Sheet Structure Research Articles

Influence of electrospun carbon nanofiber surface properties on lithium-air battery cathode behavior

The surface properties of carbons significantly influence their performance when they are used as lithium-air battery cathodes. This study used carbon nanofiber sheets derived from polyacrylonitrile (PAN) nanofiber sheets and prepared by electrospinning (ES-CNF) as a model cathode to investigate the influence of surface properties. The sheet structure enabled sufficient access of O2 to the carbon surface. For this investigation, five types of ES-CNF sheets having different surface properties were prepared by varying the heat-treatment temperature from 800 to 2200 °C. A portion of the heat-treated samples were further treated with nitric acid. The surface properties of the obtained samples were analyzed in detail by temperature programmed desorption analysis conducted under vacuum in the temperature range 100–1800 °C. The results indicated that discharge and charge voltages depend on the number of edge-H and the type and number of carbon functional groups. Oxygen-containing functional groups on the carbon promoted not only the surface-route deposition of Li2O2, which can be charged (decomposed) at voltages below 3.7 V, but also undesired side reactions, which can increase the charge voltage up to over 4.0 V. Furthermore, it was also found that carboxyl or phenol/ether groups effectively promote surface-route reactions much more efficiently than N-containing functional groups (NCFGs) and carbonyl groups. The knowledge obtained in this study can be utilized as a new guideline to design cathode carbon for lithium-air batteries.

Residue-specific binding of Ni(II) ions influences the structure and aggregation of amyloid beta (Aβ) peptides

Alzheimer’s disease (AD) is the most common cause of dementia worldwide. AD brains display deposits of insoluble amyloid plaques consisting mainly of aggregated amyloid-β (Aβ) peptides, and Aβ oligomers are likely a toxic species in AD pathology. AD patients display altered metal homeostasis, and AD plaques show elevated concentrations of metals such as Cu, Fe, and Zn. Yet, the metal chemistry in AD pathology remains unclear. Ni(II) ions are known to interact with Aβ peptides, but the nature and effects of such interactions are unknown. Here, we use numerous biophysical methods—mainly spectroscopy and imaging techniques—to characterize Aβ/Ni(II) interactions in vitro, for different Aβ variants: Aβ(1–40), Aβ(1–40)(H6A, H13A, H14A), Aβ(4–40), and Aβ(1–42). We show for the first time that Ni(II) ions display specific binding to the N-terminal segment of full-length Aβ monomers. Equimolar amounts of Ni(II) ions retard Aβ aggregation and direct it towards non-structured aggregates. The His6, His13, and His14 residues are implicated as binding ligands, and the Ni(II)·Aβ binding affinity is in the low µM range. The redox-active Ni(II) ions induce formation of dityrosine cross-links via redox chemistry, thereby creating covalent Aβ dimers. In aqueous buffer Ni(II) ions promote formation of beta sheet structure in Aβ monomers, while in a membrane-mimicking environment (SDS micelles) coil–coil helix interactions appear to be induced. For SDS-stabilized Aβ oligomers, Ni(II) ions direct the oligomers towards larger sizes and more diverse (heterogeneous) populations. All of these structural rearrangements may be relevant for the Aβ aggregation processes that are involved in AD brain pathology.

Highly selective adsorption of Hg (II) from aqueous solution by three-dimensional porous N-doped starch-based carbon.

For the first time, N-doped carbon materials with 3D porous-layered skeleton structure was synthesized through a one-step co-pyrolysis method, which was fabricated by co-pyrolysis of natural corn starch and melamine using metal catalysts (Ni (II) and Mn (II)). The 3D-NC possessed a heterogeneously meso-macroporous surface with a hierarchically connected sheet structure inside. Batch adsorption experiments suggested that highly selective adsorption of Hg (II) by the 3D-NC could be completed within 90min and had maximum adsorption capacities as high as 403.24mg/g at 293K, pH = 5. The adsorption mechanism for Hg (II) was carefully evaluated and followed the physical adsorption, electrostatic attraction, chelation, and ion exchange. Besides, thermodynamic study demonstrated that the Hg (II) adsorption procedure was spontaneous, endothermic, and randomness. More importantly, the 3D-NC could be regenerated and recovered well after adsorption-desorption cycles, showing a promising prospect in the remediation of Hg (II)-contaminated wastewater.

