Improved synthesis yield of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) must be synthesized in a controlled manner before they can be used in various industries. A recent study published in the journal Nanomaterials explains that the maximum yield of SWNT synthesis depends on the positions of the materials in a horizontal chemical vapor deposition (CVD) reactor.

Study: Variation of the yield in the synthesis of single-walled carbon nanotubes in a horizontal chemical vapor deposition reactor. Image source: Evannovostro / Shutterstock.com

The researchers synthesized SWNTs using methane and thin iron layers as a source or activator.

The fluctuation in SWNT production yield over the horizontal distance of the reactor was examined with a scanning electron microscope, while atomic force microscopy and Raman spectroscopy were used to characterize the shape and crystalline nature of the synthesized single-walled carbon nanotubes.

The results indicated that the maximum SWNT production yield was achieved in the rear section of the horizontal reactor.

(a) Schematic representation of the CVD chamber.  (b) Digital photo of the device.

(a) Schematic representation of the CVD chamber. (b) Digital photo of the device. Image source: Sung-Il, J., & Jeong, G.-H.

These findings can be used to fabricate a wide variety of single-walled nanomaterials, including conductive nanofibers and rare earth nanoparticles.

Applications of single wall carbon nanotubes (SWNTs)

Single-walled carbon nanotubes have a diverse range of applications due to their exceptional structural, mechanical and electrochemical properties. From an industrial point of view, the controlled production of SWNTs is crucial in terms of structural efficiency.

For example, the selective development of semiconducting or ferromagnetic SWNTs is beneficial for applications such as connectors, catalysts, transducers, and technologies that require adequate electrical properties.

Synthesis of SWNTs by carbon vapor deposition

Among the various manufacturing methods for single-wall carbon nanotubes, chemical vapor deposition (CVD) is widely used because of its simplicity and production control. In addition, vapor-liquid-solid processes can be used to describe the SWNT production technique in CVD.

Carbon compounds from thermally decomposed substrates are built into the reactive metallic particles, which are deposited as hexagonal networks of highly concentrated carbons to form carbon nanotubes.

Most of the manufacture of single-wall carbon nanotubes in horizontal CVD systems is done using growth surfaces installed in the center of the tank, which gives high temperature and great thermal stability.

Variation of the surface density of SWNTs in relation to gas flow rate and sample position.

Variation of the surface density of SWNTs in relation to gas flow rate and sample position. Image source: Sung-Il, J., & Jeong, G.-H.

A novel technique for SWNT growth on SiO2 substrates

In this study, the researchers focused on the development of SWNTs in relation to the sampling point in the CVD tank, since the formation properties of SWNTs are strongly influenced by small changes in growth conditions such as gas flow rate and growth temperature.

The researchers made SWNTs from thin sheets of iron grown on silicon oxide plates. Thin iron sheets were carefully applied to the substrates using the particle evaporation technique at a slow rate of dissolution. The substrates were then placed in the tank.

The iron-deposited substrates were then anodized in air at 900 degrees Celsius for 10 minutes and cooled to temperatures below 200 degrees Celsius.

After the chamber stabilized, a combination of methane and hydrogen was added for ten minutes to synthesize the single-walled carbon nanotubes.

The CVD heater was cooled to room temperature after the synthesis phase. To examine the influence of the gas flow rate and the growth temperature at each sample location within the CVD tank, the gas flow rate was changed between 150 and 500 sccm while maintaining a hydrogen-methane ratio of 10%.

For the test phase, the temperatures were changed between 850 and 925 degrees Celsius.

Study results

Based on the results of SEM, AFM and Raman spectroscopy, it was discovered that the greatest production of single-walled carbon nanotubes was achieved in the rear section of the horizontal CVD reactor, not the middle part.

The same results were obtained using silicon substrates and larger diameter CVD tanks.

The rear of the chamber had a higher concentration of SWNT than the center due to the presence of an improved thermal atmosphere which aided in the degradation of the material due to the availability of a gas flow.

The presented results can be used to synthesize a wide variety of functional nanomaterials, including semiconducting nanorods and metal oxide nanoparticles, especially when a horizontal CVD tank is used.

Variation of the surface density of SWNTs in relation to growth temperature and sample position.

Variation of the surface density of SWNTs in relation to growth temperature and sample position. Image source: Sung-Il, J., & Jeong, G.-H.

Future perspective

In order to make SWNTs a viable material for sensors, fuel cells, storage systems and electronics, future research will likely examine a variety of low-dimensional nanomaterials. In addition, extensive theoretical calculations based on flow research may be required.

However, current research on single-wall carbon nanotubes suggests that they could be used in future applications such as conductive foils or sensor manufacturing.

Read on: Carbon Nanotube Nanocomposite Ink for additive manufacturing.

References

Sung-Il, J. & Jeong, G.-H. (2021). Variation of the yield in the synthesis of single-walled carbon nanotubes in a horizontal chemical vapor deposition reactor. Nanomaterials, 11 (12), 3292.Available at: https://www.mdpi.com/2079-4991/11/12/3293

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