Full Length ArticleCo metal nanoparticles deposition inside or outside multi-walled carbon nanotubes via facile support pretreatment
Graphical abstract
Introduction
The decoration of multi-walled carbon nanotubes (MWCNTs) by cobalt nanoparticles expands the range of their functional properties by providing them with new magnetic, catalytic, electronic and electro-magnetic characteristics. MWCNTs filled with magnetic Co-containing nanoparticles have been proved to be useful for multiple innovations in nanotechnology [1], [2], [3], Li/air batteries [4], [5], [6], [7], [8], magnetic-storage devices [9], magnetic composites for drug delivery [10], [11], catalysts for different processes [12], [13], [14], [15], [16], [17], [18], as well as absorption and microwave irradiation shielding material [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30]. It is generally accepted that the magnetic properties of nanoparticles are determined by many factors, such as chemical composition [20], [31], [32], [33], [34], [35], crystallinity [36], [37], size [37], [38], [39], [40], [41] and shape [35], [42], [43], [44], [45]. The possible interaction of the nanoparticles with the surrounding matrix and neighboring nanoparticles [46], [47], [48], [49], [50] should be also mentioned in the list. Hence, changing the size, shape, composition and structure of nanoparticles, it is possible, within certain limits, to control the magnetic characteristics of the composite materials. Moreover, intimate interphase contacts between the Co nanoparticles and MWCNTs result in additional synergistic effects. It is thus possible to further tune the electrophysical properties by adjusting, on the one hand, the dielectric component via the MWCNTs structure and content and, on the other hand, the magnetic properties by means of Co nanoparticles loading. This multiplicity of possible leverage makes MWCNTs promising building blocks for the formation of new hybrid materials with new electromagnetic properties. However, this requires a good control of the location and distribution of Co nanoparticles in the structure of MWCNTs.
Depending on the MWCNTs structure parameters (the average size of outer and inner diameters, number of layers, surface area, aspect ratio, defectiveness and the functional composition of their surface) as well as the preparation method of Co/MWCNT hybrids, the size, shape and location of the Co nanoparticles can be varied. Presently, it is still a great challenge to uniformly deposit 3d group magnetic nanoparticles onto both the inner and outer surfaces of MWCNTs without altering its hollow tubular structure. A common synthetic route to produce Co/MWCNT hybrids is incipient wetness impregnation with cobalt salt solutions. However, the specific features of the cobalt nanoparticles formed by this method in, or on, MWCNTs remain unclear. It is very important to consider various factors that may influence the formation and distribution of cobalt particles in the structure of MWCNTs. Such factors include (i) processes occurring in the impregnating solution; (ii) surface charge of MWCNTs; (iii) structure and functional composition of MWCNTs. According to the literature data [51], [52], structure, surface area, surface functional composition, defects of outer layers, size distribution, agglomeration state, and purity of the samples have considerable influence on the surface charge and the reactivity of carbon nanotubes. MWCNTs are amphoteric by nature, which means that acid and basic functionalities coexist on their surface and that in an aqueous medium. Consequently, depending on the pH and the nature of the MWCNTs surface functionalities, positive or negative charges may be present. In particular, oxidation of pristine MWCNTs leads to the formation of different oxygen-containing groups in the boundary layers, namely carbonyl, carboxyl, lactone, quinone, ether, and hydroxyl groups, the content and distribution of which depend on the oxidation conditions [53], [54]. The appearance of oxygen containing groups can lead under appropriate conditions to the formation of negative charges on the MWCNTs surface, and consequently to a better adsorption of metal cations and, eventually, to a satisfactory dispersion of nanoparticles in the MWCNT structure [54], [55], [56].
Previously [22], we investigated the effect of varying Co content nanoparticles, distributed in the structure of MWCNT, on their magnetic and electromagnetic properties. The present work addresses the issue of Co dispersion when synthesizing Co/MWCNT hybrid materials. A special attention has been paid to the impact of the structure and surface functionalities of MWCNTs on the mechanism of metallic cobalt nanoparticles fixation as well as on their ultimate location and size distribution. The structure and morphology of pure and Co-containing MWCNTs has been monitored by high-resolution transmission electron microscopy (HRTEM) while the structure of the cobalt metal in the hybrids after the reduction has been essentially investigated by 59Co internal field nuclear magnetic resonance (IF-NMR). This technique provides information about the structure (fcc and hcp stackings) and the average size of Co metal nanoparticles through their magnetically single- and multidomain character. It has been complemented by in situ synchrotron X-ray diffraction (in situ XRD) to provide the evolution of all crystalline phases versus temperatures and monitor the evolution of their average sizes.
