Ion-exchange and ion-transport in silica and sulphonated-silica (ormosil) hydrogels

The effects of organosulphonate groups on the ion-exchange and ion-transport properties of silica hydrogels have been investigated by using Ru(NH3)63+, Ru(bpy)32+ and Fe(CN)63− redox probes. Silica and sulphonated ormosil hydrogels were prepared by using tetramethyl orthosilicate as a silica precursor and 2(4-chlorosulphonylphenyl)ethyl-trichlorosilane to provide sulphonate functionality for ion-exchange and ion conductivity. Both gels act as cation-exchangers and exclude Fe(CN)63−. Partition coefficients are higher for the ormosil and for the more highly charged Ru(NH3)63+ versus Ru(bpy)32+. Diffusion coefficients are higher for the unmodified silica, which is consistent with weaker interactions between the cationic probes and less anionic gel network.