Optimization of Keratin Hydrolysate Extraction from Tannery Sheep Hair Waste

Tannery hair wastes are becoming a challenge for tanners regarding environmental pollution control and human health. In this study, an experiment had been designed to hydrolyse sheep hair in an alkaline medium, and the operational condition for the alkaline extraction of KH has been modeled and optimized. The structure, morphology, functional groups, particle size, and molecular mass of the KH extracts were evaluated experimentally by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), particle size analysis, and SDS-PAGE analysis, respectively. FTIR analysis of the extract confirmed the presence of carboxylic, amide, and aldehyde functional groups and alkyl side chains of amino acids. The molecular weight of the extracted keratin ranges between 3–15 kDa, and X-ray diffraction (XRD) analysis showed an amorphous form of structure with two peaks at 2 theta of 9.36° and 21.16° due to α -helix and β - sheet structure in keratin. Response surface methodology (RSM) coupled with BOX-Behnken design was applied as a statistical tool to investigate the effect of extraction time, the concentration of the hydrolysing agent, and temperature on the response variable (yield of keratin protein). The concentration of the hydrolysing agent was found to be the most significant factor affecting the speed of extraction, but its gradual increase tends to affect the protein content of the extract. Optimum parameters of 0.5 N, 80°C, and 3.5 hr were obtained for the concentration of NaOH, temperature, and extraction time, respectively, with a maximum average protein yield of 91.5% and a percentage total nitrogen content of 14.6% using the Kjeldahl method and 86.57% using the biuret test method.

Fibronectin-Enriched Interface Using a Spheroid-Converged Cell Sheet for Effective Wound Healing.

Cell sheets and spheroids are cell aggregates with excellent tissue-healing effects. However, their therapeutic outcomes are limited by low cell-loading efficacy and low extracellular matrix (ECM). Preconditioning cells with light illumination has been widely accepted to enhance reactive oxygen species (ROS)-mediated ECM expression and angiogenic factor secretion. However, there are difficulties in controlling the amount of ROS required to induce therapeutic cell signaling. Here, we develop a microstructure (MS) patch that can culture a unique human mesenchymal stem cell complex (hMSCcx), spheroid-attached cell sheets. The spheroid-converged cell sheet structure of hMSCcx shows high ROS tolerance compared to hMSC cell sheets owing to its high antioxidant capacity. The therapeutic angiogenic efficacy of hMSCcx is reinforced by regulating ROS levels without cytotoxicity using light (610 nm wavelength) illumination. The reinforced angiogenic efficacy of illuminated hMSCcx is based on the increased gap junctional interaction by enhanced fibronectin. hMSCcx engraftment is significantly improved in our novel MS patch by means of ROS tolerative structure of hMSCcx, leading to robust wound-healing outcomes in a mouse wound model. This study provides a new method to overcome the limitations of conventional cell sheets and spheroid therapy.

Multiscale hybrid modeling of the impact response of the Earth’s magnetotail to ionospheric O+ outflow

Ionospheric outflow plays an important role in coupling the ionosphere with the solar wind-magnetosphere system. Previous multi-fluid MHD studies explored the global influence of oxygen ions of ionospheric origin (O+) on magnetospheric dynamics. A detailed exploration of the interaction of ionospheric ions with the magnetotail requires kinetic treatment for ions. We perform a self-consistent investigation of these processes with a three-dimensional space-time adaptive hybrid code, HYPERS, powered by an intelligent Event-driven Multi-Agent Planning System (EMAPS). By comparing simulations with and without outflow we conclude that oxygen ions, flowing from the ionosphere through the lobes into the tail or directly entering the inner magnetosphere, are able to significantly modify the magnetotail configuration and induce X-points and current sheet structures at locations where magnetic reconnection does not occur in a simulation without outflow, potentially very close to the Earth. This finding may have implications for interpreting substorms and magnetotail reconnection events observed for southward magnetic field simultaneously with significant contents of oxygen ions of ionospheric origin.

