Flame Synthesis Method Research Articles

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.

G060015 減圧沸騰噴霧による火炎内ナノ粒子合成法の構築

Flame synthesis method is commercially important because of its relative low cost, one-step process and it can be operated as continuous processes. However, a novel flame synthesis method for nanoparticles is proposed to solve several kinds of problem with vapor-to-particles and droplet-to-particles formation processes. For improving their problems, the new nanoparticle synthesis method by applying the flash boiling spray to flame synthesis method is proposed in this study. This method is expected that a uniform particle size, composition and non-agglomerated nanoparticles can be generated in high purity. In the construction of this method, it is important to control the particle nucleation and growth. The particle residence time is a significant process parameter affecting the particle nucleationand growth. Then, it is thought that ambient pressure change the particle residence time. The objective of this report was to investigate the influence of ambient pressure on the TiO_2 particle characteristic. In consequence, as the ambient pressure decrease, the primary particle diameter decrease because of the short particle residence time. And the agglomeration is inhibited by elongating mean free path due to the pressure drop. Moreover, since particle growth was carried out quickly by getting higher ambient pressure, the transformation of anatase to rutile phase was inhibited, and anatase content of product particles synthesized in higher ambient pressure was increased.

Hydrogen flame synthesis of few-layer graphene from a solid carbon source on hexagonal boron nitride

We report a new hydrogen flame synthesis method to successfully grow graphene on h-BN flakes in 20 seconds without using any catalyst. At the initial stage graphene layers anchored to the (100) surface plane of the h-BN crystal, and afterwards the graphene grew up beyond substrates to form high electrical conductivity quasi-freestanding nanosheets.

Flexible Solid-State Supercapacitors Based on Carbon Nanoparticles/MnO2 Nanorods Hybrid Structure

A highly flexible solid-state supercapacitor was fabricated through a simple flame synthesis method and electrochemical deposition process based on a carbon nanoparticles/MnO(2) nanorods hybrid structure using polyvinyl alcohol/H(3)PO(4) electrolyte. Carbon fabric is used as a current collector and electrode (mechanical support), leading to a simplified, highly flexible, and lightweight architecture. The device exhibited good electrochemical performance with an energy density of 4.8 Wh/kg at a power density of 14 kW/kg, and a demonstration of a practical device is also presented, highlighting the path for its enormous potential in energy management.

Flame synthesis of graphene films in open environments

Few-layer graphene is grown on copper and nickel substrates at high rates using a novel flame synthesis method in open-atmosphere environments. Transmittance and resistance properties of the transferred films are similar to those grown by other methods, but the concentration of oxygen, as assessed by X-ray photoelectron spectroscopy, is actually less than that for graphene grown by chemical vapor deposition under near vacuum conditions. The method involves utilizing a multi-element inverse-diffusion-flame burner, where post-flame species and temperatures are radially-uniform upon deposition at a substrate. Advantages of the specific flame synthesis method are scalability for large-area surface coverage, increased growth rates, high purity and yield, continuous processing, and reduced costs due to efficient use of fuel as both heat source and reagent. Additionally, by adjusting local growth conditions, other carbon nanostructures (i.e. nanotubes) are readily synthesized.

Flame synthesis of carbon nanostructures on stainless steel anodes for use in microbial fuel cells

Microbial fuel cells (MFCs) offer a promising alternative energy technology, but suffer from low power densities which hinder their practical applicability. In order to improve anodic power density, we deposited carbon nanostructures (CNSs) on an otherwise plain stainless steel mesh (SS-M) anode. Using a flame synthesis method that did not require pretreatment of SS-M substrates, we were able to produce these novel CNS-enhanced SS-M (CNS-M) anodes quickly (in a matter of minutes) and inexpensively, without the added costs of chemical pretreatments. During fed batch experiments with biomass from anaerobic digesters in single-chamber MFCs, the median power densities (based on the projected anodic surface area) were 2.9 mW m −2 and 187 mW m −2 for MFCs with SS-M and CNS-M anodes, respectively. The addition of CNSs to a plain SS-M anode via flame deposition therefore resulted in a 60-fold increase in the median power production. The combination of CNSs and metallic current collectors holds considerable promise for power production in MFCs.

