Constructing the electron donor-acceptor unit in keto-type structure COFs for enhanced photocatalytic H₂O₂ production

Engineering of functional groups is a promising way to optimize the structure and facilitate photocatalytic H₂O₂ production of covalent organic frameworks (COFs), and hydrophilic groups (such as –OH, -COOH, et al.) are easy to combine with water molecules through hydrogen bonding to improve the mass transfer efficiency between O₂ and COFs. However, the presence of -OH groups in the imine-linked COF, a keto-type structure would be formed which seriously affects the photocatalytic H₂O₂ production process. To solve this difficulty, here we use pyruvate as additive during the synthesis process of keto-type structure COFs, in which -OH would be re-exposed and the extra -COOH would be introduced meanwhile. Since the presence of these hydrophilic groups in Tz-Dha-H, the adsorption of O₂ is highly improved, and an electron donor-acceptor unit is reasonably formed, which results in a synergistically activated electron-push-pull effect and the acceleration of charge transfer and separation. As a result, the photocatalytic H₂O₂ yield of Tz-Dha-H in pure water is as high as 694.99 μmol g⁻¹ h⁻¹, which is 1.67 times higher than that of Tz-Dha. Undoubtedly, this work proposes a new idea for improving the photocatalytic activity of H₂O₂ production by the construction of electron-donor-acceptor unit in keto-type COFs.