KR20130097640A - Method for producing two-dimensional sandwich nanomaterials based on graphene - Google Patents

Abstract

(a) a mixture comprising (a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant, or
(a2) a mixture comprising graphene particles, at least one solvent useful for solution stripping of graphite and at least one cationic surfactant and / or nonionic surfactant
, ≪ / RTI >
(b) adding at least one sol precursor compound to the mixture from step (a),
(c) reacting the mixture from step (b) by a sol-gel method such that a gel is formed from at least one sol precursor compound on the graphene oxide particles or graphene particles,
(d) removing one or more surfactants, and
(e) optionally, heating the gel coated graphene oxide particles to at least 500 ° C. for at least 1 minute under an inert gas atmosphere to reduce the graphene oxide to graphene.
To prepare a two-dimensional nanomaterial by a method comprising a.

Description

Method for manufacturing two-dimensional sandwich nanomaterial based on graphene {METHOD FOR PRODUCING TWO-DIMENSIONAL SANDWICH NANOMATERIALS BASED ON GRAPHENE}

The present invention relates to a method for producing a sandwich nanomaterial based on graphene or graphene having a two-dimensional (2-D) nanomaterial and a coating of carbon, metal or metal oxide and a sandwich material thus prepared. The invention also relates to the use of 2-D sandwich nanomaterials as templates for making other 2-D sandwich materials, their use in catalysts, sensors, capacitors, primary and secondary electrochemical cells and fuel cells, and Its use for the production of graphene particles and a method for producing a single layer of graphene from 2-D sandwich nanomaterials prepared according to the invention.

Two-dimensional (2-D) nanomaterials are two-dimensionally infinite in principle, but three-dimensional (thickness) is a material limited to nanoscale. The result is a very large length to thickness ratio for these mostly particulate materials. Graphene is a 2-D nanomaterial in that it comprises a planar layer of sp ² hybrid carbon atoms bonded to a six-membered ring. Graphite consists of these graphene layers. Graphene has very high mechanical strength and high electrical conductivity. However, the broad applicability of graphene and graphene-based functionalized 2-D nanomaterials has been hampered by the difficulties encountered in the production of graphene.

Initially, graphene was prepared by attaching an adhesive strip to high oriented pyrolytic graphite (HOPG), stripping off the adhesive strip with graphite and an optional layer of graphene attached, and transferring the layer to a silicon wafer. It was. This method is still used today to obtain high purity graphene particles, but it is very time consuming and yields low.

Another method is chemical vapor deposition (CVD), in which a carbon source is evaporated to deposit on a catalyst support. In this way supported graphene particles can be obtained but no suspension of “free” graphene particles in the medium.

Graphene can also be obtained by epitaxial growth on a metal substrate. Heating SiC to a temperature above 1100 ° C. also yields graphene. Both methods yield graphene coated surfaces but do not yield the "glass" particles of graphene.

Another method for preparing graphene particles is solution exfoliation of graphite, in which graphite is a graphene particle formed by positive interaction between the solvent and the graphite surface in an organic solvent such as N-methylpyrrolidone. It is peeled off. This requires special solvents and therefore additional optional processing, for example by applying additional layers to functionalize graphene, can be problematic. In addition, only low monolayer yields are obtained since graphene particles tend to quickly reassemble into stacks.

Graphene particles can also be obtained by chemical reduction of graphene oxide particles in an aqueous suspension, but this always leaves a certain proportion of oxidized groups in graphene. Graphene oxide can be easily dispersed in water due to many oxygen groups, but due to the anionic properties formed, graphene oxide has inherent incompatibility with inorganic compounds such as SiO ₂ . In addition, graphene suspensions prepared by the reduction of aqueous graphene oxide suspensions make it very difficult to obtain individual graphene particles, because they can aggregate easily without dispersion even if they are dispersed in water.

Graphene oxide can also be converted to graphene by thermal methods [Aksay, Chem. Mater. 2007, 19, p. 4396-4404]. However, graphene particles aggregate at high temperatures, making it difficult to obtain individual graphene particles.

Nevertheless, due to the positive properties of graphene, such as the high electron mobility of graphene, the very good electrical conductivity and room temperature quantum Hall effect obtained keeps trying to functionalize graphene.

WO 2010/014215 A2 describes a process for producing nanocomposites based on graphene and metal oxides. The graphite flakes are chemically oxidized and the resulting graphite oxide is peeled off by high speed thermal expansion and partially converted to graphene. The exfoliated particles of graphene are used to make an aqueous dispersion comprising sodium dodecyl sulfate to stabilize the particles. A metal oxide precursor is added to this dispersion to deposit onto dispersed particles of graphene to form a nanocomposite material. Due to their manufacturing method, the particles of graphene have a carbon / oxygen ratio in the range of 10 to 500. Due to the oxygen atoms in the graphene particles, it is rather difficult to adsorb anionic surfactants on their surfaces.

Graphene oxide, which is obtained by oxidation of graphene and graphite and consists of layers of carbon atoms bonded to six-membered rings containing oxygen-containing groups, is also useful as a starting point for the production of functionalized 2-D nanomaterials.

However, for the graphene manufacturing method and functionalized graphene and graphene oxide manufacturing method and the 2-D nanomaterials based on graphene and graphene oxide and having excellent performance characteristics to avoid the aforementioned disadvantages of the prior art. The demand continues to exist.

