Surfactant-Mediated Crystalline Structure Evolution Enabling the Ultrafast Green Synthesis of Bismuth-MOF in Aqueous Condition.

Green synthesis of stable metal-organic frameworks (MOFs) with permanent and highly ordered porosity at room temperature without needing toxic and harmful solvents and long-term high-temperature reactions is crucial for sustainable production. Herein, a rapid and environmentally friendly synthesis strategy is reported to synthesize the complex topological bismuth-based-MOFs (Bi-MOFs), [Bi9(C9H3O6)9(H2O)9] (denoted CAU-17), in water under ambient conditions by surfactant-mediated sonochemical approach, which could also be applicable to other MOFs. This strategy explores using cetyltrimethylammonium bromide (CTAB) amphiphilic molecules as structure-inducing agents to control the removal of non-coordinated water (dehydration) and enhance the degree of deprotonation of the ligands, thereby regulating the coordination and crystallization in aqueous solutions. In addition, another two new strategies for synthesizing CAU-17 by crystal reconstruction and one-step synthesis in binary solvents are provided, and the solvent-induced synthesis mechanism of CAU-17 is studied. The as-prepared CAU-17 presents a competitive iodine capture capability and effective delivery of the antiarrhythmic drug procainamide (PA) for enteropatia due to the broad pH tolerance and the unique phosphate-responsive destruction in the intestine. The findings will provide valuable ideas for the follow-up study of surfactant-assisted aqueous synthesis of MOFs and their potential applications.

A Cucurbit[8]uril-Based Supramolecular Framework Material for Reversible Iodine Capture in the Vapor Phase and Solution.

The safe and efficient management of hazardous radioactive iodine is significant for nuclear waste reprocessing and environmental industries. A novel supramolecular framework compound based on cucurbit[8]uril (Q[8]) and 4-aminopyridine (4-AP) is reported in this paper. In the single crystal structure of Q[8]-(4-AP), two 4-AP molecules interact with the outer surface of Q[8] and the two other 4-AP molecules are encapsulated into the Q[8] cavity to form the self-assembly Q[8]-(4-AP). Iodine adsorption experiments show that the as-prepared Q[8]-(4-AP) not only has a high adsorption capacity (1.74 g· g-1) for iodine vapor but also can remove the iodine in the organic solvent and the aqueous solution with the removal efficiencies of 95% and 91%, respectively. The presence of a large number of hydrogen bonds between the iodine molecule and the absorbent, as seen in the single crystal structure of iodine-loaded Q[8]-(4-AP) (I2@Q[8]-(4-AP)), is thought to be responsible for the exceptional iodine adsorption capacity of the material. In addition, the adsorption-desorption tests reveal that the self-assembly material has no significant loss of iodine capture capacity after five cycles, indicating that it has sufficient reusability.

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.

Robust Imidazopyridinium Covalent Organic Framework as Efficient Iodine Capturing Materials in Gaseous and Aqueous Environment.

The development of a high-performing adsorbent that can capture both iodine vapor from volatile nuclear waste and traces of iodine species from water is an important challenge, especially in industrially relevant process conditions. This study introduces novel imidazopyridinium-based covalent organic frameworks (COFs) through post-modification of a picolinaldehyde-based imine COF. These COFs demonstrate excellent iodine adsorption capacity, adsorption kinetics, and a high stability/recyclability in both vapor and water phases. Notably, one imidazopyridinium COF exhibits gaseous iodine uptake of 21 wt.% under dynamic adsorption conditions at 150 °C and a relative humidity of 50%, surpassing the performance of the currently used silver-based zeolite adsorbents (Ag@MOR (17wt.%)). Additionally, the same imidazopyridinium COFs can efficiently remove iodine species at a low concentration from aqueous solution. Seawater containing triiodide ions treated under dynamic flow-through conditions resulted in decreased concentrations down to the ppb level. The adsorption mechanisms for iodine and polyiodide species are elucidated for the imine COF and imidazopyridinium COFs; involving halogen bonding, hydrogen bonding, and charge-transfer complexes.

