Au core-PtAu alloy shell nanowires for formic acid electrolysis

Inefficient electrocatalysts and high-power consumption are two thorny problems for electrochemical hydrogen(H2)production from acidic water electrolysis.Herein we report the one-pot precise synthesis of ultrafine Au core-Pt Au alloy shell nanowires(Au@PtxAu UFNWs).Among them,Au@Pt_0.077 Au UFNWs exhibit the best performance for formic acid oxidation reaction(FAOR)and hydrogen evolution reaction(HER),which only require applied potentials of 0.29 V and-22.6 m V to achieve a current density of 10 m A cm^-2,respectively.The corresponding formic acid electrolyzer realizes the electrochemical H2 production at a voltage of only 0.51 V with 10 m A cm^-2 current density.Density functional theory(DFT)calculations reveal that the Au-riched Pt Au alloy structure can facilitates the direct oxidation pathway of FAOR and consequently elevates the FAOR activity of Au@Pt_0.077 Au UFNWs.This work provides meaningful insights into the electrochemical H₂ production from both the construction of advanced bifunctional electrocatalysts and the replacement of OER.     

Layered Ag-graphene films synthesized by Gamma ray irradiation for stable lithium metal anodes in carbonate-based electrolytes

Lithium metal batteries are considered as high energy density battery systems with very promising prospects and have bee n widely studied.However,The uncon trollable plating/strippi ng behavior,infinite volume change and den drites formation of lithium metal anode restrict the applicati on.The unc on trolled n ucleati on of lithium caused by the non uniform multi-physical field distributions,can lead to the undesirable lithium deposition.Herein,a graphene composite uniformly loaded with Ag nano-particles(Ag NPs)is prepared through a facile Gamma ray irradiation method and assembled into self-supported film with layered structure(Ag-rGO film).Whe n such film is used as a lithium metal an ode host,the uncontrolled deposition is converted into a highly nucleation-induced process.On one hand,the Ag NPs distributed between the in terlayers of graphe ne can preferentially induce lithium nu cleati on and en able uniform deposition morphology of lithium between interlayers.On the other hand,the stable layered graphene structure can accommodate volume change,stabilize the interface between anode and electrolyte and inhibit dendrites formation.Therefore,the layered Ag-rGO film as anode host can reach a high Coulombic efficiency over 93.3% for 200 cycle(786 h)at a current density of 1 mA cm^-2 for 2 mAh cm^-2 in carbonate-based electrolyte.This work proposes a facile Gamma ray irradiation method to prepare metal/3D-skeleton structure as lithium anode host and demonstrates the potential to regulate the lithium metal deposition behaviors via manipulating the distribution of lithiophilic metal(e.g.Ag)in 3D frameworks.This may offer a practicable thinking for the subsequent design of the lithium metal anode.     

中国纤维素乙醇技术的研究进展

中国面临着严重的能源短缺和环境污染问题,中国政府正在局部几个省份内政策性鼓励燃料乙醇生产和使用.尽管当前主要是用玉米和谷物作为生产乙醇的原料,然而中国具有大量潜在的低成本的纤维素生物质原料,可以极大地扩大乙醇的产量,降低原料成本.近20年来,由于技术的革命性进步,已使得纤维素乙醇的生产成本从4美元/加仑以上,降低至约1.2-1.5美元/加仑.其中,每吨生物质约44美元.因此,目前乙醇掺汽油具有十分强的市场竞争力.已有几个公司正在建造首批商业纤维素乙醇工厂,虽然这些刚起步的小型设施在合理利用和管理上风险较小,但规模经济需要较大型工厂.尽管配送生物质原料的成本会随需求的增加而增加,但在乙醇生产基础上的生物精炼技术的发展,尤其是化工产品和动力的协同生产,将会使全过程的经济可行性大大提高.进一步深入的基础研究,将解决低成本下实现纤维素的完全利用,以确保在无政策性补贴的前提下,真正使纤维素乙醇成为具有市场竞争力的低成本纯液体燃料.     

