Antifluorite-type lithium chromium oxide nitrides: synthesis, structure, order, and electrochemical properties

Antifluorite-type lithium chromium oxide nitrides were prepared by solid-state reaction of Li(3)N, Li(2)O, and Cr(2)N. Depending on the reaction time and starting Li/Cr and O/Cr ratios, either an ordered or a disordered phase (or mixtures of both) is obtained. The formation of the former is favored by short reaction times and low Cr/O ratios whereas the formation of the latter is favored by higher Cr/O ratios and longer reaction times. The two phases were characterized, and the first one was confirmed to be the already reported Li(14)Cr(2)N(8)O phase, whereas the stoichiometry of the second is Li(10)CrN(4)O(2). Interestingly, even if both contain cationic vacancies in the structure, electrochemical lithium intercalation could only be achieved for Li(10)CrN(4)O(2). This phase exhibits a reversible capacity of 160 mAh/g very stable upon cycling. Bond valence and first-principles DFT calculations were carried out to understand the absence of lithium insertion in Li(14)Cr(2)N(8)O. Li-Li repulsion and destabilization of the tetrahedral CrN(4) units induced by occupation of the potential sites, as well as the absence of energetically favorable pathways for transport of the ions to these sites, are suggested to be the reasons.     

Highly Dispersible and Stable Anionic Boron Cluster–Graphene Oxide Nanohybrids

An efficient process to produce boron cluster–graphene oxide nanohybrids that are highly dispersible in water and organic solvents is established for the first time. Dispersions of these nanohybrid materials in water were extraordinarily stable after one month. Characterization of hybrids after grafting of appropriate cobaltabisdicarbollide and closo‐dodecaborate derivatives onto the surface of graphene oxide (GO) was done by FT‐IR, XPS, and UV/Vis. Thermogravimetric analysis (TGA) clearly shows a higher thermal stability for the modified‐GO nanohybrids compared to the parent GO. Of particular note, elemental mapping by energy‐filtered transmission electron microscopy (EFTEM) reveals that a uniform decoration of the graphene oxide surface with the boron clusters is achieved under the reported conditions. Therefore, the resulting nanohybrid systems show exceptional physico‐chemical and thermal properties, paving the way for an enhanced processability and further expanding the range of application for graphene‐based materials.     

The vibration-rotation spectrum of D12CP in the region of the ν2 band: The spectroscopic constants for the states 0000, 0110, 0200, and 0220 and the bond lengths of the molecule

The vibration-rotation spectrum of DCP has been recorded with a resolution of 0.004 cm^?1 in the spectral region extending from 575 to 475 cm^?1. The fundamental band ν₂ and the “hot” bands from the vibrational level (01¹0) to the levels (02⁰0) and (02²0) have been identified and analyzed. A total of 347 infrared transitions have been measured and their wavenumbers together with 13 microwave or millimeter-wave frequencies have been fit simultaneously to obtain 15 spectroscopic constants including those arising from l-type doubling and l-type resonance. The agreement between the calculated and measured wavenumbers of nonblended lines is usually within 1 × 10^?4 cm^?1. These constants, used in conjunction with the ones previously obtained for the molecule, allow the calculation of the anharmonicity constants x₂₂ and g₂₂ and of the second-order vibration-rotation interaction constants γ₂₂ and γ₁₁. Although many of the γ's are still missing because an insufficient number of bands have been analyzed, the equilibrium bond lengths for the molecule have been recalculated using the improved set of first-order vibration-rotation interaction constants: r_e(CH) = 1.06596(11)Å and r_e(CP) = 1.540452(18)Å.     

Efficient Chemical Modification of Carbon Nanotubes with Metallacarboranes

As‐produced single‐walled carbon nanotubes (SWCNTs) tend to aggregate in bundles due to π–π interactions. Several approaches are nowadays available to debundle, at least partially, the nanotubes through surface modification by both covalent and noncovalent approaches. Herein, we explore different strategies to afford an efficient covalent functionalization of SWCNTs with cobaltabisdicarbollide anions. Aberration‐corrected HRTEM analysis reveals the presence of metallacarboranes along the walls of the SWCNTs. This new family of materials presents an outstanding water dispersibility that facilitates its processability for potential applications.     

