Systems and methods for supercritical fluid promoted exfoliation and extraction

Abstract

A method for producing a high quality exfoliated layered material may include: filling a powder of a layered material into a variable volume reactor; injecting a pressurized fluid into the variable volume reactor; increasing the temperature of the variable volume reactor to a predetermined temperature; increasing the pressure of the variable volume reactor to a pressure above a critical pressure of the pressurized fluid at the predetermined temperature by reducing the volume of the variable volume reactor; obtaining an embedded layered material powder by maintaining temperature and pressure conditions within the variable volume reactor for a predetermined amount of time; and exfoliating the embedded layered material powder by expanding the pressurized fluid within the variable volume reactor by increasing the volume of the variable volume reactor. The reactor and method may be configured to perform supercritical extraction as well as nanoparticle production processes.

Description

Technical Field

[0001] The present disclosure relates to the production of nanomaterials, and in particular to the mass production of single-layer nanomaterials such as graphene nanosheets. More specifically, the present disclosure relates to a system and method for supercritical fluid-facilitated exfoliation of layered materials such as graphite. Background Art

[0002] Graphene is a sp 2 A single-layer two-dimensional hexagonal crystal array of elemental carbon atoms formed by hybridized C-C bonds. Graphene exhibits excellent mechanical, electrical, optical and thermal properties, which make it suitable for the preparation of sensitive sensors, energy storage devices, composites, conductive inks and biomedical products.

[0003] Various methods such as chemical exfoliation approach and reduction of graphene oxide (GO) by chemical oxidation of graphite can be used for mass production of graphene. However, the graphene obtained by this method contains a large number of lattice defects and oxygen-containing groups, resulting in poor mechanical, electronic and optical properties. In addition, chemical exfoliation methods use toxic chemicals and produce hazardous waste. In addition, these methods involve several steps and require 3 to 5 days to allow the intercalant and organic solvent to be fully inserted into the graphite layer.

[0004] In order to solve the lattice defects and oxygen content in the chemical exfoliation method, the liquid phase exfoliation (LPE) method has been developed to produce native and defect-free graphene. In the LPE method, the solvent is embedded in the interlayer of graphite and the graphite is exfoliated into isolated sheets. However, there are some problems with the LPE method, such as low yield, time-consuming process and the use of expensive and toxic high-boiling organic solvents.

[0005] Other methods for producing graphene sheets with high quality may include chemical vapor deposition (CVD) methods and thermal decomposition of silicon carbide (SiC), which is also known as epitaxial growth. However, the complexity of the process, high temperature and vacuum conditions, low productivity and high cost limit the possibility of industrialization of such methods. In addition, in these methods, the transfer process between different substrates may also induce additional defects. In terms of epitaxial growth, the production of high-quality graphene films requires a single-crystalline SiC substrate, which increases the cost of the process.

[0006] Another method for exfoliating and embedding layered materials such as graphite and clay is to utilize supercritical CO2 exfoliation technology. In the supercritical CO2 exfoliation method, pressurized supercritical CO2 can be inserted between graphite layers to embed graphite due to its high diffusivity, low viscosity and zero surface tension. Then, a rapid decompression step can allow the graphene sheets or layers to be peeled off from the embedded graphite. Here, the supercritical CO2 between the layers expands due to the decompression step, and thus the distance between the layers increases, which leads to effective exfoliation of the graphite. In this method, the decompression rate is a key factor.

[0007] Supercritical CO2 exfoliation is a physical process and produces high-quality native defect-free graphene, and the oxygen content of graphite (raw material) does not increase during the production process, whereas the oxygen content increases in chemical exfoliation methods due to the use of strong oxidants or in CVD methods due to high temperature processes. In addition, compared with other methods, this method is not a time-consuming process, and the method takes less than 4 hours. This green process is carried out at a low temperature process of less than 70°C, and CO2 is separated from graphene during the decompression step. Therefore, unlike chemical exfoliation and LPE methods, this green process does not produce hazardous waste. However, one disadvantage of supercritical CO2 exfoliation is that it is difficult to scale up the process to produce larger amounts of graphene. Therefore, it is necessary to develop a system and method for supercritical fluid-promoted exfoliation that can allow large-scale production of high-quality graphene. Summary of the invention

[0008] The present invention content is intended to provide an overview of the subject matter of the present disclosure, and is not intended to identify the necessary elements or key elements of the subject matter, nor is it intended to be used to determine the scope of the embodiments claimed. The proper scope of the present disclosure can be ascertained from the claims set forth below in view of the specific embodiments and the accompanying drawings.

[0009] According to one or more exemplary embodiments, the present disclosure relates to a supercritical fluid-facilitated exfoliation method. The exemplary method may include: filling a layered material powder into a variable volume reactor. The exemplary variable volume reactor may include: an elongated shell; a piston movably disposed within the elongated shell, wherein the exemplary piston may divide the interior of the elongated shell into a first chamber and a second chamber. Filling the exemplary layered material powder into the exemplary variable volume reactor may include: filling the exemplary layered material powder into the exemplary first chamber.

[0010] The exemplary method may also include: injecting the pressurized gas into the exemplary first chamber; increasing the temperature of the exemplary first chamber to a predetermined temperature by heating the exemplary first chamber; and increasing the pressure of the exemplary first chamber to a pressure above a critical pressure of the exemplary pressurized gas by injecting hydraulic fluid into the exemplary second chamber. In response to injecting the exemplary hydraulic fluid into the exemplary second chamber, the exemplary piston may move toward the exemplary first chamber, thereby reducing the volume of the exemplary first chamber.

[0011] The exemplary method may also include obtaining an embedded layered material powder by embedding an exemplary pressurized gas between layers of an exemplary layered material powder, wherein embedding the exemplary pressurized gas between layers of the exemplary layered material powder may include maintaining the temperature and pressure conditions within the exemplary first chamber for a predetermined amount of time.

[0012] The exemplary method may also include: exfoliating the exemplary embedded layered material powder by expanding the exemplary pressurized gas within the exemplary first chamber, wherein expanding the exemplary pressurized gas within the exemplary first chamber may include discharging the exemplary hydraulic fluid from the exemplary second chamber. In response to discharging the exemplary hydraulic fluid from the exemplary second chamber, the exemplary piston may move toward the exemplary second chamber, thereby increasing the volume of the exemplary first chamber.

[0013] According to one or more exemplary embodiments, the present disclosure relates to a system for producing a peelable layered material. The exemplary system may include: an elongated shell; a piston movably disposed in the exemplary elongated shell, the piston dividing the inner volume of the exemplary elongated shell into a first chamber and a second chamber; a powder inlet port, the powder inlet port is connected to the exemplary first chamber in a powder-connected manner, wherein the exemplary powder inlet port can be configured to allow powder to be introduced into the exemplary first chamber. The exemplary system may also include: a gas injection port, which can be connected to the exemplary first chamber in a fluid-connected manner. The exemplary gas injection port can be configured to allow gas to be injected into the exemplary first chamber.

