Template-based synthesis of nanomaterials

The large interest in nanostructures results from their numerous potential applications in various areas such as materials and biomedical sciences, electronics, optics, magnetism, energy storage, and electrochemistry. Ultrasmall building blocks have been found to exhibit a broad range of enhanced mechanical, optical, magnetic, and electronic properties compared to coarser-grained matter of the same chemical composition. In this paper various template techniques suitable for nanotechnology applications with emphasis on characterization of created arrays of tailored nanomaterials have been reviewed. These methods involve the fabrication of the desired material within the pores or channels of a nanoporous template. Track-etch membranes, porous alumina, and other nanoporous structures have been characterized as templates. They have been used to prepare nanometer-sized fibrils, rods, and tubules of conductive polymers, metals, semiconductors, carbons, and other solid matter. Electrochemical and electroless depositions, chemical polymerization, sol-gel deposition, and chemical vapour deposition have been presented as major template synthetic strategies. In particular, the template-based synthesis of carbon nanotubes has been demonstrated as this is the most promising class of new carbon-based materials for electronic and optic nanodevices as well as reinforcement nanocomposites. Received: 27 May 1999 / Accepted: 27 October 1999 / Published online: 8 March 2000     

Solution combustion synthesis of nanomaterials

Solution combustion (SC) is an effective method for synthesis of nano-size materials and it has been used for the production of a variety (currently more than 1000) of fine complex oxide powders for different advanced applications, including catalysts, fuel cells, and biotechnology. However, it is surprising that while essentially all of the studies on SC emphasize the characterization of the synthesized materials, little information is available on controlling combustion parameters and the reaction mechanisms. This paper is devoted to the analysis of the combustion parameters for different SC reaction modes. First, the conventional volume combustion synthesis mode, which involves uniform reaction solution preheating prior to self-ignition, is briefly discussed. Second, for the first time, results of detailed experimental studies on steady-state self-propagating mode of SC synthesis of nano-powders are presented. Finally, the so-called solution + impregnation combustion mode is considered. The relationship between combustion parameters and product microstructures are emphasized. These results are crucial not only from the application stand-point, but more importantly lead to methodological benefits, allowing application of the developed approaches to investigate steady state heterogeneous combustion waves in new classes of reaction systems.     

Mechanical properties of bulk carbon nanomaterials

Bulk carbon nanomaterials, which open prospects for the development of a new generation of supercapacitors, are actively investigated for recent years, but their mechanical properties and structure remain poorly understood. In connection with this fact, the influence of the hydrostatic and uniaxial compression on mechanical properties and structure of three bulk nanomaterials consisting of (i) bent graphene flakes, (ii) short carbon nanotubes, and (iii) fullerenes C₂₄₀ are investigated by the molecular dynamics method. It is shown that the strength of the material and its stability to graphitization depend on its constituent structural units. At large degrees of deformation, the material consisting of bent graphene sheets has the highest strength, whereas at the material density lower than 2.5 g/cm³, the highest strength is observed in the nanomaterial consisting of fullerene molecules. The differences in mechanical properties of the materials under consideration are explained by their structural features.     

Solution-phase synthesis of nanomaterials at low temperature

This paper reviews the solution-phase synthesis of nanoparticles via some routes at low temperatures, such as room temperature route, wave-assisted synthesis (γ-irradiation route and sonochemical route), directly heating at low temperatures, and hydrothermal/solvothermal methods. A number of strategies were developed to control the shape, the size, as well as the dispersion of nanostructures. Using diethylamine or n-butylamine as solvent, semiconductor nanorods were yielded. By the hydrothermal treatment of amorphous colloids, Bi₂S₃ nanorods and Se nanowires were obtained. CdS nanowires were prepared in the presence of polyacrylamide. ZnS nanowires were obtained using liquid crystal. The polymer poly (vinyl acetate) tubule acted as both nanoreactor and template for the CdSe nanowire growth. Assisted by the surfactant of sodium dodecyl benzenesulfonate (SDBS), nickel nanobelts were synthesized. In addition, Ag nanowires, Te nanotubes and ZnO nanorod arrays could be prepared without adding any additives or templates. Supported by the National Basic Research Program of China (Grant No. 2005CB623601) and the National Natural Science Foundation of China (Grant No. 20431020)     

The synthesis of hafnium nanomaterials by alkali metal reduction of hafnium tetrachloride

Hafnium tetrachloride was reduced in organic solvents with lithium powder, sodium–potassium alloy, or lithium hydride/Et₃B. All reductions required sonochemical agitation to proceed at an appreciable rate, with the notable exception of the reaction of HfCl₄ with Li in diethyl ether. Activation of C–H bonds occurred in all reactions, which resulted in carbon-containing products. HfCl₄ was reduced on a 50-g scale with LiH/Et₃B, and a 10-g scale with Li powder in pentane. All the solid products from the reductions were converted to nanomaterials by annealing under vacuum from 500 to 1,000 °C, which also resulted in the sublimation of the alkali metal salts. The nanomaterials contain a mixture of products with the α-Hf (hexagonal) structure (crystallite size 8–250 nm) and the HfC (FCC) structure (crystallite size 3–80 nm), with the amount of hafnium in the bulk annealed product varying from 88 to 99 wt%. When toluene, pentane, or triethylamine solvents were used, the presence of amorphous graphitic or carbonaceous material was also detected by solid state ¹³C NMR. Thermally annealed products were additionally characterized by electron microscopy and thermal analysis under Ar/O₂, and have BET surface areas ranging from 2.7 to 155 m²/g.     

