I2 Adsorption Research Articles

Adsorption and Detection of Iodine Species by a Thorium-Based Metal–Organic Framework

Actinide-bearing metal-organic frameworks (MOFs) encompass intriguing structures and properties, but the radioactivity of actinide cripples their applications. Herein, we have constructed a new thorium-based MOF (Th-BDAT) as a bifunctional platform for the adsorption and detection of radioiodine, a more radioactive fission product that can readily spread through the atmosphere in its molecular form or via solution as anionic species. The iodine capture within the framework of Th-BDAT from both the vapor phase and the cyclohexane solution has been verified, showing that Th-BDAT features maximum I2 adsorption capacities (Qmax) of 959 and 1046 mg/g, respectively. Notably, the Qmax of Th-BDAT toward I2 from cyclohexane solution ranks among the highest value for Th-MOFs reported to date. Furthermore, incorporating highly extended and π-electron-rich BDAT4- ligands renders Th-BDAT as a luminescent chemosensor whose emission can be selectively quenched by iodate with a detection limit of 1.367 μM. Our findings thus foreshadow promising directions that might unlock the full potential of actinide-based MOFs from the point of view of practical application.

Capture of volatile I2 by dithioglycol functionalized HKUST-1 and its polymeric composite beads

Successful sequestration of radioactive waste is one of the primary bottle necks of nuclear technologies. The present work describes the effect of dithioglycol functionalization of HKUST-1 on its I2 adsorption performance at 80 °C both in powder and composite bead form. The nature of interaction between I2 and the host matrix has been revealed employing various techniques. There observed a profound enhancement in adsorption kinetics upon functionalization compare to pristine HKUST-1. Composite bead with 60% MOF shows an adsorption capacity of 0.98 g/gbead which is 4.2 times higher than reported PVDF based composite bead of HKUST-1. Unlike HKUST-1, in present studies I2 adsorption takes place through both physic-sorption & chemi-sorption means yielding γ-CuI which acts as secondary adsorbent and converted into I2@CuI through molecular I2 adsorption. To the best of our knowledge, this is the first report describing the simple synthesis of γ-CuI homogeneously distributed throughout the polymeric composite bead.

MIL-101-NH2-TFR and MIL-101-NH2-TFR/Cu2+ as novel hybrid materials for efficient adsorption of iodine and reduction of Cr(VI)

Today, due to the earnest jeopardies of environmental contaminants from various sources and their deteriorating effects on the ecosystem, the adsorption and reduction of these highly toxic pollutants with an efficient and cost-effective protocol can be considered a desirable phenomenon. Herein, a chromium-based metal-organic framework (MIL-101-NH2) was modified with thiourea and formaldehyde to form a polymeric layer on the surface (MIL-101-NH2-TFR). The resulting nanohybrid, as an adsorbent, was applied for efficient capture of iodine (I2) molecules from cyclohexane solution. MIL-101-NH2-TFR nanohybrid signified a superior adsorption performance for the capture of I2, compared to the pristine MIL-101-NH2, with a theoretical maximum uptake value of 625 mg/g and adsorption efficiency of 96.9 % through thionyl (CS), amino, and phenyl groups. The pseudo-second-order rate equation and the Langmuir model were best fitted for the I2 adsorption over MIL-101-NH2-TFR adsorbent. Quantum chemical calculations were conducted to reveal the mechanism of I2 adsorption onto the surface of MIL-101-NH2-TFR. Moreover, MIL-101-NH2-TFR was used to anchor Cu2+ to generate a catalytic system (MIL-101-NH2-TFR/Cu2+) for detoxification of Cr(VI) in the presence of formic acid as an eco-friendly reducing reagent in an aqueous medium. MIL-101-NH2-TFR and MIL-101-NH2-TFR/Cu2+ were reused several times for the adsorption/desorption process and the catalytic reduction, respectively.

