The Influence of Weakly Coordinating Cations on the O−H⋅⋅⋅O− Hydrogen Bond of Silanol-Silanolate Anions

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol-silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol-silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate–oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol-silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol-silanolate chains in the solid state.     

Effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in GMZ bentonite

Polyaminopolycarboxylate EDTA with powerful metal-binding property, which often presents in low and intermediate-level waste, can enhance the radionuclide migration. The effect of EDTA on the diffusion behavior of ⁹⁹TcO₄ ^? and ReO₄ ^? in Gaomiaozi (GMZ) bentonite was investigated by using through-diffusion method. For ⁹⁹TcO₄ ^? in present of EDTA, the D _e values was (1.2 ± 0.1) × 10^?11 m²/s, which was 4 times higher than that in absent of EDTA. It can be explained that the complexation between ⁹⁹TcO₄ ^? and EDTA might be formed. By contrast, the D _e values of ReO₄ ^? remained unchanged in present or absent of EDTA, indicating that ReO₄ ^? could not complex with EDTA. However, the diffusion of ReO₄ ^? could be increased in present of EDTA, the D _a value was found to be increased from 1.8 × 10^?10 to 5.4 × 10^?10 m²/s. It demonstrated that ReO₄ ^? need more drastic conditions to form the Re(VII)–EDTA complexes than those used for ⁹⁹TcO₄ ^?. For both ReO₄ ^? and ⁹⁹TcO₄ ^?, the rock capacity factor α is less than the total porosity ε _tot, indicating that they has little retention/sorption on the surface of bentonite.     

Effect of LET on radiolysis of C6−C8 cycloalkane systems

The - and -radiolysis of cyclohexane, cycloheptane and cyclooctane was investigated in the absence and presence of iodine scavenger. Comparison of the distributions of products formed revealed considerable differences between - and -radiolysis, and the decomposition of strainless cyclohexane and strained cycloheptane and cyclooctane.     

Influence of Changing the Remote Substituents on Charge Transfer Properties of Cyanide-Bridged Trinuclear Fe−Ru−Fe Complexes

To investigate the effect of ligand remote (>10 Å) substituents on the bridging metal center on the metal-to-metal charge transfer (MMCT) properties in cyanidometa-bridged complexes, a series of new cyanidometal-bridged complexes and their one-electron and two-electron oxidation products have been synthesized and well characterized (namely, trans-[Cp(dppe)Fe−NC−(L)Ru(PPh₃)−CN−Fe(dppe)Cp][PF₆]_n (n=2, 3, 4) (L=dmptpy, 1[PF₆]_n ; L=meoptpy, 2[PF₆]_n ; L=t-Buptpy, 3[PF₆]_n ) (Cp=1,3-cyclopentadiene, dppe=1,2-bis(diphenylphosphino)ethane, PPh₃=triphenylphosphine, dmptpy=4′-(4-dimethylaminophenyl)-2,2′,6′,2′′-terpyridine, meoptpy=4′-(4-methoxyphenyl)-2,2′,6′,2′′-terpyridine, t-Buptpy=4′-(4-tertbutylphenyl)-2,2′,6′,2′′-terpyridine)). The investigations suggest that the cyanido-stretching (ν_CN) vibration energy for the complexes is unsensitive to the electron-donating ability change of the remote substituents of the cyanidometal bridging auxiliary ligand from tertbutyl, methoxy to dimethylamino group. However, the MMCT energies of the one- and two-electron oxidation complexes are still sensitive to the remote substituents of the ligand on the bridging metal center, and decreases with the increase of the electron-donating ability of the remote substituents from tertbutyl, methoxy to dimethylamino group. All one-electron and two-electron oxidation products belong to Class II mixed valence compounds according to the classification of Robin and Day.     

Brown pigments based on perovskite structure of BiFeO3−δ

Light brown inorganic pigments based on BiFeO₃ doped by Sr²⁺ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi_1?x Sr _x FeO_3?δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO₃ is 1046 K, whereas the substitution of 20 mol% of Bi³⁺ by Sr²⁺ ions shifted it to 1403 K and powder with composition Bi_0.65Sr_0.35FeO_3?δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi_0.85Sr_0.15FeO_3?δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).

     

Effect of γ-irradiation on optical and electrical properties of Se1−xTex

The effect of γ-irradiation on optical and electrical properties of amorphous and polycrystalline Se_1−xTe_x (0.211<x<0.802) thin films of thickness 180 nm were investigated. The analysis of the absorption coefficient data revealed the existence of indirect transition both before and after irradiating. It was observed that the value of the optical energy gap depends on the value of x, decreasing as x increases. It was found also that the optical energy gap decreases with an increase of γ-doses for all compositions. The obtained results for all Se_1−xTe_x, films have been interpreted in terms of density of states model of Mott and Davis. From the experiment of electrical conductivity σ at various temperatures, it was observed that Se_1−xTe_x. films exhibited ln σ versus T⁻¹ relationships at high temperatures and ln σ(T)^1/2 versus T^−1/4 hopping conductivity behaviour at low temperatures. It was found that the thermal activation energies ΔE decrease with increasing Te content and increases with decreasing γ-doses. X-ray diffraction patterns for the as-deposited Se_1−xTe_x, show that polycrystalline films start to appear for x>0.407.     

