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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Resolving Confined 7 Li Dynamics of Uranyl Peroxide Capsule U 24

Here, we obtained a kerosene-soluble form of the lithium salt [UO 2 (O 2 )(OH) 2 ] 24 phase (Li-U 24 ), by adding cetyltrimethylammonium bromide surfactant to aqueous Li-U 24 . Interestingly, its variable-temperature solution 7 Li NMR spectroscopy resolves two narrowly spaced resonances down to –10 °C, which shift upfield with increasing temperature, and finally coalesce at temperatures > 85 °C. Comparison with solid-state NMR demonstrates that the Li dynamics in the Li-U 24 -CTA phase involves only exchange between different local encapsulated environments. This behavior is distinct from the rapid Li exchange dynamics observed between encapsulated and external Li environments for Li-U 24 in both the aqueous and the solid-state phases. Density functional theory calculations suggest that the two experimental 7 Li NMR chemical shifts are due to Li cations coordinated within the square and hexagonal faces of the U 24 cage, and they can undergo exchange within the confined environment, as the solution is heated. Very different than U 24 in aqueous media, there is no evidence that the Li cations exit the cage, and therefore, this represents a truly confined space.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Li 15 P 4 S 16 Cl 3 , a Lithium Chlorothiophosphate as a Solid-State Ionic Conductor

Tremendous efforts have been devoted to the design of solid Li + electrolytes and the development of all-solid-state batteries. Compared with conventional Li-ion batteries, which use flammable liquid organic electrolytes, all-solid-state batteries show significant advantages in safety. In this work, a novel lithium chlorothiophosphate compound, Li 15 P 4 S 16 Cl 3 , is discovered. The crystal structure and electrochemical properties are investigated. Li 15 P 4 S 16 Cl 3 can be synthesized as a pure phase via a facile solid-state reaction by heating a ball-milled mixture of Li 2 S, P 2 S 5 , and LiCl at 360 °C. The crystal structure of Li 15 P 4 S 16 Cl 3 was refined against neutron and synchrotron powder X-ray diffraction data, revealing that it crystallizes in the space group $I\bar{4}3d$. Furthermore, the Li + transport in Li 15 P 4 S 16 Cl 3 was also investigated by multiple solid-state NMR methods, including variable-temperature NMR line-shape analysis, NMR relaxometry, and pulsed-field-gradient NMR. Li 15 P 4 S 16 Cl 3 shows good thermodynamic stability and can be synthesized at relatively low temperature. Although it exhibits a low ionic conductivity at room temperature, it can serve as a new motif crystal structure for the design and development of new solid-state electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2020

Dynamics of Cation-Induced Conformational Changes in Nanometer-Sized Uranyl Peroxide Clusters

Conformational changes of the pyrophosphate (Pp)-functionalized uranyl peroxide nanocluster [(UO 2 ) 24 (O 2 ) 24 (P 2 O 7 ) 12 ] 48– ({U 24 Pp 12 }), dissolved as a Li/Na salt, can be induced by the titration of alkali cations into solution. The most symmetric conformer of the molecule has idealized octahedral ( O h ) molecular symmetry. One-dimensional 31 P NMR experiments provide direct evidence that both K + and Rb + ions trigger an O h -to- D 4 h conformational change within {U 24 Pp 12 }. Variable-temperature 31 P NMR experiments conducted on partially titrated {U 24 Pp 12 } systems show an effect on the rates; increased activation enthalpy and entropy for the D 4 h -to- O h transition is observed in the presence of Rb + compared to K + . Two-dimensional, exchange spectroscopy 31 P NMR revealed that magnetization transfer links chemically unique Pp bridges that are present in the D 4 h conformation and that this magnetization transfer occurs via a conformational rearrangement mechanism as the bridges interconvert between two symmetries. The interconversion is triggered by the departure and reentry of K (or Rb) cations out of and into the cavity of the cluster. This rearrangement allows Pp bridges to interconvert without the need to break bonds. Cs ions exhibit unique interactions with {U 24 Pp 12 } clusters and cause only minor changes in the solution 31 P NMR signatures, suggesting that O h symmetry is conserved. Single-crystal X-ray diffraction measurements reveal that the mixed Li/Na/Cs salt adopts D 2 h molecular symmetry, implying that while solvated, this cluster is in equilibrium with a more symmetric form. Thus, these results highlight the unusually flexible nature of the actinide-based {U 24 Pp 12 } and its sensitivity to countercations in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Coupled Multimodal Dynamics of Hydrogen-Containing Ion Networks in Water-Deficient, Sodium Hydroxide-Aluminate Solutions

