Stability Of MOFs Research Articles

Ultra-sensitive detection of 5-fluorouracil by flow injection chemiluminescence immunoassay based on Fenton-like effect of single atom Co nanozyme

Single atom nanozymes (SAzymes) are considered as the most hopeful candidates for replacing natural enzymes. In this work, a flow-injection chemiluminescent immunoassay (FI-CLIA) based on a Fenton-like activity single atom cobalt nanozyme (Co SAzyme) was developed for the rapid and sensitive detection of 5-fluorouracil (5-Fu) in serum for the first time. Co SAzyme was prepared by an in-situ etching method at room temperature using ZIF-8 metal-organic frameworks (ZIF-8 MOFs). With excellent chemical stability and ultra-high porosity of ZIF-8 MOFs as the core, Co SAzyme presents high Fenton-like activity which can catalyze the decomposition of H2O2 to produce large amounts of superoxide radical anions, thus effectively amplifying the chemiluminescence of the Luminol-H2O2 system. In addition, carboxyl-modified resin beads were used as the substrate to load more antigens due to its advantages of good biocompatibility and large specific surface area. Under optimal conditions, the detection range of 5-Fu was 0.001–1000 ng mL−1 with a limit of detection of 0.29 pg mL−1 (S/N = 3). Furthermore, the immunosensor was successfully applied for the detection of 5-Fu in human serum samples with satisfactory results, displaying the potential application of this strategy for bioanalysis and clinical diagnosis.

Green synthesize of nano-MOF-ethylcellulose composite fibers for efficient adsorption of Congo red from water

Two novel MOF- ethyl cellulose (EC)- based nanocomposites have been designed and synthesized in water by electrospinning and applied for adsorption of congo red (CR) in water. Nano- Zeolitic Imidazolate Framework-67 (ZIF-67), and Materials of Institute Lavoisier (MIL-88A) were synthesized in aqueous solutions by a green method. To enhance the dye adsorption capacity and stability of MOFs, they have been incorporated into EC nanofiber to prepare composite adsorbents. The performance of both composites in the absorption of CR, a common pollutant in some industrial wastewaters, has then been investigated. Various parameters including initial dye concentration, the dosage of the adsorbent, pH, temperature and contact time were optimized. The results indicated 99.8 and 90.9% adsorption of CR by EC/ZIF-67 and EC/MIL-88A, respectively at pH = 7 and temperature at 25 °C after 50 min. Furthermore, the synthesized composites were separated conveniently and successfully reused five times without significant loss of their adsorption activity. For both composites, the adsorption behavior can be explained by pseudo-second-order kinetics, Intraparticular diffiusion and Elovich models demonstrated that the experimental data well matched to the pseudo-second-order kinetics. Intraparticular diffiusion model showed that the adsorption of CR on EC/ZIF-67 and EC/MIL-88a took place in one and two steps, respectively. Freundlich isotherm models and thermodynamic analysis indicated exothermic and spontaneous adsorption.

Linker mediated enhancement in reusability and regulation of Pb(II) removal mechanism of Cu-centered MOFs

Our study demonstrates improved hydrolytic stability of Cu-centered MOFs through linker selection, resulting in enhanced and selective Pb(II) removal with contrasting removal mechanisms. A simple one-pot solvothermal process was employed to synthesize Copper 1,3,5-Benzene-Tricarboxylic Acid (Cu-BTC) MOF, Copper Imidazolate (Cu-Im) MOF and Copper Nicotinic Acid (Cu-NA) MOF, respectively. The synthesis of these MOFs was confirmed using characterization techniques such as XPS, XRD, FTIR and ICP-OES. Water stability studies using experimental and modelling approaches demonstrated that substituting the 1,3,5-benzene-tricarboxylic acid linker with either imidazolate or nicotinic acid, enhanced the hydrostability of the Cu-centered MOF from under 2 h to over 48 h, while showing a high Pb(II) adsorption capacity of 492 mg g−1. This improved hydrostability was observed across acidic and basic pH and at elevated temperatures. The improved stability of Cu-Im significantly enhanced its reusability and showed Pb(II) adsorption for 3 cycles, with 99.5 % removal efficiency at the end of the 3rd cycle and a desorption efficiency of 92.7 %. The experimental data obtained were substantiated with modelling studies (density functional theory) to gain insights into the 2D structure of Cu-Im and compare the hydrolytic stability of Cu-BTC and Cu-Im. Cu-Im, when tested on textile effluent showed a Pb(II) removal efficiency of 99 % within 2 h of treatment. This study opens up the possibility of using linker selection and design as a strategy to enhance the hydrostability of Cu-centered MOFs and in the process improve its applicability for environmental remediation applications.

