Activated carbon catalyzing the formation of carbon nanotubes

Activated carbon (AC), a common carbon material, is employed as catalyst to synthesize carbon nanotubes (CNTs) through chemical vapor deposition (CVD) and detonation-assisted CVD methods. The results show AC can effectively catalyze CNT formation. From the microscopic observations on morphologies and structures of the formed intermediates, it is found that carbon-catalyzed CNT formation follows particle-wire-tube stepwise evolution mechanism, in which carbon nanoparticles first assemble into wire-like nanostructures, then evolve into nanotubes via particle-particle coalescence and structural crystallization.     

Effect of growth temperature on the CVD grown Fe filled multi-walled carbon nanotubes using a modified photoresist

Fe filled carbon nanotubes were synthesized by atmospheric pressure chemical vapor deposition using a simple mixture of iron(III) acetylacetonate (Fe(acac)₃) with a conventional photoresist and the effect of growth temperature (550-950 °C) on Fe filled nanotubes has been studied. Scanning electron microscopy results show that, as the growth temperature increases from 550 to 950 °C, the average diameter of the nanotubes increases while their number density decreases. High resolution transmission electron microscopy along with energy dispersive X-ray investigation shows that the nanotubes have a multi-walled structure with partial Fe filling for all growth temperatures. The graphitic nature of the nanotubes was observed via X-ray diffraction pattern. Raman analysis demonstrates that the degree of graphitization of the carbon nanotubes depends upon the growth temperature.     

Hydrothermal synthesis of titanate nanoparticle/carbon nanotube hybridized material for dye sensitized solar cell application

With the hydrothermal treatment, titanate nanostructure with distinctively different morphology and surface characteristics was successfully synthesized from commercial rutile titania powder dispersed in accommodating media which were deionized water or NaOH solution. Hybridized materials of titanate nanoparticles and carbon nanotubes (CNT) were also synthesized by the hydrothermal treatment process. Intrinsic interaction of titanate nanoparticles and CNTs could be confirmed by spectroscopic analysis. The synthesized titanate nanoparticle/CNT hybridized material was then employed for fabricating a working electrode of dye-sensitized solar cells (DSSC). Based on experimental results, DSSC fabricated from the hybridized titanate nanoparticles and carbon nanotubes could provide the highest photoconversion efficiency of approximately 3.92%.     

New synthesis of Cu2O and Cu nanoparticles on multi-wall carbon nanotubes

Cu₂O and Cu nanoparticles were deposited on the surface of multi-walled carbon nanotubes with a diameter range of 15–90 nm by the impregnate method. Multi-wall carbon nanotubes with a length of 200 μm and a diameter range of 70–110 nm were grown inside of quartz tubing by the spray pyrolysis method using ferrocene/benzene under argon flow. The nanotubes were then treated with nitric acid to clean the surface and generate carboxylic groups. The copper was impregnated on multi-walled carbon nanotubes using a xylene solution of copper(I) phenylacetylide as the precursor. Copper and cuprous oxide nanoparticles were obtained during thermal treatment.     

Novel strategy for the synthesis of vertically orientated carbon nanofibers

This paper presents a first approach of a simple way to obtain vertically orientated carbon nanotubes. The used catalytic system consisted of quartz or graphite plates, on which some iron solutions (of precursors such as nitrates or phthalocyanines) were deposited by simple impregnation, generating homogeneous films. After drying, the plates were submitted to reduction and reaction procedure, which consisted in acetylene decomposition at 750 °C during 1 h. Samples after reaction were studied by scanning electron microscopy and transmission electron microscopy, which confirmed the formation of homogeneous and vertically orientated structures of carbon nanotubes over the plates.     

