Efficient Capture of Organic Dyes and Crystallographic Snapshots by a Highly Crystalline Amino-Acid-Derived Metal-Organic Framework

Design of Multivariate Biological Metal-Organic Frameworks: Toward Mimicking Active Sites of Enzymes

Mimicking enzymatic processes carried out by natural enzymes, which are highly efficient biocatalysts with key roles in living organisms, attracts much interest but constitutes a synthetic challenge. Biological metal-organic frameworks (bioMOFs) are potential candidates to be enzyme catalysis mimics, as they offer the possibility to combine biometals and biomolecules into open-framework porous structures capable of simulating the catalytic pockets of enzymes. In this work, we first study the catalase activity of a previously reported bioMOF, derived from the amino acid L-serine, with formula {CaIICuII6[(S,S)-serimox]3(OH)2(H2O)} · 39H2O (1) (serimox = bis[(S)-serine]oxalyl diamide), which is indeed capable to mimic catalase enzymes, in charge of preventing cell oxidative damage by decomposing, efficiently, hydrogen peroxide to water and oxygen (2H2O2 → 2 H2O + O2). With these results in hand, we then prepared a new multivariate bioMOF (MTV-bioMOF) that combines two different types of bioligands derived from L-serine and L-histidine amino acids with formula CaIICuII6[(S,S)-serimox]2[(S,S)-hismox]1(OH)2(H2O)}·27H2O (2) (hismox = bis[(S)-histidine]oxalyl diamide ligand). MTV-bioMOF 2 outperforms 1 degrading hydrogen peroxide, confirming the importance of the amino acid residue from the histidine amino acid acting as a nucleophile in the catalase degradation mechanism. Despite displaying a more modest catalytic behavior than other reported MOF composites, in which the catalase enzyme is immobilized inside the MOF, this work represents the first example of a MOF in which an attempt is made to replicate the active center of the catalase enzyme with its constituent elements and is capable of moderate catalytic activity.

Stepwise construction of multi-component metal-organic frameworks

Multi-component metal-organic frameworks (MC-MOFs) are crystalline porous materials containing multiple organic ligands or mixed metals, which manifest new properties beyond the linear combination of the single component. However, the traditional one-pot synthesis method for MOFs is not always applicable for synthesizing MC-MOFs due to the competitive coordination of multiple ligands and metals. Therefore, the stepwise construction of MC-MOFs has been explored, which enables more precise control of the heterogeneity within the ordered MC-MOFs. This review provides a summary of the synthesis strategies, namely, ligand exchange, coordinative modification, covalent modification, ligand metalation, cluster metalation, and use of mixed-metal precursors, for the stepwise construction of MC-MOFs. Furthermore, we discuss the applications of MC-MOFs with ordered arrangements of multiple functionalities, focusing on gas adsorption and separation, water remediation, heterogeneous catalysis, luminescence, and chemical sensing.

Degradation of Penicillinic Antibiotics and β-Lactamase Enzymatic Catalysis in a Biomimetic Zn-Based Metal-Organic Framework

β-Lactam antibiotics are one of the most commonly prescribed drugs to treat bacterial infections. However, their use has been somehow limited given the emergence of bacteria with resistance mechanisms, such as β-lactamases, which inactivate them by degrading their four-membered β-lactam rings. So, a total knowledge of the mechanisms governing the catalytic activity of β-lactamases is required. Here, we report a novel Zn-based metal-organic framework (MOF, 1), possessing functional channels capable to accommodate and interact with antibiotics, which catalyze the selective hydrolysis of the penicillinic antibiotics amoxicillin and ceftriaxone. In particular, MOF 1 degrades, very efficiently, the four-membered β-lactam ring of amoxicillin, acting as a β-lactamase mimic, and expands the very limited number of MOFs capable to mimic catalytic enzymatic processes. Combined single-crystal X-ray diffraction (SCXRD) studies and density functional (DFT) calculations offer unique snapshots on the host-guest interactions established between amoxicillin and the functional channels of 1. This allows to propose a degradation mechanism based on the activation of a water molecule, promoted by a Zn-bridging hydroxyl group, concertedly to the nucleophilic attack to the carbonyl moiety and the cleaving of C-N bond of the lactam ring.

