Mesoporous Bubble‐like Manganese Silicate as a Versatile Platform for Design and Synthesis of Nanostructured Catalysts

Manganese silicate in bubble‐like morphology was used as a versatile platform to prepare a new class of yolk–shell hybrids. The mesoporosity of the shell was generated from the interbubble space and the bubble structure of manganese silica was used to hold and support nanoparticles (e.g., Au, Ag, Pt, Co, Ni, Au–Pd alloy, MoO₂, Fe₃O₄, carbon nanotubes and their combinations). We also used heterogeneous catalysis reactions to demonstrate the workability of these catalysts in both liquid and gas phases.     

Atomic ordering as a new way of nanostructure creation in solids

The application of atomic-vacancy ordering for generating nanostructures in non-stoichiometric compounds and substituting solid solutions is considered. The conditions under which a nanostructure is formed in powder and bulk samples and peculiarities of the nanostructure within them are exemplified with non-stoichiometric vanadium carbide VC_0.875. The formation of nanostructure in the VC_0.875 carbide has been demonstrated to originate from the first order phase transition disorder-order VC_0.875 → V₈C₇ accompanied by an abrupt volume change.     

High Loading Pt Core/Carbon Shell Derived from Platinum‐Aniline Complex for Direct Methanol Fuel Cell Application

A novel approach to high loaded Pt core/carbon shell catalyst synthesis from a Pt‐aniline complex was reported. The Pt‐aniline complex was successfully synthesized by irradiating an ultrasound to the hexachloro platinic acid and aniline monomer mixture. The highly viscous nature of aniline leads to reproducible hexagonal plate like Pt‐aniline complex crystals. The chemical composition of the Pt‐aniline complex was identified as [PtCl₂(C₆H₅NH₂)₂] with the help of NMR, XPS, HR ESI‐MS, and TGA analyses. Furthermore, the Pt‐aniline hexagonal plates were sintered at various temperatures like 400 °C, 500 °C, and 700 °C for an hour. This formed the highly dispersed carbon covered Pt nano particles with loading of 80.1 wt %, 81.3 wt %, and 83.4 wt % for HP‐4, HP‐5, and HP‐7, respectively. After supporting it on Vulcan XC‐72, Pt core/carbon shell pyrolyzed at a low temperature showed excellent performance in methanol oxidation reaction. In addition, Pt core/carbon shell prepared at a high temperature revealed excellent tolerance to methanol.     

Forming and Gathering of SnO2 Nanoparticles on External Surface of High Silica TON, MFI and FAU Type Zeolites

Tin dioxide （SnO2） nano-particles were prepared on high silica TON, MFI and FAU type zeolites by impregnation of SnC12 solution and subsequent calcination at 873 K. XRD and SAED were used to characterize the crystalline phase, and TEM was used to characterize the morphology, the particle size and the agglomerative state of the formed nano-materials. The nano-particles, which possess 8 nm, 10-80 nm and 6 nm in size, were found to form on the outer surface of TON, MFI and FAU zeolites, respectively. SnO2 microcapsules and SnOz netlike nanostructure were obtained by decomposition of SnO2-TON and SnO2-MFI in 40% hydrofluoric acid at room temperature. Compared with the nano-particles formed on NaY zeolite, the special morphology and the agglomerative state of SnO2 nanostructures on TON and MFI type zeolites with one and two dimension channel system indicate that the heterogeneous framework, surface structure and property perform important function for forming and growing SnO2 nanostructure on the outer surface of the zeolites.     

