ES2933953T3 - Reactor for the manufacture of graphene - Google Patents

Abstract

The present invention relates to a process, a reactor and a system for producing freestanding two-dimensional nanostructures, using a microwave excited plasma environment. The process is based on injecting a mixture (9) of gases and precursors in a current regime into a reactor. The current is subjected to a surface wave electric field (5), excited by the use of microwave energy (7) that is introduced into a field applicator (6), generating high energy density plasmas (2,3, 4), which break the precursors into their atomic and/or molecular constituents. The system comprises a plasma reactor with a surface wave launch zone, a transient zone with a progressively increasing cross-sectional area and a nucleation zone. The plasma reactor together with an infrared radiation source (11) provides a controlled adjustment of the spatial gradients, temperature and speed of the gas stream. Most of the two-dimensional nanostructure samples obtained have a thickness of a single atomic layer, and the process and system allow obtaining graphene production rates of the order of one gram per hour and higher. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Reactor for the manufacture of graphene

field of invention

The present invention relates generally to a reactor for the selective fabrication of autonomous two-dimensional nanostructures using plasma technology, in particular microwave plasma.

Background of the invention

Currently, the development of new two-dimensional nanostructures is considered one of the research areas in science and technology that presents the greatest demand and, therefore, with the greatest strategic value.

Graphene is the most eminent example of a two-dimensional (carbon-based) nanostructure that is in increasing demand as it possesses many extraordinary properties, with potential applications in numerous scientific and engineering disciplines.

However, the mechanical, optical, and electrical performance of graphene crucially depends on its structural characteristics, i.e., the number of monolayers (whose growth limits desirable quantum mechanical properties), the presence of sp3 carbons, defects, etc. .

Currently, the procedures used for the production of graphene are based on one of two different approaches, hereinafter referred to as 'top-down' or 'bottom-up'.

The highest quality graphene can be obtained by mechanically exfoliating highly oriented pyrolytic graphite, this procedure can be considered the most common example of the "top-down" approach. However, this procedure leads to relatively low production rates (about 1 mg/h), compared to the reference amount for industrial applications (about 1 g/h).

The production of graphene oxide from graphite, followed by thermal reduction of graphene oxide, is a second example of a "top-down" production strategy, which despite having much higher production rates (greater than 1 g /h), leads to a highly defective product (S. Mao, H. Pu, J. Chen, «Graphene oxide and its reduction: modeling and experimental progress» 2012 RSC Adv. progress 22643).

“Bottom up” approaches include epitaxial growth, chemical vapor deposition (CVD), and vacuum graphitization of silicon carbide substrates, among others. These techniques have several drawbacks, such as the degradation of the properties of the nanostructure due to the interference of transition metals, the need to use expensive catalysts (Fe, Co, Cu, Ni, etc.), the very high processing temperatures, the length and complexity of the production procedures, the use of dangerous chemicals and, above all, the very limited control over the nanostructure assembly procedure (E. Tatarova et al, «Plasmas for environmental issues: from hydrogen production to 2D materials assembly» 2014 Plasma Sources Sci. Technol. 23063002-063054).

Therefore, existing techniques cannot yet provide two-dimensional nanostructures with predefined and well-controlled structural and physicochemical properties, while at the same time guaranteeing production rates suitable for industrial applications.

To the above restrictions, it should be added that state-of-the-art "bottom-up" approaches generally require the use of a substrate, consisting of a solid surface, which may limit the success of intended applications.

For example, when the goal is to create energy storage and conversion devices, or the development of new composite materials, the use of autonomous graphene structures (i.e., without supporting substrates) is a more attractive alternative to such horizontal graphenes and substrate-supported graphenes, where one side of the graphene sheet is implanted onto a solid substrate surface.

In fact, in terms of applications, autonomous graphenes have the obvious advantage of being able to use both surfaces and at least three open edges, while substrate-bound graphenes use only one surface.

Recently, microwave plasmas have been used in the "spray through plasma" technique (a "bottom-up" approach) to produce a multitude of autonomous nanostructures that are of interest in many fields (J. Phillips, D. Mendoza, C. K. Chen, “Method for producing metal oxide nanoparticles” 2008 US Pat.

7,357,910 B2), including graphene (J. Phillips, CC Luhrse, M. Richard 2009 IEEE Trans. Plasma Sci. 37726).

In the work by Dato et al, «Substrate-free gas-phase synthesis of graphene sheets» 2008 Nano Letters 82012, it has been shown that it is possible to produce graphene autonomously, without the need to use three-dimensional materials or substrates.

However, it should be noted that this work maintains other limitations mentioned above, namely the low purity of the nanostructures produced, only some of which are graphene sheets made up of two or three layers of carbon (the rest correspond to other allotropes of carbon), and the low production rates achieved (approximately 1 mg/h).

In order to control the number of atomic monolayers and the structural quality (defects, impurities, etc.) of the two-dimensional nanostructures produced, a novel microwave plasma-assisted procedure was proposed, which enables the final product to be decisively selected.

This procedure, which was used to produce autonomous graphene sheets, is based on injecting a liquid precursor, such as ethanol, through a microwave argon plasma, where the ethanol decomposition occurs. The carbon atoms and molecules, produced by the gas phase plasma, diffuse towards colder parts of the system, where they are added to solid carbon nuclei.

