Amorphous-to-Crystalline Transformation: How Cluster Aggregation Drives the Multistep Nucleation of ZIF-8

Area of Science:

• Materials Science
• Chemical Engineering
• Crystallization Science

Background:

• Nucleation is critical for crystallization, impacting product characteristics like size, morphology, and polymorphism.
• Knowledge gaps exist in understanding crystallization, particularly for porous solids like ZIF-8.
• The exact species and transformations during ZIF-8 nucleation remain unclear.

Purpose of the Study:

• To elucidate the nucleation pathway and mechanism of nanocrystalline ZIF-8.
• To identify the key species and their transformations during ZIF-8 crystallization.
• To provide insights for controlling metal-organic framework (MOF) crystallization.

Main Methods:

• Combined harmonic light scattering (HLS) for structural insights.
• Utilized Nuclear Magnetic Resonance (NMR) spectroscopy for molecular exchange analysis.
• Employed a dual approach for concurrent structural and chemical characterization.

Main Results:

• Identified charged prenucleation clusters (PNCs) with excess ligands and positive charge.
• Demonstrated nucleation occurs via PNC aggregation, releasing ligands and protons.
• Observed formation of charge-neutral amorphous precursor particles (APPs) incorporating solution monomers and ZIF-8.

Conclusions:

• Chemical dynamics are crucial in the multistage structural evolution of MOFs.
• PNCs play a critical role in the nucleation of ZIF-8.
• Targeted chemical interactions with PNCs can control MOF crystallization.