Large π-Conjugated Metal-Organic Frameworks for Infrared-Light-Driven CO₂ Reduction

Area of Science:

• Materials Science
• Photocatalysis
• Organic Chemistry
• Chemical Engineering

Background:

• Traditional photocatalysts struggle with near-infrared (NIR) light excitation.
• NIR-light-responsive materials for photochemical reduction often have unsuitable band positions due to narrow band gaps.
• Developing efficient NIR-light-driven catalysts is crucial for CO2 reduction.

Purpose of the Study:

• To engineer metal-organic frameworks (MOFs) with large π-conjugated organic semiconductors for NIR light-driven CO2 reduction.
• To systematically tune MOF structure and properties by varying π-conjugated units.
• To elucidate the mechanism of photoinduced electron transfer in these MOFs.

Main Methods:

• Synthesis of a series of mesoporous MOFs with increasing macrocyclic π-conjugated units.
• Single-crystal X-ray diffraction for structural analysis.
• Ultrafast spectroscopy, X-ray photoelectron spectroscopy (XPS), and in situ electron paramagnetic resonance (EPR) for mechanistic studies.

Main Results:

• MOFs with precisely arranged organic semiconductor units and metal clusters were obtained.
• Spectroscopic studies confirmed charge separation and photoexcited dynamics.
• The tetrakis(4-carboxybiphenyl)naphthoporphyrin) MOF (TNP-MOF) showed a high CO2 reduction rate (>6630 μmol h⁻¹ g⁻¹) under NIR light, with AQEs over 2.03% (760 nm) and 1.11% (808 nm).

Conclusions:

• Engineered MOFs with large π-conjugated organic semiconductors are effective NIR-light-driven CO2 reduction catalysts.
• The study verified the photoinduced electron transfer pathway within the MOFs.
• TNP-MOF exhibits superior photocatalytic performance compared to other MOF-based catalysts, including visible-light-driven ones.