This procedure is described in the following papers: E. Tatarova, J. Henriques, CC Luhrs, A. Dias, J. Phillips, MV Abrashev, CM Ferreira, «Microwave plasma based single step method for free standing graphene synthesis at atmospheric conditions» 2013 appl. Phys. Lett. 103 134101-5; E. Tatarova, A. Dias, J. Henriques, AM Botelho do Rego, AM Ferraria, MV Abrashev, CC Luhrs, J. Phillips, FM Dias, CM Ferreira, «Microwave plasma applied for the synthesis of free standing graphene sheets» 2014 J. Phys D: Appl. Phys. 47385501-512.

These works partially solve the problem of the simultaneous production of different carbon allotropes (limited to approximately 30% of the total nanostructures produced), allowing graphene sheets to be produced with a high structural quality (1-3 atomic layers) comparable to that of the graphene materials available on the market, but with the advantage of being autonomous, that is, with the advantage of not having a support substrate, as mentioned above.

US Patent Application 2010/301212 A1, entitled "Substrate-free gas-phase synthesis of graphene sheets" describes a substrate-free gas-phase synthesis apparatus and method that can rapidly and continuously produce graphene under conditions environmental conditions without the use of graphite or substrates. Graphene sheets are continuously synthesized in fractions of a second by sending an aerosol consisting of argon gas and liquid ethanol droplets into a microwave-generated argon plasma field at atmospheric pressure. The ethanol droplets evaporate and dissociate in the plasma, forming sheets of graphene that are collected. The apparatus is scalable for large-scale production of clean and highly ordered graphene and its multiple applications. The graphene that is produced is clean and highly ordered with few lattice imperfections and oxygen functions, and therefore has better characteristics over graphene produced by current methods in the art. The graphene produced by the apparatus and methods was shown to be particularly useful as a supporting substrate allowing direct atomic resolution imaging of organic molecules and interfaces with nanoparticles to a degree previously unattainable.

In GB Patent Application 2527209 A, entitled "Apparatus and method for plasma synthesis of graphitic products including graphene" there is disclosed an apparatus for forming graphitic products including graphene comprising a plasma nozzle 19 coupled to a reaction chamber 7, media 14 for supplying a carbon-containing process gas to the nozzle 19 and means 1 for supplying radio frequency or microwave radiation to the process gas within the nozzle 19. The nozzle 19 is arranged so that the plasma luminescence extends towards reaction chamber 7. In use, the process gas is cracked by the plasma in nozzle 19 and passes into reaction chamber 7 where it recombines to form graphitic products in plasma luminescence. The nozzle 19 is shaped to form at least one and preferably three vortices in the process gas within the nozzle 19. The reaction chamber 7 may be cylindrical with an opening 9 at one or both ends for product removal. The luminescence quickly loses heat when leaving the nozzle 19, for example due to the diameter of the reaction chamber 7 or the means for cooling the luminescence in the chamber.

However, these proposals have not solved other problems mentioned above, such as the low production rate of graphene, of approximately 0.5 mg/h, and the relatively low degree of purity of the product obtained, which is produced with incorporated oxygen.

Therefore, there is a need in the art for a reactor for the production of autonomous two-dimensional nanostructures that solve the aforementioned problems of the prior art.

In particular, a reactor is needed that can provide higher degrees of purity of the resulting nanostructures, as well as better industrial production rates.

Additional objects, advantages and functions of the present invention will be proposed in the following description, and they can be naturally developed and improved with practical use.

The objects of the present invention are achieved by the reactor claimed in the appended independent claims, the dependent claims being used to define particular embodiments of the present invention.

Summary of the invention

The invention relates to a microwave plasma reactor for manufacturing autonomous two-dimensional nanostructures, the reactor having a hollow body (1) comprising:

• a part (19) for launching surface waves of plasma creation,

• a part (21) of nucleation of precursor constituents and

• a transitory part (20) having the first and second ends connected, respectively, to the surface wave launching part (19) and to the nucleation part (21), providing fluid communication between these parts (19, 21). ), wherein said parts (19, 20, 21) define, respectively, in the body (1) three interior operating zones (19', 20', 21'),

characterized in that the first end of the transitional part (20) has a cross-sectional area that is less than a cross-sectional area of the second end.

Preferably, the cross-sectional area of the transitory part (20) increases progressively from its first to its second end.

In one embodiment, said parts (19, 20, 21) are integrally joined together, forming a single piece.

The hollow body (1) of the reactor is formed by a dielectric material selected from the group consisting of quartz, sapphire, alumina and combinations thereof.

In another embodiment, the hollow body (1) of the reactor also comprises a part (8) for admitting a mixture of at least one inert gas and at least one precursor, the part (8) being integrated into the part (19 ) for launching surface waves or coupled to the part (19) for launching surface waves through connections.

In addition, the invention refers to a system for the production of autonomous two-dimensional nanostructures, the system comprising:

• a microwave plasma reactor having a hollow body (1) comprising at least a surface wave launching part (19), a transient plasma formation part (20) and a nucleation part (21). of precursor constituents; Said parts (19, 20, 21) define, respectively, in the reactor three interior operating zones (19', 20', 21') that are sequentially connected in fluid communication with each other,

characterized in that it also includes

• At least one source (11) of infrared radiation on the outside of the hollow body (1) of the plasma reactor, arranged to irradiate the inner area (21') defined by the nucleation part (21) of said body (1). ) from the reactor.

In one embodiment, the system further comprises a cooling device (10) outside the hollow body (1) of the plasma reactor, wherein the cooling device (10) is arranged to cool at least the area (20 ') interior defined by the transitory part (20) of said body (1) of the reactor.

