Common Metal-organic Frameworks Research Articles

Selective adsorption of mercury ion from water by a novel functionalized magnetic Ti based metal-organic framework composite

In the context of industrialization and severe wastewater pollution, mercury ions pose a major threat due to their high toxicity. However, traditional adsorbents and common metal-organic framework (MOF) materials have limited effectiveness. This study focuses on combining magnetic materials with functionalized titanium-based MOF composite (SNN-MIL-125(Ti)@Fe3O4) to improve mercury ion adsorption. Through comprehensive characterization and analysis, the adsorption performance and mechanism of the material were studied. The optimal adsorption of the material was achieved at pH 5, exhibiting a pseudo-second-order adsorption model and the Hill theoretical capacity of 668.98 mg/g. Hill and Tempkin models confirmed the presence of chemical and physical adsorption sites on the material surface. Thermodynamic experiments showed a spontaneous endothermic process. Despite the presence of interfering ions, the material exhibited high selectivity for mercury ions. After four cycles, adsorption performance decreased by only 8%, indicating excellent reusability. Nitrogen- and sulfur-containing functional groups played a key role in mercury ion adsorption. In conclusion, SNN-MIL-125(Ti)@Fe3O4, as a magnetic MOF adsorption material, showed potential for effective remediation of mercury-contaminated wastewater. This study contributes to the development of efficient adsorption materials and enhances the understanding of their mechanism.

Localized surface plasmon resonance sensing of SO2 and H2S using zeolitic imidazolate framework-8

A localized surface plasmon resonance (LSPR) sensor for SO2 and H2S has been developed by coating a Au nanopattern with zeolitic imidazolate framework-8 (ZIF-8), which is one of the most common metal–organic frameworks. SO2 and H2S were detected by the change in the absorbance at a certain wavelength in the LSPR spectrum. The sensitivity to SO2 and H2S was enhanced by ZIF-8 and with increasing relative humidity, and 0.1–20 ppm SO2 and 0.1–10 ppm H2S could be detected within 5 min at 70% relative humidity. The ZIF-8-coated sensor was more sensitive to SO2. The changes in the absorbance increased during exposure to SO2 and H2S, and only slightly decreased for SO2 and remained almost constant for H2S after stopping exposure. These responses indicate that the sensor can measure the integrated concentrations of SO2 and H2S. If the sensor was not exposed to ≥ 20 ppm SO2 or ≥ 10 ppm H2S, the sensitivity and LSPR spectrum of the sensor could be recovered approximately a dozen times by heating it at 200 °C in air. This study demonstrates the potential of metal–organic-framework-coated LSPR sensors for highly sensitive detection of SO2 and H2S.

Facile in Situ Polymer Functionalization Approach for Constructing Water-Resistant Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have been widely investigated for their use in separation, such as gas adsorption or biotechnology. However, numerous MOFs are unstable in aqueous environment or humid conditions, significantly hindering their practical application. While current methods for enhancing MOF water stability can largely decrease the pore structural parameters, herein, we proposed a strategy of in situ trace polymer functionalization for enhancing the MOF stability and demonstrated that the water stability of four common MOFs can be enhanced greatly by incorporating hydrophobic PSfCOOH molecules into the framework through a one-step synthesis. A series of investigations into the local chemical structure and bonding environment suggest that the enhanced water stability arises from the construction of hydrophobic microenvironments and the steric hindrance around the metal sites. The prepared Cu-BTC-PSfCOOH remained intact after being immersed in water for even 10 days, preserving 90% of its original pore structural parameter, such as Brunauer–Emmett–Teller (BET) surface areas. Moreover, 88% of the initial BET surface areas can be maintained after one-day immersion in 6 M HCl solution. The strategy is also demonstrated to be efficient in enhancing the water stability of three other typical MOFs, showing good universality in constructing water-resistant MOFs.

Internalization of the Metal-Organic Framework MIL-101(Cr)-NH2 by a Freshwater Alga and Transfer to Zooplankton.

