Search

Aroused by plant photosynthesis, Z-scheme heterostructures have been considered as a potential photocatalyst for solar-driven water splitting to solve the current energy crisis. Hence, based on first-principles calculations, we predict that Sc2CF2/Janus MoSSe can be used as a Z-scheme heterostructure for efficient photocatalytic water splitting. The research shows that the traditional type-II to direct Z-scheme heterostructure conversion can be realized through different stacking methods of Sc2CF2 and Janus MoSSe. Through the built-in electric field and band bending theory, the transition path of photogenerated carriers is analyzed, which reveals the completely different photocatalytic mechanism of type-II and direct Z-scheme heterostructure. Surprisingly, the direct Z-scheme heterostructure displays a high overpotential of the hydrogen evolution reaction ( χ H 2 =1.01 eV) and the oxygen evolution reaction ( χ O 2 =1.46 eV) compared with the type II heterostructure. More importantly, the direct Z-scheme heterostructure has an ultra-high solar-to-hydrogen (STH) efficiency (36.1%), which breaks through the limitation of traditional theoretical efficiency and reveals a tremendous prospect of commercial application. Furthermore, the calculation of free energy confirms that the water splitting reaction on the direct Z-scheme heterostructure occur spontaneously under the external potential, but not for type-II heterostructure. Finally, introducing the additional electronic conductor (N-doped graphene) can accelerate the electron (hole) transfer and interlayer carrier recombination, which will further improve the photocatalytic performance of Z-scheme heterostructure. These distinctive features make Sc2CF2/Janus MoSSe heterostructure as promising Z-scheme photocatalyst for water splitting.

In this work, we explore the application potential of AsP/M2CO2 (M = Sc, Zr) van der Waals heterostructures in photocatalytic water splitting through the first-principles calculations. The calculated results show that AsP/Zr2CO2 heterostructure possesses an unfavorable type-Ⅰ band alignment, whereas AsP/Sc2CO2 exhibits a desirable type-Ⅱ band alignment, which is beneficial for separating the photogenerated electron-hole pairs. Also, the band edge positions of AsP/Sc2CO2 heterostructure stride the redox potential of water, ensuring favorable reaction kinetics. Besides, the strong optical absorption of AsP/Sc2CO2 heterostructure in both visible and ultraviolet regions (especially up to 10−6 cm−1 at about 250 nm) makes it possible to utilize solar energy effectively. Meanwhile, AsP/Sc2CO2 heterostructure has an exciton binding energy as low as 0.09 eV, which quantitatively illustrates the high separation efficiency of photogenerated charge carrier. Thus, the type-Ⅱ band alignment, suitable band edge position, strong light absorption, and low exciton binding energy together indicate that AsP/Sc2CO2 heterostructure is a potential photocatalytic material. In addition, the obvious redshift phenomenon in the optical spectrum of AsP/Sc2CO2 heterostructure shows that biaxial strain can improve its light capture capability. Also, the interconversion between type-Ⅱ and type-Ⅰ can be achieved by applying different strains. All these findings suggest that the novel AsP/Sc2CO2 heterostructure has significant application prospects in next-generation photovoltaic and photocatalytic devices.

The chemical modulation associated with moiré patterns, arising at the interface of metal-supported 2D material systems, affects the interaction between molecules and 2D materials on surfaces. Since the crystallography of the support influences the interfacial chemistry of the moiré modulation, this parameter could also play a role in the graphene-molecule interaction, although studies using non-hexagonal metal supports are needed to investigate this effect. It is a key issue since graphene appears combined with organic films in most technological advances related to this material. Here, we have characterized the properties of PTCDA molecules on graphene grown on Rh(110) substrates, which exhibit a rectangular atomic packing, using scanning tunneling microscopy and spectroscopy. The results showed that PTCDA molecules are arranged on the surface into a herringbone structure exhibiting a long-range ordering, which grows continuously across substrate atomic steps edge and dislocations. The quasi-1D moiré patterns of the Gr/Rh(110) surfaces are found to provide an inert chemical landscape for the molecular arrangement. Bias voltage-dependent imaging of the orbital structure of PTCDA molecules and differential conductance spectra back up a weak molecule–substrate interaction scheme. Finally, the α-polymorph of bulk crystal PTCDA has been determined as the favored stacking configuration for bilayer molecules on Gr/Rh(110), Financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) and Fondo Europeo de Desarrollo Regional (FEDER) under grant No. MAT2016-77852-C2-2-R, as well as, from the Spanish Ministerio de Ciencia e Innovacion ´ (MICINN) through the “María de Maetzu” program for units of excellence in R&D (grant No. CEX2018-000805-M) is gratefully acknowledged. A. J. M.-G. acknowledges funding by the Spanish Ministerio de Ciencia e Innovacion ´ (MICINN) through Project No. PID2020-116619GA-C22, as well as, from the Comunidad de Madrid and the Universidad Autonoma ´ de Madrid under project SI3/PJI/2021- 00500

