Magnetic Properties Of Carbon Nanotubes Research Articles

Study of bamboo-type carbon nanotubes with magnetic iron carbide nanoparticles fabricated by a modified CVD method

This work studies the structural, microstructural, and magnetic properties of carbon nanotubes with magnetic iron carbide nanoparticles attached to their walls. The samples were fabricated in a single step using a modified chemical vapor deposition (CVD) method. The proposed method allows to obtain carbon nanotubes with iron carbide nanoparticles partially immersed in their walls. The carbon nanotubes were characterized using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). Results show that the obtained carbon nanotubes are multi-walled with a bamboo-like structure. They have an average diameter of 40 nm and inner cavities of 20 nm in diameter. The magnetic nanoparticles are firmly fixed to the nanotubes, and they have an average diameter of 15 nm with rounded borders. The iron carbide nanoparticles exhibit a ferromagnetic behavior with high magnetic saturation resulting from their morphological characteristics and their location on the walls of the nanotubes, which prevent their agglomeration and reduce dipolar interactions.

Novel Magnetic Carbon Nanotube-TiO2 Composites for Solar Light Photocatalytic Degradation of Pharmaceuticals in the Presence of Natural Organic Matter

Magnetic carbon nanotube-TiO2 (MCNT-TiO2) composites that rely on the inherent magnetic properties of carbon nanotubes were synthesized and their photocatalytic activity was evaluated for the degradation of carbamazepine and sulfamethoxazole under solar irradiation and environmentally relevant conditions. Compared with a TiO2 reference catalyst, the MCNT-TiO2 composites exhibited a higher photodegradation rate due to the high surface area and extended visible light absorption. The photodegradation rate constants for carbamazepine and sulfamethoxazole in pure water were ˜1.5 and ˜1.2 times greater than those for TiO2, respectively. The catalysts were tested in the presence of natural organic matter and rapid photodegradation rates for carbamazepine and sulfamethoxazole were observed relative to bare TiO2, indicating that MCNT-TiO2 may be suitable for practical applications. Solar and UVC reactivation were used to recover the photocatalytic activity, and UVC irradiation was more efficient and maintained the performance of MCNT-TiO2 for consecutive treatment cycles. MCNT-TiO2 with its unique fast kinetics and high photodegradation activity toward micropollutants exhibits great potential as an alternative method for water and wastewater treatment.

Defect formation in multiwalled carbon nanotubes under low-energy He and Ne ion irradiation.

The mechanical, structural, electronic and magnetic properties of carbon nanotubes can be modified by electron or ion irradiation. In this work we used 25 keV He+ and Ne+ ion irradiation to study the influence of fluence and sample thickness on the irradiation-induced damage of multiwalled carbon nanotubes (MWCNTs). The irradiated areas have been characterised by correlative Raman spectroscopy and TEM imaging. In order to preclude the Raman contribution coming from the amorphous carbon support of typical TEM grids, a new methodology involving Raman inactive Au TEM grids was developed. The experimental results have been compared to SDTRIMSP simulations. Due to the small thickness of the MWCNTs, sputtering has been observed for the top and bottom side of the samples. Depending on thickness and ion species, the sputter yield is significantly higher for the bottom than the top side. For He+ and Ne+ irradiation, damage formation evolves differently, with a change in the trend of the ratio of D to G peak in the Raman spectra being observed for He+ but not for Ne+. This can be attributed to differences in stopping power and sputter behaviour.

Carbon nanotube-based electrochemical sensors for pesticide determination in aqueous solutions: a review

Excellent mechanical, electrical and magnetic properties of carbon nanotubes (CNT) make CNTs a promising material for the development of electrochemical sensors. Pesticides are very important for an increase in crop yields. However, the intensive use of pesticides can lead to the accumulation of their remains, thus creating a severe problem and risk to human and environmental health. Those are the reasons why the monitoring of pesticides in the environment is extremely important. For that purpose, electrochemical sensors based on carbon nanotubes were designed, and their main aim is pesticide monitoring at environmental samples. A review of the recent studies of environmental monitoring of pesticides using electrochemical sensors based on carbon nanotubes is presented.

Green and facile approach for enhancing the inherent magnetic properties of carbon nanotubes for water treatment applications.

