Crystals as molecules: postsynthesis covalent functionalization of zeolitic imidazolate frameworks

A new crystalline zeolitic imidazolate framework, ZIF-90, was prepared from zinc(II) nitrate and imidazolate-2-carboxyaldehyde (ICA) and found to have the sodalite-type topology. Its 3D porous framework has an aperture of 3.5 A and a pore size of 11.2 A. The pores are decorated by the aldehyde functionality of ICA which has allowed its transformation to the alcohol functionality by reduction with NaBH4 and its conversion to imine functionality by reaction with ethanolamine to give ZIF-91 and ZIF-92, respectively. The N2 adsorption isotherm of ZIF-90 shows a highly porous material with calculated Langmuir and BET surface areas of 1320 and 1270 m2 g(-1). Both functionalized ZIFs retained high crystallinity and in addition ZIF-91 maintained permanent porosity (surface areas: 1070 and 1010 m2 g(-1)).     

3D Electron-Rich ZIF-67 Coordination Compounds Based on 2-Methylimidazole: Synthesis,Characterization and Effect on Thermal Decomposition of RDX,HMX, CL-20, DAP-4 and AP

ZIF-67 is a three-dimensional zeolite imidazole ester framework material with a porous rhombic dodecahedral structure, a large specific surface area and excellent thermal stability. In this paper, the catalytic effect of ZIF-67 on five kinds of energetic materials, including RDX, HMX, CL-20, AP and the new heat-resistant energetic compound DAP-4, was investigated. It was found that when the mass fraction of ZIF-67 was 2%, it showed excellent performance in catalyzing the said compounds. Specifically, ZIF-67 reduced the thermal decomposition peak temperatures of RDX, HMX, CL-20 and DAP-4 by 22.3 °C, 18.8 °C, 4.7 °C and 10.5 °C, respectively. In addition, ZIF-67 lowered the low-temperature and high-temperature thermal decomposition peak temperatures of AP by 27.1 °C and 82.3 °C, respectively. Excitingly, after the addition of ZIF-67, the thermal decomposition temperature of the new heat-resistant high explosive DAP-4 declined by approximately 10.5 °C. In addition, the kinetic parameters of the RDX+ZIF-67, HMX+ZIF-67, CL-20+ZIF-67 and DAP-4+ZIF-67 compounds were analyzed. After the addition of the ZIF-67 catalyst, the activation energy of the four energetic materials decreased, especially HMX+ZIF-67, whose activation energy was approximately 190 kJ·mol⁻¹ lower than that reported previously for HMX. Finally, the catalytic mechanism of ZIF-67 was summarized. ZIF-67 is a potential lead-free, green, insensitive and universal EMOFs-based energetic burning rate catalyst with a bright prospect for application in solid propellants in the future.     

Amorphization of the prototypical zeolitic imidazolate framework ZIF-8 by ball-milling

We report the rapid amorphization of the prototypical substituted zeolitic imidazolate framework, ZIF-8, by ball-milling. The resultant amorphous ZIF-8 (a(m)ZIF-8) possesses a continuous random network (CRN) topology with a higher density and a lower porosity than its crystalline counterpart. A decrease in thermal stability upon amorphization is also evident.     

Metal–Organic Framework Crystal–Glass Composite Membranes with Preferential Permeation of Ethane

Metal–organic framework (MOF) glass is an easy to process and self-supported amorphous material that is suitable for fabricating gas separation membranes. However, MOF glasses, such as ZIF-62 and ZIF-4 have low porosity, which makes it difficult to obtain membranes with high permeance. Here, a self-supported MOF crystal–glass composite (CGC) membrane was prepared by melt quenching a mixture of ZIF-62 as the membrane matrix and ZIF-8 as the filler. The conversion of ZIF-62 from crystal to glass and the simultaneous partial melting of ZIF-8 facilitated by the melt state of ZIF-62 make the CGC membrane monolithic, eliminating non-selective grain boundaries and improving selectivity. The thickness of CGC membrane can be adjusted to fabricate a membrane without the need of a support substrate. CGC membranes exhibit a C₂H₆ permeance of 41 569 gas permeation units (GPU) and a C₂H₆/C₂H₄ selectivity of 7.16. The CGC membrane has abundant pores from the glassy state of ZIF-62 and the crystalline ZIF-8, which enables high gas permeance. ZIF-8 has preferential adsorption for C₂H₆ and promotes C₂H₆ transport in the membrane, and thus the GCG membrane exhibits ultrahigh C₂H₆ permeance and good C₂H₆/C₂H₄ selectivity.     