Designing External Pores of Aluminum Oxo Polyhedrons for Efficient Iodine Capture.

Although metal-organic polyhedra (MOPs) expansion has been studied to date, it is still a rare occurrence for their porous intermolecular assembly for iodine capture. The major limitation is the lack of programmable and controllable methods for effectively constructing and utilizing the exterior cavities. Herein, the goal of programmable porous intermolecular assembly is realized in the first family of aluminum oxo polyhedrons (AlOPs) using ligands with directional H-bonding donor/acceptor pairs and auxiliary alcohols as structural regulation sites. The approach has the advantage of avoiding the use of expensive edge-directed ditopic and face-directed tritopic ligands in the general synthesis strategy of MOPs. Combining theoretical calculations and experiments, the intrinsic relationship is revealed between alcohol ligands and the growth mechanism of AlOPs. The maximum I2 uptake based on the mass gain during sorption corresponds to 2.35 g g-1, representing the highest reported I2 sorption by an MOP. In addition, it can be easily regenerated and maintained the iodine sorption capacity, revealing its further potential application. This method of constructing stable and programmable porous materials will provide a new way to solve problems such as radionuclide capture.

3D Covalent Organic Framework with "the" Topology.

Discovery of new topology covalent organic frameworks (COFs) is a mainstay in reticular chemistry and materials research because it not only serves as a stepwise guide to the designed construction of covalent-organic architectures but also helps to comprehend function from structural design point-of-view. Proceeding on this track, the first 3D COF, TUS-38, with the topology is constructed by reticulating a planar triangular 3-c node of D3h symmetry with a tetragonal prism 8-c node of D2h symmetry via [3 + 8] reversible imine condensation reaction. TUS-38 represents a twofold interpenetrated multidirectional pore network with a high degree of crystallinity and structural integrity. Interestingly, stemming from the nitrogen-rich s-triazine rings with electron-deficient character and ─C â• N─ linkages composing the TUS-38 framework that benefit to the charge-transfer and hence dipole-dipole electrostatic interactions between the framework and iodine in addition to exclusive topological characteristics of the exotic the net, TUS-38 achieves an exemplary capacity for iodine vapor uptake reaching 6.3 g g-1. Recyclability studies evidence that TUS-38 can be reused at least five times retaining 95% of its initial adsorption capacity; while density functional theory (DFT) calculations have heightened the understanding of the interactions between iodine molecules and the framework.

Porous Organic Cage as an Efficient Platform for Industrial Radioactive Iodine Capture.

Herein, we firstly develop porous organic cage (POC) as an efficient platform for highly effective radioactive iodine capture under industrial operating conditions (typically ≥150 °C), ≤150 ppmv of I2). Due to the highly dispersed and readily accessible binding sites as well as sufficient accommodating space, the constructed NKPOC-DT-(I-) (NKPOC=Nankai porous organic cage) demonstrates a record-high I2 uptake capacity of 48.35 wt % and extraordinary adsorption capacity of unit ionic site (~1.62) at 150 °C and 150 ppmv of I2. The I2 capacity is 3.5, 1.6, and 1.3 times higher than industrial silver-based adsorbents Ag@MOR and benchmark materials of TGDM and 4F-iCOF-TpBpy-I- under the same conditions. Furthermore, NKPOC-DT-(I-)Me exhibits remarkable adsorption kinetics (k1=0.013 min-1), which is 1.2 and 1.6 times higher than TGDM and 4F-iCOF-TpBpy-I- under the identical conditions. NKPOC-DT-(I-)Me thus sets a new benchmark for industrial radioactive I2 adsorbents. This work not only provides a new insight for effectively enhancing the adsorption capacity of unit functional sites, but also advances POC as an efficient platform for radioiodine capture in industry.

A Halogen-Bonded Organic Framework (XOF) Emissive Cocrystal for Acid Vapor and Explosive Sensing, and Iodine Capture.