Structural chemistry of complex carbides and related compounds

Complex carbides formed in ternary systems of a transition element (M), a B-group element (M′), and carbon and having a formula M₂M′C (H-phase) or M₃M′C (perovskite carbide) occur frequently. This reflects the simple geometry of the atomic arrangement of the metals and the filling mode by an interstitial stabilizer such as carbon or nitrogen. The phase relationship of the ternary combinations {Ti, Zr, Hf, V, Nb, Ta, Cr, Mn, and Ni}-aluminum-carbon was investigated. New complex carbides were found with the corresponding zirconium, hafnium, and tantalum combinations. The crystal structures in the case of Zr- and Hf-containing complex carbides can be characterized by a twelve-metal-layer sequence and by a ten-metal-layer sequence with carbon atoms again filling octahedral voids. The transition of structure types from TiC, Ti₂AlC, Ti₃SiC₂, ZrAlC₂, Zr₂Al₃C₅, to Al₄C₃ is also discussed.     

Assembly of a Nanoreactor System with Confined Magnetite Core and Shell for Enhanced Fenton‐Like Catalysis

Conventional solid catalysts for heterogeneous Fenton‐like reactions in bulk solution usually suffer from aggregation and vulnerability, which greatly lower the catalytic efficiency and hamper their practical application. Herein, we demonstrate a promising yolk–shell nanostructure with both the core and the shell composed of magnetite (designated as yolk‐like Fe₃O₄@Fe₃O₄/C) as a nanoreactor capable of accommodating the Fenton‐like reaction into its void space. Benefiting from the mesoporous shell and perfect interior cavity of this composite, reactants can access and be abundantly confined within the microenvironment where Fe₃O₄ sites are dispersed on the entire cavity surfaces, thus leading to a higher catalytic efficiency compared with the conventional solid catalysts in bulk solution. The chosen model reaction of chlorophenols degradation in the presence of the as‐prepared materials as well as hydrogen peroxide (H₂O₂) confirms this assumption. Under the optimal reaction conditions, more than 97 % 4‐chlorophenol (4‐CP) can be degraded in the Fe₃O₄@Fe₃O₄/C nanoreactor, whereas only 28 % can be achieved by using bare Fe₃O₄ particles within 60 min. Furthermore, owing to the existence of the outermost carbon layer and high‐magnetization properties, the nanoreactor can be re‐used for several runs. The synthesized nanoreactor displays superior catalytic activity toward the Fenton‐like reaction compared with the bare solid catalysts, and thereby holds significant potential for practical application in environmental remediation.     

Synthesis of Starburst Oligoanilino[60]fullerene and Poly(Dimethylsiloxane) Triblock Copolymers

Abstract

A new synthetic approach for the fabrication of core‐shell like conducting elastomers was described. The approach utilized the facile intermolecular self‐assembly of poly(dimethylsiloxane) (PDMS) in DMSO leading to formation of a core particle, while soluble oligoaniline (A _x ) segments dispersed in the solution phase resembling a shell overlayer for building the morphology. This morphology was demonstrated by bis[penta(tetraanilinofullereno)] bis(aminopropyl)poly(dimethylsiloxane) [PDMS‐(F5A₄)₂] triblock co‐oligomers synthesized using a functionalized C₆₀ derivative as a linker. Observation of ¹H NMR spectroscopic responses on the PDMS particle formation in DMSO‐d ₆ is consistent with the proposed core‐shell geometry with oligoaniline moieties located at the shell overlayer.     

Hydrodeoxygenation of Furfural over Unsupported,SiO2-supported or Metal-promoted Mo Carbides: Tunning the Selectivity between 2-Methylfuran and C10 Furoins Diesel Precursors

The hydrodeoxygenation of furfural (FF) over Mo carbides in liquid phase at 200 °C, 30 bar of H₂ for 4 h in 2-butanol was investigated. Unsupported and SiO₂-supported Mo carbide with different crystallographic phases (β-Mo₂C/SiO₂ and α-MoC/SiO₂), and in the presence of Cu and Ni as promoters were studied. The reactivation treatment under H₂ atmosphere of the passivated Mo carbides was investigated by XAS. The results show that Mo is present in different states of oxidation in the passivated catalysts, with more severe oxidation in the bimetallic systems, in which the original carbides are not restored after reactivation. Finally, the product distribution in the HDO of furfural is modified as a function of catalyst oxidation degree. Using the less oxidized Mo carbide (β-Mo₂C), a higher yield to 2-methylfuran is obtained, while C₁₀ condensation products are formed for the more oxidized catalysts.     

