Tailoring the dielectric properties and energy storage density of 1−x(0.94NaNbO3−0.06SZ)−xBi2O3 through substitution strategy

Energy storage using dielectric capacitors is a growing area of research and development. However, designing a highly performing dielectric capacitor is still a challenge. Despite the excellent results achieved in lead-based dielectrics, lead-free substitutes are essential because of the environmental concerns associated with lead-based products. The lead-free 1?x (0.94NaNbO₃? 0.06SrZrO₃)+ x Bi₂O₃ ceramics abbreviated NNSZ + xB for x = 0.0, 0.05, 0.1, 0.15, and 0.20 was fabricated via solid-state reaction. A recoverable energy density of 2.93 J cm?³ was obtained for NNSZ+0.1B, associated with high thermal stability (25–130 °C), excellent cycling (N = 10⁵), and high efficiency (η) of 83.5%. Moreover, the introduction of Bi₂O₃ significantly improved the electrical insulation (?_r at 1 kHz = 1608 and tan δ = 0.0038) and breakdown strength (380 kVcm?¹) of NNSZ+0.1B by minimizing the formation of sodium, bismuth, and oxygen vacancies. The results obtained in this study provide a benchmark for further investigations on NaNbO₃-based ceramics. More importantly, this study suggests that NNSZ + xB ceramics can be used in pulsed power technology.     

Photocatalytic deoxygenation of N–O bonds with rhenium complexes: from the reduction of nitrous oxide to pyridine N-oxides

The accumulation of nitrogen oxides in the environment calls for new pathways to interconvert the various oxidation states of nitrogen, and especially their reduction. However, the large spectrum of reduction potentials covered by nitrogen oxides makes it difficult to find general systems capable of efficiently reducing various N-oxides. Here, photocatalysis unlocks high energy species able both to circumvent the inherent low reactivity of the greenhouse gas and oxidant N₂O (E⁰(N₂O/N₂) = +1.77 V vs. SHE), and to reduce pyridine N-oxides (E_1/2(pyridine N-oxide/pyridine) = −1.04 V vs. SHE). The rhenium complex [Re(4,4′-tBu-bpy)(CO)₃Cl] proved to be efficient in performing both reactions under ambient conditions, enabling the deoxygenation of N₂O as well as synthetically relevant and functionalized pyridine N-oxides.

A rhenium-based photocatalyst enables the deoxygenation of several compounds containing N–O bonds, such as N₂O and pyridine N-oxides.     

Purification of Single-walled Carbon Nanotubes Grown by a Chemical Vapour Deposition (CVD) Method

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Reactivity of B‐Xanthyl N‐Heterocyclic Carbene‐Boranes

The synthesis and reactivity of mono‐ and bis‐S‐xanthyl NHC‐boranes is reported. The new NHC‐boranes are prepared through nucleophilic exchange at boron from either mono‐ or bis‐triflyl NHC‐boranes, themselves obtained by protolysis of the NHC‐BH₃ starting compounds. The B?H bond of the S‐xanthyl NHC‐boranes can be cleaved both homolytically and heterolytically, albeit the latter is more synthetically useful. The S‐xanthyl NHC‐boranes can reduce both aldehydes and imines. The B?S bond can also be cleaved homolytically. Under UV irradiation, the S‐xanthyl NHC‐boranes generate NHC‐boryl radicals that can initiate radical polymerizations of acrylates.     

One-Pot Synthesis of Metastable 2,5-Dihydrooxepines through Retro-Claisen Rearrangements: Method and Applications

A one-pot methodology to synthesize metastable bicyclic 2,5-dihydrooxepines from cyclic 1,3-diketones and 1,4-dibromo-2-butenes through the retro-Claisen rearrangement of syn-2-vinylcyclopropyl diketone intermediates is reported. DFT calculations were performed to understand the reaction selectivity and mechanisms towards [1,3]- or [3,3]-sigmatropic rearrangements, highlighting the crucial influence of the temperature. The reaction was successfully applied to a short protecting group-free total synthesis of radulanin A, a natural 2,5-dihydrobenzoxepine. Moreover, the strong herbicidal potential of this natural product is demonstrated for the first time.     

