Changes in Current Transport and Regulation of the Microstructure of Graphene/Polyimide Films under Joule Heating Treatment.

The excellent electrical properties of graphene have received widespread attention. However, the difficulty of electron transfer between layers still restricts the application of graphene composite materials to a large extent. Therefore, in this study, graphene/polyimide films were subjected to a Joule heating treatment to improve the electrical conductivity of the film by ~76.85%. After multiple Joule thermal cycle treatments, the conductivity of the graphene/polyimide film still gradually increased, but the increase in amplitude tended to slow down. Finally, after eight Joule heat treatments, the conductivity of the graphene/polyimide film was improved by ~93.94%. The Joule heating treatment caused the polyimide to undergo atomic rearrangement near the interface bonded to the graphene, forming a new crystalline phase favourable for electron transport with graphene as a template. Accordingly, a model of the bilayer capacitive microstructure of graphene/polyimide was proposed. The experiment suggests that the Joule heating treatment can effectively reduce the distance between graphene electrode plates in the bilayer capacitive micro-nanostructures of graphene/polyimide and greatly increases the number of charge carriers on the electrode plates. The TEM and WAXS characterisation results imply atomic structure changes at the graphene/polyimide bonding interface.

Non-Blinking Luminescence from Charged Single Graphene Quantum Dots.

Photoluminescence blinking behavior from single quantum dots under steady illumination is an important but controversial topic. Its occurrence has impeded the use of single quantum dots in bioimaging. Different mechanisms have been proposed to account for it, although controversial, the most important of which is the non-radiative Auger recombination mechanism whereby photocharging of quantum dots can lead to the blinking phenomenon. Here, the singly charged trion, which maintains photon emission, including radiative recombination and non-radiative Auger recombination, leads to fluorescence non-blinking which is observed in photocharged single graphene quantum dots (GQDs). This phenomenon can be explained in terms of different energy levels in the GQDs, caused by various oxygen-containing functional groups in the single GQDs. The suppressed blinking is due to the filling of trap sites owing to a Coulomb blockade. These results provide a profound understanding of the special optical properties of GQDs, affording a reference for further in-depth research.

Molecular mechanisms of the antibacterial activity of polyimide fibers in a skin-wound model with Gram-positive and Gram-negative bacterial infection in vivo.

Recently, the need for antibacterial dressings has amplified because of the increase of traumatic injuries. However, there is still a lack of ideal, natural antibacterial dressings that show an efficient antibacterial property with no toxicity. Polyimide (PI) used as an implantable and flexible material has been recently reported as a mixture of particles showing more desirable antibacterial properties. However, we have identified a novel type of natural polyimide (PI) fiber that revealed antibacterial properties by itself for the first time. The PI fiber material is mainly composed of C, N, and O, and contains a small amount of Ca and Cl; the characteristic peaks of polyimide appear at 1774 cm-1, 1713 cm-1, 1370 cm-1, 1087 cm-1, and 722 cm-1. PI fibers displayed significant antibacterial activities against Escherichia coli (as a Gram-negative bacteria model) and methicillin-resistant Staphylococcus aureus (MRSA, as a Gram-positive bacteria model) according to the time-kill kinetics in vitro, and PI fibers damaged both bacterial cell walls directly. PI fibers efficiently ameliorated a local infection in vivo, inhibited the bacterial burden, decreased infiltrating macrophages, and accelerated wound healing in an E. coli- or MRSA-infected wound model. In conclusion, PI fibers used in the present study may act as potent antibacterial dressings protecting from MRSA or E. coli infections and as promising candidates for antimicrobial materials for trauma and surgical applications.

Population Genetics Reveals That the Western Tianshan Mountains Populations of Agrilus mali (Coleoptera: Buprestidae) May Have Not been Recently Introduced.

