MOF Materials Research Articles

High-pressure study of a 3d-4f heterometallic CuEu-organic skeleton.

We prepared a 3d-4f heterobimetallic CuEu-organic framework NBU-8 with a density of 1921 kg m-3 belonging to the family of dense packing materials (dense metal-organic frameworks or MOFs). This MOF material was prepared from 4-(pyrimidin-5-yl)benzoic acid (HPBA) with a bifunctional ligand site as a tripodal ligand and Cu2+ and Eu3+ as the metal centres; the molecular formula is Cu3Eu2(PBA)6(NO3)6·H2O. This material is a very promising dimethylformamide (DMF) molecular chemical sensor. Systematic high-pressure studies of NBU-8 were carried out by powder X-ray diffraction, high-pressure X-ray diffraction and molecular dynamics simulation. The high-pressure experiment shows that the (006) diffraction peak of the crystal structure moves toward a low angle with increasing pressure, accompanied by the phenomenon that the d-spacing increases, and as the pressure increases, the (10-2) diffraction peak moves to a higher angle, the amplitude of the d-spacing is significantly reduced and finally merges with the (006) diffraction peak into one peak. The amplitude of the d-spacing is significantly reduced, indicating that NBU-8 compresses and deforms along the a-axis direction when subjected to uniform pressure. This is caused by tilting of the ligands to become more vertical along the c direction, leading to its expansion. This allows greater contraction along the a direction. We also carried out a Rietveld structure refinement and a Birch-Murnaghan solid-state equation fitting for the high-pressure experimental results. We calculated the bulk modulus of the material to be 45.68 GPa, which is consistent with the calculated results. The framework is among the most rigid MOFs reported to date, exceeding that of Cu-BTC. Molecular dynamics simulations estimated that the mechanical energy absorbed by the system when pressurized to 5.128 GPa was 249.261 kcal mol-1. The present work will provide fresh ideas for the study of mechanical energy in other materials.

Direct Synthesis of MOF-74 Materials on Carbon Fiber Electrodes for Structural Supercapacitors.

The use of fossil fuels has contributed significantly to environmental pollution and climate change. For this reason, the development of alternative energy storage devices is key to solving some of these problems. The development of lightweight structures can significantly reduce the devices' weight, thereby reducing energy consumption and emissions. Combining lightweight structures with alternative energy storage technologies can further improve efficiency and performance, leading to a cleaner and more sustainable system. In this work, for the first time, MOF-74 materials with different divalent metal ions have been synthesized directly on carbon fiber, one of the most widely used materials for the preparation of electrodes for supercapacitors with structural properties. Different techniques, such as nitrogen adsorption-desorption isotherms, cyclic voltammetry or galvanostatic charge-discharge, among others, were used to evaluate the influence of the metal cation on the electrochemical capacitance behavior of the modified electrodes. The Co-MOF-74 material was selected as the best modification of the carbon fibers for their use as electrodes for the fabrication of structural supercapacitors. The good electrochemical performance shown after the incorporation of MOF materials on carbon fibers provides a viable method for the development of carbon fiber electrodes, opening a great variety of alternatives.

Post-synthetic functionalization of UiO-66-NH2 by polyacrylamide and polyvinylimidazolium salt brushes via ATRP and adsorption behavior

Aquacultural water pollution caused by methylene blue is an urgent environmental problem, posing a serious threat to aquaculture and human health. Adsorption is a potential and promising method to remove methylene blue from aquaculture water. In this study, UiO-66-NH2@PAM and UiO-66-NH2@PVIO post-synthetic functionalized by polyacrylamide and polyvinylimidazolium salt brushes onto UiO-66-NH2 by virtue of ATRP method were successfully synthesized, and adsorption performance for methylene blue were systematically studied. Adsorption kinetic curves with trend of first increase, and decrease, and then increase was explained by capillary effect. Experimental data were fitted best by pseudo second-order kinetic and Langmuir isotherm model. UiO-66-NH2@PVIO had comparatively higher adsorption capacities than UiO-66-NH2@PAM, because UiO-66-NH2@PVIO had stronger adsorption affinity and binding energy for methylene blue than UiO-66-NH2@PAM. Adsorption driving forces were electrostatic interaction, π-π conjugation effects, hydrogen-bonding interactions, induced dipoles, van der Waals forces, sieving effect so that adsorption processes were ascribed to physical adsorption. UiO-66-NH2@PAM and UiO-66-NH2@PVIO had very good reusability and stability, and could be utilized in practical application. The results can offer better help for the synthesis of MOF materials by the technology of post-synthetic functionalization, and provide technical guidance for actual application in dye removal from aquacultural water.

