Structure and magnetic properties of carbon encapsulated Fe nanoparticles obtained by arc plasma and combustion synthesis

Carbon encapsulated Fe nanoparticles were obtained using two methods: arc plasma and combustion synthesis. These powders were characterized by the following methods: SQUID magnetization measurements, transmission electron microscopy (TEM) and Mössbauer spectroscopy. The last two methods showed that Fe nanoparticles, obtained by both techniques belong to metallic and/or carbide phases, and are partially encapsulated by graphitic carbon. The particles had 10-100 nm in diameter, and were covered by carbon 5-15 nm thick layers. The transmission Mössbauer spectra revealed two magnetic and two paramagnetic components. In the plasma samples the largest part of iron was contained in the carbide phase while in the combustion samples the bcc α-Fe encompassed most of iron. The combustion sample has much higher content of carbon, indicating that the Fe particles were not covered by graphite layer totally, and were dissolved in the etching process. The dominant portion of combustion samples was not vaporized, thus the iron phase solidified from the liquid. The plasma-arc samples were synthesized via dual mechanism: growth of nanocrystals from the vapor phase (carbide) and solidification of the liquid micro-droplets in the cold zone (α-Fe and γ-Fe).     

Improved field emission properties of double-walled carbon nanotubes decorated with Ru nanoparticles

The field emission properties of double-walled carbon nanotubes (DWCNTs) were remarkably improved by decorating their surface with ruthenium (Ru) metal nanoparticles. The Ru nanoparticles were attached effectively on the surface of DWCNTs via a chemical procedure. The Ru-decorated DWCNTs showed lower turn-on voltage, higher emission current density, and improved emission uniformity compared with pristine DWCNTs. The effect of Ru nanoparticles on the work function and density of states was evaluated by the first-principles calculation. The enhanced field emission properties of Ru-DWCNTs were mainly attributed to the Ru nanoparticles which increased the field enhancement factor and the density of emission sites. Our results indicate that the Ru-decorated DWCNTs can be used as an effective field emitter for various field emission devices.     

Electrochemical detection of Cr(VI) with carbon nanotubes decorated with gold nanoparticles

Journal of Applied Electrochemistry - A nanocomposite consisting of gold nanoparticles deposited on the side walls of functionalised multi-walled carbon nanotubes, Ox-MWCNT-Aunano, was prepared...     

The synthesis of ionic-liquid-functionalized multiwalled carbon nanotubes decorated with highly dispersed Au nanoparticles and their use in oxygen reduction by electrocatalysis

Multiwalled carbon nanotube (MWCNT)/ionic liquid/gold nanoparticle hybrid materials have been prepared by a chemical route that involves functionalization of MWCNT with amine-terminated ionic liquids followed by deposition of Au. Transmission electron microscopy revealed well-distributed Au with a narrow size distribution centered around 3.3 nm. The identity of the hybrid material was confirmed through Raman and X-ray photoelectron spectroscopy. It showed good electrocatalytic behavior toward oxygen reduction, relative to glassy carbon electrode. The results indicate that modification of MWCNT with ionic liquids and Au could play an important role in increasing the electrocatalytic activity of MWCNT.     

Facile synthesis of silicon dioxide nanoparticles decorated multi-walled carbon nanotubes with graphitization and carboxylation for electrochemical detection of gallic acid

