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Synthesis of amine-functionalized ZIF-8 with 3-amino-1,2,4-triazole by postsynthetic modification for efficient CO 2 –selective adsorbents and beyond
Abstract
The facile tuning of a gate size, as well as the chemical functionalization of zeolitic imidazolate frameworks (ZIFs), have been considered efficient strategies for various potential applications including gas membranes, sensors, and catalysts. Herein, we demonstrate the synthesis of amine-functionalized ZIF-8 (ZIF8-A) with 3-amino-1,2,4-triazole (Atz) by postsynthetic modification (PSM) towards two objectives: (1) CO2 selective adsorption by a combination of chemical interactions and controlled gate sizes and (2) potential for further chemical modifications. The acquired ZIF8-A substantially enhanced CO2/N2 and CO2/CH4 selectivity at 35 oC compared to ZIF-8 since the Atz conversion enhanced chemical interactions with CO2 due to the introduction of amine moieties while reducing both surface area and pore volume. The gate size control of ZIF-8 by the replacement of Atz was thoroughly investigated by extensive transport experiments and density functional theory (DFT)-based computational simulations. In addition, the vinyl-functionalized ZIF-8, another versatile starting material, was successfully prepared by further chemical modifications of ZIF8-A with either methacrylic anhydride or glycidyl methacrylate through nucleophilic substitution reactions. As such, we believe that our current work can provide promising platforms for designing ZIF-based materials with versatile properties including the precise control of gate size and the incorporation of various functional groups.
... As can be seen from the XRD patterns and Raman spectra (Figures 1b,c and S2b,c−S5b,c), the introduction of Atz to Fe-ZIF did not lead to loss in terms of MOF crystallinity. 23 Figure S5d). Functional groups including C� N−NH, C−NH 2 , and N−C−NH were obtained at 1545, 1511, and 1210 cm −1 in 2-mIm and Atz, respectively, and aliphatic C−H and aromatic C−H stretching oscillations of the 2-mIm ligand were also recorded at 3134 and 2928 cm −1 , respectively. ...
... In the 1 H NMR spectrum, the existence of methyl and methine groups of 2-mIm from ZIF-8 and Fe-ZIF-20 was obtained at 2.46 and 7.36 ppm, respectively. 23,26,27 After Atz was introduced, an additional peak at 8.21 ppm could be attributed to the methine group of Atz. 23,26,27 These findings also support the XRD results that the ZIF-8 structure was maintained following the insertion of Atz into Fe-ZIF. ...
... 23,26,27 These findings also support the XRD results that the ZIF-8 structure was maintained following the insertion of Atz into Fe-ZIF. 23,26 3.2. Characterization of Carbon Structures. ...
Recently, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have received great attention for the development of renewable energy and energy storage systems. In the context of catalyst standpoint, developing single-atom catalysts (SACs) with bifunctional electrocatalytic reactions (ORR/OER) has emerged as a fascinating research field in recent years. However, a majority of SACs that have been reported have a complicated synthesis route that involves many steps and harmful solvents and suffer from aggregation phenomena, which makes them unsustainable for industrial use. Herein, a bifunctional C-Atz-20 electrocatalyst was fabricated by inserting a secondary organic linker, 3-amino-1,2,4-triazole (Atz), into Fe-ZIF followed by high-temperature pyrolysis and its ORR/OER elucidated. To fully comprehend the function of Atz addition, the nanostructured materials underwent an extensive characteristic analysis. The results showed that the C-Atz-20 exhibited better long-term ORR and OER stability tests when compared with Pt/C and RuO 2 , respectively. Interestingly, the high ORR activity of C-Atz-20 originally contributed to the presence of a large fraction of pyridinic and graphitic N. Rotating ring-disk electrode (RRDE) measurement illustrates the ORR mechanism in the catalytic process, giving a better understanding of electron transport, thus paving the way for the design and development of heterogeneous catalysts with simple preparation and operating procedures.
... Only a few works demonstrate the independent light emission of PL and RT-OP for high-security encryption 27 . We envisioned that MOFs classified as porous crystalline materials constructed using metal ions or metal clusters coordinated with organic ligands [30][31][32][33] would be useful for realizing independent PL and RT-OP emission. Accordingly, when guest molecules for RT-OP were securely fixed within each periodic cavity of an MOF, the host-guest pairs were rigidified with fixed molecular separation, owing to the crystalline structure of the MOFs, resulting in stable RT-OP even without additives 14,34 . ...
... The surface areas were approximately 13.8, 11.0, 9.4, and 4.1 m 2 g −1 for the Pb-MOF (1:2), (1:3), (1:4), and (1:6) samples, respectively. These results clearly indicate that the cavities in the pristine Pb-MOFs were efficiently occupied by the CA molecules 32,34 . ...
Optical encryption technologies based on room-temperature light-emitting materials are of considerable interest. Herein, we present three-dimensional (3D) printable dual-light-emitting materials for high-performance optical pattern encryption. These are based on fluorescent perovskite nanocrystals (NCs) embedded in metal-organic frameworks (MOFs) designed for phosphorescent host-guest interactions. Notably, perovskite-containing MOFs emit a highly efficient blue phosphorescence, and perovskite NCs embedded in the MOFs emit characteristic green or red fluorescence under ultraviolet (UV) irradiation. Such dual-light-emitting MOFs with independent fluorescence and phosphorescence emissions are employed in pochoir pattern encryption, wherein actual information with transient phosphorescence is efficiently concealed behind fake information with fluorescence under UV exposure. Moreover, a 3D cubic skeleton is developed with the dual-light-emitting MOF powder dispersed in 3D-printable polymer filaments for 3D dual-pattern encryption. This article outlines a universal principle for developing MOF-based room-temperature multi-light-emitting materials and a strategy for multidimensional information encryption with enhanced capacity and security.
... Despite not reaching exceptionally high levels compared to other MOFs, the adsorption capacity of CO 2 in KAUST-7 demonstrates a distinctive isotherm behavior that distinguishes it from the majority of MOFs. Conventionally, in most MOFs, the adsorption capacity of CO 2 shows a direct correlation with pressure, i.e., the adsorption capacity increases as pressure rises [39][40][41][42]. However, KAUST-7 diverges from this pattern by showcasing a very high adsorption capacity at extremely low pressures (1 kPa). ...
To overcome the challenging trade-off between permeability and selectivity in polymer CO 2 separation membranes , CO 2-philic metal-organic framework (MOF) KAUST-7 was incorporated within polyethylene oxide (PEO)-type matrices to prepare mixed matrix membranes (MMMs). A cross-scale approach of quantum chemical calculations and molecular dynamics simulations was used to explore the behavior and mechanism of CO 2 adsorption on KAUST-7. The strong affinity between KAUST-7 and CO 2 enabled a dramatic increase in the CO 2 solubility of MMMs. The 2 wt% KAUST-7 loaded MMM exhibited CO 2 permeability and CO 2 /N 2 selectivity of 608 Barrer and 75, respectively, representing 41.7% and 54% improvement compared to the neat membrane, exceeding the 2019 upper bound. Furthermore, long-term separation tests for 100 h demonstrated the stability of these membranes.
... Metal-organic frameworks (MOFs) are crystalline materials with high porosity and large free volume and surface area [29]. With these properties, MOFs have been used in various applications, including gas separation, energy storage, and catalysis [30][31][32]. In particular, MOFs have been used in energy storage systems as silicon/MOF-based carbon composites because they mitigate the significant volume expansion of silicon while providing a channel for Li ions to move through [33,34]. ...
The high capacity of electrodes allows for a lower mass of electrodes, which is essential for increasing the energy density of the batteries. According to this, silicon is a promising anode candidate for Li-ion batteries due to its high theoretical capacity. However, its practical application is hampered by the significant volume expansion of silicon during battery operation, resulting in pulverization and contact loss. In this study, we developed a stable Li-ion anode that not only solves the problem of the short lifetime of silicon but also preserves the initial efficiency by using silicon nanoparticles covered with glassy ZIF-4 (SZ-4). SZ-4 suppresses silicon pulverization, contact loss, etc. because the glassy ZIF-4 wrapped around the silicon nanoparticles prevents additional SEI formation outside the silicon surface due to the electrically insulating characteristics of glassy ZIF-4. The SZ-4 realized by a simple heat treatment method showed 74% capacity retention after 100 cycles and a high initial efficiency of 78.7%.
... To overcome these issues, post-synthetic modifications of MOFs have been widely investigated, including the introduction of additional functional groups 19,20 , ligand (or metal) exchange 21,22 , and surface oligomer/polymer coating 12,13,15,[23][24][25] . For example, polymethyl methacrylate (PMMA)-functionalized UiO-66 nanoparticles showed excellent colloidal stability in casting solutions, which led to enhanced particle dispersion and interactions within the polymer matrix 20 . ...