Direct Electrical Sensing of Iodine Gas by a Covalent Organic Framework-Based Sensor

Rapid and highly sensitive detection of iodine gaseous species is crucial as the first response in case of nuclear accidents and nuclear waste clean-up. A robust and user-friendly sensor-based technology that allows online monitoring is highly desirable. Herein, we report the success of using a covalent organic framework (AQ-COF)-based sensor for real-time iodine gas adsorption and detection by the electrochemical impedance spectroscopy (EIS) technique. The sensor exhibits a high sensitivity and a pronounced electrical response to trace amounts of iodine vapor. Gaseous iodine was readily detected with a significant change in resistance (104×) at 70 °C within 5 min exposure to air. Notably, the EIS response is quite chemoselective to iodine over other common species such as air, methanol, ethanol, and water, with a selectivity of 320, 14, 49, and 1030, respectively. A mechanical study shows that the adsorption of iodine can reduce the optical bandgap of the AQ-COF, causing the impedance to drop significantly. This study demonstrates how the adsorption enrichment effect of selective I2 adsorption by a covalent organic framework can be leveraged to create a highly selective sensor for the direct online electrical detection of radioactive gaseous toxins.

Controlled Iodine Phase Transfer of Covalent Organic Framework Membranes for Instant but Sustained Disinfection.

Freestanding membranes of CuCl2-implanted TpPa covalent organic frameworks (COFs) were mechanochemically produced. The resulting membrane had a high I2 adsorption capacity (566.78 g·mol-1) in cyclohexane, which corresponds to 2.2I2 per unit cell with 1.3I2 immobilized on 3Cl- ions (60%) and 0.9 on 3N atoms (40%). Upon being placed in aqueous media, the membrane released 61.1% of its loaded I2 mainly by its Cl- ions within 10 min and the remaining 38.9% mainly from its N atoms within about 5 h. Thanks to that, the COF membranes loaded with 1.5 mg of I2 could be repetitively utilized to kill about 108 CFU/mL E. coli in 0.5-3 min at least five times, after which the membranes could retain their bactericidal activity for 4 h against 108 CFU/mL E. coli. This highlights the promising application of I2-loaded TpPa-CuCl2 COF membranes for instant and sustained disinfection.

A novel Cu nanoporous aerogel for high-efficient immobilization of iodide in water

The effective capture and storage of the generated radioactive contaminant (iodine) are of great significance with the extensive use of nuclear energy. In this work, a novel Cu nanoporous aerogel (Cu-NPA) was prepared by using inorganic Cu salt as precursors. The as-prepared Cu-NPA was fully characterized in detail, and the I2 adsorption and stability capability of Cu-NPA has been investigated in the solution. The results showed that Cu-NPA has high specific surface area and porosity. The structure of hierarchical pores is conducive to the rapid enrichment of pollutants in water. Adsorption experiments showed that Cu-NPA had ultra-high I2 adsorption capacity (1384 mg/g) and fast equilibrium adsorption time (10 min). The I2 in the solution (c < 1200 mg/g) can be almost completely removed. In addition, Cu-NPA exhibits good stability in the air and can be exposed to air for a long time. In general, our work demonstrated the preparation of Cu-NPA and its great potential in the field of rapidly eliminating radioactive I2.

Precise regulation of active sites of MOFs for capture of iodine

Metal-organic frameworks (MOFs) have great potential for the capture of volatile iodine. The effect of a precise regulation of active sites in JLNU-4 (MOFs) on capture of iodine was investigated by Monte Carlo (MC) method and molecular dynamics (MD), and it was found that the larger the Zn/Cd atomic ratio, the better the iodine capture. Interestingly, compared with the meta-position regulation of Zn/Cd, the ortho-positions regulation increased the free volume of the crystal and enhanced the interactions between Cd and O with I, thus improving the capture capacity of iodine. The first-principles study revealed the charge transfer of each atom in MOFs crystal with I2 during iodine capture and the secondary bonds with weak covalent interactions were all formed after I2 adsorption onto MOFs. These findings provide a reference for the capture of radioactive iodine and a theoretical basis for the strategies for precise regulation of MOFs in the future.

