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Atomically thin two-dimensional transition metal dichalcogenides (TMDCs) have been regarded as ideal and promising nanomaterials that bring broad application prospects in extensive fields due to their ultrathin layered structure, unique electronic band structure, and multiple spatial phase configurations. TMDCs with different phase structures exhibit great diversities in physical and chemical properties. By regulating the phase structure, their properties would be modified to broaden the application fields. In this mini review, focusing on the most widely concerned molybdenum dichalcogenides (MoX2: X = S, Se, Te), we summarized their phase structures and corresponding electronic properties. Particularly, the mechanisms of phase transformation are explained, and the common methods of phase regulation or phase stabilization strategies are systematically reviewed and discussed. We hope the review could provide guidance for the phase regulation of molybdenum dichalcogenides nanomaterials, and further promote their real industrial applications. [ABSTRACT FROM AUTHOR]

As an emerging zero-dimensional nano crystalline porous material, porous organic cages (POCs) with soluble properties in organic solvents, are promising candidates as molecular fillers in mixed matrix membranes (MMMs). The pore structure of POCs should be adjusted to trigger efficient gas separation performance, and the interaction between filler and matrix should be optimized. In this work, ionic liquid (IL) was introduced into the molecular fillers of CC3, to construct the IL@CC3/PIM-1 membrane to effectively separate CO2 from CH4. The advantages of doping IL include: (1) narrowing the cavity size of POCs from 4.4 to 3.9 Å to enhance the diffusion selectivity, (2) strengthening the CO2 solubility to heighten the gas permeability, and (3) improving the compatibility between filler and matrix to upgrade membrane stability. After the optimization of the membrane composite, the IL@CC3/PIM-1-10% membrane possesses the CO2 permeability of 7868 Barrer and the CO2/CH4 selectivity of 73.4, which compared to the CC3/PIM-1-10% membrane, improved by 15.9% and 106.2%, respectively. Furthermore, the membrane has maintained a stable separation performance at varied temperatures and pressures during the long-term test. The proposed method offers an efficient way to improve the performance of POCs-based MMMs in gas separation. [ABSTRACT FROM AUTHOR]

MXenes, a family of 2D transition metal carbides, are considered promising high‐rate pseudocapacitive materials because of their metallic‐like conductivity and transition metal oxide‐like surfaces. Currently, nearly 50 stoichiometric MXenes have been synthesized. However, only a few MXenes, such as Ti3C2, have shown stable pseudocapacitive charge storage so far. Further improving the inherent pseudocapacitance of MXenes without losing their cyclability remains a challenge. Herein, a mild method is reported to produce highly stable bimetallic solid‐solution MXene Ti2VC2 using a solution of potassium fluoride and hydrochloric acid. The electrochemical properties of resulting multilayered clay‐like and delaminated Ti2VC2 films are investigated, exceeding the performance of typical Ti3C2 in acidic electrolytes. These electrodes deliver up to 2000 F cm−3 and retain more than 90% of their initial capacitance after 20 000 cycles, surpassing most state‐of‐the‐art supercapacitor materials known. The pseudocapacitive charge storage of Ti2VC2 is deeply investigated through in situ and ex situ experimental studies, confirmed the pseudocapacitive mechanism is a combination of hydrated H+ intercalation and surface redox. This work provides a practical route toward future rational design on the atomic scale for high‐performance pseudocapacitive materials. [ABSTRACT FROM AUTHOR]

The construction of interfacial electric field (IEF) in semiconductor heterojunction is of great significance in boosting photocatalytic hydrogen evolution through efficient separation of photogenerated charge‐carriers. However, the exploitation of IEF in type‐I heterojunction has not been proposed for designing photocatalysts. Herein, based on the density functional theory prediction, p‐SnS with different work functions modulated by Sn‐vacancy are compounded with n‐ZnIn2S4 containing S‐vacancy to form type‐I heterojunction. The optimized SnS/ZnIn2S4 photocatalyst without co‐catalysts exhibits an impressive hydrogen evolution rate of 22.75 mmol g−1 h−1, 6.23 times of ZnIn2S4. Systematic investigations reveal that the interfacial Sn‐S bond acts as a transport channel that accelerates the interface charge‐carriers transfer under the promotion of IEF originating from the significant Fermi level difference. A large difference in the surface photovoltage signal of SnS/ZnIn2S4 and ZnIn2S4 is achieved from effective photogenerated charge‐carriers separation by IEF. The new p‐n type‐I scheme of SnS/ZnIn2S4 induced by the interfacial mediation can separate the photogenerated charge‐carriers, and retain the highly reductive electrons of ZnIn2S4 for hydrogen evolution, overcoming the disadvantage of reduction potential decline in the typical type‐I scheme. This study will afford a new theoretical basis for the achievement of high‐efficiency photocatalytic hydrogen evolution through interface modulation. [ABSTRACT FROM AUTHOR]

