Electrochemistry of mesoporous organosilica of MCM-41 type containing 4,4′-bipyridinium units:: Voltammetric response and electrocatalytic effect on 1,4-dihydrobenzoquinone oxidation

The electrochemistry of a novel organic-inorganic material in which 4,4'-bipyridinium units (BP) are covalently attached to the walls of a periodic mesoporous organisilica (PMO) of the MCM-41 type is described. The pristine material (BP@PMO), having its internal space completely filled by the cetyltrimethylammonium structure-directing agent, is almost electrochemically silent. In contrast, the extracted material obtained after removal of the structure-directing agent (BP@PMO-ex) exhibits two reduction peaks at -0.36 and -0.75 V vs AgCl/Ag in contact with aqueous electrolytes. BP@PMO-ex shows a remarkable electrocatalytic effect on the oxidation of 1,4-dihydrobenzoquinone (H(2)Q) that is studied by rotating disk voltammetry. At low scan rates the catalytic process is under diffusion/convection control, with a second-order reaction between the surface catalyst and H(2)Q acting as a rate-determining step. At high rotation rates the catalytic process becomes independent of the mass transfer, in agreement with the idea that electroactive bipyridinium centers are confined to a boundary zone of the MCM-41 grains.