RU2478571C2 - Method of producing and splitting multilayer graphane - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in motorcar, chemical, electronic and electrochemical industry. Graphite nanofibres with diameter of up to 50 nm, length of about 5 mcm and specific surface area of about 200 m²/g, which contain about 1 wt % catalyst nanoparticles with size of 10-30 nm are put into a container and held in a helium current at 773 K for pre-treatment. The catalyst used is one of the metals which dissociatively adsorb hydrogen - Pd, Pt, Ni, Ti, Fe, Co, Nb, Mo, Ta, W, Rh, Ru, Os, Ir, La, Mg and/or alloys thereof. The fibres are then hydrotreated at hydrogen pressure of 11 MPa and temperature of 298 K for 24 hours. A layer of chemisorbed hydrogen with thermal desorption activation energy of about 1.2 eV is formed in the surface regions of the nanofibres and a layer of chemisorbed hydrogen with thermal desorption activation energy of about 2.5 eV is formed on the inner surfaces of the nanofibres. Highly compact molecular hydrogen with density of up to 0.7 g/cm³ is intercalated in slit-like nanocavities in amount of about 10 wt %. Hydrogen is removed from the slit-like nanocavities by sharply reducing pressure and then annealing the sample at 295 K for 10 minutes. Chemisorbed hydrogen with thermal desorption activation energy of about 1.2 eV is removed by annealing at 800 K for 3 hours. The obtained nanofibres consist of multilayer fragments of graphane - polygraphane, in form of dark strips which are separated into separate nano-regions by slit-like nanocavities in form of light strips.

EFFECT: invention simplifies the process by excluding steps which are complex and not practically feasible.

2 cl, 7 dwg, 1 ex

Description

1. The technical field to which the invention relates.

The invention relates to certain relevant areas of nanotechnology (B82B 3/00 - manufacturing or processing of nanostructures), technical physics and hydrogen energy. It can be used in the automotive, chemical, electronic, electrical and several other areas of technology.

2. The level of science and technology

Recently, a group of scientists from England, Holland and Russia ([1] DCElias, RRNair, TMGMohiuddin, SVMorozov, P. Blake, MPHalsall, ACFerrari, DWBoukhvalov, MIKatsnelson, AKGeim, KSNovoselov, "Control of graphene's properties by reversible hydrogenation: Evidence for graphane ", // Science, 2009, v. 323, no.5914, pp610-613) it was possible to achieve a chemical reaction of a single atomic layer of graphite - graphene [2-5] (Fig. 1 ( above), Fig. 2A) - with hydrogen ([2] AKGeim, "Graphene: Status and prospects", // Science, 2009, v. 324, no. 5934, pp1530-1534; [3] M. Popov (Rusnano chief expert). Interview in 2009 for Forbes with K. Novoselov (Nobel Prize in Physics for 2010) “How the thinnest matter in the Universe was created Noah ”(based on materials [2]). // www.forbes.ru/tehno/tehnologii/5798…; [4] C. Soldano, A. Mahmood, E. Dujardin," Production, properties and potential of graphene "/ / Carbon, 2010, v. 48, iss. 8, pp2127-2150; [5] A. Samarov, “Graphene: new production methods and recent advances” // Elements - science news (http://elementy.ru/ news / 430857)).

As a result, a new two-dimensional substance with the chemical formula CH is formed - graphane [1, 6, 7] (Fig. 2B, Fig. 3), which at very low temperatures behaves like an insulator ([6] JOSofo, ASChaudhari, GDBarber , "Graphane: A two-dimensional hydrocarbon" // Physical Review B, 2007, v.75, pp153401-1 - 153401-4; [7] Y. Erin. "When interacting with hydrogen, graphene turns into graphane" (according to materials [1]) // Elements - science news (http://elementv.ru/news/431012)).

Grafan has a two-dimensional hexagonal crystalline structure (Fig. 2B, Fig. 3), but with a slightly shorter (constant) lattice period than graphene.

{Figure 1, taken from [7], shows (above) graphene (graphene), consisting of a monolayer of carbon atoms arranged in the form of a hexagonal network, which underlies the structures of graphite (graphite, lower left figure), graphite nanofibers (graphite nanofibers), carbon nanotubes (carbon nanotubes, bottom in the center of the picture) and fullerenes (buckyballs, or fullerenes, bottom right). The structures of graphite and graphite nanofibers consist of fragments of weakly bonded van der Waals interactions of graphene monolayers, i.e. from fragments of multilayer graphene, or "polygraphen"}. {Fig. 2, taken from article [1], shows the crystal structure of graphene (A), corresponding to Fig. 1 (above), and graphene (B), corresponding to Fig. 3. The larger balls show carbon atoms, the smaller balls show hydrogen atoms; a is the bond length between carbon atoms, d is the lattice constant; for graphan a = 1.42 Å, d≈2.42 Å; for graphene, a = 1.42 Å, d≈2.46 Å)}.