Integrating different modification strategies into a single step to achieve the desired properties of metal–organic frameworks (MOFs) has been very synthetically challenging, especially in developing advanced MOF/polymer mixed matrix membranes (MMMs). Herein, we report a polymer–MOF (polyMOF) system constructed from a carboxylated polymer with intrinsic microporosity (cPIM-1) ligand. This intrinsically microporous ligand could coordinate with metals, leading to ~100 nm-sized polyMOF nanoparticles. Compared to control MOFs, these polyMOFs exhibit enhanced ultramicroporosity for efficient molecular sieving, and they have better dispersion properties in casting solutions to prepare MMMs. Ultimately, integrating coordination chemistries through the cPIM-1 and polymer-based functionality into porous materials results in polyMOF/PIM-1 MMMs that display excellent CO2 separation performance (surpassing the CO2/N2 and CO2/CH4 upper bounds). In addition to exploring the physicochemical and transport properties of this polyMOF system, scalability has been demonstrated by converting the developed MMM material into large-area (400 cm²) thin-film nanocomposite (TFN) membranes.
... The conversion ratio of the MeIm to Atz was 34%, which is calculated based on the intensity ratio of the methine peaks at b and c. In addition, the FT-IR spectrum of ZIF8A exhibited higher absorbance peaks for the -NH 2 (3441 and 3328 cm − 1 ) (peak d) and -NH (3123 cm − 1 ) (peak e) stretching bends, which correspond to Atz, compared to those in the ZIF-8 spectrum [39]. The presence of Atz in ZIF-8 altered the electrical state of the frameworks. ...
... The addition of MOF particles improved the CO 2 permeability of the mixed-matrix membrane, but at the same time decreased its CO 2 selectivity, which might be due to the poor compatibility between the MOF particles and the membrane. It was found that amine-functionalized ZIF-8 could effectively improve the permeability and selectivity of the membrane, which was due to chemical interactions and the effect of the controlled fence combination that enhanced the selectivity of the membrane for CO 2 [56] . In addition, it was found that the crystal structure and thermal stability of the synthesized NH-ZIF-8 were identical to those of the pure ZIF-8 crystals. ...
Metal-organic frameworks (MOFs) are porous crystalline materials assembled from organic ligands and metallic secondary building blocks. Their special structural composition gives them the advantages of high porosity, high specific surface area, adjustable pore size, and good stability. MOF membranes and MOF-based mixed-matrix membranes prepared from MOF crystals have ultra-high porosity, uniform pore size, excellent adsorption properties, high selectivity, and high throughput, which contribute to their being widely used in separation fields. This review summarizes the synthesis methods of MOF membranes, including in situ growth, secondary growth, and electrochemical methods. Mixed-matrix membranes composed of Zeolite Imidazolate Frameworks (ZIF), University of Oslo (UIO), and Materials of Institute Lavoisier (MIL) frameworks are introduced. In addition, the main applications of MOF membranes in lithium–sulfur battery separators, wastewater purification, seawater desalination, and gas separation are reviewed. Finally, we review the development prospects of MOF membranes for the large-scale application of MOF membranes in factories.
... ZIFs can be functionalized quite easily and have many active sites, hence, the researchers had modified ZIF surface with amino group in order to form basic active sites that resulted in Lewis acid -base interaction with CO 2 which in turn increases selectivity of CO 2 [208]. ZIF-7-NH 2 /XLPEO mixed matrix membrane was fabricated by Xiang et al. [178]with high permeability and selectivity. ...
Gas separation by employing polymeric membranes is one of the most developed branches of membrane based separation technology. But, polymeric materials are unable to meet the demands of present day membrane technology. Mixed matrix membranes (MMMs) which are combination of both polymeric and inorganic materials have appeared as an emerging membrane material as it combines the dimensional stability and efficient gas separation ability of inorganic material along with facile fabrication and low cost of polymeric material. In this review, main challenges that are encountered during fabrication of MMMs and the steps taken to overcome these challenges are reviewed in detail. Also, the basic criteria for the selection of suitable polymer and inorganic material for fabrication of MMMs is also discussed pertaining to chemical and physical compatibility between them. Zeolite imidazolate frameworks (ZIFs) because of their good compatibility with polymers along with their beneficial properties such as unsaturated sites, adjustable pore channels and simple functionalization are widely incorporated into polymer matrix for fabrication of MMMs. Influence of various types of ZIFs on MMMs fabrication along with their gas separation performances are also put together in this review article from different reports. Moreover, ZIF modification techniques in order to enhance the gas separation performance of MMMs are also discussed. This study reveals that modified filler’s synergic effect can alter membrane’s structure by improving interfacial voids and thus can overcome the trade-off effect. Besides this, the influence of ZIFs morphology on gas separation performance of MMMs is also analysed in this article.
The growing demand for wearable devices designed for continuous monitoring necessitates an extended power supply, prompting the development of self-powered sensing devices capable of prolonged operation. Multifunctional materials have become a prime focus for self-powered systems. One such material is ZIF-8, a porous crystalline metal–organic framework (MOF) that holds promise for non-enzymatic glucose detection due to its expansive surface area, functional sites, electrocatalytic activity, and biocompatibility. Our research details the successful synthesis of ZIF-8 and a composite consisting of ZIF-8 and reduced graphene oxide (rGO). We extensively investigated the structural, elemental, and morphological attributes of these materials using various characterization techniques. Our examination of glucose detection involved cyclic voltammetry and amperometry studies. The hybrid electrode, benefiting from the synergistic interplay between ZIF-8 and rGO, exhibited an exceptional sensitivity of 5047.18 μA mM−1 cm−2 and a detection limit of 0.3 μM, spanning the range of 0.005 mM to 5 mM. Furthermore, we explored these materials' potential in the supercapacitance realm. The ZIF-8/rGO hybrid electrode demonstrated an impressive specific capacitance of 287F/g at a current density of 1 Ag−1, displaying pseudocapacitive behaviour. A proof-of-concept prototype device, utilizing ZIF-8/rGO, was fabricated and investigated for its potential in wearable glucose sensing. The device yielded satisfactory results, showcasing its capability as a self-powered wearable sensor. In general, ZIF-8/rGO hybrid nanostructure emerged as a promising candidate for supercapacitor and electrochemical glucose detection applications.
A bimetallic zinc and cobalt zeolitic imidazolate framework (ZnCo-ZIF-71) catalyst was synthesized using metal acetate and 4,5-dichloroimidizole in a methanol solution. Various physicochemical analytical techniques were employed to characterize the synthesized catalyst and to confirm the existence of uniform distribution of Zn and Co atoms throughout the catalyst system. CO2-epoxide cycloaddition reactions were subsequently carried out to test the performance of ZnCo-ZIF-71. The bimetallic ZIF showed a higher conversion of epoxide compared to that of the corresponding monometallic ZIF (Zn-ZIF-71 and Co-ZIF-71), likely due to the prevalence of linker defects in bimetallic ZIF system. The degree of linker defects in bimetallic ZIFs was characterized based on molecular simulations. The mechanism for the solvent-free CO2-epoxide cycloaddition reaction catalyzed by ZnCo-ZIF-71 was proposed following the XAFS analysis and DFT calculations.
CO 2 capture and storage have been regarded as promising concepts to reduce anthropogenic CO 2 emissions. However, the high cost, inferior adsorption capacity, and higher effective activation temperature of traditional sorbents limit their practical application in efficient CO 2 capture. Here, a C‐S‐H@ZIF‐8 (C‐S‐Z) sorbent is fabricated by in situ growth of the ZIF‐8 shell on the C‐S‐H (calcium‐silicate‐hydrate) surface for ultra‐high CO 2 adsorption and storage. Among the C‐S‐Z, the outer ZIF‐8 shell acts as a transport channel that promotes CO 2 absorption toward the underlying C‐S‐H substrate for accelerated carbonation while preventing nitrogen and water from reaching the interior C‐S‐H. As a consequence, C‐S‐Z possesses the merits of ample pyrrolic nitrogen, porous structure, and ultra‐high surface area (577.18 m ² g ⁻¹ ), that contribute to an ultra‐high CO 2 capture capacity, reaching 293.6 mg g ⁻¹ . DFT calculations show a high CO 2 adsorption energy and the mineral carbonation is dominant by the adsorption process. In particular, the advantages of the outstanding adsorption capacity, low cost, and high CO 2 selectivity make this C‐S‐H‐based sorbent hold great potential in the practical application for direct air CO 2 capture and storage.
The thin selective layer in mixed matrix membranes (MMMs) with high pervaporation performance is in high demand because of their high productivity. However, it has been limited because of the defective interface of sieving fillers in MMMs and the instability to permeate molecules, resulting in instability and degradation in the membrane state and pervaporation performance. Herein, we synthesized defective UiO-66 (DUiO66) by controlling the concentration of the reactants and then analyzed the characteristics of the defects. We confirmed that defects of the missing linker are induced in its structure, and DUiO66 (1.324) has a higher defect density than conventional UiO66 (1.064). Those led to the highly enhanced interface of DUiO66 with polyvinyl alcohol (PVA) matrix and water solvent, resulting in mechanical stability and a uniformed thin selective layer. Crosslinked thin-layered PVA MMMs with DUiO66 (XPDUiO66) were applied to the flat-sheet type and hollow fiber type membranes and then examined for the pervaporation performance to separate IPA/water solution (mainly 80/20 and 90/10 (w/w)). The thin-layered flat type and hollow fiber type XPDUiO66 revealed a dramatic increase in flux by 5.6 and 5.0 times compared to the free-standing type MMM while almost maintaining selectivity. Notably, the flat-sheet type XPDUiO66-2 increased around 606% and 1,664% in PSI relative to XPVA at a feed solution of 80/20 and 90/10 (w/w) IPA/water, respectively. The current work offers significant findings on the relationship between defective MOF-applied MMMs and pervaporation performance.
