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Vol. 8. Issue 6.
Pages 5893-5898 (November - December 2019)
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Vol. 8. Issue 6.
Pages 5893-5898 (November - December 2019)
Original Article
DOI: 10.1016/j.jmrt.2019.09.062
Open Access
Compounds of carbon nanotubes decorated with silver nanoparticles via in-situ by chemical vapor deposition (CVD)
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Lina Marcela Hoyos-Palacioa, Diana Paola Cuesta Castrob, Isabel Cristina Ortiz-Trujilloa, Luz Elena Botero Palacioa, Beatriz Janeth Galeano Upeguic, Nelson Javier Escobar Morac, Jesus Antonio Carlos Corneliod,
Corresponding author
iqcornelio@gmail.com

Corresponding author.
a Grupo de Investigación Biología de Sistemas, Universidad Pontificia Bolivariana, Medellín, Antioquia, Colombia
b Grupo de Investigación en Salud Pública, Universidad Pontificia Bolivariana, Medellín, Antioquia, Colombia
c Grupo de Investigaciones en Bioingeniería, Universidad Pontificia Bolivariana, Medellín, Antioquia, Colombia
d Tribology and Surfaces Group, National University of Colombia, Medellín, Colombia
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Abstract

The use of carbon nanotubes decorated with metallic particles is having a great impact as a reinforcing nanomaterial in different applications. In this work, multiwalled carbon nanotubes (MWCNTs) were synthesized by chemical vapor deposition and decorated with silver nanoparticles via in-situ. The MWCNTs-Ag were characterized by SEM, TEM, Raman, XRD, and XPS. The results indicated that the silver nanoparticles dispersed homogeneously on the outer surface of the MWCNTs.

Keywords:
Carbon nanotubes
Chemical vapor deposition
Nanoparticles
Silver
Full Text
1Introduction

Carbon nanotubes (CNTs) were first discovered by Iijima [1]. This type of material has received much interest for its use in the fabricating of new classes of materials for its properties such as high aspect ratio, ultra-lightweight, high tensile strength, excellent electrical conductivity, chemical and thermal stability [2,3]. The last outer layer of the CNTs serves as a specific anchoring network for the deposition of metallic nanoparticles. The incorporation of nanoparticles in the tubular structure of the CNT is of great interest because it forms a hybrid nanostructure which exhibits properties from both parent structures [3]. Nanocomposites have attracted much attention to several scientists, due to their novel properties. These were caused by small size, large surface area and quantum-dimension, which can improve their physical and chemical properties [4].

The doping of CNTs with various metal nanoparticles such as Au, pd, Pt, Ag is appealing due to the properties of metallic nanoparticles [5,6]. The decoration/doping of CNTs with Ag nanoparticles has a potential use due to its applications as advanced nanocomposites [6], antibacterial activity [7] and sensor [8,9]. Several authors have reported different methods to obtain these hybrid materials, in which they report the “separate methodology” which means functionalizing CNT and synthesizing nanomaterials individually and assembling them together [9]. The decoration of CNTs with Ag has also been achieved through decomposition thermal [10], chemical reduction [11] and vapor deposition [12] have been employed to decorate CNTs with Ag. However, in most cases the agglomeration of silver nanoparticles has been reported, so this factor is a disadvantage in the uniform decoration of the surface of the CNTs and in the evaluation of its properties. Conventional methods of silver nanoparticles synthesis have mainly relied on the use of synthetic chemicals and heating for a long time. Compared to the ordinary heating method, microwave synthesis as a fast emerging and widely accepted processing technology is in favor of homogeneous heating and easy nucleation of noble metal nanoparticles, however the modification of CNTs often involves the reaction of hazardous chemical agents, difficult reaction conditions and complex reaction procedures. For example, the use of ethylene glycol as reducing agent not only increases the post-treatment process but also has a harmful effect on the special properties of the new metal nanoparticles [13].

On the other hand, different physical methods such as plasma irradiation and gamma irradiation for surface modification of CNTs have also been reported and it has been shown that CNTs can be functionalized by plasma irradiation to introduce various chemical agents into CNTs [14]. One of the possible reasons is that functional groups such as carboxyl groups and amine groups can coordinate with heavy metal ions. The surface modification of carbon nanomaterials such as nanotubes with biomolecules via Mussel-inspired chemistry has also been recently reported [15]. Previous studies have reported that chemistry inspired by mussels can be a promising method for fabricating high effective decorated nanocomposites [14].

