硬质合金基体上钛过渡层碳化条件对金刚石薄膜附着力的影响

以WC-6;Co为基体,采用磁控溅射法,在酸蚀后进行氢等离子体脱碳试样上制备Ti过渡层,然后碳化过渡层为TiC.在电子辅助热丝化学气相沉积装置中制备金刚石薄膜.研究碳化条件对金刚石薄膜与基体附着力的影响.结果表明,在700℃左右的低温碳化,TiC结构致密,而在850℃左右的高温碳化,TiC呈疏松的多孔组织,在CH4-Ar等离子体中碳化则850℃左右仍能获得致密的TiC层.在致密的过渡层上沉积的金刚石薄膜具有更高的附着力.     

Pyrolysis and film growth studies of phosphinoborane compounds

Chemical vapor deposition experiments were conducted using phosphinoborane compounds of the type [R₂BPR′₂]_n, where R = CH₂CH₃ (1) or CH₃ (2), R′= C(CH₃)₃, and R = CH₂CH₃ (3) or CH₃ (4), R′ = Si(CH₃)₃. Thin films were deposited on Si substrates at 300–850°C under vacuum using 1–3, while no film formed using 4. All films contained considerable carbon (C/B = 0.67–7) and were deficient in phosphorus (P/B = 0-0.5) according to Auger electron spectroscopy. For 3, silicon was incorporated in the films (Si/B = 0.9–2). The preferential loss of phosphorus was nearly complete at higher pyrolysis temperatures that favor formation of carbon-rich films. Volatile products of the decompositions were observed by in situ mass spectroscopy and by ¹H nuclear magnetic resonance analysis of the condensate in a liquid nitrogen cooled trap. The products indicate that β-hydrogen elimination of alkene from boron is a preferred reaction pathway, while concerted elimination reactions appear to be inefficient. Although these phosphinoborane compounds do not appear to be suitable precursors for pure boron phosphide, the B-P-C films obtained are chemically inert and may be of interest as protective coatings.     

Stable Borane Adducts of Alcoholates and Carboxylates

Six adducts of B(C₆F₅)₃ and archetypical alcoholates and carboxylates, were prepared and isolated as crystalline sodium crown ether salts, [Na(15‐crown‐5)][CH₃O · B(C₆F₅)₃] ( 1 ), [Na(15‐crown‐5)][CH₃CH₂O · B(C₆F₅)₃] ( 2 ), [Na(15‐crown‐5)][HCO₂ · B(C₆F₅)₃] ( 3 ), [Na(15‐crown‐5)][(H₃CCO₂ · B(C₆F₅)₃] ( 4 ), [Na(15‐crown‐5)][(F₃CCO₂ · B(C₆F₅)₃] ( 5 ), and [Na₂(15‐crown‐5)₃][C₂O₄ · 2 B(C₆F₅)₃] ( 6 ). All compounds were fully characterized by multinuclear NMR‐ and IR spectroscopy, ESI MS spectrometry, and X‐ray crystallography.     

Synthesis,Crystal Structure of a New Structure Type,and Thermal Analysis of the Ammonium Borophosphate (NH4)2[B2P3O11(OH)]

(NH₄)₂[B₂P₃O₁₁(OH)] was synthesized as a crystalline colorless powder by reaction of (NH₄)₂HPO₄, H₃BO₃, and H₃PO₄ under hydrothermal conditions at 180 °C. According to X‐ray single‐crystal investigations (NH₄)₂[B₂P₃O₁₁(OH)] crystallizes in a new structure type in the orthorhombic space group P2₁2₁2₁ (no. 19) [Z = 4, a = 4.509(3), b = 14.490(11), c = 16.401(12) Å, R₁ = 0.046, wR₂ = 0.093, 1682 data, 200 parameters]. The crystal structure comprises infinite layers of corner‐sharing borate, phosphate and hydroxo‐phosphate tetrahedra with ammonium ions in‐between. The loop‐Branched (lB) zweier‐single layer reveals an open‐Branched (oB) vierer‐single ring as fundamental building unit (FBU), which was observed in (NH₄)₂Mn^II[B₂P₃O₁₁(OH)₂]Cl^[1] for the first time. Besides the spectroscopic properties the thermal behavior is presented as well.     