Said cooling device (10) is operable in a temperature range between 40°C and 220°C, preferably between 40°C and 200°C, more preferably between 40 and 180°C, most preferably between 40°C and 150°C

In another embodiment, the system also comprises a source of ultraviolet radiation outside the hollow body (1) of the plasma reactor, arranged to irradiate at least the interior area (21') defined by the nucleation part (21). of said body (1) of the reactor.

In yet another embodiment, said parts (19, 20, 21) of the body (1) of the reactor are integrally joined together, forming a single piece.

Said body (1) of the reactor is formed by a dielectric material selected from the group consisting of quartz, sapphire, alumina and combinations thereof.

In a highly preferred embodiment, the system for the production of autonomous two-dimensional nanostructures is characterized by comprising:

• a microwave plasma reactor that has a hollow body (1) comprising at least:

a part (19) for launching surface waves of plasma creation,

a part (21) of nucleation of precursor constituents and

a transitory part (20) having the first and second ends connected, respectively, to the surface wave launching part (19) and the nucleation part (21), providing seamless communication between these parts (19, 21) ,

wherein said parts (19, 20, 21) define, respectively, in the body (1) of the reactor three interior operating zones (19', 20', 21'); and said first end of the transitional part (20) has a cross-sectional area less than the cross-sectional area of said second end of the transitional part (20), and

• at least one source (11) of infrared radiation outside said hollow body (1) of the reactor, arranged to irradiate the interior area (21') defined by the nucleation part (21) of said body (1). of the reactor.

Preferably, the system of the previous embodiment also comprises a cooling device (10) outside the body (1) of the reactor, wherein the cooling device (10) is arranged to cool at least the area (20' ) interior defined by the transitory part (20) of said body (1) of the reactor, said cooling device (10) being operable in a temperature range between 40 °C and 220 °C, preferably between 40 °C and 200 °C C, more preferably between 40°C and 180°C, most preferably between 40°C and 150°C.

Preferably, the system of the previous embodiment also comprises a source of ultraviolet radiation outside the hollow body (1) of the plasma reactor, arranged to irradiate at least the interior zone (21') defined by the nucleation part (21). of said body (1) of the reactor.

Brief description of the drawings

The accompanying drawings and photographs illustrate exemplary embodiments and typical results of the present invention and, together with the description, serve to explain the principles of the invention.

Figures 1 to 3 show drawings of the longitudinal cross section of a preferred system of the invention, also showing some physical characteristics related to the production process of autonomous nanostructures, such as the gradients (13, 15, 16) of gas temperature within of the reactor (figure 2) also called (T1, T2 and T3); and gas velocity gradients (17, 18) (Figure 3), the control of which allows selecting the production of autonomous two-dimensional nanostructures according to the invention.

Figure 4 shows a schematic representation of an exemplary plasma reactor injection unit.

Figure 5 shows an example of a scanning electron microscopy (SEM) image, obtained from the result of the selective synthesis of graphene sheets, with a scale bar of 100 nm, controlled with strong gradients. temperature and velocity axials. This image at 40,000x magnification was obtained in SEI mode with secondary electrons and an applied working voltage of 15.0 kV.

Figure 6 shows a High Resolution Transmission Electron Microscopy (HRTEM) image, obtained using graphene sheets synthesized by the system of the present invention. As seen in the image, with a scale bar of 10 nm, these graphene sheets advantageously have only a few layers, many of them being monolayers identified by the arrows.

Figure 7 shows an example of a scanning electron microscopy (SEM) image, with a scale bar of 100 nm, obtained from the result of the state-of-the-art non-selective synthesis of carbon nanostructures (carbon nanoparticles, graphene nanosheets and nanodiamonds), adopting conditions of reduced and/or uncontrolled axial temperature/velocity gradients. The image is at 40,000x magnification and was obtained in SEI mode with secondary electrons and an applied working voltage of 15.0 kV.

Detailed description of the invention

The present invention relates to a reactor in which microwave plasmas are used to selectively produce autonomous two-dimensional nanostructures, which are advantageously made up of only a few atomic layers and created in the form of suspended flakes, with production rates of the order of one gram. per hour (1g/h).

The reactor and system of the invention allow, by monitoring the operating conditions, the selective production of nanostructures, that is, the generation of a single two-dimensional monolayer atomic allotrope.

Figures 5 and 6 show examples of nanostructures produced in accordance with the present invention, Figure 5 shows a scanning electron microscopy (SEM) image of flake-shaped graphene nanosheets, and Figure 6 shows an electron microscopy image High-resolution transmission analysis (HRTEM) of graphene nanosheets with only a few monolayers. The results presented in these figures were achieved by applying the procedure of the invention, which made it possible to select the final product in a decisive manner.

On the other hand, Figure 7 shows a scanning electron microscopy (SEM) image, obtained under non-selective production conditions according to a prior art procedure, where various carbon nanostructures can be distinguished, such as carbon nanoparticles, carbon nanosheets, graphene and nanodiamonds.

Note that while the examples presented herein relate to the production of graphene, the reactor of the present invention can be used to produce other two-dimensional nanostructures, such as graphene derivatives (for example, N-graphene, F- graphene), germanene (the two-dimensional homologue of germanium), hexagonal boron nitride, among others.

In the context of the present invention, the term "two-dimensional nanostructures" refers to nanometer-thick sheets consisting of a limited number (typically between 1 and 3) of atomic layers.

The term "autonomous nanostructures" refers to independent nanostructures capable of supporting their own weight without deteriorating, and which are created in the form of suspended flakes, without the need to use support substrates.

The term "current" refers to a fluid in motion.

The term "microwave plasma" refers to an ionized gas, generated by applying an electric field from a surface wave excited by microwave energy. The surface wave propagates at the interface between the plasma and a dielectric medium, where the electric field is strongest. When propagating, the surface wave creates a plasma and self-consistently generates its own propagation structure.

