Co metal nanoparticles deposition inside or outside multi-walled carbon nanotubes via facile support pretreatment

Abstract

Decoration of one-dimensional multi-walled carbon nanotubes (MWCNTs) with zerodimensional Co nanoparticles leads to hybrid structures with chemical and electromagnetic features that are not available to the individual components. This work addresses the influence of the nature and structure of MWCNTs on the localization of Co nanoparticles. Depending on synthesis conditions, Co can be deposited on the external or in inner surfaces of the nanotubes. Co/MWCNTs hybrids have been characterized by in situ X-ray powder diffraction, highresolution transmission electron microscopy and 59 Co internal field nuclear magnetic resonance. It has been shown that the average diameter (7.2, 9.4 and 18.6 nm), number of walls (5-7, 12-15, 15-20), and functional composition of the MWCNTs have a remarkable effect on the size of Co nanoparticles and their distribution in the structure of MWCNTs. The observed phenomenon has 2 been rationalized in terms of nanotubes surface properties. Parent MWCNTs being hydrophobic and having limited porosity do not stabilize Co nanoparticles and, therefore, they are localized on the outside surface with relatively large average size and broad size distribution. On the other hand, the oxidation of the MWCNTs resulted in the penetration of Co nanoparticles inside of the nanotubes, presumably because of pore opening as well as increased hydrophilicity of the nanotubes.

Trimetallic Mn‐Fe‐Ni Oxide Nanoparticles Supported on Multi‐Walled Carbon Nanotubes as High‐Performance Bifunctional ORR/OER Electrocatalyst in Alkaline Media

“…Oxygen functionalities were introduced by treating the obtained samples in concentrated HNO 3 aqueous solution (68 vol%) for 2 h at 120 °C in a reflux condenser. The material was subsequently washed and dried to obtain oxygen functionalized MWCNTs (MWCNTs‐Ox) with a purity higher than 99%, being catalyst residues encapsulated inside the tube core the main impurities …”

Cobalt catalysts on carbon-based materials for Fischer-Tropsch synthesis: a review

“…However, for CNTox, a significant amount of the functional groups decomposes during catalyst preparation and activation stages, and only a quarter of the initial oxygen remains on the support surface by the time the FTS starts [235]. The functionalization of CNT which is often performed with nitric acid, but also with H2O2, generally result in a narrow Co particle size distribution and a confinement in the inner cavity of the tubes (Figure 32) [63,121,236]. Indeed, Co particles were detected solely outside pristine CNT after an impregnation process [236], because internal channels of pristine CNT were closed, consequently the Co particles could not penetrate inside CNT [236].…”

“…The functionalization of CNT which is often performed with nitric acid, but also with H2O2, generally result in a narrow Co particle size distribution and a confinement in the inner cavity of the tubes (Figure 32) [63,121,236]. Indeed, Co particles were detected solely outside pristine CNT after an impregnation process [236], because internal channels of pristine CNT were closed, consequently the Co particles could not penetrate inside CNT [236]. Chernyak et al [96] compared Co-catalysts supported on untreated and CNTox in terms of Co particles size, and FTS activity and selectivity.…”

Superparamagnetic behaviour of metallic Co nanoparticles according to variable temperature magnetic resonance

“…Co IF NMR and FMR to investigate Co nanoparticles contained inside multi-walled carbon nanotubes (MWCNTs) and establish the application limits of both methods. In our previous works 23,24 , factors which affect the formation of Co nanoparticles in the MWCNTs structure such as CNT dimensions, impregnation solution concentration and postsynthetic acidic treatment, were discussed in detail. Herein, we could thus concentrate on Co/MWCNT samples containing metallic Co nanoparticles localized inside the MWCNT channels.…”

“…Co nanoparticles were deposited inside the MWCNTs by incipient wetness impregnation with an aqueous solution of Co(NO 3 ) 2 ⋅6H 2 O (98%, Sigma-Aldrich) and subsequent reduction under H 2 flow. The procedure for preparing of Co/MWCNT samples was described in detail earlier 23,24 . The resulting sample contained 4.2 wt.% of Co (as determined by X-ray fluorescence analysis).…”