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Atmospheric iodine chemistry has garnered increasing attention as a result of increased iodine emissions. A key subset of this chemistry involves iodine oxides (I₂O_2–5), which serve as precursors to particle formation. Among these, I₂O₃ is the simplest iodine oxide involved in particle formation, but it has remained undetected in the atmosphere. Previous theoretical studies have characterized this peculiar molecule, primarily using energies to refine geometries obtained at low levels of theory. Due to the reemerging interest in I₂O₃, this study presents geometries optimized at the CCSD(T)/aug-cc-pwCVTZ-PP level of theory─marking the first instance, to the best of our knowledge, where thismore » system has been studied exclusively with CCSD(T). Harmonic vibrational frequencies were computed at the same level of theory. Final energetics were obtained using the very high level CCSDT(Q) method with basis sets up to quintuple-zeta cardinality (aug-cc-pwCV5Z-PP) and extrapolated to the CBS limit to yield CCSDT(Q)/CBS//CCSD(T)/aug-cc-pwCVTZ-PP energies. These energies include harmonic zero-point vibrational energy corrections and scalar relativistic energy corrections. Additionally, this study discovers new isomers along the I₂O₃ potential energy surface, a novel contribution to the field. The performance of different computational methods and DFT functionals commonly used in atmospheric chemistry is also assessed relative to high-level theoretical methods.« less

Four promising iodine “getter” materials (Ag, Cu, Bi, and Sn) for radioiodine capture were assessed in their pure metal-iodide (MI_x) pelletized forms to compare relative chemical durabilities. To study chemical durability, commercial MI_x compounds of AgI, BiI₃, BiOI, CuI, and SnI₄ were converted to dense monolithic pellets using spark plasma sintering. Semidynamic leach testing in the form of modified ASTM C1308 tests was then performed on the pellets in two different forms including unmounted (as-pressed) specimens (i.e., “U”) and epoxy-mounted specimens (i.e., “M”) with polished surfaces. The chemical durability results and sample characterizations showed that three of the five MI_xmore » compounds tested (i.e., AgI, CuI, and BiOI) displayed moderate to high leach resistances. Further, the remaining two MI_x compounds (i.e., BiI₃ and SnI₄), which are both desirable iodine waste forms due to their high iodine loading capacities, readily decomposed during leach testing, indicated by crystallographic changes in the specimens as well as large amounts of iodine detected in the leachate solutions. The instabilities of BiI₃ and SnI₄ raise uncertainties for using the base metals/cations (i.e., Bi⁰/Bi³⁺ and Sn⁰/Sn⁴⁺, respectively) as viable getters for radioiodine capture due to likely poor waste form chemical durabilities after capture and consolidation into waste forms.« less

The preferential growth of α-phase formamidinium perovskite (α-FAPbI₃) at low temperatures can be achieved with the incorporation of chloride-based additives, with methylammonium chloride (MACl) being the most common example. However, compared to other less-volatile chloride additives, MACl only remains in the growing perovskite film for a short time before evaporating during annealing, primarily influencing the early stages of film formation. In addition, evaporation of MACl as methylamine (MA⁰) and HCl can introduce a side reaction between MA⁰ and formamidinium (FA), undermining the compositional purity and phase stability of α-FAPbI₃. In this study, it is demonstrated that addition of iodine (I₂)more » into the FAPbI₃ precursor solution containing MACl suppresses the MA-FA side reaction during annealing. Additionally, MACl evaporation is delayed owing to strong interaction with triiodide. The added I₂ facilitates spontaneous growth of α-FAPbI₃ prior to annealing, with an improved bottom morphology due to the formation of fewer byproducts. Perovskite solar cells derived from an I₂-incorporated solution deliver a champion power conversion efficiency of 25.2% that is attributed to suppressed non-radiative recombination.« less

Here, we report a set of three new mixed-valent Au^I Au^III iodides: (ClPy)₃[AuI₂]₂[AuI₄] [1], (BrPy)₃[AuI₂]₂[AuI₄] [2], and (ClPy)₂[AuI₂][AuI₄] [3], as well as three new monovalent Au^III iodides: (XPy)₂[AuI₄][I₃] (Py = 4-X-pyridinium X = Cl, Br, and I) [4–6]. Two of these mixed-valent compounds (1 and 2) incorporate both monovalent Au^I···Au^I (aurophilic bonding) and mixed-valent Au^II···Au^IIII couples (Au–I halogen bonding), to the best of our knowledge an unprecedented structural feature. These same two mixed-valent compounds also exhibit a rare low-dimensional molecular architecture with respect to second sphere Au···I interactions, namely, 1D chains of Au···I interactions, extending along a single crystallographic axis.more » All compounds were synthesized with the assistance of the I^–/I₃^– redox couple and tacit manipulation of the polyiodide content during synthesis. Air-free synthesis was used to influence the redox process of I^–/I₃^–, resulting in better selection for mixed-valent products. Compounds 1–2 and 4–5 exhibit a characteristically narrow bandgap (1.04–1.25 eV), as measured via diffuse reflectance spectroscopy (DRS). Computational analyses were used to rationalize the specific assembly modes of [AuI₂]^– and [AuI₄]^– species, and they show that the Au^I···I interaction type is favored over the Au^III···I.« less

