Composite wrapping material

Abstract

A composite sorbent comprising a few-layer 2D carbon allotrope impregnated with an ionic liquid is described. Also described are a method for manufacturing the foregoing material, a composite material comprising the foregoing material, and the use of the foregoing material for thermal energy storage, sorption cooling, adsorptive water desalination, or air dehumidification.

Description

Technical Field

[0001] The present invention relates to composite sorbents, and more particularly, but not limited thereto, to composite sorbents that may be particularly useful for thermal energy storage applications.

Background Art

[0002] Solid physical sorbents (i.e., adsorbents), chemical sorbents (i.e., absorbents), and physical / chemical sorbent composites have various applications. However, recently, the potential for use in the field of thermal energy storage has become apparent, considering high heat storage density and the possibility of no heat dissipation during the storage stage (since thermal energy is stored in the form of sorption potential rather than heat).

[0003] Despite significant scientific progress in this field, there is one consistent problem with the use of sorbents for thermal energy storage, which is that the heat storage and release rates of many sorbents may be slow due to the low thermal diffusivity (i.e., heat transfer rate) typical of many known sorbents. Slow heat storage and release rates impede the thermal energy storage process, thereby limiting the commercial viability of this technology.

[0004] For example, conventionally, porous media (e.g., silica gel, zeolite, metal-organic framework, activated carbon, expanded graphite, graphite) have been used as the host structure of chemical sorbents. For example, in L.W. Wang et al, “Thermal conductivity and permeability of consolidated expanded natural graphite treated with sulphuric acid”, the thermal conductivity and permeability of consolidated expanded natural graphite treated with sulphuric acid have been studied to examine its effectiveness for use as a heat transfer matrix. In A. Grekova et al, “Composite sorbents “Li / Ca halogenides inside Multi-wall Carbon Nano-tubes” for Thermal Energy Storage”, the use of multi-wall carbon nanotubes (MWCNT), a composite material impregnated with three specific hygroscopic salts, has been examined. However, while these known hosting structures have an extraordinary surface area and porous volume, their thermal diffusivity is still not sufficient, spoiling their high adsorption performance. Furthermore, the physical shape of these materials is often not ideal. For example, in the aforementioned literature by Wang et al, the material is in the shape of a compressed disk and is not practical for use in many industrial applications mainly due to its low permeability and the manufactured shape.

[0005] It is advantageous to provide a sorbent suitable for use in thermal energy storage applications and other applications involving periodic heating / cooling (e.g., adsorption cooling, adsorption desalination, and air dehumidification), which provides improved performance and / or has a more convenient physical shape for use in such applications.

[0006] The present invention has been conceived based on the above considerations.

Summary of the Invention

[0007] The inventor has noticed that it may be possible to produce high-performance composite materials by using a specific 2D material as the host structure of a selected chemical sorbent.

[0008] Accordingly, in a first aspect, the present invention provides a composite sorbent comprising a few-layer 2D carbon allotrope impregnated with an ionic liquid. The 2D carbon allotrope functions as a host / matrix structure for the ionic liquid. Accordingly, in the following disclosure, the terms “host structure”, “host material”, “matrix material” or “matrix structure” can be used interchangeably to refer to the 2D carbon allotrope material impregnated with the ionic liquid. The ionic liquid can be intercalated between the layers of the 2D carbon allotrope.

[0009] The inventor has found that by impregnating a few-layer 2D carbon allotrope with an ionic liquid, a sorbent having excellent sorbent performance can be provided. Furthermore, it has been found that the resulting sorbent has an improved thermal diffusivity compared to other known physical sorbents, such as graphite, metal-organic frameworks and silica gel powder. Accordingly, such materials offer great potential for use in applications such as thermal energy storage, and more generally, any application that requires periodic heating and cooling.

[0010] As used herein, the term “2D carbon allotrope” is used to define a material that has a substantially two-dimensional structure and consists essentially of carbon.

[0011] Suitable 2D carbon allotropes may include one or more materials selected from the group consisting of graphene, graphyne, graphyenylene, diamane, and mixtures thereof. Thus, the 2D carbon allotropes used in the present invention may contain one or more of the materials specified above or may consist of one or more of the materials specified above. Such 2D carbon allotropes are considered to be able to provide improved performance as compared with materials having a substantially 3D structure, for example, graphite (including expanded graphite). The composite sorbent according to the present invention preferably does not contain graphite or expanded graphite.

[0012] The term "few-layer" is generally used to refer to a material having a thickness of less than 10 atomic layers. For example, the material can include 1 to 10 atomic layers (for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 atomic layers). In a preferred arrangement, the material can have a thickness of 5 atomic layers or less. Here, an atomic layer generally refers to a single atomic layer. The number of layers can be measured by any suitable technique known in the art, including, but not limited to, transmission electron microscopy (TEM) or atomic force microscopy (AFM). Materials with fewer atomic layers may be preferred because they can have improved properties with respect to the thermal diffusivity as compared with materials having more layers.

