WO2019158794A1 - Method for obtaining a graphene oxide aerogel - Google Patents

Method for obtaining a graphene oxide aerogel Download PDF

Info

Publication number
WO2019158794A1
WO2019158794A1 PCT/ES2019/070082 ES2019070082W WO2019158794A1 WO 2019158794 A1 WO2019158794 A1 WO 2019158794A1 ES 2019070082 W ES2019070082 W ES 2019070082W WO 2019158794 A1 WO2019158794 A1 WO 2019158794A1
Authority
WO
WIPO (PCT)
Prior art keywords
temperature
pressure
reactor
mpa
graphene oxide
Prior art date
Application number
PCT/ES2019/070082
Other languages
Spanish (es)
French (fr)
Inventor
Concepción DOMINGO PASCUAL
Ana María LÓPEZ PERIAGO
Alejandro BORRÁS CABALLERO
Gerard TOBÍAS ROSSELL
Gil GONÇALVES
Stefania SANDOVAL ROJANO
Julio FRAILE SAINZ
Original Assignee
Consejo Superior De Investigaciones Científicas (Csic)
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Consejo Superior De Investigaciones Científicas (Csic) filed Critical Consejo Superior De Investigaciones Científicas (Csic)
Publication of WO2019158794A1 publication Critical patent/WO2019158794A1/en

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/0091—Preparation of aerogels, e.g. xerogels
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2204/00—Structure or properties of graphene
    • C01B2204/20—Graphene characterized by its properties

Definitions

  • the present invention relates to a process for obtaining a monolithic three-dimensional graphene oxide airgel comprising a gelation stage under supercritical conditions and a supercritical drying stage.
  • the present report describes an invention framed in the field of design and synthesis of materials with high surface area.
  • graphene-type materials it is worth mentioning the graphene, graphene oxide (GO) and reduced graphene oxide (rGO) nanollamines. These materials consist of laminar structures, where the carbon atoms bond together forming hexagons by covalent bonds, see a schematic representation of GO in Figure 1 [D. R. Dreyer et al, Chem. Soc. Rev., 39, 2010, 228]. The resulting products stand out for their excellent mechanical, thermal and electrical properties. In this field, the importance of exfoliated graphene materials is enhanced. Mass production of this compound is mainly done through the oxidation of graphite to GO by strong mineral acids.
  • the GO is reduced to rGO after treatment by pyrolysis at T> 1273 K or chemical treatment with reducing agents, such as borohydride or hydrazine [S. Pe ⁇ , H.M. Cheng, Coal 50, 2012, 3210].
  • reducing agents such as borohydride or hydrazine
  • the GO can be visualized as a large highly oxygenated macromolecule, with the presence of the most oxygenated functional groups at the edges of the network (see Figure 1), which allows the preparation of colloidal dispersions stable in water or alcohols. These oxygenated groups can be eliminated to different degrees a posteriori, resulting in the formation of reduced graphene oxide (rGO), with thermal and chemical treatments being the most used.
  • Both the GO and the rGO are materials of high technological interest, especially as dry three-dimensional (3D) porous solids [V. Chabot, D. Higgins, A. Yu, X. Xiao, Z. Chen, J. Zhang, Energy Environ. Sci. 7, 2014, 1564]
  • conventional drying of GO suspensions for example under vacuum, leads to the formation of agglomerated powders with low surface area values ( ⁇ 50 m 2 / g) and not to structures 3D
  • Freeze-drying methods the use of slaughter templates and "critical point drying” are presented as the most efficient methods for obtaining 3D stable nanostructures of exfoliated GO with optimum porosity, specific surface and interconnectivity characteristics [Y. Wu et al. Nature Commun Doi: 10.1038 / ncomms7141].
  • the most commonly used method is lyophilization, preceded or not by a hydrothermal stage, in which aqueous suspensions are started that are cryogenized at 313-323 K, subsequently sublimating the water under low pressure conditions. .
  • the method of drying at the critical point requires high pressure and very high temperature equipment, so it is less used.
  • the formation of an interface is avoided by constituting a supercritical fluid by increasing temperature and pressure before carrying out its evaporation directly as a gas.
  • direct dehydration of hydrogels under supercritical conditions in general is not feasible, since the critical point of the water is reached at 22 MPa and 647 K, parameters too high to maintain the thermal and chemical stability of many of the substances to be treated .
  • the aqueous phase is exchanged before elimination, preferably by a short chain alcohol, acetone, or mixtures thereof.
  • This temperature is high enough to produce chemical changes in the material being treated. As a consequence, this treatment causes epoxidation and the reduction of GO to rGO almost entirely, eliminating the functional groups.
  • the resulting material has a low degree of hydrophilicity and is generally unstable in water [CY Kong et al. J. Supercrit. Fluids 61, 2012, 206; A. Alazmi et alNanoscale, 8, 2016, 17782; M. Seo et al Carbon 64, 2013, 207, SP Sasikala et al Adv. Mater. 28, 2016, 2663].
  • a gel is a colloidal system where the continuous phase is solid and the discontinuous phase is liquid.
  • the gels have a density similar to liquids, however their structure is more similar to that of a solid.
  • Certain gels have the ability to pass from one colloidal state to another, that is, they remain fluid when agitated and solidify when they remain immobile. This feature is called thixotropy.
  • the process by which a gel is formed is called "gelation.”
  • the inventors of the present invention have found a method of obtaining a monolithic three-dimensional graphene oxide airgel, which is preferably carried out under isothermal and isobaric conditions and comprising the steps of preparing an alcoholic dispersion of nanoparticles or oxide platelets of graphene at room temperature, a subsequent gelation process of said dispersion with the help of compressed or supercritical carbon dioxide at a temperature T ⁇ 370 K and a pressure P> 6 MPa) and a supercritical drying carried out at a temperature T ⁇ 370 K and a P> 15 MPa to extract the liquid inside the gel.
  • the process of the present invention is ecologically sustainable, that is, it is carried out at a low temperature, less than 373 K and in the presence of green solvents.
  • green solvent an alternative to the current substance / solvent that reduces the impact caused by the use of organic solvents.
  • organic solvents are mainly obtained from renewable raw materials, have low toxicity and are not corrosive or carcinogenic. Examples are alcohols such as methanol and ethanol, soybean oil esters and ethyl lactate.
  • a supercritical fluid is that fluid that is above its critical pressure and temperature and whose phase is neither liquid nor gaseous, but shares properties of both states. It flows like a gas and is capable of dissolving substances like a liquid. Some supercritical fluids are inert and non-toxic, allowing them to be classified as green solvents. In addition, they are relatively cheap and their properties are adjustable through pressure variations.
  • the monolithic graphene oxide three-dimensional airgel that is obtained with the process of the present invention is a three-dimensional rigid sponge structure that is stable in the air and in an aqueous medium, which has an interconnected porosity of mesoporous size pores and exhibits great capacity of adsorption of C0 2 .
  • the adsorption of C0 2 measured at 273 K shows high adsorption values, resulting in values of up to 100 mL of C0 2 adsorbed per grams of graphene oxide.
  • Porous solids are classified by the IUPAC by their average pore size.
  • the monolithic graphene oxide three-dimensional airgel obtained with the process of the present invention is composed of exfoliated sheets of Graphene oxide highly anisotropic in shape, with lateral dimensions of several microns, between 10 pm and 50 pm and with a thickness of 1 -2 nm.
  • the chemical composition of the airgel obtained can be described as follows:
  • the total number of carbon atoms per 100 total atoms is> 60% measured by X-ray photoelectron spectroscopy, XPS, and
  • the chemical composition of the airgel of the present invention retains a high number of functional groups of the starting graphene oxide: the process of the invention results in a surprisingly low degree of reduction of GO to rGO.
  • the methods described in the literature result in structures of similar porous carbonaceous materials, but highly reduced since they use much higher temperatures and more aggressive solvents.
  • the low degree of reduction of the airgel obtained following the process of the present invention is an advantage, since it allows post-functionalization.
  • the airgel that is obtained exhibits a high surface area, between 100 m 2 / g and 250 m 2 / g and a high pore volume, between 0.9 ml / g and 1.5 mL / g.
  • the present invention relates to a method of obtaining a monolithic three-dimensional airgel stable in the air and in aqueous medium
  • step (b) gelation process of the dispersion obtained in step (a) by the addition of compressed or supercritical carbon dioxide at a temperature T1 ⁇ 370 K and a pressure P1> 6 MPa); Y (c) extraction of the liquid comprised within the gel obtained in step (b) by supercritical drying at a temperature T2 ⁇ 370 K and a pressure P2> 15 MPa.
  • the reactor used in steps (a) and (b) consists of a 316SS stainless steel body of 100 ml_ that withstands pressures greater than 30 MPa.
  • Two sapphire windows are placed opposite each other in the reactor body and allow visual monitoring of the reactions that occur inside.
  • the sample to be processed is placed inside the reactor being visible through the sapphire windows.
  • the reactor is heated by four resistors inserted in the reactor body.
  • the reactor consists of an input of C0 2 .
  • the C0 2 is compressed by a high pressure pump.
  • the reactor is depressurized removing C0 2 reactor by micrometering valve.
  • the pressure in the reactor is measured and controlled through a pressure gauge (PG) and a pressure transducer (PT, PIC).
  • the temperature in the reactor is measured and controlled with a thermocouple (T / C, TIC).
  • Step (a) of the process of the invention relates to the preparation of a stable alcohol dispersion comprising laminar nanoparticles or graphene oxide platelets.
  • Step (a) can be carried out by conventional solvent exchange, preferably by water / alcohol exchange.
  • step (b) is carried out, a gelation process by adding a supercritical fluid at a temperature T 1 ⁇ 370 K and a pressure P1> 6 MPa.
  • step (b) of the process of the present invention is an advantage over the state Of art.
  • a “supercritical fluid” is any substance that is under conditions of pressure and temperature above its critical point.
  • the aggregation states of matter that are currently known are five: solid, liquid, gas, plasma and Bose-Einstein condensate.
  • a fluid Supercritical is an almost state with intermediate properties between liquids and gases.
  • Density above the critical point depends basically on pressure and temperature, but in any case it is closer to that of liquids than to gases. The density increases if the pressure is at constant temperature and if the temperature decreases at constant pressure.
  • steps (b) and (c) are carried out
  • steps (b) and (c) are carried out.
  • steps (b) and (c) are carried out.
  • the final process for the formation of the graphene oxide airgel is supercritical drying. This is where the liquid inside the gel is removed, leaving only the solid three-dimensional network of the airgel.
  • Step (c) of the process of the invention refers to the extraction of the liquid comprised within the gel obtained in step (b) by supercritical drying at a temperature T2 ⁇ 370 K and P2> 15 MPa.
  • the supercritical drying treatment tries to remove the solvent from the gel obtained in step (b) without generating a two-phase system (liquid / vapor) and thus avoid the capillary forces that would cause the structure to collapse.
  • Figure 1 Molecular representation of a sheet of graphene oxide (GO), indicating the main functional groups, as well as the dimensions of the sheets.
  • Figure 2. Schematic representation of the different reaction steps used to obtain graphene oxide (GO) aerogels using the low temperature drying method with supercritical C0 2 .
  • FIG. 3 Schematization of the 100 ml_ high pressure reactor (1) with sapphire windows (2) used in the experiments of preparation of aerogels by gelation and drying with scC0 2 , in which the most important elements of resistance are indicated ( 3) and control of temperature, pressure and flow of C0 2 circulating from the inlet (4) to the outlet (6) and compressed by a high pressure pump (5).
  • FIG. 1 Two scanning electron microscopy images at different magnifications 300 (a) and 3000 magnification (b) showing the film obtained in the experiment performed in Example 3.
  • Figure 10. Two scanning electron microscopy images at different magnifications 3000 (a) and 24000 magnification (a) of the airgel obtained in the experiment performed in Example 4.
  • the dispersion used in the examples consists of GO nanoparticles with lateral dimensions approx. 30 pm and has a concentration of 4 mg / mL.
  • Two sapphire windows (2) are placed opposite each other in the reactor body and allow visual monitoring of the reactions that occur inside.
  • the sample to be processed is placed inside the reactor being visible through the sapphire windows.
  • the reactor is heated by four resistors (3) inserted in the reactor body.
  • the reactor consists of an input of C0 2 (4).
  • the C0 2 is compressed by a high pressure pump (5).
  • the reactor is depressurized removing C0 2 reactor by micrometering valve (6).
  • the pressure in the reactor in the reactor is measured and controlled through a pressure gauge (PG) and a pressure transducer (PT, PIC).
  • the temperature in the reactor is measured and controlled with a thermocouple (T / C, TIC).
  • a test tube containing the dispersion of GO in alcoholic medium is placed inside the reactor body (1), visible through the sapphire windows (2).
  • the reactor is sealed with the sample inside, being prepared to increase the pressure and temperature.
  • the reactor is then pressurized to the working pressure.
  • P 6 MPa
  • These conditions are maintained for a long period of time, generally greater than 24 h, which leads to the formation of a gel in the test tube that is inside the reactor.
  • the pressure and temperature conditions (generally increasing both slightly) may or may not change to dry the gel. If they are not modified, it is considered to work in isobaric and isothermal conditions.
  • Drying of the gel is achieved by eliminating the supercritical phase of the reactor, which carries with it the ethanol initially added in the test tube. This process can be completed by adding more C0 2 without ethanol directly from the pump (5), with the aim of completely eliminating ethanol. Finally, the reactor is depressurized by the valve (6) to ambient pressure, maintaining the working temperature. The reactor is allowed to cool to laboratory temperature, and is ready to open and recover the sample. The examples are carried out without agitation, unless otherwise specified.
  • Example 1 Obtaining an unstable graphene oxide (GO) gel 4. Increase the pressure in the reactor to 6 MPa at room temperature
  • Figure 6 shows scanning electron microscopy images of the film obtained at three months.
  • Example 3 Obtaining a graphene oxide (GO) film
  • the agitation of the reactor is started at 300 rpm, while 350 mL of C0 2 is passed over a period of 3 hours, the flow being approximately 1 , 95 mL / min.
  • Example 4 Obtaining a graphene oxide (GO) airgel using the method of temperature and pressure variation 4. Increase the reactor temperature up to 298 K and add C0 2 to a pressure of 6 MPa, maintaining these conditions for 18 h.
  • GO graphene oxide
  • Example 5 Obtaining an airgel in isobaric and isothermal conditions.