Current methods for preparing magnetic composites with carbon nanotubes (MCNT) commonly include extensive use of treatment with strong acids and result in massive losses of carbon nanotubes (CNTs). In this study we explore the potential of taking advantage of the inherent magnetic properties associated with the metal (alloy or oxide) incorporated in CNTs during their production. The as-received CNTs are refined by applying a permanent magnet to a suspension of CNTs to separate the high-magnetic fraction; the low-magnetic fraction is discarded with the solvent. The collected MCNTs were characterized by a suite of 10 diffraction and spectroscopic techniques. A key discovery is that metallic nano-clusters of Fe and/or Ni located in the interior cavities of the nanotubes give MCNTs their ferromagnetic character. After refinement using our method, the MCNTs show saturation magnetizations up to 10 times that of the as-received materials. In addition, we demonstrate the ability of these MCNTs to repeatedly remove atrazine from water in a cycle of dispersion into a water sample, adsorption of the atrazine onto the MCNTs, collection by magnetic attraction and regeneration by ethanol. The resulting MCNTs show high adsorption capacities (> 40 mg-atrazine/g), high magnetic response, and straightforward regeneration. The method presented here is simpler, faster, and substantially reduces chemical waste relative to current techniques and the resulting MCNTs are promising adsorbents for organic/chemical contaminants in environmental waters.

Characterization of Metallic and Semiconducting Single-Walled Carbon Nanotubes Separated by Electromagnet

Due to producing both metallic and semiconducting carbon nanotubes simultaneously during growth procedure, it is probably needed to separate them after synthesize. In this article a novel and efficient method for separating metallic single-walled carbon nanotubes from semiconducting is proposed. This method is based on magnetic properties of carbon nanotubes and takes advantages of an electromagnet in order to apply magnetic field on carbon nanotubes. In this work, carbon nanotubes are utilized in the solid phase. Results are discussed by analyzing field emission scanning electron microscopy images, X-ray diffraction, and Raman spectroscopy diagrams and also by measuring the resistivity of samples.

Nanomagnetism in Ge-Doped Narrow CNTs

By carrying out density functional theory (DFT) calculations, we studied the effects of Gedoping on the geometrical, electronic, and magnetic properties of carbon nanotubes (CNTs). Three different doping configurations were considered. All of these configurations were stable upon relaxation. It was found that the formation energies of Ge-doped zigzag nanotubes increased with increasing tube diameters, indicating that the doping of Ge into narrower CNTs was more energetically favorable. In the presence of impurity, the electronic properties of small gap semiconducting nanotubes could be changed and the band gap be removed, but the metallic (5, 5) nanotube remained metallic after doping. Spontaneous magnetization was found to be induced in doping Ge nanotubes. The occurrence of ferromagnetism in the absence of transition-metal atoms arose mainly from the Ge-p states and was partially due to C p-orbitals. The magnetic moments of Ge atoms vary with the radius and chirality of nanotubes and their adsorbing sites.

Control of Magnetic Properties of Carbon Nanotubes Filled with Iron

Carbon nanotubes (CNTs) filled with iron nanowires show high coercivity owing to their shape anisotropy originating from the high-aspect-ratio shapes of the iron nanowires. In this study, CNTs filled with iron were prepared by the thermal chemical vapor deposition (T-CVD) method using ferrocene as a precursor, and the magnetic properties of the synthesized CNTs were examined in detail. It was found that the CVD temperature and the amount of the ferrocene introduced into the CVD reactor influence the amount of CNT growth and the magnetic properties. The high coercivity of approximately 1.6 kOe or higher was obtained under certain CVD conditions. The selected-area electron diffraction analysis showed that the magnetic properties of the CNTs filled with iron are determined by the crystal structure (α-Fe or Fe3C) of the iron nanowires, which can be controlled by the amount of the ferrocene supplied during CVD.

Controlling the magnetic response of carbon nanotubes filled with iron-containing material

Magnetic nanoparticles and/or nanowires are being encapsulated in carbon nanotubes (CNTs) as an alternative to introduce a magnetic response to CNTs. This work proposes a novel route to control the magnetic response of CNTs filled with iron-containing nanomaterial through the synthesis process and heat treatment. CNTs were synthesized through chemical vapor deposition from ferrocene at 750°C. They were characterized by Raman spectroscopy and microscopy. In addition, the CNTs were heat treated after the synthesis; CNTs were heated at 1000°C for 10min in an inert atmosphere. The magnetic properties of CNTs as grown and after heat treatment were evaluated using the hysteresis loop and Mössbauer spectroscopy. Results show that there is a correlation between the manufacturing process – considering synthesis parameters and heat treatment – and the composition of iron-containing phases in the CNTs. By varying the temperature and dwell time of synthesis, the composition of the phases encapsulated by CNTs will be different. Heat treatment performed on the CNTs after the synthesis, also resulted in significant modification of the final phases trapped by the nanotubes. These methods enabled the control of which phases remained encapsulated by the nanotubes. This study shows it is possible to control the final magnetic properties, e.g. coercivity, of CNTs filled with magnetic material so as to synthesize the most appropriate magnetic nanomaterial for a specific application.

