Nitrogen doped carbon nano-onions as efficient and robust electrocatalysts for oxygen reduction reactions

We investigated synthesis and electrocatalytic performance of metal-free, nitrogen-doped carbon nano-onions (N-CNOs) for oxygen reduction reactions in alkaline electrolyte. N-CNOs were prepared by chemical oxidation of nanodiamond-derived carbon nano-onions (ox-CNOs), followed by thermal annealing with urea under the flow of argon gas. The chemical oxidation step was critical to successfully internalize nitrogen atoms into carbon network. Morphology, microstructure, and chemical states of carbon nano-onions (CNOs), ox-CNOs, and N-CNOs were characterized by transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Electrocatalytic activity of pristine and modified CNOs was characterized by a series of electrochemical measurements. Electrochemical characterizations were done with thin film electrodes of CNOs mounted on a glassy carbon disk. Compared to CNOs and ox-CNOs, N-CNOs showed remarkably enhanced electron-transfer kinetics with the 4-electron transfer as a dominant reaction pathway. Overall, N-CNOs exhibited electrochemical characteristics comparable to commercial Pt/C catalysts.     

Size-dependent photodegradation of CdS particles deposited onto TiO2 mesoporous films by SILAR method

Carbonaceous nanomaterials, such as fullerene C₆₀, carbon nanotubes, and their functionalized derivatives have been demonstrated to possess high sorption capacity for organic and heavy metal contaminants, indicating a potential for remediation application. The actual application of these nanomaterials, however, is often hindered by the high cost of materials and the limited understanding of their mobility in porous media. In this work, carbon nano-onions (CNOs), a relatively new addition to the carbonaceous nanomaterials, were synthesized in a cost-effective way using a laser-assisted combustion synthesis process, and carefully characterized for their potential remediation application. Surface oxidized CNOs possessed 10 times higher sorption capacity than C₆₀ for heavy metal ion contaminants including Pb²⁺, Cu²⁺, Cd²⁺, Ni²⁺, and Zn²⁺. CNOs aqueous suspension can be very stable in NaCl solution at ionic strength up to 30?mM and CaCl₂ solution at ionic strength up to 4?mM CaCl₂ when pH ranged from 5 to 9, which are consistent with environmentally relevant conditions. Interactions of CNOs with iron oxide and silica surfaces under favorable condition were found to be electrostatic in origin. Mobility of CNOs in quartz sands was controlled by electrolyte type and concentration. Approximately 4.4, 25.1, and 92.5?% of injected CNO mass were retained in the sand column in ultrapure water, 1?mM?NaCl, and 1?mM CaCl₂ solutions, respectively.     

Transition of carbon nanostructures in heptane diffusion flames

The flame synthesis has high potential in industrial production of carbon nanostructure (CNS). Unfortunately, the complexity of combustion chemistry leads to less controlling of synthesized products. In order to improve the understanding of the relation between flames and CNSs synthesized within, experiments were conducted through heptane flames in a stagnation-point liquid-pool system. The operating parameters for the synthesis include oxygen supply, sampling position, and sampling time. Two kinds of nanostructures were observed, carbon nanotube (CNT) and carbon nano-onion (CNO). CNTs were synthesized in a weaker flame near extinction. CNOs were synthesized in a more sooty flame. The average diameter of CNTs formed at oxygen concentration of 15% was in the range of 20–30 nm. For oxygen concentration of 17%, the average diameter of CNTs ranged from 24 to 27 nm, while that of CNOs was around 28 nm. For oxygen concentration of 19%, the average diameter of CNOs produced at the sampling position 0.5 mm below the flame front was about 57 nm, while the average diameters of CNOs formed at the sampling positions 1–2.5 mm below the flame front were in the range of 20–25 nm. A transition from CNT to CNO was observed by variation of sampling position in a flame. We found that the morphology of CNS is directly affected by the presence of soot layer due to the carbonaceous environment and the growth mechanisms of CNT and CNO. The sampling time can alter the yield of CNSs depending on the temperature of sampling position, but the morphology of products is not affected.     

