Pretreated clay compositions for selective removal of planar molecules from solution

Abstract

A method for forming a treated clay composition, a method for decaffeination, and a treated clay composition are disclosed. The method for forming the treated clay composition includes preparing a first solution of caffeine molecules and non-caffeine molecules, extracting the caffeine molecules to form a pre-treatment solution, and contacting the clay composition with the pre-treatment solution to form a treated clay composition, where at least a portion of the non-caffeine molecules are adsorbed. The method for decaffeination includes preparing a solution of caffeine molecules and non-caffeine molecules and contacting the solution with the treated clay composition. The treated clay composition includes organic molecules adsorbed onto the mineral layer of the clay. The organic molecules are non-caffeine molecules from the pre-treatment solution.

Description

[Technical Field]

[0001] The present disclosure relates to the decaffeination, and more particularly the selective decaffeination, of solutions using pretreated clay compositions. [Background technology]

[0002] There are various techniques for decaffeinating beverages such as coffee, tea (e.g., green tea, black tea, and white tea), and soft drinks. For example, caffeine can be extracted from coffee using solvents such as dichloromethane, ethyl acetate, chloroform, ethanol, and acetone. Other techniques for decaffeinating coffee include treatment with supercritical CO2 and the Swiss water® process, in which caffeine is captured by charcoal filtration. Additionally, caffeine can be removed from beverages using food-compatible clays and clay / polymer complexes. For example, bentonite and its polymer complexes can capture planar molecules such as caffeine. Summary of the Invention

[0003] Various embodiments are directed to a method for forming a treated clay composition, including preparing a first solution of caffeine molecules and non-caffeine molecules. The non-caffeine molecules can include chlorogenic acid lactone and its degradation products, phenols, polyphenols, lactones, tannins, and phenylindanes. The method also includes extracting the caffeine molecules from the first solution to form a pre-treatment solution, and contacting the clay composition with the pre-treatment solution to form a treated clay composition, wherein at least a portion of the non-caffeine molecules are adsorbed. The pre-treatment solution can include non-caffeine molecules. The clay composition can include clay (e.g., bentonite, montmorillonite, or nontronite, or a combination thereof) and, in some embodiments, a hydrophilic polymer. The method also includes preparing a second solution of caffeine molecules and non-caffeine molecules and extracting the caffeine molecules from the second solution by contacting it with the treated clay composition. The first and second solutions can be coffee, tea, or a soft drink.

[0004] An additional embodiment is directed to a method of decaffeination comprising providing a solution of caffeine molecules and non-caffeine molecules (e.g., chlorogenic acid lactones, phenols, polyphenols, lactones, tannins, and phenylindanes) and selectively adsorbing the caffeine molecules onto a treated clay composition. The solution may be coffee, tea, or a soft drink. The treated clay composition comprises organic molecules (e.g., chlorogenic acid lactones, phenols, polyphenols, lactones, tannins, and phenylindanes) adsorbed onto a clay (e.g., bentonite, montmorillonite, or nontronite clay, or a combination thereof). The clay may be encased in a polymer.

[0005] Further embodiments are directed to treated clay compositions comprising clay having mineral layers and organic molecules adsorbed onto the mineral layers. The mineral layers can include montmorillonite layers. The treated clay composition can also include polymers (e.g., poly(acrylic acid), polyvinyl alcohol, polyethylene glycol, polyacrylamide, etc.). The organic molecules are non-caffeine molecules from the pretreatment solution. These molecules can include chlorogenic acid lactones, phenols, polyphenols, lactones, tannins, and phenylindanes. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a flow diagram illustrating a decaffeination method according to some embodiments of the present disclosure. [Figure 2A] FIG. 1 is a schematic diagram illustrating a method of forming a treated bentonite composition according to some embodiments of the present disclosure. [Figure 2B] FIG. 1 is a schematic diagram illustrating a method of selective decaffeination according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0007] Decaffeinated beverages made from natural caffeine sources, such as coffee beans and tea leaves, require caffeine extraction.Caffeine can be extracted from green (unroasted) coffee beans or roasted coffee beans using various techniques.For example, in a technique known as the Swiss water® process, green coffee beans are soaked in hot water and then passed through a charcoal filter with pores that can capture caffeine molecules.Caffeine can also be extracted from coffee beans soaked in water by treatment with supercritical carbon dioxide (sCO2).