Objective Schisandra sphenanthera and S. chinensis are the two important medicinal plants that have long been used under the names of “Nan-Wuweizi” and “Wuweizi”, respectively. The misuse of “Nan-Wuweizi” and “Wuweizi” in herbal medical products calls for an accurate method to distinguish these herbs. Chloroplast (cp) genomes have been widely used in species delimitation and phylogeny due to their uniparental inheritance and lower substitution rates than that of the nuclear genomes. To develop more efficient DNA markers for distinguishing S. sphenanthera, S. chinensis, and the related species, we sequenced the cp genome of S. sphenanthera and compared it to that of S. chinensis. Methods The cp genome of S. sphenanthera was sequenced at the Illumina HiSeq platform, and the reference-guided mapping of contigs was obtained with a de novo assembly procedure. Then, comparative analyses of the cp genomes of S. sphenanthera and S. chinensis were carried out. Results The cp genome of S. sphenanthera was 146 853 bp in length and consisted of a large single copy (LSC) region of 95 627 bp, a small single copy (SSC) region of 18 292 bp, and a pair of inverted repeats (IR) of 16 467 bp. GC content was 39.6%. A total of 126 functional genes were predicted, of which 113 genes were unique, including 79 protein-coding genes, 30 transfer RNA (tRNA) genes, and four ribosomal RNA (rRNA) genes. Five tRNA, four protein-coding genes, and all rRNA were duplicated in the IR regions. There were 18 intron-containing genes, including six tRNA genes and 12 protein-coding genes. In addition, 45 SSRs were detected. The whole cp genome of S. sphenanthera was 123 bp longer than that of S. chinensis. A total of 474 SNPs and 97 InDels were identified. Five genetic regions with high levels of variation (Pi > 0.015), trnS-trnG, ccsA-ndhD, psbI-trnS, trnT-psbD and ndhF-rpl32 were revealed. Conclusion We reported the cp genome of S. sphenanthera and revealed the SNPs and InDels between the cp genomes of S. sphenanthera and S. chinensis. This study shed light on the species identification and further phylogenetic study within the genus of Schisandra.

Agricultural soils are a dominant source of atmospheric nitrous oxide (N2O). A clear understanding of N2O emission from fruit cropping systems is urgently needed to improve the global budget and establish mitigation options. The primary aims of this study were to (i) quantify the variations in N2O emissions from fruit orchards, (ii) evaluate the major controls of N2O emissions, and (iii) discuss potential mitigation strategies across climates, soil types and field managements. We summarized 123 determinations of N2O emissions under perennial fruit trees from peer-reviewed publications from 1997 to 2019, with measurement periods covering at least one whole growing season. Cumulative N2O emissions ranged widely from −0.116–26 kg N ha−1 per year or growing season and increased linearly with nitrogen (N) fertilizer input rates on a global basis (r2 = 0.39, p

The piezoelectric properties of two-dimensional (2D) Janus ZnBrI are predicted by the multiscale method. Based on the density functional theory, the electronic properties and piezoelectric coefficients of 2D Janus ZnBrI are calculated. It is found that the 2D Janus ZnBrI has a large in-plane piezoelectric coefficient d 11 , up to 145.85 pm/V, which is about 40 times that of 2D 2H-MoS 2 . Based on the finite element method and multi-physical field simulation, the large piezoelectric response of 2D Janus ZnBrI is shown intuitively. Based on the nonequilibrium Green's function, the device model of metal-semiconductor-metal is established, and the I-V response of the device model is calculated, which shows the modulation of piezoelectric effect on tunneling current. The simulation results show that 2D Janus ZnBrI is a 2D piezoelectric material with application potential. This multiscale prediction method can comprehensively predict other 2D piezoelectric materials.

