An oligomerization degree of carbon nitride nanosheet containing a part of supramolecular chain and a preparation method and application of photocatalytic decomposition of water while producing hydrogen and oxygen

Abstract

The application discloses oligomerization degree carbon nitride nanosheet containing partial supramolecular chains and a preparation method and application of photocatalytic decomposition of water to simultaneously produce hydrogen and oxygen, and the preparation method comprises the following steps: adding melamine and cyanuric acid into a solvent, stirring after ultrasonic treatment, and drying to obtain supramolecular precursor powder; and calcining the supramolecular precursor powder to obtain oligomerization degree carbon nitride containing partial supramolecular chains. The application retains partial supramolecular oxygen-containing structures to optimize adsorption and dissociation of oligomerization degree carbon nitride nanosheet and water molecules at a reaction liquid interface, realizes high H and OH enrichment of a local environment, and promotes performance improvement of photocatalytic complete decomposition of water.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of hydrogen energy preparation, and relates to a photocatalytic clean hydrogen energy preparation technology, that is, a hydrogen energy preparation technology for realizing photocatalytic water splitting at a low cost under full spectrum conditions, in particular to a low-polymerization-degree carbon nitride nanosheet containing a partial supramolecular chain, a preparation method and application of photocatalytic water splitting for simultaneously producing hydrogen and oxygen, which is beneficial to industrialized application of photocatalytic water splitting for hydrogen production. BACKGROUND

[0002] With the promotion of global modernization and industrialization, the demand for energy of human society is increasing day by day. Energy and environment have become two problems that are first attacked, which greatly threaten the survival and development of human society. Therefore, in order to solve these two challenging problems, countries have vigorously promoted the strategy of using sustainable renewable energy and promoted the low-carbonization of global energy industry and social development, which is also the goal of China's energy technology field. Hydrogen energy (H2) is a kind of energy with high energy density, no pollution, no toxicity, easy storage and transportation, and the combustion product of hydrogen is water, and water can also be decomposed to produce hydrogen, so it is considered as an ideal clean energy. The preparation of hydrogen by photocatalytic water splitting by semiconductor photocatalysts realizes the green conversion of light-hydrogen, which is a promising clean energy conversion technology. The core point of this technology is the semiconductor photocatalyst, so the most critical point is to prepare a high-efficiency, stable, non-polluting and toxic, and economical photocatalyst.

[0003] For photocatalytic water splitting for hydrogen production, there are mainly three key steps: after the semiconductor catalyst is irradiated by light with energy greater than its band gap, the electron-hole pairs are generated by photoexcitation; the separated electron-hole pairs are transferred from the inside of the catalyst to the surface of the catalyst, and a part of the electron-hole pairs will recombine; the electrons migrated to the surface will react with water to produce hydrogen, and the holes will react with water to produce oxygen. For a complete water splitting reaction to produce hydrogen and oxygen, in order to ensure sufficient redox driving force, the band gap of photocatalysis needs to be at least greater than 1.23 eV. In addition, it is a four-electron process (2H2O+4e - +4h + →2H2+O2), the process is relatively complex, and it is a typical uphill reaction with an increase in Gibbs free energy, and the Gibbs free energy before and after the reaction reaches 237 kJ mol -1In addition to the above dynamics and thermodynamics factors, the interface adsorption and desorption process is also a key constraint factor. For hydrogen (oxygen) evolution reaction, increasing the adsorption capacity of protons (water) further increases the probability of hydrogen (oxygen) generation by proton (water) reduction (oxidation); on the contrary, if the adsorption capacity of hydrogen (oxygen) is strong, hydrogen (oxygen) is not easy to desorb, thereby hindering the continuous progress of the photocatalytic reaction. In the complete water splitting reaction, in addition to the above process, the un-desorbed hydrogen and oxygen in the system may also have the reverse reaction to generate water, reducing the hydrogen production activity of the complete water splitting reaction. For the surface reaction mechanism of the photocatalyst, in addition to the simple adsorption and desorption process, more attention should be paid to the influence of surface atoms on the reaction. For example, in the complete water splitting reaction, how to easily break the H-O bond and promote the formation of H-H and O-O bonds is the essential reason for improving the complete water splitting activity; at the same time, how to avoid the reverse reaction and identify the core factors of the reverse reaction will help in-depth design of the photocatalyst.

