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

Abstract Hydrogen peroxide (H 2 O 2 ) photosynthesis is an attractive carbon-neutral process for decentralized applications, but suffers from insufficient activity of catalysts due to the high energy barrier of hydrogen extraction from H 2 O without sacrificial reagent. Herein, we report that mechanochemically synthesized keto-form anthraquinone covalent organic framework (Kf-AQ) is able to directly synthesize H 2 O 2 with molecular oxygen and alkaline water (pH = 13) in the absence of any sacrificial reagents, with a superior production rate of 4784 µmol h − 1 g − 1 under visible light irradiation (λ > 400 nm) and an impressive apparent quantum yield (AQY) of 15.8% at 400 nm. Characterization results revealed that the strong alkalinity resulted in the formation of OH − (H 2 O) n clusters in water, which were first adsorbed on keto moieties of Kf-AQ and then more easily dissociated into molecular oxygen and active hydrogen with the injection of photoelectrons, because the energy barrier of hydrogen extraction from OH − (H 2 O) n was largely lowered by weakening the H-bonded networks of H 2 O molecules owing to the excessive electrons in OH − . The produced active hydrogen quickly diffused to react with anthraquinone to generate anthrahydroquinone, which was subsequently oxidized by molecular oxygen to selectively produce H 2 O 2 . This study provides a novel efficient H 2 O 2 photosynthesis material, and also sheds light on the importance of hydrogen extraction from H 2 O for photocatalytic H 2 O 2 synthesis.