Methods of preparing aerogels and aerogel slurries and aerogels and slurries prepared thereby

Abstract

The present invention relates to methods of preparing aerogel and aerogel slurries, as well as to aerogels and slurries prepared thereby. More particularly, the invention relates to environmentally-friendly methods of preparing aerogels and aerogel slurries in which carbon dioxide is utilised as a reactant and is consumed during the process.

Description

[0001] Methods of Preparing Aerogels and Aerogel Slurries and Aerogels and Slurries Prepared Thereby

[0002] The present invention relates to methods of preparing aerogel and aerogel slurries, as well as to aerogels and slurries prepared thereby. More particularly, the invention relates to environmentally-friendly methods of preparing aerogels and aerogel slurries in which carbon dioxide is utilised as a reactant and is consumed during the process.

[0003] Aerogels are porous materials with a high specific surface area, which have a range of commercial applications in diverse sectors such as construction, insulation, catalysis and drug delivery. For example, aerogels can be used as an aggregate in cement applications to provide lightweight and insulating properties, while aerogel slurries can be used for rendering buildings or as water-repellent coatings for various applications.

[0004] Aerogels are conventionally manufactured via a sol-gel process, in which a three dimensional 'wet-gel' skeleton is obtained, before a solvent exchange step is carried out to replace the original sol-gel solvent in the pores of the wet gel with a drying solvent. In the final step, drying is carried out to yield the porous aerogel structure. Aerogel slurries are usually prepared from the porous aerogels, for instance by mixing the porous aerogel with wet binders, following preparation of the aerogel via the route above (i.e., via the steps wet-gel (WG) to aerogel (A) to aerogel slurry (AS)).

[0005] Conventional methods for preparing aerogels are environmentally unfriendly, often resulting in the emission of CO2 and air pollutants, and / or the use of toxic volatile organic compounds or acids. For instance, when supercritical drying is used in the drying step, a large amount of CO2 is required to be flushed through the aerogel. When ambient drying techniques are used, significant volumes of volatile organic compounds are released and even those techniques which rely on water-based solvents for drying (Han et al., Bioinspired Synthesis of Monolithic and Layered Aerogels, Advanced Materials: 2018, 30 (23)) result in the emission of CO2 as a by-product. These disadvantages also mean that the production of aerogels is limited to trained technicians and to environments where safety procedures for dealing with hazardous materials are in place.

[0006] The use of CO2 as a gelation agent in the preparation of silica aerogels has been reported (Wu et al., Silica Aerogels formed from Soluble Silicates and Methyltrimethoxysilane (MTMS) using C02gas as a gelation agent, Ceramics International: 2018, 44, 821-829). In this process, sodium silicate (waterglass), CO2 and water are reacted to form a silica wet gel. However, the sodium carbonate by-product is removed by washing with water, so CO2 is not utilised as part of the aerogel products, but is removed as an effluent in the wastewater.

[0007] More environmentally-friendly methods for the preparation of aerogels are known, such as that described by Plank et al. (Plank et al., Preparation and Characterisation of a Calcium Carbonate Aerogel, Research Letters in Materials Science: 2009, 1-3). However, this method uses supercritical drying, with the disadvantages previously noted, and the resultant calcium carbonate aerogels have lower fire resistance, lower porosity and higher density compared with conventional silica aerogels.

[0008] It is an aim of the invention to obviate or mitigate one or more of the disadvantages associated with the prior art. An environmentally friendly method for the preparation of aerogels and aerogel slurries would be useful, as would be a method which allows for an overall reduction in CO2 emissions, or even net zero for CO2 emission to be achieved. A scalable method with reduced processing or drying times, and / or which can be performed at ambient temperatures would be particularly beneficial, as would be a direct route to aerogel slurries which avoids the need to prepare a finished aerogel and then incorporate it into a slurry. A method which avoids the need for hazardous chemicals, allowing it to be carried out without specialised equipment and / or in non-laboratory settings, would be useful.

[0009] Summary

[0010] The present invention relates to methods of preparing aerogel and aerogel slurries, as well as to aerogels and slurries prepared thereby. The preparation of both the aerogels and the aerogel slurries via the methods of the invention consume CO2 as a reactant, and retain the CO2 in the resultant aerogel or slurry product, thereby resulting in significant environmental benefits compared with prior art methods in which CO2 is typically emitted. In embodiments, the invention provides a direct route for the preparation of an aerogel slurry from a wet-gel (i.e., WG to AS). Advantageously, the methods of the invention avoid the use of toxic volatile organic solvents or strong acids, and provide simple, energy-efficient and environmentally- friendly processes for the preparation of both aerogels and aerogel slurries. In certain aspects, due to the lack of volatile or hazardous liquid chemicals and no requirement for specialised equipment, the method can be performed in domestic or non-laboratory environments.