Section snippets
Synthesis of MWCNTs and functionalization
MWCNTs were synthesized by ethylene decomposition over bimetallic Fe-Co catalysts at 680 °C. The narrowest MWCNTs (labelled MWCNT-7) with an average outer diameter of 7.2 nm and the smaller number of walls (5–7) considered in this study were formed over the 30 wt% Fe2Co/Al2O3 catalyst; MWCNT with medium outer diameter 9.4 nm and wall number (12–15) over the 40 wt% Fe2Co/Al2O3 catalysts (labelled MWCNT-9); and the larger diameter MWCNT (labelled MWCNT-18) of 18.6 nm with 15–20 walls over the
Effect of the MWCNT structure on the Co particles formation
Multi-walled carbon nanotubes are amphoteric by nature, which means that acidic and basic functionalities coexist on their surface. In an aqueous medium, these functionalities, depending on the pH, provoke a distribution of charges. At pH below the point of zero charge, the balance of charges is positive while for pH above, it is negative. Consequently, electrostatic interaction favors the adsorption of anions in aqueous solutions of pH below the PZC and the one of cations at pH above the PZC.
Discussion
Many processes, such as hydrolysis, dissociation, and complexation, must be taken into consideration to determine the different ionic forms existing in aqueous solutions. Taking into account the relevant hydrolysis and dissociation constants, it can be predicted that 99.997% of the Co in the impregnation solution of Co nitrate (II) at pH 3.95 was in the form of Co2+ (see confirmatory calculations in the supplementary materials). The value of the PZC of the oxidized MWCNTs was always around of
Conclusion
The effect of the MWCNTs nature (diameter and number of walls) as well as their oxidative pretreatment on the Co nanoparticle formation by incipient wetness impregnation followed by reduction has been investigated by in situ XRD, HRTEM and 59Co IF-NMR.
Pristine MWCNTs (7, 9 and 18), hydrophobic and with limited porosity, did not stabilize Co nanoparticle which only formed outside of the MWCNTs with an average particles size of 20 nm and a very wide size distribution as well as poor resistance to
Acknowledgements
The reported study was funded by the Russian Foundation for Basic Research via grant 16-32-60046 mol_a_dk (Mariya A. Kazakova). Olga B. Lapina and Andrey S. Andreev are grateful to the Russian Foundation for Basic Research, which provided the 59Co NMR studies via grant 17-53-150018. A.S. Andreev was also supported in part by a PhD grant from the French Embassy in Moscow and by the Société des Amis de l’ESPCI.
References (91)
- et al.
Three-dimensional nanostructured graphene: synthesis and energy, environmental and biomedical applications
Synth. Met.
(2017) - et al.
NiCo2O4/CNT nanocomposites as bi-functional electrodes for Li ion batteries and supercapacitors
Carbon
(2016) - et al.
Controlling co-support interaction in Co/MWCNTs catalysts and catalytic performance for hydrogen production via NH3 decomposition
Appl. Catal. A
(2013) - et al.
Tuning catalytic performances of cobalt catalysts for clean hydrogen generation via variation of the type of carbon support and catalyst post-treatment temperature
Int. J. Hydrogen Energy
(2014) - et al.
Facile synthesis of nitrogen-doped carbon nanotubes encapsulating nickel cobalt alloys 3D networks for oxygen evolution reaction in an alkaline solution
J. Power Sour.
(2017) - et al.
Electromagnetic and microwave absorbing properties of Co-filled carbon nanotubes
J. Alloys Compd.
(2010) - et al.
Microwave-absorbing properties of Co-filled carbon nanotubes
Mater. Res. Bull.
(2008) - et al.
Microwave absorption and catalytic activity of carbon nanotubes decorated with cobalt nanoparticles
Mater. Lett.
(2012) - et al.
Magnetic and dielectric properties of carbon nanotubes with embedded cobalt nanoparticles
Carbon
(2017) Simultaneous adsorptive desulfurization of diesel fuel over bimetallic nanoparticles loaded on activated carbon
J. Clean. Prod.
(2018)
Preparation and magnetic property of multiwalled carbon nanotubes decorated by Fe3O4 nanoparticles
New Carbon Mater.
