Singlet oxygen drives photochemistry in carbon dots–TiO2 composites under visible light

Design of heterogeneous photosensitizers capable of selectively generating singlet oxygen ( 1 O 2 ) represents a holy grail in the field of industrial selective organic synthesis. In fact, this highly reactive and specific species is currently generated by using photosensitizers dissolved in homogeneous solutions, while it would be highly desirable to exploit the advantages of heterogeneous catalytic systems for industrial applications. In this work, we demonstrate that composite materials based on carbon dots (CDs) and TiO 2 , prepared via hydrothermal synthesis, selectively generate singlet oxygen over other reactive oxygen species, in contrast to conventional TiO 2 -based photocatalysts where activity is mainly driven by hydroxyl and superoxide radicals. The hybrid systems exhibit a markedly enhanced 1 O 2 photoproduction compared to the single components. This synergistic effect has been correlated with the specific interaction of CDs with TiO 2 , which in turn is related to the functional groups characterizing the CDs surface. In particular, the prevalent presence of oxygenated moieties at the surface of the CDs stabilizes Ti 3+ centers, whose population increases under visible light irradiation. In this case, electron transfer to molecular oxygen is suppressed and singlet oxygen is hypothesized to be efficiently generated through long-range energy transfer mechanisms. • CDs ’s surface functional affect charge carrier transfer between CDs and TiO2 • CDs@TiO2 composites selectively generate single oxygen • CDs@TiO2 composites are active under visible light • CDs@TiO2 show enhanced performance compared to single components • Enhanced performance due to synergic cooperation between CDs and TiO2