The (meta)stability of low water activity sodium hydroxide/aluminate (Na + OH–/Al(OH) 4 –) electrolytes dictates kinetics in the Bayer process for aluminum refining and high-level nuclear waste processing. We utilized quasi-elastic neutron scattering (QENS) and proton nuclear magnetic resonance spectroscopy ( 1 H NMR) in extremely concentrated sodium aluminate solutions to investigate the picosecond (ps) to microsecond (ms) timescale motions of H-bearing species (Al(OH) 4 – monomers/clusters, OH– and H 2 O). In the QENS data, in contrast to typical liquids, no short-time translational diffusion was observed at 293 K, but two types of localized motions were found: (i) local backbone tumbling or a formation of large hydrated ion clusters on the order of 40–60 ps; and (ii) much slower, complex, and collective dynamics of the ensemble of H-bearing species on the order of 350–750 ps. Variable temperature, pulsed field gradient, diffusion-ordered 1H NMR was used to determine the ensemble translational motion along with relaxometry to calculate rotational correlation coefficients. The ensemble rotational correlation times were on the order of 184–300 ps from 1 H NMR, which is consistent with the timescale of the QENS components. Complementary molecular dynamics simulation of NaOH solutions exhibit extensive ion networks potentially responsible for the observed dynamical coupling of water with the motion of large hydrated ion clusters. Understanding these collective motions will aid in predicting the behavior of complex solutions during aluminum production and during nuclear waste processing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Dynamics in Flexible Pillar[ n ]arenes Probed by Solid-State NMR

Pillar[n]arenes are supramolecular assemblies that can perform a range of technologically important molecular separations which are enabled by their molecular flexibility. Here, we probe dynamical behavior by performing a range of variable-temperature solid-state NMR experiments on microcrystalline perethylated pillar[n]arene (n = 5, 6) and the corresponding three pillar[6]arene xylene adducts in the 100–350 K range. This was achieved either by measuring site-selective motional averaged 13 C 1 H heteronuclear dipolar couplings and subsequently accessing order parameters or by determining 1 H and 13 C spin–lattice relaxation times and extracting correlation times based on dipolar and/or chemical shift anisotropy relaxation mechanisms. We demonstrate fast motional regimes at room temperature and highlight a significant difference in dynamics between the core of the pillar[n]arenes, the protruding flexible ethoxy groups, and the adsorbed xylene guest. Additionally, unexpected and sizable 13 C 1 H heteronuclear dipolar couplings for a quaternary carbon were observed for p-xylene adsorbed in pillar[6]arene only, indicating a strong host–guest interaction and establishing the p-xylene location inside the host, confirming structural refinements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Water Structure and Dynamics in Smectites: X-ray Diffraction and 2 H NMR Spectroscopy of Mg–, Ca–, Sr–, Na–, Cs–, and Pb–Hectorite

Variable-temperature X-ray diffraction and 2 H NMR spectroscopy of the smectite mineral, hectorite, containing interlayer Na + , K + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ , and Pb 2+ equilibrated at 43% relative humidity (RH) and mixed with 2 H 2 O to form a paste provide a comprehensive picture of the structural environments and dynamics of interlayer 2 H 2 O and the relationships of these properties to interlayer hydration state, the hydration energy and polarizability of the cation, temperature, and the formation of ice-1h in the interparticle pores. The variation in basal spacing shown by the XRD data correlates well with the 2 H NMR behavior, and the XRD data show for the first time in hectorites that crystallization of interparticle ice-1h causes a decrease in the interlayer spacing, likely due to removal of interlayer 2 H 2 O. Here, the variation of the 2 H NMR behavior of all the samples with decreasing temperature reflects decreasing frequencies of motion for the rotation of the 2 H 2 O molecules around their dipoles, reorientation of the 2 H 2 O molecules, and exchange of the 2 H 2 O molecules between interlayer sites coordinated to and not coordinated to the cations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Defects Enable Dark Exciton Photoluminescence in Single-Walled Carbon Nanotubes

