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•The oxidation process of FG is expressed by the one-half-order kinetic model R2.•The diffusion rate of MnO3+ and the oxidation rate of FG are discovered to be constant.•The ...transformation of functional groups during FG oxidation is described.•The chemical composition and defect extent of GO is adjustable using reaction conditions.
Graphite oxide (GO) is one of the most extensively studied materials and has been tested for numerous applications due to its unique properties. Nevertheless, a quantitative description of complicated transfer and reaction rates of the oxidation of graphite is still not available, which essentially hinders large-scale production of high-quality GO and other graphene related materials. In this work, GO is prepared from flake graphite (FG) by a modified Hummers method. Size and color evolutions of time-dependent complementary domains, i.e. the starting GO domain and the remaining FG domain, are monitored during the entire oxidation process. The oxidation of FG in acidic oxidizing medium can be interpreted as a contracting area process controlled by phase boundary. Reaction rate constant (k) and kinetic parameters (Ea, lnA) are obtained after a systematic investigation of the influence of reaction temperature, concentration of sulfuric acid, and oxidizing agent on the oxidation, with the aid of R2 mathematical model. Using the kinetic results, the oxidation process and the conversion rate from FG to GO thus become controllable. Both intermediate products and final GO products are studied using XRD, TGA, and XPS to reveal the oxidation mechanism. The degree of oxidation of FG and the content of major functional groups on the surface of products can thus be optimized. Our research results are valuable to understanding fundamental mechanism of graphite oxidation and to achieving industrial production of high-quality GO with controllable degree of oxidation and tunable proportion of oxygen-containing functional groups for a variety of applications.
The current work investigates a novel three-dimensional boron nitride called bulk B
N
and its corresponding two-dimensional monolayer B
N
based on the first-principles of density functional theory. ...The phonon spectra prove that bulk B
N
and monolayer B
N
are dynamically stable. The molecular dynamics simulations verify that bulk B
N
and monolayer B
N
have excellent thermal stability of withstanding temperature up to 1000 K. The calculated elastic constants state that bulk B
N
and monolayer B
N
are mechanically stable, and bulk B
N
has strong anisotropy. The theoretically obtained electronic structures reveal that bulk B
N
is an indirect band-gap semiconductor with a band gap of 5.4 eV, while monolayer B
N
has a direct band gap of 6.1 eV. The valence band maximum is mainly contributed from B-2p and N-2p orbits, and the conduction band minimum mainly derives from B-2p orbits. The electron transitions from occupied N-2p states to empty B-2p states play important roles in the dielectric functions of bulk B
N
and monolayer B
N
. The newly proposed monolayer B
N
is a potential candidate for designing optoelectronic devices such as transparent electrodes due to its high transmissivity.
An ordered hollow MoS
2
nanocages/RGO nanocomposite is constructed by a simple solvothermal-assisted assembly method combined with freeze-drying and annealing. In this novel nanostructure, hollow MoS
...2
nanocages are homogeneously distributed on graphene sheets with a tight bond of C-O-Mo. The nanosized and hollow MoS
2
nanocages can effectively accommodate the huge volume change during charge/discharge process and increase the number of electrochemical reaction active sites, accelerating the kinetics of lithiation/delithiation. The tight C-O-Mo bond between graphene and MoS
2
further reinforces the structural stability, thus improve the electrical conductivity and substantially enhance the lithium storage performance of MoS
2
anode material. As a result, this novel nanocomposite shows a long-cycle stability of 717.4 mAhg
−1
after 800 cycles at a high current density of 3 Ag
−1
, exhibiting great potential as an anode nanocomposite for advanced lithiumion batteries.
