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

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.