Recent Advances in Metal-Organic Frameworks and Their Derivatives for Adsorption of Radioactive Iodine

Radioactive iodine (131I) with a short half-life of ~8.02 days is one of the most commonly used nuclides in nuclear medicine. However, 131I easily poses a significant risk to human health and ecological environment. Therefore, there is an urgent need to develop a secure and efficient strategy to capture and store radioactive iodine. Metal-organic frameworks (MOFs) are a new generation of sorbents with outstanding physical and chemical properties, rendering them attractive candidates for the adsorption and immobilization of iodine. This review focuses on recent research advancements in mechanisms underlying iodine adsorption over MOFs and their derivatives, including van der Waals interactions, complexing interactions, and chemical precipitation. Furthermore, this review concludes by outlining the challenges and opportunities for the safe disposal of radioactive iodine from the perspective of the material design and system evaluation based on our knowledge. Thus, this paper aims to offer necessary information regarding the large-scale production of MOFs for iodine adsorption.

A Porphyrin-Based 3D Metal-Organic Framework Featuring [Cu8Cl6]10+ Cluster Secondary Building Units: Synthesis, Structure Elucidation, Anion Exchange, and Peroxidase-Like Activity

Herein, we report a rare example of cationic three-dimensional (3D) metal-organic framework (MOF) of [Cu5Cl3(TMPP)]Cl5 ⋅ xSol (denoted as Cu-TMPP; H2TMPP=meso-tetrakis (6-methylpyridin-3-yl) porphyrin; xSol=encapsulated solvates) supported by [Cu8Cl6]10+ cluster secondary building units (SBUs) wherein the eight faces of the Cl--based octahedron are capped by eight Cu2+. Surface-area analysis indicated that Cu-TMPP features a mesoporous structure and its solvate-like Cl- counterions can be exchanged by BF4 -, PF6 -, and NO3 -. The polyvinylpyrrolidone (PVP) coated Cu-TMPP (denoted as Cu-TMPP-PVP) demonstrated good ROS generating ability, producing ⋅OH in the absence of light (peroxidase-like activity) and 1O2 on light irradiation (650 nm; 25 mW cm-2). This work highlights the potential of Cu-TMPP as a functional carrier of anionic guests such as drugs, for the combination therapy of cancer and other diseases.

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.

Silver-Rich Hybrid Framework Iodide Based on [Ag8I6]2+ Clusters Displays Low-Temperature Dual Emission and Luminescence Thermochromism

Cluster-based framework metal iodides have diverse structures and excellent luminescence properties, and show promising applications in sensing and solid-state lighting. However, the design and synthesis of these materials remain great challenges because excess I^- ions introduced into the synthesis systems decrease the condensation degree of M-I units. In this work, a new strategy is developed to control the condensation behavior of Ag-I units, and a new silver-rich cluster-based framework iodide [DabcoAg₈I₆(SPh)₂]_n (1) (Dabco = 1,4-diazabicyclo [2.2.2] octane) has been synthesized under solvothermal conditions in the presence of silver thiophenolate (AgSPh)_n. Compound 1 features a three-dimensional (3-D) cluster-based framework with a pillared layer structure composed of cationic [Ag₈I₆]²⁺ clusters bridged by SPh^- and Dabco, and displays low-temperature dual emission and luminescence thermochromism.