Synthesis, characterization and magnetic properties of carbon nanotubes decorated with magnetic MIIFe2O4 nanoparticles

In this study, a simple, efficient and reproducible microemulsion method was applied for the successful decoration of carbon nanotubes (CNTs) with magnetic MIIFe2O4 (M=Co, Ni, Cu, Zn) nanoparticles. The structure, composition and morphology of the prepared nanocomposite materials were characterized using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The magnetic properties were investigated by the vibrating sample magnetometer (VSM). The SEM results illustrated that large quantity of MIIFe2O4 nanoparticles were uniformly decorated around the circumference of CNTs and the sizes of the nanoparticles ranged from 15 to 20nm. Magnetic hysteresis loop measurements revealed that all the MIIFe2O4/CNTs nanocomposites displayed ferromagnetic behavior at 300K and can be manipulated using an external magnetic field. The CoFe2O4/CNTs nanocomposite showed maximum value of saturation magnetization which was 37.47emug−1. The as prepared MIIFe2O4/CNTs nanocomposites have many potential application in magnetically guided targeted drug delivery, clinical diagnosis, electrochemical biosensing, magnetic data storage and magnetic resonance imaging.

Vibration response of double-walled carbon nanotubes subjected to an externally applied longitudinal magnetic field: A nonlocal elasticity approach

The magnetic properties of carbon nanotubes and their mechanical behaviour in a magnetic field have attracted considerable attention among the scientific and engineering communities. This paper reports an analytical approach to study the effect of a longitudinal magnetic field on the transverse vibration of a magnetically sensitive double-walled carbon nanotube (DWCNT). The study is based on nonlocal elasticity theory. Equivalent analytical nonlocal double-beam theory is utilised. Governing equations for nonlocal transverse vibration of the DWCNT under a longitudinal magnetic field are derived considering the Lorentz magnetic force obtained from Maxwell's relation. Numerical results from the model show that the longitudinal magnetic field increases the natural frequencies of the DWCNT. Both synchronous and asynchronous vibration phases of the tubes are studied in detail. Synchronous vibration phases of DWCNT are more affected by nonlocal effects than asynchronous vibration phases. The effects of a longitudinal magnetic field on higher natural frequencies are also presented. Vibration response of DWCNT with outer-wall stationary and single-walled carbon nanotube under the effect of longitudinal magnetic field are also discussed in the paper.

Magnetic properties of carbon nanotubes filled with ferromagnetic metals

Carbon nanotubes (CNTs) encapsulating Fe nanowires were prepared by the chemical vapor deposition (CVD) method using ferrocene as a precursor. The influence of the addition of Pt to an Fe catalyst, which is required for growing CNTs by CVD, on the magnetic properties of the resulting CNTs was examined from the viewpoint of enhancing coercivity. Our results showed that the addition of a Pt layer on the Fe catalyst deposited on a substrate increased the coercivity of the Fe-filled CNT. This increase is due to changes in the easy magnetization axis of the Fe nanowires in the CNTs. This result indicates that the magnetic properties of the Fe-filled CNTs can be tuned by the controlling the growth conditions, which is suitable for applications in areas such as magnetic recording media and medicine.

Metal-doped carbon nanotubes interacting with vitamin C

In this paper, the structural, electronic and magnetic properties of carbon nanotubes doped with Al, Fe, Mn and Ti atoms interacting with vitamin C molecules are studied through first principles simulations based on the density functional theory. The charge transfers are obtained from the vitamins into the tubes for adsorption and substitutional doping cases. The highest binding energies of vitamin C molecules are calculated for the Al substitutional and Ti adsorbed cases, with values of about 1.20 and 3.26 eV, respectively. The results demonstrated that, depending on doping, the spin polarizations and the conductance characters of the systems can change, which could be relevant to improve the molecule adsorption on carbon nanostructures.

Calculation of the chirality-dependent orbital magnetic anisotropy in doped semiconducting single-walled carbon nanotubes

We calculate the orbital magnetic anisotropy (Δ χ) of semiconducting single-walled carbon nanotubes at different carrier densities using a nearest-neighbor tight-binding model. Kataura plots of Δ χ exhibit 2 n + m family groupings and chiral index dependence at all carrier densities which are consistent with the trigonal warping effect. The diameter dependence of Δ χ varies strongly with carrier density. We fit our data with a symmetry-restricted model to obtain approximate analytic expressions for Δ χ as a function of nanotube chirality and carrier density. Our results illustrate the important role of doping on the magnetic properties of carbon nanotubes. Experimental studies of Δ χ should take these effects into account for accurate interpretation of their results.

