Sandwich-type CoSe2-CNWs@rGO/S composites with efficient trapping and catalytic conversion of polysulfides in lithium-sulfur batteries.

Although lithium-sulfur batteries (LSBs) are very promising in energy storage devices, their low conductivity, shuttle effect, and volume expansion unfavorably lead to sluggish kinetics and worsening electrochemical performance. To address these problems, we firstly prepared conductive carbon nanowires embedded with lithiophilic CoSe2 nanoparticles (CoSe2-CNWs), and utilized CoSe2-CNWs to construct reduced graphene oxide (rGO) sheets; thereby, sandwich-type CoSe2-CNWs@rGO composites were assembled. CoSe2-CNWs@rGO composites were taken as the sulfur host. Due to the alternating rGO sheets and active sulfur, the special sandwich structure can maximize the use of sulfur, confine polysulfides physically, favor electron transport, and cushion the volume change during cycling. The interlayer CoSe2-CNWs network also can entrap polysulfides chemically, promote the electron transfer, and improve the reaction kinetics, owing to the synergetic merits of high polarity and conductivity. Compared with CoSe2-CNWs/S and Co-CNWs/S, the CoSe2-CNWs@rGO/S cathode shows a significant improvement in cell performance. Its specific capacity decreases from 1137.9 mA h g-1 at 0.1 C to 649.7 mA h g-1 at 2 C, demonstrating the optimal rate performance. The cycling capacity also slowly reduces from 975.4 mA h g-1 to 839.7 mA h g-1 after 150 cycles at 0.5 C, showing a high retention of 86.1% with a tiny average fading rate (0.093%).

Transition in plant-plant facilitation in response to soil water and phosphorus availability in a legume-cereal intercropping system.

BACKGROUND: The tradeoff between negative and positive interactions of facilitated species and facilitators may depend on the degree of resource availability in agroecosystems. However, the rhizospheric mechanisms driving trade-offs that occur along phosphorus (P) and water availability gradients have not yet been systematically clarified. We established three types of root isolation conditions (no barrier, nylon barrier and solid barrier) at different P and water addition levels to address the above issue in a maize-grass pea intercropping system. RESULTS: The total yield and biomass net effect (NE) and the relative interaction index (RII) were significantly higher than 0 under all environmental conditions, demonstrating that plant-plant interactions generated positive effects in the intercropping system. The maize yield and biomass RII were 0.029-0.095 and 0.018-0.066, respectively, which indicated that maize growth was constantly facilitated. However, the RII for grass pea yield and biomass exhibited a different trend in comparison with maize. It was higher than 0 (as the facilitated species) under low soil P and moisture conditions and transitioned to values lower than 0 (facilitator species) under high P and moisture conditions, which showed that the type and intensity of plant-plant interactions steadily shifted with the applied stressors. Direct interactions decreased the maize rhizospheric soil pH by 1.5% and 1.9% under Low-P conditions. Notably, the rhizospheric soil acid and alkaline phosphatase secretions of maize and grass pea increased by 17.4-27.4% and 15.3-27.7%, respectively, in P-deficient soils. These results show that plant-plant interactions can effectively relieve P stress by mineralizing organophosphorus in P-deficient soils. Furthermore, the above tendency became more pronounced under drought-stressed conditions. The nylon barrier partially restricted the exchange and utilization of available nutrients and decreased the total yield and biomass by 1.8-7.8% and 1.1-7.8%, respectively. The presence of a solid barrier completely restricted interspecific rhizospheric interactions and decreased the total yield and biomass by 2.1-13.8% and 1.6-15.7%, respectively. Phytate and KH2PO4 addition intensified asymmetric interspecific competition, and grass pea was consistently subjected to competitive pressures. CONCLUSION: Briefly, the tradeoff between facilitation and competition was driven by rhizospheric interactions, and the transition in the intensity and type of interaction was highly dependent on resource availability in a biologically diverse system.

An efficient method of inducing differentiation of mouse embryonic stem cells into primitive endodermal cells.