Continuous synthesis of controlled size carbon-encapsulated iron nanoparticles

Carbon-encapsulated iron nanoparticles were continuously and selectively synthesised in a thermal plasma jet from ethanol (carbon source) and Fe powders with different grain sizes. The grain size of the Fe powder influenced the size distribution of the as-produced carbon encapsulates. The products obtained from large Fe particles (50-78 μm) were comprised of small encapsulates with diameters between 5 and 10 nm. Larger carbon encapsulates with a broad diameter distribution (10-100 nm) were synthesised from the finest Fe particles (18 μm). It was also found that Fe particle size was the most crucial parameter for determining the encapsulation yield. The encapsulation yield was also influenced by the carbon to iron ratio and the thermal conductivity of the plasma gas.     

Atomic-scale in-situ observation of carbon nanotube growth from solid state iron carbide nanoparticles

We have first observed the nucleation and growth process of carbon nanotubes (CNTs) from iron carbide (Fe 3C) nanoparticles in chemical vapor deposition with C 2H 2 by in situ environmental transmission electron microscopy. Graphitic networks are formed on the fluctuating iron carbide nanoparticles, and subsequently CNTs are expelled from them. Our atomic scale observations suggest that carbon atoms diffuse through the bulk of iron carbide nanoparticles during the growth of CNTs.     

One-pot synthesis of iron oxide-carbon core-shell particles in supercritical water

The quantitatively limited use of hydrogen peroxide in supercritical water allows for the in situ formation of iron oxides and graphitic carbon from ferrocene in one step. The structure of the particles prepared at 400-500 °C is comprised of nano- to micro-meter size of magnetite and maghemite cores covered with graphitic carbon shells. The morphology and size of the core-shell particles and the phase composition of iron-oxide cores are different dependent on the preparation conditions. The particles prepared at 400 °C contain, as dominant iron-oxide phase, the magnetite core particles ranging from nano- to micro-meter scales with no morphological regularity, while those prepared at 500 °C are comprised of hexagram shape and micro-meter size of maghemite cores. The observed morphology, the dimension of the core particles, and the dominant phase composition suggested that the iron-oxide cores would be formed through the oxidation of iron(II) to iron(III) and two different hydrolysis paths. Furthermore, the higher preparation temperature of 500 °C has shown a tendency to form smaller crystallite sizes of polycrystalline iron-oxide cores. The decrease of subcrystal sizes in the vicinity of superparamagnetic thresholds effects the reduction of coercivity in the ferromagnetic hysteresis.     

碳包覆铁纳米颗粒制备及电磁性能分析

以纤维素为基质,硝酸铁为金属颗粒前躯体,在氢气保护下进行控温炭化合成出准球形的碳包覆铁纳米颗粒．产物通过TEM、EDX和XRD表征呈核壳结构,粒径分布比较窄．通过波导法对所制备的碳包覆铁纳米颗粒进行吸波性能分析,采用矢量网络仪研究分析其在8．2～12．4GHz频率范围内的电磁性能．     

Coating and filling of carbon nanotubes with homogeneous magnetic nanoparticles

Magnetic multi-walled carbon nanotube (MWCNT) composites were obtained by decoration of metal oxide nanoparticles on or in carbon nanotubes. The method involved the dispersion of the carbon nanotubes in iron pentacarbonyl Fe(CO)₅ followed by vacuum thermolysis and subsequent oxidation. The magnetic iron oxide particle deposition was always homogeneous and could be controlled selectively on the outer, inner, or both surfaces of MWCNTs by using different MWCNTs. Since the hollow channels remained intact, these MWCNT based composites could find special applications in cellular delivery systems.     

Mass production of multi-wall carbon nanotubes by metal dusting process with high yield

Carbon nanotube materials were synthesized over Fe-Ni nanoparticles generated during disintegration of the surface of alloy 304L under metal dusting environment. The metal dusting condition was simulated and optimized through exposing stainless steel samples during long term repetitive thermal cycling in CO/H₂ = 1/1, total gas flow rate 100 cm³/min, at 620 °C for 300 h. After reaction, surface morphology of the samples and also carbonaceous deposition which had grown on sample surfaces were examined by stereoscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results revealed that multi-wall carbon nanotubes could be formed over nanocatalyst generated on the alloy surface by exploiting metal dusting process. By optimization of reaction parameters the yields of carbon nanotube materials obtained were 700-1000%. Also it has been shown herein that the amount of carbon nanotube materials remarkably increases when the reaction time is extended up to 300 h, indicating a possibility of the mass production by this easy method.     

