Regulating the Tautomerization in Covalent Organic Frameworks for Efficient Sacrificial Agent-Free Photocatalytic H₂O₂ Production

Abstract

The efficiency of photocatalytic production of H 2 O 2 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 (C�C), which serve as the primary adsorption sites and have a lower energy barrier for the reduction of the O 2 reduction. DHAA-Tp COF displayed a remarkable photocatalytic H 2 O 2 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 O 2 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 H 2 O 2 using an efficient, stable, and recyclable metal-free photocatalytic system.

Facile synthesis of naphthalene-based porous organic salts for photocatalytic oxidative coupling of amines in air

“…This work provides a new direction for the facile synthesis of many more kinds of photoactive porous organic salts by combining various π-conjugated organic building blocks for diverse photocatalytic reactions. 43–45…”