A catalyst is a substance that does not participate in the reaction and at the same time controls the rate of the reaction. Among many catalyst domains, the supported catalyst anchored to the support increases the possibility of active site exposure. Since the surface area is large, many catalyst particles can be loaded at once.
The 1D material has a small surface area, but has a small contact area with the catalyst particles and is therefore less likely to form a cluster. In addition, most of them were synthesized in the liquid phase and transferred to a 2D substrate to continue the chemical reaction. In this paper, we have demonstrated that suspended single-walled carbon nanotubes can be used as a 1D support for catalysts using iron catalysts and cobalt nanoparticle catalysts.
In addition, in the synthesized carbon nanotube supported catalyst, the secondary carbon nanotube was synthesized to a length of several tens of um using chemical vapor deposition (CVD) to confirm the catalyst reaction.
Introduction
- Catalyst support with various dimensions
- Discovery of Carbon nanotube
- Carbon nanotube properties
- CNT structure
- Electrical properties
- Raman spectroscopy of carbon nanotube
- CNT synthesis methods
- CNT catalysts
- CNT catalyst supports
- New CNT catalysts
- CNT growth mechanism
- CNT application
- Reinforcement of polymer nanocomposites
- Electronic Devices
- Limitation
Depending on the measurement method and the chirality of the SWCNTs, 1.22 TPa–1.26 TPa have been reported (Dresselhaus et al. 2001). In other words, the carbon nanotube diameter can be calculated via RBM, although the value is affected by the amount of cross-linked carbon nanotubes (Bandow et al., 1998). The elasticity and mechanical properties mentioned above are also determined by phonons (Dresselhaus et al., 2005).
SWCNT-SWCNT hybridization by arc discharge is reported by other research groups under air conditions at less cost (A et al., 2015). The disadvantage of this synthesis method is the higher possibility of defecting of the fabricated carbon nanotubes (amorphous carbon) when compared to previous methods (Collins, Arnold, & Avouris, 2001). The electrical and thermal properties are affected by these disorders along with the structural characteristics of carbon nanotubes (Avoris, Chen, & Perebeinos, 2007; Ferreira et al., 2016).
Thus, these metal catalysts are more efficient in forming carbon nanotubes with smaller diameter, which is equivalent to high curvature as SWCNTs (Ding et al., 2008). For example, In 2005, Kumare et al. reported that metal nanoparticle catalyst in zeolite supported nanopores presented a phenomenally high amount of carbon nanotubes which have a narrow diameter distribution. Although c and m planar sapphire showed low amounts of carbon nanotube growth, plane sapphire showed normal growth of carbon nanotubes in the (001) direction (Han et al., 2005).
Similarly, in single crystal MgO direction (110) a strong increase in the preference of carbon nanotubes is presented (Maret et al., 2007). To solve this problem, multiple melt mixing methods and process conditions (higher temperature, processing cut and mixing time) have been studied (Lin et al., 2016). Since the spin-casting technique can reduce the solvent evaporation time, the CNT dispersion can be maintained in the polymer matrix (Filipe V Ferreira et al., 2019).
Small- to medium-sized digital circuits based on SWCNT random network (Q. Cao et al., 2008). In the field of biomedical applications, CNT is a particularly attractive material due to its exclusive physical and chemical properties (Marchesan et al., 2017). Currently, it has been investigated that this surface modification improves the dispersion of CNTs, but also affects the properties and applications (Hashem Nia et al., 2017).
Several papers have reported that surface functionalization causes defects in the CNT structure and consequently reduces the mechanical, electrical, and thermal properties (Laudenbach et al., 2017).
SWCNT Diameter Comparison: Fe nanoparticle catalyst & Co nanoparticle catalyst
Experiment
- Cobalt nanoparticle catalyst preparation
- Fe catalyst preparation
- Synthesis of horizontal aligned carbon nanotube via CVD method
In the case of the SiO2 substrate, since the silicon dioxide film acts as an insulator, it has a different conductivity than that of the CNT. The most important thing in the synthesis of CNTs using CVD is the setting and environment of the synthesis conditions. After this point, the CNTs can be observed to grow in the desired direction on the substrate.
In addition, it is important to note that CNTs grow in the direction of the gas flow when using the CVD method. In contrast, AFM physically measures the height (diameter) of all CNTs, so that the diameter of the total CNTs present in the. In the case of the Fe catalyst, the particle size of the catalyst is not relatively constant due to the use of evaporative deposition.
Since both 'Tip-growth' and 'Base-growth' occur in the CNT synthesis mechanism, the size of the catalyst is critical to the diameter of the CNTs being synthesized. However, these TEM networks were not completely stable in the next step of catalyst lifting. The synthesized CNTs were very sensitive to strain because only both sides of the TEM grid were attached to the window frame and suspended in the air.
