Recognising timescale as an adjustable dimension in porous solids provides a new perspective to develop novel four-dimensional framework materials. The deliberate design of three-dimensional porous ...framework architectures is a developed field; however, the understanding of dynamics in open frameworks leaves a number of key questions unanswered: What factors determine the spatiotemporal evolution of deformable networks? Can we deliberately engineer the response of dynamic materials along a time-axis? How can we engineer energy barriers for the selective recognition of molecules? Answering these questions will require significant methodological development to understand structural dynamics across a range of time and length scales.
Amongst various porous materials, noble metal aerogels attract wide attention due to their concurrently featured catalytic properties and large surface areas. However, insufficient understanding and ...investigation of key factors (e.g. reductants and ligands) in the fabrication process limits on-target design, impeding material diversity and available applications. Herein, unveiling multiple roles of reductants, we develop an efficient method, i.e. the excessive-reductant-directed gelation strategy. It enables to integrate ligand chemistry for creating gold aerogels with a record-high specific surface area (59.8 m
g
), and to expand the composition to all common noble metals. Moreover, we demonstrate impressive electrocatalytic performance of these aerogels for the ethanol oxidation and oxygen evolution reaction, and discover an unconventional organic-ligand-enhancing effect. The present work not only enriches the composition and structural diversity of noble metal aerogels, but also opens up new dimensions for devising efficient electrocatalysts for broad material systems.
Functionalization of dicarboxylate linkers with proline was used to generate catalytically active metal–organic frameworks (MOFs) for diastereoselective aldol addition. Due to high robustness and ...chemical stability, zirconium based MOFs, namely UiO-67 and UiO-68, were chosen as catalyst hosts. During the MOF synthesis, utilizing Boc protected proline functionalized linkers H2bpdc-NHProBoc and H2tpdc-NHProBoc, in situ deprotection of the Boc groups without racemization is achieved, enabling direct application of the enantiopure, homochiral MOFs in catalytic reaction, without further postsynthetic treatment. Solvent screening and kinetic studies as well as cycling tests were used to evaluate the conditions for diastereoselective aldol addition using a model reaction of 4-nitrobenzaldehyde and cyclohexanone. High yields (up to 97%) were achieved in reasonable reaction time using ethanol as solvent. In comparison to homocatalytic reactions catalyzed by l-proline and its derivatives, MOFs showed opposite diastereoselectivity attributed to the catalytic sites in confined pore space rendering this class of materials as promising catalysts for fine chemicals production.
A set of porous carbons has been prepared by chemical activation of various fungi-based chars with KOH. The resulting carbon materials have high surface areas (1600–2500m2/g) and pore volumes ...(0.80–1.56cm3/g), regardless of the char precursors. The porosities mainly derived from micropores in activated carbons strongly depend on the activation parameters (temperature and KOH amount). All activated carbons have uniform micropores with pore size of 0.8–0.9nm, but some have a second set of micropores (1.3–1.4nm pore size), further broadened to 1.9–2.1nm as a result of increasing either the activation temperature to 750°C or KOH/char mass ratio to 5/1. These fungi-based porous carbons achieve an excellent H2 uptake of up to 2.4wt% at 1bar and −196°C, being in agreement with results from other porous carbonaceous adsorbents reported in the literature. At high pressure (ca. 35bar), the saturated H2 uptake reaches 4.2–4.7wt% at −196°C for these fungi-based porous carbons. The results imply a great potential of these fungi-based porous carbons as H2 on-board storage media.
A new mesoporous metal–organic framework (MOF; DUT‐60) was conceptually designed in silico using Zn4O6+ nodes, ditopic and tritopic linkers to explore the stability limits of framework architectures ...with ultrahigh porosity. The robust ith‐d topology of DUT‐60 provides an average bulk and shear modulus (4.97 GPa and 0.50 GPa, respectively) for this ultra‐porous framework, a key prerequisite to suppress pore collapse during desolvation. Subsequently, a cluster precursor approach, resulting in minimal side product formation in the solvothermal synthesis, was used to produce DUT‐60, a new crystalline framework with the highest recorded accessible pore volume (5.02 cm3 g−1) surpassing all known crystalline framework materials.
Pores for thought: Computational prediction suggests DUT‐60 as a new framework with sufficient mechanical stability to enable exceptional gas accessible porosity. With an experimentally validated specific surface area of 7839 m2 g−1 and a specific pore volume of 5.02 cm3 g−1 DUT‐60 has the highest ever achieved porosity among all crystalline porous frameworks.
Switchable metal–organic frameworks (MOFs) showing pronounced and stepwise volume changes as a response toward external stimuli such as partial pressure changes were integrated into electron ...conductive composites to generate novel threshold sensors with pronounced resistivity changes when approaching a critical partial pressure. Two “gate pressure” MOFs (DUT-8(Ni), DUT = Dresden University of Technology, and ELM-11, ELM = Elastic Layer-structured MOF) and one “breathing” MOF (MIL-53(Al), MIL = Material Institute Lavoisier) are shown to cover a wide range of detectable gas concentrations (∼20–80%) using this concept. The highest resistance change is observed for composites containing a percolating carbon nanoparticle network (slightly above the percolation threshold concentration). The volume change of the MOF particles disrupts the percolating network, resulting in a colossal resistance change up to 7500%. Repeated threshold detection is particularly feasible using MIL-53(Al) due to its high mechanical and chemical stability, even enabling application of the composite sensor concept in ambient environment for the detection of volatile organic compounds at high concentration levels.
Six novel Zr(IV)- and Hf(IV)-based MOFs, namely DUT-67, DUT-68, and DUT-69 (DUT, Dresden University of Technology) were obtained using a modulated synthesis approach with the acetic acid as a ...modulator and the bent 2,5-thiophenedicarboxylate (tdc2–) as a ligand. The modulator not only increases the size of the MOF crystallites but also plays a role of a structure directing agent, affecting both the secondary building unit (SBU) connectivity and topology of the resulting frameworks. The structure of DUT-67 is based on the reo underlying net, characteristic for its cuboctahedral and octahedral pores and is therefore isoreticular to DUT-51. The DUT-68 material has a more complicated hierarchical pore system including rhombicuboctahedral mesopore, surrounded by cuboctahedral, square-antiprismatic and octahedral microcages. DUT-69 is the first example of Zr-based MOF containing 10-connected SBU. DUT-69 has bct topology, possessing octahedral cages and channels running along one crystallographic direction. In accordance with X-ray single crystal analysis, the pores of DUT-67 and DUT-68, which were obtained at high modulator concentrations, are partially occupied by additional clusters. All novel materials are found to be robust, hydrophilic, chemically, and thermally stable. The BET specific surface area amounts to 1064 and 810 m2·g–1 for DUT-67(Zr) and DUT-67(Hf), 891 and 749 m2·g–1 for DUT-68(Zr) and DUT-68(Hf), and 560 and 450 m2·g–1 for DUT-69(Zr) and DUT-69(Hf), respectively.
As a prominent and representative example of flexible metal–organic frameworks (MOFs), DUT-49(Cu) has gained attention due to the unique phenomenon of negative gas adsorption (NGA), originating from ...an unprecedented structural contraction during the gas adsorption. Herein, postsynthetic metal exchange is demonstrated to afford DUT-49 frameworks with a wide variety of metal cations, e.g., Mn2+, Fe2+, Ni2+, Zn2+, Cu2+, and Cd2+. The single-crystal-to-single-crystal conversion allowed characterization of the new MOFs by single crystal X-ray diffraction, indicating identical structure and topology compared with that of previously explored DUT-49(Cu) framework. This approach is proven successful in achieving Mn–Mn and Cd–Cd dimers, which are rare examples of M–M paddle-wheel SBUs. The relative stability and flexibility of the resulted frameworks are observed to be highly sensitive to the metal ion of the framework, following the trends predicted by the Irving–Williams series. DUT-49(Ni) was recognized as a second material from the DUT-49 series showing adsorption-induced transitions. A sequential increase in framework flexibility from rigid to flexible and from flexible to NGA has been achieved through selective incorporation of metal centers into the structure. Finally, heterometallic structures are formed by selective and controlled exchange of metal ions to finely tune the flexibility and NGA phenomenon of the framework.
Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However, the response of such ...materials toward laser‐induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)‐based porous COFs—Por‐COF‐HH and its dual metalated congeners Por‐COF‐ZnCu and Por‐COF‐ZnNi—have been prepared and present excellent NLO properties. Notably, intensity‐dependent NLO switching behavior was observed for these Por‐COFs, which is highly desirable for optical switching and optical limiting devices. Moreover, the efficient π‐conjugation and charge‐transfer transition in ZnCu‐Por‐COF enabled a high nonlinear absorption coefficient (β=4470 cm/GW) and figure of merit (FOM=σ1/σo, 3565) value compared to other state‐of‐the‐art materials, including molecular porphyrins (β≈100–400 cm/GW), metal–organic frameworks (MOFs; β≈0.3–0.5 cm/GW), and graphene (β=900 cm/GW).
COF it up! Three regioregular porphyrin‐based porous covalent organic frameworks (COFs) with excellent nonlinear optical (NLO) properties are presented. Por‐COF‐HH and its metalated congeners, Por‐COF‐ZnCu and Por‐COF‐ZnNi, were prepared by Schiff base condensation of tetrasubstituted porphyrin aldehydes and amines. The NLO switching and high‐parameter values obtained for these Por‐COFs are promising for optical switching and optical limiting devices.
The water physisorption properties and the water stability of the metal-organic frameworks HKUST-1 (=(Cu
3(BTC)
2) (BTC = benzene-1,3,5-tricarboxylate)), ZIF-8, MIL-101, MIL-100(Fe) and DUT-4 ...(=Al(OH)(NDC)) (NDC
=
naphthalene-2,6-dicarboxylate) were studied. The water physisorption isotherms were compared to nitrogen physisorption isotherms and the chemical stability after water adsorption was investigated.
Water adsorption does not only provide information about specific surface area, pore size and pore volume, but can also be used to estimate hydrophobicity and stability towards moisture. Both HKUST-1 and DUT-4 turned out to be unstable in direct contact with water, whereas the MIL-materials and ZIF-8 do show stability. The highest water adsorption affinity was observed for HKUST-1. Even though unstable in liquid water, for applications in trace water removal or molecular sensing HKUST-1 is a promising material. ZIF-8 is highly inert but hydrophobic. The MIL-materials are both likely candidates for water adsorption applications, but higher concentrations of the adsorbate are needed to attain an effective adsorption. DUT-4 shows insufficient adsorption capacity, but stability at ambient conditions is given.
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