Slippery liquid‐infused porous surfaces (SLIPS) have received widespread attention in the antifouling field. However, the reduction in antifouling performance caused by lubricant loss limits their application in marine antifouling. Herein, inspired by the skin of a poison dart frog which contains venom glands and mucus, a porous liquid (PL) based on ZIF‐8 is prepared as a lubricant and injected into a silicone polyurethane matrix to construct a new type of SLIPS for marine antifouling applications: the slippery porous‐liquid‐infused porous surface (SPIPS). The SPIPS consists of a responsive antifoulant‐releasing switch between “defensive” and “offensive” antifouling modes to intelligently enhance the antifouling effect after lubricant loss. The SPIPS can adjust antifouling performance to meet the antifouling requirements under different light conditions. The wastage of antifoulants is reduced, thereby effectively maintaining the durability and service life of SLIPS materials. The SPIPS exhibits efficient lubricant self‐replenishment, self‐cleaning, anti‐protein, anti‐bacterial, anti‐algal, and self‐healing (97.48%) properties. Furthermore, it shows satisfactory 360‐day antifouling performance in actual marine fields during boom seasons, demonstrating the longest antifouling lifespan in the field tests of reported SLIPS coatings. Hence, the SPIPS can effectively promote the development of SLIPS for neritic antifouling.
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Cancer theranostics that combines cancer diagnosis and therapy is a promising approach for personalized cancer treatment. However, current theranostic strategies suffer from low imaging sensitivity for visualization and an inability to target the diseased tissue site with high specificity, thus hindering their translation to the clinic. In this study, we have developed a tumor microenvironment-responsive hybrid theranostic agent by grafting water-soluble, low-fouling fluoropolymers to pH-responsive zeolitic imidazolate framework-8 (ZIF-8) nanoparticles by surface-initiated RAFT polymerization. The conjugation of the fluoropolymers to ZIF-8 nanoparticles not only allows sensitive in vivo visualization of the nanoparticles by 19F MRI but also significantly prolongs their circulation time in the bloodstream, resulting in improved delivery efficiency to tumor tissue. The ZIF-8-fluoropolymer nanoparticles can respond to the acidic tumor microenvironment, leading to progressive degradation of the nanoparticles and release of zinc ions as well as encapsulated anticancer drugs. The zinc ions released from the ZIF-8 can further coordinate to the fluoropolymers to switch the hydrophilicity and reverse the surface charge of the nanoparticles. This transition in hydrophilicity and surface charge of the polymeric coating can reduce the "stealth-like" nature of the agent and enhance specific uptake by cancer cells. Hence, these hybrid nanoparticles represent intelligent theranostics with highly sensitive imaging capability, significantly prolonged blood circulation time, greatly improved accumulation within the tumor tissue, and enhanced anticancer therapeutic efficiency.
Due to the powerful redox homeostasis and inefficiency of monotherapy, chemodynamic therapy (CDT) is clinically limited. Despite great efforts, the design of CDT nanosystems with specific H2O2 homeostasis and effective integration of multiple treatments remains a great challenge. Therefore, herein, we engineer a novel pH-responsive nanocatalyst to disrupt intracellular H2O2 homeostasis through consuming glutathione (GSH), elevating H2O2 and restraining H2O2 elimination, as well as achieving a combination of CDT and chemotherapy (CT) through sensitized DSF. In the formulation, amplified CDT synergized enhanced CT significantly, strengthening the tumor therapeutic efficacy in vitro and in vivo. This work not only solves intracellular redox homeostasis disruption, but also realizes the re-use of old drugs, providing new insights for CDT-based multimodal cancer therapy.
Antibody‐nanoparticle conjugates are promising candidates for precision medicine. However, developing a controllable method for conjugating antibodies to nanoparticles without compromising the antibody activity represents a critical challenge. Here, a facile and generalizable film‐coating method is presented using zeolitic imidazole framework‐8 (ZIF‐8) to immobilize antibodies on various nanoparticles in a favorable orientation for enhanced cell targeting. Different model and therapeutic antibodies (e.g., Herceptin) are assembled on nanoparticles via a biomineralized film‐coating method and exhibited high antibody loading and targeting efficiencies. Importantly, the antibodies selectively bind to ZIF‐8 via their Fc regions, which favorably exposes the functional Fab regions to the biological target, thus improving the cell targeting ability of antibody‐coated nanoparticles. In combination, molecular dynamics simulations and experimental studies on antibody immobilization, orientation efficiency, and biofunctionality collectively demonstrate that this versatile site‐specific antibody conjugation method provides effective control over antibody orientation and leads to improved cell targeting for a variety of nanoparticles. A film‐coating method by using ZIF‐8 to immobilize antibodies on various nanoparticles in a favorable orientation is developed for cell targeting. The underlying mechanism of orientated antibody conjugation is revealed to be unique site‐selective binding of antibodies to ZIF‐8. Its broad applicability is demonstrated by conjugating antibodies on a range of nanoparticles to realize cell‐specific targeting for potential biomedical applications.
Polymer microspheres equipped with a porous skeleton network to build fluid channels for efficient water treatment.
Zeolitic Imidazolate Frameworks (ZIFs) owing to their crystalline morphology have well designed pore architecture. ZIFs show great potential for applications in gas separation, gas storage, catalysis and sensors because of their high surface area, pore volume and well defined pore network. In order to utilize ZIFs for aforementioned applications, investigation of pore architecture (pore size, pore size distribution and interconnectivity) of ZIFs in powder or film form is highly essential. Conventional gas adsorption techniques are found to be incapable for providing complete pore architecture of ZIFs due to ultra-microporosity and pressure dependent framework flexibility. In recent years, positron annihilation lifetime spectroscopy (PALS) has been used to investigate the porosity of few ZIFs. In order to establish the applicability of PALS for pore architecture investigation of ZIFs in general, a systematic study in a number of ZIFs (ZIF-67, ZIF-8, ZIF-7l, ZIF-7n ZIF-62, ZIF-90, ZIF-70.52-8, Zn0.25Co0.75-ZIF-8, and ZIF-8A) have been carried out. These frameworks have been synthesized at room temperature or using solvothermal methods. PALS measurements of these ZIFs confirm the presence of different types of interconnected pores in these frameworks. The estimated pore sizes are compared with the pore sizes determined from other conventional techniques. The present study suggests that PALS is a powerful technique for the investigation of tuning of the pore architecture of all type of ZIFs. The determined pore sizes are the factual average pore size of desolvated bulk ZIF samples free from artifacts. These pore sizes could be correlated with the pore size dependent separation performance of ZIFs.
To simultaneously purify H2 and capture CO2 in the steam methane reforming (SMR) process for H2 production, a bifunctional metal organic framework (MOF) membrane ([Ni(tzba)0.5(F)(bpy)]) was proposed via an in-situ synthesis method to efficiently permeate H2 through ultramicropores and selectively adsorb CO2 with the strong affinity of uncoordinated N-Ni-F⁻ active sites. Ni(tzba)0.5(F)(bpy) exhibited a good CO2 uptake capacity (4.3 mmol/g at 273 K and 110 kPa) because the F⁻ anionic and exposed uncoordinated tetrazolate N atoms in ligands have an excellent affinity to CO2. Dynamic breakthrough experiments suggested that Ni(tzba)0.5(F)(bpy) achieved efficient separation of CO2 from H2, CH4, and N2. Ni(tzba)0.5(F)(bpy) MOF membrane also shows outstanding H2/CO2 separation performance because the high adsorption capacity of CO2 reduced CO2 mobility. The H2 permeability of 1.59 × 10⁵ Barrer and H2/CO2 ideal selectivity of 14.43 greatly exceeded the latest upper bound. Continuous permeability tests of up to 100 hours demonstrated the long-term stability of the Ni(tzba)0.5(F)(bpy) MOF membrane for H2 separation applications. Density functional theory (DFT) calculations clarified the adsorption mechanism of Ni(tzba)0.5(F)(bpy) towards gases.
Solvent-assisted linker exchange (SALE) is a powerful tool to increase the structural complexity of metal-organic frameworks (MOF) and expand their functionality, while amounts of organic solvent and energy-intensive heating are needed in this process. In this work, we propose a solvent-free and environment-friendly mechanochemistry-assisted linker exchange strategy (MALE) for MOF post-synthetic modification in a green and sustainable manner at room temperature, which is demonstrated by the efficient linker exchange in ZIF-8 (ZIF = Zeolitic imidazolate frameworks) with imidazole-2-formaldehyde (Im-CHO) ligand. Importantly, contrast experiments show that the linker exchange reaction rate of the MALE method is much faster and more efficient than the conventional SALE method. In addition, the versatility of the MALE method is certified by successfully extending to robust UiO-66 (UiO = University of Oslo) and other functional ZIF-8 analogues, including ZIF-8/Br, ZIF-8/CF3, ZIF-8/CH2OH, ZIF-8/Cl, and ZIF-8/Et. Besides, the obtained ZIF-8/CF3 shows a boosting kinetic separation performance for C3H6/C3H8 gas mixtures compared with pristine ZIF-8. This work not only proposes a green, efficient, and solvent-free linker exchange method of MOF, but also develops a potential adsorbent for efficient kinetic separation of C3H6/C3H8 mixtures.