Abstract

The present invention relates to a method for obtaining a three-dimensional monolithic graphene oxide aerogel, which comprises a step of gelling in supercritical conditions and a step of supercritical drying. The invention described herein belongs to the field of design and synthesis of materials with a high surface area.

Description

Procedimiento de obtención de un aeroael de óxido de arafeno  Procedure for obtaining an araane oxide aeroael
La presente invención se refiere a un procedimiento de obtención de un aerogel tridimensional monolítico de óxido de grafeno que comprende una etapa de gelación en condiciones supercríticas y una etapa de secado supercrítico. The present invention relates to a process for obtaining a monolithic three-dimensional graphene oxide airgel comprising a gelation stage under supercritical conditions and a supercritical drying stage.
La presente memoria describe una invención enmarcada en el campo del diseño y la síntesis de materiales con alta área superficial. The present report describes an invention framed in the field of design and synthesis of materials with high surface area.
ANTECEDENTES DE LA INVENCIÓN BACKGROUND OF THE INVENTION
En el contexto actual de desarrollo de nuevos materiales, se observa un creciente esfuerzo enfocado a formular materiales carbonaceos porosos con interés tecnológico, de los que destacan los nanotubos, las nanofibras, los fullerenos y el grafeno en sus diferentes formas. Todos ellos exhiben valores elevados de superficie específica, alta estabilidad química y térmica y relativo bajo coste, lo que los convierte en materiales adecuados en aplicaciones de a(b)dsorción. In the current context of development of new materials, there is a growing effort focused on formulating porous carbonaceous materials with technological interest, of which nanotubes, nanofibers, fullerenes and graphene in their different forms stand out. All of them exhibit high specific surface values, high chemical and thermal stability and relative low cost, which makes them suitable materials in applications of a (b) dsorption.
En lo concerniente a los materiales tipo grafeno, cabe mencionar las nanoláminas de grafeno, de óxido de grafeno (GO) y de óxido de grafeno reducido (rGO). Estos materiales consisten en estructuras laminares, donde los átomos de carbono se enlazan formando hexágonos mediante uniones covalentes, véase una representación esquemática de GO en Figura 1 [D. R. Dreyer et al, Chem. Soc. Rev., 39, 2010, 228]. Los productos resultantes destacan por sus excelentes propiedades mecánicas, térmicas y eléctricas. En este campo, se realza la importancia de los materiales de grafeno exfoliados. La producción en masa de este compuesto se realiza principalmente a través de la oxidación de grafito a GO mediante ácidos minerales fuertes. As regards graphene-type materials, it is worth mentioning the graphene, graphene oxide (GO) and reduced graphene oxide (rGO) nanollamines. These materials consist of laminar structures, where the carbon atoms bond together forming hexagons by covalent bonds, see a schematic representation of GO in Figure 1 [D. R. Dreyer et al, Chem. Soc. Rev., 39, 2010, 228]. The resulting products stand out for their excellent mechanical, thermal and electrical properties. In this field, the importance of exfoliated graphene materials is enhanced. Mass production of this compound is mainly done through the oxidation of graphite to GO by strong mineral acids.
En caso de ser necesario para aplicaciones específicas, el GO se reduce a rGO después de tratarlo mediante pirólisis a T > 1273 K o tratamiento químico con agentes reductores, tales como el borohidruro o la hidracina [S. Peí, H.M. Cheng, Carbón 50, 2012, 3210]. If necessary for specific applications, the GO is reduced to rGO after treatment by pyrolysis at T> 1273 K or chemical treatment with reducing agents, such as borohydride or hydrazine [S. Peí, H.M. Cheng, Coal 50, 2012, 3210].
El GO se puede visualizar como una gran macromolécula altamente oxigenada, con presencia de los grupos funcionales más oxigenados en los bordes de la red (véase Figura 1 ), lo que permite la preparación de dispersiones coloidales estables en agua o alcoholes. Estos grupos oxigenados se pueden eliminar en distintos grados a posteriori, resultando en la formación de óxido de grafeno reducido (rGO), siendo los tratamientos térmicos y químicos los más utilizados. Tanto el GO como el rGO son materiales de elevado interés tecnológico, sobre todo como sólidos porosos tridimensionales (3D) secos [V. Chabot, D. Higgins, A. Yu, X. Xiao, Z. Chen, J. Zhang, Energy Environ. Sci. 7, 2014, 1564] Sin embargo, el secado convencional de las suspensiones de GO, por ejemplo al vacío, conduce a la formación de polvos aglomerados con valores bajos de área superficial (< 50 m2/g) y no a estructuras 3D. The GO can be visualized as a large highly oxygenated macromolecule, with the presence of the most oxygenated functional groups at the edges of the network (see Figure 1), which allows the preparation of colloidal dispersions stable in water or alcohols. These oxygenated groups can be eliminated to different degrees a posteriori, resulting in the formation of reduced graphene oxide (rGO), with thermal and chemical treatments being the most used. Both the GO and the rGO are materials of high technological interest, especially as dry three-dimensional (3D) porous solids [V. Chabot, D. Higgins, A. Yu, X. Xiao, Z. Chen, J. Zhang, Energy Environ. Sci. 7, 2014, 1564] However, conventional drying of GO suspensions, for example under vacuum, leads to the formation of agglomerated powders with low surface area values (<50 m 2 / g) and not to structures 3D
Los métodos de liofilización, el uso de plantillas de sacrificio y el "secado en el punto crítico" se presentan como los métodos más eficientes para la obtención de nanoestructuras estables 3D de GO exfoliado con características óptimas de porosidad, superficie específica e interconectividad [Y. Wu et al. Nature Commun. Doi: 10.1038/ncomms7141 ]. Freeze-drying methods, the use of slaughter templates and "critical point drying" are presented as the most efficient methods for obtaining 3D stable nanostructures of exfoliated GO with optimum porosity, specific surface and interconnectivity characteristics [Y. Wu et al. Nature Commun Doi: 10.1038 / ncomms7141].
Para la obtención de esponjas 3D de GO el método más utilizado es la liofilización, precedida o no de una etapa hidrotermal, en el que se parte de suspensiones acuosas que se criogenizan a 313-323 K, sublimándose posteriormente el agua en condiciones de baja presión. To obtain 3D GO sponges, the most commonly used method is lyophilization, preceded or not by a hydrothermal stage, in which aqueous suspensions are started that are cryogenized at 313-323 K, subsequently sublimating the water under low pressure conditions. .
El método de secado en el punto crítico, a pesar de ser muy efectivo, requiere de equipamiento de alta presión y muy alta temperatura, por lo que es menos utilizado. En este proceso, la formación de una interfase se evita al constituirse un fluido supercrítico por aumento de temperatura y presión antes de llevar a cabo su evaporación directamente como gas. Sin embargo, la deshidratación directa de hidrogeles en condiciones supercríticas en general no es viable, ya que el punto crítico del agua se alcanza a 22 MPa y 647 K, parámetros demasiado elevados para mantener la estabilidad térmica y química de muchas de las sustancias a tratar. Para solucionar este inconveniente, la fase acuosa se intercambia antes de su eliminación, preferentemente por un alcohol de cadena corta, acetona, o mezclas de estos. El disolvente se puede eliminar así a presiones y temperaturas inferiores, 5-7 MPa y 510-520 K (Figura 2) [H.D. Gesser et al., Chem. Rev. 89, 1989, 765]. Para reducir la temperatura de procesado se han desarrollado métodos que utilizan tecnología basada en C02 supercrítico (scC02) para el secado de geles [M.A. Worsley, et al J. Phys.Chem. Lett. 2, 201 1 , 921 ] Los métodos supercríticos no han sido previamente aplicados al secado de suspensiones que no estén previamente gelificadas. El único método que se ha encontrado descrito para la producción de aerogeles de grafeno es el de secado en el punto crítico a partir de geles en etanol. La utilización de este método conlleva el uso de altas temperaturas (T > 500 K), lo que ya de por sí es una desventaja energética. Esta temperatura es suficientemente elevada para producir cambios químicos en el material que se está tratando. Como consecuencia, este tratamiento causa la epoxidación y la reducción de GO a rGO casi en su totalidad, eliminándose los grupos funcionales. El material resultante tiene un bajo grado de hidrofilicidad y es generalmente inestable en agua [C.Y. Kong et al. J. Supercrit. Fluids 61 , 2012, 206; A. Alazmi et alNanoscale, 8, 2016, 17782; M. Seo et al Carbón 64, 2013, 207, S.P. Sasikala et al Adv. Mater. 28, 2016, 2663]. The method of drying at the critical point, despite being very effective, requires high pressure and very high temperature equipment, so it is less used. In this process, the formation of an interface is avoided by constituting a supercritical fluid by increasing temperature and pressure before carrying out its evaporation directly as a gas. However, direct dehydration of hydrogels under supercritical conditions in general is not feasible, since the critical point of the water is reached at 22 MPa and 647 K, parameters too high to maintain the thermal and chemical stability of many of the substances to be treated . To solve this inconvenience, the aqueous phase is exchanged before elimination, preferably by a short chain alcohol, acetone, or mixtures thereof. The solvent can thus be removed at lower pressures and temperatures, 5-7 MPa and 510-520 K (Figure 2) [HD Gesser et al., Chem. Rev. 89, 1989, 765]. To reduce the processing temperature, methods using technology based on supercritical C0 2 (scC0 2 ) have been developed for drying gels [MA Worsley, et al J. Phys.Chem. Lett. 2, 201 1, 921] Supercritical methods have not previously been applied to drying suspensions that are not previously gelled. The only method that has been found described for the production of graphene aerogels is that of drying at the critical point from gels in ethanol. The use of this method involves the use of high temperatures (T> 500 K), which in itself is an energy disadvantage. This temperature is high enough to produce chemical changes in the material being treated. As a consequence, this treatment causes epoxidation and the reduction of GO to rGO almost entirely, eliminating the functional groups. The resulting material has a low degree of hydrophilicity and is generally unstable in water [CY Kong et al. J. Supercrit. Fluids 61, 2012, 206; A. Alazmi et alNanoscale, 8, 2016, 17782; M. Seo et al Carbon 64, 2013, 207, SP Sasikala et al Adv. Mater. 28, 2016, 2663].
