Organic porous solid as promising iodine capture materials

Facile fabrication of morphology-adjustable viologen-based ionic polymers for carbon dioxide immobilization and iodine vapor adsorption

Viologens, also referred as 1,1'-disubstituted-4,4'-bipyridinium salts, exhibit exceptional redox properties, identifying them as building blocks for functional organic polymer materials with a wide range of potential applications, including carbon dioxide (CO2) conversion and iodine capture. Herein, a series of viologen-derived ionic porous organic polymers (VIPOP-n), assembled from viologen derivatives, were designed and synthesized using a straightforward one-step strategy. The constructed polymer materials were subsequently characterized by Fourier Transform Infrared Spectroscopy (FT-IR), solid-state 13C nuclear magnetic resonance (13C NMR), X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), and nitrogen adsorption-desorption isotherms, among other techniques. Notably, the variation of synthetic solvents significantly influences the construction of polymer materials, resulting in observable changes in morphology and structure, which in turn affect their potential applications in CO2 cycloaddition reaction and iodine adsorption. The polymer VIPOP-3 exhibits superior catalytic performance under conditions of 80 °C and 1 atm CO2, producing valuable cyclic carbonates with yields reaching 94%. Density Functional Theory (DFT) calculations indicate that inert-hydrogen bonding can effectively activate both the epoxide and CO2, lowering the activation energy (Ea) of the cycloaddition reaction to 87.5 kJ mol-1, as corroborated by kinetic evaluations. Additionally, all polymers exhibited effective iodine vapor adsorption capacities, with VIPOP-7 emerging as the most efficient material, displaying an adsorption capacity of 2.96 g g-1. The adsorption process was investigated through various kinetic models, revealing that both physical and chemical adsorption were involved, with physical adsorption being the predominant process.

Crystalline Porous Materials for Gaseous Iodine Capture: A Comprehensive Review

The growing reliance on nuclear energy necessitates efficient strategies for managing spent nuclear fuel, particularly the capture of volatile radioactive iodine, which poses significant environmental and health risks. Crystalline porous materials have emerged as promising candidates for iodine adsorption due to their high surface areas, tunable porosity, and abundant active sites. This review comprehensively summarizes recent advancements in the design and application of four classes of crystalline porous materials for iodine capture: metal-organic frameworks, covalent organic frameworks, hydrogen-bonded organic frameworks, and porous organic cages. The discussion focuses on key adsorption mechanisms, structural modifications, and functionalization strategies that enhance iodine adsorption capacity, retention, and recyclability. While significant progress has been made, challenges remain in scaling up synthesis, improving stability under industrial conditions, and achieving cost-effective large-scale applications. Future research should emphasize on scalable synthesis, industrial validation, and development of multifunctional adsorbents with enhanced selectivity and reusability. This review provides insights into the rational design of next-generation porous materials for efficient iodine capture, contributing to advancements in nuclear waste management and environmental sustainability.

Synthesis of a Novel Zwitterionic Hypercrosslinked Polymer for Highly Efficient Iodine Capture from Water

Cationic porous organic polymers have a unique advantage in removing radioactive iodine from the aqueous phase because iodine molecules exist mainly in the form of iodine-containing anions. However, halogen anions will inevitably be released into water during the ion-exchange process. Herein, we reported a novel and easy-to-construct zwitterionic hypercrosslinked polymer (7AIn-PiP)-containing cationic pyridinium-type group, uncharged pyridine-type group, pyrrole-type group, and even an electron-rich phenyl group, which in synergy effectively removed 94.2% (456 nm) of I2 from saturated I2 aqueous solution within 30 min, surpassing many reported iodine adsorbents. Moreover, an I2 adsorption efficiency of ~95% can still be achieved after three cyclic evaluations, indicating a good recycling performance. More importantly, a unique dual 1,3-dipole was obtained and characterized by 1H/13C NMR, HRMS, and FTIR, correlating with the structure of 7AIn-PiP. In addition, the analysis of adsorption kinetics and the characterization of I2@7AIn-PiP indicate that the multiple binding sites simultaneously contribute to the high affinity towards iodine species by both physisorption and chemisorption. Furthermore, an interesting phenomenon of inducing the formation of HIO2 in unsaturated I2 aqueous solution was discovered and explained. Overall, this work is of great significance for both material and radiation protection science.

