In situ redox growth of mesoporous Pd-Cu2O nanoheterostructures for improved glucose oxidation electrocatalysis

Interfaces of metal-oxide heterostructured electrocatalyst are critical to their catalytic activities due to the significant interfacial effects. However, there are still obscurities in the essence of interfacial effects caused by crystalline defects and mismatch of electronic structure at metal-oxide nanojunctions. To deeply understand the interfacial effects, we engineered crystalline-defect Pd-Cu2O interfaces through nonepitaxial growth by a facile redox route. The Pd-Cu2O nanoheterostructures exhibit much higher electrocatalytic activity toward glucose oxidation than their single counterparts and their physical mixture,which makes it have a promising potential for practical application of glucose biosensors.Experimental study and density functional theory(DFT) calculations demonstrated that the interfacial electron accumulation and the shifting up of d bands center of Cu-Pd toward the Fermi level were responsible for excellent electrocatalytic activity. Further study found that Pd(3 1 0) facets exert a strong metaloxide interface interaction with Cu2O(1 1 1) facets due to their lattice mismatch. This leads to the sinking of O atoms and protruding of Cu atoms of Cu2O, and the Pd crystalline defects, further resulting in electron accumulation at the interface and the shifting up of d bands center of Cu-Pd, which is different from previously reported charge transfer between the interfaces. Our findings could contribute to design and development of advanced metal-oxide heterostructured electrocatalysts.

Multi-hybrid method for investigation of EM scattering from inhomogeneous object above a dielectric rough surface

An iterative strategy combining Kirchhoff approximation(KA) with the hybrid finite element-boundary integral(FE-BI) method is presented in this paper to study the interactions between the inhomogeneous object and the underlying rough surface.KA is applied to study scattering from underlying rough surfaces,whereas FE-BI deals with scattering from the above target.Both two methods use updated excitation sources.Huygens equivalence principle and an iterative strategy are employed to consider the multi-scattering effects.This hybrid FE-BI-KA scheme is an improved and generalized version of previous hybrid Kirchhoff approximation-method of moments(KA-MoM).This newly presented hybrid method has the following advantages:(1) the feasibility of modeling multi-scale scattering problems(large scale underlying surface and small scale target);(2) low memory requirement as in hybrid KA-MoM;(3) the ability to deal with scattering from inhomogeneous(including coated or layered) scatterers above rough surfaces.The numerical results are given to evaluate the accuracy of the multi-hybrid technique;the computing time and memory requirements consumed in specific numerical simulation of FE-BI-KA are compared with those of MoM.The convergence performance is analyzed by studying the iteration number variation caused by related parameters.Then bistatic scattering from inhomogeneous object of different configurations above dielectric Gaussian rough surface is calculated and the influences of dielectric compositions and surface roughness on the scattering pattern are discussed.

Ionic liquids on uncharged and charged surfaces: In situ microstructures and nanofriction

In situ changes in the nanofriction and microstructures of ionic liquids(ILs)on uncharged and charged surfaces have been investigated using colloid probe atomic force microscopy(AFM)and molecular dynamic(MD)simulations.Two representative ILs,[BMIM][BF_(4)](BB)and[BMIM][PF_(6)](BP),containing a common cation,were selected for this study.The torsional resonance frequency was captured simultaneously when the nanoscale friction force was measured at a specified normal load;and it was regarded as a measure of the contact stiffness,reflecting in situ changes in the IL microstructures.A higher nanoscale friction force was observed on uncharged mica and highly oriented pyrolytic graphite(HOPG)surfaces when the normal load increased;additionally,a higher torsional resonance frequency was detected,revealing a higher contact stiffness and a more ordered IL layer.The nanofriction of ILs increased at charged HOPG surfaces as the bias voltage varied from 0 to 8 V or from 0 to−8 V.The simultaneously recorded torsional resonance frequency in the ILs increased with the positive or negative bias voltage,implying a stiffer IL layer and possibly more ordered ILs under these conditions.MD simulation reveals that the[BMIM]+imidazolium ring lies parallel to the uncharged surfaces preferentially,resulting in a compact and ordered IL layer.This parallel“sleeping”structure is more pronounced with the surface charging of either sign,indicating more ordered ILs,thereby substantiating the AFM-detected stiffer IL layering on the charged surfaces.Our in situ observations of the changes in nanofriction and microstructures near the uncharged and charged surfaces may facilitate the development of IL-based applications,such as lubrication and electrochemical energy storage devices,including supercapacitors and batteries.

Insights into the nucleation,grain growth and phase transformation behaviours of sputtered metastableβ-W films

Metastable phase in tungsten film is of great interests in recent years due to its giant spin Hall effects,however,little information has been known on its nucleation,growth and phase transformation.In this paper,a 900 nm-thick tungsten film with double-layer structure(α-W underlayer andβ-W above it)was produced on SiO_(2)/Si substrate by high vacuum magnetron sputtering at room temperature.The structural properties ofβ-W were systemically investigated by X-ray diffraction,transmission electron microscopy,thermodynamic calculation,first-principle and phase-field simulations.It is found that theβ-W nucleation is energetically favoured on the SiO_(2)surface compared to theα-W one.As the film thickening proceeds,β-W[211]turns to be preferred direction of growth owing to the elastic strain energy minimization,which is verified by phase-field simulations.Moreover,theβ→αphase transformation takes place near the film-substrate interface while the rest of the film keeps theβ-W phase,leading to a doublelayer structure.This localized phase transition is induced by lower Gibbs free energy ofα-W phase at larger grain sizes,which can be confirmed by thermodynamic calculation.Further in-situ heating TEM analysis of the as-deposited film reveals that theβ→αphase transformation is fulfilled byα/βinterface propagation rather than local atomic rearrangements.Our findings offer valuable insights into the intrinsic properties of metastable phase in tungsten.