We proposed an efficient and scalable ultrasound-assisted approach for the synthesis of functionally integrated nanohybrid of silicon dioxide (SiO₂) nanoparticles and multi-walled carbon nanotubes with graphitization and carboxylation (GCMCN), which was employed to modify the glassy carbon electrode (GCE) for the fabrication of GCMCN@SiO₂/GCE sensor. Graphitization of GCMCN contributed to the reduction of defect density and enhancement of electrical conductivity, and carboxylation of GCMCN improved the dispersion degree of carbon nanomaterial due to the hydrophilicity of carboxyl groups. SiO₂ nanoparticles possessed abundant binding active sites for target analytes due to the surface hydroxyl groups or silanol groups, which were beneficial for the enrichment of gallic acid (GA) molecules. For the functionally integrated GCMCN@SiO₂ nanocomposite, the interconnected conductive networks of GCMCN presented more efficient charge transport channels, which recompensed the non-conductive property of SiO₂ nanoparticles. Based on the functional collaboration of GCMCN and SiO₂ nanoparticles, the fabricated GCMCN@SiO₂/GCE sensor presented good GA detection property (GA concentration: 0.01–15 μM, LOD value: 1.99 nM). The proposed sensor exhibited acceptable repeatability, reproducibility, and selectivity. Moreover, the good practicability performance could be effectuated at the GCMCN@SiO₂/GCE sensor for the quantitative analysis of GA in black tea and green tea samples.     

Single-step synthesis of germanium nanowires encapsulated within multi-walled carbon nanotubes

We report the single-step synthesis of Ge nanowires encapsulated within multi-walled carbon nanotubes (MWCNTs) from a phenyltrimethylgermane (C₆H₅Ge(CH₃)₃) precursor, using a simple chemical vapor deposition (CVD) method. The MWCNT/germanium nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) measurements. TEM analysis reveals that the nanowires consist of well crystallized Ge cores which are completely encapsulated by the sheath-like MWCNTs, the latter corresponding to a layer thickness of 5-10 nm. SEM images, corresponding to various stages of nanowire growth, indicate that MWCNT growth occurs at Ge nanoparticles and that the growing MWCNTs carry Ge as nanowires away from the nanoparticles. By optimizing the CVD parameters, nanowires can be produced with uniform length and diameter in the range 6-10 μm and 200-300 nm, respectively.     

Controlled assembly of graphene shells encapsulated gold nanoparticles and their integration with carbon nanotubes

Controlled growth and uniform patterning of graphene/carbon shells encapsulated gold nanoparticles (GNPs) on silicon wafer or on high curvature carbon nanotubes (CNTs) is reported here. This was achieved by utilizing patterned gold nanoparticles with controlled sizes (∼30–600 nm) via gold film dewetting process. Surface-oxidized and patterned nanoparticles were used as sacrificial catalysts for the chemical vapor deposition (CVD) growth of graphene/carbon shells. The shell morphological evolution and thickness as well as surface migration of nanoparticles during the CVD process were studied as a function of the gold nanoparticles size. Reduced surface migration and coalescence was observed for gold nanoparticles after the CVD growth and this was attributed to the initial formation of graphene/carbon shells as well as stable dispersion of the dewetted gold nanoparticles. It is proposed that graphene/carbon shell growth was controlled by Ostwald’s ripening, surface gold oxide, and reducing CVD growth environment. Furthermore, complex heterostructures based on CNTs coated with GNPs were fabricated by dewetting Au films on CNTs and followed by surface oxidation and CVD growth steps. CNTs successfully survived multiple processing steps and selective growth of graphene shells around Au nanoparticles was achieved and studied using microscopic and spectroscopic methods.     

Noncovalently silylated carbon nanotubes decorated with quantum dots

A nanoassembly of single-walled carbon nanotubes coated by a thin layer of silica followed by quantum dots was prepared. That the quantum dots retained their photoluminescent properties after deposition onto the silylated carbon nanotubes suggests that the thin layer of silica prevented the quenching of the fluorescence by the nanotubes. This fluorescent nanoassembly represents an excellent building block for photoelectric and optical devices and biological nanoprobes.     