A novel approach towards the production of luminescent silicon nanoparticles: sputtering, gas aggregation and co-deposition with H2O

Silicon clusters were produced by sputtering of a p-doped Si target and aggregation of the Si atoms in an argon gas atmosphere. The clusters were deposited in ultra high vacuum onto either (i) carbon transmission electron microscope (TEM) grids or (ii) a liquid nitrogen cooled finger on which a thick layer of ice was co-deposited during the exposure to the cluster beam. The ice layer containing the clusters was melted to form a liquid sample which showed luminescence peaking at 421 nm when excited at 307.5 nm. The luminescence is attributed to electron-hole recombination in oxygen deficient defects in the Si–SiO₂ interface region. TEM images of the nanoparticles deposited on the carbon grids show spherical particles with diameters ranging from 4 to 50 nm, flake-like structures or nanotube-like shapes. Grids with higher deposited densities reveal clusters that are agglomerated into chains, TEM images of the dried liquid sample show a network of fibres indicating that growth into fibres is further promoted when the clusters gain mobility in the melted ice.     

溅射法制备Ag/Ag2O超微粒子的分析

用Ｘ射线衍射、Ｘ射线光电子能谱、透射电子显微镜和差示扫描量热法对溅射法制备的Ａｇ超微粒子的晶体学结构、表面组成、微粒形态和热力学性质进行了分析。结果表明，所制备的微粒为内部为Ａｇ、表面为Ａｇ₂Ｏ的两相微粒，以及单一的Ａｇ₂Ｏ微粒，粒径在１０ｎｍ以上的微粒没有确定的外形，粒径在１０ｎｍ以下的微粒为球形。微粒有不同于块体金属Ａｇ的异常热效应。到４０天时，沉积在碳膜上的Ａｇ，Ａｇ₂Ｏ两相微粒有一部份还原形成了单一的金属Ａｇ超微粒子。 关键词：     

Plasma characterization and room temperature growth of carbon nanotubes and nano-onions by excimer laser ablation

The deposition of carbon nanotubes and carbon nano-onions at room temperature using excimer laser radiation to ablate mixed graphite-metal targets is described. Our deposition conditions are in contrast to other investigations on the pulsed laser deposition of carbon nanotubes that have employed high temperatures and high pressures. We find that the formation of these carbon nanostructures is dependent on the ambient gas employed during ablation. In the presence of O₂ gas, carbon nanotubes and nano-onions are produced, while inert atmospheres such as Ar yield amorphous carbon. High-resolution, in situ, time-resolved emission spectroscopy has been used to track the evolution of species (C₂, C₃, Ni/Co) in the ablation plume. Spectral fits on low and high-resolution spectra reveal that the vibrational-rotational temperatures for C₂ produced in O₂ remain at ∼5000 K for nearly 20 μs but drop rapidly in Ar. Details of the formation of carbon nanotubes and nano-onions, and in situ time-resolved optical emission spectroscopy are described.     

Occurrence of particle debris field during focused Ga ion beam milling of glassy carbon

To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to FIB milling. Two ion beam scanning modes - slow single scan and fast repetitive scan - have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness (R_a) of FIB milled areas after cleaning is less than 2 nm.     

Spontaneous Agglomeration of Silver Nanoparticles Deposited on Carbon Film Surface

The spontaneous aggregation of silver nanoparticles on a two-dimensional surface at room temperature is investigated. The nanoparticles were deposited on a carbon film and have been observed by a transmission electron microscope (TEM) for over one year. These particles were about 10nm, spherical and well dispersed initially, and an obviously spontaneous agglomeration was observed at the 12th day, the values, coverage rate of the silver particles on carbon film, were increased with time (before 40th day), but reduced with time (after 40th day). These show that the aggregates of the particles tend to have the smallest surface to reduce their surface free energy and are compact three-dimensional cluster in which the most size is above 100nm. Agglomerating is a successively slow diffusion-limited aggregation (DLA) growth. Another phenomenon, a big aggregate gathering some particles and a small aggregate to form a still bigger one, is observed. This indicates that the aggregating processes are controlled by migration of the particles on carbon film surface and surface energy of the particles.     