[0008] In addition, absorbent clays such as bentonite can be used to extract caffeine from solution. Bentonite is a clay primarily composed of montmorillonite, although other smectite minerals, such as nontronite, hectorite, saponite, and beidellite, may also be present. Bentonite may also contain variable amounts of other minerals, such as quartz, feldspar, calcite, and gypsum. Bentonite has a nanoscale layered structure. For example, bentonite layers are approximately 100 nm thick. 2 and a thickness of about 1 nm. The condensation of these layers forms particles on the micrometer to millimeter scale. The layers are held together primarily by van der Waals and electrostatic forces.

[0009] Each of these layers may have an octahedral sheet between two tetrahedral sheets. The octahedral sheets may contain aluminum, magnesium, or iron cations, or a combination thereof. Each cation is surrounded by an oxygen atom and a hydroxyl ion, which are shared by the octahedral unit cell. The tetrahedral sheets may be silica sheets, with a unit cell formula of SiO. Montmorillonite, the main component of bentonite, has the formula (Al,Mg)(SiO). 10 )4(OH)8·12H2O. Water molecules and exchangeable cations (e.g., sodium and calcium cations) can move between the layers, resulting in separation of the layers and swelling of the particles. Organic molecules can enter the spaces between the layers and adsorb onto the large planar surfaces of the mineral sheets. Therefore, caffeine can be extracted from solutions mixed with bentonite due to adsorption on the layer surfaces.

[0010] However, other molecules may be adsorbed onto the bentonite layer as well. These include a variety of planar, aromatic, non-caffeinated compounds. Therefore, when bentonite is used to remove caffeine from coffee, compounds that provide other characteristics (e.g., flavor, color, and aroma) may also be removed. Compounds that may be removed include chlorogenic acid lactones and their degradation products (e.g., phenylindanes). In addition, there is evidence that phenylindanes and other compounds present in coffee may provide physiological benefits when consumed. Therefore, there is a need for technologies to more selectively remove caffeine from coffee to avoid the adverse quality effects of removing other components during decaffeination.

[0011] Disclosed herein is a technology for selectively removing caffeine from a solution (e.g., a beverage) using a treated clay composition. The clay composition includes an absorbent clay, such as bentonite, montmorillonite, or nontronite, or a combination thereof. The clay composition can also be a clay / polymer composite, in which the absorbent clay is encased in a hydrophilic polymer, such as poly(acrylic acid), polyvinyl alcohol, polyethylene glycol, or polyacrylamide. The treatment process involves adding the clay composition to a solution to be decaffeinated, e.g., a pretreatment solution containing non-caffeine molecules typically found in coffee, tea, and soft drinks. Examples of these compounds include phenols, polyphenols, lactones, tannins, phenylindanes, and other aromatic hydrocarbons. Non-caffeine molecules in this solution can adsorb onto a layer of the clay composition, producing a clay composition with a reduced affinity for the adsorbed non-caffeine compounds. To preferentially remove caffeine, the treated clay composition can be added to another solution containing both caffeine and non-caffeine molecules.

[0012] FIG. 1 is a flow diagram illustrating a decaffeination method 100 according to some embodiments of the present disclosure. A pretreatment solution is prepared. This is illustrated in operation 110. The pretreatment solution can be prepared from a first solution containing caffeine molecules and non-caffeine molecules. The first solution can be a caffeine-containing beverage, such as coffee, tea, or a soft drink. For example, the first coffee solution can be prepared by extraction, in which hot water is poured over roasted and ground coffee beans. In some embodiments, the coffee solution extraction can be performed using whole roasted beans or unroasted beans. These extraction techniques can also be used to prepare the first tea solution. The coffee solution can also be prepared by dissolving soluble (“instant”) coffee in water. In some embodiments, the caffeine concentration in the first solution is approximately 20 kg / m 3 ~50kg / m 3 However, solutions with other caffeine concentrations can also be used (e.g., approximately 0.2 kg / m 3 ~5kg / m 3 , approximately 5 kg / m 3 ~20kg / m 3 , approximately 50 kg / m 3 ~100kg / m 3 etc.).