Binary ligand strategy toward interweaved encapsulation-nanotubes structured electrocatalyst for proton exchange membrane fuel cell

Hierarchically porous architecture of ir on-nitroge n-carb on(Fe-N-C)for oxyge n reducti on reaction(ORR)is highly desired towards efficient mass transfer in the fuel cell device manner.Herein,we reported a binary ligand strategy to prepare zeolitic imidazolate frameworks(ZIFs)-derived precursors,wherein the addition of secondary ligand endows precursors with the capabilities to transform into porously interweaved encapsulation-nanotubes structured composites after calcination.The optimal catalyst,i.e.,termed as Fe₆-M/C-3,exhibits excellent durability with 88.8%current retention after 50,000 seconds in 0.1 M HClO₄solution by virtue of nanoparticles-encapsulation features,which is more positive than the benchmark commercial 20 wt%Pt/C catalyst.Moreover,a promising maximum power density of Fe₆-M/C-3 as cathode catalyst was also dem on strated in proton exchange membrane fuel cells(PEMFCs)measurements.Therefore,this binary ligand approach to the fabrication of hierarchically porous structures would also have significant implications for various other electrochemical reactions.     

Molten salt as ultrastrong polar solvent enables the most straightforward pyrolysis towards highly efficient and stable single-atom electrocatalyst

Currently,pyrolysis as the most widely used method still has some key issues not well resolved for synthesis of carbon-supported single-atom catalysts(C-SACs),e.g.,the sintering of metal atoms at high temperature as well as the high cost and complicated preparations of precursors.In this report,molten salts are demonstrated to be marvellous medium for preparation of C-SACs by pyrolysis of small molecular precursors(ionic liquid).The ultrastrong polarity on one hand establishes robust interaction with precursor and enables better carbonization,resulting in largely enhanced yield.On the other hand,the aggregation of metal atoms is effectively refrained while no nanoparticle or cluster is formed.By this strategy,a C-SAC with atomically dispersed Fe-N₄ sites and a high specific area over 2000 m² g^-1 is obtained,which illustrates high ORR activity in both acid and alkaline media.Moreover,this SAC exhibits superior methanol tolerance and stability after acid soaking at 85℃ for 48 h.It is believed that the molten-salts-assisted pyrolysis can be developed into a routine strategy as it not only can largely simply the synthesis of C-SACs,but also can be extended to prepare other types of SACs.     

镧对Mg-Si合金中Mg2Si相变质的影响

研究了Mg-5Si合金中La的添加对初生Mg2Si相变质的影响。结果表明,适量的La能够有效地变质初生Mg2Si相。基于本文的研究,在添加约0.5%La时,获得了最佳的变质效果,此时,初生Mg2Si相的尺寸减小到25μm以下,其形态从粗大的树枝形状变为多面体形状。然而,当La增加到0.8%或者更高时,初生Mg2Si相又生长为粗大的树枝形态。而且,在凝固过程中发现形成了一些LaSi2化合物,这些化合物的数量随着La的增加而呈现逐渐增加的趋势。     

电感耦合等离子体质谱法测定天然水体中19种元素

建立STD/KED模式-电感耦合等离子体质谱（ICP-MS）法同时测定天然水体中铍、硼、钛、钒、铬、锰、钴、镍、铜、锌、钼、镉、锑、钡、铊、铅、铁、砷和硒19种元素的分析方法。仪器调谐校准后,样品在线加入锂、钪、铑、铋校准溶液校正,以标准曲线内标法定量分析。标准曲线相关系数均大于0.999,样品加标回收率为92.6%～103.6%,质控样品测定值相对标准偏差为0.20%～2.6%(n=6),方法检出限为0.01～0.70μg/L。该方法灵敏度高,操作简便,节省人力,能满足天然水体中19种元素的同时检测需要。     

电解质-非电解质混合溶液活度系数的关联及溶解的推算 II:NH3-NaCl-Na2SO4-H2O体系的液固平衡热力学

由于在研究的体系中, Na2SO4是非对称电解质, 且能生成水合盐, 故推导了由非对称型电解质与非电解质所构成的混合溶液的各组分的活度系数关联通式, 并在此基础上讨论了水合盐液固平衡的计算方法.     

黄花棘豆化学成分的研究II:两种三萜皂苷的结构

从黄花棘豆的总皂苷中分离出两个新皂苷1和2.经光谱分析及化学方法确证,1为3-O-[α-L-鼠李吡喃糖基(1→2)-β-D-葡萄吡喃糖基(1→4)-β-D-葡萄吡喃糖醛酸基]-黄豆醇B;2为3-O-[α-L-鼠李吡喃糖基(1→2)-α-L-阿拉伯吡喃糖基(1→4)-β-D-葡萄吡喃糖醛酸基]-黄豆醇B.     

二氧化钛纳米管的研究进展

二氧化钛纳米管由于其新奇的光电、催化、气敏等性能引起了广泛的关注,在太阳能电池、光催化、环境净化、气体传感器等领域有潜在的应用价值.本文概述了近年来在制备方法、反应机理和组成、晶型和形貌及掺杂和应用方面的进展,并讨论了今后可能的研究发展方向.     

