阅读说明：本技术 卷曲状氮化碳薄片、制备方法及其在光催化分解水产氢中的应用 (Curled carbon nitride thin sheet, preparation method and application thereof in hydrogen production through photocatalytic water decomposition ) 是由 张宗弢 刘文博 王润伟 张德广 于 2019-12-16 设计创作，主要内容包括：一种卷曲状氮化碳薄片、制备方法及其在光催化分解水产氢中的应用,属于光催化技术领域。该卷曲状氮化碳薄片的制备是以三聚氰胺和三聚氰酸为原料,在低温常压下,通过在煅烧下气化丙三醇将氮化碳剥离来制备卷曲状氮化碳薄片。与通常的方法相比采用了更加安全的常压低温自组装,操作简便产量高,以水为溶剂相比于在有机溶剂中自组装前驱体更加环保。同时也极大的增强了氮化碳的可见光催化的能力。卷曲的薄片结构大大提升了材料的比表面积也减小了材料的带隙宽度,从而大幅度的增加了材料对可见光的吸收也为光催化分解水反应提供了充足的反应位点,进而提高了可见光催化分解水的速率。易于实现工业化生产,具有广阔的应用前景。(A curled carbon nitride thin sheet, a preparation method and application thereof in hydrogen production by photocatalytic water decomposition belong to the technical field of photocatalysis. The preparation method of the curled carbon nitride sheet is characterized in that melamine and cyanuric acid are used as raw materials, and carbon nitride is stripped by gasifying glycerol under low temperature and normal pressure and calcining to prepare the curled carbon nitride sheet. Compared with the common method, safer normal-pressure low-temperature self-assembly is adopted, the operation is simple and convenient, the yield is high, and compared with self-assembly of a precursor in an organic solvent, the method using water as the solvent is more environment-friendly. And simultaneously, the visible light catalytic capability of the carbon nitride is greatly enhanced. The curled thin sheet structure greatly improves the specific surface area of the material and also reduces the band gap width of the material, thereby greatly increasing the absorption of the material to visible light and providing sufficient reaction sites for the photocatalytic water decomposition reaction, and further improving the rate of the photocatalytic water decomposition by the visible light. Is easy to realize industrial production and has wide application prospect.)

1. A preparation method of a curled carbon nitride sheet comprises the following steps:

(1) respectively dissolving melamine and cyanuric acid in deionized water in a water bath to prepare a melamine solution and a cyanuric acid solution;

(2) adding the melamine solution obtained in the step (1) into a melamine solution, continuously heating the obtained suspension in a water bath, centrifuging the obtained white product, washing the white product with water and ethanol for several times, and drying to obtain a white solid;

(3) dispersing the white solid obtained in the step (2) in a mixed solution of ethanol and glycerol, uniformly dispersing by ultrasonic, heating and refluxing the obtained suspension in an oil bath, centrifuging the obtained white product, washing the white product for a plurality of times by using water and ethanol, and drying to obtain a white product;

(4) grinding the white product obtained in the step (3) into fine powder, and heating the fine powder at the temperature of 400-600 ℃ in the air to obtain the curled carbon nitride flake photocatalyst.

2. A method of preparing a rolled carbon nitride sheet according to claim 1, wherein: in the step (1), the mass ratio of melamine to cyanuric acid is 1: 0.8-1.2, and dissolving in deionized water in water bath at 60-80 ℃.

3. A method of preparing a rolled carbon nitride sheet according to claim 1, wherein: in the step (2), the water bath heating temperature is 60-80 ℃, the water bath heating time is 1.5-3.0 hours, and finally, the white solid is obtained by drying for 12-24 hours at 80-100 ℃.

4. A method of preparing a rolled carbon nitride sheet according to claim 1, wherein: in the step (3), the volume ratio of the ethanol to the glycerol is 1: (0.2-0.4), the oil bath temperature is 80-120 ℃, the oil bath time is 2-4 hours, and finally, the white product is obtained by drying at 80-100 ℃ for 12-24 hours.