It is an object of the present invention to provide a method for producing graphene particles and functionalized graphene and graphene oxide particles in a high yield in a relatively simple manner. It is further an object to provide functionalized 2-D nanomaterials based on graphene and graphene oxide, for example, which have particularly good performance characteristics in the anode materials of lithium ion secondary batteries.

The inventors have found that the above object is

(a) a mixture comprising (a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant, or

(a2) a mixture comprising graphene particles, at least one solvent useful for solution stripping of graphite and at least one cationic surfactant and / or nonionic surfactant

To provide,

(b) adding at least one sol precursor compound to the mixture from step (a),

(c) reacting the mixture from step (b) by a sol-gel method such that a gel is formed from at least one sol precursor compound on the graphene oxide particles or graphene particles,

(d) removing one or more surfactants, and

(e) optionally, heating the gel coated graphene oxide particles to at least 500 ° C. for at least 1 minute under an inert gas atmosphere to reduce the graphene oxide to graphene.

It was found that it is achieved by the method of manufacturing a two-dimensional sandwich nanomaterial comprising.

In a preferred embodiment, the at least one sol precursor compound is selected from SiO ₂ precursor compounds. Starting from this embodiment, the present invention also includes steps (a)-(d) and further

(f) impregnating SiO ₂ coated graphene oxide particles or SiO ₂ coated graphene particles with at least one precursor compound selected from the group consisting of metal oxide precursor compounds, metal precursor compounds and carbon precursor compounds,

(g) converting at least one precursor compound into the corresponding metal oxide, corresponding metal or carbon, and

(h) removing SiO ₂ from graphene oxide particles or graphene particles

It provides a method for producing a 2-D sandwich nanomaterial comprising a.

The invention further relates to its use as a template for the preparation of 2-D sandwich nanomaterials and other nanolayer materials obtainable according to the process of the invention, catalysts, sensors, capacitors, primary and secondary electrochemical cells and fuels. Its use as a cell, and catalysts, sensors, capacitors, primary and secondary electrochemical cells and fuel cells comprising the 2-D sandwich nanomaterial of the present invention.

The present invention further provides the use of the 2-D sandwich nanomaterial of the present invention for producing graphene particles and the steps (a) to (d), wherein at least one sol precursor compound in step (b) Selected from SiO ₂ precursor compounds), further steps:

(h) removing SiO ₂

Is performed, wherein step (e) is carried out when step (a) provides a mixture according to (a1).

The present invention can be carried out with a relatively high throughput in a simple manner and a method for producing 2-D nanomaterials and 2-D sandwich nanomaterials based on graphene or graphene oxide which yields coated 2-D nanomaterials in high yield. To provide. Such coated 2-D nanomaterials can be obtained with a wide variety of coatings, in which case repeated executions of impregnation and removal by the nanocasting process can form coatings that are not even directly obtainable. For example, nanocasting is used to make graphene particles coated with mesoporous Co ₃ O ₄ by using 2-D sandwich nanomaterials formed from SiO ₂ coated graphene. Other 2-D nanomaterials coated with metals and metal oxides can be obtained in a similar manner, for example 2-D coated with Sn, Ge, Co, SnO ₂ , TiO ₂ , Fe ₂ O ₃ and Fe ₃ O ₄ . There is a nanomaterial. In particular, embodiments of the invention wherein a mixture according to (a1) is provided in step (a) and graphene oxide is converted to graphene in step (d), starting from widely available starting material graphene oxide at a relatively low cost It is a simple method for obtaining coated 2-D nanomaterials based on graphene.

2-D sandwich nanomaterials obtainable according to the invention have a very large specific surface area with a very large length to thickness ratio and a very uniformly formed mesoporous structure, which is the surfactant initially used in step (a). It is due to the molecule and can be altered through the use of different surfactants. The 2-D sandwich nanomaterials obtainable by the process of the invention show that the graphene particles of the invention coated with mesoporous carbon, for example, exhibit very good properties when used as anode materials in lithium ion secondary electrons. It has excellent performance characteristics in that respect.

Hereinafter, the present invention will be described in detail.

In the context of the present invention, "graphite" is to be understood to mean carbon consisting of a plurality of planar, mutually overlapped layers formed of bonded six-membered rings of sp ² hybrid carbon atoms.

"Graphene" is to be understood strictly as meaning a single layer of carbon from the graphite structure, ie a monolayer of junction rings arranged in a hexagon consisting of six carbon atoms with sp ² hybridization.

For the purposes of the present invention, "graphene" means up to 10 layers, preferably up to 5 layers, more preferably up to 2, of junction rings arranged in a hexagon each consisting of 6 sp ² hybrid carbon atoms And a layer of still more preferably one material.

"Graphite oxide" is a three-dimensional structure consisting of layers, each of which consists of a conjugated C ₆ ring functionalized with partially carbonyl, carboxyl, alcohol and epoxy groups. These individual layers are no longer planar as in graphite and completely protrude or partially zigzag from the plane depending on the degree of oxidation.

For the purposes of the present invention, "graphene oxide" means up to 10 layers, preferably up to 5 layers, formed from conjugated C ₆ rings having oxygen functional groups such as epoxy, alcohol, carboxyl and / or carbonyl groups, It is to be understood that it means more preferably two or more layers, even more preferably a material formed from a single layer.

The term "particle" is used in the context of the present invention as a generic term for graphene oxide particles and graphene particles.

The term "two-dimensional nanomaterials and sandwich nanomaterials" in the context of the present invention is in principle infinite in two directions, but includes a third coating up to dimensions ranging from 0.3 nm to 500 nm, including any coating present when measured under an electron microscope. It is a small plate-shaped particle defined in the direction of. Sandwich particles of the present invention based on graphene or graphene oxide are coated on their top and bottom surfaces and have a sandwich-like layered structure with a sequence of coating / graphene or graphene oxide / coating. The coating may consist of one or more layers.

