COMPOSITE SORBENT MATERIAL

Abstract

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

Claims

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

2. The composite sorbent material according to claim 1 wherein the 2D carbon allotrope comprises graphene, graphyne, graphyenylene, diamane, or mixtures thereof.

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

4. The composite sorbent material according to claim 1 wherein the ionic liquid comprises one or more salts having a melting point of 100 C. or less.

5. The composite sorbent material according to to claim 1 wherein the ionic liquid comprises one or more cations selected from the group consisting of: imidazolium, pyridinium, ammonium, phosphonium, or pyrrolodinium cations.

6. The composite sorbent material according to to claim 1 wherein the ionic liquid comprises one or more anions selected from the group consisting of: tetrafluoroborate [BF.sub.4].sup., hexafluorophosphate [PF.sub.6].sup., Chloride [Cl].sup., Bromide [Br].sup., Methylsulfate [CH.sub.3OSO.sub.3].sup., methanesulfonate [CH.sub.3SO.sub.3].sup., Trifluoromethanesulfonate [CF.sub.3SO.sub.3].sup., bis(trifluoromethylsulfonyl) imide [(CF.sub.3SO.sub.2).sub.2N].sup., Benzoate [C.sub.7H.sub.5O.sub.2].sup., Nitrate [NO.sub.3].sup., or Acetate [C.sub.2H.sub.3O.sub.2].sup. anions.

7. The composite sorbent material according to to claim 1 wherein the ionic liquid cation or anion comprises one or more aliphatic side chains groups selected from the group consisting of: methylene [CH.sub.2], methyl [CH.sub.3], ethyl [C.sub.2H.sub.5], propyl [C.sub.3H.sub.7], butyl [C.sub.4H.sub.9], Benzyl [C.sub.6H.sub.5CH.sub.2], Methoxy [OCH.sub.3], ethoxy [OC.sub.2H.sub.5], propoxy [OC.sub.3H.sub.7], butoxy [OC.sub.4H.sub.9], or hydroxyl [OH].

8. The composite sorbent material according to claim 1 wherein the ionic liquid is selected from 1-ethyl-3-methylimidazolium methanesulfonate (EMIM CH.sub.3SO.sub.3), 1-ethyl-3-methylimidazolium-chloride (EMIM Cl), 1-ethyl-3-methylimidazolium methyl sulfate (EMIM CH.sub.3OSO.sub.3), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM CF.sub.3SO.sub.3) or mixtures thereof.

9. The composite sorbent material according to claim 1 wherein the material is particulate in form.

10. The composite sorbent material according to claim 8 wherein the composite sorbent material has a particle size or agglomerated particles size in a range of from 5 to 70 m.

11. The composite sorbent material according to claim 1 wherein the composite sorbent material has a thermal diffusivity of 3 mm.sup.2/s or more.

12. A method for producing a composite sorbent material according to claim 1, the method including steps of: providing a few-layer 2D carbon allotrope; and impregnating the 2D carbon allotrope with an ionic liquid to form the composite sorbent material.

13. The method according to claim 12 wherein the step of impregnating the 2D carbon allotrope with an ionic liquid is performed as one of: (i) a wet impregnation step; (ii) an incipient wetness 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 an ionic liquid is performed as a wet impregnation step, including a step of immersing the 2D carbon allotrope in an aqueous solution comprising the ionic liquid.

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

16. A composite material comprising the composite sorbent material of claim 1 in combination with one or more further materials.

17. The composite material of claim 16 wherein the composite material comprises a metallic or graphite foam supporting the composite sorbet material of any one of claims 1 to 11

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

19. The composite material of claim 18 wherein the binder material comprises polyvinyl acetate (PVA).

20. Use of a composite sorbent material according to claim 1 for thermal energy storage, sorption cooling, adsorption water desalination or air dehumidification.

Description

SUMMARY OF THE FIGURES

[0057] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0058] FIGS. 1 (a) and (b) show the thermal diffusivity of composites according to the invention compared to a conventionally used silica gel adsorbent.

