Tautomeric-State Engineering of Anthraquinone Covalent Organic Frameworks Enables Efficient H2O2 Photosynthesis from Water and Oxygen.

Abstract

Hydrogen peroxide photosynthesis from water and oxygen represents a sustainable route toward decentralized chemical manufacturing, yet its efficiency is severely restricted by sluggish water oxidation reaction. Herein, we report an alkaline-triggered keto-form reconstruction strategy in an anthraquinone-based covalent organic framework (TpAQ) to promote H2O2 photosynthesis. Under strongly alkaline conditions (pH = 13), hydroxide ions induce spontaneous enol-to-keto tautomerization, generating a keto-dominant framework with reconstructed electronic structures and interfacial catalytic microenvironments. The resulting keto-form-rich TpAQ exhibits broadened visible-light absorption, positively shifted valence band positions, accelerated charge separation, and substantially enhanced water adsorption and activation capability. Benefiting from the synergistic enhancement of water oxidation and two-electron oxygen reduction kinetics, the optimized photocatalyst achieves an H2O2 production rate of 678 μM h-1 under visible-light irradiation, which is 3.12-fold higher than that under neutral conditions. Isotope-labeling experiments combined with in situ spectroscopy reveal that the promoted water oxidation continuously supplies O2 for subsequent H2O2 generation via a one-step two-electron oxygen reduction pathway. This work establishes tautomeric-state engineering as an effective strategy for regulating charge dynamics and water oxidation kinetics in covalent organic framework photocatalysts toward efficient H2O2 photosynthesis.