Carbon-dots encapsulated luminescent metal–organic frameworks@surface molecularly imprinted polymer: A facile fluorescent probe for the determination of chloramphenicol

In this study, carbon dots (CDs)-encapsulated luminescent metal–organic frameworks@surface molecularly imprinted polymer (CDs@MOF@SMIP) was facilely prepared and applied as fluorescent probe for specific identification and sensitive detection of chloramphenicol (CAP) in food. Fluorescent CDs, serving as signal tags, were encapsulated within metal–organic backbones (ZIF-8), yielding luminescent MOF materials (CDs@ZIF-8). The synthesized CDs, CDs@ZIF-8 and CDs@ZIF-8@SMIP were investigated by morphological and structural characterizations (UV–Vis, XRD, FT-IR, BET, TEM). The CDs@ZIF-8@SMIP probe was demonstrated to have remarkable selectivity and sensitivity towards CAP. Its fluorescence decreased linearly with CAP concentration from 0.323 μg L-1 (0.001 μM) to 8075.0 μg L-1 (25.0 μM), featuring a low detection limit of 0.08 μg L-1. The CDs@ZIF-8@SMIP-based fluorescence strategy achieved satisfactory recoveries (95.5 % − 101.0 %) in CAP-spiked commercial foods with RSD < 4.4 % (n = 3). These results indicate that this method can effectively detect trace CAP in food matrices and has broad application prospects.

Enhancement of adsorption performance for I2 and Cr(VI) by the metal-organic framework UiO-66-NH2 via post-synthetic modification

Excessive emissions of radioactive I2 and toxic Cr(VI) have been a significant threat to the environment and human health. Thus, the adsorption of I2 and Cr(VI) has attracted great attention. Here a new functionalized UiO-66-NH2 MOF with pyrazole and amide groups were fabricated through postsynthetic modification (PSM) (denoted as UiO-66-AMmpz) and used to study the adsorption of gaseous I2 and aqueous phase Cr(VI). UiO-66-AMmpz exhibited good adsorption capacities of 1.21 g·g−1 for I2 at 75 °C and 291.2 mg·g−1 for Cr(VI) at pH 2, which significantly surpasses the pristine UiO-66-NH2. By analyzing the IR, XPS, EPR, Raman spectra of UiO-66-AMmpz before and after I2 adsorption, it was deduced that the good adsorption performance was attributed to the strong interactions between the adsorbed I2 and abundant N and O sites in the surface and pores of UiO-66-AMmpz, which mainly came from post-introduced the pyrazole and amide groups. In addition, the Cr(VI) adsorption process followed the pseudo-second-order kinetics and its adsorption data also fit well the Langmuir model. Simultaneously, the thermodynamic parameters suggested that the Cr(VI) adsorption process is spontaneous and endothermic process. Moreover, XPS and IR analysis revealed that the adsorbed Cr(VI) was partially reduced to Cr(III) and then fixed on UiO-66-AMmpz. This work can aid us to appreciate the surface interaction between I2 and Cr(VI) and the framework of MOFs and provide a promising MOF material to adsorb gaseous I2 and remove Cr(VI) from water.

Rare earth element-modified MOF materials: synthesis and photocatalytic applications in environmental remediation

Rare earth element-modified MOF materials: synthesis and photocatalytic applications in environmental remediation

Desalination performance investigation of TpPa-1 COF and MIL-47(V) MOF bilayer membranes using molecular dynamics simulation

The efficiency of reverse osmosis (RO) desalination heavily depends on the advancement of innovative membrane materials. In this study, we utilized molecular dynamics simulations to assess the desalination performance of pure and hybrid bilayers made from two-dimensional (2D) TpPa-1 COF and MIL-47 (V) MOF materials. Our findings show that a pure TpPa-1 COF bilayer exhibits a water permeability (348 L/cm2/day/MPa) that is over four orders of magnitude higher than commercially-used seawater RO membranes, while still maintaining an 88 % ion rejection rate. On the other hand, the MIL-47(V) MOF bilayer demonstrates an impressive 97 % ion rejection rate with significantly higher water permeability (160 L/cm2/day/MPa) compared to existing membrane materials such as cellulose acetate, polysulfone aromatic polyamides, MoS2, graphene, HAB-derived MOF, and carbon nanotubes. As a result, MIL-47(V) stands out as a promising nanoporous material for advanced RO water desalination with both high water permeability and exceptional rejection efficiency. However, when the COF and MOF materials are combined in a hybrid bilayer configuration, the water permeability becomes lower than bilayers of the same material due to pore misalignment. Our findings indicate that the pore-sieving effect is the primary governing factor for the rejection in the bilayer membrane. The electrostatic interactions and hydrogen bonding formation between water molecules and the oxygen atoms in the bilayers play vital roles in regulating water transport and ion passage across the examined bilayers.