Small molecule‐mediated control of hydroxyapatite growth: Free energy calculations benchmarked to density functional theory

The unique, plate‐like morphology of hydroxyapatite (HAP) nanocrystals in bone lends to the hierarchical structure and functions of bone. Proteins enriched in phosphoserine (Ser‐OPO₃) and glutamic acid (Glu) residues have been proposed to regulate crystal morphology; however, the atomic‐level mechanisms remain unclear. Previous molecular dynamics studies addressing biomineralization have used force fields with limited benchmarking, especially at the water/mineral interface, and often limited sampling for the binding free energy profile. Here, we use the umbrella sampling/weighted histogram analysis method to obtain the adsorption free energy of Ser‐OPO₃ and Glu on HAP (100) and (001) surfaces to understand organic‐mediated crystal growth. The calculated organic‐water–mineral interfacial energies are carefully benchmarked to density functional theory calculations, with explicit inclusion of solvating water molecules around the adsorbate plus the Poisson–Boltzmann continuum model for long‐range solvation effects. Both amino acids adsorb more strongly on the HAP (100) face than the (001) face. Growth rate along the [100] direction should then be slower than in the [001] direction, resulting in plate‐like crystal morphology with greater surface area for the (100) than the (001) face, consistent with bone HAP crystal morphology. Thus, even small molecules are capable of regulating bone crystal growth by preferential adsorption in specific directions. Furthermore, Ser‐OPO₃ is a more effective growth modifier by adsorbing more strongly than Glu on the (100) face, providing one possible explanation for the energetically expensive process of phosphorylation of some proteins involved in bone biomineralization. The current results have broader implications for designing routes for biomimetic crystal synthesis. © 2013 Wiley Periodicals, Inc.     

Interfacial reactions of a MAX phase/superalloy hybrid

Oxidation resistant, strain tolerant MAX phase coatings are of general interest for high temperature applications. Accordingly, Cr₂AlC MAX phase coupons were vacuum diffusion bonded to an advanced turbine disk alloy at 1100 °C for compatibility studies. The interface revealed an inner diffusion zone consisting of ~10 µm of β‐Ni(Co)Al, decorated with various γ′ (Ni,Co)₃Al, Ta(Ti,Nb)C, and W(Cr,Mo)₃B₂ precipitates. On the Cr₂AlC side, an additional ~40‐µm Al‐depletion zone of Cr₇C₃ formed an interconnected network with the β‐Ni(Co)Al. On the superalloy side, enhanced carbide precipitation developed over a depth of ~80 µm. Subsequent annealing for 100 h and 1000 h at 800 °C coarsened some features, enhanced TCP precipitation in the superalloy, but only enlarged the diffusion layers by ~5 µm at most. Because of Al depletion from the MAX phase and corresponding Al enrichment of the alloy, the reaction zone displayed similarities to an oxidized Cr₂AlC surface and an aluminized superalloy, respectively. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

Electrolytic Formation of Crystalline Silicon/Germanium Alloy Nanotubes and Hollow Particles with Enhanced Lithium‐Storage Properties

Crystalline silicon(Si)/germanium(Ge) alloy nanotubes and hollow particles are synthesized for the first time through a one‐pot electrolytic process. The morphology of these alloy structures can be easily tailored from nanotubes to hollow particles by varying the overpotential during the electro‐reduction reaction. The continuous solid diffusion governed by the nanoscale Kirkendall effect results in the formation of inner void in the alloy particles. Benefitting from the compositional and structural advantages, these SiGe alloy nanotubes exhibit much enhanced lithium‐storage performance compared with the individual solid Si and Ge nanowires as the anode material for lithium‐ion batteries.     