[0013] The few-layer 2D carbon allotropes may be in the shape of platelets. The size of the platelets is not particularly limited, but in some embodiments, the platelets can have a lateral extent in the range of 0.5 nm to 20 μm. For example, the platelets can have a lateral extent of 1 nm or more, 5 nm or more, 10 nm or more, 50 nm or more, 100 nm or more, 200 nm or more, 500 nm or more, 1 μm or more, or 5 μm or more. The platelets can have a lateral extent of 15 μm or less, 10 μm or less, 5 μm or less, or 1 μm or less. Generally, if the bulk volume of the particles is the same, the smaller the particles, typically the larger the overall surface area.

[0014] Each of the two longest dimensions of the platelet is at least about 10 times larger, or at least about 50 times larger, or at least about 100 times larger, or at least about 1000 times larger, or at least about 5000 times larger, or at least about 10,000 times larger than the shortest dimension (i.e., thickness) of the platelet. The size of the few-layer 2D carbon allotrope platelets can be determined by any suitable method known in the art, such as SEM or TEM analysis.

[0015] In some preferred embodiments, the 2D carbon allotropes include or consist of graphene. Graphene can be obtained or prepared according to any technique that is obvious to those skilled in the art. For example, it can be obtained from natural or synthetic graphite, graphite oxide, expandable graphite, exfoliated graphite, etc. It can be obtained by physical exfoliation of graphite, for example, by peeling, grinding, or pulverizing graphene from graphite. It can be made from inorganic precursors, such as silicon carbide, etc. It can be made by chemical vapor deposition (e.g., by the reaction of methane and hydrogen on a metal surface, etc.). It can be made by reducing an alcohol, such as ethanol, etc., with a metal (such as an alkali metal like sodium), and then thermally decomposing the alkoxide product. It can be made by exfoliation of graphite in a dispersion, or exfoliation of graphite oxide in a dispersion and subsequent reduction of the exfoliated graphite oxide. Graphene can be made by exfoliation of expandable graphite, subsequent intercalation, and ultrasonic treatment or other means of separating the intercalated sheets. It can be made by intercalation of graphite and subsequent exfoliation of the product in a suspension or by heat, etc. Further useful processes include those described or referenced in F. Bonaccorso et al, Materials Today (2012) 15, 564 - 589; A.C. Ferrari et al., Nanoscale, (2015), 7, 4598 - 4810.

[0016] In a preferred embodiment, the composite sorbent comprises few-layer graphene (FLG) as the matrix of the composite material (or, in other words, as the host structure for the ionic liquid). FLG is composed of a plurality of stacked graphene layers, typically 2 to 6 graphene layers. As described above, few-layer graphene (FLG) can include graphene sheets with less than 10 atomic layers. For example, FLG can include 1 to 6 atomic layer graphene sheets. FLG may be composed of pure carbon or may be substantially composed of pure carbon. Alternatively, FLG may contain elements selected from the group consisting of one or more trace elements, such as nitrogen, boron, oxygen, and hydrogen, and combinations thereof. Preferably, FLG contains at least 98%, at least 99%, at least 99.5%, or at least 99.9% carbon.

[0017] The term "ionic liquid" is a technical term used to define a salt in a liquid state. Typically, the term "ionic liquid" is used to refer to salts that usually have a melting point of 100°C or lower. However, in some cases, the term is used to refer to salts that are liquid at or near room temperature (i.e., salts that are liquid in the range of about 10°C to about 40°C, or in the range of about 20°C to about 30°C). Therefore, the melting point of one or more ionic liquids used in the present invention is preferably 100°C or lower, more preferably 80°C or lower, more preferably 70°C or lower, more preferably 60°C or lower, more preferably 50°C or lower, or more preferably 40°C or lower.

[0018] Ionic liquids are basically composed of ions (cations and anions). In some applications, ionic liquids may be referred to as liquid electrolytes, ionic melts, ionic fluids, fused salts, liquid salts, or molten salts. An ionic liquid can contain at least one ion with delocalized charge. It can further contain at least one organic ion.

[0019] In particular, one advantage of using ionic liquids is that the properties (ionic structure) of the ionic liquids impregnated in few-layer 2D materials can be specifically tailored to the intended applications. For example, Mehrkesh, Amirhossein & Karunanithi (2016), as well as Gao et al. (2015) and Seo et al. (2014), have described how to tune ionic liquids (ILs) by appropriate selection of cations, anions, and aliphatic alkyl side chain groups attached to the normal cations to impart specific functions for a given application. A further advantage is that due to these relatively low melting points, crystallization of these liquids during use can be more easily avoided, leading to a reduced risk of damage to the host matrix material impregnated with the liquid as a result of unwanted crystallization of the liquid during use. A further advantage is the excellent thermal diffusivity of ionic liquids compared to other hydrated salts (e.g., hydrated salts such as LiCl). Impregnating few-layer 2D carbon allotropes with ionic liquids has been found to provide composite sorbents with surprisingly good thermal diffusivities compared to similar composite materials that do not contain ionic liquids but contain hydrated salts such as LiCl.