Peptide-derived coordination frameworks for biomimetic and selective separation

Peptide-derived metal-organic frameworks (PMOFs) have emerged as a class of biomimetic materials with attractive performances in analytical and bioanalytical chemistry. The incorporation of biomolecule peptides gives the frameworks conformational flexibility, guest adaptability, built-in chirality, and molecular recognition ability, which greatly accelerate the applications of PMOFs in enantiomeric separation, affinity separation, and the enrichment of bioactive species from complicated samples. This review focuses on the recent advances in the engineering and applications of PMOFs in selective separation. The unique biomimetic size-, enantio-, and affinity-selective performances for separation are discussed along with the chemical structures and functions of MOFs and peptides. Updates of the applications of PMOFs in adaptive separation of small molecules, chiral separation of drug molecules, and affinity isolation of bioactive species are summarized. Finally, the promising future and remaining challenges of PMOFs for selective separation of complex biosamples are discussed.

Metal-organic frameworks as chemical nanoreactors for the preparation of catalytically active metal compounds

Since the emergence of metal-organic frameworks (MOFs), a myriad of thrilling properties and applications, in a wide range of fields, have been reported for these materials, which mainly arise from their porous nature and rich host-guest chemistry. However, other important features of MOFs that offer great potential rewards have been only barely explored. For instance, despite the fact that MOFs are suitable candidates to be used as chemical nanoreactors for the preparation, stabilization and characterization of unique functional species, that would be hardly accessible outside the functional constrained space offered by MOF channels, only very few examples have been reported so far. In particular, we outline in this feature recent advances in the use of highly robust and crystalline oxamato- and oxamidato-based MOFs as reactors for the in situ preparation of well-defined catalytically active single atom catalysts (SACS), subnanometer metal nanoclusters (SNMCs) and supramolecular coordination complexes (SCCs). The robustness of selected MOFs permits the post-synthetic (PS) in situ preparation of the desired catalytically active metal species, which can be characterised by single-crystal X-ray diffraction (SC-XRD) taking advantage of its high crystallinity. The strategy highlighted here permits the always challenging large-scale preparation of stable and well-defined SACs, SNMCs and SCCs, exhibiting outstanding catalytic activities.

(Multivariate)-Metal-Organic Framework for Highly Efficient Antibiotic Capture from Aquatic Environmental Matrices

Contamination of aquatic environments by pharmaceuticals used by modern societies has become a serious threat to human beings. Among them, antibiotics are of particular concern due to the risk of creating drug-resistant bacteria and, thus, developing efficient protocols for the capture of this particular type of drug is mandatory. Herein, we report a family of three isoreticular MOFs, derived from natural amino acids, that exhibit high efficiency in the removal of a mixture of four distinct families of antibiotics, such as fluoroquinolones, penicillins, lincomycins, and cephalosporins, as solid-phase extraction (SPE) sorbents. In particular, a multivariate (MTV)-MOF, prepared using equal percentages of amino acids l-serine and l-methionine, also exhibits outstanding recyclability, surpassing the benchmark material activated carbon. The good removal performance of the MTV-MOF was rationalized by means of single-crystal X-ray diffraction. These results highlight the situation of MOFs as a real and promising alternative for the capture of antibiotics from environmental matrices, especially wastewater streams.

Uncommon 3D Twofold Interpenetrated Zinc Phosphate Consisting of Inorganic Chains and Mixed Ligands for Highly Efficient Dye Removal Ability Using Its Nanosized Particles

The flexible blocks are the primary building units for constructing crystalline solids with interpenetrating structures. Herein, we reported a novel class of crystalline material with such structural features, which was made of two tetradentate ligands and one-dimensional (1D) rigid chains of zinc phosphate. This is also the first example of transition metal phosphate incorporating a squarate linker. Furthermore, efficient dye removal ability has been presented.