Mobile iron nanoparticle and its role in the formation of SiO2 nanotrench via carbon nanotube-guided carbothermal reduction

The detailed role of iron nanoparticles (NPs) involved with the formation of SiO2 nanotrenches is revealed. The physical movements of iron NPs, such as levitation and adsorption, turn out to be responsible for the initiation of carbothermal reduction (C (carbon nanotube, s) + SiO2(s) <--> SiO(g) + CO(g)), which results in SiO2 nanotrenches that are fully guided by carbon nanotubes. Under the chemical vapor deposition condition with 0.1% of O2 gas, iron NPs are liberally levitated from SiO2/Si substrate then adsorbed on the sidewalls of carbon nanotubes. Depending on the numbers of iron NPs attached to carbon nanotubes, two different types of nanotrenches are determined. When multiple iron NPs are assembled on carbon nanotubes and involved in carbothermal reduction, aligned nanohole type of nanotrenches is produced (Type I). On the contrary, when single iron NPs initiate the carbothermal reduction, nanotrenches having smooth pathways and high shoulders are commonly formed (Type II).     

Room-temperature ferromagnetism in doped face-centered cubic fe nanoparticles

The magnetism of Fe and its alloys has been at the center of scientific and technological interest for decades. Along with the ferromagnetic nature of body-centered cubic Fe, the magnetic properties of face-centered cubic (fcc) Fe have attracted much attention. It is well known that fcc Fe is thermodynamically unstable at ambient conditions and not ferromagnetic. Contrary to what is known, we report that elongated nanoparticles of fcc Fe, grown within graphitic nanotubes, remain structurally stable and appear ferromagnetic at room temperature. The magnetic moment (2+/-0.5 microB) in these nanoparticles and the hyperfine fields for two different components of 57Fe (33 and 21 T), measured by M?ssbauer spectroscopy, are explained by carbon interstitials in the expanded fcc Fe lattice, that is, FeC(x) where x approximately 0.10, which result in the formation of a dominant Fe4C stoichiometry. First-principles calculations suggest that the ferromagnetism observed in the fcc Fe is related to both lattice expansion and charge transfer between iron and carbon. The understanding of strain- and dopant-induced ferromagnetism in the fcc Fe could lead to the development of new fcc Fe-based alloys for magnetic applications.     

Carbon nanotube formation over laser ablated M and M/Pd (M = Fe,Co, Ni) catalysts: The effect of Pd addition

Monometallic and bimetallic M and M/Pd (M = Fe, Co, Ni) nanoparticles were prepared by pulsed Nd:YAG laser ablation of bulk M and Pd targets in acetone and transferred onto Si wafers to catalyze carbon nanotubes from decomposition of liquid petroleum gas via thermal chemical vapor deposition at 750°C. Transmission electron microscopy and optical extinction study revealed that the prepared M and M/Pd nanoparticles have rather spherical shape and their aspect ratios are nearly one. In comparison to monometallic M catalysts by addition of Pd, the average sizes of produced bimetallic M/Pd catalysts increased. Carbon nanotubes' characterization revealed that by addition of Pd to laser ablated M catalysts the average diameter, the yield, and quality of end product carbon nanotubes were increased. The average diameter of grown carbon nanotubes increases as: Ni < Ni/Pd < Co < Co/Pd < Fe < Fe/Pd and the quality of them increases as: Ni < Co < Fe < Ni/Pd < Fe/Pd < Co/Pd.     

