CN109806897B - Graphene-based composite material and preparation method and application thereof - Google Patents

Graphene-based composite material and preparation method and application thereof Download PDF

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CN109806897B
CN109806897B CN201711159257.1A CN201711159257A CN109806897B CN 109806897 B CN109806897 B CN 109806897B CN 201711159257 A CN201711159257 A CN 201711159257A CN 109806897 B CN109806897 B CN 109806897B
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graphene
composite material
hydrogen
carbon
water
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CN109806897A (en
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江俊
杨丽
罗毅
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Hefei Jiqian Quantum Technology Co ltd
Jiang Jun
Luo Yi
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University of Science and Technology of China USTC
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/32—Hydrogen storage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/133—Renewable energy sources, e.g. sunlight

Abstract

The invention belongs to the field of photocatalytic materials and hydrogen storage materials, and particularly relates to a graphene-based composite material as well as a preparation method and application thereof. The graphene-based composite material provided by the invention comprises a single-layer carbon-nitrogen material; and graphene bonded to both sides of the single layer of carbon nitrogen material by van der waals forces. The composite material provided by the invention has good light absorption capacity in the ultraviolet and visible light range of solar energy, and can efficiently collect solar energy, so that the composite material is suitable for the field of photocatalysis. On the other hand, by utilizing the efficient selective permeability of the graphene, the composite material provided by the invention allows protons to penetrate through the graphene to participate in the reaction, and newly generated hydrogen cannot escape, and OH and O are blocked2And the reverse reaction is inhibited when the composite material enters a system, and the effective purification and safe storage of hydrogen can be realized, so that the composite material is also suitable for the field of hydrogen storage.

Description

Graphene-based composite material and preparation method and application thereof
Technical Field
The invention belongs to the field of photocatalytic materials and hydrogen storage materials, and particularly relates to a graphene-based composite material as well as a preparation method and application thereof.
Background
The shortage of fossil energy and environmental pollution are two major problems facing the development of human beings, and the photocatalytic water splitting reaction can activate water molecules H by solar energy2O, promoting the reaction, lowering the potential barrier and generating hydrogen which is a clean energy carrier. Because clean water is generated by combustion and utilization of hydrogen, the photolysis water technology has great potential in the aspects of new energy and environmental management, low cost, environmental friendliness, sustainable development and the like.
Utilization of TiO from Fujishima, university of Tokyo, Japan2Subjecting the single crystal to lightAfter the catalytic reaction decomposes water into hydrogen and oxygen, a large number of theories and experiments are dedicated to the development and application research of photocatalytic materials. In recent years, there have been developed photocatalysts such as metal oxides, sulfides, pure metals, and metal-free semiconductor materials. Meanwhile, the graphene-like two-dimensional material also shows excellent photocatalytic performance with higher chemical stability, semiconductivity and excellent optical properties. The recent professor Kangzhenghui of Suzhou university synthesizes a novel carbon nanodot-carbon nitride (C)3N4) The nano composite photocatalyst realizes efficient and complete water decomposition by utilizing solar energy, and the energy conversion efficiency from the solar energy to the hydrogen can reach 2%.
However, the technical bottleneck of hydrogen collection and storage inhibits the wide-range application of hydrogen production by photolysis of water. The generation of hydrogen relies on the separation of photogenerated electron holes, and in order for the electron holes to drive the reaction efficiently, the photocatalyst reduction and oxidation active site spacing is limited by the maximum charge mobility range. In addition, the protons generated at the oxidation site migrate to the reduction site to evolve hydrogen, and the distance between the reduction and oxidation sites is also required to be not too large. Shorter active site spacing increases the probability of reverse reactions occurring, while also collecting and storing pure H for oxygen removal2Presenting difficulties.
Therefore, efficient hydrogen production and H purification are designed and developed2Before the safe hydrogen storage method, the photocatalytic water splitting hydrogen production cannot be really implemented in a large range.
Disclosure of Invention
In view of the above, the present invention provides a graphene-based composite material, and a preparation method and an application thereof, and the graphene-based composite material provided by the present invention can be used for preparing hydrogen by catalytic cracking of water under an illumination condition, and can be used for effectively purifying and safely storing the prepared hydrogen.
The invention provides a graphene-based composite material, which comprises:
a single layer of carbon nitrogen material;
and graphene bonded to both sides of the single layer of carbon nitrogen material by van der waals forces.
Preferably, the sheetThe carbon-nitrogen-containing material comprises a single layer of C3N4。
Preferably, the graphene comprises unmodified graphene and/or functional group modified graphene; the functional group modified graphene comprises one or more of graphene oxide, metal-doped graphene, non-metal-doped graphene, metal and non-metal co-intercalated graphene and defective graphene.
Preferably, the graphene oxide comprises hydroxylated graphene oxide and/or epoxidized graphene oxide;
the doped metal of the metal-doped graphene comprises one or more of Zn, Cu, Fe, Co and Ni;
the doped nonmetal of the nonmetal-doped graphene comprises Si and/or N;
the embedding material for embedding the metal and the nonmetal into the graphene comprises TiN4。
The invention provides a preparation method of the graphene-based composite material in the technical scheme, which comprises the following steps:
a1) mixing the single-layer carbon-nitrogen material with water and then atomizing to obtain mist;
a2) and contacting the fog with the single-layer graphene film, then covering the fog contact side of the single-layer graphene film with another single-layer graphene film, and drying to obtain the graphene-based composite material.
