Weakly Hydrophilic Imine-Linked Covalent Benzene-Acetylene Frameworks for Photocatalytic H2O2 Production in the Two-Phase System

Abstract

Conversing oxygen (O₂) to hydrogen peroxide (H₂O₂) driven by solar energy is a promising H₂O₂ onsite production route but often short of efficient and durable photocatalysts. Herein, strong π-π conjugate polycyclic aromatic benzene and acetylene units have been constructed into new covalent organic frameworks (COFs) linked by imine C═N bonding. These COFs demonstrated two-dimensional hexagonal crystalline frameworks with higher crystallinity and larger surface area (>600 m² g^-1). Covalent benzene-acetylene frameworks possessed appropriate visible light-responsive band structure and the suppressed charge recombination rate. The -OH groups on their frameworks enable them to be weakly hydrophilic. As a result, it served as high-performance but durable photocatalysts for H₂O₂ production in the water-benzyl alcohol (BA) two-phase system. It delivered a H₂O₂ production rate of 1240 μmol h^-1 g_cat^-1 and durable catalytic efficiency within 60 h, comparable to the best COF-based catalysts. This study provides an efficient two-phase photocatalytic system for H₂O₂ production based on weakly hydrophilic imine-linked benzene-acetylene organic photocatalysts.

Keywords: covalent organic frameworks; hydrogen peroxide; photocatalyst; two-electron oxygen reduction; two-phase.