[0011] Accordingly, the invention relates to a method of preparing a silica or alumina wet-gel for use in the preparation of an aerogel or aerogel slurry, the method comprising: providing a precursor solution comprising an alkylsilane and / or a metal alkoxide and reacting the precursor solution in the presence of a sol-gel solvent to form a reaction mixture; and adding a gelation agent to the reaction mixture; to form a wet-gel, wherein the gelation agent is an alkaline earth metal oxide solid.

[0012] Accordingly, in a first aspect of the present invention there is provided a method of preparing a silica or alumina wet-gel for use in the preparation of an aerogel or aerogel slurry, the method comprising: providing a precursor solution comprising an alkylsilane and / or a metal alkoxide and reacting the precursor solution in the presence of a sol-gel solvent to form a reaction mixture having a pH of from 3 to 9; and adding a gelation agent to the reaction mixture; to form a wet-gel, wherein the gelation agent is an alkaline earth metal oxide solid.

[0013] The gelation agent is added in its alkaline earth metal oxide solid form, i.e., it is not formed in situ.

[0014] The reaction mixture has a pH of from 3 to 9. The method does not use an acid. In an embodiment, the reaction mixture does not include an acid. Advantageously, the method avoids the use of acids, and in particular strong acids, which were previously considered necessary when preparing silica gels.

[0015] In an embodiment, the reaction mixture has a pH of from 3 to 7.

[0016] In an embodiment, the reaction mixture has a pH of from 4 to 9. In an embodiment, the reaction mixture has a pH of from 4.5 to 9.

[0017] In an embodiment, the reaction mixture has a pH of from 5 to 8.75.

[0018] The wet-gel comprises a silicon dioxide (silica) or alumina gel skeleton and an alkaline earth metal hydration solution comprising alkaline earth metal hydroxide.

[0019] The alkaline earth metal oxide solid may be selected from calcium oxide, magnesium oxide, barium oxide and strontium oxide.

[0020] In an embodiment, the alkaline earth metal solid is calcium oxide.

[0021] In an embodiment, the alkaline earth metal solid is added to the reaction mixture at a molar concentration of from 0.002 M to 195 M.

[0022] In an embodiment, the alkaline earth metal solid is added to the reaction mixture at a molar concentration of from 0.002 M to 20 M.

[0023] In an embodiment, the alkaline earth metal solid is added to the reaction mixture at a molar concentration of from 0.01 M to 2 M.

[0024] In an embodiment, the precursor solution comprises an alkylsilane.

[0025] The alkylsilane may be selected from triethoxymethylsilane (MTES) and trimethoxymethylsilane (MTMS). A mixture of alkylsilanes may also be used.

[0026] In an embodiment, the alkylsilane is triethoxymethylsilane (MTES).

[0027] In an embodiment, the precursor solution comprises a metal alkoxide.

[0028] The metal alkoxide may be selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), polyethoxydisiloxane (PEDS) and aluminium-tri-sec-butoxide. A mixture of metal alkoxides may also be used.

[0029] In an embodiment, the precursor solution comprises an alkylsilane and a metal alkoxide.

[0030] In an embodiment, the metal alkoxide is in the form of a liquid.

[0031] In an embodiment, the sol-gel solvent comprises an alcohol.

[0032] Suitable alcohols are known to those skilled in the art and include, but are not limited to, Cl- C4 alcohols, ethanol, methanol, propanol, butanol. In an embodiment, the sol-gel solvent is a mixture of water and an alcohol.

[0033] In an embodiment, the sol-gel solvent is a mixture of carbonated water and an alcohol.

[0034] In an embodiment, the alcohol is ethanol, and preferably bioethanol. By 'bioethanol' is meant ethanol which has been produced in an environmentally friendly manner, for instance by fermentation of a biomass, such as plant by-products, containing sugar and starch components.

[0035] In an embodiment, in the sol-gel solvent, the molar ratio of water or carbonated water: alcohol is in the region of from 100:1 to 1: 100, from 50:1 to 1:50 or from 20:1 to 1:20. In an embodiment, the ratio is from 10:1 to 1: 10, or from 5: 1 to 1: 5.