Covalently linked MOF@COF direct Z-scheme heterojunction for visible light-driven photocatalytic degradation of flotation agents

It is necessary to find a green, highly efficient and cost-effective way to treat the water pollution caused by flotation agents that are widely used in mineral processing, coal desulfurization and water treatment. Herein, by wrapping an amino group-containing MOF core with a visible light active triazine COF through imine bonds, a covalently linked MOF@COF composite was prepared and found to work as a direct Z-scheme heterojunction photocatalyst for highly efficient visible light-driven degradation of flotation agents. As prepared MOF@COF not only inherits the merits of parent MOF and COF such as large specific surface area, porous framework, good crystallinity, and strong visible light-harvesting capability, but also shows other attractive advantages including robust stability, highly efficient photogenerated electron-hole pair separation and enhanced redox ability due to its covalently linking mode. After carefully selecting the COF content in the composite and optimizing reaction conditions, the resultant MOF@COF composite was successfully used for the photocatalytic degradation and mineralization of flotation agent pollutes in a wide concentration range, giving an apparent rate constant that was 3.2 and 3.5 times higher than those of parent MOF and COF, respectively. In view of systematical characterization and experimental analysis, the underlying reaction mechanism concerning Z-scheme heterojunction was proposed. This work provides a promising way to prepare high-performance photocatalytic materials for the degradation and removal of flotation agent pollutants using inexhaustible solar energy, and to broaden the applications of MOF and COF-based materials.

Turning Normal to Abnormal: Reversing CO2/C2‐Hydrocarbon Selectivity in HKUST‐1

AbstractMetal–organic frameworks (MOFs) can efficiently purify hydrocarbons from CO2, but their rapid saturation, driven by preferential hydrocarbon adsorption, requires energy‐intensive adsorption–desorption processes. To address these challenges, an innovative approach is developed, enabling control over MOF flexibility through densification and defect engineering, resulting in an intriguing inverse CO2/C2 hydrocarbon selectivity. In this study, the densification process induces the shearing of the crystal lattice and contraction of pores in a defective CuBTC MOF. These changes have led to a remarkable transformation in selectivity, where the originally hydrocarbon‐selective CuBTC MOF becomes CO2‐selective. The selectivity values for densified CuBTC are significantly reversed when compared to its powder form, with notable improvements observed in CO2/C2H6 (4416 vs 0.61), CO2/C2H4 (15 vs 0.28), and CO2/C2H2 (4 vs 0.2). The densified material shows impressive separation, regeneration, and recyclability during dynamic breakthrough experiments with complex quinary gas mixtures. Simulation studies indicate faster CO2 passage through the tetragonal structure of densified CuBTC compared to C2H2. Experimental kinetic diffusion studies confirm accelerated CO2 diffusion over hydrocarbons in the densified MOF, attributed to its small pore window and minimal interparticle voids. This research introduces a promising strategy for refining existing and future MOF materials, enhancing their separation performance.

Metal-organic framework-derived two-dimensional in-plane Janus catalysts promoting oxygen electroreduction to hydrogen peroxide.

We use MOFs material as precursor to synthesize carbon based two-dimensional (2D) materials loaded with In2 S3 -In2 O3 (In-S-O) nanoparticles. The In-S-O nanoparticles have exhibited Janus architecture composed of two compounds with different crystal structures that are combined in-plane on 2D carbon material surface. The excellent properties of this in-plane Janus material include 2D nanoarchitecture and its Janus properties formed by combining two different crystal structures. It has exhibited excellent electrochemical performances due to its abundant electrochemical active sites and large specific surface area. According to experiments, the electron transfer number of the material for two-electron oxygen reduction is about 2.4, and the hydrogen peroxide yield is 32 mg/h cm2 . In the further test of liquid flow electrolytic cell, the yield can reach up to 172 mg/h cm2 .

Metal-organic frameworks (MOFs) for photoelectrocatalytic (PEC) reducing carbon dioxide (CO2) to hydrocarbon fuels.

