CN109550516B

CN109550516B - Carbon/carbon nitrogen (C)xNy) Composite nanotube composite material and preparation method and application thereof

Info

Publication number: CN109550516B
Application number: CN201811555774.5A
Authority: CN
Inventors: 江俊; 罗毅; 杨丽; 李鑫; 谢李燕; 王翕君
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2018-12-19
Filing date: 2018-12-19
Publication date: 2021-09-24
Anticipated expiration: 2038-12-19
Also published as: CN109550516A

Abstract

The invention belongs to the field of composite materials and application, and particularly relates to carbon/carbon nitrogen (C)_xN_y) A composite nanotube composite material and a preparation method and application thereof. The composite material of the present invention consists of carbon nitrogen (C) of the inner layer_xN_y) The carbon nanotubes are combined with the carbon nanotubes on the outer layer through van der Waals force. The composite structure has good light absorption capacity and can efficiently capture solar energy, so that the composite material can be used in the field of photocatalysis. Meanwhile, the carbon nano tube has high-efficiency selective penetrability to protons, only allows the protons to pass through the outer carbon nano tube under the action of electrostatic attraction to move to the carbon nitrogen material, and inhibits newly generated H₂Detachment and OH^‑And O₂The molecules enter the composite material to realize safe hydrogen storage, so the composite material is also suitable for the field of hydrogen storage.

Description

Carbon/carbon nitrogen (C)xNy) Composite nanotube composite material and preparation method and application thereof

Technical Field

The invention relates to the field of composite materials, in particular to carbon/carbon nitrogen (C)_xN_y) A composite nanotube composite material and a preparation method and application thereof.

Background

Since the 20 th century, the dependence on fossil fuels (coal, petroleum, natural gas, etc.) brings about various problems such as energy crisis and environmental pollution, and restricts the sustainable development of global economy. The search for alternative energy sources has become an urgent need of people at present. Among them, hydrogen energy is considered as one of the most promising clean energy sources in the future. The hydrogen is taken as an energy carrier and is mainly extracted from water, and meanwhile, the combustion product is also water, so that the hydrogen is pollution-free and recyclable. As a clean green energy with abundant reserves, wide sources and high energy density, the hydrogen energy has important strategic significance on the development of the economy in the whole world.

The use of hydrogen energy includes the aspects of hydrogen preparation, storage and transportation, and the key problem for developing hydrogen energy is the preparation, collection and storage of hydrogen gas. The photocatalysis hydrogen production technology for producing hydrogen by water by driving inexhaustible solar energy shows great potential due to the characteristics of low cost, environmental friendliness and the like. However, the technical bottleneck of hydrogen collection and storage limits its large-area application. The hydrogen is difficult to separate from the oxygen after being generated, thereby not only increasing the probability of reverse reaction, but also bringing the difficulty of purifying the hydrogen; meanwhile, safe and effective hydrogen storage is a long-term challenge, hydrogen and oxygen are mixed and then easily react to generate explosion, and the common pressure tank for hydrogen storage is low in safety and convenience. Therefore, before the two problems are really solved, the solar energy water-splitting hydrogen production can not be effectively applied in large scale.

Fortunately, the progress of the preparation technology of the large-area carbon nano-material brings new opportunities for storing hydrogen. Among them, the carbon nanotube has a hollow tubular structure and a large specific surface area, providing a natural excellent condition for storage of hydrogen. Since Dillon et al pioneered in 1977 that single-walled carbon nanotubes were used for hydrogen storage, the hydrogen storage properties of carbon nanotubes have gradually attracted much attention as a metal-free, inexpensive material.

The unique metallic and one-dimensional structure of carbon nanotubes makes them have strong electron transport properties. In addition, carbon nanotubes have high compressive strength, good mechanical properties and chemical properties, and thus are widely used in photocatalysis, chemical sensing and energy storage. Through the modification of functional groups of the carbon nano tube, such as doping, defects and the like, the hydrogen storage capacity of the carbon nano material is improved, and a good active site is provided for a water cracking reaction.