[0036] The method comprises reacting the precursor solution in the presence of the sol-gel solvent. When the precursor solution is reacted in the presence of a sol-gel solvent, it can be used in a molar ratio of precursor: sol-gel solvent of from 100:1 to 1:100, from 50:1 to 1:50, or from 20:1 to 1:20. In an embodiment, the ratio is from 10: 1 to 1: 10, or from 1:4 to 1:10.

[0037] The inventors have advantageously demonstrated that when an alkaline earth metal oxide solid is used as the gelation agent, a wet-gel is formed comprising a silicon dioxide (silica) or alumina gel skeleton and an alkaline earth metal hydration solution. Excess alkaline earth metal oxide solid, along with its alkaline earth metal hydroxide products, can react with carbon dioxide to generate the corresponding alkaline earth metal carbonate, which is retained within the final aerogel or aerogel slurry product. Beneficially, unlike other processes in which CO2 is used (for instance as a gelation agent as described by Wu et al. where the CO2 is utilised and subsequently released as a side-product) in the process of the present invention, the alkaline earth metal oxide and its hydroxide product in the wet-gel can react with and consume CO2, which is retained in the form of carbonate in the final aerogel an aerogel slurry products. This means that the production of the aerogel and aerogels slurries results in the net consumption of CO2, with significant environmental advantages when atmospheric CO2 is used. For instance, where CaO is used as the alkaline earth metal solid, 1 mole of CO2 is captured by 1 mole of CaO to produce 1 mole of CaCOs, which is retained or trapped in the final aerogel or aerogel slurry product. The CO2 can be introduced prior to gelation (for example by adding carbonated water to the reaction mixture, either as part of the sol-gel solvent or otherwise), and / or after gelation (for example in an aging step). The wet-gel prepared by the method of the invention in its first aspect, can be used in the preparation of an aerogel or an aerogel slurry.

[0038] When the wet-gel is to be used in the preparation of an aerogel slurry, the method may comprise the step of blending the wet-gel to form a slurry mixture.

[0039] Blending the wet-gel can be performed by any suitable means, for instance by breaking up the gel using a spoon or a stirrer, by mechanical means, or any other appropriate means which would be apparent to one skilled in the art. As would be understood by a person skilled in the art, while the blending step is not essential, blending the wet-gel breaks up the gel and exposes more surface area to undergo further reaction.

[0040] In an embodiment, the method comprises adding a drying agent, and optionally water, to the slurry mixture.

[0041] In an embodiment, the drying agent may an alkaline earth metal oxide. The alkaline earth metal oxide solid which is used as the drying agent may be the same alkaline earth metal oxide solid which is used as the gelation agent; however, it does not need to be, and in embodiments, a different alkaline earth metal solid can be used. This can be advantageous to impart desired characteristics on the resultant aerogel product.

[0042] In an embodiment, the drying agent is an alkaline earth metal solid selected from calcium oxide, magnesium oxide, barium oxide and strontium oxide.

[0043] Advantageously, the alkaline earth metal oxide solid reacts with water in the pores of the wetgel in the slurry mixture in an exothermic reaction which can self-heat the slurry and facilitate drying. Additional water can be added if necessary or desired, to maximise the exothermic reaction and speed up the drying time. Any residual water can be absorbed by the by-product hydroxide.

[0044] In an embodiment, the drying agent is calcium oxide.

[0045] The drying agent can be added to the wet-gel at a molar concentration of from 0.016 M to 162.114 M.

[0046] The drying agent can be added to the wet-gel at a molar concentration of from 0.016 M to 35 M. The drying agent can be added to the wet-gel at a molar concentration of from 0.016 M to 20 M.

[0047] In an embodiment the method further comprises introducing carbonated water to the reaction mixture, and / or introducing carbon dioxide to the wet-gel or to the wet or dried slurry mixture; to form the aerogel or aerogel slurry.

[0048] In an embodiment, the step of introducing carbon dioxide to the wet-gel, or to the wet or dried slurry mixture, comprises introducing CO2 gas or exposing the wet-gel or the slurry mixture to atmospheric CO2.

[0049] In an embodiment, carbon dioxide gas is introduced into the wet-gel or to the slurry mixture. While high purity or industrial CO2 can be used, i.e., and introduced to the wet-gel or slurry mixture from a canister or by similar appropriate means, advantageously, the CO2 can be derived from the atmosphere. In this embodiment, the wet-gel or slurry mixture can be exposed to the atmosphere and allowed to age. In embodiments, the aging takes place at ambient temperature and pressure. During the aging step, the CO2 reacts with the alkaline earth metal hydroxide to form the corresponding carbonate which is trapped within the pores of the aerogel and within the pores and surrounding the silica skeleton of the aerogel slurry.