Multivariate Metal-Organic Framework/Single-Walled Carbon Nanotube Buckypaper for Selective Lead Decontamination

The search for efficient technologies empowering the selective capture of environmentally harmful heavy metals from wastewater treatment plants, at affordable prices, attracts wide interest but constitutes an important technological challenge. We report here an eco-friendly single-walled carbon nanotube buckypaper (SWCNT-BP) enriched with a multivariate amino acid-based metal-organic framework (MTV-MOF) for the efficient and selective removal of Pb²⁺ in multicomponent water systems. Pristine MTV-MOF was easily immobilized within the porous network of entangled SWCNTs, thus obtaining a stable self-standing adsorbing membrane filter (MTV-MOF/SWCNT-BP). SWCNT-BP alone shows a moderately good removal performance with a maximum adsorption capacity of 180 mg·g^-1 and a considerable selectivity for Pb(II) ions in highly concentrated multi-ion solutions over a wide range of lead concentration (from 200 to 10000 ppb). Remarkably, these features were outperformed with the hybrid membrane filter MTV-MOF/SWCNT-BP, exhibiting enhanced selectivity and adsorption capacity (310 mg·g^-1, which is up to 42% higher than that of the neat SWCNT-BP) and consequently enabling a more efficient and selective removal of Pb²⁺ from aqueous media. MTV-MOF/SWCNT-BP was able to reduce [Pb²⁺] from the dangerous 1000 ppb level to acceptable limits for drinking water, below 10 ppb, as established by the current EPA and WHO limits. Thus, the eco-friendly composite MTV-MOF/SWCNT-BP shows the potential to be effectively used several times as a reliable adsorbent for Pb²⁺ removal for household drinking water or in industrial treatment plants for water and wastewater lead decontamination.

Stable Crystalline Organic-Inorganic Hybrid Indium Phosphate with Dye Removal and Ractopamine Detection Applications

A highly stable framework of an organic-inorganic hybrid indium phosphate (NTOU-7) was synthesized under hydro(solvo)thermal conditions and structurally characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy. This is the first example of a post-transition-metal phosphate incorporating tetradentate organic molecules. The In atoms in the inorganic layers are coordinated by imidazole rings of the 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene linkers to generate a new solid-state material. NTOU-7 showed high chemical stability and displayed excellent performance for both dye removal and ractopamine (RAC) detection, which are interesting environmental and biosensing applications. The sensitivity and ultralow limit of detection were 607.9 μA·μM·cm^-2 and 2.74 × 10^-10 mol·L^-1 (0.08 ppb), which meet the requirements stated by the Codex Alimentarius Commission (10 ppb RAC residue in beef and pork). The detection performance was confirmed by sensing spiked-in RAC in real pork samples. We also reported the synthesis, characterization, structural stability, dye removal, and sensing properties of NTOU-7.

Facile and Green Synthesis of Starfruit-Like ZIF-L, and Its Optimization Study

Due to its excellent characteristics, zeolitic imidazole framework-L (ZIF-L) is widely used in various applications, such as drug delivery, wastewater treatments and energy storage. In the synthesis of ZIF-L, the molar ratio of ligand to metal, the reaction time and the temperature are essential parameters to produce excellent ZIF-L. In this work, ZIF-L was synthesized using a facile and green synthesis method. It was statistically investigated and optimized to obtain the best operating conditions. The optimization was carried out toward the amount of adsorbed crystal violet (CV) dye (q) as the response in the statistics. The optimal ZIF-L was obtained using a molar ratio of ligand to metal of 8.2220 for 97 min at 29 °C, where the q value of the CV adsorption onto this optimal ZIF-L reached 823.02 mg/g. The obtained ZIF-L was characterized using SEM, XRD, FTIR and TGA analyses to ensure its excellent characteristics.