Por tanto, es necesario desarrollar nuevos procedimientos de obtención de aerogeles de óxido de grafeno que superen las desventajas mencionadas anteriormente. Therefore, it is necessary to develop new procedures for obtaining graphene oxide aerogels that overcome the above-mentioned disadvantages.
DESCRIPCIÓN DE LA INVENCIÓN Un gel es un sistema coloidal donde la fase continua es sólida y la discontinua es líquida. Los geles presentan una densidad similar a los líquidos, sin embargo su estructura se asemeja más a la de un sólido. Ciertos geles presentan la capacidad de pasar de un estado coloidal a otro, es decir, permanecen fluidos cuando son agitados y se solidifican cuando permanecen inmóviles. Esta característica se denomina tixotropía. El proceso por el cual se forma un gel se denomina “gelación”.DESCRIPTION OF THE INVENTION A gel is a colloidal system where the continuous phase is solid and the discontinuous phase is liquid. The gels have a density similar to liquids, however their structure is more similar to that of a solid. Certain gels have the ability to pass from one colloidal state to another, that is, they remain fluid when agitated and solidify when they remain immobile. This feature is called thixotropy. The process by which a gel is formed is called "gelation."
Reemplazando el líquido con gas es posible crear aerogeles: materiales con propiedades excepcionales como densidades muy bajas, elevada porosidad y excelente aislamiento térmico. Los inventores de la presente invención han encontrado un procedimiento de obtención de un aerogel tridimensional monolítico de óxido de grafeno, que se lleva a cabo preferiblemente en condiciones isotérmicas e isobáricas y que comprende las etapas de preparación de una dispersión alcohólica de nanopartículas o plaquetas de óxido de grafeno a temperatura ambiente, un posterior proceso de gelación de dicha dispersión con la ayuda de dióxido de carbono comprimido o supercrítico a una temperatura T < 370 K y una presión P > 6 MPa) y un secado supercrítico llevado a cabo a una temperatura T< 370 K y una P > 15 MPa para extraer el líquido que se encuentra dentro del gel. El procedimiento de la presente invención es sostenible ecológicamente, es decir, se lleva a cabo a baja temperatura, menor de 373 K y en presencia de disolventes verdes. By replacing the liquid with gas it is possible to create aerogels: materials with exceptional properties such as very low densities, high porosity and excellent thermal insulation. The inventors of the present invention have found a method of obtaining a monolithic three-dimensional graphene oxide airgel, which is preferably carried out under isothermal and isobaric conditions and comprising the steps of preparing an alcoholic dispersion of nanoparticles or oxide platelets of graphene at room temperature, a subsequent gelation process of said dispersion with the help of compressed or supercritical carbon dioxide at a temperature T <370 K and a pressure P> 6 MPa) and a supercritical drying carried out at a temperature T <370 K and a P> 15 MPa to extract the liquid inside the gel. The process of the present invention is ecologically sustainable, that is, it is carried out at a low temperature, less than 373 K and in the presence of green solvents.
En la presente invención se denomina“disolvente verde” a una sustancia/disolvente alternativo a los actuales que reduce el impacto ocasionado por el empleo de disolventes orgánicos. Se obtienen principalmente a partir de materias primas renovables, presentan baja toxicidad y no son corrosivos ni cancerígenos. Ejemplos son alcoholes como el metanol y etanol, ásteres de aceite de soja y lactato de etilo. Un fluido supercrítico es aquel fluido que se encuentra por encima de su presión y temperatura crítica y cuya fase no es ni líquida ni gaseosa, sino que comparte propiedades de ambos estados. Fluye como un gas y es capaz de disolver sustancias como un líquido. Algunos fluidos supercríticos son inertes y no tóxicos, lo que permite clasificarlos como disolventes verdes. Además, son relativamente baratos y sus propiedades son ajustables mediante variaciones de presión. In the present invention, an alternative to the current substance / solvent that reduces the impact caused by the use of organic solvents is called "green solvent". They are mainly obtained from renewable raw materials, have low toxicity and are not corrosive or carcinogenic. Examples are alcohols such as methanol and ethanol, soybean oil esters and ethyl lactate. A supercritical fluid is that fluid that is above its critical pressure and temperature and whose phase is neither liquid nor gaseous, but shares properties of both states. It flows like a gas and is capable of dissolving substances like a liquid. Some supercritical fluids are inert and non-toxic, allowing them to be classified as green solvents. In addition, they are relatively cheap and their properties are adjustable through pressure variations.
El aerogel tridimensional monolítico de óxido de grafeno que se obtiene con el procedimiento de la presente invención es una estructura de esponja rígida tridimensional que es estable al aire y en medio acuoso, que presenta una porosidad interconectada de poros de tamaño mesoporoso y que exhibe gran capacidad de adsorción de C02. La adsorción de C02 medida a 273 K muestra valores elevados de adsorción, resultando en valores de hasta 100 mL de C02 adsorbido por gramos de óxido de grafeno. Los sólidos porosos son clasificados por la IUPAC por su promedio en el tamaño de poro. Materiales con un diámetro de aproximadamente 2 nm son microporosos, con poros en un rango mayor a 50 nm son macroporosos y con poros con un rango comprendido entre 2 nm y 50 nm son mesoporosos. El aerogel tridimensional monolítico de óxido de grafeno que se obtiene con el procedimiento de la presente invención está compuesto por láminas exfoliadas de óxido de grafeno altamente anisotrópicas en su forma, con dimensiones laterales de varias mieras, de entre 10 pm y 50 pm y con un grosor de 1 -2 nm. The monolithic graphene oxide three-dimensional airgel that is obtained with the process of the present invention is a three-dimensional rigid sponge structure that is stable in the air and in an aqueous medium, which has an interconnected porosity of mesoporous size pores and exhibits great capacity of adsorption of C0 2 . The adsorption of C0 2 measured at 273 K shows high adsorption values, resulting in values of up to 100 mL of C0 2 adsorbed per grams of graphene oxide. Porous solids are classified by the IUPAC by their average pore size. Materials with a diameter of approximately 2 nm are microporous, with pores in a range greater than 50 nm are macroporous and with pores with a range between 2 nm and 50 nm are mesoporous. The monolithic graphene oxide three-dimensional airgel obtained with the process of the present invention is composed of exfoliated sheets of Graphene oxide highly anisotropic in shape, with lateral dimensions of several microns, between 10 pm and 50 pm and with a thickness of 1 -2 nm.
La composición química del aerogel obtenido se puede describir de la siguiente manera: The chemical composition of the airgel obtained can be described as follows:
• el número total de átomos de oxígeno por cada 100 átomos totales es > 25 % medido por Espectroscopia de fotoelectrones emitidos por rayos X (del inglés X-ray photoelectron spectroscopy, XPS),  • the total number of oxygen atoms per 100 total atoms is> 25% measured by X-ray photoelectron Spectroscopy (XPS),
• el número total de átomos de carbono por cada 100 átomos totales es > 60 % medido por X-ray photoelectron spectroscopy, XPS, y  • The total number of carbon atoms per 100 total atoms is> 60% measured by X-ray photoelectron spectroscopy, XPS, and
• los grupos oxigenados predominantes pertenecen al grupo funcional C=0 (OH).  • The predominant oxygenated groups belong to the functional group C = 0 (OH).
Por tanto, la composición química del aerogel de la presente invención conserva un elevado número de grupos funcionales del óxido de grafeno de partida: el procedimiento de la invención se traduce en un sorprendente bajo grado de reducción de GO a rGO. Los métodos descritos en la literatura resultan en estructuras de materiales carbonaceos porosos similares, pero altamente reducidos ya que utilizan temperaturas mucho más elevadas y disolventes más agresivos. El bajo grado de reducción del aerogel obtenido siguiendo el procedimiento de la presente invención supone una ventaja, puesto que permite post-funcionalizarlos. Therefore, the chemical composition of the airgel of the present invention retains a high number of functional groups of the starting graphene oxide: the process of the invention results in a surprisingly low degree of reduction of GO to rGO. The methods described in the literature result in structures of similar porous carbonaceous materials, but highly reduced since they use much higher temperatures and more aggressive solvents. The low degree of reduction of the airgel obtained following the process of the present invention is an advantage, since it allows post-functionalization.
El aerogel que se obtiene exhibe un área superficial elevada, de entre 100 m2/g y 250 m2/g y un alto volumen de poro, de entre 0,9 ml/g y 1 ,5 mL/g. The airgel that is obtained exhibits a high surface area, between 100 m 2 / g and 250 m 2 / g and a high pore volume, between 0.9 ml / g and 1.5 mL / g.