MOF-based photoelectrocatalysis (PEC) using CO2 as an electron donor offers a green, clean, and extensible way to make hydrocarbon fuels under more tolerant conditions. Herein, basic principles of PEC reduction of CO2 and the preparation methods and characterization techniques of MOF-based materials are summarized. Furthermore, three applications of MOFs for improving the photoelectrocatalytic performance of CO2 reduction are described: (i) as photoelectrode alone; (ii) as a co-catalyst of semiconductor photoelectrode or as a substrate for loading dyes, quantum dots, and other co-catalysts; (iii) as one of the components of heterojunction structure. Challenges and future wave surrounding the development of robust PEC CO2 systems based on MOF materials are also discussed briefly.

Fabrication of bimetallic MOF-74 derived materials for high-efficiency adsorption of iodine.

Owing to their high porosity, open metal sites, and huge surface area, metal-organic framework (MOF) materials are commonly employed in iodine adsorption processes. Bimetallic MOFs have drawn a lot of attention since mono-metal MOFs have been unable to keep up with the demand. Bimetallic MOF materials still have drawbacks, including limited adsorption capacity, extended adsorption time, poor stability, and poor selectivity, despite their positive performance in radioactive iodine capture. It has been therefore difficult to develop adsorbents with quick iodine adsorption rates and high iodine adsorption efficiency. This study investigated the adsorption properties of a series of bimetallic MOF-74 materials (Mn-Co-MOF-74, Mn-Zn-MOF-74, and Mn-Ni-MOF-74) for radioactive iodine, as well as their design and synthesis utilizing the reflux approach. It was discovered that the adsorption performance of Mn-Ni-MOF-74 for radioiodine was superior to that of the other two bimetallic MOF-74 materials. Using the bimetallic Mn-Ni-MOF-74 as a precursor, a variety of bimetallic MOF-74 derived carbon compounds (Mn-Ni-CX) were prepared by high-temperature pyrolysis. Simultaneously, the structure of the material and the iodine adsorption characteristics have been thoroughly studied.

Cyclodextrin metal-organic framework@SiO2 nanocomposites for poorly soluble drug loading and release.

The development of non-toxic drug carrier materials with high loading capacity, sustained release properties, stability, and biocompatibility holds significant medical value and potential for loading and releasing poorly soluble drugs. In this study, we synthesized a biocompatible, non-toxic, environmentally friendly CD-MOF porous material with high specific surface area and tunable structure. By incorporating SiO2 to enhance the stability of MOF materials, the synthesized CD-MOF@SiO2 material shows promising applications in drug delivery. The obtained CD-MOF@SiO2 nanocomposite was utilized as a carrier for the poorly soluble drug, folic acid. Characterization of the drug-loaded composite before and after drug loading was performed using scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, N2 adsorption-desorption, and X-ray diffraction analyses, showing improved stability as indicated by thermogravimetric analysis and derivative thermogravimetry data. UV spectrophotometry was used to investigate the loading and sustained release of folic acid under different conditions in PBS buffer, demonstrating that the well-structured CD-MOF@SiO2 material exhibits high drug loading and controllable release properties. The CD-MOF@SiO2 achieved a high drug loading efficiency (166.78%) and encapsulation rate (83.39%) for folic acid, leading to a significant increase in apparent solubility from 1.6 μg mL-1 in its free form to 21.74 mg mL-1, a 13 588-fold expansion. This work presents a novel, efficient, and highly valuable approach for the development of carrier materials for loading and releasing poorly soluble drugs.

A label-free electrochemical biosensor based on a bimetallic organic framework for the detection of carbohydrate antigen 19-9.

Carbohydrate antigen 19-9 (CA19-9) is an important marker for pancreatic cancer, ovarian cancer and other tumors, and its rapid and stable detection is the basis for early diagnosis and treatment. In this paper, a label-free electrochemical immunosensor for the sensitive detection of CA19-9 has been developed. First, the synthesis of two novel core-shell bimetallic nanomaterials, namely Ce-MOF-on-Fe-MOF and Fe-MOF-on-Ce-MOF, was accomplished using the MOF-on-MOF approach. The poor electrical conductivity of MOF materials was addressed by incorporating polyethylenimide (PEI) functionalized rGO with Ce-MOF-on-Fe-MOF and Fe-MOF-on-Ce-MOF nanomaterials. Simultaneously, toluidine blue (Tb) was employed as a redox probe and physically adsorbed onto the synthesized materials, resulting in the formation of two nanomaterials: rGO@Ce-MOF-on-Fe-MOF@Tb and rGO@Fe-MOF-on-Ce-MOF@Tb. The fundamental characterization reveals that the sensing performance of the rGO@Ce-MOF-on-Fe-MOF@TB-based immune sensor surpasses that of the rGO@Fe-MOF-on-Ce-MOF@TB-based immune sensor, which is attributed to the fact that, unlike the interlayer-constrained structure of Fe-MOF-on-Ce-MOF, in Ce-MOF-on-Fe-MOF, Ce-MOF penetrates into Fe-MOF to form a heterogeneous structure due to the relatively large pore size of Fe-MOF, which better combines the excellent biocompatibility and strong anchoring effect of Fe MOFs on antibodies, as well as the high electrochemical activity and conductivity of Ce-MOF, to enhance sensing performance. The proposed label-free immunosensor based on rGO@Ce-MOF-on-Fe-MOF@Tb has a wide linear range (1-100 000 mU mL-1), a low detection limit (0.34 mU mL-1), good stability, reproducibility, and repeatability, and satisfactory applicability, which provides a potential platform for clinical applications.