With the continuous development of the Internet financial industry, its impact on people's daily life is growing. Under the influence of the information technology and the financial innovation, the volatility of the financial market has been significantly enhanced, and the financial risk has become increasingly serious. The COVID-19 in 2020 still has a profound impact on the global financial market. The reasonable measurement of the financial risks is the most important step in the financial risk management. Based on the sample analysis of the Standard & Poor's 500 Index from January 3, 2013 to June 30, 2020, this paper measures the risks by analyzing and calculating the value at risk (VaR) of the sample data by different methods. This paper mainly establishes the ARMA model, the GARCH model based on bayese statistics, and the POT model based on the extreme value theory, and compares and analyzes the VaR values obtained by the three models. Finally, the effectiveness of VaR is tested by VaR backtracking test, and the advantages and disadvantages of the methods are compared and evaluated.

Nanoclusters involve finite metal atoms are of great importance in chemical synthesis and catalysis due to their unique structure-dependent properties. Knowing how nanoclusters work in reaction conditions is no doubt one of the most important challenges, which requires deep insight into atomic-scale dynamics during the process. State-of-the-art in-situ transmission electron microscope (TEM) can realize the real-time study, which is expected to reveal insights into the underlying mechanisms of catalysis and design efficient catalysts. In this minireview, we aim to give a critical review and recent progress on nanocluster dynamics unveiled by in-situ and environmental TEM from two aspects: evolutions of metal single atoms and nanoclusters in high-temperature reaction conditions and the well-defined molecular clusters in confined space. We emphasize the cluster-environment interaction and the cluster structure–property relationships. In the end, we also summarize the present achievements and propose future challenges. We expect this review will fuel the excitement and stimulate research in the fields of cluster and catalysis. [ABSTRACT FROM AUTHOR]

The low stability of hydrogen bonded organic frameworks (HOFs) greatly limits their practical application. Herein, we synthesized a sulfonate-containing HOF and further improved its stability by crosslinking its crystal particles based on an in situ reaction of ammonia on its surface. The obtained HOF-based composite HDSD-1@Tp can maintain stability in common organic solvents, boiling water and acid solutions (3 M), the mixed solution of DMF and water (1 : 1) and basic solutions up to pH = 12. The pore structure formed by the organic linkages between HDSD-1 crystal particles not only enhances the stability of HDSD-1, but also is conducive to the storage of guest water molecules. When NH4+ that can serve as a proton source and improve the hydrophilicity of the material is introduced into HDSD-1@Tp, the obtained HDSD-1@Tp-NH3 exhibits an ultrahigh proton conductivity of 3.8 × 10−1 S cm−1 at 80 °C 98% RH. In this work a new strategy for the synthesis of novel HOF-based proton conducting materials with excellent stability and high proton conductivity has been developed. [ABSTRACT FROM AUTHOR]

This paper discusses the optimal dividend and capital injection problems when an insurance company has two lines of business with common shock dependence. Suppose that the manager of the company has time-inconsistent preference, which can be described by a quasi-hyperbolic discount function. The value of the company is measured by the expected discounted dividend payments minus the expected discounted costs of capital injection. The goal is to find out the optimal strategies for maximizing the value of the company. By using the stochastic control techniques, we solve the problems in all cases of time-consistent preference manager, naive manager and sophisticated manager, respectively. The closed-form solutions of the value functions are presented. Our results show that the sophisticated manager is inclined to pay out dividends earlier than the naive manager, time-inconsistent preference manager is more likely to pay dividends in advance than time-consistent preference manager. Furthermore, we provide some numerical analysis to reveal the sensitivity of the optimal dividend strategies to the dependence intensity and the cost of capital injection. The results show that, as the cost of capital injection increases, sophisticated manager will give up capital injection first, followed by naive manager. In addition, we also find that: when the cost of capital injection is low, managers think that the value of the company that undertakes two kinds of insurance with high correlation is higher; while, managers have opposite evaluations, when the cost of capital injection is high. [ABSTRACT FROM AUTHOR]

The long–term stability of proton conductors is one of the most important factors in evaluating materials. Guest molecules can act as "bridges" for proton conduction channels and reside in the channels of covalent organic frameworks, but they are prone to leakage. Therefore, it is important to develop proton conductors with intrinsic proton conductivity. In this paper, we synthesized an intrinsically sulfonated covalent organic framework, TpPa–SO3H, which has a more stable proton conducting performance than that of TpPa@H2SO4 by loading guest molecules. Meanwhile, the proton conductivity of TpPa–SO3H was further improved by coating a superabsorbent polymer through an in situ reaction to obtain PANa@TpPa–SO3H (PANa: sodium polyacrylate). As a result, the modified composite exhibits an ultrahigh proton conductivity of 2.33 × 10−1 S cm−1 at 80 °C under 95% relative humidity (RH). The stability of PANa@TpPa–SO3H makes it an efficient proton transport platform with excellent proton conductivity and long–term durability. [ABSTRACT FROM AUTHOR]

