Interfacial Microenvironment-Regulated Coordinate Structures Dictate the Metal-Organic Framework Facet Orientation...

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• High-quality, oriented metal-organic framework (MOF) thin films are crucial for advanced functional devices.
• Understanding the microscopic evolution of MOFs at solid-liquid interfaces is essential but challenging.
• Controlling MOF oriented growth pathways is key to unlocking their full potential.

Purpose of the Study:

• To investigate the critical early growth stages of HKUST-1 MOF on a COOH-functionalized gold substrate.
• To elucidate the molecular-level mechanisms governing MOF orientation during thin film formation.
• To correlate MOF crystal facet orientation with catalytic performance in CO2 fixation.

Main Methods:

• In situ surface-enhanced infrared spectroscopy (SEIRs)
• X-ray photoelectron spectroscopy (XPS)
• Photoinduced force microscopy (PIFM)

Main Results:

• Identified that both the COOH-terminated self-assembled monolayer (SAM) and interfacial coordination layers dictate initial MOF growth.
• Demonstrated that solvent polarity (aprotic vs. protic) influences interfacial layer structure and subsequent MOF orientation ([111], [100], polycrystal).
• Observed that HKUST-1 films exhibit crystal facet-dependent catalytic activity for CO2 conversion to cyclic carbonate.

Conclusions:

• The study provides molecular-level insights into MOF thin film growth control.
• Interfacial engineering via solvent choice and SAM functionalization enables precise control over MOF orientation.
• Facet-dependent catalysis highlights the importance of oriented MOF films for functional applications, guiding the design of anisotropic devices.