Keto-anthraquinone covalent organic framework for H2O2 photosynthesis with oxygen and alkaline water

Abstract

Hydrogen peroxide photosynthesis suffers from insufficient catalytic activity due to the high energy barrier of hydrogen extraction from H₂O. Herein, we report that mechanochemically synthesized keto-form anthraquinone covalent organic framework which is able to directly synthesize H₂O₂ (4784 μmol h⁻¹ g⁻¹ at λ > 400 nm) from oxygen and alkaline water (pH = 13) in the absence of any sacrificial reagents. The strong alkalinity resulted in the formation of OH^-(H₂O)_n clusters in water, which were adsorbed on keto moieties within the framework and then dissociated into O₂ and active hydrogen, because the energy barrier of hydrogen extraction was largely lowered. The produced hydrogen reacted with anthraquinone to generate anthrahydroquinone, which was subsequently oxidized by O₂ to produce H₂O₂. This study ultimately sheds light on the importance of hydrogen extraction from H₂O for H₂O₂ photosynthesis and demonstrates that H₂O₂ synthesis is achievable under alkaline conditions.