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revised on 14.10.2019 and posted on 16.10.2019by Francisco Yarur, John Manioudakis, Rafik Naccache, Marek Majewski
Visible light photosensitization of metal oxides to create heterostructures for the conversion of solar-to-chemical energy is a promising approach to produce solar fuels and other valuable chemicals. Carbon dots have recently been considered as suitable candidates to sensitize wide bandgap metal oxide semiconductors due to their low cost and tunable optical properties. While photocatalytic systems using carbon dots as sensitizers have been reported, transformations involving the production of value-added chemicals as well as the electron transfer mechanisms underpinning photocatalysis within such heterostructures remain underexplored. Here we report the sensitization of zinc oxide nanowires with carbon dots for the α-heteroarylation of 1-phenylpyrrolidine with 2-chlorobenzothiazole under visible light illumination at room temperature. The carbon dots improve the light absorption of the nanowires in the visible region of the spectrum affording the use of white light to drive catalysis. From optical spectroscopy and electrochemistry investigations of the resulting nanohybrid material, the photocatalytic properties are explained by the band alignment at the zinc oxide-carbon dot junction where a series of single-electron transfers creates the necessary potential to oxidize 1-phenylpyrrolidine. The resulting cascade of electron transfers into and from the carbon dots drives the α-heteroarylation to a 97% yield after 24 hrs.