Primitive Endoderm (PrE) is an extraembryonic structure derived from inner cell mass (ICM) in the blastocysts. Its interaction with the epiblast is critical to sustain embryonic growth and embryonic pattern. In this study, we reported a simple and efficient method to induce the differentiation of mouse Embryonic Stem Cells (mESCs) into PrE cells. In the process of ESC monolayer adherent culture, 1 µM atRA and 10 µM CHIR inducers were used to activate RA and Wnt signaling pathways respectively. After 9 days of differentiation, the proportion of PrE cells was up to 85%. Further studies indicated that Wnt signaling pathway acted as a switch that RA induces mESCs differentiation between SMC and PrE cell. In the presence of only RA signaling, mESCs adopted the fate of smooth muscle cells (SMCs); Simultaneous activation of the Wnt signaling pathway changed the differentiation fate of mESCs into PrE cells. This efficient induction method can provide new cellular resources and models for relevant studies of PrE.

Employing synergetic effect of ZnSe quantum dots and layered Ni(OH)2to boost the performance of lithium-sulfur cathodes.

The low sulfur utilization, cycling instability, and sluggish kinetics are the critical obstructions to practical applications of lithium-sulfur batteries (LSBs). Constructing sulfur hosts with high conductivity, suppressed shuttle effect, and rapid kinetics is essential for their practical application in LSBs. Here, we synthetically utilized the merits of ZnSe quantum dots (QDs) and layered Ni(OH)2to boost the performance of LSBs. A novel core-shell ZnSe-CNTs/S@Ni(OH)2was constructed using the ZnSe-CNTs network as framework to load sulfur and following with Ni(OH)2encapsulation. The CNT network decorated with ZnSe QDs not only serves as a conductive framework providing fast electron/ion transfer channels, but also limits polysulfide diffusion physically and chemically. Layered Ni(OH)2, the wrinkled encapsulation, not only permits fast electron/ion transfer, but also buffers the expansion, confines active materials, and limits the polysulfide dissolution chemically. When used as a cathode, ZnSe-CNTs/S@Ni(OH)2presents enhanced electrochemistry performance compared with ZnSe-CNTs/S and CNTs/S. The average specific capacity decreases from 1021.9 mAh g-1at 0.2 C to 665.0 mAh g-1at 2 C, showing rate capacity much higher than ZnSe-CNTs/S and CNTs/S. After 150 cycles, the capacity at 0.5 C slowly reduces from 926.7 to 789.0 mAh g-1, showing high retention of 85.1%. Therefore, our investigation provides a new strategy to construct a promising sulfur cathode for LSBs.

A special core-shell ZnS-CNTs/S@NH cathode constructed to elevate electrochemical performances of lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) are regarded as promising candidates for next-generation electrochemical energy storage systems due to their low cost and high energy density. However, the insulative sulfur, the volume expansion and high soluble polysulfides are three roots impeding their practical applications, and consequently bring challenges of low sulfur utilization, poor cyclic stability and sluggish redox kinetics. Herein, a special core-shell ZnS-CNTs/S@Ni(OH)2 (labeled as ZnS-CNTs/S@NH) cathode has been designed to overcome above obstacles and elevate the electrochemical performance. The ZnS-CNTs/S@NH cathode is synthesized via a facile step-by-step strategy, in which ZnS-decorated CNTs was used as a framework to load sulfur and followed with a ultrathin Ni(OH)2 (NH) layer encapsulation. The ZnS-CNT core combines merits of CNT network and polar ZnS quantum dots (QDs), accommodating the volume change, offering efficient pathways for fast electron/ion transport, and anchoring polysulfides through polar interactions. The outer Ni(OH)2 shell physically confines the active material and meanwhile provides plenty of catalytic sites for effective polysulfide chemisorption. Benefiting from these merits, the ZnS-CNTs/S@NH cathode exhibits excellent cell performances in comparison with ZnS-CNTs/S and CNTs/S. Its discharge capacity at different C-rates is optimal in the three cathodes, which decreases from 1037.0 mAh g-1 at 0.1 C to 646.1 mAh g-1 at 2.0 C. Its cyclic capacity also manifests the slowest reduction from 861.1 to 760.1 mAh g-1 after 150 cycles at 0.5 C, showing a high retention (88.3%) and a tiny average fading rate (0.078%). The strategy in this work provides a feasible approach to design and construct core-shell cathode materials for realizing practically usable Li-S batteries.

