p‐π Conjugated Covalent Organic Frameworks Expedite Molecular Triplet Excitons for H ₂ O ₂ Production Coupled with Biomass Upgrading

Abstract

Abstract High‐efficiency production of triplet states in covalent organic framework photocatalysts is crucial for high‐selectivity oxygen (O 2 ) reduction to hydrogen peroxide (H 2 O 2 ). Herein, fluorine and partial fluorine atoms are incorporated into an olefin‐linked triazine covalent organic framework (F‐ol‐COF and HF‐ol‐COF), in which the adjacent fluorine (F) atoms‐olefinic bond forms p‐π conjugation that induces spin‐polarization under irradiation, thus expediting triplet excitons for activating O 2 to singlet oxygen ( 1 O 2 ) and contributing to a high H 2 O 2 selectivity (91%). Additionally, the feasibility of coupling H 2 O 2 production with the valorization of 5‐hydroxymethylfurfural (HMF) is exhibited. The F‐ol‐COF demonstrates a highly stable H 2 O 2 yield rate of 12558 µmol g −1 h −1 with the HMF‐to‐functionalized furan conversion yield of 95%, much higher than the partially fluorinated COF (HF‐ol‐COF) and the non‐fluorinated COF (H‐ol‐COF). Mechanistic studies reveal that F‐incorporation promotes charge separation, intensifies the Lewis acidity of the carbon atoms on the olefinic bond as active sites for O 2 adsorption, and provides highly concentrated holes at the triazine unit for HMF oxidation upgrading. This study suggests the attractive potential of rational design of porous‐crystalline photocatalysts for high‐efficiency photocatalytic O 2 reduction to H 2 O 2 and biomass upgrading.