[en] A process characterized by variable-valence metal (Mn, Co, Ni, etc) ion assisted reduction of graphene oxide with NaBH₄ heated at 90 deg. C for a short period of 1 h was developed to produce reduced graphene oxide (RGO), and the RGO sheets exhibited a homogeneous and stable dispersibility in water.

[en] Nanocomposites of CoNi alloy nanoparticles loaded on Ketjenblack carbon (CoNi/KB) are successfully prepared through one-pot thermal decomposition of organic precursor solution. It can be proved, through a serious of characterization methods, that the introduction of porous carbon nanospheres with high specific surface area effectively prevents the serious agglomeration and oxidation of alloy nanoparticles. Highly dispersed CoNi alloy nanoparticles are evenly distributed on the surface of carbon nanospheres with a size of about ca. 5 nm. The CoNi/carbon nanosphere composites exhibit excellent electromagnetic wave absorbability when the doping mass is merely 15 wt% with the minimum reflection loss of −39.5 dB at 12.4 GHz and the effective absorption bandwidth ( < −10.0 dB) is 5.6 GHz for a thickness of 2 mm. This study demonstrates that rational compositions, surface defects, mesoporous structure, enhanced interfacial polarization and synergistic effect can optimize impedance matching of CoNi/KB, and improve the wave absorption performance. Consequently, the CoNi/KB nanocomposites have vast potential applications as a novel high-efficiency microwave absorbing materials.

[en] A simple, highly efficient, and eco-friendly method is prepared to divide bulk boron nitride (BN) into boron nitride nanosheets (BNNSs). Due to the anisotropy of the hexagonal BN expansion coefficient, bulk BN is exfoliated utilizing the rapid and tremendous change in temperature, the extreme gasification of water, and ice thermal expansion pressure under freeze drying. The thickness of most of the BNNSs was less than ∼3 nm with a yield of 12–16 wt%. The as-obtained BNNS/polyacrylamide (PAAm) composite hydrogels exhibited outstanding mechanical properties. The tensile strength is fives times the bulk of the BN/PAAm composite hydrogels and the elongations are more than nine-fold the bulk of the BN/PAAm composite hydrogels. The BNNS/PAAm nanocomposite hydrogels also exhibited excellent elastic recovery, and the hysteresis of the BNNS nanocomposite hydrogels was negligible even after 30 cycles with a maximum tensile strain (ε _max) of 700%. This work provides new insight into the fabrication of BN/polymer nanocomposites utilizing the excellent mechanical properties and transparency of BN. The results confirm that a few layers of BNNSs can also efficiently and directly improve the mechanical properties of composite polymer due to its stronger surface free energy and better wettability. (paper)

[en] Highlight• Electronic behaviors between intrinsic graphene and single atom vacancy graphene. • The fragment orbital analysis of molecules adsorption to understand interaction. • Conjugated π bond shield effect causes the laminate to be inert. • The mechanism of single atom vacancy improving molecule adsorption performance. Non-metal carbon materials have been widely utilized in diversified electrocatalytic reaction in virtue of property advantages. And the defective structure has greatly affected the physicochemical properties. Thus, it is of great significance to understand the mechanism of defective effect. Herein, we constructed graphene structural model to in-depth understand the electronic characteristics of vacancy defect sites and further comprehend the molecular interaction during the adsorption process. Our results indicate that the vacancy defect can effectively turn off conjugated π bond shield and form defect state, including π state and σ state. According to the fragment orbital analysis, due to the conjugated π bond shielding effect of perfect graphene, it cannot bond to nonpolar molecule. Even polar molecules, it needs to induce polar π defect on the surface of perfect graphene firstly. However, whether it's polar or nonpolar molecular, it can easily track coupling with the defect sites where the shield is turned on. The findings point out a new avenue to understand the catalytic behavior for carbon materials.

[en] Lithium-rich manganese-based layered materials have been considered as the most promising cathode materials for future high-energy-density lithium-ion batteries. However, a great loss of irreversible capacity at the initial cycle, poor cycle stability, and rate performance severely restrict its application. Herein, we develop a new strategy to synthesize hierarchical hollow Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ microspheres using sucrose and cetyltrimethylammonium bromide as a soft template combined with hydrothermal assisted homogeneous precipitation method. The hollow microspheres are assembled by the primary particles with the size of 50 nm. As a result, the as-prepared material exhibits high reversible capacity, good cycling stability, and excellent rate property. It delivers a high initial discharge capacity of 305.9 mAh g⁻¹ at 28 mA g⁻¹ with coulombic efficiency of 80%. Even at high current density of 560 mA g⁻¹, the sample also shows a stable discharge capacity of 215 mAh g⁻¹. The enhanced electrochemical properties are attributed to the stable hierarchical hollow sphere structure and the appropriate contact area between electrode and electrolyte, thus effectively improve the lithium-ion intercalation and deintercalation kinetics.

