posted on 2024-02-21, 13:37authored bySong Yang, Zhu Gao, Zeyou Hu, Chunyue Pan, Jiayin Yuan, Kam Chiu Tam, Younian Liu, Guipeng Yu, Juntao Tang
The efficiency of photocatalytic production of H2O2 is constrained by the low selectivity toward
oxygen reduction,
and the active sites are still under debate. Herein, analogous covalent
organic framework photocatalysts were synthesized from triformylphloroglucinol
(Tp) and predesigned diamines, in which a molecular engineering strategy
was employed to manipulate the energy barrier for the targeted proton
transfers. The tautomerization of enol-imine to keto-enamine introduced
abundant alkene bonds (CC), which serve as the primary adsorption
sites and have a lower energy barrier for the reduction of the O2 reduction. DHAA-Tp COF displayed a remarkable photocatalytic
H2O2 production rate of 219.5 μmol h–1 g–1 without any sacrificial reagent,
which stands out among the structure-related materials. A switch from
a concerted one-step 2e– to a two-step single e– process in O2 reduction was observed in
TCNAQ-Tp COF, which is presumably ascribed to the suppressed tautomerization
mediated by the strong electron-withdrawing cyano groups. The results
demonstrate a novel concept for the photocatalytic production of H2O2 using an efficient, stable, and recyclable metal-free
photocatalytic system.