Synthesis of Hybrid Materials Based on Iron Nanoparticle-Decorated Multiwalled Carbon Nanotubes

Fe-containing nanoparticles have been grown for the first time on the surface of multiwalled carbon nanotubes by metalorganic chemical vapor deposition using iron acetylacetonate, Fe(acac)₃, as a precursor. The resultant hybrid nanomaterial has been characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the synthesized material consists of multiwalled carbon nanotubes whose surface is decorated with iron nanoparticles.     

Bulk synthesis of carbon nanocapsules and nanotubes containing magnetic nanoparticles via low energy laser pyrolysis of ferrocene

A one-step synthesis route to carbon nanocapsules and nanotubes containing Fe and Fe₃C nanoparticles is reported. Low power laser assisted pyrolysis of ferrocene yielded carbon nanocapsules (30-100 nm in diameter) and multi-wall carbon nanotubes (30-80 nm in diameter). The developed route is fast and enables one to synthesize the products at a rate of 84 mg/min. The iron content in the product (10-42 wt.%) can be varied by modulating the buffer gas pressure during the synthesis process.     

Synthesis of zirconia nanoparticles on carbon nanotubes and their potential for enhancing the fracture toughness of alumina ceramics

Nanoparticles of zirconia (ZrO₂) were in situ synthesized on the surface of carbon nanotubes by means of liquid phase reactions and a proper heat treatment process. The size of the nanoparticles could be controlled by the amount of zirconium source materials in a solution and its reaction times. In this study, the size of the nanoparticles ranged from several nanometers to twenty nanometers. It was particularly noted that the synthesized zirconia possessed a cubic structure (c-phase) which generally existed as a stable form of zirconia crystals at high temperatures (above 2370 °C) as well as a form of zirconia that could be used for enhancing the fracture toughness of alumina ceramics. Experimental results showed that the mechanical properties of alumina ceramics mixed with in situ synthesized nanoparticles on the surface of carbon nanotubes were much better than that of pristine nanotubes or zirconia nanoparticles alone. The existence of the nanoparticles on the surface of nanotubes results in improving the dispersion and bonding properties of the nanotubes in alumina matrix environment. The fracture toughness of CNT/ZrO₂ alumina ceramics was also improved by the mechanism of bridging effect.     

Fe-sapphire and C-Fe-sapphire interactions and their effect on the growth of single-walled carbon nanotubes by chemical vapor deposition

We previously reported that the quantity of single-walled carbon nanotubes grown on Fe-coated sapphire by chemical vapor deposition depended on the crystallographic faces of sapphires. In this report, we show that the interaction of Fe, sapphire, and carbon depended on the sapphire faces. We deduce that the quantity of Fe available to catalyze the growth of single-walled carbon nanotubes was suppressed by the formation of Fe-Al alloys and whether the Fe-Al alloys were formed on Fe-coated sapphire or not depended on the sapphire-surface structure.     

Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.     

用于制备优质单壁碳纳米管管束的MgO负载Fe3O4纳米粒子的合成

采用沉淀方法制备了直径分布狭窄的均匀Fe3O4纳米颗粒.Fe3O4纳粒形体几近一致,平均粒径为10.33 nm±2.99 nm(平均粒径±标准偏差).在超声作用下将MgO纳米颗粒分散在一定量Fe3O4纳米颗粒的水溶液中获得MgO负载Fe3O4的纳米颗粒.以甲烷为碳源,Fe3O4/MgO为催化剂,经化学气相沉积,在Fe3O4纳粒上制得了大量直径近乎均匀的单壁碳纳米管(SWCNTs)束.TEM显示:SWCNTs的平均直径1.22rm.热重分析显示:样品在400℃～600℃温度区间失重量约19％.拉曼光谱显示:SWCNTs的ID/IG的强度比为0.03,表明采用Fe3O4/MgO催化剂可制得高石墨化程度的单壁碳纳米管.