Agrilus mali Matsumura is a wood-boring beetle that aggressively attacks species of the genus Malus, that has recently caused serious damage to the wild apple tree M. sieversii (Lebed.) in the western Tianshan Mountains in Xinjiang. It was first detected there in the early 1990s and spread rapidly, being thus considered a regional invasive pest. To explore the possible outbreak mechanism of the local population and characterize the genetic differentiation of A. mali across different regions of China, we used three mitochondrial genes (COI, COII, and CytB) to investigate the genetic diversity and genetic structure of 17 A. mali populations containing 205 individuals collected from five Chinese provinces. Among them, nine populations were from the western Tianshan Mountains. Ultimately, of the 136 pairwise F st comparisons, 99 showed high genetic differentiation among overall populations, and Tianshan populations exhibited significant differentiation with most of the non-Tianshan populations. Furthermore, A. mali populations represented relatively abundant haplotypes (54 haplotypes). Nine populations from the Tianshan Mountains showed 32 haplotypes (26 of which were unique), displaying relatively high genetic diversity. Additionally, the Mantel test revealed population genetic differentiation among either overall populations or the Tianshan Mountains populations, likely caused by geographical isolation. Phylogenic relationships showed that all populations clustered into three clades, and Tianshan Mountains populations, including CY, occupied one of the three clades. These results suggest that A. mali in the western Tianshan region has possibly been present in the area for a long period, and may not have been introduced recently. Highly frequent gene flows within Tianshan populations are possibly caused by human activities and may enhance the adaptability of A. mali along the western Tianshan Mountains, leading to periodic outbreaks. These findings enhance our understanding of jewel beetle population genetics and provide valuable information for pest management.

The conserved mitochondrial genome of the jewel beetle (Coleoptera: Buprestidae) and its phylogenetic implications for the suborder Polyphaga.

In this study, we sequenced the mitochondrial (mt) genome of Agrilus mali (Coleoptera: Buprestidae) using next-generation sequencing, and accordingly annotated 13 protein-coding, 22 tRNA, and 2 rRNA genes and a 1458-bp non-coding region. Comparative analysis indicated that the mt genome of A. mali is relatively conserved, with a typical gene content and order identical to those of other coleopterans. However, the newly sequenced mt genome is characterized by a relatively higher A + T content compared with that of other species within the family Buprestidae. Phylogenetic analysis based on Bayesian inference revealed that the evolutionary relationship among the six infraorders of the suborder Polyphaga is (Scirtiformia + (Elateriformia + ((Scarabaeiformia + Staphyliniformia) + (Bostrichiformia + (Cucujiformia))))). However, the topology indicated that the family Buprestidae is a sister group to other Polyphaga infraorders, excluding Scirtiformia as a monophyly, and thus the monophyly of Elateriformia was not supported. This study not only presents the mt genome of a species in the family Buprestidae and a comparative analysis of jewel beetles but also examines the contribution of mt genomes in elucidating phylogenetic relationships within the suborder Polyphaga of Coleoptera.

MOF-Derived Co3O4 Polyhedrons as Efficient Polysulfides Barrier on Polyimide Separators for High Temperature Lithium-sulfur Batteries.

The incorporation of highly polarized inorganic compounds in functional separators is expected to alleviate the high temperature safety- and performance-related issues for promising lithium-sulfur batteries. In this work, a unique Co3O4 polyhedral coating on thermal-stable polyimide (PI) separators was developed by a simple one-step low-temperature calcination method utilizing metal-organic framework (MOF) of Co-based zeolitic-imidazolate frameworks (ZIF-Co) precursors. The unique Co3O4 polyhedral structures possess several structural merits including small primary particle size, large pore size, rich grain boundary, and high ionic conductivity, which endow the ability to adequately adsorb dissolved polysulfides. The flexible-rigid lithium-lanthanum-zirconium oxide-poly(ethylene oxide) (LLZO-PEO) coating has been designed on another side of the polyimide non-woven membranes to inhibit the growth of lithium dendrites. As a result, the as-fabricated Co3O4/polyimide/LLZO-PEO (Co3O4/PI/LLZO) composite separators displayed fair dimensional stability, good mechanical strength, flame retardant properties, and excellent ionic conductivity. More encouragingly, the separator coating of Co3O4 polyhedrons endows Li-S cells with unprecedented high temperature properties (tested at 80 °C), including rate performance 620 mAh g-1 at 4.0 C and cycling stability of 800 mAh g-1 after 200 cycles-much better than the state-of-the-art results. This work will encourage more research on the separator engineering for high temperature operation.

Pt nanoparticles decorated rose-like Bi2O2CO3 configurations for efficient photocatalytic removal of water organic pollutants.