Step (a) of the method of the present invention

(a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant, or

(a2) graphene particles, at least one solvent useful for solution stripping of graphite, and at least one cationic surfactant and / or nonionic surfactant

It includes providing a mixture comprising a.

Graphite oxide particles are generally used to provide a mixture according to (a1). The preparation of graphite oxide particles is known to those skilled in the art; Generally, graphite oxide is produced by oxidation of graphite. Oxidation causes oxygen atoms to be introduced into the graphite to form primarily alcohol, epoxy, carbonyl and carboxyl groups. These groups expand the gap between the individual layers, and the layers are likely to be separated from each other. The oxide layer of graphite also becomes more hydrophilic so that it can be better dispersed in water by oxygen-containing groups.

The preparation of oxidized graphite is known to those skilled in the art; Generally this method involves treating graphite with oxidizing agents and acids, more particularly strong acids. The oxidants used are more particularly chlorate and permanganate, in particular sulfuric acid and nitric acid being used as the acid.

L. Staudenmaier, Ber. Dt. Chem. Ges. 31, (1898), 1481 and L. Staudenmaier, Ber. Dt. Chem. Ges. 32, (1899), 1394 describe a process for producing graphite oxide (called graphite acid in this reference) by reaction of graphite with potassium chlorate in the presence of fuming nitrogen and concentrated sulfuric acid.

W.S. Hummers, R.E. Offeman, J. Am. Chem. Soc. 80 (1958), 1339, describe a process for producing graphite oxide by reaction of sodium nitrate with potassium permanganate in the presence of sulfuric acid.

It is also possible to use expandable graphite as a precursor for the production of graphite oxide. In this case, graphite is expanded in the first step. The product obtained is then ground, for example in a ball mill. The last step is chemical denaturation as described above by thermal oxidation or oxidation in the presence of sulfuric acid.

The mixture further comprises water and one or more cationic surfactants and / or nonionic surfactants. Suitable surfactants are described below.

When providing a mixture according to (a1) starting from graphite oxide particles, the graphite oxide particles are at least partly peeled off with graphene oxide particles, thus the mixture comprises graphene oxide particles.

In order to provide a mixture according to (a2), the graphite particles are generally suspended in one or more suitable solvents. In this method, the graphite particles are solution peeled into individual layers in an organic solvent to provide a suspension of graphene particles in one or more aprotic solvents. This can be achieved using a solvent whose surface energy is approximately equal to the surface energy of graphene. A solvent with a surface energy of 55-90 mJ / m ² ensures the exfoliation of graphite particles into graphene particles (Hernandez et al., ArXiV: 0805.2850 v1). Examples of suitable solvents are N, N-dimethylacetamide, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone and N-methylpyrrolidone.

Solvents useful for solution stripping of graphite further include dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, dimethylacetamide and cyclohexane.

According to the invention it is preferred to use a solvent selected from the group consisting of N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, dimethylacetamide and cyclohexane; Dimethylformamide is particularly preferred.

Natural graphite and artificially produced graphite can be used with pyrographite, with electrographite and expanded graphite being particularly suitable.

In (a), the mixture provided according to (a1) or according to (a2) further comprises at least one cationic and / or nonionic surfactant.

The cationic surfactant is preferably a group consisting of quaternary ammonium compounds, more preferably C _n H _{2n + 1} N (R) ₃ Hal (where n is 12, 14, 16 and 18, and Hal is Cl And Br, R is CH ₃ or C ₂ H ₅ , wherein each R is the same or different), cetyltrimethylammonium chloride, cetyltrimethylammonium bromide and cetyltriethylammonium bromide are particularly preferred.

The at least one nonionic surfactant preferably consists of a C ₂ -C ₄ -alkylene oxide block copolymer comprising ethylene, for example marketed under the trade name Pluronic ^® by BASF SE. Selected from the group.

The presence of one or more cationic and / or nonionic surfactants prevents problems in terms of incompatibility of graphene / graphene oxide and inorganic materials and aggregation problems. Cationic and / or nonionic surfactants are either electrostatically adsorbed on the surface of the strongly negatively charged graphene oxide or adsorbed on the surface of graphene through interaction with π-electrons of the graphene structure Or self-assemble into a regular microstructure on the upper and lower surfaces of the graphene oxide particles. For example, cetyltrimethylammonium bromide adsorbed on graphene oxide particles forms tubular micelles that form mesopores of about 2 nm size after coating application.

A mixture according to (a1) comprising graphene oxide particles, water and one or more cationic surfactants and / or nonionic surfactants, or graphene particles, one or more solvents useful for solution stripping of graphite, and one In order to provide a mixture according to (a2) comprising the above cationic surfactant and / or nonionic surfactant, each mixture starting from the graphite oxide particles or the graphite particles is generally a graphite oxide particle or Treatment of the graphite particles with graphene oxide particles or graphene oxide particles is carried out through energy input so that the exfoliation to graphene oxide particles can be promoted and improved. This can be done, for example, via ultrasound, stirring, shaking and other methods known to those skilled in the art. Stirring, grinding and dispersing devices known to those skilled in the art, such as Ultra-Turrax ^® stirrers, can be used.