Synthesis and Electrochemical Study of Antifluorite‐type Phases in the Li‐M‐N‐O (M = Ti,V) Systems

Antifluorite‐type phases have been prepared in the Li‐M‐N‐O (M = Ti, V) systems by solid state reaction under nitrogen starting from mixtures of lithium nitride, different amounts of lithium oxide and the transition metal nitride. The two series of samples obtained can be formulated as Li₅TiN₃ · xLi₂O and Li₇VN₄ · xLi₂O solid solutions. X‐ray diffraction data indicate that, as the amount of oxygen increases, the superstructure peaks decrease in intensity without changing their position, whereas the peaks corresponding to the simple anti‐fluorite structure increase. Thus, samples with low oxygen content are a mixture of two phases: the corresponding ternary nitride (either Li₅TiN₃ or Li₇VN₄) and the quaternary oxinitride with a disordered antifluorite structure and hence structural disorder does not seem to be induced progressively, as previously believed. In agreement with previous studies, a decrease of the cell parameter with oxygen content is observed in both solid solutions. Even though no deintercalation/intercalation reactions were expected (no cationic vacancies exist in the sample and the transition metals are present in their highest oxidation states) an evaluation of the electrochemical performances of the samples vs. metallic lithium was done to test the possibility of conversion reactions taking place. However, none of them showed any electroactivity.     

Urea-assisted fabrication of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@ZnO@Au composites for the catalytic photodegradation of Rhodamine-B

A new chemical approach for the fabrication of Fe₃O₄ embedded ZnO magnetic semicondutctor composite is reported. The method consists in increasing the pH of the synthesis solution by the thermal decomposition of urea instead of using common alkaline agents, such as NaOH and NH₄OH. The material (Fe₃O₄@ZnO) was used as a platform for the fabrication of highly dispersed gold nanoparticles (~5?nm). The catalytic efficiency of the material, Fe₃O₄@ZnO@Au, was tested in the photodegradation of Rhodamine-B solutions, and prominent catalytic efficiency, stability, and recycling were achieved. A single portion of the catalyst could be used up to five times without significant loss of activity and its photodegradation efficiency was considered high even after the 12th cycle (56%). Catalyst separation after each batch could be easily achieved because of the intrinsic magnetic property of the material. Leaching monitoring of free Zn species during the fabrication of the catalyst suggests that the use of urea decreased substantially the formation of non-magnetic-semiconducting species and provided a higher mass yield of the magnetic composite compared to an analogous protocol using NaOH. The catalyst was also characterized by detailed structural and chemical analyses, such as transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and vibration sample magnetometer (VSM).

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Liquid chromatography-tandem mass spectrometry determination for multiclass pesticides from insect samples by microwave-assisted solvent extraction followed by a salt-out effect and micro-dispersion purification

The effects of phyto-pharmaceutic compounds (PPCs), such as neonicotinoids, on wildlife reproduction and survival are a rising concern. Yet, understanding the biological consequences of PPC use is particularly complex given the large diversity of PPCs and their derivatives to which wildlife can be exposed. Here, we present a simple and sensitive method for the simultaneous detection and quantification of multiclass PPCs (54 molecules) in single insect boluses (<0.05 g dry mass) by ultra-high pressure liquid chromatography coupled to a tandem mass spectrometer (LC-MS/MS). A key part of this new method is the use of a two-step extraction method combining (i) the high efficiency of a microwave-assisted solvent extraction (MAE) for extracting analytes that might be tightly bound to environmental matrices and (ii) the versatility of a salt-out effect adapted from the QuEChERS methodology allowing the extraction and purification of a wide array of analytes. This microwave-assisted salt-out extraction (MASOE) approach was compared to classical extraction methods including matrix solid phase dispersion (MSPD), microwave-assisted extraction (MAE), and the QuEChERS method. Average recoveries for 54 analytes ranged from 49% to 106%, (relative standard deviations <22%). The limits of detection (LODs) and quantification (LOQs) were in the ranges of 0.10–3.00 ng g⁻¹ and 0.40–7.00 ng g⁻¹, respectively. We applied this method to analyse 881 insect boluses collected from Tree Swallow (Tachycineta bicolour) nestlings along an agricultural intensification gradient in southern Québec (Canada). We detected 25 PPCs out of the 54 considered. We detected at least one PPC in 30% of samples and were able to quantify at least one of them in 17% of samples. Our study shows that the MASOE method should prove to be a powerful tool for studying the fate and impacts of PPCs on wildlife.     

The ν1 and ν1 + ν2 − ν2 infrared absorption bands of H12CP

The vibration-rotation spectrum of HCP was recorded in the region of the ν₁ band with a resolution of about 0.035 cm^?1. All the data available were combined to calculate spectroscopic constants for the 00⁰0, 10⁰0, 01^1e0, 01^1f0, 11^1e0, and 11^1f0 states.