A Comprehensive Review on Novel Graphene‐Hydroxyapatite Nanocomposites For Potential Bioimplant Applications

AbstractThe advancements in medical treatment necessitated the development of advanced bio‐implant materials for hard tissue replacement and bone regeneration. Hydroxyapatite (HA), an extreme bioresorbable material having physicochemical similarities with natural bone, seems to be a good bioimplant. Still, the ineffective mechanical properties, viz. fracture toughness, wear resistance, and tensile strength, restrict its practical utility in bioimplants. Recently, graphene‐HA nanocomposites have been explored for potential bioimplant applications ascribed to their superior biocompatibility, bioactivity, osteoconductivity, and enhanced mechanical properties. The huge surface area with a two‐dimensional sheet structure facilitates graphene's strong integration with HA, thus enhancing mechanical properties. These enhanced mechanical properties of graphene‐HA nanocomposite are chiefly attributed to the pull‐out, ridge growth, crack deflection, and grain bridging characteristics exhibited by graphene filler in the HA matrix. Further, graphene is neutral and biocompatible, thus improving the graphene‐HA nanocomposite‘s biocompatibility. These qualities made this nanocomposite a rising star among bio‐ceramic implant materials. This review presents the current scenario on the synthesis and mechanical and biological properties of graphene‐hydroxyapatite nanocomposite, which seems to be a propitious material for implants in orthopaedic applications.

Effect of thermal oxygen aging on the crystallization and insulation properties of polyether ether ketone

AbstractAs an engineering material, polyether ether ketone (PEEK) has been widely used in many fields. It is important to study its thermal oxidative aging law for its material service optimization. The changes of chemical structure and relative properties of PEEK sheets after thermal oxygen aging at 280°C for different times were measured by universal tensile machine, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and resistance meter. The results showed that the elongation at break of the aged samples decreased with the extension of thermal aging time, while the tensile strength continuously increased within 336 h of thermal aging and then decreased gradually. Moreover, the crystallization temperature, melting enthalpy, and crystallinity of the samples decreased with the increase of thermal aging time. The crystallinity decreased to 2.3% after 2852 h aging and the initial decomposition temperature and the maximum decomposition temperature of PEEK gradually decreased from 554.3 to 523.5°C and 572.9 to 558.2°C, respectively. The increase of tan δ was more significant in the low frequency band (10−2–101) Hz. With the increase of aging time, the zeta potential of PEEK surface constantly moved to the negative direction and the volume resistivity and the dielectric strength similarly increased first and then decreased.

The construction of scale-like Fe7S8/C composite nanotubes and their electrochemical properties

Iron sulfides is promising anode material for lithium-ion battery. However, the shortcomings of low electronic conductivity and severe volume expansion effect, restrict their electrochemical performance. Herein, we report an in situ growth strategy for fabricating scale-like Fe7S8/C composite nanotubes. The hierarchical structure of scale-like Fe7S8/C composite nanotubes combine the structural advantages of sheet structure and tubular structure. As lithium-ion battery anodes, the prepared scale-like Fe7S8/C composite nanotubes deliver superior reversible capacity of 688 ​mA ​h ​g−1 even after 500 cycles at a current density of 1 ​A ​g−1. These outstanding electrochemical performances can be attributed to the synthetic effects of the structure. The sheet structure can provide large active area and abundant Li-ion storage sites, and the tubular structure can provide buffer space for the volume expansion effect. Moreover, the combination with carbon improves the electrical conductivity of the material effectively. Therefore, the results show that the scale-like Fe7S8/C composite nanotubes are excellent electrode materials.