Construction of imide-functionalized aromatic conjugation tetracarboxylate frameworks and adsorption behavior for iodine and selective cationic dyes

Metal-organic frameworks (MOFs) show great potential in environmental contaminants removal owing to their outstanding pore properties and tunable chemical performance. Two new imide-functionalized aromatic conjugation tetracarboxylate frameworks: [Cd4(BDCPPI)2(DMF)2(H2O)3]·2DMF·8H2O (1) and [Zn4(BDCPPI)2(DMF)6]·3DMF·4H2O (2) were designed and synthesized under solvothermal conditions. Due to the micropore size and aromatic conjugation properties with the 3D network structures, complexes 1 and 2 have abundant active sites, resulting in strong iodine capture and dye adsorption capacity. The excellent iodine capture ability on complexes 1 and 2 might due to the interaction of iodine with the carbonyl oxygen atom (I⋯O) and the benzene ring (I···π). The materials were charge and size selective for the adsorption of dyes, and the presence of abundant imide-functionalized groups in the channels can form hydrogen-bonding interactions with dye molecules to promote their adsorption properties. In addition, the high I2 adsorption and release capacity of complexes 1 and 2 indicate their wide application prospects in nuclear waste management. Therefore, the as-synthesized MOFs can be used as potential multifunctional adsorbents for further removal of organic dyes and iodine from wastewater.

Capture of iodine gas by Bi0 modified silica with different morphologies: Influence of pore characteristic on the stable and unstable forms of adsorption

Exploring efficient iodine gas adsorbent is a meaningful and challenging topic in the field of radioactive waste treatment. Herein, Bi0 modified SiO2 with different morphologies (platelet-like, rod-like, and sphere-like) were fabricated by an improved impregnation method using SnCl2 as reductant. The iodine gas adsorption behaviors of the obtained materials were systematically investigated. The effects of pore characteristic, temperature and time on the adsorption capacity including total, chemical (stable form) and physical (unstable form) were studied. Pore characteristic and temperature affected not only the total adsorption, but also the stable and unstable forms of adsorption. The results demonstrated that the platelet-like Bi0 modified SiO2 (Bi0@SiO2-P) with ordered, short and straight pore characteristics had the highest total adsorption capacity (up to 960 mg/g), while sphere-like (Bi0@SiO2-S) with disordered pore showed the highest ratio of stable form of adsorption (94.8 %). Furthermore, with increasing temperature, the total and unstable form adsorption decreased slightly, but stable form increased. The adsorption processes were better fitted by the pseudo-second-order kinetic equation. The results demonstrated that I2 adsorption for Bi0 modified SiO2 materials was mainly chemical (Bi + I2 = BiI3).

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Highly Efficient Iodine Capture and CO2 Adsorption using a Triazine‐Based Conjugated Microporous Polymers

AbstractTriazine‐based conjugated microporous polymers (CMPs) are a class of promising materials for adsorptive separation of CO2, which could be an effective alternative to chemisorption based approaches. Three novel CMPs were synthesized based on mixed building‐block approach under ionothermal conditions (ZnCl2, 400 °C). CMP@1‐3 possess moderate BET surface area of 325–707 m2 g−1. These polymers have a permanent porous structure, plenty of nitrogen atoms in the skeletons as effective sorption sites, and display a high adsorption performance for CO2 and iodine. Among them, CMP@3 displays outstanding CO2 adsorption capacity with uptake up to 120.8 cm3 g−1 at 1 bar and 273 K. In addition, CMP@3 exhibits a superior iodine uptake up to 308 wt.%. After adsorption and release, the structure of CMPs materials does not change and has high stability, which can be used as a convenient, economic and environmentally friendly material to develop its application in the field of I2 adsorption.

Iodine Uptake by Zr-/Hf-Based UiO-66 Materials: The Influence of Metal Substitution on Iodine Evolution.

