Molecular Compartments Created in Metal-Organic Frameworks for Efficient Visible-Light-Driven CO₂ Overall Conversion

Area of Science:

• Materials Science
• Nanotechnology
• Catalysis
• Photochemistry

Background:

• Metal-organic frameworks (MOFs) offer tunable porous structures for hosting catalytic nanoparticles.
• Visible-light-driven CO2 conversion is a key area for sustainable chemical production.
• Precise control over nanoparticle size, location, and integration within porous materials is crucial for enhanced catalytic performance.

Purpose of the Study:

• To construct molecular compartments by growing tungsten oxide hydrate (WO3·H2O) semiconductor nanoparticles within the mesopores of MIL-100-Fe MOF.
• To investigate the precise location and spatial arrangement of these nanoparticles within the MOF structure.
• To evaluate the photocatalytic efficiency of the resulting composite for the overall conversion of CO2 and H2O under visible light.

Main Methods:

• Synthesis of WO3·H2O nanoparticles within the mesopores of MIL-100-Fe.
• Powder X-ray diffraction (PXRD) to determine nanoparticle location within the MOF pores.
• Small-angle neutron scattering (SANS) to analyze the spatial arrangement of nanoparticles across the MOF crystal.
• Gas-phase photoreduction experiments using visible light (λ > 420 nm) to assess catalytic activity and quantum efficiency.

Main Results:

• Successfully integrated WO3·H2O nanoparticles into MIL-100-Fe mesopores, creating well-defined molecular compartments.
• PXRD and SANS confirmed the precise pore-level location and distribution of the semiconductor nanoparticles.
• The composite (24%-WO3·H2O-in-MIL-100-Fe) achieved a CO2 reduction rate of 0.49 mmol·g−1·h−1 and an apparent quantum efficiency of 1.5% at 420 nm.
• Coordinated water species within the MOF structure were identified as critical for high catalytic activity.

Conclusions:

• The precise, pore-level integration of semiconductor nanoparticles within MOFs enables efficient visible-light-driven CO2 overall conversion.
• The developed composite material sets new benchmarks for CO2 reduction rates and quantum efficiencies under visible light.
• The role of coordinated water in MOFs is highlighted as a significant, often overlooked, factor for enhancing photocatalytic performance.