Leonardite powder as an efficient adsorbent for cationic and anionic dyes

This paper aims to investigate the uses of leonardite powder (LP) as an effective adsorbent for the removal of basic red 18 (BR18) and reactive red 180 (RR180) dyes. LP was characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Zeta potential, Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). The adsorption process was assessed based on pH, size and the amount of the adsorbent, BR18 and RR180 concentration, and the contact time. BR18 dye was completely adsorbed onto the LP (the removal efficiency equals 100%) after 45 min at the optimum condition (original pH [6.5], the particle size of 45 μm, the adsorbent dose of 0.25 g/L, and the initial concentration of 10 mg/L). For RR180, the maximum removal efficiency (74%) was obtained when 1 g/L LP with 45 um size was added to an RR180 solution of 10 mg/L concentration. Temkin isotherm was used to explain the adsorption of BR18. In contrast, RR180 adsorption was described by the Freundlich model. The adsorptions of both dyes followed the pseudo-second-order kinetics. The reusability of the LP was assessed. For BR18, the efficiency decreased to 96% in the second cycle and reached 42% in the fifth cycle. In RR180, LP was not able to be reused efficiently. As a result, the LP ability for BR18 removal is higher than the RR180 in terms of uptake and reusability. PRACTITIONER POINTS: BR18 and RR180 dyes elimination was carried out with leonardite powder (LP). The maximum removal efficiencies for BR18 and RR180 were 100% and 74%, respectively. The LP ability for BR18 removal is higher than the RR180 in terms of uptake and reusability.

Iodine-Chemisorption, Interpenetration and Polycatenation: Cationic MOFs and CPs from Group 13 Metal Halides and Di-Pyridyl-Linkers

Eight cationic, two-dimensional metal-organic frameworks (MOFs) were synthesized in reactions of the group 13 metal halides AlBr3 , AlI3 , GaBr3 , InBr3 and InI3 with the dipyridyl ligands 1,2-di(4-pyridyl)ethylene (bpe), 1,2-di(4-pyridyl)ethane (bpa) and 4,4'-bipyridine (bipy). Seven of them follow the general formula 2 ∞ [MX2 (L)2 ]A, M=Al, In, X=Br, I, A- =[MX4 ]- , I- , I3 - , L=bipy, bpa, bpe. Thereby, the porosity of the cationic frameworks can be utilized to take up the heavy molecule iodine in gas-phase chemisorption vital for the capture of iodine radioisotopes. This is achieved by switching between I- and the polyiodide I3 - in the cavities at room temperature, including single-crystal-to-single-crystal transformation. The MOFs are 2D networks that exhibit (4,4)-topology in general or (6,3)-topology for 2 ∞ [(GaBr2 )2 (bpa)5 ][GaBr4 ]2 ⋅bpa. The two-dimensional networks can either be arranged to an inclined interpenetration of the cationic two-dimensional networks, or to stacked networks without interpenetration. Interpenetration is accompanied by polycatenation. Due to the cationic character, the MOFs require the counter ions [MX4 ]- , I- or I3 - counter ions in their pores. Whereas the [MX4 ]- , ions are immobile, iodide allows for chemisorption. Furthermore, eight additional coordination polymers and complexes were identified and isolated that elaborate the reaction space of the herein reported syntheses.

Rapid synthesis of polyimidazole functionalized MXene via microwave-irradiation assisted multi-component reaction and its iodine adsorption performance

The adsorption applications of MXene-based adsorbents have intensively investigated recently. However, the performance of MXene-based adsorbents has been largely limited owing to their lack of functional groups and adsorptive sites. Therefore, surface functionalization of MXene is an important route to achieve better performance for environmental adsorption. Herein, polyionic liquid functionalized MXene (named as MXene-PIL) was prepared through a multi-component reaction and adsorptive removal of iodine by MXene-PIL was also evaluated. The successful generation of PIL on MXene was confirmed by a series of characterization measurements. Furthermore, the effects of contact time, iodine concentration, environmental temperature and other factors on the adsorption performance of MXene-PIL were investigated. Adsorption kinetic analysis including pseudo-first-order dynamic model, pseudo-second-order dynamic model and Weber-Morris model, adsorption thermodynamic analysis such as Langmuir and Freundlich models and Van't Hoff equation were used for further analysis the adsorption behavior of iodine by MXene-PIL. We demonstrated that the adsorption capacity could be as high as about 170 mg/g, which is obviously larger than the unmodified MXene and most of other reported adsorbents. Taken together, a simple strategy has been developed for in-situ generation of PIL on MXene and the resultant composites show potential application for adsorptive removal of iodine.

