Liquid- and vapour-phase conversion of aligned Cu(OH) 2 nanobelts into crystalline coatings of Cu-BDC and Cu-CDC MOFs, leads to differences in the crystal phase, morphology and crystallographic orientation.

The preparation of thin films is often associated with the appearance of unknown polymorphs, as both the substrate and deposition method can heavily influence crystallization processes. Here, chemical vapor deposition is used to obtain thin films of a copper‐isonicotinate (Cu‐INA) metal–organic framework (MOF). Starting from copper‐based precursor layers (copper oxide and hydroxide), a solid‐vapor conversion with vaporized isonicotinic acid in either a dry or humidified atmosphere, yields a new Cu‐INA MOF polymorph. It is found that the crystalline order of the precursor layer has a strong impact on the texture of Cu‐INA thin films. Furthermore, a novel methodology is introduced to determine the structure of a previously unknown thin‐film phase of Cu‐INA. Although only a few diffraction peaks are found via synchrotron grazing incidence X‐ray diffraction (GIXRD), a triclinic unit cell can be determined, and Patterson functions can be calculated. The latter reveals the position of the copper atoms within the unit cell and the alignment of the INA linkers defining the coordination network structure. This work introduces how the combination of GIXRD data with Patterson functions can be used to identify the structure of an unknown thin‐film MOF polymorph.

Since the advent of thin-film composite polyamide membranes brought forth a breakthrough in desalination and water purification membranes nearly half a century ago, recent years have only witnessed marginal improvements in the water-salt selectivity of these membranes. The slow progression is partly attributable to limited understanding of membrane synthesis–structure–performance relationships. A centralized archive of reverse osmosis membrane (RO) characterization data may lead to a shared understanding of features that maximize RO performance and unify research efforts. The Open Membrane Database (OMD), which can be found at www.openmembranedatabase.org, is a growing database of over 600 water purification and desalination membranes that are sourced from peer-reviewed journals, patents, and commercial product data. Here, we outline the detailed functionality of the database, the transport theory underlying the membrane performance calculations, and best practices for membrane performance testing and reporting. The user-sourced, open-access database may be used to benchmark novel RO membranes against the state of the art, conduct meta-analyses, and develop synthesis–structure–performance relationships, each of which will be critical to advancing membrane development.

ZIF-8 was synthesized by subjecting ZnO thin films deposited via plasma-enhanced atomic layer deposition to a 2-methylimidazole vapor. The impact of the conversion time as well as the density and thickness of the ZnO precursor on the resulting ZIF-8 layers were investigated. Grazing Incidence X-ray diffraction reveals a preferred (100) or (111) orientation of the ZIF-8 crystals, depending on thickness and density of the precursor, and with a more prominent orientation at longer conversion times. The onset of crystallization occurs after 20 min of conversion for the less dense precursor, compared to 40 min for the denser one. The ZIF-8 thickness and roughness increase with conversion time. The final thickness of the ZIF-8 layer depends on the thickness and density of the precursor layer, and can be up to 15-fold higher than the precursor thickness.

Thin films of crystalline porous materials have great potential in membranes, sensors, and microelectronics. Still, characterizing their pore size, pore volume, and specific surface area is challenging. In article number 2006993, Rob Ameloot and co-workers discuss positron annihilation lifetime spectroscopy, represented by the bees lighting up inside the honeycomb, in comparison to physisorption methods, symbolized by the quantification of honey in the pores.