Excitation wavelength dependence and magnetic field effect on aerosol particle formation from a gaseous mixture of carbon disulphide and glyoxal

Upon excitation of carbon disulphide (CS₂) molecules under UV light irradiation at 313?nm a gaseous mixture of CS₂ and glyoxal deposited sedimentary aerosol particles only. The nucleation process of the aerosol particles was investigated by measuring the He–Ne laser light intensity scattered by the aerosol particles formed under light irradiation at 313?nm, and the chemical structure of the sedimentary particles was analysed by measuring the FT-IR and X-ray photoelectron spectra. On application of a magnetic field of up to 5?T, the nucleation process was decelerated and the chemical species originating from CS₂ were less abundant. The results were compared with those obtained under visible light irradiation at 435.8?nm reported previously. Chemical reactions between CS₂ and glyoxal molecules, which were responsive to the magnetic field, are discussed briefly.     

Scanning force microscopy of catalytic nickel particles prepared from carbon nanotubes

The method of scanning force microscopy (SFM) is used to study catalytic nickel nanoparticles deposited on a substrate of quartz glass by decomposition of carbon nanotubes. The SFM images so obtained were computer processed using an original numerical deconvolution algorithm which allowed us to determine the actual dimensions and shape of the nanoparticles. Nonoverlapping particles with diameters from 20 to 200 nm were recorded. Analysis of the SFM images revealed that the shape of the nickel particles is nearly spherical, which is in good agreement with transmission electron microscopy data. Fiz. Tverd. Tela (St. Petersburg) 39, 2065–2071 (November 1997)     

Synchrotron,X-Ray,and Electron Microscopic Studies of Catalyst Systems Based on Multiwalled Carbon Nanotubes Modified by Copper Nanoparticles

Physics of the Solid State - The results of the studies of a composite based on multiwalled carbon nanotubes (MWCNTs), onto the outer surface of which nanosized copper particles are deposited by...     

Calibration and numerical simulation of Nanoparticle Surface Area Monitor (TSI Model 3550 NSAM)

TSI Nanoparticle Surface Area Monitor (NSAM) Model 3550 has been developed to measure the nanoparticle surface area deposited in different regions of the human lung. It makes use of an adjustable ion trap voltage to match the total surface area of particles, which are below 100 nm, deposited in tracheobronchial (TB) or alveolar (A) regions of the human lung. In this paper, calibration factors of NSAM were experimentally determined for particles of different materials. Tests were performed using monodisperse (Ag agglomerates and NaCl, 7–100 nm) and polydisperse particles (Ag agglomerates, number count mean diameter below 50 nm). Experimental data show that the currents in NSAM have a linear relation with a function of the total deposited nanoparticle surface area for the different compartments of the lung. No significant dependency of the calibration factors on particle materials and morphology was observed. Monodisperse nanoparticles in the size range where the response function is in the desirable range can be used for calibration. Calibration factors of monodisperse and polydisperse Ag particle agglomerates are in good agreement with each other, which indicates that polydisperse nanoparticles can be used to determine calibration factors. Using a CFD computer code (Fluent) numerical simulations of fluid flow and particle trajectories inside NSAM were performed to estimate response function of NSAM for different ion trap voltages. The numerical simulation results agreed well with experimental results.     