Changes in the structure and properties of the thick sheets of bainitic/martensitic steel at a cross-section

To expand the grade of rolled low-carbon low-alloy steels chrome-nickel-molybdenum composition. The analysis of changes the mechanical properties and structure in the thickness of rolled sheets of 15, 50 and 60 mm produced using quenching with furnace heating and high tempering was performed.

Promoted photocatalytic hydrogen evolution via double-electron migration in Ag@g-C3N4 heterojunction

The unsaturated edge Ag introduced on the surface of photocatalysts plays an important role in boosting photo-excited electrons for the photoreduction H2O reaction. However, a moderate and tractable strategy to efficiently expose edge Ag remains an enormous challenge. For this purpose, a core skeleton with ‘Ag conductive nanosphere array’ inside and a two-dimensional sheet structure with g-C3N4 layer outside are formed. The introduction of Ag nanospheres into g-C3N4 not only enlarges the distance between g-C3N4 nanolayers, but also increases the exposure of Ag nanospheres. When Ag intimately contacts with g-C3N4, the electrons of g-C3N4 voluntarily flow to the Ag. Consequently, a built-in electric field (IEF) has been formed at interface of Ag@g-C3N4 heterojunction, which prevents the continuous flow of electrons from g-C3N4 to Ag. Under irradiation, the e− accumulated in Ag tend to recombine with the h+ in the valence band of g-C3N4 which is driven by Coulomb interaction and IEF. Ag nanospheres are fabricated as a co-catalyst to decorate the g-C3N4 nanolayer, which hinder the conglomeration of g-C3N4 nanolayers. Moreover, Ag@g-C3N4 heterojunction provides polyunsaturated edge Ag as active sites, inducing prolonged lifetime of photogenerated electrons and formed the unique charge transfer channels. In addition, abundant nitrogen vacancies are formed, which strengthens the chemisorption of H2O. As a result, supreme Ag@g-C3N4 realizes a high H2 evolution of 312.5 μmol and preserves a good sustainability. This paper emphasizes the importance of unique electron transfer pathway and chemisorption of water for photoreduction H2O.

Tribological properties of metal-organic framework nanosheets functionalized by oleic acid

<p indent="0mm">Terephthalic acid and copper acetate were used as raw materials, and copper-based metal-organic framework (Cu-MOF) nanosheets were synthesized by ultrasonic-assisted self-assembly. Afterward, oleic acid (OA) molecules were successfully modified on the surface of Cu-MOF by ultrasonic treatment to acquire Cu-MOF@OA nanosheets. The morphology of Cu-MOF@OA maintained its sheet structure; however, the size of the nanosheets was reduced, and the agglomeration problem was considerably alleviated compared with Cu-MOF nanosheets. The Cu-MOF@OA nanosheets exhibited good dispersion stability in <sc>500 N</sc> base oil. The tribological tests indicated that Cu-MOF@OA showed the best tribological properties at the addition concentration of 1.0 wt.%. Moreover, the friction coefficient and wear volume were reduced to 3/5 and 1/6 of the base oil, respectively. Finally, scanning electron microscopy and X-ray photoelectron spectroscopy were applied to characterize the morphology and characteristic elements of wear scar lubricated by Cu-MOF@OA nanosheets and explore the lubrication mechanism. The results indicated that complex tribochemical reactions occur among Cu-MOF@OA, base oil, and iron substrate under the action of load and shear stress during the friction experiment, forming a tribofilm composed of nitrogenous substances, carbonaceous substances, and iron oxides, which reduce the friction and wear of metal surfaces.