[0013] An amount of the clay composition is contacted with the first solution. In some embodiments, the amount of the clay composition is about 100 kg / m 3 However, other amounts of clay composition can be used (e.g., about 50 kg / m 3 ~100kg / m 3 , about 100kg / m 3 ~150kg / m 3This can be done at room temperature, although other solution temperatures can be used as well (e.g., about 50-200°C). In some embodiments, the clay composition is bentonite or a bentonite / polymer composite (e.g., poly(acrylic acid)-bentonite, polyvinyl alcohol-bentonite, polyethylene glycol-bentonite, polyacrylamide-bentonite, etc.). However, other clay compositions, such as montmorillonite, nontronite, or clay / polymer composites thereof, can also be used. In some embodiments, the clay composition and the first solution are combined and allowed to contact in a container for about 1-5 minutes. The first solution and the clay composition can be mixed by stirring, shaking, or otherwise agitating. For large volumes of solution (e.g., greater than about 1 L), longer contact times may be required. In other embodiments, the first solution can be passed through a filtration column containing clay / polymer composite particles. Clay / polymer composites with non-particulate structures can also be used (e.g., porous clay / polymer composites).

[0014] The caffeine and a portion of the non-caffeinated molecules in the first solution are adsorbed onto the clay composition to obtain a decaffeinated solution. A portion of the non-caffeinated molecules (e.g., about 50-90%) remain in the decaffeinated solution. The clay composition is then separated from the decaffeinated first solution. The remaining solution is referred to herein as the pretreated solution. For example, the clay composition can be filtered out of the solution through at least one filtration step. Centrifugation can also be used to remove the clay composition from the solution (e.g., prior to filtration). When using column filtration using a clay / polymer complex, the pretreated solution is collected from the column.

[0015] The removal of non-caffeine molecules from the first solution can be measured via nuclear magnetic resonance (NMR) spectroscopy (e.g., proton or carbon-13 NMR, or both) by observing signals at chemical shifts characteristic of aromatic molecules other than caffeine. In an example involving a first coffee solution and a corresponding pretreatment solution, the proton NMR spectrum of the pretreatment solution may show an approximately 97-98% decrease in the signal intensity of peaks characteristic of caffeine (e.g., at approximately 7.5 ppm) and an approximately 50% decrease in the signal intensity of non-caffeine aromatic peaks at approximately 8.01 ppm or approximately 4.0-4.2 ppm, or both. Other techniques for measuring the amount of organic molecules in solution (e.g., gas chromatography-mass spectroscopy) can also be used. The removal of non-caffeine molecules may also be indicated by a color change. For example, if color-producing non-caffeine molecules (e.g., from coffee or tea) are adsorbed onto the clay composition layer, the clay composition may darken in color.

[0016] In other embodiments, the pretreatment solution may be prepared directly in operation 110 by dissolving desired non-caffeinated molecules. This pretreatment solution may include non-caffeinated molecules known to be partially extracted from beverages during decaffeination with clay compositions. For example, the pretreatment solution may be prepared by providing a solution of molecules commonly adsorbed onto bentonite during coffee decaffeination, such as phenols, polyphenols, lactones, tannins, phenylindanes or other aromatic hydrocarbons, or combinations thereof.

[0017] A treated clay composition is then prepared. This is illustrated in operation 120. In some embodiments, a quantity of an untreated clay composition (e.g., bentonite, montmorillonite, or nontronite, or a combination thereof) is mixed with the pretreatment solution. In other embodiments, the clay / polymer complex is combined with the pretreatment solution through mixing or column filtration. The addition of the untreated clay composition and mixing with the pretreatment solution can be performed using techniques substantially similar to those used to mix the clay composition and the first solution in operation 110. Organic molecules from the decaffeinated pretreatment solution adsorb onto a layer of the clay composition. As a result, the resulting treated clay composition has a reduced affinity for the adsorbed decaffeinated molecules. The treated clay composition is removed from the pretreatment solution (e.g., through filtration or centrifugation, or both). The treated clay composition can optionally be dried after removal from the pretreatment solution (e.g., through heating, evaporation under ambient conditions, evaporation under reduced pressure, addition of a drying agent, etc.).

[0018] The treated clay composition is used for selective decaffeination of a second solution. This is illustrated in operation 130. The second solution can be a coffee solution (e.g., a coffee solution substantially similar to the first coffee solution before the addition of the untreated bentonite in operation 110). However, in some embodiments, other solutions (e.g., tea or soft drinks) can also be decaffeinated with the treated bentonite. This is discussed in more detail above. The addition of the treated clay composition and mixing with the second solution can be performed using techniques substantially similar to those used to mix the untreated clay composition with the first solution.