In this work an alternative to obtaining carbon nanotubes (MWCNTs) decorated with silver nanoparticles of in-situ form is described, where the dispersion and size of the nanoparticles are homogeneous. The CNTs were grown in a chemical vapor deposition (CVD) equipment. The carbon nanotubes were doped with a silver precursor during the synthesis process.

2Materials and methods2.1CNTs synthesis

CNTs were synthesized by chemical vapor deposition. A furnace with high precision temperature control (1100 °C ± 1 °C accuracy) and equipped with a quartz tube was used to grow CNTs at 700 °C. Acetylene was used as carbon source. Nickel was employed as catalyst to produce MWCNTs. The gas mixture was composed of 80 cc/min nitrogen, 20 cc/min acetylene and 15 cc/min hydrogen. The processing sequence included reduction time of 20 min, acetylene time of 30 min and cooling time of 60 min (Fig. 1).

Fig. 1.

Schematic diagram of a Chemical Vapor Deposition unit used for growing of CNTs.

(0.12MB).

In this method, the metal catalyst (nickel) is deposited on a quartz tube. The CVD reaction furnace is heated to a temperature of 700 °C where nano-sized catalytic metal particles are found. Typically, the formation of carbon nanotubes facilitates the motor-assisted decomposition of hydrocarbons, usually carbon monoxide or methane gases, under conditions of high temperature that cause the growth of MWCNTs upon cooling. The doping/decoration process of the carbon nanotubes is carried out once the automated system activates the carbon source (acetylene). The doping system consists of a nebulizer that vaporizes the silver source (silver nitrate solution at 30% wt-Merck ACS, ISO, Reag. Ph Eur) allowing the flow of nitrogen to pass through. This process is achieved by pulsating vaporizations of the silver nitrate solution every 30 s during a period of 20 min, the required time for CNTs to grow.

2.2Morphological analysis

Carbon nanotubes (CNTs) were characterized by SEM-EDX and TEM. The scanning electron microscope (SEM) used was JEOL JSM-6490 LV and the Transmission electron microscopy (TEM) Tecnai F20 Super Twin TMP from FEI to verify the structural characteristics of the CNTs.

2.3Structural analysis

X-ray diffraction patterns (XRD) were obtained through the XPert PANalytical Empyrean Serie II-Alpha1 diffractometer. Rama Spectroscopy using a Horman Jobin Yvon confocal Raman spectrometer, Labram HR high resolution model with a focal length of 800 mm, Laser spot size from 1 to 300 mm, CCD detector with a resolution of 1024 × 256 pixels, optimized spectral range of 400–1100 nm and diffraction gratings of 1800 and 600 lines/m. The surface chemical information was determined by X-ray photoelectron spectroscopy (XPS, SPECS) with a PHOIBOS 150 1D-DLD analyzer and monochromatic Al Kα radiation (1486.7 eV) operated at 100 W. The XPS spectra were recorded with a pass energy of 90 eV and a step size of 0.01 eV. A charge compensation was achieved by a low-energy electron flood gun (3 eV cathode voltage and 20 mA emission current).

3Results and discussion3.1Morphology and structural analysis of MWCNTs-Ag

Fig. 2 shows SEM images of CNTs grown with a Ni catalyst. A mixture of carbon nanotubes and catalysts residues can be observed in the image. Fig. 2b shows the EDX analysis which determines the sample composition. The presence of carbon and silver can be observed mainly, which suggests the presence of silver nanoparticles in the structure of the CNTs. Finally, the presence of nickel and silicon from the catalyst is also observed.

Fig. 2.

Characterization of Carbon Nanotubes a) SEM images of CNTs (arrows show the catalyst residues) b) EDX spectra of CNTs.

(0.29MB).

Structural analysis by TEM is a necessary technique to characterize the morphology and microstructure of the CNTs-Ag nanocomposite. The TEM image (Fig. 3) indicates that the obtained CNTs are of the multi-all nature (MWCNTs) since the central opening is clearly observed. The CNTs exhibit a high degree of crystallinity considering that the carbon layers are highly aligned. The diameter of the silver nanoparticles is more homogeneous with respect to the nickel particles. Through this technique the decoration of the carbon nanotubes with silver, during the growing phase, via in-situ was successfully carried out (See Fig. 3a). In Fig. 3b the spherical silver nanoparticles with an average diameter of about 3 nm can be clearly seen. In addition, silver nanoparticles were distributed homogeneously on the surface of the MWCNTs without agglomeration. It is observed that the silver nanoparticles have homogeneously adhered to the outer surface of the MWCNTs, which confirms that the process of decorating via in-situ in the CVD method may be a viable option for doping CNTs with metal nanoparticles. Finally, the EDX analysis confirmed that the nanoparticles present in the CNTs are silver nanoparticles distributed throughout the structure (Fig. 3c).

