Preferential SOx Adsorption in Mg-MOF-74 from a Humid Acid Gas Stream

Dual-Action NO Delivery from One Mixed Metal Metal-Organic Framework

Owing to their varied and controllable reticular chemistry, metal-organic frameworks (MOFs) represent excellent, structurally precise material platforms for creating multifunctional devices. This flexibility allows the design of MOFs to feature two different delivery mechanisms for the medicinal gas nitric oxide (NO) within one structure: a rapid, kinetic release of preadsorbed NO and subsequent continuous, catalytic generation of NO on exposure to a suitable substrate. In our approach, this was realized by preparing mixed metal MOF-74 analogues (also known as CPO-27) combining two metals, namely, nickel and copper. The introduction of 10 atom % nickel into Cu-MOF-74 provides a material platform with a number of excellent properties: (i) a high capacity of NO can be released with a moisture-triggered mechanism; (ii) the available copper sites allow the (potentially indefinite) catalytic generation of NO in the presence of S-nitrosoglutathione (GSNO), a store of NO in the human body; and (iii) it features prolonged material stability on exposure to phosphates. This material therefore shows great promise as part of the next generation of multifunctional MOF-based medicinal devices.

Comprehensive DFT investigation of small-molecule adsorption on the paradigm M-MOF-74 family of metal-organic frameworks

The capture of toxic chemicals such as NH3, H2S, NO2 and SO2 is essential due to the tremendous threats they pose to human health and the environment. The M-MOF-74 family of metal-organic frameworks has recently gained attention as a promising category of sorbent materials for the capture of toxic chemicals; however, no clear and comprehensive relationships have been established between the capability of the M-MOF-74 to capture all target toxic chemicals and their properties such as the nature and magnetic state of the metal sites. Density-functional theory (DFT) is employed to investigate the binding energy of target molecules on M-MOF-74 with different metals including Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn. The Hubbard U correction is employed to properly treat d electrons of transition metals and its effect explored on the bandgap of M-MOF-74. The magnetic properties of M-MOF-74 are investigated in detail along with their impact on the target molecule adsorption. Our calculations with DFT+U lead to good agreement with available experimentally determined bandgaps and structural properties. M-MOF-74 (M = Ti, V, Cr, Mn, Fe, Co and Cu) exhibit antiferromagnetic behavior, while ferromagnetic behavior prevails for Ni-MOF-74. Not surprisingly, the coordinatively unsaturated metals (M = Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) are the most likely sites for chemical adsorption of the target adsorbates, and V-MOF-74 and Ti-MOF-74 predicted to be efficient adsorbents for the target molecules, which can be rationalized on the basis of the metal d-band features. The spin configuration of transition metals in M-MOF-74 is found to have a negligible effect on adsorbate binding energies, which suggests that common DFT calculations without careful consideration of the material magnetic states can indeed be used to rapidly screen binding energies of adsorbates on such MOFs, with some notable exceptions; for instance, V-MOF-74 shows potential for magnetic sensing of NO2. This study provides further insight into the role of different unsaturated metals and their magnetic state for the removal of target toxic molecules by metal-organic frameworks.

Cu-UiO-66 Catalyzed Synthesis of Imines via Acceptorless Dehydrogenative Coupling of Alcohols and Amines

Herein, the Cu-UiO-66 catalyst was developed for acceptorless dehydrogenative coupling (ADC) between alcohols and amines to produce imines. The Cu-UiO-66 catalyst was synthesized by installing Cu2+ onto Zr-oxo clusters in UiO-66, and the catalyst efficiently catalyzes the ADC reaction under mild and environmentally friendly conditions with excellent selectivity. Mechanistic studies reveal that the O2⋅- radicals and porosity of formed in Cu-UiO-66 participate cooperatively during the catalytic cycle. Meanwhile, the only by-product of the system is environmentally benign water. Cycling tests and hot filtration tests showed that the Cu-UiO-66 catalyst exhibited excellent stability and catalytic activity during the reaction. Importantly, the Cu-UiO-66 catalyst might provide a promising strategy for the ADC reaction between alcohols and amines to produce imines.