[0014] The exemplary system may also include: a hydraulic mechanism that can be connected to the exemplary second chamber in a fluid-connected manner. The exemplary hydraulic mechanism can be configured to cause the exemplary piston to move along the longitudinal axis of the exemplary elongated housing. The exemplary hydraulic mechanism may include: a hydraulic fluid reservoir and a hydraulic pump, the hydraulic fluid reservoir containing hydraulic fluid, and the hydraulic pump can be connected between the exemplary hydraulic fluid reservoir and the exemplary second chamber. The exemplary hydraulic pump can be configured to pump the exemplary hydraulic fluid into the exemplary second chamber and pump out the exemplary second chamber. In response to pumping the exemplary hydraulic fluid into the exemplary second chamber, the exemplary piston can move toward the exemplary first chamber. In response to pumping the hydraulic fluid out of the exemplary second chamber, the exemplary piston can move toward the exemplary second chamber. The exemplary system may also include: a temperature control mechanism that can be connected to the elongated housing. The exemplary temperature control mechanism can be configured to control the temperature of the exemplary first chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The novel features which are believed to be characteristic of the present disclosure, as to its structure, organization, use and method of operation, together with further objects and advantages thereof, will be better understood from the following drawings, in which present exemplary embodiments of the present disclosure are shown by way of example. It is to be expressly understood, however, that the drawings are for illustration and description only and are not intended as a definition of the limits of the present disclosure. Embodiments of the present disclosure will now be described by way of example with reference to the accompanying drawings, in which:

[0016] Figure 1 A schematic diagram of a system for producing high-quality exfoliated layered materials consistent with one or more exemplary embodiments of the present disclosure is shown;

[0017] Figure 2 A flow chart showing a supercritical fluid-facilitated exfoliation method for producing high-quality nanomaterials consistent with one or more exemplary embodiments of the present disclosure is shown;

[0018] Figure 3 shows Raman spectra of artificial graphite and native graphene nanosheets consistent with one or more exemplary embodiments of the present disclosure;

[0019] Figure 4 showing an atomic force microscope (AFM) image of graphene nanosheets produced consistent with one or more exemplary embodiments of the present disclosure; and

[0020] Figure 5 Transmission electron microscopy (TEM) images of produced graphene nanosheets consistent with one or more exemplary embodiments of the present disclosure are shown. DETAILED DESCRIPTION

[0021] The novel features which are believed to be characteristic of the disclosure, as to its structure, organization, use, and method of operation, together with further objects and advantages thereof, will be better understood from the following discussion.

[0022] In general, supercritical CO2 exfoliation techniques may involve exposing a graphite material to supercritical CO2 in a pressurized container for a predetermined period of time, and then exfoliating graphene sheets or layers from the intercalated graphite by rapidly depressurizing the container to ambient pressure. As mentioned previously, the rate of depressurization plays an important role in effectively exfoliating the graphite.

[0023] Current methods for producing graphene by supercritical CO2 exfoliation are typically utilized on a small scale because most systems and methods utilize valves (such as ball valves) to rapidly depressurize the container in which graphite is exposed to supercritical CO2. For larger scales, a relatively large amount of CO2 must be released via the valve in a relatively short period of time. Due to the Joule-Thomson effect, during the rapid discharge of gas from the container, the temperature drops sharply, which may lead to blockage of the valve and inconsistency of the discharge flow rate. This blockage may lead to longer discharge times, and as mentioned above, rapid discharge of gas is crucial for the successful exfoliation of graphite. In addition, the sharp drop in temperature during the decompression step may sometimes be as high as 100°C, which may damage the seal of the valve. Not to mention, the discharge of the mixture of CO2 and powder through the restricted flow path of the ball valve may further cause blockage in the valve.

[0024] Furthermore, in large-scale production, the release of a large amount of CO2 in a short period of time through a valve may be similar to the release of a large amount of gas through a pressure relief valve. Such a release of a large amount of gas requires special equipment for control and safety. To better understand the necessity of controlling such an operation, imagine that at 40°C, a volume of 1m 3 The reactor with a pressure of 120 bar was depressurized instantaneously. The reactor contained supercritical CO2 (717.8 kg CO2, 365.4 m 3 Normal volume) and powder. For comparison, at ambient temperature (20°C), a normal CO2 cartridge has a volume of 50 liters (34 kg CO2, 17.3 m 3 Normal volume) and a pressure of about 55 to 60 bar. This comparison shows the unusual conditions that would arise if one tried to scale up a conventional supercritical CO2 stripping system.

[0025] A large amount of CO2 is released during this process, increasing CO2 emissions. Since the CO2 pressure is reduced to ambient pressure, a cryogenic cooling system and pressurization by CO2 pumps will be necessary in order to capture and recover atmospheric CO2. Therefore, capturing and recovering CO2 may become expensive and energy-intensive.

[0026] The conversion yield of graphite exfoliated in one stage to graphene is usually low and the number of graphene layers is high, which means that the produced graphene is of low quality. To solve this problem, the exfoliation step needs to be repeated several times, which means that a large amount of CO2 must be consumed as raw material. Not to mention that after each exfoliation step, a large amount of CO2 must be released into the atmosphere. In addition, after each exfoliation step, the produced graphene powder must be collected from the container, and then the graphite powder must be reloaded into the high-pressure container, which is time-consuming.

[0027] The present disclosure relates to exemplary embodiments of systems and methods for performing supercritical fluid-promoted exfoliation of layered materials such as graphite to produce high-quality nanomaterials such as graphene. Exemplary systems and methods can utilize supercritical fluid-promoted exfoliation techniques in variable volume reactors to produce graphene from graphite powder. Such utilization of exemplary variable volume reactors can allow supercritical CO2 exfoliation techniques to be performed on a larger scale without facing any of the problems mentioned in the preceding paragraphs. The exemplary system can be further used to produce other exfoliated materials, such as hexagonal boron nitride (h-BN), tungsten disulfide (WS2), molybdenum disulfide (MoS2), etc.

[0028] An exemplary system for producing high-quality exfoliated layered materials can include a variable volume reactor, which can be a rodless piston-cylinder system, in which a pressurized gas (such as supercritical CO2) can be inserted between the layers of the exemplary layered material to obtain an exemplary embedded material. The exemplary variable volume reactor can be a jacketed reactor, in which the fluid circulation system of the exemplary jacket connected to the exemplary jacketed variable volume reactor can be used to control the temperature of the exemplary variable volume reactor. In the exemplary system, the exemplary rodless piston can divide the inner volume of the exemplary cylinder into two chambers. The first chamber can be used as an exemplary variable volume reactor for exposing layered material powder to supercritical CO2, and the second chamber can be used to load and discharge high-pressure hydraulic fluid to change the volume of the exemplary first chamber. As used herein, a cylinder can refer to a cylindrical shell or a conical shell.

