Heterometallic and Hydrophobic Metal–Organic Frameworks as Durable Photocatalysts for Boosting Hydrogen Peroxide Production in a Two-Phase System

Reductive production of hydrogen peroxide (H2O2) from dioxygen (O2) coupled with the oxidative synthesis of value-added products using hydrophobic metal–organic frameworks (MOFs) is very important for energy production. Herein, a hydrophobic iron-doped zirconium-based MOF (OPA/Fe-Zr-MOF), in which Zr clusters are modified by octadecylphosphonic acid (OPA), is prepared and used for photocatalytic H2O2 production in a two-phase system composed of water and benzyl alcohol (BA). It allows the formation of H2O2 in the water phase and the oxidation product of BA, benzaldehyde, in the BA phase. The hydrophobic OPA/Fe-Zr-MOF exhibited a high H2O2 production rate of 13.1 mmol L–1·h–1 under visible-light irradiation (λ > 420 nm), while the pristine Zr-MOF did not show any activity. Such high activity is attributed to the Fe3+-doping and the unique hydrophobicity of OPA/Fe-Zr-MOF. The doped Fe3+ ions conferred Zr-MOF with visible-light absorption and acted as an electron donor for O2 reduction to H2O2. The unique hydrophobicity, as evidenced by a water contact angle of 109°, enabled the spatial separation of OPA/Fe-Zr-MOF in the BA and H2O2 in the water phase, which inhibited the Fenton-like reaction induced by Fe3+ ions. Thus, H2O2 was not easily decomposed. This research enriches the application of hydrophobic MOFs for the solar-to-chemical energy conversion.