En un primer aspecto, la presente invención se refiere a un procedimiento de obtención de un aerogel tridimensional monolítico estable al aire y en medio acuosoIn a first aspect, the present invention relates to a method of obtaining a monolithic three-dimensional airgel stable in the air and in aqueous medium
• compuesto por láminas exfoliadas de óxido de grafeno • composed of exfoliated graphene oxide sheets
• con una porosidad interconectada  • with an interconnected porosity
• y poros en el rango de los mesoporos  • and pores in the range of mesopores
caracterizado por que comprende las siguientes etapas: characterized in that it comprises the following stages:
(a) preparación de una dispersión alcohólica estable que comprende nanopartículas laminares o plaquetas de óxido de grafeno;  (a) preparation of a stable alcohol dispersion comprising laminar nanoparticles or graphene oxide platelets;
(b) proceso de gelación de la dispersión obtenida en la etapa (a) mediante la adición de dióxido de carbono comprimido o supercrítico a una temperatura T1 < 370 K y una presión P1 > 6 MPa); y (c) extracción del líquido comprendido dentro del gel obtenido en la etapa (b) mediante secado supercrítico a una temperatura T2 < 370 K y una presión P2 > 15 MPa. (b) gelation process of the dispersion obtained in step (a) by the addition of compressed or supercritical carbon dioxide at a temperature T1 <370 K and a pressure P1> 6 MPa); Y (c) extraction of the liquid comprised within the gel obtained in step (b) by supercritical drying at a temperature T2 <370 K and a pressure P2> 15 MPa.
Preferiblemente, el reactor utilizado en las etapas (a) y (b) consta de un cuerpo de acero inoxidable 316SS de 100 ml_ que aguanta presiones superiores a los 30 MPa. En el cuerpo del reactor se sitúan dos ventanas de zafiro de manera opuesta y que permiten hacer un seguimiento visual de las reacciones que ocurren en el interior. La muestra a procesar se sitúa dentro del reactor siendo visible a través de las ventanas de zafiro. El reactor se calienta mediante cuatro resistencias insertadas en el cuerpo del reactor. El reactor consta de una entrada de C02. El C02 se comprime mediante una bomba de alta presión. El reactor se despresuriza eliminando el C02 del reactor mediante una válvula micrométrica. La presión en el reactor se mide y se controla a través de un manómetro (PG) y un transductor de presión (PT, PIC). La temperatura en el reactor se mide y se controla con un termopar (T/C, TIC). Preferably, the reactor used in steps (a) and (b) consists of a 316SS stainless steel body of 100 ml_ that withstands pressures greater than 30 MPa. Two sapphire windows are placed opposite each other in the reactor body and allow visual monitoring of the reactions that occur inside. The sample to be processed is placed inside the reactor being visible through the sapphire windows. The reactor is heated by four resistors inserted in the reactor body. The reactor consists of an input of C0 2 . The C0 2 is compressed by a high pressure pump. The reactor is depressurized removing C0 2 reactor by micrometering valve. The pressure in the reactor is measured and controlled through a pressure gauge (PG) and a pressure transducer (PT, PIC). The temperature in the reactor is measured and controlled with a thermocouple (T / C, TIC).
La etapa (a) del procedimiento de la invención se refiere a la preparación de una dispersión alcohólica estable que comprende nanopartículas laminares o plaquetas de óxido de grafeno. Step (a) of the process of the invention relates to the preparation of a stable alcohol dispersion comprising laminar nanoparticles or graphene oxide platelets.
La etapa (a) se puede llevar a cabo mediante intercambio convencional de disolventes, preferiblemente mediante intercambio agua/alcohol. Step (a) can be carried out by conventional solvent exchange, preferably by water / alcohol exchange.
Una vez obtenida la dispersión alcohólica, ésta se transfiere a un reactor, donde se lleva a cabo la etapa (b), un proceso de gelación mediante la adición de un fluido supercrítico a una temperatura T 1 < 370 K y una presión P1 > 6 MPa. Once the alcoholic dispersion is obtained, it is transferred to a reactor, where step (b) is carried out, a gelation process by adding a supercritical fluid at a temperature T 1 <370 K and a pressure P1> 6 MPa.
La gelación convencional descrita en la literatura (estado del arte) requiere el uso de aditivos contaminantes, o bien altas temperaturas en tratamientos hidrotermales y solvotermales, por lo que la etapa (b) del procedimiento de la presente invención supone una ventaja con respecto al estado del arte. The conventional gelation described in the literature (state of the art) requires the use of contaminating additives, or high temperatures in hydrothermal and solvothermal treatments, so that step (b) of the process of the present invention is an advantage over the state Of art.
Un“fluido supercrítico” es cualquier sustancia que se encuentre en condiciones de presión y temperatura superiores a su punto crítico. A "supercritical fluid" is any substance that is under conditions of pressure and temperature above its critical point.
Los estados de agregación de la materia que se conocen actualmente son cinco: sólido, líquido, gas, plasma y condensado de Bose-Einstein. Un fluido supercrítico es un casi estado con propiedades intermedias entre líquidos y gases. The aggregation states of matter that are currently known are five: solid, liquid, gas, plasma and Bose-Einstein condensate. A fluid Supercritical is an almost state with intermediate properties between liquids and gases.
En un diagrama de fases clásico, las curvas de fusión, sublimación y vaporización muestran las zonas de coexistencia de dos fases. Tan solo hay un punto de coexistencia de tres fases, el llamado punto triple (PT). El cambio de fase se asocia a un cambio brusco de entalpia y densidad. Pero por encima del punto crítico (PC) este cambio no se produce, por tanto, podríamos definir este punto como aquel por encima del cual no se produce licuefacción al presurizar, ni gasificación al calentar; y por ende un fluido supercrítico es aquel que se encuentra por encima de dicho punto. In a classic phase diagram, the melting, sublimation and vaporization curves show the coexistence zones of two phases. There is only one point of coexistence of three phases, the so-called triple point (PT). The phase change is associated with a sharp change in enthalpy and density. But above the critical point (PC) this change does not occur, therefore, we could define this point as the one above which no liquefaction occurs when pressurizing, nor gasification when heating; and therefore a supercritical fluid is one that is above that point.
A continuación se resumen las características de un fluido supercrítico. The characteristics of a supercritical fluid are summarized below.
• No existe interfase gas-líquido  • There is no gas-liquid interface
• La compresibilidad isotérmica se hace infinitamente positiva  • Isothermal compressibility becomes infinitely positive
· El coeficiente de expansión térmica es infinito y positivo  · The coefficient of thermal expansion is infinite and positive
• La entalpia de vaporización es cero  • The enthalpy of vaporization is zero
• Si la densidad se mantiene constante e igual a la densidad crítica la capacidad calorífica a volumen constante tiende al infinito  • If the density remains constant and equal to the critical density the heat capacity at constant volume tends to infinity
• La densidad por encima del punto crítico depende básicamente de la presión y la temperatura, pero en cualquier caso está más cercana a la de los líquidos que a la de los gases. La densidad aumenta si lo hace la presión a temperatura constante y si disminuye la temperatura a presión constante.  • Density above the critical point depends basically on pressure and temperature, but in any case it is closer to that of liquids than to gases. The density increases if the pressure is at constant temperature and if the temperature decreases at constant pressure.
• La viscosidad es mucho más baja que la de los líquidos, lo que le confiere propiedades hidrodinámicas muy favorables  • The viscosity is much lower than that of liquids, which gives it very favorable hydrodynamic properties
· La bajísima tensión superficial permite una alta penetrabilidad a través de sólidos porosos y lechos empaquetados.  · The very low surface tension allows high penetrability through porous solids and packed beds.
• Mayores coeficientes de difusión (difusividad) que en líquidos por lo que la transferencia de materia es más favorable En una realización preferida del procedimiento de la invención, las etapas (b) y (c) se llevan a cabo  • Higher diffusion coefficients (diffusivity) than in liquids so that the transfer of matter is more favorable In a preferred embodiment of the process of the invention, steps (b) and (c) are carried out
• en condiciones isobáricas, donde la primera presión P1 es igual a la segunda presión P2, siendo ambas presiones P1 y P2 mayores de 15 MPa y  • in isobaric conditions, where the first pressure P1 is equal to the second pressure P2, both pressures P1 and P2 being greater than 15 MPa and
• en condiciones isotérmicas, donde la primera temperatura T1 es igual a la segunda temperatura. En otra realización preferida del procedimiento de la invención, las etapas (b) y (c) se llevan a cabo • in isothermal conditions, where the first temperature T1 is equal to the second temperature. In another preferred embodiment of the process of the invention, steps (b) and (c) are carried out.
• en condiciones isobáricas, donde la primera presión P1 es igual a la segunda presión P2, siendo ambas presiones P1 y P2 mayores de 15 MPa.  • in isobaric conditions, where the first pressure P1 is equal to the second pressure P2, both pressures P1 and P2 being greater than 15 MPa.
En otra realización preferida del procedimiento de la invención, las etapas (b) y (c) se llevan a cabo In another preferred embodiment of the process of the invention, steps (b) and (c) are carried out.
• en condiciones isotérmicas, donde la primera temperatura T1 es igual a la segunda temperatura T2.  • in isothermal conditions, where the first temperature T1 is equal to the second temperature T2.
