Salts as linker sources allow the preparation of high-quality carboxylate-based MOFs under unprecedented sustainable conditions: room temperature and water as the sole solvent.

The real industrial establishment of MOFs requires significant advances in economic and chemical sustainability. This work describes a novel and simple method to prepare one of the most widely studied MOF material, i.e. MIL-100(Fe), which significantly improves the sustainability of the conventional process in several aspects. Interestingly, the only difference in the preparation method of MIL-100(Fe) compared with that of semi-amorphous Fe-BTC (MOF material commercialized as Basolite F300 having the same metal and linker, and which can be also prepared under similar sustainable conditions), is to start from Fe(II) or Fe(III) sources, respectively, which opens certain versatility options in the room temperature synthesis procedures of MOF materials. The prepared samples were characterized using XRD, TGA, N 2 adsorption/ desorption isotherms, Cs-aberration corrected STEM and UV-Vis DRS. These two room-temperature-made Fe-BTC materials were tested in the industrially-demanded photocatalytic degradation of methyl orange under both ultraviolet and solar light radiation. MIL-100(Fe) was a very active photocatalyst in comparison with its homologue. That difference was mainly attributed to the presence of larger cavities within its structure.

This paper describes the preparation and characterization of nano-scaled M-MOF-74/CPO-27-M (M = Mg, Mn, Co, Ni and Zn) materials at room temperature. Some of the soformed crystals are the smallest ones of any MOF material (and, to the best of our knowledge, of any microporous material) ever reported. They are in the limit of being able to diffract, particularly these forming the Co-and Ni-MOF-74 samples. Consequently, unequivocal identification as crystalline MOF-74 phase was deduced by combining other characterization techniques rather than powder X-ray diffraction. These small crystals are unstable as isolated ones, so they form steady and robust aggregates, whose mechanical properties strongly depend on the crystal size. The particles that results from the 'fusion' of nanocrystals smaller than 10 nm (more properly denoted as nanodomains) could not be disaggregated by conventional ultrasonic and graining techniques. On the contrary, agglomerates of crystals larger than 10 nm are dissociable in discrete crystals. It allows characterizing Zn-MOF-74 nanocrystals by advanced electron microscopy methods. Cs-corrected STEM provided, for the first time, 'quasi' atomic resolution images of MOFs, which are especially unstable under electronic radiation. The magnitude of the crystal size of M-MOF-74 is tentatively associated to the solubility of the metal source.

In some aspects, the potential of metal–organic framework (MOF) materials as heterogeneous catalysts has been realized, at least in an academic context. However, one of their most promising catalytic properties, that is, the presence of open metal sites, is far from understood properly. In this work, a series of M–MOF‐74 (M=Mn, Co, Ni, Cu, Zn) materials, prepared under sustainable conditions, was tested systematically in the oxidation of cyclohexene, which can proceed by either radical or epoxidation routes. Under the optimized reaction conditions, the radical route is spontaneous to some extent and it is enhanced in the presence of any M–MOF‐74 that has a metal with a redox character but not Zn. However, the epoxidation of cyclohexene is also promoted by a redox catalyst in such a way that the conversion correlates qualitatively with the redox potential of the metal. Thus, for the first time, a chemical property of M is correlated with the catalytic activity of the M–MOF‐74 family.

BACKGROUND: Very recently, metal-organic framework (MOF) materials have been postulated as emerging supports to achieve solid-state enzyme-contained biocatalysts. In this work, post-synthesis and in situ strategies to immobilize -glucosidase and laccase on different MOF materials were studied. The MOF-based supports, i.e. MIL-53(Al), NH 2 -MIL-53(Al) and Mg-MOF-74, were prepared under soft and sustainable conditions (room temperature and pH values compatible with enzymatic activity), allowing development of the in situ strategy. RESULTS:In both post-synthesis and in situ approaches, the intercrystalline mesoporosity of the MOF-based support favored the immobilization efficiency or the specific activity. The latter expressed as units per milligram of immobilized enzyme was higher in the post-synthesis immobilization, whereas the biocatalysts prepared in situ gave much higher enzyme loading (over 85%) and lower enzyme leaching (around 5%). The in situ approach even worked in a non-aqueous (N,N-dimethylformamide) media in which the free enzyme was completely inactive. The immobilized enzymes are much larger than the structural pores of the MOFs. CONCLUSIONS: Enzymes can be efficiently immobilized on nanocrystalline MOFs prepared under soft and sustainable conditions despite the supports lacking large enough pores to host the enzymes. The in situ approach is very efficient capturing enzymes and preserving some of their activity even under adverse conditions. Electrophoresis test of enzyme retention in biocatalystsThe efficiency of the enzyme encapsulation was studied by means of SDS-PAGE electrophoresis. Since the solid samples are not suitable for electrophoresis, the enzyme was forced to leave the pores by the following procedure. First, the biocatalysts were suspended in the electrophoresis buffer solution (containing sodium dodecyl sulfate, mercaptoethanol, bromophenol blue, tris buffer pH 6.8 and glycerol) and boiled for 10 min. In such denaturing conditions including the split of disulfide bonds, the tertiary structure of the protein should be lost and the random coil chain should then be easily released from the pores. The supernatants of these suspensions were withdrawn and run in 10 % SDS-PAGE electrophoresis.