Variable temperature photoluminescence excitation spectroscopy of three (n,m) species of single-walled carbon nanotubes revealed that at resonant S 22 excitation, in addition to allowed excitonic optical transitions, several sidebands that should be forbidden based on selection rules were observed and appeared to have a strong temperature dependence. In particular, we found that a sideband located approximately 130 meV away from the bright S 11 exciton peak relating to the K-momentum dark exciton state, called X 1 , decreased in intensity five-fold as the samples were cooled. Direct optical excitation of this dark state is nominally forbidden, thus calling into question how the state is populated, and why it is so prominent in the photoluminescence spectrum. Interestingly, the ratio of the integrated photoluminescence intensities of X 1 to S 11 scales with a Boltzmann factor unrelated to the phonon that is thought to be responsible for depopulating the K-momentum dark exciton state: an in-plane transverse optical phonon, A 1 ’. Furthermore, photoluminescence spectra from individual (7,5) nanotubes show that only a small fraction exhibit the X 1 feature, with varying oscillator strength, thus suggesting that intrinsic processes such as phonon scattering are not responsible for populating the dark state. Alternatively, we suggest that populating the K-momentum dark exciton state requires scattering from defects, which is consistent with the increased magnitude of the X 1 feature for samples with increased sample purification and processing. Thus, the presence of an X 1 peak in photoluminescence is an extremely sensitive spectroscopic indicator of defects on single-walled carbon nanotubes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Unraveling the Nature of Vibrational Dynamics in CsPbI 3 by Inelastic Neutron Scattering and Molecular Dynamics Simulations

Cesium lead iodide, CsPbI 3 , is an optoelectronic material of large interest for various technological applications; however, fundamental questions surrounding the vibrational dynamics of this material, especially regarding its role in structural phase transitions, remain to be elucidated. Here, in a combined variable temperature inelastic neutron scattering (INS) and machine-learning based molecular dynamics (MD) simulation study, we show that the stable phase at room temperature, i.e., the nonperovskite δ-phase, exhibits phonon modes with weak anharmonicity with only a weak temperature dependence from 10 K all the way up to the transition to the cubic perovskite α-phase at approximately 600 K. In contrast, the α-phase features anharmonic and damped vibrational dynamics, mainly associated with overdamped tilting motions of the PbI 6 octahedra. Crucially, these overdamped tilting modes, which relate to the tetragonal and orthorhombic distorted perovskite phases (β- and γ-phase, respectively) formed at lower temperatures, stay overdamped by more than 100 K above the respective phase transition. This suggests a flat energy landscape of octahedral tilting motions in α-CsPbI3 and with structural fluctuations on the picosecond time scale with tilting patterns that locally resemble the structure of the β- and γ-phases. The vibrational dynamics of α-CsPbI 3 are also characterized by pronounced anharmonic motions with large thermal displacements of the Cs + ions, but these modes remain underdamped at 600 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Amine Dynamics in Diamine-Appended Mg 2 (dobpdc) Metal–Organic Frameworks

In this work, variable-temperature 15 N solid-state NMR spectroscopy is used to uncover the dynamics of three diamines appended to the metal–organic framework Mg 2 (dobpdc) (dobpdc 4– = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate), an important family of CO 2 capture materials. The results imply both bound and free amine nitrogen environments exist when diamines are coordinated to the framework open Mg 2+ sites. There are rapid exchanges between two nitrogen environments for all three diamines, the rates and energetics of which are quantified by 15 N solid-state NMR data and corroborated by density functional theory calculations and molecular dynamics simulations. The activation energy for the exchange provides a measure of the metal–amine bond strength. The unexpected negative correlation between the metal–amine bond strength and CO 2 adsorption step pressure reveals that metal–amine bond strength is not the only important factor in determining the CO 2 adsorption properties of diamine-appended Mg 2 (dobpdc) metal–organic frameworks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Growth of Extra-Large Chromophore Supramolecular Polymers for Enhanced Hydrogen Production

