Cyclodextrin silica-based materials: advanced characterizations and study of their complexing behavior by diffuse reflectance UV-Vis spectroscopy

The modification of a silica gel by beta-cyclodextrin has been performed in a two-step procedure, by grafting the epoxy functions on the silica gel following by the reaction with the alcoholate of beta-cyclodextrin. A detailed characterization of these hybrid materials has been undertaken by FTIR. Raman, C-13 MAS NMR, TGA, N-2 sorption experiments. Before reaction with beta-cyclodextrin, the mean loading of the epoxy groups covalently bonded to the mineral surface, is about 580 mumol g((SiO2))(-1), corresponding to a surface coverage of 2.0 mumol m(-2). After the coupling reaction, materials with cyclodextrin group loadings up to 67 mumol g((SiO2))(-1) have been prepared. This indicates that about 11% of the immobilized glycidyl appears to be effective in covalently linking to the cyclodextrin moieties. Adsorption experiments, using methyl orange as a guest molecule, agree with the fact that the cyclodextrin silica-based materials present a greater ability for removing the organic compound from water. Nevertheless, additional interactions, other than inclusion process, could be involved at the highest concentrations of the dye. By diffuse reflectance, the UV-Vis spectral investigation of methyl orange coated on the materials with cyclodextrins gives rise to marked changes, ascribed to the formation of inclusion complexes inside the accessible beta-cyclodextrin cavities anchored to the mineral support. (C) 2004 Elsevier Inc. All rights reserved.