Gamma detection of select fission products or activation products such as ¹⁵³Sm and ²³⁹Np in a fission sample is difficult due to gamma interferences from radiotellurium and radioiodine. To aid in the detection of these difficult-to-detect nuclides, the radiotellurium and radioiodine were removed using Cu metal turnings. This method is highly effective at the removal of the interfering radionuclides removing > 98% of the radiotellurium and radioiodine. A mechanistic study was conducted. Determining the deposition mechanism, using a number of techniques including XANES and electrochemistry providing an understanding of the electrochemical path for the Te deposition. Initial work focused onmore » the use of stable Te, further expanding into activated TeO₂, and a fresh fission sample. Importantly, this method presents a rapid method for the direct detection of select fission products that could have a significant impact on nuclear related fields including nuclear forensics.« less

Efficient management of radionuclides that are released from various processes in the nuclear fuel cycle is of significant importance. Among these nuclides, radioactive iodine (mainly ¹²⁹I and ¹³¹I) is a major concern due to the risk it poses to the environment and to human health; thus, the development of materials that can capture and safely store radioactive iodine is crucial. Herein, a novel silver-thione-functionalized zeolitic imidazole framework (ZIF) was synthesized via post-synthetic modification and assessed for its iodine uptake capabilities alongside the parent ZIF-8 and intermediate materials. A solvent-assisted ligand exchange procedure was used to replace the 2-methylimidazole linkers inmore » ZIF-8 with 2-mercaptoimidazole, forming the intermediate compound ZIF-8=S, which was reacted with AgNO₃ to yield the ZIF-8=S-Ag⁺ composite for iodine uptake. Despite possessing the lowest BET surface area of the derivatives, the Ag-functionalized material demonstrated superior I₂ adsorption in terms of both maximum capacity (550 g I₂/mol) and rapid kinetics (50% loading achieved in 5 hrs, saturation in 50 hrs) compared to our pristine ZIF-8, which reached 450 g I₂/mol after 150 hours and 50% loading in 25 hours. This improvement is attributed to the presence of the Ag⁺ ions, which provide a strong chemical driving force to form stable Ag-I species. In conclusion, the results of this study contribute to a broader understanding of the strategies that can be employed to engineer adsorbents with robust iodine uptake behavior.« less

Mechanism of hexavalent chromium removal (Cr(VI) as CrO₄^2-) by the weak-base ion exchange (IX) resin ResinTech® SIR-700-HP (SIR-700) from simulated groundwater is assessed in the presence of radioactive contaminants iodine-129 (as IO₃^-), uranium (U as uranyl UO₂²⁺), and technetium-99 (as TcO₄^-), and common environmental anions sulfate (SO₄^2-) and chloride (Cl-). Batch tests using the acid sulfate form of SIR-700 demonstrated Cr(VI) and U(VI) removal exceeded 97%, except in the presence of high SO₄^2- concentrations (536 mg/L) where Cr(VI) and U(VI) removal decreased to ≥ 80%. However, Cr(VI) removal notably improved with co-mingled U(VI) that complexes with SO₄^2- at the protonatedmore » amine sites. These U–SO₄^2- complexes are integral to U(VI) removal, as confirmed by the decrease in U(VI) removal (<40%) when the acid chloride form of SIR-700 was used instead. Solid phase characterization revealed that CrO₄^2- is removed by IX with SO₄^2- complexes and/or reduced to amorphous Cr(III)(OH)₃ at secondary alcohol sites. Tc(VII)O₄^- and I(V)O₃^- also undergo chemical reduction, following a similar removal mechanism. Oxyanion removal preference is determined by the anion reduction potential (CrO₄^2->TcO₄^->IO₃^-), geometry, and charge density. For these reasons, 39% and 69% of TcO₄^- and 17% and 39% of IO₃^- are removed in the presence and absence of Cr(VI), respectively.« less

While iodine speciation is important for a wide range of nuclear activities, understanding the mechanisms of the transformations of iodine between chemical forms and the sensitivity of these transitions to solution conditions and exposure to radiation remains an active area of research. This work curates spectroscopic data from several experimental techniques and establishes their sensitivity and limitations in detecting changes in iodine speciation in both neutral and acidic regimes. The techniques include Raman spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, ¹²⁷I NMR spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy. Analysis of these data indicates that these commonly accessible spectroscopies often have dynamic rangesmore » of measurable concentrations that do not always overlap between all techniques. The experimental techniques are disparately sensitive to iodide (I^-), molecular iodine (I₂), iodate (IO₃^-), and periodate (IO₄^-) species. Raman, FTIR, and NMR spectra were subsequentially analyzed using two-dimensional correlation analyses to generate high-resolution autocorrelation spectra. Here, the use of these spectroscopies is then extended to tracking acidification-induced and gamma irradiation-induced transformations of dissolved sodium iodate in deionized water and concentrated nitric acid. Both dissolution into nitric acid and irradiation with a gamma source are demonstrated to perturb the iodine speciation promoting their assembly into molecular iodine (I₂) and/or triiodide (I₃^-). While I₂ and I₃^- species are undetectable with FTIR spectroscopy and ¹²⁷I NMR spectroscopy, the species can be detected with UV-Vis spectroscopy, and in some instances, I₃^- can be detected with Raman spectroscopy in the low wavenumber region. Ultimately, the results of this work provide a path to designing optimal combinations of techniques to detect forms of iodine across a wide range of concentrations and conditions.« less