In another aspect, in g-C₃N₄Carbon and nitrogen (e.g. CN, C) as typified₂N，C₃N, etc.) exhibit high chemical stability, semiconductivity and excellent optical properties in photoelectrocatalysisExcellent performance. The novel nanotube structure formed by curling the two-dimensional carbon and nitrogen material inherits the good physical and chemical properties of the planar carbon and nitrogen material and is widely used for the photolysis water reaction. After the two materials are compounded, the van der Waals interaction between the two materials can realize ultra-fast charge transfer, and further effectively promote the separation of electrons and holes. Previous researches also show that after the carbon nano tube is compounded with a carbon and nitrogen material, the compounding of carriers can be inhibited, the charge transfer is enhanced, the service life of the carriers is prolonged, and the hydrogen generation speed is increased. In addition, the carbon nanotube structure also has highly effective selective permeability, which can only allow protons to pass through, but prevent other gases and functional groups from entering, so that the safe separation and storage of protons in the water splitting reaction can be facilitated by utilizing this characteristic.

Disclosure of Invention

The invention aims to provide carbon/carbon nitrogen (C)_xN_y) A composite nanotube composite material and a preparation method and application thereof. The composite material of the invention can be used in the field of photocatalysis, and simultaneously realizes cheap carbon/carbon nitrogen (C)_xN_y) The application of the safety hydrogen production and storage integration of the composite nanotube structure provides a theoretical basis.

The technical scheme adopted by the invention is as follows:

carbon/carbon nitrogen (C)_xN_y) The composite nanotube composite material is characterized in that: the composite material consists of carbon and nitrogen (C) of an inner layer_xN_y) The nano-tube and the carbon nano-tube wrapped on the outer surface of the nano-tube are formed by two parts, wherein x is any one of

natural numbers

1, 2 or 3, and y is a

natural number

1 or 4.

Preferably, the carbon nitrogen nanotubes of the inner layer and the carbon nanotubes of the outer surface are bonded together through Van der Waals force.

Preferably, the mass percentage of the carbon nitrogen nanotubes in the inner layer and the carbon nanotubes in the outer surface ranges from 28% to 30%.

Preferably, the outer layer nanotube material is unmodified carbon nanotube or carbon nanotube modified by functional groups.

Preferably, the functional group is modifiedThe carbon nano tube is a metal nitrogen doped carbon nano tube, and the metal nitrogen is selected from FeN₃、CoN₃、NiN₃、ZnN₃And CuN₃One or more of (a).

Preferably, the carbon nitrogen (C)_xN_y) The nanotube is C₃N₄A nanotube.

Carbon/carbon nitrogen (C)_xN_y) The preparation method of the composite nanotube composite material comprises the following steps:

a1) after depositing a metal film on the carbon nitride nanotube material, putting the carbon nitride nanotube material into a reaction kettle;

a2) introducing C in a certain proportion₂H₂And N₂The mixed gas enters a reaction kettle, and the temperature is increased to 480 ℃ and 520 ℃ for reaction for 4-6min to obtain the carbon nano tube deposited on the metal film;

a3) in N₂And cooling the reaction kettle under protection, soaking the carbon nano tube deposited on the metal film by using HCl solution to remove the metal catalyst, centrifuging, washing with water, and drying to obtain the carbon/carbon nitrogen CxNy composite nano tube material.

Preferably, C₂H₂And N₂The volume ratio of the mixed gas is (4-6): (94-96)

Preferably, the CVD reaction time is 5min at 500 ℃, and the length of the time influences the length of the nanotube.

The composite material of the invention is used as a photocatalyst. The composite material has good light absorption capacity in the ultraviolet light and visible light range, and can efficiently capture solar energy, so that the composite material is suitable for the field of photocatalysis.

The composite material disclosed by the invention is applied to hydrogen production by photolysis of water.

The process of catalytic cracking water in the composite material of the invention is as follows: the carbon nano tube modified by functional groups in the composite system has stronger coupling effect with the carbon nitrogen nano tube, so that interface polarization is generated, electrons and holes are induced to generate different flow directions, the holes are stably distributed on the carbon nano tube material in an aggregation manner, and most of corresponding electrons are distributed on the carbon nitrogen nano tube. Next functional groupThe modified carbon nano tube can efficiently catalyze and crack water with the help of the photoproduction cavity to generate protons. And then protons generated by the driving of the photogenerated holes can penetrate through the carbon nano tube modified by the functional groups under the action of the electrostatic attraction of the carbon nano tube, migrate to the carbon nano tube and generate reduction reaction with photogenerated electrons on the carbon nano tube to generate hydrogen. Newly generated H₂Since the carbon nanotube modified by the functional group cannot be penetrated, it will be stored in a composite structure, and OH and O₂Etc. are also isolated on the outer layer of the carbon nano tube, thereby realizing the purpose of safe hydrogen storage.

