Achieving efficient H2O2 production by a visible-light absorbing, highly stable photosensitized TiO2

In this paper we propose titanium dioxide modified with cobalt(II) 2-ethylhexanoate (Co@TiO2) as photoactive material for the efficient visible light driven production of H2O2. We demonstrate that visible light activity can be achieved thanks to a photoinduced electron transfer from the excited complex towards the TiO2 conduction band that corresponds to a cobalt-to-titanium-charge-transfer transition. H2O2 is synthetized by a combination of oxygen reduction and water oxidation, that is possible thanks to the correct band position of Co@TiO2. A mechanism of H2O2 formation is suggested on the basis of experimental evidences. Reactive oxygen intermediates, together with H2O2 are responsible for the photocatalytic degradation of a nonionic surfactant, methylene blue and phenol for wastewater treatments. Finally, and quite interestingly, Co@TiO2 can be also used in a photoelectrochemical setup, where it can be adopted both as photoanode and photocatode, and the switching potential corresponds to the redox potential of the adsorbed complex Co(III)/Co(II) couple.