By "precursor" is meant an atomic or molecular product that constitutes the raw material for the construction of nanostructures.

By “precursor constituents” is meant the chemical elements from which the precursor is made, ie one or more of the following chemical elements: carbon, boron, germanium, nitrogen, oxygen, hydrogen and fluorine.

By "nucleation of precursor constituents" or simply "nucleation" is meant the step in which assemblies of one or more precursor constituents dispersed in the inert gas are brought together into agglomerates, on a nanometer scale.

By "selective" production is meant the decisive selection of the desired final product, for example, avoiding the appearance of allotropic variants. That is, the controlled production of a single type of allotrope for which the respective operating parameters have been defined, namely flow rate, microwave power and power of the infrared radiation source.

Note that, regardless of the explicit presentation of the quantitative expression "about X", any value of X presented in the course of the present description must be interpreted as an approximate value of the real value of X, since such an approximation to the real value would be reasonably expected due to experimental and/or measurement conditions that introduce deviations from the true value.

In the context of the present description, the term "comprising" and its verbal variations should be understood as "including, among others". As such, the term should not be construed as "consisting solely of".

In the context of this application, the use of the expression "and/or" means that both conditions are met or that only one of them occurs. For example, the term "cooling device and/or ultraviolet radiation source" means "cooling device and ultraviolet radiation source" or "cooling device" or "ultraviolet radiation source".

The procedure for the production of autonomous two-dimensional nanostructures using plasma technology comprises the following steps:

(a) producing a stream of a mixture of at least one inert gas and at least one precursor,

(b) breaking down the precursor into its atomic and molecular constituents by means of a microwave plasma, said plasma being created from the stream of the mixture from the previous step,

(c) exposing the precursor constituents formed in the previous step to infrared radiation and, subsequently,

(d) collecting the nanostructures resulting from the nucleation of precursor constituents.

In step a) of production of a current, the inert gas is selected from the group comprising helium, neon, argon, krypton, xenon or a mixture of these, and the precursor can have a chemical composition that contains one or more of the following elements: carbon, boron, germanium, nitrogen, oxygen, hydrogen and fluorine. By way of example, gaseous precursors can be used, such as methane, ethylene, acetylene or diborane; or liquid precursors, such as ethanol, propanol, butanol, or methanol, or solid precursors, such as germanium monoxide or germanium dioxide.

The mixture of gases and precursors can be injected in a flow regime, for example, in a part (8) of admission of a reactor, with a flow rate between 4.2 x 10.6 and 8.3 x 10-4 cubic meters. standard per second (m3/s), preferably between 8.3x10-6 m3/s and 3.3x10-4 m3/s, more preferably between 1.7x10-5 m3/s and 1.7x10-4 m3/s.

Said current is exposed to a high frequency electric field, with a frequency that is between 10 MHz and 28 GHz, preferably between 100 MHz and 14 GHz, more preferably between 500 MHz and 3 GHz, most preferably 2.45 GHz, belonging to a surface wave (5), excited by microwave power (7), with a power that is between 100 W and 60000 W, preferably between 500 W and 10000 W, more preferably between 1000 W and 6000 W, the most preferably between 2000 W and 6000 W.

This microwave power (7) is applied, for example, by means of a field applicator (6), to generate a plasma (2, 3, 4) of high energy density (between 0.1 GW/m3 and 1 GW/ m3) that breaks down the precursor or precursors present in the stream into its atomic and molecular constituents.

The atomic and molecular constituents of the precursors flow from the zone (20') of hot plasma, where they were produced in the gas phase, to a colder nucleation zone (21'), where the two-dimensional nanostructures are produced and grow independently. autonomous.

The control of the spatial gradients, of the temperature and of the velocity of the flow of the gas mixture, allows to selectively produce the desired two-dimensional nanostructures.

The adjustment of these spatial gradients is achieved by applying, for example, around the reactor, a source (11) of infrared radiation and, optionally, a cooling device (10) and/or a source of ultraviolet radiation.

In one embodiment of the process, the precursor constituents are further subjected to ultraviolet radiation in step (c). The ultraviolet radiation is generated by a source of ultraviolet radiation operating in a power range between 50 W and 3000 W, preferably between 100 W and 2500 W, more preferably between 150 W and 2000 W, most preferably between 200 W and 1500W

In addition, the current can be subjected, between step (a) and step (b), to cooling by means of a cooling device that operates in a temperature range between 40 °C and 220 °C, preferably between 40°C to 200°C, more preferably between 40°C and 180°C, most preferably between 40°C and 150°C.

In a preferred embodiment of the method, in step (c) both infrared and ultraviolet radiation are applied, as well as current cooling between step (a) and step (b).

Surprisingly, the application of infrared radiation provides high quality nanostructures, clearly above the state of the art. Without pretending to be a theory, infrared radiation seems to intervene favorably in controlling the number of monolayers per sheet and the percentage of carbon sp3 bonds.

The infrared radiation required for the procedure is generated by a source (11) of infrared radiation that operates in a power range between 50 W and 3000 W, preferably between 100 W and 2500 W, more preferably between 150 W and 2000 W, most preferably between 200 W and 1500 W.

The combination of ultraviolet radiation with infrared radiation provides even better results, such a combination seems to intervene to improve the efficiency of removal of the oxygen groups that are attached to the graphene structure, which contributes to further improve the quality of the graphene. Final product.

The spatial temperature gradient of the gas is between 15,000 K/m and 75,000 K/m, and the reactor wall temperature is between 300 K and 1,200 K.