Fabrication of carbon encapsulated Co3O4 nanoparticles embedded in porous graphitic carbon nanosheets for microwave absorber

Carbon-encapsulated Co₃O₄ nanoparticles homogeneously embedded 2D (two-dimensional) porous graphitic carbon (PGC) nanosheets were prepared by a facile and scalable synthesis method. With assistance of sodium chloride, the Co₃O₄ nanoparticles (10–20 nm) with magnetic loss were well encapsulated by onion-like carbon shells homogeneously embedded porous graphitic carbon nanosheets (thickness of less than 50 nm) with dielectric loss. In the architecture, the well impedance matching for microwave absorption can be obtained by the synergetic effect between Co₃O₄ nanoparticles and encapsulated porous carbon nanosheets. The minimum reflection loss value of −32.3 dB was observed at 11.4 GHz with a matching thickness of 2.3 mm for 2D Co₃O₄@C@PGC nanosheets. The 2D Co₃O₄@C@PGC nanosheets can be used as a kind of candidate for microwave absorbing materials.     

Direct synthesis of high-quality single-walled carbon nanotubes by the physical nucleation of iron nanoparticles in an atmospheric pressure carbon monoxide flow

We demonstrate a direct and stable aerosol synthesis of single-walled carbon nanotubes (SWCNTs) using a hot wire generator (HWG) method, with iron physically evaporated in a carbon monoxide (CO) atmosphere as the catalyst source. A small amount of added carbon dioxide increased the lifetime of the Fe wire in reacting CO up to several weeks. This approach allowed us to significantly increase the yield of SWCNTs as compared to the previously employed inert hydrogen-containing flow through the wire. High quality and purity SWCNTs were produced, as demonstrated by high-resolution transmission electron microscopy and Raman and optical absorption spectroscopy.     

Formation of graphitic rods in carbon/carbon composites reinforced with carbon nanotubes

The formation of graphitic rods with a carbon nanotube (CNT) in the center was observed in CNT-reinforced phenolic resin-based carbon/carbon composites heat treated at 2000 °C. TEM characterization indicated that the carbon surrounding the CNT has a much better degree of graphitization compared to the carbon in most of the matrix. The formation temperature (2000 °C) of the graphitic rod is lower than for stress graphitization and normal graphitization of phenolic resin.     

Facile synthesis of graphitic carbons decorated with SnO2 nanoparticles and their application as high capacity lithium-ion battery anodes

A facile and potentially scalable synthesis route to obtain SnO₂–carbon composites was developed. SnO₂ nanoparticles were deposited on the surface of two types of graphitic carbon: (a) commercial porous graphite (HG) and (b) graphitic carbon nanostructures. The synthesis procedure consists of two simple steps: (i) room temperature formation/deposition of SnO₂ nanocrystals and (ii) thermal treatment at 350 °C to generate SnO₂ nanoparticles (size ~3.5 nm) over the carbon surface. The electrochemical performance of the graphitic carbons and the SnO₂–carbon composites as anode materials in Li-ion rechargeable batteries was investigated. In all cases, tape casting electrode fabrication allowed almost full active material utilization. Good cyclabilities were achieved, with HG and HG–SnO₂ showing capacities of 356 and 545 mAh g⁻¹, respectively after 50 cycles.     

Direct synthesis of self-aligned single-walled carbon nanotubes on paper

A technique of micro chemical vapor deposition (μCVD) is reported for the direct synthesis of self-aligned SWCNTs on various substrates including plastics and paper. With the guidance of micro flow channels, self-aligned SWCNTs up to hundreds of microns in length have been collected. Both Raman spectral and transmission electron microscopy have validated the high quality of these SWCNTs. In conclusion, μCVD could be a versatile method to synthesize pristine SWCNTs for various applications.     

Effect of carbon nanotubes decorated with silver nanoparticles as hybrid filler on properties of natural rubber nanocomposites

Decoration of carbon nanotube (CNT) surfaces with silver nanoparticles (AgNPs) was performed using N,N-dimethylformamide reducing agent. The CNT-decorated with AgNP (CNT-AgNP) was then used to prepare natural rubber (NR) nanocomposites via latex mixing method. Cure characteristics, mechano-thermal relaxation, electrical conductivity, and thermal properties of the composites were investigated. It was found that the CNT-AgNP gave cure properties improved over plain NR compounds in terms of scorch time, degree of vulcanization, and activation energy. In addition, temperature scanning stress relaxation measurement revealed stronger network formation after incorporation of AgNP into the NR matrix due to the interaction among CNT and AgNP particles. This also provided high conductivity and low percolation threshold concentration for the CNT-AgNP filled NR, relative to plain CNT filled NR composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47281.     