The hypersensitivity of state-of-the-art polyamide-based membranes to chlorine is a major source of premature membrane failure and module replacement in water desalination plants. This problem can currently only be solved by implementing pre- and post-treatment processes involving additional chemical use and energy input, thus increasing environmental, capital, and operational costs. Herein, we report a chlorine-, acid-, and base-resistant desalination membrane comprising a cross-linked epoxide-based polymer-selective layer with permanent positive charges. These novel membranes exhibit high mono- and divalent salt rejection (81% NaCl, 87% CaCl2, 89% MgCl2) and a water permeance of similar to 2 L m(-2) h(-1) bar(-1), i.e., desalination performance comparable to that of commercially available nanofiltration membranes. Unlike conventional polyamide-based membranes, this new generation of epoxide-based membranes takes advantage of the intrinsic chemical stability of ether bonds while achieving the polymer and charge density needed for desalination. In doing so, the stability of these membranes opens new horizons for sustainable water purification and many other separations in harsh media in a variety of applications (e.g., solvent recovery, gas separations, redox flow batteries).

The landscape of possible polymorphs for some metal–organic frameworks (MOFs) can pose a challenge for controlling the outcome of their syntheses. Demonstrated here is the use of a template to control in the vapor-assisted formation of zeolitic imidazolate framework (ZIF) powders and thin films. Introducing a small amount of either ethanol or dimethylformamide vapor during the reaction between ZnO and 4,5-dichloroimidazole vapor results in the formation of the porous ZIF-71 phase, whereas other conditions lead to the formation of the dense ZIF-72 phase or amorphous materials. Time-resolved in situ small-angle X-ray scattering reveals that the porous phase is metastable and can be transformed into its dense polymorph. This transformation is avoided through the introduction of template vapor. The porosity of the resulting ZIF powders and films was studied by N2 and Kr physisorption, as well as positron annihilation lifetime spectroscopy. The templating principle was demonstrated for other members of the ZIF family as well, including the ZIF-7 series, ZIF-8_Cl, and ZIF-8_Br.

Thin films of crystalline and porous metal–organic frameworks (MOFs) have great potential in membranes, sensors, and microelectronic chips. While the morphology and crystallinity of MOF films can be evaluated using widely available techniques, characterizing their pore size, pore volume, and specific surface area is challenging due to the low amount of material and substrate effects. Positron annihilation lifetime spectroscopy (PALS) is introduced as a powerful method to obtain pore size information and depth profiling in MOF films. The complementarity of this approach to established physisorption‐based methods such as quartz crystal microbalance (QCM) gravimetry, ellipsometric porosimetry (EP), and Kr physisorption (KrP) is illustrated. This comprehensive discussion on MOF thin film porosimetry is supported by experimental data for thin films of ZIF‐8.

A simple solvent- and catalyst-free method is presented for the synthesis of the mesoporous metal-organic framework (MOF) MAF-6 (RHO-Zn(eIm)2) based on the reaction of ZnO with 2-ethylimidazole vapor at temperatures ≤ 100 °C. By translating this method to a chemical vapor deposition (CVD) protocol, mesoporous crystalline films could be deposited for the first time entirely from the vapor phase. A combination of PALS and Kr physisorption measurements confirmed the porosity of these MOF-CVD films and the size of the MAF-6 supercages (diam. ~2 nm), in close agreement with powder data and calculations. MAF-6 powders and films were further characterized by XRD, TGA, SEM, FTIR, PDF and EXAFS. The exceptional uptake capacity of the mesoporous MAF-6 in comparison to the microporous ZIF-8 is demonstrated by vapor-phase loading of a molecule larger than the ZIF-8 windows.

MAF-252, a non-porous crystalline coordination polymer, is obtained from the solvent-free reaction of ZnO with 3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole. MAF-252 can be synthesized in powder form and deposited as thin films, starting from ZnO powder and layers, respectively. Chemical vapour deposition (CVD) of MAF-252 enables conformal and patterned thin films, even on high aspect ratio features.