Opening the gate: framework flexibility in ZIF-8 explored by experiments and simulations

ZIF-8 is a zeolitic imidazole-based metal-organic framework with large cavities interconnected by narrow windows. Because the small size of the windows, it allows in principle for molecular sieving of gases such as H(2) and CH(4). However, the unexpected adsorption of large molecules on ZIF-8 suggests the existence of structural flexibility. ZIF-8 flexibility is explored in this work combining different experimental techniques with molecular simulation. We show that the ZIF-8 structure is modified by gas adsorption uptake in the same way as it is at a very high pressure (i.e., 14,700 bar) due to a swing effect in the imidazolate linkers, giving access to the porosity. Tuning the flexibility, and so the opening of the small windows, has a further impact on the design of advanced molecular sieving membrane materials for gas separation, adjusting the access of fluids to the porous network.     

Mn3O4/金属有机骨架材料活化过一硫酸盐降解水中难降解有机污染物罗丹明B

锰氧化物是一类环境友好型材料,可以有效活化过一硫酸盐(PMS)降解水中难降解有机污染物.但是锰氧化物在单独使用时容易出现严重的团聚现象,进而降低其对PMS的催化活性,不利于水中污染物的降解.因此,人们通常将锰氧化物负载于多孔的载体材料上.金属有机骨架材料(MOFs)因具有巨大的比表面积和温和的制备条件而广受关注.本文采用温和的溶剂热法首次成功制备了Mn3O4与MOF的复合材料Mn3O4/ZIF-8,并通过X射线衍射、扫描电镜、透射电镜、X射线光电子能谱和红外光谱等手段对其进行了表征,探究了Mn3O4/ZIF-8的形成机理.考察了Mn3O4负载量对Mn3O4/ZIF-8催化性能的影响,以及Mn3O4/ZIF-8投加量、PMS投加量、初始罗丹明B(RhB)浓度和反应温度对RhB去除效果的影响,同时探究了Mn3O4/ZIF-8的重复使用性能,分析了RhB的降解途径、去除机理以及最终的降解副产物.结果表明,边长为50?150 nm的片状Mn3O4均匀分散在粒径为250 nm的六边形ZIF-8的外表面;当Mn3O4负载量为0.5时,所制备的复合材料0.5-Mn/ZIF-120活化PMS对RhB的降解效果最好,反应60 min时RhB降解率可达到99.4%,且Mn的浸出量可以忽略不计.在该体系中,RhB的降解过程符合一级动力学反应方程,其降解速率常数随催化剂和PMS投加量的增加、反应温度的提高和初始RhB浓度的减小而增大.在0.5-Mn/ZIF-120催化剂投加量为0.4 g/L、PMS投加量为0.3 g/L、初始RhB浓度为10 mg/L、初始溶液pH为5.18及室温(23oC)条件下,水中RhB的降解率在40 min时即可达到98%.淬灭实验表明,该体系中HO?起主导作用,而其主要来源于活化PMS所产生的SO4–?.此外,通过简单的二次水冲洗方式对0.5-Mn/ZIF-120催化剂进行回收使用,在连续5次循环使用后仍然可见较高的催化活性和稳定性,RhB的去除率保持在96%以上,且Mn的浸出百分率始终低于5%.     