Incorporation ZnS quantum dots into carbon nanotubes for high-performance lithium-sulfur batteries.

Constructing sulfur hosts with high electronic conductivity, large void space, strong chemisorption, and rapid redox kinetics is critically important for their practical applications in lithium-sulfur batteries (LSBs). Herein, by coupling ZnS quantum dots (QDs) with carbon nanotubes (CNTs), one multifunctional sulfur host CNT/ZnS-QDs is designed via a facile one-step hydrothermal method. SEM and TEM analyses reveal that small ZnS-QDs (<5 nm) are uniformly anchored on the CNT surface as well as encapsulated into CNT channels. This special architecture ensures sulfur direct contacting with highly conductive CNTs; meanwhile, the catalytic effect of anchored ZnS-QDs improves the chemisorption and confinement to polysulfides. Benefiting from these merits, when used as sulfur hosts, this special architecture manifests a high specific capacity, superior rate capability, and long-term cycling stability. The ZnS-QDs dependent electrochemical performance is also evaluated by adjusting the mass ratio of ZnS-QDs, and the host of CNT/ZnS-QDs 27% owns the optimal cell performance. The specific capacity decreases from 1051 mAh g-1 at 0.2 C to 544 mAh g-1 at 2.0 C, showing rate capability much higher than CNT/S and other CNT/ZnS-QDs/S samples. After 150 cycles, the cyclic capacity at 0.5 C exhibits a slow reduction from 1051 mAh g-1 to 771 mAh g-1, showing a high retention of 73.4% with a coulombic efficiency of over 99%. The electrochemical impedance spectroscopy analyses demonstrate that this special architecture juggles high conductivity and excellent confinement of polysulfides, which can significantly suppress the notorious shuttle effect and accelerate the redox kinetics. The strategy in this study provides a feasible approach to design efficient sulfur hosts for realizing practically usable LSBs.

Self-Assembled Vanadium Oxide Nanoflakes for p-Type Ammonia Sensors at Room Temperature.

VO2(B), VO2(M), and V2O5 are the most famous compounds in the vanadium oxide family. Here, their gas-sensing properties were investigated and compared. VO2(B) nanoflakes were first self-assembled via a hydrothermal method, and then VO2(M) and V2O5 nanoflakes were obtained after a heat-phase transformation in nitrogen and air, respectively. Their microstructures were evaluated using X-ray diffraction and scanning and transmission electron microscopies, respectively. Gas sensing measurements indicated that VO2(M) nanoflakes were gas-insensitive, while both VO2(B) and V2O5 nanoflakes were highly selective to ammonia at room temperature. As ammonia sensors, both VO2(B) and V2O5 nanoflakes showed abnormal p-type sensing characteristics, although vanadium oxides are generally considered as n-type semiconductors. Moreover, V2O5 nanoflakes exhibited superior ammonia sensing performance compared to VO2(B) nanoflakes, with one order of magnitude higher sensitivity, a shorter response time of 14⁻22 s, and a shorter recovery time of 14⁻20 s. These characteristics showed the excellent potential of V2O5 nanostructures as ammonia sensors.

Novel photoluminescence properties and enhanced photocatalytic activities for V2O5-loaded ZnO nanorods.

Three different kinds of V2O5/ZnO heteronanorods were synthesized through a CVD process and oxidized in air at temperatures of 350, 420 and 500 °C. These 1D heteronanorods were formed from ZnO nanorods (NRs) coated with V2O5 nanoparticles (NPs). With the rise of oxidation temperature, the coated V2O5 NPs were found to be growing and their crystallinity gradually improved. Photoluminescence (PL) spectra for these V2O5/ZnO samples exhibited some novel characteristics, such as the appearance of new emission peaks, the variation in PL intensity, and the tremendously enhanced visible emission for the 500 °C sample. Photocatalysis investigation for all V2O5/ZnO samples showed enhanced photocatalytic activities compared to their single-component counterparts. Furthermore, their photocatalytic activities were also influenced by the oxidation temperature. The 350 °C sample showed the highest photocatalytic activity, and gradually decreased photocatalytic activities were observed for the other two samples. The novel PL properties and enhanced photocatalytic activities were attributed to the coupling between ZnO NRs and V2O5 NPs, and can be attributed to the collective effect of the V-doped ZnO layer near the interface, the decreased defect concentration in V2O5 NPs, and the improved particle crystallinity.