Preferably, in step a2), ethanol is added to the mist contact side before another single-layer graphene film is covered.
The invention provides a preparation method of the graphene-based composite material in the technical scheme, which comprises the following steps:
b1) mixing and reacting the single-layer carbon-nitrogen material, the graphene, the ammonia and the hydrazine in water to obtain a reaction solution;
b2) and filtering the reaction solution to form a film, and drying to obtain the graphene-based composite material.
Preferably, in the step b1), the reaction temperature is 90-99 ℃; the reaction time is 4-8 h.
Preferably, step b1) specifically comprises:
mixing the single-layer carbon and nitrogen material, graphene and ammonia in water to obtain a mixed solution; and then mixing the mixed solution with hydrazine for reaction to obtain a reaction solution.
The invention provides a method for producing hydrogen and storing hydrogen, which comprises the following steps:
under the illumination condition, water is cracked in the presence of the composite material or the composite material prepared by the method in the technical scheme to obtain hydrogen; the hydrogen gas is stored in the composite material.
Compared with the prior art, the invention provides a graphene-based composite material and a preparation method and application thereof. The graphene-based composite material provided by the invention comprises a single-layer carbon-nitrogen material; and graphene bonded to both sides of the single layer of carbon nitrogen material by van der waals forces. In the invention, the graphene and the carbon and nitrogen material in the composite material have an action mode of intermolecular van der Waals force, the carbon and nitrogen material is positioned between two layers of graphene, the binding energy is strong, and a composite structure can exist stably; and the composite material has good light absorption capacity in the ultraviolet and visible light range of solar energy, and can efficiently collect solar energy, so that the composite material is suitable for the field of photocatalysis. In the invention, the process of the composite material for catalytically cracking water is as follows: the graphene and the carbon and nitrogen material in the composite material have a difference of work functions, the carbon and nitrogen material generates charge polarization after absorbing photon energy, photo-generated electron holes are separated in the composite material, the holes are transmitted to the outer layer graphene, and electrons stay in the carbon and nitrogen material wrapped in the inner layer; then, the graphene in the composite material can be efficiently catalytically cracked to generate protons with the help of the photo-generated holes; then, protons generated by the driving of the photogenerated holes in the composite material can penetrate through the graphene and migrate to the carbon-nitrogen material under the action of the electrostatic attraction of the carbon-nitrogen material, and then the protons and the photogenerated electrons on the carbon-nitrogen material undergo a reduction reaction to generate hydrogen. In the present invention, H is generated in the composite material2Cannot penetrate graphene, will be stored in the inner layer structure of the composite material, and OH and O2Etc. are also isolated outside the graphene, and thusThe composite material can effectively purify and safely store hydrogen prepared by water splitting.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 shows a GR/GO-C device according to an embodiment of the present inventionxNy-uv-vis absorption spectrum of GR/GO;
FIG. 2 is a g-C representation of an embodiment of the present inventionxNyAnd GR/GO-CxNy-band structure diagram of GR/GO;
FIG. 3 shows GR, GO, and C provided by embodiments of the present inventionxNyWork function graph of (a);
FIG. 4 is a differential charge distribution diagram of GR/GO-CN-GR/GO according to an embodiment of the present invention;
FIG. 5 shows a GR/GO-C device according to an embodiment of the present invention2Differential charge profile of N-GR/GO;
FIG. 6 shows a GR/GO-C device according to an embodiment of the present invention3N4-differential charge profile of GR/GO;
FIG. 7 is a hole evolution diagram of GR-CN according to an embodiment of the present invention;
FIG. 8 is a diagram illustrating a catalytic cracking water adsorption configuration and a photo-generated hole distribution of a graphene material according to an embodiment of the present invention;
FIG. 9 shows proton penetration GR-C provided by practice of the invention3N4A process diagram;
FIG. 10 shows GR-C provided for practicing the invention3N4-the most stable pattern of GR adsorption of one H atom and storage of one hydrogen molecule;
FIG. 11 shows GR-C provided for practicing the invention3N4-the GR stores the optimum pattern for different amounts of hydrogen;
FIG. 12 shows GR-C provided for practicing the invention3N4-graph of graphene deformation energy at different hydrogen storage rates for GR;
FIG. 13 is a schematic representation of a preferred embodiment of the present invention
Figure BDA0001474221270000041
Graph of the change of applied external pressure at different hydrogen storage rates at the interlamellar spacing.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a graphene-based composite material, which comprises:
a single layer of carbon nitrogen material;
and graphene bonded to both sides of the single layer of carbon nitrogen material by van der waals forces.