Confined Nanospace Pyrolysis for the Fabrication of Coaxial Fe3O4@C Hollow Particles with a Penetrated Mesochannel as a Superior Anode for Li‐Ion Batteries

In this study, a method is developed to fabricate Fe₃O₄@C particles with a coaxial and penetrated hollow mesochannel based on the concept of “confined nanospace pyrolysis”. The synthesis involves the production of a polydopamine coating followed by a silica coating on a rod‐shaped β‐FeOOH nanoparticle, and subsequent treatment by using confined nanospace pyrolysis and silica removal procedures. Typical coaxial hollow Fe₃O₄@C possesses a rice‐grain morphology and mesoporous structure with a large specific surface area, as well as a continuous and flexible carbon shell. Electrochemical tests reveal that the hollow Fe₃O₄@C with an open‐ended nanostructure delivers a high specific capacity (ca. 864 mA h g^?1 at 1 A g^?1), excellent rate capability with a capacity of about 582 mA h g^?1 at 2 A g^?1, and a high Coulombic efficiency (>97 %). The excellent electrochemical performance benefits from the hollow cavity with an inner diameter of 18 nm and a flexible carbon shell that can accommodate the volume change of the Fe₃O₄ during the lithium insertion/extraction processes as well as the large specific surface area and open inner cavity to facilitate the rapid diffusion of lithium ions from electrolyte to active material. This fabrication strategy can be used to generate a hollow or porous metal oxide structure for high‐performance Li‐ion batteries.     

异质哑铃型纳米颗粒合成中的关键因素(英文)

哑铃型纳米颗粒由一种包含强相互作用的异质结构成,它两端是不同物质的纳米颗粒.这两种不同功能的纳米颗粒紧密相连,形成一种哑铃形的外观.这种结构的纳米颗粒在电子、磁性、光学及催化等方面有着不同于单一组分纳米颗粒的独特性质,因此受到人们广泛关注.哑铃型纳米颗粒的这些独特性质是由两种物质交界面处的电子转移引起的,得益于较强的界面相互作用,两种物质都可以通过界面处的电子转移得到改良,使得这种结构的催化剂在较低温度下催化氧化有机废气时活性很高.以CO氧化反应为例,Au纳米颗粒通常情况下对该反应没有催化活性,但是被负载到金属氧化物上面以后,却表现出了很高的催化活性.这正是氧化物载体与Au纳米颗粒之间电子传输的结果.通常在核壳结构中,核心物质以及两种物质的交界面都被外壳所包裹,而哑铃型结构当中的两种物质的功能面以及它们之间活泼的交界面均可以充分地暴露在反应物中,从而极大提升了其催化效果.这种独特的结构优势也在疾病诊断与治疗中的多功能探针上得到了广泛应用.由于哑铃型结构的两种物质的纳米颗粒相对位置是固定的,当用作催化剂时可以发挥出很好的抗烧结性能,还可使这两种物质更协调地均匀分布.因此哑铃型结构催化剂不仅催化活性更高,而且在较高温度下具有较高的稳定性.哑铃型结构可以看作是独立纳米颗粒与核壳型纳米颗粒之间的一种中间状态,它通常是由一种物质的纳米颗粒在另一种种子颗粒上面经过外延生长得到的.这与核壳结构纳米颗粒的合成很相似,但是必须准确地控制成核过程,使得成核可以各向异性地发生在种子颗粒的某一个晶面上.而在核壳结构的合成中,这一成核过程是均匀分布的.所以在制备哑铃型结构纳米颗粒时,很重要的就是要促进非均质成核,同时抑制均相成核.由于哑铃型纳米颗粒的特殊结构,在制备时想要准确控制上述成核条件是非常困难的,所以到目前为止,仅有很少种类的物质可以被制成哑铃型结构,比如Au(Ag,Pt,Pd)-Fe3O4(Co3O4),Au-PbS(PbSe),FePt-CdS和Cu-Ag等,这些物质中大多数都是由贵金属纳米颗粒和磁性纳米粒子组成的.哑铃型纳米颗粒由于受限于物质种类,它在催化氧化方面的应用也被局限在了很少一部分气体上,如CO.而通过其它很多种催化剂已经可以在较低温度(甚至零下数摄氏度)下实现CO催化氧化.因此,哑铃型结构的优势在CO催化氧化中并不能得到很好利用和体现,而用于甲烷等一些在较低温度下更难氧化的气体的催化氧化尚未见报道.这正是由合成多种多样的哑铃型纳米颗粒的巨大困难所致.因此,找到合成哑铃型纳米颗粒的困难所在以及合成过程中的一些重要影响因素非常有意义,这将帮助我们使用更多的物质合成出一些新的哑铃型纳米颗粒,进而利用其高催化活性,使得更多难以氧化的气体在较低温度下被氧化.本文总结了合成哑铃型纳米颗粒时的多种影响因素,并介绍了相关的一些合成方法.种子颗粒的尺寸以及两种颗粒之间的尺寸比例可以影响制备过程中外延生长的可控性,颗粒尺寸以及两种颗粒的尺寸差别越小,反应越容易控制.反应温度和反应时间需要根据反应物的性质进行精确控制才可以得到合适的尺寸以及较好的粒径分布.而两种不同的物质最终能不能形成哑铃型结构则是由很多种因素决定的,比如反应溶剂的极性、两种物质之间的晶格错配度以及反应中所用乳化剂的含量.除此之外,合适的前驱体、氧化还原剂以及操作环境等都可以影响哑铃型纳米颗粒的合成结果     

