Description:FIELD OF INVENTION
The invention relates generally to the field of formation of single wall carbon nanotubes, and more particularly to a method for regulated nucleation of a catalyst for a single wall carbon nanotube formation reaction.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to India patent application number 202341004533 and provisional patent application number 202541059503.
BACKGROUND
The high-pressure carbon monoxide (HiPCO) process is a gas-phase process that uses the floating catalyst approach, whereby the catalytic particles are formed in situ by thermal decomposition of the catalyst precursor. The catalyst precursor, usually metal carbonyl, undergoes decomposition at temperatures as low as 100oC, even in an atmosphere of carbon monoxide. After decomposition, the metal atoms in catalyst are in the gas phase where they are highly unstable and tend to cluster together forming catalyst nanoparticles. The catalyst nanoparticles rapidly grow and increase in size till they reach about 1 nanometer in diameter. At this stage, if the temperature of the catalyst nanoparticles is of the order of 900oC, the catalyst nanoparticles will catalyze the growth of single wall carbon nanotubes. Otherwise, the catalyst nanoparticle will continue to grow in size and once they reach the temperature of 900oC, catalyze the growth of other undesirable forms of carbon such as multiwall carbon nanotubes, and amorphous carbon.
Due to the inefficient heating of the catalyst nanoparticles, in majority of cases, only a minor fraction of the carrier gas transporting catalyst precursor effectively contributes to the formation of single wall carbon nanotubes. The remainder is largely inefficient, either being wasted or leading to the formation of unwanted byproducts that require subsequent removal.
Previously, rapid heating of catalyst nanoparticles has been achieved by modulating the flow rates of hot and cold gas streams, utilizing strategically placed holes and nozzles to generate gas jets, and engineering surface features on the reactor walls to promote rapid mixing of the hot and cold gases.
However, none of the above cited methods have been found to be effective in rapid heating of the catalyst nanoparticles.
Hence, there is a need for a production technology that induces rapid heating of the catalyst nanoparticle thus regulating the catalyst nucleation for increasing the efficiency of single wall carbon nanotubes formation.
BRIEF DESCRIPTION OF DRAWINGS
So that the manner in which the recited features of the invention can be understood in detail, some of the embodiments are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1 shows a schematic diagram of an arrangement of a moving surface placed inside a HIPCO reactor for regulated nucleation of a catalyst for single wall carbon nanotubes formation, according to an embodiment of the invention.
FIG. 2 shows a schematic representation of a moving surface for regulated nucleation of a catalyst, according to an embodiment of the invention.
FIG. 3. shows a schematic representation of a moving surface for regulated nucleation of a catalyst, according to another embodiment of the invention.
FIG. 4. shows a schematic diagram of an arrangement of drive mechanism for moving surface, according to an embodiment of the invention.
FIG. 5 shows a SEM image of single wall carbon nanotube obtained through regulated nucleation of a catalyst, according to an embodiment of the invention.
FIG. 6 shows a Raman spectrum of single wall carbon nanotube obtained through regulated nucleation of a catalyst, according to an embodiment of the invention.
FIG. 7 shows an EDAX data of single wall carbon nanotube obtained through regulated nucleation of a catalyst, according to an embodiment of the invention.
SUMMARY OF THE INVENTION
One aspect of the invention provides a method for regulated nucleation of a catalyst for single wall carbon nanotubes formation. The regulated nucleation of a catalyst nanoparticle is achieved through rapid heating of the catalyst nanoparticle by enabling a turbulent mixing of a low temperature gas carrying the catalyst with a high temperature gas. The turbulent mixing causes rapid heating of the catalyst nanoparticle to a temperature of about 900oC to allow growth of single wall carbon nanotubes.
Another aspect of the invention provides for regulated nucleation of a catalyst nanoparticle by enabling a turbulent mixing, through at least one moving surface of a low temperature gas carrying a catalyst precursor with a high temperature gas. The turbulent mixing enables rapid heating of the catalyst nanoparticle for catalyzing the growth of a single wall carbon nanotube.
The regulated nucleation of a catalyst includes selecting a catalyst precursor that is capable of being readily vaporized, providing the catalyst precursor along with a low temperature gas stream, decomposing the catalyst precursor by increasing the temperature and trigger the growth of a catalyst nanoparticle, rapidly heating the nanoparticle in presence of a carbon source to a temperature of about 900oC for catalyzing the growth of a single wall carbon nanotube. The said temperature is attained to obtain a nucleated catalyst nanoparticle having a size of about 1 nm and allow the growth of single wall carbon nanotubes on the nucleated catalyst nanoparticle. The rapid heating is achieved by turbulent mixing through at least one moving surface of the low temperature gas carrying the catalyst nanoparticles and high temperature gas.