The common metal-organic framework (MOF) MIL-101(Cr)-NH2 has attracted considerable attention due to its great potential applications in the environmental field. Nevertheless, its behavior and fate in aquatic systems are unknown. This study quantified and visualized the interactions of MIL-101(Cr)-NH2 with the freshwater phytoplanktonic alga Chlamydomonas reinhardtii and its potential trophic transfer to zooplankton. The unicellular alga absorbed and accumulated the MOF by surface attachment, forming agglomerates and eventually cosettling out from water. Bioimaging revealed that MIL-101(Cr)-NH2 was internalized by the algal cells and mainly occurred in the pyrenoid. Without algae in a freshwater system, MIL-101(Cr)-NH2 was ingested by Daphnia magna, showing steadily increasing concentrations approaching 1-9% of dry body weight. Addition of algae substantially suppressed D. magna uptake of MIL-101(Cr)-NH2 by 63.8-97.9%. Such inhibition could be explained by the competitive uptake of MOF by the algae and the inductive effects of algal food on MOF elimination by D. magna. The MOF (≤1 mg/L) ingested by D. magna was centered in the gut regions, whereas large MOF or algae-MOF aggregates were adsorbed onto the carapace and appendages, including the antennae, at 10 mg/L. Overall, the algae were the major targets for MIL-101(Cr)-NH2, with nearly all algal cells settling out at 10 mg/L within 24 h. The possibility of trophic transfer of MIL-101(Cr)-NH2 to D. magna in aquatic systems with algae present was limited due to its low accumulation potential and short retention time in D. magna.

UiO-66-NH2: An easily attainable and label-free turn-on probe for facile fluorescence sensing of alkaline phosphatase

Alkaline phosphatase (ALP) is now a well acknowledged indicator for diverse clinical diseases correlated with its abnormal expression. Compared to the assays by traditional and lately emerging methods, the fluorescent (FL) sensing, especially in the turn-on mode, has become more favored due to its simplicity, low cost, and high sensitivity and precision. However, the feasible FL probes are still limited and suffering from poor biological compatibility, complex preparation, additional modification or function-alization. Herein, we found that one common metal–organic framework, UiO-66-NH2 at nanoscale, could act as a new and label-free FL probe for facile sensing of ALP in the turn-on mode, based on the simple aid by phenyl phosphate which could be hydro-lyzed by ALP, with the product of phosphate ion enhancing the FL emission of UiO-66-NH2 via simple adsorption. Unlike many other FL probes in the turn-on mode, it was unnecessary to quench the FL of the probes in advance, greatly simplifying the sensor design. Moreover, by use of a new method based on dielectric barrier discharge (DBD), the UiO-66-NH2 could be prepared in 10 min, much shorter than that (usually hours) for preparing most other FL probes for ALP assay. The limit of detection was 0.4 U L-1, superior or at least rivalrous to the previously reported ones, and the ALP assay was also accomplished for real serum samples, with the analytical results highly consistent with those obtained by the clinical procedures, revealing its high practical utility.

Metal-organic frameworks properties from hybrid density functional approximations.

The chemical versatility and modular nature of Metal-Organic Frameworks (MOFs) make them unique hybrid inorganic-organic materials for several important applications. From a computational point of view, ab initio modeling of MOFs is a challenging and demanding task, in particular, when the system reaches the size of gigantic MOFs as MIL-100 and MIL-101 (where MIL stands for Materials Institute Lavoisier) with several thousand atoms in the unit cell. Here, we show how such complex systems can be successfully tackled by a recently proposed class of composite electronic structure methods revised for solid-state calculations. These methods rely on HF/density functional theory hybrid functionals (i.e., PBEsol0 and HSEsol) combined with a double-zeta quality basis set. They are augmented with semi-classical corrections to take into account dispersive interactions (D3 scheme) and the basis set superposition error (gCP). The resulting methodologies, dubbed "sol-3c," are cost-effective yet reach the hybrid functional accuracy. Here, sol-3c methods are effectively applied to predict the structural, vibrational, electronic, and adsorption properties of some of the most common MOFs. Calculations are feasible even on very large MOFs containing more than 2500 atoms in the unit cell as MIL-100 and MIL-101 with reasonable computing resources. We propose to use our composite methods for the routine in silico screening of MOFs targeting properties beyond plain structural features.

Applications of nanocomposites based on zeolitic imidazolate framework-8 in photodynamic and synergistic anti-tumor therapy.

