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The scaling-up issue, mechanical instability, and possible packing capacity loss during pelletization remain as the major obstacles for the application of metal–organic frameworks (MOFs) in practic...

Stimulated by novel properties in topological insulators, experimentally realizing quantum phases of matter and employing control over their properties have become a central goal in condensed matte...

The crystal quality of Cu2ZnSn(S,Se)4 (CZTSSe) thin film is crucially important to the high-performance CZTSSe solar cell. After the selenization, a bi-layer CZTSSe thin film consisting of a large-...

Although many studies on luminescent metal–organic frameworks (MOFs) have been reported for chemical sensing applications, it has yet to be realized in MOFs the precise linearity control over photo...

State-of-the-art chemical sensors based on covalent organic frameworks (COFs) are restricted to the transduction mechanism relying on luminescence quenching and/or enhancement. Herein, we present an alternative methodology via a combination of in situ-grown COF films with interdigitated electrodes utilized for capacitive benzene detection. The resultant COF-based sensors exhibit highly sensitive and selective detection at room temperature toward benzene vapor over carbon dioxide, methane, and propane. Their benzene detection limit can reach 340 ppb, slightly inferior to those of the metal oxide semiconductor-based sensors, but with reduced power consumption and increased selectivity. Such a sensing behavior can be attributed to the large dielectric constant of the benzene molecule, distinctive adsorptivity of the chosen COF toward benzene, and structural distortion induced by the custom-made interaction pair, which is corroborated by sorption measurements and density functional theory (DFT) calculations. This study provides new perspectives for fabricating COF-based sensors with specific functionality targeted for selective gas detection.

The density, viscosity, and refractive index data of binary mixtures for the main components of biodiesel (ethyl caprylate, ethyl caprate, and ethyl myristate) with ethylcyclohexane in the whole ra...

Droplets sliding on surfaces always exhibit an advancing and a receding contact angle. When exerting different driving forces on the droplet to force it to slide at different velocities, the droplet would alter its shape to adapt to the new motion. Hence, different advancing/receding contact angles are likely to be observed, leading to the multiple contact angle hysteresis on a given surface. To verify this hypothesis, many-body dissipative particle dynamics is employed to perform the sliding simulation on both chemically homogeneous and heterogeneous surfaces. By ensuring the droplet sliding in uniform motions under different driving forces, the advancing/receding contact angles are recorded for analysis. Simulation results show that, for homogeneous surfaces, a larger driving force can result in both larger advancing contact angle and smaller receding contact angle, while for heterogeneous surfaces, increasing the driving force only results in smaller receding contact angles. For both cases, multiple contact angle hysteresis can be observed. These observations are contrary to the currently prevailing opinion, which believes that the contact angle hysteresis should be unique on given surfaces. Our findings would advance the understanding of wetting phenomena and possibly inspire new guidance for the design of functional interfaces.

Engineering metal–organic frameworks (MOFs) for adsorptive ethylene/ethane separation has shown bright prospects for replacing the energy-intensive cryogenic distillation process. Herein, we demons...

Advanced porous materials (APMs) constructed from structure-encoded building blocks present an unprecedented degree for molecular design, and have demonstrated class-leading performance in numerous applications. However, the development of economically viable and sustainable synthetic means of production is a critical prerequisite to translate APMs to real-world applications. In this Perspective, we first consider the diverse synthetic routes to APMs—metal/covalent organic frameworks (MOFs/COFs), porous organic polymers (POPs) and porous molecular solids—and highlight the challenges for scalable and sustainable synthesis. Subsequently, we illustrate concepts to guide the sustainable synthesis of APMs with recent examples in the literature. Lastly, we present our outlook for the translation of molecular design to scalable APM production.

Mixed matrix membranes (MMMs) have gained great attention for the efficient CO2 removal from raw nature gas or biogas (CO2/CH4 separation) and flue gas (CO2/N2 separation). Nevertheless, the development of high-performance MMMs for industrial applications is largely limited by the lack of suitable porous fillers. Herein, a novel ionic covalent organic polymer (ICOP-1) consisting of gas selective pores and hollow cavities is facilely fabricated using a metal triflate catalyzed condensation reaction. Considering its unique structural properties, ICOP-1 is explored as a novel filler to enhance the gas separation properties of polysulfone (PSf) membranes. Defect-free MMMs are successfully prepared owing to the high polymer–filler affinity originating from the organic nature of these two phases. Besides, the large cavities and size-selective pores of ICOP-1 lead to a simultaneous increase in membrane CO2 permeability and CO2/CH4, CO2/N2 selectivities. With the addition of only 0.5 wt % of ICOP-1 fillers, the a...

