Hollow and Threadlike Nanostructures of Boron Carbide

An original low-temperature method is proposed for the synthesis of boron carbide from simple materials. It made it possible to obtain a powdered product in the form of hollow and threadlike nanostructures. The boron carbide nanotubes are shorter than bundles of nanotubes. The boron carbide nanostructures are grown from vapor-phase reagents at a high-temperature nanocenter, the enhanced reactivity of which is maintained as a result of the exothermic effect of the reaction.     

碳化硅和碳化硼在电催化中的应用

燃料电池是具有广泛应用前景的新能源技术。碳载铂基催化剂（Pt/C）是最常用的燃料电池电极催化剂,不过Pt/C稳定性较差、且成本高昂,严重限制了燃料电池的规模化应用。共价型碳化物碳化硅和碳化硼,由于具有极强的共价键,其物化稳定性优异,成为制备高稳定性、低成本的燃料电池催化剂的重要基础材料。本文总结了相关研究成果,介绍了碳化硅和碳化硼的独特优势,讨论了相关研究的发展方向。     

碳化硅和碳化硼在电催化中的应用

燃料电池是具有广泛应用前景的新能源技术。碳载铂基催化剂(Pt/C)是最常用的燃料电池电极催化剂,不过Pt/C稳定性较差、且成本高昂,严重限制了燃料电池的规模化应用。共价型碳化物碳化硅和碳化硼,由于具有极强的共价键,其物化稳定性优异,成为制备高稳定性、低成本的燃料电池催化剂的重要基础材料。本文总结了相关研究成果,介绍了碳化硅和碳化硼的独特优势,讨论了相关研究的发展方向。     

六方硼碳氮化合物的溶剂热合成与表征

采用溶剂热合成方法,以无水乙腈、叠氮化钠和四氟硼酸钠为原料,以苯为溶剂,在温度为400℃条件下,成功合成出了硼碳氮(BCN)三元化合物.利用X射线粉末衍射(XRD)、Fourier变换红外光谱(FTIR)、透射电子显微镜(TEM)、选区电子衍射(SAED)、X射线能谱(EDS)和电子能量损失谱(EELS)对合成产物进行了表征.XRD和SAED分析表明,合成产物为六方相,晶格常数为a=0.2678nm,c=0.6639nm;TEM结果表明,合成产物中存在纳米棒和四方柱状块体BCN;EELS和EDS分析表明,产物由B,C,N三种元素组成,化学式为B0.23C0.60N0.17;FTIR分析表明样品中存在C—N,B—C和B—N键,表明B,C,N三元素之间达到了原子级化合.     

碳化硼纳米线的制备和结构

以碳纳米管为模板，通过加热碳纳米管与硼粉的混合物，获得了笔直的硼碳纳米线.对纳米线的结构和成分进行研究，结果表明纳米线主要为B4C纳米线.在部分B4C纳米线的端部存在Ni颗粒，这些端部具有Ni颗粒的纳米线构成了纳米磁针.讨论了B4C纳米线的生长机制，B4C纳米线的生长主要为硼原子在碳纳米管中扩散并发生化学反应，使得碳纳米管晶格结构发生重组，形成B4C纳米线.反应后，硼原子部分取代了碳纳米管中碳原子，修补了碳纳米管中的晶格缺陷，获得了形态笔直的B4C纳米线.     

碳化硼成分分析标准物质的研制

介绍碳化硼成分分析标准物质的制备方法。以硼酸和蔗糖为原材料,酯化反应得到硼酸酯沉淀,经过烧结制备碳化硼粉体。用低温前驱体裂解法制备碳化硼成分分析标准物质,并进行了均匀性检验、稳定性考察,采用8家实验室协作定值,对定值结果的不确定度进行了评定。结果表明,研制的碳化硼成分分析标准物质具有良好的均匀性和稳定性,量值准确可靠,定值结果的相对扩展不确定度为0.003 1%~0.13%(k=2)。     

Atomic force microscopy and transmission electron microscopy of cellulose from Micrasterias denticulata; evidence for a chiral helical microfibril twist