Many works reported the encapsulation of iodine in metal-organic frameworks as well as the I2 → I3- chemical conversion. This transformation has been examined by adsorbing gaseous iodine on a series of UiO-66 materials and the different Hf/Zr metal ratios (0-100% Hf) were evaluated during the evolution of I2 into I3-. The influence of the hafnium content on the UiO-66 structure was highlighted by PXRD, SEM images, and gas sorption tests. The UiO-66(Hf) presented smaller lattice parameter (a = 20.7232 Å), higher crystallite size (0.18 ≤ Φ ≤ 3.33 μm), and smaller SSABET (818 m2·g-1) when compared to its parent UiO-66(Zr) ─ a = 20.7696 Å, 100 ≤ Φ ≤ 250 nm, and SSABET = 1262 m2·g-1. The effect of replacing Zr atoms by Hf in the physical properties of the UiO-66 was deeply evaluated by a spectroscopic study using UV-vis, FTIR, and Raman characterizations. In this case, the Hf presence reduced the band gap of the UiO-66, from 4.07 eV in UiO-66(Zr) to 3.98 eV in UiO-66(Hf). Furthermore, the UiO-66(Hf) showed a blue shift for several FTIR and Raman bands, indicating a stiffening on the implied interatomic bonds when comparing to UiO-66(Zr) spectra. Hafnium was found to clearly favor the capture of iodine [285 g·mol-1, against 230 g·mol-1 for UiO-66(Zr)] and the kinetic evolution of I2 into I3- after 16 h of I2 filtration. Three iodine species were typically identified by Raman spectroscopy and chemometric analysis. These species are as follows: "free" I2 (206 cm-1), "perturbed" I2 (173 cm-1), and I3- (115 and 141 cm-1). It was also verified, by FTIR spectroscopy, that the oxo and hydroxyl groups of the inorganic [M6O4(OH)4] (M = Zr, Hf) cluster were perturbed after the adsorption of I2 into UiO-66(Hf), which was ascribed to the higher acid character of Hf. Finally, with that in mind and considering that the EPR results discard the possibility of a redox phenomenon involving the tetravalent cations (Hf4+ or Zr4+), a mechanism was proposed for the conversion of I2 into I3- in UiO-66─based on an electron donor-acceptor complex between the aromatic ring of the BDC linker and the I2 molecule.

Synchronous Moderate Oxidation and Adsorption on the Surface of γ-MnO2 for Efficient Iodide Removal from Water.

Long-term exposure to excessive iodine via drinking water presents health risks. Moderate oxidation of iodide (I-) to iodine (I2) has a better iodine removal effect than excessive oxidation to iodate (IO3-). This study combines computational and experimental methods to construct a heterogeneous interface with synchronous I- moderate oxidation and I2 adsorption to increase the total iodine removal. Compared to other forms of crystal manganese dioxide (MnO2), theoretical calculations predict that MnO2 with a γ-crystal structure has the lowest adsorption energy, that is, -1.20 eV, and a slight overlap between the conduction and valence bands, which favors electron transfer between I- and Mn(IV) and I2 adsorption. Thus, γ-type MnO2 was designed by adjusting the precursor Mn sources and hydrothermal reaction conditions. The liquid chromatography-inductively coupled plasma-mass spectrometry and high-performance liquid chromatography confirmed that the total iodine concentration in water decreased from 173.7 to 36.3 μg/L after 2 h, with 200 mg/L γ-MnO2 dosage lower than the national standard of 0.1 mg/L. A minute proportion of I- in water was converted to IO3- (approximately 1.1 μg/L). The current I- adsorbent performed better than previously reported ones. During iodine removal, most of the I- migrated from water to the surface of γ-MnO2, and the ratio of I- to I2 was determined to be 1:0.6 by X-ray photoelectron spectroscopy. This study evaluates iodine species transformation and an optimum strategy for heterogeneous interface design; it is promising for treating high-iodine groundwater.

Efficient and simultaneous capture of iodine and methyl iodide achieved by a covalent organic framework

Radioactive molecular iodine (I2) and organic iodides, mainly methyl iodide (CH3I), coexist in the off-gas stream of nuclear power plants at low concentrations, whereas few adsorbents can effectively adsorb low-concentration I2 and CH3I simultaneously. Here we demonstrate that the I2 adsorption can occur on various adsorptive sites and be promoted through intermolecular interactions. The CH3I adsorption capacity is positively correlated with the content of strong binding sites but is unrelated to the textural properties of the adsorbent. These insights allow us to design a covalent organic framework to simultaneously capture I2 and CH3I at low concentrations. The developed material, COF-TAPT, combines high crystallinity, a large surface area, and abundant nucleophilic groups and exhibits a record-high static CH3I adsorption capacity (1.53 g·g−1 at 25 °C). In the dynamic mixed-gas adsorption with 150 ppm of I2 and 50 ppm of CH3I, COF-TAPT presents an excellent total iodine capture capacity (1.51 g·g−1), surpassing various benchmark adsorbents. This work deepens the understanding of I2/CH3I adsorption mechanisms, providing guidance for the development of novel adsorbents for related applications.