[0059] FIG. 2. shows water vapour adsorption characteristics of the developed composites compared to the conventionally used silica gel adsorbent, in the form of sorption isotherms.

[0060] FIG. 3 shows ethanol adsorption characteristics of the developed composites compared to the conventionally used silica gel adsorbent, in the form of sorption isotherms.

[0061] FIG. 4 shows a graph of uptake % against time indicating stability for water sorption for (a) GP-CL-10 and (b) GP-CL-20.

[0062] FIG. 5 shows a graph of uptake % against time indicating stability for water sorption for (a) GP-CH3SO3-10 and (b) GP-CH3SO3-20.

[0063] FIG. 6 shows SEM images of various samples of materials according to the present invention: (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

[0064] FIG. 7 shows an SEM image of pristine graphene platelets used to form composite materials according to the present invention.

EXAMPLES

Synthesis of Materials

[0065] A series of samples were synthesised following the below protocol: [0066] 1) Dry 1 g of graphene platelets (i.e., host matrix, host structure) in an oven at 150 C. for 12 h. [0067] 2) Prepare 25 g of aqueous solution of ionic liquid in water at 10 wt % concentration: (2.5 g ionic liquid and 22.5 waterionic liquids used in the present samples include ethyl-methylimidazolium methanesulfonate (EMIM CH.sub.3SO.sub.3) and Ethyl-methylimidazolium-chloride (EMIM Cl)). [0068] 3) Immerse the dried host matrix into the aqueous solution and stir it for 1 hr to attain a homogenous blend comprises graphene platelets and aqueous solution. [0069] 4) Leave the mixture to rest for one hour to ensure complete impregnation. [0070] 5) Filter the excess solution to separate the composite sorbent material. [0071] 6) Dry the composite in the oven at 150 C. for 1 hr to remove excess solvent (water).

[0072] To obtain further samples, steps 2-6 were repeated to impregnate fresh (un-impregnated) host matrix with ionic liquid in aqueous solutions having different concentrations of ionic liquid: 20 wt %, 30 wt%, 40 wt %.

[0073] The samples were named following the following naming conventions: GP-CL-X=graphene platelets impregnated with Ethyl-methylimidazolium-chloride in aqueous solution at X wt % concentration.

[0074] GP-CH3SO3-X=graphene platelets impregnated with ethyl-methylimidazolium methanesulfonate in aqueous solution at X wt % concentration.

Quantification of Amount of Ionic Liquid in Samples

[0075] The wt % of ionic liquid of a number of the composite sorbent material samples was quantified according to the following equation:

[00003]$\mathrm{IL}\mathrm{content}=\frac{m_{\mathrm{composite}}-m_{\mathrm{dry}\mathrm{matrix}}}{m_{\mathrm{dry}\mathrm{matrix}}}$

[0076] The amount of ionic liquid in the remaining samples was then calculated by extrapolated from the experimentally obtained results. The following results were obtained. * indicates results obtained from calculation by extrapolation.

TABLE-US-00001 Sample Ionic Liquid content (wt %) GP-CL-10 2 GP-CL-20 19 GP-CL-30 30* GP-CL-40 43* GP- CH3SO3-10 3 GP- CH3SO3-20 15 GP- CH3SO3-30 25* GP- CH3SO3-40 35*

Characterisation of Thermal Diffusivity

[0077] The thermal diffusivity of the samples was characterised as follows:

[0078] Laser flash thermal diffusivity analyser LFA 467 NETZSCH was used to determine the thermal diffusivity of the developed composites. The geometry of the sample holder used is that suggested in the equipment's user manual, comprising: (1) a sample holder plate, (2) lower support plate, (3) powdery sample, (4) upper support plate, and (5) fixing screw. The use of this kind of sample holder was chosen to provide a consistent measurement condition for all samples (a homogenised particle distribution compacted at a pressure of 0.1 MPa). The equipment is widely used in academia and industry that measures the thermal diffusivity at 3% accuracy and 2% repeatability. The sample mass typically ranges between 0.2 g and 0.7 g, the thickness of the sample ranges between 1.5 mm and 3 mm, and the packing density ranges between 0.6 and 1.4 g/cm.sup.3. These parameters are factored in determining the thermal diffusivity of the sample. The variation in the sample density is mainly depends on the salt concentration in the sample.

