A Novel Efficient and Effective Preprocessing Algorithm for Text Classification

Text classification is an essential task of natural language processing. Preprocessing, which determines the representation of text features, is one of the key steps of text classification architecture. It proposed a novel efficient and effective preprocessing algorithm with three methods for text classification combining the Orthogonal Matching Pursuit algorithm to perform the classification. The main idea of the novel preprocessing strategy is that it combined stopword removal and/or regular filtering with tokenization and lowercase conversion, which can effectively reduce the feature dimension and improve the text feature matrix quality. Simulation tests on the 20 newsgroups dataset show that compared with the existing state-of-the-art method, the new method reduces the number of features by 19.85%, 34.35%, 26.25% and 38.67%, improves accuracy by 7.36%, 8.8%, 5.71% and 7.73%, and increases the speed of text classification by 17.38%, 25.64%, 23.76% and 33.38% on the four data, respectively.

Growing Biomorphic Transition Metal Dichalcogenides and Their Alloys Toward High Permeable Membranes and Efficient Electrocatalysts Applications

3D architecratured transition metal dichalcogenides constructed by atomically thin layers are appealing building blocks in various applications,such as catalysts,energy storage,conversions,sensors,and so on.However,the direct growth of 3D transition metal dichalcogenides architectures with high crystal quality and well-controlled size/thickness remains a huge challenge.Herein,we report a facile,highly-repeatable,and versatile chemical vapor deposition strategy,for the mass production of high-quality 3D-architecratured transition metal dichalcogenides(e.g.,MoS_(2),WS_(2),and ReS_(2))and their alloys(e.g.,W_(x)Mo(1–x)S_(2)and Rex Mo_((1–x))S_(2))nanosheets on naturally abundant and low-cost diatomite templates.Particularly,the purified transition metal dichalcogenides products exhibit unique and designable 3D biomorphic hierarchical microstructures,controllable layer thicknesses,tailorable chemical compositions,and good crystallinities.The weak interlayer interactions endow them with good dispersity in solutions to form stable additive-free inks for solution-processing-based applications,for example,high-permeable and high-stable separation membranes for water purification,and efficient electrocatalysts for hydrogen evolution reactions.This work paves ways for the low-cost,mass production of versatile transition metal dichalcogenides powder-like materials with designable structures and properties,toward energy/environmental-related applications and beyond.

面向电极接触应用的二维金属性过渡金属硫属化合物的制备和器件研究进展

二维(two-dimensional,2D)层状半导体材料因具有原子级厚度、优异的光电性质和良好的热/化学稳定性等,被认为是延续摩尔定律的重要候选材料之一.基于超薄2D半导体材料构建的电子器件本质上是一种界面器件,其性能与金属-半导体接触的质量密切相关.常规蒸镀法制备金属电极通常涉及高能原子(团簇)轰击,该过程往往导致沟道材料的损伤和界面缺陷的产生,使得接触质量下降,接触电阻增大,器件性能显著恶化.2D金属性过渡金属硫属化合物(metallic transition metal dichalcogenides,MTMDCs)和半导体性TMDCs具有类似的材料组成、相同的层间范德华相互作用、可兼容的制备方法等,有望作为金属-半导体接触的界面材料,有效改善接触问题.目前,面向电极接触应用的高质量2D-MTMDCs的制备与应用已取得重要进展.本文综述了近年来基于化学气相沉积(chemical vapor deposition,CVD)法制备MTMDCs的一些研究成果,包括不同材料体系的制备、结构表征以及作为电极接触的应用等,最后讨论了该领域目前存在的问题,展望了未来可能的发展方向.

