Defect-Engineered Metal-Organic Frameworks Fang, Zhenlan; Bueken, Bart; De Vos, Dirk E. ...
Angewandte Chemie (International ed.),
June 15, 2015, Letnik:
54, Številka:
25
Journal Article
Recenzirano
Odprti dostop
Defect engineering in metal–organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in ...controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of “defect‐engineering” concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect‐engineered CNCs.
Designer defects: Defects in coordination network compounds (CNCs) are defined as “sites that locally break the regular periodic arrangement of atoms or ions of the static crystalline parent framework due to missing or incorrectly dislocated atoms or ions”. This Review provides both a concise overview of defects in CNCs (including their classification and characterizations) and applications of defective CNCs/MOFs.
The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis ...results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions.
The influence of internal (genetic and developmental) and external (environmental) factors on levels of flavonoid gene transcripts, enzyme activity and metabolites was studied in fruit of six ...cultivated strawberry (Fragaria x ananassa Duch.) genotypes grown at two Italian locations. Gene expression and enzyme activity showed development- and genotype-associated patterns, revealing gene coordination. Analysis clarified the regulation mechanism of the hydroxylation status of the B-ring of the major flavonoid pools and pointed out examples of genotype-specific post-transcriptional regulation mechanisms and key steps of pathway regulation in strawberry fruits. Metabolite profiles were strongly affected by development and genotype. Flavan-3-ols, their proanthocyanidin (PA) derivatives and anthocyanins were the most abundant metabolites. Flavonol levels and PA-associated traits (epicatechin/catechin ratio and mean degree of polymerization) showed significant environmental effects. Multivariate and correlation analyses determined the relationships among genes, enzymes and metabolites. The combined molecular and biochemical information elucidated more in depth the role of genetic and environmental factors on flavonoid metabolism during strawberry fruit development, highlighting the major impact of developmental processes, and revealing genotype-dependent differences and environmental effects on PA-related traits.
Functionalized linkers can greatly increase the activity of metal–organic framework (MOF) catalysts with coordinatively unsaturated sites. A clear linear free‐energy relationship (LFER) was found ...between Hammett σm values of the linker substituents X and the rate kX of a carbonyl‐ene reaction. This is the first LFER ever observed for MOF catalysts. A 56‐fold increase in rate was found when the substituent is a nitro group (see picture).
Perfluorinated alkylated substances (PFASs) are widely used in industrial and commercial applications, leading to a widespread occurrence of these persistent and harmful contaminants in our ...environment. Removal of these compounds from surface and waste waters is being mandated by European and U.S. governments. Currently, there are no treatment techniques available that lower the concentrations of these compounds for large water bodies in a cost‐ and energy‐efficient way. We hereby propose a hydrophobic, all‐silica zeolite Beta material that is a highly selective and high‐capacity adsorbent for PFASs, even in the presence of organic competitors. Advanced characterization data demonstrate that the adsorption process is driven by a very negative adsorption enthalpy and favorable steric factors.
Perfluorinated compounds have found wide application but have adverse effects on health and environment. There is a need to selectively recover them from process and surface waters. We now show that a microporous zeolite Beta, in its all‐silica form, shows outstanding capacity and affinity for the uptake of PFASs like perfluorooctanoic acid and perfluorooctanesulfonic acid, even in the presence of other organics.
Use of imidazolium ionic liquids as solvents for organic transformations with tetravalent cerium salts as oxidizing agents was evaluated. Good solubility was found for ammonium hexanitratocerate(IV) ...(ceric ammonium nitrate, CAN) and cerium(IV) triflate in 1-alkyl-3-methylimidazolium triflate ionic liquids. Oxidation of benzyl alcohol to benzaldehyde in 1-ethyl-3-methylimidazolium triflate was studied by in-situ FTIR spectroscopy and 13C NMR spectroscopy on carbon-13-labeled benzyl alcohol. Careful control of the reaction conditions is necessary because ammonium hexanitratocerate(IV) dissolved in an ionic liquid can transform benzyl alcohol not only into benzaldehyde but also into benzyl nitrate or benzoic acid. The selectivity of the reaction of cerium(IV) triflate with benzyl alcohol in dry ionic liquids depends on the degree of hydration of cerium(IV) triflate: anhydrous cerium(IV) triflate transforms benzyl alcohol into dibenzyl ether, whereas hydrated cerium(IV) triflate affords benzaldehyde as the main reaction product. Reactions of ammonium hexanitratocerate(IV) with organic substrates other than benzyl alcohol have been explored. 1,4-Hydroquinone is quantitatively transformed into 1,4-quinone. Anisole and naphthalene are nitrated. For the cerium-mediated oxidation reactions in ionic liquids, high reaction temperatures are an advantage because under these conditions smaller amounts of byproducts are formed.
The near-unlimited availability of CO2 has stimulated a growing research effort in creating value-added products from this greenhouse gas. This paper presents the trends on the most important methods ...used in the electrochemical synthesis of carboxylic acids from carbon dioxide. An overview is given of different substrate groups which form carboxylic acids upon CO2 fixation, including mechanistic considerations. While most work focuses on the electrocarboxylation of substrates with sacrificial anodes, this review considers the possibilities and challenges of implementing other synthetic methodologies. In view of potential industrial application, the choice of reactor setup, electrode type and reaction pathway has a large influence on the sustainability and efficiency of the process.
Imperfections in the spotlight: Fluorescence microscopy was used to detect defects in metal–organic frameworks formed during synthesis. In contrast to currently available techniques, confocal ...fluorescence microscopy offers the advantage of three‐dimensional imaging at the single‐crystal level combined with the sensitivity required to study the start of defect formation.
Herein, a new group of visible light photocatalysts is described. Iron(III) oxides could be promising visible light photocatalysts because of their small band gap enabling visible light excitation. ...However, the high electron–hole recombination rate limits the yield of highly oxidizing species. This can be overcome by reducing the particle dimensions. In this study, metal–organic frameworks (MOFs), containing Fe3-μ3-oxo clusters, are proposed as visible light photocatalysts. Their photocatalytic performance is tested and proven via the degradation of Rhodamine 6G in aqueous solution. For the first time, the remarkable photocatalytic efficiency of such Fe(III)-based MOFs under visible light illumination (350 up to 850 nm) is shown.
While titanium‐based metal–organic frameworks (MOFs) have been widely studied for their (photo)catalytic potential, only a few TiIV MOFs have been reported owing to the high reactivity of the ...employed titanium precursors. The synthesis of COK‐47 is now presented, the first Ti carboxylate MOF based on sheets of TiIVO6 octahedra, which can be synthesized with a range of different linkers. COK‐47 can be synthesized as an inherently defective nanoparticulate material, rendering it a highly efficient catalyst for the oxidation of thiophenes. Its structure was determined by continuous rotation electron diffraction and studied in depth by X‐ray total scattering, EXAFS, and solid‐state NMR. Furthermore, its photoactivity was investigated by electron paramagnetic resonance and demonstrated by catalytic photodegradation of rhodamine 6G.
COK‐47, the first Ti carboxylate sheet‐based MOF, can be synthesized as pristine or inherently defective nanoparticulate material. Its structure was extensively characterized and its defects render it a highly efficient catalyst for the oxidation of thiophenes. The material also features photocatalytic activity.
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