Hierarchically porous FeNi3@FeNi layered double hydroxide nanostructures: one-step fast electrodeposition and highly efficient electrocatalytic performances for overall water splitting

FeNi-layered double hydroxide (LDH) is thought to be an excellent electrocatalyst for oxygen evolution reaction (OER) but it always shows extremely poor electrocatalytic activity toward hydrogen evolution reaction (HER) in alkaline media. Hence, it is significant to improve its HER activity to make it a bifunctional electrocatalyst for the decomposition of water. Here, a simple galvanostatic electrodeposition method was designed for the successful construction of the bifunctional FeNi₃@FeNi LDH electrocatalyst. The as-prepared catalyst displayed excellent electrocatalytic activity for HER/OER in 1.0 M KOH. To drive the current density of 10 mA cm^-2 for HER/OER, an overpotential of 106/199 mV was needed, respectively. In a two-electrode system with the FeNi₃@FeNi LDH/NF as the anode and the cathode simultaneously, the overpotential hardly changed after continuously working for 168 h at 10 mA cm^-2. Compared with other FeNi-based catalysts, the present catalyst possessed close or better electrocatalytic activity.

The role of coordination compounds in virus research. Different approaches and trends

This article aims to provide an overview of the studies focused on using coordination compounds as antiviral agents against different types of viruses. We present various strategies so far used to this end. This article is divided into two sections. The first collects the series of designed antiviral drugs based on coordination compounds. This approach has been developed for many years, starting from the 70s with the discovery of cis-platin (cis-DDP). It has been mainly focused on studying the synergistic effect of a wide variety of new compounds obtained by combining metal ions with organic antiviral ligands. Then, we collect various strategies analyzing the coordination compounds interacting with viruses using different processes such as wrapping viruses, rapid detection of RNA or DNA virus, or nanocarriers. These recent and novel insights help to study viruses from other points of view, allowing to measure their physical and chemical properties. We also highlight a section in which the issue of viruses from a disinfection viewpoint is addressed, using coordination compounds as a tool able to control the release of antiviral and biocide agents. This is an emerging and promising field but this approach is actually little developed. We finally provide a section with a general conclusion and perspectives.

Biocompatible MOF-808 as an iodophor antimicrobial agent with controlled and sustained release of iodine

I2@MOF-808 was prepared to investigate the amount of I2 adsorbed on MOF-808. By antibacterial tests, it was also confirmed that it could be considered as a biocide without the problem of microbial resistance and instability of iodine.

Template effect of innocent and coordinating anions on the formation of interpenetrated 2D and 3D networks: methyl orange and iodine sorption studies

A pyridyl based Schiff base resulted in a 2D staircase network (CP1) with Cd(ii) when ClO₄⁻ is the counter anion while the use of benzene-1,3-disulphonate counter anion resulted in a novel 3D Cd(ii) coordination polymer with threefold interpenetration (CP2).

Design and properties of multiple-emitter luminescent metal–organic frameworks

This feature article reviews the design strategies by which multiple different emission sources could be combined for creating multi-emitter luminescent metal–organic frameworks (LMOFs).

Bisimidazole-based phosphorescent thiocyanatocadmates

Simple room-temperature self-assemblies between Cd2+ salts, SCN- and bisimidazole molecules at pH = 2 created three new organically templated thiocyanatocadmates [H2(L1)][Cd(SCN)4]·H2O (L1 = 1,4-bis(1H-imidazol-1-yl)benzene) 1, [H2(L2)][Cd(SCN)4] (L2 = 1,3-bis(2-methylimidazol-1-yl)propane) 2, and [H2(L3)][Cd2(SCN)6] (L3 = 1,4-bis(2-methyl-1H-imidazol-1-yl)butane) 3. X-ray single-crystal diffraction analysis reveals that (i) in 1-3, the SCN- groups doubly bridge the Cd2+ centers to form different thiocyanatocadmates: a linear chain in 1; a zigzag chain in 2; and a 2-D layer network (63 net) in 3; and (ii) in 1, via Nbase-HNSCN interactions, the L1 molecules extend the thiocyanatocadmate chains into a 2-D supramolecular layer, whereas in 2, the zigzag thiocyanatocadmate chains self-assemble into a 3-D supramolecular network via weak SS interactions. Photoluminescence analysis indicates that the three title compounds all emit light: blue light for 1 and 2 and green light for 3. At low temperatures, the emission positions of the three compounds hardly change, but the emission intensities are largely enhanced. Interestingly, after turning off the UV lamp, 1 and 2 still briefly emit light (ca. 2 s), which means that 1 and 2 possess phosphorescence properties. Phosphorescence lifetimes at 77 K are 1619 ms for 1 and 247 ms for 2.