Atomic force microscopy (AFM), tapping mode atomic force microscopy (TM-AFM) and transmission electron microscopy (TEM) have been used to image the cell wall, ultrathin sections of whole cells and cellulose microfibrils prepared from the green alga Micrasterias denticulata. Measurements of the microfibril dimensions are in agreement with earlier observations carried out by electron microscopy. Images at the molecular level of the surface of the microfibrils were obtained with AFM and show regular periodicities along the microfibril axis that correspond to the fibre and glucose repeat distances of cellulose. Twisted regions visible at intervals along the microfibrils dried down onto substrates were noted to be right-handed in over 100 observations by TEM, AFM and TM-AFM. This revised version was published online in August 2006 with corrections to the Cover Date.     

Oxidation Behaviour of A Boron Carbide Based Material in Dry and Wet Oxygen

The oxidation behaviour of a B₄C based material was investigated in a dry atmosphere O₂(20 vol.%)-CO₂(5 vol.%)-He and also in the presence of moisture H₂O (2.3 vol%) as boron oxide is very sensitive to water vapour. The mass changes of samples consisting of a chemical vapour deposit of B₄C on silicon nitride substrates were continuously monitored in the range 500–1000°C during isothermal experiments of 20 h. The stability of boron oxide formed by oxidation of B₄C was also studied in dry and wet atmospheres to explain the kinetic curves. In both atmospheres, oxidation is diffusion controlled at 700 and 800°C and enhanced by water vapour. At 900°C and higher temperatures, boron oxide volatilisation and consumption by reaction with water vapour modifies the properties of the oxide film and the material is no more protected. At 600°C, B₄C oxidation is weak but the process remains diffusion controlled in dry conditions as boron oxide volatilisation is negligible. However, in the presence of water vapour, B₂O₃ consumption rate is significant and mass losses corresponding to this consumption and to the combustion of the excess carbon are observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

石墨基底对碳/碳化硼复合纳米绳形成的影响

利用邻碳硼烷(C₂H₁₂B₁₀)作为反应原料,二茂铁(C₁₀H₁₀Fe)作为催化剂,通过化学气相沉积法在石墨基片上生长出一种新颖的碳化硼纳米绳。用X射线衍射仪分析纳米绳的相结构,用场发射扫描电子显微镜(FESEM)和高分辨透射电子显微镜(HRTEM)观察纳米绳的微观形貌和结构,结果发现纳米绳的中心部分是碳化硼纳米线,在线的表面有非晶碳绳结,故纳米绳为碳/碳化硼复合物。研究了绳状产物的生长机理,表明石墨基片对产物的形成有至关重要的作用。     

Structure and Electron Transport at Metal Atomic Junctions Doped with Dichloroethylene

We have investigated the structure and electron transport at dichloroethylene-doped metal atomic junctions at low temperatures (20 K) in ultra-high vacuum, using Fe, Ni, Pd, Cu, Ag, and Au. The metal atomic junctions were fabricated using the mechanically controllable break junction technique. After introducing the dichloroethylene (DCE), the conductance behavior of Fe, Ni, and Pd junctions was considerably changed, whereas little change was observed for Cu, Ag, and Au. For the Pd and Cu junctions, a clear peak was observed in their conductance histograms, showing that the single-molecule junction was selectively formed. To investigate the structure of the metal atomic junctions further, their plateau lengths were analyzed. The length analysis revealed that the Au atomic wire was elongated, and the metal atomic wires were formed for the other transition metals: those that do not normally form metal atomic wires without DCE doping, as DCE adsorption stabilized the metal atomic states. There is a strong interaction between DCE and the metals, where DCE supports the formation of the metal atomic wire for Fe, Ni, and Pd.     

