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Mechanistic Insights into Growth of Surface‐Mounted Metal‐Organic Framework Films Resolved by Infrared (Nano‐) Spectroscopy
Author(s) -
Delen Guusje,
Ristanović Zoran,
Mandemaker Laurens D. B.,
Weckhuysen Bert M.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201704190
Subject(s) - copper , infrared spectroscopy , materials science , thin film , infrared , adsorption , monolayer , chemical engineering , nanotechnology , absorption spectroscopy , agglomerate , spectroscopy , chemistry , organic chemistry , optics , composite material , physics , engineering , quantum mechanics , metallurgy
Control over assembly, orientation, and defect‐free growth of metal‐organic framework (MOF) films is crucial for their future applications. A layer‐by‐layer approach is considered a suitable method to synthesize highly oriented films of numerous MOF topologies, but the initial stages of the film growth remain poorly understood. Here we use a combination of infrared (IR) reflection absorption spectroscopy and atomic force microscopy (AFM)‐IR imaging to investigate the assembly and growth of a surface mounted MOF (SURMOF) film, specifically HKUST‐1. IR spectra of the films were measured with monolayer sensitivity and <10 nm spatial resolution. In contrast to the common knowledge of LbL SURMOF synthesis, we find evidence for the surface‐hindered growth and large presence of copper acetate precursor species in the produced MOF thin‐films. The growth proceeds via a solution‐mediated mechanism where the presence of weakly adsorbed copper acetate species leads to the formation of crystalline agglomerates with a size that largely exceeds theoretical growth limits. We report the spectroscopic characterization of physisorbed copper acetate surface species and find evidence for the large presence of unexchanged and mixed copper‐paddle‐wheels. Based on these insights, we were able to optimize and automatize synthesis methods and produce (100) oriented HKUST‐1 thin‐films with significantly shorter synthesis times, and additionally use copper nitrate as an effective synthesis precursor.