Effects of Carbide Formation in Graphene Growth

Besides carbon solubility, the carbide formation possibility is another important factor to differentiate various substrate materials in graphene growth. A recent experiment indicates that the formation of transition metal carbides (TMCs) can suppress carbon precipitation. In this study, Mo₂C, a representative of TMCs, is used to study the effects of carbide formation in graphene growth from first principles. Carbon diffusion in Mo₂C bulk turns out to be very difficult and it becomes much easier on the Mo₂C(001) surface. Therefore, carbon precipitation suppression and graphene growth can be realized simultaneously. A direction depended diffusion behavior is observed on the Mo₂C(101) surface, which makes it less favorable for graphene growth compared to the (001) surface.     

Using Simple Spray Pyrolysis to Prepare Yolk–Shell‐Structured ZnO–Mn3O4 Systems with the Optimum Composition for Superior Electrochemical Properties

A spray‐pyrolysis process is introduced as an effective tool for the preparation of yolk–shell‐structured materials with electrochemical properties suitable for anode materials in Li‐ion batteries (LIBs). Yolk–shell‐structured ZnO–Mn₃O₄ systems with various molar ratios of the Zn and Mn components are prepared. The yolk–shell‐structured ZnO–Mn₃O₄ powders with a molar ratio of 1:1 of the Zn and Mn components are shown to have high capacities and good cycling performances.     

A novel spinel coating on cobalt‐based Superalloy GH605 via an in‐situ oxidation approach

Cr‐Mn‐O spinel coating was prepared on the surface of cobalt‐based superalloy GH605 via an in‐situ oxidation method in H₂O‐H₂ environment. The composition, morphology, and chemical value state of the oxide spinel coatings were investigated by SEM, EDS, XRD, Raman spectra, and XPS. It indicated that the morphology of coating varied with oxidation temperature, and granular surface appeared when oxidation temperature increased to 1100°C. The formed Cr‐Mn‐O spinel coating was composed of Cr₂O₃ and MnCr₂O₄, and the thickness increased significantly with oxidation temperature. In the coating, Cr element existed in the state of Cr³⁺ ions and Cr⁶⁺ ions, while Mn element only existed in the form of Mn²⁺ ions.     

Manganese(II) complexes with diethylamine in aqueous solutions

Interaction between MnCl₂ and diethylamine (DEA) in aqueous solutions has been studied by UV, IR, and EPR spectroscopy as part of the design and research program on models of natural photosystems. The composition of the precipitate for comparable concentrations of reagents and solute oxygen has been investigated. Mn(II) was found to be oxidized with oxygen to give MnO₂·H₂O as a precipitate. In the solution over the precipitate, Mn(III) complexes with DEA are formed; the complex molecule has four and six amine molecules in the coordination sphere.     

