Isolated Fe Sites in 2D Metal-organic Layers: Structural Regulation Governing Hydrocarbon Photooxidation

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) offer tunable structures for catalysis.
• Incorporating Fe into Zr-based MOFs enhances light absorption and redox activity.
• Precise control over Fe active sites (number, oxidation state, coordination) in MOFs is challenging due to dynamic ligands.

Purpose of the Study:

• To construct and investigate atomically defined Fe configurations within a 2D triazine-based zirconium carboxylate MOF (ZrTATB).
• To establish the structure-performance relationship for photocatalytic toluene oxidation with varying Fe active sites.
• To elucidate the mechanistic pathways governing activity and selectivity.

Main Methods:

• Post-synthetic modification of ZrTATB to create three distinct Fe configurations (Fe1, Fe2, Fe3).
• Photocatalytic toluene oxidation experiments.
• Mechanistic studies involving adsorption analysis and intermediate identification.

Main Results:

• A non-linear structure-performance relationship was observed, with Fe2 exhibiting optimal photocatalytic activity.
• Fe2 achieved a balanced coordination environment, enabling efficient water activation (•OH generation) and selective C-H bond cleavage.
• Fe1 showed excessive toluene adsorption, while Fe3 exhibited weak substrate binding due to saturated coordination spheres.
• Water availability was identified as a key factor influencing product selectivity (benzaldehyde vs. benzoic acid).

Conclusions:

• Atomically precise engineering of Fe active sites in Zr-based MOFs is crucial for optimizing photocatalytic performance.
• The Fe2 configuration provides an ideal balance for efficient toluene oxidation.
• Understanding the interplay between coordination environment, substrate adsorption, and water activation is key to designing advanced MOF catalysts.