Benzenesulfonic acid-grafted UIO-66 with improved hydrophobicity as a stable Brønsted acid catalyst

Hydrothermal and catalytic stability of UIO-66 MOFs with defective structures are critical aspects to be considered in their catalytic applications, especially under the conditions involving water, moisture and/or heat. Here, we report a facile strategy to introduce the macromolecular acid group to UIO-66 to improve the stability of the resulting UIO-66—PhSO3H MOF in aqueous phase catalysis. In detail, UIO-66—PhSO3H was obtained by grafting benzenesulfonic acid on the surface of the pristine UIO-66 to introduce the hydrophobicity, as well as the Brønsted acidity, then assessed using catalytic hydrolysis of cyclohexyl acetate (to cyclohexanol) in water. The introduction of hydrophobic molecules to UIO-66 could prevent the material from being attacked by hydroxyl polar molecules effectively, explaining its good structural stability during catalysis. UIO-66—PhSO3H promoted the conversion of cyclohexyl acetate at ca. 87%, and its activity and textural properties were basically intact after the cyclic stability tests. The facile modification strategy can improve the hydrothermal stability of UIO-66 significantly, which can expand its catalytic applications in aqueous systems.

Electronic and Topological Properties of UIO66-ILs Interaction through a Computational Study

A high surface area adsorbent, such as MOFs, is an attractive option to evacuate heavy metals from wastewater. However, due to the possibility of the MOF structure collapsing when exposed to water, the stability and selectivity of MOFs for wastewater treatment remain a debatable task. Depending on the application, it has been shown that the consolidation of IL into MOF could improve the stability and reusability of pure MOF; nevertheless, research on the molecular interactions between the MOF framework and IL is still lacking. The stability, compatibility, and selectivity of this hybrid material are significantly influenced by the fundamental interactions between the MOFs and ILs moieties (cation and anion molecules), particularly the sorts of interactions. In this work, we focused on the topological properties of ILs and utilization of molecular docking calculations to assess the binding energy (ΔGbind) and binding affinity between UIO66 with TFSI-imidazole and TFSI-pyridinium ILs studied. The properties of ILs such as aromaticity of the structures, bond critical point (BCP), and electrostatic potential map surface were carried out using the Gaussian and Multiwfn software while the binding energies were computed using the AutoDock software to identify particular binding sites for IL toward MOF. The Autodock software's default setting was used to prepare all of the structures. To determine the binding locations of MOF, the IL was successively incorporated into the MOF pores inside the grid box of 90 x 90 x 90 Å (x, y, and z) dimensions. The results showed that both ILs; TFSI-imidazole, and TFSI-pyridinium IL, interacted favorably with the MOFs, having binding energies varying from -4.12 to -8.60 kcal mol-1. The stability of UIO66-ILs system increases with the addition of anion and cation. According to docking molecular structures, both cation and anion tend to bind in the corner of the MOF pore, which is in line with the previous work.

ZIF-8@Rhodamine B as a Self-Reporting Material for Pollutant Extraction Applications.

Herein, we have evaluated the potential of dye-encapsulation as a simple mechanism to self-report the stability of MOFs for pollutant extraction applications. This enabled the visual detection of material stability issues during the selected applications. As proof-of-concept, the zeolitic imidazolate framework (ZIF-8) material was prepared in aqueous medium and at room temperature in the presence of the dye rhodamine B. The total amount of loaded rhodamine B was determined using UV-vis spectrophotometry. The prepared dye-encapsulated ZIF-8 showed a comparable extraction performance with bare ZIF-8 for the removal of hydrophobic endocrine-disrupting phenols, such as 4-tert-octylphenol and 4-nonylphenol, and improved the extraction performance of more hydrophilic endocrine disruptors, such as bisphenol A and 4-tert-butylphenol.

