Graphitic Carbon Nitride Doped with Biphenyl Diimide: Efficient Photocatalyst for Hydrogen Peroxide Production from Water and Molecular Oxygen by Sunlight

Photocatalytic hydrogen peroxide (H2O2) production from water and molecular oxygen (O2) by sunlight is a promising strategy for green, safe, and sustainable H2O2 synthesis. We prepared graphitic carbon nitride (g-C3N4) doped with electron-deficient biphenyl diimide (BDI) units by a simple calcination procedure. The g-C3N4/BDI catalyst, when photoirradiated by visible light (λ >420 nm) in pure water with O2, successfully promotes water oxidation by the photogenerated valence band holes and selective two-electron reduction of O2 by the conduction band electrons, resulting in successful production of millimolar levels of H2O2. Electrochemical analysis, Raman spectroscopy, and ab initio calculation results revealed that, upon photoexcitation of the catalyst, the photogenerated positive holes are localized on the BDI unit while the conduction band electrons are localized on the melem unit. This spatial charge separation suppresses rapid recombination of the hole–electron pairs and facilitates efficient H2O2 production. The solar-to-chemical energy conversion efficiency for H2O2 production is 0.13%, which is comparable to that for photosynthetic plants. This metal-free photocatalysis therefore shows potential as an artificial photosynthesis for clean solar fuel production.