Energy-efficient indoors temperature control can be realised through adsorption chillers or adsorption heat pumps based on the reversible adsorption and desorption of water in porous materials. Stable microporous aluminium-based metal-organic frameworks (MOFs) present promising water sorption properties for this goal. The development of synthesis routes that make use of available and affordable building blocks and avoid the use of organic solvents is crucial to advance this field. In this work, two scalable synthesis routes under mild reaction conditions were developed for aluminium-based MOFs: (1) in aqueous solutions using a continuous flow reactor and (2) through the vapour-assisted conversion of solid precursors. Fumaric acid, its methylated analogue mesaconic acid, as well as mixtures of the two were used as linkers. The synthesis conditions determine the crystal structure (symmetry and topology), either the MIL-53 or MIL-68 type with square-grid or kagome-grid topology, respectively. Fine-tuning resulted in new MOF materials thus far inaccessible through conventional synthesis routes. Furthermore, by varying the linker ratio, the water sorption properties can be continuously adjusted while retaining the sigmoidal isotherm shape advantageous for heat transformation applications.

The performance of modern chips is strongly related to the multi-layer interconnect structure that interfaces the semiconductor layer with the outside world. The resulting demand to continuously reduce the k-value of the dielectric in these interconnects creates multiple integration challenges and encourages the search for novel materials. Here we report a strategy for the integration of metal-organic frameworks (MOFs) as gap-filling low-k dielectrics in advanced on-chip interconnects. The method relies on the selective conversion of purpose-grown or native metal-oxide films on the metal interconnect lines into MOFs by exposure to organic linker vapor. The proposed strategy is validated for thin films of the zeolitic imidazolate frameworks ZIF-8 and ZIF-67, formed in 2-methylimidazole vapor from ALD ZnO and native CoOx, respectively. Both materials show a Young's modulus and dielectric constant comparable to state-of-the-art porous organosilica dielectrics. Moreover, the fast nucleation and volume expansion accompanying the oxide-to-MOF conversion enable uniform growth and gap-filling of narrow trenches, as demonstrated for 45 nm half-pitch fork-fork capacitors.

Here we present a novel, solvent-free approach to post-synthetic linker exchange in ZIF-8 through exposure to linker vapor. As in the solvent-based approach, this vapor-phase linker exchange (VPLE) method retains the parent SOD topology and proceeds in a single-crystal to single-crystal manner. The scope of linkers that can be incorporated through VPLE was studied and criteria for the selection of further candidates were formulated. In large crystals, the incoming linker was found to form domains instead of distributing homogeneously, similar as for solution-based linker exchange. In contrast to the latter approach, VPLE yields a higher concentration of the incoming linker in the crystal core instead of the shell.

Metal-organic frameworks (MOFs) enable the design of host-guest systems with specific properties. In this work, we show how the confinement of anthracene in a well-chosen MOF host leads to reversible yellow-to-purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host-guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.

Robust and scalable thin film deposition methods are key to realize the potential of metal-organic frameworks (MOFs) in electronic devices. Here, we report the first integration of the chemical vapor deposition (CVD) of MOF coatings in a custom reactor within a cleanroom setting. As a test case, the MOF-CVD conditions for ZIF-8 are optimized to enable smooth, pinhole-free, and uniform thin films on full 200 mm wafers under mild conditions. The single-chamber MOF-CVD process and the impact of the deposition parameters are elucidated via a combination of in situ monitoring and ex situ characterization. The resulting process guidelines will pave the way for new MOF-CVD formulations and a plethora of MOF-based devices.

Copper dicarboxylate metal-organic framework films are deposited via chemical vapour deposition. Uniform films of CuBDC and CuCDC with an out-of-plane orientation and accessible porosity are obtained from the reaction of Cu and CuO with vaporised dicarboxylic acid linkers.

Porous materials have attracted tremendous scientific and industrial interest due to their broad commercial applicability. However, some applications require that these materials are deposited on surfaces to create thin films. Here, the recent progress of new porous thin-film material classes is described: porous organic molecular materials, porous organic polymers, covalent organic frameworks, and nanoporous carbon. In each case, the state of the art and current barriers in their thin-film fabrication, as well as intrinsic material advantages that are suited for different applications are presented. By highlighting the unique structural characteristics and properties of these materials, it is hoped that increased research development and industrial interest will be fostered, which will lead to new methods of thin-film synthesis and consequently to new applications.