Cyanide gases are colorless and toxic gases, which are widely used in the industry, thus efficiently detecting them has become a pressing issue. The sensitivity and selectivity of β-tellurene toward cyanide gases are reported in this work. Adsorption energy, charge transfer, and electronic properties of the cyanide gases (HCN, (CN)2, CNBr) as well as common gases (CO2, N2, CO) adsorption systems are calculated based on the density functional theory (DFT). The significantly larger adsorption energy (−0.26 eV for HCN, −0.36 eV for CNBr) and charge transfer (0.11 |e| for HCN, 0.10 |e| for CNBr) show that the tellurene is a well sensitive material for cyanide gases detection. The change of I–V curves made by gas adsorption further confirms the selectivity and sensitivity of tellurene to cyanide gases, especially the HCN. Moreover, different biaxial strains could effectively regulate the adsorption behavior of cyanide gases on tellurene, as the adsorption energy of the HCN molecule is enhanced to be −0.52 eV. Based on these results, we predict that tellurene could be a practical material to detect cyanide gases.

In this study, we propose an innovative Hf2CO2/WS2 heterostructure with excellent photocatalytic performance for water splitting based on first-principles calculations. The binding energy, and ab initio molecular dynamics (AIMD) simulations exhibit this material's excellent ambient stability. Furthermore, the band structure confirms that the Hf2CO2/WS2 heterostructure possesses the intrinsic type-II semiconductor and are well satisfied with the requirements of redox energy level in water splitting reaction. Meanwhile, the charge transfer occurs from Hf2CO2 to WS2 monolayer, which further induces the separation of photogenerated carriers and prolong the lifetime of carriers. Dramatically high visible-light absorption (~6.3 × 105 cm−1) and carrier mobility (~2.2 × 103 cm2 V-1 s-1) are found, which means that the heterostructure has adequate motive force to make the photogenerated carriers separate into different monolayers quickly before recombination. Moreover, according to Gibbs free energy calculation, HER and OER can be triggered spontaneously under the driving of external potential. The results confirm that the thermodynamic feasibility of water splitting on Hf2CO2/WS2 heterostructure surface. Hence, these distinctive features endow Hf2CO2/WS2 heterostructure with the potential ability of photocatalytic water splitting, which provides a potential avenue for the future experimental project.

Zinc–cobalt slag, a hazardous waste from hydrometallurgical zinc smelting, is an important secondary source of cobalt; however, the separation of zinc and cobalt is a serious problem in cobalt recovery. A novel approach was proposed to separate zinc and cobalt via an alkaline glycine solution. This innovative method selectively dissolves zinc and cadmium from the slag with a high yield, leaving most of the cobalt and manganese in the residue. The dissolution ratios of zinc and cadmium are 93.81% and 87.64%, respectively, under optimal conditions (pH 10, 45 °C, glycine concentration of 100 g/L, L/S ratio of 40:1, and a reaction time of 180 min). In contrast, the dissolution ratios of cobalt and manganese are almost negligible. Substantial separation of zinc and cobalt occurred as the separation factor reached a value of 736.8. The recovery of zinc and cadmium from the glycine leachate was accomplished by precipitation with an oxalic acid solution, and the precipitation ratios were 97.7% and 99.0%, respectively. The use of glycine as the leaching agent successfully separated zinc and cobalt, which allowed for the recovery of cobalt, and also enabled the recovery of zinc and cadmium.

Thermoelectric devices based on thermoelectric materials, which can be utilized to transform heat to electric energy, are regarded as the clean and reliable energy-harvestings that reduce greenhouse gas and noxious gas missions. In this work, thermoelectric properties of square-Ag2X (X = S, Se) monolayers have been systematically studied through uniting Boltzmann transport theory and first-principles. The results show that square-Ag2X (X = S, Se) monolayers possess ultrahigh electrical conductivities due to their ultralight electron effective masses, together with high Seebeck coefficients, resulting in ultrahigh power factors (0.014 and 0.018 W/m K2). Moreover, phonon transport calculations unveil that square-Ag2X (X = S, Se) monolayers exhibit low lattice thermal conductivities (3.46 and 2.33 W/m K) at 300 K, which can be traced back to their small Debye temperature, low acoustic group velocities, short phonon relaxation times and large Gruneisen parameters. Accordingly, the obtained figure of merit of monolayer square-Ag2Se for optimal n-type doping at 700 K can approach 2.81, which is larger than the well-known n-type thermoelectric monolayer SnSe (2.32) and Mg3Sb2 (2.21). Therefore, the excellent thermoelectric properties of square-Ag2Se monolayer along with its all-round stability verified by the phonon dispersion, ab initio molecular dynamic simulation and accordance of Born–Huang criteria highlight its prominent potential for thermoelectric applications.