Fast doping of Cu into ZnSe NCs by hydrazine promoted cation exchange in aqueous solution at room temperature.

Controllable doping is an effective way of tuning the properties of semiconductor nanocrystals (NCs). In this work, a simple strategy of fast doping Cu ions into ZnSe NCs under ambient conditions was proposed. The principle of doping is based on hydrazine (N2H4) promoted cation exchange reaction. By direct addition of Cu ion stock solution into the preformed ZnSe NCs, Cu doped ZnSe NCs can be obtained. Furthermore, the emission of doped NCs can be tuned by changing the amount of impurity ion addition. The cation exchange reaction is facilitated by three factors: 1) N2H4 addition, 2) fast impurity ions, and 3) partial stabilizer removal. The proposed cation exchange reaction in aqueous solution could be an alternate route for NC doping as well as synthesis of ionic NCs.

Low-temperature CVD synthesis of patterned core-shell VO2@ZnO nanotetrapods and enhanced temperature-dependent field-emission properties.

VO2 nanostructures are attractive materials because of their reversible metal-insulator transition (MIT) and wide applications in devices. When they are used as field emitters, a new type of temperature-controlled field emission device can be fabricated. Vapor transport methods used to synthesize traditional VO2 nanostructures are energy-intensive, low yield, and produce simple morphology (quasi-1D) that exhibits substrate clamping; thus they are not suitable for field emission applications. To overcome these limitations, ZnO nanotetrapods were used as templates, and patterned core-shell VO2@ZnO nanotetrapods were successfully grown on an ITO/glass substrate via a low-temperature CVD synthesis. SEM, TEM, EDX, XPS analyses and X-ray diffraction revealed that the cores and shells of these nanotetrapods were single crystal wurtzite-type ZnO and polycrystalline VO2, respectively. The VO2@ZnO nanotetrapods show strongly MIT-related FE properties, the emission current density at low temperature is significantly enhanced in comparison with pure VO2 nanostructures, and the emission current density increased by about 20 times as the ambient temperature increased from 25 to 105 °C at a fixed field of 5 V µm(-1). Although the VO2@ZnO nanotetrapods show a worse FE performance at low temperatures compared with pure ZnO nanotetrapods, the FE performance was substantially improved at high temperatures, which was attributed to the MIT-related band bending near the interface and the abrupt resistance change across the MIT.

Synthesis of Au-decorated V2O5@ZnO heteronanostructures and enhanced plasmonic photocatalytic activity.

A ternary plasmonic photocatalyst consisting of Au-decorated V2O5@ZnO heteronanorods was successfully fabricated by an innovative four-step process: thermal evaporation of ZnO powders, CVD of intermediate on ZnO, solution deposition of Au NPs, and final thermal oxidization. SEM, TEM, EDX, XPS, and XRD analyses revealed that the interior cores and exterior shells of the as-prepared heteronanorods were single-crystal wurtzite-type ZnO and polycrystalline orthorhombic V2O5, respectively, with a large quantity of Au NPs inlaid in the V2O5 shell. The optical properties of the ternary photocatalyst were investigated in detail and compared with those of bare ZnO and V2O5@ZnO. UV-vis absorption spectra of ZnO, V2O5@ZnO, and Au-decorated V2O5@ZnO showed gradually enhanced absorption in the visible region. In addition, gradually decreased emission intensity was also observed in the photoluminescence (PL) spectra, revealing enhanced charge separation efficiency. Because of these excellent qualities, the photocatalytic behavior of the ternary photocatalyst was studied in the photodegradation of methylene blue under UV-vis irradiation, which showed an enhanced photodegradation rate nearly 7 times higher than that of bare ZnO and nearly 3 times higher than that of V2O5@ZnO, mainly owing to the enlarged light absorption region, the effective electron-hole separation at the V2O5-ZnO and V2O5-Au interfaces, and strong localization of plasmonic near-field effects.