石墨炉原子吸收法测定植物样品中硼的研究

本文比较了四种石墨和三种基体改进剂对石墨炉法测硼的影响。结果表明，使用涂层石墨管并采用Ｃａ－Ｍｇ－抗坏血酸作基体改进剂，可获得最高的灵敏度和最好的回收率，讨论了硼的最佳工作条件和干扰情况，对植物标准样品进行了测定，所得结果与标准值吻合，植物中硼含量为３４～５３μｇ／ｇ时，方法的相对标准偏差为２．１％～３．８％，检出限为３７８ｐｇ（Ｋ＝３）。     

Growth of Single-Walled Carbon Nanotubes with Controlled Structure: Floating Carbide Solid Catalysts

Single-walled carbon nanotube (SWNT) horizontal arrays with specific chirality can be enriched using solid carbide catalysts on substrates. However, scale-up production by continuous loading of the solid catalysts onto the substrates is challenging. Described here is the preparation of a floating carbide solid catalyst (FSC) for the controlled growth of SWNTs. The FSC, titanium carbide (TiC) nanoparticle, was directly obtained in the carrier gas phase by decomposition and carbonization of the titanocene dichloride precursor at high temperature. By using the TiC nanoparticle FSC, both SWNT horizontal arrays and randomly distributed networks can be obtained. The chirality of the as-grown SWNTs were thermodynamically controlled to have fourfold symmetry. Further optimization of growth condition resulted in an abundance of (16,8) tubes with about a 74 % content. This FSC chemical vapor deposition (FSCCVD) method has potential for realizing mass growth of SWNTs with controlled structures.     

Structure and Electronic Characteristics of New Graphyne-Like Fullerenes of Boron Nitride: Quantum-Chemical Modelling

Atomic models are proposed and quantum-chemical modelling is undertaken for hypothetical graphyne-like fullerenes of boron nitride. The electronic structure and interatomic interactions are discussed for the case of the B₁₆N₁₆ and B₄₈N₄₈ molecules. The proposed polyhedral boron–nitrogen molecules, having stable dielectric characteristics and highly porous structure, may be of interest for the creation a family of new intercalated nanomaterials based on these nanoparticles.     

甘草多糖螺旋结构的原子力显微镜研究

用原子力显微镜(AFM)对甘草多糖的微观结构进行观察, 实验结果表明, 甘草多糖主要由葡萄糖、阿拉伯糖和半乳糖组成. 甘草多糖分子的稀溶液铺展在Ni^2＋处理的云母片上, 经干燥, 乙醇固定后, 获得稳定、重复的图像. 甘草多糖分子具有高度分枝的结构, 并且糖链间形成环状、柱状或近似于螺旋状的结构. 甘草多糖链呈多股紧密的螺旋结构, 这种现象可能与该多糖中分子间的Van der Waals相互作用以及糖链间氢键缔合有关.     

Growth of Single‐Walled Carbon Nanotubes with Controlled Structure: Floating Carbide Solid Catalysts

Single‐walled carbon nanotube (SWNT) horizontal arrays with specific chirality can be enriched using solid carbide catalysts on substrates. However, scale‐up production by continuous loading of the solid catalysts onto the substrates is challenging. Described here is the preparation of a floating carbide solid catalyst (FSC) for the controlled growth of SWNTs. The FSC, titanium carbide (TiC) nanoparticle, was directly obtained in the carrier gas phase by decomposition and carbonization of the titanocene dichloride precursor at high temperature. By using the TiC nanoparticle FSC, both SWNT horizontal arrays and randomly distributed networks can be obtained. The chirality of the as‐grown SWNTs were thermodynamically controlled to have fourfold symmetry. Further optimization of growth condition resulted in an abundance of (16,8) tubes with about a 74 % content. This FSC chemical vapor deposition (FSCCVD) method has potential for realizing mass growth of SWNTs with controlled structures.     

A New Class of Boron Nanotube

The configurations, stability and electronic structures of a new class of boron sheet and related boron nanotubes are predicted within the framework of density functional theory. This boron sheet is sparser than those of recent proposals. Our theoretic results show that the stable boron sheet remains flat and is metallic. There are bands similar to the π‐bands in graphite near the Fermi level. Stable nanotubes with various diameters and chiral vectors can be rolled from the sheet. Within our study, only the thin (8, 0) nanotube with a band gap of 0.44 eV is semiconducting, while all the other thicker boron nanotubes are metallic, independent of their chirality. It indicates the possibility, in the design of nanodevices, to control the electronic transport properties of the boron nanotube through the diameter.     