[0004] According to the existing research and foundation, among the many types of photocatalyst materials, the band gap width of graphite phase carbon nitride (g-C3N4) photocatalyst is about 2.7 eV, which can completely split water to produce hydrogen and oxygen under visible light, and has the characteristics of non-toxic, cheap, simple preparation, abundant raw materials and stability, and has great application prospect and research value. However, due to the molecular structure of carbon nitride mainly composed of amino- connected triazine structural units, which forms a highly symmetrical internal structure, seriously hindering the migration of internal photo-generated carriers, thereby reducing the CN photocatalytic hydrogen production activity. However, it is difficult to optimize the molecular structure of CN by traditional methods, and most of them are in the form of heteroatoms incorporated into the molecular structure, showing single group and atomic characteristics, and it is difficult to retain the characteristics of individual molecules, and the optimization of the surface is slightly insufficient. Recently, according to the report of Lotsch of Munich University, by controlling the synthesis temperature of melon, low molecular weight CN is synthesized, emphasizing the role of defects (chain end groups) in improving the catalytic activity of CN, and also indicating that there is sufficient potential to essentially improve the photocatalytic activity of CN by selective synthesis of active phases. At present, the synthesis of CN from traditional raw materials mainly has two nodes, one is the generation of melamine at 400°C, and the other is the generation of CN at 525°C, so temperature can change the molecular structure of CN and selectively retain the desired groups. Obviously, it is worth exploring to change the temperature to optimize the molecular structure and surface interface reaction to achieve high photocatalytic complete water splitting performance after synthesizing the basic framework structure of CN. SUMMARY

[0005] In order to overcome the problem of serious photogenerated carrier recombination in the prior art, the present application aims to provide a low degree of oligomerization carbon nitride nanosheet containing partial supramolecular chains and a preparation method and application in photocatalytic decomposition of water to simultaneously produce hydrogen and oxygen, so as to realize efficient photocatalytic hydrogen production of the photocatalyst.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solution:

[0007] A preparation method of a low degree of oligomerization carbon nitride nanosheet containing partial supramolecular chains, comprising the following steps:

[0008] Melamine and cyanuric acid are added to a solvent, stirred after ultrasonic, dried, and a supramolecular precursor powder is obtained;

[0009] The supramolecular precursor powder is calcined to obtain a low degree of oligomerization carbon nitride containing partial supramolecular chains.

[0010] Further, the ultrasonic time is 5-10 min, and the stirring time is 8-10 h.

[0011] Further, the solvent is ethanol.

[0012] Further, the molar ratio of melamine to cyanuric acid is 1:1.

[0013] Further, the dosage ratio of melamine to solvent is 0.04 mol:0.04 mol.

[0014] Further, the calcination is carried out under N2 atmosphere.

[0015] Further, the calcination temperature is 350-550 o C, and the time is 2 h.

[0016] Further, the temperature is raised to 400-550 o C at a temperature rising rate of 3-5 o C / min.

[0017] A low degree of oligomerization carbon nitride nanosheet containing partial supramolecular chains.

[0018] Application of a low degree of oligomerization carbon nitride nanosheet containing partial supramolecular chains in photocatalytic decomposition of water to simultaneously produce hydrogen and oxygen.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] The application realizes the control of the polymerization degree of carbon nitride by pre-synthesizing a supramolecular precursor, connecting melamine and cyanuric acid by hydrogen bonds, and controlling the calcination temperature, optimizes the molecular structure, and strengthens the surface optimization of the photocatalytic water splitting reaction. The application first prepares an oligomeric carbon nitride nanosheet containing a partial supramolecular chain, optimizes the adsorption and dissociation of water molecules on the interface of the oligomeric carbon nitride nanosheet and the reaction solution by retaining part of the supramolecular oxygen-containing structure, realizes the enrichment of local environment of high *H and *OH, and promotes the improvement of the photocatalytic complete water splitting performance. The characterization results and theoretical analysis show that the retained oxygen-containing functional groups in the oligomeric carbon nitride nanosheet promote the adsorption of water molecules, the dissociation energy barrier of water molecules is reduced, the local environment of high *H and *OH is realized, and the production of hydrogen and oxygen is promoted. Therefore, under the synergistic action of the oxygen-containing structure and the carbon nitride structure, the oligomeric carbon nitride nanosheet obtains a stable and relatively efficient single-photon system complete water splitting ability.