[0019] The treated clay composition includes adsorbed non-caffeinated molecules present in the first solution. These non-caffeinated molecules include compounds that contribute to the qualitative characteristics of the first solution, such as taste, aroma, and appearance. Examples of these compounds are discussed in more detail above. The treated clay composition has a reduced affinity for previously adsorbed compounds. Because the pre-treatment solution is decaffeinated, the treated clay composition does not adsorb more than trace amounts of caffeine molecules. Therefore, the treated clay composition and the untreated clay composition do not have substantially different affinities for caffeine. This allows the treated clay composition to preferentially remove caffeine from the second solution. Continuing with the NMR example above, selective decaffeination can be observed by comparing the proton NMR spectra of a coffee solution and a coffee solution decaffeinated with the treated clay composition. A decaffeinated coffee solution may exhibit a 97-98% reduction in signal intensity of the caffeine peak at about 7.5 ppm and less than a 50% reduction (e.g., a 0-10% reduction in signal intensity) in the signal intensities of the aromatic peaks at 8.01 ppm and about 4.0-4.2 ppm.

[0020] In some embodiments, operation 130 can be performed on an industrial scale, for example, in the preparation of decaffeinated brewed coffee or decaffeinated instant coffee granules. In other embodiments, the treated clay composition can be provided to a consumer who can then decaffeine a beverage of their choice by mixing the beverage with the treated clay composition and then filtering the mixture to remove the clay composition and any adsorbed caffeine.

[0021] Figure 2A is a schematic diagram illustrating a method 200 for preparing a treated bentonite composition according to some embodiments of the present disclosure. For purposes of illustrating method 200, but not by way of limitation, Figure 2A is described within the context of method 100 illustrated in Figure 1. Where elements referenced in Figure 2A are identical to elements shown in Figure 1, the same reference numbers are used in both figures.

[0022] A coffee solution 210 is prepared and mixed with a first portion (B1) of untreated bentonite to form a decaffeinated mixture 220. Caffeine molecules are adsorbed onto the surface of the bentonite in this solution 220 to form a bentonite / caffeine composition (BCaf). For example, approximately 90-100% of the caffeine molecules in the decaffeinated mixture 220 can be adsorbed onto the bentonite. A portion of the non-caffeinated molecules in the mixture 220 (e.g., approximately 10-50%) can similarly be adsorbed onto the surface of the BCaf.

[0023] The B-Caf is removed from mixture 220 (e.g., by filtration) to form pretreated solution 230. Techniques for preparing pretreated solution 230 from the first coffee solution are discussed in more detail with respect to operation 110 of method 100 (FIG. 1). In FIG. 2A, pretreated solution 230 is lighter in color than coffee solution 210 and decaffeinated mixture 220. This is intended to represent the removal of color-forming non-caffeinated molecules adsorbed onto B-Caf. However, this is for illustrative purposes, and in some embodiments, the appearance of pretreated solution 230 is substantially the same as the appearance of coffee solution 210.

[0024] A second portion of untreated bentonite (B2) is prepared. This untreated bentonite is added to the pretreatment solution 230 to form the treated mixture 240. The non-caffeine molecules present in the treated mixture 240 adsorb onto the untreated bentonite. The amount of non-caffeine molecules adsorbed onto the bentonite depends, at least in part, on the concentration of the molecules and the amount of bentonite in the treated mixture 240. The amount of adsorption may also depend on parameters such as mixing time and temperature. The bentonite with adsorbed non-caffeine molecules is referred to herein as treated bentonite (tB).

[0025] The treated bentonite is then separated from the mixture 240. After the treated bentonite is removed from the mixture 240, it may optionally be dried. Preparation of treated bentonite is discussed in more detail with respect to operation 120 of method 100 (FIG. 1). The remaining solution 250 may be discarded in some embodiments. In other embodiments (not shown), the remaining solution may be mixed with a next portion of treated or untreated bentonite to extract additional non-caffeine molecules remaining in the solution 250.