Infrared analysis of CO ice particles in the aerosol phase

Fourier transform infrared extinction spectra of a variety of CO ice aerosols, generated at low temperatures in a liquid helium cooled collisional-cooling cell, have been analyzed. Different operation modes of the cooling system were used for the generation of spherical and nonspherical CO nanoparticles at temperatures between 5 and 35 K and with diameters between 10 and 1000 nm. In contrast to the predominantly amorphous CO films described in the literature the presented CO particles are (poly)crystalline. A Mie inversion iterative scheme is presented and used to infer the optical constants of CO ice for the cases compact particles have been produced. The spectra of nonspherical CO aerosol particles are interpreted by modeling the extinction using the discrete dipole approximation procedure combined with the retrieved optical constants. A global positive matrix factorization scheme allows us to infer the dominant shapes in the observed particle distribution and can be used as a guide for further experiments. Near 25 K a pronounced shape evolution of smaller particles from spherical toward longish structures was observed at low buffer-gas pressure over 400 s.     

Capture of the complex [Ni(dto)2]2- (dto2- = dithiooxalato ligand) in a Mo12 ring: synthesis, characterizations, and application toward the reduction of protons

The encapsulation of the complex [Ni(dto)(2)](2-) within an oxothiododecamolybdic cyclic cluster has been investigated. The resulting molybdenum ring, [Mo(12)O(12)S(12)(OH)(12)(Ni(dto)(2))](2-), corresponds to the first example of the {Mo(2)O(2)S(2)}-based assembly arranged around a 3d transition-metal complex. It was unambiguously characterized in the solid state and in solution by FT-IR spectroscopy, single-crystal X-ray diffraction, NMR, UV-visible spectroscopy, and electrospray ionization-high-resolution mass spectrometry (ESI-HRMS). The latter technique revealed to be a powerful tool for the characterization of templated molybdenum ring systems in solution and gave excellent results in high resolution. The electronic spectrum of [Mo(12)O(12)S(12)(OH)(12)(Ni(dto)(2))](2-) evidenced a strong red shift of the LMCT bands attributed to the complex [Ni(dto)(2)](2-), suggesting significant variations of the electronic properties upon its encapsulation within the Mo(12) ring. These differences were demonstrated by electrochemical studies in CH(3)CN, which also revealed, for both compounds [Ni(dto)(2)](2-) and [Mo(12)O(12)S(12)(OH)(12)(Ni(dto)(2))](2-), electrocatalytic properties for the reduction of protons. These results evidence the ability of dithioxalato complexes to act as electrocatalysts for the hydrogen evolution reaction (HER) and confirm such a property for oxothiomolybdenum rings.     

Proton-coupled electron transfer of flavodoxin immobilized on nanostructured tin dioxide electrodes: thermodynamics versus kinetics control of protein redox function

In this paper, we report a spectroelectrochemical investigation of proton-coupled electron transfer in flavodoxin D. vulgaris Hildenborough (Fld). Poly-L-lysine is used to promote the binding of Fld to the nanocrystalline, mesoporous SnO(2) electrodes. Two reversible redox couples of the immobilized Fld are observed electrochemically and are assigned by spectroelectrochemistry to the quinone/semiquinone and semiquinone/hydroquinone couples of the protein's flavin mononucleotide (FMN) redox cofactor. Comparison with control data for free FMN indicates no contamination of the Fld data by dissociated FMN. The quinone/semiquinone and semiquinone/hydroquinone midpoint potentials (E(q/sq) and E(sq/hq)) at pH 7 were determined to be -340 and -585 mV vs Ag/AgCl, in good agreement with the literature. E(q/sq) exhibited a pH dependence of 51 mV/pH. The kinetics of these redox couples were studied using cyclic voltammetry, cyclic voltabsorptometry, and chronoabsorptometry. The semiquinone/quinone reoxidation is found to exhibit slow, potential-independent but pH-sensitive kinetics with a reoxidation rate constant varying from 1.56 s(-)(1) at pH 10 to 0.0074 s(-)(1) at pH 5. The slow kinetics are discussed in terms of a simple kinetics model and are assigned to the reoxidation process being rate limited by semiquinone deprotonation. It is proposed that this slow deprotonation step has the physiological benefit of preventing the undesirable loss of reducing equivalents which results from semiquinone oxidation to quinone.