[0050] In an embodiment, the CO2 in the carbonated water or that is added to the wet-gel or slurry mixture reacts with the alkaline earth metal hydroxide to form a carbonate which is retained in the aerogel or aerogel slurry.

[0051] In an embodiment, when an aerogel is being prepared, the method further comprises the step of drying the wet-gel or aged wet-gel to form the aerogel. In an embodiment, the method comprises one or more drying steps. The drying step(s) can be performed by conventional means, such as in an oven or on a heat plate. Suitable heating methods would be apparent to one skilled in the art. In an embodiment, the drying step can be selected from subcritical drying, ambient pressure drying, supercritical drying and freeze drying. Subcritical and ambient pressure drying techniques may be preferred due to their low environmental impact.

[0052] In an embodiment, the drying step comprises heating under ambient pressure. The heating may be carried out at a temperature of from 60°C to 500 °C. In an embodiment, the heating is carried out at from 60°C to 150°C.

[0053] Temperatures around 100°C (e.g., from 80°C to 120°C) may be preferred, since the liquid phase has a boiling point no higher than 100°C.

[0054] The drying step may be performed for from 15 minutes to 24 hours. As would be understood by one skilled in the art, the length of the drying step will depend on the heating temperature, with lower temperatures requiring longer drying times. In an embodiment, the drying step is performed for from 15 minutes to 12 hours, or from 15 minutes to 6 hours. In an embodiment, the drying step is carried out for from 20 minutes to 3 hours, or from 30 minutes to 2 hours. When the drying temperature ranges from 60°C to 150°C, the drying time may be from 30 minutes to 12 hours, from 30 minutes to 8 hours, from 30 minutes to 6 hours or from 30 minutes to 2 hours.

[0055] As the aerogel slurry has already undergone a drying step before aging with CO2, there is no requirement for a separate drying step for the aerogel slurry product. However, if desired, a subsequent drying step can be performed since the dried slurry product exhibits different water affinity characteristics as discussed in more detail below.

[0056] In embodiments of the invention, the aerogels may be prepared with fibres to allow for the preparation of fibre-reinforced products. In these embodiments, the fibres can be added during the step of forming the wet-gel, i.e., by adding fibres when reacting the precursor solution in the presence of the sol-gel solvent; and adding the gelation agent. Alternatively, or additionally, the fibres can be added at a later stage, for instance when blending the wetgel to form a slurry. Suitable fibres for use in the methods of the invention include ceramic fibres, organic fibres, carbon fibres and fibre glass.

[0057] In an embodiment, the fibres are ceramic fibres. Triton™ ceramic short fibres are an illustrative example of fibres which can be used. In an embodiment, the fibres are fibre glass.

[0058] 6 mm fibre glass strands are another illustrative example of fibres which can be used. One skilled in the art would appreciate that these examples are illustrative, and alternative fibres can be used. Advantageously, when fibres are used, the methods of the invention allow for the rapid production of reinforced aerogel or aerogel slurry composites. The term composite is used to describe an aerogel with one or more additional components, such as the fibres which can be introduced into the aerogel structure.

[0059] Figures:

[0060] The invention will now be described by way of example only with reference to the accompanying figures, in which:

[0061] Figure 1 shows the reaction schematic for the preparation of an aerogel according to an embodiment of the invention;

[0062] Figure 2 shows the reaction schematic for the preparation of an aerogel slurry according to an embodiment of the invention;

[0063] Figure 3 shows elasticity testing of the aerogel prepared in Example 1.2;

[0064] Figure 4 shows the results of X-ray diffraction performed on the aerogel prepared in Example 1.2;

[0065] Figure 5 shows SEM imaging of the aerogel prepared in Example 1.2;

[0066] Figure 6 shows the aerogel slurry prepared in Example 3.2 after drying;

[0067] Figure 7 shows the results of X-ray diffraction performed on the aerogel slurry prepared in Example 3.2 (after drying);

[0068] Figure 8 shows SEM imaging of the aerogel slurry prepared in Example 1.2 (after drying);

[0069] Figure 9 shows a photograph of the aerogel prepared in Example 2;

[0070] Figure 10 shows a photograph of the fibre-reinforced aerogel prepared in Example 4 Detailed Description:

[0071] An embodiment of the invention will now be described in detail with reference to Figure 1, which illustrates schematically the preparation of an aerogel according to the invention. In Figure 1 a wet-oxide gel is obtained by a sol-gel process carried out using a precursor and solvent. The precursor is an alkylsilane, a metal alkoxide, or mixtures thereof. The sol-gel solvent is a mixture of an alcohol and water, for example, bioethanol and water. In certain embodiments, CO2 can be introduced in this step, for instance in the form of carbonated water. The carbonated water may be part of the sol-gel solvent. No acids are used in the reaction mixture, the pH of which ranges from 4 to 9.

