Efficient Photosynthesis of Hydrogen Peroxide by Cyano-Containing Covalent Organic Frameworks from Water, Air and...

The insufficient exciton (e^- -h⁺ pair) separation/transfer and sluggish two-electron water oxidation are two main factors limiting the H₂ O₂ photosynthetic efficiency of covalent organic frameworks (COFs) photocatalysts. Herein, we present an alternative strategy to simultaneously facilitate exciton separation/transfer and reduce the energy barrier of two-electron water oxidation in COFs via a dicyano functionalization. The in situ characterization and theoretical calculations reveal that the dicyano functionalization improves the amount of charge transfer channels between donor and acceptor units from two in COF-0CN without cyano functionalization to three in COF-1CN with mono-cyano functionalization and four in COF-2CN with dicyano functionalization, leading to the highest separation/transfer efficiency in COF-2CN. More importantly, the dicyano group activates the neighbouring C atom to produce the key *OH intermediate for effectively reducing the energy barrier of rate-determining two-electron water oxidation in H₂ O₂ photosynthesis. The simultaneously enhanced exciton separation/transfer and two-electron water oxidation in COF-2CN result in high H₂ O₂ yield (1601 μmol g^-1  h^-1 ) from water and oxygen without using sacrificial reagent under visible-light irradiation. COF-2CN can effectively yield H₂ O₂ in water with wide pH range, in different real water samples, in scaled-up reactor under natural sunlight irradiation, and in continuous-flow reactor for consecutively producing H₂ O₂ solution for water decontamination.