En otra realización preferida del procedimiento de la invención, donde el fluido supercrítico de las etapas (b) y (c) es C02 supercrítico. In another preferred embodiment of the process of the invention, wherein the supercritical fluid of steps (b) and (c) is supercritical C0 2 .
El proceso final para la formación del aerogel de óxido de grafeno es el secado supercrítico. Aquí es donde el líquido que hay dentro del gel es retirado, dejando únicamente la red tridimensional sólida del aerogel. The final process for the formation of the graphene oxide airgel is supercritical drying. This is where the liquid inside the gel is removed, leaving only the solid three-dimensional network of the airgel.
La etapa (c) del procedimiento de la invención se refiere a la extracción del líquido comprendido dentro del gel obtenido en la etapa (b) mediante secado supercrítico a una temperatura T2 < 370 K y P2 > 15 MPa. El tratamiento de secado supercrítico trata de eliminar el disolvente del gel obtenido en la etapa (b) sin generar un sistema de dos fases (líquido/vapor) y evitar así las fuerzas capilares que generarían el colapso de la estructura. Step (c) of the process of the invention refers to the extraction of the liquid comprised within the gel obtained in step (b) by supercritical drying at a temperature T2 <370 K and P2> 15 MPa. The supercritical drying treatment tries to remove the solvent from the gel obtained in step (b) without generating a two-phase system (liquid / vapor) and thus avoid the capillary forces that would cause the structure to collapse.
A lo largo de la descripción y las reivindicaciones la palabra "comprende" y sus variantes no pretenden excluir otras características técnicas, aditivos, componentes o pasos. Para los expertos en la materia, otros objetos, ventajas y características de la invención se desprenderán en parte de la descripción y en parte de la práctica de la invención. Los siguientes ejemplos y figuras se proporcionan a modo de ilustración, y no se pretende que sean limitativos de la presente invención. Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.
BREVE DESCRIPCIÓN DE LAS FIGURAS BRIEF DESCRIPTION OF THE FIGURES
Figura 1. Representación molecular de una lámina de óxido de grafeno (GO), indicando los principales grupos funcionales, así como las dimensiones de las láminas. Figura 2. Representación esquemática de los distintos pasos de reacción utilizados para obtener aerogeles de óxido de grafeno (GO) utilizando el método de secado a baja temperatura con C02 supercrítico. Figure 1. Molecular representation of a sheet of graphene oxide (GO), indicating the main functional groups, as well as the dimensions of the sheets. Figure 2. Schematic representation of the different reaction steps used to obtain graphene oxide (GO) aerogels using the low temperature drying method with supercritical C0 2 .
Figura 3. Esquematización del reactor de 100 ml_ de alta presión (1 ) con ventanas de zafiro (2) utilizado en los experimentos de preparación de aerogeles por gelificación y secado con scC02, en el que se indican los elementos más importantes de resistencias (3) y control de temperatura, presión y flujo de C02 circulando desde la entrada (4) hasta la salida (6) y comprimido mediante una bomba de alta presión (5). Figure 3. Schematization of the 100 ml_ high pressure reactor (1) with sapphire windows (2) used in the experiments of preparation of aerogels by gelation and drying with scC0 2 , in which the most important elements of resistance are indicated ( 3) and control of temperature, pressure and flow of C0 2 circulating from the inlet (4) to the outlet (6) and compressed by a high pressure pump (5).
Figura 4. Tres fotografías ópticas del gel inestable obtenido en el experimento realizado en el Ejemplo 1 , fotografiado a distintos tiempos t: t = 0 (inmediatamente después de sacarlo del reactor), después de 1 h (t = 1 h) y después de 10 h (t = 10 h). Figure 4. Three optical photographs of the unstable gel obtained in the experiment performed in Example 1, photographed at different times t: t = 0 (immediately after removing it from the reactor), after 1 h (t = 1 h) and after 10 h (t = 10 h).
Figura 5. Cuatro fotografías ópticas del gel estable obtenido en el experimento realizado en el Ejemplo 2, fotografiado a distintos tiempos t: t = 0 (inmediatamente después de sacarlo del reactor), y después de mantener dicho gel en la nevera durante 1 (t = 1 mes), 2 (t = 2 meses) y 3 (t = 3 meses) meses. Figure 5. Four optical photographs of the stable gel obtained in the experiment performed in Example 2, photographed at different times t: t = 0 (immediately after removing it from the reactor), and after keeping said gel in the refrigerator for 1 (t = 1 month), 2 (t = 2 months) and 3 (t = 3 months) months.
Figura 6. Dos imágenes de microscopía electrónica de barrido a distintas magnificaciones, 400 (a) y 800 de magnificación (b) mostrando la película obtenida en el experimento realizado en el Ejemplo 2. Figure 6. Two scanning electron microscopy images at different magnifications, 400 (a) and 800 magnification (b) showing the film obtained in the experiment performed in Example 2.
Figura 7. Una fotografía óptica de la película obtenida en el experimento realizado en el Ejemplo 3, fotografiado a un tiempo t = 0 (inmediatamente después de sacarlo del reactor). Figure 7. An optical photograph of the film obtained in the experiment performed in Example 3, photographed at a time t = 0 (immediately after removing it from the reactor).
Figura 8. Dos imágenes de microscopía electrónica de barrido a distintas magnificaciones 300 (a) y 3000 de magnificación (b) mostrando la película obtenida en el experimento realizado en el Ejemplo 3. Figure 8. Two scanning electron microscopy images at different magnifications 300 (a) and 3000 magnification (b) showing the film obtained in the experiment performed in Example 3.
Figura 9. Ocho fotografías ópticas representando la formación del aerogel descrito en el experimento realizado en el Ejemplo 4, fotografiado a distintos tiempos t: t = 0 (inmediatamente después de meterlo en el reactor), y después de periodos de 1 h (t = 1 h) y 2 h (t = 2 h), en el intervalo que va de las 20 h a las 35 h de reacción (t = 20-35 h), e inmediatamente después de sacarlo del reactor (t = 50 h). Figura 10. Dos imágenes de microscopía electrónica de barrido a distintas magnificaciones 3000 (a) y 24000 de magnificación (a) del aerogel obtenido en el experimento realizado en el Ejemplo 4. Figure 9. Eight optical photographs representing the formation of the airgel described in the experiment performed in Example 4, photographed at different times t: t = 0 (immediately after putting it in the reactor), and after periods of 1 h (t = 1 h) and 2 h (t = 2 h), in the range from 20 h to 35 h of reaction (t = 20-35 h), and immediately after removing it from the reactor (t = 50 h). Figure 10. Two scanning electron microscopy images at different magnifications 3000 (a) and 24000 magnification (a) of the airgel obtained in the experiment performed in Example 4.
Figura 11. Gráfica de adsorción de C02 de la muestra obtenida en el Ejemplo 4. Figure 11. C0 2 adsorption plot of the sample obtained in Example 4.
Figura 12. Cinco fotografías ópticas del aerogel obtenido en el experimento realizado en el Ejemplo 5, fotografiado a distintos tiempos t: t = 0 (inmediatamente después de meterlo en el reactor), y después de periodos de t = 1 h, t = 2 h y t = 35 h de reacción, e inmediatamente después de sacarlo del reactor a t = 50 h. Figure 12. Five optical photographs of the airgel obtained in the experiment performed in Example 5, photographed at different times t: t = 0 (immediately after putting it in the reactor), and after periods of t = 1 h, t = 2 hyt = 35 h of reaction, and immediately after removing it from the reactor at = 50 h.
Figura 13. Dos imágenes de microscopía electrónica de barrido obtenidas a distintas magnificaciones 1500 (a) y derecha 20000 de magnificación (b) del aerogel obtenida en el experimento realizado en el Ejemplo 5. Figure 13. Two scanning electron microscopy images obtained at different magnifications 1500 (a) and right 20000 magnification (b) of the airgel obtained in the experiment performed in Example 5.
Figura 14. Gráfica de adsorción de C02 de la muestra obtenida en el Ejemplo 5. Figure 14. C0 2 adsorption plot of the sample obtained in Example 5.
EJEMPLOS A continuación se describe una serie de ensayos realizados por los inventores, que se consideran representativos de la efectividad del método de la invención para la utilización de procesos supercríticos en la preparación de aerogeles de óxido de grafeno (GO). Se detalla el procedimiento de la invención a título de ejemplo no limitativo y puramente ilustrativo. El procedimiento utilizado está esquematizado en Fig. 2. El procedimiento comienza con una etapa de preparación de muestra previa al tratamiento supercrítico de la siguiente manera: EXAMPLES The following describes a series of tests carried out by the inventors, which are considered representative of the effectiveness of the method of the invention for the use of supercritical processes in the preparation of graphene oxide (GO) aerogels. The process of the invention is detailed by way of non-limiting and purely illustrative example. The procedure used is schematized in Fig. 2. The procedure begins with a sample preparation stage prior to supercritical treatment as follows:
1. Toma de una alícuota de óxido de grafeno (GO) dispersado en agua. La dispersión utilizado en los ejemplos consta de nanopartículas de GO con dimensiones laterales aprox. de 30 pm y tiene una concentración de 4 mg/mL. 1. Take an aliquot of graphene oxide (GO) dispersed in water. The dispersion used in the examples consists of GO nanoparticles with lateral dimensions approx. 30 pm and has a concentration of 4 mg / mL.