Cadmium(II) three-dimensional coordination polymers constructed from 1,3,5-tris(4-carboxyphenoxy)benzene: synthesis, crystal structure, fluorescence and I2 sorption characterization

Two three-dimensional (3D) CdII coordination polymers, namely poly[[di-μ-aqua-diaquabis{μ5-4,4′,4′′-[benzene-1,3,5-triyltris(oxy)]tribenzoato}tricadmium(II)] dihydrate], {[Cd3(C27H15O9)2(H2O)4]·2H2O} n , (I), and poly[[aqua{μ6-4,4′,4′′-[benzene-1,3,5-triyltris(oxy)]tribenzoato}(μ-formato)[μ-1,1′-(1,4-phenylene)bis(1H-imidazole)]dicadmium(II)] dihydrate], {[Cd2(C27H15O9)(C12H10N4)(HCOO)(H2O)]·2H2O} n , (II), have been hydrothermally synthesized from the reaction system containing Cd(NO3)2·4H2O and the flexible tripodal ligand 1,3,5-tris(4-carboxyphenoxy)benzene (H3tcpb) via tuning of the auxiliary ligand. Both complexes have been characterized by single-crystal X-ray diffraction analysis, elemental analysis, IR spectra, powder X-ray diffraction and thermogravimetric analysis. Complex (I) is a 3D framework constructed from trinuclear structural units and tcpb3− ligands in a μ5-coordination mode. The central CdII atom of the trinuclear unit is located on a crystallographic inversion centre and adopts an octahedral geometry. The metal atoms are bridged by four syn–syn carboxylate groups and two μ2-water molecules to form trinuclear [Cd3(COO)4(μ2-H2O)2] secondary building units (SBUs). These SBUs are incorporated into clusters by bridging carboxylate groups to produce pillars along the c axis. The one-dimensional inorganic pillars are connected by tcpb3− linkers in a μ5-coordination mode, thus forming a 3D network; its topology corresponds to the point symbol (42.62.82)(44.62)2(45.66.84)2. In contrast to (I), complex (II) is characterized by a 3D framework based on dinuclear cadmium SBUs, i.e. [Cd2(COO)3]. The two symmetry-independent CdII ions display different coordinated geometries, namely octahedral [CdN2O4] and monocapped octahedral [CdO7]. The dinuclear SBUs are incorporated into clusters by bridging formate groups to produce pillars along the c axis. These pillars are further bridged either by tcpb3− ligands into sheets or by 1,4-bis(imidazol-1-yl)benzene ligands into undulating layers, and finally these two-dimensional surfaces interweave, forming a 3D structure with the point symbol (4.62)(47.614). Compound (II) exhibits reversible I2 uptake of 56.8 mg g−1 with apparent changes in the visible colour and the UV–Vis and fluorescence spectra, and therefore may be regarded as a potential reagent for the capture and release of I2.