The graphene-based composite material provided by the invention comprises a single-layer carbon-nitrogen material and graphene combined on two sides of the single-layer carbon-nitrogen material to form a sandwich structure. Wherein the single-layer carbon-nitrogen material is preferably graphite-like phase carbon-nitrogen material, including but not limited to single-layer CN and single-layer C2N or a single layer of C3N4. The source of the single layer carbon nitrogen material is not particularly limited in the present invention, and may be commercially available or prepared by a method well known to those skilled in the art, as a single layer C3N4For example, the preparation method can be as follows:
I) carbonizing melamine to obtain a bulk phase C3N4；
II) subjecting said bulk phase C3N4Grinding into powder, and heating to obtain C3N4Nanosheets;
III) adding said C3N4Nanosheet liquid-basedUltrasonic centrifugation is carried out on the phases to obtain a monolayer C3N4。
In the preparation method provided by the invention, the carbonization temperature in the step I) is preferably 500-600 ℃, and more preferably 550-560 ℃; the carbonization time in the step I) is preferably 2-6 h, and more preferably 3-4 h. The heating temperature in the step II) is preferably 480-580 ℃, and more preferably 530-540 ℃; the heating time in the step II) is preferably 100-200 min, and more preferably 150-160 min. The liquid phase in step III) is preferably an aqueous isopropanol solution; the time of the ultrasonic centrifugation in the step III) is preferably 2-6 h. More preferably 3 to 4 hours.
In the present invention, the graphene is bonded to both sides of the single layer of carbon nitrogen material by van der waals forces. Wherein the graphene comprises unmodified Graphene (GR) and/or graphene modified by functional groups. In the present invention, the functional group-modified graphene includes, but is not limited to, one or more of graphene oxide, metal-doped graphene, non-metal-doped graphene, metal and non-metal co-intercalated graphene, and defective graphene. In the present invention, the graphene oxide includes but is not limited to hydroxylated graphene oxide (abbreviated as GO)OH) And/or epoxylated graphene oxide (GOo for short); the doping metal of the metal-doped graphene includes but is not limited to one or more of Zn, Cu, Fe, Co and Ni; doped non-metals of the non-metal doped graphene include, but are not limited to, Si and/or N; the embedding material for embedding the metal and the nonmetal into the graphene comprises but is not limited to TiN4. In the present invention, the source of the graphene is not particularly limited, and the graphene may be commercially available, or may be prepared according to a method known to those skilled in the art, and for example, unmodified graphene may be prepared according to the following method:
i) depositing nickel on the substrate to form a nickel layer;
ii) depositing graphene on the nickel layer to form a graphene layer;
iii) transferring the graphene layer to a transfer substrate.
In the above production process provided by the present invention, the group in step i)The slice can be SiO2a/Si sheet; the deposition in step i) is preferably by electron beam evaporation deposition. The deposition in step ii) is preferably carried out by vapor deposition, the vapor deposition preferably comprising charging Ar and H into a reactor in which a nickel layer is placed2Then is refilled with CH4And H2Carrying out vapor deposition reaction; wherein Ar and H are charged2The temperature is preferably 900-1000 ℃, and the time is preferably 20-30 min; is charged into the CH4And H2The temperature of the reaction is preferably 1000-1100 ℃, and the time is preferably 5-10 min. The transfer substrate in step iii) is preferably a polyethylene terephthalate (PET) film.
Taking graphene oxide as an example, the graphene oxide can be prepared according to the following method:
s1), mixing graphite and concentrated sulfuric acid, and adding KMnO into the mixed system4Obtaining a mixed solution;
s2), heating the mixed solution for reaction to obtain a first reaction solution;
s3), mixing the first reaction solution with water and hydrogen peroxide for reaction to obtain a second reaction solution;
s4), and sequentially carrying out standing and solid-liquid separation on the second reaction solution to obtain a solid;
s5) and washing and drying the solid to obtain the graphene oxide.
In the preparation method provided by the invention, the using amount ratio of the graphite to the concentrated sulfuric acid in the step s1) is preferably (1-5) g: (20-100) mL, more preferably (2-3) g: (50-60) mL; step s1) of the graphite and KMnO4Is preferably 1: (0.5 to 2), and more preferably 1: 1. The reaction temperature in the step s2) is preferably 25-50 ℃, and more preferably 35-40 ℃; the reaction time in the step s2) is preferably 10-60 min, and more preferably 30-40 min. The dosage ratio of the water in the step s3) to the graphite in the step s1) is preferably (400-600) mL: (1-5) g, more preferably (450-500) mL: (2-3) g; the dosage ratio of the hydrogen peroxide in the step s3) to the graphite in the step s1) is preferably (10-30) mL: (1-5) g, more preferably (15-20) mL: (2-3) g; described in step s3)The reaction temperature is preferably 25-50 ℃, and more preferably 35-40 ℃; the time for the reaction in step s3) is not particularly limited, but the reaction is preferably stopped when the color of the reaction solution turns to a golden yellow color; in step s3), the first reaction solution is preferably mixed with part of water, and then hydrogen peroxide and the balance of water are mixed with the first reaction solution, wherein the ratio of the part of water to the graphite in step s1) is preferably (80-150) mL: (1-5) g, more preferably (100-120) mL: (2-3) g, and the time for mixing the first reaction liquid and part of water is preferably 15-20 min. The standing time in the step s4) is preferably 8-20 h, and more preferably 12-15 h. The manner of washing in step s5) preferably comprises acid washing and water washing in sequence, wherein the acid washing solution of the acid washing is preferably 5 wt% hydrochloric acid aqueous solution.
The invention also provides a method for preparing the graphene-based composite material in the technical scheme, which comprises the following steps:
a1) mixing the single-layer carbon-nitrogen material with water and then atomizing to obtain mist;
a2) and contacting the fog with the single-layer graphene film, then covering the fog contact side of the single-layer graphene film with another single-layer graphene film, and drying to obtain the graphene-based composite material.
In the preparation method of the composite material provided by the invention, firstly, the single-layer carbon-nitrogen material and water are mixed and atomized. The device for carrying out the atomization is preferably a humidifier. Atomizing to obtain mist containing the single-layer carbon and nitrogen material.
And after obtaining the fog, contacting the fog with the single-layer graphene film, so that a single-layer carbon and nitrogen material can be adhered to the contact side of the single-layer graphene film and the fog. In the present invention, the contacting is preferably performed by introducing the mist into the container and then covering the single-layer graphene film on the mist. And then covering another single-layer graphene film on the fog contact side of the single-layer graphene film. In the invention, in order to reduce the surface tension, a single-layer graphene film can be flatly paved on the surface of a single-layer carbon and nitrogen material, and ethanol is preferably added to the mist contact side before another single-layer graphene film is covered. After covering another single-layer graphene film, drying is performed. Wherein the drying temperature is preferably 50-60 ℃; the drying time is preferably 0.5-1 h. And (5) after drying is finished, obtaining the graphene-based composite material.
The invention also provides another method for preparing the graphene-based composite material in the technical scheme, which comprises the following steps:
b1) mixing and reacting the single-layer carbon-nitrogen material, the graphene, the ammonia and the hydrazine in water to obtain a reaction solution;
b2) and filtering the reaction solution to form a film, and drying to obtain the graphene-based composite material.
In the preparation method of the composite material provided by the invention, firstly, a single-layer carbon-nitrogen material, graphene, ammonia and hydrazine are mixed and reacted in water, and the process specifically comprises the following steps:
firstly, mixing a single-layer carbon and nitrogen material, graphene and part of water to obtain a mixed suspension; the concentration of the mixed suspension is preferably 0.05-5 mg/mL, and more preferably 0.1-0.2 mg/mL. And then mixing the mixed suspension with ammonia, wherein the ammonia is preferably ammonia water, the concentration of the ammonia water is preferably 25-26 wt%, and the volume ratio of the ammonia water to the mixed suspension is preferably (0.5-2): (100-500), more preferably (0.7-1): (200-300); the mixing is preferably carried out under the ultrasonic condition, and the mixing time is preferably 1-2 h. And then mixing a mixture consisting of the mixed suspension and ammonia with hydrazine for reaction, wherein the volume ratio of the hydrazine to the mixed suspension is preferably (0.05-0.2): (100-500), more preferably (0.08-0.1): (200-300); the reaction temperature is preferably 90-95 ℃, and the reaction time is preferably 4-8 h, and more preferably 5-6 h. After the reaction, a reaction solution was obtained.
And after the reaction solution is obtained, filtering the reaction solution to form a membrane. Wherein the filtration device is preferably a mixed cellulose ester membrane filter; the filtration is preferably by vacuum filtration. And (3) stripping the membrane from the filtering device after membrane formation, and drying to obtain the graphene-based composite material. Wherein the drying mode is preferably freeze-drying.
The composite material provided by the inventionThe graphene and the carbon and nitrogen material have the action mode of intermolecular van der Waals force, the carbon and nitrogen material is positioned between two layers of graphene, the binding energy is strong, and a composite structure can exist stably; and the composite material has good light absorption capacity in the ultraviolet and visible light range of solar energy, and can efficiently collect solar energy, so that the composite material is suitable for the field of photocatalysis. On the other hand, by utilizing the efficient selective permeability of the graphene, the composite material disclosed by the invention allows protons to penetrate through the graphene to participate in a reaction, and newly generated hydrogen cannot escape, and OH and O are blocked2And the reverse reaction is inhibited when the hydrogen enters the system, and the effective purification and safe storage of the hydrogen are realized, so that the composite material is also suitable for the field of hydrogen storage.
The working mechanism of the composite material catalytic cracking water provided by the invention is as follows: (1) the composite material generates photo-induced excitons by absorbing visible light and ultraviolet light, and the photo-induced excitons are rapidly separated into high-energy holes and electrons and respectively migrate to the outer graphene-based material (oxidation sites) and the inner carbon and nitrogen material (reduction sites); (2) the photogenerated holes migrated to the graphene-based material are gathered near the active site and attack the water molecules adsorbed on the surface to drive water to generate protons through cracking; (3) driven by the electrostatic attraction on the carbon and nitrogen material of the inner layer, the newly generated protons can penetrate through the graphene-based material of the outer layer and move to the carbon and nitrogen material; (4) the protons migrated to the carbon and nitrogen material are gathered around the N atoms enriched with photo-generated electrons, and are driven by the photo-generated electrons to react to generate hydrogen; (5) since hydrogen cannot penetrate the graphene-based material, it will be retained within the graphene on both sides of the outer layer, while at the same time O2OH and the like can not enter the composite material, so that the occurrence of reverse reaction is inhibited, and the effective purification and safe storage of hydrogen under high hydrogen storage rate are realized.
The graphene-based composite material provided by the invention mainly has the following advantages:
1) the high-efficiency selective permeability of the graphene material is skillfully utilized, namely, only protons are allowed to penetrate to participate in the reaction, the generated hydrogen cannot escape, and OH and O are blocked2The reverse reaction is inhibited and the composite material is realizedEffective purification and safe storage of hydrogen.
2) Clean solar energy is converted into hydrogen energy by using low-cost materials containing little metal, hydrogen production and safe hydrogen storage are integrated by collecting light catalytic cracking water, the hydrogen production and storage cost is effectively reduced, and the large-scale application of the hydrogen energy is favorably realized.
3) The two bottleneck problems of the most difficult hydrogen separation and safe storage and transportation in hydrogen energy utilization are solved, and a new way is opened up for the concept design and the practical application of converting solar energy cracked water into hydrogen energy.
The invention also provides a method for producing hydrogen and storing hydrogen, which comprises the following steps:
under the illumination condition, water is cracked in the presence of the composite material or the composite material prepared by the preparation method in the technical scheme to obtain hydrogen; the hydrogen gas is stored in the composite material.
In the hydrogen production and storage method provided by the invention, the composite material is used as a photocatalytic material for water cracking, so that hydrogen can be produced by catalytically cracking water under the illumination condition, and the produced hydrogen can be effectively purified and safely stored. The method provided by the invention simultaneously solves two bottleneck problems of difficult hydrogen separation and safe storage and transportation in hydrogen energy utilization, and opens up a new way for realizing the concept design and practical application of converting solar energy cracked water into hydrogen energy.
The invention also provides an application of the composite material prepared by the technical scheme or the composite material prepared by the preparation method in hydrogen production by photolysis of water.
In the application provided by the invention, the composite material can be used as a photocatalytic material, and not only can be used for preparing hydrogen by catalytic cracking of water under the illumination condition, but also can be used for effectively purifying and safely storing the prepared hydrogen. The application provided by the invention simultaneously solves two bottleneck problems of difficult hydrogen separation and safe storage and transportation in hydrogen energy utilization, and opens up a new way for realizing the concept design and practical application of converting solar energy cracked water into hydrogen energy.
For the sake of clarity, the following examples are given in detail.
Example 1
Preparation of the monolayer C3N4：
(1) Melamine is taken as a precursor, put into a crucible, covered with a cover, put into a muffle furnace to be heated to 550 ℃, carbonized for 4 hours, and then kept stand and cooled to obtain bulk phase C3N4；
(2) C prepared in the previous step3N4Grinding into powder, placing into crucible, covering with cover, heating in tubular furnace at 530 deg.C for 150min, standing, and cooling to obtain C3N4Nanosheets;
(3) c is to be3N4Placing the nanosheet into isopropanol solution, ultrasonically centrifuging for 4h, and vacuum drying to obtain monolayer C3N4。
Example 2
Preparation of Graphene (GR):
in SiO2Depositing a layer of nickel on the Si sheet by electron beam evaporation, and then filling Ar and H at about 900-1000 DEG C2About 20min, then filling CH for 5-10 min at 1000 DEG C4And H2Then CVD reaction can be carried out, and graphene is deposited on the nickel sheet.
And (3) wet transferring the generated graphene onto a PET carrier to obtain the graphene/PET film.
Example 3
Preparing Graphene Oxide (GO):
2g of graphite is added into 50mL of concentrated sulfuric acid, and the mixture is fully stirred until the mixture is dispersed. Then, 2g of KMnO was slowly added thereto while stirring in an ice bath4. Then reacting the mixed solution in a water bath at 35-40 ℃ for 30min, adding 100mL of water, stirring and reacting for 15min, and then continuously adding 350mL of water and 15mL of H2O2And (4) stirring vigorously, standing for 12h when the solution turns golden yellow, and pouring out the supernatant. And washing the rest bottom solid by using 5 wt% hydrochloric acid, washing the bottom solid by using high-purity water for multiple times, then centrifugally washing, and drying in vacuum to obtain the graphene oxide.
Example 4
Preparation of graphene-based compositeMaterial (GR-C)3N4–GR)：
The monolayer C obtained in example 13N4Dissolved in water and nebulized with a commercial humidifier. Then atomized C3N4The mixture is introduced into a beaker and covered by the graphene film prepared in example 2 to obtain GR-C3N4And (3) a membrane.
Then in the GR-C obtained3N4C of the film3N4And (3) dropwise adding ethanol, quickly covering another layer of graphene film prepared in example 2, and finally drying at 60 ℃ for half an hour to obtain the graphene-based composite material.
Referring to the method provided in this example, the graphene/PET film was replaced with the functional group-modified graphene/PET film, and the monolayer C was formed3N4And replacing the graphene with other single-layer carbon and nitrogen materials to prepare other graphene-based composite materials.
Example 5
Preparation of graphene-based composite (GR-C)3N4–GR)：
Monolayer C prepared in example 13N4And graphene oxide prepared in example 3 was mixed in water to prepare 200mL of a mixed suspension of 0.1mg/mL, then 700 μ L of 25 wt% ammonia was added, the mixture was uniformly mixed by sonication for 1 hour, then 80 μ L of hydrazine was added, after reaction for 6 hours at 95 ℃, the mixture was vacuum-filtered through a mixed cellulose ester membrane filter, and the product was peeled off from the filter membrane and lyophilized to obtain a graphene-based composite material.
Referring to the method provided in this example, graphene oxide was replaced with graphene modified with other functional groups or unmodified graphene, and the monolayer C was formed3N4And replacing the graphene with other single-layer carbon and nitrogen materials to prepare other graphene-based composite materials.
Example 6
Constructing an initial configuration through Material Studio, and performing structural optimization by using a VASP software package to verify that the composite Material can exist stably; based on the stable configuration, calculating the optical properties, charge distribution, hole evolution process and the like of the material, and confirming the efficient light absorption performance and charge separation capability of the composite material; adhesion meterCalculating the adsorption energy, the activation energy, the Gibbs energy and the like of the photo-generated cavity driven cracked water of the functional group modified graphene material, and analyzing the photolysis water reaction performance of the composite material; then simulating the process that protons are electrostatically attracted to penetrate through the graphene material to enter the inner-layer carbon and nitrogen material, verifying that the protons can penetrate through the graphene material, and investigating the protons moving to the carbon and nitrogen material to generate hydrogen (H) under the assistance of electrons2) Performance of (d); and finally, researching the hydrogen storage rate of the composite material and simulating the hydrogen storage performance of the composite material. The method specifically comprises the following steps:
1. electron hole separation
(a) Stability of composite materials
According to known formula CxNy(single layer carbon nitrogen material) and GRF(graphene material) configuration, construction of GRF–CxNy–GRFAnd (3) a composite material model, and optimizing under the condition of considering Van der Waals correction. With CxNyAnd GR (unmodified graphene)/GO (graphene oxide) for example, we selected the relatively stable graphite-like carbon-nitrogen material (g-CN, g-C)2N,g-C3N4) The interlamellar spacing and binding energy of the optimized composite material are shown in table 1:
TABLE 1 GR/GO-C in the practice of the inventionxNyBinding energy and interlayer spacing of-GR/GO
Figure BDA0001474221270000111
As can be seen from Table 1, example CxNyAnd GR/GO layers spacing and binding energy ranges, respectively
Figure BDA0001474221270000112
And 1.02-3.73 eV, which shows that the composite material can exist stably.
(b) Light absorption Properties
Calculating the light absorption properties and band information of the composite material based on the stable configuration, as CxNy，GR，GR/GO–CxNyFor example, GR/GO is shown in FIGS. 1 and 2, and FIG. 1 shows the present inventionGR/GO-C provided by the illustrative embodimentxNy-GR/GO, UV-visible absorption spectrum, FIG. 2 is a graph of g-C provided by an example of the inventionxNy(graphite-like carbon and nitrogen material) and GR/GO-CxNy-band structure of GR/GO.
As can be seen from the figure, pure CxNyPrimarily absorbing ultraviolet light. When the composite material is compounded with GR/GO, the band gap of the composite material is narrowed due to the coupling effect between the GR/GO and the GR/GO, the composite material has good absorption capacity in the visible light and ultraviolet light ranges of solar energy reflected on light absorption, solar energy can be effectively captured, and photogenerated excitons are generated.
(c) Electron hole separation
The generated photogenerated excitons need to be separated and respectively transferred to the oxidation active site and the reduction active site, and the driving force is the work function difference between the graphene material and the carbon-nitrogen material. With CxNyGR/GO is taken as an example, the results are shown in FIG. 3, FIG. 3 is GR, GO and C provided by the embodiment of the inventionxNyWork function diagram of (2).
As can be seen from FIG. 3, CxNyThe GR/GO has a large work function and a phase difference range of 1.7-2.91 eV. Driven by the difference of work functions, when the two materials are compounded, charge polarization occurs, and electrons and holes are induced to generate different flow directions, so that separation is realized.
The results of the composite structure's Bader charge and differential charge also validate this conclusion. With GR/GO-CxNyFor example, the GR/GO is shown in table 2 and fig. 4 to 6, wherein fig. 4 is a differential charge distribution diagram of GR/GO-CN-GR/GO provided by the embodiment of the present invention, and fig. 5 is a differential charge distribution diagram of GR/GO-C provided by the embodiment of the present invention2Differential charge distribution diagram of N-GR/GO, FIG. 6 is a schematic diagram of GR/GO-C provided by an embodiment of the present invention3N4-differential charge profile of GR/GO. In FIGS. 4-6, the neutral finger system is in the ground state, 1 e-finger system is added, one photo-generated electron is added, and 1h is added+The system adds a photogenerated hole, a blue area represents a hole, and a yellow area represents an electron; FIGS. 4-6 are divided into 9 small images by two horizontal and two vertical dotted lines, each small image is composed of an upper image and a lower imageThe composition, taking the upper left small figure in fig. 4 as an example, the upper image of the figure resembling a "diamond" is a top view of the GR-CN-GR composite, and the lower image resembling a "sandwich" structure is a side view of the GR-CN-GR composite.
TABLE 2 GR/GO-CxNyBader Charge analysis Table of-GR/GO
Figure BDA0001474221270000121
Figure BDA0001474221270000131
As can be seen from Table 2 and FIGS. 4 to 6, the inner layer of the composite material was transferred by 0.34 to 0.72 (with CN) and 0.18 to 0.20 (with C) before photoexcitation2N complex) and 0.16 to 0.25 (with C)3N4Recombination) unit positive charges (holes) to the GR/GO material of the outer layer, verifying the good electron-hole separation capability of the composite structure.
Further simulation of hole evolution further supports this ability of the composite. Taking GR-CN as an example, the result is shown in fig. 7, fig. 7 is a hole evolution distribution diagram of GR-CN provided by the embodiment of the present invention, and fig. 7a and 7b are evolution processes of low-energy and high-energy holes, respectively. As can be seen in fig. 7, approximately 14% of the low energy holes in the composite will move from the CN material to the GR layer within 3 ps; at higher hole energies, more than 80% of the holes are rapidly transferred to the GR layer within a few ps. This ultra-fast charge transfer is sufficient to compete with electron-hole recombination, enabling efficient separation of electron holes.
As can be seen from Table 2 and FIGS. 4 to 7, when the inner layer carbon nitride material absorbs photon energy, charge polarization is generated, and photo-generated electron holes in the composite material are induced to be separated. With GR/GO-CxNyFor example, the addition of a photogenerated hole can be 1.17-1.59 (in combination with CN), 1.01-1.10 (in combination with C)2N complex) and 1.01 to 1.23 (with C)3N4Recombination) of the unit cavities to the GR/GO material of the outer layer; and, correspondingly, addAfter photo-generated electrons, 0.68-0.87, 0.33-0.45 and 0.32-0.33 unit of electrons are respectively gathered in CN, C of the inner layer2N and C3N4On the material.
As can be seen from fig. 3-7 and table 2, the composite material of the present invention can generate effective electron-hole separation driven by the work function difference, the electrons stay in the carbon-nitrogen material wrapped in the inner layer, and the holes are transported to the outer graphene-based material.
2. Photo-generated hole-driven cracking water
(a) Surface water adsorption
The water splitting reaction in the composite material starts from the adsorption of water molecules on the surface of the graphene modified by the functional group. By GRZn(Zn-doped graphene), GRCu(Cu-doped graphene), GRFe(Fe-doped graphene), GRCo(Co-doped graphene), GRNi(Ni-doped graphene), GRSi(Si-doped graphene), GRN(N-doped graphene), GRTiN4(TiN4Doped graphene), GRCv(defective graphene), GOOH、GOOFor example, the adsorption energy range of the water molecules is 0.07-1.05 eV, which indicates that the water molecules can be stably adsorbed on the graphene modified by the functional group to participate in the reaction.
(b) Distribution of photogenerated holes
On the other hand, photogenerated holes transported to the outer graphene material will collect near the active site, providing the energy required for water splitting. By GRCo/GO–CN–GRCoFor example,/GO, the stable configuration of the graphene material after water adsorption and the charge distribution after adding one photo-generated hole are shown in fig. 8, fig. 8 is a catalytic cracking water adsorption configuration and a photo-generated hole distribution diagram of the graphene material according to the embodiment of the present invention, where the upper diagram is the stable configuration of the graphene material after water adsorption, and the lower diagram is the charge distribution diagram after adding one photo-generated hole to the graphene material. As can be seen from the figure, the photogenerated holes are localized in the reactive site region, driving the water to undergo an oxidation reaction.
(c) Water splitting energy barrier
In addition, the existence of the functional group can effectively reduce the energy barrier of water cracking. To be provided withGRZn，GRCu，GRFe，GRCo，GRNi，GRSi，GRN，GRTiN4，GRCv，GOOH，GOOFor example, the energy barrier for the cleavage water is shown in table 3:
table 3 adsorption energy of graphene material to water molecule (E)ads) And the energy barrier to cracking water (E)b)
Figure BDA0001474221270000141
Known as the water splitting energy barrier (E)b) From 5.13eV for pure water to 3.64eV for graphene and finally to a comparatively lower about 0.5 eV. In an actual photolytic water reaction, photogenerated holes accumulated on the graphene-based material can overcome the energy barriers and drive water to crack.
(d) Gibbs free energy of water splitting
The addition of holes also contributes to the reduction of the Gibbs free energy of the water splitting reaction. Using GO as an example, the results are shown in table 4:
TABLE 4 GO cleavage Water Gibbs free energy
Neutral property GOOH GOO
ΔG(eV) 1.55 2.34
Adding for 1h+ GOOH GOO
ΔG(eV) 1.08 1.67
It can be seen that after injection of holes, the water-cleaved Gibbs can be removed from GO under previously neutral conditionsOHAnd GOODecreases to 1.08eV and 1.67eV, indicating that holes can also thermodynamically assist the hydrolysis reaction.
Comprehensively, the photo-generated holes in the composite material drive water molecules adsorbed at the active sites of the graphene material to be cracked, and protons are generated.
3. Proton penetrating graphene-based materials
Protons generated by the driving of the photogenerated holes are under the action of the electrostatic attraction of the carbon and nitrogen material of the inner layer, penetrate through the graphene-based material of the outer layer and move to the carbon and nitrogen material of the inner layer. With GR/GO-CxNyFor example, at equilibrium spacing, the coulombic interaction energy range of protons with the GR/GO inner layer is shown in table 5:
TABLE 5 GR/GO-CxNy-GR/GO intermediate CxNyCoulomb electrostatic interaction energy to proton
Figure BDA0001474221270000151
As can be seen from Table 5, the coulomb interaction energy range of the proton and the GR/GO of the inner layer is 1.48-4.04 eV at the equilibrium distance. This interaction energy is sufficient to overcome the proton penetration graphene-based energy barrier (about 1.23eV), so that the proton penetration process is successfully achieved.