After nucleation of the precursor constituents, the solid nanostructures are collected, for example, in a membrane filtration device (22).

In summary, the procedure is based on injecting, into a microwave plasma reactor, a mixture (9) of at least one inert gas and at least one precursor under current.

The current is subjected to an electric field of surface waves (5), excited by the use of microwave energy (7), which is introduced, for example, into a field applicator (6), generating plasmas (2, 3, 4 ) of high energy density that break the precursor into its atomic and/or molecular constituents. These precursor constituents produced in the gas phase by the plasma in the zones (19', 20') of the reactor (see figure 2) diffuse to a zone (21') reactor nucleation, where they are added into solid nanostructures, which are then collected, for example, in a membrane filtration device (22).

Surprisingly, the use of an infrared radiation source (11) arranged in the referred nucleation zone (21') of the reactor provides high-quality nanostructures, allowing control of the number of monolayers per sheet and the percentage of carbon sp3 bonds.

The optional use of a cooling device (10) and/or a source of ultraviolet radiation, provides an even more controlled adjustment of the spatial gradients, of the temperature and of the velocity of the flow of the mixture of gas and precursor. , which favorably contributes to the decisive selection of the desired final product.

The present invention relates to a microwave plasma reactor for the fabrication of autonomous two-dimensional nanostructures.

With reference to figure 2, the reactor of the invention for the production of autonomous two-dimensional nanostructures has a hollow body (1), which body (1) comprises:

• a part (19) for launching surface waves of plasma creation,

• a part (21) of nucleation of precursor constituents and

• a transitory part (20) having the first and second ends connected, respectively, to the surface wave launching part (19) and to the nucleation part (21), providing fluid communication between these parts (19, 21). ),

wherein said parts (19, 20, 21) define, respectively, three interior operating zones (19', 20', 21') in the reactor, the reactor is characterized in that it has a cross-sectional area at the first end of said transitory part (20) smaller than in the second extreme.

In a preferred embodiment of the invention, the cross-sectional area of the transitory part (20) increases progressively from its first to its second end.

In one aspect of the reactor of the invention, said parts (19, 20, 21) are integrally connected to each other, forming a single piece.

In another preferred embodiment of the reactor of the invention, its hollow body (1) also comprises an intake part (8), to admit a mixture of at least one inert gas and at least one precursor, the intake part (8) being integrated into the part (19) for launching surface waves or coupled to the part (19) for launching surface waves through connections.

The hollow body (1) of the reactor is formed by a dielectric material selected from the group consisting of quartz, sapphire, alumina and combinations thereof.

In operation, said stream of a mixture of a gas and a precursor passes through various zones (19', 20', 21') of the reactor, the hollow body (1) of which has an increasing hollow cross-sectional area.

The procedure to produce autonomous two-dimensional nanostructures begins in the area (19') of smallest cross section (a), where surface waves are launched; following a transitory zone (20'), with a cross-sectional area that gradually increases, for example, according to the mathematical expression A = na (where n represents the ratio A/a with values between 1 and 20) (see figures 2 and 3); and finally to a nucleation zone (21'), with a cross-sectional area (A) greater than the cross-sectional area (a) of the zone (19').

This geometry of the body (1) of the reactor provides a controlled reduction of the speed and temperature of the current with a positive impact on the selective production of the desired two-dimensional nanostructures, in particular, on the significant increase in their production rate.

The present invention also relates to a system for the production of autonomous two-dimensional nanostructures.

A described system comprises:

• a microwave plasma reactor having a hollow body (1) comprising at least a surface wave launching part (19), a transient plasma formation part (20) and a nucleation part (21). of precursor constituents; Said parts (19, 20, 21) define, respectively, in the reactor three interior operating zones (19', 20', 21') that are sequentially connected in fluid communication with each other,

wherein the system further comprises

• at least one source (11) of infrared radiation outside the hollow body (1) of the plasma reactor, arranged to irradiate said interior zone (21') defined by the nucleation part (21) of said body (1). ) from the reactor.

The infrared radiation source (11) operates in a power range between 50 W and 3000 W, preferably between 100 W and 2500 W, more preferably between 150 W and 2000 W, most preferably between 200 W and 1500 W.

In an embodiment of the system, it also comprises a cooling device (10) outside the hollow body (1) of the plasma reactor, wherein the cooling device (10) is arranged to cool, at least, the area (20 ') interior defined by the transitory part (20) of said body (1) of the reactor.

The cooling device (10) operates in a temperature range between 40°C and 220°C, preferably between 40°C and 200°C, more preferably between 40°C and 180°C, most preferably between 40°C C and 150°C.

In yet another embodiment, the system also comprises a source of ultraviolet radiation on the outside of the hollow body (1) of the plasma reactor, arranged to irradiate, at least, the interior zone (21') defined by the part (21 ) for nucleation of said body (1) of the reactor. The ultraviolet radiation source operates in a power range between 50 W and 3000 W, preferably between 100 W and 2500 W, more preferably between 150 W and 2000 W, most preferably between 200 W and 1500 W.

The parts (19, 20, 21) of the body (1) of the reactor can be integrally joined together to form a single piece.

Said microwave plasma reactor body (1) is constructed from a dielectric material selected from the group comprising quartz, sapphire, alumina and similar materials and combinations thereof.