2. Intercambio de la fase acuosa por un volumen similar de etanol mediante una secuencia de centrifugado (12000 rpm, 30 min), decantación por extracción con pipeta, redispersión en etanol y sonicación (30 min), toda ella repetida un mínimo de 3 veces. 3. Trasvase de alícuotas de 1 mL de la dispersión en etanol de concentración aproximada 3 mg/ml_ a un tubo de ensayo de vidrio de 2 mL con diámetro de 0,7 cm, e introducción del mismo en el reactor de alta presión. Los elementos más importantes de este reactor se han esquematizado en la Figura 3: El reactor consta de un cuerpo de acero inoxidable 316SS (1 ) de 100 mL que aguanta presiones superiores a los 30 MPa (300 bar). En el cuerpo del reactor se sitúan dos ventanas de zafiro (2) de forma opuesta y que permiten hacer un seguimiento visual de las reacciones que ocurren en el interior. La muestra a procesar se sitúa dentro del reactor siendo visible a través de las ventanas de zafiro. El reactor se calienta mediante cuatro resistencias (3) insertadas en el cuerpo del reactor. El reactor consta de una entrada de C02 (4). El C02 se comprime mediante una bomba de alta presión (5). El reactor se despresuriza eliminando el C02 del reactor mediante una válvula micrométrica (6). La presión en el reactor en el reactor se mide y se controla a través de un manómetro (PG) y un transductor de presión (PT, PIC). La temperatura en el reactor se mide y se controla con un termopar (T/C, TIC). 2. Exchange of the aqueous phase for a similar volume of ethanol by means of a spin sequence (12000 rpm, 30 min), decantation by pipette extraction, redispersion in ethanol and sonication (30 min), all repeated a minimum of 3 times . 3. Transfer of 1 mL aliquots of the ethanol dispersion of approximate concentration 3 mg / ml_ to a 2 mL glass test tube with a diameter of 0.7 cm, and insertion into the high pressure reactor. The most important elements of this reactor have been schematized in Figure 3: The reactor consists of a 316SS (1) 100 mL stainless steel body that withstands pressures greater than 30 MPa (300 bar). Two sapphire windows (2) are placed opposite each other in the reactor body and allow visual monitoring of the reactions that occur inside. The sample to be processed is placed inside the reactor being visible through the sapphire windows. The reactor is heated by four resistors (3) inserted in the reactor body. The reactor consists of an input of C0 2 (4). The C0 2 is compressed by a high pressure pump (5). The reactor is depressurized removing C0 2 reactor by micrometering valve (6). The pressure in the reactor in the reactor is measured and controlled through a pressure gauge (PG) and a pressure transducer (PT, PIC). The temperature in the reactor is measured and controlled with a thermocouple (T / C, TIC).
En un experimento estándar, un tubo de ensayo conteniendo la dispersión de GO en medio alcohólico se sitúa dentro del cuerpo del reactor (1 ), visible a través de las ventanas de zafiro (2). El reactor se sella con la muestra dentro, quedando preparado para aumentar la presión y la temperatura. Se añade C02 al reactor a presión de botella (P=6 MPa) y se sube la temperatura hasta la temperatura de trabajo. A continuación se presuriza el reactor hasta la presión de trabjao. Estas condiciones se mantienen durante un periodo de tiempo largo, generalmente superior a 24 h, lo que conduce a la formación de un gel en el tubo de ensayo que esta dentro del reactor. A continuación, se pueden o no modificar las condiciones de presión y temperatura (generalmente aumentando ambas ligeramente) para llevar a cabo el secado del gel. Sino se modifican, se considera que se trabaja en condiciones isobáricas e isotérmicas. El secado del gel se consigue eliminando la fase supercrítica del reactor, que se lleva consigo el etanol añadido inicialmente en el tubo de ensayo. Este proceso se puede completar añadiendo mas C02 sin etanol directamente de la bomba (5), con el objetivo de eliminar en su totalidad el etanol. Finalmente, el reactor se despresuriza por la válvula (6) hasta presión ambiental, manteniendo la temperatura de trabajo. El reactor se deja enfriar a temperatura de laboratorio, y está listo para abrirlo y recuperar la muestra. Los ejemplos se llevan a cabo sin agitación, a no ser que se especifique lo contrario. In a standard experiment, a test tube containing the dispersion of GO in alcoholic medium is placed inside the reactor body (1), visible through the sapphire windows (2). The reactor is sealed with the sample inside, being prepared to increase the pressure and temperature. C0 2 is added to the reactor under bottle pressure (P = 6 MPa) and the temperature is raised to the working temperature. The reactor is then pressurized to the working pressure. These conditions are maintained for a long period of time, generally greater than 24 h, which leads to the formation of a gel in the test tube that is inside the reactor. Then, the pressure and temperature conditions (generally increasing both slightly) may or may not change to dry the gel. If they are not modified, it is considered to work in isobaric and isothermal conditions. Drying of the gel is achieved by eliminating the supercritical phase of the reactor, which carries with it the ethanol initially added in the test tube. This process can be completed by adding more C0 2 without ethanol directly from the pump (5), with the aim of completely eliminating ethanol. Finally, the reactor is depressurized by the valve (6) to ambient pressure, maintaining the working temperature. The reactor is allowed to cool to laboratory temperature, and is ready to open and recover the sample. The examples are carried out without agitation, unless otherwise specified.
Ejemplo 1 : Obtención de un gel inestable de óxido de grafeno (GO) 4. Incremento de la presión en el reactor hasta 6 MPa a temperatura ambienteExample 1: Obtaining an unstable graphene oxide (GO) gel 4. Increase the pressure in the reactor to 6 MPa at room temperature
(aproximadamente 298 K), seguido de un incremento de la temperatura hasta 368 K y otro de la presión hasta 20 MPa, manteniéndose estas condiciones durante 2 h. (approximately 298 K), followed by an increase in temperature to 368 K and another pressure up to 20 MPa, maintaining these conditions for 2 h.
5. Con el reactor a una temperatura de 368 K y una presión de 20 MPa, se pasan 350 mL de CO2 en un periodo de 3 h, siendo el flujo aprox. de 1 ,95 mL/min. 5. With the reactor at a temperature of 368 K and a pressure of 20 MPa, 350 mL of CO2 is passed over a period of 3 h, the flow being approx. of 1.95 mL / min.
6. Despresurización lenta del reactor 0,08-0,1 MPa/min a una temperatura de 308 K, dejándolo enfriar finalmente a temperatura ambiente. Con este protocolo se obtiene un gel inestable que colapsa en unos minutos debido a la evaporación del alcohol que todavía contiene, formando un pequeño monolito de porosidad insignificante. La estructura 3D no se mantiene debido al poco tiempo de gelificación empleado. La Figura 4 muestra la evolución del gel a distintos tiempos t: t = 0 (al sacarlo del reactor), t = 1 h (húmedo y parcialmente colapsado) y t = 10 h (seco y totalmente colapsado). 6. Slow depressurization of the reactor 0.08-0.1 MPa / min at a temperature of 308 K, finally allowing it to cool to room temperature. With this protocol an unstable gel is obtained that collapses in a few minutes due to the evaporation of the alcohol that it still contains, forming a small monolith of insignificant porosity. The 3D structure is not maintained due to the short gelation time used. Figure 4 shows the evolution of the gel at different times t: t = 0 (when removed from the reactor), t = 1 h (wet and partially collapsed) and t = 10 h (dry and fully collapsed).
Ejemplo 2: Obtención de un gel estable de óxido de grafeno (GO) Example 2: Obtaining a stable graphene oxide (GO) gel
4. Incremento de la presión en el reactor hasta 6 MPa a temperatura ambiente (aprox. 298 K), manteniéndose estas condiciones durante 18 h. 4. Increase the pressure in the reactor to 6 MPa at room temperature (approx. 298 K), maintaining these conditions for 18 h.
5. Presurización del reactor a 20 MPa y temperatura de 323 K y paso a través del reactor de un flujo de 350 mL de C02 en un periodo de 3 h, siendo el flujo aprox. de 1 ,95 mL/min. 5. Pressurization of the reactor to 20 MPa and temperature of 323 K and passage through the reactor a flow of 350 mL of C0 2 in a period of 3 h, with the flow approx. of 1.95 mL / min.
6. Enfriamiento del reactor hasta una temperatura de 308 K. Despresurización lenta del reactor 0,08-0,1 MPa/min a una temperatura de 308 K, dejándolo finalmente enfriar a temperatura ambiente. Con este protocolo se obtiene un alcogel estable que, guardado a una temperatura de 279 K en nevera, tarda varios meses en colapsar. En este caso, las etapas de secado y consolidación no han sido eficientes en la obtención de un aerogel 3D seco debido a las bajas temperaturas de proceso empleadas durante todo el proceso. 6. Cooling the reactor to a temperature of 308 K. Slow depressurization of the reactor 0.08-0.1 MPa / min at a temperature of 308 K, finally allowing it to cool to room temperature. With this protocol a stable alcogel is obtained which, stored at a temperature of 279 K in a refrigerator, takes several months to collapse. In this case, the drying stages and consolidation have not been efficient in obtaining a dry 3D airgel due to the low process temperatures used throughout the process.
La Figura 5 muestra la evolución del gel a distintos tiempos t: t = 0 (al sacarlo del reactor), a t = 1 mes en nevera, mostrando un gel con apariencia similar al observado al sacarlo del reactor, y a t = 3 meses en nevera, donde se observa que finalmente el gel ha colapsado. Figure 5 shows the evolution of the gel at different times t: t = 0 (when removed from the reactor), at = 1 month in the refrigerator, showing a gel with an appearance similar to that observed when removed from the reactor, yat = 3 months in the refrigerator, where it is observed that the gel has finally collapsed.
La Figura 6 muestra imágenes de microscopía electrónica de barrido de la película obtenida a los tres meses. Figure 6 shows scanning electron microscopy images of the film obtained at three months.
Ejemplo 3: Obtención de una película de óxido de grafeno (GO) Example 3: Obtaining a graphene oxide (GO) film
4. Incremento de la temperatura del reactor hasta 368 K y adición de C02 hasta una presión de 12 MPa, manteniéndose estas condiciones durante 18 h. 4. Increase the reactor temperature up to 368 K and add C0 2 to a pressure of 12 MPa, maintaining these conditions for 18 h.