Two-dimensional molecular space with regular molecular structure

A novel two-dimensional molecular space (layered carboxylpropylamidephenylsilica, CPAPhS) with regular carboxyl groups was successfully synthesized through grafting carboxyl groups in the structure of layered (aminophenyl)silica using butanedioic anhydride. The carboxyl groups regularly arranged in the layered CPAPhS can react with various organic molecules with amino and hydroxyl groups through formation of reactive intermediate with catalyzers, such as SOCl2. In this research, an example was used to prove the reaction properties of regular carboxyl groups in layered CPAPhS. The layered CPAPhS was reacted with SOCl2 to form layered acyl chloridepropylamidephenylsilica (ACPAPhS) and then reacted with n-butylamine and n-butyl alcohol to form layered n-butylamidepropylamidephenylsilica (BAPAPhS) and n-butylesterpropylamidephenylsilica (BEPAPhS) with regular molecular structures. Layered CPAPhS showed the potential as a starting material for formation of a series of novel two-dimensional molecular space with various regular molecular structures, and as a solid acceptor for chemical reagent with amino and hydroxyl groups for chemical processes.     

A theorem on the Gram matrix of a polyhedron

A theorem concerning the Gram matrix of a general set of vectors: a vector polyhedron, is described. Generally speaking, the demonstration is performed by means of a non-negative vector definition: the variance vector, which can be associated to any vector polyhedron belonging to a vector space where a scalar product can be defined. The complete sum of the variance vector, the condensed variance index of any polyhedron, permits to construct the Gram matrix theorem.     

Search strategies in structural bioinformatics

Optimisation problems pervade structural bioinformatics. In this review, we describe recent work addressing a selection of bioinformatics challenges. We begin with a discussion of research into protein structure comparison, and highlight the utility of Kolmogorov complexity as a measure of structural similarity. We then turn to research into de novo protein structure prediction, in which structures are generated from first principles. In this endeavour, there is a compromise between the detail of the model and the extent to which the conformational space of the protein can be sampled. We discuss some developments in this area, including off-lattice structure prediction using the great deluge algorithm. One strategy to reduce the size of the search space is to restrict the protein chain to sites on a regular lattice. In this context, we highlight the use of memetic algorithms, which combine genetic algorithms with local optimisation, to the study of simple protein models on the two-dimensional square lattice and the face-centred cubic lattice.     

Topological analysis of some special graphs: III. Regular polyhedra

A regular polyhedron is isomorphic to a cluster on which every face has same number of bonds and every atom has an equal number of coordinating atoms. A general strategy for generating the eigenvectors and the eigenvalues of regular polyhedra is given. Not sign analyses are also performed on the eigenvectors of regular polyhedra. The results provide us a quick way to grasp the topological feature of the electronic structure of clusters having interesting topology.     

Topological analysis of some special graphs. III. Regular polyhedra

A regular polyhedron is isomorphic to a cluster on which every face has same number of bonds and every atom has an equal number of coordinating atoms. A general strategy for generating the eigenvectors and the eigenvalues of regular polyhedra is given. Net sign analyses are also performed on the eigenvectors of regular polyhedra. The results provide us a quick way to grasp the topological feature of the electronic structure of clusters having interesting topology.     

Modern solid state NMR techniques and concepts in structural studies of synthetic polymers

In this mini‐review, we present the solid state nuclear magnetic resonance (NMR) methods which trace the new tendency in structural studies of synthetic polymers. The review is organized into three sections. In the first part, short theoretical background and introduction to very fast magic angle spinning NMR technique with sample rotation 60 kHz are shown. The second part presents method for enhancing the sensitivity of NMR experiments by application of dynamic nuclear polarization magic angle spinning technique. In the third section, the power of the NMR crystallography approach which can be used for fine refinement of polymers structure on the atomic level is discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Low voltage and high transmittance transflective blue-phase liquid crystal display with opposite polar electrodes

A single-cell-gap transflective polymer-stabilised blue-phase liquid crystal display with opposite polar pixel electrodes on an etched substrate is proposed. In the proposed structure, the space between common electrodes is adopted as transmissive region, and the space above the common electrode is adopted as reflective region. By optimising the electrode parameters of the transmissive and reflective regions, well-matched voltage-dependent transmittance and reflectance curves can be obtained. In addition, the device has good performances of low operating voltage (~3.2 V), high optical efficiency and a wide viewing angle.     

