COMPOSITE MATERIALS
20220267607 · 2022-08-25
Inventors
- Sam Burrow (Bristol, GB)
- Elena Mogort-Valls (Bristol, GB)
- Conor Brady (Bristol, GB)
- Thomas Bryant (Bristol, GB)
- Vaiva Nagyte (Bristol, GB)
- Mehrdad Alibouri (Bristol, GB)
Cpc classification
C08J5/005
CHEMISTRY; METALLURGY
C08J2327/16
CHEMISTRY; METALLURGY
C08K3/30
CHEMISTRY; METALLURGY
C08J3/215
CHEMISTRY; METALLURGY
International classification
C08J5/00
CHEMISTRY; METALLURGY
Abstract
The present invention relates to processes for forming composites. The invention also relates to composites obtained by the processes described herein. Also provided are composites comprising 2D materials.
Claims
1. A process for forming a composite, the process comprising the following steps: a) providing a 2D material in a solvent; b) adding a particulate material to the solvent; c) providing a flocculating agent in the solvent, wherein the flocculating agent is a non-basic flocculating salt; wherein the presence of the flocculating agent in the solvent results in an interaction between the particulate material and 2D material to form a composite.
2. The process according to claim 1, wherein the 2D material is selected from one or more of: graphene, graphene oxide, reduced graphene oxide, functionalised graphene, partially oxidised graphene; metal oxide nanosheets which are composed of sheets of edge/corner sharing MO.sub.6 octahedra, (where M is a transition metal, and O is oxygen), where the sheets are separated by alkali metal cations, protons, water, solvent or any combination thereof; metal double hydroxides which are composed of octahedral hydroxide layers of divalent and trivalent metal cations, where charge is balanced with anions between the layers, represented by the general formula M.sup.2+.sub.1−xM.sup.3+.sub.x(OH).sub.2A.sup.n−.sub.x/n.mH.sub.2O (where M.sup.2+=Mg.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Zn.sup.2+, etc.; M.sup.3+=Al.sup.3+, Fe.sup.3+, Co.sup.3+, etc.; and A=(CO.sub.3).sup.2−, Cl.sup.−, (NO.sub.3).sup.−, (ClO.sub.4).sup.−, etc.); hexagonal boron nitride; and transition metal dichalcogenides with the general stoichiometry MX.sub.2, where M is a transition metal atom and X is a chalcogen atom.
3. The process according to claim 1 or claim 2, wherein the 2D material is selected from hBN, graphene or a transition metal dichalcogenide.
4. The process according to any preceding claim, wherein the non-basic flocculating salt is selected from alkali hydrogen phosphates, ethyltriphenylphosphonium halides, Borax, non-basic ammonium salts, tetraethylammonium halides, alkaline earth metal nitrates, alkali metal nitrates, alkaline earth metal halides, alkali metal halides, MOF precursors and combinations thereof, with the proviso that if the non-basic flocculating salt is ammonium chloride, it is formed in-situ in the solvent.
5. The process according to any preceding claim, wherein the non-basic flocculating salt is selected from one or more of sodium hydrogen phosphate, Ethyltriphenylphosphonium iodide, Borax, ammonium acetate, tetraethylammonium bromide, magnesium nitrate, lithium chloride, ammonium thiocyanate, zinc nitrate, diaminobutane, 2-methylimidazole, and combinations thereof.
6. A process for forming a composite, the process comprising the following steps: a) providing a 2D material that is not graphene-based in a solvent; b) adding a particulate material to the solvent; c) providing a flocculating agent into the solvent, wherein the flocculating agent is a basic material, wherein the presence of the flocculating agent in the solvent results in an interaction between the particulate material and 2D material to form a composite.
7. The process according to claim 6, wherein the 2D material that is not graphene based is selected from: metal oxide nanosheets which are composed of sheets of edge/corner sharing MO.sub.6 octahedra, (where M is a transition metal, and O is oxygen), where the sheets are separated by alkali metal cations, protons, water, solvent or any combination thereof; metal double hydroxides which are composed of octahedral hydroxide layers of divalent and trivalent metal cations, where charge is balanced with anions between the layers, represented by the general formula M.sup.2+.sub.1−xM.sup.3+.sub.x(OH).sub.2A.sup.n−.sub.x/n.mH.sub.2O (where M.sup.2+=Mg.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Zn.sup.2+, etc.; M.sup.3+=Al.sup.3+, Fe.sup.3+, Co.sup.3+, etc.; and A=(CO.sub.3).sup.2−, Cl.sup.−, (NO.sub.3).sup.−, (ClO.sub.4).sup.−, etc.); hexagonal boron nitride; and transition metal dichalcogenides with the general stoichiometry MX.sub.2, where M is a transition metal atom and X is a chalcogen atom.
8. The process of claim 7, wherein the 2D material that is not graphene is selected from hBN or a transition metal dichalcogenide.
9. The process of any of claims 6 to 8, wherein the basic material is a basic solution.
10. The process of any one of claims 6 to 9, wherein the basic material is a basic flocculating salt.
11. The process of any preceding claim, wherein the 2D material is present in the solvent as a dispersion.
12. The process of any preceding claim, wherein the 2D material and particulate material are substantially insoluble in the solvent at the operating temperature of the process.
13. The process according to any preceding claim, wherein the 2D material and particulate material are mixed prior to addition of the flocculating salt to form a dispersion.
14. The process according to any preceding claim, wherein the 2D material is provided by exfoliation of a bulk layered material in the solvent.
15. A process according to any one of claims 1 to 5, the process comprising: a) providing a dispersion of a bulk layered material in a solvent; b) adding a particulate material to the dispersion; c) exfoliating the layered material, before or after the addition of the particulate material, to form a 2D material in the dispersion; wherein the process comprises introducing a non-basic flocculating salt into the dispersion prior to or following any one of steps a) to c); wherein the presence of the flocculating salt to the solvent results in an interaction between the particulate material and 2D material to form a composite.
16. A process according to any one of claims 6 to 9, the process comprising; a) providing a dispersion of a bulk layered material in a solvent; b) adding a particulate material to the dispersion; c) exfoliating the layered material, before or after the addition of the particulate material, to form a 2D material in the dispersion; wherein the process comprises introducing a basic material into the dispersion prior to or following any one of steps a) to c); wherein the presence of the basic material in the solvent results in an interaction between the particulate material and 2D material to form a composite.
17. The process according to any one of claims 13 to 16, wherein the exfoliation comprises sonication, shear mixing, or high-pressure homogenisation, optionally at a shear rate of at least 10.sup.4s.sup.−1.
18. The process of any one of claims 13 to 15 when ultimately dependent on claim 1, wherein the exfoliation of the bulk layered material is performed in the presence of a non-basic flocculating salt which also acts as an exfoliant.
19. The process of any one of claim 13 or 16 when ultimately dependent on claim 6, wherein the exfoliation of the bulk layered material is performed in the presence of a basic flocculating salt which also acts as an exfoliant.
20. The process of any preceding claim, wherein the particulate material and the 2D material are mixed together to form a dispersion.
21. The process of any one of claim 1 to 5 or 9, wherein the flocculating salt is generated in the solvent in-situ by transforming a source of salt into a flocculating salt by any one or more of: heat, pressure, reaction of an acid with a base, reaction with non-salts, reaction with precursor salts, catalysis, enzymes or light.
22. The process of claim 20, wherein the flocculating salt is generated in the solvent by; adding two or more precursor salts to the solvent, adding an antisolvent to the solvent, wherein addition of the antisolvent causes the precursor salts to react and form the flocculating salt in the solvent.
23. The process of any preceding claim, wherein the solvent comprises one or more of organic solvents and water.
24. The process of claim 23, wherein the solvent is selected from Cyrene; DMSO; NMP; butyl lactate; dimethyl isosorbide; triacetin; DMF; 1,2-dichlorobenzene; benzonitrile; pyridine; triethyl citrate; THF, cyclohexanone; cyclopentanone; olefins including pentane, hexane, cyclohexane, heptane, cyclooctane; ethyl acetate; ethyl lactate; furfual; eugenol; isoeugenol; levulinic acid; chloroform; 1,2-dischloromethane; toluene; methyl-t-butyl ether; methyl ethyl ketone; trichloroethylene; xylene; IPA; Water; Acetone; Methanol The process of claim 22 or 23, wherein the solvent is selected from Water, dichloromethane, chloroform, pentane, hexane, IPA, methanol, toluene, ethyl acetate, trichloroethylene, xylene, acetone, and combinations thereof.
25. The process of any preceding claim, wherein the particulate material is a metal oxide.
26. The process of any one of claims 1 to 25 wherein the particulate material is a polymeric material.
27. The process of any preceding claim, wherein the composite is dried following flocculation.
28. The process of any preceding claim, further comprising removing and/or recovering the flocculating salts present in the solvent.
29. The process of any preceding claim, wherein the process is performed in the absence of a surfactant.
30. The process of any preceding claim, wherein the ratio of 2D material to particulate material in the solvent is 1:1000 by atom to 10:1 by atom.
31. A process as claimed in any one of the preceding claims, wherein the process is conducted at a temperature in the range 0° C. to 260° C., preferably 0° C. to 110° C., more preferably 0° C. to 50° C.
32. A process as claimed in any one of the preceding claims, wherein the particulate material has a particle size in the range 5 nm to 1 pm, preferably 10 nm to 500 nm, ore preferably 15 nm to 250 nm.
33. A process according to any one of the preceding claims, wherein the interaction between the 2D material and particulate material results in an increase in particle size of the formed composite relative to the particle size of the particulate material.
34. A composite obtained by, obtainable by or directly obtained by the process according to any of the preceding claims.
35. A composite comprising a 2D material, a particulate material and a solid salt.
36. The composite of claim 35, wherein the 2D material, particulate material and solid salt are attached to one another in a flocculated product.
37. The composite of claim 35 or 36, wherein the 2D material is graphene, the solid salt is a non-basic flocculating salt and the particulate material is a metal oxide.
38. The composite of claim wherein the particle size of the composite is from 10 to 1000 microns
39. A composite comprising a 2D material, a particulate material and a metal organic framework.
40. The composite of claim 39, wherein the 2D material, particulate material and metal organic framework are attached to one another in a flocculated product.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0239] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:
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DETAILED DESCRIPTION
[0308] The term ‘two-dimensional material” (2D material) may mean a compound in a form which is so thin that it may exhibit different properties than the same compound when in bulk. Typically, two-dimensional inorganic compounds are in a form which is single- or few layers thick, i.e. up to 10 layers thick. A two-dimensional crystal of a layered material (e.g. an inorganic compound or graphene) is a single or few layered particles of that material.
[0309] 2D materials do exhibit thicknesses, however the dimensions of those thicknesses are significantly lower than the widths and lengths of these materials, thus the origin of the name ‘2D materials’.
[0310] The term ‘few-layered particle’ means a particle which is so thin that may exhibit different properties than the same compound when in bulk. Not all of the properties of the compound will differ between a few-layered particle and a bulk compound, but one or more properties are likely to be different. A more convenient definition would be that the term ‘few layered’ refers to a crystal that is from 2 to 9 atomic or molecular layers thick in cross-section (e.g. 2 to 5 layers thick). Crystals of graphene, for example, which have more than 9 molecular layers (i.e. 10 atomic layers; 3.5 nm) generally exhibit properties more similar to graphite than to graphene. An atomic or molecular layer is the minimum thickness chemically possible for the compound. In the case of boron-nitride one molecular layer is a single atom thick. In the case of the transition metal dichalcogenides (e.g. MoS.sub.2 and WS.sub.2), a molecular layer is three atoms thick (one transition metal atom and two chalcogen atoms). Thus, few-layer crystals of 2D materials are generally less than 50 nm thick, depending on the compound and are preferably less than 20 nm thick, e.g. less than 10 or 5 nm thick.
[0311] The ‘inorganic compounds’ referred to throughout this specification are inorganic layered compounds. Thus, the term ‘inorganic compound’ refers to any compound made up of two or more elements which forms layered structures in which the bonding between atoms within the same layer is stronger than the bonding between atoms in different layers. Many examples of inorganic layered compounds have covalent bonds between the atoms within the layers but van der Waals bonding between the layers. The term ‘inorganic layered compound’ is not intended to encompass graphene.
[0312] Many inorganic compounds exist in a number of allotropic forms, some of which are layered and some of which are not. For example boron nitride can exist in a layered graphite-like structure or as a diamond-like structure in which the boron and nitrogen atoms are tetrahedral orientated.
[0313] Examples of layered inorganic compounds to which the present invention can be applied include: hexagonal boron nitride (hBN), bismuth strontium calcium copper oxide (BSCCO), transition metal dichalcogenides (TMDCs), Sb.sub.2Te.sub.3, Bi.sub.2Te.sub.3 and MnO.sub.2.
[0314] TMDCs are structured such that each layer of the compound consists of three atomic planes: a layer of transition metal atoms (for example Mo, Ta, W . . . ) sandwiched between two layers of chalcogen atoms (for example S, Se or Te). Thus in one embodiment, the TM DC is a compound of one or more of Mo, Ta and W with one or more of S, Se and Te. There is strong covalent bonding between the atoms within each layer of the transition metal chalcogenide and predominantly weak Van der Waals bonding between adjacent layers. Exemplary TMDCs include NbSe.sub.2, WS.sub.2, MoS.sub.2, TaS.sub.2, PtTe.sub.2, VTe.sub.2.
[0315] A layer of graphene consists of a sheet of sp.sup.2-hybridized carbon atoms. Each carbon atom is covalently bonded to three neighbouring carbon atoms to form a ‘honeycomb’ network of tessellated hexagons. Carbon nanostructures which have more than 10 graphene layers (i.e. 10 atomic layers; 3.5 nm) generally exhibit properties more similar to graphite than to mono-layer graphene. Thus, throughout this specification, the term graphene is intended to mean a carbon nanostructure with up to 10 graphene layers. Graphene is the ‘ultimate’ 2D material as it is defined by having one carbon atom thickness layer/sheet, which is a structural unit of graphite.
[0316] The level of graphene defects in a composite can be assessed using Raman spectroscopy in a manner similar to L. G. Cancado et al. 2011, “Quantifying Defects in Graphene via Raman Spectroscopy at Different Excitation Energies”, Nano Letters, which is incorporated herein by reference. The ratio of the intensity of the observed D peak Raman intensity, referred to as I(D), to the G peak Raman intensity, referred to as 1(G), indicates the amount of defects present within the graphene. This is referred to as the I(D)/I(G) ratio. The distance between defects is a measure of the amount of disorder. Given the distance between defects is greater than approximately 4 nm; the lower the I(D)/I(G) ratio, the greater the distance between defects, thus, the amount of disorder is lower. In addition to this, the full width atof half maximum (FWHM) of D, G, 2D (also referred to asin some literature called G′), D′ peaks can be used to evaluate the level of disorder as discussed in E. H. Martins Ferreira et al. 2010, “Evolution of the Raman spectra from single-, few-, and many-layer graphene with increasing disorder”, PHYSICAL REVIEW B work. If FWHM of D, G, 2D (in some literature called also referred to as G′), and D′ Raman peaks at a laser excitation wavelength of 514.5 nm (2.41 eV), are reaching values lowerhigher than 20 cm-1, 20 cm-1, 35 cm-1, and 10 cm-1 respectively, then the distance between zero dimensional pointlike defects is expected to be greater than approximately 4 nm.
[0317] The composites formed by the method of the present invention may have an I(D)/I(G) ratio of less than 0.75, less than 0.6 or preferably less than 0.5 , at a laser excitation wavelength of 532 nm (2.33 eV). Thus, the composites formed by the method of the present invention may have an I(D)/I(G) ratio of from 0.01 to 0.75, 0.02 to 0.65 or 0.04 to 0.55, at a laser excitation wavelength of 532 nm (2.33 eV). Given the distance between defects is greater than approximately 4 nm and a laser excitation wavelength of 532 nm (2.33 eV); an I(D)/I(G) ratio less than 1 indicates that the defects are greater than 9.5 nm apart.