[0020] Ionic liquids can contain cations that include one or more aromatic rings. Alternatively or in addition, ionic liquids can contain nitrogen-containing cations. Alternatively or in addition, ionic liquids can contain phosphorus-containing cations. In a preferred arrangement, ionic liquids can contain one or more cations selected from the group consisting of imidazolium, pyridinium, pyrrolidinium, ammonium, or phosphonium cations.

[0021] Ionic liquids are tetrafluoroborate [BF 4 - 、hexafluorophosphate [PF 6 - 、chloride [Cl] - 、bromide [Br] - 、methyl sulfate [CH 3 OSO 3 - 、methanesulfonate [CH 3 ​​​SO 3 - , trifluoromethanesulfonate [CF 3 SO 3 - , bis(trifluoromethylsulfonyl)imide [(CF 3 SO 2 ) 2 N - , benzoate [C 7 H 5 O 2 - , nitrate [NO 3 - , or acetate [C 2 H 3 O 2 - and may contain one or more anions selected from the group consisting of anions of. Cl - , Br - , triflate, and the use of methanesulfonate anions, considering their performance in enabling sorption of water in ionic liquids containing these anions - that is, considering the typical hydrophilicity of these anions, may be particularly preferred. More generally, the use of hydrophilic anions may be preferred compared to hydrophobic anions.

[0022] In some arrangements, the ionic liquid can include a mixture of two or more ionic liquids. In other words, the ionic liquid can include two or more different cations and / or two or more different anions. The ionic liquid may be a binary mixture of two ionic liquids, also referred to in the art as a "double salt ionic liquid" (DSIL). Also, mixtures of three or more components of ionic liquids may be considered suitable for use in the present invention.

[0023] The ionic liquid can include one or more aliphatic side chains. The aliphatic side chain may be provided to the cation and / or anion forming the ionic liquid, but can typically be provided to the cation. These aliphatic chains may be linear or branched, or may form a non-aromatic ring, but linear aliphatic groups may be preferred in some cases. The aliphatic side chain is methylene [CH​​​​​2 , methyl [CH 3 , ethyl [C 2 H 5 , propyl [C 3 H 7 , butyl [C 4 H 9 , benzyl [C 6 H 5 CH 2 , methoxy [OCH 3 , ethoxy [OC 2 H 5 , propoxy [OC 3 H 7 , butoxy [OC 4 H 9 , or one or more alkyl groups selected from the group consisting of hydroxyl [OH]. For example, one preferred cation is ethyl-methylimidazolium, which contains an imidazolium ion having both ethyl and methyl alkyl side chain groups.

[0024] Preferred side chain groups may vary depending on the intended use of the composite sorbent. For example, the absorption and solubility of water in an ionic liquid can depend on the hydrophobicity of any cationic aliphatic side chain present (which may vary with the length of the aliphatic chain - the longer the chain, the lower the hydrophilicity), and thus, to obtain improved performance in water absorption, the use of short aliphatic side chains (e.g., C4 or shorter) may be preferred. However, longer aliphatic side chains (e.g., up to C4 or in some cases exceeding C4) can nevertheless provide suitable performance for the absorption and solubility of ethanol. This is because this alcohol also has an aliphatic chain, which supports its absorption (and solubility) in the ionic liquid.

[0025] Suitable ionic liquids include, but are not limited to, 1-ethyl-3-methylimidazolium methanesulfonate (EMIM CH 3 SO 3 ), 1-ethyl-3-methylimidazolium chloride (EMIM Cl), 1-ethyl-3-methylimidazolium methyl sulfate (EMIM CH3 OSO 3 )), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM CF 3 SO 3 )). Therefore, the ionic liquid used in the present invention can be selected from one or more of these ionic liquids, or mixtures thereof, for example, binary mixtures thereof.

[0026] The ionic liquid can be impregnated into the host structure provided by the few-layer 2D carbon allotropes by any suitable method known in the art.

[0027] Therefore, in a second aspect, the present invention is a method for producing a composite sorbent, the method comprising providing a few-layer 2D carbon allotrope; impregnating the 2D carbon allotrope with an ionic liquid to form a composite sorbent; and providing a method.

[0028] It is preferred to use the wet impregnation (WI) method to develop the composite material. This is because such a method can provide both interfacial deposition and bulk deposition of the ionic liquid on the host material (the 2D carbon allotrope in the present invention) at a high level. However, the use of other impregnation approaches (e.g., incipient wetness impregnation (IWI) and equilibrium deposition filtration (EDF)) is also conceivable. It should be noted that, as reported by (Bourikas 2006), incipient wetness impregnation can achieve more bulk deposition, and equilibrium deposition filtration can achieve more interfacial deposition.

[0029] The wet impregnation method can include the step of immersing the matrix material (here, the 2D carbon allotrope) in a solution containing an ionic liquid in a solvent for impregnation into the matrix material. The solution containing the ionic liquid may be an aqueous solution, i.e., here, the solvent is water.