Influence of ligands within Al-based metal-organic frameworks for selective separation of methane from unconventional natural gas

Efficient CH4/N2 separation from unconventional natural gas is vital for both energy recycling and climate change control. Figuring out the reason for the disparity between ligands in the framework and CH4 is the crucial problem for developing adsorbents in PSA progress. In this study, a series of eco-friendly Al-based MOFs, including Al-CDC, Al-BDC, CAU-10, and MIL-160, were synthesized to investigate the influence of ligands on CH4 separation through experimental and theoretical analyses. The hydrothermal stability and water affinity of synthetic MOFs were explored through experimental characterization. The active adsorption sites and adsorption mechanisms were investigated via quantum calculation. The results manifested that the interactions between CH4 and MOFs materials were affected by the synergetic effects of pore structure and ligand polarities, and the disparities of ligands within MOFs determined the separation efficiency of CH4. Especially, the CH4 separation performance of Al-CDC with high sorbent selection (68.56), moderate isosteric adsorption heat for CH4 (26.3 kJ/mol), and low water affinity (0.1 g/g at 40% RH) was superior to most porous adsorbents, which was attributed to its nanosheet structure, proper polarity, reduced local steric hindrance, and extra functional groups. The analysis of active adsorption sites indicated that hydrophilic carboxyl groups and hydrophobic aromatic ring were the dominant CH4 adsorption sites for liner ligands and bent ligands, respectively. The methylene groups with saturated C–H bonds enhanced the wdV interaction between ligands and CH4, resulting in the highest binding energy of CH4 for Al-CDC. The results provided valuable guidance for the design and optimization of high-performance adsorbents for CH4 separation from unconventional natural gas.

Controllable preparation of nickel cobalt manganese ternary metal-organic frameworks for high-performance supercapacitor

In this study, Ni, Co and Mn metal-organic frameworks (MOFs, Ni2Co1-XMnX-MOFs-S, X = 0, 0.25, 0.5) nanorods are successfully obtained by a one-step hydrothermal method under the aid of C12H25SO4Na (SDS). The morphology and the size of the nanorods can be controlled by changing the doping method and content of Mn, resulting in the different electrochemical performances. The study proves that SDS has a great influence on the capacitance of the ternary metal NiCoMn-MOFs. Research results show that the optimized Ni2Co0.75Mn0.25-MOFs-S displays a capacitance of 1428 F·g−1 at current density of 1 A·g−1. Meanwhile, controlling partial substitution of Mn is beneficial to improve the stability of MOFs, such as the charge-discharge cycle stability of Ni2Co0.75Mn0.25-MOFs-S is high to 83.5 % after 3000 cycles. The energy density of the asymmetric supercapacitor (Ni2Co0.75Mn0.25-MOFs-S//AC) is 38.10 Wh·kg−1 at a power density of 884.38 W·kg−1. In addition, the act of Mn on improving material stability is studied.

Thermal stability of copper-based MOF under different atmospheres

Thermal stability of copper-based MOF under different atmospheres

Effects of High Gamma Doses on the Structural Stability of Metal-Organic Frameworks.

Four different MOFs were exposed to γ rays by a cobalt-60 source reaching a maximum dose of 5 MGy. The results showed that the MIL-100 (Cr) and MIL-100 (Fe) did not exhibit obvious structural damage, suggesting their excellent radiation stability. MIL-101 (Cr) showed good radiation stability up to 4 MGy, but its structure started degrading with increasing radiation dose. Furthermore, the results showed that the structure of AlFu MOFs started to decompose at a gamma dose of 1 MGy, exhibiting a much lower tolerance to γ radiation. At this radiation energy, the dominant interaction of the gamma-ray with MOFs is the Compton effect and the radiation stability of MOFs can be improved by prolific aromatic linkers, high linker connectivity, and good crystallinity. The results of this study indicate that MIL-100 and MIL-101 MOFs have a good potential to be employed in nuclear applications, where relatively high radiation doses play a role, for example, nuclear waste treatment and radionuclides production.