Covalent organic frameworks (COFs) have emerged as promising crystalline porous materials with well-defined structures, high porosity, tunable topology, and functionalities suitable for various applications. However, studies of few-layered ultrathin two-dimensional (2D) COF nanosheets, which may lead to unprecedented properties and applications, are still limited. Herein, we report the targeted synthesis of three azine-linked and imine-linked 2D COFs named NUS 30–32 using monomers containing aggregation-induced emission (AIE) rotor-active tetraphenylethylene (TPE) moieties, affording micro- and meso-dual pores in NUS-30 and NUS-32 and triple pores in NUS-31. For the first time, we demonstrate that these isostructural bulk COF powders can be exfoliated into ultrathin 2D nanosheets (2–4 nm thickness) by a temperature-swing gas exfoliation approach. Compared with TPE monomers and COF model compounds, the AIE characteristic of NUS 30–32 nanosheets is distinctly suppressed because of the covalent restriction o...

Differentiation of xylene isomers remains as one of the most important challenges in the chemical industry, mainly due to the similar molecular sizes and boiling points of the three xylene isomers. Fluorescence-based chemical sensors have attracted wide attention due to their high sensitivity and versatile applications. Here, we report a novel fluorescent metal-organic framework named NUS-40, which is able to selectively detect and discriminate o-xylene from other xylene isomers. Suspension of NUS-40 in o-xylene produces a distinct red shift in the fluorescence emission compared to that in either m-xylene or p-xylene. Moreover, the extent of peak shift is dependent on the concentration of o-xylene in xylene isomer mixtures, and the observed linear correlation between fluorescence intensity and o-xylene concentration is beneficial for quantitative detection. The possible mechanism of such responsive fluorescence behavior was investigated by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and vapor sorption experiments. In addition, facile metalation of the porphyrin centers with metal ions provides an additional route to fine-tune the sensing properties.

Phase and porosity control in titanium dioxide (TiO2) is essential for the optimization of its photocatalytic activity. However, concurrent control over these two parameters remains challenging. Here, a novel metal-organic framework templating strategy is demonstrated for the preparation of highly microporous anatase TiO2. In situ encapsulation of Ti precursor in ZIF-8 cavities, followed by hydrolysis and etching, produces anatase TiO2 with a high Brunauer-Emmett-Teller surface area of 335 m2·g-1 and a micropore surface area ratio of 48%. Photocatalytic hydrogen generation catalyzed by the porous TiO2 can reach a rate of 2459 μmol·g-1·h-1. The measured photocatalytic activity is found to be positively correlated to the surface area, highlighting the importance of porosity control in heterogeneous photocatalysts.

Postcombustion CO2 capture from wet flue gas is a daunting challenge that metal–organic-framework-based (MOF-based) adsorbents need to address, because the moisture in the gas stream may not only hydrolyze the coordination bonds of MOFs but also be competitively adsorbed in MOFs leading to compromised CO2 capture performance. In this study, two isostructural water-stable MOFs decorated with alkyl groups, namely, UiO-66(Zr)-(OAc)2 and UiO-66(Zr)-(OPr)2, are synthesized from UiO-66(Zr)-(OH)2 via a facile postsynthetic esterification strategy and evaluated for their water affinity and CO2 capture performance. The increased water contact angle and reduced water vapor capacity at 60% relative humidity indicate the positive role of the propionyl group of UiO-66(Zr)-(OPr)2 in reducing material hydrophilicity. When the adsorbent beds are not fully saturated with water, breakthrough experiments using simulated wet flue gas reveal that UiO-66(Zr)-(OPr)2 possesses a CO2/N2 adsorption selectivity of 76.6, which is 22...

Microporous metal-organic frameworks (MOFs) as building materials for molecular sieving membranes offer unique opportunities to tuning the pore size and chemical property. The recently reported polycrystalline Zr-MOF membranes have greatly expanded their applications from gas separation to water treatment. However, Zr-MOFs are notoriously known for their intrinsic defects caused by ligand/cluster missing, which may greatly affect the molecular sieving property of Zr-MOF membranes. Herein, we present the mitigation of ligand-missing defects in polycrystalline UiO-66(Zr)-(OH)2 membranes by postsynthetic defect healing (PSDH), which can help in increasing the membranes’ Na+ rejection rate by 74.9%. Intriguingly, the membranes also exhibit excellent hydrothermal stability in aqueous solutions (>600 h). Our study proves the feasibility of PSDH in improving the performance of polycrystalline Zr-MOF membranes for water-treatment applications.