Thermal conduction of one-dimensional carbon nanomaterials and nanoarchitectures

This review summarizes the current studies of the thermal transport properties of one-dimensional(1D) carbon nanomaterials and nanoarchitectures. Considering different hybridization states of carbon, emphases are laid on a variety of 1D carbon nanomaterials, such as diamond nanothreads, penta-graphene nanotubes, supernanotubes, and carbyne. Based on experimental measurements and simulation/calculation results, we discuss the dependence of the thermal conductivity of these 1D carbon nanomaterials on a wide range of factors, including the size effect, temperature influence, strain effect, and others. This review provides an overall understanding of the thermal transport properties of 1D carbon nanomaterials and nanoarchitectures, which paves the way for effective thermal management at nanoscale.     

功能纳米材料的可控制备及性能研究

功能纳米材料以其独特的结构和优异的性能在催化、能源、传感等领域具有广泛的应用前景.通过控制其制备和组装过程,可以有效地调节其性能.文章介绍了作者所在实验室在新型纳米材料合成方面的研究进展,深入探索了纳米晶体、生物络合高分子和生物分子-无机杂化纳米结构的可控性制备过程,对金属-半胱氨酸生物络合高分子的自组装与超结构手性进行了系统的研究和探讨.另外,文章作者还发现了无机杂化纳米结构的可逆光开关荧光效应,该效应在光信息记录方面具有潜在的应用价值.     

功能纳米材料的可控制备及性能研究

功能纳米材料以其独特的结构和优异的性能在催化、能源、传感等领域具有广泛的应用前景.通过控制其制备和组装过程,可以有效地调节其性能.文章介绍了作者所在实验室在新型纳米材料合成方面的研究进展,深入探索了纳米晶体、生物络合高分子和生物分子-无机杂化纳米结构的可控性制备过程,对金属-半胱氨酸生物络合高分子的自组装与超结构手性进行了系统的研究和探讨.另外,文章作者还发现了无机杂化纳米结构的可逆光开关荧光效应,该效应在光信息记录方面具有潜在的应用价值.     

Phase composition and structure of Fe-Ni alloys in a unique Antarctic meteorite Yamato 791694

Phase composition and structure of iron-nickel alloys in the Antarctic meteorite Y-791694 are discussed and compared to other non-Antarctic Ni-rich ataxites using the results obtained by Mössbauer spectroscopy, X-ray diffraction and other techniques.     

Influence of processing parameters on nanomaterials synthesis efficiency by a carbothermal reduction process

In this work, the influence of synthesis parameters on the synthesis efficiency of tin oxide nanomaterials was studied by using the carbothermal reduction method in a sealed tube furnace. The parameters were the starting material, temperature and time of synthesis as well as the gas flux. The starting material was tin dioxide mixed with carbon black in a molar proportion of 1.5:1 and 1:1. The temperature range was from 950 to 1,125 °C with a step of 25 °C, and the synthesis times used were 15, 30, 45, 60, 75, 90, and 120 min. Using optimum values of the above parameters, the gas flux was changed to verify its influence. After completion of the syntheses, we found a grayish-black material inside the tube which was characterized by X-ray diffraction and scanning electron microscopy. The results showed that the collected material is composed of nanobelts (with width around 60 nm) and disks that grew preferentially in the SnO phase. A model based on the oxide vapor pressure was proposed to evaluate the efficiency of the process, and the results showed good agreement between experimental data and the proposed model. Based on the results obtained, the best conditions to obtain a homogeneous material with 95% efficiency is using a starting material in the molar proportion Sn:C of 1.5:1, a temperature of 1,132 °C for 75 min, and a N₂ gas flux of 80 sccm.     

