Photocatalytic Synthesis of Hydrogen Peroxide by Re-doped Metal-Organic Frameworks Incorporating Bianthracene Ligands

Photocatalytic synthesis of hydrogen peroxide (H²O²) from oxygen (O2) is a challenging process. Metal-organic framework (MOF) materials are emerging photocatalysts with potential tuneable light absorption properties. Herein, we report a Re-modified Zr-based MOF, Re10-MFM-67, in which active Re sites are incorporated into MFM-67 by partial replacement of the highly conjugated ligand 9,9’-bianthracene-10,10’-dicarboxylic acid (H₂L1) with a [(H₂L²)Re^I(CO)₃Cl] (H₂L² = 2,2’-bipyridine-5,5’-dicarboxylic acid) moiety. Re10-MFM-67 (10 refers to the molar percentage content of Re complex within the material) exhibits broadband light absorption with an exceptional rate of formation of H₂O₂ from O₂ of 8.50 mmol gcat⁻¹ h⁻¹ and a record turnover frequency (TOF) of 28.7 h⁻¹ under visible light irradiation (λ &gt; 400 nm). Synchrotron powder X-ray diffraction (SPXRD) and neutron powder diffraction (NPD) confirms the structure of Re10-MFM-67 and together with extended X-ray absorption fine structure (EXAFS) analysis confirm the coordination environment and binding of the [Re^I(CO)₃Cl] moiety within the framework structure.<i> In situ</i> electron paramagnetic resonance (EPR) spectroscopy confirms that photocatalytic H₂O₂ generation on Re10-MFM-67 occurs <i>via </i>a two-step oxygen reduction reaction (ORR) pathway with the superoxide anion formed as an intermediate. This study promotes the design of MOF-based photocatalysts with conjugated ligands for efficient photosynthesis.<br/><br/>