Structure and magnetism of Fe–Co alloy nanoparticles
J. Alloys Compd.
Magnetoresponsive conductive colloidal suspensions with magnetized carbon nanotubes
J. Magn. Magn. Mater.
Tuning of single to multi-domain behavior for monodispersed ferromagnetic cobalt nanoparticles
Chem. Phys. Lett.
Influence of crystallite size on the magnetic properties of Fe3O4 nanoparticles
J. Alloys Compd.
Influence of intrinsic parameters on the particle size of magnetic spinel nanoparticles synthesized by wet chemical methods
Particuology
Ab initio calculations of dimensional and adsorbate effects on the workfunction of single-walled carbon nanotube
Diamond Relat. Mater.
Surface charge model of a carbon nanotube: self-consistent field from Thomas-Fermi theory
J. Phys. Chem. Solids
Characterization of functional groups on oxidized multi-wall carbon nanotubes by potentiometric titration
Catal. Today
The role of carbon materials in heterogeneous catalysis
Carbon
The effect of oxygen surface groups of the support on platinum dispersion in Pt/carbon catalysts
J. Catal.
Internal field 59Co NMR study of cobalt-iron nanoparticles during the activation of CoFe2/CaO catalyst for carbon nanotube synthesis
J. Catal.
Oxidation behavior of multiwall carbon nanotubes with different diameters and morphology
Appl. Surf. Sci.
Some aspects of the surface chemistry of carbon blacks and other carbons
Carbon
The control of platinum impregnation by PZC alteration of oxides and carbon
J. Mol. Catal. A: Chem.
Effect of the nature of carbon support on the formation of active sites in Pd/C and Ru/C catalysts for hydrogenation of furfural
Catal. Today
Effect of γ-Al2O3 hydrothermal treatment on the formation and properties of platinum sites in Pt/γ-Al2O3 catalysts
Appl. Catal., A
Purification of single walled carbon nanotubes: the problem with oxidation debris
Chem. Phys. Lett.
Chemical modification of multiwalled carbon nanotubes for sorption of Zn2+ from aqueous solution
Chem. Eng. J.
A study of the electrical properties of carbon nanotube-NiFe2O4 composites: effect of the surface treatment of the carbon nanotubes
Carbon
Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions. V. hydrolysis and hydroxo-complexes of Co2+ at 298.15 K
Hydrometallurgy
Cobalt nanoparticles with preferential hcp structure: a confirmation by X-ray diffraction and NMR
Chem. Phys. Lett.
Effect of Co crystallinity on Co/CNT catalytic activity in CO/CO2 hydrogenation and CO disproportionation
Appl. Surf. Sci.
Effect of support surface treatment on the synthesis, structure, and performance of Co/CNT Fischer-Tropsch catalysts
J. Catal.
Optimal ferromagnetically-coated carbon nanotube tips for ultra-high resolution magnetic force microscopy
Nanotechnology
Magnetic force microscopy of nanostructured Co/Pt multilayer films with perpendicular magnetization
Materials
A magnetic force microscope using CoFe-coated carbon nanotube probes
Nanotechnology
Carbon nanotube/Co3O4 composite for air electrode of lithium-air battery
Nanoscale Res. Lett.
Self-Templated formation of interlaced carbon nanotubes threaded hollow Co3S4 nanoboxes for high-rate and heat-resistant lithium-sulfur batteries
J. Am. Chem. Soc.
In Situ transmission electron microscopy investigation of the electrochemical lithiation-delithiation of individual Co9S8/Co-filled carbon nanotubes
ACS Nano
Hydrogen storage in decorated multiwalled carbon nanotubes by Ca Co, Fe, Ni, and Pd nanoparticles under ambient conditions
J. Phys. Chem. C
Preparation of magnetic carbon nanotubes (Mag-CNTs) for biomedical and biotechnological applications
Int. J. Mol. Sci.
Design of covalently functionalized carbon nanotubes filled with metal oxide nanoparticles for imaging, therapy, and magnetic manipulation
ACS Nano
Pronounced size dependence in structure and morphology of gas-phase produced partially oxidized cobalt nanoparticles under catalytic reaction conditions
ACS Nano
Facile synthesis of Co3O4@CNT with high catalytic activity for co oxidation under moisture-rich conditions
ACS Appl. Mater. Interf.
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