Copper-Containing Polyoxometalate-Based Metal-Organic Frameworks as Heterogeneous Catalysts for the Synthesis of N-Heterocycles.

Three new polyoxometalate-based metal-organic frameworks (POMOFs) [Cu4(μ3-OH)2(tba)3(H2O)5(SiW12O40)0.5](H2SiW12O40)0.5·2.5H2O (CuSiW), [Cu3(μ3-OH)(tba)3(Htba)(H2O)2(HPMo12O40)]·7H2O (CuPMo), and [Cu4(μ3-OH)2(tba)3(H2O)3(PW12O40)0.5]2(PW12O40)·0.5H2O (CuPW) were constructed using multinuclear copper clusters, 3-(4H-1,2,4-triazol-4-yl)benzoic acid (Htba), and Keggin polyoxometalates (POMs). Different POMs regulate the formation of different multinuclear copper clusters ("boat" tetranuclear clusters in CuSiW, trinuclear clusters in CuPMo, and "chair" tetranuclear clusters in CuPW) and different topological structures of CuSiW, CuPMo, and CuPW (3-connected two-dimensional (2D) network for CuSiW, 4-connected 2D network for CuPMo, and (4,6)-connected three-dimensional network for CuPW). CuSiW, CuPMo, and CuPW as heterogeneous catalysts combine the high stability of MOFs in polar solvents and excellent catalytic activity of POMs and could be used for the synthesis of nitrogen-heterocycle compounds. The condensation cyclization reactions of 2-aminophenols/benzenesulfonyl hydrazines with 1,3-diketones produce benzoazoles and pyrazoles in good to excellent yields under the catalysis of CuPMo. Moreover, the catalyst could be reused at least for 7 runs, and this protocol was suitable for gram-scale reactions.

Fabrication and adsorption mechanism of chitosan/Zr-MOF (UiO-66) composite foams for efficient removal of ketoprofen from aqueous solution

• The ultralight porous chitosan/(UiO-66) foams (CSF@UiO-66) were synthesized. • CSF@UiO-66 foam testified lightweight, good flexibility and high stability. • CSF@UiO-66 foam could efficiently remove ketoprofen (KTP) from water. • DFT calculations were applied to reveal the adsorption mechanism. Porous chitosan/Zr-MOF (UiO-66) composite foams (CSF@UiO-66) were facilely prepared by grafting UiO-66 into polymerized chitosan using epichlorohydrin as the linking agent. The flexible foams with high loadings of UiO-66 exhibited low density (15.0 ∼ 23.4 mg/cm 3 ) and superior liquid–solid separation performance. The hierarchical pores and abundant functional groups contributed to the effective removal of ketoprofen (KPF) from water by the composite foams, achieving a maximum adsorption capacity of 209.7 mg/g at pH 4, outperforming most reported adsorbents. Batch adsorption experiments demonstrated that the adsorption of KPF could be described by the Langmuir isotherm and pseudo-second-order kinetic model. Importantly, the composite foams showed excellent performance even in the presence of some ions and good reusability for engineering applications. Furthermore, density functional theory (DFT) calculations revealed that the adsorption mechanism between the composite foams and KPF could be attributed to hydrogen bonding and π-π interaction. In essence, this work provides an innovative strategy for the fabrication of a blocky composite foam with high loadings of MOF for efficient adsorptive removal of KPF in liquids, which can overcome the disadvantages of agglomeration due to small particle size and poor stability of MOFs.

CuII Ion Doping Enhances the Water Stability of Luminescent Metal-Organic Framework, Realizing the Detection of Fe3+ and Antibiotics in Aqueous Solutions.

