Supramolecular structures on silica surfaces and their adsorptive properties

The study of adsorptive and chemical immobilization of β-cyclodextrin on a surface of hydroxylated silicas with various porous structure is described. Using IR spectroscopy, thermal gravimetrical analysis with a programmed heating, and chemical analysis of the silica surface, it is shown that the process of adsorption-desorption of β-cyclodextrin depends on the porous structure of the silica. The reaction of esterification was used for chemical grafting of β-cyclodextrin on the surface of hydroxylated silicas. Hydrolytic stability of silicas chemically modified by β-cyclodextrin apparently is explained by simultaneous formation of chemical and hydrogen bonds between surface silanol groups and hydroxyl groups of β-cyclodextrin. The uptake of the cations Cu(II), Cd(II), and Pb(II) and the anions Cr(VI) and As(V) by silicas modified with β-cyclodextrin is investigated as a function of equilibrium ion concentrations. The increase of ion uptake and selectivity of ion extraction in comparison with starting silicas is established. It is due to the formation of surface inclusion complexes of the “host-guest” type in which one molecule of β-cyclodextrin interacts simultaneously with several ions.