5. A method of preparing a rolled carbon nitride sheet according to claim 1, wherein: in the step (4), the heating time is 1.5-3.0 hours.

6. A curled carbon nitride sheet characterized by: is prepared by the method of any one of claims 1 to 5.

7. Use of the rolled carbon nitride sheet according to claim 6 for photocatalytic decomposition of water to produce hydrogen.

Technical Field

The invention belongs to the technical field of photocatalysis, and particularly relates to a curled carbon nitride thin sheet, a preparation method and application thereof in hydrogen production through photocatalytic water decomposition.

Background

Carbon nitride has been the most widely studied visible-light photocatalyst so far due to its good thermal stability, chemical stability and appropriate band gap width. At present, the most convenient synthesis method of carbon nitride is a thermal polycondensation method, and nitrogen-rich precursors such as urea, melamine, dicyandiamide and cyanamide are directly calcined at 500-600 ℃. However, since the carbon nitride synthesized by the method is in a bulk structure, the band gap is wider, the response to visible light is weaker, the specific surface area is low, and sufficient reaction sites cannot be provided, so that the photocatalytic reaction activity is low. In order to improve this phenomenon, the photocatalytic activity of carbon nitride is increased, the specific surface area of carbon nitride is increased to increase the surface active sites, and the band gap of carbon nitride is adjusted to decrease the band gap width of carbon nitride to increase the response to visible light. However, the preparation process of high-activity carbon nitride has involved the steps of high pressure, organic solvent and the like, which pollute the environment or increase the cost. Therefore, the invention develops a simple, cheap, safe and pollution-free method for preparing the curled carbon nitride thin sheet photocatalyst.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a simple, cheap, safe and pollution-free curled carbon nitride thin sheet, a preparation method and application thereof in hydrogen production by photocatalytic water decomposition.

The curled carbon nitride sheet is prepared by using melamine and cyanuric acid as raw materials, inserting glycerol into the interlayer of a self-assembly precursor at low temperature and normal pressure, and gasifying the glycerol under calcination to strip carbon nitride. Compared with the common method, the method adopts safer normal-pressure low-temperature self-assembly, is simple and convenient to operate, has high yield, and is more environment-friendly compared with self-assembly of the precursor in an organic solvent by taking water as the solvent. The method for stripping the carbon nitride from bottom to top can better strip the bulk phase carbon nitride into sheets, and simultaneously greatly enhances the visible light catalytic capability of the carbon nitride. The method has the advantages of safe and simple process, easily obtained raw materials, no toxic substances and organic waste liquid generated in the production process, easy realization of industrial production and wide application prospect.

The invention relates to a preparation method of a curled carbon nitride sheet, which comprises the following steps:

(1) respectively dissolving melamine and cyanuric acid in deionized water in a water bath to prepare a melamine solution and a cyanuric acid solution;

(2) adding the melamine solution obtained in the step (1) into a melamine solution, continuously heating the obtained suspension in a water bath, centrifuging the obtained white product, washing the white product with water and ethanol for several times, and drying to obtain a white solid;

(3) dispersing the white solid obtained in the step (2) in a mixed solution of ethanol and glycerol, uniformly dispersing by ultrasonic, heating and refluxing the obtained suspension in an oil bath, centrifuging the obtained white product, washing the white product for a plurality of times by using water and ethanol, and drying to obtain a white product;

(4) grinding the white product obtained in the step (3) into fine powder, and heating the fine powder at the temperature of 400-600 ℃ in the air to obtain the curled carbon nitride flake photocatalyst.

In the step (1), the mass ratio of melamine to cyanuric acid is 1: 0.8-1.2, respectively dissolving in deionized water in a water bath at 60-80 ℃;

in the step (2), the water bath heating temperature is 60-80 ℃, and the water bath heating time is 1.5-3.0 hours; drying the mixture at 80-100 ℃ for 12-24 hours;

in the step (3), the volume ratio of the ethanol to the glycerol is 1: (0.2-0.4), the oil bath temperature is 80-120 ℃, and the oil bath time is 2-4 hours; drying for 12-24 hours at 80-100 ℃;

in the step (4), the heating time is 1.5-3.0 hours.