With GR-C3N4For example, further molecular dynamics calculations simulated the movement of protons through graphene into carbon nitride material, and the results are shown in fig. 9, where fig. 9 provides proton penetration GR-C for the practice of the present invention3N4The process diagram, wherein the left diagram is the proton does not penetrate the graphene, and the middle diagram is the protonThe proton has just penetrated the graphene and the right picture is the proton movement onto the carbon nitride material. It can be known from fig. 9 that protons can penetrate through the graphene material, achieving separation and transmission.
Comprehensively, the protons in the composite material can penetrate through the outer graphene-based material and move to the inner carbon nitrogen material.
4. Electron driven hydrogen evolution reaction
The protons transferred to the inner layer carbon nitrogen material react with the help of photo-generated electrons to generate hydrogen. With GR-C3N4FIG. 10 shows the results of the GR example, FIG. 10 is the GR-C provided by the present invention3N4-GR scheme for the adsorption of one H atom (FIG. 10a) and storage of the most stable configuration of one hydrogen molecule (FIG. 10 b). As can be seen from fig. 10, after the proton penetrates the graphene, the stable configuration is C3N4The upper N atom is bonded to a bond. At this time, electrons will gather and distribute around the N atom, and these gathered electrons attract other protons by electrostatic action, are driven by the photo-generated electrons, and combine with the previously adsorbed protons to generate hydrogen. Since hydrogen cannot penetrate the graphene-based material, and OH and O2And the like are also isolated at the outer side of the graphene group, so that the occurrence of reverse reaction is inhibited, and the effective purification and separation of the hydrogen are realized.
In conclusion, the protons transferred to the inner layer carbon and nitrogen material in the composite material of the invention are driven by the photo-generated electrons to precipitate hydrogen and remain in the composite material.
5. Composite material for storing hydrogen safely
After the inner layer carbon nitrogen material absorbs sunlight, enough photoproduction holes and electrons can be provided to respectively drive the outer layer water cracking reaction and the inner layer hydrogen evolution reaction, and more hydrogen is generated. Due to the efficient selective permeability of graphene-based materials, newly generated hydrogen that cannot escape will be safely stored within the composite. With GR-C3N4Taking GR as an example, the hydrogen storage performance of the composite material is simulated through quantitative calculation, the results are shown in FIGS. 11-12, FIG. 11 is GR-C provided by the invention3N4FIG. 12 is a graph of the optimum structure of GR for storing different amounts of hydrogen, the GR-C3N4-graphene deformation energy diagram at different hydrogen storage rates of GR. As can be seen from FIGS. 11 to 12, when the composite structure is completely released and the hydrogen storage rate is from 0 to 5.2 wt% (mass%), the interlayer distance is increased to the maximum
Figure BDA0001474221270000161
The deformation energy of the outer layer graphene is only 0.001-0.012 eV, which shows that the stored hydrogen hardly causes deformation of the outer layer graphene under the condition.
In addition, the range of interlayer spacing can be maintained on the outer graphene layer under conditions that store varying amounts of hydrogen when pressure is applied. With GR-C3N4-GR composite with interlayer spacing
Figure BDA0001474221270000162
For example, the results are shown in FIG. 13, FIG. 13 is a graph of the results of the present invention
Figure BDA0001474221270000171
Graph of the change of applied external pressure at different hydrogen storage rates at the interlamellar spacing. As can be seen in fig. 13, when an external pressure of about 56bar is applied to the outer graphene layer, the external pressure may be applied to the outer graphene layer
Figure BDA0001474221270000172
A hydrogen storage rate of 5.2 wt% was achieved at the interlamellar spacing, which is comparable to the applied pressure values reported in the literature for other materials. More importantly, the hydrogen storage rate at this point is already approaching the U.S. agency's commercial hydrogen storage standard (6.5 wt%).
In conclusion, the composite material utilizes the efficient selective penetrability of the graphene, allows protons to penetrate and participate in the reaction, and prevents newly generated H2Escape and outer OH, O2And the hydrogen can be effectively purified and safely stored by entering the hydrogen storage tank.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (3)

1. A preparation method of a graphene-based composite material comprises the following steps:
1) mixing and reacting the single-layer carbon-nitrogen material, the graphene oxide, ammonia and hydrazine in water to obtain a reaction solution;
the reaction temperature is 90-99 ℃; the reaction time is 4-8 h;
2) filtering the reaction solution to form a film, and drying to obtain the graphene-based composite material;
the graphene-based composite material includes a single layer of carbon nitrogen material and graphene bonded to both sides of the single layer of carbon nitrogen material by van der waals forces.
2. The method of claim 1, wherein the single layer of carbon and nitrogen material comprises a single layer of C3N4。
3. The method according to claim 1, wherein step 1) comprises:
mixing the single-layer carbon and nitrogen material, graphene oxide and ammonia in water to obtain a mixed solution; and then mixing the mixed solution with hydrazine for reaction to obtain a reaction solution.
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