MOF thin films: existing and future applications

Abstract

The applications and potentials of thin film coatings of metal-organic frameworks (MOFs) supported on various substrates are discussed in this critical review. Because the demand for fabricating such porous coatings is rather obvious, in the past years several synthesis schemes have been developed for the preparation of thin porous MOF films. Interestingly, although this is an emerging field seeing a rapid development a number of different applications on MOF films were either already demonstrated or have been proposed. This review focuses on the fabrication of continuous, thin porous films, either supported on solid substrates or as free-standing membranes. The availability of such two-dimensional types of porous coatings opened the door for a number of new perspectives for functionalizing surfaces. Also for the porous materials themselves, the availability of a solid support to which the MOF-films are rigidly (in a mechanical sense) anchored provides access to applications not available for the typical MOF powders with particle sizes of a few μm. We will also address some of the potential and applications of thin films in different fields like luminescence, QCM-based sensors, optoelectronics, gas separation and catalysis. A separate chapter has been devoted to the delamination of MOF thin films and discusses the potential to use them as free-standing membranes or as nano-containers. The review also demonstrates the possibility of using MOF thin films as model systems for detailed studies on MOF-related phenomena, e.g. adsorption and diffusion of small molecules into MOFs as well as the formation mechanism of MOFs (101 references).

Mechanistic Insights into Growth of Surface‐Mounted Metal‐Organic Framework Films Resolved by Infrared (Nano‐) Spectroscopy

“…This band is present in fully reacted mixtures of Cu−btc (Figure 2 c), and also for the films grown with drying each whole cycle (Figure 2 a); the vibration at 1620 cm −1 (mode v 2 ) is prominent for the hindered‐grown films (Figure 3 c) and belongs to COO − (from Cu−btc) in the partially exchanged [Cu 2 Ac 2 (btc) 2 ]; similarly, the band at 1550 cm −1 (mode v 4 ) likely belongs to the COO − (from Cu−Ac) vibrations in the partially exchanged [Cu 2 (btc) 2 Ac 2 ], whereas the band at around 1580 cm −1 (mode v 3 ) is attributed to an asymmetric COO − mode of [Cu 2 Ac 4 ], based on the IRRAS spectra of copper acetate (Figure 2 c). The arrangement and chemistry of these species could be responsible for the previously observed surface diffusion barriers and defects in [Cu 3 (btc) 2 ] films with unclear chemical origin 4, 33…”

“…MOFs are highly porous crystalline materials consisting of inorganic metal nodes coordinated to organic linkers‐ functionalities that enable highly versatile chemical properties. The synthesis of oriented MOF films received significant attention due to their potential use as membranes, sensing and photo‐responsive devices, and (electro)catalysts 4, 5, 6, 7. Surface‐anchored films of metal‐organic frameworks (SURMOFs) can be synthesized in a straightforward manner by using a liquid phase layer‐by‐layer (LbL) synthesis approach 8, 9.…”

The surface barrier phenomenon at the loading of metal-organic frameworks

“…Uptake was determined using a quartz crystal microbalance 24 Here we use surface-mounted MOFs (SURMOFs) of different thicknesses to quantitatively analyse the importance of surface barriers. SURMOFs are highly crystalline, oriented, thin MOF films grown by liquid-phase epitaxy on solid substrates in a well-defined layer-by-layer manner 22 . Suitable functionalization of the substrate is required for nucleating SURMOF growth on the substrate surface and controlling crystal orientation.…”

A smart microelectromechanical sensor and switch triggered by gas

“…to traditional organics and polymers. [23][24][25][26][27] Drop-on-demand inkjet printer with a nozzle of 20 lm diameter is used to coat the microstructure. Fig.…”