核壳结构碳化钨/碳化钨铁复合材料的制备与电催化活性

以铁黄为载体,偏钨酸铵为钨源,将直接包覆与原位还原碳化技术相结合制备了碳化钨/碳化钨铁复合材料.经X射线衍射(XRD)分析和透射电子显微镜(TEM)观察,复合材料的主要物相为碳化钨铁(Fe3W3C)、碳化钨(WC)和碳化二钨(W2C),且构成了以Fe3W3C为核、WC和W2C为壳的核壳结构.采用三电极体系循环伏安法测试了复合材料在酸性、中性和碱性体系中对甲醇的电催化氧化活性.结果表明,与颗粒状碳化钨和介孔空心球状碳化钨相比,复合材料的电催化活性有了明显的提高;进一步研究发现,复合材料的电催化活性不仅受到体系性质的影响,还与其物相组成和微结构相关.上述结果说明,通过控制复合材料的物相组成及微结构,以及反应体系的性质可实现对其电催化活性的调控;同时表明,核壳结构是提高碳化钨催化材料活性的有效途径之一.     

Synergistic Effect of Boron Nitride and Carbon Domains in Boron Carbide Nitride Nanotube Supported Single-Atom Catalysts for Efficient Nitrogen Fixation

Developing the low-cost and efficient single-atom catalysts (SACs) for nitrogen reduction reaction (NRR) is of great importance while remains as a great challenge. The catalytic activity, selectivity and durability are all fundamentally related to the elaborate coordination environment of SACs. Using first-principles calculations, we investigated the SACs with single transition metal (TM) atom supported on defective boron carbide nitride nanotubes (BCNTs) as NRR electrocatalysts. Our results suggest that boron-vacancy defects on BCNTs can strongly immobilize TM atoms with large enough binding energy and high thermal/structural stability. Importantly, the synergistic effect of boron nitride (BN) and carbon domains comes up with the modifications of the charge polarization of single-TM-atom active site and the electronic properties of material, which has been proven to be the essential key to promote N₂ adsorption, activation, and reduction. Specifically, six SACs (namely V, Mn, Fe, Mo, Ru, and W atoms embedded into defective BCNTs) can be used as promising candidates for NRR electrocatalysts as their NRR activity is higher than the state-of-the art Ru(0001) catalyst. In particular, single Mo atom supported on defective BCNTs with large tube diameter possesses the highest NRR activity while suppressing the competitive hydrogen evolution reaction, with a low limiting potential of −0.62 V via associative distal path. This work suggests new opportunities for driving NH₃ production by carbon-based single-atom electrocatalysts under ambient conditions.     

Highly Dispersible and Stable Anionic Boron Cluster–Graphene Oxide Nanohybrids

An efficient process to produce boron cluster–graphene oxide nanohybrids that are highly dispersible in water and organic solvents is established for the first time. Dispersions of these nanohybrid materials in water were extraordinarily stable after one month. Characterization of hybrids after grafting of appropriate cobaltabisdicarbollide and closo‐dodecaborate derivatives onto the surface of graphene oxide (GO) was done by FT‐IR, XPS, and UV/Vis. Thermogravimetric analysis (TGA) clearly shows a higher thermal stability for the modified‐GO nanohybrids compared to the parent GO. Of particular note, elemental mapping by energy‐filtered transmission electron microscopy (EFTEM) reveals that a uniform decoration of the graphene oxide surface with the boron clusters is achieved under the reported conditions. Therefore, the resulting nanohybrid systems show exceptional physico‐chemical and thermal properties, paving the way for an enhanced processability and further expanding the range of application for graphene‐based materials.     

The Effect of Boron on the Properties of Glucomannan： An Experimental and Molecular Dynamics Simulation Study

1 INTRODUCTION gel using KGM and borax at 60 ℃, which can be used as slow-released reagent of theophylline and Generally, the mixture of Konjac Glucomanan dibucaine. And Hogi Tsuneo utilized KGM and tetra- (KGM) and salts that could be hydrolyzed to form valent boric acid to prepare artificial crystal[1]. This multi-hydroxyl hydrates leads to the generation of kind of crystal has good light transmission property, gelatum. Among the familiar salts, such as borate, elasticity, intensi…