Role of Metal-Organic Frameworks (MOFs) in treating and diagnosing microbial infections

This review article highlights the innovative role of metal-organic frameworks (MOFs) in addressing global healthcare challenges related to microbial infections. MOFs, comprised of metal nodes and organic ligands, offer unique properties that can be applied in the treatment and diagnosis of these infections. Traditional methods, such as antibiotics and conventional diagnostics, face issues such as antibiotic resistance and diagnostic limitations. MOFs, with their highly porous and customizable structure, can encapsulate and deliver therapeutic or diagnostic molecules precisely. Their large surface area and customizable pore structures allow for sensitive detection and selective recognition of microbial pathogens. They also show potential in delivering therapeutic agents to infection sites, enabling controlled release and possible synergistic effects. However, challenges like optimizing synthesis techniques, enhancing stability, and developing targeted delivery systems remain. Regulatory and safety considerations for clinical translation also need to be addressed. This review not only explores the potential of MOFs in treating and diagnosing microbial infections but also emphasizes their unique approach and discusses existing challenges and future directions.

In Situ Single-crystal X-ray Diffraction Studies of Physisorption and Chemisorption of SO2 within a Metal-Organic Framework and Its Competitive Adsorption with Water

Living on an increasingly polluted planet, the removal of toxic pollutants such as sulfur dioxide (SO2) from the troposphere and power station flue gas is becoming more and more important. The CPO-27/MOF-74 family of metal-organic frameworks (MOFs) with their high densities of open metal sites is well suited for the selective adsorption of gases that, like SO2, bind well to metals and have been extensively researched both practically and through computer simulations. However, until now, focus has centered upon the binding of SO2 to the open metal sites in this MOF (called chemisorption, where the adsorbent-adsorbate interaction is through a chemical bond). The possibility of physisorption (where the adsorbent-adsorbate interaction is only through weak intermolecular forces) has not been identified experimentally. This work presents an in situ single-crystal X-ray diffraction (scXRD) study that identifies discrete adsorption sites within Ni-MOF-74/Ni-CPO-27, where SO2 is both chemisorbed and physisorbed while also probing competitive adsorption of SO2 of these sites when water is present. Further features of this site have been confirmed by variable SO2 pressure scXRD studies, DFT calculations, and IR studies.

Nanoarchitectonics Design Strategy of Metal-Organic Framework and Bio-Metal-Organic Framework Composites for Advanced Wastewater Treatment through Adsorption

Freshwater depletion is an alarm for finding an eco-friendly solution to treat wastewater for drinking and domestic applications. Though several methods like chlorination, filtration, and coagulation-sedimentation are conventionally employed for water treatment, these methods need to be improved as they are not environmentally friendly, rely on chemicals, and are ineffective for all kinds of pollutants. These problems can be addressed by employing an alternative solution that is effective for efficient water treatment and favors commercial aspects. Metal organic frameworks (MOFs), an emerging porous material, possess high stability, pore size tunability, greater surface area, and active sites. These MOFs can be tailored; thus, they can be customized according to the target pollutant. Hence, MOFs can be employed as adsorbents that effectively target different pollutants. Bio-MOFs are a kind of MOFs that are incorporated with biomolecules, which also possess properties of MOFs and are used as a nontoxic adsorbent. In this review, we elaborate on the interaction between MOFs and target pollutants, the role of linkers in the adsorption of contaminants, tailoring strategy that can be employed on MOFs and Bio-MOFs to target specific pollutants, and we also highlight the effect of environmental matrices on adsorption of pollutants by MOFs.

The L-proline modified Zr-based MOF (Basu-proline) catalyst for the one-pot synthesis of dihydropyrano[3,2-c]chromenes

A novel, reusable, and efficient L-proline-modified Zr-based metal-organic framework (Basu-proline) was designed, synthesized, and characterized by Fourier Transform-Infrared spectroscopy (FT-IR), Energy-Dispersive X-ray spectroscopy (EDX), elemental mapping, Field Emission Scanning Electron Microscopy (FE-SEM), X-ray Diffraction analysis (XRD), Thermo-Gravimetric-Differential Thermal Analysis (TGA-DTA), and N2 adsorption-desorption isotherms. Then, its catalytic performance was assessed in the synthesis of dihydropyrano[3,2-c]chromenes via the one-pot, three-component tandem condensation reaction of 4-hydroxycoumarin, aromatic aldehydes and malononitrile. The Basu-proline catalyst exhibited a better efficiency than some reported protocols regarding higher yields, lower reaction times, and simple separation.

