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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The potential of Tunisian prickly pear cactus as a low-cost adsorbent for Pb(II) ions from aqueous solution was investigated in batch mode. To determine the optimum adsorption conditions, experiments were conducted varying the operating parameters, as follows: pH of the solutions (2-10), initial concentration of metal ions (0.98-2.4 mmol/L) and temperature (30-60 °C). The adsorption isotherm data were analyzed by applying the Langmuir, Freundlich, Dubinin–Raduskevich, Temkin and Redlich–Peterson models. The experimental results were better fitted by the Freundlish model. The pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models were applied to the description of the kinetic data. The best fit was achieved for the pseudo-second order model, and the presence of both film and intraparticle diffusion mechanisms was demonstrated. Thermodynamic studies indicated that the biosorption on the cladode powder is an exothermic and chemical process. The desorption/regeneration process was also investigated. The obtained results revealed over 90% desorption of Pb(II) metal ions from the total metal-loaded mass of the adsorbent and good stability of the cactus adsorbent for four successive adsorption/desorption cycles.