Through the test of a Beijing Popley light hydrogen production system and the detection of a Japan Shimadzu GC-81 chromatograph, the curly carbon nitride sheet photocatalyst prepared by the invention has the advantages that the rate of catalytic photolysis water is obviously improved compared with the rate of bulk phase carbon nitride generated by pure melamine pyrolysis under the conditions that 1 wt% of platinum is loaded by reducing chloroplatinic acid by using sodium borohydride and triethanolamine is used as a sacrificial agent, and the performance is improved by over 37.5 times.

The catalyst of the invention can greatly improve the efficiency of photocatalytic water decomposition and further meet the industrial requirement. The curled thin sheet structure greatly improves the specific surface area of the material and also reduces the band gap width of the material, thereby greatly increasing the absorption of the material to visible light and providing sufficient reaction sites for the photocatalytic water decomposition reaction, and further improving the rate of the photocatalytic water decomposition by the visible light. Therefore, the invention is a significant invention.

Drawings

FIG. 1: a hydrogen rate characterization chart is obtained by carrying out photocatalytic decomposition on water under the conditions that 1 wt% platinum-loaded curled carbon nitride sheets and bulk-phase carbon nitride are used as sacrificial agents in triethanolamine, a 300W xenon lamp is used as a light source, and light below 420nm is filtered out by a 420nm filter. It can be seen that the activity of photocatalytic hydrogen production is greatly improved by the curled carbon nitride sheet compared with bulk phase carbon nitride.

FIG. 2: curled carbon nitride flakes (NS-C)₃N₄Curve 2) and bulk phase carbon nitride (B-C)₃N₄Fluorescence spectrum of curve 1); the fluorescence spectrum intensity of the curled carbon nitride thin sheet is greatly reduced compared with that of bulk-phase carbon nitride, and the structure and the energy band position of the curled carbon nitride thin sheet greatly reduce the recombination of photo-generated electrons and holes, so that the efficiency of photocatalytic hydrogen production is improved.

FIG. 3: scanning electron micrographs (a) and transmission electron micrographs (b) of the curled carbon nitride flakes;

in FIG. 3(a) it can be seen that the sample is coiled and uniformly dispersed; in fig. 3(b), it can be seen that the curled carbon nitride has a lamellar structure, and the number of layers of the lamellar structures is small, and the structure is thin, so that the specific surface area of the sample is greatly increased, and the photocatalytic hydrogen production efficiency is improved.

FIG. 4: curled carbon nitride flakes (NS-C)₃N₄Curve 2) and bulk phase carbon nitride (B-C)₃N₄The characterization plot of the X-ray diffractometer of curve 1); as can be seen from the figure, the characteristic peak intensity of the curled carbon nitride sheet is lower than that of bulk phase carbon nitride, and the lower peak intensity indicates lower crystallinity, which indirectly indicates the less-layer structure of the curled carbon nitride sheet.

FIG. 5: curled carbon nitride flakes (NS-C)₃N₄Curve 2) and bulk phase carbon nitride (B-C)₃N₄Graph (a) of the ultraviolet-visible diffuse reflection spectrum and graph (b) of the band gap of curve 1). It can be seen from FIG. 5a that curve 2 has a significantly higher absorption in the visible region than curve 1, indicating a curled carbon nitride sheet (NS-C)₃N₄Curve 2) absorption of visible light is much higher than that of bulk phase carbon nitride (B-C)₃N₄Curve 1), it can be seen from fig. 5b that the curled carbon nitride sheet has a narrower band gap than the bulk phase carbon nitride, which also indirectly illustrates that the curled carbon nitride sheet has a higher visible light utilization than the bulk phase carbon nitride.

Detailed Description

The present invention will be described in detail with reference to specific examples, but the use and purpose of these embodiments are merely to exemplify the present invention, and do not limit the actual scope of the present invention in any way, and the scope of the present invention is not limited thereto.