[en] Large over-potentials during battery operation remain a big obstacle for aprotic Li–O₂ batteries. Herein, a nanocomposite of about 4 nm cobalt monoxide nanocrystals grown  in situ on reduced graphene oxide substrates (CoO/RGO) has been synthesized via a thermal decomposition method. The CoO/RGO cathode delivers a high initial capacity of 14 450 mAh g⁻¹ at a current density of 200 mA g⁻¹. Simultaneously it displays little capacity fading after 32 cycles with a capacity restriction of 1000 mAh g⁻¹. Additionally, compared with Ketjenblack and general CoO nanoparticles, ultrathin CoO nanoparticle-decorated RGO electrode materials with a delaminated structure display an observable reduction of over-potential in Li–O₂ batteries. These results demonstrate that the introduction of RGO improves the performance of CoO, which is a promising strategy for optimizing the design of electrocatalysts for aprotic rechargeable Li–O₂ batteries. (paper)

[en] Two kinds of coumarin derivatives, 7-hydroxy coumarin and 7-hydroxy-4-methyl coumarin, were intercalated into the layered europium hydroxide by ion exchange reaction. The two organic compounds, despite with the same basic structure of benzopyrone but only varied substituent groups, demonstrated much different intercalation structures. The 7-hydroxy coumarin molecules may deposite on the external surface of the layers and 7-hydroxy-4-methyl coumarin molecules corresponded to a vertical mono-layered arrangement. In addition, co-intercalation of surfactant 1-octane sulfonic acid sodium with coumarin anions into layered europium hydroxide can enlarge the interlayer distance, both of the coumarin anions located vertically in the interlayer. The thermal stability of organics was enhanced after intercalation. The combination of the coumarin anions with the positively-charged layers generated hybrid materials exhibiting versatile luminescence properties. In solid state, the luminescence of the organics and Eu³⁺ were co-quenched for 7-hydroxy coumarin composites, but surfactant co-intercalated 7-hydroxy-4-methyl coumarin composite showed strong violet emission. In formamide, all of the composites displayed blue emission. The energy transfer between Eu³⁺ and organics and the change of microenvironment were proposed to account for the versatile luminescence properties. This work benefits the improvement of stability and fluorescence property of coumarin dyes and offers a beneficial approach to fabricate organic-inorganic hybrid materials with controllable structures and luminescence properties. - Graphical abstract: Intercalation of coumarin derivatives into LEuH forms organic-inorganic hybrid materials with versatile structures and luminescence properties, which benefits the improvement of stability and fluorescence property of such dyes.

[en] Graphical abstract: Monodispersed CoZr₄(PO₄)₆ porous microspheres with shell structure were synthesized via a combined solvothermal method and calcination route. The radar-wave absorbability of the purple sample calcined at 900 °C was strongest at the frequency of about 8.5 GHz. Highlights: ► In this study we synthesized monodispersed CoZr₄(PO₄)₆ porous microspheres as microwave absorber. ► The relationship between microstructures and the electromagnetic properties was indicated. ► The radar-wave absorbability of the sample was included. -- Abstract: Monodispersed CoZr₄(PO₄)₆ microspheres with a diameter of 40 μm were achieved via a combining solvothermal and calcination route. The crystallinity of the calcined microspheres with shell structure was improved, while the monodisperse property and morphologies remained. The possible formation mechanism of the porous CoZr₄(PO₄)₆ microspheres with nanoshell was proposed. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR) technologies, thermal analysis (TG and DSC), nitrogen adsorption–desorption isotherms and network analyzer. The sample calcined at 900 °C shows a strongest absorbability in the radar-wave absorbability test.

[en] Magnetic metals (Fe, Co, Ni) and alloys thereof are easily synthesized as nanoparticles, but obtaining highly dispersed graphene-based magnetic nanomaterials remains challenging. Here, three CoNi/graphene nanocomposites (CoNi/GN) are successfully assembled for the first time via a one-pot strategy without templating by manipulating the reaction time and solvents used for the same precursors. Moreover, the reduction of graphene oxide utilizing this method is more effective than that by conventional methods and the alloy particles are firmly embedded on the GN substrate. Compared to n- and p-CoNi/GN nanocomposites, o-CoNi/GN nanocomposites show the best electromagnetic wave absorption properties with the maximum reflection loss of −31.0 dB at 4.9 GHz for a thickness of 4 mm; the effective absorption bandwidth (< 10.0 dB) is 7.3 GHz (9.5–16.8 GHz) for a thickness of 2 mm. The structures and electromagnetic wave absorption mechanisms of the three composites were also investigated. This research provides a new platform for the development of magnetic alloy nanoparticles in the field of microwave-absorbing devices. .

[en] Highlights: • LaSrNiO are prepared via sol-gel way accompanied by high-temperature calcination. • LaSrNiO nanoparticles possess mixed perovskite and spinel phase for Sr doping. • Unique crystal structure of LaSrNiO effectively boost Li-O₂ battery performance. -- Abstract: LaSrNiO nanoparticles with different doping amount of strontium are synthesized through sol-gel method accompanied by high-temperature calcination. With the increase of Sr content, the crystal structure of samples changes from perovskite to spinel phase that promote both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) property. As a cathode catalyst for Li-O₂ battery, LaSrNiO nanoparticles show a capacity performance of 9000 mAh·g⁻¹ and significantly enhanced cyclability. The improved battery performance with Sr-doped nanoparticles can be ascribed to the high surface area of Sr-doped LaSrNiO nanoparticles combined with mixed spinel and perovskite phased structure which facilitate specific capacity and OER performance obviously. This research work is believed to shed light on a new thought to boost the performance of Li-O₂ battery.