A microporous -topology metal–organic framework with an unprecedented high-nuclearity Co10-cluster for iodine capture and histidine detection

Two Metal-Organic Frameworks with a Fused Cis-Decalin Conformation for Multimedia Iodine Capture

The extensive growth of nuclear power plants has a severe detrimental effect on human health and the surroundings due to the uncontrolled and unfiltered release of radioactive wastes into the environment. One such radioactive waste is 129I which has a fatal effect when released into the air or water bodies. Hence, molecular and ionic iodine capture from multimedia has become an important area of interest in the recent past. This work is aimed at introducing two 2D metal-organic frameworks with a fused cis-decalin conformation, {[Zn2(tpbn)(fdc)2]·6H2O}n (1) and {[Cd2(tpbn)(fdc)2(H2O)2]·2H2O}n (2), synthesized at room temperature utilizing a combination of M(OAc)2·2H2O (M: Zn/Cd), a neutral flexible ligand, tpbn, and a simple commercially available furan dicarboxylate, fdc2-, for the target application. The polarizing nature of the furan moieties and the oxygen rich pores in 1 and 2 facilitate the easy capture of molecular iodine from both the vapor phase and aqueous media with high uptake values. Furthermore, their efficiency was tested for the practical application under real-world conditions using river and seawater. In addition to confirming their recyclability with the retention of structural integrity, the interaction between 1 and 2 with iodine has also been established with experimental and theoretical calculations.

Optimizing Iodine Enrichment through Induced-Fit Transformations in a Flexible Ag(I)-Organic Framework: From Accelerated Adsorption Kinetics to Record-High Storage Density

Efficient capture and storage of radioactive I2 is a prerequisite for developing nuclear power but remains a challenge. Here, two flexible Ag-MOFs (FJI-H39 and 40) with similar active sites but different pore sizes and flexibility are prepared; both of them can capture I2 with excellent removal efficiencies and high adsorption capacities. Due to the more flexible pores, FJI-H39 not only possesses the record-high I2 storage density among all the reported MOFs but also displays a very fast adsorption kinetic (124 times faster than FJI-H40), while their desorption kinetics are comparable. Mechanistic studies show that FJI-H39 can undergo induced-fit transformations continuously (first contraction then expansion), making the adsorbed iodine species enrich near the Ag(I) nodes quickly and orderly, from discrete I- anion to the dense packing of various iodine species, achieving the very fast adsorption kinetic and the record-high storage density simultaneously. However, no significant structural transformations caused by the adsorbed iodine are observed in FJI-H40. In addition, FJI-H39 has excellent stability/recyclability/obtainability, making it a practical adsorbent for radioactive I2. This work provides a useful method for synthesizing practical radioactive I2 adsorbents.

Bacterial Cellulose-Based MOF Hybrid as a Sensitive Switch Off-On Luminescent Sensor for the Selective Recognition of l-Histidine

In this study, a stable and luminescent UiO-66-NH2 (UN) and its derivative Cu2+@UN were prepared and utilized successfully as an Off-On luminescent sensing platform for effective, selective, as well as rapid (5 min) detection of l-Histidine (l-His). The UN reveals efficient quenching in the presence of Cu2+ ions through photoinduced electron transition (PET) mechanism as a dynamic quenching process (in the range of 0.01-1 mM) forming Cu2+@UN sensing platform. However, due to the remarkable affinity between l-His and Cu2+, the luminescence of Cu2+@UN is recovered in the presence of l-His indicating Turn-On behavior via a quencher detachment mechanism (QD). A good linear relationship between the l-His concentration and luminescence intensity was observed in the range of 0.01-40 μM (R2 = 0.9978) with a detection limit of 7 nM for l-His sensing. The suggested method was successfully utilized for l-His determination in real samples with good recoveries and satisfying consequences. Moreover, the result indicates that only l-His induces a significant luminescence restoration of Cu2+@UN and that the signal is significantly greater than that of the other amino acids. Also, the portable test paper based on bacterial cellulose (BC) as the Cu2+@UNBC sensing platform was developed to conveniently evaluate the effective detection of l-His.

Highly Emissive and Robust Cd-Based MOF with an Unprecedented Topology for Tetracycline Sensing

Herein, an unprecedented cadmium-based metal-organic framework (JNU-106) fabricated by utilizing pyrazole-functionalized tetraphenylethylene ligands (Py-TPE) and rod-shaped secondary building units is reported, possessing a new (3,3,3,6,6,8)-connected topological network. Thanks to the ingeniously designed intramolecular charge transfer behavior, which originates from the congruent coplanarity between Py and TPE, JNU-106 exhibits intense green luminescence with a quantum yield increased by 1.5 times. The phenomenon of remarkable fluorescence quenching of JNU-106 reveals that it possesses extremely high anti-interference performance, superior sensitivity, and dedicated selectivity toward tetracycline antibiotics (TCAs) in aqueous solutions, which are comparable to those of the state-of-the-art porous sensing compounds. Taking the theoretical calculations and experimental results into account, the luminescence quenching is mainly attributed to the internal filtration effect and the static quenching effect. Considering the portable and rapid performance of JNU-106-based testing strips for sensing TCAs, the fabricated JNU-106 provides an alternative for ecological monitoring and environmental governance.