Nonequilibrium Ionization Modeling of Petschek-type Shocks in Reconnecting Current Sheets in Solar Eruptions

Nonequilibrium ionization (NEI) is essentially required for astrophysical plasma diagnostics once the plasma status departs from the assumption of ionization equilibrium. In this work, we perform fast NEI calculations combined with magnetohydrodynamic (MHD) simulations and analyze the ionization properties of a Petschek-type magnetic reconnection current sheet during solar eruptions. Our simulation reveals Petschek-type slow-mode shocks in the classical Spitzer thermal conduction models and conduction flux-limitation situations. The results show that under-ionized features can be commonly found in shocked reconnection outflows and thermal halo regions outside the shocks. The departure from equilibrium ionization strongly depends on plasma density. In addition, this departure is sensitive to the observable target temperature: the high-temperature iron ions are strongly affected by the effects of NEI. The under-ionization also affects the synthetic SDO/AIA intensities, which indicates that the reconstructed hot reconnection current sheet structure may be significantly underestimated either for temperature or apparent width. We also perform an MHD-NEI analysis on the reconnection current sheet in the classical solar flare geometry. Finally, we show the potential reversal between the under-ionized and over-ionized states at the lower tip of reconnection current sheets where the downward outflow collides with closed magnetic loops, which can strongly affect multiple SDO/AIA band ratios along the reconnection current sheet.

Fabrication of graphene oxide/copper synergistic antibacterial coating for medical titanium substrate

Titanium (Ti) was an excellent medical metal material, but the lack of good antibacterial activity confined its further practical application. To solve this dilemma, a coating containing graphene oxide (GO) and copper (Cu) was prepared on the surface of Ti sheet (Ti/APS/GO/Cu). First, physical sterilization could be carried out through the sharp-edged sheet structure of GO. Second, the oxygen-containing functional group on the surface of GO and the released Cu2+ would generate reactive oxygen species for chemical sterilization. The synergistic effect of GO and Cu substantially enhanced the in vitro and in vivo antibacterial property of Ti sheet, thereby reducing bacterial-related inflammation. Quantitatively, the antibacterial rate of Ti/APS/GO/Cu against E. coli or S. aureus reached over 99%. Besides, Ti/APS/GO/Cu showed excellent biocompatibility and no toxicity to cell. Such work developed multiple sterilization avenues to design non-antibiotic, safe and efficient antibacterial implant material for the biomedical domain.

Simulation-ready graphene oxide structures with hierarchical complexity: a modular tiling strategy

Graphene oxide (GO) sheet structures are highly variable and depend on preparation conditions. The use of molecular simulation is a complementary strategy to explore how this complexity influences the ion transport properties of GO membranes. However, despite recent advances, computational models of GO typically lack the required complexity as suggested by experiment. The labor required to create such an ensemble of such structural models with the required complexity is impractical without recourse to automated approaches, but no such code currently can meet this challenge. Here, a modular tiling concept is introduced, along with the HierGO suite of code; an automated approach to producing highly complex hierarchically-structured models of GO with a high degree of control in terms of holes and topological defects, and oxygen-group placement, that can produce simulation-ready input files. The benefits of the code are exemplified by modeling and contrasting the properties of three types of GO membrane stack; the widely-modeled Lerf–Klinowski structure, and two types of highly heterogeneous GO sheet reflecting differing processing conditions. The outcomes of this work clearly demonstrate how the introduction of the complexity modeled here leads to new insights into the structure/property relationships of GO with respect to permeation pathways of water, ions and molecular agents that are inaccessible using previously-considered models.

Differential effects of DTT on HEWL amyloid fibrillation and fibril morphology at different pH

Proteins can transform from their native state to a state having fibrillar aggregates characterized by cross β sheet structure. The fibrillar aggregates are known as amyloid and have been linked to several disorders. Disulfide bonds in proteins are one of the important factors that determine the propensity of aggregation. Hen Egg White Lysozyme (HEWL) was used by us as a model protein to decipher the role disulfide bonds play in the amyloid fibril formation and fibril morphology by using Dithiothreitol (DTT) as reducing agent at pH 2.7 and pH 7.4. We found that DTT can have different effects on HEWL amyloid depending on pH and the buffer used for preparing the amyloid fibrils. Our studies highlight the critical role of non-native disulfide bonds in amyloidogenesis and how disruption of these bonds can greatly affect the fibrillation process. Overall, these studies throw light on the fibrillation mechanism and can be explored further in designing effective inhibitors against amyloidosis.

Efficient removal of Hg0 in flue gas using a novel Sn-based porphyrin polymer

A Sn-based porphyrin polymer (TAPP(Sn)-FAC) synthesized in a mild condition was introduced for the Hg0 removal in flue gas. The properties characterization of materials revealed the two-dimensional sheet structure, an amorphous structure and high stability of TAPP(Sn)-FAC, and Sn was successfully incorporated into TAPP-FAC in the form of SnN. The removal performance of Hg0 under different conditions was investigated using a lab-scale fixed-bed reactor. TAPP(Sn)-FAC presented an excellent Hg0 removal efficiency from 100 °C to 250 °C, which can reach 8 mg/g of Hg0 capture capacity at 100 °C for 300 min. Besides, TAPP(Sn)-FAC had a strong sulfur and water resistance, and the presence of NO and O2 had a facilitating effect for Hg0 removal. Moreover, the existence of Sn can enhance the Hg0 adsorption and oxidation capacity of TAPP(Sn)-FAC by promoting the electron transfer process. Furthermore, TAPP(Sn)-FAC presented an excellent chemical stability, which was a promising material in the Hg0 removal in flue gas.

Assembly–disassembly switching of chiral sheet assembly for controlled circularly polarized luminescence

AbstractAlthough substantial advances have been made regarding synthetic chiral assemblies, obtaining the two‐dimensional (2D) system with a sophisticated supramolecular chirality remains challenging. Herein, we report the switchable supramolecular chiral 2D materials via donor‐acceptor interaction between a pyrene amphiphile and 7,7,8,8‐tetracyanoquinodimethane (TCNQ). The resulting supramolecular chiral sheets spontaneously disassemble when TCNQ is irreversibly photo‐reduced to its anion. Subsequent additions of TCNQ drive the disassembled molecules to repeatedly form optically active sheet structures, demonstrating that the assembled materials exist transiently only while TCNQ is supplied. The chiral sheets emit intense circularly polarized light with a large luminescence dissymmetric factor (glum).

The Mo as electron trapper and donor to modulate the electron of CoP2 in phosphating process

To prepare bifunctional electrocatalyst towards HER and OER is extremely important for promoting the development of electrochemical water splitting technology. Herein, the element doping method is employed to tune the electron environment of cobalt phosphide (CoP). The Mo-doped CoP supported on carbon cloth (CC) is constructed by solvothermal and annealing method. The effect of Mo on the electron modulation of CoP during different phosphating time was studied carefully. It is noted that the Mo play an important role in tuning the electron state of Co and P elements which can trap the electron and was reduced to low valence, then transfer the electron to Co and P. With increasing the phosphating time, the electron transfer phenomenon between Mo and CoP is obvious. Benefiting from the electron engineering of Mo, Co and P as well as thin and wrinkle sheets structure, the optimal electrocatalyst only requires 39 mV and 251 mV to deliver 10 mA cm−2 for HER and OER, respectively. Also, as for the whole water splitting performance, it delivers 10 mA cm−2 at cell voltage of 1.56 V. Importantly, Faraday efficiency of the optimal catalyst achieves 99.9% for HER due to the tuned electron state of Co and P, high ECSA and low Rct.

Actuation of shape memory poly(vinyl alcohol) and graphene oxide film in water

The PVA/GO film prepared by vacuum-assisted self-assembly exhibits quick thermo-/water- responsive shape memory effect. The anisotropic lamellar structure of GO sheets and plenty of chemical groups containing oxygen in the PVA/GO film facilitate rapid recovery in water. The lamellar structure of GO sheets improves the recovery stress of composite and results in a 16-fold increase in Young’s modulus. PVA molecular chain slides along the direction of the laminated GO sheets, consistent with the extension direction, ensuring that the composite film maintains a large fracture strain. The straight film is programmed into a spiral shape by the plasticization of water on PVA instead of ordinary heating and the spiral film can drive a weight 160 times its own weight to rotate in water at room temperature (about 25[Formula: see text]C).