In order to provide the mixture according to (a1), the present invention is preferably 0.005 to 5% by weight graphite oxide, more preferably 0.01 to 5% by weight graphite oxide particles, even more preferred, based on the total weight of the mixture Preferably starting from a mixture comprising from 0.01 to 2% by weight graphite oxide particles. The concentration of at least one cationic surfactant and / or nonionic surfactant is preferably 0.1 to 10% by weight, more preferably 0.2 to 5% by weight, most preferably 0.2 to 1, based on the total weight of the mixture Range by weight.

In order to provide a mixture according to (a2), the present invention preferably provides 0.01% by weight of graphite particles, more preferably 0.5% by weight of graphite particles, most preferably 1% by weight, based on the total weight of the mixture. Begin with a mixture comprising graphite particles. The mixture is preferably from 0.1 to 10% by weight, more preferably from 0.2 to 5% by weight, most preferably from 0.2 to 1% by weight, based on the total weight of the mixture, of at least one cationic and / or nonionic surfactant It includes.

In providing the mixture, at least some of the non-peeled particles are removed from the mixture, for example by careful centrifugation, unless all graphite oxide particles or graphite particles are stripped into a single layer of graphene oxide particles and graphene particles. Can be removed

According to the invention, the mixtures provided in step (a1) all preferably comprise from 0.005 to 5% by weight, more preferably from 0.01 to 5% by weight of graphene oxide particles, based on the total weight of the mixture, The mixture provided in (a2) preferably comprises from 0.001 to 5% by weight, more preferably from 0.01 to 1% by weight of graphene particles, based on the total weight of the mixture.

Step (b) of the process of the invention comprises adding at least one sol precursor compound to the mixture obtained from step (a). As used herein, "sol precursor compound" refers to a compound that forms a so-called sol under conditions predominantly present in a particular mixture. "Sol" is to be understood herein as a term used in the context of the "sol gel method" known to those skilled in the art. In the "sol gel method", the sol precursor is first converted to a sol and then to a gel. The sol-gel method is described, for example, in W. Stober et al., J. Colloid Interf. Sci 26 (1968), p. 62, which is incorporated herein by reference.

According to the invention, the at least one sol precursor compound is a SiO ₂ precursor compound, a ZrO ₂ precursor compound, a TiO ₂ precursor compound, a CeO ₂ precursor compound, an Al ₂ O ₃ precursor compound, a Fe ₂ O ₃ precursor compound, Fe ₃ O ₄ Precursor compound, MgO precursor compound, ZnO precursor compound, chromium oxide precursor compound, Co ₂ O ₃ precursor compound, molybdenum oxide precursor compound, tungsten oxide precursor compound, hafnium oxide precursor compound, Y ₂ O ₃ precursor compound and water soluble crosslinkable polymer And a polymer precursor. The at least one sol precursor compound is preferably selected from the group consisting of metal halides, metal nitrates, metal carboxylates, metal oxysulfates, metal acetylacetonates and metal alkoxides and water glass for Si, wherein the metal is Zn, Mg, Al, Y, Fe, Cr, Co, Si, Zr, Ti, Ce, Mo, W and Hf.

According to the invention, the metal alkoxide is preferably selected from Me (OR) _n ,

Where

When Me is Zn, Mg, n is 2,

N is 3 when Me is Al, Y, Fe, Cr, Co,

When Me is Si, Zr, Ti, Ce, Mo, W, Hf, n is 4,

R is C ₁ -C ₈ -alkyl, which may be substituted with one or more OH groups, wherein each R may be the same or different.

At least one sol precursor compound comprises water glass and Si (OR) ₄ , wherein R is HCH ₃ , C ₂ H ₅ , C ₂ H ₄ OH, nC ₃ H ₇ , iC ₃ H ₇ , nC ₄ H ₉ and tC Very particular preference is given to ₄ H ₉ , wherein R may be the same or different.

According to the invention, the water soluble crosslinkable polymer and the polymer precursor are preferably selected from melamine-formaldehyde resin precursors and resorcinol-formaldehyde resin precursors.

In step (b) the one or more sol precursor compounds are generally added slowly in the liquid state to the mixture from step (a). It can be added in solution or without solvent. The concentration of at least one sol precursor compound added in step (b) is generally from 0.1 to 10% by weight, preferably from 0.2 to 5% by weight, based on graphene oxide particles or graphene particles present in the mixture (a). More preferably, it is 0.2 to 1 weight% of range.

Depending on the sol precursor compound used, a catalyst for sol and / or gel formation, such as acid or base, may be added in step (b) or before step (b).

Surfactant molecules adsorbed on graphene oxide particles or graphene particles and self-assembled into mesoporous structures are controlled nuclei of sol or gel formed from graphene oxide particles or one or more sol precursor compounds on the surface of graphene particles. A molecular template is formed for formation and growth.

Step (c) of the process of the invention comprises reacting the mixture from step (b) by the sol-gel method, wherein the surface of the graphene oxide or graphene particles is not deposited in a solvent by a homogeneous nucleation process. Due to the surfactant molecules adsorbed on the phase, the gel deposits on the surface of graphene oxide or graphene particles in a heterogeneous nucleation process. This is known to those skilled in the art as a liquid-crystalline templating mechanism [GS Arttard, Nature 378 (1995), p. 366-368]. In this process, the sol precursor compound is converted to a sol and further to a gel.

Step (c) is generally carried out for a period of 0.5 hours to 2 days, preferably 1 hour to 24 hours, more preferably 2 hours to 18 hours. The temperature in step (c) is generally from 10 to 80 ° C., depending on the system, more particularly on the solvent and / or dispersant used.