The system described could comprise:

• A microwave plasma reactor that has a hollow body (1) comprising at least:

a part (19) for launching surface waves of plasma creation,

a part (21) of nucleation of precursor constituents and

a transitory part (20) having the first and second ends connected, respectively, to the surface wave launching part (19) and the nucleation part (21), providing seamless communication between these parts (19, 21) ,

wherein said parts (19, 20, 21) define, respectively, in the body (1) of the reactor three interior operating zones (19', 20', 21'); and said first end of the transitional part (20) has a cross-sectional area less than the cross-sectional area of said second end of the transitional part (20), and

• at least one source (11) of infrared radiation outside said hollow body (1) of the reactor, arranged to irradiate the interior area (21') defined by the nucleation part (21) of said body (1). of the reactor.

In a variant of the previous embodiment, in addition to the source (11) of infrared radiation outside the hollow body (1), a cooling device (10) can also be arranged outside the body (1) of the reactor, cooling at least the interior zone (20') defined by the temporary part (20) of said body (1) of the reactor. In addition to the cooling device (10), or as an alternative to it, a source of ultraviolet radiation can also be arranged outside the hollow body (1) of the plasma reactor, to irradiate at least the zone (21'). interior defined by the nucleation part (21) of said body (1) of the reactor.

In another variant of the previous embodiment, said parts (19, 20, 21) of the body (1) of the reactor are integral with each other, forming a single piece of dielectric material. Optionally, the parts (19, 20, 21) of the body (1) of the reactor are connected to one another by means of suitable connection means known to the person skilled in the art.

The following are several examples of selective production of autonomous two-dimensional nanostructures using plasma technology according to the present invention. Of course, the examples described below should not be construed as constituting any kind of limitation on the scope of the present invention, which is defined by the independent claims.

examples

1. For the production of graphene with a production rate greater than 1 gram per hour, a plasma reactor consisting of a quartz tube was used, comprising a part (19) for launching surface waves with an internal radius of 18, 0mm, a transitional part (20), with an increasing internal radius, from 18.0mm to 75.0mm; and a nucleation part (21) was used, with an internal radius of 75.0 mm. First, a mixture composed of ethylene or acetylene as precursors, with a rate of incorporation into the mixture of 8.3 x 10.6 m3/s and argon as carrier gas, with a flow rate of 8.3 x 10-4 m3/s. Flow rates were monitored by a controller coupled to two flow meters. Next, said mixture formed by ethylene or acetylene and argon was introduced in current regime (12) through a connection (14), using an injection unit (see figure 4), in an intake part (8). of the reactor, made up of a quartz tube and installed in the part (19) for launching surface waves. Optionally, any other gas injection system capable of performing this function could be used. Subsequently, the stream of said mixture was advanced through the part (20) of a microwave plasma torch (5) induced by a surface wave at atmospheric pressure. This plasma torch comprised a microwave generator, operating at a frequency of 2.45 GHz, a waveguide system (7) including an isolator, directional couplers, and a tuner, and a type field applicator (6). surfatron. The system was closed by an adjustable component that shorted out the microwave. The microwave power provided to the plasma was 60 kW. The current is subjected to infrared radiation (IR), through a source (11) of infrared radiation operating with an applied power of 3000 W, together with ultraviolet radiation (UV), also operating with an applied power of 3000 W. IR and UV radiation was generated by an array of electric lamps. The thus formed two-dimensional graphene nanostructures were collected by means of a membrane filtering device (22) coupled to a vacuum pump.

2. For the production of germanene, with a production rate of more than 2 milligrams per hour, a plasma reactor made up of a quartz tube was used, comprising a part (19) for launching surface waves with an internal radius of 18.0 mm, a transitory part (20), with an increasing internal radius, from 18.0 mm to 32.0 mm, and a nucleation part (21), with an internal radius of 32.0 mm. The mixture used was composed of a solid precursor, in this case germanium monoxide, with a rate of incorporation into the mixture of 8.0 milligrams/hour, and argon was used as carrier gas, with a flow rate of 8.3 x 10- 5m3/s. Said mixture was injected, under current (12), into an inlet part (8) of the reactor, located in the part (19) for launching surface waves, then passing through the hot area (20') of a torch. of microwave plasma, the plasma being generated by a surface wave (5) at atmospheric pressure. The plasma torch comprised a microwave generator, operating at a frequency of 2.45 GHz, a waveguide system (7) including an isolator, directional couplers and a tuner, and a type field applicator (6). surfatron. The system was closed by an adjustable component that shorted out the microwave. The microwave power provided to the plasma was 6 kW. The quartz tube wall temperature was maintained at 220 °C using a cryostat device (10). The current was subjected to infrared radiation (IR) generated by an array of electric lamps, with an applied power of 1000 W. Finally, the two-dimensional nanostructures were collected by means of a membrane filtering device (22) coupled to a vacuum pump. .

3. For alternative production of germanene with a production rate of more than 2 milligrams per hour, the system described above (example 2) with the smallest radius of 18.0 mm and the largest of 32 was used in the system. .0mm. The mixture used was made up of a solid precursor, in this case germanium dioxide, with a rate of incorporation into the mixture of 8.0 milligrams/hour, and argon was used as the carrier gas, with a flow rate of 8.3 x 10 '5 m3/s. The plasma torch used was the same as the one described above (example 2), operating at the same frequency of 2.45 GHz, and with the same type of field applicator (6). The microwave power provided to the plasma was 6 kW. The stream was subjected to infrared (IR) radiation, generated by an array of electric lamps with an applied power of 1500 W. Finally, the two-dimensional nanostructures were collected by means of a membrane filtering device (22) coupled to a vacuum pump.