Ethanol flame synthesis of highly transparent carbon thin films

Large area (the order of centimeters), flexible thin films of amorphous carbon were prepared on copper foils by an ethanol flame synthesis method. The carbon films exhibit high transmittance in the visible and near infrared range (up to 90% at 550 nm). Schottky diodes formed by combining the carbon films with n-type silicon wafers show high on/off ratio (up to 150) photocurrents at air-mass 1.5 and illumination intensity of 100 mW/cm 2.

Flame synthesis of tungsten oxide nanostructures on diverse substrates

One-dimensional (1D) tungsten oxide nanostructures show great potential for applications in the areas of batteries, photoelectrochemical water-splitting, electrochromic devices, catalysts and gas sensors. 1D tungsten oxide nanostructures are currently synthesized by physical or chemical vapor deposition, which are limited by low temperatures, the need for vacuum conditions, frequently expensive catalysts, and difficulty in scaling up for mass-production. These limitations, however, can be overcome by flame synthesis. Here, using a co-flow multi-element diffusion burner, we demonstrate the atmospheric, catalyst-free, rapid, mild and scalable flame synthesis of diverse, quasi-aligned, large density, and crystalline tungsten oxide nanostructures on a variety of substrates. Specifically, under fuel-rich conditions, monoclinic 1D W 18O 49 nanowires and nanotubes were grown on tungsten, iron, steel and fluorinated tin oxide (FTO) substrates, with controlled diameters ranging from 10 to 400 nm and axial growth rates ranging from 2 to 60 μm/h. Monoclinic 1D WO 3 nanowires and nanotubes were grown, instead, on silicon and silicon dioxide substrates. Under fuel-lean conditions, diverse WO 3 nanostructures, including monoclinic 1D nanowires, cubic 2D nanobelts and monoclinic 3D nanocones were grown on tungsten and FTO substrates. The success of this versatile flame synthesis method is attributed to the large tunability of several synthesis parameters, including the flame stoichiometry, the tungsten source and growth substrate temperatures, the tungsten oxide vapor concentration, and the material of the growth substrate. This flame synthesis method can be extended to synthesize other 1D transition metal oxides as well, enabling many large-scale electronic and energy conversion applications.

Charge–discharge characteristics of nanocrystalline Co 3O 4 powders via aerosol flame synthesis

Nanocrystalline Co 3O 4 powders were synthesized by aerosol flame synthesis (AFS) method for the anode of lithium ion batteries and the basic electrochemical properties were investigated. The effects of synthesis conditions and heat-treatment temperature on the morphology, crystallite size and electrochemical properties were investigated. As-prepared soot contained Co 3O 4, CoO and Co(OH) 2, which were eventually converted into cubic spinel Co 3O 4 by post heat treatment. The as-prepared particle size was in the range of 10–30 nm and grew to 50–85 nm by the heat treatment. With growing particle size and improved crystallinity, charge–discharge capacity and cycle performance were improved and the discharge capacity of the powder heat-treated at 700 °C was 571 mAh/g after 30 cycles, which was better than Co 3O 4 powder reported in the previous literature.

Flame synthesis of carbon nanofibers on carbon paper: Physicochemical characterization and application as catalyst support for methanol oxidation

We developed a simple, rapid and highly efficient flame synthesis method for direct growing carbon nanofibers (CNFs) on carbon paper (CP) using a common laboratory ethanol flame as both heat and carbon sources. High density CNFs with tangled solid-cored structure were uniformly formed over the Ni-plated CP surface in ∼20 s. The morphologies of the CNFs were characterized by scanning electron microscopy and transmission electron microscopy. X-ray diffraction study revealed the graphitic nature of the CNFs. Raman spectroscopy analysis confirmed that the CNFs are disordered graphitic nanocrystallites with high degree of exposed edges. Electrochemical impedance spectroscopy and cyclic voltammetry were used to show that growing CNFs directly on CP facilitates electron transfer with concomitant increase in double-layer capacitance. The CNF/CP was used as support for Pt nanoparticles to study their supporting effect on the catalyst performance. The as prepared Pt/CNF electrocatalyst exhibited much improved electrocatalytic activity for methanol oxidation compared to Pt/CP and commercial Pt/C on CP. High electronic conductivity and improved electrochemical behavior of the CNF/CPs, resulted from direct contact of the nanofibers with CP, combined with unique properties of CNFs, make the synthesized CNF/CPs promising for fuel cell applications.