Cu paste has been considered as the most promising die-attach material for high-power devices. To investigate the influences of Cu paste layer thickness on bonding qualities of joint, the large-area joints (10 × 10 mm2) were bonded by multiscale Cu paste with a layer thickness varying from 30 to 200 μm, and the mechanical properties and microstructure characteristics of joints were analyzed. A layer thickness between 80 and 100 μm is considered the optimal thickness, in which, the shear strength of joint reaches the maximum value of 26.1Mpa and the bond layer is the most tightly connected. We believe that a suitable thickness not only ensures the complete sintered of the Cu particles, but also inhibits the coursing on the pores, which enhance the joint bonding strength. The results of this work help to determine the thickness of paste and are useful for power electronics packaging.

Li-garnet Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for lithium metal batteries owing to its excellent stability and high ionic conductivity. However, there exists serious lithium dendrite problem in LLZO electrolyte under elevated current density, easily leading to internal short-circuit and poor cycling performance. In this work, we demonstrated that Ta-doped LLZO with 4 wt% MgO additive delivered superior endurance to lithium dendrite due to its improved mechanical properties and lower electronic conductivity. The critical current density (CCD) of LLZTO-MgO composite electrolyte reached as high as 1.95 mA⸳cm−2 at room temperature (RT). It also realized stable lithium plating/stripping performance for 1000h under 0.5 mA⸳cm−2. Moreover, the full cell paired with LiNi0·6Co0·2Mn0·2O2 cathode exhibited better cycling stability especially at a high rate. Our work provided an alternative strategy for dendrite-suppression in solid electrolyte besides interfacial modification.

This paper presents an improved semantic segmentation model for medical images named PRDNet. Common semantic segmentation algorithms only feed the features of the last layer of convolutional neural network into the decoder, which results in the position information of the first several layers of convolutional neural network is not utilized. While in our work, ResNet and dilated convolution are simultaneously used to extract multi-layer features of medical images in parallel. In the decoding stage, the multi-layer features are fused according to the structure of feature pyramid network. Moreover, several classic semantic segmentation algorithms were selected for comparison, such as UNet, Attention UNet, FPN, Deeplab v3, SENet and DANet. After a series of experiments on CHAOS and ISIC2017 datasets, the algorithm proposed by us has a 1%–4% improvement in different evaluation metrics compared with other algorithms.

To extend the application range of h-BN monolayer which possesses a wide bandgap (5.9 eV), constructing lateral heterostructures is proved to be a feasible and novel method. Here, considering C3B monolayer possessing an indirect narrow bandgap (0.67 eV), the lateral heterostructure is proposed by using h-BN monolayer to hybridize with C3B monolayer. The structural, electronic, optical and transport properties of the h-BN/C3B lateral heterostructures are systematically investigated by performing first-principles calculation. The calculated results demonstrate that the electronic properties of the studied lateral heterostructures can be easily modulated by strain and external electric field. Specifically, the (ABNM)2-(AC3BM)2 exhibits metal-to-semiconductor transition under different strain conditions and the bandgap of the (ABNM)2-(AC3BM)2 can be adjusted from 1.03 to 2.62 eV by applying external electric field vertically. In addition, the optical calculations reveal that (ABNM)2-(AC3BM)n behave outstanding optical-absorption capacity in visible region. Furthermore, the calculated asymmetrical carrier effective masses suggest that the migratory directions of electron and hole are parallel to the interface. These highly-tunable electronic properties and favorable optical performances of the (ABNM)2-(AC3BM)n lateral heterojunctions may facilitate their practical applications for nanoelectronics and optoelectronics.

We theoretically explored the possibility of monolayer tellurene detecting nucleobases and amino acids by means of first-principles calculation. The obvious differences of adsorption energy between nucleobases indicate that monolayer tellurene can be used for DNA sequencing. The order of adsorption strength is G > A > C > T > U. Moreover, monolayer tellurene exhibits more excellent sensing performance to TYR, PHE and TRP than to HIS, which means that tellurene can be used for detecting amino acids. Besides, we explored the adsorption mechanism of nucleobases and amino acids on tellurene by ELF, which demonstrate nucleobases and amino acids are all physically adsorbed on tellurene. The calculated results of PDOS show that orbital hybridization is the primary cause of charge transfer between each biomolecule and monolayer tellurene. Furthermore, the results of absorption coefficient and refractive index further prove that tellurene can detect nucleobases and amino acids. Therefore, we conclude that monolayer tellurene can be a promising candidate for biosensor to detect nucleobases and amino acids.