[0030] The concentration of the ionic liquid in the aqueous solution may be in the range of 1 wt% to 99 wt%, for example, it may be about 10 wt%, about 20 wt%, about 30 wt%, about 40 wt%, about 50 wt%, or about 60 wt%. The higher the concentration of the ionic liquid in the solution, the greater the amount of the ionic liquid that can be impregnated into the host structure. Therefore, in some cases, it may be preferable for the ionic liquid to be present in the solution in an amount of at least 15 wt% or at least 20 wt%. Furthermore, increasing the wt% of the ionic liquid in the solution impregnated into the matrix material can lead to improved sorption performance of the resulting composite material, but it has been found that it can also lead to a decrease in the thermal diffusivity. Therefore, in a preferred embodiment, the concentration of the ionic liquid in the aqueous solution impregnated into the matrix material to form the composite sorbent is in the range of 20 wt% to 30 wt%, for example, about 25% - this amount has been found to provide a good balance between sorption performance and thermal diffusivity.

[0031] The solution containing the matrix material and the ionic liquid can be mixed at a ratio of 1 g of the matrix material: 5 g or more of the solution, for example, at a ratio of 1:10, 1:15, 1:20, 1:25, 1:50 or more. By providing an excess amount of the solution relative to the amount of the matrix material, it may be possible to ensure more complete impregnation of the matrix material.

[0032] The immersion process can be carried out to obtain a homogeneous blend of the host matrix / ionic liquid solution. The immersion process may be carried out for a time of, for example, 1 minute or more, for example, 10 minutes or more, 30 minutes or more, or 1 hour or more.

[0033] Stirring can be carried out while the matrix material is being immersed in the solution containing the ionic liquid. This can help to ensure more complete impregnation of the matrix material.

[0034] Before the impregnation process, the host matrix / structure can be dried to remove unwanted moisture or absorbed gases. Drying can be carried out in an oven or by any other suitable method. Drying can be carried out at a temperature of 50 °C or higher, 100 °C or higher, or 150 °C or higher. Drying can be carried out for a period of 1 hour or longer, 2 hours or longer, 5 hours or longer, 10 hours or longer, or 12 hours or longer.

[0035] After the impregnation process, the impregnated host matrix (composite material) can be separated from the mixture by any suitable technique (e.g., a filtration process). The composite material can then be dried to remove excess solvent (e.g., remove excess water).

[0036] An example of the complete method is shown below: a) Dry the host matrix / structure in an oven at 150 °C for 12 hours. b) To ensure the achievement of wet impregnation, prepare an excess volume of an aqueous ionic liquid solution compared to the host structure (e.g., 1 g of graphene: 25 g of solution). The aqueous solution concentration can be varied (e.g., 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%) as a higher salt concentration results in a higher degree of salt impregnation. c) Immerse the dried host matrix in the aqueous solution and stir it for nearly 1 hour to obtain a homogeneous blend of the host matrix / aqueous solution. d) Leave the mixture for 1 hour to ensure complete impregnation of the host matrix. e) Filter the excess solution and gently dry the composite material in an oven at 150 °C for at least 1 hour.

[0037] In some embodiments, the weight percentage (mass fraction) of the ionic liquid in the composite sorbent material may be at least 1% to 60% based on the total weight of the composite sorbent material. It has been found that increasing the weight percentage of the ionic liquid in the composite sorbent material can lead to improved sorption performance but can also lead to a decrease in the thermal diffusivity. For example, the ionic liquid can be present at a weight percentage of 1% or more, 2% or more, 3% or more, 5% or more, 10% or more, 15% or more, 20% or more, 30% or more, 40% or more, or 50% or more. The weight percentage of the ionic liquid in the composite material can be quantified according to the following formula:

Number

[0038] The estimation of the IL liquid mass can be based on the measured density of the dry matrix, the final composite material, and the density of the IL using the following formula:

Number

[0039] In some embodiments, the composite sorbent material has a thermal diffusivity of 3 mm 2 / s or more, more preferably 4 mm 2 / s or more, 5 mm 2 / s or more, 6 mm 2 / s or more, 7 mm 2 / s or more, 8 mm 2 / s or more, 9 mm 2 / s or more, or 10 mm 2 / s or more. In some embodiments, the composite sorbent material can have a thermal diffusivity of up to about 12 mm 2 / s or more. The thermal diffusivity can be measured by a laser flash analyzer using a method as discussed in more detail below.

[0040] A high thermal diffusivity can provide improved performance of the composite sorbent material when used, for example, in thermal energy storage applications or other applications that require thermal cycling.

[0041] In some embodiments, the composite sorbent material may be particulate. That is, the composite sorbent material can include a plurality of particles. The particles may be formed as single, individual particles or as aggregates that include two or more smaller particles. The particles or agglomerated particles can have a size (maximum dimension) of about 5 to 70 μm as measured by SEM imaging - for example, by measuring the maximum dimension of n platelets and calculating the average of the measurements, where n is a value of 5 or more. Generally, for the same bulk volume of particles, the smaller the particles, typically the larger the overall surface area. Thus, in a preferred arrangement, the particles can have a size (maximum dimension) of about 5 to 50 μm, for example, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. The particle size of the composite sorbent material can mainly depend on the particle size of the few-layer 2D carbon allotropes before impregnation.