Due to the limitations resulting from hypoxia and the self-aggregation of photosensitizers, photodynamic therapy (PDT) has not been applied clinically to treat most types of solid tumors. Zeolitic imidazolate framework-8 (ZIF-8) is a common metal–organic framework that has ultra-high porosity, an adjustable structure, good biocompatibility, and pH-induced biodegradability. In this review, we summarize the applications of ZIF-8 and its derivatives in PDT. This review is divided into two parts. In the first part, we summarize progress in the application of ZIF-8 to enhance PDT and realize theranostics. We discuss the use of ZIF-8 to avoid the self-aggregation of photosensitizers, alleviate hypoxia, increase the PDT penetration depth, and combine PDT with multi-modal imaging. In the second part, we summarize how ZIF-8 can achieve synergistic PDT with other anti-tumor therapies, including chemotherapy, photothermal therapy, chemodynamic therapy, starvation therapy, protein therapy, gene therapy, and immunotherapy. Finally, we highlight the challenges that must be overcome for ZIF-8 to be widely applied in PDT. To the best of our knowledge, this is the first review of ZIF-8-based nanoplatforms for PDT.

Stability and Degradation of Metal–Organic‐Framework Films under Ambient Air Explored by Uptake and Diffusion Experiments

AbstractThe loading with guest molecules is the key feature for most applications of metal–organic frameworks (MOFs). The limited stability of MOFs against environmental factors, like humid air, is often a severe problem which hinders real‐life applications. Here, the stability of four common MOFs, UiO‐66, UiO‐67, HKUST‐1, and ZIF‐8, under long‐term exposure to humid air and under exposure to water vapor is explored. Transient uptake experiments with toluene and other volatile organic compounds as probe molecules are combined with structural investigations via X‐ray diffraction and infrared spectroscopy. In line with previous publications showing the structural stability of ZIF‐8 and UiO‐66, it is found that its uptake properties are not affected by exposure to air. On the other hand, HKUST‐1 shows clear structural decomposition in air and degradation of the uptake properties. Unexpectedly, while the diffraction and spectroscopy data of UiO‐67 do not suggest a corrosion of the structure upon air exposure, the guest‐loading data show a strong decrease of the uptake amount and a deceleration of the uptake rate. Both features strongly indicate the formation of surface barriers for the mass transfer in UiO‐67, like in HKUST‐1. The study underlines the importance of transient uptake experiments for characterizing the stability of MOF materials.

Study on preparation of metal-organic framework membrane and pore size adjustment method

Metal-organic framework materials have the advantages of large specific surface area, high porosity, strong adjustability of framework structure, adjustable chemical and thermal properties, etc., and can be used as ideal membrane materials. In this paper, the preparation methods and conditions of several common metal-organic framework materials, as well as how to adjust the pore size, are reviewed, and the advanced membrane treatment technology is prospected.

Microporous Metal-Organic Framework with a Completely Reversed Adsorption Relationship for C2 Hydrocarbons at Room Temperature.

As a new type of porous material, metal-organic frameworks (MOFs) have been widely studied in gas adsorption and separation, especially in C2 hydrocarbons. Considering the stronger interaction between the unsaturated molecules and the metal sites, and the smaller molecular size of unsaturated molecules, the usual relationship of affinities and adsorption capacities among C2 hydrocarbons in most common MOFs is C2H2 > C2H4 > C2H6. Herein, a unique microporous metal-organic framework, NUM-7a (activated NUM-7), with a completely reversed adsorption relationship for C2 hydrocarbons (C2H6 > C2H4 > C2H2) has been successfully synthesized, which breaks the traditional concept of the adsorption relationship of MOFs for C2 hydrocarbons. Based on this unique adsorption relationship, a green and simple one-step separation purification for a large amount of C2H4 can be expected to be achieved through the selective adsorption of C2H6. In addition, NUM-7a also shows good selectivities in C2H2/CO2 and CO2/CH4.