Facile synthesis of novel MoS2@SnO2 hetero-nanoflowers and enhanced photocatalysis and field-emission properties.

A novel hierarchical MoS2@SnO2 hetero-nanoflower was successfully synthesized by a facile, two-step hydrothermal method without using any additives or surfactants. One possible growth mechanism of the hetero-nanostructure was presented in detail based on OH(-) ion-dependent experimental facts. Due to the formation of the p-n junctions and the increased specific surface area in the composites, an outstanding photocatalytic activity of the as-prepared sample was obtained by monitoring the photodegradation of methylene blue (MB). According to the data, after irradiation for 100 min, the remaining MB in solution is about 26% for MoS2 nanoflowers and 9.5% for MoS2@SnO2 hetero-nanoflowers. Moreover, an excellent field-emission performance was obtained from MoS2@SnO2 hetero-nanoflower relative to the pure MoS2 with the turn-on field decreasing from 4.2 V µm(-1) to 3.4 V µm(-1) and the threshold field decreasing from 6.2 V µm(-1) to 5.2 V µm(-1), which is mainly attributed to the increased field-emission points and MoS2-SnO2 heterojunction.

Morphology-controlled synthesis of ZnO replicas with photonic structures from butterfly (Papilio paris) wing scales for tunable optical properties.

ZnO replicas with photonic structures were fabricated from Papilio paris butterfly wing scales and their tunable optical properties were studied. Through modification of the fabrication method, the reticular porous network structure was successfully replicated from dark black (DB) wing scales. The DB wing scale replicas exhibit a photonic band gap (PBG) in the visible region, which overlaps with the visible emission range of ZnO. Both DB and GB (greenish-blue) wing scale replicas can work as one-dimensional diffraction gratings in optical diffraction experiments, whose spot distances can be tuned by different periodic sizes of butterfly wing structure. Moreover, the ZnO DB wing scale replicas exhibit improved photoluminescence (PL) spectra with reduced visible emission and enhanced UV emission, which can both be attributed to the existence of a PBG produced by the reticular porous network structure in DB wing scales. These results can be very helpful in the research of applications of ZnO materials in UV lasing and optical diffraction devices.

Fabrication of ZnO photonic amorphous diamond nanostructure from parrot feathers for modulated photoluminescence properties.

A ZnO photonic amorphous diamond nanostructure was successfully synthesised using a feather barb of the Rosy-Faced Lovebird as supporting template via a facile sol-gel process. Different from ordered structures, an isotropic PBG around 500 nm was evidenced from reflectance spectra and an optical metallurgical microscopy image, which overlaps with the visible emission peak of ZnO. As a result, the inhibition of visible emission inside the PBG and the enhancement of UV emission at the PBG edges have both been observed, which is independent from the incident angle. Moreover, the rapid thermal annealing can also help improve the crystallinity of ZnO and raise the UV/visible emission ratio without affecting the structure. These results can be very useful for the study of the modification of the optical emission properties of ZnO and other semiconductor materials as well as research on ZnO random lasing.

Fabrication and temperature-dependent field-emission properties of bundlelike VO2 nanostructures.

Bundlelike VO(2)(B) nanostructures were synthesized via a hydrothermal method, and VO(2)(M(1)/R) nanobundles were obtained after a heat-treatment process. Structural characterization shows that these nanobundles are self-assembled by VO(2) nanowires, and VO(2)(M(1)/R) nanobundles have better crystallinity. Temperature-dependent field-emission (FE) measurement indicates that FE properties of these two phases of nanobundles can both be improved by increasing the ambient temperature. Moreover, for the VO(2)(M(1)/R) nanobundles, their FE properties are also strongly dependent on the temperature-induced metal-insulator transitions process. Compared with poor FE properties found in the insulating phase, FE properties were significantly improved by increasing the temperature, and about a three-orders-of-magnitude increasing of the emission current density has been observed at a fixed field of 6 V/µm. Work function measurement and density-functional theory calculations indicated that the decrease of work function with temperature is the main reason that caused the improvement of FE properties. These characteristics make VO(2)(M(1)/R) a candidate material for application of new type of temperature-controlled field emitters, whose emission density can be adjusted by ambient temperature.