H2S oxidation by multi-wall carbon nanotubes decorated with tungsten sulfide

Tungsten sulfide catalysts decorated on single and multiwall carbon nanotubes (SWNTs & MWNTs) and activated carbon were synthesized, and XRD, ICP, SEM, TEM and ASAP analyses were employed to acquire the characteristics of each catalyst. Afterwards a gas flow containing 5,000 ppm of H₂S was passed over the catalyst in gas hour space velocity (GHSV) of 5,000 h^?1, temperature of 65 °C, steam volume percent of 20 and O₂/H₂S ratio equal to 2. The results revealed that the catalyst supported on MWNTs exhibited higher conversion amongst its counterparts. Then effects of GHSV, steam volume percent in the feed, catalyst loading and temperature were investigated on conversion of hydrogen sulfide to elemental sulfur for tungsten sulfide catalyst decorated on MWNTs.     

Formation of bamboo-like conducting carbon nanotubes decorated with Au nanoparticles by the thermal decomposition of sucrose in an AAO template

An easy method is reported for the preparation of bamboo-like conducting carbon nanotubes decorated with Au nanoparticles (Au-CNT), by carbonization of sucrose inside of anodic aluminum oxide (AAO) nanochannels (～80 nm and ～30 μm in diameter and length, respectively). First, the AAO membrane nanochannels were coated with Au nanoparticles (～10 nm in diameter) and the carbon nanotubes were then formed in the same channels below 973 K. Electron microscopy shows long bamboo-like carbon nanotubes, ～30 μm in length, decorated with crystalline gold nanoparticles, ～50 nm in diameter. The coalescence of the precoated small Au nanoparticles inside the channel results in the attached large Au nanoparticles. The apparent resistivity of the Au-CNT prepared at 973 K, was ～16.8 Ω cm. The electrical conductivity of the structure is discussed with relation to electrochemical and micro Raman experiments.     

粒径可控的铜纳米粒子的液相还原法制备

在一定温度的水溶液中,采用铜离子前躯体,水合肼为还原剂,在PVP存在下,进行了粒径、形貌可控的纯铜纳米粒子的合成,获得了粒径在7～70nm的铜纳米粒子.通过X射线衍射仪、紫外一可见分光光度计、透射电子显微镜、扫描电子显微镜和电子衍射等手段对产物测试与表征,证实了上述结果.同时证明,粒径可由奥斯瓦尔德老化过程控制,保护剂可在一定程度上控制粒子形貌.     

Evidence for large hydrogen capacity in single-walled carbon nanotubes encapsulated by thin Pd layers onto a Pd substrate

We report a study of hydrogen storage and its mechanism in a novel material, representing single-walled carbon nanotubes (SWCNTs) encapsulated by thin Pd layers onto a Pd substrate. A synergetic effect resulting in combination of the Pd and the SWCNT properties with regard to hydrogen has been achieved. We showed that adding SWCNTs increases the H₂-capacity of the Pd–SWCNT composite under electrochemical loading only by up to 25% relative to the Pd metal alone. At the same time, with regard to the added SWCNTs, such synergetic approach (providing high H₂ pressure from highly H-loaded massive Pd substrate into a small fraction of deposited SWCNT) allowed us to achieve a net capacity of 8–12 wt.%. H₂, thus, bringing a unique chance to study hydrogen storage mechanism in highly H-loaded SWCNT. Using ESR technique it was established that the Pd–C_x π-complexes forming at the openings of SWCNTs could be considered as hydrogen adsorption sites, providing both high gravimetric capacity (H/C > 1) and low hydrogen binding energy in the Pd encapsulated SWCNT.