There is a strong and urgent need for efficient materials that can capture radioactive iodine atoms from nuclear waste. This work presents a novel strategy to develop porous materials for iodine capture by employing halogen bonding, mechanochemistry and crystal engineering. 3D halogen-bonded organic frameworks (XOFs) with guest-accessible permanent pores are exciting targets in crystal engineering for developing functional materials, and this work reports the first example of such a structure. The new-found XOF, namely TIEPE-DABCO, exhibits enhanced emission in the solid state and turn-off emission sensing of acid vapors and explosives like picric acid in nanomolar quantity. TIEPE-DABCO captures iodine from the gas phase (3.23 g g-1 at 75 °C and 1.40 g g-1 at rt), organic solvents (2.1 g g-1 ), and aqueous solutions (1.8 g g-1 in the pH range of 3-8); the latter with fast kinetics. The captured iodine can be retained for more than 7 days without any leaching, but readily released using methanol, when required. TIEPE-DABCO can be recycled for iodine capture several times without any loss of storage capacity. The results presented in this work demonstrate the potential of mechanochemical cocrystal engineering with halogen bonding as an approach to develop porous materials for iodine capture and sensing.

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.

Superfast Capture of Iodine from Air, Water, and Organic Solvent by Potential Dithiocarbamate-Based Organic Polymer.

Organic polymers are widely explored due to their high stability, scalability, and more facile modification properties. We developed cost-effective dithiocarbamate-based organic polymers synthesized using diamides, carbon disulfide, and diamines to apply for environmental remediation. The sequestration of radioiodine is a serious concern to tackle when dealing with nuclear power for energy requirements. However, many of the current sorbents have the problem of slower adsorption for removing iodine. In this report, we discuss the utilization of an electron-rich dithiocarbamate-based organic polymer for the removal of iodine in a very short time and with high uptake. Our material showed 2.8 g/g uptake of vapor iodine in 1 h, 915.19 mg/g uptake of iodine from cyclohexane within 5 s, 93% removal of saturated iodine from water in 1 min, and 1250 mg/g uptake of triiodide ions from water within 30 s. To the best of our knowledge, the iodine capture was faster than previously observed for any existing material. The material was fully recyclable when applied for up to four cycles. Hence, this dithiocarbamate-based polymer can be a promising system for the fast removal of various forms of iodine and, thus, enhance environmental security.

Two New 1D Supramolecular Compounds Based on PbI2 for Efficient Iodine Capture.

Two new inorganic-organic hybrid crystals based on PbI2 were assembled through the solvent evaporation method, namely, {[L1]·[Pb2I6]}n (1) and {[L2]2·[Pb3I10]}n (2). L1-L2 are a series of multivalent nitrogen-containing cationic ligands. Compounds 1-2 were characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR, powder X-ray diffraction, and thermogravimetric microanalysis. The results showed that the adsorption rate of 80 mg compound 1 to iodine reached 96.59%, indicating a high iodine capture performance in cyclohexane solution. In the meantime, the adsorption kinetics is most suitable for a pseudo-second-order model, and the adsorption process is mainly chemisorption. Adsorption thermodynamics is most suitable for the Langmuir model, indicating that adsorption occurs on the surface of the monolayer. According to the adsorption mechanism, it can be inferred that the structure of compound 1 contains amino, benzene, N heterocyclic, and other active groups, that is, indirectly increases the adsorption site with iodine, and the chemical reaction with iodine improves the removal rate of iodine in cyclohexane solution. In addition, compound 1 was found to have good iodine adsorption and recyclability by cyclic experiments. Therefore, the synthesized compound 1 can be used as a potential and excellent iodide capture adsorbent, which may have a good application prospects in the future.

Calix[4]arene Derivative for Iodine Capture and Effect on Leaching of Iodine through Packaging.

