Fe-filled Multiwalled Carbon Nanotubes Research Articles

Carboxylated, Fe-filled multiwalled carbon nanotubes as versatile catalysts for O2 reduction and H2 evolution reactions at physiological pH.

The development of new electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at physiological pH is critical for several fields, including fuel cells and biological applications. Herein, the assembly of an electrode based on carboxyl-functionalised hydrophilic multiwalled carbon nanotubes (MWCNTs) filled with Fe phases and their excellent performance as electrocatalysts for ORR and HER at physiological pH are reported. The encapsulated Fe dramatically enhances the catalytic activity, and the graphitic shells play a double role of efficiently mediating the electron transfer to O2 and H2 O reactants and providing a cocoon that prevents uncontrolled Fe oxidation or leaching.

X-ray diffraction study of the evolution of Fe-filled multiwalled carbon nanotubes under pressure

We present in situ high pressure X-ray diffraction experiments on multi-walled carbon nanotubes (MWNTs) filled with iron-based nanowires. In addition to our diffraction results, we provide a detailed characterization of our samples in terms of nanotube length, iron contents, nanotube number of walls and radial dimension. Both carbon nanotubes and encapsulated iron-based nanowires were found to be stable under high pressure conditions, in contrast with previous experiments performed on Fe-filled MWNTs where structural transitions of nanotubes and Fe3C nanowires were recorded around 9 GPa. We point out the importance of providing a complete structural characterization of the studied material and we propose an explanation for the contradictory results found in the literature based on different structural characteristics of the samples and on recent results on the non-hydrostaticity of some pressure transmitting media.

Sharp Carbon‐Nanotube Tips and Carbon‐Nanotube Soldering Irons

The nano-electron beam assisted fabrication of atomically sharp iron-based tips (see figure) and the creation of a nano-soldering iron for nano-interconnects using Fe-filled multiwalled carbon nanotubes (MWCNTs) is reported. The technique allows carving of a MWCNT and a control of the flow of the encapsulated metal outward by regulating the e-beam exposure time and spot size.

Synthesis of different magnetic carbon nanostructures by the pyrolysis of ferrocene at different sublimation temperatures

Various magnetic nanostructures such as Fe nanoparticles (Fe-NPs) adhering to single-walled carbon nanotubes, carbon-encapsulated Fe-NPs, Fe-NP decorated multi-walled carbon nanotubes (MWCNTs), and Fe-filled MWCNTs have been synthesized by the pyrolysis of pure ferrocene. It is found that the formation of the nanostructures can be selectively controlled by simply adjusting the sublimation temperature of ferrocene, while keeping all other experimental parameters unchanged. Magnetic characterization reveals that these nanostructures have an enhanced coercivity, higher than that of bulk Fe at room temperature. Based on the experimental results, the formation mechanism of the nanostructures is discussed in detail.

Synthesis and characteristics of Fe-filled multi-walled carbon nanotubes for biomedical application

Multifunctional nanocontainers can be produced based on partially filled Fe-multi walled carbon nanotubes (MWCNTs). Using thermal decomposition ferrocene filled nanotubes can be grown aligned on substrates. The encapsulated metal nanowires have diameters of 5-30 nm and a length up to few microns. They consist of single-crystalline of α and γ-Fe- phases. Using heat treatment, it is possible to transform γ-Fe into α-Fe. With the aid of wet chemical methods the nanotubes can be opened and additionally filled with an agent, e.g., therapeutic agents (carboplatin) or other metals (copper). Initial studies do not show a high toxicity over a period of 440 days. These materials can be used for drug delivery and hyperthermia. The specific absorption rate (SAR) is greater than 100W/(g-α-Fe) in a magnetic field of 18kA/m (f = 250kHz).

Structure and magnetic properties of iron nanowires encased in multiwalled carbon nanotubes

By using X-ray diffraction, transmission electron microscopy, ferromagnetic and electron paramagnetic resonances, Fe-filled multiwalled carbon nanotubes were studied. The iron within the nanotubes was found to be in three phases: the austenite γ-Fe is located at the top of the nanotubes, while the ferrite α-Fe and cementite θ-Fe 3C are found close to the substrate. The morphology of the α + θ mixture suggests that the eutectoid reaction γ → α + θ occurs. Two ferromagnetic signals were observed and identified as those belonging to ferrite and cementite. Ferromagnetic signals revealed a surprising temperature dependence: with decreasing temperature, their integral intensity decreases nearly linearly, and the signals disappear at temperatures below 70 K. Possible reasons for this behaviour are discussed. Two paramagnetic signals appear at low temperatures. Based on their temperature behaviour and on the values of the g-factors, the first signal is related to localized spin moments and the second one to free electrons.