[0072] The wet-gel reaction leads to the formation of a wet oxide gel, Figure 1, comprising an oxide gel skeleton and an alkaline earth metal hydration solution. During both the sol-gel step and after formation of the wet oxide gel, the alkaline earth metal solid (e.g., calcium oxide in Figure 1) and its hydroxide products (e.g., calcium hydroxide in Figure 1) capture and react with carbon dioxide to generate the alkaline earth metal carbonate, e.g., calcium carbonate in Figure 1. 1 mole of CO2 is captured by 1 mole of CaO to produce 1 mole of CaCCh. The CO2 can be high purity or industrial CO2, e.g., introduced from a canister, or preferably can be CO2 from the atmosphere to which the reaction is exposed.

[0073] The formed carbonate is trapped within the pores of the aerogel, meaning that CO2 is consumed during the process and unlike prior art methods, is retained within the aerogel rather than being released. This has significant environmental benefits and allows the method to act as a carbon capture and utilisation process. The method can use atmospheric CO2 as a direct air capture technology. The aerogel can then be dried to form the final aerogel product using any conventional drying means, such as ambient pressure drying, subcritical drying, supercritical drying, freeze drying etc.

[0074] The steps can therefore be summarised as:

[0075] In the above scheme, CO2 is introduced into the system in the aging step, and reacts with the alkaline earth metal oxide and its hydroxide product in the wet-gel to form a carbonate which is retained in the final aerogel and aerogel slurry products. However, alternatively, or additionally, CO2 could be introduced prior to the gelation stage, for instance by introducing carbonated water into the reaction mixture. When carbonated water is introduced into the reaction mixture, it can be used for example in the sol-gel solvent.

[0076] An embodiment of the invention in which the wet-gel is used in the preparation of an aerogel slurry will now be described with reference to Figure 2. In Figure 2 a wet-oxide gel is obtained by a sol-gel process carried out using a precursor and solvent, in the same manner as described in Figure 1. The precursor is an alkylsilane, a metal alkoxide, or mixtures thereof. The sol-gel solvent is a mixture of an alcohol and water, for example, bioethanol and water (or again carbonated water could be used). The reaction mixture does not include an acid and has a pH of from 4 to 9.

[0077] The wet-gel reaction leads to the formation of a wet oxide gel, Figure 2, comprising an oxide gel skeleton and an alkaline earth metal hydration solution. An alkaline earth metal oxide solid is then added to the formed wet oxide gel to act as a drying agent. The alkaline earth metal oxide solid reacts with the water in the pores of the wet oxide gel in an exothermic reaction which can self-heat the slurry mixture and facilitate drying. Additional water can be added if necessary or desired, to maximise the exothermic reaction and speed up the drying time. Any residual water can be absorbed by the by-product hydroxide.

[0078] The alkaline earth metal solid (e.g., calcium oxide in Figure 2) and its hydroxide products (calcium hydroxide in Figure 2) in the slurry mixture can capture and react with carbon dioxide to generate the corresponding alkaline earth metal carbonate (e.g., calcium carbonate in Figure 2). The CO2 can be high purity or industrial CO2, e.g., introduced from a canister, or can preferably be CO2 from the atmosphere to which the reaction is exposed. The formed carbonate is trapped within the pores of the slurry and surrounding the silica skeleton, meaning that CO2 is consumed during the process and unlike prior art methods, is retained within the final product rather than being released. This has significant environmental benefits. In addition, this method allows for the direct preparation of an aerogel slurry, i.e., from wet-gel (WG) to aerogel slurry (AS) without the need to prepare an aerogel product and then mix it with a wet binder, as per conventional methods. This has significant benefit is terms of commercialisation and scale-up. The wet slurry can be used directly in coating applications, such as for render etc.

[0079] Alternatively, it can be dried and used in the form of a dried slurry. If drying is required, the aerogel slurry can be dried using known techniques, such as ambient pressure drying, subcritica I drying, supercritical drying, freeze drying etc. Ambient pressure and temperature may be preferred for any optional drying step due to the environmental benefits.

[0080] The steps can therefore be summarised as:

[0081] In the above scheme, CO2 is introduced into the system in the aging step, and reacts with the alkaline earth metal oxide and its hydroxide product in the wet-gel to form a carbonate which is retained in the final aerogel and aerogel slurry products. However, alternatively, or additionally, CO2 could be introduced prior to the gelation stage, for instance by introducing carbonated water into the reaction mixture. When carbonated water is introduced into the reaction mixture, it can be used in the sol-gel solvent.

