Binding and removal of octahedral, tetrahedral, square planar and linear anions in water by means of activated carbon functionalized with a pyrimidine-based receptor

Binding of S2O32-, SeO42-, Pt(CN)42-, Co(CN)63-, Au(S2O3)23- and Fe(CN)64- anions by the protonated(positively charged) forms of tren (tris(2-aminoethyl)amine) and of the tren-derivative (HL) containing apyrimidine residue was studied by means of potentiometric measurements in 0.1 M NMe4Cl solutions at298.1 0.1 K. Both ligands form stable complexes with these anions which appear to be mostlystabilized by electrostatic forces. In the case of HL, an anion–p interaction with the pyrimidine residue ofthe ligand also affords a significant contribution to complex stability. Some shape preference fortetrahedral and octahedral anions over square planar ones is observed. A hybrid AC/HL material obtainedby adsorption of HL on commercial activated carbon (AC) was used to study the extraction of theseanions from water. AC/HL shows enhanced adsorption capacity toward all the anions studied withrespect to AC. This behavior is ascribed to the stronger interaction of anions with the HL function of AC/HL than with the Cp-H3O+ sites of unfunctionalized AC. Of special interest is the enhancement of theadsorption capacities found for Au(S2O3)23- and Pt(CN)42-, two anions of great relevance for theextraction of platinum and gold from ores and from metallic wastes.