Phase composition and magnetic characteristics of Fe-filled multi-walled carbon nanotubes

The work addresses the correlation between the phase composition and the magnetic characteristics of aligned Fe-filled multi-walled carbon nanotubes (Fe-MWCNTs) grown by pyrolysis of ferrocene on oxidized Si substrates. In a combinatorial approach we exploited the extremely high gradients of the technological parameters temperature and ferrocene flow across the surface of a substrate positioned close to the reactor wall to obtain a large variation in the structural and magnetic properties of the Fe-MWCNTs. In this way, we established several clear correlations between the Fe-filling phase composition and the overall magnetic characteristics of the aligned Fe-MWCNTs. The α-Fe rich samples, which possess a more ordered graphitic sheet structure, a higher degree of preferred crystalline orientation of the metal filling and much larger metal crystallites in comparison with the carbide-rich samples, show a much stronger magnetic anisotropy with easy axis perpendicular to the substrate and unusually high values of the coercive field H c and the saturation field H s. The changes in the measured saturation magnetisation M s and the H c values correlate well with the variation of the α-Fe content and the filling crystallinity. A special annealing treatment of the samples causes a distinct increase of the α-Fe quantity and an increase of the measured average grain size. The respective magnetic characteristics show a significant increase of the overall magnetic moment and decrease of the coercive field. The correlation between the structural and the magnetic characteristics of the annealed samples matches quite well the respective correlations in the case of as-deposited samples.

Ferromagnetic filled carbon nanotubes and nanoparticles: synthesis and lipid-mediated delivery into human tumor cells

We describe the synthesis and the properties of Fe-filled multi-walled carbon nanotubes (MWNTs) and nanoparticles (NP) produced by chemical vapor deposition (CVD). We have employed ferrocene as a starting substance and oxidized Si-wafers as substrates. The magnetic properties and the interaction of the material with bladder cancer cells were determined. After the addition of NP suspensions to cultured cells, no adhesion of the nanoparticles/nanotubes (NT/NP) to the cell membrane and also no cellular uptake were observed. However, the preincubation of the (NT/NP) suspension with cationic lipid caused an efficient delivery of the lipid-nanostructure complexes into the cytoplasm within 2h after adding to the culture medium.

Mössbauer transmission and back scattered conversion electron study of Fe nanowires encapsulated in multiwalled carbon nanotubes

Fe 57 transmission Mössbauer spectroscopy (TMS) and back scattered conversion electron Mössbauer spectroscopy (CEMS) measurements were carried out on Fe-filled multiwalled carbon nanotubes (Fe-MWCNTs) grown by chemical vapor deposition with ferrocene as precursor. Samples of Fe-MWCNTs material deposited on the inner wall of the quartz tube reactor and samples of aligned Fe-MWCNTs grown perpendicularly to the oxidized Si substrate were characterised by the TMS method. The data show that Fe phases encapsulated within the carbon nanotubes comprise α-Fe, γ-Fe, and Fe3C in different percentage ratio depending on the sample preparation. These results are in a good accordance with the previously measured magnetic characteristics and with the structural data found by x-ray diffraction as well by selected area electron diffraction methods and allow a new complementary characterization of the Fe(Fe-alloy)-MWCNT systems. The CEMS method applied for the characterization of metal containing MWCNTs reveals that close to the top surface of the aligned Fe-MWCNTs samples only the γ-Fe phase is found. This technique shows an additional potential for further investigation of the spatial distribution of the crystalline phases in the depth of aligned Fe-MWCNT samples.

Magnetic properties of aligned Fe-filled carbon nanotubes

We report on the magnetic properties of Fe-filled multiwalled carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD) on Si substrates with ferrocene as precursor. The MWNTs are aligned perpendicularly to the substrate plane. X-ray diffraction analyses indicate the presence of both bcc and fcc iron with a relatively strong texture. Magnetometry measurements show a pronounced magnetic anisotropy with the easy axis perpendicular to the substrate plane and parallel to the axis of the aligned MWNTs, respectively. The low-temperature behavior suggests a negligible coupling between the two iron phases. We accessed the magnetic properties of individual Fe-filled MWNTs by electron holography using a transmission electron microscope (TEM).

Synthesis and characterization of aligned Fe-filled carbon nanotubes on silicon substrates

We describe the preparation and the properties of Fe-filled multi-walled carbon nanotubes on Co-coated oxidized silicon substrates. The material was grown by pyrolysis of ferrocene, using a chemical vapor deposition process. Scanning and transmission electron microscopy studies indicate that the material consists of filled and aligned MWNTs. They have outer diameters of 40–100 nm and diameters of the metal core of 20–40 nm. Energy dispersive X-ray analysis of individual tubes reveals that their filling consists of pure Fe. Alternating gradient magnetometry investigations demonstrate the ferromagnetic behavior of the filled tubes. We observe unique magnetic properties differing from those of bulk Fe.