[0082] The methods of the invention will now be described by way of example only.

[0083] Examples:

[0084] Materials:

[0085] Methyltriethoxysilane (MTES 99%) was purchased from Hubei Co-Formula Material Tech Co., Ltd, China. Bioethanol (ethanol, 96.6%) was purchased from Bioethanol Fireplace, UK. Calcium oxide (CaO 99%) was purchased from Minerals Water, UK. Carbon dioxide (CO2 100%) gas was purchased from AUTOart, UK. Carbonated water used was Aqua Vale™ Sparkling Spring Water.

[0086] Methodology: pH was measured directly using a Vleoak pH Meter with 0.01 High Accuracy and 0-14 measurement range.

[0087] Example 1:

[0088] 1.1 Preparation of wet-gel:

[0089] MTES was used as the precursor and mixed with a sol-gel solvent consisting of bioethanol and water, wherein the molar ratio of MTES, bioethanol and water was 1: 8: 22. The pH of the reaction mixture was measured and determined to be 8.75. CaO powder was added as a gelation agent to the precursor mixture liquid at a molar concentration of 0.016 M.

[0090] 1.2 Preparation of aerogel from wet-gel:

[0091] The silica wet gel prepared in Example 1.1 was aged in gaseous CO2, by covering the container holding the wet-get with cling-film and blowing CO2 from a canister into the container. Aging was carried out for 7 days.

[0092] Finally, the aged wet-gel was directly dried at 100 °C in a closed container for 2 hours, to yield a silica aerogel. The CO2 captured in the process was theoretically determined to be 0.013 g CO2 per gram of silica aerogel generated, based on the capture of 1 mole of CO2 by 1 mole of CaO.

[0093] 1.3 Characterisation of aerogel

[0094] 1.3.1

[0095] The bulk density of the aerogel of Example 1.2 was calculated from measurement weight by measurement volume and was determined to be 0.08 g / cm3.

[0096] The porosity of the aerogel, calculated from the bulk density using the equation: porosity = (l-(bu Ik density / theoretical density))*100 was determined to be 96%.

[0097] Flexibility of the aerogel was demonstrated by manual compression, as shown in Figure 3.

[0098] Hydrophobicity of the aerogel was measured using opensource analysis (Stalder et al., "Low- Bond Axisymmetric Drop Shape Analysis for Surface Tension and Contact Angle Measurements of Sessile Drops", Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010), with the product exhibiting a contact angle of 141°.

[0099] X-Ray diffraction of the aerogel was carried out by Empyrean Powder XRD using Cu radiation at a scanning speed of 1.3° / min and step width of 0.02°. The results, shown in Figure 4, illustrate that the aerogel product comprises amorphous silica gel as the main component, with calcium carbonate (CaCCh) also present as demonstrated by the peak at 29.5°.

[0100] SEM imaging was carried out using a Zeiss 500 Scanning Electron Microscope - Field Emission Gun to image the samples in high vacuum mode with a 5keV accelerating voltage. Before SEM imaging, all samples were coated in gold to increase electrical conductivity. The results are shown in Figure 5 and show a clear nanoporous structure consisting of a silica skeleton.

[0101] Example 2:

[0102] 2.1 Preparation of wet-gel

[0103] MTES was used as the precursor and mixed with a sol-gel solvent consisting of bioethanol and carbonated water (pH 4.6), wherein the molar ratio of MTES, bioethanol and water was 1: 8: 22. The pH of the reaction mixture was measured and determined to be 5.14. CaO powder was added as a gelation agent to the precursor mixture liquid at a concentration of 0.016 M.

[0104] 2.2 Preparation of aerogel from wet-gel:

[0105] The silica wet gel prepared in Example 2.1 was aged in gaseous CO2, by covering the container holding the wet-get with cling-film and blowing CO2 from a canister into the container. Aging was carried out for 7 days.

[0106] Finally, the aged wet-gel was directly dried at 100 °C in a closed container for 2 hours, to yield a silica aerogel.

[0107] The CO2 captured in the process was determined to be 0.013 g CO2 per gram of silica aerogel based on the capture of 1 mole of CO2 by 1 mole of CaO.

[0108] 2.3 Characterisation of aerogel

[0109] 2.3.1

[0110] The bulk density of the aerogel of Example 2.2 was calculated from measurement weight by measurement volume and was determined to be 0.089 g / cm3.

