Tunable axial symmetry β-ketoamine covalent organic frameworks for efficient photocatalytic H2O2 synthesis in seawater

Abstract

Photocatalytic production of hydrogen peroxide (H₂O₂) from seawater represents a sustainable approach for solar energy conversion. However, complex ionic composition hinders charge transport and accelerates catalyst degradation, undermining efficiency and posing a major challenge to the development of effective photocatalysts. Here, we explore the role of axial symmetry in stabilized β-ketoamine covalent organic frameworks (COFs) for efficient seawater photocatalysis. Three COFs with identical chemical compositions but distinct symmetries, uniaxial (1KtTb), meta-uniaxial (2KtTb), and meta-triaxial (3KtTb), were synthesized. Comprehensive experiments and theoretical analyses reveal that axial symmetry significantly influences light absorption, photocarrier recombination, and the energy barriers of key intermediate pathways (*OOH and *OH). The uniaxial symmetric framework exhibits a narrower bandgap, improved charge separation, and lower reaction barriers, enabling enhanced solar utilization and photocatalytic performance. In real seawater tests from the Zhoushan Sea, the uniaxial symmetric COF achieved record H₂O₂ production rates of 12 865.2 µmol g⁻¹ h⁻¹ under oxygen and 8557.4 µmol g⁻¹ h⁻¹ in air, with over 90% activity retained after 20 cycles and 30 days of immersion. Our results demonstrate the application potential of structural symmetry in photocatalysis and guide the design of marine-adapted COFs for efficient H₂O₂ synthesis and photoelectric conversion.