Effect of sulfur on enhancing nitrogen-doping and magnetic properties of carbon nanotubes

Sulfur (S) is introduced as an additive in the growth atmosphere of carbon nanotubes (CNTs) in the range of 940-1020°C. CNT products with distorted sidewalls can be obtained by S-assisted growth. Moreover, many fascinating CNT structures can also be found in samples grown with S addition, such as bamboo-like CNTs, twisted CNTs, arborization-like CNTs, and bead-like CNTs. Compared with CNTs grown without S, more nitrogen-doping content is achieved in CNTs with S addition, which is beneficial for the properties and applications of nitrogen-doped CNTs. In addition, S can also enhance the encapsulation of ferromagnetic materials and thus improve the soft magnetic properties of CNTs, which is favorable to the applications of CNTs in the electromagnetic wave-absorbing and magnetic data storage areas.

Magnetic properties of carbon nanotubes with and without catalyst

In this paper we report on the magnetic properties of single- and multiwalled carbon nanotubes synthesized using different chemical vapour deposition methods and with variety of catalyst materials (ferromagnetic Fe, FeCo and diamagnetic Re). Different methods yield carbon nanotubes with different morphologies and different quantity of residual catalyst material. Catalyst particles are usually encapsulated in the nanotubes and influence the magnetic respond of the samples. Varying ferromagnetic properties depending on the shape, size and type of catalyst are discussed in detail. The data are compared with M(H) characteristics of carbon nanotubes without catalysts and with nonmagnetic rhenium, as a reference.

Magnetic Properties of Carbon Nanotubes with Low Content of Fe

Films of oriented carbon nanotubes containing different concentrations of ferrocene (0.5%, 1%, 1.5%, 2%, 2.5% and 5%) have been synthesized by CVD method and studied by means of SQUID and force microscopy. Strong dependence of magnetization process on nanotubes parameters is observed. Magnetic anisotropy of low-doped nanotubes is shown to have an easy magnetic axis perpendicular to the aligned nanotubes.

The influence of electron irradiation on the magnetic properties of carbon nanotubes filled with Fe-phases composite

The arrays of multi-wall carbon nanotubes (CNTs) filled with Fe-containing nanocomposite have been studied from the point of view of their magnetic properties stability to electron irradiation. CNTs with different content of magnetic component were synthesized by CVD method using ferrocene/xylene mixture of varied proportion. The structure, composition and magnetic properties of CNTs irradiated with a dose of 1015 cm-2 were investigated by TEM, X-ray analysis and ponderomotive method, correspondingly. It was revealed that the morphology of the magnetic particles inside CNTs were changed what, along with radiation defects, lead the deterioration the magnetic properties of CNTs.

Phase states and magnetic properties of iron nanoparticles in carbon nanotube channels

The structure, phase composition, and magnetic properties of carbon nanotubes filled with iron nanoparticles and obtained by thermolysis of a mixture of ferrocene and C60 fullerene or ferrocene and orthoxylene at a temperature of 800°C are investigated. Electron microscopy, X-ray diffraction, and Mossbauer spectroscopy data lead to the conclusion that carbon nanotubes are multilayer systems partially filled with iron nanoparticles and/or nanorods. Metallic inclusions in nanotube channels form α-Fe, γ-Fe, and Fe3C phases. The concentration of each phase in the samples is determined. It is shown that 10–20-nm iron clusters in nanotubes exhibit magnetic properties typical of bulk phases of iron. High elasticity of carbon nanotube walls facilitates stabilization of the high-temperature γ-Fe phase; the relative concentration of this phase in a sample can be increased by lowering the concentration of ferrocene in the initial reaction mixture.

Edge States and Magnetism in Carbon Nanotubes with Line Defects

We apply first-principles calculations to investigate the interplay between electronic and magnetic properties of carbon nanotubes with line defects. We consider three types of defects: lines of C--O--C epoxy groups, and defects resulting from the substitution of the oxygen atoms by CH2 or C2H4 divalent radicals. We find that the line defects behave as pairs of coupled graphene edge states, and a variety of electronic and magnetic ground states is predicted as a function of defect type, nanotube diameter, and a possibly applied transverse electric field.