In order to tailor metal-organic framework (MOF) materials for a myriad of potential applications, recent studies have expanded on the advantages of using MOF particles in the nano-size regime. These ...so-called nanoMOFs may be prepared using a variety of synthetic methodologies; many analogous to those used for the preparation of their bulk counterparts. However, many of these techniques lack the refinement to consistently produce monodisperse particle sizes. Here we discuss recent advances in some of these synthetic methods with a particular emphasis on methods exhibiting increased levels of size-control while producing crystallites ranging in size from tens to hundreds of nanometers. Additionally, we highlight some specific applications that benefit from the inherent properties of nano-sized MOFs.
Synthetic methods for the preparation of metal-organic framework crystallites in the nano-size regime and their potential applications are reviewed.
CD-MOF, an extended framework incorporating the C
symmetric cyclic oligosaccharide, γ-cyclodextrin (γ-CD), is based on the coordination of alkali metal cations to alternating α-1,4-linked ...d-glucopyranosyl units on the primary and secondary faces of the γ-CD tori. Here, we report the synthesis and characterisation of an amino-functionalised CD-MOF that is isostructural with pristine CD-MOF and adsorbs CO
permanently.
Because of their efficient energy-transport properties, porphyrin-based metal–organic frameworks (MOFs) are attractive compounds for solar photochemistry applications. However, their absorption bands ...provide limited coverage in the visible spectral range for light-harvesting applications. We report here the functionalization of porphyrin-based MOFs with CdSe/ZnS core/shell quantum dots (QDs) for the enhancement of light harvesting via energy transfer from the QDs to the MOFs. The broad absorption band of the QDs in the visible region offers greater coverage of the solar spectrum by QD–MOF hybrid structures. We show through time-resolved emission studies that photoexcitation of the QDs is followed by energy transfer to the MOFs with efficiencies of more than 80%. This sensitization approach can result in a >50% increase in the number of photons harvested by a single monolayer MOF structure with a monolayer of QDs on the surface of the MOF.
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We report the synthesis and characterization of two thin films (DA-MOF and L2-MOF) of porphyrin-based MOFs on functionalized surfaces using a layer-by-layer (LbL) approach. Profilometry measurements ...confirm that the film thickness increases systematically with number of growth cycles. Polarization excitation and fluorescence measurements indicate that the porphyrin units are preferentially oriented, while X-ray reflectivity scans point to periodic ordering. Ellipsometry measurements show that the films are highly porous. Since there are currently few methods capable of yielding microporous MOFs containing accessible free-base porphyrins, it is noteworthy that the LbL growth permits direct MOF incorporation of unmetalated porphyrins. Long-range energy transfer is demonstrated for both MOF films. The findings offer useful insights for subsequent fabrication of MOF-based solar energy conversion devices.
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Given that energy (exciton) migration in natural photosynthesis primarily occurs in highly ordered porphyrin-like pigments (chlorophylls), equally highly ordered porphyrin-based metal–organic ...frameworks (MOFs) might be expected to exhibit similar behavior, thereby facilitating antenna-like light-harvesting and positioning such materials for use in solar energy conversion schemes. Herein, we report the first example of directional, long-distance energy migration within a MOF. Two MOFs, namely F-MOF and DA-MOF that are composed of two Zn(II) porphyrin struts 5,15-dipyridyl-10,20-bis(pentafluorophenyl)porphinatozinc(II) and 5,15-bis4-(pyridyl)ethynyl-10,20-diphenylporphinatozinc(II), respectively, were investigated. From fluorescence quenching experiments and theoretical calculations, we find that the photogenerated exciton migrates over a net distance of up to ∼45 porphyrin struts within its lifetime in DA-MOF (but only ∼3 in F-MOF), with a high anisotropy along a specific direction. The remarkably efficient exciton migration in DA-MOF is attributed to enhanced π-conjugation through the addition of two acetylene moieties in the porphyrin molecule, which leads to greater Q-band absorption intensity and much faster exciton-hopping (energy transfer between adjacent porphyrin struts). The long distance and directional energy migration in DA-MOF suggests promising applications of this compound or related compounds in solar energy conversion schemes as an efficient light-harvesting and energy-transport component.