Chemically Stable Guanidinium Covalent Organic Framework for the Efficient Capture of Low-Concentration Iodine at High Temperatures

The capture of radioactive I2 vapor from nuclear waste under industrial operating conditions remains a challenging task, as the practical industrial conditions of high temperature (≥150 °C) and low I2 concentration (∼150 ppmv) are unfavorable for I2 adsorption. We report a novel guanidinium-based covalent organic framework (COF), termed TGDM, which can efficiently capture I2 under industrial operating conditions. At 150 °C and 150 ppmv I2, TGDM exhibits an I2 uptake of ∼30 wt %, which is significantly higher than that of the industrial silver-based adsorbents such as Ag@MOR (17 wt %) currently used in the nuclear fuel reprocessing industry. Characterization and theoretical calculations indicate that among the multiple types of adsorption sites in TGDM, only ionic sites can bond to I2 through strong Coulomb interactions under harsh conditions. The abundant ionic groups of TGDM account for its superior I2 capture performance compared to various benchmark adsorbents. In addition, TGDM exhibits exceptionally high chemical and thermal stabilities that fully meet the requirements of practical radioactive I2 capture (high-temperature, humid, and acidic environment) and differentiate it from other ionic COFs. Furthermore, TGDM has excellent recyclability and low cost, which are unavailable for the current industrial silver-based adsorbents. These advantages make TGDM a promising candidate for capturing I2 vapor during nuclear fuel reprocessing. This strategy of incorporating chemically stable ionic guanidine moieties in COF would stimulate the development of new adsorbents for I2 capture and related applications.

Ultrafast solid-phase synthesis of 2D pyrene-alkadiyne frameworks towards efficient capture of radioactive iodine

Iodine (I2) capture over adsorbents has great potential for the treatment of radioactive nuclear wastes. Herein, we develop a direct synthesis of 2D structured pyrene-alkadiyne frameworks, poly(1,3,6,8-tetraethynylpyrene) (PTEP), through a facile and ultrarapid solid-phase thermal polymerization of 1,3,6,8-tetraethynylpyrene (TEP) monomers in air. With this way, only single chemical of TEP is used without any catalysts, templates, solvents, and waste emissions. The PTEP frameworks feature high content of periodically distributed pyrene groups, regular intra-plane big rings, and 2D interlamellar structure, which endow PTEP with abundant electron-donors, high and accessible specific surface area as well as low resistance of mass transfer. PTEP exhibits high I2 capture capacity (3380 mg g−1 for vaporous I2 at 75 °C and 2570 mg g−1 for aqueous solution at 25 °C), fast adsorption kinetics (1350 mg g-1h−1 at 75 °C), strong water tolerance, thermal stability, and reliable reusability for the adsorption of vaporous I2 and I2 aqueous solution, which are superior to most of current sorbents. The experiments and modellings suggest that I2 adsorption on PTEP refers to the Langmuir adsorption model and the pseudo-second-order adsorption kinetics, in which the adsorbed iodine exists as polyiodide I5-via accepting electrons mainly from pyrenes.

Activated carbon from almond shells using an eco-compatible method: screening, optimization, characterization, and adsorption performance testing.

Activated carbon as a low-cost adsorbent prepared from almond shells using H3PO4 as a chemical activator and room vacuum pyrolysis as a physical activator, which is considered to be an eco-compatible preparation process. Experimental design methodology was used to study and optimize the effects of eight preparation parameters on I2 adsorption expressed by the iodine index (mg g-1). It was found that optimum activated carbon was obtained by chemical activation with H3PO4 at first, followed by physical treatment at 420 °C under a vacuum pressure of -0.8 bar. The obtained activated carbon was characterized by a thermogravimetric analyzer, scanning electron microscopy coupled to EDX, X-ray diffraction, and Fourier transform infrared absorption spectroscopy. The zero-charge pH and the characteristics of surface chemistry by Boehm titration were determined to predict the acid-base properties of the prepared material. An adsorption efficiency study of crystal violet dye on the optimally produced activated carbon was carried out. The obtained results of physicochemical characterization showed interesting properties of our activated carbon in comparison with those produced by other methods. Among these properties, an important porous surface, high thermal stability, and a disorganized graphitic crystalline structure were revealed. In addition to the carbon and oxygen elements, EDX analysis revealed the presence of phosphorus element, and the FTIR analysis indicated the existence of phosphonate groups and an acidic character, which resulted from chemical activation by H3PO4. An iodine index of 824.85 mg g-1 was achieved for optimal preparation. Crystal violet adsorption studies show a pseudo-first-order kinetic process and fit well with the Freundlich isotherm model, and thus, the predicted adsorption capacity was 364.27 mg g-1.