Pyrazine Functionalization in Eu-MOF for Exclusive Ratiometric Luminescence Sensing of PO43

Single-emission luminescence sensors are less than satisfactory for complex systems due to their susceptibility to environmental disturbances. Lanthanum-based metal-organic frameworks (Ln-MOFs) with highly stable ratiometric dual-emission are regarded as promising luminescence probes owing to their fascinating ligand-to-metal energy transfer behaviors (also known as the antenna effect). Herein, we report the synthesis of a pair of isostructural europium-based MOFs (termed JNU-219 and JNU-220) by utilizing two X-shaped tetracarboxylate linkers, 4,4',4″,4‴-benzene-2,3,5,6-tetrayl-tetrabenzoate (BTEB) and 4,4',4″,4‴-pyrazine-2,3,5,6-tetrayl-tetrabenzoate (BTTB). Both JNU-219 and JNU-220 present the characteristic red luminescence of Eu3+, yet the pyrazine functionalization of the BTTB linker renders JNU-220 with significantly increased luminescence emission, almost 30 times that of JNU-219. As a result, the detection limit of JNU-220 for the ratiometric luminescence sensing of PO43- was determined to be as low as 0.22 μM, which is far superior to those of other reported MOF materials. Additionally, we demonstrate the excellent stability and reusability of JNU-220, further verifying its potential as a robust ratiometric luminescence probe.

Linker Engineering for Reactive Oxygen Species Generation Efficiency in Ultra-Stable Nickel-Based Metal-Organic Frameworks

Interfacial charge transfer on the surface of heterogeneous photocatalysts dictates the efficiency of reactive oxygen species (ROS) generation and therefore the efficiency of aerobic oxidation reactions. Reticular chemistry in metal-organic frameworks (MOFs) allows for the rational design of donor-acceptor pairs to optimize interfacial charge-transfer kinetics. Herein, we report a series of isostructural fcu-topology Ni8-MOFs (termed JNU-212, JNU-213, JNU-214, and JNU-215) with linearly bridged bipyrazoles as organic linkers. These crystalline Ni8-MOFs can maintain their structural integrity in 7 M NaOH at 100 °C for 24 h. Experimental studies reveal that linker engineering by tuning the electron-accepting capacity of the pyrazole-bridging units renders these Ni8-MOFs with significantly improved charge separation and transfer efficiency under visible-light irradiation. Among them, the one containing a benzoselenadiazole unit (JNU-214) exhibits the best photocatalytic performance in the aerobic oxidation of benzylamines with a conversion rate of 99% in 24 h. Recycling experiments were carried out to confirm the stability and reusability of JNU-214 as a robust heterogeneous catalyst. Significantly, the systematic modulation of the electron-accepting capacity of the bridging units in donor-acceptor-donor MOFs provides a new pathway to develop viable noble-metal-free heterogeneous photocatalysts for aerobic oxidation reactions.

Porous amorphous metal-organic frameworks based on heterotopic triangular ligands for iodine and high-capacity dye adsorption

The research on amorphous metal-organic frameworks (aMOFs) is still in its infancy, and designing and constructing aMOFs with functional pores remains a challenge. Two aMOFs based on Co(II) and heterotopic triangular ligands with large conjugated aromatic planes, namely aMOF-1 and aMOF-2, were constructed and characterized by IR, XPS, EA, ICP, XANS and so on. aMOF-1 possesses mesopores, whereas aMOF-2 possesses micropores. The porosity, conjugated aromatic plane and uncoordinated N atoms in the framework allow these aMOFs to adsorb iodine and dyes. The iodine adsorption capacity of aMOF-1 is 3.3 g per g, which is higher than that of aMOF-2 (0.56 g per g), mainly due to the expansion or swelling of aMOF-1 after iodine adsorption. The uptake of cationic dyes by aMOF-2 showed more rapid kinetics and a higher removal rate than that by aMOF-1, mainly due to the difference in the porosity and surface charge. Although the surface charges of aMOF-1 and aMOF-2 are negative, both of them showed significantly faster adsorption kinetics toward anionic dyes, among which methyl orange (MO) and Congo red (CR) can be removed in 5 min. This occurs possibly because the quick adsorption of Na+ ions alters the surface charge of the framework and promotes dye uptake. The adsorption capacities of aMOF-1 for MO and CR reached 921 and 2417 mg g-1, respectively. The correlation data for aMOF-2 are 1042 and 1625 mg g-1, respectively. All adsorption capacities are among the highest compared to many cMOFs. Adsorption in mixed dye solution is found to be charge-dependent, kinetic-dependent, and synergetic in these systems. The porosity, surface charge regulation during adsorption, weak interactions and multiple adsorption processes contribute to the dye adsorption performance.