Synthesis of an IRMOF-1@SiO2 Core-Shell and Amino-Functionalization with APTES for the Adsorption of Urea and Creatinine Using a Fixed-Bed Column Study

Kidney dysfunction is a clinical disease that disables the kidneys to remove the waste products and uremic toxins from the circulation and may lead to fatal kidney failure. Hemodialysis is advantageous in this circumstance since it prevents the accumulation of waste products in the body and facilitates the removal of uremic toxins. However, hemodialysis cannot entirely remove some uremic toxins, such as urea and creatinine. In this paper, a high-performance fixed-bed column for urea and creatinine removal was offered. As a result, a MOF layer was built on SiO₂, which was then amino-functionalized using APTES. Numerous assays were used to characterize the final adsorbent. The adsorption of urea and creatinine was evaluated in batch and continuous conditions. Thus, it was demonstrated that the adsorption behavior of A(0.2)-IRMOF-1@SiO₂ followed the Langmuir isotherm, and it exhibited the maximum adsorption capacity. The batch experiment determined that urea and creatinine had an adsorption capacity of 1325.73 and 625.00 mg·g^-1, respectively. The adsorption capacity was increased, which was due to the presence of amino groups (APTES) on the MOF surface. The continuous operation was evaluated using the A(0.2)-IRMOF-1@SiO₂ fixed-bed column. Thomas and Nelson's models were examined to achieve a better understanding of the adsorption behaviors. The A(0.2)-IRMOF-1@SiO₂ fixed-bed column successfully removed 92.57% of urea and 80.47% of creatinine. The separation factor for urea in comparison to creatinine was 2.40 in the A(0.2)-IRMOF-1@SiO₂ fixed-bed column.

Gas sensing based on metal-organic frameworks: Concepts, functions, and developments

Effective detection of pollutant gases is vital for protection of natural environment and human health. There is an increasing demand for sensing devices that are equipped with high sensitivity, fast response/recovery speed, and remarkable selectivity. Particularly, attention is given to the designability of sensing materials with porous structures. Among diverse kinds of porous materials, metal-organic frameworks (MOFs) exhibit high porosity, high degree of crystallinity and exceptional chemical activity. Their strong host-guest interactions with guest molecules facilitate the application of MOFs in adsorption, catalysis and sensing systems. In particular, the tailorable framework/composition and potential for post-synthetic modification of MOFs endow them with widely promising application in gas sensing devices. In this review, we outlined the fundamental aspects and applications of MOFs for gas sensors, and discussed various techniques of monitoring gases based on MOFs as functional materials. Insights and perspectives for further challenges faced by MOFs are discussed in the end.

Iodide-enhanced Cu-MOF nanomaterials for the amplified colorimetric detection of Fe3

In this paper, a novel colorimetric strategy based on iodide ion (I^-) and Cu-MOF catalysis was developed for simple, low-cost, and naked-eye detection of Fe³⁺. Both I^- and MOFs display catalytic activity toward peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB). Adsorption and embedding of I^- in Cu-MOF generates Cu-MOF/I with a three-dimensional porous structure that exhibits higher specific surface area, providing more active sites to facilitate interaction with TMB, resulting in enhanced catalytic efficiency. Reports have shown that Fe³⁺ can oxidize TMB in the absence of H₂O₂. We found that as Fe³⁺ concentration increases, the color of the system gradually deepens and the UV absorption peak gradually increases, thus providing a colorimetric sensor for quantitative Fe³⁺ detection. The detection limit (LOD) obtained in the presence of I^- is 200 nM; however, in the absence of I^-, the LOD is approx. 10 μM. Thus, the sensing system is ideal for signal amplified analysis of Fe³⁺. In the presence of various interfering metal ions, the developed sensing system displays excellent selectivity. Additionally, the practical application to Fe³⁺ detection in real samples is explored.

Kinetically Controlled Linker Binding in Rare Earth-2,5-Dihydroxyterepthalic Acid Metal-Organic Frameworks and Its Predicted Effects on Acid Gas Adsorption

In the pursuit of highly stable and selective metal-organic frameworks (MOFs) for the adsorption of caustic acid gas species, an entire series of rare earth MOFs have been explored. Each of the MOFs in this series (RE-DOBDC; RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; DOBDC = 2,5-dihydroxyterepthalic acid) was synthesized in the tetragonal space group I4/m. Crystallized MOF samples, specifically Eu-DOBDC, were seen to have a combination of monodentate and bidentate binding when synthesized under typical reaction conditions, resulting in a contortion of the structure. However, extended crystallization times determined that this binding is kinetically controlled and that the monodentate binding option was crystallographically eliminated by extended reaction times at higher temperatures. Furthermore, this series allows for the direct study of the effect of the metal center on the structure of the of the MOF; herein, the lanthanide metal ionic radii contraction across the periodic table results in a reduction of the MOF pore size and lattice parameters. Scanning electron microscopy-energy-dispersive spectroscopy was used to investigate the stages of crystal growth for these RE-DOBDC MOFs. All MOFs, except Er-DOBDC had a minimum of two stages of growth. These analogues were demonstrated by analysis of neutron diffraction (PND) to exhibit a cooperative rotational distortion of the secondary building unit, resulting in two crystallographically distinct linker sublattices. Computational modeling efforts were used to show distinct differences on acid gas (NO₂ and SO₂) binding energies for RE-DOBDC MOFs when comparing the monodentate/bidentate combined linker with the bidentate-only linker crystal structures.