{Figure 3, taken from article [6], shows the structure of the graphane corresponding to Figure 2B, so-called chair-like modification (the chair conformation). Carbon atoms are shown by dark balls, and hydrogen atoms by light balls}.

It should be noted that the authors of [1] include A.K. Geim and K.S. Novoselov - scientists who were the first to receive graphene, the thinnest and most durable of all known materials [2-5], and who were awarded the Nobel Prizes in Physics for 2010.

The term “grafan” first appeared in 2006, in an article [6] by American theoretical physicists. In this work, it was theoretically shown that as a result of the interaction of graphene with atomic hydrogen, a new substance with the chemical formula CH can be formed - this substance was called graphane. It was shown in [6] that the crystalline structure of graphan, like graphene, is two-dimensional hexagonal. In this case, hydrogen atoms are attached on both sides of the plane (monolayer) of carbon atoms (Fig. 2B, Fig. 3).

In [1], the initial material — graphene crystals — was prepared by micromechanical exfoliation (using adhesive tape) of loosely bonded graphene layers of graphite (Fig. 1) located on a silicon oxide substrate. The fact that just a single layer of carbon atoms (graphene) was obtained, the researchers were convinced by optical methods and using Raman spectroscopy. Then, the obtained graphene was annealed at a temperature of 573 K in an argon atmosphere for 4 h (to rid the crystals of the starting material of possible impurities and impurities). Then, the graphene samples were exposed (2 h) to the so-called “direct-current” plasma — a mixture of argon and hydrogen (the proportion of hydrogen was 10%), which was at a pressure of about 100 Pa, and as a result, graphene was obtained.

It was also shown [1] that the graphene hydrogenation reaction is “reversible,” and graphane can again be converted to graphene by thermal desorption annealing at a temperature of 723 K for 24 h.

The method [1, 2] of mechanical peeling (using adhesive tape) makes it possible to obtain graphene monolayers (sheets with an area of up to 1 mm ² ) of high quality, obviously intended only for functional studies. The epitaxial method for growing graphene [2-5] is based on the deposition of a substance evaporated in a molecular source on a crystalline substrate. However, the implementation of this technology requires extremely complex technical solutions. There are also significant difficulties in obtaining graphene by chemical methods [2-5]: first, it is necessary to achieve complete separation of graphite placed in a solution; secondly, to ensure that the peeled graphene in the solution retains the shape of the sheet, and does not curl and does not stick together.

It should be noted that there are currently no serial devices based on the use of graphene (and / or graphene), although the list of promising technologies is quite extensive [2-5].

Note that the technical difficulties and the relatively low technological and economic efficiency of the methods [1, 7] for producing graphane are mainly due to technical (technological) difficulties and certain restrictions on the preparation of the starting material — sheets (atomic thickness) of defect-free graphene [2-5].

Further advancement in the study and practical application of graphane obviously requires the development of a more efficient new method for producing a graphane-like carbon material — multilayer graphane, or “polygraph”, consisting of multilayer fragments of weakly bonded van der Waals interaction layers of graphane. The new method is free from a number of technological difficulties and limitations (drawbacks) inherent in the known methods [1, 7] for producing graphane from graphene [2-5], since it is based on the production of multilayer graphane (“polygraph”) from the original multilayer graphene (“polygraph” ) contained in carbon structures (in graphite nanofibres, etc.), as well as in the subsequent splitting of polygraph with "megabar" hydrogen. This new method is devoted to the present invention, which uses the work [1] as a prototype, as well as the results of [6] (for thermodynamic estimates).

3. Disclosure of invention

A fundamentally new method is proposed for producing graphane in a multilayer rather than a monolayer form by means of hydrogenation of fragments of the initial multilayer graphene contained in carbon structures (in graphite nanofibers, etc.), and subsequent splitting of the fragments of polygraph with "megabar" hydrogen.

The proposed method is technologically and economically more efficient than the currently used methods for producing graphene [1, 6, 7] by hydrogenation of graphene, the production methods of which are characterized by known technological difficulties and certain limitations [2-5]. Therefore, the proposed method differs from the prototype [1] in higher technical, technological and economic efficiency, including with respect to the real possibilities of further detailed (stationary) study of graphane (in multilayer form) and its practical use.

