Heterogenization of a functionalized copper(II) Schiff base complex by direct immobilization onto an oxidized activated carbon

A copper(II) Schiff base complex bearing hydroxyl groups [bis(4-hydroxysalicylaldehyde)ethylenediaminatel copper(II), [Cu(4-HOsalen)], was directly anchored onto an air-oxidized activated carbon. Oxidation of the activated carbon was done with a mixture of air and N-2 (with 5% O-2) to increase the oxygenated surface functional groups, and complex immobilization was made by attachment of the metal complex hydroxyl groups to carbon surface groups. The adsorption/desorption of the metal complexes onto the oxidized activated carbon was monitored by UV-vis spectroscopy. Carbon-based materials were characterized by elemental analysis, surface techniques (scanning electron microscopy and X-ray photoelectron microscopy), nitrogen adsorption isotherms, and thermal analysis (temperature-programmed desorption and thermogravimetry), EPR spectra of both free and carbon-supported [Cu(4-HOsalen)] complexes were recorded. A comparative study with the unfunctionalized copper complex, [Cu(salen)], was also performed to assess the role of the hydroxyl groups in copper complex anchorage. Data from all the techniques have provided evidence that copper complexes with the hydroxyl functionalized Schiff base are chemically bound to carbon surface groups through the ligand substituent, whereas the unfunctionalized complex, [Cu(salen)], was only physically adsorbed onto the activated carbon and was leached during Soxhlet extraction.