We theoretically explored the possibility of monolayer antimonide phosphorus (SbP) detecting SF6 decomposition components based on the first-principles calculations. The calculated results indicate that monolayer SbP exhibits more excellent gas sensing performance to SO2 than to other gas molecules, with the adsorption energy of −0.541 eV and the charge transfer of −0.232 e. In addition, we predict that SbP is suitable for SO2 sensing to detect SF6 decompositions by comparing adsorption energy and charge transfer of different substrates. Therefore, monolayer SbP can be a promising candidate for high sensitivity SO2 sensor to detect SF6 decompositions.

Electroshock treatment (EST) can influence the microstructure of a material in a short time through the coupling of the thermal and nonthermal effects of a high-density pulsed current. In this study, a Ti-55531 near-β titanium alloy manufactured by a laser-based directed energy deposition was processed via EST, and the microstructure was characterized via scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). After the EST, small subgrains were precipitated in the large columnar β grains. With an increase in the EST time, the α phase precipitated along the grain boundary tended to grow, the curvature radius of the α tips increased, and distinct spheroidization occurred. The EBSD results indicated that after the EST, the maximum texture intensity of the β phase decreased from 23.18 to 13.15, and the texture intensity exhibited a uniform distribution. The foregoing results were attributed to the thermal and nonthermal effects of the EST, which led to an energy concentration on the tips of the needle-like α phase and the phase transformation of the tips. When the high current passes through the sample, both the thermal and nonthermal effects are introduced, the thermal effect cause the increase of sample's temperature, and the nonthermal effect shows as the form of special forces such as the electrostatic and electronic wind forces, which can influence the movement of dislocation. This work is expected to provide a new method for optimizing the microstructure of the near-β titanium alloys manufactured by a laser-based directed energy deposition.

Despite the ever-increasing measurements of denitrification and nitrous oxide (N2O) emissions globally, boundary line analyses of these important processes have only been applied to a limited number of agroecosystems. The primary aims of this study were to determine the responses of denitrification and N2O emissions from a subtropical cropland to several soil parameters through boundary line analyses, and to evaluate the ability of site-specific boundary line models for simulating gaseous nitrogen (N) losses using available soil parameters. We performed 403 measurements of denitrification and N2O emissions from two fields cropped with a winter wheat-summer maize rotation in the Sichuan Basin, Southwest China, from October 2004 to September 2005. Boundary lines were fitted for denitrification and N2O emission data against soil temperature, water content, ammonium and/or nitrate substrates, and heterotrophic respiration rates. The boundary lines were largely in agreement with existing theoretical concepts. By incorporating the regulatory effects of soil temperature, water content, N substrates, and an unknown factor that could be related to ammonium content, the boundary line models reasonably simulated the seasonal variations in denitrification and N2O emissions that were collected from a field trial in the same region during the maize season in 2012. The models overestimated the denitrification and N2O emissions on the sampling dates by 8% and 22% on average, respectively. We conclude that boundary line models are useful tools for estimating gaseous N losses from a given cropland. However, the application of the models is limited by the availability of input data.

This paper studies a un-stirred chemostat with two species competing for two growth-limiting, non-reproducing resources. We determine the conditions for positive steady states of the two species, and then consider the global attractors of the model. In addition, we obtain the conditions under which the two populations uniformly strongly persist or go to extinction. Since the diffusion mechanism with homogeneous boundary conditions inhibits the growth of the organism species, it can be understood that the coexistence will be ensured by proportionally smaller diffusions for the two species. In particular, it is found that both instability and bi-stability subcases of the two semitrivial steady states are included in the coexistence region. The two populations will go to extinction when both possess large diffusion rates. If just one of them spreads faster with the other one diffusing slower, then the related semitrivial steady state will be globally attracting. The techniques used for the above results consist of the degree theory, the semigroup theory, and the maximum principle.

This paper deals with a multiple food chain model in un-stirred chemostat, where the prey feeds on two growth-limiting, nonreproducing resources. The conditions for existence of positive steady states are established. The global bifurcation of positive solutions is considered also. Furthermore, we obtain the conditions under which the predator possesses uniformly strong persistence or goes to extinction. The techniques used in this paper include the degree theory, the global bifurcation theory, the semigroup theory, and the maximum principle.