Centimeter-Scale Pillared-Layer Metal-Organic Framework Thin Films Mediated by Hydroxy Double Salt Intermediates for...

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Fabricating metal-organic framework (MOF) thin films over large areas is crucial for gas sensor applications.
• Synthesizing anisotropic MOF films, like pillared-layer structures, at ambient conditions presents significant challenges.

Purpose of the Study:

• To demonstrate a facile method for constructing dense, continuous pillared-layer MOF thin films on a centimeter scale at room temperature.
• To optimize MOF film formation for carbon dioxide (CO2) sensor applications using Cu(II)-based MOFs and various ligands.
• To translate the developed MOF film synthesis to practical sensing platforms.

Main Methods:

• Utilized an aluminum-doped zinc oxide template and hydroxy double salt (HDS) intermediates for room-temperature MOF film synthesis.
• Explored a series of Cu(II)-based pillared MOFs with different 1,4-benzenedicarboxylic acid (bdc) ligands.
• Investigated the effect of ligand polarity and water solubility on MOF film crystallinity and morphology.
• Integrated the optimized MOF thin films onto quartz crystal microbalance and optical fiber sensor platforms.

Main Results:

• Successfully fabricated dense and continuous pillared-layer MOF thin films on centimeter-scale areas at room temperature.
• Identified that nonpolar ligands with lower water solubility favored crystalline pillared MOF structures from HDS intermediates.
• Achieved the most uniform and dense film growth with Cu2(ndc)2(dabco) MOF (ndc = 1,4-naphthalene-bdc; dabco = 1,4-diazabicyclo[2.2.2]octane) over a 1 cm² area.
• Demonstrated CO2 sensing capabilities with rapid response/recovery times (seconds) on integrated quartz crystal microbalance and optical fiber sensors, even at moderate humidity.

Conclusions:

• Developed a scalable and ambient-condition synthesis for continuous, anisotropic MOF thin films.
• The Cu2(ndc)2(dabco) MOF films are suitable for developing high-performance CO2 sensors.
• This approach provides a roadmap for utilizing MOF thin films in various sensor devices and other applications.