Optimizing Fe-Based Metal-Organic Frameworks through Ligand Conformation Regulation for Efficient Dye Adsorption and C2 H2 /CO2 Separation

Regulating the structure of metal-organic frameworks (MOFs) by adjusting the ligands reasonably is expected to enhance the interaction of MOFs on special molecules/ions, which has significant application value for the selective adsorption of guest molecules. Herein, two tricarboxylic ligands H₃ L-Cl and H₃ L-NH₂ were designed and synthesized based on the ligand H₃ TTCA by replacing part of the benzene rings with C=C bonds and modifying the chlorine and amino groups on the 4-position of the benzene ring. Two 3D Fe-MOFs (UPC-60-Cl and UPC-60-NH₂ ) with the new topology types were constructed. As the C=C bonds of the ligands have flexible torsion angles, UPC-60-Cl features three types of irregular 2D channels, while UPC-60-NH₂ has a cage with two types of windows on the surface. The synergistic effect of unique channels and modification of functional groups endows UPC-60-Cl and UPC-60-NH₂ with high adsorption capacity for organic dyes. Compound UPC-60-Cl shows high adsorption capacity for CV (147.2 mg g^-1 ), RHB (100.3 mg g^-1 ), and MO (220.9 mg g^-1 ), whereas UPC-60-NH₂ exhibits selective adsorption of MO (158.7 mg g^-1 ). Meanwhile, based on the diverse pore structure and modification of active sites, UPC-60-Cl and UPC-60-NH₂ show the selective separation of equimolar C₂ H₂ /CO₂ . Therefore, reasonable regulation of organic ligands plays a significant role in guiding the structure diversification and performance improvement of MOFs.

Highly Efficient Removal of Neonicotinoid Insecticides by Thioether-Based (Multivariate) Metal-Organic Frameworks

Circumventing the impact of agrochemicals on aquatic environments has become a necessity for health and ecological reasons. Herein, we report the use of a family of five eco-friendly water-stable isoreticular metal-organic frameworks (MOFs), prepared from amino acids, as adsorbents for the removal of neonicotinoid insecticides (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid) from water. Among them, the three MOFs containing thioether-based residues show remarkable removal efficiency. In particular, the novel multivariate MOF {Sr^IICu^II₆[(S,S)-methox]_1.5[(S,S)-Mecysmox]_1.50(OH)₂(H₂O)}·36H₂O (5), featuring narrow functional channels decorated with both -CH₂SCH₃ and -CH₂CH₂SCH₃ thioalkyl chains-from l-methionine and l-methylcysteine amino acid-derived ligands, respectively-stands out and exhibits the higher removal efficiency, being capable to capture 100% of acetamiprid and thiacloprid in a single capture step under dynamic solid-phase extraction conditions-less than 30 s. Such unusual combination of outstanding efficiency, high stability in environmental conditions, and low-cost straightforward synthesis in 5 places this material among the most attractive adsorbents reported for the removal of this type of contaminants.

Recent advances in metal-organic frameworks as adsorbent materials for hazardous dye molecules

Water is vital for the sustenance of all forms of life. Hence, water pollution is a universal crisis for the survival for all forms of life and a hurdle in sustainable development. Textile industry is one of the anthropogenic activities that severely pollutes water bodies. Inefficient dyeing processes result in thousands of tons of synthetic dyes being dumped in water bodies every year. Therefore, the efficient removal of synthetic dyes from wastewater has become a challenging research field. Owing to their tuneable structure-property aspects, metal-organic frameworks (MOFs) have emerged as promising adsorbents for the adsorptive removal of dyes from wastewater and textile effluents. In this perspective, we highlight recent studies involving the application of MOFs for the adsorptive removal of hazardous dye molecules. We also classify the developed MOFs into cationic, anionic, and neutral framework categories to comprehend their suitability for the removal of a given class of dyes.

