Electronic structure of surface complexes between CeO2 and benzene derivatives: A comparative experimental and DFT study

Surface modification of CeO2 nano-powder, synthesized by a self-propagating room temperature method with salicylate-type ligands (salicylic acid and 5-aminosalicylic acid) as well as catecholate-type ligands (catechol, 3,4-dihydroxybenzoic acid, caffeic acid and 2,3-dihydroxy naphthalene), induces the appearance of absorption in the visible spectral region due to the interfacial charge transfer (ICT) complex formation. Thorough characterization involving transmission electron microscopy, XRD analysis, and nitrogen adsorption-desorption isotherms, revealed that loosely agglomerated CeO2 particles of the size ranging from 2 to 4 nm have cubic fluorite structure and specific surface area of 140 m2/g. The attachment of salicylate- and catecholate-type of ligands to the surface of CeO2 powders leads to the formation of colored powders with tunable absorption in the visible spectral region. The density functional theory calculations with properly design model systems were performed to estimate the alignment of energy levels of various inorganic/organic hybrids. A reasonably good agreement between calculated values and experimental data was found.