G0600-8-5 カーボンナノチューブ生成への直流電場付与の効果(熱工学部門一般講演(8):プラズマ・熱現象)

The purpose of this study is to reveal the effects of DC electric field on carbon nanotube (CNT) synthesis. In flame synthesis method, it is considered that there are two effects of DC electric field which promotes CNT growth; i.e. generating ionic wind and enhancing catalytic activity. To distinguish the effect of DC bias on catalytic activity promotion, chemical vapor deposition (CVD) synthesis with high voltage DC bias is used in the present study. DC bias voltage is varied from -1.0 kV to +1.0 kV. It is confirmed that CNT growth is promoted by applying electric field. Moreover, it is suggested that catalytic activity may increase with increasing the intensity of electric field.

914 減圧沸騰噴霧の火炎内ナノ粒子合成法への展開(FM-1 燃焼による材料微粒子合成)

914 減圧沸騰噴霧の火炎内ナノ粒子合成法への展開(FM-1 燃焼による材料微粒子合成)

Flame Synthesis of Nanosized Cu−Ce−O, Ni−Ce−O, and Fe−Ce−O Catalysts for the Water-Gas Shift (WGS) Reaction

A flame synthesis method has been used to prepare nanosized, high-surface-area Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts from aqueous solutions of metal acetate precursors. The particles were formed by vaporization of the precursors followed by reaction and then gas to particle conversion. The specific surface areas of the synthesized powders ranged from 127 to 163 m(2)/g. High-resolution transmission electron microscope imaging showed that the particle diameters for the ceria materials are in the range of 3-10 nm, and a thin layer of amorphous material was observed on the surface of the particles. The presence and surface enrichment of the transition-metal oxides (CuO, NiO, and Fe(2)O(3)) on the ceria particles were detected using X-ray photoelectron spectroscopy. Electron energy-loss spectroscopic studies suggest the formation of a core-shell structure in the as-prepared particles. Extended X-ray absorption fine structure studies suggest that the dopants in all M-Ce-O systems are almost isostructural with their oxide counterparts, indicating the doping materials form separate oxide phases (CuO, Fe(2)O(3), NiO) within the host matrix (CeO(2)). Etching results confirm that most of the transition-metal oxides are present on the surface of CeO(2), easily dissolved by nitric acid. The performance of the flame-synthesized catalysts was examined toward water-gas shift (WGS) activity for fuel processing applications. The WGS activity of metal ceria catalysts decreases in the order Cu-Ce-O > Ni-Ce-O > Fe-Ce-O > CeO(2) with a feed mixture having a hydrogen to carbon monoxide (H(2)/CO) ratio of 1. There was no methane formation for these catalysts under the tested conditions.

Volumetric flame synthesis of well-defined molybdenum oxide nanocrystals

Well-defined faceted inorganic Mo oxide nanocrystals are synthesized in the gasphase using a solid-fed-precursor flame synthesis method. The solid crystals haverectangular cross-section with characteristic size of 10–20 nm and with lengths rangingfrom 50 nm to a few hundred nanometres. A 1 mm diameter high purity Mo probeintroduced in the oxygen-rich part of the flame serves as the material source. Acombination of the strong temperature gradient and varying chemical speciesconcentrations within the flame volume provides the ideal conditions for the rapidand direct formation of these unique nanocrystals. Oxidation and evaporation ofMoO3 in the oxygen-rich zone are followed by reduction toMoO2 in the lower temperature, more fuel-rich zone. TheMoO3 vapours formed are pushed in the direction of the gas flow and transformed into maturewell-defined convex polyhedron nanocrystals bounded with six faces resembling rectangularparallelepipeds.

Rapid Catalyst-Free Flame Synthesis of Dense, Aligned α-Fe2O3 Nanoflake and CuO Nanoneedle Arrays

This paper describes a simple and yet rapid flame synthesis method to produce one-dimensional metal oxide nanostructures by directly oxidizing metals in the postflame region of a flat flame. Single and bicrystal alpha-Fe(2)O(3) nanoflakes and CuO nanoneedles were grown in the postflame region by a solid diffusion mechanism and were aligned perpendicularly to the substrate with a surface coverage density of 10 nanostructures per square micrometer. The alpha-Fe(2)O(3) nanoflakes reached lengths exceeding 20 microm after only 20 min of growth. This rapid growth rate is attributed to a large initial heating rate of the metal substrate in the flame and to the presence of water vapor and carbon dioxide in the gas phase that together generate thin and porous oxide layers that greatly enhance the diffusion of the deficient metal to the nanostructure growth site and enable growth at higher temperatures than previously demonstrated.