Croconic Acid Integrated Zwitterionic Conjugated Porous Polymer for Effective Iodine Adsorption

Given the rapid growth of the nuclear sector, effective treatment of radioactive iodine is critical. Herein, we report the synthesis and the iodine adsorption properties of croconic acid (CTPB) and squaric acid (STPB) containing π-conjugated novel zwitterionic conjugated porous polymers (CPPs). The CPPs have been synthesized through a condensation reaction of tris(4-aminophenyl)benzene with croconic acid or squaric acid in high yields (~95 %). The ionic nature of the polymers promoted high iodine/polyiodide vapour adsorption capacity of up to 4.6 g/g for CTPB and 3.5 g/g for STPB under ambient pressure at 80 °C. The zwitterionic framework (croconic acid or squaric acid units) coupled with the aromatic units is expected to effectively capture molecular iodine (I2) and polyiodides (I3 - and I5 -). The iodine adsorption properties of the polymers have been studied using Fourier-Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Brauner-Emmett-Teller (BET) analysis, and Raman Spectroscopy. Besides this work, there are only three ionic units for effective iodine adsorption. This work demonstrates the importance of zwitterionic units in the porous network reported for iodine adsorption and separation.

Direct Observation of Enhanced Iodine Binding within a Series of Functionalized Metal-Organic Frameworks with Exceptional Irradiation Stability

Optimization of active sites and stability under irradiation are important targets for sorbent materials that might be used for iodine (I2) storage. Herein, we report the direct observation of I2 binding in a series of Cu(II)-based isostructural metal-organic frameworks, MFM-170, MFM-172, MFM-174, NJU-Bai20, and NJU-Bai21, incorporating various functional groups (-H, -CH3, - NH2, -C≡C-, and -CONH-, respectively). MFM-170 shows a reversible uptake of 3.37 g g-1 and a high packing density of 4.41 g cm-3 for physiosorbed I2. The incorporation of -NH2 and -C≡C- moieties in MFM-174 and NJU-Bai20, respectively, enhances the binding of I2, affording uptakes of up to 3.91 g g-1. In addition, an exceptional I2 packing density of 4.83 g cm-3 is achieved in MFM-174, comparable to that of solid iodine (4.93 g cm-3). In situ crystallographic studies show the formation of a range of supramolecular and chemical interactions [I···N, I···H2N] and [I···C≡C, I-C═C-I] between -NH2, -C≡C- sites, respectively, and adsorbed I2 molecules. These observations have been confirmed via a combination of solid-state nuclear magnetic resonance, X-ray photoelectron, and Raman spectroscopies. Importantly, γ-irradiation confirmed the ultraresistance of MFM-170, MFM-174, and NJU-Bai20 suggesting their potential as efficient sorbents for cleanup of radioactive waste.

Construction of hydroxyl-functionalized hyper-crosslinked networks from polyimide for highly efficient iodine adsorption

The rapid development of nuclear energy posed a great threat to the environment and human health. Herein, two hydroxyl-functionalized hyper-crosslinked polymers (PIHCP-1 and PIHCP-2) containing different electron active sites have been synthesized via Friedel-Crafts alkylation reaction of the polyimides. The resulting polymers showed a micro/mesoporous morphology and good thermal and chemical stability. Rely on the high porosity and multi-active sites, the PIHCPs show an ultrahigh iodine uptake capacity reached 6.73 g g-1 and the iodine removal efficiency from aqueous solution also reaches 99.7%. Kinetic analysis demonstrates that the iodine adsorption on PIHCPs was happened on the heterogeneous surfaces in the form of multilayer chemisorption. Electrostatic potential (ESP) calculation proves the great contribution of hydroxyl groups on the iodine capture performance. In addition, the iodine capture efficiency of both adsorbents can be maintained over 91% after four cyclic experiments which ensures their good recyclability for further practical applications.

Nonporous amorphous superadsorbents for highly effective and selective adsorption of iodine in water

Adsorbents widely utilized for environmental remediation, water purification, and gas storage have been usually reported to be either porous or crystalline materials. In this contribution, we report the synthesis of two covalent organic superphane cages, that are utilized as the nonporous amorphous superadsorbents for aqueous iodine adsorption with the record-breaking iodine adsorption capability and selectivity. In the static adsorption system, the cages exhibit iodine uptake capacity of up to 8.41 g g-1 in I2 aqueous solution and 9.01 g g-1 in I3- (KI/I2) aqueous solution, respectively, even in the presence of a large excess of competing anions. In the dynamic flow-through experiment, the aqueous iodine adsorption capability for I2 and I3- can reach up to 3.59 and 5.79 g g-1, respectively. Moreover, these two superphane cages are able to remove trace iodine in aqueous media from ppm level (5.0 ppm) down to ppb level concentration (as low as 11 ppb). Based on a binding-induced adsorption mechanism, such nonporous amorphous molecular materials prove superior to all existing porous adsorbents. This study can open up a new avenue for development of state-of-the-art adsorption materials for practical uses with conceptionally new nonporous amorphous superadsorbents (NAS).