Graphene oxide particles and graphene particles then exhibit a coating with this particular gel on both the top and bottom surfaces. The gel will be arranged according to the template formed by one or more cationic surfactants and / or nonionic surfactants on the particle surface. This forms a homogeneous, structured coating of the particle surface by the gel.

The coated graphene oxide particles and graphene particles can then be further treated, for example separated and / or dried.

After step (c), the surfactant molecules are removed from the coated graphene oxide particles or coated graphene particles by washing or heating in step (d). The coated particles can be washed with solvent or water such as methanol, ethanol and propanol, for example. However, the surfactant molecules can also be removed by heating to a temperature of 50 to 500 ° C. under inert atmosphere. Removal of the surfactant particles may be carried out while heating the graphene oxide particles so that the graphene oxide is converted to graphene in step (e), that is, the steps (d) and (e) may be performed together. The surfactant molecule may optionally be removed in a calcination step carried out (see below).

After the coated particles are removed and dried, a calcination process can be further performed, in which case the coated particles are calcined at high temperature in the presence of an oxygen containing gas or an inert gas. In the case of SiO ₂ coated particles, for example, calcination for at least 2 hours at 5 to 600 ° C. in air, for example 2 to 8 hours, is suitable.

The coated particles generally comprise 75% to 95% by weight, preferably 80% to 92% by weight, more preferably 85% to 90% by weight of graphene oxide or graphene, Coatings formed from gels generally comprise from 5% to 25% by weight, preferably from 8% to 20% by weight, more preferably from 10% to 15% by weight.

If step (a) provides a mixture according to (a1), the coated graphene oxide particles are optionally held for at least 1 minute above 500 ° C. under an inert gas atmosphere so that the graphene oxide can be reduced to graphene. Heating (step (e)). Preferably, the coated graphene oxide particles are heated under an inert gas atmosphere for at least 30 minutes, more preferably at least 1 hour. The heating is generally not performed longer than 12 hours, preferably no longer than 6 hours. The temperature used is preferably in the range of 500 to 1000 ° C.

In this embodiment of the invention, the method

(a) a mixture comprising (a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant

To provide,

(b) adding at least one sol precursor compound to the mixture from step (a),

(c) reacting the mixture from step (b) by a sol-gel method such that a gel is formed on the graphene oxide particles,

(d) removing one or more surfactants, and

(e) optionally, heating the coated graphene oxide particles to at least 500 ° C. for at least 1 minute under an inert gas atmosphere to reduce the graphene oxide to graphene.

It is particularly preferable to actually carry out step (e).

In a particularly preferred embodiment, the process described above is carried out in step (b) from the SiO ₂ precursor compound, more particularly water glass and Si (OR) ₄ , wherein R is H, CH ₃ , C ₂ H ₅ , C ₂ H ₄ OH, nC ₃ H ₇ , iC ₃ H ₇ , nC ₄ H ₉ and tC ₄ H ₉ , wherein R can be the same or different).

SiO ₂ coated 2-D sandwich nanomaterials based on graphene and / or graphene oxide according to the invention are particularly suitable for use as a template for making other 2-D sandwich nanomaterials. Thus, the present invention comprises the steps described above, wherein the at least one sol precursor compound in step (b) is selected from SiO ₂ precursor compounds, the following steps:

(f) impregnating SiO ₂ coated graphene oxide particles or SiO ₂ coated graphene particles with at least one precursor compound selected from the group consisting of metal oxide precursor compounds, metal precursor compounds and carbon precursor compounds,

(g) converting at least one precursor compound into the corresponding metal oxide, corresponding metal or carbon, and

(h) removing SiO ₂ from graphene oxide particles or graphene particles

It further provides a method comprising a.

Thus, the method according to this embodiment

(a) a mixture comprising (a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant, or

(a2) a mixture comprising graphene particles, at least one solvent useful for solution stripping of graphite and at least one cationic surfactant and / or nonionic surfactant

To provide,

(b) adding at least one sol precursor compound selected from SiO ₂ precursor compounds to the mixture from step (a),

(c) reacting the mixture from step (b) by a sol-gel method such that a gel is formed from at least one sol precursor compound on the graphene oxide particles or graphene particles,

(d) removing at least one surfactant,

(e) optionally, heating the gel coated graphene oxide particles for at least one minute at a temperature of at least 500 ° C. under an inert atmosphere to reduce the graphene oxide to graphene,

(f) impregnating SiO ₂ coated graphene oxide particles or SiO ₂ coated graphene particles with at least one precursor compound selected from the group consisting of metal oxide precursor compounds, metal precursor compounds and carbon precursor compounds,

(g) converting at least one precursor compound into the corresponding metal oxide, corresponding metal or carbon, and

(h) removing SiO ₂ from graphene oxide particles or graphene particles

Include together.

Step (f) comprises impregnating the SiO ₂ coated graphene oxide particles or the SiO ₂ coated graphene particles with at least one metal oxide precursor compound, at least one metal precursor compound and / or at least one carbon precursor compound. The individual precursor compounds will fill the spaces / pores in the SiO ₂ coating that was originally filled by the surfactant molecules.

The at least one metal oxide precursor compound and / or the at least one metal precursor compound is preferably selected from the group consisting of metal halides, metal nitrates, metal alkoxides, metal sulfates, metal carboxylates and metal oxysulfates. The at least one carbon precursor compound is preferably selected from the group consisting of sucrose, glucose and pitch.