[0021] Further, by controlling the calcination temperature of the supramolecular precursor, the conversion degree of cyanuric acid is controlled, and an oligomeric carbon nitride nanosheet with part of the supramolecular structure retained is synthesized, realizing the coexistence of a supramolecular chain and a carbon nitride structure. The optimization of the chemical structure of carbon nitride makes the interface reaction optimized. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the infrared spectrum (FT-IR) diagram of the carbon nitride with different polymerization degrees in examples 1-4 and comparative example 1;

[0023] Figure 2 is the X-ray diffraction (XRD) diagram of the carbon nitride with different polymerization degrees in examples 1-4 and comparative example 1;

[0024] Figure 3 is the scanning electron microscope (SEM) diagram of the carbon nitride with different polymerization degrees in examples 1-4 and comparative example 1;

[0025] Figure 4 is the complete water splitting hydrogen production diagram of the carbon nitride with different polymerization degrees in examples 1-4 and comparative example 1 under full spectrum conditions;

[0026] Figure 5 is the complete water splitting hydrogen production diagram of the oligomeric carbon nitride containing a partial supramolecular chain in examples 1, examples 7-9 under different catalyst dosages under full spectrum conditions. DETAILED DESCRIPTION

[0027] For the purpose of facilitating the understanding of the present application, a more complete description of the present application will be given below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0028] The application discloses a preparation method of an oligomeric nitrogenated carbon nanosheet containing partial supramolecular chains, comprising:

[0029] Melamine and cyanuric acid are added to an ethanol solution, ultrasonic treatment is performed for 5-10 min, 25 o C, the product is washed and vacuum dried to obtain a supramolecular precursor powder, the obtained supramolecular precursor powder is heated to 350-550 o C at a heating rate of 3-5 o C / min under a N2 atmosphere, and calcination is performed for 2-3 h to obtain an oligomeric nitrogenated carbon containing partial supramolecular chains. The molar ratio of melamine to cyanuric acid is 1:1, and the dosage ratio of melamine to ethanol is 0.04 mol:0.04 mol.

[0030] The present application synthesizes a supramolecular precursor in advance, and then controls the polymerization temperature of the nitrogenated carbon to prepare an oligomeric nitrogenated carbon containing partial supramolecular chains, which has good photocatalytic activity, can catalyze the decomposition of pure water to produce hydrogen and oxygen under full-spectrum conditions, and exhibits good catalytic hydrogen and oxygen production activity, with a photocatalytic hydrogen production rate of 12.5 μmol h -1 , and a corresponding photocatalytic oxygen production rate of 6.0 μmol h -1 , and a photocatalytic hydrogen production rate of 28.3 μmol h -1 , and a corresponding photocatalytic oxygen production rate of 13.5 μmol h -1 , and a quantum efficiency of 3.65% at 420 nm. The present application is simple in operation and good in repeatability, and provides a reliable scheme for improving the photocatalytic water decomposition hydrogen production efficiency and the development and application of a new type of photocatalyst for simultaneously producing hydrogen and oxygen.

[0031] The following is a specific implementation case.

[0032] Example 1

[0033] Step one: 0.04 mol melamine (Mel) and 0.04 mol cyanuric acid (CU) were added into 100 mL anhydrous ethanol, dispersed by ultrasonic for 5 min, and stirred vigorously at 25 °C for 8 h. Then centrifuged, washed with ethanol for 2-3 times, and collected after vacuum drying at 60 °C for 12 h. The final white product was a supramolecular precursor, and was named as CM.

[0034] Step two: the CM obtained in step one was ground uniformly, and the ground powder was calcined at 400 °C for 2 h under N2 atmosphere (heating rate 3 °C / min), and the obtained sample was collected after furnace cooling. The obtained sample was the oligomeric g-C3N4 nanosheets CM-400 containing partial supramolecular chains. o C / min), and the obtained sample was collected after furnace cooling. The obtained sample was the oligomeric g-C3N4 nanosheets CM-400 containing partial supramolecular chains. o C / min), and the obtained sample was collected after furnace cooling. The obtained sample was the oligomeric g-C3N4 nanosheets CM-400 containing partial supramolecular chains.

[0035] Step three: the oligomeric g-C3N4 nanosheets CM-400 containing partial supramolecular chains prepared in step two were added into 100 mL pure water solution for photocatalytic water splitting and hydrogen and oxygen production test. The specific steps were as follows:

[0036] 1) 10 mg CM-400 photocatalyst was added into the reactor customized for the online system, 100 mL pure solution was added, and 3% Pt was added.

[0037] 2) The system was vacuumed by vacuum pump before light irradiation to remove the gas in the system.

[0038] 3) The magnetic stirrer and xenon lamp power were turned on.

[0039] Example 2

[0040] Step one: 0.04 mol melamine (Mel) and 0.04 mol cyanuric acid (CU) were added into 100 mL anhydrous ethanol, dispersed by ultrasonic for 5 min, and stirred vigorously at 25 °C for 8 h. Then centrifuged, washed with ethanol for 2-3 times, and collected after vacuum drying at 60 °C for 12 h. The final white product was a supramolecular precursor, and was named as CM.

[0041] Step two: the CM obtained in step one was ground uniformly, and the ground powder was calcined at 450 °C for 2 h under N2 atmosphere (heating rate 3 °C / min), and the obtained sample was collected after furnace cooling. The obtained sample was the oligomeric g-C3N4 nanosheets CM-450 containing partial supramolecular chains. o C / min), and the obtained sample was collected after furnace cooling. The obtained sample was the oligomeric g-C3N4 nanosheets CM-400 containing partial supramolecular chains. o C / min), and the obtained sample was collected after furnace cooling. The obtained sample was the oligomeric g-C3N4 nanosheets CM-400 containing partial supramolecular chains.

[0042] Step three: the oligomeric g-C3N4 nanosheets CM-450 containing partial supramolecular chains prepared in step two were added into 100 mL pure water solution for photocatalytic water splitting and hydrogen and oxygen production test. The specific steps were as follows:

[0043] 1) Add 10 mg of CM-450 photocatalyst to the reactor customized for the online system, add 100 mL of pure water solution with a total volume of 100 mL, and add 3% Pt;

[0044] 2) Before irradiation, remove the gas in the system by vacuum pumping;

[0045] 3) Turn on the magnetic stirrer and the xenon lamp power supply.

[0046] Example 3

[0047] Step one: Add 0.04 mol of melamine (Mel) and 0.04 mol of cyanuric acid (CU) to 0.04 mol of anhydrous ethanol, ultrasonic dispersion for 5 min, and vigorous stirring at 25°C for 8 h. Then centrifuge, ethanol wash 2-3 times, and collect after vacuum drying at 60°C for 12 h. The final white product is a supramolecular precursor, named CM.

[0048] Step two: Grind the CM obtained in step one uniformly, and grind the powder under N2 atmosphere at 500 o C for 2 h (heating rate 3 o C / min), and after cooling in the furnace, grind and collect the obtained sample, which is the higher degree of polymerization carbon nitride CM-500.

[0049] Step three: Add the higher degree of polymerization carbon nitride CM-500 prepared in step two to 100 mL of pure water solution for photocatalytic water decomposition and hydrogen and oxygen production test. The specific steps are as follows:

[0050] 1) Add 10 mg of CM-500 photocatalyst to the reactor customized for the online hydrogen production system, add pure water with a total volume of 100 mL, and add 3% Pt;

[0051] 2) Before irradiation, remove the gas in the system by vacuum pumping;

[0052] 3) Turn on the magnetic stirrer and the xenon lamp power supply.

[0053] Example 4

[0054] Step one: Add 0.04 mol of melamine (Mel) and 0.04 mol of cyanuric acid (CU) to 100 mL of anhydrous ethanol, ultrasonic dispersion for 5 min, and vigorous stirring at 25°C for 8 h. Then centrifuge, ethanol wash 2-3 times, and collect after vacuum drying at 60°C for 12 h. The final white product is a supramolecular precursor, named CM.

[0055] Step two: The CM obtained from step one was grinded evenly, and the grinded powder was calcined at 550 °C for 2 h (heating rate 3 °C / min) under N2 atmosphere. After the furnace cooling, the obtained sample was collected by grinding. The obtained sample was high polymerization degree carbon nitride CM-550. o C / min), and after the furnace cooling, the obtained sample was collected by grinding. The obtained sample was low polymerization degree carbon nitride CM-420 containing part of supramolecular chains. o C / min), and after the furnace cooling, the obtained sample was collected by grinding. The obtained sample was low polymerization degree carbon nitride CM-420 containing part of supramolecular chains.

[0056] Step three: The high polymerization degree carbon nitride CM-550 prepared in step two was added into 100 mL pure water solution for photocatalytic decomposition of water and hydrogen and oxygen production test. The specific steps are as follows:

[0057] 1) 10 mg of CM-550 photocatalyst was added into the reactor customized for the online hydrogen production system, 100 mL of pure water was added, and 3% Pt was added.

[0058] 2) Before light irradiation, the system was vacuumed by a vacuum pump to remove the gas in the system.

[0059] 3) The magnetic stirrer was turned on, and the xenon lamp power supply was turned on.