[0318] It is also possible to assess the nature of the graphene defects using Raman spectroscopy. In general, defects in graphene are considered to be anything that breaks the symmetry of the infinite carbon hexagonal lattice. This therefore includes edges, vacancies and changes in carbon-hybridization (e.g. sp.sup.2 into sp.sup.3). An sp.sup.3 defect is due to an additional atom being present out-of-plane of the graphene layer resulting in an sp.sup.3 hybridized carbon atom or atoms. A vacancy defect is due to one or more missing atoms of a 2D material layer. An edge defect is due to a graphene sheet not being infinitely large and therefore having an edge.
[0319] Partially oxidised graphene and pristine graphene can be distinguished from graphene oxide, functionalised graphene and reduced graphene oxide using Raman spectroscopy, as discussed herein. Graphene oxide and functionalised graphene contain high amounts of sp.sup.3 defects. Reduced graphene oxide is formed from the reduction of graphene oxide with reducing agent or temperature treatment. Reduced graphene oxide also includes a large amount of vacancy defects, as a result of the removal of oxygen to leave holes in the hexagonal lattice. Thus, graphene oxide and reduced graphene oxide typically have an I(D)/I(G) ratio of above 0.8 or FWHM of D, G, 2D (in some literature called G′) peaks values higher than 70, 70, 150 cm.sup.−1 respectively. Conversely, partially oxidised graphene oxide has fewer oxygen atoms compared to graphene oxide but has not undergone harsh reduction processes like reduced graphene oxide. Thus, more of the hexagonal structure is maintained, meaning fewer sp.sup.3 and vacancy defects. The number of defects can be assessed by measuring the I(D)/I(G) ratio or FWHM of peaks as discussed above.
[0320] The presence of sp.sup.3 defects and vacancy defects can have a detrimental impact on the usefulness of the final composite. Thus, it is desirable for the number of sp.sup.3 and/or vacancy defects to be minimised.
[0321] The ratio of the intensity of the Raman D peak, referred to as I(D), to the Raman D′ peak, referred to as I(D′), signifies the type of defects present in the sample. This is referred to as the I(D)/I(D′) ratio. A ratio less than approximately 3.5, at a laser excitation wavelength of 514.5 nm (2.41 eV) indicates contributions from edge defects dominate. A ratio of approximately 7 indicates the presence of vacancy defects and a ratio of approximately 13 or more suggests sp3 defects.
[0322] The graphene composites of the present invention may have a FWHM-(G) (Full Width at Half Maximum of the graphene Raman G peak of a raman spectra) of lower than 70 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). Preferably, the FWHM-(G) will be lower than 60 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). More preferably, the FWHM-G will be lower than 50 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). Even more preferably, the FWHM-(G) will be lower than 40 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). Most preferably, the FWHM-(G-) will be lower than 30 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV).
[0323] The graphene composites of the present invention may have a FWHM-(2D) (Full Width at Half Maximum of the graphene Raman 2D peak) of the present invention graphene composites may be lower than 100 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). Preferably, the FWHM-(2D) will be lower than 80 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). More preferably, the FWHM-(2D) will be lower than 60 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). Even more preferably, the FWHM-(2D) will be lower than 50 cm.sup.−1 at a laser excitation wavelength of 514.5 nm (2.41 eV). The graphene composites of the present invention may have an I(D)/I(D) ratio of from 0.01 to 7, 0.01 to 4.5, 0.01 to 3.5 or preferably from 0.1 to 3.45 at a laser excitation wavelength of 532 nm (2.33 eV). Thus, the composites of the present invention will preferably have minimal sp3 defects and more preferably minimal vacancy defects.
[0324] Graphene oxide typically comprises a weight percentage of oxygen of above 15 wt. %. In the scope of the present invention, the term “partially oxidised graphene” can be interpreted as a graphene oxide which only comprises oxygen in an amount of up to 15% of the total weight of the graphene, e.g. 5 to 15 wt. %. Typically, partially oxidised graphene would include oxygen in an amount of up to 10% of the total weight of the graphene. As discussed above, the term “pristine graphene” refers to graphene which has not been chemically modified.
[0325] The processes described within may be performed without the use of graphene that is substantially chemically modified. However, some graphene production methods may introduce some degree of oxidation (below 15%) as a result of slight oxidation facilitating faster exfoliation. However, unlike previous work involving graphene oxide, this degree of oxidation does not necessarily increase the processability of the graphene, and preferably the degree of oxidation/the degree of defects is reduced to as low as possible to reduce the impact on the conductive properties of the final composite material.
[0326] Flocculation is a widely used effect used in water purification, cheesemaking, brewing, and throughout other areas of chemistry to collect a product from a dispersion or fine suspension in a liquid fluid. It may involve one or more of a combination of steps: [0327] Changing the pH of a dispersion, to such a value that the surface charge on the particulate components no longer repulses nearby particles, [0328] Adjusting the temperature of a dispersion, to such a value that particles can overcome the particle-particle repulsion to stick together, [0329] Adding an excess of any of the components, such that stabilisation is no longer possible, [0330] Adding a non-solvent to the dispersion to reduce the stabilisation effect of surfactants and/or solvent-surface interactions [0331] Providing a highly charged solid, which the various solid components of the dispersion are attracted to.
These steps perform the general function of bringing together suspended particulates, to create larger ‘flocs’ which (depending on the relative density of particle to fluid) collectively rise to the top or fall to the bottom of the suspending fluid. The present inventors have advantageously identified methods to induce flocculation to assist in the formation of 2D composite materials.
[0332] Flocculation is an advantageous step to include in a process as it permits the utilization of large amounts of solvent without the need for significant liquid evaporation or otherwise physical means of obtaining a product. This makes flocculation a widely used process at industrial scales, where time and energy used for the reaction are ideally as small as possible. Given that it is often difficult to obtain a good dispersion of 2D materials in solvents, flocculation of a product will permit recycling of the large volume of solvent likely needed when scaling up the production of 2D-particulate material composites.
[0333] The interaction between the particulate material and the 2D material (in the presence of the flocculating agent) results in an increase in the particle size of the composite relative to the particulate material. This arises due to the formation ‘secondary particles’ (aggregates of composite material) in the solvent. Thus, the use of flocculation is advantageous over simple high shear mixing of particulate materials and 2D materials, because larger, bound particles can be formed. These larger particles are beneficial for further processing steps, as larger particles are known to have more predictable properties than nano-sized particles (e.g. nano-sized particles can be difficult to stabilise).
[0334] In the methods described herein, the addition of a flocculating agent to the solvent will induce the 2D material and the particulate material to flocculate and form a composite material. Without wishing to be bound by theory, it is thought that inducing flocculation in this manner results in improved interaction between the 2D material and the particulate. This will often result in an increase in particle size due to the interaction between 2D and particulate materials. This results in a more efficient process for making composites of 2D materials than previously demonstrated in the prior art. The increase in particle size may be observed under a microscope, where observable flocs (groups of particles) growing beyond 10 microns in metal oxides and with polymers can be observed. Before addition of the salt, the particle size within dispersion is expected to be the size at which it was made, e.g. 10 nm particles and higher. Generally, only small, unflocculated, particles (e.g. less than 500 nm) are observed with the microscope before addition of the salt. However, larger particles may be visible depending on the preparation method used to form the dispersion.
[0335] Flocculated products are advantageous because solvents can be recycled efficiently, as the formed flocculated material is naturally separated from the dispersion mixture during flocculation. This also means that a relatively large amount of solvent can be used for the dispersion of the 2D material, which reduces the risk of aggregation of the 2D material and ensures a homogeneous mixture of the composite.
[0336] It will be understood by a skilled person that a 2D material may be defined as a layered material with an in-plane modulus significantly higher than the shear modulus between the layers. Such materials include but not are restricted to, graphene, WS.sub.2, MoS.sub.2 and hexagonal boron nitride. Typically, a 2D material will comprise from 1-10 molecular layers.
[0337] A “graphene-based” material refers to a 2D layered material which comprises a hexagonal carbon skeleton, such as graphene, graphene oxide, reduced graphene oxide, functionalised graphene (e.g. fluorinated graphene). Thus, a material that is “not graphene based” refers to materials which could be termed as “inorganic layered compounds”. Thus, the term ‘inorganic compound’ refers to any compound made up of two or more elements which forms layered structures in which the bonding between atoms within the same layer is stronger than the bonding between atoms in different layers. Many examples of inorganic layered compounds have covalent bonds between the atoms within the layers but van der Waals bonding between the layers. The term ‘inorganic layered compound’ is not intended to encompass graphene or graphene derivatives.
[0338] The term “non-basic” means that when the flocculating salt is added to deionised water, the pH of the resulting solution is from 1 to 7.5, suitably from 1 to 7.
[0339] The term “substantially insoluble” in the context of the present invention means that at least 1000 mass parts of solvent is required to dissolve 1 mass part of solute at standard operating temperatures (e.g. 25° C. and latm pressure). The term “insoluble”, in the context of the present invention means that greater than 10000 mass parts of solvent is required to dissolve 1 mass part of solute.
[0340] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
[0341] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. 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. The invention is not restricted to the details of any foregoing embodiments. 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.
[0342] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
EXAMPLES
Example 1
[0343] A Nickel Oxide/MoS2 composite was obtained with the following method, which used sodium hydroxide as the flocculating agent.
[0344] A dispersion of MoS2 was prepared by high-shear mixing in DMSO, with sodium citrate used as an exfoliation aid. Briefly:
200 ml of sodium citrate (1.84 mg/ml) in DMSO was prepared. To this mixture, 1.005 g of MoS2 (Sigma, 234842, <2 micron powder, 98%) was added. The solution was homogenised for 1 hour at maximum RPM using a L4R mixer, equipped with a ¾ tubular square-hole high-shear stator (Silverson Machines). The solution was kept in a cold water bath throughout homogenising, to maintain the solution temperature below 30-40 degrees centigrade. After homogenising, the solution was transferred to four 50 ml centrifuge tubes and centrifuged for 30 minutes at 2000 RPM (Premiere, Model XC-2450 Series Centrifuge), to yield a brown dispersion. The top 80% in each supernatant was used as the ‘MoS2 dispersion’ This method normally yields a MoS2 dispersion of 0.01-0.02 mg/ml
[0345] 2 ml MoS2 dispersion and 0.01 g nickel oxide (Sigma, <50 nm, 637130) were added into a glass vial and dispersed with a bath sonicator for 10 minutes. 0.2 ml NaOH solution (1M in deionised water) was added, rapidly forming a precipitate from the mixture. The supernatant was removed, and the resulting slurry transferred to a vacuum oven to dry in a vacuum oven at 80 degrees centigrade for 30 hours. The product was analysed with Raman spectroscopy. (
Example 2
[0346] A ZnO/Graphene composite was obtained with the following method, which used ammonium acetate as the flocculating agent.
[0347] A ZnO/Graphene composite was obtained with the following method, which used ammonium acetate as the flocculating agent.
[0348] A dispersion of graphene was prepared by high-shear mixing of graphite in DMSO. Briefly:
[0349] 25 g graphite flakes (<50 micron, Sigma) were added to 500 ml DMSO in a beaker. The solution was homogenised for 30 minutes at maximum RPM using a L4R mixer, equipped with a 32 mm square-hole high-shear rotor/stator assembly (Silverson Machines). A water bath was used to maintain the temperature of the dispersion close to room temperature. After homogenising, the solution was transferred to 50 ml centrifuge tubes and centrifuged for 30 minutes at 2000 RPM (Premiere, Model XC-2450 Series Centrifuge). The top ⅔.sup.rd of supernatant in each vial was then centrifuged for a further 30 minutes at 3500 RPM. The top ⅔.sup.rd of the resulting supernatants were used as ‘graphene dispersion’. This method usually yields a graphene dispersion of 0.01-0.05 mg/ml
[0350] 2 ml of the graphene dispersion and 0.01 g zinc oxide (sigma, <100 nm, 544906) were added into a glass vial and bath-sonicated for 10 minutes. 0.2 ml of saturated ammonium acetate was then added to the dispersion to initiate the flocculation. The product formed slowly, yielding large suspended particles which could be observed with a microscope. The suspension was left to evaporate in a vacuum oven for 30 hours at 80 degrees centigrade, yielding a solid which was analysed with Raman spectroscopy (
Example 3
[0351] hBN/ZrO2 composite was obtained using the following method, which used ammonium carbonate as the flocculating agent.
[0352] A dispersion of hBN was first achieved by high-shear mixing of hBN in DMSO. Briefly:
[0353] 200 ml DMSO was added to a 250 ml glass beaker. To this, 1.015 g of hBN (Sigma, 255475, ˜1 micron powder, 98%) was added. The solution was homogenised for 1 hour at maximum RPM using a L4R mixer with ¾ tubular square-hole high-shear stator (Silverson Machines). The solution was kept in a cold-water bath throughout homogenising, to maintain the solution temperature below 30-40 degrees centigrade. After homogenising, the solution was transferred to four 50 ml centrifuge tubes and centrifuged for 30 minutes at 2000 RPM, followed by 15 minutes at 4000 RPM (Premiere, Model XC-2450 Series Centrifuge), to yield a white dispersion. The top 80% in each supernatant was used as the TON dispersion'. This method usually yields a hBN dispersion of 0.008-0.03 mg/ml
[0354] 2 ml of the hBN dispersion and 0.01 g ZrO2 (5 micron powder, 230693, Sigma-Aldrich, 99%) were added into a glass vial and sonicated for 10 minutes. 0.2 ml saturated ammonium carbonate was then added to the dispersion to initiate the flocculation. The product was dried with a vacuum oven and then analysed with Raman spectroscopy, shown in
Example 4
[0355] A hBN/ZrO2 composite was also obtained using the following method, which used NaOH as the flocculating agent.
[0356] 500 ml of NaOH solution (2M in deionised water) is prepared. Then, 1.011 g hBN (Sigma, 255475, ˜1 micron powder, 98%) is added, and the solution was homogenised for 30 minutes at maximum RPM using a L4R mixer, equipped with a 32 mm square-hole high-shear rotor/stator assembly (Silverson Machines). A water/ice bath was used to maintain the temperature of the dispersion close to room temperature. Then, 1.057 g ZrO2 (5 micron powder, 230693, Sigma-Aldrich, 99%) was added to the mixture, and homogenisation was continued under the same conditions for an additional 30 minutes.
[0357] A white flocculation was seen to rapidly form, once homogenisation ceased. An aliquot of precipitate was collected and dried on a hotplate at 70 degrees centigrade. The product was then analysed with Raman spectroscopy, shown in
Example 5
[0358] A composite between MoSe2 and Polyurethane was formed with the following method, which used ammonium acetate as the flocculating agent, with sodium citrate to enhance the yield of layered material.
[0359] A water-based biodegradable polyurethane nanoparticle emulsion was synthesised following the protocol described by Chen et al (2014).
[0360] Under inert atmosphere, 10.24 g of Poly-e-caprolactone diol (5 mmol) and 3.99 ml IPDI (19 mmol) were reacted for 3 hours (180 rpm) at 75C. Approximately 0.8 ml of 2-Butanol and 0.71 g of DMPA (5 mmol) were then added against high nitrogen flow. The reaction was cooled down to 45C, 0.696 ml triethylamine (TEA, 5 mmol) was syringed into the reaction flask and the mixture was stirred for 30 minutes. 36 ml DI water was quickly added against vigorous sitting (1200 rpm) for 2 minutes, after which the stirring was brought back to 180 rpm. 0.51 ml ethylenediamine (EDA, 8 mmol) was added and the reaction was stirred for further 30 minutes. The milky colloidal dispersion was collected, centrifuged and washed twice with DI water (3000 rpm, for 15 and 30 minutes) to yield a 15 w % emulsion.
[0361] Adapted from Chen, Y.-P., & Hsu, S. (2014). ‘Preparation and characterization of novel water-based biodegradable polyurethane nanoparticles encapsulating superparamagnetic iron oxide and hydrophobic drugs.’ J. Mater. Chem. B, 2(21), 3391-3401. Doi:10.1039/c4tb00069b
[0362] A dispersion of MoSe2 was prepared with the following method:
200 ml of sodium citrate (1.84 mg/ml) in DMSO was prepared. To this mixture, 1.005 g of MoSe2 (Alfa, 13112, 325 mesh powder, 99.9%) was added. The solution was homogenised for 1 hour at maximum RPM using a L4R mixer, equipped with a 19 mm square-hole high-shear stator (Silverson Machines). The solution was kept in a cold water bath throughout homogenising, to maintain the solution temperature below 30-40 degrees centigrade. After homogenising, the solution was transferred to four 50 ml centrifuge tubes and centrifuged for 30 minutes at 2000 RPM (Premiere, Model XC-2450 Series Centrifuge), to yield a brown dispersion. The top 80% in each supernatant was then centrifuged at 4000 RPM for a further 15 minutes. Dispersions were left to settle further overnight, then the supernatant was used directly as ‘MoSe2 dispersion’.
[0363] To form the composite:
2 ml MoSe2 dispersion and 0.5 ml PU dispersion were added together into a vial and sonicated for 5 minutes. Saturated ammonium acetate (0.2 ml) was added to the mixture under mild agitation. A precipitate formed slowly, and the contents were transferred to a vacuum oven for drying for 30 hours at 80 degrees C. This yielded a transparent, brown film weighing 0.0912 grams. The product was further analysed with Raman spectroscopy, shown in
Example 6, MOF-Initiated Flocculation in DMSO Graphene Dispersion
[0364] Images of this dispersion were taken throughout the procedure of making the dispersion and the interaction. The metal oxide used was titanium oxide (anatase) and the flocculating agent was the zinc nitrate hexahydrate which instigated the formation of a MOF, ZIF-8. The experimental procedure is as follows:
[0365] 25 g graphite flakes (<50 micron, Sigma) were added to 500 ml DMSO in a beaker. The solution was homogenised for 30 minutes at maximum RPM using a L4R mixer, equipped with a 35 mm square-hole high-shear stator (Silverson Machines). A water bath was used to maintain the temperature of the dispersion close to room temperature. After homogenising, the solution was transferred to 50 ml centrifuge tubes and centrifuged for 30 minutes at 2000 RPM (Premiere, Model XC-2450 Series Centrifuge). The top ⅔.sup.rd of supernatant in each vial was then centrifuged for a further 30 minutes at 3500 RPM. The top ⅔.sup.rd of the resulting supernatants were used as ‘graphene dispersion’, yielding solution 1. This method normally yields a graphene dispersion of 0.01-0.05 mg/ml
[0366] In a separate beaker, 0.66 g of 2-methylimidazole was then added to 44 g (40 ml) of DMSO, yielding solution 2. 0.375 ml of 1,4-diaminobutane was added to 25 ml of solution 2, yielding solution 3.
[0367] In a separate beaker, 0.30 g of Zinc nitrate hexahydrate was added to 44g (40 ml) DMSO, yielding solution 4.
[0368] Images of 100 ml graphene dispersion were captured using the camera. 0.5 g of Anatase (Sigma, ˜25 nm, powder) was added to the dispersion, and the mixture was mixed using a sonication bath for 10 minutes. The dispersion was left to rest for a further 10 minutes. Images of the mixture were captured using the camera.
[0369] Solution 3 was added to the mixture and mixed for 5 minutes using the sonication bath. Then, 25 ml of solution 4 was added to the mixture, and the mixture was mixed for 5 minutes using a magnetic stirrer and stirrer bar. This initiates the formation of solid crystals of the MOF, ZIF-8, from soluble precursors. Formation of ZIF-8 acted as a flocculant to form a composite between TiO2 and graphene sheets. Photos were taken at regular intervals to show formation of the flocculated product from the dispersion (
Example 7: Ammonium Chloride-Initiated Flocculation when Using Graphene Dispersion in a Acetone:Water Mixture
[0370] Images of this dispersion were taken throughout the interaction procedure. The metal oxide used was titanium oxide (anatase) and the interaction agent was ammonium chloride, produced in-situ by reaction of HCl with ammonia.
[0371] The experimental procedure is as follows:
In a thoroughly cleaned 500 ml beaker, 2 g Graphite (<50 micron, Sigma) is added to a 3:1 by weight Acetone:water mixture (316 g Acetone to 105 g water). The mixture is shear mixed for 30 minutes at maximum RPM using a L4R mixer, equipped with a 35 mm square-hole high-shear stator (Silverson Machines). A water/ice bath was used to maintain the temperature of the dispersion close to room temperature. After homogenising, the solution was transferred to 50 ml centrifuge tubes and centrifuged for 30 minutes at 2000 RPM (Premiere, Model XC-2450 Series Centrifuge). The top ⅔.sup.rd of supernatant in each vial was then centrifuged for a further 30 minutes at 3500 RPM. The top ⅔.sup.rd of the resulting supernatants were used as ‘graphene dispersion’. This method normally yields a graphene dispersion of 0.01-0.05 mg/ml
[0372] 0.2 g TiO2 (Sigma, ˜25 nm, powder) is added to the mixture and it is dispersed by sonication for 10 minutes. Images were taken immediately after and then after 10 minutes. Exfoliated graphene was found to stay in dispersion, while a layer of non-dispersed TiO2 sinks at the bottom, indicating little/no interaction between graphene and TiO2. While mixing with a magnetic stirrer/stirrer bar, 10 ml 1M (aqueous) HCl was added, followed by 10 ml 1M (aqueous) ammonia. The mixture was left to stir for 5 minutes. This formed a precipitate of ammonium chloride which caused the formation of a composite. This is seen to precipitate rapidly, over the course of 10 minutes. Photos from this reaction can be found in
Example 8: MoS2 and PU Microscope Study
[0373] Reaction procedure: [0374] 1. 1 ml MoS2 dispersion (as prepared from example 1) was added to a glass vial. [0375] 2. 0.1 ml of polyurethane dispersion (as prepared from example 5) was added and dispersed using a bath sonicator for a total of 5 minutes. [0376] 3. Images of the dispersion were taken under the microscope using two different magnifications. To image the dispersion, a few drops were placed on a glass slide and a cover slip was placed on top to allow the imaging to take place. (
Example 9: MoSe2 and TiO2 Microscope Study
[0379] 1. 1 ml MoSe2 dispersion (as prepared from example 5) was added to a glass vial. Images were attempted to be recorded with a microscope, but no material was observed. [0380] 2. 0.0015 g of anatase powder (Sigma, 637254, anatase, <25 nm particle size) was added to the dispersion and dispersed using a bath sonicator for a total of 5 minutes. [0381] 3. Images of the dispersion were taken using the higher magnification (yielding images roughly 140 microns across). To image the dispersion, a few drops were placed on a glass slide and a transparent cover slip was placed on top to allow the imaging to take place. (
Example 10: Synthesis of MoS2/TiO2 Composite
[0384] 2 ml MoS2 dispersion (as prepared from example 1) was added into a glass vial. 0.01 g anatase (Sigma, 637254, anatase, <25 nm particle size) was added to the dispersion, and the mixture was mixed for 5 minutes in a sonication bath. After sonication, 0.2 ml NaOH solution (1M, in deionised water) was added to the mixture, and flocculation was observed. The solid product settled out rapidly, and it was dried with a vacuum oven for 30 hours at 80 degrees centigrade. UV/Vis Diffuse Reflectance Spectroscopy was performed on the solid product, and the spectrum (
Example 11: Synthesis of a MoS2/PU Composite
[0385] 2 ml MoS2 dispersion (as prepared from example 1) was added into a glass vial. 0.5 ml PU dispersion (from example 5) was added also, and the mixture was mixed in a sonication bath for 5 minutes. 0.2 ml saturated ammonium carbonate solution (aqueous) was added, and a flocculation was observed to occur rapidly. The product was collected, then dried in a vacuum oven for 30 hours at 80 degrees centigrade, yielding a dark, slightly transparent, flexible film. UV/Vis Diffuse Reflectance Spectroscopy was performed on the solid product, and the spectrum (
Example 12: Synthesis of a WSe2/ZnO2 Composite
[0386] WSe2 dispersion was synthesised using the same method as used to produce MoS2 dispersion in example 1. Briefly, sodium citrate (0.37 g) was added into 200 ml of DMSO. 1g WSe2 (Alfa, 13084, 10-20 micron powder, 99.8%) was added, and the mixture homogenised for 1 hour in a cold water bath. The resulting suspension was centrifuged for 30 minutes at 2000 RPM. 2 ml of the WSe2 dispersion was added into a glass vial, and 0.01 g ZnO (<100 nm powder, 544906, Sigma-Aldrich) was also added, forming a mixture which was mixed in a sonication bath for 5 minutes. Saturated ammonium carbonate solution (aqueous) was added while gently mixing the vial, yielding a precipitate. The product was transferred to an oven and dried at 80 degrees Celsius for 30 hours, and the solid was analysed with UV/Vis reflectance spectroscopy. The troughs in the spectrum between 500 nm and 800 nm indicate the presence of exfoliated WSe2, while the feature between 300 nm and 500 nm is likely the ZnO bandgap.
Example 13: Synthesis of a WSe2/PU Composite
[0387] WSe2 dispersion (as prepared from example 12) was added to a glass vial. 0.5 ml PU dispersion (from example 5) was added also, and the mixture was mixed in a sonication bath for 5 minutes. 0.2 ml saturated ammonium carbonate solution (aqueous) was added under mild agitation, and a flocculation was observed to occur rapidly. The product was collected, then dried in a vacuum oven for 30 hours at 80 degrees Celsius in a vacuum oven, yielding a brown, slightly transparent, flexible film. UV/Vis Diffuse Reflectance Spectroscopy was performed on the solid product, and the spectrum (
Example 14: Synthesis of a MoSe2/SnO Composite
[0388] 2 ml MoSe2 dispersion (as prepared from example 5) was added to a glass vial. 0.01 g Tin oxide (Sigma-Aldrich, 549657, <100 nm powder) was also added, forming a mixture, which was mixed for 5 minutes in a sonication bath. 0.2 ml sodium citrate (1M, aqueous) was added under mild agitation, and a precipitate formed slowly which was dried for 30 hours at 80 degrees Celsius in a vacuum oven. UV/Vis Diffuse Reflectance Spectroscopy was performed on the solid product, and the spectrum (
Example 15: Synthesis of a MoSe2/PU Composite
[0389] 2 ml MoSe2 dispersion (as prepared from example 5) was added to a glass vial. 0.5 ml PU was also added, and the mixture mixed for 5 minutes in a sonication bath. 0.2 ml saturated ammonium carbonate solution (aqueous) was added under mild agitation, and flocculation was observed to rapidly occur. The product was collected, then dried in a vacuum oven for 30 hours at 80 degrees Celsius in a vacuum oven, yielding a dark, slightly transparent, flexible film. UV/Vis Diffuse Reflectance Spectroscopy was performed on the solid product, and the spectrum (
Example 16: PEDOT:PSS and MoS2 Composite with Magnesium Hydroxide as a Flocculating Salt
[0390] 2 g MoS2 was shear mixed at 11 k rpm using a IKA T25 ultra-turrax shear mixer in 250 ml of 3:7 Water:IPA by volume solvent with temperature control (Temperature was maintained below 30 C). Then, the dispersion was centrifuged (Eppendorf 5702) for 20 minutes at 4 k rpm. 80% of the supernatant was collected and centrifuged again at 4 k rpm for 20 minutes. Supernatant was collected and, UV/Vis absorbance recorded was 0.325 at 672 nm. The concentration was estimated to be 0.01 g/L by using an extinction coefficient of 3400 L g m UV/Vis spectroscopy was collected and is reproduced in
[0391] Three samples are prepared with 10 ml of the above dispersion by adding 1 ml of a 2.4 g/L PEDOT:PSS aqueous solution produced by dispersing dry pellets (purchased from Sigma Aldrich, product number 768618) in deionized water. The samples are sonicated for 10 s and magnetically stirred for 5 minutes. Then, selected amounts of 0.01 M LiOH(aq) and 0.01 M Mg(NO.sub.3).sub.2 are simultaneously added following:
[0392] M1: 430 μL LiOH/215 μL Mg(NO.sub.3).sub.2
[0393] M2: 860 μL LiOH/430 μL Mg(NO.sub.3).sub.2
[0394] M3: 1720 μL LiOH/860 μL Mg(NO.sub.3).sub.2
[0395] Solid formation is observed immediately after addition (see
Example 17: Synthesis of a Combined Composite Between TiO2, Graphene, NiO, and LiCl, with Acetone as an Antisolvent for LiCl
[0396] 25 g graphite flakes (<50 micron, Sigma) were added to 500 ml NMP in a water jacketed beaker. The solution was homogenised for 30 minutes at maximum RPM using a L4R mixer, equipped with a 32 mm square-hole high-shear rotor/stator assembly (Silverson Machines). Water flow in a cooling jacket was used to maintain the temperature of the dispersion close to room temperature (˜22 degrees Celcius). After homogenising, the solution was transferred to 50 ml centrifuge tubes and centrifuged for 30 minutes at 4400 RPM (Eppendorf 5702). The top ⅔rd of supernatant in each vial was then centrifuged for a further 30 minutes at 4400 RPM. The top ⅔rd of the resulting supernatants were used as ‘graphene dispersion’. This method usually yields a graphene dispersion of 0.25-0.35 mg/ml.
[0397] 250 mg of titanium oxide and 250 mg nickel oxide (sigma) were added to a suspension of 35 ml of NMP containing 0.3 mg/ml of graphene dispersion, detailed in step 1.
[0398] 0.12 ml of 5 M LiCl (aq) was added to the suspension to provide an antisolvent interaction species which yielded no more than 5 wt % of the final composite.
[0399] This mixture was stirred at 1000 rpm for 15 minutes using a magnetic stirring bar and sonicated periodically for 1 minute after each 5 minutes stirring.
[0400] 35 ml of acetone (sigma-aldrich) was added rapidly to the suspension under stirring at 200 rpm.
[0401] The suspension was left to stand while the antisolvent-accelerated flocculation produced a cascading deposition of dual oxide/graphene composite.
Example 18: ‘Bottom-Up’ Graphene Mixed with SnO Nanoparticles
[0402] Bottom-up multi-layer graphene (obtained from Goodfellow Cambridge Ltd, product number GR006096) is produced from gaseous precursors with a plasma-based process. It has no/little impurities, so is useful for applications requiring high purity. Bottom-up graphene is an alternative method to graphite-based ‘top-down’ approaches to obtaining graphene.
[0403] Multi-layer graphene was added to a 1:1 volume solvent blend of water:IPA, at a 0.3g.L-1 concentration.
[0404] 200 ml of this dispersion was sonicated for 30 minutes while being stirred at 900 RPM with an overhead stirrer. The dispersion was kept at room temperature with a water bath to counteract the heat from the sonication activity.
[0405] After this point SnO2 was added to 15 ml of this dispersion to achieve a graphene loading of 2 wt %, and the resulting mixture was sonicated and stirred for a further 5 min and 900 rpm. After this, the solution was sampled for microscopy and left to stand for 5 minutes.
[0406] After this time, the solution was again sonicated and stirred for 5 m and 900 rpm. After which, 0.5M aqueous solutions of Li2SO4 and CaCl2 were added to achieve a theoretical wt % of 2% CaSO4. This was again stirred for 5 m at 900 rpm, before being left to stand for 5 m after which the resulting composite was collected for microscopy.
[0407]
Example 19: Tin Oxide with Electrochemically Exfoliated Graphene
[0408] Electrochemically exfoliated graphene (EEG) in NMP (G-DISP-NMP-EG-2+) was obtained from Sixonia Gmbh. As received, it was a suspension of exfoliated graphene at ˜8 mg/ml. This graphene is characterised in
[0409] 22.5 mg tin oxide (<100 nm, Sigma) was then added to 15 ml of the dispersion from step 1. The mixture was sonicated and stirred/agitated until agglomerates of tin oxide could no longer be seen. Microscopy characterisation of the mixture can be seen in
[0410] 0.5 ml each of 0.5 M phosphoric acid and 0.5 M calcium chloride were added simultaneously over 10 seconds into the mixture, under agitation to ensure good mixing. Within a few seconds, a flocculation could be observed in the suspension. Flocs formed were characterised with optical microscopy in
[0411] Addition of phosphoric acid and calcium chloride salts likely caused formation of calcium phosphate, which is substantially insoluble in water and IPA. It is believed that this rapid precipitation of insoluble salt is what causes such a dramatic change in the suspension, causing flocculation of the particles and thereby forming a well-mixed composite between EEG and SnO particles. Microscopy images (
Example 20: Tungsten Disulfide and Polystyrene Composite
[0412] Aqueous tungsten disulphide dispersion was prepared for this example. In 500 ml of DI water, 5 g sodium cholate was added. Then, 25 g WS2 (2 μm, 99% from Merck) was added and shear was applied for an hour using a Silverson LR4 high shear square-hole mixing head under maximum RPM. To avoid foaming, shear was stopped after 20 minutes, and thereafter shear was pulsed on/off in 10 minute intervals. Temperature of the mixture is kept at 30 C throughout exfoliation. The dispersion is then centrifuged at 2 k rpm for 20 minutes, 1.3 k rpm for 100 minutes and 4 k rpm for 10 minutes to remove any unexfoliated material.
[0413] Lithium carbonate was attempted for use as a flocculating salt. Briefly:
[0414] A 20 ml of the aqueous WS.sub.2 dispersion and 360 ul of a 1.1% aqueous polystyrene solution (200 nm particle size, purchased from Merk) is slightly sonicated and stirred magnetically. 1.260 ml of 0.1 M LiOH is added and the dispersion is stirred for 10 minutes. Then, CO.sub.2(g) is bubbled through for a few minutes in order for the Li.sub.2CO.sub.3 to form. Foaming issues caused loss of product, but rest of dispersion is left to settle. No clear solid is formed immediately, but a white solid is observed after settling overnight and a white solid is observed. The white colour indicates not much WS2 has been removed from the dispersion and incorporated within the solid.
[0415] To improve the amount of product collected, this procedure was repeated with sodium aluminate as the flocculating salt. Briefly:
[0416] 20 ml of the aqueous WS.sub.2 dispersion and 360 ul of a 1.1% aqueous polystyrene solution (200 nm particle size, purchased from Merk) is sonicated for 10 seconds then agitated on a magnetic stirrer for 5 minutes. 0.320 ml of a 0.1 M NaAlO.sub.2 solution is added and solution is stirred further over 5 minutes to ensure homogeneous dispersion of components. Then, 0.320 ml of 0.1 M HCl was added and solid formation was observed within a few seconds. The supernatant also becomes clear, and no inhomogeneity in the formed particles is seen, indicating that WS2 and PS have been integrated together into a composite. Optical and scanning electron microscopy are reproduced in
Example 21: Zirconium Oxide and Electrochemically Exfoliated Graphene (EEG) and Barium Sulphate
[0417] Electrochemically exfoliated graphene (EEG) in NMP (product code G-DISP-NMP-EG-2+) was obtained from Sixonia Gmbh. As received, it was a suspension of exfoliated graphene at ˜9 mg/ml. This suspension was diluted to 0.15 mg/ml with a 1:1 mixture of distilled water and IPA.
[0418] This solution was sonicated and stirred for 30 m and 900 rpm (stirred with an overhead stirrer)
[0419] ZrO2 (<5 micon, Sigma-Aldrich, product number 230693) was then added to achieve a graphene loading of 10 wt %. The mixture was then sonicated and stirred for a further 5 min at 900 rpm (stirred with an overhead stirrer). After this, 15 ml of this solution was removed for microscopy and left to stand for 5 minutes.
[0420] 30 ml of the parent solution was combined with 105 uL of aqueous 0.1M H2SO4 and Ba(OH)2 to achieve a 2 wt % theoretical barium sulfate loading. Solution was stirred and then sampled, before being left to settle for 30 minutes.
[0421] This was repeated with 210 ul of H2SO4 and Ba(OH)2 to achieve a 4 wt % barium sulphate loaded material.
[0422]
Example 22: Comparative Examples: ‘bottom-up’ Graphene with Lithium Phosphate and Zinc Oxide
[0423] Bottom-up multi-layer graphene (MLG) (obtained from Goodfellow Cambridge Ltd, product number GR006096) is produced from gaseous precursors with a plasma-based process. It has no/little impurities, so is useful for applications requiring high purity. Bottom-up graphene is an alternative method to graphite-based lop-down' approaches to obtaining graphene.
[0424] MLG is added to 3:7 IPA:Water volumetric mixture to make a 0.3 mg/ml suspension. This mixture is sonicated and stirred for 30 minutes to make a graphene dispersion.
[0425] 294 mg ZnO (<50 nm, Sigma-Aldrich) is added to 20 ml of the graphene dispersion. This mixture is sonicated and agitated for a further 10 minutes. This ensures dispersion of the ZnO in the first graphene dispersion. After 4 hours of being left with no agitation, no settling can be observed in the mixed dispersion. Microscope imaging of the dispersion indicates that there is little flocculation in the liquid.
[0426] A small amount of this dispersion is removed and dried on a hotplate to make a continuous film. Significant aggregation of graphene can be seen as large black shapes in the film surface. These are imaged further in
[0427] To compare with the effect of adding a flocculating salt, the above steps are repeated, but this time with the formation of lithium phosphate as a flocculating salt (from addition of LiOH and phosphoric acid). This time, no large-scale aggregates can be observed. The sample looks the same across the whole film, indicating that graphene is well-adhered to the zinc oxide. This homogeneous film is imaged in
[0428] IPA/water in 3:7 volumetric mixture is a useful dispersing medium for graphene as it is constituent of cheap, environmentally benign solvents. However, there are more expensive alternatives that offer better dispersion of graphene. To compare the effect of using a ‘better’ solvent for graphene, FLG (Few Layer Graphene, obtained from Goodfellow Cambridge Ltd, product number GR006094) was dispersed in Cyrene (Dihydrolevoglucosenone; Sigma-Aldrich, product number 807796) at 0.1 mg/ml concentration. Without the use of cyrene, preparation of graphene of this type (few-layer, rather than multi-layer) is impossible. This graphene was characterised by Raman spectroscopy in
[0429] Quality improvements summary of graphene material in ZnO metal oxide:
[0430] Bad solvent (Water:IPA 70:30)<Good solvent (Cyrene)<Bad solvent+lithium phosphate<<Good solvent+Lithium phosphate
Example 24: ZrO2 with Calcium Phosphate—Comparative Screening of Salt Addition and Composition
[0431] Electrochemically exfoliated graphene (EEG) in NMP (product code G-DISP-NMP-EG-2+) was obtained from Sixonia Gmbh. As received, it was a suspension of exfoliated graphene at ˜8 mg/ml. This suspension was diluted to 0.1 mg/ml with distilled water. This suspension was sonicated for 30 mins to form a ‘graphene dispersion’.
[0432] 100 ml of this graphene dispersion was combined with 190 mg of ZrO2 (5 micron, sigma) to give a theoretical Gr weight percentage of 5%. This was sonicated for 5 minutes with additional agitation from an overhead stirrer.
[0433] Several samples were produced from this mixture. Calcium phosphate (theoretical product: CaHPO4.2H2O) was produced from different amounts of calcium chloride (0.5 M, aqueous) and ammonium phosphate (0.1 M, aqueous). Increasing salt content (0%, ˜2%, ˜4%, ˜8%) showed a clear increase in ‘graphene incorporation’ between 0% and ˜4%, but showed little obvious increase in graphene incorporation between ˜4% and ˜8%. Images can be seen clearly in
Example 25: SnO with Bottom-Up Graphene—Conductivity Comparison
[0434] Bottom-up multi-layer graphene (MLG, obtained from Goodfellow Cambridge Ltd, product number GR006096) is produced from gaseous precursors with a plasma-based process. It has no/little impurities, so is useful for applications requiring high purity. Bottom-up graphene is an alternative method to graphite-based lop-down' approaches to obtaining graphene.
[0435] MLG was dispersed in 100 ml NMP for 30 minutes using sonication and stirring to give a concentration of 0.3 g.L-1. Tin oxide was added to give a 2% Gr to solid ratio, and the mixture was sonicated and stirred for a further 5 minutes.
[0436] 10 ml of the mixture was removed to function as the control sample. To the remaining solution, 1M Li2SO4 (aqueous, to make 4% theoretical solid loading of salt) was added to flocculate the product. Both samples were left to settle for 24 hours.
