Direct Measurement of Adsorbed Gas Redistribution in Metal–Organic Frameworks

Observation of a Reversible Order-Order Transition in a Metal-Organic Framework - Ionic Liquid Nanocomposite Phase-Change Material

Metal-organic framework (MOF) composite materials containing ionic liquids (ILs) have been proposed for a range of potential applications, including gas separation, ion conduction, and hybrid glass formation. Here, an order transition in an IL@MOF composite is discovered using CuBTC (copper benzene-1,3,5-tricarboxylate) and [EMIM][TFSI] (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide). This transition - absent for the bare MOF or IL - provides an extended super-cooling range and latent heat at a capacity similar to that of soft paraffins, in the temperature range of ≈220 °C. Structural analysis and in situ monitoring indicate an electrostatic interaction between the IL molecules and the Cu paddle-wheels, leading to a decrease in pore symmetry at low temperature. These interactions are reversibly released above the transition temperature, which reflects in a volume expansion of the MOF-IL composite.

Improving the efficiency and environmental safety of emamectin benzoate through a pH-responsive metal-organic framework microencapsulation strategy

Herein, we developed a technique for loading nanopesticides onto Metal-Organic Frameworks (MOFs) to control Spodoptera litura. The average short-axis length of the synthesized carrier emamectin benzoate@PCN-222 @hyaluronic acid (EB@PCN-222 @HA) was ∼40 nm, with an average long-axis length of ∼80 nm. This enabled the manipulation of its size, contact angle, and surface tension on the surface of leaves. Pesticide-loading capacity, determined via thermogravimetric analysis, was measured at ∼16 %. To ensure accurate pesticide release in the alkaline intestine of Spodoptera litura, EB@PCN-222 @HA was engineered to decompose under alkaline conditions. In addition, the carrier delayed the degradation rate of EB, enhancing EB's stability. Loading Nile red onto PCN-222 @HA revealed potential entry into the insect body through feeding, which was supported by bioassay experiments. Results demonstrated the sustained-release performance of EB@PCN-222 @HA, extending its effective duration. The impact of different carrier concentrations on root length, stem length, fresh weight, and germination rate of pakchoi and tomato were assessed. Promisingly, the carrier exhibited a growth-promoting effect on the fresh weight of both the crops. Furthermore, cytotoxicity experiments confirmed its safety for humans. In cytotoxicity assays, PCN-222 @HA showed minimal toxicity at concentrations up to 100 mg/L, with cell survival rates above 80 %. Notably, the EB@PCN-222 @HA complex demonstrated reduced cytotoxicity compared to EB alone, supporting its safety for human applications. This study presents a safe and effective approach for pest control using controlled-release pesticides with extended effective durations.

High-Performance Room Temperature Ammonia Sensors Based on Pure Organic Molecules Featuring B-N Covalent Bond

Exploring organic semiconductor gas sensors with high sensitivity and selectivity is crucial for the development of sensor technology. Herein, for the first time, a promising chemiresistive organic polymer P-BNT based on a novel π-conjugated triarylboron building block is reported, showcasing an excellent responsivity over 30 000 (Ra/Rg) against 40 ppm of NH3, which is ≈3300 times higher than that of its B-N organic small molecule BN-H. More importantly, a molecular induction strategy to weaken the bond dissociation energy between polymer and NH3 caused by strong acid-base interaction is further executed to optimize the response and recovery time. As a result, the BN-H/P-BNT system with rapid response and recovery times can still exhibit a high responsivity of 718, which is among the highest reported NH3 chemiresistive sensors. Supported by in situ FTIR spectroscopy and theoretical calculations, it is revealed that the N-H fractions in BN-H small molecule promoted the charge distribution on phenyl groups, which increases charge delocalization and is more conducive to gas adsorption in such molecular systems. Notably, these distinctive small molecules also promoted charge transfer and enhanced electron concentration of the P-BNT sensing polymer, thus achieving superior B-N-containing organic molecules with excellent sensing performance.

The Molecular Path Approaching the Active Site in Catalytic Metal-Organic Frameworks

How molecules approach, bind at, and release from catalytic sites is key to heterogeneous catalysis, including for emerging metal-organic framework (MOF)-based catalysts. We use in situ synchrotron X-ray scattering analysis to evaluate the dominant binding sites for reagent and product molecules in the vicinity of catalytic Ni-oxo clusters in NU-1000 with different surface functionalization under conditions approaching those used in catalysis. The locations of the reagent and product molecules within the pores can be linked to the activity for ethylene hydrogenation. For the most active catalyst, ethylene reagent molecules bind close to the catalytic clusters, but only at temperatures approaching experimentally observed onset of catalysis. The ethane product molecules favor a different binding location suggesting that the product is readily released from the active site. An unusual guest-dependence of the framework negative thermal expansion is documented. We hypothesize that reagent and product binding sites reflect the pathway through the MOF to the active site and can be used to identify key factors that impact the catalytic activity.

Synthesis of fluorescent MOFs: live-cell imaging and sensing of a herbicide

Various metal–organic frameworks of Zn(ii) and Cd(ii) have been synthesized hydrothermally for the detection of herbicide (simazine) as well as nitro-aromatic compounds. Also these MOFs show live-cell imaging for MCF-7 cells.

In situ visualization of loading-dependent water effects in a stable metal-organic framework

Competitive water adsorption can have a significant impact on metal-organic framework performance properties, ranging from occupying active sites in catalytic reactions to co-adsorbing at the most favourable adsorption sites in gas separation and storage applications. In this study, we investigate, for a metal-organic framework that is stable after moisture exposure, what are the reversible, loading-dependent structural changes that occur during water adsorption. Herein, a combination of in situ synchrotron powder and single-crystal diffraction, infrared spectroscopy and molecular modelling analysis was used to understand the important role of loading-dependent water effects in a water stable metal-organic framework. Through this analysis, insights into changes in crystallographic lattice parameters, water siting information and water-induced defect structure as a response to water loading were obtained. This work shows that, even in stable metal-organic frameworks that maintain their porosity and crystallinity after moisture exposure, important molecular-level structural changes can still occur during water adsorption due to guest-host interactions such as water-induced bond rearrangements.

Mechanical Properties in Metal-Organic Frameworks: Emerging Opportunities and Challenges for Device Functionality and Technological Applications

Some of the most remarkable recent developments in metal-organic framework (MOF) performance properties can only be rationalized by the mechanical properties endowed by their hybrid inorganic-organic nanoporous structures. While these characteristics create intriguing application prospects, the same attributes also present challenges that will need to be overcome to enable the integration of MOFs with technologies where these promising traits can be exploited. In this review, emerging opportunities and challenges are identified for MOF-enabled device functionality and technological applications that arise from their fascinating mechanical properties. This is discussed not only in the context of their more well-studied gas storage and separation applications, but also for instances where MOFs serve as components of functional nanodevices. Recent advances in understanding MOF mechanical structure-property relationships due to attributes such as defects and interpenetration are highlighted, and open questions related to state-of-the-art computational approaches for quantifying their mechanical properties are critically discussed.

Real-time powder diffraction studies of energy materials under non-equilibrium conditions

Energy materials form the central part of energy devices. An essential part of their function is the ability to reversibly host charge or energy carriers, and analysis of their phase composition and structure in real time under non-equilibrium conditions is mandatory for a full understanding of their atomic-scale functional mechanism. Real-time powder diffraction is increasingly being applied for this purpose, forming a critical step in the strategic chemical engineering of materials with improved behaviour. This topical review gives examples of real-time analysis using powder diffraction of rechargeable battery electrodes and porous sorbent materials used for the separation and storage of energy-relevant gases to demonstrate advances in the insights which can be gained into their atomic-scale function.

An In-Depth Structural Study of the Carbon Dioxide Adsorption Process in the Porous Metal-Organic Frameworks CPO-27-M

The CO₂ adsorption process in the family of porous metal-organic framework materials CPO-27-M (M=Mg, Mn, Co, Ni, Cu, and Zn) was studied by variable-temperature powder synchrotron X-ray diffraction under isobaric conditions. The Rietveld analysis of the data provided a time-lapse view of the adsorption process on CPO-27-M. The results confirm the temperature-dependent order of occupation of the three adsorption sites in the pores of the CPO-27-M materials. In CPO-27-M (M=Mg, Mn, Co, Ni, and Zn), the adsorption sites are occupied in sequential order, primarily because of the high affinity of CO₂ for the open metal sites. CPO-27-Cu deviates from this stepwise mechanism, and the adsorption sites at the metal cation and the second site are occupied in parallel. The temperature dependence of the site occupancy of the individual CO₂ adsorption sites derived from the diffraction data is reflected in the shape of the volumetric sorption isotherms. The fast kinetics and high reversibility observed in these experiments support the suitability of these materials for use in temperature- or pressure-swing processes for carbon capture.

Hierarchically porous materials: synthesis strategies and structure design

This review addresses recent advances in synthesis strategies of hierarchically porous materials and their structural design from micro-, meso- to macro-length scale.