[0029] An exemplary method for performing supercritical fluid-facilitated exfoliation may include: a step of filling an amount of layered material powder within an exemplary first chamber of an exemplary system; a step of injecting a pressurized gas (such as carbon dioxide) into the exemplary first chamber from a pressurized gas source (such as a pressurized gas cylinder connected in fluid communication with the exemplary first chamber); a step of increasing the temperature of the exemplary first chamber to a predetermined temperature by utilizing an exemplary circulation system; a step of increasing the pressure of the exemplary first chamber to a pressure above the critical pressure of the exemplary injected gas by reducing the volume of the exemplary first chamber. The volume of the exemplary first chamber may be reduced by injecting a high-pressure hydraulic fluid into an exemplary second chamber of the exemplary system to push the exemplary rodless piston toward the pressurized gas side of the exemplary rodless piston. The exemplary method for performing supercritical fluid-facilitated exfoliation may also include: a step of maintaining the pressure and temperature conditions within the exemplary first chamber at the supercritical conditions of the pressurized gas within the exemplary first chamber to insert the pressurized gas molecules between the layers of the exemplary layered material within the exemplary first chamber. In other words, the exemplary method for performing supercritical fluid-facilitated exfoliation may also include an embedding step, which may involve maintaining the pressure and temperature conditions within the exemplary first chamber at supercritical conditions of the pressurized gas within the exemplary first chamber to insert the pressurized gas molecules between layers of the exemplary layered material within the exemplary first chamber.

[0030] In the exemplary method, after the embedding step, instead of quickly releasing the exemplary pressurized gas from the exemplary first chamber as is commonly done in the art, the exemplary pressurized hydraulic fluid within the exemplary second chamber is quickly discharged, which can result in a sudden expansion of the exemplary pressurized gas within the exemplary first chamber. Such rapid expansion of the gas within the exemplary first chamber can result in the peeling of a single layer of the exemplary layered material. Here, the exemplary steps can be repeated several times to ensure a high yield of the peeling process.

[0031] In exemplary embodiments, such rapid expansion of the gas within the exemplary variable volume reactor, rather than by utilizing a valve to rapidly discharge the exemplary pressurized gas, can allow all of the mentioned problems associated with rapid discharge of the exemplary pressurized gas, such as valve clogging and seal breakage, to be overcome. In addition, in exemplary embodiments, since the exemplary pressurized gas is not discharged into the atmosphere, the exemplary pressurized gas can be reused repeatedly.

[0032] For example, in the case of utilizing supercritical carbon dioxide, in the exemplary method, the pressurized carbon dioxide may not be released into the environment, but the exemplary pressurized carbon dioxide may be decompressed within the exemplary variable volume reactor. Here, in order to prepare an exemplary system for repeating the stripping step, the pressure of the carbon dioxide gas may be simply increased by pumping an exemplary hydraulic fluid into the exemplary second chamber. In other words, the exemplary system may be pressurized and decompressed by loading and discharging the exemplary hydraulic fluid rather than loading and discharging the exemplary pressurized gas. Since the density of the exemplary hydraulic fluid may be 1000 times the density of the exemplary pressurized gas, the flow rate of discharging the exemplary hydraulic fluid from the exemplary system may be 1000 / 1 of the flow rate of discharging the exemplary pressurized gas. Such lower flow rates may address the safety and control issues of conventional supercritical CO2 stripping systems.

[0033] Figure 1 A schematic diagram of a system 100 for producing high-quality exfoliated layered materials consistent with one or more exemplary embodiments of the present disclosure is shown. In an exemplary embodiment, the system 100 may include a variable volume reactor 102, which can be used vertically or horizontally to perform supercritical gas exfoliation technology. In an exemplary embodiment, the variable volume reactor 102 may include an elongated shell 104 and a piston 106, which is movably disposed within the elongated shell 104. In an exemplary embodiment, the piston 106 can divide the inner volume of the elongated shell 104 into a first chamber 108 and a second chamber 110. In an exemplary embodiment, the piston 106 can be a rodless piston because the piston 106 is not connected to any external actuator and can be caused to move along the longitudinal axis 103 of the elongated shell 104 in response to the pressure difference between the first chamber 108 and the second chamber 110. For example, the variable volume reactor 102 can be configured as a cylinder-piston mechanism, wherein the elongated housing 104 can be an elongated cylinder or cone, and the piston 106 can be an annular piston disposed within the elongated cylinder that divides the elongated cylinder or cone into two cylindrical or conical chambers, such as a first chamber 108 and a second chamber 110. In an exemplary embodiment, an O-ring 107 can be used to enable the piston 106 to move along the longitudinal axis 103 while maintaining a fluid-tight seal between the first chamber 108 and the second chamber 110. In an exemplary embodiment, the elongated housing 104 can be an elongated open-ended cylinder that can be sealed by utilizing a cap 146. In other words, the elongated housing 104 can include a closed-end cone.

[0034] In an exemplary embodiment, a layered material powder (such as graphite powder) and a pressurized gas (such as pressurized CO2) can be introduced into the first chamber 108, while a pressurized hydraulic fluid (such as water) can be introduced into the second chamber 110. In an exemplary embodiment, the linear movement of the piston 106 along the longitudinal axis 103 of the elongated housing 104 can be controlled by changing the pressure within the second chamber 110 by charging and discharging the hydraulic fluid into the second chamber 110. For example, charging the hydraulic fluid into the second chamber 110 can cause the piston 106 to move toward the first chamber 108, and thereby reduce the volume of the first chamber 108 and compress the contents of the first chamber 108. At the same time, discharging the hydraulic fluid from the second chamber 110 can cause the piston 106 to move back toward the second chamber 110, and thereby increase the volume of the first chamber 108 and expand the contents of the first chamber 108.

[0035] In an exemplary embodiment, a mixture of gas and powder may be introduced into a first chamber 108 on one side of the piston 106, and pressurized hydraulic fluid may be introduced into a second chamber 110 on the opposite side of the piston 106. Here, an O-ring 107 may prevent the pressurized hydraulic fluid from leaking into the first chamber 108.

[0036] In an exemplary embodiment, the hydraulic fluid can be water, a mixture of water and ethylene glycol, hydraulic oil, high temperature oil, or any other high boiling point liquid that can be pumped into the second chamber 110, as will be discussed. In an exemplary embodiment, the variable volume reactor 102 can be used to exfoliate various layered materials, such as graphite powder, hexagonal boron nitride (h-BN), tungsten disulfide (WS2), and molybdenum disulfide (MoS2) powder. In an exemplary embodiment, the pressurized gas that can be heated and compressed to its supercritical condition can be CO2 or any other suitable fluid, such as water, ethanol, methanol, propanol, methane, ethane, propane, butane, ethylene, or a mixture thereof. In an exemplary embodiment, additives such as surfactants, stabilizers, coating agents, and / or reactive substances such as ozone, oxygen, acid vapor, or SO3 can be further added to the pressurized gas.

[0037] In an exemplary embodiment, the system 100 may also include a temperature control mechanism that may be coupled to the variable volume reactor 102 and may be configured to regulate and control the temperature within the variable volume reactor 102, particularly within the first chamber 108. In an exemplary embodiment, the temperature control mechanism may include a jacket 112 that may surround the outer surface of the elongated housing 104, wherein the jacket 112 may be connected in fluid communication with a water circulation system 115. In an exemplary embodiment, the water circulation system 115 may be configured to control the temperature of the variable volume reactor 102 by circulating water at a predetermined temperature within the jacket 112. In an exemplary embodiment, the water circulation system 115 may include: a water tank 116, which is heated by a heater 118 that may be disposed within the water tank 116; a water thermocouple 120, which may be configured to measure the temperature of the water within the water tank 116, and may be further connected in communication with a temperature controller 121. In an exemplary embodiment, the temperature controller 121 may be configured to control the temperature of the water within the water tank 116 at a given set point using the heater 118. In an exemplary embodiment, the water circulation system 115 may include a circulation pump 122, which may be connected between the water tank 116 and the jacket 112 and may be configured to circulate water within the jacket 112. For example, the temperature of the circulating water within the jacket 112 may be adjusted by using the temperature controller 121, so that the operating temperature within the first chamber 108 may be adjusted to a temperature within a range of 31° C. to 90° C. For example, the operating temperature within the first chamber 108 may be adjusted to a temperature of approximately 40° C.