A hydrophobic calix[4]arene derivative was investigated for its iodine (I2) capture efficiency from gaseous and liquid phase. The iodine uptake was followed by UV-vis spectroscopy. Additionally, the influence of the calix[4]arene derivative-polyolefin system on the leaching of iodine through packaging from a povidone-iodine-based (PVP-I) formulation was evaluated. In fact, iodine is a low-cost, multi-target, and broad-spectrum antiseptic. However, it is volatile, and the extended storage of I2-based formulations is challenging in plastic packaging. Here, we investigated the possibility of reducing the loss of I2 from an iodophor formulation by incorporating 4-tert-butylcalix [4]arene-tetraacetic acid tetraethyl ester (CX) and its iodine complex in high-density polyethylene (HDPE) or polypropylene (PP) via a swelling procedure. Surface and bulk changes were monitored by contact angle, thermogravimetric analysis (TGA), and UV-vis diffuse reflectance spectra. The barrier effect of the different polymeric systems (embedded with CX, iodine-CX complex, or I2) was evaluated by monitoring the I2 retention in a buffered PVP-I solution by UV-vis spectroscopy. Overall, experimental data showed the capability of the calix[4]arene derivative to complex iodine in solution and the solid state and a significant reduction in the iodine leaching by the PP-CX systems.

Effective Iodine Capture Behavior by a Censer-shaped Macrocycle in Vapor Phase and Aqueous Solution.

Iodine capture is of great significance for disposal of the hazardous radioactive iodine. CTX[P(O)Ph], one kind of censer-shaped macrocycle cyclotrixylohydroquinoylene (CTX) derivatives, was applied as an efficient iodine adsorbent. It showed satisfactory iodine adsorption capacity in vapor phase and could be reused without obvious adsorption capacity loss. Besides, the adsorbent could also uptake iodine in water. Fortunately, two iodine loading CTX[P(O)Ph] crystal structures were obtained under different conditions to explore the mechanism of iodine adsorption. This work provides a relatively rare example of iodine adsorption by macrocycle. It is promising that the results with crystal information might be meaningful for exploring and designing new kinds of iodine adsorbents.

Halogen Bonding Adsorbent Pyridine N-oxides for Iodine Capture in Water.

Rapid capture of 129 I with high volatility and toxicity in the environment has attracted much attention. Herein we reported a firstly synthesized nonporous material: pyridine N-oxides (NTPO and ATPO) as iodine adsorbent. Both of NTPO and ATPO exhibit remarkable performance on the adsorption of iodine in aqueous solution, vapor state and organic solvents. Upon the capture of iodine, pyridine N-oxides were transformed to binary cocrystals combined with the pyridine N-oxides and iodine which is driven by halogen bond between iodine and oxygen atoms. Moreover, pyridine N-oxides shows high chemical, thermal and moisture stability.

Two Facile Aniline-Based Hypercrosslinked Polymer Adsorbents for Highly Efficient Iodine Capture and Removal.

Effective capture and safe disposal of radioactive iodine (129I or 131I) during nuclear power generation processes have always been a worldwide environmental concern. Low-cost and high-efficiency iodine removal materials are urgently needed. In this study, we synthesized two aniline-based hypercrosslinked polymers (AHCPs), AHCP-1 and AHCP-2, for iodine capture in both aqueous and gaseous phases. They are obtained by aniline polymerization through Friedel-Crafts alkylation and Scholl coupling reaction, respectively, with high chemical and thermal stability. Notably, AHCP-1 exhibits record-high static iodine adsorption (250 wt%) in aqueous solution. In the iodine vapor adsorption, AHCP-2 presents an excellent total iodine capture (596 wt%), surpassing the most reported amorphous polymer adsorbents. The rich primary amine groups of AHCPs promote the rapid physical capture of iodine from iodine water and iodine vapor. Intrinsic features such as low-cost preparation, good recyclability, as well as excellent performance in iodine capture indicate that the AHCPs can be used as potential candidates for the removal of iodine from radioactive wastewater and gas mixtures.

Synthesis of a Triazaisotruxene-Based Porous Organic Polymer and Its Application in Iodine Capture.

A new triazaisotruxene-based porous organic polymer (POP) was designed and successfully synthesized by a FeCl3-promoted crosslinking reaction. As a result of its porosity and good thermal stability, the designed POP can be utilized as a promising adsorbent for iodine, not only in the gaseous phase, but also in organic and aqueous solutions. Compared to its triazatruxene (TN) analogue, the ITN-based POP shows equal iodine uptake in the gaseous phase and in hexane solution, and better uptake in aqueous solution.