Luminescent metal–organic frameworks (LMOFs) have been widely developed in the field of chemical sensing owing to their outstanding photoluminescence performance, high selectivity, anti-interference, high sensitivity, and fast response, and have become one of the research hotspots of emerging functional materials. However, in practical applications, many tests are carried out in the water environment, and fragile water stability greatly limits the application of MOFs in the field. Therefore, it is important to develop a method to enhance the water stability of MOFs. Herein, a new complex {[Zn(L)]·CH3CN} n (Zn-MOF, H2L = 5-(benzimidazol-1-yl) isophthalic acid) with a superior photophysical property has been synthesized first. Its water stability was highly enhanced by the doping of CuII ions by the one-pot method. In addition, the detection performances of doping material Cu0.1/Zn-MOF for sixteen metal ions and thirteen antibiotics were well studied. It was found that Cu0.1/Zn-MOF displays high sensitivity, fast response, lower detection limit, and long-term stability for the detection of Fe3+, NFT, NFZ, FZD, and TC in the aqueous medium.

Fluorescence analysis for characterizing the alkali stability of metal–organic frameworks: an informative complement to X-ray diffraction

Based on pH-responsive fluorescence associated with alkaline hydrolysis, a fluorometric method is proposed for characterizing the stability of MOFs. It can be used to monitor the whole process from nondestructive local hydrolysis to complete destructive hydrolysis.

Mind the gap! tailoring sol–gel ceramic mesoporous coatings on labile metal–organic frameworks through kinetic control

Kinetic control allows for the synthesis of mesoporous silica shells on top of labile ZIF-8 cores without compromising MOF stability.

Using Machine Learning and Data Mining to Leverage Community Knowledge for the Engineering of Stable Metal-Organic Frameworks.

Although the tailored metal active sites and porous architectures of MOFs hold great promise for engineering challenges ranging from gas separations to catalysis, a lack of understanding of how to improve their stability limits their use in practice. To overcome this limitation, we extract thousands of published reports of the key aspects of MOF stability necessary for their practical application: the ability to withstand high temperatures without degrading and the capacity to be activated by removal of solvent molecules. From nearly 4000 manuscripts, we use natural language processing and image analysis to obtain over 2000 solvent-removal stability measures and 3000 thermal degradation temperatures. We analyze the relationships between stability properties and the chemical and geometric structures in this set to identify limits of prior heuristics derived from smaller sets of MOFs. By training predictive machine learning (ML, i.e., Gaussian process and artificial neural network) models to encode the structure-property relationships with graph- and pore-structure-based representations, we are able to make predictions of stability orders of magnitude faster than conventional physics-based modeling or experiment. Interpretation of important features in ML models provides insights that we use to identify strategies to engineer increased stability into typically unstable 3d-transition-metal-containing MOFs that are frequently targeted for catalytic applications. We expect our approach to accelerate the time to discovery of stable, practical MOF materials for a wide range of applications.

Enzyme immobilization on metal organic frameworks: Laccase from Aspergillus sp. is better adapted to ZIF-zni rather than Fe-BTC

Laccase from Aspergillus sp. (LC) was immobilized within Fe-BTC and ZIF-zni metal organic frameworks through a one-pot synthesis carried out under mild conditions (room temperature and aqueous solution). The Fe-BTC, ZIF-zni MOFs, and the LC@Fe-BTC, LC@ZIF-zni immobilized LC samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The kinetic parameters (KM and Vmax) and the specific activity of the free and immobilized laccase were determined. Immobilized LCs resulted in a lower specific activity compared with that of the free LC (7.7µmolmin-1 mg-1). However, LC@ZIF-zni was almost 10 times more active than LC@Fe-BTC (1.32µmolmin-1 mg-1 vs 0.17µmolmin-1 mg-1) and only 5.8 times less active than free LC. The effect of enzyme loading showed that LC@Fe-BTC had an optimal loading of 45.2mgg-1, at higher enzyme loadings the specific activity decreased. In contrast, the specific activity of LC@ZIF-zni increased linearly over the loading range investigated. The storage stability of LC@Fe-BTC was low with a significant decrease in activity after 5 days, while LC@ZIF retained up to 50% of its original activity after 30 days storage. The difference in activity and stability between LC@Fe-BTC and LC@ZIF-zni is likely due to release of Fe3+ and the low stability of Fe-BTC MOF. Together, these results indicate that ZIF-zni is a superior support for the immobilization of laccase.