Novel and global approach of the complex and interconnected phenomena related to the contact line movement past a solid surface from hydrophobized silica gel

In this work a generalized hydrodynamic theory for water flow into a mesoporous matrix from hydrophobized silica gel is suggested. Although we examine a fluid dynamics problem, the motion of the water-gas-solid contact line past a hydrophobized silica gel surface, motivation for such research derives from the investigation of a novel principle of mechanical energy dissipation, called surface dissipation, and its attached machine element, named a colloidal damper (CD). Similar to a hydraulic damper, this absorber has a cylinder-piston structure, but oil is replaced by a colloid consisting of a mesoporous matrix and a lyophobic liquid. Here, the mesoporous matrix is from silica gel modified by linear chains of alkyldimethylchlorosilanes and water is the associated lyophobic liquid. Mainly, the colloidal damper energy loss can be explained by the dynamic contact angle hysteresis in advancing (liquid displaces gas) and receding motion (gas displaces liquid); such hysteresis occurs due to the geometrical and chemical heterogeneities of the solid surface. Although this new kind of dissipation could be attractive for many applications, the subject remains almost unexplored in the scientific literature. Many different, complex, and interconnected aspects are related to this subject: capillary hydrodynamics, slippage effect, contact angle hysteresis, estimation of dissipated energy, thickness optimization of the grafted layer on the surface of the mesoporous matrix, etc. For this reason, a novel and global approach to all the complex and interconnected phenomena related to the contact line movement past a solid surface from hydrophobized silica gel is proposed. Our approach has a modest experimental basis but this is compensated for with rich references to other experimental and theoretical work oriented to the study of surface phenomena in such systems. We tried to sort the existing results and to find the right place for each in building our global view of the problem. This work is structured as follows. The measurement technique of the hysteresis loop is described. From experimental data one calculates the dissipated energy versus length of the grafted molecule on the silica gel surface. These results are justified by flow analysis. Generalized hydrodynamic theory means here that the basic structure of the Navier-Stokes equations is kept, but in order to include the relation between macroscopic flow and molecular interactions, slip is allowed on the solid wall. The nanopillar architecture of the silica gel hydrophobic coating is described. Concepts of slip and contact angle hysteresis are detailed and their connection is revealed. During adsorption, water penetrates the pore space by maintaining contact with the top of the coating molecules (region of -CH(3) groups); after that, water is forced into and partially or totally fills the space between molecules (region of -CH(2) groups). In such circumstances, at the release of the external pressure, desorption occurs. An original energetic-barriers approach is proposed to understand the filling of the nanosize canals which occur in the hydrophobic grafted layer. Employing this energetic-barriers approach, one finds the optimum length of the grafted molecule which maximizes the dissipated energy of the CD reversible cycle. Such results are useful for the appropriate design of ultrahydrophobic surfaces in general, and for the optimal design of a hydrophobic coating of a mesoporous matrix destined for CD use.     

固体酸催化剂结构与催化反应机理的核磁共振研究

Solid acid catalysts have been widely used in advanced petrochemical processes because of their environmental friendliness, high product selectivity, and easy product separation. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a well-established tool for structure determination and dynamic study of various functional materials. In this review, we focus mainly on our research using solid-state NMR to characterize the acid properties and elucidate the catalytic reaction mechanism of solid acid catalysts. The acid strength of solid acids can be quantitatively measured from the chemical shifts of adsorbed probe molecules such as pyridine, acetone, trialkylphosphine oxides, and trimethylphosphine. The spatial proximity and synergetic effect of various acid sites on solid acid catalysts can be ascertained by two-dimensional (2D) double-quantum magic angle spinning (DQ MAS) NMR spectroscopy. Additionally, in situ solid-state NMR spectroscopy can be used to explore heterogeneous catalytic reaction mechanisms by monitoring the evolution of the reactants, intermediates, and products.     

序列结构对液晶共聚酯性能的影响

本文通过熔融酯交换和Schottern-Baumann缩聚反应合成了两类组成相同而序列结构不同的基于对羟基苯甲酸、对苯二甲酸和二元酚的三元共聚酯,用热台偏光显微镜、DSC和X-射线衍射,较详细地研究了序列结构对液晶相类型、转变温度和固态结构等的影响。结果表明,无规共聚酯较规则共聚酯的熔化温度普遍降低;但序列结构的差异并不改变液晶相类型,规则共聚酯和无规共聚酯均为热致向列型液晶,两类共聚酯固态结构的差异可用结构单元的相似性进行解释。