Supramolecular assembling of molecular ion-ligands on graphite-based solid materials directed to specific binding of metal ions

Abstract

Molecular ligands with a particular topology, based on a polar heteroaromatic nucleus linked to hydrophilic (metal-complexing) substituents, form very stable assemblies with activated carbons (ACs) due to strong π–π interactions between the planar pyrimidine moiety and the arene centers of the AC surfaces. Heteroatomic functions at the edges of the AC graphitic sheets do not alter the interaction mode with the ligands nor the stability of the assemblies. That results in the formation of stable hybrids, AC/ligand, whose surface chemical properties, specially the acid base behavior and the affinity to metal ions, reflect those of the non-conjugated, hydrophilic moieties of the ligands. Consequently, such hybrid materials show metal ion adsorptivities that are superior to those of the parent AC and correlate with the metal-binding abilities of the non-conjugated substituents. Significant amounts of meso- and macropores are required in the parent AC to efficiently transfer the chemical properties of the ligand non-conjugated substituents to the hybrid AC/ligand. After adsorption of metal ions, new hybrids, AC/ligand/metal, emerge with interesting potential applications. Thus, an AC/triamine ligand/Pd(II) hybrid showed high catalytic activity in hydrogenation reactions due to the formation of highly stable Pd nanoparticles at the AC surface during the first reaction cycle.