In connection with the foregoing, it is necessary first of all to expand and detail the definition of graphane, as well as the definition of multilayer graphane (polygraph), consisting of fragments of loosely coupled (van der Waals interaction) layers of graphane, in the thermodynamic and crystal chemical plan, using the results of [1, 2, 6], in particular, to identify the material according to data (spectra) of temperature-programmed desorption (TPD spectroscopy) of hydrogen.

According to the theoretical results [6] presented in Fig. 4, the standard energy (enthalpy ΔH ₁ ) of the formation of graphane (chemical compound СН _(graphane) ) from graphite (С _(graphite) ) and gaseous molecular hydrogen (Н _{2 (gas)} ) at the hydrogen pressure of 0.1 MPa and a temperature of 298 K is ΔH _{1 (cr.)} = -0.15 eV / atom (for the "arm-like" graphene) and ΔH _{1 (lod.)} = -0.09 eV / atom (for the "boat-like" graphene).

{Figure 4 (from article [6]) shows the formation energy (in eV / atom) of some hydrogen compounds with carbon as a function of the hydrogen content in the compound (in atomic%). It can be seen that graphane, i.e. the monolayer compound CH, in both versions (Fig. 2B, Fig. 3), is more stable than the compounds C ₅ H, C ₄ H, C ₃ H and C ₂ H}.

Using the ΔH ₁ value (from [6]) and the known (from the Handbooks of thermodynamic quantities) values of the enthalpy of molecular hydrogen dissociation (~ 2.3 eV / atom) and the enthalpy of the van der Waals interaction of graphene layers in graphite (-0.1 eV / atom), it is possible to determine the standard energy (enthalpy) ΔH _{2 of the} formation of graphane (C ₍ graphene ₎ ) from graphene (C _(graphene) ) and atomic hydrogen (H _(gas) ), i.e. binding energy (enthalpy) of a hydrogen atom with graphan ΔH ₂ ≈-2.5 eV / atom (hydrogen) ≈-240 kJ / mol (N) (both for "arm-like" and for "boat-like" graphene).

Note that ΔН ₂ ≈-240 kJ / mol (N) can also be determined from experimental data (in the description link [1] DC Elias et al. "Control of graphene's properties by reversible hydrogenation: Evidence for graphane" // Science, 2009 , v.323, p.611) on the temperature-time conditions (Т = 773 K, τ = 24 h (p. 3 of the description)) of the reverse conversion of experimental graphane to graphene using the Polyany-Wigner kinetic equation (1 / τ = ν exp [ΔH ₂ / RT]) and data [1] (Fig.3) on the Raman spectrum of graphane (ν≈10 ¹³ s ^-1 ).

In this connection, it should be emphasized that the value of ΔH ₂ characterizes the chemisorption of atomic hydrogen by graphene, corresponding to the theoretical model “F *” for the chemisorption of hydrogen atoms on graphite (in the graphene plane of the material), schematically shown in Fig. 5. In this case, graphane can be considered as a two-dimensional carbohydride, which can also be formed in multilayer carbon structures (i.e., in polygraph). {Fig. 5 presents theoretical models of chemisorption of hydrogen atoms on graphite (in the graphene plane of the material). In the “F *” model, the activation energy of thermal desorption of hydrogen atoms is ~ 2.5 eV (TPD peak γ (Fig. 6)); in the N model, ~ 1.2 eV (TPD peak β (Fig. 6)); in models “C” and “D” - ~ 3.6 eV; in models “G” and “F” - ~ 0.2 eV. The complex (С-Н *) in the “F *” model corresponds to the critical one-dimensional graphane nucleus in multilayer carbon structures (ie, in polygraph)}.

The value (characteristic) ΔH ₂ can be used to identify the chemisorption and diffusion of hydrogen in fragments (regions) of the initial polygraph in carbon nanomaterials and graphite, since (as was emphasized in [6]), the van der Waals interaction can be neglected in an acceptable approximation (~ - 0.1 eV / atom) between graphene (or graphane) monolayers in a multilayer material. Moreover, the value of -ΔH ₂ can correspond to the activation energy of thermal desorption of hydrogen from graphane, or graphane-like, multilayer regions (fragments) of the material, determined from the data on temperature-programmed desorption (TPD peak γ in Fig. 6), which may indicate the presence of polygraph in the material.

{Fig. 6 (from the “Implementation Example”) shows the temperature-programmed desorption curves — TPD peaks β (~ 1.2 eV) and γ (~ 2.5 eV) of chemisorbed hydrogen from samples of the initial graphite nanofibers (GNF), hydrogenated at 298 K for 24 hours at a hydrogen gas pressure of P _H2 ≈11 MPa (curve 1) and at P _H2 ≈0.1 MPa (curve 2). The TPD peak γ with an activation energy of ~ 2.5 eV corresponds to hydrogen desorption from graphane-like multilayer regions (fragments), or regions (fragments) of multilayer graphane, in samples}.