DETAILED DESCRIPTION OF INVENTION
Various embodiments of the invention relate to regulated nucleation of a catalyst for a single wall carbon nanotube formation reaction.
Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals are understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.
One embodiment of the invention provides a method for regulated nucleation of a catalyst during a single wall carbon nanotube formation reaction. The method includes selecting a catalyst precursor. The catalyst precursor is capable of being readily vaporized and includes but is not limited to a metal carbonyl and a metallocene. The metal carbonyl includes but is not limited to iron pentacarbonyl, nickel tetra carbonyl, chromium hexa carbonyl and dicobalt octacarbonyl. The metallocene includes but is not limited to ferrocene, and cobaltocene. In one embodiment of the invention, iron pentacarbonyl is selected as the catalyst precursor. The catalyst precursor is provided in a stream of a low temperature gas. The gas includes but is not limited to carbon monoxide, carbon dioxide, methane or a combination thereof. In one embodiment of the invention, the iron pentacarbonyl is provided in a stream of carbon monoxide at a temperature of about 30oC. The catalyst precursor is decomposed by raising the temperature to above 100 °C (depending on the pressure conditions ranging from 10 bars to 60 bars) which initiates the growth of catalyst nanoparticles. Iron pentacarbonyl being volatile decomposes readily, once decomposition occurs, individual iron atoms are left in the gas phase where they are extremely unstable and nucleate to form iron nanoparticles. At this temperature, the catalyst nanoparticles continue to grow in size. Once the catalyst nanoparticles reach 1nm diameter, they are ready to catalyze the growth of a single wall carbon nanotube. The catalyst nanoparticle is rapidly heated to a temperature above 900 °C. This high temperature activates the nanoparticle, enabling it to catalyze the growth of single-walled carbon nanotubes. The rapid heating is achieved through a heated carbon source. The carbon source includes but is not limited to carbon monoxide, carbon dioxide, methane or a combination thereof. The carbon source is maintained at a temperature ranging from 800-10000C. In one embodiment of the invention, the stream carrying nucleated catalyst nanoparticle is rapidly heated by turbulent mixing with the carbon monoxide gas stream maintained at a temperature of 9000C. The turbulent mixing is achieved through at least one moving surface. The moving surface is selected from a list comprising of a shaft having a fan, an impellor, a stirrer, a mixer, or other surfaces that generate turbulence by moving. In one embodiment of the invention, the moving surface includes a shaft having an impeller. In another embodiment of the invention, the moving surface includes a hollow shaft for enabling the gas to exit directly into the impeller blades. The moving surface is operated either in a pulsed mode or a continuous mode. The moving surface can perform a translational motion, a rotational motion or a roto-translational motion to enable a turbulent mixing of the catalyst nanoparticle carried in low temperature carbon monoxide gas stream with the carbon monoxide gas maintained at a high temperature of about 9000C. The moving surface is positioned in a reactor in such a way that the moving surface intercepts the low temperature gas carrying the catalyst precursor and/or growing nanoparticles as they emerge from an injector into zone containing the hot carbon monoxide gas and cause turbulence even in the low-pressure regions that extends a few micrometers behind the moving surface so as to rapidly heat the maximum number of catalyst nanoparticles to a temperature of about 900 0C. Rapidly heating the nanoparticle when it attains a size of 1nm diameter from a temperature of about 1000C to 9000C regulates the nucleation of the catalyst nanoparticle to the size of 1nm diameter to allow growth of single wall carbon nanotubes. The turbulent mixing achieved through moving surface maximizes the number of nanoparticles that can grow single wall carbon nanotubes, thus increasing the yield of single wall carbon nanotubes formed.