Boron nitride nanotube-based amphiphilic hybrid nanomaterials for superior encapsulation of hydrophobic cargos

We report an organic-inorganic hybrid core-shell nanomaterial obtained by conjugation of an amphiphilic monomethoxy-poly(ethylene glycol)-b-poly(epsilon-caprolactone) diblock copolymer to hydroxylated boron nitride nanotubes (BNNTs). The extent of copolymer grafting reached 64% w/w, an exceptionally high value. The hybrid materials exhibit excellent physical stability in water and an outstanding loading capacity (31.3% w/w) for curcumin, a hydrophobic drug. Moreover, they present good compatibility with the Caco2 cell line, a model of intestinal epithelium. Our findings demonstrate the potential of multifunctional hybrid BNNTs to serve as a platform for complex amphiphilic nanoparticle architectures with improved features.     

A Redox‐anchoring Approach to Well‐dispersed MoCx/C Nanocomposite for Efficient Electrocatalytic Hydrogen Evolution

Here we report a redox‐anchoring strategy for synthesizing a non‐noble metal carbide (MoC_x) nanocomposite electrocatalyst for water electrolysis in acidic media, using glucose and ammonium heptamolybdate as carbon and Mo precursors, respectively, without the need of gaseous carbon sources such as CH₄. Specifically, the aldehyde groups of glucose are capable of reducing Mo⁶⁺ to Mo⁴⁺ (MoO₂), and thus molybdenum species can be well anchored by a redox reaction onto a carbon matrix to prevent the aggregation of MoC_x nanoparticles during the following carbonization process. The morphology and chemical composition of the electrocatalysts were well characterized by BSE‐SEM, TEM, XRD and XPS. The obtained MoC_x−2 sample showed a reasonably high hydrogen evolution reaction (HER) activity and excellent stability in an acidic electrolyte, and its overpotential required for a current density output of 20 mA cm⁻² is as low as 193 mV. Such a prominent performance is ascribed to the excellent dispersity and nano‐size, and the large reactive surface area of MoC_x particles. This work may open a new way to the design and fabrication of other non‐noble metal carbide nanocatalysts for various electrochemical applications.     

羟基化氮化硼催化乙烷氧化脱氢制乙烯

乙烯是最为重要的化工原料之一,目前其工业来源主要来自于烃类的水蒸汽裂解过程.该过程本质上是一个高温均相裂解过程,温度(>800?℃)高,能耗大,碳排放严重.乙烷氧化脱氢制乙烯属于放热反应,反应温度低,速率快,无积碳等限制,是一条更富有竞争力的工艺路线.然而,常用的金属或金属氧化物催化剂容易导致乙烯深度氧化,从而降低了乙烯选择性.纳米碳材料在烃类氧化脱氢反应中展现出一定的催化活性,但容易被氧化,难以用于反应温度高的乙烷氧化脱氢反应.本文报道了羟基化的氮化硼(BNOH)可高效催化乙烷氧化脱氢制乙烯.氮化硼边沿羟基官能团脱氢生成了动态活性位,从而引发了乙烷的脱氢反应.BNOH对乙烷氧化脱氢制乙烯显示出高选择性.当乙烷转化率在11%,乙烯选择性可高达95%;当乙烷转化率增加到40%,乙烯选择性保持在90%.重要的是,当乙烷转化率超过60%时,BNOH仍然可保持80%的乙烯选择性以及50%的乙烯收率.这些性能指标与现有工业乙烷水蒸气裂解过程运行性能相当.进一步优化反应条件,BNOH催化剂能够实现高达9.1 gC2H4 gcat-1 h-1的时空收率.经过200 h的氧化脱氢反应测试,BNOH催化剂活性和选择性基本恒定,表明其具有非常好的稳定性.X射线粉末衍射结果显示,反应前后BNOH催化剂的物相没有发生变化.透射电子显微镜测试证实,反应后BNOH催化剂的形貌和微观结构也没有明显改变.X射线光电子能谱结果显示,反应200 h后BNOH催化剂表面的氧含量仅从反应前的6.9 atom%微增到8.3 atom%.1H固体核磁共振谱测试显示,反应200 h后,BNOH催化剂上羟基含量无明显改变.结合原位透射红外光谱和同位素示踪实验,初步确定了BNOH催化剂上引发乙烷氧化脱氢反应的活性中心.氮化硼边沿的氧官能团并不能引发乙烷的氧化脱氢反应,而羟基官能团才是氧化脱氢反应发生的活性位.在乙烷氧化脱氢条件下,分子氧脱除羟基官能团上的氢原子动态生成BNO·?和HO2·?活性位.密度泛函理论计算表明,乙烷首先在BNO·?或HO2·?位活化生成乙基自由基,这些中间物进一步与气相氧物种发生反应脱氢生成乙烯.动力学测试结果也验证了上述实验和理论结果.     

