The fabrication of thin film coatings of metal–organic frameworks (MOFs) on various substrates is discussed in this critical review. Interestingly, the relatively few studies on MOF films that have appeared in the literature are limited to the following cases: [Zn₄O(bdc)₃] (MOF-5; bdc = 1,4-benzenedicarboxylate), [Cu₃(btc)₂] (HKUST-1; btc = 1,3,5-benzenetricarboxylate), [Zn₂(bdc)₂(dabco)] (dabco = 1,4-diazabicyclo[2.2.2]octane), [Mn(HCOO)], [Cu₂(pzdc)₂(pyz)] (CPL-1; pzdc = pyrazine-2,3-dicarboxylate, pyz = pyrazine), [Fe(OH)(bdc)] (MIL-53(Fe)) and [Fe₃O(bdc)₃(Ac)] (MIL-88B; Ac = CH₃COO⁻). Various substrates and support materials have been used, including silica, porous alumina, graphite and organic surfaces, i.e. self-assembled monolayers (SAMs) on gold, as well as silica surfaces. Most of the MOF films were grown by immersion of the selected substrates into specifically pre-treated solvothermal mother liquors of the particular MOF material. This results in more or less densely packed films of intergrown primary crystallites of sizes ranging up to several μm, leading to corresponding film thicknesses. Alternatively, almost atomically flat and very homogenous films, with thicknesses of up to ca. 100 nm, were grown in a novel stepwise layer-by-layer method. The individual growth steps are separated by removing unreacted components via rinsing the substrate with the solvent. The layer-by-layer method offers the possibility to study the kinetics of film formation in more detail using surface plasmon resonance. In some cases, particularly on SAM-modified substrates, a highly oriented growth was observed, and in the case of the MIL-53/MIL-88B system, a phase selective deposition of MIL-88B, rather than MIL-53(Fe), was reported. The growth of MOF thin films is important for smart membranes, catalytic coatings, chemical sensors and related nanodevices (63 references).

Surface-supported metal–organic framework thin films are receiving increasing attention as a novel form of nanotechnology, which hold great promise for photovoltaics, electronic devices, CO ₂ reduction, energy storage, water splitting and membranes.

Cu/CeO₂ catalysts are highly active for the low-temperature water–gas shift—a core reaction in syngas chemistry for tuning the H₂/CO/CO₂ proportions in feed streams—but the direct identification and quantitative description of the active sites remain challenging. Here we report that the active copper clusters consist of a bottom layer of mainly Cu⁺ atoms bonded on the oxygen vacancies (O_v) of ceria, in a form of Cu⁺–O_v–Ce³⁺, and a top layer of Cu⁰ atoms coordinated with the underlying Cu⁺ atoms. This atomic structure model is based on directly observing copper clusters dispersed on ceria by a combination of scanning transmission electron microscopy and electron energy loss spectroscopy, in situ probing of the interfacial copper–ceria bonding environment by infrared spectroscopy and rationalization by density functional theory calculations. These results, together with reaction kinetics, reveal that the reaction occurs at the copper–ceria interfacial perimeter via a site cooperation mechanism: the Cu⁺ site chemically adsorbs CO whereas the neighbouring O_v–Ce³⁺ site dissociatively activates H₂O.