Ultralong Persistent Room Temperature Phosphorescence of Metal Coordination Polymers Exhibiting Reversible pH-Responsive Emission

Ultra-long-persistent room temperature phosphorescence (RTP) materials have attracted much attention and present various applications in illumination, displays, and the bioimaging field; however, the persistent RTP is generally from the inorganic phosphor materials to date. Herein, we show that the metal coordination polymers (CPs) could be new types of emerging long-lived RTP materials for potential sensor applications. First, two kinds of Cd-based CPs, Cd(m-BDC)(H2O) (1) and Cd(m-BDC)(BIM) (2) (m-BDC = 1,3-benzenedicarboxylic acid; BIM = benzimidazole), were obtained through a hydrothermal process, and the samples were found to exhibit two-dimensional layered structures, which are stabilized by interlayer C-H···π interaction and π···π interaction, respectively. The CPs show unexpected second-time-scale ultra-long-persistent RTP after the removal of UV excitation, and this persistent emission can be detected easily on a time scale of 0-10 s. The CPs also feature a tunable luminescence decay lifetime by adjusting their coordination situation and packing fashion of ligands. Theoretical calculation further indicates that the introduction of the second ligand could highly influence the electronic structure and intermolecular electron transfer toward tailoring the RTP of the CP materials. Moreover, CP 2 exhibits well-defined pH- and temperature-dependent phosphorescence responses. Therefore, this work provides a facile way to develop new type of CPs with steady-state and dynamic tuning of the RTP properties from both experimental and theoretical perspectives, which have potential applications in the areas of displays, pH/temperature sensors, and phosphorescence logic gates. On account of suitable incorporation of inorganic and organic building blocks, it can be expected that the ultra-long-persistent RTP CPs can be extended to other similar systems due to the highly tunable structures and facile synthesis routes.

Ionothermal synthesis, magnetic transformation and hydration–dehydration properties of Co(ii)-based coordination polymers

A series of low-coordinated coordination polymers obtained under an ionic liquid medium exhibit interesting hydration–dehydration behaviour and magnetic transformations.

Patterned growth of luminescent metal–organic framework films: a versatile electrochemically-assisted microwave deposition method

Electrochemically-assisted microwave deposition technology, a facile method for spatially locating the microcrystals of luminescent metal–organic framework (LMOF) films on a surface, was reported.

Copper-based energetic MOFs with 3-nitro-1H-1,2,4-triazole: solvent-dependent syntheses, structures and energetic performances

Three energetic compounds assembled with 3-nitro-1H-1,2,4-triazole have exemplified that coordinated solvent molecules may have a vital effect on the detonation properties.

Crystal engineering on superpolyhedral building blocks in metal–organic frameworks applied in gas adsorption

Two metal–organic frameworks [PCN-426(Ni) and PCN-427(Cu)] have been designed and synthesized to investigate the structure predictability using a SBB (supermolecular building blocks) approach. Tetratopic ligands featuring 120° angular carboxylate moieties were coordinated with a [Ni3(μ3-O)] cluster and a [Cu2O2] unit, respectively. As topologically predicted, 4-connected networks with square coordination adopted the nbo net for the Ni-MOF and ssb net for the Cu-MOF. PCN-426(Ni) was augmented with 12-connected octahedral SBBs, while PCN-427(Cu) was constructed with tetragonal open channels. After a CO2 supercritical drying procedure, the PCN-426(Ni) possessed a Brunauer–Emmett–Teller (BET) surface area as high as 3935 m2 g−1 and impressively high N2 uptake of 1500 cm3 g−1. This work demonstrates the generalization of the SBB strategy, finding an alternative to inconvenient synthetic processes to achieve the desired structural features.

Design and synthesis of purely inorganic 3D frameworks composed of reduced vanadium clusters and manganese linkers

Two purely inorganic three-dimensional (3D) frameworks [Mn4(H2O)11V(IV)(18)O42(PO4)](7-) (1) and [Mn2(H2O)7V(IV)(18)O42(PO4)](11-) (2) were synthesized under hydrothermal conditions and fully characterized by single-crystal X-ray structural analysis, IR spectroscopy, thermogravimetric analysis and PXRD. Structural analysis revealed that these two compounds contained a similar all reduced polyoxoanion [V(IV)(18)O42(PO4)](15-) linked by different amounts of manganese centers to form 3D framework materials. The V centers in these two compounds were all reduced to the +IV oxidation state, resulting in an all reduced polyoxoanion, which was firstly used as the building block for constructing 3D framework materials. The all reduced typical polyoxoanion [V(IV)(18)O42(PO4)](15-) with 15 negative charges supplied enough charge amount to accept TM cations. In these two structures, the anions were surrounded by 12 and 5 Mn(2+) ions, respectively, adjusted by varying the feeding amount of MnCl2·4H2O. An electrocatalytic study revealed that compound 1 exhibits electrocatalytic activity for reduction of H2O2.