A comparative STM study of Ru nanoparticles deposited on HOPG by mass-selected gas aggregation versus thermal evaporation

Scanning tunneling microscopy was used to compare the morphologies of Ru nanoparticles deposited onto highly-oriented graphite surfaces using two different physical vapour deposition methods; (1) pre-formed mass-selected Ru nanoparticles with diameters between 2 nm and 15 nm were soft-landed onto HOPG surfaces using a gas-aggregation source and (2) nanoparticles were formed by e-beam evaporation of Ru films onto HOPG. The particles generated by the gas-aggregation source are round in shape with evidence of facets resolved on the larger particles. Annealing these nanoparticles when they are supported on unsputtered HOPG resulted in the sintering of smaller nanoparticles, while larger particles remained immobile. Nanoparticles deposited onto sputtered HOPG surfaces were found to be stable against sintering when annealed. The size and shape of nanoparticles deposited by e-beam evaporation depend to a large extent on the state of the graphite support and the temperature. Ru deposition onto unsputtered HOPG is characterised by bimodal growth with large flat particles formed on the substrate terraces and smaller diameter particles aligned along the substrate steps. Evaporation onto sputtered HOPG results in the formation of 2 nm round particles with a narrow size distribution. Finally, thermal deposition onto both sputtered and unsputtered HOPG at 660 °C results in larger particles showing a flat Ru(0 0 0 1) top facet.     

Grain size and its distribution in NiTi thin films sputter-deposited on heated substrates

Grain size and its distribution in NiTi thin films sputter-deposited on a heated substrate have been investigated using the small angle x-ray scattering technique. The crystalline particles have a small size and are distributed over a small range of sizes for the films grown at substrate temperatures 370 and 420℃. The results show that the sizes of crystalline particles are about the same. From the x-ray diffraction profiles, the sizes of crystalline particles obtained were 2.40nm and 2.81nm at substrate temperatures of 350 and 420℃, respectively. The morphology of NiTi thin films deposited at different substrate temperatures has been studied by atomic force microscopy. The root mean square roughness calculated for the film deposited at ambient temperature and 420℃ are 1.42 and 2.75nm, respectively.     

水热合成碳颗粒的结构和发光性能

用生物试剂氨基葡萄糖盐酸盐和葡萄糖在水溶液中合成了碳颗粒,用场发射扫描电子显微镜、高分辨透射电子显微镜、显微Raman光谱仪和傅立叶红外光谱仪对样品的结构和组成进行了研究。结果表明,碳颗粒是球形非晶结构,直径为0.3~1.4μm。利用He-Cd激光器的325 nm线,在显微Raman光谱仪中对碳颗粒的光致发光(PL)性能进行了研究。光谱显示出中心在420 nm的弱的蓝色PL带、中心在575 nm和650 nm的强而宽的绿光和红光PL带,它们分别与官能团和带与带之间的跃迁有关。绿光和红光PL带的宽化与sp2碳颗粒的非均匀性有关。     

Structure of fullerene-containing soot at different formation stages of arc discharge vaporization of graphite

Electron microscopy is used in a study of nanoclusters of the carbon soot deposited on a probe in different areas of arc discharge during graphite vaporization under conditions favorable for fullerene synthesis. It is found that the spatial network of soot nanoclusters consists of alternating regions of higher density or associates of carbon particles. Two types of nanoclusters have been identified with the correlation radii of the associates equal to 0.6–0.8 and 1.6–2.2 nm, respectively. Type I nanoclusters are dominant in the soot microparticles, and their structure shows practically no variations with increasing separation r of the soot collector from the discharge axis over the range of distances studied, r=1–9 cm. The effective radius R ₀ of the “elementary” particles making up the associates in the soot nanoclusters of Type I calculated with the use of scaling relationships is 0.15–0.17 nm and is close to the gas-kinetic radius of carbon atoms. Type II nanoclusters have been identified in soot collected at r>3 cm. Values of R ₀ calculated in this case are 0.6–0.9 nm and decrease with increasing r, which indicates the presence of fullerene molecules in these nanocluster associates.     

