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Although transition metal sulfides have prodigious potential for use as electrode materials because of their low electronegativities, their large volume changes inhibit broad application. Moreover, there is only limited knowledge of the ageing processes of these materials at the nanoscale. Herein, nano-C/FeS2 materials were prepared via one-pot syntheses from green biodegradable carbon precursors, followed by activation and sulfidation. The increased activation/sulfidation time led to an increase in the size of the nanoparticles (7 to 17 nm) and their aggregation, as well as in an increase in the specific surface area. The materials were then used as electrodes in 2-electrode symmetric supercapacitors with 2 M KOH. The activation process resulted in improved capacitance (60 F g−1 at 0.1 A g−1) and rate capability (36%) depending on the composite porosity, conductivity, and size of the FeS2 particles. The ageing of the FeS2 nanoparticles was investigated under air, and a progressive transformation of the nano-FeS2 into hydrated iron hydroxy sulfate with a significant morphological modification was observed, resulting in drastic decreases in the capacitance (70%) and retention. In contrast, the ageing of nano-FeS2 during cycling led to the formation of a supplementary iron oxyhydroxide phase, which contributed to the enhanced capacitance (57%) and long-term cycling (132% up to 10,000 cycles) of the device.

Individual groups must choose an article drawn from a periodical that describes one of the newest and most promising products within a limited topic, theme, or range of topics. This activity fosters interaction between the group of students as they choose the article, makes them more aware of resources, and leads to greater cultural knowledge. (SR)

A time-dependent oxidation of carbon fibers in boiling nitric acid was used to investigate the influence of a modification of the fiber surface properties on the adhesion strength with an acrylate resin cured by electron beam (EB). For each time of treatment, a characterization of the surface topography and the surface chemistry was done (topography at a micrometric and nanometric scale, specific surface area, temperature programmed desorption, X-ray photoelectron spectroscopy analysis). The oxidation of the fiber surface in boiling nitric acid created a rough surface, which significantly increased the specific surface area, and also generated a high density of hydroxyl groups, carboxylic acids and lactones in comparison to untreated fibers. The adhesion strength with the acrylate resin cured by EB was measured by a pull-out test. For comparison, an isothermal ultraviolet curing of the matrix was also investigated. The value of the interfacial shear strength, determined by the Greszczuk's model, was increased by the oxidation of the carbon fiber surface for both curing processes, but lower values were systemically obtained with EB curing. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Potassium vanadium oxyfluoride phosphate of composition KVPO 4 F 0.5 O 0.5 was modified by a carbon coating to enhance its electrochemical performance. Two distinct methods were used, first, chemical vapor deposition (CVD) using acetylene gas as a carbon precursor and second, an aqueous route using an abundant, cheap, and green precursor (chitosan) followed by a pyrolysis step. The formation of a 5 to 7 nm-thick carbon coating was confirmed by transmission electron microscopy and it was found to be more homogeneous in the case of CVD using acetylene gas. Indeed, an increase of the specific surface area of one order of magnitude, low content of C sp 2 , and residual oxygen surface functionalities were observed when the coating was obtained using chitosan. Pristine and carbon-coated materials were compared as positive electrode materials in potassium half-cells cycled at a C/5 (C = 26.5 mA g -1 ) rate within a potential window of 3 to 5 V vs K + /K. The formation by CVD of a uniform carbon coating with the limited presence of surface functions was shown to improve the initial coulombic efficiency up to 87% for KVPFO 4 F 0.5 O 0.5 -C 2 H 2 and to mitigate electrolyte decomposition. Thus, performance at high C-rates such as 10 C was significantly improved, with ∼50% of the initial capacity maintained after 10 cycles, whereas a fast capacity loss is observed for the pristine material.

C-rich graphitic carbonitride materials (CN x ) with a large range of compositions have been prepared thanks to the self-assembly, in different ratios, of melamine (M) and a panel of polycarboxylic acids (A) such as oxalic, tartaric and citric acid. The thermal conversion of the formed adducts (MA y ), led to CN x phases, with x ranging from 0.66 to 1.4 (x=1.33 for g-C 3 N 4 for comparison). The properties of these materials were examined by different techniques (XRD, Raman spectroscopy, TEM, TGA, XPS and DRIFT). It appears that the increase in the C content is associated with the disappearance of the long-range order of heptazine units and an increase in the sub-nanometer carbon-rich cluster size within the graphitic g-C 3 N 4 structure. This trend is followed by a significant increase in the interlayer spacing and a lower proportion of N=C-N bonds compared to C=C bonds. The thermal stability under an inert atmosphere of these phases and their UV-Visible absorbance properties were also investigated., (© 2022 Wiley-VCH GmbH.)

The reduction of nitroarenes is the most efficient route for the preparation of aromatic primary amines. These reductions are generally performed in the presence of heterogeneous transition metal catalysts, which are rather efficient but long and tedious to prepare. In addition, they contain very expensive metals that are in most cases difficult to reuse. Therefore, the development of efficient, easily accessible and reusable Pd catalysts obtained rapidly from safe and non-toxic starting materials was implemented in this report. Two bottom-up synthesis methods were used, the first consisted in the impregnation of a micro/mesoporous carbon support with a Pd salt solution, followed by thermal reduction (at 300, 450 or 600 °C) while the second involved a direct synthesis based on the co-assembly and pyrolysis (600 °C) of a mixture of a phenolic precursor, glyoxal, a surfactant and a Pd salt. The obtained composites possess Pd nanoparticles (NPs) of tunable sizes (ranging from 1-2 to 7.0 nm) and homogeneously distributed in the carbon framework (pores/walls). It turned out that they were successfully used for mild and environment-friendly hydrogenations of nitroarenes at room temperature under H 2 (1 atm) in EtOH in the presence of only 5 mequiv. of supported Pd. The determinations of the optimal characteristics of the catalysts constituted a second objective of this study. It was found that the activity of the catalysts was strongly dependent on the Pd NPs sizes, i.e. , catalysts bearing small Pd NPs (1.2 nm obtained at 300 °C and 3.4 nm obtained at 450 °C) exhibited an excellent activity, while those containing larger Pd NPs (6.4 nm and 7.0 nm obtained at 600 °C, either by indirect or direct methods) were not active. Moreover, the possibility to reuse the catalysts was shown to be dependent on the surface chemistry of the Pd NPs: the smallest Pd NPs are prone to oxidation by air and their surface was gradually covered by a PdO shell decreasing their activity during reuse. A good compromise between intrinsic catalytic activity ( i.e . during first use) and possibility of reuse was found in the catalyst made by impregnation followed by reduction at 450 °C since the hydrogenation could be performed in only 2 h in EtOH or even in water. The catalyst was quantitatively recovered after reaction by filtration, used at least 7 times with no loss of efficiency. Advantageously, almost Pd-free primary aromatic amines were obtained since the Pd leaching was very low (<0.1% of the introduced amount). Compared to numerous reports from the literature, the catalysts described here were both easily accessible from eco-friendly precursors and very active for hydrogenations under mild and "green" reaction conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)