[0038] In an exemplary embodiment, the variable volume reactor 102 may also include a powder inlet port 114 that may be connected to the first chamber 108 in a powder communication manner, wherein the powder inlet port 114 may be configured to allow a powder (such as graphite powder) to be introduced into the first chamber 108. In an exemplary embodiment, the powder inlet port 114 may be equipped with an on / off ball valve, and the exemplary powder may be poured into the first chamber 108 through the ball valve using a funnel. In an exemplary embodiment, after the powder is introduced into the first chamber 108, the powder inlet port 114 may be closed.

[0039] In an exemplary embodiment, the variable volume reactor 102 may also include a gas injection port, which may be equipped with a gas injection valve 128, which may be connected to the first chamber 108 in a fluid-connected manner, wherein the gas injection valve 128 may be configured to allow pressurized gas (such as pressurized CO2) to be introduced into the first chamber 108. To this end, in an exemplary embodiment, the gas injection port may be connected to a pressurized gas reservoir 126 (such as a pressurized gas cylinder) in a fluid-connected manner, and the fluid communication between the gas injection port and the pressurized gas reservoir 126 may be intercepted by the gas injection valve 128 and an optional gas filter 132, which may be configured to remove unwanted impurities from the gas stream. As used herein, the fluid communication intercepted by the valve may refer to a valve configured to connect and disconnect the fluid communication. In other words, pressurized CO2 or any other desired gas may be supplied to the first chamber 108 of the variable volume reactor 102 from a pressurized gas source.

[0040] In the case of pressurized CO2, the pressurized gas reservoir 126 may contain a mixture of liquid and gaseous CO2 at a pressure in the range of 5 bar to 73 bar. For example, the pressurized gas reservoir 126 may contain a mixture of liquid and gaseous CO2 at a pressure of about 35 bar. In an exemplary embodiment, in response to the gas injection valve 128 being opened, the gaseous CO2 may be gradually drawn out from the top of the pressurized gas reservoir 126 and may be introduced into the first chamber 108. In an exemplary embodiment, in response to the pressurized gas being gradually introduced into the first chamber 108, the piston 106 may be urged to move toward the second chamber 110, wherein the piston 106 may reach the extreme end of the elongated housing 104. In this state where the piston 106 is pushed toward the second chamber 110 in response to the pressurized gas being injected into the first chamber 108, the volume of the first chamber 108 may reach a maximum value, and the volume of the second chamber 110 may reach a minimum value close to zero. After a predetermined period of time, for example, after 5 minutes, the gas injection valve 128 may be closed. At this point, the pressures in the first chamber 108 and the pressurized gas reservoir 126 are equal.

[0041] In an exemplary embodiment, a pressure gauge 130 and a reactor thermocouple 124 may be coupled to the first chamber 108 to monitor the pressure and temperature of the first chamber 108. For example, when pressurized CO2 is used to perform the stripping technique, when the pressurized CO2 is initially injected into the first chamber 108 and the gas injection valve 128 is closed, the temperature of the variable volume reactor 102 may be set at a temperature in the range of 31° C. to 300° C. by utilizing the temperature control mechanism of the system 100, and the pressure may be in the range of 5 bar to 73 bar. For example, the temperature of the variable volume reactor 102 may be set at 40° C. by utilizing the temperature control mechanism of the system 100, and the pressure may be approximately 20 bar.

[0042] In an exemplary embodiment, the system 100 can be further coupled to a hydraulic mechanism that can be connected in fluid communication with the second chamber 110, wherein the hydraulic mechanism can be configured to cause the piston 106 to move along the longitudinal axis 103 of the elongated housing 104 and thereby compress the contents of the first chamber 108. In other words, the volume of the first chamber 108 can be reduced by causing the piston 106 to move toward the first chamber 108, wherein the pressure within the first chamber 108 can be increased in response to the reduction in volume caused by the movement of the piston 106.

[0043] In an exemplary embodiment, the hydraulic mechanism may include a hydraulic fluid reservoir that may contain a hydraulic fluid. In an exemplary embodiment, the water tank 116 may further be configured to function as a hydraulic fluid reservoir if the fluid circulating in the jacket 112 and the hydraulic fluid used to move the piston 106 are similar. For example, both the circulating fluid and the pressurized hydraulic fluid may be water. However, in exemplary embodiments where the circulating fluid and the pressurized hydraulic fluid are not the same, a separate hydraulic fluid reservoir must be utilized.

[0044] In an exemplary embodiment, the hydraulic mechanism may further include a hydraulic pump 134, which may be connected between a hydraulic fluid reservoir (e.g., a water tank 116) and the second chamber 110. In an exemplary embodiment, the hydraulic pump 134 may be configured to pump hydraulic fluid into the second chamber 110. In an exemplary embodiment, in response to the hydraulic fluid being pumped into the second chamber 110, the piston 106 may move toward the first chamber 108. In an exemplary embodiment, the pressure in the first chamber 108 may be increased to a pressure in the range of 73 bar to 400 bar (e.g., 130 bar). In an exemplary embodiment, the hydraulic mechanism may further include a back pressure regulator 136 that may be configured to adjust a target pressure. In an exemplary embodiment, when the target pressure is reached in the first chamber 108, the flow of hydraulic fluid may be diverted back to the hydraulic fluid reservoir. For example, in the case of using water as the hydraulic fluid, the water may be diverted back to the water tank 116 after the target pressure is reached.

[0045] In an exemplary embodiment, in the case of using CO2, when CO2 is pressurized in response to the movement of the piston 106, the temperature of CO2 may be increased during a short period of time when pressurized by the hydraulic fluid, and then the temperature of CO2 is reduced to the target temperature in a short period of time. In other words, the heat generated by the pressurization of CO2 can be quickly dissipated into the circulating water in the jacket 112. During the temperature reduction to the target operational temperature, the CO2 pressure may be slightly reduced, which can be compensated by charging the hydraulic fluid into the second chamber 110 using the hydraulic pump 134.

[0046] In an exemplary embodiment, the pressurized gas within the first chamber 108 can be maintained at its critical condition for a predetermined amount of time by utilizing the hydraulic mechanism and temperature control mechanism of the system 100. For example, in the case of graphite intercalation utilizing supercritical CO2, the CO2 can be maintained at its supercritical condition of 73 bar to 400 bar and 31° C. to 300° C. for a predetermined amount of time. For example, the CO2 can be maintained at its supercritical condition of 130 bar and 40° C. for a predetermined amount of time. During this period, the supercritical CO2 can be intercalated between the graphite layers.