[0042] Providing the composite sorbent material in powder form can have significant advantages over known sorbent materials provided as bulk masses. This is because it can facilitate industrial processes that involve the material (for example, it can facilitate the manufacturing process of a heat exchanger that includes the material). Further, providing the material in powder form may enable the material to be incorporated into other materials or articles - for example, by incorporating the powder as a filler material into a matrix material to provide a further composite material. For example, the powder can be incorporated as part of a coating for another material by combining the powder with a suitable binder material or by packing it into a binding form, such as a metal or graphite form.

[0043] Accordingly, in a further aspect of the invention, a further composite material is provided that includes the composite sorbent material of the first aspect in combination with one or more additional materials.

[0044] Additional composite materials can have a matrix-filler structure, where the composite sorbent of the first aspect functions as a filler material in matrix materials of different compositions.

[0045] In one preferred arrangement, a coating material is provided that includes the composite sorbent according to the first aspect of the invention in combination with a binder material. Suitable binder materials are not particularly limited, but examples include epoxy-based binder materials, silicon-based binder materials, and / or polymer binder materials. An example of a suitable binder material is polyvinyl acetate (PVA). The coating material can be manufactured by mixing the composite sorbent with the binder material in any suitable manner. The coating material can be applied to other structures by any suitable method, including, for example, dip coating or spray coating.

[0046] Another preferred arrangement is a metal or graphite foam that supports the composite sorbent. The composite sorbent can be applied to and supported by the foam by any suitable method, including (e.g., by dip or spray coating) coating the foam, or by granular packing of the composite sorbent into the foam.

[0047] The composite materials can find use in many applications, including, but not limited to, thermal energy storage applications, sorption cooling, adsorptive water desalination, and air dehumidification.

[0048] Accordingly, in a further aspect, the invention provides for the use of the composite sorbent according to the first aspect for any of the above applications.

[0049] The invention includes the described aspects and combinations of preferred features, except where such combinations are clearly unacceptable or explicitly avoided.

Brief Description of the Drawings

[0050] Embodiments and experiments explaining the principles of the present invention will be discussed with reference to the accompanying drawings.

[0051]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Example

[0052] Synthesis of materials A series of samples were synthesized according to the following protocol: 1) Dry 1 g of graphene platelets (i.e., the host matrix, the host structure) in an oven at 150 °C for 12 hours. 2) Prepare 25 g of an aqueous solution of the ionic liquid in water at a concentration of 10% by weight: (2.5 g of the ionic liquid and 22.5 of water - The ionic liquids used in this sample were ethyl - methylimidazolium methanesulfonate (EMIM CH 3 SO 3 ) and ethyl - methylimidazolium chloride (EMIM Cl).) 3) Immerse the dried host matrix in the aqueous solution and stir it for 1 hour to obtain a homogeneous blend containing the graphene platelet and the aqueous solution. 4) Leave the mixture for 1 hour to ensure complete impregnation. 5) Filter off the excess solution and separate it from the composite sorbent. 6) Dry the composite material in an oven at 150 °C for 1 hour to remove the excess solvent (water).

[0053] To obtain further samples, steps 2 - 6 were repeated, impregnating fresh (unimpregnated) host matrices with ionic liquids in aqueous solutions having different concentrations (20 wt%, 30 wt%, 40 wt%).

[0054] The samples were named according to the following naming convention: GP - CL - X = Graphene platelet impregnated with ethyl - methylimidazolium chloride in an aqueous solution of X wt% concentration. GP - CH3SO3 - X = Graphene platelet impregnated with ethyl - methylimidazolium methanesulfonate in an aqueous solution of X wt% concentration.

[0055] Quantification of the amount of ionic liquid in the sample The weight percentage of the ionic liquid in some of the composite sorbent samples was quantified according to the following formula:

Equation

[0056] Next, the amount of ionic liquid in the remaining samples was calculated by extrapolation from the results obtained in the experiment. The following results were obtained. * indicates the result obtained from the calculation by extrapolation.

[0057]

Table 1

[0058] Characteristic evaluation of thermal diffusivity The thermal diffusivity of the samples was characterized as follows:

[0059] To determine the thermal diffusivity of the developed composite material, the laser flash thermal diffusivity analyzer LFA 467 NETZSCH TM was used. The shape of the sample holder used was as shown in the equipment user manual, and it had (1) a sample holder plate, (2) a lower support plate, (3) a powder sample, (4) an upper support plate, and (5) fixing screws. The use of this type of sample holder was selected to provide consistent measurement conditions (compressed at a pressure of 0.1 MPa and a homogenized particle distribution) for all samples. The device measures the thermal diffusivity with an accuracy of ±3% and a reproducibility of ±2%, and is widely used in academia and industry. The sample mass is typically in the range of 0.2 g to 0.7 g, the sample thickness is in the range of 1.5 mm to 3 mm, and the packing density is in the range of 0.6 to 1.4 g / cm 3 of the range. These parameters are considered when determining the thermal diffusivity of the sample. The change in sample density mainly depends on the salt concentration in the sample.

