Experimental and Theoretical Study on the Interchange between Zr and Ti within the MIL-125-NH₂ Metal Cluster

Area of Science:

• Materials Science
• Photocatalysis
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) like MIL-125-NH2 are promising for photocatalysis.
• Tuning MOF composition is crucial for enhancing their performance in CO2 reduction.

Purpose of the Study:

• To investigate the impact of substituting titanium (Ti) with zirconium (Zr) in the secondary building unit (SBU) of MIL-125-NH2.
• To establish the relationship between material composition, light-induced charge carrier dynamics, and photocatalytic CO2 reduction efficiency.

Main Methods:

• Mixed metal synthesis of MIL-125-NH2 with Ti and Zr.
• Experimental characterization of framework structure and morphology.
• Femtosecond transient absorption spectroscopy to study charge carrier dynamics.
• Photocatalytic CO2 reduction experiments under visible light.
• Density Functional Theory (DFT) calculations for electronic structure analysis.

Main Results:

• Successfully synthesized mixed Ti-Zr MIL-125-NH2, confirming structural integrity.
• Zr incorporation introduced structure defects, primarily missing linkers.
• Mixed metal samples exhibited shorter charge carrier lifetimes compared to pure MIL-125-NH2.
• The -NH2 group enhanced photocatalytic activity, while Zr incorporation showed no significant improvement in CO2 reduction yield.
• DFT calculations indicated that defects, not electronic structure changes, are responsible for reduced photocatalytic activity.

Conclusions:

• Zr substitution in MIL-125-NH2 does not enhance visible-light photocatalytic CO2 reduction.
• Structure defects arising from Zr incorporation are the primary cause of decreased photocatalytic performance.
• The -NH2 functional group remains a key factor for improved activity in this MOF system.