Abstract
We present the study of pristine and calcined f-MWCNTs functionalized by nitrogen-containing functional groups. We focus on the structural and microstructural modification tuned by the previous annealing. However, our primary goal was to analyze the electronic structure and magnetic properties in relation to the structural properties using a multi-technique approach. The studies carried out by X-ray diffraction, XPS, and 57Fe Mössbauer spectrometry revealed the presence of γ-Fe nanoparticles, Fe3C, and α-FeOOH as catalyst residues. XPS analysis based on the deconvolution of core level lines confirmed the presence of various nitrogen-based functional groups due to the purification and functionalization process of the nanotubes. The annealing procedure leads to a structural modification mainly associated with removing surface impurities as purification residues. Magnetic studies confirmed a significant contribution of Fe3C as evidenced by a Curie temperature estimated at TC = 452 ± 15 K. A slight change in magnetic properties upon annealing was revealed. The detailed studies performed on nanotubes are extremely important for the further synthesis of composite materials based on f-MWCNTs.
Highlights
Carbon nanotubes (CNTs) were intensively studied immediately after their discovery by Suimo Ijima in 1990 [1]
In view of the ongoing discussion on the form of Fe as a catalyst precursor in MWCNTs, in the following paper, we have focused on a comprehensive study of pristine and calcined f-MWCNTs functionalized with COONH4 groups
Published results point out the presence of iron carbides cementite during the synthesis of CNTs [35]
Summary
Carbon nanotubes (CNTs) were intensively studied immediately after their discovery by Suimo Ijima in 1990 [1]. CNTs can be considered as a hexagonal array of carbon atoms wound in a hollow cylinder in two ways: single-walled nanotubes (SWCNTs) and multi-walled (MWCNTs) nanotubes [1]. These materials are characterized in particular by (i) outstanding mechanical and structural properties; (ii) good surface to area ratio; (iii) unique electrical conductivity; (iv) chemical and thermal stability, making them attractive components for nanohybrids [4,5,6,7,8,9,10,11,12,13,14,15]. Schaper et al [31] reported in situ electron microscopy studies demonstrating the role of cementite as an intermediate in the catalytic formation of nanotubes by promoting the successive segregation of new well-ordered graphene layers on its surface
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