{Fig. 7 (from the “Implementation Example”) shows microphotographs of nanofibers composed of alternating nano-regions (nanofragments) of multilayer graphane (dark bands in the photographs) and slit-like nanocavities separating them (light bands marked by arrows in the photographs). Such a nanostructure is formed under certain hydrogenation conditions of the initial graphite nanofibers (GNF) and is characterized by the TPD peak γ with an activation energy of ~ 2.5 eV (Fig. 6). The splitting of graphan regions into nanoscopes separated by slit-like nanocavities occurs under the influence of high-density (“megabar”, i.e., corresponding to megabar compression) molecular hydrogen intercalated into the material and localized (in the form of nanoplasts) in slot-like nanocavities formed in the material due to the association energy atomic hydrogen, and leaving the material under certain dehydration conditions}.

The process of dissociative chemisorption of hydrogen by a carbon multilayer sorbent (fragmented polygraph), corresponding to the TPD peak γ with an activation energy of ~ 2.5 eV (Fig. 6), is characterized by the standard enthalpy of volume dissolution, or dissociative chemoabsorption, mole of hydrogen atoms (from the initial state H _{2 (gas)} ) in fragments of polygrafen ΔH _(γ) = -19 ± 1 kJ / mol (N), as well as the value of the effective energy (enthalpy) of activation of volume diffusion of hydrogen atoms in fragments of polygrafen Q _(γ) = 250 ± 3 kJ / mol (N) ≈ΔH ₂ .

Under certain conditions, the process can go right up to the formation of graphane-like (carbohydride) regions in the predominant part of the fragments of the starting material — fragmented polygraphen.

The law of "acting masses" for the "reaction" of chemoabsorption of hydrogen in

fragments polygraph _(. C _(printing) + _^1/2 H _{2 (gas)} ⇔SN _{(grafan.obl))} can be described by the expression corresponding to the Langmuir isotherm dissociative absorption:

where X _γ is the equilibrium concentration (Н / С ^lat ) of _γ absorbed hydrogen atoms in the lattice (lat) of multilayer fragments in the carbon material at a pressure of P _H2 (in Pa) and temperature T (in K), i.e. the ratio of the number of multilayer fragments dissolved in the lattice in the material of hydrogen atoms (H) to the number of carbon atoms (C ^lat ≤ C) in the fragment lattice in the material, close to the total number of carbon atoms (C) in the material; X _γm = (H / C ^lat ) _γm ≤1,0 - limiting (“carbohydride”, or graphane) concentration of hydrogen in the lattice of multilayer fragments in the material; P ⁰ _H2 = 1 Pa - standard pressure.

The equilibrium constant K _(γ) in expression (1) can be represented as:

where ΔS _(γ) ≈ -15 R is the standard entropy for this "reaction"; R is the universal gas constant.

The time of diffusion saturation by hydrogen of the lattice and other regions of multilayer fragments in the carbon material at relatively low temperatures, at which there is an “irreversible” capture of the diffusant by chemisorption centers (graphan-like, etc.), can be estimated (up to an order of magnitude) using the expression:

where L is the characteristic diffusion path (of the order of the thickness of the sample);

D ₀ ≈2 · 10 ^-4 cm ² / s; Q≈10 kJ / mol.

The time of diffusion desorption (departure) of chemisorbed hydrogen from the lattice of multilayer fragments (polygraph and / or polygraph) in a carbon material at elevated temperatures, at which there is a “reversible” capture of the diffusant by chemisorption graphane-like centers, can be estimated (up to an order of magnitude) as:

where L _(γ) is the characteristic diffusion path (L _{(γ) of the} order of the diameter of the fibers in the case of GNF); D _{0 (γ)} ≈3 · 10 ^-3 cm ² / s; Q _(γ) = 250 + 3 kJ / mol (N) ≈-ΔH ₂ .

The process of dissociative-associative chemoadsorption of hydrogen by a multilayer fragmented carbon sorbent corresponding to the TPD peak β with an activation energy of ~ 1.2 eV (Fig. 6) is characterized by the standard enthalpy of chemoadsorption of a mole of Н _{2 (gas)} in the boundary defect (def) regions (surface layers) of fragments of polygraphen in a carbon material ΔH _(β) ≈-110 kJ / mol (Н ₂ ), as well as the value of the effective energy (enthalpy) of activation of hydrogen diffusion in the boundary defect regions (layers) of fragments of polygraph Q _(β) ≈120 kJ / mole (H ₂ ).

The law of “acting masses” for the “reaction” of chemoadsorption (C _{(def.polygraphhene)} + Н _{2 (gas)} ⇔CH _{2 (def._obl.)} ) Can be described by expressions corresponding to the isotherm of non-dissociative (formally) Langmuir adsorption:

where X _β is the equilibrium concentration (Н ₂ / С ^def ) _{β of} adsorbed hydrogen molecules in the boundary defective (def) regions (surface layers) of polygraphen fragments in the carbon material at a pressure of P _H2 (in Pa) and temperature T (in K)), those. the ratio of the number of adsorbate molecules (H ₂ ) to the number of carbon atoms (C ^def ) in the defective areas (layers) of fragments of polygraph; X _βm = (Н ₂ / С ^def ) _βm ≤0.5 - limiting (“carbohydride”) local concentration; ΔS _(β) ≈ -30 R.

Under certain conditions, the process can go right up to the formation of carbohydride concentrations in the predominant part of the defective areas (surface layers) of fragments of the initial polygraph; the necessary and sufficient duration of the process at relatively low temperatures is determined (up to an order of magnitude) by expression (3).

The time of diffusion desorption (departure) of chemisorbed hydrogen from defective regions - the surface layers of fragments of the initial polygraph in the carbon material (at elevated temperatures) can be estimated (up to an order of magnitude) using the expression:

where L _(β) ≈L is the characteristic diffusion path (of the order of the thickness of the sample); D _{0 (β)} ≈1.8 · 10 ³ cm ² / s.

Using expressions (1-7), it is possible to determine the optimal hydrogenation regimes of the initial multilayer carbon material (fragmented polygraph), which ensure the formation of graphane-like regions with carbohydride concentrations (X _γm = (Н / С ^lat ) _{γm ≈} 1) inside the multilayer fragments of the material achievement of local carbohydride concentrations (X _βm = (H ₂ / C ^def ) _βm ≈0.5) in defective areas (surface layers) in fragments of the material.

To justify and optimize the process of splitting graphene and / or graphene layers in multilayer fragments in carbon materials, the “law of acting masses” is considered for sorption (transition) of hydrogen from the initial atomic gaseous state (H _(gas) ) to the lattice of fragments in carbon materials with subsequent association hydrogen atoms in a highly compact (“megabar”) molecular state (H _{2 (graph.)} ), localized between graphene (and / or graphane) layers of material fragments. The physics of the process (2 Н _(gas) → Н _{2 (graph.)} ) Consists in the fact that atomic hydrogen easily penetrates through graphene (graphene) layers of material fragments, and the molecular formed between graphene (graphene) layers (as a result of the association of hydrogen atoms) is molecular hydrogen is (under certain conditions) “locked” between graphene (and / or graphene) layers of carbon material fragments.

The law of mass action for the “reaction” (2 Н _(gas) ⇔Н _{2 (graph.)} ) Can be represented in the form convenient for the corresponding estimates as:

where P _{H (gas)} , P ⁰ _{H (gas)} is the equilibrium and standard pressure of atomic hydrogen gas, respectively; P * _{H2 (graph.)} - equilibrium fugacity (effective pressure of molecular hydrogen), corresponding to a highly compact molecular state of hydrogen between graphene (and / or graphane) layers of material fragments; P ⁰ _{H2 (gas)} is the standard pressure of molecular hydrogen; ΔH _(diss.) , ΔS _(diss.) - standard energy and entropy of dissociation of molecular hydrogen gas, respectively (ΔH _(diss.) ≈4.6 eV, ΔS _(diss.) ≈0 (to a first approximation)); ΔV is the corresponding change in the volume of the material (of the order of the gram-atomic volume of carbon).

It follows that the megabar values of local stresses (P * _{H2 (graph.)} ) Necessary for splitting fragments of polygraphen and / or polygraphane in a carbon material can be obtained (due to the energy of association of hydrogen atoms in the material) at technological temperatures and real (for practical implementation ) atomic hydrogen pressure P _{H (gas)} ~ 10-100 Pa.

Such a pressure of atomic hydrogen (P _{H (gas)} ~ 10-100 Pa) can be obtained, for example, by the catalytic atomization of molecular hydrogen, by hydrogenation of carbon material in gaseous molecular hydrogen with a pressure P _{H2 (gas)} ~ 10 MPa.

With a sharp decrease in hydrogen pressure (by tens of percent or more), the intercalated (int.) Highly compact “megabar” hydrogen is desorbed (leaves) from the multilayer carbon material in a time that can be estimated (order of magnitude) using the expression:

where L _(int.) ≈L is the characteristic diffusion path (of the order of the sample thickness); D _{0 (int.)} ≈9 * 10 ^-3 cm ² / s; Q _(int.) ≈ -7 kJ / mol (H ₂ ).

The density of the highly compact “megabar” hydrogen (ρ _H ) intercalated between the graphene (and / or graphene) layers in the multilayer fragments of the material (GNF) can be determined (after removal of the “megabar” hydrogen from the material (Fig. 7)) using expressions (using electron microscopic and gravimetric data):

where ρ _C = 2.3 g / cm ³ is the known density of carbon nanofibers; f _vH = 0.4 ± 0.1 is the volume fraction of slit-like nanocavities (ie, the “hydrogen” part) in nanofibers, determined from Fig. 7; ν _C , v _h are the volumes of the carbon part of the nanofibers and the “hydrogen” part of the nanofibres, respectively; f _mH = 0.17 ± 0.01 is the mass fraction of intercalated hydrogen in slit-like nanocavities in nanofibers in the sample corresponding to Fig. 7 (experimental value); m _C , m _H are the masses of the carbon part of the nanofibers and the “hydrogen” part of the nanofibres, respectively.

From this, one can obtain the value ρ _H = 0.7 ± 0.2 g / cm ³ , which in the case of comprehensive compression of the sample corresponds to megabar external pressures of hydrogen, and in our case, to internal local megabar pressures of high-density hydrogen intercalated into the material, i.e. internal local megabar stresses in nanomaterial.

Using the known data [1–7] on the superhigh strength characteristics of graphene (or graphene), we can estimate the internal stresses necessary for the effect of mechanical “bloating” of slit-like nanocavities in their middle part to a lenticular shape observed in microphotographs of nanofibers (Fig. 7), and get close to megabar values of internal pressures (stresses).

Chemisorbed hydrogen corresponding to the TPD peak β with an activation energy of ~ 1.2 eV (Fig. 6) can be removed from the material by desorption annealing, in which only chemisorbed hydrogen corresponding to the TPD peak γ with an activation energy of ~ 2 remains in the material. 5 eV (Fig. 6), i.e. only nano-regions of multilayer fragmented graphane are preserved, separated by slit-like nanocavities (Fig. 7). The optimal mode of thermal desorption annealing of the material can be determined using expressions (7) and (4).

The method of formation and splitting of a multilayer fragmented graphane - polygraph in the initial multilayer carbon material - fragmented polygraph (Fig. 1-5) is carried out by means of a set of the following operations.

1. Use carbon materials as a material object, consisting of multilayer fragments of graphene - fragmented polygraphen (Fig. 1) such as graphite nanofibers or carbon nanotubes.

2. A certain amount of metal catalyst nanoparticles, at least one of the group of metals dissociatively absorbing hydrogen, including Pd, Pt, Ni, Ti, Fe, Co, Nb, Mo, Ta, is introduced into the interfragment surface regions of the carbon material by a chemical or electrochemical method, W, Rh, Ru, Os, Ir, La, Mg, and / or their alloys, necessary and sufficient to create a partial pressure of atomic hydrogen with a pH of about 10-100 Pa during subsequent hydrogenation of the material in gaseous molecular hydrogen (expression (8)).

3. The material is purified from the attached functional groups of the oxide type by annealing it in an inert gas.

4. Create by hydrogenation of the carbon material in gaseous molecular hydrogen (expressions (1-8)) at pressures P _H2 , temperatures and hydrogenation times not exceeding 30 MPa, 1000 K and 300 h, respectively, a carbohydride layer of chemisorbed hydrogen with an activation energy of thermal desorption ~ 1.2 eV in the surface regions of polygraphic material fragments (Fig. 5, 6), a carbohydride layer of chemisorbed hydrogen with an activation energy of thermal desorption of ~ 2.5 eV on the internal graphene surfaces of material fragments (Fig. 5 5, 6), as well as a nanolayer of a highly compact molecular “megabar” hydrogen intercalated into the material with a density of up to ~ 0.7 g / cm ³ (expressions (10-12)) in an amount of about 10 wt.% (Fig. 7).

5. Remove from the nanosized layers — slit-like nanocavities of the material — the highly compact molecular hydrogen intercalated there by drastically reducing the pressure of molecular hydrogen gas by tens or more%, preferably by ~ 100%, and subsequent low-temperature annealing (expression (9)) of the material, preferably at T≈ 298 K.

6. Remove chemisorbed hydrogen from the material with an activation energy of thermal desorption of ~ 1.2 eV by annealing (expression (7)) at elevated temperatures, preferably at T≈800 K, in which only chemisorbed hydrogen with an activation energy of thermal desorption of ~ 2 remains in the material, 5 eV (expression (4)), i.e. only multilayer fragments of graphane are preserved, separated by slit-like nanocavities into separate nanoscopic regions (Fig. 7);

7. Control the completeness of the process by periodically conducting temperature-programmed hydrogen desorption (Fig. 6), gravimetric and electron microscopic studies of the material (Fig. 7).

4. The implementation of the invention

Implementation example

A sample with a thickness of ~ 0.45 cm from ~ 1 g of carbon fragmented nanomaterial — graphite nanofibers (GNF) with a fiber diameter of up to ~ 50 nm, a fiber length of ~ 5 μm and a specific surface area of ~ 200 m ² / g) containing ~ 1 wt.% inclusions of nanoparticles (~ 10-30 nm in size) of a palladium catalyst are placed in a container made of hydrogen-resistant steel and incubated for 2 hours in a helium stream at 773 K (for cleaning the carbon sorbent).

Then, a sample (in a container) is hydrogenated in gaseous molecular hydrogen at a pressure of P _{H2 (gas)} ≈11 MPa and a temperature of T≈298 K for 24 h (until the formation of graphite nanofibers of a carbon-hydride layer of a chemo-adsorbed hydrogen with energy activation of thermal desorption ~ 1.2 eV (Fig. 5, 6), as well as the formation on the internal graphene surfaces of nanofibers of a carbohydride layer of chemisorbed hydrogen with an activation energy of thermal desorption of ~ 2.5 eV (Fig. 5, 6), i.e., the formation of graphane areas in the predominant part of the material. Modes of such hydrogenation of the material are determined using the expressions (1), (2), (3), (5) and (6). The specified completeness of the process of hydrogenation of the material is controlled by means of temperature-programmed desorption (TPD ) hydrogen from the material (Fig. 6) .In this case, the amount and local concentrations of chemisorbed hydrogen are determined from the calibrated areas of the TPD peaks β and γ (Fig. 6) using expressions (1), (2), (5-6).

When hydrogenated material from gaseous molecular hydrogen at a pressure of P _{H2 (gas)} ≈11 MPa and a temperature of T≈298 K for 24 hours provides (through catalytic atomization of a part of molecular hydrogen) the partial pressure of atomic hydrogen (P _{H (gas)} ≈10-100 Pa (expression (8)) for multilayer intercalation into the material of highly compact (megabar, i.e. corresponding to megabar compression) molecular hydrogen with a density of up to ~ 0.7 g / cm ³ (expressions (10-12) in an amount of ≥10 wt.%, causing the splitting of nanofibers (due to the energy of assoc tion of atomic hydrogen (expression (8)) on graphyne nanoregions separated nanoplastami intercalated hydrogen - slotted nanofields (Fig.7).

The intercalated highly compact “megabar” hydrogen is removed from the nanomaterial by means of a sharp decrease in the hydrogen pressure (to zero), i.e. depressurization, and subsequent annealing of the nanomaterial at T≈295 K for 10 min; the annealing mode is determined using expression (9). After such processing, microphotographs of the nanofibers (Fig. 7) show the multilayer graphane nano-regions (dark bands in the photographs) and the slit-like lenticular nanocavities separating them (light bands, some of which are indicated by arrows in the photographs).

The density of the highly compact “megabar” hydrogen (pH) intercalated in the slit-like nanocavities of the material (Fig. 7) is determined using expressions (10), (11) and (12). In this case, the characteristic values are used: ρ _C = 2.3 g / cm ³ — known density of carbon (or graphane) nanofibers; f _vH = 0.4 ± 0.1 - volume fraction of slit-like nanocavities in nanofibers, which is determined from Fig. 7; f _mH = 0.17 ± 0.01 is the mass fraction of intercalated hydrogen in slit-like nanocavities in nanofibers in the sample corresponding to Fig. 7, which is determined from gravimetric measurements.

This yields the value ρ _H = 0.7 ± 0.2 g / cm ³ , which, in the case of comprehensive compression of the sample, corresponds to megabar external pressures of hydrogen, and in the case under consideration, to internal local pressures of high-density hydrogen intercalated into the material, i.e. internal local megabar stresses in nanomaterial.

They evaluate (using known data [1–7] on the superhigh “super-megabar” strength characteristics of graphene (or graphene)) the internal stresses necessary for the effect of mechanical “bloating” of slit-like lenticular nanocavities in their middle part to the lenticular shape observed in microphotographs of nanofibres (Fig. .7), and they obtain close to megabar values of internal pressures (stresses).

Then chemisorbed hydrogen corresponding to the TPD peak β with an activation energy of ~ 1.2 eV (Fig. 6) is removed from the nanomaterial by annealing the nanomaterial (sample with a thickness of ~ 0.45 cm) at 800 K for 3 hours. In this case, the mode of desorption annealing of the sample nanomaterial is determined using expressions (7) and (4).

As a result of the complex of all the operations described above, a sample is obtained from nanofibers consisting of multilayer fragments of graphane - polygraph, split (divided) into separate nanobas (dark bands in Fig. 7) with slit-like lenticular nanocavities (light bands in Fig. 7, some of which marked by arrows).

Claims (2)

1. The method of obtaining and splitting multilayer graphane - polygraph, consisting of loosely interconnected graphane layers, characterized in that:
use carbon materials as a material object, consisting of multilayer fragments of graphene - graphite nanofibres or carbon nanotubes;
at least one of the group of metals dissociatively absorbing hydrogen, and including Pd, Pt, Ni, Ti, Fe, Co, Nb, Mo, Ta, W, Rh, is introduced chemically or electrochemically into the interfragment near-surface regions of the carbon material , Ru, Os, Ir, La, Mg and / or their alloys, in an amount necessary and sufficient to create, with subsequent hydrogenation of the material in gaseous molecular hydrogen, a partial pressure of atomic hydrogen P _{H of the} order of 10-100 Pa;
carry out a preliminary purification of the carbon material from the attached functional groups of the oxide type by annealing in an inert gas;
create by means of hydrogenation of carbon material in gaseous molecular hydrogen at pressures Р _H2 , temperatures and hydrogenation times not exceeding 30 MPa, 1000 K and 300 h, respectively, a carbohydride layer of chemisorbed hydrogen with an activation energy of thermal desorption of ~ 1.2 eV in the surface regions of polygraphic material fragments, a carbohydride layer of chemisorbed hydrogen with an activation energy of thermal desorption of ~ 2.5 eV on the internal graphene surfaces of material fragments, as well as intercalated a slit-shaped nanocavities material highly compact with a density of molecular hydrogen to ~ 0.7 g / cm ³ in an amount of about 10 wt.%;
remove highly compact molecular hydrogen intercalated there from the slit-like nanocavities of the material by drastically reducing the pressure of molecular hydrogen gas by tens or more%, up to ~ 100%, and subsequent low-temperature annealing of the material, for example, at T≈295 K;
chemisorbed hydrogen with an activation energy of thermal desorption of ~ 1.2 eV is removed by annealing at elevated temperatures, for example, at T≈800 K, at which only chemisorbed hydrogen with an activation energy of thermal desorption of ~ 2.5 eV remains in the material, i.e. save only multilayer fragments of graphane, divided by slit-like nanocavities into separate nanoscopes;
control the completeness of the process of hydrogenation of the material and the process of intercalation of highly compact molecular hydrogen by means of temperature-programmed hydrogen desorption, gravimetric measurements and electron microscopy. 2. The method according to claim 1, characterized in that:
use a sample with a thickness of ~ 0.45 cm from ~ 1 g of carbon fragmented nanomaterial — graphite nanofibers with a fiber diameter of up to ~ 50 nm, a fiber length of ~ 5 μm and a specific surface of ~ 200 m ² / g, containing ~ 1 wt.% inclusions of nanoparticles of size ~ 10-30 nm palladium catalyst;
place the sample in a container of hydrogen-resistant steel and incubate for 2 hours in a helium stream at 773 K;
hydrogenating the sample in a steel container in gaseous molecular hydrogen at a pressure of P _H2 ≈11 MPa and a temperature of T≈298 K for 24 h until the formation of carbon-hydride layer of chemisorbed hydrogen in the surface regions of graphite nanofibers with an activation energy of thermal desorption of ~ 1.2 eV, forming the internal graphene surfaces of nanofibers of a carbohydride layer of chemisorbed hydrogen with an activation energy of thermal desorption of ~ 2.5 eV, as well as the formation of interlayers of intercalation into slot-like nanowires the material of highly compact molecular hydrogen with a density of ~ 0.7 g / cm ³ in an amount of ≥10 wt.%;
highly compact molecular hydrogen is removed from the slit-like nanocavities of the material by drastically reducing the hydrogen pressure in the steel container to zero, i.e. pressure relief, and subsequent annealing of the sample at T≈295 K for 10 min;
chemisorbed hydrogen with an activation energy of thermal desorption of ~ 1.2 eV is removed from the nanomaterial by annealing the sample at 800 K for 3 h;
get a sample of nanofibers, consisting of multilayer fragments of graphane - polygraph, divided into separate nanobas with slit-like nanocavities;
control the given completeness of the process by conducting temperature-programmed hydrogen desorption, gravimetric measurements and electron microscopy.

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