Silicon anode is widely used in advanced energy conversion and storage devices such as lithium-ion batteries due to its high specific capacity. Nevertheless, the volume expansion and the poor electrical...
The deep purification of trace heavy metals in drinking water is of great significance and has received considerable attention worldwide. 2,5-dimercapto-1,3,4-thiadiazole (DMTD) functionalized magnetic ZIF-8 adsorbent (Fe3O4@ZIF-8-DMTD) using a novel one-pot post coordination modulation method at room temperature could effectively adsorb trace heavy metals from drinking water through cooperating with the abundant functional groups and surface charges. The negative surface charges promoted the rapid accumulation of trace heavy metals on the surface of the adsorbent, meanwhile, the abundant thiol/nitrogen sites contributed to their adsorption, thus the adsorption rate and adsorption capacity of trace heavy metals were greatly improved. For trace Pb(II) (150 ppb), the effluent concentration could meet the World Health Organization (WHO) standard (≤10 ppb) within 10 s after adsorption by Fe3O4@ZIF-8-DMTD, and the cumulative adsorption capacity that met WHO standard was 12.11 mg/g. Fe3O4@ZIF-8-DMTD also showed high stability in a broad pH range and excellent adsorption performance in a wide low concentration range. The effluent concentration still could meet the WHO standard when the initial Pb(II) concentration was 11.70 ppm, and the corresponding adsorption capacity reached 35.00 mg/g. Moreover, the capture experiments for multiple heavy metals that coexisted in tap water showed that the effluent concentrations of Hg(II), Pb(II), Cu(II), Cd(II), and Cr(III) could be lower than the allowable limits in a few minutes. The adsorbent could also be easily recovered using magnets and regenerated by thiourea solution, which showed great application potential for the purification of trace heavy metals in drinking water.
The design of functionalized metallic nanoparticles is considered an emerging technique to ensure the interaction between metal and semiconductor material. In the literature, this interface interaction is mainly governed by electrostatic or van der Waals forces, limiting the injection of electrons under light irradiation. To enhance the transfer of electrons between two compounds, close contact or chemical bonding at the interface is required. Herein, a new approach was reported for the synthesis of chemically bonded plasmonic Au NPs/ZIF‐67 nanocomposites. The structure of ZIF‐67 was grown on the surface of functionalized plasmonic Au NPs using 1H‐1,2,4‐triazole‐3‐thiol as the capping agent, which acted as both stabilizer of Au nanoparticles and a molecular linker for ZIF‐67 formation. As a result, the synthesized material exhibited outstanding photocatalytic CO2 reduction with a methanol production rate of 2.70 mmol h⁻¹ g⁻¹cat under sunlight irradiation. This work emphasizes that the diligent use of capping agents, with suitable functional groups, could facilitate the formation of intimate heterostructure for enhanced photocatalytic CO2 reduction.
Herein, a new approach for the in situ synthesis of zeolitic imidazolate framework (ZIF) nanoparticles with triple ligands, referred to as Sogang ZIF‐8 (SZIF‐8), is reported for enhanced C2H4/C2H6 kinetic separation. SZIF‐8 consists of tetrahedral zinc metals coordinated with tri‐butyl amine (TBA), 2,4‐dimethylimidazole (DIm), and 2‐methylimidazole (MIm). SZIF‐8(x) with different DIm contents in x (up to 23.2 mol%) are synthesized in situ because TBA preferably deprotonates DIm ligands due to the much lower pKa of DIm over MIm, allowing for the Zn‐DIm coordination. The Zn‐DIm coordination reduces the window size of ZIF‐8 with suppressed linker flipping motion due to bulky DIm ligands and simultaneously enhances the interfacial interaction between 6FDA‐DAM polyimide (6FDA) and SZIF‐8 via electron donor–acceptor interactions. Consequently, 6FDA/SZIF‐8(13) mixed matrix membrane exhibits an excellent C2H4 permeability of 60.3 Barrer and C2H4/C2H6 selectivity of 4.5. The temperature‐dependent transport characterization reveals that such excellent C2H4/C2H6 kinetic separation is attained by the enhancement in size discrimination‐based energetic selectivity. Our hybrid multi‐ligand approach can offer a useful tool for the fine‐tuning of molecular structures and textural properties of other metal organic frameworks.
Amine-functionalized zeolite imidazolate frameworks (ZIF) are known to improve the mixed matrix membranes (MMM) separation performances for CO2/CH4 applications. In this study, 3,5-diamino-1,2,4-triazole, a ligand with -NH2 functionality and uncoordinated -NH group, was used in the postsynthetic modification of dual metal Zn/Co-ZIF for partial substitution of 2-methylimidazole to obtain a biligand Zn/Co-ZIF (Zn/Co-TZ1h) with retained crystallinity, tunable pore size and enhanced CO2 adsorption capacity. A series of mixed matrix membranes were then fabricated at a single concentration (7.5 wt %) of parent Zn/Co-ZIF or Zn/Co-TZ1h in 6FDA-ODA or Matrimid polyimides to compare the effect of modified ZIF to its unmodified analogue on the MMM properties and CO2/CH4 separation performance. Zn/Co-TZ1h MMM showed enhanced mechanical properties and better filler integration into the polymer matrix as a result of better interfacial interactions via hydrogen bonding while retaining the same thermal stability as Zn/Co-ZIF MMM. Moreover, the combination of ZIF gate size control, improved size discrimination, and specific chemical interaction gave the NH2-functionalized Zn/Co-ZIF MMM the possibility to significantly overcome the CO2/CH4 separation performance of the pure polymer. Postsynthetic modification of ZIF by amine-functionalized ligands can be an effective strategy to improve the filler/polymer interface quality resulting in improved MMM separation properties.
A high-quality mixed matrix membrane (MMM) with high flux and separation factor is fostered to enhance ethanol pervaporation. In this study, a fluorinated and defect-free ZIF-8/PDMS membrane was prepared by the covalent bonding among fluoromonomer, ZIF-8 particles and PDMS using a one-pot method. ZIF-8 is first modified with 3-amino-1,2,4-triazole (Atz) to graft –NH2 groups, and then modified with glycidyl methacrylate (GMA). This was achieved by the amine-epoxide addition reaction (named GZIF-8) to facilitate covalent bonding with methacrylate-functionalized PDMS, where the interfacial compatibility ZIF-8 and PDMS is improved. Moreover, 1H,1H,2H,2H-perfluorooctyl methacrylate (13F) as F-monomer is introduced into the membrane formation process by the polymerization of methacrylate groups among 13F, ZIF-8 and PDMS, where a fluorinated structure with high hydrophobicity and low surface energy is formed. The pervaporation performance for a 5 wt% ethanol solution at 60 °C shows that the resulting MMM has a high separation factor of 9.5 and total flux of 1681 g m⁻² h⁻¹ under the optimized parameters of 3 wt% GZIF-8 loading and 12 wt% 13F amounts.
Today, the new emergence of metal-organic frameworks (MOFs), a new class of highly porous crystalline nanomaterials, has been gaining momentous popularity in the gas adsorption research. As advanced organic-inorganic hybrid solids, MOFs exhibit a string of fascinating properties hardly found in traditional materials, notably the unprecedentedly high designability and huge porosity. These advanced crystalline solids have been tailored with superior performance to the adsorption of different targeted gaseous pollutants. The present work provides a summary on the structural features and unique properties of MOFs, and their effective roles in the purification of different categories of gaseous pollutants. By relating to the governing adsorption mechanism, the innovative strategies for the specific design of MOFs for performance enhancement will be discussed from the perspective of stability enhancement, pore surface functionalization, pore geometry control, and composite fabrication. The regeneration steps and multicyclic operation, along with the opportunities and future prospects will be highlighted.
A transition between a micron-leaf-like structure (ZIF-L) at room temperature to the nano-zeolitic imidazolate framework-8 (n-ZIF-8) was produced by using a water-based synthesis without modulating agents. Polymorphisms of ZIF structures were produced in an hour by mixing varying molar ratios of 2-methylimidazole and zinc nitrate hexahydrate (8:1, 21:1, and 35:1). The polymorphic phase transition of the ZIFs was identified using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and surface and pore characteristics from a nitrogen adsorption analyzer. The sizes of the particles range from micron to nano (ZIF-L = 2 µm, n21ZIF-8 = 400 nm, and n35ZIF-8 = 100 nm). The n35-ZIF-8 has amongst the highest surface area of any ZIF-8 currently reported, with approximately 1776 m²g⁻¹ and is thermally stable up to 400 °C. Meanwhile, n21ZIF-8 demonstrated the greatest CO2 absorption capacity by absorbing up to 22.71 mmolg⁻¹ of CO2 at 273 K.
Molecular sieving is based on mobility differences of species under extreme confinement, i.e. within pores of molecular dimensions. The pore properties of a material determine its separation efficiency, while pore network engineering provides a way to optimize the sieving performance. Unlike rigid and structurally limited carbon and zeolite molecular sieves, metal organic frameworks (MOFs) offer flexible networks with unlimited pore tailoring possibilities, by using different linkers, functional groups and metals/clusters. Nevertheless, knowledge-based pore optimization towards highly selective materials is hampered by the complex relationship between structural modifications and molecular diffusivity. Machine learning (ML) approaches can elucidate this correlation, but pertinent research in MOFs has so far focused solely on sorption properties. Herein, we report the first ML-assisted work towards understanding how the replacement of basic MOF building units affects the pore structure and consequently the molecular diffusivity. The ML approach developed is general; the work is however focused on zeolitic-imidazolate frameworks (ZIFs) with SOD topology. Since there is no database of relevant ZIF variations, we constructed a new ensemble of 72 existing and new ZIFs through systematic sub-unit replacement, developed a force-field for each of these structures and performed molecular dynamics (MD) simulations on fully flexible systems to calculate framework properties and the diffusivity of different molecules (ranging from helium to n-butane). Based on this new database, a predictive multi-step ML model was developed and trained. The model can rapidly and efficiently estimate the diffusivity of molecules in any possible ZIF structure with SOD topology by using readily accessible input information.
To promote CO2/N2 selectivity of MOF (metal organic framework)-on-MOF hybrids, ZIF-8 (Zeolitic imidazolate frameworks-8) @NH2-MIL-125 (Materials of Institute Lavoisier-125) with ordered hierarchically-porous structures were originally fabricated and in-situ loaded as nanofillers in mixed matrix membranes (MMMs) to efficiently separate CO2 from N2 based on selection-diffusion-selection mechanism. The guest ZIF-8 nanoparticles (theoretical pore size = 0.34 nm) were uniformly grown on surfaces of the host NH2-MIL-125 nanoparticles and acted as molecular sieves owing to its small pore size, which kept larger N2 molecules (theoretical kinetic diameter = 0.36 nm) out and allowed smaller CO2 molecules (theoretical kinetic diameter = 0.33 nm) to pass through, while the host NH2-MIL-125 with relatively large pores (theoretical pore size = 0.60 nm) provided low-resistance channels for rapid CO2 transfer. The CO2/N2 adsorption selectivity of [email protected]2-MIL-125 heterostructures exhibited 12% and 300% higher than that of NH2-MIL-125 and ZIF-8, respectively. The Pebax-based MMMs loaded with [email protected]2-MIL-125 nanofillers had an increased CO2/N2 ideal selectivity by 42% and 61% compared to that of [email protected]2-MIL-125 and [email protected], respectively.
The separation of ethane/ethene mixtures (as well as other paraffin/olefin mixtures) is one of the most important but challenging processes in the petrochemical industry. In this work, we report the synthesis of ZIF-318, isostructural to ZIF-8 but built from the mixed linkers of 2-methylimidazole (L1) and 2-trifluoromethylimidazole (L2) (ZIF-318 = [(Zn(L1)(L2)]n. The synthesis has been optimized to proceed without ZnO-formation. Using only the L2 linker under solvothermal conditions afforded ZnO-embedded in the H-bonded and non-porous coordination polymer ZnO@[Zn2(L2)2(HCOO)(OH)]n. The slight differences in the size of the substituents (-CH3 vs -CF3) and possibly in combination with different electronic inductive effects led to small but significant changes to the pore size and properties respectively, though the effective pore opening (aperture) size of ZIF-318 remained the same in comparison with ZIF-8. ZIF-318 is chemically (boiling water, methanol, benzene, and wide pH range at room temperature for 1 day), thermally (up to 310 °C) stable, and more hydrophobic than ZIF-8 which is proven by contact angle measurement. ZIF-318 can be activated for N2, CO2, CH4, H2, ethane, ethane, propane, and propene gases sorptions. Consequently, in breakthrough experiments, the ethane/ethene mixtures can be separated.
Metal–organic framework (MOF) membranes have received increasing attention as adsorbents, yet single phase MOF membranes have certain limitations, which frustrate their capacity performance. In this work a MOF composite membrane was successfully prepared by a facile and green strategy through reasonable design. At first, a defect-free ZIF-8 membrane was fabricated on an ionic liquid modified pencil bar by a solvothermal method. Then, a novel poly(ethylenglycol) functionalized ZIF-8 composite membrane (ZIF-8/PEG-NH2) was prepared through a flexible coordination-based post-synthetic modification strategy. We found that reaction time and temperature were two crucial factors for successfully fabricating well-defined ZIF-8/PEG-NH2 membrane. Besides, the adsorption of phenolic endocrine disruptors (e.g., 4-nonylphenol) on original ZIF-8 membrane and ZIF-8/PEG-NH2 membrane was investigated, and the good adsorption selectivity of ZIF-8/PEG-NH2 membrane towards 4-nonylphenol was demonstrated, with high adsorption capacity and fast adsorption dynamics. Excitingly, such ZIF-8/PEG-NH2 membrane was successfully employed for the selective detection of 4-nonylphenol from environmental water samples, demonstrating its great application potential in environmental monitoring.
Zeolitic imidazolate frameworks (ZIFs), a subclass of metal–organic frameworks
(MOFs) built with tetrahedral metal ions and imidazolates, offer
permanent porosity and high thermal and chemical stabilities. While ZIFs
possess some attractive physical and chemical properties, it remains important
to enhance their functionality for practical application. Here, an overview
of the extensive strategies which have been developed to improve the
functionality of ZIFs is provided, including linker modifications, functional
hybridization of ZIFs via the encapsulation of guest species (such as metal
and metal oxide nanoparticles and biomolecules) into ZIFs, and hybridization
with polymeric matrices to form mixed matrix membranes for industrial gas
and liquid separations. Furthermore, the developed strategies for achieving
size and shape control of ZIF nanocrystals are considered, which are important
for optimizing the textural characteristics as well as the functional performance
of ZIFs and their derived materials/hybrids. Moreover, the recent
trends of using ZIFs as templates for the derivation of nanoporous hybrid
materials, including carbon/metal, carbon/oxide, carbon/sulfide, and carbon/
phosphide hybrids, are discussed. Finally, some perspectives on the potential
future research directions and applications for ZIFs and ZIF-derived materials
are offered.
Bridging ligand replacement in zeolitic imidazolate frameworks, ZIF-8 and ZIF-67, by 1,2,3-triazole was investigated. A complete substitution of 2-methylimidazole by 1,2,3-triazole resulted in a topological transformation of the parent framework from a sodalite (SOD) network to a diamond (DIA) network.
The burgeoning field of metal-organic frameworks or porous coordination polymers has received increasing interest in recent years. In the last decade these microporous materials have found several applications including storage and separation of gases, sensors, catalysis and functional materials. In order to better design new metal-organic frameworks and porous coordination polymers with specific functionalities a fundamental issue is to achieve a basic understanding of the relationship between molecular parameters and structures, preferred adsorption sites and properties by using using modern theoretical methods. The focus of this mini-review is a description of the potential and emerging applications of metal-organic frameworks.
A series of well-defined hard-soft-hard triblock copolymers were synthesized by Ru-based atom transfer radical polymerization (ATRP) (MWD < 1.26) in order to examine their electromechanical properties under electric fields. The obtained methacrylate based triblock copolymers consisted of poly(dodecyl methacrylate) (PDMA) soft middle block segments and three different hard block segments with poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PtBMA), and their random copolymers (PMTDTMTs). Polar acidified triblock copolymers were also prepared by deprotecting tert-butyl groups in tBMA-incorporating hard block segments through simple thermal treatment at 200 °C for 120 min, which in situ gave poly(methacrylic acid) (PMAA) and its random copolymers (PAMDMA) in the hard block segments. SAXS and AFM studies indicated that these triblock copolymers showed well-organized phase separations with different domain sizes, which were strongly dependent on the amount of bulky PtBMA or polar PMAA in the hard block segments. In addition, these triblock copolymers had a variety of morphologies affecting their mechanical (elastic modulus) and electrical (dielectric constant) properties, leading to a tuning of their electromechanical properties. The transverse strains of these triblock random copolymers as a function of an applied electric field indicated that the PTMDMT series possessed the best electromechanical properties, exhibiting an 11-fold enhancement relative to the corresponding acidified polymer PAMDMA at 50 Vpp μm⁻¹ due to a dramatic decrease of the elastic modulus from 4.04 to 0.05 MPa in spite of an increase of the dielectric constant from 3.6 to 5.1. In situ SAXS analysis under an electric field showed that these bulk strains originated from nano-structured microdomain changes.
Zeolitic imidazolate frameworks (ZIFs) represent a new and special class of metal organic frameworks comprised of imidazolate linkers and metal ions, with structures similar to conventional aluminosilicate zeolites. Their intrinsic porous characteristics, abundant functionalities as well as exceptional thermal and chemical stabilities, have led to a wide range of potential applications for various ZIF materials. Explosive research activities ranging from synthesis approaches to attractive applications of ZIFs have been emerged in this rapidly developing field in the past 5 years. In this review, the development and recent progress towards the different synthesis strategies to generate both powder and membrane/film-based ZIF materials are analysed and summarised. Their attractive and potential applications in gas separation, catalysis, sensing and electronic devices, and drug delivery in the past years are discussed and reviewed. In addition, the prospect and potential new development of ZIF materials are presented.
This contribution serves as an update to a previous review (Polym. Chem. 2010, 1, 17–36) and highlights recent applications of thiol–ene ‘click’ chemistry as an efficient tool for both polymer/materials synthesis as well as modification. This current contribution covers examples from the literature published up to ca. mid 2013. It is not intended to be exhaustive but rather serves to highlight many of the new and exciting applications where researchers have applied thiol–ene chemistry in advanced macromolecular engineering and materials chemistry.
Metal-organic frameworks (MOFs) are hybrid porous materials with many potential applications, which intimately depend on the presence of chemical functionality either at the organic linkers and/or at the metal nodes. Functionality that cannot be introduced into MOFs directly via de novo syntheses can be accessed through post-synthesis modification (PSM) on the reactive moieties of the linkers and/or nodes without disrupting the metal-linker bonds. Even more intriguing methods that go beyond PSM are herein termed building block replacement (BBR) which encompasses (i) solvent-assisted linker exchange (SALE), (ii) non-bridging ligand replacement, and (iii) transmetalation. These one-step or tandem BBR processes involve exchanging key structural components of the MOF, which in turn should allow for the evolution of protoMOF structures (i.e., the utilization of a parent MOF as a template) to design MOFs composed of completely new components, presumably via single crystal to single crystal transformations. The influence of building block replacement on the stability and properties of MOFs will be discussed, and some insights into their mechanistic aspects are provided. Future perspectives providing a glimpse into how these techniques can lead to various unexplored areas of MOF chemistry are also presented.
Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic
and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical
stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage,
and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to
expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical
composition and shape of building units can be multiply varied within a particular structure already exist and may lead to
materials that offer a synergistic combination of properties.
A cross-platform program, VESTA, has been developed to visualize both structural and volumetric data in multiple windows with tabs. VESTA represents crystal structures by ball-and-stick, space-filling, polyhedral, wireframe, stick, dot-surface and thermal-ellipsoid models. A variety of crystal-chemical information is extractable from fractional coordinates, occupancies and oxidation states of sites. Volumetric data such as electron and nuclear densities, Patterson functions, and wavefunctions are displayed as isosurfaces, bird's-eye views and two-dimensional maps. Isosurfaces can be colored according to other physical quantities. Translucent isosurfaces and/or slices can be overlapped with a structural model. Collaboration with external programs enables the user to locate bonds and bond angles in the `graphics area', simulate powder diffraction patterns, and calculate site potentials and Madelung energies. Electron densities determined experimentally are convertible into their Laplacians and electronic energy densities.
A well-defined PNIPAM-PS star block copolymer with a porphyrin core was synthesized by a reversible addition–fragmentation chain-transfer (RAFT) process, and was found to efficiently capture and decompose environmentally toxic organic materials such as benzene, toluene, ethylbenzene, and xylene (BTEX) in water under UV irradiation and was easily recycled by filtration after simple thermal treatment.
We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order N-atoms(3) operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ''metric'' and a special ''preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order N-atoms(2) scaling is found for systems up to 100 electrons. If we take into account that the number of k points can be implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
The method of dispersion correction as an add-on to standard Kohn-Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C(6) coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.
Various failure modes derived from the electrochemical migration (ECM) through the dielectric polymer layers have been considered critical issues in the electronic devices. Herein, we for the first time suggested the rationally designed epoxy/zeolitic imidazolate framework-8 (ZIF-8) nanocomposite materials for efficient suppression of copper ion migration based on the plausible reaction mechanisms of metal metathesis addressed by sequential cleaving and ligating between metal ions (Zn²⁺ and Cu²⁺) and 2-methylimidazole (2-mim) ligands. The fabrication process for epoxy/ZIF-8 (EZ) nanocomposites was first examined to optimize the crosslinking system. The capability of the metal ion capture in the EZ nanocomposites was examined using the aqueous solution containing Cu²⁺ ions. In addition, the ECM suppression properties were evaluated using the thermal humidity bias (THB) model testing. The representative model investigations with the EZ nanocomposites exhibited substantially enhanced copper ion adsorption and suppression of copper migration in comparison to those of epoxy. Hence, the EZ nanocomposites can be one promising material to alleviate the undesired ECM behavior in electronic device applications.
The metal-organic framework (MOF), ZIF-67 with different morphologies was synthesized via a solvent-induced method at room temperature. The photocatalytic performances towards the reduction of CO2 were evaluated by using ZIF-67 as cocatalyst cooperating with ruthenium-based complex as photosensitizer. It has been demonstrated that the two-dimensional ZIF-67 with leaf-like morphology exhibited the best photocatalytic activity and stability due to the highest CO2 adsorption capability and efficient electron transfer from the excited [Ru(bpy)3]2+ to ZIF-67.
Mixed matrix membranes (MMMs) provide an efficient implementation that overcomes the bottleneck of individual inorganic or polymeric membrane for gas separation, but still face challenges. Here, we put forward a strategy by using in situ synthesized polymer grafted metal organic frameworks (MOFs) to eliminate both interfacial and carrier problems existing in the MMMs. Specially, polyethyleneimine (PEI) grafted ZIF-8 (PEI-g-ZIF-8) was in situ synthesized by using Zn2+, 2-methylimidazole and hyperbranched PEI through a rapid room-temperature method. The chemical composition and porous structure of PEI-g-ZIF-8 were investigated by Fourier transform infrared spectroscopy, powder X-ray diffraction, N2 adsorption-desorption measurement, etc. The results indicated that the synthesized PEI-g-ZIF-8 achieves an enlarged pore volume and aminated surface. The improved interfacial compatibility between PEI-g-ZIF-8 nanoparticles and poly(vinylamine) (PVAm) was confirmed through high-sensitivity differential scanning calorimetry and zeta potential measurements. According to the CO2/gas separation tests, the MMMs incorporating with PEI-g-ZIF-8 achieved 1990 GPU of CO2 permeance and 79.9 of selectivity for CO2/N2 (15/85 vol.%) separation, and 1790 GPU of CO2 permeance and 40.7 of selectivity for CO2/CH4 (10/90 vol.%) separation, under 0.30 MPa gas pressure.
This review explores the features and corresponding application of ZIF-67 and its derivatives. Thermally and chemically stable zeolitic imidazolate framework (ZIF) materials has received extensive research and application. In particular, ZIF-67 can be synthesized by facile and environmentally friendly organic synthesis. The nanostructures and mean particle sizes of ZIF-67 can be adjusted by controlling experimental conditions carefully. The resulting ZIF-67 possesses the characteristics of tunable pore aperture, high stable structure, catalytic activity and so on. Futhermore, by combining the advantages of ZIF-67 and various components or structures, the resulting compounds have a potential better performance than that of pure ZIF-67. Therefore, ZIF-67 and its derivatives have aroused great interest of scientists and have the potential to be applied to gas adsorption, molecular separation, electrochemistry, catalysts and so on.
Highly permeable and selective, as well as plasticization-resistant membranes are desired as promising alternatives for cost- and energy-effective CO2 separation. Here, robust mixed-matrix membranes based on an amino-functionalized zeolitic imidazolate framework ZIF-7 (ZIF-7-NH2 ) and crosslinked poly(ethylene oxide) rubbery polymer are successfully fabricated with filler loadings up to 36 wt%. The ZIF-7-NH2 materials synthesized from in situ substitution of 2-aminobenzimidazole into the ZIF-7 structure exhibit enlarged aperture size compared with monoligand ZIF-7. The intrinsic separation ability for CO2 /CH4 on ZIF-7-NH2 is remarkably enhanced as a result of improved CO2 uptake capacity and diffusion selectivity. The incorporation of ZIF-7-NH2 fillers simultaneously makes the neat polymer more permeable and more selective, surpassing the state-of-the-art 2008 Robeson upper bound. The chelating effect between metal (zinc) nodes of fillers and ester groups of a polymer provides good bonding, enhancing the mechanical strength and plasticization resistance of the neat polymer membrane. The developed novel ZIF-7 structure with amino-function and the resulting nanocomposite membranes are very attractive for applications like natural-gas sweetening or biogas purification.
Metal–organic frameworks (MOFs) as porous fillers possessing molecular sieving properties have been combined with polymers to give mixed-matrix membranes (MMMs) with enhanced separation performance. This field of research has produced a large number of different membranes and many MOF/polymer combinations have been tested and reported to show potential application to industrial gas separation. Although MOFs have been proposed as novel additives with high porosity and tunable pore size, which were supposed to outperform other porous fillers, due to restrictions in separation performance of the filler and challenges concerning the compatibility of polymer and MOF, only a small fraction of these works report both improved permeability and selectivity. In this review these challenges are set into the context of MOF synthesis and membrane fabrication, by the choice of appropriate polymer/MOF combinations, utilization of the MOF functional sites, modification of the MOF surface chemistry or pore texture and size, and also targeted influence of the size and shape of the filler particles. The effect of the highlighted MOF additives on the gas separation performance is analyzed and discussed by comparison of the gas permeability and selectivity to outline strategies by which high performing MMMs can be achieved by accessing the full potential of the porous MOF fillers.
Aza-Michael reaction is a simple and accessible addition reaction performed at moderate temperature, possibly without a catalyst and without releasing by-products. Its versatility allows for the design of specific structures thanks to the availability of a multitude of Michael acceptors and Michael donors. The reaction rate of the aza-Michael reaction can be improved by adding different co-reactants (polar protic solvents, catalysts) and/or adjusting the external energy sources (e.g. moderate to high temperatures or high pressures). Here, we show that this addition reaction is efficient for modifying or curing silicon-containing molecules, oligomers and polymers. The pros and cons of applying the aza-Michael reaction to silicon-containing molecules (including alkoxysilanes and PDMS) are highlighted. A large variety of intermediates such as coupling agents, reactive diluents, and sol-gel precursors prepared by the aza-Michael reaction are presented. Finally, applications of these, including products ranging from functional silicone intermediates to soft (unfilled) elastomers, are reported.
Recently, the ZIF-67 molecular sieve has emerged as an excellent substitute for the ZIF-8 counterpart due to its potentially high C3H6/C3H8 separation performance. Here, for the first time, we investigated the effect of ZIF-67 in mixed matrix membranes (MMMs) for C3H6/C3H8 separations by integrating them into 6FDA-DAM polymer matrix. The 6FDA-DAM/ZIF-67 (80/20 wt/wt) MMMs achieved an ideal selectivity of 29.9 and a separation factor of 19 under single and equimolar mixed gas conditions, respectively, at 35 °C. The intrinsic C3H6/C3H8 separation performance of ZIF-67 was estimated from our experimental transport results based on the Maxwell model. The calculation demonstrated its superior C3H6/C3H8 selectivity of 251, which is twice of that of ZIF-8, supporting the high molecular sieving capacity of ZIF-67 containing MMMs. Moreover, a thorough investigation on the temperature-dependent gas transports elucidated that the energetic selectivity is a major contributor for the high C3H6/C3H8 diffusivity selectivity in ZIF-67 containing MMMs. However, the minimum aperture size of ZIF-67 (4.5 Å), derived by the cuboid dimensions of C3H6 and C3H8, substantially sacrificed the C3H6/C3H8 entropic selectivity of ZIF-67 containing MMMs. Lastly, the defect-free incorporation of ZIF-67 nanoparticles into 6FDA-DAM polymer matrix effectively retarded physical aging process, maintaining the excellent separation performance of the associated MMMs for 75 days.
Tuning the pore structure of zeolitic imidazolate frameworks (ZIFs) enables unique control of their material properties. In this work, we used computational methods to examine the gate structure of ZIF-8 tuned by substitution terminal groups. The substitution position and electron affinity of the added groups were shown to be key factors in gate size. Electrostatic interactions are responsible for the variation in gate opening. These results suggest that the post-modification of terminal group in ZIFs can be used to finely tune the pore gate, opening up new strategies in the design of ZIFs with desired properties.
The electron-density distribution in a prototypical porous coordination polymer ZIF-8 has been obtained in an approach combining high-resolution X-ray diffraction data and Invariom refinement. In addition, the periodic quantum-chemical calculation has been used to describe the theoretical density features of ZIF-8 in the same geometry (m1) and also in a "high-pressure" form of ZIF-8 (m2) characterized by conformational change with respect to the methylimidazolate linker. A thorough comparison of the electronic and electrostatic properties in two limiting structural forms of ZIF-8 proposes additional aspects on diffusion and adsorption processes occurring within the framework. The dimensions of the four-membered (FM) and six-membered (SM) apertures of the β cage are reliably determined from the total electron-density distribution. The analysis shows that FM in m2 becomes competitive in size to the SM aperture and should be considered for the diffusion of small molecules and cations. Bader's topological analysis (quantum theory of atoms in molecules) shows similar properties of both ZIF-8 forms. On the other hand, analysis of their electrostatic properties reveals tremendous differences. The study suggests exceptional electrostatic flexibility of the ZIF-8 framework, where small conformational changes lead to a significantly different electrostatic potential (EP) distribution, a feature that could be important for the function and dynamics of the ZIF-8 framework. The cavity surface in m1 contains 38 distinct regions with moderately positive, negative, or neutral EP and weakly positive EP in the cavity volume. In contrast to m1, the m2 form displays only two regions of different EP, with the positive one taking the whole cavity surface and the strong negative one localized entirely in the FM apertures. The EP in the cavity volume is also more positive than that in m1. A pronounced influence of the linker reorientation on the EP of the ZIF-8 forms is related to the high symmetry of the system and to an amplification of the electrostatic properties by cooperative effects of the proximally arranged structural fragments.
The incorporation of 2,3-dimercaptoterephthalate (thiocatecholate, tcat) into a highly robust UiO-type metal-organic framework (MOF) has been achieved via postsynthetic exchange (PSE). The anionic, electron-donating thiocatecholato motif provides an excellent platform to obtain site-isolated and coordinatively unsaturated soft metal sites in a robust MOF architecture. Metalation of the thiocatechol group with palladium affords unprecedented Pd-mono(thiocatecholato) moieties within these MOFs. Importantly, Pd-metalated MOFs are efficient, heterogeneous, and recyclable catalysts for regioselective functionalization of sp(2) C-H bond. This material is a rare example of chelation-assisted C-H functionalization performed by a MOF catalyst.
Industrial separation processes comprise approximately 10 % of the global energy demand, driven largely by the utilization of thermal separation methods (e.g., distillation). Significant energy and cost savings can be realized using advanced separation techniques such as membranes and sorbents. One of the major barriers to acceptances of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. One promising class of emerging materials is zeolitic imidazolate frameworks (ZIFs), an important thermally and chemically stable subclass of metal organic frameworks (MOFs). The objectives of this paper are (i) to provide a current understanding of the synthetic methods that enable the immense tunability of ZIFs, (ii) to identify areas of success and areas for improvement when ZIFs are used as adsorbents, (iii) to identify areas of success and areas for improvement in ZIF membranes. A review is given of the state-of-the-art in ZIF synthesis procedures and novel ZIF formation pathways as well as their application in energy efficient separations.
We studied molecular sieving properties of zeolitic imidazolate framework-8 (ZIF-8) by estimating the thermodynamically corrected diffusivities of probe molecules at 35 °C. From helium (2.6 Å) to iso-C4H10 (5.0 Å), the corrected diffusivity drops 14 orders of magnitude. Our results further suggest that the effective aperture size of ZIF-8 for molecular sieving is in the range of 4.0 to 4.2 Å, which is significantly larger than the XRD-derived value (3.4 Å) and between the well-known aperture size of zeolite 4A (3.8 Å) and 5A (4.3 Å). Interestingly, because of aperture flexibility, the studied C4 hydrocarbon molecules that are larger than this effective aperture size still adsorb in the micropores of ZIF-8 with kinetic selectivities for iso-C4H8/iso-C4H10 of 180 and n-C4H10/iso-C4H10 of 2.5 × 106. These unexpected molecular sieving properties open up new opportunities for ZIF materials for separations that cannot be economically achieved by traditional microporous adsorbents such as synthetic zeolites.
Imidazolate framework ZIF-8 is modified via postsynthetic method using etheylenediamine to improve its adsorption performance toward CO2. Results show that the BET surface area of the modified ZIF-8 (ED-ZIF-8) increases by 39%, and its adsorption capacity of CO2 per surface area is almost two times of that on ZIF-8 at 298 K and 25 bar. H2O uptake on the ED-ZIF-8 become obviously lower compared to the ZIF-8. The ED-ZIF-8 selectivity for CO2/N2 adsorption gets significantly improved, and is up to 23 and 13.9 separately at 0.1 and 0.5 bar, being almost twice of those of the ZIF-8. The isosteric heat of CO2 adsorption (Qst) on the ED-ZIF-8 becomes higher, while Qst of N2 gets slightly lower compared to those on the ZIF-8 Furthermore, it suggests that the postsynthetic modification of the ZIF-8 not only improves its adsorption capacity of CO2 greatly, but also enhances its adsorption selectivity for CO2/N2/H2O significantly. ©2013 American Institute of Chemical Engineers AIChE J, 59: 2195–2206, 2013
A series of ABA triblock copolymers of methyl methacrylate (MMA) and dodecyl methacrylate (DMA) [poly(MMA-b-DMA-b-MMA)] (PMDM) were synthesized by Ru-based sequential living radical polymerization. For this, DMA was first polymerized from a difunctional initiator, ethane-1,2-diyl bis(2-chloro-2-phenylacetate) with combination of RuCl2(PPh3)3 catalyst and nBu3N additive in toluene at 80 °C. As the conversion of DMA reached over about 90%, MMA was directly added into the reaction solution to give PMDM with controlled molecular weight (Mw/Mn ≤ 1.2). These triblock copolymers showed well-organized morphologies such as body centered cubic, hexagonal cylinder, and lamella structures both in bulk and in thin film by self-assembly phenomenon with different poly(methyl methacrylate) (PMMA) weight fractions. Obtained PMDMs with 20–40 wt % of the PMMA segments showed excellent electroactive actuation behaviors at relatively low voltages, which was much superior compared to conventional styrene-ethylene-butylene-styrene triblock copolymer systems due to its higher polarity derived from the methacrylate backbone and lower modulus. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
ZIF-8 has been rapidly developed as a potential candidate for CO2 capture due to its low density, high surface area, and robust structure. Considering the electron-donating effect of amino functional groups, amino-modification is expected to be an efficient way to improve CO2 adsorption of ZIF-8. In this work, grand canonical Monte Carlo (GCMC) simulation was performed to study the CO2 adsorption isotherm based on ZIF-8, ZIF-8-NH2, and ZIF-8-(NH2)2. ZIF-8 was synthesized and CO2 adsorption isotherms based on ZIF-8 was measured. The experimental surface area, pore volume, and CO2 adsorption isotherm were used to validate the force field. Adsorptive capacity of ZIF-8-NH2, and ZIF-8-(NH2)2 were first estimated. The GCMC simulation results indicated that the order of increasing CO2 capacity of the ZIF-8 in the lower pressure regime is: ZIF-8 < ZIF-8-NH2 < ZIF-8-(NH2)2, and in the high pressure is: ZIF-8 < ZIF-8-(NH2)2 < ZIF-8-NH2. New adsorption sites can be generated with the existence of-NH2 groups. In addition, for non-modified and amino-modified ZIF-8, it was the first time to use density functional theory (DFT) calculations to investigate their CO2 adsorption sites and CO2 binding energies. The present work indicates that appropriate amine-functionalized can directly enhanced CO2 capacity of ZIF-8.
The separation of olefins from paraffins is energy intensive, and consequently polymer membrane based separations have been considered as an attractive alternative. Although much research has been conducted on polymer membranes for the C3H6/C3H8 separation in recent years, no comprehensive review exists that considers and evaluates all of the available literature data. A review is necessary in order to define the challenges that must be overcome to achieve adequate separation performance using polymer membranes. The goal of this paper is to present the experimentally observed C3H6/C3H8 upper bound based on available literature data, as well as C3H6/C3H8 permeation measurements reported herein. A mathematical prediction of the C3H6/C3H8 upper bound curve was also developed, and it compares very well to the most credible experimentally observed C3H6/C3H8 upper bound.
Herein, we report a general postsynthetic exchange (PSE) approach to introduce a redox-active transition metal, specifically Mn(II), into "inert" zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs). It is shown that metal ion PSE occurs in ZIF-71 (RHO topology) and ZIF-8 (SOD topology) under ambient conditions. The metal exchanged ZIFs are the first porous, Mn(II)-based ZIFs and a rare example of ZIFs with two transition metal centers in a single lattice. Exchanged materials are characterized by scanning electron microscopy-energy dispersed X-ray spectroscopy (SEM-EDX), aerosol time-of-flight mass spectrometry (ATOFMS), X-ray fluorescence spectroscopy (XRF), and Brunauer-Emmett-Teller (BET) surface area analysis. In addition, stepwise "tandem" PSE strategies are described to exchange of metal ions and organic linkers consecutively in ZIFs. These findings are important for probing the chemical dynamics of ZIFs, despite their high crystallinity and robustness, and inspire the more widespread use of PSE to prepare multimetallic and multifunctional MOFs.
Mixed-matrix membranes (MMMs) with metal-organic frameworks (MOFs) as additives (fillers) exhibit enhanced gas permeabilities and possibly also selectivities when compared to the pure polymer. Polyimides (Matrimid®) and polysulfones are popular polymer matrices for MOF fillers. Presently investigated MOFs for MMMs include [Cu(SiF(6))(4,4'-BIPY)(2)], [Cu(3)(BTC)(2)(H(2)O)(3)] (HKUST-1, Cu-BTC), [Cu(BDC)(DMF)], [Zn(4)O(BDC)(3)] (MOF-5), [Zn(2-methylimidazolate)(2)] (ZIF-8), [Zn(purinate)(2)] (ZIF-20), [Zn(2-carboxyaldehyde imidazolate)(2)] (ZIF-90), Mn(HCOO)(2), [Al(BDC)(μ-OH)] (MIL-53(Al)), [Al(NH(2)-BDC)(μ-OH)] (NH(2)-MIL-53(Al)) and [Cr(3)O(BDC)(3)(F,OH)(H(2)O)(2)] (MIL-101) (4,4'-BIPY = 4,4'-bipyridine, BTC = benzene-1,3,5-tricarboxylate, BDC = benzene-1,4-dicarboxylate, terephthalate). MOF particle adhesion to polyimide and polysulfone organic polymers does not represent a problem. MOF-polymer MMMs are investigated for the permeability of the single gases H(2), N(2), O(2), CH(4), CO(2) and of the gas mixtures O(2)/N(2), H(2)/CH(4), CO(2)/CH(4), H(2)/CO(2), CH(4)/N(2) and CO(2)/N(2) (preferentially permeating gas named first). Permeability increases can be traced to the MOF porosity. Since the porosity of MOFs can be tuned very precisely, which is not possible with polymeric material, MMMs offer the opportunity of significantly increasing the selectivity compared to the pure polymeric matrix. Additionally in most of the cases the permeability is increased for MMM membranes compared to the pure polymer. Addition of MOFs to polymers in MMMs easily yields performances similar to the best polymer membranes and gives higher selectivities than those reported to date for any pure MOF membrane for the same gas separation. MOF-polymer MMMs allow for easier synthesis and handability compared to pure MOF membranes.
An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way. The method allows high-quality first-principles molecular-dynamics calculations to be performed using the original fictitious Lagrangian approach of Car and Parrinello. Like the LAPW method it can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function. The augmentation procedure is generalized in that partial-wave expansions are not determined by the value and the derivative of the envelope function at some muffin-tin radius, but rather by the overlap with localized projector functions. The pseudopotential approach based on generalized separable pseudopotentials can be regained by a simple approximation.
Using the difference Fourier analysis of neutron powder diffraction data along with first-principles calculations, we reveal detailed structural information such as methyl group orientation, hydrogen adsorption sites, and binding energies within the nanopore structure of ZIF8 (Zn(MeIM)(2)). Surprisingly, the two strongest adsorption sites that we identified are both directly associated with the organic linkers, instead of the ZnN4 clusters, in strong contrast to classical MOFs, where the metal-oxide clusters are the primary adsorption sites. These observations are important and hold the key to optimizing this new class of ZIF materials for practical hydrogen storage applications. Finally, at high concentration H-2-loadings, ZIF8 structure is capable of holding up to 28 H-2 molecules (i.e., 4.2 wt %) in the form of highly symmetric novel three-dimensional interlinked H-2-nanoclusters with relatively short H-2-H-2 distances compared to solid H-2. Hence, ZIF compounds with robust chemical stability can be also an ideal template host-material to generate molecular nanostructures with novel properties.
Replacing the organic linker in sodalite-type zinc 2-methylimidazolate by 3-methyl-1,2,4-triazolate produces isomorphous pure triazolate or solid solution imidazolate/triazolate frameworks functionalized by uncoordinated nitrogen donors. These show dramatically enhanced and fine-tuned sorption performance for practical adsorptive applications.
Metal-organic frameworks (MOFs) are an important class of hybrid inorganic-organic materials. In this tutorial review, a progress report on the postsynthetic modification (PSM) of MOFs is provided. PSM refers to the chemical modification of the MOF lattice in a heterogeneous fashion. This powerful synthetic approach has grown in popularity and resulted in a number of advances in the functionalization and application of MOFs. The use of PSM to develop MOFs with improved gas sorption, catalytic activity, bioactivity, and more robust physical properties is discussed. The results reported to date clearly show that PSM is an important approach for the development and advancement of these hybrid solids.
Zeolites are one of humanity’s most important synthetic products. These aluminosilicate-based materials represent a large segment of the global economy. Indeed, the value of zeolites used in petroleum refining as catalysts and in detergents as water softeners is estimated at $350 billion per year. A major current goal in zeolite chemistry is to create a structure in which metal ions and functionalizable organic units make up an integral part of the framework. Such a structure, by virtue of the flexibility with which metal ions and organic moieties can be varied, is viewed as a key to further improving zeolite properties and accessing new applications.
The modification of metal-organic frameworks (MOFs) in a postsynthetic scheme is discussed in this critical review. In this approach, the MOF is assembled and then modified with chemical reagents with preservation of the lattice structure. Recent findings show amide couplings, isocyanate condensations, 'click' chemistry, and other reactions are suitable for postsynthetic modification (PSM). In addition, a number of MOFs, from IRMOF-3 to ZIF-90, are amenable to PSM. The generality of PSM, in both scope of chemical reactions and range of suitable MOFs, clearly indicates that the approach is broadly applicable. Indeed, the rapid increase in reports on PSM demonstrates this methodology will play an increasingly important role in the development of MOFs for the foreseeable future (117 references).
We present ab initio quantum-mechanical molecular-dynamics calculations based on the calculation of the electronic ground state and of the Hellmann-Feynman forces in the local-density approximation at each molecular-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using subspace alignment. This approach avoids the instabilities inherent in quantum-mechanical molecular-dynamics calculations for metals based on the use of a fictitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows us to perform simulations over several picoseconds.
Generalized gradient approximations (GGA{close_quote}s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. {copyright} {ital 1996 The American Physical Society.}
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