[0060] As shown in FIGS. 1(a) and 1(b), it was found that the material according to the present invention exhibits a very good thermal diffusivity over a wide range of operating temperatures, but it was found that the thermal diffusivity decreases as the concentration of the ionic liquid during impregnation increases.

[0061] The following table shows an overview of the measured thermal diffusivity of the developed composite materials made from various salt concentrations (i.e., the concentration values given in the following table are the concentrations of a given ionic liquid in an aqueous solution during the wet impregnation of the 2D carbon allotropes) measured at approximately 25 °C (i.e., corresponding to the values plotted on the far left in FIGS. 1(a) and 1(b)). From this data, it can be seen that the measured thermal diffusivity of the materials according to the present invention is much larger than that of silica gel, indicating the excellent thermal performance of the composite materials according to the present invention.

[0062]

Table 2

[0063] Some further studies were also conducted to compare the thermal diffusivity of the materials according to the present invention with similar materials using hydrated salts instead of ionic liquids. In this study, by using the same graphene derivative host matrix impregnated with 20 wt% LiCl (hydrated salt), a composite material with a measured thermal diffusivity of only 3.02 mm 2 / s was obtained at approximately 25 °C. As can be seen from the comparison with the values in the above table, the thermal diffusivity of the similar materials according to the present invention is much higher than this. At the same temperature and concentration (20%), GP-CH3SO3-20 exhibits a thermal diffusivity of 6.4 mm 2 / s, and GP-CL-20 exhibits a thermal diffusivity of 6.78 mm 2 / s.

[0064] Characteristic evaluation of adsorption characteristics The adsorption characteristics of the samples were characterized as follows:

[0065] The adsorption characteristics of the samples were determined using a Dynamic Vapor Sorption (DVS) gravimetric analyzer DVS Resolution from Surface Measurements Systems TM The accuracy of the microbalance of the DVS analyzer was confirmed to be ±0.05 mg by using a 100 mg standard calibration mass before the test run. The adsorption characteristics include adsorption rate, desorption rate, heat of sorption, and adsorption isotherm.

[0066] Samples were placed in the DVS reaction chamber for each test and locally dried at room temperature by continuously flowing dry nitrogen gas at a rate of 200 sccm (standard cubic centimeters) until the mass state stopped changing. The mass at the end of the drying process was regarded as the dry mass (i.e., the reference mass) for the following tests to determine the change in sample mass. After the drying process, adsorption / desorption tests were conducted at various pressure ratios. The sample mass was recorded every minute to determine the adsorption rate at a predetermined temperature and pressure ratio. It should be noted that, as reported by Rezk (2013), the effect of the carrier gas on the adsorption rate is less than 10%, so DVS uses nitrogen as the carrier gas for ethanol vapor during the adsorption / desorption process.

[0067] Figure 2 shows the water vapor adsorption characteristics of the developed composite material compared with the conventionally used silica gel adsorbent. In particular, from this graph, it can be seen that the composite material shows a high sorption affinity for water vapor adsorption quality, but it varies depending on the concentration of the chemisorbent during impregnation; the higher the concentration, the higher the impregnated chemisorbent and the better the adsorption performance.

[0068] The excellent performance of the developed composite material can be evaluated against silica gel. The following table shows the maximum equilibrium water absorption of the developed composite material prepared from various salt concentrations (i.e., the concentration values given in the following table are the concentrations of a predetermined ionic liquid in an aqueous solution during the wet impregnation of the 2D carbon allotropes). The maximum equilibrium absorption of silica gel RD benchmark (Fuji Silica Gel of Fuji Silysia Chemical Ltd) is 0.36 g 水 / g シリカゲル is.

[0069]

Table 3

[0070]

Table 4

[0071] From this data, the maximum equilibrium absorption amount g of all the tested samples 水 / g 吸着材 and g エタノール / g 吸着材 were found to be much larger than the maximum equilibrium absorption amount of silica gel, indicating the excellent sorption performance of the composite material according to the present invention.

[0072] Also, the stability of the water sorption capacity of the samples was tested by changing the water vapor pressure ratio in the medium at 25 °C from 90% to 0%. The results of this stability test are shown in FIGS. 4 and 5, indicating that there is substantially no loss of water absorption over 20 consecutive sorption / desorption cycles. Therefore, it has been demonstrated that the material according to the present invention has excellent sorption stability.

[0073] SEM analysis The samples were also analyzed by SEM imaging. A small spatula of the sample was placed on double-sided copper tape adhered to a microscope stub and placed in a Thermo Scientific TM Quattro S microscope equipped with a field emission filament (FEG).

[0074] Secondary electron images were obtained at magnifications of 250 - 6500 times using an Everhart-Thornley (EDT) detector in high vacuum. The acceleration voltage of the beam was selected to be 10 kV with a spot size of 3. This apparatus and technique are widely used in academia and industry for visualizing small-scale objects.

