Graphene effectively activating "dead" water molecules between manganese dioxide layers in potassium-ion battery

Aqueous potassium-ion batteries(APIBs),recognized as safe and reliable new energy devices,are considered as one of the alternatives to traditional batteries.Layered MnO_(2),serving as the main cathode,exhibits a lower specific capacity in aqueous electrolytes compared to organic systems and operates through a different reaction mechanism.The application of highly conductive graphene may effectively enhance the capacity of APIBs but could complicate the potassium storage environment.In this study,a MnO_(2) cathode pre-intercalated with K~+ions and grown on graphene(KMO@rGO) was developed using the microwave hydrothermal method for APIBs.KMO@rGO achieved a specific capacity of 90 mA h g^(-1) at a current density of 0.1 A g^(-1),maintaining a capacity retention rate of>90% after 5000 cycles at 5 A g^(-1).In-situ and exsitu characterization techniques revealed the energy-storage mechanism of KMO@rGO:layered MnO_(2)traps a large amount of "dead" water molecules during K~+ions removal.However,the introduction of graphene enables these water molecules to escape during K~+ ions insertion at the cathode.The galvanostatic intermittent titration technique and density functional theory confirmed that KMO@rGO has a higher K~+ions migration rate than MnO_(2).Therefore,the capacity of this cathode depends on the interaction between dead water and K~+ions during the energy-storage reaction.The optimal structural alignment between layered MnO_(2) and graphene allows electrons to easily flow into the external circuit.Rapid charge compensation forces numerous low-solvent K~+ions to displace interlayer dead water,enhancing the capacity.This unique reaction mechanism is unprecedented in other aqueous battery studies.

Photovoltaic Properties of the Modified n-Si(111) Electrodes with Ethyl and Carboxyls

n-Si（111） surface tailed -C2H5, -C2H4COOH, -C2H2COOH were prepared by the reactions among Si-H to ethyl-Grignard, methyl acrylate and ethyl propionate, and the carboxyls were formed under the existence of trifluoroacetic acid. The composite n-Si（111） electrodes were obtained by depositing Pt nanodots and the photovoltaic characteristics for these electrodes were studied in I^-/I3^- redox electrolyte. The j-U （photo current density-potential） behaviors of photo-voltage and photocurrent densities to the electrodes under solar illumination varied regularly with groups of -C2H2COOH〉-C2H4COOH〉-H〉-C2H5. The photo-voltage and photocurrent density of the electrode tailed -C2 H2COOH were -0.641 V and 5.25 mA/cm^2, respectively, more negative than those of the non-conjugated modification.

Mechanism investigation of A-site doping on modulating electronic band structure and photocatalytic performance towards CO_(2) reduction of LaFeO_(3) perovskite

Three kinds of metal atoms with different valence electronic configurations,Bi(6s^(2)6p^(3)),Y(4d^(1)5s^(2)),and Ce(4f^(1)5d^(1)6s^(2)),were selected to investigate the effect of A-site(La^(3+))doping on electronic band structure,photoelectric properties,and photocatalytic performance of LaFeO_(3) perovskite.It was identified that the Bi doped LaFeO_(3) presented significantly improved photocatalytic activity towards the reduction of CO_(2),while the Y or Ce doped LaFeO_(3) displayed decreased photocatalytic activity compared to the pristine LaFeO_(3).It was revealed that doping of all the three metal atoms resulted in narrowed band gap and thus extended light absorption of LaFeO_(3) by lowering its conduction band minimum(CBM).The recombination rate and mobility of the charge carriers were represented by the relative effective mass(D)between holes and electrons for pristine and A-site doped LaFeO_(3).The doping of Bi resulted in increased D value,attributed to the Bi 6s electron states at the valence band maximum(VBM),and thus promoted separation and transfer of the charge carriers and improved photocatalytic activity of LaFeO_(3).In contrast,the doping of Ce resulted in significantly decreased D value,induced by the highly localized Ce 4f hole states at the CBM,and thus higher recombination rate of the charge carriers and decreased photocatalytic activity of LaFeO_(3).Furthermore,the Y doped LaFeO_(3) with a slightly decreased D value presented slightly increased recombination rate of the charge carriers and thus decreased photocatalytic activity.Such a work provides new insights into the A-site doping in LaFeO_(3) perovskite,which should be helpful for optimizing the electronic band structure and activity of perovskite-type photocatalysts at atomic level.

Tungsten separation behavior on preparation of high-purity cerium by combined vacuum gravity sedimentation-directional solidification

In light of the difficult removal of harmful impurity tungsten(W)in Ce metal,in this paper a combined vacuum gravity sedimentation-directional solidification method was innovatively designed and the W separation behavior was investigated.By reducing the electron beam power instantly and gradually at reduction rates of 1,3 and 5 kW/min,it is found that W is enriched at the bottom of ingots as the melt solidifies.The enrichment effect is much better than that of single purification method and the enrichment degree increases as the beam reduction rate decreases,attributed to the k0(W)>1 andρ(W)>ρ(Ce).Overall,the minimum content of W impurity can decrease from 630 to 0.1 ppm at the top of the ingot,and the purity of Ce increases from 99.932 wt%to 99.995 wt%by this combined method.Additionally,this paper provides a new method for the removal of high density and low evaporation coefficient impurities in low vapor pressure rare earth metals.