Electrocatalytic water splitting, as a sustainable, pollution-free and convenient method of hydrogen production, has attracted the attention of researchers. However, due to the high reaction barrier and slow four-electron transfer process, it is necessary to develop and design efficient electrocatalysts to promote electron transfer and improve reaction kinetics. Tungsten oxide-based nanomaterials have received extensive attention due to their great potential in energy-related and environmental catalysis. To maximize the catalytic efficiency of catalysts in practical applications, it is essential to further understand the structure–property relationship of tungsten oxide-based nanomaterials by controlling the surface/interface structure. In this review, recent methods to enhance the catalytic activities of tungsten oxide-based nanomaterials are reviewed, which are classified into four strategies: morphology regulation, phase control, defect engineering, and heterostructure construction. The structure–property relationship of tungsten oxide-based nanomaterials affected by various strategies is discussed with examples. Finally, the development prospects and challenges in tungsten oxide-based nanomaterials are discussed in the conclusion. We believe that this review provides guidance for researchers to develop more promising electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

Interfacial atomic configuration plays a vital role in the structural stability and functionality of nanocomposites composed of metal nanoparticles (NPs) and two−dimensional semiconductors. In situ transmission electron microscope (TEM) provides a real−time technique to observe the interface structure at atomic resolution. Herein, we loaded bimetallic NiPt truncated octahedral NPs (TONPs) on MoS2 nanosheets and constructed a NiPt TONPs/MoS2 heterostructure. The interfacial structure evolution of NiPt TONPs on MoS2 was in situ investigated using aberration−corrected TEM. It was observed that some NiPt TONPs exhibited lattice matching with MoS2 and displayed remarkable stability under electron beam irradiation. Intriguingly, the rotation of an individual NiPt TONP can be triggered by the electron beam to match the MoS2 lattice underneath. Furthermore, the coalescence kinetics of NiPt TONPs can be quantitatively described by the relationship between neck radius (r) and time (t), expressed as rn = Kt. Our work offers a detailed analysis of the lattice alignment relationship of NiPt TONPs on MoS2, which may enlighten the design and preparation of stable bimetallic metal NPs/MoS2 heterostructures. [ABSTRACT FROM AUTHOR]

Constructing a heterogeneous interface using different components is one of the effective measures to achieve the bifunctionality of nanocatalysts, while synergistic interactions between multiple interfaces can further optimize the performance of single-interface nanocatalysts. The non-precious metal nanocatalysts MoS2/NiSe2/reduced graphene oxide (rGO) bilayer sandwich-like nanostructure with multiple well-defined interfaces is prepared by a simple hydrothermal method. MoS2 and rGO are layered nanostructures with clear boundaries, and the NiSe2 nanoparticles with uniform size are sandwiched between both layered nanostructures. This multiple-interfaced sandwich-like nanostructure is prominent in catalytic water splitting with low overpotential for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and almost no degradation in performance after a 20 h long-term reaction. In order to simulate the actual overall water splitting process, the prepared nanostructures are assembled into MoS2/NiSe2/rGO||MoS2/NiSe2/rGO modified two-electrode system, whose overpotential is only 1.52 mV, even exceeded that of noble metal nanocatalyst (Pt/C||RuO2~1.63 mV). This work provides a feasible idea for constructing multi-interface bifunctional electrocatalysts using nanoparticle-doped bilayer-like nanostructures. [ABSTRACT FROM AUTHOR]

As a typical planar 4-connected ligand that possesses D4h symmetry, the squarate ligand is expected to construct some interesting topologies. Here, we report that the assembly of the squarate ligand with rare-earth ions can produce a series of (4, 8)-connected frameworks with the "smallest" scu type topology. Among these compounds, the Tb based analogue not only possesses a good proton conductivity, but also exhibits luminescence responses toward MnO4− and Cr2O72−, making it a candidate for multifunctional materials. [ABSTRACT FROM AUTHOR]