Adsorption and pH-Responsive Release of Tinidazole on Metal–Organic Framework CAU-1

Herein, a porous hydrostable metal–organic framework (MOF), CAU-1, was systematically studied for its adsorption performance of tinidazole (TNZ). Owing to the abundant −OH and −NH2 groups as well as the strong positively charged surface of the framework, the H-bond interaction and electrostatic interaction can play important roles in the adsorption process of TNZ. As a result, CAU-1 exhibits an excellent saturated adsorption capacity of TNZ (∼450 mg·g–1), superior to all of the previous reported porous adsorbents including other common MOFs. Meanwhile, the loaded TNZ molecules in CAU-1 can be released under simulated physiological conditions and the cumulative release amount can be controlled via the pH value of solution. This work demonstrates that such an MOF may be promising in TNZ removal, and rational selection of organic functional groups is an efficient strategy to design high-capacity adsorbents for the removal of antibiotics. Additionally, further study indicates that CAU-1 can serve as a pH-resp...

Biocompatible MOFs for Storage and Separation of O2: A Molecular Simulation Study

Metal organic frameworks (MOFs) are great candidates for capturing O2 due to their highly porous structures and tunable physical and chemical properties. In this study, we assessed the performance of 1525 biocompatible MOFs which have endogenous linkers and nontoxic metal centers for adsorption-based and membrane-based O2 separation and also for high-pressure O2 storage. We initially computed Henry’s constants of O2 and N2 at zero coverage and 298 K by performing Grand Canonical Monte Carlo (GCMC) simulations and estimated infinite dilution adsorption selectivities for O2/N2 mixture. We performed binary mixture GCMC simulations for the top 15 candidates at various pressures and 298 K and compared mixture adsorption selectivities with those obtained from infinite dilution. We then estimated O2 working capacities of 315 biocompatible MOFs obtained at 298 K and 140 bar for storage and 5 bar for release pressures. Our results showed that 15 biocompatible MOFs outperform gravimetric O2 working capacities of the traditional adsorbent materials such as activated carbon and NaX and some common MOFs such as NU-125 and UMCM-152 at 298 K. We finally calculated O2 and N2 permeabilities and membrane selectivities of 45 promising MOF candidates for O2/N2 separation. Seventeen biocompatible MOF membranes were identified to exceed the Robeson’s upper bound established for polymers. This computational study will be useful to identify the promising biocompatible MOFs for storage and separation of O2. The bio-MOF library constructed in this study will also guide both experimental and computational studies for design and development of biocompatible MOFs for various medical applications.

An Exceptionally Water Stable Metal-Organic Framework with Amide-Functionalized Cages: Selective CO2 /CH4 Uptake and Removal of Antibiotics and Dyes from Water.

As the main organic pollutants in wastewater, antibiotics and organic dyes are harmful to the environment and public health, and their removal is important but challenging. In this work, highly porous 3D metal-organic frameworks (MOFs) [M2 (PDAD)(H2 O)]n (PCN-124-stu; M=Cu, Zn; H4 PDAD = 5,5'-(pyridine-3,5-dicarbonyl)bis(azanediyl)diisophthalic acid) were synthesized, and PCN-124-stu(Cu) shows excellent chemical and thermal stability. PCN-124-stu(Cu) was used as a host for efficient extraction of various organic dyes, especially the large-molecule dye Coomassie brilliant blue, and fluoroquinolones from water, in comparison with five common MOFs, zeolite 13X, and activated carbon. PCN-124-stu(Cu) exhibits absolute predominance for fluoroquinolone adsorption among these microporous materials because of the H-bonds between fluoroquinolone molecules and the amide groups in the frameworks, except for MIL-100(Cr), which is a mesoporous MOF. Moreover, PCN-124-stu(Cu) could release fluoroquinolones slowly in physiological saline and retained its framework structure after four adsorption/desorption cycles. In addition, PCN-124-stu(Cu) can be used as a platform for selective adsorption of CO2 /CH4.

Pd Nanocubes@ZIF-8: Integration of Plasmon-Driven Photothermal Conversion with a Metal-Organic Framework for Efficient and Selective Catalysis.

