Abstract
A new photocatalytic reactivity of carbon-nanodot-doped graphitic carbon nitride (CD-C3N4) with alkenes and dienes, has been disclosed. We have shown that CD-C3N4 photosensitizes the oxidation of unsaturated substrates in a variety of solvents according to two competing mechanisms: the energy transfer via singlet oxygen (1O2) and/or the electron transfer via superoxide (O·−2). The singlet oxygen, derived by the CD-C3N4 photosensitized process, reacts with alkenes to form allylic hydroperoxides (ene products) whereas with dienes, endoperoxides. When the electron transfer mechanism operates, cleavage products are formed, derived from the corresponding dioxetanes. Which of the two mechanisms will prevail depends on solvent polarity and the particular substrate. The photocatalyst remains stable under the photooxidation conditions, unlike the most conventional photosensitizers, while the heterogeneous nature of CD-C3N4 overcomes usual solubility problems.
Highlights
Graphitic carbon nitride (g-C3 N4 ) is recently one of the most studied heterogeneous, metal-free photocatalysts. g-C3 N4 is a polymeric material, composed of highly abundant elements such as carbon and nitrogen, thermally stable and nontoxic
The relatively low band gap energy Eg of 2.7 eV and high conduction and valence bond positions of the photocatalyst [4] prompted many research groups to improve the photocatalytic activity of g-C3 N4
We demonstrate chemically that 3 in photosensitized reactions, electron and singlet and oxygen mechanisms are in competition, CD-C3N4 photosensitized reactions,transfer electron transfer singlet oxygen mechanisms are in depending on themostly natureon of the nature substrate the polarity thepolarity solvent.ofInthe addition, competition,mostly depending of and the substrate andofthe solvent.the mediated photooxygenation results were compared with those derived using conventional addition, 3 4 the CD-C3N4 mediated photooxygenation results were compared with those derived using singlet oxygensinglet photosensitizers
Summary
Graphitic carbon nitride (g-C3 N4 ) is recently one of the most studied heterogeneous, metal-free photocatalysts. g-C3 N4 is a polymeric material, composed of highly abundant elements such as carbon and nitrogen, thermally stable and nontoxic. The relatively low band gap energy Eg of 2.7 eV and high conduction and valence bond positions of the photocatalyst [4] prompted many research groups to improve the photocatalytic activity of g-C3 N4. This was achieved by doping the surface of the catalyst with a variety of metallic elements [3,5,6,7,8,9,10,11], oxides [12,13], sulfides [14] even graphene [15] and carbon nanotubes [16]. In a more recent article [18], the metal-free carbon-nanodot-doped graphitic carbon nitride (CD-C3 N4 )
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