[0079] It was found that materials according to the present invention displayed remarkably good thermal diffusivity performance over a wide range of operating temperatures, as shown in FIG. 1(a) and FIG. 1(b), although thermal diffusivity was found to decrease with increasing ionic liquid concentration during impregnation.

[0080] The table below shows a summary of the measured thermal diffusivity for the developed composites developed from various salt concentrations (i.e. the concentration values given in the tables below are the concentration of the given ionic liquid in aqueous solution during wet impregnation of the 2D carbon allotrope) as measured at about 25 C. (i.e. corresponding to the leftmost plotted values in FIGS. 1(a) and 1(b). It can be seen from this data that the measured thermal diffusivity is much greater for material according to the present invention as compared with that of silica gel, indicating strong thermal performance of composites according to the present invention.

TABLE-US-00002 Thermal Thermal diffu- diffu- sivity sivity mm.sup.2/s mm.sup.2/s (see (see EMIM CI FIG. EMIM CH3SO.sub.3 FIG. concentration 1(a)) concentration 1(b)) 10 wt % [GP-CL-10] 9.96 10 wt % [GP-CH3SO3-10] 11.84 20 wt % [GP-CL-20] 6.78 20 wt % [GP-CH3SO3-20] 6.40 30 wt % [GP-CL-30] 5.98 30 wt % [GP-CH3SO3-30] 5.92 40 wt % [GP-CL-40] 3.95 40 wt % [GP-CH3SO3-40] 3.45 Silica gel benchmark = 0.443 mm.sup.2/s

[0081] Some further work was also done to compare the thermal diffusivity of materials according to the present invention with analogous materials using salt hydrates instead of ionic liquids. For this work, using the same graphene derivative host matrix impregnated with LiCl (a salt hydrate) at 20 wt % concentration yielded a composite having a thermal diffusivity of only 3.02 mm.sup.2/s as measured at about 25 C. As can be seen by comparison with the figures in the table above, the thermal diffusivity of analogous materials according to the present invention are found to be much higher than this, with GP-CH3SO3-20 displaying a thermal diffusivity of 6.4 mm.sup.2/s and GP-CL-20 a thermal diffusivity of 6.78 mm.sup.2/s at the same temperature and concentration (20%).

Characterisation of Adsorption Characteristics

[0082] The adsorption characteristics of the samples was characterised as follows:

[0083] The sorption characteristics of the samples were determined using dynamic vapor sorption (DVS) gravimetric analyser DVS Resolution by Surface Measurements Systems. The accuracy of the DVS analyzer microbalance was verified 0.05 mg by using 100 mg standard calibration mass prior to test execution. The adsorption characterisation included the rate of adsorption, the rate of desorption, heat of sorption and adsorption isotherms.

[0084] Sample was placed in the reaction chamber of the DVS for every test and was locally dried at room temperature by means of continuous flow of dry nitrogen gas at a rate of 200 sccm (standard cubic centimetre) until no change of the mass condition was reached. The mass at the end of the drying process was considered the dry mass (i.e., reference mass) for the following test to determine the change in sample mass. The drying process was followed by adsorption/desorption tests at various pressure ratios. The sample masses were recorded every 1 min to determine the adsorption kinetics at the predefined temperature and pressure ratio. It is noteworthy that the DVS utilizes Nitrogen as a carrier gas for the Ethanol vapor during the adsorption/desorption processes, as the effect of carrier gas on the adsorption kinetics is less than 10%, as reported by Rezk (2013).

[0085] FIG. 2 shows water vapour adsorption characteristics of the developed composites compared to the conventionally used silica gel adsorbent. In particular from this graph it can be seen that the composites show a high sorption affinity to the water vapour adsorbate but vary according to chemical sorbent concentration during the impregnation; the higher the concentration, the higher the impregnated chemical sorbent and the better the adsorption performance.