Copper(i)-polymers and their photoluminescence thermochromism properties

Under hydro(solvo)thermal conditions, four organic bidentate bridging N,N'-donor ligands 1,3-bis(2-methylimidazol-1-yl)propane (L1), 4,4'-di(1H-imidazol-1-yl)-1,1'-biphenyl (L2), 1,2-bis(2-methyl-1H-imidazol-1-ylmethyl)benzene (L3) and 5,6,7,8-tetrahydroquinoxaline (L4) were employed to react with CuBr/CuI, generating four 2-D layered copper(i)-polymer coordination polymer materials [Cu2Br2(L1)] 1, [CuI(L2)] 2, [CuI(L3)] 3 and [CuI(L4)0.5] 4. In 1-4, different Cu-X motifs are found: a cubic Cu4Br4 core in 1; a castellated Cu-I single chain in 2; a rhombic Cu2I2 core in 3; and a staircase-like Cu-I double chain in 4. The 2-D layer networks of 1-3 can all be simplified into a simple 44 topology (planar for 1 and 3; wave-like for 2), while the 2-D layer network of 4 has a 63 topology. The photoluminescence behaviors of 1-4 under a UV lamp suggest that 1 and 2 possess fluorescence thermochromism properties. Under the UV lamp, with the decrease in temperature, (i) 1 exhibits a yellow-to-red emission; (ii) 2 exhibits a yellow-to-green emission; (iii) 3 always emits green light; and (iv) 4 never emits light. These are further confirmed by their emission spectra. From 297 K to 77 K, the emission of 1 exhibits a large red shift from 561 nm to 623 nm; the emission of 2 exhibits a large blue shift from 571 nm to 515 nm; only a minor red shift is observed for the emission of 3; and no peaks appear in the emission spectra of 4. The crystal data of 1 and 2 at different temperatures have been collected for revealing the origination of their fluorescence thermochromism properties. Based on the above investigations, the effect of the rigidity/flexibility of the organic ligand on the fluorescence thermochromism properties of copper(i)-polymer coordination polymer materials is discussed. The quantum yields at 297 K and the photoluminescence lifetimes at 297 K and 77 K for 1-3 were also measured for better understanding their photoluminescence properties.

Two CuxIy-based copper–organic frameworks with multiple secondary building units (SBUs): structure, gas adsorption and impressive ability of I2 sorption and release

Two Cu_xI_y-based copper–organic frameworks with multiple SBUs have been successfully synthesized. Both the compounds exhibit high performance for I₂ sorption and release.

Insight into the structure and bonding of copper(i) iodide clusters and a cluster-based coordination polymer

The structure and chemical bonding pattern of selected copper(i) iodide clusters and a cluster-based coordination polymer are investigated using DFT.

Design, synthesis and characterization of copper-based coordination compounds with bidentate (N,N and N,O) ligands: reversible uptake of iodine, dye adsorption and assessment of their antibacterial properties

This work presents the synthesis of close-packed copper complexes with an uncommon ability for dye and iodine adsorption and antibacterial activities.

Irreversible solvent-assisted structural transformation in 3D metal-organic frameworks: Structural modification and enhanced iodine-adsorption properties

In this work, we demonstrate a solvent-assisted structural transformation between two 3D metal-organic frameworks (MOFs) ([Zn₄(α-bptc)₂(H₂O)₃]_n (1) → {[Zn₂(α-bptc)(H₂O)₄]·(pra)}_n (2)) (α-H₄bptc = 2,3,3',4'-biphenyl tetra-carboxylic acid and pra = pyridin-2-amine) at room temperature by immersing complex 1 in a mother solution. The structural transformation involves not only solvent exchange but also the cleavage and formation of coordination bonds, which is confirmed by infrared spectroscopy, single-crystal X-ray diffraction analysis, powder X-ray diffraction patterns, and thermogravimetric analysis. Structural analyses revealed that significant modifications occurred during the transformation including the changes in lattice parameters, unit cell volume, space group, coordination number, secondary building units, and topological type. In the case of drastic structural transitions, significant changes in properties were also observed. Complex 2 displayed the interesting uptake and release of iodine with the changes in visible color, UV and fluorescence spectra, and fully reversible I2 uptake of 8.5 mg g-1, which further suggested about its future application as iodine absorbing material.

A metal–organic framework based multifunctional catalytic platform for organic transformation and environmental remediation

Given the need for an efficient reaction platform, a multifunctional material has been developed through the integration of iodine into a Cd²⁺ based MOF as a new catalytic system for organic transformation.