Carbon/carbon Nitrogen (C) of the invention_xN_y) In the composite nanotube system, the carbon nanotube modified by the functional group is a metal nitrogen-doped carbon nanotube; carbon-nitrogen nanotube of C₃N₄A nanotube. The carbon nano tube modified by functional groups in the nano tube composite system and the carbon nitrogen nano tube material have the action mode of intermolecular van der Waals force, and the carbon nitrogen nano tube is wrapped by the carbon nano tube and can stably exist. The composite system has good light absorption capacity in ultraviolet and visible light ranges, and can efficiently capture solar energy, so that the composite material is suitable for the field of photocatalysis.

Has the advantages that:

1. according to the composite material, the carbon nitrogen nanotubes on the inner layer and the carbon nanotubes modified by the functional groups coated on the outer layer form a nanotube composite structure which is combined by Van der Waals force and stably exists, the composite structure has good light absorption capacity, and solar energy can be efficiently captured, so that the composite material is suitable for the field of photocatalysis, and a novel efficient photocatalyst is provided for hydrogen production by photolysis of water.

2. The composite material consists of the inner carbon nitrogen nano tube layer and the outer carbon nano tube layer, the outer carbon nano tube layer has high-efficiency selective penetrability to protons, only allows the protons to pass through the outer carbon nano tube layer to move to the inner carbon nitrogen material layer under the action of electrostatic attraction, and inhibits newly generated H₂Free from OH and O₂The molecules enter the composite material to realize safe hydrogen storage, so the composite material is also suitable for the field of hydrogen storage.

Compared with the existing graphene-based composite material, the gas stored in the carbon nanotube material can be transmitted and collected through unique pipeline conduction, so that the phenomenon that local gas is too much and strong pressure is generated is effectively avoided, and the material is damaged and collapsed.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiment or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings according to the provided drawings without creative efforts.

The acronyms appearing herein are notes: CNT represents an unmodified carbon nanotube; CNT (carbon nanotube)_FRepresents a metallic nitrogen-doped carbon nanotube; CNNT represents carbon nitrogen nanotube.

FIG. 1 is an XRD pattern of carbon/carbon nitrogen and iron nitrogen doped/carbon nitrogen composite nanotube material provided in example 2 of the present invention;

FIG. 2 is a graph of the UV-visible absorption spectrum of a carbon/carbon-nitrogen and iron-nitrogen doped/carbon-nitrogen composite nanotube material provided in example 2 of the present invention;

FIG. 3 shows a CNT provided in example 3 of the present invention_F-uv-vis absorption spectrum of CNNT;

FIG. 4 shows CNT-CNNT and CNT provided in example 3 of the present invention_FeN3-charge distribution profile of CNNT conduction band bottom and valence band top;

FIG. 5 is a hole evolution diagram of CNT-CNNT provided by embodiment 3 of the present invention;

FIG. 6 shows a carbon nanotube material CNT and a CNT provided in example 3 of the present invention_FeN3The catalytic cracking water adsorption configuration and the photoproduction cavity distribution diagram;

FIG. 7 shows CNTs according to example 3 of the present invention_FeN3，CNT_CoN3，CNT_NiN3， CNT_CuN3And CNT_ZnN3Cracking water energy barrier diagram;

FIG. 8 is a diagram illustrating the reaction path and energy barrier of the proton penetrating the CNT provided in example 3 of the present invention;

fig. 9 is a diagram of the reaction process and energy barrier for forming hydrogen by combining protons driven by electrons provided in example 3 of the present invention.

Detailed Description

The technical solutions of the present invention are described below clearly and completely by using specific embodiments, 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.