The control of morphology in bioinspired chromophore assemblies is key to the rational design of functional materials for light harvesting. Here, we investigate here morphological changes in perylene monoimide chromophore assemblies during thermal annealing in aqueous environments of high ionic strength to screen electrostatic repulsion. We found that annealing under these conditions leads to the growth of extra-large ribbon-shaped crystalline supramolecular polymers of widths from about 100 nm to several micrometers and lengths from 1 to 10 μm while still maintaining a unimolecular thickness. This growth process was monitored by variable-temperature absorbance spectroscopy, synchrotron X-ray scattering, and confocal microscopy. The extra-large single-crystal-like supramolecular polymers are highly porogenic, thus creating loosely packed hydrogel scaffolds that showed greatly enhanced photocatalytic hydrogen production with turnover numbers as high as 13 500 over ~110 h compared to 7500 when smaller polymers are used. Our results indicate great functional opportunities in thermally and pathway-controlled supramolecular polymerization.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Reversible 1,2-Addition of Water To Form a Nucleophilic Mn(I) Hydroxide Complex: A Thermodynamic and Reactivity Study

( iPr PN H P)Mn(CO) 2 (OH) (2; iPr PN H P = HN{CH 2 CH 2 (P i Pr 2 )} 2 ) was formed from the reversible 1,2-addition of water to ( iPr PNP)Mn(CO) 2 (1; iPr PNP = the deprotonated, amide form of the ligand, –N{CH 2 CH 2 (P i Pr 2 )} 2 ). This reversible reaction was probed via variable-temperature NMR experiments, and the energetics of the 1,2-addition/elimination was found to be slightly exothermic (-0.8 kcal/mol). The corresponding manganese hydroxide was found to react with aldehydes, yielding the corresponding manganese carboxylate complexes ( iPr PN H P)Mn(CO) 2 (CO 2 R), where R = H, methyl, phenyl. While no reaction between 1 and neat benzaldehyde was observed, in the presence of water, conversion to the corresponding manganese-bound benzoate with formation of H 2 was observed. The catalytic oxidation of benzaldehyde by water without additives was unsuccessful due to strong product inhibition, with the manganese benzoate formed under a variety of reaction conditions. Upon addition of base, a catalytic cycle for the conversion of aldehyde to carboxylate and hydrogen can be devised.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

An Efficient Copper-Based Redox Shuttle Bearing a Hexadentate Polypyridyl Ligand for DSCs under Low-Light Conditions

A Cu complex featuring a hexadentate ligand was synthesized and evaluated as a redox shuttle in dye-sensitized solar cell (DSC) devices, which exhibited excellent performance under low-light conditions. Cu-based redox shuttles (RSs) have been shown to perform remarkably well under low-light conditions; however, most of the known Cu-based RSs employ bidentate pyridyl ligands and often require bulky flanking groups adjacent to the nitrogen donors of these ligands to prevent distortion and binding of exogenous Lewis bases such as 4- tert -butylpyridine (TBP) that are added to enhance cell performance. Without the bulky substituents, the bidentate ligands are susceptible to ligand exchange with TBP. In this context, we have developed a Cu-based RS with a preorganized multidentate ligand designed to facilitate efficient electron transfer kinetics and high stability via the chelate effect. The Cu system, [Cu(bpyPY4)] 2+/+ , reported here is supported by the hexadentate polypyridyl ligand bpyPY4 (6,6'-bis(1,1-di(pyridine-2-yl)ethyl)-2,2'-bipyridine) and examined as a RS in DSCs. From X-ray crystallography and variable-temperature 1 H NMR studies, bpyPY4 provides a dynamic coordination environment around the metal center. Cyclic voltammetry and UV–visible and NMR spectroscopy indicate that noncoordinated pyridyl donors block binding of TBP to copper. DSC devices using [Cu(bpyPY4)] 2+/+ as the redox electrolyte gave a power conversion efficiency (PCE) value of 4.9% under 1 sun illumination (100 mW/cm 2 ). Strikingly, the device performance increased to 11.11% when irradiated with 2400 lux (0.5 mW/cm 2 ) via a fluorescent lamp light source and improved further to 15.2% PCE at 13500 lux (2.10 mW/cm 2 ). In conclusion, the Cu redox shuttle is an intriguing candidate for implementation with narrow band gap sensitizers with low oxidation potentials, which are important for high photocurrent DSC devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Understanding Electron Transport in Disk-Shaped Triphenylene-Tris(naphthaleneimidazole)s through Structural Modification and Theoretical Investigation