In this paper, we study a general mean-variance reinsurance, new business and investment problem, where the claim processes of original and new businesses are modeled by two different risk processes and the safety loadings of reinsurance and new business are different. The retention level of the insurer is constrained in [ 0 , 1 ] and the controls of new business and risky investment are required to be non-negative. This model relaxes the limitations of those in existing research. By using the projection onto the convex set controls valued in, we obtain an open-loop equilibrium reinsurance-new business-investment strategy explicitly. We also show that the obtained equilibrium strategy is the optimal one among all deterministic strategies in the sense that it yields the smallest mean-variance cost. In the case where original and new businesses are the same, the equilibrium strategy is given in closed-form and its sensitivities to safety loadings are shown by numerical examples. At last, by comparing with the case where acquiring new business is prohibited, we show that allowing writing new policies indeed improves the performance of the insurer's risk management. [ABSTRACT FROM AUTHOR]

Li et al. [[3]] fabricated a CoFe SB 2 sb O SB 4 sb /g-C SB 3 sb N SB 4 sb composite catalyst with CoFe SB 2 sb O SB 4 sb particles supported on the flaky g-C SB 3 sb N SB 4 sb using a scalable facile method. However, currently, Li-S batteries suffer from low volumetric energy density and poor cycling stability due to the intrinsic low conductivity of sulfur and its discharge product, lithium polysulfide shuttle effect, and so on. Developing efficient and low-cost energy conversion and storage devices and technologies is all-important issue in order to achieve a low-carbon society, whose performance essentially depends on the properties of materials. Zhao et al. [[8]] designed a single-atom catalyst Au/WSSe by filling the single Au atom at the S vacancy site in the Janus WSSe monolayer. [Extracted from the article]

The heterostructure of transition metal nanocrystal on two-dimensional (2D) materials exhibits unique physical and chemical properties through various interfacial interactions. It has been established that the atomic structure and strain in the vicinity of the interface determine the band structure and phonon modes of the nanocrystal, regulating the optical and electrical properties of such heterostructures. Hence, metal—support interfacial engineering is a demonstrated approach to acquiring desired properties of the nanocrystals. However, a fundamental understanding of the interfacial structures remains elusive and precise control of the interactions has yet achieved. Herein, we explore the regulation of interface on MoS2 supported Pt nanocrystals which were prepared by reducing ultrasonic dispersed potassium chloroplatinate. The Pt-MoS2 heterostructure interface was systematically studied by aberration corrected transmission electron microscopy. Three types of Pt-MoS2 interfaces with distinct atomic configurations were identified. The strain within the Pt nanocrystals is sensitive to the atomic configuration of the supporting MoS2, which regulates the size of the Pt nanocrystals. These results provide insights on tuning of nanocrystal strain, paving the way for precise control of 2D semiconductor heterostructures. [ABSTRACT FROM AUTHOR]

Controllable synthesis of carbon nanostructures is expected to achieve high electrical, optical, and mechanical performance for various applications. Despite great progress in this field, controllable synthesis of carbon nanostructures, i.e., graphite shells (GSs) and carbon nanotubes (CNTs), is still demanded to be deeply revealed. Here, a strategy is demonstrated to achieve GSs and bamboo CNTs by regulating the interface interaction via in situ pyrolysis of Co phthalocyanine (CoPc) in an environmental transmission electron microscopy (ETEM) at atomic resolution. The results indicate that the catalyst involves the nucleation, combination, and reconstruction of Co/Co3C, the growth modes of the carbon, i.e., base‐growth or tip‐growth, and nanostructures are dependent on the interface interaction between catalyst and substrate controlled by temperature. High temperature favors tip‐growth of bamboo CNTs with larger catalyst nanoparticles (NPs) (≈20 nm), while low temperature favors the base‐growth of GSs with smaller NPs (≈10 nm). The average growth rate of 131.3 nm s−1 at 850 °C is about 60 times compared with that at 750 °C. The work provides a comprehensive understanding of distinct growth mode of GSs and CNTs at different temperatures, which would be valuable for the controllable growth of carbon nanostructures by catalyst design and engineering. [ABSTRACT FROM AUTHOR]

Understanding the mechanism of nucleation and growth of nanocrystals is crucial for designing and regulating the structure and properties of nanocrystals. However, the process from molecules to nanocrystals remains unclear because of the rapid and complicated dynamics of evolution under reaction conditions. Here, the complete evolution process of solid‐phase chloroplatinic acid during the electron beam irradiation triggered reduction and nucleation of platinum nanocrystals is recorded. Aberration‐corrected environmental transmission electron microscopy is used for direct visualization of the dynamic evolution from H2PtCl6 to Pt nanocrystals at the atomic scale, including the formation and growth of amorphous clusters, crystallization, and growth of clusters, and the ripening of Pt nanocrystals. At the first two stages, there exists a critical size of ≈2.0 nm, which represents the start of crystallization. Crystallization from the center and density fluctuation are observed in the second stage of the crystallization of a few clusters with a size obviously larger than the critical size. The work provides valuable information to understand the kinetics of the early stage of nanocrystal nucleation and crystallization at atomic scale. [ABSTRACT FROM AUTHOR]