Molecular Iodine Capture by Covalent Organic Frameworks.

The effective capture and storage of volatile molecular iodine from nuclear waste is of great significance. Covalent organic frameworks (COFs) are a class of extended crystalline porous polymers that possess unique architectures with high surface areas, long-range order, and permanent porosity. Substantial efforts have been devoted to the design and synthesis of COF materials for the capture of radioactive iodine. In this review, we first introduce research techniques for determining the mechanism of iodine capture by COF materials. Then, the influencing factors of iodine capture performance are classified, and the design principles and strategies for constructing COFs with potential for iodine capture are summarized on this basis. Finally, our personal insights on remaining challenges and future trends are outlined, in order to bring more inspiration to this hot topic of research.

Synthesis of Electron-Rich Porous Organic Polymers via Schiff-Base Chemistry for Efficient Iodine Capture.

As one of the main nuclear wastes generated in the process of nuclear fission, radioactive iodine has attracted worldwide attention due to its harm to public safety and environmental pollution. Therefore, it is of crucial importance to develop materials that can rapidly and efficiently capture radioactive iodine. Herein, we report the construction of three electron-rich porous organic polymers (POPs), denoted as POP-E, POP-T and POP-P via Schiff base polycondensations reactions between Td-symmetric adamantane knot and four-branched "linkage" molecules. We demonstrated that all the three POPs showed high iodine adsorption capability, among which the adsorption capacity of POP-T for iodine vapor reached up to 3.94 g·g-1 and the removal rate of iodine in n-hexane solution was up to 99%. The efficient iodine capture mechanism of the POP-T was investigated through systematic comparison of Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after iodine adsorption. The unique π-π conjugated system between imine bonds linked aromatic rings with iodine result in charge-transfer complexes, which explains the exceptional iodine capture capacity. Additionally, the introduction of heteroatoms into the framework would also enhance the iodine adsorption capability of POPs. Good retention behavior and recycling capacity were also observed for the POPs.

A Carbazole-Functionalized Porous Aromatic Framework for Enhancing Volatile Iodine Capture via Lewis Electron Pairing.

Nitrogen-rich porous networks with additional polarity and basicity may serve as effective adsorbents for the Lewis electron pairing of iodine molecules. Herein a carbazole-functionalized porous aromatic framework (PAF) was synthesized through a Sonogashira-Hagihara cross-coupling polymerization of 1,3,5-triethynylbenzene and 2,7-dibromocarbazole building monomers. The resulting solid with a high nitrogen content incorporated the Lewis electron pairing effect into a π-conjugated nano-cavity, leading to an ultrahigh binding capability for iodine molecules. The iodine uptake per specific surface area was ~8 mg m-2 which achieved the highest level among all reported I2 adsorbents, surpassing that of the pure biphenyl-based PAF sample by ca. 30 times. Our study illustrated a new possibility for introducing electron-rich building units into the design and synthesis of porous adsorbents for effective capture and removal of volatile iodine from nuclear waste and leakage.

Ionic Functionalization of Multivariate Covalent Organic Frameworks to Achieve an Exceptionally High Iodine-Capture Capacity.

Adsorption-based iodine (I2 ) capture has great potential for the treatment of radioactive nuclear waste. In this study, we apply a "multivariate" synthetic strategy to construct ionic covalent organic frameworks (iCOFs) with a large surface area, high pore volume, and abundant binding sites for I2 capture. The optimized material iCOF-AB-50 exhibits a static I2 uptake capacity of 10.21 g g-1 at 75 °C and a dynamic uptake capacity of 2.79 g g-1 at ≈400 ppm I2 and 25 °C, far exceeding the performances of previously reported adsorbents under similar conditions. iCOF-AB-50 also exhibits fast adsorption kinetics, good moisture tolerance, and full reusability. The promoting effect of ionic groups on I2 adsorption has been elucidated by experimentally identifying the iodine species adsorbed at different sites and calculating their binding energies. This work demonstrates the essential role of balancing the textural properties and binding sites of the adsorbent in achieving a high I2 capture performance.