Bifunctional 3D-MOF-based nanoprobes for electrochemical sensing and nanozyme enhanced with peroxidase mimicking for colorimetric detection of acetaminophen

The outgrowth of the zeolitic imidazole framework (ZIF-67) with substantial benefits was significantly used in the present study. The attractive properties of ZIF-67 are envisioned to develop a dual-functional sensing platform as electrochemical and colorimetric for acetaminophen detection. Co-ZIF-67 was developed as a synthesis-controlled material via three different preparation techniques as ZIF-67-C, ZIF-67-A, and ZIF-67-H. ZIF-67-C prepared via simple co-precipitation strategy in room temperature acquired rhombic dodecahedral structure with increased electrocatalytic activity. ZIF-67-C nanozyme exhibits enzymatic activity with intrinsic peroxidase mimicking and higher electron affinity than ZIF-67-A and ZIF-67-H. The well-developed ZIF-67-C without further aggregation and a steadily build structure resulted in an enhanced response. While the higher chance of aggregation and irregular arrangements of ZIF-67-A and ZIF-67-H resulted in lower performance toward acetaminophen detection. Moreover, the absorption of 3, 3 ', 5, 5' – tetramethylbenzidine (TMB) molecules could lower the diffusion distance leading to improved peroxidase mimicking activity. Nanozyme ZIF-67-C effectively oxidizes TMB to TMBox product and with hydroxyl radicals (^?OH) generation from H₂O₂ decomposition. Michaelis-Menten and Lineweaver Burk's model was estimated. The LOD was 0.014 μM (electrochemical) and 0.034 μM (calorimetric). The real samples as river water and lake water show good recovery in both sensing modes. The high surface area, improved electrical conductivity, high porosity of the prepared ZIF-67-C sample is beneficial for dual sensing applications and determined to be used in several applications.     

Synthesis of Cu^Ⅱ/ZIF-8 Metal-organic Framework Catalyst and Its Application in the Aerobic Oxidation of Alcohols

The tliree-dimensional copper-doped zeolitic imidazolate framework ZIF-8(Cu^Ⅱ/ZIF-8) was prepared by a metal ion exchange process, using reaction of three different copper salts, zinc nitrate hexahydrate[Zn(NO)3·6H2O] and 2?methylimidazole(2-MelM) under nitrogen atmosphere at the room temperature. The TEM and PXRD results indicated that the morphology of Cu^Ⅱ/ZIF-8 was rhombic dodecahedron and the structure was intact after copper was doped into the porous ZIF-8. The synthesized Cu(NO3)2/ZIF-8 heterogeneous catalyst showed an excellent activity for tlie aerobic oxidation of primary alcohols employing molecular oxygen as oxidant. Moreover, tlie Cu(NO3)2/ZIF-8 heterogeneous catalyst can cycled 15 times without leaching of copper.     

ZIF-8对向列相液晶电-光性能的提升

ZIF-8（沸石咪唑酯骨架结构材料）是一种金属有机物骨架结构材料,因其极高的比表面积、出色的热稳定性而被广泛应用于各种性质研究中。ZIF-8通过传统的水热法在甲醇溶液中合成,其颗粒尺寸约为250nm,形貌为菱形十二面体。研究发现,合成的ZIF-8材料具有良好的热稳定性及相当大的比表面积。将其掺杂进液晶中会增强液晶的电-光性能,增强效果与掺杂浓度有关。在向列相液晶4-氰基-4'-戊基联苯（5CB）中,ZIF-8可以吸附杂质离子,抑制屏蔽效应,最终使液晶驱动电压降低,响应加快。在掺杂浓度为0.05%（w,质量分数）时,液晶体系的电-光性能改善最明显,阈值电压（V_th）最小达到0.92 V,饱和电压（V_sat）达到1.31 V,响应时间仅为10.04 ms。而当掺杂浓度大于0.05%（w）时,ZIF-8在液晶盒中发生团聚,影响液晶分子的有序排布,同时吸附杂质离子减少,不利于液晶电-光性能的改善。     

A Combined Experimental and Computational Study on the Adsorption Sites of Zinc-Based MOFs for Efficient Ammonia Capture

