Polarity-Enhanced Covalent Organic Frameworks for Sacrificial-Agent-Free Synthesis of Hydrogen Peroxide under Visible...

This study presents three sulfone- or cyanodecorated photoactive covalent organic frameworks (COFs) with adjustable arm lengths and linkages for photocatalytic synthesis of hydrogen peroxide (H₂O₂). It is found that, upon replacing imine linkage with cyanated vinylene, under the irrdation of visible light, the H₂O₂ production rates (HPR) considerably increases from 2261 μmol h^-1g^-1 to 7613 μmol h^-1g^-1 in pure water and O₂ atmosphere without the assistance of any sacrificial agent. Even though in air atmosphere, its HPR value still reaches 6339 μmol h^-1 g^-1 with good recyclability. The improved catalytic performance is attributed to the enhanced polarity through the incorporation of strong polar sulfone or cyano groups in the COF frameworks, which brings about the effective separation of photogenerated electrons and holes, high photocurrent intensity, and low charge resistance as well as the increased surface hydrophilicity. The photocatalytic mechanism is studied by means of the theoretical calculations and comparative experiments conducted under the aerobic and anaerobic conditions in the presence and absence of the various scavengers for electron, hole, superoxide radical, and hydroxyl radical in the reaction system.