含钨SBA-15介孔分子筛催化剂的表面酸性和羟基分布

分别以浸渍法和水热晶化法制备了SBA-15介孔分子筛孔中插入氧化钨和碳化钨的催化剂,采用NH3-TPD测定了表面酸性和总酸量,并采用FT-IR研究了它们的表面羟基分布情况.NH3-TPD结果表明,浸渍法制备的含氧化钨的SBA-15介孔分子筛催化剂表面只有SBA-15介孔分子筛的弱酸位,而含碳化钨的SBA-15介孔分子筛催化剂表面还出现了W2C的强酸位.水热晶化法制备的含氧化钨的SBA-15介孔分子筛催化剂表面SBA-15介孔分子筛的弱酸位随W含量的增大略有增强, W含量较高时还出现了钨物种的强酸位;含碳化钨的SBA-15介孔分子筛催化剂表面除了SBA-15介孔分子筛的弱酸位外, W含量较低时有W2C的强酸位, W含量较高时有W2C和WC两种强酸位.傅里叶变换红外光谱结果表明,浸渍法和水热晶化法制备的含氧化钨和碳化钨的SBA-15介孔分子筛催化剂除表面自由硅羟基外,还存在着α, β和γ三种不同类型的氢键羟基,并且氢键羟基和催化剂的制备方法以及催化剂的W含量都有一定的关系.     

Synthesis, crystal structure, and properties of two modifications of MgB(12)C(2)

Single crystals of two modifications of the new magnesium boride carbide MgB(12)C(2) were synthesized from the elements in a metallic melt by using tantalum ampoules. Crystals were characterized by single-crystal X-ray diffraction and electron microprobe analysis (energy-dispersive (EDX) and wavelength-dispersive (WDX) X-ray spectroscopy). Orthorhombic MgB(12)C(2) is formed in a Cu/Mg melt at 1873 K. The crystal structure of o-MgB(12)C(2) (Imma, Z=4, a=5.6133(10), b=9.828(2), c=7.9329(15) A, 574 reflections, 42 variables, R(1)(F)=0.0208, wR(2)(I)=0.0540) consists of a hexagonal primitive array of B(12) icosahedra with Mg atoms and C(2) units in trigonal-prismatic voids. Each icosahedron has six exohedral B--B and six B--C bonds. Carbon is tetrahedrally coordinated by three boron atoms and one carbon atom with a remarkably long C--C distance of 1.727 A. Monoclinic MgB(12)C(2) is formed in an Al/Mg melt at 1573 K. The structure of m-MgB(12)C(2) (C2/c, Z=4, a=7.2736(11), b=8.7768(13), c=7.2817(11) A, beta=105.33(3) degrees , 1585 reflections, 71 variables, R(1)(F)=0.0228, wR(2)(I)=0.0610) may be described as a distorted cubic close arrangement of B(12) icosahedra. Tetrahedral voids are filled by C atoms and octahedral voids are occupied by Mg atoms. The icosahedra are interconnected by four exohedral B--B bonds to linear chains and by eight interstitial C atoms to form a three-dimensional covalent network. Both compounds fulfill the electron-counting rules of Wade and Longuet-Higgins.     

The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties

The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI₃ and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln₁₂(C₂)₃I₁₇-type compounds (C 2/c, a=19.610(1) and 19.574(4) Å, b=12.406(2) and 12.393(3) Å, c=19.062(5) and 19.003(5) Å, β=90.45(3)° and 90.41(3)°, for Pr₁₂(C₂)₃I₁₇ and Nd₁₂(C₂)₃I₁₇, respectively). All compounds contain infinite zigzag chains of C₂-centered metal atom octahedra condensed by edge-sharing into the [tcc]_∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd₁₂(C₂)₃I₁₇ sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln³⁺)₁₂(C₂^6-)₃(I⁻)₁₇(e⁻) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd₁₂(C₂)₃I₁₇, Gd₁₂(C₂)₃I₁₇ and Dy₁₂(C₂)₃I₁₇ indicate the coexistence of competing magnetic interactions leading to spin freezing at T_f=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at T_N=25 and 29 K, respectively. For Dy₁₂(C₂)₃I₁₇, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe.