A liquid phase exfoliation method and an exfoliating medium

Abstract

The invention relates to a liquid phase exfoliation method comprising cellulose, SiO2 amorphous powder, NaOH, 2DLM precursor and water as input materials and including following steps: adding 0.01 towt.% of cellulose, calculated with respect to the total weight of the SiO2+NaOH dry mix, into a 10M NaOH water solution and stirring for at leastminutes, preferably from 30 to 60 minutes; adding 0.001 to 1 wt.% of 2DLM's precursor, calculated with respect to the total weight of the SiO2+NaOH dry mix, to the alkali cellulose suspension and stirring for at least minutes, preferably from 30 to 60 minutes, at min. 50°C, preferably at 70°C; adding SiO2 powder to the mixture in a quantity to ensure a waterglass modulus n from 1.5 to 2, heating it to the temperature of at least 50°C, preferably 70°C, and stirring it at that temperature until complete dissolution of the SiO2 powder; evaporating water from the suspension at a temperature 90 to 150°C until evaporation is no longer possible due to the hygroscopic properties of the cellulose / waterglass system; exposing the system to a mechanical work, preferably at a room temperature, for at leastto 30 minutes, to obtain a paste-like exfoliating medium containing 2DLM. The invention also relates to an exfoliating medium.

Description

[0001] A liquid phase exfoliation method and an exfoliating medium

[0002] Technical field

[0003] The invention relates to the field of nanotechnology, nanomaterials and nanocomposites fabrication.

[0004] Background Art

[0005] 2D-layered materials (2DLMs) are atomically thin materials where intramolecular interactions are covalent / ionic forces, whereas the intermolecular interactions are weaker van der Waals forces. This peculiar configuration makes them prone to exfoliation into single or few atomic layers, with lateral size ranging from hundreds of nanometres (top down approach, Chen et al. 2012; Coleman 2013a; Yi et al. 2013).

[0006] Bottom-up methods growth were also attempted, such as chemical vapor deposition, pulsed laser deposition, or wet chemical method. These methods were found to as effective for the production of highly pure 2DLMs with negligible number of defects. However, the main limitation intrinsic to the bottom-up approach is the very low yield, which hinders their use in industrial applications.

[0007] An example of 2DLM is Graphene (G), monoatomic planes of sp2carbon atoms, disposed as hexagonal two-dimensional honeycomb lattice. This has shown many exclusive properties, such as the quantum hall effect (QHE), large specific surface area, high carrier mobility at room temperature, high mechanical strength, optical transparency, high flexibility, abundant surface functional groups and excellent thermal and electrical conductivity. Stacks of G planes held together by short-range intermolecular forces (Van der Walls interactions) then form graphite particles. Boron nitride nanosheets (BNNSs) are the structural analogous of G, obtained from the exfoliation of hexagonal boron nitride (h-BN). In the last decade, the development of industrially scalable methods to produce large quantities of 2DLMs has become a technological challenge. Different mechanical approaches have been proposed for 2DLMs exfoliation from powder precursors, such as low energy ball milling (Li et al. 2011a), sonication in polar organic (Lin and Connell 2012) or aqueous (Lin et al. 2011) systems, and high shear homogenization (Li et al. 2011b; Paton et al. 2014).

[0008] In the recent years, it has been found out that shearing of precursor particles at high- shear rates (> 105s4) in suitable stabilizing liquids could promote the formation of concentrated suspensions of few-layer sheets with limited number of defects. The suitability of a solvent is generally determined on the basis of Hansen solubility theory, i.e. a weighted assessment of the three main interactions between molecules (dispersion forces, dipolar intermolecular forces and H-bonds) defined by the three Hansen's solubility parameters (HSPs) (Louwerse et al. 2017). Solvents suitable for exfoliation are those with HSPs closely matching with the material to be exfoliated. For example, among suitable solvents for G exfoliation, N-methylpyrrolidone, have generally low viscosities (values ranging from 0.5 to 2 mPa-s (Smith et al. 2011)) and exhibit toxicity and low boiling points. Toxicity sets risks related to handling and sustainability. Low viscosity implies shearing at high shear rates, in order to generate sufficiently high shear stresses to initiate exfoliation (Paton et al. 2014; Arao et al. 2016). This approach has serious limitations due to its high energy consumption. As far as inventor's knowledge is concerned, very few attempts have tried to elucidate the effect of superior viscosity / macromolecular media on the exfoliation of 2DLMs.

[0009] Nevertheless, a universal cheap and effective method for the mass production of defect-less 2DLMs with large-size and high dispersibility still remains a key challenge. Recent endeavours are thus devoted to the utilization of more sustainable exfoliating media. To this aim, cellulose has been recently used as an additive in liquid-phase exfoliation for graphite, exploiting the non-polar domains of cellulose, which have affinity toward graphene (Yu et al. 2021; Ferreira et al. 2017), showing promising results in terms of yield and quality of the exfoliated nanosheets. Cellulose is the most diffused polymer on earth. Billions of tons of cellulose are yearly produced. Properties such as biocompatibility, flexibility, transparency, high mechanical strength, biodegradability are observed in cellulose. According to their origin, cellulose fibres are found in nature combined with lignin, hemicellulose and other organic compounds, to different extents. Cellulose nanofibrils (CNFs) are the building blocks of all types of cellulosic fibres. When isolated, possess a huge aspect ratio (being long micrometric-millimetric chains of glucose molecules) and a fairly high Young's modulus - simulated theoretical Young's modulus of 138 GPa (Tanaha et al. 2006), measured Young's modulus of 78±17 GPa through atomic force microscopy (AFM) (Guhados et al. 2005) - and therefore they have been widely used in mechanical reinforcement.

[0010] Thus, the object of this invention to provide a cost-friendly and effective exfoliation method for manufacturing 2DLMs, and a non-toxic exfoliating medium containing said 2DLMs.

[0011] Summary of the Invention

[0012] This invention proposes a highly versatile, low-cost, eco-friendly strategy for the high- yield exfoliation of 2DLMs up to mono- or few-layers- nanosheets using a highly viscous water-based semi-solid paste containing sodium silicate (waterglass) and cellulose fibres.

[0013] A liquid phase exfoliation method, according to the present invention, comprises as input materials cellulose, amorphous SiO2 powder, NaOH, 2DLM precursor and water, and includes the following steps: i. Adding 0.01 to 10 wt.% of cellulose, calculated with respect to the total weight of the SiO2+NaOH dry mix, into a 10M NaOH water solution and stirring for at least 5 minutes, preferably from 30 to 60 minutes, ii. Adding 0.001 to 1 wt.% of 2DLM's precursor, calculated with respect to the total weight of the SiO2+NaOH dry mix, to the alkali cellulose suspension and stirring for at least 5 minutes, preferably 30 to 60 minutes, at least at 50°C, preferably at 50 to 100°C, more preferably at 60 to 80°C, the most preferably at 70°C, iii. Adding SiO2 powder to the mixture in a quantity to ensure a waterglass modulus n (molar ratio SiO2 / Na2O) from 1.5 to 2, heating it to the temperature of at least 50°C, preferably from 50 to 100°C, more preferably from 60 to 80°C, the most preferably 70°C, and stirring it at that temperature until complete dissolution of the SiO2 powder, iv. Evaporating water from the suspension at a temperature from 90 to 150°C until evaporation is no longer possible due to the hygroscopic properties of the cellulose / waterglass system, v. Exposing the system to a mechanical work for at least 15 minutes, preferably from 20 to 30 minutes, at a temperature range 80 to 10°C, preferably at a temperature range 40 to 20°C, the most preferably at a room temperature, to obtain a paste-like exfoliating medium containing 2DLMs.

[0014] During the first step, the transition from a parallel Cell (I) to an antiparallel Cell (II) crystal structure and swelling of the cellulose superstructure occurs, as a result of sodium adsorption.

[0015] During the second step, all graphite becomes stabilized in the aqueous solution, given to the amphiphilic nature of cellulose fibres, able to physically bond with graphite. This could be seen by a progressive darkening of the cellulose fibre suspension and the disappearance of graphite particles floating on the surface. Moreover, the alkalinity of the system plays an additional beneficial role by establishing alkali-n bounds with sp2carbon structures, very much desirable especially in case of Gs or BNNSs.

[0016] During the third step, the waterglass is formed "in-situ" i.e. monomeric and oligomeric silicate anions has access to intrafibrillar domain, initiating the cellulose deconstruction process. Monomeric and oligomeric silicate anions form upon amorphous silica dissolution, diffusing towards the Na-rich cellulose surface as counterions layer, according to the DLVO model. As the water keeps on evaporating, the viscosity increases and the solution transits from a liquid state to very viscous consistence (similar to honey). At nanoscale, the process leads to the formation of a mesogenic phase comprised of parallel arrays of silicate intercalated straightened cellulose nanofibrils. These ordered alkali-cellulose / silicate structures bind to graphite exposed surfaces establishing adhesion.

[0017] During the fourth step, the mixtures is further shrunk, by exposing it to temperatures as high as 90-100 °C (on a hot plate for example), a doughy and sticky paste is obtained. When further evaporation of the water is no longer allowed due to the high hygroscopic properties of cellulose / waterglass system, the paste is ready to be worked.

[0018] During the fifth step, the paste is let to cool down at room temperature while kept under constant mechanical work (hand-mixing with a spatula or using a homogenizer). As cooling proceeds, the system experiences an additional viscous transition, in which the paste assumes a cohesive putty-like consistency. For increasing the efficiency of the process, the paste can be also deformed using machineries that could impart a controlled and homogeneous mechanical work (such as homogenizers, extruders, laminating rollers etc...) for at least fifteen minutes.

[0019] Under these conditions, the shear forces generated within this system are sufficient to overcome the interplanar short-range interactions and induce massive exfoliation of the embedded 2DLM flakes. A hint of some microstructural changes is given by the transition from a sticky to an extremely plastic and cohesive (i.e. no longer sticky) solid, elastic material, after 5 minutes of repeated straining (step 5). A hint of the exfoliation is provided by the colour of the paste, which transits from a dark grey to a silvery grey (a distinctive feature of the exfoliated graphene) after deformation, in the case of graphite exfoliation.

[0020] In this way, it is possible to harvest a high-quality nanosheets or to fabricate a highly ordered cellulose fibres-nanosheets mixtures. Suitable types of 2DLM precursors are i.e. graphite, graphene oxide, boron nitride, cloisite, MXenes and montmorillonite. They can be in the form of powder or flakes. MXenes are a relatively new class of two-dimensional inorganic compounds. These materials consist of atomically thin layers of transition metal carbides, nitrides, or carbonitrides. MXenes accept a variety of hydrophilic terminations.

[0021] The further aspect of this invention is an exfoliating medium containing 2DLM obtainable by the process above - steps i to v.

[0022] The exfoliating medium can work also as a storage medium., i.e. a matrix in which nanosheets could be stored once exfoliated. The high viscosity of this matrix suppresses in fact all diffusion kinetics, preventing their restacking. This exfoliating medium is easy to remove or exchange with other solvents after exfoliation.

[0023] The method according to the present invention has several advantages, such as:

[0024] - The method offers a solution for the exfoliation of both apolar (Gs, BNNSs) or polar (montmorillonites, cloisites) precursors, owing to the amphiphilic character of cellulose fibres.

[0025] - The method is cost-effective and eco-friendly - using an aqueous medium and inexpensive raw materials (no toxic and expensive solvents are used).

[0026] - Exfoliation can be accomplished up to mono and few-layer nanosheets in few minutes without utilization of expensive machineries, therefore highly cost and energy efficient.

[0027] - Being a low shear-rate exfoliation method, the products are essentially intact, unfolded and defect-free nanosheets.

[0028] - A controlled slow deformation of these mixtures can lead to the formation of aligned cellulose fibres / 2DLMs structure, with planar direction parallel to the shear directory, which could be used as template for nanocomposites fabrication.

[0029] - The paste could be re-diluted, recovered by filtration, and reused. Subsequent processing of the so-obtained exfoliating medium can follow different parallel routes, depending on the desired product:

[0030] 1- The waterglass medium is utilized as a matrix for fabrication of cellulose / 2DLMs nanocomposite, by drying the paste at 150-250°C, preferably 200°C to remove the chemical water, or the waterglass is treated in any hydrogen halide acids (HCI, HF etc...) with tuned concentration to form highly water-soluble sodium salts and thus to remove the desired quantity of sodium from the system with precipitation of silica powder.

[0031] 2- The semi-solid paste is diluted in water and treated with diluted phosphoric (H3PO4) or sulfuric (H2SO4) acid to carry out an anionic exchange in the waterglass with silicate anions (SiC4), thus precipitating silica and sodium phosphate or sodium sulphate salts. These salts are able to freeze the highly ordered cellulose tactoids along with homogenously dispersed 2DMLs. The precipitates are then dried for further processing, or the salts are separated from the silica precipitates through a selective chemical dissolution of silica (in diluted HCI or NaOH) and then filtered and washed.

[0032] 3- To obtain the 2DLMs / cellulose mixture the following steps are needed:

[0033] - dissolving the exfoliating medium containing 2DLM in water to obtain a liquid suspension of cellulose fibres and 2DLM in diluted sodium silicate,

[0034] - filtering off the sodium silicate,

[0035] - washing out the resulting mixture in water.

[0036] 4- Following the synthesis route 3, the cellulose-graphene mixture can be redispersed in any suitable solvent such as N-methyl pyrrolidone (NMP) or dimethysulfoxide (DMSO). For example, it can be homogenized in suitable organic solvents to synthesize polymeric matrix for the fabrication of polymer-based nanocomposites possessing both the benefits of cellulose fibres and graphene nanosheets (such as mechanical reinforcement and improved electrical conductivity, respectively), rendering the product suitable for several applications, including fabrication of electronic sensors, biosensor, polymeric solid electrolyte films for energy storage and / or capacitors etc.. 5- Following the synthesis route 3, the cellulose-BNNSs mixture can be redispersed in suitable inorganic and organic solvents such as NMP (N- methyl pyrrolidone) or DMSO (dimethysulfoxide), THF (tetra hydrofuran). For example, an organic solvent can be used to synthesize a polymer matrix homogenously embedding the cellulose-BNNSs mixture to form a polymeric nanocomposites possessing both the advantages of cellulose microfibres and BNNSs (such as mechanical resistance, thermal conductivity, electric insulation, optical properties), making it suitable for several applications, including electronic sensors, biomedicine, automotive, energy storage etc..

[0037] 6- Following the synthesis route 3, other mixtures could be produced through exfoliation of other 2DLMs, such as MXene nanosheets, aluminosilicate-clay nanosheets, 2D-layered silica nanocompounds etc...

[0038] 7- Exfoliated 2DLMs can be collected through removal of the cellulose fibres following the route 3, by means of two methods:

[0039] - exposing the mixture to the temperature from 300 to 450 °C for 10 min. to burn out the cellulose fibres

[0040] - immersing the mixture in Schweizer's reagent to dissolve the cellulose fibres and filtering out the supernatants.

[0041] 8- 2DLMs nanocomposite with glass or glass-ceramic matrix can be obtained following the synthesis routes 1 or 2. The products are calcined in air to burn the cellulose out or in Argon at 650°C to 750°C, preferably at 700 °C to pyrolize cellulose, then melt-quenched to obtain a silicate or sodiumsilicate or sodium-silicate-phosphate or silicate-phosphate glasses with dispersed 2DLMs. The glass can be then recrystallized by annealing at temperature slightly high its glass-transition temperature. These materials thus processed possess optical (UV and IR absorption and / or transparency, light filtering etc...) electric properties (insulating or conductive glasses), mechanical properties (strengthening and toughening of brittle glasses), chemical stability (bioglass and bioceramics for bone grafting) and thermal properties (thermal conductive glasses). 9- 2DLMs nanocomposite with glass or glass-ceramic matrix can be obtained following the synthesis routes 1 or 2. The precipitated SiO2 is then converted to metallic silicon in argon at 650-750°C for 30-120 minutes using metallic magnesium (Mg) as reducing agent (according to the magnesiothermic reduction). The result is a 2DLMs with or without pyrolized cellulose homogenously dispersed in a metal silicon matrix for the production of electrodes for energy storage devices, capacitors and supercapacitors.

[0042] 10-Similarly, ceramic-matrix nanocomposites with dispersed 2DLMs are synthesized following the synthesis routes 1 and / or 2. The matrix is formed through calcination. In particular, calcination in air burns the ordered cellulose tactoids, therefore using them as templates for synthesis of hierarchical microstructure; when calcined in inert gas, it prompts the formation of a hierarchically structured carbon from pyrolized cellulose. Meanwhile, the ceramic matrix is also formed on the basis of the waterglass or phosphate / sulphate (if precipitated with HsPC or H2SO4, see section 1.1) salts surrounding and fixing the highly ordered cellulose tactoids. This matrix can be tailored in its composition for several different applications, such as aerospace (thermally-resistant binary and ternary ceramics), bio-application (biocompatible and bioactive ceramics) and energy storage (semiconductors for cathode or anode in Na / Li-ion batteries, for solid electrolytes in Na / Li all-solid-state-batteries, capacitors and super-capacitors, etc...).

[0043] 11- Moreover, the concurrent exfoliation of more than one type of 2DLM is also feasible if required.

[0044] Brief description of the drawings

[0045] Fig. 1 - SEM image of sample of the Example 3.

[0046] Fig. 2 - SEM image of graphite.

[0047] Fig. 3 - TEM image of a few-layers graphene of the Example 3.

[0048] Fig. 4 - TEM image of a graphene monolayer on the grid substrate of the Example 3 - borders are not visible due to the high aspect ratio of this specific graphene nanosheet. Fig. 5 - RAMAN spectra of graphite (dashed line) and the product of exfoliation (solid line).

[0049] Detailed description

[0050] Example 1

[0051] Preparation of exfoliating medium containing 2DLM material

[0052] The waterglass was prepared so as to have a chemical modulus n= 1.8 (molar ratio SiO2 / Na2O). The weight percentages of cellulose and 2DLM was calculated with respect to the total weight of the SiO2+NaOH dry mix.

[0053] The precursor 2DLM of choice is here graphite, which is the main common precursor for the production of graphene by mechanical methods.

[0054] The mixture of exfoliating medium and graphite, was produced as follows:

[0055] 1. 0.06 wt.% of micro-fibrillated cellulose (MFC) (3 g of MFC pulp containing 2 wt.% of cellulose) was added to a 10M NaOH solution (10 mL H2O, 4 g NaOH) and stirred for 30 minutes, then

[0056] 2. 0.006 g of graphite powder was added to the alkali cellulose suspension and kept stirring for 30 minutes.

[0057] 3. SiO2 powder was added in a quantity to ensure a chemical modulus of the waterglass n=1.8 and kept under stirring at 70°C until complete dissolution.

[0058] 4. The mixture was then exposed to higher temperature as 100 °C (on a hot plate) while kept under continuous stirring, to further shrink it.

[0059] 5. When further evaporation of the water is no longer allowed at the given temperature due to its high hygroscopicity, the mixture was removed from the heat source and mechanically worked (hand-mixing with a spatula) while cooling for 0.5 hours.

[0060] For this particular SiO2 / Na2O ratio n=1.8), the waterglass shows a minimum in the static viscosity ensuring flow capability even at high solid loading. Example 2

[0061] The process of Gs harvesting, i.e. the separation of them from the paste-like exfoliating medium was accomplished by re-dissolving the wrought paste in water to the point to obtain a liquid suspension of cellulose fibres and Gs in diluted watereglass, and then filtering away the waterglass. The MFC / Gs mixture was then washed firstly in a 0.5M HCI solution to remove excess of Na and / or waterglass, and secondly in distilled water. If MFC / Gs is the desired end-product, no further processing is needed, and the mixture can be used to form highly ordered nanocomposites, and / or highly homogenous cellulose-nanosheets mixtures for several applications.

