Deciphering Metal-Organic Framework Synthesis from Hydroxy Double Salts: In-Situ Insights via Synchrotron X-ray...

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Sustainable manufacturing of metal-organic frameworks (MOFs) requires rapid, room-temperature synthesis methods.
• Hydroxy double salts (HDSs) accelerate MOF formation kinetics and reduce synthesis temperatures.
• A deeper understanding of the reaction mechanisms is crucial for developing novel MOF synthesis routes.

Purpose of the Study:

• To investigate the dynamic processes involved in MOF formation from HDS precursors using in-situ synchrotron X-ray techniques.
• To elucidate the reaction mechanism for the conversion of a (Zn,Co) HDS to a mixed-metal zeolitic imidazolate framework-8 (mmZIF-8).
• To determine the activation energies for nucleation and growth during MOF synthesis.

Main Methods:

• Combined in-situ synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS).
• Time-resolved diffraction pattern analysis to monitor crystalline phase evolution.
• X-ray absorption spectroscopy to track changes in local coordination environments.
• Kinetic analysis to determine activation energies for nucleation and growth.

Main Results:

• The conversion of (Zn,Co) HDS to mmZIF-8 proceeds rapidly at room temperature without detectable crystalline intermediates.
• Activation energies for nucleation and growth were determined to be 25.5 ± 2.5 and 64.0 ± 7.9 kJ·mol⁻¹, respectively.
• Local structural evolution from mixed coordination in HDS to tetrahedral coordination in mmZIF-8 was observed, with two plausible reaction pathways proposed.

Conclusions:

• In-situ synchrotron X-ray techniques provide unprecedented insight into the mechanism of HDS-based MOF synthesis.
• The findings validate the use of HDSs for rapid, low-temperature MOF fabrication.
• This fundamental understanding is expected to facilitate the development of new MOF synthesis strategies.