Porous silicon microparticles synthesis by solid flame technique

Porous silicon microparticles have been prepared from SiO 2 + αMg ( α is mole number of Mg) exothermic mixture by solid flame synthesis method. Two interconnected strategies were followed to initiate morphology changes of as-produced silicon particles, namely changing the concentration of Mg in 0.75–2.0 mol range, and leaching of the combustion products with hydrochloric and/or hydrofluoric acids. The effects of synthesis conditions and chemical treatment procedure on product morphology and composition were evaluated using scanning electron microscopy and X-ray diffraction analysis. Porous silicon microparticles with uniform network structure and pore size distribution ranging from 0.1 to 1.5 μm were prepared after acid treatment of final combustion product. A comprehensive model for pore formation is proposed and discussed in context to the combustion temperature.

Polyhedral Maghemite Nanocrystals Prepared by a Flame Synthetic Method: Preparations, Characterizations, and Catalytic Properties

Highly uniformed polyhedral γ-Fe(2)O(3) nanocrystals are prepared via a flame synthesis method by directly combusting the organic solution of iron-precursor. Systematic investigations reveal that the polyhedral γ-Fe(2)O(3) nanocrystals are 26-facet particles enclosed by six {100}, eight {111}, and twelve {110} facets, and these 26-facet γ-Fe(2)O(3) nanocrystals present excellent catalytic activities associated with their polyhedral structures.

화염법을 이용한 Pt/C 촉매 제조

Abstract Carbon black, activated carbon and carbon nanotube have been used as supporting materials for precious metal catalysts used in fuel cell electrodes. One-step flame synthesis method is used to coat 2-5nm Pt dots on flame-generated carbon particles. By adjusting flame temperature, gas flow rates and resident time of particles in flame, we can obtain Pt/C nano catalyst-support composite particles. Additional injection of hydrogen gas facilitates pyrolysis of Pt precursor in flame. The size of as-incepted Pt dots increases along the flame due to longer resident time and sintering in high temperature flame. Surface coverage and dispersion of the Pt dots is varied at different sampling heights and confirmed by Transmission electron microscopy (TEM), Energy-dispersive spectra (EDS) and X-ray diffraction (XRD). Crystalinity and surface bonding groups of carbon are investigated through X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. 1. 서 론 연료전지는 높은 효율과 자연 친화적인 방법으로 화학 에너지를 직접 전기에너지로 변환할 수 있다는 점에서 차세대 동력원으로 생각되어왔다.

Pt Coating on Flame-Generated Carbon Particles and Their Application for a Catalytic Electrode of Proton Exchange Membrane Fuel Cell (PEMFC)

Carbon black, activated carbon and carbon nanotube have been used as supporting materials for precious metal catalysts used in fuel cell electrodes. One-step flame synthesis method is used to coat 2-5nm Pt dots on flame-generated carbon particles. By adjusting flame temperature, gas flow rates and resident time of particles in flame, we can obtain Pt/C nano catalyst-support composite particles. Additional injection of hydrogen gas facilitates pyrolysis of Pt precursor in flame. The size of as-incepted Pt dots increases along the flame due to longer resident time and sintering in high temperature flame. Surface coverage and dispersion of the Pt dots is varied at different sampling heights and confirmed by Transmission electron microscopy (TEM), Energy-dispersive spectra (EDS) and X-ray diffraction (XRD). Crystalline and surface bonding groups of carbon are investigated through X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The electro-catalytic property of Pt/C composites for the application to catalytic electrode PEMFC are also investigated by Cyclic voltammetry (CV).

Flame-synthesis of carbon nanotubes on silicon substrates and their field emission properties

We reported the flame-synthesis of patterned multiwalled carbon nanotubes (CNTs) on silicon substrate by a shadow mask and their field emission properties. It was found that CNTs with tangled and curved morphology were preferentially grown around the cracked edges of Ni dot pattern. A crack-induced catalyst-activation growth mechanism was proposed. The patterned CNTs fabricated by such a simple flame-synthesis method exhibited good field emission characteristics with uniform emission patterns and reproducible and stable emission behaviors, although the CNTs possessed many defective graphite layers and showed relatively higher turn-on and threshold field than other reported CNTs grown by chemical vapor deposition. Our results demonstrated that such a low-cost and scaleable CNT pattern fabrication process can be expected to have favorable applications in field emission devices.