[0047] In an exemplary embodiment, the variable volume reactor 102 may also include a fluid discharge port connected in fluid communication with the second chamber 110. In an exemplary embodiment, the fluid discharge port may be blocked by a fluid discharge valve 140, which may be an on / off ball valve. In an exemplary embodiment, the fluid discharge valve may block fluid communication between the second chamber 110 and a hydraulic fluid reservoir (e.g., a water tank 116), and may be configured to allow rapid discharge of hydraulic fluid from the second chamber 110 into the hydraulic fluid reservoir.

[0048] In an exemplary embodiment, after the pressure and temperature within the first chamber 108 are maintained for a predetermined amount of time to intercalate supercritical gas molecules between the layers of the layered powder material within the first chamber 108, the fluid discharge valve 140 can be opened to quickly discharge hydraulic fluid from the second chamber 110. In an exemplary embodiment, opening the fluid discharge valve 140 can result in rapid discharge of hydraulic fluid from the second chamber 110, which in turn can result in rapid expansion of the supercritical gas within the first chamber 108. Such rapid expansion can result in exfoliation of the intercalated layered powder material within the first chamber 108. For example, after supercritical CO2 and graphite powder are maintained under supercritical conditions of CO2 for a predetermined amount of time so that CO2 molecules can be intercalated between graphite layers, the fluid discharge valve 140 can be opened to quickly discharge water from the second chamber 110, and thus rapidly expand the CO2 within the first chamber 108. Such rapid expansion of CO2 can result in exfoliation of intercalated graphite. During such rapid expansion, the temperature of CO2 suddenly decreases and is rapidly raised again to the target operating temperature by the circulating water within the jacket 112. During the rapid expansion step, the CO2 molecules embedded between the graphene layers suddenly expand, accompanied by a temperature shock, which can ultimately lead to the effective exfoliation of individual graphene layers.

[0049] In an exemplary embodiment, in response to the rapid discharge of hydraulic fluid from the second chamber 110 , the piston 106 may rapidly move toward the second chamber 110 and may collide with the base end of the elongated housing 104 .

[0050] In an exemplary embodiment, as mentioned above, in order to achieve a higher conversion yield of graphite to graphene or a higher stripping yield of any other suitable layered material, the embedding step and the stripping step can be repeated several times. To this end, after the rapid expansion, the fluid discharge valve 140 can be closed, and the hydraulic pump 134 can be used to pump water or any selected hydraulic fluid into the second chamber 110 to move the piston 106 toward the first chamber 108 and compress the contents of the first chamber 108 back to the operating pressure and temperature. For example, in the case of supercritical CO2, 130 bar and 40°C. Similarly, supercritical conditions can be maintained for a given time period of 2 minutes to 600 minutes (e.g., 60 minutes) to embed. After repeating the embedding step, the fluid discharge valve 140 can be opened again to allow rapid expansion to occur again. This repetition of the embedding step and the stripping step can be performed several times to achieve a desired conversion yield. In an exemplary embodiment, since these steps are repeated without the need to charge fresh CO 2 gas from the pressurized gas reservoir 126 , operating time, cost, CO 2 consumption, and CO 2 emissions may be significantly reduced.

[0051] In an exemplary embodiment, the elongated housing 104 may also include a product discharge port in communication with the first chamber 108. In an exemplary embodiment, the product discharge port may be equipped with a product discharge valve 148 that may intercept communication between the first chamber 108 and the product collection box 152. In an exemplary embodiment, after the exfoliation of the layered material is repeated any desired number of times, in order to collect the produced exfoliation product, the fluid discharge valve 140 is closed and the gas injection valve 128 is opened. It should be noted that the pressure of the first chamber 108 is approximately the pressure of the pressurized gas reservoir 126. Then, the hydraulic pump 134 may be used to pump water into the second chamber 110 to push the piston 106 toward the first chamber 108. Here, the CO2 gas may return to the pressurized gas reservoir 126 after passing through the gas filter 132 until the piston 106 contacts the stopper 147. In this state, the volume of the first chamber 108 may exceed the pile volume of the exfoliated product by at least 25%. Therefore, the exfoliated product may not be compressed, and the pressure of the first chamber 108 may be the same as the pressure of the pressurized gas reservoir 126, which may be in the range of 5 bar to 73 bar. For example, the pressure of the first chamber 108 may be 35 bar.

[0052] In an exemplary embodiment, in order to collect the exfoliated product from the first chamber 108, the gas injection valve 128 can be closed and the exhaust valve 149 can be gradually opened to reduce the pressure to a pressure of approximately less than 5 bar. Then, the product exhaust valve 148 can be gradually opened. All the exfoliated products at a pressure of approximately less than 5 bar can be discharged into the product collection box 152, and the excess CO2 can be discharged from the product collection box 152 after passing through the filter 156. Finally, the product valve 154 installed at the bottom of the product collection box 152 can be opened to collect the exfoliated powder product. It should be noted that during product collection, the maximum volume of the first chamber 108 can be 15% of the total volume of the elongated shell 104, and therefore, 85% of the CO2 can be recycled back to the pressurized gas reservoir 126. This relatively high recycling percentage can allow for a significant reduction in CO2 consumption and CO2 emissions. In an exemplary embodiment, the pressurized gas reservoir 126 may be equipped with a CO 2 make-up line 158 that may be utilized when necessary to compensate for the amount of CO 2 exhausted from the filter 156 .

[0053] Figure 2 A flow chart of a supercritical fluid-facilitated exfoliation method 200 for producing high-quality nanomaterials consistent with one or more exemplary embodiments of the present disclosure is shown. In an exemplary embodiment, method 200 can be performed by a system similar to system 100.

[0054] In an exemplary embodiment, method 200 may include: step 202, which is to fill the layered material powder into the variable volume reactor; step 204, which is to inject a pressurized fluid into the variable volume reactor, and the pressurized fluid may include gas or any other suitable fluid, such as water, ethanol, methanol, propanol, methane, ethane, propane, butane, ethylene or a mixture thereof; step 206, which is to increase the temperature of the variable volume reactor to a predetermined temperature; step 208; which is to increase the pressure of the variable volume reactor to a pressure higher than the critical pressure of the pressurized fluid at the predetermined temperature by reducing the volume of the variable volume reactor; step 210; which is to obtain the embedded layered material powder by maintaining the temperature and pressure conditions within the variable volume reactor for a predetermined amount of time; and step 212, which is to exfoliate the embedded layered material powder by increasing the volume of the variable volume reactor to expand the pressurized fluid within the variable volume reactor.

[0055] In an exemplary embodiment, the step 202 of filling the layered material powder into the variable volume reactor may include filling the layered material powder into a variable volume reactor similar to the variable volume reactor 102. For example, the powder inlet port 114 may be opened, and the layered material powder may be filled into the first chamber 108 by utilizing a funnel. Then, the powder inlet port 114 may be closed. In an exemplary embodiment, the step 202 of filling the layered material powder into the variable volume reactor may also include filling a stacked two-dimensional material powder into the variable volume reactor, the stacked two-dimensional material powder including at least one of graphite powder, dichalcogenide powder, silicate clay powder, hexagonal boron nitride powder, tungsten disulfide powder, and molybdenum disulfide powder.