Example 1

Preparation of carbon nitride nanotubes

(1) 150mg of NiCl₂Grinding into fine powder, adding into cyclohexane of about 50mL together with 1.5g of metal Na, and ultrasonically dispersing for 30 min;

(2) putting the dispersed mixture in the step (1) into an autoclave, sealing and heating to 230 ℃, and fully reacting for 6-7 hours;

(3) after the reaction, naturally cooling the sealed autoclave to room temperature, then adding 2.25g of anhydrous cyanuric chloride into the autoclave, then adding cyclohexane to enable the autoclave to be filled to about 2/3 of the volume, sealing again, and heating to 230 ℃ for reaction for 10 hours;

(4) after the reaction is finished, cooling the reaction kettle to room temperature, then taking out the product, respectively and sequentially washing the product with absolute ethyl alcohol, hot cyclohexane, dilute sulfuric acid and hot distilled water, and drying in vacuum to obtain the product, namely the carbon nitride nanotube.

Example 2

Preparation of carbon/carbon nitrogen composite nano tube material

A layer of cobalt film is evaporated and deposited on the carbon nitride nanotube sample prepared in the example 1 by using electron beams, and then mixed gas (C) is introduced into a reaction kettle₂H₂:5％,N₂95 percent of carbon nano tube and 80 sccm), heating to 500 ℃ for about 5min for reaction, then generating CVD reaction, depositing the carbon nano tube on the cobalt film, then slowly cooling the reaction kettle to room temperature under the protection of pure nitrogen, soaking the obtained product in 0.6mol/L HCl solution to remove metal cobalt, then centrifuging and washing with waterDrying to obtain the carbon/carbon nitrogen C₃N₄Composite nanotube composites. Adding polypyrrole into the composite material for coating, dripping ammonium ferrous sulfate solution while stirring, adjusting the pH value to about 12, heating in a water bath to 60 ℃, stirring for 22 hours, cooling to room temperature, centrifuging, washing with water, and drying to obtain the iron-nitrogen doped/carbon nitrogen C₃N₄Composite nanotube composites. The XRD and absorption spectra of the two composites are shown in fig. 1 and fig. 2. In fig. 1, a strong diffraction peak at about 26 degrees is shown as a (002) peak, and the presence of the nanotube structure is verified. Fig. 2 shows that the composite structure can effectively absorb ultraviolet light and visible light, so as to efficiently capture light energy, and the existence of strong coupling of the composite structure is proved.

Example 3

And constructing an initial configuration through Material Studio, and performing structural optimization by using a VASP software package to obtain a stable composite configuration. Calculating the electronic property, the optical property, the transition state, the energy information and the like of the material based on the stable configuration, and confirming the efficient light absorption performance and the electron hole separation of the composite material; calculating the evolution of electron holes and the process of attacking water molecules, and analyzing the photolysis water reaction performance of the composite material; then simulating the process that protons are attracted by static electricity and penetrate through the carbon nanotube material to enter the inner carbon nitrogen material, verifying that the protons can penetrate through the carbon nanotube material, and investigating the protons moving to the inner carbon nitrogen nanotube material to generate hydrogen (H) under the assistance of electrons₂) The performance and hydrogen storage performance of (1) specifically include:

1. electron hole separation

(a) Stability of composite materials

Construction of nanotube structures, i.e., CNTs, by Material Studio based on known carbon and carbon-nitrogen nanotube configurations_FCNNT model, optimized under consideration of Van der Waals' corrections. With CNNT (C)₃N₄) And CNT (unmodified carbon nanotube)/CNT_F(metallic nitrogen doped carbon nanotubes) as an example, the binding energy of the optimized composite material is shown in table 1:

TABLE 1 CNT/CNT in the practice of the invention_FBinding energy of-CNNT

As can be seen from Table 1, CNNT (C) in the examples₃N₄) And CNT/CNT_FThe binding energy ranges are 3.00-3.12 eV respectively, which shows that the composite material can exist stably.

(b) Light absorption Properties

The light absorption properties of the composite were calculated based on the stable configuration as CNNT (C)₃N₄) And CNT (unmodified carbon nanotube)/CNT_F(metallic nitrogen doped carbon nanotube) as an example, the absorption spectrum is shown in FIG. 3, and FIG. 3 shows CNT/CNT provided by the embodiment of the present invention_F-UV-VIS absorption spectrum of CNNT.

As can be seen from the figure, the carbon nanotube composite structure absorbs in the visible light and ultraviolet light ranges, and can effectively capture solar energy to generate photogenerated excitons.

