Keto-anthraquinone covalent organic framework for H ₂O ₂ 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 H ₂O. Herein, we report that mechanochemically synthesized keto-form anthraquinone covalent organic framework which is able to directly synthesize H ₂O ₂ (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 ^-(H ₂O) _n clusters in water, which were adsorbed on keto moieties within the framework and then dissociated into O ₂ 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 O ₂ to produce H ₂O ₂. This study ultimately sheds light on the importance of hydrogen extraction from H ₂O for H ₂O ₂ photosynthesis and demonstrates that H ₂O ₂ synthesis is achievable under alkaline conditions.

Abstract

Hydrogen peroxide photosynthesis is an important reaction that suffers from poor activity due to the high energy barrier of hydrogen extraction in water. Here, we report a keto-form anthraquinone framework that shows promising performance in alkaline conditions.