[0026] Figure 2B is a schematic diagram illustrating a method 201 for preparing a selectively decaffeinated coffee solution according to some embodiments of the present disclosure. For purposes of illustrating method 201, but not by way of limitation, Figure 2B is described within the context of methods 100 and 200 illustrated in Figures 1 and 2A, respectively. Where elements referenced in Figure 2B are identical to elements shown in Figures 1 and 2A, the same reference numbers are used in both figures.

[0027] A second coffee solution 260 is prepared. This coffee solution 260 can be substantially similar to the coffee solution 210 illustrated in FIG. 2A. However, any type of coffee solution can be used. Treated bentonite (tB) is added to the coffee solution 260 to form a selectively decaffeinated mixture 270. The preparation of treated bentonite is discussed in more detail with respect to FIG. 2A and operation 120 of method 100 (FIG. 1). The mixing conditions (e.g., time, temperature, amount of bentonite, etc.) of method 201 can be substantially similar to the mixing conditions of mixtures 220 and / or 240 (method 200). However, in some embodiments, various mixing and / or column filtration conditions can be used. This is discussed in more detail with respect to FIG. 1.

[0028] Caffeine molecules adsorb onto the surface of the treated bentonite in the selective decaffeinated mixture 270 to form a treated bentonite / caffeine composition (tBCaf). For example, approximately 90-100% of the caffeine molecules in the selective decaffeinated mixture 270 can be adsorbed onto the treated bentonite. While there may be non-caffeine molecules adsorbed onto the tBCaf as well, the amount of non-caffeine molecules adsorbed onto the tBCaf will be less than the proportion of non-caffeine molecules adsorbed onto untreated bentonite under similar conditions (e.g., coffee solution 260 concentration, bentonite to solution ratio, temperature, mixing time, etc.). This is because the treated bentonite has a reduced affinity for the non-caffeine molecules present in coffee relative to untreated bentonite. In some embodiments, approximately 0-10% of the non-caffeine molecules adsorb onto the treated bentonite, although other amounts can be adsorbed as well (e.g., approximately 0-5%, 10-15%, 15-20%, etc.).

[0029] The tBCaf composition is removed from the selectively decaffeinated mixture 270 through filtration. In some embodiments, centrifugation can be used to separate the tBCaf from the mixture 270. This can be followed by filtration. Additionally, in some embodiments, two or more filtration steps are performed to remove the tBCaf from the mixture. Removing the tBCaf from the mixture 270 results in a decaffeinated coffee solution 280, which can be consumed or dried to form soluble coffee granules. The decaffeinated coffee solution 280 can be qualitatively more similar to the coffee solution 260 than a decaffeinated coffee solution prepared using untreated bentonite. This is because the preferential adsorption of caffeine molecules on the treated bentonite separates from the non-caffeinated molecules responsible for coffee's characteristics, e.g., taste, appearance, aroma, and other physiological effects. Techniques for preparing the selectively decaffeinated coffee solution 280 are discussed in more detail with respect to operation 130 of method 100 (FIG. 1).

[0030] Methods 200 and 201 can also be performed with beverages other than coffee and can involve clay compositions other than treated bentonite or bentonite / polymer complexes. For example, in method 200, a tea pretreatment solution can be prepared, followed by tea-treated bentonite. The tea-treated bentonite can then be used in method 201 to selectively decaffeinate the tea solution. Additionally, montmorillonite clay, nontronite, other smectite clays, and their polymer complexes can be used instead of or in addition to bentonite or bentonite / polymer complexes. Solutions that can be decaffeinated and clay compositions that can be treated are discussed in more detail with respect to FIG. 1.

[0031] Unless otherwise noted, processes (e.g., mixing, filtration, etc.) are carried out at ambient conditions or with slight heating without special atmosphere or headspace, and standard procedures for solvent removal and purification are followed. Room temperature can be between about 15°C and 30°C. Unless otherwise indicated, the modifiers "about," "approximately," and "approximately" refer to a stated value, range of values, or one or more endpoints of a range of values ±10%. Ranges (e.g., time, concentration, temperature, etc.) stated herein include both endpoints and all numbers between the endpoints. Unless otherwise specified, the use of "about," "approximately," or the tilde (~) in relation to ranges applies to both ends of the range (e.g., "approximately 1 g to 5 g" should be interpreted as "approximately 1 g to approximately 5 g"), and in relation to lists of ranges, applies to each range in the list (e.g., "approximately 1 g to 5 g, 5 g to 10 g, etc." should be interpreted as "approximately 1 g to about 5 g, about 5 g to about 10 g, etc.").