Behavior of Ultrafine Particles generated from organic vapors by corona ionizers

This paper reports an experimental study on the stability, coagulation and diffusion of molecular clusters and ultrafine particles generated from organic vapors by corona ionizers. Upon leaving the ionizer, particles are made to flow within several types of vessels: depending on the specific geometry of the flow system, clusters either coagulate into large particles or are deposited on the walls. Particles larger than 4nm and molecular clusters penetrate through a wire-screen type diffusion battery, but particles in the size range between 2 and 4nm are collected. Among the organic compounds tested (aromatics, alcohols, ketones and others), only aromatic compounds appear to yield unstable clusters which grow into detectable particles (>2nm) through Brownian coagulation. The other compounds either do not undergo the gas-to-particle conversion process or are too small to be detected. Furthermore, the presence of moisture seems to be of fundamental importance in the particle generation phenomenon. The addition of alcohols to the vapor mixture inhibits particle formation.     

Photo-chemical synthesis and deposition of noble metal nanoparticles

Highly dispersed nanoparticles of transition and noble metals are utilized for hydrocarbon reactions and rearrangements important to the chemical industry. The need to obtain 1 to 3 nm particles with narrow size distributions has prompted the development of alternative processing methods. In this paper, a novel, dry method to synthesize nanoparticles from a frozen salt solution is reported. Pd nanoparticles were synthesized by photo-chemical decomposition of palladium acetate (PdAc) within a host matrix of chloroform using an excimer laser operating at 248 nm. Frozen composite targets were ablated at fluences ranging from 0.25 J/cm² to 0.75 J/cm² at a processing pressure of 10 mTorr. The ejected nanoparticles were deposited on continuous carbon coated and lacey carbon transmission electron microscopy (TEM) grids at ambient temperature. Characterization was performed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDXS). High-resolution TEM analysis showed definitive evidence that the size distributions of the nanoparticles were narrow, exhibiting mean diameters ranging from 2.15 nm to 2.62 nm. PACS 81.15.Fg; 68.37.Lp; 81.07.Wx; 81.07.Bc; 81.10.Dn     

Carbon-coated Non-magnetic Iron Oxide Particles for the Substrate of Multi-layered Magnetic Recording Media

Non-magnetic particles with finer size (less than 200 nm), higher dispersibility, higher blackness and lower electrical resistance are required to produce better multi-layered magnetic tape media which have non-magnetic substrate using non-magnetic sub-layer materials. A special method to prepare acicular hematite particles, whose cross-sectional diameter is about 150 nm, coated with carbon black using a surface modification agent is reported in this paper. Transmission electron microscopy photographs of carbon-coated hematite particles indicate that all of the carbon black is firmly bound to the surface in a distinct layer. The thickness of carbon-coating layer was about 1 to 2 nm if 15% by weight of carbon black is coated onto the particle surface.Non-magnetic substrates for multi-layered magnetic recording media prepared using the carbon-coated particles exhibit improvements in both light transparency and electrical resistance. A decrease in transparency of about 30% as well as a reduction in the electrical resistance of about 1.5 orders of magnitude relative to conventionally prepared substrates was achieved. The surface smoothness and the viscosity were also improved because the dispersibility of these particles in non-magnetic lacquer became better than that of the physical mixture of uncoated hematite particles and carbon black.     

Synthesis of nanoparticles in an atmospheric pressure glow discharge

Nanopowders are produced in a low temperature, non-equilibrium plasma jet (APPJ), which produces a glow discharge at atmospheric pressure, for the first time. Amorphous carbon and iron nanoparticles have been synthesized from Acetylene and Ferrocene/H₂, respectively. High generation rates are achieved from the glow discharge at near-ambient temperature (40–80°C), and rise with increasing plasma power and precursor concentration. Fairly narrow particle size distributions are measured with a differential mobility analyzer (DMA) and an aerosol electrometer (AEM), and are centered around 30–35 nm for carbon and 20–25 nm for iron. Particle characteristics analyzed by TEM and EDX reveal amorphous carbon and iron nanoparticles. The Fe particles are highly oxidized on exposure to air. Comparison of the mobility and micrograph diameters reveal that the particles are hardly agglomerated or unagglomerated. This is ascribed to the unipolar charge on particles in the plasma. The generated particle distributions are examined as a function of process parameters.