[0075] The obtained SEM images are shown in FIG. 6. FIG. 6 shows (a) GP-CL-10; (b) GP-CH3SO3-10; (c) GP-CL-20; (d) GP-CH3SO3-20; (e) GP-CL-30; (f) GP-CH3SO3-30; (g) GP-CL-40; (h) GP-CH3SO3-40. FIG. 7 shows, for comparison, the SEM image of the as-received graphene platelet used to form the composite material according to the present invention.

[0076] The figure shows the degree of intercalating IL into graphene platelets with solutions of various weight percentages, compared to the original platelets. At a low IL concentration of 10 - 20 wt%, it can be seen that the IL is sufficiently confined within the interlayer spacing. At a high IL concentration of 30 - 40 wt%, excess IL precipitates on the external surface, indicating a high level of interfacial deposition.

[0077] Overview of the characteristic evaluation of materials As can be seen from the above data and discussion, increasing the concentration of ionic liquid during the impregnation into the 2D carbon allotropes decreased the thermal diffusivity, but it was found that the adsorption performance increased with the increase in ionic liquid concentration.

[0078] Considering this point, by impregnating the 2D carbon allotropes by immersion in a solution containing an ionic liquid at a concentration of 20 wt% - 30 wt%, an optimal balance of the amount of ionic liquid that provides good thermal diffusivity while maintaining good sorption performance is thought to be achieved. However, it was also found that materials formed from ionic liquids of other weight percentages also have satisfactory performance that provides good practicality for some applications.

[0079] The features disclosed in the above description, or the claims, or the accompanying drawings, which are expressed from the perspective of their specific forms, or the means for performing the disclosed functions, or the methods or processes for obtaining the disclosed results, can be used, if necessary, individually or in any combination of such features, to implement the present invention in various forms.

[0080] Although the present invention has been described in connection with the above exemplary embodiments, many equivalent modifications and variations will be apparent to those skilled in the art given this disclosure. Accordingly, the exemplary embodiments of the present invention shown above are to be considered illustrative and not limiting. Various changes can be made to the described embodiments without departing from the spirit and scope of the present invention.

[0081] To avoid any ambiguity, any theoretical explanations provided herein are for the purpose of enhancing the reader's understanding. The inventors do not wish to be bound by any of these theoretical explanations.

[0082] Any section headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described.

[0083] Throughout this specification, including the claims, unless the context requires otherwise, the words "comprise", "include", and variations such as "comprises", "comprising", "including" etc. are to be understood to mean that the stated integer or step or group of integers or steps is included, but not to the exclusion of any other integer or step or group of integers or steps.

[0084] It should be noted that the singular forms "a", "an", and "the" as used in this specification and the appended claims include plural referents unless the context clearly dictates otherwise. Here, a range may be expressed as from and / or to one particular value with "about" attached and / or another particular value with "about" attached. When such a range is expressed, another embodiment includes from one particular value and / or to another particular value. Similarly, when a value is expressed as an approximation by the use of the preceding "about", that particular value is understood to form another embodiment. The term "about" is optional with respect to a numerical value and, for example, means + / - 10%.

[0085] References To more fully describe and disclose the present invention and the state of the art to which it pertains, a number of publications have been cited above. The complete citations of these references are provided below. Each of these references is hereby incorporated herein by reference in its entirety. Mehrkesh, Amirhossein & Karunanithi, Arunprakash. (2016). Optimal Design of Ionic Liquids for Thermal Energy Storage. Computers & Chemical Engineering. 93. 10.1016 / j.compchemeng.2016.04.008. Gao, Jubao & Cao, Lingdi & Dong, Haifeng & Zhang, X.P. & Zhang, Suojiang. (2015). Ionic liquids tailored amine aqueous solution for pre-combustion CO2 capture: Role of Imidazolium-Based Ionic Liquids. Applied Energy. 154. 771-780. 10.1016 / j.apenergy.2015.05.073. Seo, Samuel & Quiroz-Guzman, Mauricio & Desilva, M & Lee, Tae & Huang, Yong & Goodrich, Brett & Schneider, William & Brennecke, Joan. (2014). Chemically Tunable Ionic Liquids with Aprotic Heterocyclic Anion (AHA) for CO2 Capture. The journal of physical chemistry. B. 118. 10.1021 / jp502279w. Wang, L.W., Metcalf, S.J., Critoph, Robert, Thorpe, Roger, & Tamainot-Telto, Zacharie. (2011). Thermal conductivity and permeability of consolidated expanded natural graphite treated with sulphuric acid. Carbon. 49. 4812 - 4819. 10.1016 / j.carbon.2011.06.093. Grekova, Alexandra, Gordeeva, Larisa, & Aristov, Yuri. (2016). Composite sorbents “Li / Ca halogenides inside Multi-wall Carbon Nano-tubes” for Thermal Energy Storage. Solar Energy Materials and Solar Cells. 155. 176 - 183. 10.1016 / j.solmat.2016.06.006. Bonaccorso, Francesco, Lombardo, Antonio, Hasan, Tawfique, Sun, Zhipei, Colombo, Luigi, & Ferrari, Andrea. (2012). Production and processing of graphene and 2d crystals. Materials Today. 15. 564 - 589. 10.1016 / S1369-7021(13)70014-2. Andrea C Ferrari, Francesco Bonaccorso, Vladimir Fal’Ko, Konstantin S Novoselov, Stephan Roche,et al. Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems. Nanoscale, Royal Society of Chemistry, 2014, 7 (11), pp.4598-4810. Bourikas, K., Kordulis, C. & Lycourghiotis, A. 2006. The Role of the Liquid‐Solid Interface in the Preparation of Supported Catalysts. Catalysis Reviews, 48, 363-444. A. Rezk, R. AL-Dadah, S. Mahmoud, A. Elsayed, Investigation of Ethanol / metal organic frameworks for low temperature adsorption cooling applications, Applied Energy 112 (2013) 1025-1031

