No abstract

The results presented in this work are related to the design of a guideline to develop specific properties at the surface of an activated carbon (AC). For this, two model aromatic compounds have been synthesized and their electrolytic behavior in aqueous solutions was studied by a potentiometric method. The textural characteristics of the activated carbon were determined by porosimetry methods. The nature of oxygen-carrying functions and the acid-base behavior of the AC surface were characterized by TPD and potentiometric titration methods, respectively. The adsorption and desorption equilibria of the aromatic compounds on activated carbon were measured in aqueous solutions, and the hysteresis between adsorption and desorption, which reveals irreversible adsorption, was discussed on the basis of the frontier orbital theory. HOMO and LUMO orbitals of the adsorbent and adsorbates were calculated, and irreversible adsorption was attributed to the small energy difference between HOMO and LUMO of the aromatic adsorbates and the adsorbent. Adsorption equilibria of K2CrO4 in aqueous solution on the AC alone and on the AC-aromatic ligand adsorbents, respectively, prove the efficient development of specific chemical functions at the carbon surface provided by the adsorbed aromatic compounds.

A new G-(H2L)-Pd heterogeneous catalyst has been prepared via a self-assembly process consisting in the spontaneous adsorption, in water at room temperature, of a macrocyclic H2L ligand on graphene (G) (G + H2L = G-(H2L)), followed by decoration of the macrocycle with Pd2+ ions (G-(H2L) + Pd2+ = G-(H2L)-Pd) under the same mild conditions. This supramolecular approach is a sustainable (green) procedure that preserves the special characteristics of graphene and furnishes an efficient catalyst for the Cu-free Sonogashira cross coupling reaction between iodobenzene and phenylacetylene. Indeed, G-(H2L)-Pd shows an excellent conversion (90%) of reactants into diphenylacetylene under mild conditions (50 °C, water, aerobic atmosphere, 14 h). The catalyst proved to be reusable for at least four cycles, although decreasing yields down to 50% were observed.

The adsorption of five Nalpha-substituted amino acids with a 5-nitroso-6-oxo pyrimidine as substituent on a commercial activated carbon (AC) has been studied in aqueous solution at several pH values. The adsorption processes of these organic compounds have been analyzed on the basis of the electrolytic behavior of the adsorbates. In all cases, the adsorption process is highly irreversible due to strong pi-pi interactions between the arene centers of the AC and the pyrimidine residue of the adsorbates. This interaction is consistent with XPS data and HOMO-LUMO theoretical calculations. The adsorption of these organic compounds provides a new route for the functionalization of the AC surface with carboxyl groups. In addition, the adsorption capacity of the AC/organic compound systems for Cu(II) ions in aqueous solution has been studied at different pH values. These systems show an increase of the adsorption capacity for Cu(II) compared to the AC, which is related to the AC functionalization with carboxyl groups due to the adsorbed organic compounds.