Cyclic voltammetry of tris(2,2′-bipyridyl)ruthenium(II) cations adsorbed in electrodes modified with mesoporous molecular sieve silicas

The electrochemical behavior of [Ru(bpy)(3)](2+) was examined in electrodes modified with two mesoporous molecular sieves, HMS and Al-HMS. [Ru(bpy)(3)](2+) was adsorbed by both molecular sieves, resulting in increased peak currents for the Ru(II)/Ru(III) redox process at the HMS- or Al-HMS-modified electrodes relative to the bare ITO electrode. The peak currents obtained with the Al-HMS-modified electrode were 20 times larger than those obtained with the corresponding blank ITO electrode coated with only polystyrene. No increase in the peak currents was found for electrodes modified with a microporous NaY zeolite under the same conditions. For HMS, extensive washing of the powder prior to the preparation of the modified electrodes resulted in the complete disappearance of the voltammetric waves. This demonstrates that the electroactive [Ru(bpy)(3)](2+) ions in HMS were weakly held cations physisorbed in the neutral mesoporous silicate. In Al-HMS electrodes, however, large voltammetric waves remained, showing that unlike what was previously reported for clay-modified electrodes, the electrostatically bound ions adsorbed by cation exchange in Al-HMS were electrochemically active.