Keto–enol tautomerism in low-cost melamine-based COFs for highly efficient H2O2 photosynthesis

Abstract

Developing cost-effective photocatalysts for H₂O₂ production is essential for sustainable chemistry. Here, we employ the exceptionally inexpensive industrial precursor melamine to synthesize two triazine-based covalent organic frameworks (COFs), MA-COF-2 and MA-COF-3. By modulating hydroxyl functionalization in the aldehyde monomers, we successfully induce β-ketoenamine tautomerism within the frameworks. The higher hydroxyl density in MA-COF-3 drives a more exhaustive enol-to-keto conversion, which promotes the spatial separation of HOMO–LUMO orbitals and effectively suppresses photogenerated charge recombination. Consequently, MA-COF-3 achieves a superior H₂O₂ production rate of 21.59 mmol g⁻¹ h⁻¹, which is 3.6-fold higher than the performance of MA-COF-2 (5.98 mmol g⁻¹ h⁻¹) and ranks among the top tier of reported COF-based photocatalysts. This work demonstrates a cost-efficient strategy to bypass the dependence on expensive building blocks, offering a scalable blueprint for the industrial-scale photosynthesis of H₂O₂ using readily available organic materials.