[0111] Example 3:

[0112] 3.1 Preparation of wet-gel:

[0113] MTES was used as a precursor and mixed with a sol-gel solvent which consists of bioethanol and water, wherein the molar ratio of MTES, bioethanol and water is 1: 8: 22. The pH of the reaction mixture was measured and determined to be 8.75. CaO powder was added as a gelation agent into the precursor mixture liquid at a molar concentration of 0.016 M.

[0114] 3.2 Preparation of aerogel slurry directly from wet-gel (WG to AS):

[0115] The obtained silica wet-gel was blended to break up the gel structure and form a slurry, before being mixed with 5.9 g of CaO as a drying agent with drying being facilitated by both the desiccant properties of the CaO and by the exothermic reaction between the CaO and water, which dries the internal pores. After mixing with the CaO, the external surface of the slurry started to get warmer (increase of between 2°C to 5°C). After one hour, the external temperature of the slurry had returned to ambient temperature, leaving a partially dried slurry, which still appears wet. Once the step of mixing the slurry with the alkaline earth metal solid as drying agent was complete, an aging step was performed, by covering the container holding the dried slurry mixture with cling-film and blowing CO2 from a canister into the container. Aging was carried out for 7 days, at which point the aerogel slurry was obtained, with no need for a further drying step.

[0116] In this example, the aging step was performed once drying of the internal pores had taken place, and a partially dried slurry had been obtained. However, as a skilled person would appreciate, the aging step can commence at any point after the addition of the alkaline earther metal solid drying agent.

[0117] The CO2 captured in the process was theoretically determined to be 1.56 g CO2 per gram of silica aerogel slurry generated based on the capture of 1 mole of CO2 by 1 mole of CaO.

[0118] 3.3 Characterisation of aerogel slurry

[0119] In order to carry out characterisation of the wet-gel, the slurry was first allowed to dry in air under ambient pressure and temperature for 14 days without any additional heating.

[0120] The bulk density of the dried aerogel slurry of Example 3.2 was calculated from measurement weight by measurement volume and was determined to be 0.04 g / cm3.

[0121] The porosity of the aerogel slurry, calculated from the bulk density using the equation: porosity = (l-(bu Ik density / theoretical density))*100 was determined to be 85%.

[0122] Figure 6 is a photograph of the dried slurry showing its external structure. The dried slurry shows monolithic performance, i.e., the dried slurry was found to be porous with a biscuitlike texture. The monolithic properties illustrate that the formed calcium carbonate acts as a binder in the aerogel slurry.

[0123] Hydrophilicity of the aerogel was measured by using opensource analysis (Stalder et al., "Low-Bond Axisymmetric Drop Shape Analysis for Surface Tension and Contact Angle Measurements of Sessile Drops", Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010), with the product having a contact angle of 80°.

[0124] X-Ray diffraction was carried out by Empyrean Powder XRD using Cu radiation at a scanning speed of 1.3° / min and step width of 0.02°. The results, shown in Figure 7, illustrate that the aerogel product comprises amorphous silica gel, with calcium carbonate (CaCCh) as the main component with amorphous silica gel also present.

[0125] SEM imaging was carried out using a Zeiss 500 Scanning Electron Microscope - Field Emission Gun to image the samples in high vacuum mode with a 5keV accelerating voltage. Before SEM imaging, all samples were coated in gold to increase electrical conductivity. The results are shown in Figure 8. These illustrate that a nanoporous microstructure is achieved and demonstrates the involvement of the formed calcium carbonate in the resultant structure. The method of the present invention can be used to prepare a silica or alumina wet-gel for use in the preparation of aerogels, or aerogel slurries. The method has a number of advantages, and in particular, consumes CO2, which is extremely beneficial from an environmental perspective. The method also avoids the use of volatile chemicals, and does not require specialised equipment, allowing for its use in domestic and commercial environments, for example where it can be used to prepare render in situ at a residential or construction site. In embodiments, the method can be used to prepare an aerogel slurry directly from a wet-gel (i.e., WG to AS), avoiding the need for the intermediate preparation of an aerogel which is then mixed with a wet binder.

[0126] Example 4:

[0127] 4.1 Preparation of wet-gel:

[0128] MTES was used as the precursor and mixed with a sol-gel solvent consisting of bioethanol and water, wherein the molar ratio of MTES, bioethanol and water was 1: 8: 22. The pH of the reaction mixture was measured and determined to be 8.75. CaO powder (1.6 g) was added as a gelation agent to the precursor mixture liquid at a molar concentration of 0.016 M. Additionally, 2.36 g of short ceramic fibre (Triton ™ Kaowol Epsilon Ceramic Fibre, Pure, Fisher Chemical ™) was added. 4.2 Preparation of aerogel from wet-gel:

[0129] The fibre-reinforced silica wet gel prepared in Example 4.1 was aged in gaseous CO2, by covering the container holding the wet-get with cling-film and blowing CO2 from a canister into the container. Aging was carried out for 7 days.