4. For the production of graphene with a production rate of approximately 0.1 grams per hour, the system consisted of a plasma reactor formed by a quartz tube that included a part (19) for launching surface waves with a 7.5mm internal radius, a transitional part (20), with increasing internal radius, from 7.5mm to 21.0mm; and a nucleation part (21) was used, with an internal radius of 21.0 mm. The system worked with a mixture made up of a gaseous precursor, in this case methane, with a rate of incorporation into the mixture of 3.3 x 10-7 m3/s and argon was used as carrier gas, with a flow rate of 6.7 x 10-5 m3/s. Flow rates were monitored by a controller coupled to two flow meters. Said mixture was injected, under current, into an inlet part (8) of the reactor located in the part (19) for launching surface waves, then passing through the hot area (20') of a microwave plasma torch. , generated by a surface wave (5) at atmospheric pressure. The plasma torch comprised a microwave generator, operating at a frequency of 2.45 GHz, a waveguide device (7) including an isolator, directional couplers and a tuner, and a type field applicator (6). surfatron. The system was closed by an adjustable component that shorted out the microwave. The microwave power provided to the plasma was 4 kW. The stream was subjected to infrared (IR) radiation generated by an array of electric lamps, with an applied power of 500 W. Finally, the two-dimensional nanostructures were collected by means of a membrane filtering device (22) coupled to a vacuum pump.

5. For the production of hexagonal boron nitride with a production rate of approximately 20 milligrams per hour, the assembly described above (example 4) with the smallest internal radius of 7.5 mm and the largest internal radius of 7.5 mm was used in the system. 21.0mm. The mixture used was made up of a gaseous precursor, in this case diborane, with a rate of incorporation into the mixture of 1.7 x 10-7 m3/s and argon was used as carrier gas, with a flow rate of 3.3 x 10 -5m3/s. The plasma torch used was the same as that described above (example 4), operating at the same frequency of 2.45 GHz, and with the same type of field applicator (6). The power of microwave provided to the plasma was 2 kW. The stream was subjected to infrared (IR) radiation, generated by an array of electric lamps, with an applied power of 1000 W. Finally, the two-dimensional nanostructures were collected by means of a membrane filtering device (22) coupled to a vacuum pump.

6. For the production of graphene with a production rate of approximately 2 milligrams per hour, the system consisted of a plasma reactor made up of a quartz tube comprising a part (19) for launching surface waves with an internal radius of 7.5 mm, a transitory part (20), with a constant inner radius of 7.5 mm, and a nucleation part (21) was used, with the same inner radius of 7.5 mm. The system worked with a mixture composed of a liquid precursor, in this case ethanol, which, after being vaporized by means of an ultrasonic bath, had a rate of incorporation into the mixture of 1.7 x 10-8 m3/s. argon as carrier gas, with a flow rate of 4.2 x 10-6 m3/s. Flow rates were monitored by a controller coupled to two flow meters. Said mixture was injected, under current, into an inlet part (8) of the reactor located in the part (19) for launching surface waves, then passing through the hot area (20') of a microwave plasma torch. , generated by a surface wave (5) at atmospheric pressure. The plasma torch included a microwave generator, operating at a frequency of 2.45 GHz, a waveguide device (7) including an isolator, directional couplers and a tuner, and a type field applicator (6). surfatron. The system was closed by an adjustable component that shorted out the microwave. The microwave power delivered to the plasma was 0.4 kW. The quartz tube wall temperature was maintained at 60 °C using a cryostat device. The current was subjected to infrared (IR) radiation, operating with an applied power of 50 W, along with ultraviolet (UV) radiation, also operating with an applied power of 50 W, the IR and UV radiation was generated by an array of lamps. electrical. Finally, the two-dimensional nanostructures were collected by means of a membrane filtering device (22) coupled to a vacuum pump.

7. For the production of graphene with a production rate of approximately 1 milligram per hour, the previously described assembly (Example 6) with a constant internal radius of 7.5 mm in all areas was used in the system (19, 20 , twenty-one). The system worked with a mixture composed of a liquid precursor, in this case butanol or propanol, which, after being vaporized by means of an ultrasonic bath, had a rate of incorporation into the mixture of 1.7 x 10-8 m3/s and was used argon as carrier gas, with a flow rate of 4.2 x 10-6 m3/s. The plasma torch used was the same as that described above (example 6), operating at the same frequency of 2.45 GHz, and with the same type of field applicator (6). The microwave power delivered to the plasma was 0.4 kW. The quartz tube wall temperature was maintained at 40 °C using a cryostat device. The stream was subjected to infrared (IR) radiation, generated by an array of electric lamps with an applied power of 50 W. Finally, the two-dimensional nanostructures were collected by means of a membrane filtering device (22) coupled to a vacuum pump.

8. For the production of graphene with a production rate of approximately 1 gram per hour, a plasma reactor consisting of a quartz tube comprising a surface wave launching part (19) with an internal radius of 18, was used. 0mm, a transitional part (20), with an increasing internal radius, from 18.0mm to 32.0mm; and a nucleation part (21) was used, with an internal radius of 32.0 mm. First, a mixture composed of ethylene as a precursor was produced, with an incorporation rate in the mixture of 8.3 x 10-6 m3/s, and a mixture of carrier gases composed of 90% argon with 5% carbon dioxide. helium and 5% neon, with a total flow rate of 3.3 x 10-4 m3/s. Flow rates were monitored by a controller coupled to two flow meters. Next, said mixture formed by ethylene with the carrier gases was introduced in a current regime (12) through a connection (14), using an injection unit (see figure 4), in an intake part (8). of the reactor, made up of a quartz tube and installed in the part (19) for launching surface waves. Subsequently, the stream of said mixture was advanced through part (20) of a microwave plasma torch generated by a surface wave (5) at atmospheric pressure. This plasma torch comprises a microwave generator, operating at a frequency of 2.45 GHz, a waveguide device (7) including an isolator, directional couplers and a tuner, and a type field applicator (6). surfatron. The system was closed by an adjustable component that shorted out the microwave. The microwave power supplied to the plasma was 20 kW. The stream was subjected to infrared (IR) radiation through a source (11) of infrared radiation generated by electric IR lamp arrays, operating with an applied power of 2500 W. The two-dimensional graphene nanostructures thus formed were collected using a extraction device.

