Silica-bound complexing agents: some aspects of synthesis, stability and pore size

A number of factors related to the metal-ion reactivity of silica-bound complexing agents are discussed. The metal-uptake capacity of alkylamines immobilized on silica is shown to be reduced by hydrolysis of bound ligand from the surface, by protonation in aqueous buffers, and by an apparent air oxidation of the amine group or other deactivation process. A one-step silylation reaction using triethoxysilylpropyl-p-nitrobenzamide is shown to produce nitrobenzamide silica gel (NBSG) and azo-coupled material equivalent to that obtained by the former two-step process. Significant time saving is realized. Organic solvent washing of the NBSG, and the azo-coupled chelating agents derived from it, removes organic matter from the surface. Adsorbed or weakly bound polymers or oligomers present in the original silane or formed during the silylation are apparently dissolved slowly by these washing solvents. Finally, metal uptake (and presumably surface coverage), expressed as mumole m (2), of a series of 8-quinolinol controlled-pore glasses was found to decrease with decrease in pore size.