[0062] Example 3

[0063] In order to prepare a high quality Gs powder, the resulting mixture of Example 2 was placed in oven at 400°C in air atmosphere (10 minutes are usually enough) to burn the cellulose away.

[0064] Alternatively, the MFC / Gs mixture was immerged in Schweizer's reagent to dissolve cellulose, and the solution filtered away from the supernatants (see the annex for further details regarding Schweizer's reagent preparation).

[0065] To assess the quality of the Gs, the black residue deprived of MFC was characterized by scanning electron microscopy (SEM) - Fig. 1 and Fig. 2, high resolution transmission electron microscopy (HR-TEM) - Fig. 3 and Fig. 4, and Raman spectroscopy - Fig. 5. HR-TEM imaging evidenced the predominance of mono- and few-layer Gs with lateral size > 2 |i and defect-free texture. Raman analysis exhibited no evident change in the ratios of the intensities of the main Raman peaks D, G and 2D (i.e. IG / ID and IG / I2D) between pristine graphite and the Gs, confirming that no additional defects were brought about by the exfoliation process - calculated ratios IG / ID and IG / I2D for pristine graphite are 5.39 and 3.42 respectively and for exfoliated product are 5.61 and 3.43 respectively. The throughput of this exfoliation methodology can be used for further synthesis of nanocomposites and beyond. Example 4

[0066] The mixture of exfoliating medium and BNNSs, was produced as follows:

[0067] 1 . 0.06 wt.% of MFC (3 g of MFC pulp containing 2 wt.% of cellulose) was added to a 10M NaOH solution (10 mL H2O, 4 g NaOH) and stirred for 30 minutes, then

[0068] 2. 0.06 g of h-BN powder was added to the alkali cellulose suspension and kept stirring for 30 minutes.

[0069] 3. SiO2 powder was added in a quantity to ensure a chemical modulus of the waterglass n=1.8 and kept under stirring at 70 °C until complete dissolution.

[0070] 4. The mixture was then exposed to higher temperature as 100 °C (on a hot plate) while kept under continuous stirring, to further shrink it.

[0071] When further evaporation of the water is no longer allowed at the given temperature due to its high hygroscopicity, the mixture was removed from the heat source and mechanically worked (hand-mixing with a spatula) while cooling for 0.5 hours.

[0072] Example 5

[0073] The process of BNNSs harvesting, i.e. the separation of them from the paste-like exfoliating medium was accomplished by re-dissolving the wrought paste in water to the point to obtain a liquid suspension of cellulose fibres and BNNSs in diluted waterglass, and then filtering away the waterglass. The MFC / BNNSs mixture was then washed firstly in a IM HCI solution to remove excess of Na and / or waterglass, and secondly in distilled water. If MFC / BNNSs is the desired end-product, no further processing is needed, and the mixture can be used to form highly ordered nanocomposites, and / or highly homogenous cellulose-BNNS mixtures for several applications.

[0074] Example 6

[0075] In order to prepare a high quality BNNSs powder, the resulting mixture of Example 5 was placed in oven at 400°C in air atmosphere (10 minutes are usually enough) to burn the cellulose away. Alternatively, the MFC / BNNSs mixture was immerged in Schweizer's reagent to dissolve cellulose, and the solution filtered away from the supernatants (see the annex for further details regarding Schweizer's reagent preparation).