[0056] In an exemplary embodiment, the step 204 of injecting the pressurized gas into the variable volume reactor may include injecting the pressurized gas into a variable volume reactor similar to the variable volume reactor 102. For example, the pressurized gas may be injected from a pressurized gas source, such as the pressurized gas reservoir 126, via the pressurized gas injection valve 128. In an exemplary embodiment, the step 204 of injecting the pressurized gas into the variable volume reactor may include opening the injection valve 128 to allow the pressurized gas to be introduced into the first chamber 108. In an exemplary embodiment, the step 204 of injecting the pressurized gas into the variable volume reactor may include injecting at least one of carbon dioxide, water, ethanol, methanol, propanol, methane, ethane, propane, butane, and ethylene into the variable volume reactor.

[0057] In an exemplary embodiment, step 206 of increasing the temperature of the variable volume reactor to a predetermined temperature may include heating the variable volume reactor via a temperature control mechanism. For example, the variable volume reactor may also include a jacket similar to jacket 112 of variable volume reactor 102, through which a circulating fluid (such as water) at a predetermined temperature may be circulated. In an exemplary embodiment, step 206 of increasing the temperature of the variable volume reactor to a predetermined temperature may include circulating water at a predetermined temperature through jacket 112 of variable volume reactor 102.

[0058] In an exemplary embodiment, step 208 of increasing the pressure of the variable volume reactor to a pressure above the critical pressure of the pressurized gas at the predetermined temperature may involve reducing the volume of the variable volume reactor. For example, increasing the pressure of the pressurized gas to a pressure above the critical pressure of the gas at the predetermined temperature may include pumping hydraulic fluid into the second chamber 110 of the variable volume reactor 102 by using the hydraulic pump 134 to push the piston 106 toward the first chamber 108 and thereby reducing the volume of the first chamber 108 and increasing the pressure of the pressurized gas within the first chamber 108.

[0059] In an exemplary embodiment, the step 210 of obtaining an embedded layered material powder can be achieved by maintaining the supercritical conditions in the variable volume reactor for a predetermined amount of time. As mentioned above, maintaining the supercritical conditions in the first chamber 108 can allow supercritical gas molecules to have a chance to be embedded between the layers of the layered material powder.

[0060] In an exemplary embodiment, step 212 of exfoliating the embedded layered material powder by expanding the pressurized gas within the variable volume reactor may involve increasing the volume of the variable volume reactor. For example, increasing the volume of a variable volume reactor such as variable volume reactor 102 may refer to increasing the volume of first chamber 108 by rapidly discharging hydraulic fluid from second chamber 110, which may result in rapid movement of piston 106 toward second chamber 110. To this end, fluid discharge valve 140 may be opened to allow hydraulic fluid to be discharged from second chamber 110.

[0061] Example

[0062] In this embodiment, the supercritical fluid-facilitated exfoliation method 200 is performed in a system similar to the system 100 for producing high-quality graphene from graphite powder. Here, 241.5 g of artificial graphite powder with a mesh size of 325 and an equivalent pile volume of 500 ml is filled into the first chamber 108 by using a funnel through the powder inlet port 114. In this embodiment, the maximum volume of the elongated housing 104 is about 7 liters. The temperature controller 121 is used to adjust the temperature of the water in the water tank 116 to be at a temperature of about 40° C. Then, the injection valve 128 is opened to introduce CO2 gas from the pressurized gas reservoir 126 into the first chamber 108. After 5 minutes, the temperature and pressure of the CO2 gas in the first chamber 108 reached 35° C. and 35 bar, respectively. Then, in order to fully pressurize the CO2 gas beyond its critical pressure, water is pumped into the second chamber 110 by using a hydraulic pump 134, which pushes the piston 106 toward the first chamber 108. It takes about one minute to reach a stable pressure of 130 bar in the first chamber 108. During the pressurization step described above, the temperature of CO2 suddenly increases to 90°C and then decreases to 35°C within 4 minutes. Then, the graphite powder is kept exposed to supercritical CO2 at 130 bar and 35°C for 60 minutes to obtain embedded graphite. Then, the fluid discharge valve 140 is opened, which causes the discharge of water from the second chamber 110 and the rapid expansion of CO2 gas in the first chamber 108. During this rapid expansion, the temperature and pressure of CO2 drop to -5°C and 30 bar, respectively. However, in less than 15 seconds, the temperature and pressure of CO2 rise back to 20°C and 33 bar, respectively. The process described above is repeated four times, and after the fourth and final cycle, all the exfoliated graphene is collected in the product box 152 by gradually decompressing the first chamber 108 to a very low pressure using the exhaust valve 149 and then opening the exhaust valve 148. The low pressure CO 2 flow may assist in discharging the graphene powder from valve 148 .

[0063] Figure 3 The Raman spectra of artificial graphite and native graphene nanosheets consistent with one or more exemplary embodiments of the present disclosure are shown. Figure 3 It is clearly visible in the graphite spectrum that the 2D peak shifts clearly from 2707.7 (graphite) to 2689.5 (graphene), which can be considered as evidence of the generation of graphene. In addition, compared with the graphite spectrum, the I D / I G There is no change, because the present invention uses CO2 at low temperature (inert gas) and does not use strong oxidants or operate at high temperatures. Therefore, there is no chance of adding oxygen and defects in the produced graphene. In other words, if high-quality graphite is used as the raw material, the present invention can produce defect-free native graphene. As in Figure 3 It is obvious that I D / IG =0.26 is very low and confirms the production of very low-defect graphene. 2D / I G The ratio of = 0.54 is quite high for large-scale production of pristine graphene, which demonstrates the production of pristine graphene with very few layers.

[0064] Figure 4 An atomic force microscope (AFM) image of graphene nanosheets produced consistent with one or more exemplary embodiments of the present disclosure is shown. Figure 4 As can be clearly seen in the graphene nanosheets, the maximum thickness of the native graphene nanosheets is less than 2.0 nm, which means that the average number of layers of the native graphene nanosheets should be less than 5. Therefore, the native graphene produced has not been processed and separated (separation of graphite from graphene) before AFM and Raman analysis, and it can be inferred that the yield of graphene production is high and most of the graphite particles have been exfoliated into a few-layer native graphene with an average value of less than 5 layers.

[0065] Figure 5 Transmission electron microscopy (TEM) images of graphene nanosheets produced consistent with one or more exemplary embodiments of the present disclosure are shown. The wrinkles on the flakes demonstrate the thin thickness of the native graphene.

[0066] In an exemplary embodiment, an exemplary system (such as system 100) and an exemplary method (such as method 200) for supercritical fluid-facilitated stripping of a layered material (such as graphite) can allow problems associated with conventional stripping methods to be overcome. Specifically, system 100 can allow the exemplary supercritical gas in a closed variable volume reactor to expand rapidly without the risk of clogging or any inconsistency during decompression. In addition, decompression can be performed via a commonly used commercial valve, which is designed for the required flow of an exemplary pure and clean hydraulic fluid that does not contain additional particles (such as graphite or graphene powder), so there is no risk of valve clogging. In addition, the density of the exemplary hydraulic fluid (such as water) is about 1000 times higher than the density of CO2 gas under standard conditions. Therefore, decompressing an incompressible fluid (such as water) at a temperature of less than 95°C can be considered a safe and conventional process. Therefore, it is possible to scale up the exemplary system to include a variable volume reactor capable of producing 300kg of graphene per day without worrying about safety issues.