Two-dimensional Cu-porphyrin nanosheet membranes for nanofiltration

A kind of two-dimensional(2D)metal-organic framework(MOF)material,Cu-meso-tetrakis(4-carboxyphenyl)porphine(Cu-TCPP)nanosheets with wrinkled and flat morphologies are used as building blocks to assemble membranes by vacuum filtration(VF)and electrophoretic deposition(EPD)as energy-efficient nanofiltration(NF)membranes to remove dyes from water.Since the nanosheets with wrinkled structure can provide additional water transport channels,thereby increasing the water permeance,in the premise of a high rejection(>97.0%)for the dye brilliant blue G(BBG)(1.60 nm×1.90 nm),the water permeance of the membrane assembled by the wrinkled nanosheets(~1170 nm)is about 4 times that of the membrane assembled by the flat nanosheets(~530 nm),reaching 16.39 L·m^(−2)·h^(−1)·bar^(−1).Additionally,the use of the relatively flat nanosheets and the membrane preparation method of electrophoretic deposition is more conducive to stack nanosheets orderly and reduce defects.Therefore,the water permeance of the membrane prepared by EPD(~1170 nm)with flat nanosheets is about twice that of the membrane prepared by VF(~530 nm),achieving 9.40 L·m^(−2)·h^(−1)·bar^(−1)with similar rejection(>97.0%)of dye evans blue(EB)(3.10 nm×1.20 nm).Furthermore,these membranes still exhibit good separation performance at high pressure of 0.6 MPa.Nanosheets with diverse structures and various membrane fabrication processes provide new directions for the separation performance optimization of 2D MOF materials for water purification.

Recent advances of Rh-based intermetallic nanomaterials for catalytic applications

Rhodium(Rh)has received widespread attention in fundamental catalytic research and numerous industrial catalytic applications.Compared to homogeneous catalysts,Rh-based nanomaterials as heterogeneous catalysts are much easier to separate and collect after usage,making them more suitable for commercial use.To this purpose,there has been a constant demand in constructing stable and highly active Rh-based nanomaterials.In contrast to Rh-based solid solutions with a random distribution of metallic atoms in the lattice,Rh-based intermetallic compounds(IMCs)with a fixed stoichiometric ratio and an ordered atomic arrangement can ensure the homogenous distribution of active sites and structural stability in the catalytic process.In this review,we concentrate on the fabrication of Rh-based IMCs for catalytic applications.Various synthetic methods and protocols for the controlled preparation of Rh-based IMC are illustrated.Meanwhile,the catalytic applications and corresponding catalytic mechanisms are discussed.In addition,personal perspectives about the remaining challenges and prospects in this field are provided.We believe this review will be useful in directing the development of Rh-based IMC catalysts for heterogeneous catalysis.

二维金属性过渡金属硫属化合物的可控制备和潜在应用

二维金属性过渡金属硫属化合物(metal transition metal dichalcogenides,MTMDCs)由于其独特的物性(如电荷密度波相转变、超导和磁性等),以及在先进纳米电子学和能源相关领域的应用潜力而受到研究者的广泛关注.为了实现基本物性研究和多方面的应用探索,化学气相沉积(CVD)技术被引入到高质量二维MTMDCs材料的制备中,成功地合成了厚度可调的超薄MTMDCs纳米片、大面积均匀的超薄薄膜、垂直取向的纳米片阵列和高质量的纳米片粉体等.CVD方法可以兼顾大畴区、层厚可调和高晶体质量的材料制备需求,还能与目前的半导体工艺相兼容,因而受到人们广泛关注.二维MTMDCs材料具有高的电导率,可以作为单层/少层半导体性过渡金属硫属化合物(transition metal dichalcogenides,TMDCs)的电极材料,改善晶体管器件的电极接触,从而提升器件性能.此外,二维MTMDCs纳米片也可作为高效的催化剂应用于电化学析氢反应,其催化性能显著优于单层/少层MoS2等半导体性TMDCs催化剂.本文综述了二维MTMDCs材料的CVD制备方法和新奇物理特性,以及其在场效应晶体管、电催化析氢应用中的研究进展;最后讨论了相关领域存在的问题和未来发展方向.