Claims

1. A composite sorbent comprising a few-layer 2D carbon allotrope impregnated with an ionic liquid.

2. The composite sorbent according to claim 1, wherein the 2D carbon allotrope comprises graphene, graphyne, graphylenene, diamond, or a mixture thereof.

3. The composite sorbent according to claim 1 or 2, wherein the 2D carbon allotrope has a thickness of 1 to 10 atomic layers.

4. The composite sorbent according to any one of claims 1 to 3, wherein the ionic liquid comprises one or more salts having a melting point of 100 °C or lower.

5. The composite sorbent according to any one of claims 1 to 4, wherein the ionic liquid comprises one or more cations selected from the group consisting of cations of imidazolium, pyridinium, ammonium, phosphonium, or pyrrolidinium.

6. The ionic liquid is tetrafluoroborate [BF 4 ] - , hexafluorophosphate [PF 6 ] - , chloride [Cl] - , bromide [Br] - , methyl sulfate [CH 3 OSO 3 ] - , methanesulfonate [CH 3 SO 3 ] - , trifluoromethanesulfonate [CF 3 SO 3 ] - , bis(trifluoromethylsulfonyl)imide [(CF 3 SO 2 ) 2 N] - , benzoate [C 7 H 5 O 2 ] - , nitrate [NO 3 ] - , or acetate [C 2 H 3 O 2 ] - The composite sorbent material of any one of claims 1 to 5, comprising one or more anions selected from the group consisting of:

7. The cation or anion of the ionic liquid contains one or more aliphatic side chain groups selected from the group consisting of methylene [CH 2 , methyl [CH 3 , ethyl [C 2 H 5 , propyl [C 3 H 7 , butyl [C 4 H 9 , benzyl [C 6 H 5 CH 2 , methoxy [OCH 3 , ethoxy [OC 2 H 5 , propoxy [OC 3 H 7 , butoxy [OC 4 H 9 , or hydroxyl [OH]. The composite adsorbent according to any one of claims 1 to 6.

8. The ionic liquid is 1-ethyl-3-methylimidazolium methanesulfonate (EMIM CH 3 SO 3 ), 1-ethyl-3-methylimidazolium chloride (EMIM Cl), 1-ethyl-3-methylimidazolium methyl sulfate (EMIM CH 3 OSO 3 ), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM CF 3 SO 3 ), or a mixture thereof, and the composite adsorbent according to any one of claims 1 to 7.

9. The composite sorbent according to any one of claims 1 to 8, wherein the composite sorbent is particulate.

10. The composite sorbent according to claim 8, wherein the composite sorbent has a particle size or agglomerated particle size in the range of 5 to 70 μm.

11. The composite dressing material is 3 mm 2 / s or more in thermal diffusivity, and the composite dressing material according to any one of claims 1 to 10.

12. A method for producing the composite sorbent according to any one of claims 1 to 11, the method comprising: providing a few-layer 2D carbon allotrope; and impregnating the 2D carbon allotrope with an ionic liquid to form the composite sorbent. A method comprising the above steps.

13. The method according to claim 12, wherein the step of impregnating the 2D carbon allotrope with the ionic liquid is performed as any one of (i) a wet impregnation step, (ii) an initial wet impregnation step, or (iii) an equilibrium deposition filtration step.

14. The method according to claim 13, wherein the step of impregnating the 2D carbon allotrope with the ionic liquid is performed as a wet impregnation step comprising immersing the 2D carbon allotrope in an aqueous solution containing the ionic liquid.

15. The method according to claim 14, wherein the concentration of the ionic liquid in the aqueous solution is in the range of 10 wt% to 40 wt%, optionally 20 wt% to 30 wt%.

16. A composite material comprising in combination the composite sorbent according to any one of claims 1 to 11 with one or more additional materials.

17. The composite material according to claim 16, wherein the composite material comprises a metal or graphite foam supporting the composite sorbent according to any one of claims 1 to 11.

18. The composite material according to claim 16 or 17, wherein the composite material includes the composite sorbent according to any one of claims 1 to 11 in combination with a binder material.

19. The composite material according to claim 18, wherein the binder material includes polyvinyl acetate (PVA).

20. Use of the composite sorbent according to any one of claims 1 to 10 for thermal energy storage, sorption cooling, adsorptive water desalination or air dehumidification.

Images