Fig. 3.

TEM images of MWCNTs decorated with Ag nanoparticles.

(0.88MB).
3.2XRD

The structure and chemical composition of the MWCNTs-Ag nanocomposite was verified by XRD as shown in Fig. 4. The graphitized nature of the MWCNT is confirmed by the crystalline planes C (002), C (100) at the 2θ values of 26° and 44°, corresponding to an interplanar space of 3.41 Å and 2.05 Å, respectively. Reflection peaks at 2θ values 38°, 45°, 64° and 77° which are identified as (111), (200), (220) and (311) correspond to FCC Ag nanoparticles [3,16,17]. Finally, other (unlabeled) peaks are present in the spectrum, these peaks can be associated to the presence of catalytic particles, nickel and silicon.

Fig. 4.

XRD pattern of carbon nanotubes decorated with silver nanoparticles.

(0.11MB).
3.3Raman spectroscopy

Fig. 5 shows the Raman spectrum of the CNTs. The spectrum shows the three characteristic peaks related to the formation of CNTs, the D band at ˜1340 cm−1, which corresponds to the phonon mode induced by disorder (A1g), the G band at ˜1580 cm−1 assigned to the phonon mode allowed by Raman (E2g) and the band G´ at ˜2660 cm−1 assigned to the first overtone of mode D [18,19].

Fig. 5.

Raman spectrum of MWCNTs and MWCNTs-Ag.

(0.1MB).

It is evident that the deposition of silver in the MWCNTs changed the intensity of the bands at 2660 cm−1, 1580 cm−1 and 1340 cm−1, resulting in lower wavenumbers. These changes involve a charge transfer process and chemical interaction between the silver nanoparticles and the surface of the MWCNTs after the deposition process [16,20,21]. A smaller ID/IG band ratio indicates a greater graphitic crystallinity of the CNTs. The MWCNTs have an ID/IG ratio of 0.78. The doping of CNTs with Ag nanoparticles showed a ratio of 0.84 because the Ag nanoparticles structural defects in the carbon wall. However, the Raman spectrum indicate a good crystallinity with a change in maximum intensities after decorating with Ag [21,22].

3.4XPS analysis

The XPS technique was used to characterize the chemical composition of the composite and confirm the presence of silver nanoparticles in the carbon nanotubes (Fig. 6). Fig. 6a shows the XPS spectrum of the MWCNTs-Ag compound in a wide scan. The binding energies of 368.2 and 373.3 eV correspond to the peaks of Ag 3d5/2 and Ag 3d3/2[23,24], respectively, indicating the presence of silver nanoparticles in the composite. The C 1s peak was also detected at a binding energy of 284.6 eV [25,26], which was corresponding to the C component of MWCNTs.

Fig. 6.

XPS spectrum of MWCNTs-Ag: a) wide scan spectrum, b) Ag 3d, c) C1s, d) N1s.

(0.31MB).
4Conclusion

In summary, it was possible to obtain CNTs decorated with silver nanoparticles. The results obtained by TEM, XRD and Raman confirmed that the silver nanoparticles were deposited in the superficial layers of the CNTs. Obtaining CNTs-Ag compounds decorated via In-Situ in the CVD process reduces production costs. With this method, it is possible to obtain homogeneous silver nanoparticles without agglomerations, which would avoid additional processes to achieve the decoration of the CNTs. Given that, CNTs decorated with metallic particles are having a great impact on the development of new materials, this process could simplify the methods of obtaining doped CNTs. Finally, the obtained CNT-Ag could have potential uses in applications such as advanced nanocomposites, antibacterial and sensors.

Statement of funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by UPB-INNOVA 2015, filed with CIDI 438B-08/15-65. To Colciencias for financing through the call Science, Technology and Innovation in Health 711–2015 [project number 121071149742].

Declaration of conflicting interests

The Authors declares that there is no conflict of interest.

Acknowledgements

The authors are grateful to Universidad Pontificia Bolivariana and the Consejo Nacional de Ciencia y Tecnología - CONACYT - Mexico [grant number 711190].

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Copyright © 2019. The Authors
Journal of Materials Research and Technology

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