[0060] Example 5

[0061] Step one: 0.04 mol of melamine (Mel) and 0.04 mol of cyanuric acid (CU) were added into 100 mL of anhydrous ethanol, ultrasonically dispersed for 10 min, and stirred vigorously at 25 °C for 10 h. Then, centrifugation was performed, and the ethanol was washed twice. After vacuum drying at 60 °C for 12 h, the white product was collected. The final obtained white product was a supramolecular precursor, and was named as CM.

[0062] Step two: The CM obtained from step one was grinded evenly, and the grinded powder was calcined at 420 °C for 2 h (heating rate 4 °C / min) under N2 atmosphere. After the furnace cooling, the obtained sample was collected by grinding. The obtained sample was low polymerization degree carbon nitride CM-420 containing part of supramolecular chains. o C / min), and after the furnace cooling, the obtained sample was collected by grinding. The obtained sample was low polymerization degree carbon nitride CM-420 containing part of supramolecular chains. o C / min), and after the furnace cooling, the obtained sample was collected by grinding. The obtained sample was low polymerization degree carbon nitride CM-420 containing part of supramolecular chains.

[0063] Example 6

[0064] Step one: 0.04 mol of melamine (Mel) and 0.04 mol of cyanuric acid (CU) were added into 100 mL of anhydrous ethanol, ultrasonically dispersed for 10 min, and stirred vigorously at 25 °C for 10 h. Then, centrifugation was performed, and the ethanol was washed twice. After vacuum drying at 60 °C for 12 h, the white product was collected. The final obtained white product was a supramolecular precursor, and was named as CM.

[0065] Step two: The CM obtained from step one was grinded evenly, and the grinded powder was calcined at 420 °C for 2 h (heating rate 4 °C / min) under N2 atmosphere. After the furnace cooling, the obtained sample was collected by grinding. The obtained sample was low polymerization degree carbon nitride CM-420 containing part of supramolecular chains. oC calcined at 2 h (heating rate 5 o C / min), after furnace cooling, the obtained sample was collected by grinding, and the obtained sample was low degree of polymerization carbon nitride CM-480 containing part of the supramolecular chain.

[0066] Example 7

[0067] Application of photocatalytic decomposition of water to simultaneously produce hydrogen and oxygen:

[0068] The same as step three in example 1, except that step 1) 20 mg of CM-400 photocatalyst was added to the reactor customized for the online hydrogen production system, and a total volume of 100 mL of pure water solution was added, and 3% Pt was added.

[0069] Example 8

[0070] Application of photocatalytic decomposition of water to simultaneously produce hydrogen and oxygen:

[0071] The same as step three in example 1, except that step 1) 30 mg of CM-400 photocatalyst was added to the reactor customized for the online hydrogen production system, and a total volume of 100 mL of pure water solution was added, and 3% Pt was added.

[0072] Example 9

[0073] Application of photocatalytic decomposition of water to simultaneously produce hydrogen and oxygen:

[0074] The same as step three in example 1, except that step 1) 40 mg of CM-400 photocatalyst was added to the reactor customized for the online hydrogen production system, and a total volume of 100 mL of pure water solution was added, and 3% Pt was added.

[0075] Comparative example 1

[0076] Step one: 0.04 mol of melamine (Mel) and 0.04 mol of cyanuric acid (CU) were added to 100 mL of anhydrous ethanol, ultrasonic dispersion for 5 min, and stirred vigorously at 25°C for 8 h. Then centrifuged, washed with ethanol 2-3 times, and collected after vacuum drying at 60°C for 12 h. The final white product obtained was a supramolecular precursor, and was named CM.

[0077] Step two: the CM obtained in step one was ground evenly, and the ground powder was calcined at 350 o C / min), after furnace cooling, the obtained sample was collected by grinding, and the obtained sample was low degree of polymerization carbon nitride CM-480 containing part of the supramolecular chain. o C / min), after furnace cooling, the obtained sample was collected by grinding, and the obtained sample was low degree of polymerization carbon nitride CM-480 containing part of the supramolecular chain.

[0078] Step three: The prepared cyanuric acid and melamine supramolecular chain CM-350 in step two was added to 100 mL pure water solution for photocatalytic water decomposition test for hydrogen and oxygen production. The specific steps are as follows:

[0079] 1) 10 mg of CM-350 photocatalyst was added to the reactor customized for the online system, and 100 mL of pure water solution was added, and 3% Pt was added;

[0080] 2) Vacuum was removed by vacuum pump before light irradiation to remove the gas in the system;

[0081] 3) Turn on the magnetic stirrer and the xenon lamp power supply.