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To grow films of Cu
O, bis-(dimethylamino-2-propoxide)Cu(ii), or Cu(dmap), is used as an atomic layer deposition precursor using only water vapor as a co-reactant. Between 110 and 175 °C, a growth ...rate of 0.12 ± 0.02 Å per cycle was measured using an in situ quartz crystal microbalance (QCM). X-ray photoelectron spectroscopy (XPS) confirms the growth of metal-oxide films featuring Cu(i).
We successfully demonstrate an approach based on linker fragmentation to create defects and tune the pore volumes and surface areas of two metal–organic frameworks, NU-125 and HKUST-1, both of which ...feature copper paddlewheel nodes. Depending on the linker fragment composition, the defect can be either a vacant site or a functional group that the original linker does not have. In the first case, we show that both surface area and pore volume increase, while in the second case they decrease. The effect of defects on the high-pressure gas uptake is also studied over a large temperature and pressure range for different gases. We found that despite an increase in pore volume and surface area in structures with vacant sites, the absolute adsorption for methane decreases for HKUST-1 and slightly increases for NU-125. However, the working capacity (deliverable amount between 65 and 5 bar) in both cases remains similar to parent frameworks due to lower uptakes at low pressures. In the case of NU-125, the effect of defects became more pronounced at lower temperatures, reflecting the greater surface areas and pore volumes of the altered forms.
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The synthesis of molybdenum oxo-amidinate complexes MoO
(R
AMD)
AMD = N,N'-di-R-acetamidinate; R = Cy (2; cyclohexyl) and
Pr (3), and their characterization by
H,
C NMR, X-ray diffraction, and ...thermogravimetric analysis is reported. Quartz-crystal microbalance and X-ray photoelectron spectroscopic studies confirm that 3 is an improved ALD precursor versus the R = t-butyl derivative for MoO
film growth. Complex 3 is accessible in higher yields (80%+), is easier to handle without mass loss, and in conjunction with O
as the second ALD reagent, yields nitride-free MoO
films.
A metal–organic framework (MOF) with high volumetric deliverable capacity for methane was synthesized after being identified by computational screening of 204 hypothetical MOF structures featuring ...(Zr6O4)(OH)4(CO2)n inorganic building blocks. The predicted MOF (NU-800) has an fcu topology in which zirconium nodes are connected via ditopic 1,4-benzenedipropynoic acid linkers. Based on our computer simulations, alkyne groups adjacent to the inorganic zirconium nodes provide more efficient methane packing around the nodes at high pressures. The high predicted gas uptake properties of this new MOF were confirmed by high-pressure isotherm measurements over a large temperature and pressure range. The measured methane deliverable capacity of NU-800 between 65 and 5.8 bar is 167 cc(STP)/cc (0.215 g/g), the highest among zirconium-based MOFs. High-pressure uptake values of H2 and CO2 are also among the highest reported. These high gas uptake characteristics, along with the expected highly stable structure of NU-800, make it a promising material for gas storage applications.
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We have synthesized and characterized a new metal-organic framework (MOF) material, NU-125, that, in the single-crystal limit, achieves a methane storage density at 58 bar (840 psi) and 298 K ...corresponding to 86% of that obtained with compressed natural gas tanks (CNG) used in vehicles today, when the latter are pressurized to 248 bar (3600 psi). More importantly, the deliverable capacity (58 bar to 5.8 bar) for NU-125 is 67% of the deliverable capacity of a CNG tank that starts at 248 bar. (For crystalline granules or powders, particle packing inefficiencies will yield densities and deliverable capacities lower than 86% and 67% of high-pressure CNG.) This material was synthesized in high yield on a gram-scale in a single-batch synthesis. Methane adsorption isotherms were measured over a wide pressure range (0.1-58 bar) and repeated over twelve cycles on the same sample, which showed no detectable degradation. Adsorption of CO sub(2) and H sub(2) over a broad range of pressures and temperatures are also reported and agree with our computational findings.
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