Now referring collectively to FIG. 1 to FIG. 4, show schematic of an arrangement for achieving regulated nucleation of a catalyst for single wall carbon nanotube formation. FIG. 1 shows a schematic diagram of an arrangement of moving surface placed inside a HiPCO reactor for regulated nucleation of a catalyst for single wall carbon nanotubes formation, according to an embodiment of the invention. The arrangement is configured to be placed inside a reactor for synthesizing a single wall carbon nanotube through HiPCO process. The reactor includes an outer tube 1, an injector tube 3 connected to an injector 5 and an inner tube 7 for collecting the synthesized single wall carbon nanotubes. The injector tube 3 is configured for flow of CO gas along with a catalyst to the injector 5 and is provided with a water-cooling mechanism 9 for maintaining the stream of CO gas along with the catalyst to a temperature below the decomposition temperature of the catalyst. A carbon source preferably CO is provided at a temperature ranging from 800-10000C through a plurality of holes 11. A moving surface is positioned inside the injector for turbulent mixing of cold stream of gas carrying catalyst nanoparticle with hot stream of gas to enable rapid heating of the catalyst nanoparticle to a temperature of 9000C. The moving surface includes a shaft 13 having an impeller 15. In one embodiment of the invention, the impeller 15 has a plurality of blades 17 (FIG. 2). In another embodiment of the invention, the impeller has a plurality of spikes 17 (FIG. 3) arranged longitudinally in a predefined pattern to give the impeller, the appearance of a bottle brush. The blades/spikes 17 are configured to cause turbulence in the regions immediately around the blades/spikes, primarily in the low-pressure regions that extend a few micrometers behind the trailing surface of each blade. The blades of the impeller pull the low temperature gas carrying the catalyst precursor and/or growing nanoparticles as they emerge into the reactor at the same time hot carbon monoxide gas is also pulled within the impeller blades. The impeller blades induce turbulent mixing of the cold gas and the hot gas to enable rapid heating of the catalyst nanoparticle. The shaft 13 uses a sleeve bearing, a ball bearing or a fluid to lubricate and/or levitate the drive shaft in an air bearing configuration. The movement of the shaft 13 is through a power source 19 situated externally to the reactor. The power source is an AC source, a DC source or a hybrid source and the power transmission is thorough the reactor wall. Further, a drive mechanism 21 is operably coupled with the power source 19 (FIG.4) to enable power transmission. The drive mechanism 21 is provided with a seal (not shown) when penetrating the reactor wall. Alternatively, the drive mechanism may use magnetic coupling 23 to avoid the need to penetrate the reactor wall for purposes of power transmission.
Characterization:
Characterization of the single walled carbon nanotubes is carried out using Scanning Electron Microscopy (SEM), Raman Spectroscopy and Energy Dispersive X-ray Spectroscopy.
FIG. 5 shows a SEM image of single wall carbon nanotube obtained through regulated nucleation of a catalyst, according to an embodiment of the invention. The SEM image of the synthesized single-walled carbon nanotubes reveal a randomly entangled and highly porous network morphology. The nanotubes are predominantly uniform in diameter, ranging between 1–3 nm, occasionally forming bundles. The network demonstrates a high degree of interconnectedness, forming nanoscale mesh structures advantageous for mechanical reinforcement and functional applications. In addition to the nanotube network, residual metallic catalyst particles and amorphous carbon impurities are evident, manifesting as brighter regions and faceted particles. These impurities are typical artifacts from catalytic chemical vapor deposition (CVD) processes and can be minimized with post-synthesis purification. The observed morphology confirms the successful synthesis of SWCNTs with a high aspect ratio and structural integrity suitable for advanced material applications.
FIG. 6 shows a Raman spectrum of single wall carbon nanotube obtained through regulated nucleation of a catalyst, according to an embodiment of the invention. The Raman spectroscopic analysis of the synthesized single-walled carbon nanotubes demonstrates characteristic vibrational modes confirming their structural integrity. The presence of radial breathing modes (RBM) within the 100-350 cm⁻¹ range confirms the formation of single-walled structures with a distribution of nanotube diameters.
A strong and sharp G-band at approximately 1580 cm⁻¹ corresponds to the tangential vibrational modes of sp²-hybridized carbon, indicative of a highly ordered graphitic structure. The D-band observed near 1350 cm⁻¹ reflects minor defect presence or amorphous carbon impurities typical of CVD-synthesized single-walled carbon nanotubes. The G′ (2D) band further substantiates the graphitic character.
The high G/D intensity ratio substantiates that the produced single-walled carbon nanotubes possess high structural purity and crystallinity, with minimal defect concentration. This Raman signature aligns with the SEM morphology observations and supports the high quality of the synthesized material suitable for advanced nanotechnological and aerospace applications.
FIG. 7 shows an EDAX data of single wall carbon nanotube obtained through regulated nucleation of a catalyst, according to an embodiment of the invention. The elemental analysis of the synthesized single-walled carbon nanotube, conducted via energy dispersive X-ray spectroscopy (EDX), confirms a predominant carbon composition of approximately 94.40 wt%, affirming the carbonaceous nature of the nanotube network. Metallic elements including iron (1.94 wt%), nickel (1.97 wt%), and chromium (1.38 wt%) are present, corresponding to residual catalyst materials utilized during chemical vapor deposition synthesis. Trace elements of aluminum (0.16 wt%) and sulfur (0.14 wt%) are detected, attributed to synthesis precursors or processing artifacts. The observed elemental profile aligns with Raman and SEM analyses, corroborating the formation of structurally intact SWCNTs with minor residual impurities. The above compositions could vary depending on process conditions and in general, carbon content is the major component.