5. A una temperatura de 368 K y una presión de 20 MPa, se pone en marcha la agitación del reactor a 300 rpm, a la vez que se pasan 350 mL de C02 en un periodo de 3 h siendo el flujo aproximadamente de 1 ,95 mL/min. 5. At a temperature of 368 K and a pressure of 20 MPa, the agitation of the reactor is started at 300 rpm, while 350 mL of C0 2 is passed over a period of 3 hours, the flow being approximately 1 , 95 mL / min.
6. Despresurización lenta del reactor 0,08 - 0,1 MPa/min a una temperatura de 308 K, dejándolo enfriar a temperatura ambiente. 6. Slow depressurization of the reactor 0.08-0.1 MPa / min at a temperature of 308 K, allowing it to cool to room temperature.
Con este protocolo se obtiene un film seco, sin estructura 3D ni porosidad. En este caso, la agitación que se ha mantenido en las etapas de consolidación y secado lleva al colapso de la estructura 3D, formándose un film donde las láminas de grafeno se alinean y agregan para reducir el área superficial. With this protocol a dry film is obtained, without 3D structure or porosity. In this case, the agitation that has been maintained in the stages of consolidation and drying leads to the collapse of the 3D structure, forming a film where graphene sheets are aligned and added to reduce the surface area.
La Figura 7 muestra el film obtenido a un tiempo t = 0 (al sacarlo del reactor). Figure 7 shows the film obtained at a time t = 0 (when removed from the reactor).
Las imágenes de microscopía electrónica de barrido se muestran en la Figura 8. En ellas se observa un sistema no poroso. Scanning electron microscopy images are shown in Figure 8. A non-porous system is observed.
Ejemplo 4: Obtención de un aerogel de óxido de grafeno (GO) aplicando el método de variación de temperatura y presión 4. Incremento de la temperatura del reactor hasta 298 K y adición de C02 hasta una presión de 6 MPa, manteniéndose estas condiciones durante 18 h. Example 4: Obtaining a graphene oxide (GO) airgel using the method of temperature and pressure variation 4. Increase the reactor temperature up to 298 K and add C0 2 to a pressure of 6 MPa, maintaining these conditions for 18 h.
5. Aumento de la temperatura y presión del reactor hasta 368 K y 20 MPa, y paso de 350 ml_ de C02 en un periodo de 3 h, siendo el flujo aproximado de 1 ,95 mL/min, manteniendo a continuación el reactor en estas condiciones durante 18 h sin flujo. 5. Increase of the temperature and pressure of the reactor up to 368 K and 20 MPa, and passage of 350 ml_ of C0 2 in a period of 3 h, the flow being approximately 1.95 mL / min, then keeping the reactor in these conditions for 18 h without flow.
6. Enfriamiento del reactor hasta una temperatura de 313 K y despresurización lenta 0,08-0,1 MPa/min a esta temperatura, dejándolo finalmente enfriar a temperatura ambiente. 6. Cooling the reactor to a temperature of 313 K and slow depressurization 0.08-0.1 MPa / min at this temperature, finally allowing it to cool to room temperature.
Con este protocolo se obtiene un monolito 3D de grafeno altamente poroso. En la formación de este aerogel se pueden observar las distintas etapas de reacción descritas anteriormente. El proceso empieza situando la dispersión alcohólica dentro del reactor y presurizándolo con C02 comprimido. El C02, fase mayoritaria, se va disolviendo en la fase líquida alcohólica lo que expande el etanol, observándose un menisco de líquido por encima del nivel de la dispersión de grafeno (véase Figura 9 t = 0 h). Esta fase líquida disminuye con el paso del tiempo (véase Figura 9, t = 1 h), y prácticamente no es visible después de un periodo de aproximadamente 2 h (véase Figura 9, t = 2 h). Paralelamente, se observa el inicio de la formación de un sistema rígido tipo gel acompañado de un cierto hinchamiento de la fase dispersada. La mezcal bidireccional de C02 y etanol continúa durante la etapa de secado y consolidación, produciéndose cierto encogimiento radial del gel debido a la menor densidad del C02 supercrítico que substituye al etanol (véase Figura 9, t = 20-35 h). Finalmente se obtiene un sólido poroso (véase Figura 9, t = 50 h), con un volumen de aproximado de 75 % del volumen ocupado por la dispersión inicial. Las imágenes de microscopía electrónica de barrido de la muestra obtenida se muestran en la Figura 10. En ellas se observa un sistema poroso interconectado. La deconvolución del espectro de alta resolución correspondiente al carbono C1 s obtenida por XPS muestra un contenido en Csp2 de 22,7 átomos %, mientras que los grupos funcionales oxigenados predominantes C=0(0H) corresponden a 21 ,8 átomos %. El método de adsorción/desorción de N2 a baja temperatura da unas propiedades texturales para esta muestra definidas como 8 nm de tamaño medio de poro, 262 m2/g de área superficial y 1 ,5 mL/g de volumen de poro (Tabla 1 ). Tabla 1. Resultados de la caracterización de los materiales obtenidos en los distintos Ejemplos de esta invención, incluyendo las medidas de las propiedades texturales y de la adsorción de C02. Sa: superficie específica, Vp: volumen de poro, D: diámetro medio de poro, VadC02: volumen adsorbido de C02, así como los resultados más representativos de XPS expresados como % atómico. With this protocol a highly porous graphene 3D monolith is obtained. In the formation of this airgel, the different reaction steps described above can be observed. The process begins by placing the alcoholic dispersion within the reactor and pressurizing with compressed C0 2. The C0 2 , majority phase, dissolves in the alcoholic liquid phase which expands the ethanol, observing a meniscus of liquid above the level of the graphene dispersion (see Figure 9 t = 0 h). This liquid phase decreases with time (see Figure 9, t = 1 h), and is practically not visible after a period of approximately 2 h (see Figure 9, t = 2 h). In parallel, the onset of the formation of a rigid gel-type system accompanied by a certain swelling of the dispersed phase is observed. The bidirectional mezcal of C0 2 and ethanol continues during the drying and consolidation stage, producing some radial shrinkage of the gel due to the lower density of the supercritical C0 2 that replaces ethanol (see Figure 9, t = 20-35 h). Finally, a porous solid is obtained (see Figure 9, t = 50 h), with a volume of approximately 75% of the volume occupied by the initial dispersion. Scanning electron microscopy images of the sample obtained are shown in Figure 10. There is an interconnected porous system. The deconvolution of the high resolution spectrum corresponding to the C1 s carbon obtained by XPS shows a Csp 2 content of 22.7% atoms, while the predominant oxygenated functional groups C = 0 (0H) correspond to 21.8% atoms. The adsorption / desorption method of N 2 at low temperature gives textural properties for this sample defined as 8 nm of average pore size, 262 m 2 / g surface area and 1.5 mL / g pore volume (Table one ). Table 1. Results of the characterization of the materials obtained in the different Examples of this invention, including the measurements of the textural properties and the adsorption of C0 2 . Sa: specific surface area, Vp: pore volume, D: average pore diameter, VadC0 2 : adsorbed volume of C0 2 , as well as the most representative results of XPS expressed as atomic%.
Figure imgf000016_0001
Figure imgf000016_0001
La adsorción de C02 a 273 K es de 1 14 mL/g (Tabla 1 ), mostrándose la gráfica de adsorción (fisisorción) en la Figura 11. The adsorption of C0 2 at 273 K is 1 14 mL / g (Table 1), showing the graph of adsorption (fisisorption) in Figure 11.
Ejemplo 5: Obtención de un aerogel en condiciones isobáricas e isotérmicas. Example 5: Obtaining an airgel in isobaric and isothermal conditions.
4. Incremento de la temperatura del reactor hasta 333 K y adición de C02 hasta una presión de 20 MPa, manteniéndose estas condiciones durante 48 h. 4. Increase the reactor temperature to 333 K and add C0 2 to a pressure of 20 MPa, maintaining these conditions for 48 h.
5. A una temperatura de 333 K el reactor se despresuriza lentamente (0,08-0,1 MPa/min), dejándolo finalmente enfriar a temperatura ambiente. 5. At a temperature of 333 K the reactor depressurizes slowly (0.08-0.1 MPa / min), finally allowing it to cool to room temperature.
Con este protocolo, se obtiene un monolito 3D de grafeno altamente poroso. En la formación de este aerogel se pueden observar las distintas etapas de reacción descritas anteriormente en el Ejemplo 4 (véase Figura 12). El encogimiento del monolito con respecto al volumen ocupado por la dispersión inicial es de aproximadamente 15-20 %. Las imágenes de microscopía electrónica de barrido de la muestra obtenida se muestran en la Figura 13. En ellas se observa un sistema poroso interconectado. With this protocol, a highly porous graphene 3D monolith is obtained. In the formation of this airgel, the different reaction steps described above in Example 4 can be observed (see Figure 12). The shrinkage of the monolith with respect to the volume occupied by the initial dispersion is approximately 15-20%. Scanning electron microscopy images of the sample obtained are shown in Figure 13. There is an interconnected porous system.
La deconvolución del espectro de alta resolución correspondiente al carbono C1 s obtenida por XPS muestra un contenido en Csp2 de 15,8 átomos %, mientras que los grupos funcionales oxigenados predominantes C=0(0H) corresponden a 22,8 átomos %. El método de adsorción/desorción de N2 a baja temperatura da unas propiedades texturales para esta muestra definidas como 8 nm de tamaño medio de poro, 218 m2/g de área superficial y 0,7 ml_/g de volumen de poro (Tabla 1 ). The deconvolution of the high resolution spectrum corresponding to the C1 s carbon obtained by XPS shows a Csp 2 content of 15.8% atoms, while the predominant oxygenated functional groups C = 0 (0H) correspond to 22.8% atoms. The adsorption / desorption method of N 2 at low temperature gives properties Textures for this sample defined as 8 nm of average pore size, 218 m 2 / g of surface area and 0.7 ml_ / g of pore volume (Table 1).
La adsorción de C02 a 273 K es de 1 10 mL/g (Tabla 1 ), mostrándose la gráfica de adsorción (fisisorción) en la Figura 14. The adsorption of C0 2 at 273 K is 1 10 mL / g (Table 1), showing the graph of adsorption (fisisorption) in Figure 14.