A Mesoporous Lead-Doped Titanium Oxide Compound with High Performance and Recyclability in I2 Uptake and Photocatalysis.

A three-dimensional (3D) mesoporous material with an atomically precise structure, Ti16Pb5O16(C6H5CO2)2(OCH3)40 (Ti16Pb5), comprised of a novel high-nuclearity Pb-doped titanium oxide cluster (TOC), was synthesized. Ti16Pb5 exhibited a surface area of 45 m2 g-1 and a pore diameter of 3.5 nm. It exhibited an uptake capacity of I2 of ≤2.2 g g-1 in vapor, and the performance was maintained after seven uptake-release cycles. Ti16Pb5 also showed a high adsorption ratio and capacity (93% and 3.1 g g-1) in hexane. The characterization data, including Fourier transform infrared, Raman, and powder X-ray diffraction, suggested the lattice structure of Ti16Pb5 was rigid and I2 was accommodated in the pores of Ti16Pb5. To the best of our knowledge, this is the first example of using a TOC in I2 adsorption. In addition, Ti16Pb5 showed excellent activity and recyclability in visible-light degradation of dye pollutants and photocurrent generation. Our structural analysis suggested the alkoxide ligands within the channels of Ti16Pb5 build up a confined polar environment and thereby facilitate I2 accommodation, and meanwhile, the improved performances and stabilities of Ti16Pb5 are correlated with its cluster-based, 3D hierarchical structure.

Высоковольтная деградация электродов, обусловленная электрохимической инжекцией в жидких диэлектриках

The results of experimental studies of the electrode degradation caused by electrochemical reactions under the action of high-voltage fields are presented. Under study were technical hydrocarbon and polymethylsiloxane (PMS) liquids, their solutions with iodine (I2) at chemically active (Cu) and indifferent (Ti) electrodes. It is shown that in hydrocarbons the Cu electrodes interact intensively with I2, and the cathodic degradation is more intense than the anodic one. The Ti electrodes do not degrade, but physical adsorption of I2 occurs on them in hydrocarbons, and a polymer film forms on them in PMS. The kinetics of degradation in time was studied.

Facile preparation of oxygen-rich porous polymer microspheres from lignin-derived phenols for selective CO2 adsorption and iodine vapor capture

Lignin is a natural O-containing aromatic amorphous polymers from the residues of biorefinery and industrial papermaking, it can derive lots of aromatic phenol chemicals used as industrial raw materials by an efficient depolymerization, and then produce synthetic polymers. Here, we selected six aromatic units from the liquid products of lignin depolymerization, and tried to prepare diversified O-rich hyper-cross-linked polymers (HCPs) by one-pot Friedel-Crafts alkylation reaction for CO2 and iodine vapor capture. HCP1, HCP2, and HCP3 microspheres possessed similar porous structure with Brunauer-Emmett-Teller (BET) surface areas (SBET) of 14.1–20.6 m2/g and high O content (26.34–30.68 wt%), while HCP4, HCP5, and HCP6 were composed of many bulks with 3D networks structure, and showed larger SBET of 15.4–246.9 m2/g and relatively low O content (18.48–26.38 wt%). The results indicated that the chemical position and quantities of substituent groups (methoxy and alkyl) into lignin-derived units had evident impact on their morphology and textural parameters. These HCPs exhibited considerable CO2 uptake (64.1 mg/g) and selectivity (35.2) at 273 K， and high iodine vapor uptake (192.3 wt%). Moreover, the performance analysis implied that the SBET and pore volume of these HCPs had not played the dominated roles in the CO2 and I2 adsorption, while their pore size distribution, O-functional groups, and electron density will be more important for the capture of the both. This study will offer a facile synthesis of O-rich polymer microsphere adsorbents based on the green and sustainable lignin.