[0130] Finally, the aged fibre-reinforced wet-gel was directly dried at 100 °C in a closed container for 2 hours, to yield a fibre-reinforced silica aerogel.

[0131] The CO2 captured in the process was theoretically determined to be 0.013 g CO2 per gram of fibre-reinforced silica aerogel generated based on the capture of 1 mole of CO2 by 1 mole of CaO.

[0132] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0133] With respect to the use of substantially any plural and / or singular terms herein, those having skill in the art can translate from the plural to the singular and / or from the singular to the plural as is appropriate to the context and / or application. The various singular / plural permutations may be expressly set forth herein for sake of clarity.

[0134] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and / or "an" should be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations).

[0135] It will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

Claims:

1. A method of preparing a silica or alumina wet-gel for use in the preparation of an aerogel or aerogel slurry, the method comprising: providing a precursor solution comprising an alkylsilane and / or a metal alkoxide and reacting the precursor solution in the presence of a sol-gel solvent to form a reaction mixture, having a pH of from 3 to 9; and adding a gelation agent to the reaction mixture, to form a wet-gel, wherein the gelation agent is an alkaline earth metal oxide solid.

2. The method as claimed in claim 1, wherein the alkaline earth metal oxide solid is selected from calcium oxide, magnesium oxide, barium oxide and strontium oxide.

3. The method as claimed in claim 1 or claim 2, wherein the precursor solution comprises an alkylsilane selected from triethoxymethylsilane (MTES), and trimethoxymethylsilane (MTMS); a metal alkoxide selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), aluminium-tri-sec-butoxide and polyethoxydisiloxane (PEDS); and mixtures thereof.

4. The method as claimed in any preceding claim, wherein the sol-gel solvent comprises an alcohol.

5. The method as claimed in any claim 4, wherein the sol-gel solvent is a mixture of an alcohol and water or an alcohol and carbonated water.

6. The method as claimed in claim 4 or claim 5, wherein the alcohol is selected from ethanol, methanol, propanol and butanol.

7. The method as claimed in any preceding claim wherein the silica or alumina wet-gel is for use in the preparation of an aerogel slurry, and the method further comprises the step of blending the wet-gel to form a slurry mixture.

8. The method as claimed in claim 7, wherein the method comprises adding a drying agent, and optionally water, to the slurry mixture.

9. The method as claimed in claim 8, wherein the drying agent is an alkaline earth metal oxide solid.

10. The method as claimed in claim 9, wherein the drying agent is calcium oxide.

11. The method as claimed in any preceding claim, wherein the method further comprises introducing carbonated water to the reaction mixture of any of claims 1 to 6, and / or introducing carbon dioxide to the wet-gel of any of claims 1 to 6, or to the slurry mixture of any of claims 7 to 10, to form an aerogel or aerogel slurry.

12. The method as claimed in claim 11, wherein the step of introducing carbon dioxide to the wet-gel, or to the slurry mixture, comprises introducing CO2 gas to the wet-gel or slurry mixture, or exposing the wet-gel or slurry mixture to atmospheric CO2.

13. The method as claimed in any preceding claim, wherein the method comprises the addition of fibres.

14. The method as claimed in claim 13, wherein the step of reacting the precursor solution in the presence of the sol-gel solvent and adding the gelation agent, to form a wet-gel; and / or the step of blending the wet-gel to form a slurry mixture; is carried out in the presence of fibres.

15. The method as claimed in claim 13 or claim 14, wherein the fibres are ceramic fibres, organic fibres, carbon fibres or fibre glass.

16. The method as claimed in any of claims 11 to 15, wherein the method further comprises drying the aerogel.

17. A kit comprising: an alkylsilane and / or a metal alkoxide; an alkaline earth metal oxide solid; an alcohol; and instructions for performing the method according to any of claims 1 to 16.

18. A method of capturing CO2 in a silica or alumina aerogel or aerogel slurry, the method comprising reacting CO2 with an alkaline earth metal solid in the process of preparing a silica or alumina aerogel or aerogel slurry, to obtain an alkaline earth metal carbonate which is trapped in the pores of the aerogel or aerogel slurry product.

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