(c) The photoproduction excitons generated by the separation of the electron holes need to be separated and respectively migrate to the oxidation active site and the reduction active site to drive the subsequent reaction, and the realization of the separation process of the electron holes is verified by the charge distribution result of the conduction band bottom and the valence band top of the composite structure. With CNT-CNNT and CNT_FeN3For the case of-CNNT, the charge distribution results of conduction band bottom and valence band top are shown in FIG. 4. FIGS. 4a and 4b are the CNT-CNNT and CNT, respectively, in this example_FeN3-charge distribution at the bottom and top of the conduction band of CNNT, yellow area in the diagram representing electrons, and in the small diagram of FIG. 4, the double circle diagram is CNT-CNNT and CNT_FeN3-top view of CNNT composite, and the jagged rectangular plot is a side view of the composite.

As can be seen from fig. 4, in the composite material, photo-generated electrons are distributed on the inner CNNT after light absorption, and photo-generated holes are distributed on the outer CNT or CNT_FeN3Above, the electron and hole are separated.

Further simulation of electron hole evolution further verified the charge separation. Taking CNT-CNNT as an example, the result is shown in fig. 5, fig. 5 is a hole evolution distribution diagram of CNT-CNNT provided by the embodiment of the present invention, and fig. 5a and 5b are evolution processes of holes and electrons, respectively. As can be seen from fig. 5, holes are substantially occupied on the CNTs in the composite material, and as time progresses, the holes are still mainly occupied on the CNTs as a driving force for the oxidation reaction. The electrons can rapidly migrate from the CNT to the CNNT within 200fs, and finally most of the electrons are accumulated on the CNNT for subsequent reduction reaction, thereby realizing effective separation of electron holes.

It can be known that, in the nanotube composite material of the present invention, photogenerated electrons move to the carbon-nitrogen nanotube, and photogenerated holes move to the carbon nanotube modified by the functional group, and due to van der waals interaction between the materials, the carrier is quickly transmitted between the two, and the holes can be quickly moved to the carbon nanotube material.

2. Photo-generated hole cracking water

Surface photo-generated hole distribution

The water splitting reaction in the composite material starts from the adsorption of water molecules on the surface of the metal nitrogen-doped carbon nanotube. With CNT_FeN3，CNT_CoN3，CNT_NiN3，CNT_CuN3，CNT_ZnN3For example, water molecules can be stably adsorbed on the metallic nitrogen-doped carbon nanotube to participate in the reaction.

The photogenerated holes that are then transported to the outer carbon nanotube material will collect near the active sites, providing the energy required for water splitting. With CNT and CNT_FeN3For example, the stable configuration of the carbon nanotube material after adsorbing water and the charge distribution after adding a photogenerated hole are shown in fig. 6, and fig. 6 is the charge distribution diagram of the carbon nanotube material provided by the embodiment of the present invention after adding a photogenerated hole. 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.

Water splitting to produce protons

The existence of the functional group can effectively reduce the energy barrier of the water cracking of the carbon nano tube. With CNT_FeN3，CNT_CoN3，CNT_NiN3，CNT_CuN3，CNT_ZnN3For example, the water-splitting energy barrier is shown in FIG. 7, and the water-splitting energy barrier (E) is shown_b) From 5.13eV for pure water to 2.86eV for carbon nanotubes and finally to a comparatively lower value of about 0.36 eV. In actual photolysisIn the water reaction, photogenerated holes gathered on the carbon nano tube material can overcome the energy barriers to drive water to be cracked to generate protons.

3. Proton-penetrating carbon nanotube material

Protons generated by water splitting on the surface of the carbon nano tube material are under the action of the electrostatic attraction of the carbon and nitrogen material of the inner layer, penetrate through the carbon nano tube of the outer layer and move to the carbon and nitrogen nano tube of the inner layer. Taking CNT-CNNT as an example, the energy barrier and movement process of proton penetrating carbon nanotube after neutral and one hole are shown in FIG. 8. As is clear from FIG. 8, the incorporation of holes can lower the proton penetration energy barrier to about 0.7eV, which is more advantageous for the proton penetration.

