Novel active carbon/crown ether derivative hybrid material for the selective removal of Cu(II) ions: The crucial role of the surface chemical functions

Abstract

The selective elimination of metal ions from solution is a subject of large interest from both theoretical and practical points of view. For this purpose it is desirable to have solid materials having specific functions able of capturing the ions. This paper reports the preparation of a crown ether derivative/active carbon hybrid material and the application for the selective elimination of Cu(II). The hybrid material has been prepared by adsorption of the crown ether derivative N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-15-crown-5 (HL) onto an activated carbon (Merck). This adsorption process is not dependent on the pH and it is highly irreversible due to strong π–π interactions between the arene centers of the activated carbon and the pyrimidine moiety of HL. This means that the pyrimidine groups of HL are blocked on the surface of the activated carbon due to the adsorption while the 15-crown-5 ether functions remain ready for coordination of metal ions. Thus, the Merck/HL hybrid has a much larger adsorption capacity of Cu(II) than this of the unfunctionalized activated carbon. In addition, the adsorption of Cu(II) ions in the presence of K(I) and Ca(II) is highly selective. It is shown that this selectivity for Cu(II) is related to the size of the 15-crown-5 ether cavity is very appropriate to house this ion. The desorption of Cu(II) from the loaded Merck/HL hybrid material in the presence of EDTA allows the regeneration of most of the actives sites of the hybrid due to the formation of the more stable Cu(II)–EDTA complex. This paper also reports the preparation of HL, its behavior in aqueous solution, its complexing behavior and its adsorption on the active carbon. These studies are the cornerstones to explain the behavior of the Merck/HL hybrid material in the adsorption of Cu(II).