Scalable salt-templated directed synthesis of high-quality MoS_(2) nanosheets powders towards energetic and environmental applications

Two-dimensional(2D)transition metal dichalcogenides(TMDCs)have emerged as perfect platforms for developing applications in nano-electronics,catalysis,energy storage and environmental-related fields due to their superior properties.However,the low-cost,batch production of high-quality 2D TMDCs remains a huge challenge with the existing synthetic strategies.Herein,we present a scalable chemical vapor deposition(CVD)approach for the batch production of high-quality MoS_(2) nanosheet powders,by using naturally abundant,water-soluble and recyclable NaCl crystal powders as templates.The high-quality MoS_(2) nanosheets powders are achieved by a facile water dissolution-filtration process,by virtue of the excellent dispersibility of the as-grown products in water.The internal mechanism for the scalable synthesis strategy is explored.The applications of the MoS_(2) nanosheets powders are also demonstrated as catalysts or adsorbents in hydrogen evolution reaction(HER)and organic dyes adsorption,respectively.This work should hereby pave ways for the mass production and application of powdery TMDCs in energetic and environmental related fields.

Graded interface engineering of 3D/2D halide perovskite solar cells through ultrathin(PEA)_(2)PbI_(4) nanosheets

2D halide perovskites have emerged as promising materials because of their stability and passivation effect in perovskite solar cells(PSCs).However,the introduction of bulky organic ammonium cations from 2D halide perovskites would decrease the device performance generally compared to the traditional 3D MAPbI_(3).Incorporation of ultrathin 2D halide perovskite nanosheets(NSs)with 3D MAPbI_(3)could address this issue.Herein,we re port a rationally designed PSCs with dimensional graded 3D/2D MAPbI_(3)/(PEA)_(2)PbI_(4)heterojunction,in which 2D(PEA)_(2)PbI_(4)NSs were synthesized and incorporated between 3D MAPbI_(3)and hole-transporting layer.Besides the significantly improved stability,a notable increasement in power conversion efficiency(PCE)of 20%was obtained for the 3D/2D perovskite solar cells due to the favourable band alignment among(PEA)_(2)PbI_(4)NSs and the other components.The graded structure of MAPbI_(3)/(PEA)_(2)PbI_(4)would upshift the energy level continuously,which enhances the hole extraction efficiency thus reduces the interface charge recombination,leading to the increasements of VOC from1.04 V to 1.07 V,Jsc from 21.81 mA/cm^(2) to 23.15 mA/cm^(2) and the fill factor from 67.89% to 74.78%,and therefore an overall PCE of 18.53%.

Wafer-Scale Uniform Synthesis of 2D Transition Metal Dichalcogenides Single Crystals via Chemical Vapor Deposition

CONSPECTUS:Two-dimensional(2D)semiconducting transition metal dichalcogenides(TMDCs),most with a formula of MX2(M=Mo,W;X=S,Se,etc.),have emerged as ultrathin channel materials in next-generation electronics,due to their atomic thickness,tunable bandgap,and relatively high carrier mobility,etc.To propel their practical applications in integrated circuits,large-scale preparation of large-domain MX2 single crystals and singlecrystal films is significantly important.Among all the synthetic methods,chemical vapor deposition(CVD)has shown great promise for the controllable syntheses of large-area uniform 2D materials with electronic-grade quality and reasonable cost.So far,intensive efforts have been devoted to the controllable growth of MX2 single crystals with large sizes,controlled thicknesses,fast growth rates,and unidirectional orientations.However,due to the complexity of the precursor species(mostly like solid powders)and their gradient feeding distributions along the gas flow direction,it is still a huge challenge to synthesize large-area MX2 samples with centimeter-scale uniformity,which inevitably hinders their practical applications in industry.More significantly,due to the noncentrosymmetric structures of MX2,antiparallel domains and twin grain boundaries usually evolved on most substrates(e.g.,mica,C-sapphire).These defective grain boundaries usually exhibit metallic characteristics and serve as conducting channels,seriously impairing the electrical and optical properties of related devices.