Composite nanomaterials usually possess synergetic properties resulting from the respective components and can be used for a wide range of applications. In this work, a Pd nanocubes@ZIF-8 composite material has been rationally fabricated by encapsulation of the Pd nanocubes in ZIF-8, a common metal-organic framework (MOF). This composite was used for the efficient and selective catalytic hydrogenation of olefins at room temperature under 1 atm H2 and light irradiation, and benefits from plasmonic photothermal effects of the Pd nanocube cores while the ZIF-8 shell plays multiple roles; it accelerates the reaction by H2 enrichment, acts as a "molecular sieve" for olefins with specific sizes, and stabilizes the Pd cores. Remarkably, the catalytic efficiency of a reaction under 60 mW cm(-2) full-spectrum or 100 mW cm(-2) visible-light irradiation at room temperature turned out to be comparable to that of a process driven by heating at 50 °C. Furthermore, the catalyst remained stable and could be easily recycled. To the best of our knowledge, this work represents the first combination of the photothermal effects of metal nanocrystals with the favorable properties of MOFs for efficient and selective catalysis.

Pd Nanocubes@ZIF‐8: Integration of Plasmon‐Driven Photothermal Conversion with a Metal–Organic Framework for Efficient and Selective Catalysis

AbstractComposite nanomaterials usually possess synergetic properties resulting from the respective components and can be used for a wide range of applications. In this work, a Pd nanocubes@ZIF‐8 composite material has been rationally fabricated by encapsulation of the Pd nanocubes in ZIF‐8, a common metal–organic framework (MOF). This composite was used for the efficient and selective catalytic hydrogenation of olefins at room temperature under 1 atm H2 and light irradiation, and benefits from plasmonic photothermal effects of the Pd nanocube cores while the ZIF‐8 shell plays multiple roles; it accelerates the reaction by H2 enrichment, acts as a “molecular sieve” for olefins with specific sizes, and stabilizes the Pd cores. Remarkably, the catalytic efficiency of a reaction under 60 mW cm−2 full‐spectrum or 100 mW cm−2 visible‐light irradiation at room temperature turned out to be comparable to that of a process driven by heating at 50 °C. Furthermore, the catalyst remained stable and could be easily recycled. To the best of our knowledge, this work represents the first combination of the photothermal effects of metal nanocrystals with the favorable properties of MOFs for efficient and selective catalysis.

Using degrees of rate control to improve selective n-butane oxidation over model MOF-encapsulated catalysts: sterically-constrained Ag3Pd(111).

Metal nanoparticles encapsulated within metal organic frameworks (MOFs) offer steric restrictions near the catalytic metal that can improve selectivity, much like in enzymes. A microkinetic model is developed for the regio-selective oxidation of n-butane to 1-butanol with O2 over a model for MOF-encapsulated bimetallic nanoparticles. The model consists of a Ag3Pd(111) surface decorated with a 2-atom-thick ring of (immobile) helium atoms which creates an artificial pore of similar size to that in common MOFs, which sterically constrains the adsorbed reaction intermediates. The kinetic parameters are based on energies calculated using density functional theory (DFT). The microkinetic model was analysed at 423 K to determine the dominant pathways and which species (adsorbed intermediates and transition states in the reaction mechanism) have energies that most sensitively affect the reaction rates to the different products, using degree-of-rate-control (DRC) analysis. This analysis revealed that activation of the C-H bond is assisted by adsorbed oxygen atoms, O*. Unfortunately, O* also abstracts H from adsorbed 1-butanol and butoxy as well, leading to butanal as the only significant product. This suggested to (1) add water to produce more OH*, thus inhibiting these undesired steps which produce OH*, and (2) eliminate most of the O2 pressure to reduce the O* coverage, thus also inhibiting these steps. Combined with increasing butane pressure, this dramatically improved the 1-butanol selectivity (from 0 to 95%) and the rate (to 2 molecules per site per s). Moreover, 40% less O2 was consumed per oxygen atom in the products. Under these conditions, a terminal H in butane is directly eliminated to the Pd site, and the resulting adsorbed butyl combines with OH* to give the desired 1-butanol. These results demonstrate that DRC analysis provides a powerful approach for optimizing catalytic process conditions, and that highly selectivity oxidation can sometimes be achieved by using a mixture of O2 and H2O as the oxidant. This was further demonstrated by DRC analysis of a second microkinetic model based on a related but hypothetical catalyst, where the activation energies for two of the steps were modified.