Identifying the Types and Characterization of the Active Sites on M−X−C Single-Atom Catalysts

Single atom catalysts (SACs) have attracted much attention in recent years. As an essential group in SACs, M−X−C (X=nonmetallic element) materials have been demonstrated to be efficient in many reactions. However, identifying the active sites on M−X−C, especially under working conditions, is still challenging, which is crucial for chemists to further understand the mechanism underlying the reaction and better design proper SACs for specific reactions. Herein, the types and characterization of M−X−C are comprehensively summarized and discussed in this review. In addition to the basic information above, the challenges and opportunities remaining in this field will be also proposed to present a perspective to the research on the next step.     

After effects of β− on time differential perturbed angular correlation spectra

The after effects of β⁻ -decay on time differential perturbed angular correlation (TDPAC) spectra of II–VI semiconductor CdS have been studied using β⁻ -emitting¹¹¹Ag as well as^111mCd as probe nuclei. The TDPAC spectrum of¹¹¹Ag in CdS exhibits a time dependent interaction indicating that the preceding β⁻ -decay leaves the daughter nucleus in an excited state. The recovery time (τ_g) of the probe atom was found to be 16±6 ns while Abragam and Pound's relaxation time (τ_kr) was found to be 9±2 ns. The results show that β⁻ -decay does change the chemical environment around the probe atom.     

Longitudinal conductivity of thin films of La1 − x Sr x F3 − x solid solutions on glass ceramics

The longitudinal conductivity of La_{1 ? x} Sr _x F_{3 ? x} solid solution films (x = 0–0.24) with thicknesses of 40–260 nm grown on glass ceramics at temperatures from room temperature to 300°C and frequencies of 10^?1–10⁶ Hz was studied by impedance spectroscopy. The concentration dependence of film conductivity on the SrF₂ content had a maximum near x = 0.05. An equivalent circuit was constructed on the basis of the impedance plots to describe migration processes. The DC conductivity was evaluated for all samples under study. The activation energies were estimated from the temperature dependences of the DC conductivities of the films. The resulting dependences of electrophysical parameters were compared with those for bulk materials in terms of the relaxation conductivity model.     

Reactivity of O2 − radical anions on hydrated ZrO2 surface

The concentration of O₂ ^? radical anions generated on the surface of hydrated ZrO₂ in an H₂O₂ solution was found to depend on H₂O₂ concentration. It was shown that this method can be used for detecting H₂O₂ in solutions at concentration as low as 0.01 wt%. The radical anions were found to react with organic molecules, even at room temperature. The decomposition kinetics of O₂ ^? radical anions was double-exponential with two reaction rate constants. The existence of two distinct rate constants suggests that two types of O₂ ^? radical anions with similar spectroscopic properties but different reactivity are present on the surface of hydrated ZrO₂. It is highly likely that different arrangements of hydroxyl groups near the radical anions account for the presence of the two types of O₂ ^? with different reactivity. The rate constants obtained in the presence of the organic compounds studied were found to conform with the expected order of reactivity: toluene > benzene ? hexane.     

Adsorption Behavior of Nitrogen Monoxide on KxGaxSn8−xO16 Hollandite

Fine powder of K _x Ga _x Sn_8–x O₁₆ hollandite was prepared by the sol-gel process using metal alkoxides, and the adsorption behavior of nitrogen monoxide (NO) on it was examined by temperature programmed desorption (TPD) method and in situ diffuse reflectance fourier transform infrared spectroscopy. Any species other than nitrogen monoxide were not detected in the TPD measurement, and the profile showed three stages between 420 and 880 K which were regarded as the desorption of chemically adsorbed NO _x species. This desorption behavior seems well consistent with the spectral changes in the FT-IR measurement. The absorption band at 1270 cm^–1 was decayed in the first stage from 420 to 640 K, and the bands at 1235 and 1570 cm^–1 in the second stage from 640 and 770 K. In the third stage above 770 K, the strong band at 1340 cm^–1 disappeared. These NO _x species on the hollandite were estimated to have a form of NO₃ ^– in the first and second stages and a form of NO₂ ^– in the third stage, considering the data on adsorption of nitrogen oxides on La₂O₃ and CaO.     

A DFT Study on the Activity Origin of Fe−N−C Sites for Oxygen Reduction Reaction

Iron-nitrogen-carbon materials have been known as the most promising non-noble metal catalyst for proton-exchange membrane fuel cells (PEMFCs), but the genuine active sites for oxygen reduction reaction (ORR) are still arguable. Herein, by the thorough density functional theory investigations, we unravel that the planar Fe₂N₆ site exhibits excellent ORR catalytic activity over both FeN₃ and FeN₄ sites, and the potential-determining step is determined to be the *OH hydrogenation step with an overpotential of 0.415 V. The ORR activity of Fe₂N₆ site originates from the low spin magnetic moment (1.11 μ_B), which leads to high antibonding states and low d-band center of the Fe center, further leads to weak binding strength of *OH species. The density of FeN₄ sites only has little influence on the ORR activity owing to the similar interaction between active site and intermediates in ORR. Our research sheds light on the activity origin of iron-nitrogen-carbon materials for ORR.     

