Magnetic properties of iron particles embedded in multiwall carbon nanotubes

Oxygenated Surface of Carbon Nanotube Sponges: Electroactivity and Magnetic Studies

We report the synthesis of nitrogen-doped carbon nanotube sponges (N-CNSs) by pyrolysis of solutions of benzylamine, ferrocene, thiophene, and isopropanol-based mixture at 1020 °C for 4 h using an aerosol-assisted chemical vapor deposition system. The precursors were transported through a quartz tube using a dynamic flow of H₂/Ar. We characterized the N-CNSs by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. We found that isopropanol, isopropanol-ethanol, and isopropanol-acetone as precursors promote the formation of complex-entangled carbon fibers making knots and junctions. The N-CNSs displayed an outstanding oxygen concentration reaching a value of 9.2% for those synthesized with only isopropanol. We identified oxygen and nitrogen functional groups; in particular, the carbon fibers produced using only isopropanol exhibited a high concentration of ether groups (C-O bonds). This fact suggests the presence of phenols, carboxyl, methoxy, ethoxy, epoxy, and more complex functional groups. Usually, the functionalization of graphitic materials is carried out through aggressive acid treatments; here, we offer an alternative route to produce a superoxygenated surface. The understanding of the chemical surface of these novel materials represents a huge challenge and offers an opportunity to study complex oxygen functional groups different from the conventional quinone, carboxyl, phenols, carbonyl, methoxy, ethoxy, among others. The cyclic voltammetry measurements confirmed the importance of oxygen in N-CNSs, showing that with high oxygen concentration, the highest anodic and cathodic currents are displayed. N-CNSs displayed ferromagnetic behavior with an outstanding saturation magnetization. We envisage that our sponges are promising for anodes in lithium-ion batteries and magnetic sensor devices.

DETERMINATION OF GROWTH DIRECTION OF CARBON NANOTUBES FROM THE SHAPE OF THE CATALYST PARTICLE

We present a mechanism that can explain the growth direction of the carbon nanotubes (CNT), based on the observation of the catalyst particle's shape, that is present along with the CNT. We claim the mechanism holds good for the tip growth as well as the base growth model for CNTs formation. The morphological studies performed using simple geometry show that for encapsulated catalyst, (i) the contact angle is less along the forward direction than that of backward direction, (ii) the growth direction of CNT is along the flow direction of the catalyst particle in the fluid state, (iii) the distance between the centre of two imaginary spheres (circles in 2D) drawn at the front and back of the catalyst particle, qualitatively predicts the difference in growth rate of the CNT and flow of the catalyst particle inside the CNT. In order to support the above claims, a generalized model is proposed, irrespective of the position of the catalyst.

Large-Scale Synthesis of Carbon Nanomaterials by Catalytic Chemical Vapor Deposition: A Review of the Effects of Synthesis Parameters and Magnetic Properties

The large-scale production of carbon nanomaterials by catalytic chemical vapor deposition is reviewed in context with their microwave absorbing ability. Factors that influence the growth as well as the magnetic properties of the carbon nanomaterials are discussed.