[0437] Settled material from both samples (control and with Li2SO4) were both washed with acetone and dried in ambient conditions. The resulting solids were then each diluted with NMP to form a slurry with ˜25% solids content. 33 uL of each slurry was applied using a doctor blade to an interdigitated electrode (DropSens: DRP-IDEAU200) and dried on a hotplate at 80 degrees C. for one hour. Dried electrodes coated with samples can be seen in
[0438] Resistance of the materials on the electrodes was measured with a multimeter (Keithlev DMM6500). Results are reported in the table below:
TABLE-US-00001 Sample number Electrical resistance Control (No Li2SO4) 3.4 MΩ Improved sample (With Li2SO4) 1.3 MΩ
[0439] Electrical conductivity is one of the most desired results from the addition of graphene to a composite material. These data show that, the use of a flocculating salt advantageously facilitates the creation of higher conductivity composite materials. This is believed to be due to the greater inclusion of graphene and the higher homogeneity of a composite assembled using a flocculating salt.
Example 26: Surfactant-Stabilised Graphene with Copper Oxide, Using Barium Sulphate as a Flocculating Salt
[0440] A surfactant-stabilised aqueous dispersion of FLG (same type as used in example 22) was prepared by adding 20 mg of the graphene powder to 200 ml of deionised water containing 20 mg of polyvinylpyrrolidone (Sigma) while under sonication and stirring at 1500 rpm. Stirring was carried out by a SciQuip Basic overhead stirrer and sonication in a Cole-Palmer 40 kHz sonication bath. Stirring and sonication were performed for 30 minutes in total. Graphene dispersion quality and homogeneity were validated under high resolution optical microscopy.
[0441] 200 mg of copper (II) oxide (Sigma) was added to 40 ml of the dispersion formed in step 1 for a final graphene composite content of <2%.
[0442] 0.1 M Barium hydroxide was added to the mixture in molar quantities to yield a (theorised) maximum of 10 wt % barium sulphate in the final composite, according to the reaction: Ba(OH)2+H2SO4.fwdarw.BaSO4+2H2O
[0443] The above mixture was stirred at 1200 rpm using a magnetic stirrer bar for 15 minutes and sonicated for one minute for every 5 minutes of stirring.
[0444] The mixture was divided into two; a control sample with only Ba(OH)2 was set aside. The other 20 ml was processed as below:
[0445] A 1.2 molar excess of 1 M sulphuric acid was added slowly under gentle stirring to the mixture to facilitate the complete reaction and the formation of a barium sulphate flocculating agent of no more than 10 wt % final composite.
[0446] The two mixtures were left to stand for 8 hours. Photographs of the product formed with and without the addition of sulphuric acid are included in
[0447] The absence of significant flocculation in the control sample (with only Ba(OH)2) suggests that formation of insoluble salts is dramatically more efficient than soluble salts. Barium sulphate is known to be substantially insoluble in water, so serves as a useful flocculating salt to make graphene-metal oxide composites from water-based dispersions of graphene.
Example 27: MOF-199 with ZrO2 and Graphene
[0448] MOFs are an exciting new class of materials, with many varied properties and uses. MOFs are useful flocculating salts as they are insoluble in many solvents. The resulting composite with inclusion of a MOF is likely to have many uses. A well-known MOF (HKUST-1, otherwise known as MOF-199) with Cu.sup.2+ as the metal centre is used in this example.
[0449] 30 ml of graphene-PVP dispersion (as prepared in example 26) was combined with 147mg of ZrO2 to achieve a graphene loading of ˜2%, this mixture was sonicated and stirred to achieve a uniformly distributed solution. To this, 21 mg of trimesic acid and 450 ul of 1M Copper nitrate trihydrate was also added, and the mixture was vigorously stirred for 5 minutes with a magnetic stirrer bar.
[0450] To this mixture, 32 ul of diaminobutane was added, causing immediate flocculation throughout the mixture, leaving behind a clear supernatant. The mixture was stirred for a further minute, before being allowed to settle, then washed with acetone and spread into a film and dried, before being analysed with optical microscopy (
[0451] Microscope images show a blue-grey colour. This indicates inclusion of graphene (white zirconia becomes grey, and small black particles of graphene and partially aggregated graphene can be seen). The blue tint shows the inclusion of MOF-199. SEM (
Example 28: Comparative Example: Multi-Layer Graphene (MLG) with TiO2
[0452] Graphene dispersion from example 18 (0.3 mg/ml solids, in 1:1 IPA:water volumetric mixture) is used in this example.
[0453] TiO2 (25 nm, Anatase structure, Sigma-Aldrich) is added to make a 2w % gr to total mass of combined TiO2/graphene solids.
[0454] This mixture is sonicated and stirred for five minutes at 900 rpm to ensure good mixing.
[0455] Centrifugation (a common solid-liquid separation technique) is then used to attempt to collect the two mixed materials in the form of a composite. Centrifugation is performed at 4.4 k RPM over 30 minutes in a (Eppendorf 5702) centrifuge.
[0456] A photograph of the centrifuge tube after centrifugation (
[0457] This demonstrates one of the typical issues with processing mixtures of metal oxides and graphene—as metal oxides are typically twice as dense as graphene, unequal separation of the two materials is likely during centrifugation. Centrifugation is normally necessary to remove highly dispersed materials from a dispersion. However, in this example, separation in this manner does not lead to a well-mixed composite material.
Example 29: Comparative Example: MLG with TiO2—Ground in Mortar/Pestle
[0458] An alternative to solution processing of 2D/particulate materials is mechanical grinding of the materials.
[0459] 10 mg of MLG (the same as used in example 18) was added to 490 mg TiO2 (the same as used in example 28).
[0460] 750 uL of IPA and 750 uL of distilled water were added to the powders, and the mixture ground thoroughly for 5 minutes by hand in a mortar and pestle.
[0461] The resulting grey paste was spread into a film and dried.
[0462] Low-magnification microscopy of the formed film (
Example 30: PVDF/MLG Composites with Phosphate Flocculating Salt
[0463] PVDF is an important engineering polymer with high chemical resistance and inertness. Compositing with graphene is expected to be difficult as both graphene and
[0464] PVDF are extremely inert. Beyond PVDF, this type of solid-state mixing of 2D materials and pre-polymerised polymers is expected to be beneficial for many other types/classes of polymers. Of particular note is the absence of a dissolving/melting step for the polymer. This increases process scalability and facilitates use of high melting point polymers or polymers that are difficult to dissolve.
[0465] 1) PVP (Average mw 10,000-Sigma-Aldrich) was added to distilled water to make a 3 g/L solution. MLG (the same used in example 18) was added to 60 ml of this solution to make a 0.3 g/L suspension. This mixture was sonicated at room temperature for 30 minutes to disperse the graphene material.
[0466] 2) 882 mg PVDF was added to 3 ml IPA (to assist mixing with water), and the slurry added into the dispersion from step 1. The mixture was then sonicated and agitated for a further 10 minutes.
[0467] 3) 21 ml of the mixture from step 2 was used to demonstrate a flocculating salt. Calcium phosphate (substantially insoluble in water) was formed from 0.108 ml 1M CaCl2 and 0.845 ml 0.1M Na2HPO4 under vigorous stirring over 2 minutes.
[0468] 4) An additional 21 ml of the mixture from step 2 was set aside to be a control mixture. This sample and the mixture from step 3 were left to settle for ˜16 hours. Very little settling was observed in the control mixture, but the supernatant from the sample from step 2 appeared to become transparent due to the increased speed of settled solids (
[0469] Solids from both control and CaPO samples were analysed via optical microscopy in
[0470] Washing of the solids was performed, as might be done in an industrial process in order to reduce the content of surfactant. Residual surfactants are known to be undesirable in many products. Washing was achieved by adding ˜0.3 ml of the solid slurries at the bottom of the sample containers into ˜50 ml of water. Despite the same volume of sample being washed, and the large volume of liquid used to wash the materials, the supernatant appeared dark in the control sample, where a whiteish pellet was seen at the bottom of the centrifuge tube. This is in stark contrast to the CaPO salt-flocculated sample, that appears to have no graphene in the supernatant (supernatant is clear) and a homogeneous grey solid pellet at the bottom of the centrifuge tube.
[0471] These results alone indicate that: [0472] In the control sample, any ‘associated’ graphene in the settled solids has low cohesion to the PVDF, especially during washing conditions. [0473] In the CaPO salt-flocculated sample from step 3, graphene and the PVDF are adhered together into a homogeneous solid, which resists separation during washing and centrifugation steps.
[0474] These results are corroborated by optical microscopy (
[0475] Order of graphene content in each sample, as is seen with optical microscopy in
[0476]