Ammonia (NH₃) is a common pollutant mostly derived from pig manure composting under humid conditions, and it is absolutely necessary to develop materials for ammonia removal with high stability and efficiency. To this end, metal–organic frameworks (MOFs) have received special attention because of their high selectivity of harmful gases in the air, resulting from their large surface area and high density of active sites, which can be tailored by appropriate modifications. Herein, two synthetic metal–organic frameworks (MOFs), 2-methylimidazole zinc salt (ZIF-8) and zinc-trimesic acid (ZnBTC), were selected for ammonia removal under humid conditions during composting. The two MOFs, with different organic linkers, exhibit fairly distinctive ammonia absorption behaviors under the same conditions. For the ZnBTC framework, the ammonia intake is 11.37 mmol/g at 298 K, nine times higher than that of the ZIF-8 framework (1.26 mmol/g). In combination with theoretical calculations, powder XRD patterns, FTIR, and BET surface area tests were conducted to reveal the absorption mechanisms of ammonia for the two materials. The adsorption of ammonia on the ZnBTC framework can be attributed to both physical and chemical adsorption. A strong coordination interaction exists between the nitrogen atom from the ammonia molecule and the zinc atom in the ZnBTC framework. In contrast, the absorption of ammonia in the ZIF-8 framework is mainly physical. The weak interaction between the ammonia molecule and the ZIF-8 framework mainly results from the inherent severely steric hindrance, which is related to the coordination mode of the imidazole ligands and the zinc atom of this framework. Therefore, this study provides a method for designing promising MOFs with appropriate organic linkers for the selective capture of ammonia during manure composting.     

Efficient oxidation of ethylbenzene catalyzed by cobalt zeolitic imidazolate framework ZIF-67 and NHPI

Efficient catalytic oxidation of ethylbenzene to acetophenone was realized using the catalytic system of cobalt zeolitic imidazolate framework ZIF-67/N-hydroxyphthalimide （NHPI） under mild conditions. 95.2% conversion of ethylbenzene with 90.3% selectivity to acetophenone could be obtained at 373 K under 0.3 MPa 02 for 9 h. The results show that there exists synergetic effect between ZIF-67 and NHPI. 1-Phenylethyl hydroperoxide （PEHP） was generated via a radical process involving the hydrogen abstraction from ethylbenzene by phthalimide N-oxyl, and subsequently effectively decomposed to acetophenone by ZIF-67.     

Growing ZIF-8 Seeds on Charged COF Substrates toward Efficient Propylene-Propane Separation Membranes

We report a covalent organic framework (COF) induced seeding strategy to fabricate metal–organic framework (MOF) membranes. Contrary to graphene oxide nuclei-depositing substrate, COF substrate has uniform pore size, high microporosity and abundant functional groups. We designed a series of charged COF nanosheets to induce the formation of ZIF-8@COF nanosheet seeds with high aspect ratio over 150, which were readily processed into a compact and uniform seed layer. The resulting ZIF-8 membranes with thickness down to 100 nm exhibit an ultrahigh C₃H₆/C₃H₈ separation performance and superior long-term stability. Our strategy is also validated by fabricating ultrathin ZIF-67 and UiO-66 membranes.     

多孔材料表面修饰聚酰亚胺非对称混合基质膜对CO2/N2和CO2/CH4的气体分离

兼具高通量和高选择性的气体分离膜是研究膜分离材料的目标.采用相转化法制备了聚酰亚胺非对称膜,并将其作为基底膜材料,分别在其表面修饰掺有金属有机框架材料Cu₃(BTC)₂ (1, 3, 5-均苯三甲酸合铜),沸石咪唑酯骨架材料ZIF-8以及镁铝水滑石MgAl-LDHs的聚酰胺酸溶液,经热亚胺化后制成非对称混合基质膜.研究了该系列非对称混合基质膜的结构特性和对CO₂、CH₄和N₂气体分离性能;考察了ZIF-8的掺杂量对非对称混合基质膜透气性能的影响.结果表明非对称聚酰亚胺膜的表面修饰可有效地改变膜的表面性质,掺杂ZIF-8的非对称混合基质膜气体的透气性能和选择性都增加,且掺杂量为5% (w)时CO₂/N₂和CO₂/CH₄的理想选择性分别高达24和83,为合成高效的CO₂分离膜提供了借鉴.     