Analysis of Radioactive Iodine Trapping Mechanism by Zinc-Based Metal-Organic Frameworks with Various N-Containing Carboxylate Ligands

This study aimed to develop effective adsorbents for capturing radioactive iodine in nuclear power waste gas. Two zinc metal-organic frameworks (Zn-MOFs) were synthesized and found to have favorable properties such as a large surface area, thermal stability, surface rich in π-electron-containing nitrogen, and redox potential. Adsorption experiments revealed maximum capacities of 1.25 and 1.96 g g^-1 for the MOFs at 75 °C, with the pseudo-second-order kinetic model fitting the data well. The Langmuir equation provided a better fit in cyclohexane, with maximum adsorption amounts of 249 and 358 mg g^-1 for Zn-MOF-1 and Zn-MOF-2, respectively. The MOFs were also stable during six cycles of adsorption and desorption. Furthermore, electron transfer occurred due to the synergistic adsorption of Zn, N, and O atoms, resulting in the conversion of some iodine to polyiodide. Zn-MOF-2 exhibited better chemisorption than Zn-MOF-1 due to a smaller highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap. Notably, it was discovered that N-containing radicals had stronger interactions with iodine compared to radicals without N. These findings provide valuable insights into MOF synthesis and environmental protection.

Two Co-Based Metal-Organic Framework Isomers with Similar Metal-Carboxylate Sheets: Turn-On Ratiometric Luminescence Sensing Activities toward Biomarker N-Acetylneuraminic Acid and Discrimination of Ga3+ and In3

Two supramolecular Co-MOF isomers, namely, {[Co(L)_0.5(m-bimb)]·3H₂O}_n (LCU-115) and {[Co(L)_0.5(p-bimb)]·3H₂O}_n (LCU-116), were synthesized from an amide-containing carboxylic acid N,N″-(3,5-dicarboxylphenyl)benzene-1,4-dicarboxamide (H₄L) and two flexible positional isostructural N-containing ligands m-bimb and p-bimb (m-bimb = 1,3-bis((1H-imidazol-1-yl)methyl)benzene; p-bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene). The carboxylate ligands connect Co(II) centers to form 2D metal-carboxylate sheets, which are extended further by m-bimb and p-bimb to form a 2D bilayer with parallel stacking (LCU-115) and a 3D framework (LCU-116), respectively. Luminescence measurements indicated that these two complexes exhibited interesting multiresponsive sensing activities toward pH, biomarker N-acetylneuraminic acid, and trivalent cations Ga³⁺/In³⁺. They show highly sensitive turn-on fluorescence responses in the acidic range and can also be regarded as on-off-on vapoluminescent sensors to typical acidic and basic gases HCl and Et₃N. It is worth noting that these complexes have excellent turn-on ratiometric fluorescence sensing ability for N-acetylneuraminic acid (NANA) with detection limits as low as 7.39 and 8.06 μM, respectively. Furthermore, they were successfully applied for the detection of NANA in simulated urine and serum samples with satisfactory results. For ion detection, LCU-116 could detect both Ga³⁺ and In³⁺, while LCU-115 could distinguish Ga³⁺ from In³⁺ with the latter showing luminescence quenching. The sensing mechanism was investigated in detail by XRD, UV-vis, EDS, XPS, SEM, and TEM. The results of interday and intraday precision studies gave low RSD values in the range of 1.19-3.53%, ascertaining the reproducibility of these sensors. The recoveries for the sensing analytes in simulated urine/serum or real water are satisfactory from 96.7 to 103.3% (toward NANA) and 96.6 to 115.0% (toward Ga³⁺ and In³⁺), indicating that these two complexes also possess acceptable reliability for monitoring in real samples. The results indicated that the supramolecular isomers LCU-115 and LCU-116 are promising material candidates for application in biological and environmental monitoring.

