Dottorato in MATERIALS FOR SUSTAINABLE DEVELOPMENT

Electron transfer is generally invoked to explain most of the reported photocatalytic reactions. However, upon interaction of an electronically excited species (e.g. irradiated TiO2) with another in its ground state, both electron or energy transfer could in principle take place. These events are mechanistically and conceptually related, but they evolve differently along the reaction coordinate depending on several factors. This contribution will provide some paradigmatic examples showing how surface modification could address the photocatalytic activity towards prevailing energy transfer based reactions. For instance, even if with evident differences, surface modifications of TiO2 with silane moieties or with carbon dots induce similar structural and photoinduced functional features of the resulting photocatalytic material. In both cases, surface modification changes locally the crystal field of the titanium atoms and stabilize Ti3+ defects in the sub-surface region. The amount of these paramagnetic centers appears to be correlated with the formation rate of singlet oxygen, while electron transfer to superoxide is suppressed. Surface modification is therefore a useful tool to exploit energy transfer driven reactions. For instance, energy transfer driven isomerization of caffeic acid has been found to occur effectively in the presence of modified TiO2. More importantly, the preferential formation of singlet oxygen at the surface of the irradiated modified semiconductor is an indirect proof of the occurrence of energy transfer driven reactions. This has been exploited for the epoxidation of limonene and for the design of oxygen getting nanocomposites. Even if more direct evidences are required to corroborate these results, the presentation will show that it is possible to control the nature of the oxidizing species in photocatalytic processes by simple surface engineering, with extremely intriguing consequences in the field of green organic chemistry.

18/06/2026