Perfluoroalkyl-functionalization of zirconium-based metal–organic framework nanosheets for photosynthesis of hydrogen peroxide from dioxygen and water

Abstract

Solar-light-driven photosynthesis of hydrogen peroxide (H₂O₂) from dioxygen (O₂) and water (H₂O) is a sustainable process. Metal–organic frameworks (MOFs) are promising candidates for the photosynthesis of H₂O₂ because of their unlimited design flexibility. However, MOF-driven H₂O₂ production from O₂ and H₂O remains a challenge because MOF photocatalysts need to exhibit high structural stability in aqueous reaction systems while suppressing H₂O₂ decomposition. In addition, the efficiency of H₂O₂ production in pure water has suffered from low O₂ solubility in aqueous solution and difficult-to-inhibit side reactions. In the present study, we demonstrate that hydrophobic Zr-based MOF (Zr-MOF) nanosheets modified with perfluoroalkyl carboxylates substantially accelerate the photocatalytic production of H₂O₂ from O₂ and H₂O under visible-light (λ > 420 nm) irradiation without any additives. Perfluoroalkyl-functionalization improves the hydrophobicity of the MOF, leading to suppression of H₂O₂ decomposition on Zr–oxo clusters. The high hydrophobicity enhances the enrichment of O₂ on the photocatalyst surface and the selectivity of two-electron oxidation of H₂O to generate H₂O₂, which promotes photocatalytic H₂O₂ synthesis. The length of the perfluoroalkyl chain plays a critical role in the enhancement of photocatalytic H₂O₂ production, and optimization of the chain length led to a 7.2-fold increase in activity compared with that of the pristine hydrophilic Zr-MOF. This study provides a noble design strategy for achieving highly selective photocatalytic H₂O₂ production via O₂ reduction and H₂O oxidation.