In the case of iron catalysts, these were deposited to a thickness of 5 Å using thermal evaporation. This is because, due to the nature of CNTs, it is oxidized and lost when annealing is carried out in air. Then, as the desired outcome, the growth of CNTs starting from the catalyst crossed the TEM lattice and proceeded in the opposite direction.
This is the result of confirming again that the catalyst particle size is a very important factor in the synthesis of carbon nanotubes. Then, it can be used as a platform to observe the movement of electrons in the catalyst using the electrical properties of CNT.
Result
- SEM image
- Raman peak
CNT: Role of one-dimensional catalyst support
Experiment
- TEM grid selection
- Synthesis of carbon nanotube via CVD method
The TEM grid used at the beginning of the experiment was a TEM grid with a square window (200 um × 200 um). At first, the entire TEM grid on which the CNT exists was immersed in a catalyst solution to deposit a catalyst. Furthermore, to confirm the synthesis of new CNTs by the catalyst on the CNTs, the catalyst was only placed in half of the window.
Since the CNT is simply placed on top of the TEM grid, masking techniques using photolithography and PR are not available. The last method I tried was to use a glass capillary and syringe to drop just one drop into the TEM grid window and dry it. The SEM image also clearly showed that only half of the window surface was in contact.
The synthesis of the second CNT was performed by placing a catalyst on the first CNT and then rotating it 90°. However, only the TEM grid was put into the input glass cylinder and tried to synthesize, but it did not grow properly. The same as a common method to synthesize horizontally aligned carbon nanotubes, the TEM grid was placed on a SiO2 substrate and the catalyst was placed in only one corner of SiO2.
Second, to perform the CVD synthesis, CNTs were synthesized in the same method by turning 90° to the direction in which the synthesis was originally performed, to perform the CVD synthesis. The expected result at this stage is to observe that a new CNT grows in a 90° direction on the ConP particles to the existing CNT. In particular, when using the CVD method, hydrogen is first injected at a high flow rate to remove the oxygen present in the chamber.
In addition, when annealing is carried out in a nitrogen atmosphere in the last step, the nitrogen flow rate is not determined and it is injected at a very high flow rate. Therefore, in the second synthesis, the flow rate was adjusted so that it was comparable to the hydrogen flow rate (4.2 sccm) in the initial and final stages.
Result
- SEM image
- TEM image
In this case, it is difficult to check the direction with the naked eye, so it is pointless to rotate the sample 90°. The CNTs that are intensively investigated in the SEM images after the first synthesis are several threads located at both ends of the window. Even if the window width is 50 um, it is a very long length in terms of CNTs with an average diameter of about 2 nm.
However, CNTs synthesized at both ends of the window are often formed at the corners, so they can be observed to have a relatively short length. Thus, a peripheral window was used, which usually changed its shape due to the influence of the catalyst. CNTs suspended in the air vary in distance depending on their position, so the strands are invisible in the SEM image.
Impurities in CNT walls, including carbon particles initiated by unvaporized graphite rod, amorphous carbon, and open tips, could also be explored (Goornavar, Jeffers, Biradar, & Ramesh, 2014). Some other structural parameters such as tube diameter and length, number of walls, entanglement and curvature can also be observed using TEM (Chong et al., 2017). In order to reduce the number of impurities in the walls of carbon nanotubes, Boncel et al. annealed MWCNTs at 2100 °C in an argon atmosphere.
The biggest difference in this experiment is the synthesis of new CNTs from CNTs suspended in air, which has become the biggest limitation in performing TEM imaging. In the case of TEM, like SEM, it is a device that fires an electron beam into the sample and projects a current into the image. Therefore, it is easy to observe only if the pattern is fixed to some extent.
However, in the case of CNTs suspended in air, it is very shaky every time the energy is applied, so it is difficult to get a clear image for TEMs that get high-resolution images. However, the difference from SEM imaging is that it is possible to visually confirm that a cobalt catalyst exists at the junction of the newly synthesized CNT.
Discussion & Conclusion
Synthesis of thin bundles of single-walled carbon nanotubes and nanohorn hybrids using an open-air arc discharge technique. Effect of growth temperature on the diameter distribution and chirality of single-walled carbon nanotubes. Nanoindentation creep, nanoimpact and thermal properties of multiwalled carbon nanotube–polypropylene nanocomposites prepared by melt blending.
Cobalt supported on carbon nanotubes for methane chemical vapor deposition for the production of new carbon nanotubes. An explanation of dispersion states of single-walled carbon nanotubes in solvents and aqueous surfactant solutions using solubility parameters. Electroanalytical wire device for estriol determination using screen-printed carbon electrodes modified with carbon nanotubes.
Nanodynamic mechanical and thermal responses of single-walled carbon nanotube reinforced polymer nanocomposite thin films.
