Vapor-Phase Processing of Metal–Organic Frameworks

Abstract

Porous metal−organic frameworks (MOFs), formed from organic linkers and metal nodes, have attracted intense research attention. Because of their high specific surface areas, uniform and adjustable pore sizes, and versatile physicochemical properties, MOFs have shown disruptive potential in adsorption, catalysis, separation, etc. For many of these applications, MOFs are synthesized solvothermally as bulk powders and subsequently shaped as pellets or extrudates. Other applications, such as membrane separations and (opto)electronics, require the implementation of MOFs as (patterned) thin films. Most thin-film formation methods are adapted from liquid-phase synthesis protocols. Precursor transport and nucleation are difficult to control in these cases, often leading to particle formation in solution. Moreover, the use of solvents gives rise to environmental and safety challenges, incompatibility issues with some substrates, and corrosion issues in the case of dissolved metal salts. In contrast, vapor-phase processing methods have the merits of environmental friendliness, control over thickness and conformality, scalability in production, and high compatibility with other workflows. In this Account, we outline some of our efforts and related studies in the development and application of vapor-phase processing of crystalline MOF materials (MOF-VPP). We first highlight the advances and mechanisms in the vapor-phase deposition of MOFs (MOF-VPD), mainly focusing on the reactions between a linker vapor and a metal-containing precursor layer. The characteristics of the obtained MOFs (thickness, porosity, crystallographic phase, orientation, etc.) and the correlation of these properties with the deposition parameters (precursors, temperatures, humidity, post-treatments, etc.) are discussed. Some in situ characterization methods that contributed to a fundamental understanding of the involved mechanisms are included in the discussion. Second, four vapor-phase postsynthetic functionalization (PSF) methods are summarized: linker exchange, guest loading, linker grafting, and metalation. These approaches eliminate potential solubility issues and enable fast diffusion of reactants and guests as well as a high loading or degree of exchange. Vapor-phase PSF provides a platform to modify the MOF porosity or even introduce new functionalities (e.g., luminescence photoswitching and catalytic activity). Third, since vapor-phase processing methods enable the integration of MOF film deposition into a (micro)fabrication workflow, they facilitate a range of applications with improved performance (low-k dielectrics, sensors, membrane separations, etc.). Finally, we provide a discussion on the limitations, challenges, and further opportunities for MOF-VPP. Through the discussion and analysis of the vapor-phase processing strategies as well as the underlying mechanisms in this Account, we hope to contribute to the development of the controllable synthesis, functionalization, and application of MOFs and related materials.

Recent progress on MOF-based optical sensors for VOC sensing

“…To avoid post-deposition treatments, Ameloot et al fabricated a uniform and compact ZIF-8 film through a vapourphase transformation from ALD ZnO films to ZIF-8, as shown in Figure 1b. 81 A recent review by Su et al 82 is suggested for further insight regarding this strategy. The solvent-free strategy makes ALD/MLD appealing for the microelectronics industry, 86 as it can lead to a meticulous tuning of thickness and possess a good potential for scaleup.…”

Investigating the vapour phase synthesis of copper terephthalate metal organic framework thin films by atomic/molecular layer deposition

“…This later approach is less desirable, as it somehow cancels the great advantage of all-gas phase processing. Indeed, vapour phase synthesis of MOFs thin films is a highly attractive strategy when contemplating MOF integration into devices [22][23][24] . In conjunction with reducing environmental impact, solvents should be avoided for device fabrication regarding the contamination and corrosion risks 25 as well as the generated surface tension during evaporation 26 .…”

Sub 150 nm Nanoscale Gallium Based Metal–Organic Frameworks Armored Antibiotics as Super Penetrating Bombs for Eradicating Persistent Bacteria

“…However, one key issue in the application of MOF in nano‐vehicles involves nanoscale synthesis, [ 7 ] especially for nanoscale MOF with a monodispersed morphology. This is a challenge because conventional soluble metal salt precursors are difficult to control spatially, always leading to bulky MOF, [ 8 ] which limits the application of MOF serving as drug delivery vehicles to combat intracellular bacteria.…”