Electronic driving carbon nitrogen nano tube hydrogen production

The protons transferred to the inner carbon nitrogen nanotubes react with the help of photo-generated electrons to generate hydrogen. With CNNT (C)₃N₄) For example, as shown in fig. 9, the reaction process in which protons adsorbed on carbon nitrogen nanotubes N are combined with other protons to form hydrogen gas is shown in fig. 9, and it is understood from fig. 9 that the energy barrier for hydrogen evolution by electron-driven protons is only 0.71eV, and the reaction is very likely to occur, and hydrogen gas is generated. The generated hydrogen hardly penetrates through the carbon nanotube material on the outer layer, has an extremely high energy barrier of 11.54eV, and is extremely difficult to overcome, so that the hydrogen can only be stored in the carbon nanotube system. On the other hand, OH and O₂And the like are isolated on the outer layer of the carbon nano tube and cannot enter a composite system, so that the occurrence of reverse reaction is inhibited, and effective purification, separation and safe storage of hydrogen are realized.

Comprehensively, driven by solar energy, the composite system can continuously generate photo-generated electrons and holes, and then water on the peripheral carbon nanotube material is cracked to generate protons, and the protons penetrate through the carbon nanotubes and move to the carbon nitrogen nanotube material on the inner side to generate more hydrogen with the help of the photo-generated electrons. The carbon nano tube has higher compressive strength and excellent mechanical property, so the generated hydrogen can not cause the collapse of the material; on the other hand, hydrogen can also be conveyed through the carbon nano tube, so that the pressure of the hydrogen on the outer-layer carbon nano tube is reduced, and finally, the hydrogen which cannot penetrate through the carbon nano tube material can react with the carbon nano tube materialOH and O₂And the like, and the oil is safely stored in a composite system.

The nanotube composite material of the present invention can realize the integration of hydrogen production and hydrogen storage safely, and obviously, the described embodiments are only a part of embodiments of the present invention, but not all embodiments. 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

1. A carbon/carbon nitrogen CxNy composite nanotube composite material is characterized in that: the composite material consists of two parts of carbon nitrogen CxNy nanotubes at the inner layer and carbon nanotubes wrapped on the outer surface of the carbon nitrogen CxNy nanotubes, wherein x is any one of natural numbers 1, 2 or 3, y is a natural number 1 or 4,

the carbon-nitrogen nanotubes of the inner layer and the carbon nanotubes of the outer surface are bonded together through Van der Waals force,

the mass percentage of the carbon nitrogen nano tubes of the inner layer and the carbon nano tubes of the outer surface is (28-30) 100,

the outer layer nanotube material is a carbon nanotube modified by functional groups,

the carbon nanotube modified by the functional group is a metal nitrogen-doped carbon nanotube, and the metal nitrogen is selected from one or more of FeN3, CoN3, NiN3, ZnN3 and CuN 3.

2. The carbon/carbon nitrogen CxNy composite nanotube composite material of claim 1, wherein the carbon nitrogen CxNy nanotubes are C3N4 nanotubes.

3. A method of making the carbon/carbon nitrogen CxNy composite nanotube composite of claim 1 comprising the steps of:

a1) depositing a metal film on the carbon nitride nanotube material, and putting the carbon nitride nanotube material into a reaction kettle;

a2) introducing a certain proportion of C₂H₂And N₂Mixed gas (es)The body enters a reaction kettle, the temperature is raised to 480-520 ℃ to carry out CVD reaction for 4-6min, and carbon nano tubes are deposited on the metal film;

a3) in N₂And cooling the reaction kettle under protection, taking out a reaction product, soaking the reaction product in HCl solution to remove metals, centrifuging, washing with water, and drying to obtain the carbon/carbon nitrogen CxNy composite nanotube.

4. The method for preparing carbon/carbon nitrogen CxNy composite nanotube composite material according to claim 3, wherein C in the step a2)₂H₂And N₂The volume ratio of the mixed gas is (4-6): (94-96).

5. The method for preparing the carbon/carbon nitrogen CxNy composite nanotube composite material according to claim 3, wherein the temperature of the CVD reaction in the step a2) is 500 ℃, and the CVD reaction time is 5 min.

6. The use of the carbon/carbon nitrogen CxNy composite nanotube composite of any of claims 1-2 for photolytic hydrogen production and storage.