Pt nanoparticles decorated with rose-like Bi2O2CO3 configurations were synthesized via a simple photoreduction method at room temperature. The structure, morphology, optical and electronic properties, and photocatalytic performance of the as-prepared materials were characterized. Compared to pure Bi2O2CO3, the Pt/Bi2O2CO3 photocatalysts show better performance in decomposing RhB, BPA and OTC under visible light (λ > 420 nm). The enhanced photocatalytic activity of Pt/Bi2O2CO3 could be attributed to the modification in light absorption (λ > 420 nm) charge migration and the separation of photo-generated electrons (e-) and holes (h+). Free radical trapping experiments demonstrated that the main active species of the catalytic reaction are different in decomposing RhB and BPA.

Percolation channels: a universal idea to describe the atomic structure and dynamics of glasses and melts.

Understanding the links between chemical composition, nano-structure and the dynamic properties of silicate melts and glasses is fundamental to both Earth and Materials Sciences. Central to this is whether the distribution of mobile metallic ions is random or not. In silicate systems, such as window glass, it is well-established that the short-range structure is not random but metal ions cluster, forming percolation channels through a partly broken network of corner-sharing SiO4 tetrahedra. In alumino-silicate glasses and melts, extensively used in industry and representing most of the Earth magmas, metal ions compensate the electrical charge deficit of AlO4- tetrahedra, but until now clustering has not been confirmed. Here we report how major changes in melt viscosity, together with glass Raman and Nuclear Magnetic Resonance measurements and Molecular Dynamics simulations, demonstrate that metal ions nano-segregate into percolation channels, making this a universal phenomenon of oxide glasses and melts. Furthermore, we can explain how, in both single and mixed alkali compositions, metal ion clustering and percolation radically affect melt mobility, central to understanding industrial and geological processes.

Facile electrosynthesis of silicon carbide nanowires from silica/carbon precursors in molten salt.

Silicon carbide nanowires (SiC NWs) have attracted intensive attention in recent years due to their outstanding performances in many applications. A large-scale and facile production of SiC NWs is critical to its successful application. Here, we report a simple method for the production of SiC NWs from inexpensive and abundantly available silica/carbon (SiO2/C) precursors in molten calcium chloride. The solid-to-solid electroreduction and dissolution-electrodeposition mechanisms can easily lead to the formation of homogenous SiC NWs. This template/catalyst-free approach greatly simplifies the synthesis procedure compared to conventional methods. This general strategy opens a direct electrochemical route for the conversion of SiO2/C into SiC NWs, and may also have implications for the electrosynthesis of other micro/nanostructured metal carbides/composites from metal oxides/carbon precursors.

Solid oxide membrane-assisted controllable electrolytic fabrication of metal carbides in molten salt.

Silicon carbide (SiC), titanium carbide (TiC), zirconium carbide (ZrC), and tantalum carbide (TaC) have been electrochemically produced directly from their corresponding stoichiometric metal oxides/carbon (MOx/C) precursors by electrodeoxidation in molten calcium chloride (CaCl2). An assembled yttria stabilized zirconia solid oxide membrane (SOM)-based anode was employed to control the electrodeoxidation process. The SOM-assisted controllable electrochemical process was carried out in molten CaCl2 at 1000 °C with a potential of 3.5 to 4.0 V. The reaction mechanism of the electrochemical production process and the characteristics of these produced metal carbides (MCs) were systematically investigated. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses clearly identify that SiC, TiC, ZrC, and TaC carbides can be facilely fabricated. SiC carbide can be controlled to form a homogeneous nanowire structure, while the morphologies of TiC, ZrC, and TaC carbides exhibit porous nodular structures with micro/nanoscale particles. The complex chemical/electrochemical reaction processes including the compounding, electrodeoxidation, dissolution-electrodeposition, and in situ carbonization processes in molten CaCl2 are also discussed. The present results preliminarily demonstrate that the molten salt-based SOM-assisted electrodeoxidation process has the potential to be used for the facile and controllable electrodeoxidation of MOx/C precursors to micro/nanostructured MCs, which can potentially be used for various applications.

Hybrid glasses from strong and fragile metal-organic framework liquids.

Hybrid glasses connect the emerging field of metal-organic frameworks (MOFs) with the glass formation, amorphization and melting processes of these chemically versatile systems. Though inorganic zeolites collapse around the glass transition and melt at higher temperatures, the relationship between amorphization and melting has so far not been investigated. Here we show how heating MOFs of zeolitic topology first results in a low density 'perfect' glass, similar to those formed in ice, silicon and disaccharides. This order-order transition leads to a super-strong liquid of low fragility that dynamically controls collapse, before a subsequent order-disorder transition, which creates a more fragile high-density liquid. After crystallization to a dense phase, which can be remelted, subsequent quenching results in a bulk glass, virtually identical to the high-density phase. We provide evidence that the wide-ranging melting temperatures of zeolitic MOFs are related to their network topologies and opens up the possibility of 'melt-casting' MOF glasses.

Hydrothermal fabrication of MnCO3@rGO composite as an anode material for high-performance lithium ion batteries.

The layer structure of graphene or reduced graphene oxide (rGO) opens an avenue for the development of advanced functional materials. In this paper, a MnCO3@rGO composite (MGC) was fabricated by anchoring MnCO3 nanoparticles (NPs) on rGO sheets in the hydrothermal reduction process of graphene oxide by using NaBH4. MnCO3 NPs with an average diameter of 8-20 nm were anchored onto the surface of rGO. The layer structure of rGO was maintained in MGC. The MGC was employed as an anode active material for lithium ion batteries. Excellent performances were obtained with a high specific capacity up to 857 mA·h·g(-1) after 100 cycles. The various charging-discharging current rates of 0.2-5.0 C exhibited no clear negative effect on the recycling stability of the MGC. The enhanced structure stability and ion and electron conductivity of the MGC are responsible for the superior electrochemical properties.

Counteracting stagnation in genetic algorithm calculations by implementation of a micro genetic algorithm strategy.

A new strategy for implementing the concept of a "micro genetic algorithm" within a standard genetic algorithm (GA) procedure is proposed. The strategy operates by applying criteria to test for the occurrence of stagnation within the population of a standard GA calculation, and triggering the micro-GA procedure whenever stagnation is detected. The micro-GA is implemented in terms of the parallel evolution of a number of small sub-populations (comprising predominantly new randomly generated structures together with a few of the best structures from the stagnated population), and the sub-population of highest quality following the micro-GA procedure is used in the construction of the next population of the standard GA calculation. The micro-GA procedure is applied in the context of a GA for carrying out direct-space structure solution from powder X-ray diffraction data, and the results demonstrate that this strategy is an effective means of promoting structural diversity within a stagnated population, leading to significantly improved evolutionary progress. This strategy may prove to be more generally applicable as an approach for alleviating problems due to stagnation in GA calculations in other fields of application.

Residue-based charge flipping: a new variant of an emerging algorithm for structure solution from X-ray diffraction data.

There is currently substantial interest and activity in the development and application of a new technique, called "charge flipping" (CF), that has emerged in the past few years for carrying out structure solution from X-ray diffraction data. We report here a new variant of this technique, termed "residue-based charge flipping" (RBCF), in which the residues of calculated and experimental structure factor amplitudes, together with the corresponding electron density residues, are introduced within the CF algorithm. An important feature of this approach is that it does not require a positive threshold electron density value (delta) to be specified to control the charge-flipping step within the algorithm (in contrast, it is well established that the success of standard CF calculations can depend critically on choosing a suitable value of delta for a given structural problem). Methodological details of the RBCF algorithm are described, and the results of the application of this technique for structure solution of three test structures are reported. The RBCF technique is shown to lead to the correct structure solution in all cases, with success rates of at least 90% (for independent calculations from different sets of initial random phases). Significantly, the convergence behavior of RBCF calculations is found to contrast markedly with that generally observed for standard CF calculations. In particular, convergence (assessed from the evolution of R-factor versus iteration number) typically progresses rapidly and immediately from the earliest iterations of RBCF calculations, rather than displaying an extended plateau region. This feature, and the fact that the RBCF technique does not use the delta parameter that is required in standard CF calculations, suggest that the RBCF algorithm may be a promising approach in future applications.