the acidic surface functions.

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Abstract:In the present paper, porous materials were prepared from the hydrothermal treatment of aqueous solutions of tannin, a renewable phenolic resource extracted from tree barks, containing dissolved salts of transition metals: V, Cr, Ni and Fe. Hydrothermal treatment produced carbonaceous particles doped with the aforementioned metals, and such materials were treated according to two different routes: (i) calcination in air in order to burn the carbon and to recover porous oxides; (ii) pyrolysis in inert atmosphere so as to recover porous metal/carbon hybrid materials. The nature of the metal salt was found to have a dramatic impact on the structure of the materials recovered by the first route, leading either to nano-powders (V, Cr) or to hollow microspheres (Ni, Fe). The second route was only investigated with iron, leading to magnetic Fe-loaded micro/mesoporous carbons whose texture, pore volumes and surface areas gradually changed with the iron content.

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In this study, the successful preparation of activated carbons from Corn Stigmata, either through direct pyrolysis and activation or through a preliminary additional hydrothermal carbonisation (HTC) step, was reported. It was shown that the latter allowed producing higher carbon yield, higher carbon content and higher BET area (A BET) after 2h of activation with CO 2 than what was observed for activated carbons (ACs) prepared in the same conditions but without HTC. The AC having the most developed porous texture, A BET = 1111 m 2 /g, was further investigated by FTIR, SEM and potentiometric titration, and its pH at point of zero charge was determined. Its performances in terms of methylene blue (MB) adsorption were studied and discussed in relation to its textural and chemical characteristics. Due to its very heterogeneous surface, the fractal Brouers-Sotolongo model was the most relevant for describing both kinetic and equilibrium adsorption data. The calculated thermodynamic parameters also showed that MB adsorption was spontaneous on this material. The high MB uptake at room temperature, compared to many other results published in the literature, further confirmed the interest of Corn Stigmata-derived hydrochars as precursors of activated carbons.