Tuning of Delicate Host-Guest Interactions in Hydrated MIL-53 and Functional Variants for Furfural Capture from Aqueous Solution

Capture of high-boiling-point furfural from diluted aqueous solution is a critical but challenging step in sustainable bio-refinery processes, but conventional separation methods such as distillation and liquid-liquid extraction requires prohibitive energy consumption. We report control over the microenvironment of hydrated MIL-53 and isoreticular variants with diversified functional terephthalic acid linkers for the purpose of preferential binding of furfural through delicate host-guest interactions. Methyl-bounded MIL-53 with improved binding energy in the hydrated form results in highly efficient capture ratio (ca. 98 %) in the extremely low concentration of furfural solution (0.5-3 wt %) and 100 % furfural specificity over xylose. The distinct hydrogen bonding sites and multiple Van de Wall interactions for furfural adsorption was testified by computational modeling. Furthermore, the recovery ratio of furfural reaches ca. 93 % in desorption.

Reverse osmosis and nanofiltration membranes for highly efficient PFASs removal: overview, challenges and future perspectives

PFASs are called “forever chemicals” because they do not fully degrade. They have become so ubiquitous in the environment that it is difficult to prevent exposure. This review aims to provide a set of improved technologies to remove PFASs from water.

Hydrolase-like catalysis and structural resolution of natural products by a metal-organic framework

The exact chemical structure of non-crystallising natural products is still one of the main challenges in Natural Sciences. Despite tremendous advances in total synthesis, the absolute structural determination of a myriad of natural products with very sensitive chemical functionalities remains undone. Here, we show that a metal-organic framework (MOF) with alcohol-containing arms and adsorbed water, enables selective hydrolysis of glycosyl bonds, supramolecular order with the so-formed chiral fragments and absolute determination of the organic structure by single-crystal X-ray crystallography in a single operation. This combined strategy based on a biomimetic, cheap, robust and multigram available solid catalyst opens the door to determine the absolute configuration of ketal compounds regardless degradation sensitiveness, and also to design extremely-mild metal-free solid-catalysed processes without formal acid protons.

The Nanosized Dye Adsorbents for Water Treatment

Clean water is a vital element for survival of any living creature and, thus, crucially important to achieve largely and economically for any nation worldwide. However, the astonishingly fast trend of industrialization and population growth and the arisen extensive water pollutions have challenged access to clean water across the world. In this regard, 1.6 million tons of dyes are annually consumed. Thereof, 10%–15% are wasted during use. To decolorize water streams, there is an urgent need for the advanced remediation approaches involving utilization of novel materials and technologies, which are cost and energy efficient. Nanomaterials, with their outstanding physicochemical properties, can potentially resolve the challenge of need to water treatment in a less energy demanding manner. In this review, a variety of the most recent (from 2015 onwards) opportunities arisen from nanomaterials in different dimensionalities, performances, and compositions for water decolorization is introduced and discussed. The state-of-the-art research studies are presented in a classified manner, particularly based on structural dimensionality, to better illustrate the current status of adsorption-based water decolorization using nanomaterials. Considering the introduction of many newly developed nano-adsorbents and their classification based on the dimensionality factor, which has never been employed for this sake in the related literature, a comprehensive review will be presented.

Coordinatively Unsaturated Metal Site-Promoted Selective Adsorption of Organic Molecules on Supported Metal-Organic Framework Nanosheets

Metal-organic frameworks (MOFs) are a class of customizable porous material, which have shown good performance in separation processes, because of their large surface area and molecular recognition property. Although the effects of chemical structure of MOFs on their separation performance were extensively studied, the exploration of their surface properties was still limited. This work demonstrated a MOF nanosheet with large amount of coordinatively unsaturated metal sites, Cu(BDC) (copper(II) benzenedicarboxylate), where the unsaturated Cu sites were utilized to selectively adsorb organic molecules with Lewis basicity. This work also investigated the direct growth of Cu(BDC) on the cellulose substrate, where the MOF nanosheets were immobilized on the cellulose substrate, enabling the composite material for practical applications. The heterogeneous nucleation and growth of MOF nanosheets on the cellulose were achieved by tuning the basicity of solution and reaction temperature. We believe this direct growth approach can be applied to other MOF composite materials for separation and purification purposes, as well as other applications involving molecular recognition properties of MOFs, such as sensing, catalysis, and enzyme immobilization.