SiO ₂ coated particles can be impregnated using conventional methods known to those skilled in the art for this type of process. An example is wet impregnation, in which the porous material to be impregnated is suspended in an excess of the corresponding precursor solution and stirred therein for a period of time, for example for 1 to 24 hours, and then The solution is removed by filtration. Another suitable method is the incipient-wetness method, in which the porous material to be impregnated is mixed with a solution of the precursor compound, wherein the amount of the solution of the precursor compound is equal to the pore volume of the porous material. The suspension obtained in this method can be mixed mechanically.

Useful solvents for metal and / or metal oxide precursor compounds and / or carbon precursor compounds include water and / or alcohols such as methanol, ethanol and propanol. The concentration of precursor compound (s) in the impregnation solution is generally 10-30% by weight, preferably 15-25% by weight, based on the total weight of the impregnation solution.

In general, the precursor compound is comprised of precursor compound to uncoated particles in the range of 0.1: 1 to 50: 1, preferably in the range of 0.5: 1 to 20: 1, more preferably in the range of 1: 1 to 10: 1. Used in weight ratio.

After impregnation, the particles are generally separated, optionally washed and dried.

Step (g) involves treating the impregnated particles at high temperature so that the particular precursor compound can be converted to the desired compound. Particles impregnated with the carbon precursor compound are generally brought to a temperature in the range from 600 to 900 ° C., preferably from 650 to 850 ° C., for 1 to 5 hours, preferably 2 to 4 hours, under an inert gas atmosphere. Preferably it is heated to a temperature in the range from 700 to 800 ° C. To convert the metal oxide precursor compound, the impregnated particles are generally brought to a temperature in the range 200-500 ° C. under an oxygen containing atmosphere, for example, generally for 2 to 10 hours, preferably for 4 to 8 hours, in air, Preferably it is heated to a temperature in the range from 300 to 400 ° C. In order to convert the metal precursor compounds, the impregnated coating particles are generally brought to a temperature in the range of 200 to 600 ° C., generally in a reducing atmosphere, for example in the presence of hydrogen, for 4-10 hours, preferably 5-8 hours, Preferably it is heated to a temperature in the range from 300 to 500 ° C.

In step (h) the silicon dioxide is removed, for example by dissolving in aqueous sodium hydroxide solution or HF. The coated particles can be stirred, for example, in an excess of aqueous sodium hydroxide solution at room temperature for 12-24 hours, at which time the aqueous sodium hydroxide solution is exchanged repeatedly.

The processes described in steps (f)-(h) are well known to those skilled in the art and are called nanocasting. Description of this process can be found, for example, in A. Rumplecker et al., Chem. Mater. 19 (2007), p. 485].

In one embodiment of the invention, the steps (f), (g) and (h) are independently repeated one or more times or independently. For example, the impregnation step may be performed repeatedly so that a large amount of precursor compound is loaded into the coated particles. Likewise, the conversion of one or more precursor compounds can be performed repeatedly so that a very substantially complete conversion can be achieved. Step (h) may also be carried out in succession repeatedly, in which case the same or different solvents for SiO ₂ may be used in the repetition.

The coated particles generally comprise 70% to 95% by weight, preferably 80% to 95% by weight, more preferably 85% to 90% by weight of graphene oxide or graphene in the dry state, Coatings selected from carbon, metal and / or metal oxides generally comprise from 5% to 30% by weight, preferably from 5% to 20% by weight, more preferably from 10% to 15% by weight.

The present invention further provides a two-dimensional sandwich nanomaterial obtainable by the method described above.

The present invention further provides the use of a sandwich nanomaterial obtainable by the method described above as a template for the production of other nanolayer materials. This can be done according to the principles mentioned above, known to the person skilled in the art as nanocasting. In nanocasting, in each case in step (a) "positive" and "negative" of the structure formed by the self-assembling surfactant molecules are produced. Thus, in step (c), SiO ₂ is filled, after removal of the surfactant molecules, by the impregnation with the carbon precursor compound, for example the space / pore that was originally filled with the surfactant molecules. The carbon precursor compound can then be converted to carbon having a three dimensional structure originally formed by the surfactant molecule. Thereafter, SiO ₂ may be removed to leave a microporous carbon structure. The structure can then be impregnated with a precursor compound, for example, a metal oxide precursor compound, and can be removed under carbon atmosphere by heating under an oxygen containing atmosphere to leave a metal oxide layer having the structure of the original SiO ₂ layer.

The present invention provides catalysts, sensors, capacitors, primary and secondary electrochemical cells and fuel cells according to the use of the two-dimensional sandwich nanomaterial obtainable by the method described above and the method described above. Further provided are catalysts, sensors, capacitors, primary and secondary electrochemical cells and fuel cells comprising two-dimensional sandwich nanomaterials.

Two-dimensional sandwich nanomaterials obtainable by the methods described above can also be used to produce graphene particles. This method for producing graphene particles is also the preferred practice described above comprising steps (a)-(e) above, wherein the at least one sol precursor compound in step (b) is selected from SiO ₂ precursor compounds. Start with the form. If step (a) provides a mixture according to (a1), step (e) is carried out so that the graphene oxide particles can be converted to graphene particles. Thereafter, immediately after step (e), step (h) (removal of SiO ₂ from graphene oxide particles) is performed. Specifically, this embodiment of the present invention

(a) a mixture comprising (a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant, or

(a2) a mixture comprising graphene particles, at least one solvent useful for solution stripping of graphite and at least one cationic surfactant and / or nonionic surfactant

To provide,

(b) adding at least one sol precursor compound selected from SiO ₂ precursor compounds to the mixture from step (a),

(c) reacting the mixture from step (b) by a sol-gel method so that a gel is formed on the graphene oxide particles or the graphene particles,

(d) removing one or more surfactants, and

(e) Optionally, the coated graphene oxide particles were subjected to 500 ° C. for at least 1 minute under an inert gas atmosphere in order to reduce the graphene oxide to graphene when step (a) provides a mixture according to (a1). Heating above, and

(g) removing SiO ₂

.