Metal–organic frameworks (MOFs) are a class of crystalline inorganic–organic hybrid materials that have demonstrated huge potential in gas separation due to their ultrahigh porosity, boundless chemical tunability, as well as surface functionality. Most gas separations realized in MOFs are under an equilibrium state and are dependent on the difference in thermodynamic affinities of gases to MOFs, whereas nonequilibrium separation such as kinetic and molecular sieving separation attracting growing attention in the past decade is achieved based on the difference in the size and diffusivity of gas molecules. In this perspective, we first discuss the pore size, temperature, and pressure effect on gas diffusion as well as nonequilibrium gas separation in MOFs. Second, we introduce current techniques reported to measure intracrystalline gas diffusivity. Third, we review recent progress in MOF-based nonequilibrium N2/O2 separation, CO2 capture, and hydrocarbon separation. In addition, we describe the hydrogen iso...

At present, the dominant technology for olefin/paraffin separations is cryogenic distillation, which is extremely energy-intensive. Developing advanced adsorbent materials would be a first step toward cost-effective alternatives such as pressure swing adsorption or temperature swing adsorption. In this work, we report a silver-decorated hafnium metal–organic framework, NUS-6(Hf)-Ag, as a C2H4-selective adsorbent for C2H4/C2H6 separation. NUS-6(Hf)-Ag was synthesized by the modulated hydrothermal approach followed by ion-exchange reactions. The successful introduction of Ag(I), confirmed by X-ray photoelectron spectroscopy and energy-dispersive spectroscopy, increased the ideal C2H4/C2H6 selectivity of the resultant NUS-6(Hf)-Ag material to 6, which was 5 times that of NUS-6(Hf). Breakthrough experiments further confirmed the C2H4/C2H6 separation performance of NUS-6(Hf)-Ag, indicating coadsorption C2H4/C2H6 selectivities greater than 3. In addition, NUS-6(Hf)-Ag was found to maintain its crystallinity and...

It is a challenging topic to disconnect a linear polymer selectively at the mechanophore site by an external force in a “cold” fashion. In this work, the effect of the power output of ultrasonication on the selective cleavage at the centered urfuryl-maleimide Diels–Alder (DA) mechanophore of poly(methyl acrylate)s (DA-PMA-a and DA-PMA-b) were quantitatively investigated by comparative study on experimental and simulated chain scission kinetics as well as high-resolution 1H NMR spectroscopy (600 MHz). At low power output of the ultrasonication (2.10 W), DA-PMA-a with Mn of ca. 2Mlim (Mlim, below which no further chain scission was observed) presented a DI (degradation index)−t (sonication time) plot with a turnover point at ca. 1.0 and no clear variation of the molecular weight after the turnover, which met well with the calculated center cleavage mode. At 5.52 W, DA-PMA-a and a poly(methyl acrylate) that contained two centered ester bonds (ester-PMA) presented similar DI–t plots with turnover points less ...

The direct synthesis of metal–organic frameworks (MOFs) with strong Bronsted acidity is challenging because the functional groups exhibiting Bronsted acidity (e.g., sulfonic acid groups) often jeopardize the framework integrity. Herein, we report the direct synthesis of two hierarchically porous MOFs named NUS-6 composed of either zirconium (Zr) or hafnium (Hf) clusters with high stability and strong Bronsted acidity. Via the modulated hydrothermal (MHT) synthesis, these two MOFs can be easily synthesized at a low temperature (80 °C) with high throughput. They exhibit BET surface areas of 550 and 530 m2 g–1 for Zr and Hf one, respectively, and a unique hierarchically porous structure of coexisting micropores (∼0.5, ∼0.7, and ∼1.4 nm) and mesopores (∼4.0 nm) with dangling sulfonic acid groups. Structural analysis reveals that the hierarchical porosity of NUS-6 is a result of missing linkers and clusters of the parental UiO-66 framework. These unique features make NUS-6 highly efficient and selective solid ...

The modulated synthesis of metal–organic frameworks (MOFs) remains empirical and challenging. Modulators are often applied and assumed capable of facilitating crystal growth by adjusting the reaction kinetics. However, most of the current studies are based on qualitative analysis and performance-leading synthesis, while no quantitative insights between modulator feature and MOF performance have been offered. In this work, we carried out a comprehensive study of the effects of three modulators (acetic acid, formic acid, trifluoroacetic acid) on the water-based modulated synthesis of UiO-66-type MOFs by using Zr or Hf as the building block and fumarate as the ligand. The modulator effects on crystallinity, yield, morphology, pore size, defects, porosity, stability, and gas separation performance of resultant MOFs have been discussed. A relationship between optimal molar ratio y and pKa value of modulator x is modeled as y = 12.72 + 0.193 × exp(1.276x). For MOF synthesis using ligands of different acidity, i...