We report that disk-shaped molecules with large aromatic π-surfaces are a class of organic semiconductors in which the charge-carrier transport properties could be greatly facilitated by preferred intermolecular stacking of the π-surfaces. The optical and electronic properties are not only determined by the core aromatic structure of these disk-shaped molecules but are also strongly dependent on the side chains, which directly impact the molecular self-assembly behavior in condensed phases. Triphenylene-tris(naphthaleneimidazole) (TP-TNI) is a recently reported n-type semiconductor featuring a large π-core and branched side chains, with an electron-transporting mobility reaching 10 -4 cm 2 V -1 s -1 . To further improve material performance, a detailed study is needed to understand the dependence of carrier transport properties on both the core electronic structure and side chain. Here, we present the detailed synthesis and characterization of a TP-TNI derivative bearing linear side chains, which has demonstrated a field-effect electron-transport mobility of up to 1.3 × 10 -3 cm 2 V -1 s -1 . The more than 1 order improvement in electron-transport properties over the branched side chain homologue can be correlated to ordered twisted packing in the thin film, as revealed by in situ variable temperature grazing incidence wide-angle X-ray scattering studies. In conclusion, in-depth theoretical understanding of the frontier orbitals, reorganization energies, and charge-transfer integrals of TP-TNI molecules has provided further insight into the relationship between the molecular stacking geometry and charge-transport properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interface-Dependent Radiative Lifetimes of Yb3+, Er3+ Co-doped Single NaYF4 Upconversion Nanowires

The development of upconversion nanomaterials for many photonic applications requires a detailed understanding of their radiative lifetimes that in turn depend critically on local environmental conditions. In this work, hexagonal (ß-phase) sodium-yttrium-?uoride (NaYF4) nanowires (NWs) were synthesized and substitutionally co-doped with a luminescent solid solution of trivalent erbium and ytterbium ions. A single-beam laser trapping instrument was used in tandem with a piezo-controlled, variable-temperature stage to precisely vary the nanowire’s distance from the substrate. The spontaneous photoluminescence lifetime of the 4S3/2 ? 4I15/2 transition from Er3+ ions was observed to change by >60% depending on the ions’ separation distance from a planar (water/glass) dielectric interface. The 4S3/2 state lifetime is observed to increase by a factor of 1.62 ± 0.01 as the distance from the quartz coverslip increases from ~0 nm to~40 µm. Less signi?cant changes in the luminescence lifetime (=10%) were observed over a temperature range between 25 and 50 °C. The distance dependence of the lifetime is interpreted quantitatively in the context of classical electromagnetic coupling between Er3+ ions within the nanowire and the adjacent dielectric interface. We also demonstrate potential applications of the NaYF4 NWs for both controlling and probing temperatures at nanometer scales by integrating them within a poly(dimethylsiloxane) composite matrix.

upconversion, nanowires, radiative lifetime, optic↗
DOE OSTI2022

Force-Modulated Selectivity of the Rhodium-Catalyzed Hydroformylation of 1-Alkenes

Here we quantify the regio- chemo-, and enantioselectivity of the hydroformylation of 1-alkenes catalyzed by Rh(I) complexes containing chiral macrocyclic biaryl bis(phosphine) ligands as a function of mechanical force applied to the biaryl backbone of these ligands. Extension forces increase the regioselectivity of the hydroformylation of 1-octene from l:b = 1.2 to 1.9 and decrease the chemoselectivity for C 9 aldehyde relative to 2-octene from 96% to 20% across a ~230 pN change in applied force. Extension forces decrease the enantioselectivity of the hydroformylation of styrene from 28% to 18% ee across a similar force range. Variable temperature 1 H and 31 P NMR analysis of five-coordinate rhodium complexes of the form (P–P)Rh(CO) 2 H established structures in which the bisphosphine ligand occupies one equatorial and one apical position in the trigonal bipyramid with rapid interconversion of the equatorial and apical phosphorus atoms ($ΔG^‡_{223 \text{K}}$ = 9.6–9.9 kcal/mol). Neither the isomeric composition nor fluxional behavior of these complexes was detectably perturbed across a ~300 pN change in applied force.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Crystallographic Evidence of Size-Dependent Bond Flexibility in Metal–Organic Framework Nanocrystals