[0032] The methods discussed herein and their accompanying drawings should not be construed as limiting. Those skilled in the art will recognize that a variety of techniques may be used, varying in conditions, components, methods, etc., ultimately resulting in treated bentonite for selective decaffeination. Additionally, conditions may optionally be varied throughout the course of the method. Furthermore, those skilled in the art will understand that in some embodiments, methods may be added, omitted, or performed in a different order while still remaining within the scope of the present disclosure. It should also be noted that the method may be performed by a single entity or by multiple entities. For example, a first entity may prepare the treated bentonite, and a second entity may prepare the selective decaffeination solution.

[0033] The molecular compounds described herein may contain one or more chiral centers. Unless otherwise noted, the disclosed structures encompass all stereoisomers, conformers, rotamers, isomers, and enantiomers of the depicted compounds. Furthermore, polymers or other materials containing the disclosed compounds may include racemic forms of the compounds and mixtures containing any of these, in addition to individual stereoisomers. Substituents in the compounds described herein may participate in further chemical reactions, transformations, or interactions, which may include synthesis, decomposition, mono- or di-substitution, or both, oxidation / reduction, acid / base, nucleophilic, electrophilic, and radical substitution, addition / elimination reactions, crosslinking reactions, and polymerization reactions.

[0034] Where isomers of a named alkyl, alkenyl, alkoxy, aryl or other functional group exist (e.g., n-butyl, isobutyl, sec-butyl, and tert-butyl), a reference to a member of a group (e.g., butyl) without specifying a particular isomer is intended to include all isomers within the family (e.g., n-butyl, isobutyl, sec-butyl, and tert-butyl). Further, unless otherwise specified, a reference to one member of a group (e.g., n-butyl) includes the remaining isomers within the family (e.g., isobutyl, sec-butyl, and tert-butyl).

Claims

1. 1. A method of forming a treated clay composition, comprising: providing a first solution comprising caffeine molecules and non-caffeine molecules; extracting the caffeine molecules from the first solution to form a pre-treatment solution; contacting a clay composition with the pretreatment solution to form the treated clay composition, wherein at least a portion of the non-caffeine molecules are adsorbed onto the treated clay composition; Including, The non-caffeine molecule comprises at least one molecule selected from the group consisting of chlorogenic acid lactone, phenols, polyphenols, lactones, tannins, and phenylindanes. method.

2. The method of claim 1 , wherein the pretreatment solution comprises the non-caffeine molecule.

3. 10. The method of claim 1, wherein the clay composition comprises a clay selected from the group consisting of bentonite, montmorillonite, and nontronite.

4. The method of claim 3 , wherein the clay composition further comprises a hydrophilic polymer.

5. The method described in claim 4, wherein the hydrophilic polymer is poly(acrylic acid), polyvinyl alcohol, polyethylene glycol or polyacrylamide.

6. providing a second solution comprising caffeine molecules and non-caffeine molecules; extracting the caffeine molecules from the second solution by contacting the second solution with the treated clay composition; The method of claim 1 further comprising:

7. 2. The method of claim 1, wherein extracting the caffeine molecules from the first solution comprises mixing another clay composition with the first solution, the clay composition having the same or different composition.

8. The method of claim 1, wherein the first solution is selected from the group consisting of coffee, tea and soft drinks.

9. The method of claim 6, wherein the second solution is selected from the group consisting of coffee, tea and soft drinks.

10. 1. A method of decaffeination comprising: Providing a caffeine-containing solution; contacting the caffeine-containing solution with a treated clay composition produced by the method of any one of claims 1 to 9, wherein the treated clay composition comprises the non-caffeine molecules adsorbed onto the clay; A method comprising:

11. 11. The method of claim 10, wherein the caffeine-containing solution is selected from the group consisting of coffee, tea, and soft drinks.

12. 11. The method of claim 10, wherein the clay is selected from the group consisting of bentonite, montmorillonite, and nontronite.

13. The method of claim 10, wherein the clay has a layered structure.

14. The method of claim 10, wherein the clay comprises a mineral layer.

15. The method of claim 14, wherein the mineral layer comprises a montmorillonite layer.

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