Adsorption of S2− and HS− ions on the (111) face of coinage metals: A quantum-chemical study

The interactions of S^2? and HS^? ions with gold, silver, and copper were studied by density functional theory using the cluster model of the metal surface. The geometrical and energy characteristics of the interactions of these ions with the surface metal atoms were evaluated. The S^2? ions form stronger chemical bonds with the surface metal atoms than HS^? ions. A significant charge transfer from anion to metal occurs during the adsorption. The adsorbability increased in the series Ag < Cu < Au for both anions. The HS^? ion showed greater ability to be transferred to the surface during the electrochemical adsorption due to the strong hydration of the S^2? ion. In alkaline media, however, the dissociation of the adsorbed HS^? leads to its conversion to S^2?.     

F− Preference of Polyamide Cryptand to Cl−

The variations in geometry structure, IR spectra, as well as the molecular orbitals upon anion recognition for polyamide cryptand are explored with the hybrid density functional theory. The cavity generated by six amide NH groups shrinks upon F ^? recognition because of the strong hydrogen bonds between the amide protons and F ^? , while the cavity expands upon Cl ^? binding because of the strong electron repulsion between the p electron of Cl ^? and the lone pair electrons of the nitrogen atom of the pyridine moieties. The “electropositive field space” …Cl ^? coupling exists when Cl ^? is recognized. The strong anion binding energy with F ^? indicates that the polyamide cryptand prefers F ^? to Cl ^? .     

Effect of Silver Nanoparticles on the Sorption Characteristics of La1 − xAgxMnO3 ± y

The effect silver nanoparticles have on the sorption characteristics of perovskite lanthanum manganite relative to methanol, benzene, and hexane vapors is studied by means of gravimetric equilibrium interval sorption. The state of silver particles is investigated using spectroscopic tools. Sorption data are compared to the catalytic activity in deep oxidation reactions of organic compounds over lanthanum manganite-based catalysts.

     

Investigation of Inhomogeneites in Epitaxial AlxGa1−xN Layers Grown on Sapphire

 Procedures for the preparation of bevels and the determination of their geometrical parameters have been developed. Using these procedures study of compositional and optical spatially resolved inhomogeneities of Al_xGa_1−xN layers grown on (0001) sapphire have been studied by EPMA and cathodolu-minescence. It has been found that the nonuniform distribution in depth of Al in epitaxial layers grown under constant conditions is connected with presence of stresses in the layer.     

Ab initio simulation of the photoelectron spectra of HCO− and DCO−

Large scale, vibrational CI calculations using a global ab initio potential energy surface are used to calculate multidimensional Franck-Condon overlaps from the ground vibrational state of HCO⁻ and DCO⁻ to all final bound and several quasibound vibrational states of HCO and DCO. The resulting Franck-Condon spectra are compared with recent experimental photoelectron spectra of HCO⁻ and DCO⁻.     

Chemistry-Performance Relationships of Polymer Gel-Electrolytes for Mg−S and Li−S Batteries: Influence of Network Cation Solvation Capacity on Polymer-Polysulfide Interactions

Metal-sulfur batteries are a promising next-generation energy storage technology, offering high theoretical energy densities with low cost and good sustainability. An active area of research is the development of electrolytes that address unwanted migration of sulfur and intermediate species known as polysulfides during operation of metal-sulfur batteries, a phenomenon that leads to low energy efficiency and short life-spans. A particular class of electrolytes, gel polymer electrolytes, are especially attractive for their ability to repel polysulfides on the basis of structure, electrostatics, and other polymer properties. Herein, within the context of magnesium- and lithium-sulfur batteries, we investigate the impact of gel polymer electrolyte cation solvation capacity, a property related to network dielectric constant and chemistry, on sulfur/polysulfide-polymer interactions, an understudied property-performance relationship. Polymers with lower cation solvation capacity are found to permanently absorb less polysulfide active material, which increases sulfur utilization for Li−S batteries and significantly increases charge efficiency and life-span for Li−S and Mg−S batteries.     

Generation of FeIV=O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron−N−C Catalyst

Generating Fe^IV=O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the Fe^IV=O generation pathway and oxidation behavior remain obscure. Employing an Fe−N−C catalyst with a typical Fe−N₄ moiety to activate peroxymonosulfate (PMS), we demonstrate that generating Fe^IV=O is mediated by an Fe−N−C−PMS* complex—a well-recognized nonradical species for induction of electron-transfer oxidation—and we determined that adjacent Fe sites with a specific Fe₁−Fe₁ distance are required. After the Fe atoms with an Fe₁-Fe₁ distance <4 Å are PMS-saturated, Fe−N−C−PMS* formed on Fe sites with an Fe₁-Fe₁ distance of 4–5 Å can coordinate with the adjacent Fe^II−N₄, forming an inter-complex with enhanced charge transfer to produce Fe^IV=O. Fe^IV=O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidation potential.