Here, it is particularly preferable to prepare graphene particles from graphene oxide. The process

(a) a mixture comprising (a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant

Providing a, or

(b) adding at least one sol precursor compound selected from SiO ₂ precursor compounds to the mixture from step (a),

(c) reacting the mixture from step (b) by a sol-gel method such that a gel is formed on the graphene oxide particles,

(d) removing one or more surfactants, and

(e) heating the coated graphene oxide particles to at least 500 ° C. for at least 1 minute under an inert gas atmosphere to reduce the graphene oxide to graphene, and

(f) removing SiO ₂

.

The present invention also encompasses the use of two-dimensional sandwich nanomaterials obtainable by the methods described above for producing graphene particles.

Hereinafter, embodiments of the present invention will be described in more detail by way of examples.

Example 1 SiO ₂  Preparation of Coated Graphene Oxide Particles

Hummers' method [Hummers, WS & Offeman, RE; J. Am. Chem. Soc. 80 (1958), p. 1339-1139], graphene oxide was prepared from natural graphite flakes. Thus synthesized 30 mg of graphene oxide was first suspended in an aqueous solution containing 1 g of cetyltrimethylammonium bromide and 40 mg of NaOH in 500 ml of demineralized water and sonicated for 3 hours. The suspension was then stirred at 40 ° C. using a magnetic stir bar for 2 hours, and 1 ml of tetraethyl orthosilicate (TEOS) was slowly added to the suspension. The mixture was reacted for 12 hours, and then SiO ₂ coated graphene oxide particles were separated by washing with warm ethanol and dried at 80 ° C. for 6 hours.

Electron microscopic observation by field emission scanning electron microscopy and transmission electron microscopy confirmed that the particles had a mesoporous structure with a size of 200 nm to several μm and a size of about 2 nm. No free silica particles or uncoated graphene oxide particles were observed. As expected, most of the surfactant molecules were adsorbed on the graphene oxide particle surface through electrostatic interaction, so that heterogeneous nucleation of tetraethyl orthosilicate on the graphene oxide surface in solution was preferred over homogeneous nucleation. Suggests that The thickness of the particles was measured by atomic force microscopy analysis perpendicular to the principal plane of the flat particles and found to be a uniform thickness of 28 ± 1 nm.

Example 2: SiO ₂  SiO from coated graphene oxide particles ₂  Preparation of Coated Graphene Particles

Graphene oxide particles prepared according to Example 1, coated with mesoporous SiO ₂ , were prepared by pyrolysing the coated graphene oxide particles at 800 ° C. for 3 hours under argon. This resulted in efficient reduction of graphene oxide to graphene without agglomeration of the particles because the particles are protected by SiO ₂ coating. As evidenced by scanning electron micrographs and transmission electron micrographs, the morphology and structure of SiO ₂ coated graphene particles remained stable during heat treatment, and the mesoporous structure remained intact during pyrolysis. SiO ₂ coated graphene particles obtained from Example 2 were observed by nitrogen adsorption and were found to exhibit type IV nitrogen adsorption isotherm properties of uniform mesopores. Pore size distribution was calculated according to Barrett-Joyner-Halenda at 2 nm. Adsorption data showed a very large specific surface area of 980 m ² g ⁻¹ , which is similar to the value for mesoporous silicon dioxide produced in a conventional manner.

Example 3: Preparation of Graphene Particles Coated with Mesoporous Carbon

The SiO ₂ coated graphene particles of Example 2 were repeatedly impregnated by stirring the sucrose solution in ethanol at 40 ° C. in an impregnation method in which the ratio of sucrose to SiO ₂ coated graphene particles in the final product was fixed at 2: 1. Impregnated. The sucrose impregnated particles were then dried and pyrolyzed at 700 ° C. for 3 hours under argon atmosphere. Thereafter, SiO ₂ was removed from the obtained particles in an aqueous NaOH solution to obtain graphene particles coated with mesoporous carbon.

Electron microscopy of the carbon coated particles confirmed that the carbon layer had a high monodisperse structure with the same size as the SiO ₂ coated particles used as the template. X-ray studies showed that the carbon in the coating was present in amorphous form therein. Observation by nitrogen adsorption and desorption confirmed a specific surface area of 910 m ² g ⁻¹ (according to Brunauer-Emmett-Teller). The particles exhibited type IV isotherms, suggesting the presence of multiple mesopores and micropores in the carbon coated graphene particles.

Example 4: Co ₃ O ₄  Preparation of Coated Graphene Particles

The SiO ₂ coated graphene particles of Example 2 were repeatedly impregnated with a solution of cobalt nitrate in ethanol by stirring at 40 ° C. by an impregnation method in which the weight ratio of cobalt nitrate to SiO ₂ coated graphene particles was 2.3: 1. The particles impregnated with cobalt nitrate were heated in air at 350 ° C. for 5 hours. Thereafter, SiO ₂ was removed from the particles in an aqueous NaOH solution. Observation using a high resolution electron microscope confirmed that Cu ₃ O ₄ had a mesoporous or crystalline structure.