[0086] The outstanding performance of the developed composite can be benchmarked against the silica gel. The table below shows the maximum equilibrium water uptake for the developed composites developed from various salt concentration (i.e. the concentration values given in the tables below are the concentration of the given ionic liquid in aqueous solution during wet impregnation of the 2D carbon allotrope). The maximum equilibrium uptake of silica gel RD benchmark (Fuji Silica-gel by Fuji Silysia Chemical Ltd) is 0.36 g.sub.water/g.sub.silica gel.

TABLE-US-00003 Maximum Maximum water water equilibrium EMIM CH3SO.sub.3 equilibrium EMIM CI uptake concen- uptake concentration g.sub.water/g.sub.ads tration g.sub.water/g.sub.ads 10 wt % [GP-CL-10] 0.57 10 wt % 0.54 20 wt % [GP-CL-20] 0.99 20 wt % 0.80 30 wt % [GP-CL-30] 0.95 30 wt % 0.95 40 wt % [GP-CL-40] 1.14 40 wt % 0.95 10 wt % 1.02 10 wt % 0.67 20 wt % 1.59 20 wt % 1.00 30 wt % 1.94 30 wt % 1.20 40 wt % 2.12 40 wt % 1.20

[0087] It can be seen from this data that the maximum equilibrium uptake g.sub.water/g.sub.ads and g.sub.ethanol/g.sub.ads is much greater than the maximum equilibrium uptake for silica gel for all samples tested, indicating strong sorption performance of composites according to the present invention.

[0088] The stability of the water sorption capabilities of the samples was also tested, by varying the water vapor pressure ratio in the medium between 90% and 0% at 25 C. The results of this stability testing are shown in FIG. 4 and FIG. 5, which demonstrate that substantially no loss in the water uptake exists over 20 consecutive sorption/desorption cycles. Materials according to the present invention are therefore demonstrated to have excellent sorption stability.

SEM Analysis

[0089] The samples were also analysed using SEM imaging. A small spatula of the sample was placed on double-sided copper tape glued to the microscope stub and placed in a Thermo Scientific Quattro S microscope equipped with a field emission filament (FEG).

[0090] An Everhart-Thornley (ETD) detector was used in the high vacuum to obtain images from secondary electrons at a magnification between 250 and 6500. The acceleration voltage for the beam was selected as 10 kV with spot size 3. This equipment and technique is widely used in academia and industry to visualise small scale objects.

[0091] The resulting 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 an SEM image of pristine graphene platelets used to form composite materials according to the present invention.

[0092] The images demonstrate the degree of intercalating IL into graphene platelets at various wt % solutions compared with pristine platelets. It can be seen that at a low IL concentration of 10-20 wt %, the ILs are well confined into the interlayer spacing. At higher IL concentration of 30-40 wt %, excess IL precipitates on the external surfaces indicating a high level of interfacial deposition.

Summary of Material Characterisation

[0093] From the above data and discussions, it can be seen that the thermal diffusivity was found to decrease with increasing ionic liquid concentration during impregnation of the 2D carbon allotrope, but that adsorption performance was found to increase with increasing ionic liquid concentration.

[0094] In view of this, it is considered that an optimal balance of amount of ionic liquid which provides good thermal diffusivity whilst retaining good sorption performance is achieved by impregnating the 2D carbon allotrope by immersion in a solution comprising ionic liquid in a concentration of from 20 wt % to 30 wt %, although materials formed from other wt % ionic liquid were nevertheless found to have satisfactory performance providing good utility for some applications.

[0095] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0096] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0097] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0098] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0099] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word comprise and include, and variations such as comprises, comprising, and including will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0100] It must be noted that, as used in the specification and the appended claims, the singular forms a, an, and the include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent about, it will be understood that the particular value forms another embodiment. The term about in relation to a numerical value is optional and means for example +/10%.

REFERENCES

[0101] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

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