Enhanced aqueous stability and long-acting antibacterial of silver-based MOFs via chitosan-crosslinked for fruit fresh-keeping

Silver-based MOFs (Ag-MOFs) is a kind of excellent antimicrobial agent, but the application is limited in fresh-keeping due to its poor aqueous stability and short antibacterial time. Herein, we have developed a novel one-pot synthesis method to enhance aqueous stability and long-acting antibacterial of silver-based MOFs by crosslinking Ag-MOFs and chitosan. The water stability of Ag-MOFs@CS is based on the cross-linking of Ag-MOFs and active groups (amino and hydroxyl) in CS. Compared with Ag-MOFs, the aqueous stability of chemical structure, antibacterial time and validity of Ag-MOFs@CS are well enhanced. Ag-MOFs@CS can be maintained for more than 168 h in water environment, while Ag-MOFs can only be maintained for 6 h. In addition, the Ag-MOFs@CS suspension can still maintain good antibacterial properties after being placed for 100 days of storage. Specifically, spraying Ag-MOFs@CS suspension could effectively extend the shelf life of pitaya for 14 days, while the untreated pitaya has mold on the 7th day. Therefore, this research provides the possibility to solve the problem of Ag-MOFs in practical applications, which illustrates this cost-effective and eco-friendly product holds immense potential value for fruit fresh-keeping application.

A unified topology approach to dot-, rod-, and sheet-MOFs

<h2>Summary</h2> Metal-organic frameworks made from multi-metal-ion units in the shape of clusters and rods (termed dot-MOFs and rod-MOFs) are well known. Here, we introduce MOFs with multi-metallic units in the form of sheets—sheet-MOFs. We show exemplars of all three types of units based on structures containing Y³⁺, Ce³⁺, or Gd³⁺ linked by benzene-1,2,4,5-tetracarboxylate to give crystals of a dot-MOF in H₂NMe₂[Y(btec)(H₂O)] <b>CTH-14</b>, a sheet-MOF in [Ce₃(btec)(Hbtec)(OAc)(HCO₂)] <b>CTH-15</b>, and a rod-MOF in 4,4′-azopyridinium[Gd₂(btec)₂] <b>CTH-16</b>. Cyclic voltammetry shows that <b>CTH-15</b> stabilizes Ce(IV). Given the fact that sheet-MOFs represent an intellectual advance in the evolution of MOFs, a unified approach is proposed for the topological classification of dot-, rod-, and sheet-MOFs. It is suggested that the stability of MOFs follow in the trend dot < rod < sheet. For CTH-14-16, the sheet- and the rod-MOF have higher thermal stability. We suggest sheet-MOFs as an additional strategy for making robust MOFs.

Enhancing in the hydrogen storage by SWCNT/HKUST-1 composites: Effect of SWCNT amount

Functionalized single-walled carbon nanotubes into HKUST-1 ([Cu3-(btc)2]; btc= 1,3,5-benzenetricarboxylate) metal organic framework composite materials were synthesized by solvothermal method and characterized using different techniques such as XRD, BET,TG, SEM, and in situ Raman spectroscopy. It is important to mention that for the first time the thermal stability of the materials was determined by in situ Raman spectroscopy. Our results demonstrated that the incorporation of functionalized SWCNTs into HKUST-1 a slight increase in the thermal stability of MOF was observed. Too, a significant enhancement in the hydrogen adsorption capacity from 23.5% at 77 K and 1 bar of in the composite materials was observed. After of 5 cycles, hydrogen uptake is still above 2.98 wt% for 0.5SW/HKUST-1 sample. The hydrogen adsorption isotherms in the composite materials were completely reversible, reflecting only the physisorption of hydrogen molecule in the structure surface. Our results showed that the composite material with small amount of carbon nanotubes can be a promising candidate for the hydrogen storage.