A linker selective retention strategy to construct hierarchical porous metal-organic frameworks with high catalytic activity for oxidative desulfurization.

In order to improve the oxidative desulfurization (ODS) performance of MOF materials, an effective way is to convert a microporous MOF into a hierarchical porous MOF (HP-MOF) by utilizing the linker selective retention strategy. Herein, UiO-66 with the introduction of an unstable linker ligand (dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate, dhtz) can selectively remove dhtz ligands to form HP-MOF (HP-UiO-66-dhtz) through heat treatment at high temperature. While maintaining the original structure of UiO-66, HP-UiO-66-dhtz features mesopores and abundant Lewis acid sites, showing excellent ODS performance for diphenylthiophene (DBT).

Metal–organic frameworks constructed using acid–base mixed ligands, carboxylic acids and N-containing chalcone, and their catalytic performance for Knoevenagel condensation

Metal–organic frameworks constructed using acid–base mixed ligands, carboxylic acids and N-containing chalcone, and their catalytic performance for Knoevenagel condensation

Construction of a novel nickel-based MOF with accessible oxygen sites for efficient CH4/N2 separation

A novel Ni-based MOF material, TUTJ-201Ni, with accessible oxygen sites, was constructed. The material displayed ultrahigh thermal stability, showing a high separation performance for CH4/N2 mixture.

An in-depth physicochemical investigation of drug-loaded core-shell UiO66 nanoMOFs.

Nanosized UiO66 are among the most studied MOF materials. They have been extensively applied in various areas, such as catalysis, gas absorption, electrochemistry, chemical sensing, and biomedical applications. However, the preparation of stable nano-sized UiO66 for drug delivery applications is challenging because of the high tendency of UiO66 to aggregate during storage. To address this issue, we coated UiO66 with oligomers made of crosslinked cyclodextrins. The coated UiO66 exhibited a good stability upon storage for more than three weeks, even for low quantities of coating materials. The resulting core-shell UiO66 were characterized using a set of complementary methods including microscopies, spectroscopies, X-ray diffraction, and thermogravimetric investigations. Size distribution was assessed by orthogonal methods. Cisplatin was loaded in the core-shell nanoparticles, followed by an in-depth analysis by asymmetric flow field-flow fractionation (AF4) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS). This method combines the extremely high elemental selectivity and ultratrace detection limits of mass spectrometry with the capacity of AF4 to differentiate the diverse populations present in the sample. Free cisplatin and UiO66-associated cisplatin could be well separated by AF4. AF4-ICP-MS/MS analysis provided the exact drug loading, without the need of separating the nanoparticles from their suspension media. These data suggest the potential of AF4-ICP-MS/MS in the optimization of drug delivery systems.

Encapsulation of luminol and Co2+ within a metal–organic framework for enhanced chemiluminescence and imaging of inflammation

By encapsulating luminol and Co2+ within UiO-67-bpydc, we construct an enhanced chemiluminescence MOF material. UiO-67-bpydc⊃Co+Lu exhibits excellent sensing properties for H2O2 and glucose, and can accurately image skin inflammation.

Construction of a redox-active metal-organic framework with an octanuclear lithium one-dimensional building block.

A stable lithium metal-organic framework, constructed using a redox-active N,N,N',N'-tetrakis(4-carboxyphenyl)-1,4-phenylenediamine linker and Li8 cluster-based one-dimensional rod secondary building unit, exhibits good stability and reversible redox activity. The Li8-MOF, which can be oxidized by AgNO3, has the potential to function as an electrochromic device, thereby advancing the development of smart MOF materials.