Claims

REIVINDICACIONES
1. Un procedimiento de obtención de un aerogel tridimensional monolítico estable al aire y en medio acuoso 1. A procedure for obtaining a monolithic three-dimensional airgel stable in the air and in an aqueous medium
· compuesto por láminas exfoliadas de óxido de grafeno  · Composed of exfoliated graphene oxide sheets
• con una porosidad interconectada  • with an interconnected porosity
• y poros en el rango de los mesoporos  • and pores in the range of mesopores
caracterizado por que comprende las siguientes etapas: characterized in that it comprises the following stages:
(a) preparación de una dispersión alcohólica estable que comprende nanopartículas laminares o plaquetas de óxido de grafeno;  (a) preparation of a stable alcohol dispersion comprising laminar nanoparticles or graphene oxide platelets;
(b) proceso de gelación de la dispersión obtenida en la etapa (a) mediante la adición de un fluido supercrítico a una primera temperatura T1 < 370 K y una primera presión P1 > 6 MPa; y  (b) process of gelation of the dispersion obtained in step (a) by adding a supercritical fluid at a first temperature T1 <370 K and a first pressure P1> 6 MPa; Y
(c) extracción del líquido comprendido dentro del gel obtenido en la etapa (b) mediante secado supercrítico a una segunda temperatura T2 < 370 K y una segunda presión P2 (c) extraction of the liquid included in the gel obtained in step (b) by supercritical drying at a second temperature T2 <370 K and a second pressure P2
> 15 MPa. > 15 MPa.
2. El procedimiento según la reivindicación 1 , donde la etapa (a) del procedimiento se lleva a cabo mediante intercambio agua/alcohol. 2. The process according to claim 1, wherein step (a) of the process is carried out by water / alcohol exchange.
3. El procedimiento según cualquiera de las reivindicaciones 1 ó 2, donde las etapas (b) y (c) se llevan a cabo 3. The method according to any of claims 1 or 2, wherein steps (b) and (c) are carried out
• en condiciones isobáricas, donde la primera presión P1 es igual a la segunda presión P2, siendo ambas presiones P1 y P2 mayores de 15 MPa, y  • under isobaric conditions, where the first pressure P1 is equal to the second pressure P2, with both pressures P1 and P2 being greater than 15 MPa, and
· en condiciones isotérmicas, donde la primera temperatura T1 es igual a la segunda temperatura T2.  · In isothermal conditions, where the first temperature T1 is equal to the second temperature T2.
4. El procedimiento según cualquiera de las reivindicaciones 1 ó 2, donde las etapas (b) y (c) se llevan a cabo en condiciones isobáricas, donde la primera presión P1 es igual a la segunda presión P2, siendo ambas presiones P1 y P2 mayores de 15 MPa. 4. The method according to any of claims 1 or 2, wherein steps (b) and (c) are carried out under isobaric conditions, where the first pressure P1 is equal to the second pressure P2, both of which are pressures P1 and P2 over 15 MPa.
5. El procedimiento según cualquiera de las reivindicaciones 1 ó 2, donde las etapas (b) y (c) se llevan a cabo en condiciones isotérmicas, donde la primera temperatura T1 es igual a la segunda temperatura. 5. The method according to any of claims 1 or 2, wherein steps (b) and (c) are carried out under isothermal conditions, where the first temperature T1 is equal to the second temperature.
6. El procedimiento según cualquiera de las reivindicaciones 1 a 5, donde el fluido supercrítico de las etapas (b) y (c) es C02 supercrítico. 6. The method according to any of claims 1 to 5, wherein the supercritical fluid of steps (b) and (c) is supercritical C0 2 .
PCT/ES2019/070082 2018-02-16 2019-02-14 Method for obtaining a graphene oxide aerogel WO2019158794A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ES201830140A ES2722998B2 (en) 2018-02-16 2018-02-16 PROCEDURE FOR OBTAINING A GRAPHENE OXIDE AEROGEL
ESP201830140 2018-02-16

Publications (1)

Publication Number Publication Date
WO2019158794A1 true WO2019158794A1 (en) 2019-08-22

Family

ID=67612940

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/ES2019/070082 WO2019158794A1 (en) 2018-02-16 2019-02-14 Method for obtaining a graphene oxide aerogel

Country Status (2)

Country Link
ES (1) ES2722998B2 (en)
WO (1) WO2019158794A1 (en)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102941042A (en) * 2012-10-25 2013-02-27 北京理工大学 Graphene/metal oxide hybrid aerogel, preparation method and applications thereof
CN107500280A (en) * 2017-08-31 2017-12-22 北京化工大学 A kind of arbitrary shape three-dimensional grapheme and its preparation method and application

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102941042A (en) * 2012-10-25 2013-02-27 北京理工大学 Graphene/metal oxide hybrid aerogel, preparation method and applications thereof
CN107500280A (en) * 2017-08-31 2017-12-22 北京化工大学 A kind of arbitrary shape three-dimensional grapheme and its preparation method and application

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
CHENG ET AL.: "Enhanced mechanical, thermal, and electric properties of graphene aerogels via supercritical ethanol drying and high-temperature thermal reduction", SCIENTIFIC REPORTS, vol. 7, 1439, 3 May 2017 (2017-05-03), pages 1 - 11, XP055636084 *
CHENWU YUE: "Low-thermal-conductivity nitrogen-doped graphene aerogels for thermal insulation", RSC ADVANCES, vol. 6, 2016, pages 9396 - 9401, XP055636085 *
SARNO ET AL.: "Supercritical C02 Processing to Improve the Electrochemical Properties of Graphene Oxide", J. OF SUPERCRITICAL FLUIDS, vol. 118, 2016, pages 119 - 127, XP029709420, doi:10.1016/j.supflu.2016.08.002 *

Also Published As

Publication number Publication date
ES2722998A1 (en) 2019-08-20
ES2722998B2 (en) 2020-01-15

Similar Documents

Publication Publication Date Title
Tsioptsias et al. Development of micro-and nano-porous composite materials by processing cellulose with ionic liquids and supercritical CO 2
WO2018080592A1 (en) Devices and methods for ambient pressure carbon dioxide freeze drying and composite materials made therefrom
Fan et al. Multiphased assembly of nanoporous silica particles
Deschamps et al. A thermodynamic limit of the melting/freezing processes of water under strongly hydrophobic nanoscopic confinement
Wu et al. A new rapid and economical one-step method for preparing SiO2 aerogels using supercritical extraction
Oschatz et al. Evolution of porosity in carbide-derived carbon aerogels
Choma et al. Microporosity development in phenolic resin-based mesoporous carbons for enhancing CO2 adsorption at ambient conditions
Gorbunova et al. Poly (ethylene glycol) as structure directing agent in sol–gel synthesis of amorphous silica
Seraji et al. Investigation of microstructure and mechanical properties of novolac/silica and C/SiO2/SiC aerogels using mercury porosimetry method
Zhu et al. A pressurized carbonation sol–gel process for preparing large pore volume silica and its performance as a flatting agent and an adsorbent
Ganesh et al. Synthesis, characterization and drug release capability of new cost effective mesoporous silica nano particle for ibuprofen drug delivery
CN110980705A (en) Difunctional graphene aerogel, and preparation method and application thereof
ES2722998B2 (en) PROCEDURE FOR OBTAINING A GRAPHENE OXIDE AEROGEL
Kumar et al. A simple process to prepare silica aerogel microparticles from rice husk ash
Gao et al. Synthesis of silica aerogel monoliths with controlled specific surface areas and pore sizes
Maheshwari et al. Robust mesoporous silica compacts: multi-scale characterization of microstructural changes related to physical–mechanical properties
AL-Sharuee Specifications study of Hydrophobic Silica Aerogel Doped with Rhodamine 6G Prepared via Sub-Critical Drying Technique
Li et al. Dual templating synthesis of hierarchical porous silica materials with three orders of length scale
Blin et al. Fluorinated emulsions: Templates for the direct preparation of macroporous–mesoporous silica with a highly ordered array of large mesopores
Enterría et al. One-pot endo/exotemplating of hierarchical micro-mesoporous carbons
Karout et al. Porous texture of silica aerogels made with ionic liquids as gelation catalysts
Tripathi et al. Synthesis of large pore carbon nanoparticles for removal of malachite green
Kalaparthi et al. Self-assembly of multi-hierarchically structured spongy mesoporous silica particles and mechanism of their formation
Winkler et al. Synthesis of silica by pressured carbonation and the influence of CO2 pressure on the silica properties
CN114633468B (en) Method for preparing stereoscopic aramid aerogel by suspension 3D printing and application

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19754349

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19754349

Country of ref document: EP

Kind code of ref document: A1