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Porous sulfonic acid functionalized silica spheres have been prepared by oxidation ofthiol-functionalized mesoporous silica samples obtained by co-condensation of (mercaptopropyl)trimethoxysilane and tetraethoxysilane in the presence ofcetyltrimethylammonium as a template. The physicochemical characteristics of the resulting ion exchangers have been analyzed by various techniques and discussed with respect to the amount of functional groups in the materials. Their ion exchange behavior was then studied from batch experiments (determination of cation exchange capacities) and by electrochemistry at carbon paste electrodes modified with these solids. In particular, ion exchange voltammetry applied to two model electroactive cations, Cu2+ and Ru(NH3)6(3+), has pointed out the key role played by the content of organofunctional groups in the materials (which strongly affects their structure and porosity) on their performance as electrode modifiers for preconcentration of target analytes prior to electrochemical detection.

Transient [1:1] complexes formed in the bimolecular interactions of electron acceptors (A) with their reduced anion radicals (A(-.)) are detected and characterized in solution for the first time. The recognition of such metastable intermediates as the heretofore elusive precursor complex (A(2)(-.)) in electron-transfer processes for self-exchange allows the principal parameters lambda (Marcus reorganization energy) and H(DA) (electronic coupling element) to be experimentally determined from the optical (charge-transfer) transitions inherent to these intermolecular complexes. The satisfactory correspondence of the theoretically predicted with the experimentally observed rate constants validates these ET parameters and the Marcus-Hush-Sutin methodology for strongly coupled redox systems lying in the (Robin-Day) Class II category. Most importantly, the marked intermolecular electronic interaction (H(DA)) within these precursor complexes must be explicitly recognized, since it dramatically affects the electron-transfer dynamics by effectively lowering the activation barrier. As such, the numerous calculations of the reorganization energy previously obtained from various self-exchange kinetics based on lambda = 4DeltaG must be reconsidered in the light of such a precursor complex, with the important result that ET rates can be substantially faster than otherwise predicted. On the basis of these studies, a new mechanistic criterion is proposed for various outer-sphere/inner-sphere ET processes based on the relative magnitudes of H(DA) and lambda.

Functionalized cobalt porphyrin immobilized multiwalled carbon nanotubes are synthesized and characterized. These new materials efficiently electrocatalyze oxygen reduction and they have potential to replace conventional Pt–C catalyst in fuel cells.