Dihydroanthracene bridged bis-naphthopyrans:A multimodal chromophore with mechano-and photo-chromic properties

Mechanochromophores based on bichromic molecular switches,such as bis-naphthopyanes,allow multimodal mechanochromic behavior beyond the typical binary response from single chromophores,which is important for distinguishing between multiple stress states through discrete changes in color.Spontaneously generated persistent and distinguishable multi-colors from activated bis-naphthopyanes remain challenging.And the versatility of bis-mechanophore design for advanced optical molecular systems and the fundamental insights into the corresponding mechano-reactivity are not enough.Here,we identify a dihydroanthracene bridged bis-naphthopyrans as a multimodal mechanochromophore in polymers.Bridging two pyrans with the sterically constrained dihydroanthracene is helpful to control the steric effect for the favorable formation of a distinctly appreciable bis-merocyanine(bis-MC)product.By varying the length of the polymer chains,the force delivered to the mechanophore is modulated,resulting in a gradient change in the relative distribution of two distinctly colored MC products and a multicolor mechanochromism.Mechanical activation of this bis-naphthopyanes proceeds via a mechanistically distinct pathway compared to the photochemical process.In addition,the bulk films can also achieve pronounced color changes when subjected to mechanical force.This study thus further expands the molecular diversity of mechanochromophores and tune the multimodal switch properties of bis-naphthopyrans based polymers.

High expression of GPR160 in prostate cancer is unrelated to CARTp-mediated signaling pathways

To the Editor:G protein-coupled receptors(GPCRs)are the largest group of membrane proteins with over 800 members,characteristic of a seven transmembrane domain1.By playing crucial roles in regulation of various physiological processes,GPCRs have been implicated in many diseases including diabetes,obesity,depression and cancer.To initiate different intracellular responses,GPCRs mainly interact with three families of effector proteins upon agonist binding:the heterotrimeric G proteins,G protein-coupled receptor kinases(GRKs)and arrestins1.

World’s first implementation of close-fit pipe jacking of twin tunnels for construction of subway station--Innovation in equipment and construction technology

1 Project overview The Shasan station of Phase II of Shenzhen’s urban rail transit Line 12 is situated in Bao’an District,Shenzhen.It comprises a two-level underground island platform station,measuring 212 m in length,and 22.6 m in width,with an overburden thickness of about 7.0 m.Fig.1 illustrates the presence of a large underground reinforced concrete stormwater culvert,measuring 11.5 m by 3.6 m,traversing the station’s center.

A facile method to introduce a donor-acceptor system into polymeric carbon nitride for efficient photocatalytic overall water splitting

It is a prospective strategy to produce sustainable energy by photocatalytic overall water splitting(POWS).This work aims to develop a simple method for integrating a donor-acceptor system into polymeric car-bon nitride(PCN)structure,which could accelerate the charge separation significantly.In the as-prepared photocatalyst(COCNT),carbon and oxygen were successfully incorporated into the framework of PCN,and the chemical environment of C and O was well probed by X-ray absorption near-edge structure(XANES)and X-ray photoelectron spectroscopy(XPS).It showed that the C-containing and O-containing segments of COCNT played the role of a donor,while the heptazine part played the role of an acceptor.In addition,Density-functional-theory(DFT)calculations confirmed the spatial split of the highest occupied molec-ular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)for promoting charge separation.Impressively,COCNT could efficiently split pure water to generate hydrogen and oxygen.And,the photo-catalytic hydrogen evolution rate over COCNT(1550.9μmol g^(-1)h^(-1))is about 17-fold higher than that of PCN.Finally,we proposed a possible photocatalytic mechanism to explain the above results.

The impact of fear effect on the dynamics of a delayed predator-prey model with stage structure

In this paper,a stage structure predator-prey model consisting of three nonlinear ordinary differential equations is proposed and analyzed.The prey populations are divided into two parts:juvenile prey and adult prey.From extensive experimental data,it has been found that prey fear of predators can alter the physiological behavior of individual prey,and the fear effect reduces their reproductive rate and increases their mortality.In addition,we also consider the presence of constant ratio refuge in adult prey populations.Moreover,we consider the existence of intraspecific competition between adult prey species and predator species separately in our model and also introduce the gestation delay of predators to obtain a more realistic and natural eco-dynamic behaviors.We study the positivity and boundedness of the solution of the non-delayed system and analyze the existence of various equilibria and the stability of the system at these equilibria.Next by choosing the intra-specific competition coeficient of adult prey as bifurcation parameter,we demonstrate that Hopf bifurcation may occur near the positive equilibrium point.Then by taking the gestation delay as bifurcation parameter,the suficient conditions for the existence of Hopf bifurcation of the delayed system at the positive equilibrium point are given.And the direction of Hopf bifurcation and the stability of the periodic solution are analyzed by using the center manifold theorem and normal form theory.What's more,numerical experiments are performed to test the theoretical results obtained in this paper.