Cluster-Based Crystalline Materials for Iodine Capture

The treatment of radioactive iodine in nuclear waste has always been a critical issue of social concern. The rational design of targeted and efficient capture materials is of great significance to the sustainable development of the ecological environment. In recent decades, crystalline materials have served as a molecular platform to study the binding process and capture mechanism of iodine molecules, enabling people to understand the interaction between radioactive iodine guests and pores intuitively. Cluster-based crystalline materials, including molecular clusters and cluster-based metal-organic frameworks, are emerging candidates for iodine capture due to their aggregative binding sites, precise structural information, tunable pores/packing patterns, and abundant modifications. Herein, recent progress of different types of cluster materials and cluster-dominated metal-organic porous materials for iodine capture is reviewed. Research prospects, design strategies to improve the affinity for iodine and possible capture mechanisms are discussed.

AIE -active TPA modified Schiff base for successive sensing of Cu2+ and His via an on-off-on method and its application in bioimaging

In this article, a novel triphenylamine-modified salicylaldehyde Schiff base 2-(((4-(diphenylamino)phenyl)imino)methyl)-4-(pyridine-4-yl)phenol (HL) was synthesized and structurally characterized. HL possessed D-π-A structure and exhibited typical AIE property in THF/H₂O. It was applied to selectively recognize Cu²⁺ through an on-off mode in THF/H₂O (1/9, v/v), and the fluorescence attenuation was attributed to a paramagnetic quenching effect of Cu²⁺ together with the abatement of HL aggregates. Hence, the detection limit achieved was as low as 1.32 × 10^-7 M. The spectroscopic and ESI-HRMS results revealed a 1 : 2 complexation ratio of Cu²⁺ with HL. The mechanism for sensing Cu²⁺ was further confirmed by performing DFT calculations. Owing to the large affinity between Cu²⁺ and His, the resultant CuL2 system was further used to detect His via the off-on method based on the displacement of ligands. The detection limit for His reached 5.14 × 10^-8 M. Furthermore, HL was available to prepare handy indicator papers for the on-site recognition of Cu²⁺ and His. Confocal fluorescent imaging demonstrated that HL could sequentially respond to intracellular Cu²⁺ and His.

Stable bifunctional ZnII-based sensor toward acetylacetone and L-histidine by fluorescence red shift and turn-on effect

A new coordination polymer [Zn(bbip)(NH2-BDC)]n (JXUST-15, bbip = 2,6-bis(benzimidazol-1-yl)pyridine and NH2-H2BDC = 2-aminoterephthalic acid) has been synthesized by mixed ligand strategy. The structure analysis shows that JXUST-15 takes a two-dimensional...

Amorphous metal-organic frameworks obtained from a crystalline precursor for the capture of iodine with high capacities

Two amorphous metal−organic frameworks (aMOFs) were obtained from crystalline Co-MOF (SCNU-Z6) via temperature-induced (aT-SCNU-Z6) and water-immersed (aW-SCNU-Z6) approaches. They exhibited high iodine uptake, with the adsorption capacities of aT-SCNU-Z6 and...

Multifunctional AIEgen-based luminescent metal–organic frameworks with coordination-induced emission for chemical sensing

Aggregation-induced emission luminogens (AIEgens) offer a timely remedy to tackle aggregation-caused quenching of traditional organic fluorescence probes.

An yttrium-organic framework based on a hexagonal prism second building unit for luminescent sensing of antibiotics and highly effective CO2 fixation

An yttrium-organic framework based on a hexagonal prism second building unit was constructed from nonanuclear yttrium(iii) and 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine for the luminescent sensing of antibiotics and highly effective CO2 fixation.

A Ni(ii) metal–organic framework with helical channels for the capture of iodine via guest exchange induced amorphization

A Ni(ii) MOF based on a imidazole–tetrazole heterotopic tripodal ligand was constructed. It exhibits abilities for the stable capture of iodine molecules present in cyclohexane, water, and vapor, via amorphization induced by guest exchange.

Pyrazine Functionalization to Boost Antenna Effect in Rare-Earth Metal-Organic Frameworks for Tetracyclines Detection

Here we report a generalizable strategy for the synthesis of rare-earth metal-organic frameworks (RE-MOFs) with 12-connected RE9 clusters and shp-topology. A total of 26 isostructural RE-MOFs (JNU-205-RE and JNU-206-RE) were...

Sodalite Cd66-Cage-Based Metal-Organic Framework Constructed by Cd9 and Cd5 Metal-Organic Clusters

A sodalite Cd₆₆-cage-based metal-organic framework (MOF), namely, CPM-9S, has been constructed based on Cd₉ and Cd₅ metal-organic clusters (MOCs), which, to the best our knowledge, represents the first Cd-cage-based MOF that contains the highest-nuclear Cd-based MOC and the largest number of Cd²⁺ ions in a cage. The iodine adsorption performances in terms of the iodine adsorption capacity, adsorption isotherm, and adsorption kinetics, as well as the adsorption mechanism, have been further studied.