Flame synthesis of 1-D complex metal oxide nanomaterials

One dimensional (1-D) complex metal oxide nanomaterials, such as ternary oxides, doped oxides, and hierarchical structures containing several oxides, not only benefit from large aspect ratios, but also offer exciting opportunities to design materials with desired properties by tuning their chemical compositions and tailoring their sizes and morphologies at the nanometer scale. Flame synthesis is an attractive method to grow 1-D complex metal oxide nanostructures because of its high temperature, scalability, low-cost and rapid growth rate. Here, we present three new combined flame synthesis methods: (1) simultaneous vapor–vapor growth, (2) simultaneous solid–vapor growth, and (3) sequential solid–vapor growth, to grow 1-D complex metal oxide nanostructures with well-defined compositions and morphologies. These three methods combine the previously reported flame vapor deposition and solid diffusion growth methods that were separately used to grow 1-D simple binary metal oxide nanostructures, and significantly advance the capabilities of existing flame synthesis methods for the growth of 1-D nanomaterials. The first method, simultaneous vapor–vapor growth, combines the flame vapor deposition growth of two different metal oxides by oxidizing and evaporating two different metal sources. With this we have successfully grown W-doped MoO₃ nanoplates and nanoflowers. In the second method, simultaneous solid–vapor growth, one precursor is again provided by oxidizing and evaporating metal oxide from a metal, while the other precursor diffuses out from a different growth substrate. With this we have successfully grown ternary Cu₃Mo₂O₉ nanowires. The third method, sequential solid–vapor growth, essentially uses the 1-D nanostructures firstly grown by solid diffusion as the substrates for subsequent flame vapor deposition. With this we have successfully grown hierarchical CuO/MoO₃ core/shell nanowires and MoO₃-branched CuO nanowires. We believe that these three new combined flame synthesis methods will provide a general platform for the synthesis of 1-D complex metal oxide nanostructures with tailored properties.     

Scaling of magnetoresistance of carbon nanomaterials in Mott-type hopping conductivity region

A method for analyzing data on Mott hopping conduction in a magnetic field, ρ ～ exp[(T ₀/T)^α], based on scaling relation ln[ρ(H)/ρ(0)] = (T ₀/T)^α F(H/T) for the spin-polarized contribution to the magnetore-sistance is proposed. This general approach is tested for a carbon nanomaterial synthesized from single-wall carbon nanotubes under high pressure (up to 7 GPa). The experiments confirmed the theoretical predictions over the temperature range 1.8–12.0 K in a magnetic field of up to 70 kOe and made it possible to correctly determine all parameters of the localized states involved in the model. The experimental data obtained for carbon nanomaterials synthesized from single-wall carbon nanotubes and a mixture of C_2N fullerenes indicate the possible renormalization of the magnetic moment of electrons involved in hopping transport.     

Study of carbon nanostructures obtained by pyrolytic synthesis

The structure and phase composition of a carbon nanomaterial obtained by the thermal decomposition of toluene-ferrocene mixtures are studied by Mössbauer spectroscopy, high-resolution electron microscopy, and x-ray diffraction. Variations in the structural state of the catalyst and in the quantitative yield of the nanomaterial are analyzed as functions of the synthesis time.     

Production of carbon nanotubes by self-propagating high-temperature synthesis

Carbon nanotubes are prepared by the method of self-propagating high-temperature synthesis for the first time. The initial components for this synthesis are carboniferous materials (soda, limestone, and Teflon) and reducers (magnesium, lithium, and sodium) with addition of a nickel or iron catalyst. The morphology of the nanotubes (straight multiwall nanotubes apparently free of a catalyst, bent nanotubes completely filled with a catalyst, and carbon nanofibers) is similar to that of nanotubes grown by chemical methods. The nanotubes account for 2–4 wt % of the product synthesized.     

Mechanical properties and structures of bulk nanomaterials based on carbon nanopolymorphs

Bulk nanomaterials based on sp² carbon nanopolymorphs are promising candidates for supercapacitors due to their unique properties such as extremely high specific surface area, high conductivity and stability against graphitization. However, the mechanical response of such materials to external loading is not understood well. This Letter studies the effect of hydrostatic pressure on the mechanical properties and structures of these materials via molecular dynamics simulations. Three types of nanopolymorphs‐based nanomaterials that are composed of bended graphene flakes, short carbon nanotubes and fullerenes are considered. It is found that these three materials show a distinct relation between the pressure and volume strain. Moreover, their resistance to graphitization depends on the structure of their constituent components. The phenomena are explained by analysing the radial distribution function and coordination numbers of the atoms. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Near-field Raman spectroscopy of biological nanomaterials by in situ laser-induced synthesis of tip-enhanced Raman spectroscopy tips

We report a new approach in tip-enhanced Raman spectroscopy (TERS) in which TERS-active tips with enhancement factors of ～10(-5)× can be rapidly (1-3 min) produced in situ by laser-induced synthesis of silver nanoparticles at the tip apex. The technique minimizes the risks of tip contamination and damage during handling and provides in situ feedback control, which allows the prediction of the tip performance. We show that TERS tips produced by this technique enable the measurement of spatially resolved TERS spectra of self-assembled peptide nanotubes with a spatial resolution of ～20 nm.     

Collision of extremely short optical pulses in semiconductor carbon nanotubes

The interaction of extremely short optical pulses in semiconductor carbon nanotubes is discussed. An equation is derived for the dynamics of the electromagnetic field in a system of semiconductor carbon nanotubes at low temperatures, whose solutions are analogs to the solitons of the sine-Gordon equation. The behavior of extremely short optical pulses in semiconductor carbon nanotubes on collision is analyzed.