Non-injection gram-scale synthesis of cesium lead halide perovskite quantum dots with controllable size and composition

Metal-halide perovskites are novel optoelectronic materials that are considered good candidates for solar harvesting and light emitting applications. In this study, we develop a reproducible and low-cost approach for synthesizing high- quality cesium lead halide perovskite （CsPbX3, X = CI, Br, and I or C1/Br and I/Br） nanocrystals （NCs） by direct heating of precursors in octadecene in air. Experimental results show that the particle size and composition of as-prepared CsPbX3 nanocrystals can be successfully tuned by a simple variation of reaction temperature. The emission peak positions of the as-prepared nanocrystals can be conveniently tuned from the UV to the NIR （360-700 nm） region, and the quantum yield of the as-obtained samples （green and red emissions） can reach up to 87%. The structures and chemical compositions of the as-obtained NCs were characterized by transmission electron microscopy, X-ray diffraction, and elemental analysis. This proposed synthetic route can yield large amounts of high-quality NCs with a one-batch reaction, usually on the gram scale, and could pave the way for further applications of perovskite-based light-emitting and photovoltaic solar cells.

A Co-N/C hollow-sphere electrocatalyst derived from a metanilic CoAl layered double hydroxide for the oxygen reduction reaction, and its active sites in various pH media

Transition-metal-coordinating nitrogen-doped carbon catalysts （M-N/C, M = Co, Fe, Mn, Ni, etc.） are considered one of the most promising nonprecious-metal electrocatalysts for the oxygen reduction reaction （ORR）. However, they suffer from low ORR catalytic activity, and their active sites have not been fully identified. Herein, we report the synthesis of a porous Co-N/C hollow-sphere electrocatalyst by carbonization of metanilic anions between the layers of a Co-A1 layered double hydroxide. The as-prepared Co-N/C catalyst exhibited excellent ORR catalytic activity with a high half-wave potential and a large diffusion-limited current in alkaline and neutral solutions. The performance of the catalyst was comparable to those of commercial Pt/C electrocatalysts. Through investigating the effects of mask ions （SCN- and F-） on the ORR activity of the Co-N/C catalyst, and comparing the ORR activity before and after the destruction of Co-Nx sites in different pH media, we concluded that the Co-Nx sites act directly as the ORR active sites in acidic and neutral solutions, but have a negligible effect on the ORR activity in alkaline conditions.

Accumulation of localized charge on the surface of polymeric carbon nitride boosts the photocatalytic activity

The random mobility of charge carriers is a main factor causing the low photocatalytic efficiency of gCN.Thus,the controllable migration of charge carriers is a rational strategy to suppress the charge recombination and facilitate charge separation.Herein,an ethylenediamine modified g-C_(3)N_(4)displays improved photocatalytic activity.The excellent charge separation efficiency is confirmed to be a key factor for the enhancement.The TEM observation after photo-depositing Pt nanoparticles and DFT calculations verify the accumulation of electrons on some areas of g-C_(3)N_(4)surface.The increased-NH_(2)groups significantly tune the electronic structure of g-C_(3)N_(4)after the modification.The generation of midgap states also affects the charge separation.Our reports provide a simple method to manage the migration of charge carriers and enable electrons directional transfer,which suppresses the recombination and improves the photocatalytic activity.

Self-Assembly of Luminescent Twisted Fibers Based on Achiral Quinacridone Derivatives

It is a great challenge to spontaneously assemble achiral molecules into twisted nanostructures in the absence of chiral substances.Here we show that two achiral centrosymmetric quinacridone(QA)derivatives,N,N’-di(n-hexyl)-1,3,8,10-tetramethylquinacridone(C6TMQA)and N,N’-di(n-decyl)-1,3,8,10-tetramethylquinac ridone(C10TMQA),can be employed as building blocks to fabricate well-defi ned twisted nanostructures by controlling the solvent composition and concentration.Bowknot-like bundles with twisted fiber arms were prepared from C6TMQA,whilst uniform twisted fibers were generated from C10TMQA in ethanol/THF solution.Spectroscopic characterization and molecular simulation calculations revealed that the introduction of ethanol into the solution could induce a staggered aggregation of C6TMQA(or C10TMQA)molecules and the formation of twisted nanostructures.Such twisted materials generated from achiral organic functional molecules may be valuable in the design and fabrication of new materials for optoelectronic applications.