Lithium metal batteries (LMBs) are considered to be a substitute for lithium-ion batteries (LIBs) and the next-generation battery with high energy density. However, the commercialization of LMBs is ...seriously impeded by the uncontrollable growth of dangerous lithium dendrites during long-term cycling. The generation and growth of lithium dendrites are mainly derived from the unstable solid-electrolyte interphase (SEI) layer on the metallic lithium anode. The SEI layer is a key by-product formed on the surface of the lithium metal anode during the electrochemical reactions and has been the barrier to development in this area. An ideal SEI layer should possess electrical insulating, superior mechanical modulus, high electrochemical stability, and excellent Li-ion conductivity, which could improve the structural stability of the electrode upon a long cycling time. This mini-review carefully summarizes the recent developments in the SEI layer for LMBs, and the relationship between SEI layer optimization and electrochemical property is discussed. In addition, further development direction of a stable SEI layer is proposed.
The physiological role of miRNAs is widely understood to include fine-tuning the post-transcriptional regulation of a wide array of biological processes. Extensive studies have indicated that ...exosomal miRNAs in the bodily fluids of various organisms can be transferred between living cells for the delivery of gene silencing signals. Here, we illustrated the expression characteristics of exosomal miRNAs in giant panda breast milk during distinct lactation periods and highlighted the enrichment of immune- and development-related endogenous miRNAs in colostral and mature giant panda milk. These miRNAs are stable, even under certain harsh conditions, via the protection of extracellular vesicles. These findings indicate that breast milk may facilitate the dietary intake of maternal miRNAs by infants for the regulation of postnatal development. We also detected exogenous plant miRNAs from the primary food source of the giant panda (bamboo) in the exosomes of giant panda breast milk that were associated with regulatory roles in basic metabolism and neuron development. This result suggested that dietary plant miRNAs are absorbed by host cells and subsequently secreted into bodily fluids as potential cross-kingdom regulators. In conclusion, exosomal miRNAs in giant panda breast milk may be crucial maternal regulators for the development of intrinsic 'slink' newborn cubs.
Glucose metabolism is a basic biological process that shows substantial variation within and between species. Using pig as a model organism, we investigated differences in glucose metabolic genes in ...seven tissues from domesticated pigs (Rongchang pig and Tibetan pig, meanwhile, the Tibetan pig just as a special case of the domesticated pig under plateau condition) and wild boar. We found large differences in the expression of genes involved in multiple aspects of glucose metabolism, including genes associated with glucose transport, gluconeogenesis, and glycolysis. In addition, we identified microRNAs (miRNAs) that may be involved in the divergence of glucose metabolism in pig. A combined analysis of mRNA and miRNA expression indicated that some miRNA:mRNA pairs showed ab facto function in it. Our results provide a valuable resource for further determination of miRNA regulatory roles in pig glucose metabolism and reveal the divergence of glucose metabolism in pigs under domestication.
•Octagonal-C (-Si) and dodecagonal-C (-Si) are four novel two-dimensional carbon or silicon monolayer materials with sp2-like hybrid chemical bonds.•Octagonal-C (-Si) and dodecagonal-C (-Si) have ...good mechanical and dynamic stability.•Dodecagonal-C has very small band gap of 0.09 eV, and it can be a candidate for commercial optical filters and infrared detectors.
Two-dimensional materials play increasingly important roles in the fields of electronic and photoelectric applications. Four two-dimensional carbon and silicon monolayers with sp2-like hybrid chemical bonds have been predicted by the first-principles calculations based on density functional theory in the current work. One type of two-dimensional monolayer materials is composed of four- and eight-membered rings called octagonal-C and octagonal-Si, and another type of two-dimensional structures consists of regular triangles and twelve-membered rings named dodecagonal-C and dodecagonal-Si. The theoretical phonon dispersions show that all predicted structures are dynamically stable. The molecular dynamics simulation confirms that octagonal-C (-Si) and dodecagonal-C have good thermal stability to maintain their crystal structures lower than 1000 K, while dodecagonal-Si has slightly worse thermal stability. The analysis of electron density differences manifests that the covalent C-C and Si-Si bonds are dominant in these two-dimensional monolayer structures. All these four structures are mechanically stable, and the mechanical properties of octagonal-C are superior to the other three. The electronic band structures indicate that octagonal-C (-Si) and dodecagonal-Si are metallic. Interestingly, dodecagonal-C has a very small band gap of 0.09 eV, and it maybe have potential applications in infrared optical devices such as commercial optical filters and infrared detectors.
Extensive and in-depth investigations of high-altitude adaptation have been carried out at the level of morphology, anatomy, physiology and genomics, but few investigations focused on the roles of ...microRNA (miRNA) in high-altitude adaptation. We examined the differences in the miRNA transcriptomes of two representative hypoxia-sensitive tissues (heart and lung) between yak and cattle, two closely related species that live in high and low altitudes, respectively. In this study, we identified a total of 808 mature miRNAs, which corresponded to 715 pre-miRNAs in the two species. The further analysis revealed that both tissues showed relatively high correlation coefficient between yak and cattle, but a greater differentiation was present in lung than heart between the two species. In addition, miRNAs with significantly differentiated patterns of expression in two tissues exhibited co-operation effect in high altitude adaptation based on miRNA family and cluster. Functional analysis revealed that differentially expressed miRNAs were enriched in hypoxia-related pathways, such as the HIF-1α signaling pathway, the insulin signaling pathway, the PI3K-Akt signaling pathway, nucleotide excision repair, cell cycle, apoptosis and fatty acid metabolism, which indicated the important roles of miRNAs in high altitude adaptation. These results suggested the diverse degrees of miRNA transcriptome variation in different tissues between yak and cattle, and suggested extensive roles of miRNAs in high altitude adaptation.
•Crystal structures and physical properties of Cs2Au2X6 were figured out.•AuX2− and AuX4− clusters dominate dielectric properties of Cs2Au2X6.•Cs2Au2X6 with direct band gaps have wide visible light ...absorption.•Cs2Au2X6 possess potential applications as solar cells.
In this work, we investigate the X-dependent crystal, electronic, elastic and optical properties of mixed-valence double perovskites Cs2Au2X6 (X=F, Cl, Br, I) based on first principles. The effects of all atomic sites, especially the AuX2− and AuX4− clusters with different valences of Au atoms, in the crystal structures of Cs2Au2X6 on their electronic and optical properties have been clarified. Meanwhile, Cs2Au2X6 double perovskites with direct band gaps have strong absorptions, low loss functions and low reflections, and they promise to be used as photoelectric absorption layers of solar cells.
High-capacity cathode materials of metal fluorides generally undergo low conductivities and sluggish kinetics derived from a multielectron-transfer conversion reaction mechanism, which severely ...hinder the cycling stability and rate performance towards their commercialization. Herein, a flexible free-standing FeF3/chitosan pyrolytic carbon/reduced graphene oxide (FeF3/C/RGO) film as an additive-free cathode was designed and prepared by a facile hydrothermal strategy followed by sequential freeze-drying, thermal reduction and fluorination post-treatments. The ultrafine FeF3 nanoparticles (NPs, ~30 nm) are confined within highly ordered RGO film, effectively reducing the Li+ diffusion pathway while the RGO sheets act as a matrix to restrict the complicated interlamination reaction (Fe3+⇄Fe2+⇄Fe) between adjacent interlayers with the spacing of ~30 nm. Benefiting from the free-standing structure, the FeF3/C/RGO film can achieve an admirable capacity up to 220 mAh g–1 over 200 cycles at 100 mA g–1, showing great potential for wearable and flexible electronic devices.
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•A flexible free-standing FeF3/C/RGO film was prepared by a facile strategy.•This film was fabricated by the covalent cross-linking effect of chitosan with GO.•The film delivers a long-term stability of 220 mAh g−1 over 200 cycles.•This novel free-standing film exhibits great potential for high-performance LIBs.
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