9. For the production of N-graphene with a production rate of approximately 1 gram per hour, a plasma reactor formed by a quartz tube was used, comprising a part (19) for launching surface waves with an internal radius of 18.0mm, a transitional part (20), with an increasing internal radius, from 18.0mm to 75.0mm; and a nucleation part (21) was used, with an internal radius of 75.0 mm. The system worked with a mixture made up of a carrier gas, in this case argon, with a flow rate of 3.3 x 10-4 m3/s and two precursors, a liquid precursor, in this case ethanol, plus a gaseous precursor, in this case. In the nitrogen case, the ethanol after being vaporized by means of an ultrasonic bath, had a rate of incorporation into the mixture of 7.5 x 10-6 m3/s. Nitrogen had a rate of incorporation into the mixture of 8.3 x 10 -7 m3/s. Flow rates were monitored by a controller coupled to two flow meters. Next, said mixture formed by the carrier gas plus the two precursors was introduced in a current regime (12) through a connection (14), by means of an injection unit (see figure 4), in a part (8) admission of the reactor, made up of a quartz tube and installed in the part (19) for launching surface waves. Subsequently, the stream of said mixture was advanced through the part (20) of a microwave plasma torch generated by a surface wave (5) at atmospheric pressure. this torch The plasma generator comprised a microwave generator, operating at a frequency of 2.45 GHz, a waveguide device (7) including an isolator, directional couplers, and a tuner, and a surfatron-type field applicator (6). The system was closed by an adjustable component that shorted out the microwave. The microwave power provided to the plasma was 6 kW. The stream was subjected to infrared (IR) radiation through a source (11) of infrared radiation generated by arrays of electric IR lamps, operating with an applied power of 2000 W. The two-dimensional graphene nanostructures thus formed were collected using a extraction device.

Figure 5 shows a scanning electron microscopy (SEM) image, obtained from the result of the selective synthesis of graphene sheets, controlled by strong axial gradients of temperature and gas velocity. On the other hand, Figure 7 shows an SEM image obtained by non-selective synthesis of carbon nanostructures (carbon nanoparticles, graphene nanosheets and nanodiamonds) carried out under conditions of reduced and/or uncontrolled axial temperature/velocity gradients. . SEM characterization was performed using a field emission gun scanning electron microscope, operating in secondary electron imaging mode with applied voltages in the (10-15) kV range.

Figure 6 shows a high-resolution transmission electron microscopy (HRTEM) image, obtained using graphene sheets synthesized with the system described herein. The image was obtained using an HRTEM microscope, operating at an accelerating voltage of 200 kV. As can be seen, the edges of the sheets are clearly folded upwards, making it possible to determine the number of atomic layers in each sheet. The HRTEM image revealed that many of the sheets are single atomic layers, some of the monolayers are identified by arrows in the figure.

Claims (8)

1. Microwave plasma reactor for the production of graphene, wherein the reactor has a hollow body (1) comprising: • a part (19) for launching surface waves of plasma creation, • a part (21) of nucleation of precursor constituents and • a transitory part (20) having the first and second ends connected, respectively, to the surface wave launching part (19) and to the nucleation part (21), providing fluid communication between these parts (19, 21). , so that in operation said parts (19, 20, 21) define, respectively, in the body (1), three internal zones of operation (19', 20', 21'), characterized in that the first end of the transitional part (20) has a cross-sectional area that is less than the cross-sectional area of the second end. Plasma reactor according to claim 1, characterized in that the cross-sectional area of the transitional part (20) increases progressively from its first to its second end. 3. Plasma reactor according to claim 1 or 2, characterized in that said parts (19, 20, 21) are integral with each other, forming a single piece. 4. Plasma reactor according to any of claims 1 to 3, characterized in that its hollow body (1) is formed by a dielectric material selected from the group consisting of quartz, sapphire, alumina and combinations thereof. 5. Plasma reactor according to any of claims 1 to 4, characterized in that its hollow body (1) further comprises a part (8) for admitting a mixture of at least one inert gas and at least one precursor, the part being (8) for admission integrated into the part (19) for launching surface waves or coupled to the part (19) for launching surface waves through connections. Plasma reactor according to any of claims 1 to 5, characterized in that it further comprises at least one source (11) of infrared radiation outside said hollow body (1) of the plasma reactor, the source being arranged ( 11) of infrared radiation to irradiate the interior zone (21') defined by the nucleation part (21) of said reactor body (1). 7. Plasma reactor according to claim 6, characterized in that it further comprises a cooling device (10) outside the body (1) of the reactor, wherein the cooling device (10) is arranged to cool, at least , the interior zone (20') defined by the transitory part (20) of said body (1) of the reactor. 8. Plasma reactor according to claim 7, characterized in that it further comprises an ultraviolet radiation source outside the hollow body (1) of the plasma reactor, said ultraviolet radiation source arranged to irradiate at least the area (21 ') interior defined by the nucleation part (21) of the referred body (1) of the reactor.