Size-dependent electronic, magnetic, and optical behavior suggests that metal–organic frameworks become softer materials as their particle sizes decrease, but direct evidence is lacking. Here, we report variable-temperature powder X-ray diffraction data of Fe(1,2,3-triazolate)2 particles that offer crystallographic insight into size-dependent bond flexibility. Rietveld refinement reveals size-dependent positive thermal expansion upon downsizing the crystalline domains from 178 to 9 nm, with a 6-fold increase from 16 MK –1 to 96 MK –1 . Here, this behavior occurs in tandem with size-dependent elongation of metal–ligand bonds and increasing thermal displacement parameters, consistent with pronounced metal-linker bond lability. We propose that these effects, as well as size-dependent annealing of crystallite sizes, originate from the high charge density and surface stress of smaller particles. Taken together, these results provide structural evidence that size reduction serves as a synthetic route to controlling the dynamic response of materials to external stimuli.

Crystals↗
DOE OSTI2023

Light-Induced Transient Lattice Dynamics and Metastable Phase Transition in CH 3 NH 3 PbI 3 Nanocrystals

In this study, methylammonium lead iodide (MAPbI 3 ) perovskite nanocrystals (NCs) offer desirable optoelectronic properties with prospective utility in photovoltaics, lasers, and light-emitting diodes (LEDs). Structural rearrange-ments of MAPbI 3 in response to photoexcitation, such as lattice distortions and phase transitions, are of particular interest, as these engender long carrier lifetime and bolster carrier diffusion. Here, we use variable temperature X-ray diffraction (XRD) and synchrotron-based transient X-ray diffraction (TRXRD) to investigate lattice response following ultrafast optical excitation. MAPbI 3 NCs are found to slowly undergo a phase transition from the tetragonal to a pseudocubic phase over the course of 1 ns under 0.02-4.18 mJ/cm 2 fluence photoexcitation, with apparent nonthermal lattice distortions attributed to polaron formation. Lattice recovery exceeds time scales expected for both carrier recombination and thermal dissipation, indicating meta-stability likely due to the proximal phase transition, with symmetry-breaking along equatorial and axial directions. These findings are relevant for fundamental understanding and applications of structure-function properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Highly Efficient Iodine Capture by Layered Double Hydroxides Intercalated with Polysulfides

We demonstrate strong iodine (I-2) vapor adsorption using Mg/Al layered double hydroxide (MgAl-LDH) nanocomposites intercalated with polysulfide (S-x(2-)) groups (S-x-LDH, x = 2, 4, 6). The as-prepared LDH/polysulfide hybrid materials display highly efficient iodine capture resulting from the reducing property of the intercalated polysulfides. During adsorption, the I-2 molecules are reduced to I-3(-) anions by the intercalated [S-x](2-) groups that simultaneously are oxidized to form S8. In addition to the chemical adsorption, additional molecular I-2 is physically captured by the LDH composites. As a result of these parallel processes, and despite their very low BET surface areas, the iodine capture capacities of S-2-LDH, S-4-LDH, and S-6-LDH are similar to 1.32, 1.52, and 1.43 g/g, respectively, with a maximum adsorption of 152% (wt %). Thermogravimetric and differential thermal analysis (TG-DTA), energy dispersive X-ray spectroscopy (EDS), and temperature-variable powder X-ray diffraction (XRD) measurements show the resulting I-3(-) ions that intercalated into the LDH gallery have high thermal stability (>= 350 degrees C). The excellent iodine adsorption performance combined with the facile preparation points to the S-x-LDH systems as potential superior materials for adsorption of radioactive iodine, a waste product of the nuclear power industry.

Ma, Shulan↗