[0067] In an exemplary embodiment, because the exemplary supercritical gas (such as supercritical CO2) is decompressed in the exemplary variable volume reactor (contrary to the conventional method that supercritical gas is discharged to the environment), CO2 discharge is close to zero. CO2 can be further circulated for the next operation. In addition, by simply pressurizing and decompressing the system with an exemplary hydraulic fluid, the stripping process can be repeated several times in the exemplary variable volume reactor. This ability can allow the production of graphene with higher conversion rate and higher quality, and without any restrictions, additional processes, and without high CO2 discharge or consumption.

[0068] According to one or more exemplary embodiments, an exemplary system similar to system 100 can be configured to extract one or more substances from a solid matrix using a supercritical fluid as a solvent. In an exemplary embodiment, system 100 can be configured to perform a supercritical extraction method, wherein supercritical CO with or without a co-solvent (such as methanol, ethanol and acetone) can be used in the extraction of aromatics, food additives, surfactants and degreasing. In the supercritical extraction method, a supercritical CO stream passes through a packed bed of a solid matrix including one or more target substances. As used herein, an exemplary target substance can refer to an exemplary substance to be extracted from an exemplary solid matrix. The exemplary target substance diffuses from the solid matrix and dissolves into an exemplary fresh supercritical CO stream. Then, the obtained supercritical solution stream is decompressed to ambient pressure, and the exemplary target substance is separated from the CO gas. Supercritical CO has high transfer characteristics and easy permeability characteristics in a solid matrix. Therefore, due to the high density and diffusion characteristics of supercritical CO, an exemplary target substance (such as phospholipids) can be easily dissolved into supercritical CO. Although supercritical extraction methods are promising methods in food and medicine compared to common liquid extraction, however, the transfer of target substances from the interior of a solid matrix to the bulk of a supercritical CO2 flow is controlled by molecular diffusion, which may result in low extraction rates and subsequent low extraction yields. In other words, a large amount of CO2 may be consumed in common supercritical extraction methods, which is undesirable from a practical point of view.

[0069] In an exemplary embodiment, a variable volume reactor (such as variable volume reactor 102) can be configured to perform a supercritical extraction method. In an exemplary embodiment, the use of a variable volume reactor (such as variable volume reactor 102) for performing a supercritical extraction method can allow for a lower amount of CO2 and accelerate the rate of extraction and production in a shorter time. To this end, in an exemplary embodiment, instead of an exemplary layered material, the variable volume reactor 102 can be loaded with a solid matrix, such as buttermilk powder with or without a co-solvent (such as methanol, ethanol or acetone). In an exemplary embodiment, an exemplary method for supercritical extraction can be similar to method 200, wherein the step 210 of obtaining an embedded layered material is replaced by the infiltration step of a solid matrix utilizing a supercritical CO2 fluid. However, due to the larger pore size of the solid matrix compared to the interlayer space of the layered material, the infiltration time should be shorter. In addition to the molecular diffusivity of the target substance into a large amount of supercritical CO2 (molecular extraction), the volume of the variable volume reactor 102 is increased in a very short time, and convective mass transfer (convective extraction) occurs during the expansion of the supercritical CO2 in the variable volume reactor 102. In response to this rapid expansion, all of the supercritical solution of the target substance is pushed out from the interior of the solid matrix into the variable volume reactor 102, while the supercritical CO2 is converted into a CO2 gas phase, and the target substance (such as phospholipid) is extracted. This process can be repeated several times to complete the extraction. The final product is discharged from the variable volume reactor 102 for further processing.

[0070] According to one or more exemplary embodiments, system 100 can be further configured to produce nanometer-scale drug particles. Here, system 100 can be used to perform supercritical solution rapid expansion (RESS) technology. In an exemplary embodiment, variable volume reactor 102 can also include a stirrer 162 that can be arranged in first chamber 108. In an exemplary embodiment, solute and suitable fluid (preferably CO2 with or without co-solvent) can be loaded into variable volume reactor 102. Then, variable volume reactor 102 can be pressurized to a critical pressure higher than the fluid by reducing its volume at a supercritical temperature adjusted by a water jacket. In an exemplary embodiment, stirrer 162 can help dissolve exemplary solutes into supercritical fluids. This process is followed by very rapid expansion of variable volume reactor 102, which can lead to instantaneous decompression, supersaturation of fluids, and the generation of solute nanoparticles. Since the diameter of variable volume reactor 102 can be much larger than the ordinary nozzle used for ordinary RESS method, there is no chance to reach supersonic speed in variable volume reactor 102 and particles grow by condensation. This configuration of system 100 may allow for the production of very small nanoparticles with a narrow size distribution, which is desirable in the pharmaceutical industry.

[0071] Embodiments have been described above by means of functional building blocks illustrating the specific implementation of specified functions and their relationships. For ease of description, the boundaries of these functional building blocks have been arbitrarily defined in this article. As long as the specified functions and their relationships are properly performed, alternative boundaries can be defined.

[0072] The foregoing description of specific embodiments will fully reveal the general nature of the present disclosure, so that others can easily modify and / or adapt various applications of such specific embodiments by applying knowledge in the art, without excessive experimentation, and without departing from the general concepts of the present disclosure. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments. It should be understood that the wording or terminology herein is used for description rather than limitation, so that the terms or wording of this specification will be interpreted by those skilled in the art based on teaching and guidance.

[0073] The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

[0074] Throughout this specification and the claims that follow, unless the context requires otherwise, the word "comprise" and variations such as "comprising" or "containing", will be understood to imply the inclusion of stated integers or steps or groups of integers or steps but not the exclusion of any other integers or steps or groups of integers or steps.

[0075] In addition, when used with an adjective or adverb, the word "substantially" is intended to enhance the scope of a particular characteristic, for example, substantially planar is intended to mean planar, nearly planar, and / or exhibiting characteristics associated with planar elements. Further use of relative terms such as "vertical," "horizontal," "upper," "lower," and "side to side" are used in the sense of being relative to the normal orientation of the device.

Claims

1. A supercritical fluid-promoted exfoliation method, the method comprising: The layered material powder is filled into a variable volume reactor, the variable volume reactor comprising: An elongated shell; a piston movably disposed within the elongated housing, the piston dividing the interior of the elongated housing into a first chamber and a second chamber, wherein filling the layered material powder into the variable volume reactor comprises filling the layered material powder into the first chamber; injecting a pressurized fluid into the first chamber; increasing the temperature of the first chamber to a predetermined temperature by heating the first chamber; increasing the pressure of the first chamber to a pressure above the critical pressure of the pressurized fluid by injecting a hydraulic fluid into the second chamber, wherein in response to injecting the hydraulic fluid into the second chamber, the piston moves toward the first chamber, thereby reducing the volume of the first chamber; obtaining an embedded layered material powder by embedding the pressurized fluid between the layers of the layered material powder, wherein embedding the pressurized fluid between the layers of the layered material powder includes maintaining the temperature and pressure conditions within the first chamber for a predetermined amount of time; and The embedded layered material powder is exfoliated by expanding the pressurized fluid within the first chamber, wherein expanding the pressurized fluid within the first chamber includes discharging the hydraulic fluid from the second chamber, wherein in response to discharging the hydraulic fluid from the second chamber, the piston moves toward the second chamber, thereby increasing the volume of the first chamber.