Persistence and Recovery of ZIF-8 and ZIF-67 Phytotoxicity

Zeolitic imidazolate frameworks (ZIFs) have been developed quickly and have attracted considerable attention for use in the detection and removal of various pollutants. Understanding the environmental risks of ZIFs is a prerequisite to their safe application by industry and new chemical registration by governments; however, the persistence and recovery of toxicity induced by ZIFs remain largely unclear. This study finds that typical ZIFs (e.g., ZIF-8 and ZIF-67) at a concentration of 0.01-1 mg/L induce significant algal growth inhibition, plasmolysis, membrane permeability, chloroplast damage, and chlorophyll biosynthesis, and the above alterations are recoverable. Unexpectedly, a persistent decrease in reactive oxygen species (ROS) is observed due to the quenching of hydroxyl free radicals. The adverse effects of ZIF-8 are weak and easily alleviated compared with those of ZIF-67. ZIF-8 is internalized mainly by caveolae-mediated endocytosis, while ZIF-67 is internalized mainly by clathrin-mediated endocytosis. Omics studies reveal that the downregulation of mRNA associated with oxidative phosphorylation and the inhibition of chlorophyll and adenosine triphosphate (ATP) synthesis in mitochondria are related to the persistence of phytotoxicity. These findings highlight the phenomena and mechanisms of the persistence and recovery of phytotoxicity, indicating the need to reconsider the environmental risk assessments of ZIFs.

Introducing High Density of Very Active Sites and Stepwise Postmodification for Tailoring the Porosity of Highly Demanding Cr3+-Based Metal-Organic Frameworks

Chromium(III)-based metal-organic frameworks (Cr-MOFs) are highly robust and porous and have been very attractive in a wide range of investigations. However, the harsh direct synthetic conditions not only impede the synthesis of new Cr-MOFs but also restrict the introduction of functional groups into them. Postsynthetic modification has somewhat alleviated such difficulties; nevertheless, it still suffered from procedures that are tedious and conditions that are not mild, which often result in low concentration of the functional groups introduced. To overcome these shortcomings, here, in this paper, we supplied a new route and prepared a benzyl alcohol functionalized Cr-SXU-2 from the judiciously designed benzyl alcohol functionalized Fe-SXU-2 through solvent-assisted metal metathesis strategy. The functionalized Cr-SXU-2 shows well-preserved crystallinity, porosity, and high chemical stability. The benzyl alcohol group can be converted into a very active benzyl bromide group in an almost quantitative yield and thus for the first time produce the benzyl bromide functionalized MOF, Cr-SXU-2-Br, in which the -Br group can be exchanged by a nucleophilic group. As a proof of concept, -N₃ was introduced and transformed into other active sites via "click reaction" to further tailor the interior of Cr-SXU-2. All these functionalized Cr-MOFs showed improved adsorption performance in contrast to the nonfunctionalized one. This step-by-step postmodification process not only diversifies the functionalization of robust MOFs but also opens a new route to employ many different functional groups in the demanding highly stable Cr-MOF platforms.

Zinc Metal-Organic Framework Growing on the Surface of Fruit Peels and Its Photocatalytic Activity

The development of water treatment materials using environmentally friendly natural biomasses as substitutes plays an increasingly important role in environmental protection. Zeolitic imidazolate framework-8 (ZIF-8) is often used for the catalytic degradation of dye wastewater, but due to its small particle size, its disadvantage of easy agglomeration prevents it from being fully functional. Herein, we report an efficient method for synthesizing biomasses/ZIF-8 using four different fruit peels as carriers. ZIF-8 nanoparticles are in-situ grown uniformly on their surface. The Brunauer-Emmett-Teller surface area of shaddock peel/ZIF-8 was found to be 752.15 m²g^-1. After catalytic activity comparison, the loose shaddock peel/ZIF-8 showed the fastest and most significant degradation efficiency of 94% in methylene blue aqueous solution and could be used multiple times through a simple washing process.