[0082] Figure 1 is the infrared spectrum (FT-IR) of CM-350, CM-400, CM-450, CM-500, and CM-550. When the temperature is 350 ℃, CM-350 still exhibits similar stretching vibration peak characteristics as CM, but the peak intensity of CM-350 changes due to the change in hydrogen bond connection. After the temperature reaches 400 ℃, the stretching vibration peak of melamine-cyanurate disappears, and the characteristic peaks of 3-s-triazine monomer appear at 810, 1313, 1455, 1599 and 3200 cm -1 , but the hydrogen bond characteristics between 2900-3200 cm -1 are still retained, which indicates that CM-400 is in a state of low polymerization. After the temperature reaches 550 ℃, the hydrogen bond connection impurity peak in CM-550 disappears, and the characteristic peaks are concentrated at 3000-3500 -1 , 1100-1800 -1 and 800 cm -1 , which indicates the presence of s-triazine ring structure and amino structure. In summary, it is shown that CM-400 is a low degree of polymerization of carbon nitride containing part of the supramolecular chain.

[0083] Figure 2XRD patterns of CM-350, CM-400, CM-450, CM-500 and CM-550. When the temperature is 350℃, the hydrogen bond structure is changed due to the formation of melamine amide in the presence of ammonia, so that the crystal structure becomes the crystal structure of melamine-triazine acid salt, but the crystal structure of carbon nitride is not formed due to the absence of polycondensation reaction. With the further increase of temperature to 400℃, the interlayer stacking of melem appears, and the typical (002) peak of the interlayer stacking of carbon nitride appears, but due to the increase of the degree of polymerization with the increase of temperature, the (100) peak of the atomic arrangement order slowly appears when the temperature reaches 450℃, and finally the relatively perfect melon structure of CM-550 is formed. This further proves that CM-400 is a crystal structure with low degree of polymerization.

[0084] Figure 3 SEM patterns of CM-350, CM-400, CM-450, CM-500 and CM-550. CM-350 is a large-sized and thick flake structure. When the temperature reaches 400 o C The supermolecular crystal structure unit changes, the carbon nitride structure begins to form, the polymer phase is generated, and the pores begin to appear. At the same time, the mass loss of the substances during the polycondensation process leads to the appearance of large voids in CM-400, so that the carbon nitride flake becomes a concave flake.

[0085] Figure 4 The hydrogen production rate of CM-400 reaches 12.5 μmol h -1 -1 under pure water condition, and the corresponding photocatalytic oxygen production rate reaches 6.0 μmol h -1 . It is shown that the carbon nitride with low degree of polymerization containing part of the supermolecular chain has excellent performance of complete decomposition of water for hydrogen production.

[0086] Figure 5 The hydrogen production rate of CM-400 reaches 12.5 μmol h -1 -1 under pure water condition, and the corresponding photocatalytic oxygen production rate reaches 6.0 μmol h -1 .

[0087] The above only describes the best embodiments of the present application, but cannot be understood as the limitation of the claims. The present application is not limited to the above embodiments, and the specific structure allows changes. Any changes made within the protection scope of the independent claims of the present application are within the protection scope of the present application.

[0088] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for preparing an oligomeric carbon nitride nanosheet comprising a partial supramolecular chain, characterized in that, The method comprises the following steps: melamine and cyanuric acid are added into a solvent, stirred after ultrasonic treatment, dried to obtain a supramolecular precursor powder; The supramolecular precursor powder is calcined at 400-450 o C to obtain oligomerized carbon nitride containing partial supramolecular chains; ultrasonic treatment time is 5-10 min, stirring time is 8-10 h; the solvent is ethanol; the molar ratio of melamine to cyanuric acid is 1:1; the dosage ratio of melamine to solvent is 0.04 mol:0.04 mol.

2. The method of claim 1, wherein the method is characterized by, calcination is carried out under N2 atmosphere.

3. The method of claim 1, wherein the method is characterized by, calcination time is 2 h.

4. The method of claim 3, wherein the method is characterized by, at a ramp rate of 3-5 o C / min to 400-450 o C.

5. An oligomeric carbon nitride nanosheet comprising a partial supramolecular chain, which is prepared by the method according to any one of claims 1-4.

6. Application of an oligomeric carbon nitride nanosheet comprising a partial supramolecular chain, which is prepared by the method according to any one of claims 1-4, in photocatalytic decomposition of water to simultaneously produce hydrogen and oxygen.

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