Iodine-loaded metal organic framework as growth-triggered antimicrobial agent

Zeolitic imidazolate framework-8 (ZIF-8) is one of easily available metal organic frameworks because of its facile preparation via mixing aqueous solutions of zinc nitrate and 2-methylimidazole. It turned into a very effective pH-responsive bactericide after loading with iodine. Approximately, 0.9g of iodine could be readily loaded into one gram of ZIF-8 from iodine dissolved n-heptane solution. Both Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis and Staphylococcus aureus could be very effectively killed by iodine loaded ZIF-8 (ZIF-8@I) at pH6.0 within 3min. In contrast, at pH above 7.0, no appreciable antimicrobial activity could be detected. The bacteria killing effect is resulted from the iodine released from ZIF-8@I disintegrated at acidic pH. ZIF-8@I coated surface also showed its acidic pH-triggered antimicrobial activity against deposited bacterial cells. The antimicrobial activity of ZIF-8@I against actively grown bacterial lawns on a pH neutral agar plate was also observed. The result demonstrates that iodine was released from the disintegrated ZIF-8@I to kill bacteria in response to the bacterial growth-induced pH lowering.

The water-based synthesis of chemically stable Zr-based MOFs using pyridine-containing ligands and their exceptionally high adsorption capacity for iodine

Zr-MOFs with inherent pyridine moieties were synthesized by a water-based approach, and exhibited exceptionally high adsorption capacity for I₂.

Synthesis, Crystal Structure, and Photoluminescent Properties of a Series of LnIII–CuI Heterometallic Coordination Polymers Based on Cu4I3 Clusters and Ln–ina Rod Units

A novel series of LnIII–CuI heterometallic coordination polymers (HCPs) {[Ln2Cu4I3(ina)7(DMA)2]n·nDMA, Ln = La (1), Ce (2), Pr (3) Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9) Ho (10), Er (11), Yb (12), Hina = isonicotinic acid, DMA = N,N-dimethylacetamide} were synthesised by a solvothermal reaction. The structures of compounds 1–12 were characterised by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Single crystal X-ray diffraction studies revealed that 1–12 are isomorphous and are 3D heterometallic coordination polymers based on inorganic Cu4I3 clusters and Ln2(ina)7(DMA) rod units. In addition, the luminescent properties of compounds 5–9 have been investigated in detail. All of them exhibited green light emission due to the synergistic effects of characteristic emissions of lanthanide ions and iodide-to-copper charge transfer.

Capture of volatile iodine by newly prepared and characterized non-porous [CuI]n-based coordination polymers

Four new non-porous copper(i) iodide coordination polymers have been synthesized and demonstrate volatile iodine capture with simultaneous fluorescence quenching.

An unusual coordination polymer containing Cu(+) ions and featuring possible Cu...Cu `cuprophilic' interactions: poly[di-μ-chlorido-(μ4-3,5-diaminobenzoato-κ(4)O:O':N:N')tricopper(I)(3 Cu-Cu)]

Compounds containing copper(I) are of interest for their role in biological processes. The nature of short (< ∼ 3.2 Å) Cu...Cu contacts within these compounds has been debated, being either described as weakly attractive (bonding) `cuprophilic' interactions, or simply as short metal-metal distances constrained by ligand geometry or largely ionic in nature. The title three-dimensional Cu(+)-containing coordination polymer, [Cu3(C7H7N2O2)Cl2]n, was formed from the in situ reduction of CuCl2 in the presence of 3,5-diaminobenzoic acid and KOH under hydrothermal conditions. Its complex crystal structure contains ten distinct Cu(I) atoms, two of which lie on crystallographic inversion centres. The copper coordination geometries include near-linear CuOCl and CuN2, T-shaped CuOCl2 and distorted tetrahedral CuOCl3 groups. Each Cu(I) atom is also associated with two adjacent metal atoms, with Cu...Cu distances varying from 2.7350 (14) to 3.2142 (13) Å; if all these are regarded as `cuprophilic' interactions, then infinite [-101] zigzag chains of Cu(I) atoms occur in the crystal. The structure is consolidated by N-H...Cl hydrogen bonds.

Recent advances in metal–organic frameworks based on pyridylbenzoate ligands: properties and applications

In this mini-review we discuss the properties and applications of metal–organic frameworks based on pyridylbenzoate.