Synthesis of pH‐responsive magnetic yolk–shell nanoparticles: A comparison between conventional etching and new deswelling approaches

Iron oxide (Fe₃O₄) magnetic nanoparticles as movable cores were used to synthesize yolk–shell nanoparticles with pH‐responsive shell composed of ethylene glycol dimethacrylate (EGDMA)‐crosslinked poly(acrylic acid) (PAA) via two different routes. In the first more common route, Fe₃O₄ nanoparticles were coated with silica layer via the Stöber process to yield Fe₃O₄@SiO₂ core–shell nanoparticles, subsequently used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe₃O₄@SiO₂@P(AA‐EGDMA). The silica layer was selectively removed through alkali etching to yield Fe₃O₄@air@P(AA‐EGDMA). In the second route, Fe₃O₄ nanoparticles without any stabilization were used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe₃O₄@P(AA‐EGDMA) core–shell nanoparticles. The nanoparticles were subsequently dispersed in acidic medium of pH = 2. Yolk–shell Fe₃O₄@air@P(AA‐EGDMA) nanoparticles were formed through deswelling of crosslinked PAA because of protonation of carboxyl groups at low pH values. Various techniques were utilized to investigate the characteristics of the synthesized core–shell nanoparticles. Formation of yolk–shell nanostructure was observed for both synthesis routes, namely etching of silica layer and deswelling approaches, from vibrating sample magnetometry and transmission electron microscopy results. Both types of nanoparticles showed pH‐responsive behaviour, i.e. decrease in absorption with increase in pH, as examined using UV–visible spectroscopy.     

Zn–HA–TiO2 nanocomposite coatings electrodeposited on a NiTi shape memory alloy

In this work, zinc–hydroxyapatite (Zn–HA) and zinc–hydroxyapatite–titania (Zn–HA–TiO₂) nanocomposite coatings were electrodeposited onto a NiTi shape memory alloy, using a chloride zinc plating bath. The structure of the composite coatings was characterized by X‐ray diffraction, scanning electron microscopy and high‐resolution transmission electron microscopy. According to the results, the Zn–HA–TiO₂ coating exhibited a plate‐like surface morphology, where the addition of the nanoparticles caused to an increase in roughness. It was also found that due to applying a proper stirring procedure during co‐deposition, a homogenous dispersion of the nanoparticles in the coatings was achieved. Also, the addition of the TiO₂ nanoparticles to the Zn–HA–TiO₂ coating enhanced the microhardness and wear resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

A Self‐Assembly Phase Diagram from Amphiphilic Perylene Diimides

Supramolecular forces govern self‐assembly and further determine the final morphologies of self‐assemblies. However, how they control the morphology remains hitherto largely unknown. In this paper, we have discovered that the self‐assembled nanostructures of rigid organic semiconductor chromophores can be finely controlled by the secondary forces by fine‐tuning the surrounding environments. In particular, we used water/methanol/hydrochloric acid to tune the environment and observed five different phases that resulted from versatile molecular self‐assemblies. The representative self‐assembled nanostructures were nanotapes, nanoparticles and their 1D assemblies, rigid microplates, soft nanoplates, and hollow nanospheres and their 1D assemblies, respectively. The specific nanostructure formation is governed by the water fraction, R_w, and the concentration of hydrochloric acid, [HCl]. For instance, nanotapes formed at low [HCl] and R_w values, whereas hollow nanospheres formed when either the HCl concentration is high, or the water fraction is low, or both. The significance of this paper is that it provides a useful phase diagram by using R_w and [HCl] as two variables. Such a self‐assembly phase diagram maps out the fine control that the secondary forces have on the self‐assembled morphology, and thus allows one to guide the formation toward a desired nanostructure self‐assembled from rigid organic semiconductor chromophores by simply adjusting the two key parameters of R_w and [HCl].