Structural evolution of zeolitic imidazolate framework-8

We report the structural evolution of zeolitic imidazolate framework-8 (ZIF-8) as a function of time at room temperature. We have identified the different stages of ZIF-8 formation (nucleation, crystallization, growth, and stationary periods) and elucidated its kinetics of transformation. We hypothesize that the observed semicrystalline-to-crystalline transformation may take place via solution- and solid-mediated mechanisms, as suggested by the observed phase transformation evolution and Avrami's kinetics, respectively. A fundamental understanding of ZIF-8 structural evolution as demonstrated in this study should facilitate the preparation of functional metal-organic framework phases with controlled crystal size and extent of crystallinity.     

In situ high pressure study of ZIF-8 by FTIR spectroscopy

ZIF-8 as a promising storage material was investigated at high pressures up to ~39 GPa by in situ FTIR spectroscopy for the first time. Structural modifications are found to be reversible in a low-pressure region but irreversible in a high-pressure region. Overall, the ZIF-8 framework exhibits an unusual chemical stability even under extreme compression.     

Supramolecular Materials Chemistry in the MacLachlan Group

This invited Team Profile was created by the MacLachlan group at the University of British Columbia . They recently published an article on the uniform growth of a metal–organic framework, ZIF-8, on the surface of individual cellulose nanocrystals (CNCs). After the ZIF-8/CNC fibers had been coated with a microporous organic polymer, the ZIF-8 was removed to leave a microporous polymer with CNCs encapsulated in a ship-in-a-bottle architecture. This material proved to be effective for CO₂ fixation. “Uniform Growth of Nanocrystalline ZIF-8 on Cellulose Nanocrystals: Useful Template for Microporous Organic Polymers”, K. Cho, L. J. Andrew, M. J. MacLachlan, Angew. Chem. Int. Ed. 2023 , e202300960 .     

Facile Synthesis of Metal–Organic Framework (ZIF-11) and Ag NPs Encapsulated-ZIF-11 Composite as an Effective Heterogeneous Catalyst for Photodegradation of Methylene Blue

Facile synthesis of metal–organic framework based on zeolitic imidazolate (ZIF-11) has been optimized to get a material with rho topology. For the first time AgNPs in various dosing amounts (using 150, 300 and 500 μL of its suspension in methanol) have been successfully encapsulated within ZIF-11 matrix at room temperature using binary solvent (methanol and toluene) yielding novel multi-core-shell AgNPs@ZIF-11 (AZ1, AZ2 and AZ3) composites. Encapsulation of AgNPs (particle size: 11.76 ± 2.3 nm) has been confirmed by TEM and ultraviolet diffuse reflectance spectroscopic (UV-DRS) analysis. The lowering of band gap of ZIF-11 from 4.36 to 4.21 eV indicates the micro-environment of AgNPs within ZIF-11 framework, which has also been ensured by XPS analysis. ZIF-11 and AgNPs@ZIF-11 composites are highly stable up to 500 °C under air and N₂ atmosphere. It has been found that AZ1 composite exhibits excellent photocatalytic activity (almost 100% degradation) toward MB (1.6 mg/L) at pH ≥ 8. Further, various factors such as loading amount of AgNPs (150, 300 and 500 μL suspension in methanol), amount of catalysts (5 mg, 10 mg and 15 mg) and concentration (1.6 mg L⁻¹, 3.19 mg L⁻¹ and 6.38 mg L⁻¹) of methylene blue (MB) dye during photodegradation experiments have been investigated. The capacious achievement of AZ1 composite is its reusability and recyclability; it can be reutilized up to three cycles with the same efficiency (100%) while under fourth and fifth cycle, it can degrade off 92.12% and 72.75% MB, respectively. AgNPs may act as a mediator to promote the quick transfer of photo-induced electrons and electron–hole pairs separation in ZIF-11. This work opens a new type of easily fabricated core-shell composites utilizing ZIF-11 for wastewater remediation process.     