Claims

Claims1. A liquid phase exfoliation method comprising cellulose, amorphous SiO2 powder, NaOH, 2DLM precursor and water as input materials and including following steps: i. Adding 0.01 to 10 wt.% of cellulose, calculated with respect to the total weight of the SiO2+NaOH dry mix, into a 10M NaOH water solution and stirring for at least 5 minutes, preferably from 30 to 60 minutes; ii. Adding 0.001 to 1 wt.% of 2DLM's precursor, calculated with respect to the total weight of the SiO2+NaOH dry mix, to the alkali cellulose suspension and stirring for at least 5 minutes, preferably 30 to 60 minutes, at min. 50°C, preferably at 70°C; iii. Adding SiO2 powder to the mixture in a quantity to ensure a waterglass modulus n from 1.5 to 2, heating it to the temperature of at least 50°C, preferably 70°C, and stirring it at that temperature until complete dissolution of the SiO2 powder; iv. Evaporating water from the suspension at a temperature 90 to 150°C until evaporation is no longer possible due to the hygroscopic properties of the Cellulose / Waterglass system; v. Exposing the system to a mechanical work for at least 15 minutes, at a temperature range 80 to 10°C, preferably at a room temperature, to obtain a paste-like exfoliating medium containing 2DLM.

2. The method according to claim 1, wherein 2DLM's precursor is in the form of powder or flakes and is selected from the group comprising: graphite, graphene oxide, boron nitride, cloisite, MXenes and montmorillonite.

3. The method according to any of the preceding claims, wherein the mechanical work in the step v. is effected by hand-mixing or using a machinery that imparts a controlled and homogeneous mechanical work, such as homogenizer, extruder or laminating roller.

4. The method according to any of the preceding claims, wherein the further steps are:- dissolving the paste-like exfoliating medium containing 2DLM in a water to obtain a liquid suspension of cellulose fibres and 2DLM in diluted sodium silicate,- filtering off the sodium silicate, and optionally- washing out the resulting mixture in a water, to obtain the 2DLMs / cellulose mixture.

5. The method according to any of the claims 1 to 3, wherein the further step is drying the exfoliating medium at a temperature 150 to 250°C, preferably 200°C to remove chemical water, to obtain a cellulose / 2DLM nanocomposite.

6. The method according to any of the claims 1 to 3, wherein the further step is treating the exfoliating medium with tuned concentration of hydrogen halide acids to form water soluble sodium salts to remove desired quantity of sodium for the system with precipitation of SiO2 powder, to obtain a cellulose / 2DLM nanocomposite.

7. The method according to any of the claims 1 to 3, wherein the further step is diluting the exfoliating medium in water and treating it with 5% solution of phosphoric or sulfuric acid in order to precipitate SiO2 and sodium phosphate or sodium sulphate salts, to obtain highly ordered cellulose tactoids along with homogenously dispersed 2DLM.

8. The method according to claim 4, wherein the further steps are:- exposing the mixture to the temperature from 300 to 450 °C for at least 5 minutes, preferably 10 minutes to burn out the cellulose fibres, or- immersing the mixture in Schweizer's reagent to dissolve the cellulose fibres and filtering out supernatant, to obtain exfoliated 2DLM.

9. The method according to claim 4, wherein the 2DLM precursor is graphite or graphene oxide and cellulose / graphene nanocomposite is further re-dispersed and homogenized in organic solvent, suitable for polymeric synthesis, to synthesize polymeric matrix for the fabrication of polymer-based nanocomposites.

10. The method according to claim 4, wherein the 2DLM precursor is boron nitride and cellulose / boron nitride nanocomposite is further re-dispersed and homogenized in organic or inorganic solvent, suitable for polymeric synthesis, to synthesize polymeric matrix for the fabrication of polymer-based nanocomposites.

11. The method according to claim 5, 6 or 7, wherein the product is further calcinated in air to burn cellulose out, or in Argon atmosphere at 650°C to 750°C, preferably at 700°C to pyrolyze the cellulose, then melt-quenched to obtain a silicate or sodium-silicate or sodium-silicate-phosphate or silicate-phosphate glasses with dispersed 2DLM.

12. The method according to claim 6 or 7 wherein the precipitated SiO2 is then converted to metallic silicon in argon at 650-750°C for 30-120 minutes using metallic magnesium as reducing agent to obtain a 2DLMs.

13. An exfoliating medium containing 2DLM obtainable by the process according to any of the claims 1 to 3.

14. Use of the exfoliating medium according to the claim 13, as a storage medium for 2DLMs.

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