Example 5: Use of Carbon Coated Graphene Particles in Lithium Ion Secondary Batteries

Electrochemical observations were performed on 2032 button cells. The carbon-coated graphene particles of Example 3, carbon black (Super-P) and poly (vinyl difluoride) (PVDF) were mixed in a weight ratio of 80:10:10 by brushing on copper foil (99.6%, Goodfellow). Working electrodes were prepared. Lithium foil was used as a counter electrode. The electrolyte consisted of an equimolar solution of LiPF ₆ in ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1; Industries Ltd). The cells were assembled in an argon filled glovebox with concentrations of water and oxygen maintained at 1 ppm or less, respectively. The electrochemical power output was measured at various charge and discharge rates in the voltage range of 0.01 to 3.00 V. The results are shown in Tables 1 and 2 below.

Claims (19)

(a) a mixture comprising (a1) graphene oxide particles, water and at least one cationic surfactant and / or nonionic surfactant, or
(a2) a mixture comprising graphene particles, at least one solvent useful for solution stripping of graphite and at least one cationic surfactant and / or nonionic surfactant
, ≪ / RTI >
(b) adding at least one sol precursor compound to the mixture from step (a),
(c) reacting the mixture from step (b) by a sol-gel method such that a gel is formed from at least one sol precursor compound on the graphene oxide particles or graphene particles,
(d) removing one or more surfactants, and
(e) optionally, heating the gel coated graphene oxide particles to at least 500 ° C. for at least 1 minute under an inert gas atmosphere to reduce the graphene oxide to graphene.
Method for producing a two-dimensional nanomaterial comprising a. The method of claim 1, wherein the at least one cationic surfactant is selected from the group consisting of quaternary ammonium compounds. The process according to claim 1 or 2, wherein the at least one nonionic surfactant is selected from the group consisting of C ₂ -C ₄ -alkylene oxide block copolymers comprising ethylene oxide. The method according to any one of claims 1 to 3, wherein the at least one sol precursor compound is a SiO ₂ precursor compound, a ZrO ₂ precursor compound, a TiO ₂ precursor compound, a CeO ₂ precursor compound, a Fe ₂ O ₃ precursor compound, a MgO precursor Compound, Al ₂ O ₃ precursor compound, Fe ₂ O ₃ precursor compound, Fe ₃ O ₄ precursor compound, MgO precursor compound, ZnO precursor compound, chromium oxide precursor compound, Co ₂ O ₃ precursor compound, molybdenum oxide precursor compound, tungsten oxide And a precursor compound, a hafnium oxide precursor compound, a Y ₂ O ₃ precursor compound, and a water-soluble crosslinkable polymer and a polymer precursor. 5. The water glass of claim 1, wherein the at least one sol precursor compound is a metal halide, metal nitrate, metal carboxylate, metal oxysulfate, metal acetylacetonate, and water glass for metal alkoxides and Si. Wherein the metal is selected from the group consisting of Zn, Mg, Al, Y, Fe, Cr, Co, Si, Zr, Ti, Ce, Mo, W and Hf. 6. The process according to claim 1, wherein at least one sol precursor compound is selected from SiO ₂ precursor compounds. 7. The compound of claim 1, wherein the at least one sol precursor compound is selected from water glass and Si (OR) ₄ , wherein R is H, CH ₃ , C ₂ H ₅ , C ₂ H ₄ OH , nC ₃ H ₇ , iC ₃ H ₇ , nC ₄ H ₉ and iC ₄ H ₉ , wherein R can be the same or different. 8. The method according to claim 6 or 7,
(f) impregnating SiO ₂ coated graphene oxide particles or SiO ₂ coated graphene particles with at least one precursor compound selected from the group consisting of metal oxide precursor compounds, metal precursor compounds and carbon precursor compounds,
(g) converting at least one precursor compound into the corresponding metal oxide, corresponding metal or carbon, and
(h) removing SiO ₂ from graphene oxide particles or graphene particles
≪ / RTI > The method according to claim 8, wherein steps (f), (g) and (h) are independently repeated one or more times independently or jointly. 10. The metal oxide precursor compound and the metal precursor compound in step (f) are selected from the group consisting of metal halides, metal nitrates, metal alkoxides, metal sulfates, metal carboxylates and metal oxysulfates. The production method selected. 10. The process according to claim 8 or 9, wherein the carbon precursor compound in step (f) is selected from the group consisting of sucrose, glucose and pitch. The process according to any one of claims 8 to 11, wherein converting at least one precursor compound in step (g) is carried out by heating the impregnated graphene oxide particles or graphene particles. The process according to claim 8, wherein SiO ₂ is removed by dissolving in aqueous solution of sodium hydroxide or HF in step (h). A two-dimensional sandwich nanomaterial obtained by the method according to any one of claims 1 to 13. Use of the two-dimensional sandwich nanomaterial according to claim 14 as a template for producing another nanolayer material. Use of the two-dimensional sandwich nanomaterial according to claim 14 in catalysts, sensors, capacitors, primary and secondary electrochemical cells and fuel cells. Catalysts, sensors, capacitors, primary and secondary electrochemical cells and fuel cells comprising the two-dimensional sandwich nanomaterial according to claim 14. Use of the two-dimensional sandwich nanomaterial according to claim 14 for producing graphene particles. A method comprising the steps (a) to (e) according to claim 6 or 7, wherein the steps are as follows:
(h) removing SiO ₂ from the graphene particles
Wherein said step (e) is carried out when step (a) provides a mixture according to (a1).