Development of a force field for zeolitic imidazolate framework-8 with structural flexibility

A force field is developed for zeolitic imidazolate framework-8 (ZIF-8) with structural flexibility by combining quantum chemical calculations and classical Amber force field. The predicted crystalline properties of ZIF-8 (lattice constants, bond lengths, angles, dihedrals, and x-ray diffraction patterns) agree well with experimental results. A structural transition from crystalline to amorphous as found in experiment is observed. The mechanical properties of ZIF-8 are also described fairly well by the force field, particularly the Young's modulus predicted matches perfectly with measured value. Furthermore, the heat capacity of ZIF-8 as a typical thermophysical property is predicted and close to experimental data available for other metal-organic frameworks. It is revealed the structural flexibility of ZIF-8 exerts a significant effect on gas diffusion. In rigid ZIF-8, no diffusive behavior is observed for CH(4) within the simulation time scale of current study. With the structural flexibility, however, the predicted diffusivities of CH(4) and CO(2) are close to reported data in the literature. The density distributions and free energy profiles of CH(4) and CO(2) in the pore of ZIF-8 are estimated to analyze the mechanism of gas diffusion.     

Metal-Organic Framework Glass Catalysts from Melting Glass-Forming Cobalt-Based Zeolitic Imidazolate Framework for Boosting Photoelectrochemical Water Oxidation

Sluggish oxygen evolution kinetics and serious charge recombination restrict the development of photoelectrochemical (PEC) water splitting. The advancement of novel metal–organic frameworks (MOFs) catalysts bears practical significance for improving PEC water splitting performance. Herein, a MOF glass catalyst through melting glass-forming cobalt-based zeolitic imidazolate framework (Co-a_gZIF-62) was introduced on various metal oxide (MO: Fe₂O₃, WO₃ and BiVO₄) semiconductor substrates coupled with NiO hole transport layer, constructing the integrated Co-a_gZIF-62/NiO/MO photoanodes. Owing to the excellent conductivity, stability and open active sites of MOF glass, Co-a_gZIF-62/NiO/MO photoanodes exhibit a significantly enhanced photoelectrochemical water oxidation activity and stability in comparison to pristine MO photoanodes. From experimental analyses and density functional theory calculations, Co-a_gZIF-62 can effectively promote charge transfer and separation, improve carrier mobility, accelerate the kinetics of oxygen evolution reaction (OER), and thus improve PEC performance. This MOF glass not only serves as an excellent OER cocatalyst on tunable photoelectrodes, but also enables promising opportunities for PEC devices for solar energy conversion.     

Metal–organic frameworks as efficient materials for drug delivery: Synthesis,characterization, antioxidant,anticancer, antibacterial and molecular docking investigation

Metal–organic framework (MOF) nano particles are a class of promising porous nano materials for biomedical applications. Owing to its high loading potential and pH-sensitive degradation, most promising of the MOFs is the zeolitic imidazolate crystal framework (ZIF-8), a progressive useful material for small molecule distribution. Doxorubicin (DOX), designated as a classical drug, was jobwise entrapped in ZIF-8 nano particles. ZIF-8 nano particles, as a novel carrier, were used to monitor the release of the anticancer drug DOX and prevent it from dissipating before reaching its goal. ZIF-8 nano particles with encapsulated DOX (DOX@ZIF-8) can be synthesized in a single pot by incorporation of DOX into the reaction mixture. MOFs and the designed drug delivery (DOX@ZIF-8) system were characterized by Fourier transfer infrared, scanning electron microscopy, N₂ sorption isotherm and X-ray diffraction. The impact of MOFs and the engineered drug delivery system on the viability of human breast and liver cancer cell lines was evaluated. The loaded drug was released at pH 5 faster than at pH 7.4. The nano particles of ZIF-8 showed low cytotoxicity, while DOX@ZIF-8 showed high cytotoxicity to HepG-2 and MCF-7 cells compared with free DOX at the equivalent concentration of DOX of >12.5 μg/ml. These findings indicate that DOX@ZIF-8 nano particles are a promising method for the delivery of cancer cells to drugs. Furthermore, ZIF-8, DOX and encapsulated DOX@ZIF-8 compounds were screened for their potential antibacterial activities against pathogenic bacteria compared with standard antibiotics by the agar well diffusion technique. The results demonstrate that the DOX@ZIF-8 exhibits a strong inhibition zone against Gram-negative strains (Escherichia coli) in comparison with the reference drug gentamycin. The docking active site interactions were evaluated to predict the binding between DOX with the receptor of breast cancer 3hb5-oxidoreductase and liver cancer 2h80-lipid binding protein for anticancer activity.