Facile one-pot synthesis of superfine palladium nanoparticles on polydopamine-functionalized carbon nanotubes as a nanocatalyst for the Heck reaction

Heterogeneous Pd nanocatalysts are efficient catalysts for the Heck reaction but require multi-step,sophisticated procedures and harsh reaction conditions.In this work,a green and facile strategy has been developed to decorate Pd nanoparticles on polydopamine(PDA)-coated multi-walled carbon nanotubes(Pd/CNTs-PDA)via a one-pot method.The obtained nanoparticles were characterized by various techniques including transmission electron microscopy,X-ray diffraction,and X-ray photoelectron spectroscopy,which proved that Pd NPs are well-dispersed on the PDA and between the surfaces of the PDA and CNTs.The resultant Pd/CNTs-PDA catalysts exhibit excellent catalytic reactivity toward the Heck reaction at low temperatures.Moreover,by DFT simulation,we found that during the PDA polymerization process,a large number of unsaturated—N=and C=O species are more active than the groups on the PDA end product to anchor Pd NPs.The results provide evidence that the catalyst synthesized by the onepot method exhibited good activity because sufficient active sites could be created to effectively promote Pd NPs dispersion during the dopamine polymerization process.Additionally,the Pd/CNTs-PDA catalyst was successfully employed in Heck cross-coupling reactions with various functionalized substrates.This method opens a window for the fabrication of high-performance nanocomposite catalysts under mild conditions using simple methods and has several potential applications.

从四方到立方:高性能太阳能电池的钙钛矿相结构演变

Crystal structure, which is generally determined by the composition, ionic radius and valence state of constituent elements, plays a significant role in the material’s fundamental properties such as optical, electronic, and mechanical characters. The manipulation of the crystal structure through compositional engineering, and understanding the relationship between crystal structure and properties are essential for the development of materials.

ASBase:The universal database for aggregate science

This paper reports the first universal and versatile database on aggregate materials for the field of aggregate science research.At the current stage,the database(http://119.91.135.188:8080/)contains over 1000 entries of organic aggregate material systems(mainly luminescent systems at the current stage)with a unique data structure which is designed particularly for aggregate materials and containing the photophysics and physicochemical properties of the compounds in different statuses of aggregation,including dilute solution form,pristine solid-state,stable crystalline,and nanoaggregates formed in solvents.The web-based interface of the database provided functions to index,search,manipulate,fetch and deposit data entries.In addition,a background calculation service optimizes the chemical structure of new entries on different levels of accuracies.The database also provided background API for interactive developments of prediction or regression models based on machine-learning algorithms.

Time-synchronous-averaging-spectrum based on super-resolution analysis and application in bearing fault signal identification

Time-synchronous-averaging(TSA)is based on the idea of denoising by averaging,and it extracts the periodic components of a quasiperiodic signal and keeps the extracted waveform undistorted.This paper studies the mathematical properties of TSA,where three propositions are given to reveal the nature of TSA.This paper also proposes a TSA-spectrum based on super-resolution analysis and it decomposes a signal without using any base function.In contrast to discrete Fourier transform spectrum(DFT-spectrum),which is a spectrum in frequency domain,TSA-spectrum is a period-based spectrum,which can present more details of the cross effects between different periodic components of a quasiperiodic signal.Finally,a case study is carried out using bearing fault analysis to illustrate the performance of TSA-spectrum,where the rotation speed fluctuation of the shaft is estimated,which is about 0.12 ms difference.The extracted fault signals are presented and some insights are provided.We believe that this paper can provide new motivation for TSA-spectrum to be widely used in applications involving quasiperiodic signal processing(QSP).

大规模中药转录组研究揭示中药抑制新冠肺炎细胞因子风暴的分子机制

中药抑制新冠肺炎相关细胞因子风暴的分子机制尚不清晰.本文首先通过HTS2技术,在基因表达层面上,大规模检测了578味中药提取物对与细胞因子风暴紧密相关的信号通路的调控作用,发现53味中药对这些通路具有显著抑制作用;评估了国家及地方新冠肺炎诊疗方案中出现的338个方剂,发现理中汤、六君子汤、黄连解毒汤、清肺排毒汤在抑制细胞因子风暴方面排在前列;鉴别了相关中药的潜在活性成分,进一步揭示了中药抑制新冠肺炎相关细胞因子风暴的化学基础.本研究系统探究了中药调节新冠相关细胞因子风暴的分子机制,为中药治疗新冠肺炎药效机制的解析提供了科学依据.