The invention thus provides a method for regulated nucleation of catalyst nanoparticles for synthesis of single-walled carbon nanotubes during HiPCO process. The regulated nucleation achieved through rapid heating of the catalyst nanoparticle within few microseconds of coming in contact with hot carbon source through a moving surface enable growth of single wall carbon nanotube on the catalyst nanoparticle, thus increasing the yield of single-walled carbon nanotubes.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
, Claims:1. A method for regulated nucleation of a catalyst during a single wall carbon nanotube formation reaction, the method comprising:
selecting a catalyst precursor that is capable of being readily vaporized;
decomposing the catalyst precursor by increasing the temperature and triggering the growth of a catalyst nanoparticle;
rapidly heating the nanoparticle in presence of a carbon source to a temperature for catalyzing the growth of a single wall carbon nanotube, the said temperature is attained to obtain a nucleated catalyst nanoparticle wherein the rapid heating is achieved through at least one moving surface that enables turbulent mixing of a low temperature gas carrying the catalyst nanoparticles and high temperature gas; and
allowing the growth of single wall carbon nanotube on the nucleated catalyst nanoparticle.
2. The method as claimed in claim 1, wherein the catalyst precursor is selected from a group comprising of metal carbonyl including iron pentacarbonyl, nickel tetra carbonyl, chromium hexa carbonyl, dicobalt octacarbonyl; and metallocene including ferrocene and cobaltocene.
3. The method as claimed in claim 1, wherein the catalyst precursor is provided in a stream of low temperature gas.
4. The method as claimed in claim 1, wherein the low temperature gas comprises carbon monoxide, carbon dioxide, methane or a combination thereof.
5. The method as claimed in claim 1, wherein the carbon source is selected from a group comprising of carbon monoxide, carbon dioxide, methane or a combination thereof.
6. The method as claimed in claim 1, wherein the carbon source is maintained at a temperature ranging from 800-10000C.
7. The method as claimed in claim 1, wherein the nucleated nanoparticle is achieved by regulation of the growth of catalyst nanoparticle to a size of about 1 nm.
8. The method as claimed in claim 1, wherein the moving surface is selected from a list comprising of a shaft having a fan, an impeller, a stirrer, a mixer, or other surfaces that generate turbulence by moving.
9. The method as claimed in claim 1, wherein the shaft uses a sleeve bearing, a ball bearing, a fluid to lubricate and/or levitate the drive shaft in an air bearing configuration
10. The method as claimed in claim 1, wherein the motion is induced by means other than a drive shaft or rotational motion.
11. The method as claimed in claim 1, wherein the moving surface is configured for a translational motion, a rotational motion and a roto-translational motion
12. The method as claimed in claim 1, wherein the moving surface is configured to cause turbulence in low-pressure regions that extend a few micrometers behind the moving surface.
13. The method as claimed in claim 1, wherein the moving surface can be operated in a pulsed mode or a continuous mode.
14. The method as claimed in claim 1, wherein the moving surface is positioned to intercept the low temperature gas carrying the catalyst precursor and/or growing nanoparticles as they emerge from an injector into zone containing the hot gas.
15. The method as claimed in claim 1, wherein the movement of the shaft is through a power source situated external to a reactor.
16. The method as claimed in claim 1, wherein the power source is an AC source, a DC source or a hybrid source.
17. The method as claimed in claim 1, wherein the power transmission is thorough the reactor wall.
18. The method as claimed in claim 1, wherein a drive mechanism is operably coupled to the power source to enable the power transmission, the said drive mechanism is provided with a seal when penetrating the reactor wall.
19. The method as claimed in claim 1, wherein the drive mechanism uses magnetic coupling to avoid the need to penetrate the reactor wall for purposes of power transmission.
20. The method as claimed in claim 1, wherein the single wall carbon nanotubes formation reaction is carried out under a pressure ranging from 10 to 60 bars.
21. The method as claimed in claim 1, wherein the regulated nucleation of the catalyst results in growth of single wall carbon nanotubes of uniform dimension, wherein the dimension is of the order of 0.8 nm to 1.2 nm.