2. The method according to claim 1, wherein filling the layered material powder into the variable volume reactor includes filling a stacked two-dimensional material powder into the first chamber, the stacked two-dimensional material powder comprising at least one of the following: graphite powder, dichalcogenide powder, silicate clay powder, hexagonal boron nitride powder, tungsten disulfide powder and molybdenum disulfide powder.

3. The method of claim 1, wherein injecting the pressurized fluid into the first chamber comprises injecting at least one of carbon dioxide, water, ethanol, methanol, propanol, methane, ethane, propane, butane, and ethylene into the first chamber.

4. The method according to claim 3, wherein filling the layered material powder into the variable volume reactor includes filling a stacked two-dimensional material powder into the first chamber, and the stacked two-dimensional material powder includes at least one of the following: graphite powder, dichalcogenide powder, silicate clay powder, hexagonal boron nitride powder, tungsten disulfide powder and molybdenum disulfide powder. 5 . The method of claim 1 , wherein filling the layered material powder into the variable volume reactor comprises filling graphite powder into the first chamber.

6. The method of claim 5, wherein injecting the pressurized fluid into the first chamber comprises injecting pressurized CO2 into the first chamber.

7. The method of claim 6, wherein increasing the temperature of the first chamber comprises heating the first chamber to a temperature in a range of 31°C to 300°C.

8. The method of claim 7, wherein increasing the pressure of the first chamber comprises injecting the hydraulic fluid into the second chamber to increase the pressure in the first chamber to 400 bar.

9. The method of claim 8, wherein injecting the hydraulic fluid into the second chamber comprises injecting at least one of water, a mixture of water and ethylene glycol, hydraulic oil, and high temperature oil into the second chamber.

10. The method of claim 1, wherein the elongated housing includes a jacket surrounding an outer surface of the elongated housing, wherein increasing the temperature of the first chamber to the predetermined temperature includes circulating at least one of water, a mixture of water and ethylene glycol, hydraulic oil, and high temperature oil at the predetermined temperature through the jacket.

11. The method of claim 1, wherein maintaining the temperature and pressure conditions within the first chamber comprises maintaining the temperature and pressure conditions within the first chamber for a period of time in a range of 2 minutes to 600 minutes.

12. A method for producing graphene, the method comprising: Graphite powder is filled into a variable volume reactor, the variable volume reactor comprising: An elongated shell; a piston movably disposed within the elongated housing, the piston dividing the interior of the elongated housing into a first chamber and a second chamber, wherein filling the graphite powder into the variable volume reactor comprises filling the graphite powder into the first chamber; injecting pressurized CO2 into the first chamber; increasing the temperature of the first chamber to a temperature in the range of 31° C. to 300° C. by heating the first chamber; increasing the pressure of the first chamber to a pressure above a critical pressure of the pressurized CO2 by injecting at least one of water, a mixture of water and ethylene glycol, hydraulic oil, and high temperature oil into the second chamber, wherein in response to injecting water into the second chamber, the piston moves toward the first chamber, thereby reducing the volume of the first chamber; maintaining the temperature and pressure conditions within the first chamber for a predetermined amount of time in the range of 2 minutes to 600 minutes; and The pressurized CO2 within the first chamber is expanded by discharging at least one of water, a mixture of water and ethylene glycol, hydraulic oil, and high temperature oil from the second chamber, wherein in response to discharging the at least one of water, a mixture of water and ethylene glycol, hydraulic oil, and high temperature oil from the second chamber, the piston moves toward the second chamber, thereby increasing the volume of the first chamber.

13. A system for producing a peelable layered material, the system comprising: An elongated shell; a piston movably disposed within the elongated housing, the piston being configured to divide an inner volume of the elongated housing into a first chamber and a second chamber; a powder inlet port connected to the first chamber in powder communication, the powder inlet port being configured to allow powder to be introduced into the first chamber; a fluid injection port connected in fluid communication with the first chamber, the fluid injection port being configured to allow injection of a fluid into the first chamber; a hydraulic mechanism connected in fluid communication with the second chamber, the hydraulic mechanism being configured to cause the piston to move along the longitudinal axis of the elongated housing, the hydraulic mechanism comprising: a hydraulic fluid reservoir containing hydraulic fluid; and a hydraulic pump connected between the hydraulic fluid reservoir and the second chamber, the hydraulic pump configured to pump the hydraulic fluid into and out of the second chamber, wherein the piston moves toward the first chamber in response to pumping the hydraulic fluid into the second chamber, and wherein the piston moves toward the second chamber in response to pumping the hydraulic fluid out of the second chamber; and A temperature control mechanism is coupled to the elongated housing, the temperature control mechanism being configured to control a temperature of the first chamber.

14. The system according to claim 13, further comprising: A powder discharge port is connected to the first chamber, the powder discharge port being configured to allow discharge of the powder from the first chamber.

15. The system of claim 14, wherein the temperature control mechanism comprises a jacket surrounding an outer surface of the elongated shell and a circulation system connected to the jacket in fluid communication, the circulation system being configured to control the temperature of the first chamber by circulating at least one of water, a mixture of water and ethylene glycol, hydraulic oil, and high temperature oil within the jacket.

16. The system of claim 15, wherein the fluid comprises at least one of CO2, CH4, N2, H2, water, ethanol, methanol, propanol, ethane, propane, butane, and ethylene.

17. The system of claim 16, wherein the powder comprises a stacked two-dimensional material.

18. The system of claim 17, wherein the stacked two-dimensional material powder comprises at least one of: graphite powder, dichalcogenide powder, silicate clay powder, hexagonal boron nitride powder, tungsten disulfide powder, and molybdenum disulfide powder.

19. A system for producing graphene, the system comprising: An elongated shell; a piston movably disposed within the elongated housing, the piston being configured to divide an inner volume of the elongated housing into a first chamber and a second chamber; a powder inlet port connected to the first chamber in powder communication, the powder inlet port being configured to allow graphite to be introduced into the first chamber; a gas injection port connected in fluid communication with the first chamber, the gas injection port being configured to allow injection of CO2 into the first chamber; a hydraulic mechanism connected in fluid communication with the second chamber, the hydraulic mechanism being configured to cause the piston to move along the longitudinal axis of the elongated housing, the hydraulic mechanism comprising: Water reservoir; a pump connected between the water reservoir and the second chamber, the pump configured to pump water into and out of the second chamber, wherein the piston moves toward the first chamber in response to pumping water into the second chamber, and wherein the piston moves toward the second chamber in response to pumping water out of the second chamber; a temperature control mechanism coupled to the elongated housing, the temperature control mechanism configured to control a temperature of the first chamber; and A powder discharge port is connected to the first chamber, the powder discharge port being configured to allow discharge of powder from the first chamber.

20. The system of claim 19, wherein the temperature control mechanism is configured to control the temperature of the first chamber to be at a temperature in the range of 31°C to 95°C, and wherein the hydraulic mechanism is configured to increase the pressure in the first chamber to a pressure in the range of 73 bar to 400 bar by injecting water from the water reservoir into the second chamber.

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