TiO2 nanoparticles as electron pools: Single- and multi-step electron transfer processes

The one electron reduction of the viologen compounds methylviologen (MV2+) and benzylviologen (BV2+) mediated by electrons loaded on TiO2 nanoparticles has been studied employing the stopped flow mixing technique. Details of the underlying reaction kinetics such as the concentration and the ionic strength dependence have been studied. The role of V2+ as an electron relay for the hydrogen production was verified, i.e., the subsequent decay of V+ was observed in the presence of noble metal nanoparticles (Aun0, Ptn0). It could be shown that the latter process is due to the electron transfer from V+ to adsorbed H+ ions on the surface of the metal particles forming H2. The rate constant of H2 production in the presence of V2+ was found to be 3 times higher than that in the V2+ free system evincing the advantages of multi-step electron transfer processes.