Preparation of rod-like g-C by microwave hydrothermal method3N4Method and application of nanosheet
阅读说明：本技术 一种微波水热法制备棒状g-C3N4纳米片的方法及应用 (Preparation of rod-like g-C by microwave hydrothermal method3N4Method and application of nanosheet ) 是由 陈红梅 薛晨阳 崔丹凤 范燕云 范正 于 2020-11-16 设计创作，主要内容包括：本发明公开了一种微波水热法制备棒状g-C-3N-4纳米片的方法,首先采用氮含量丰富的原料如二氰二胺、三聚氰胺或者硫脲等,在空气气氛中焙烧2～6h,即可得到原始体相氮化碳；然后,采用微波水热合成仪,将体相氮化碳在150～220℃和80～150 W下处理0.5～2h,得到的产物经过洗涤,干燥即可得到厚度约为3μm的氮化碳纳米片。与体相氮化碳相比,用这种技术方案处理的光催化剂的比表面积明显增大。与此同时,该技术可以降低g-C-3N-4电子空穴的复合率并加快界面电荷传输。将g-C-3N-4纳米片应用到光催化产氢反应中取得了优良的结果,产氢速率比体相氮化碳高出10倍以上。(The invention discloses a method for preparing rodlike g-C by a microwave hydrothermal method 3 N 4 Firstly, roasting raw materials with rich nitrogen content such as dicyanodiamine, melamine or thiourea for 2-6 hours in an air atmosphere to obtain original bulk-phase carbon nitride; then, treating the bulk-phase carbon nitride at 150-220 ℃ and 80-150W for 0.5-2 h by adopting a microwave hydrothermal synthesizer, washing and drying the obtained product to obtain the product with the thickness of aboutIs a 3 μm carbon nitride nanosheet. The photocatalyst treated by the technical scheme has obviously increased specific surface area compared with bulk-phase carbon nitride. At the same time, the technique can reduce g-C 3 N 4 The recombination rate of electron holes and the accelerated interface charge transport. G to C 3 N 4 The nano-sheet is applied to the photocatalytic hydrogen production reaction to obtain excellent results, and the hydrogen production rate is more than 10 times higher than that of bulk phase carbon nitride.)
1. Preparation of rod-like g-C by microwave hydrothermal method3N4A method of nanosheet, characterized by: and roasting and cooling the nitrogen-rich compound to obtain bulk-phase carbon nitride, and then preparing the carbon nitride nanosheet by a microwave hydrothermal method.
2. The microwave hydrothermal process of claim 1, wherein the rod-shaped g-C is prepared3N4A method of nanosheet, characterized by: the nitrogen-rich compound comprises one or more of dicyandiamide, melamine or thiourea.
3. The microwave hydrothermal process of claim 2, wherein the rod-shaped g-C is prepared3N4A method of nanosheet, characterized by: the roasting temperature is 500-580 ℃.
4. The microwave hydrothermal process of claim 3, wherein the rod-shaped g-C is prepared3N4A method of nanosheet, characterized by: the heating rate is 2-10 ℃/min, and the roasting time is 2-6 h.
5. The microwave hydrothermal process of claim 4, wherein the rod-shaped g-C is prepared3N4A method of nanosheet, characterized by: the microwave hydrothermal temperature is 150-200 ℃.
6. The microwave hydrothermal process of claim 5, wherein the rod-shaped g-C is prepared by the microwave hydrothermal process3N4A method of nanosheet, characterized by: the microwave power is 80-150W.
7. The microwave hydrothermal process of claim 6Rod-like g-C3N4A method of nanosheet, characterized by: the microwave hydrothermal time is 0.5-2 h.
8. A microwave hydrothermal rod-shaped g-C prepared by the method of any one of claims 1-73N4The nano-sheet is applied to the aspect of being used as a hydrogen production catalyst.
9. A hydrogen-producing catalyst characterized by: microwave hydrothermal rod-shaped g-C prepared by the method of any one of claims 1 to 73N4Precious metals are deposited on the nano-sheets in a photoreduction mode, and the precious metals are one or more of Au, Ag and Pt.
10. The hydrogen-producing catalyst according to claim 9, characterized in that: the deposited amount of the noble metal is rod-like g-C3N40.5-5% of the weight of the nanosheet.
Technical Field
The invention relates to the field of nano materials and application thereof in photocatalytic reaction, in particular to a method for constructing a carbon nitride nanosheet by a microwave hydrothermal method and application thereof in preparation of hydrogen by photocatalytic water decomposition.
Background
The global economy is rapidly developed, brings great convenience and progress to the life of people, and is accompanied by energy crisis and unavoidable environmental problems caused by the rapid reduction of non-renewable fossil energy represented by coal, petroleum and natural gas. Therefore, the development of new clean energy is urgent, and the preparation of hydrogen by decomposing water by using renewable solar energy through a photocatalytic technology is a green, efficient and low-cost technical route, and one of the core problems of the technology is the research and development of semiconductor nano materials. g-C3N4The organic semiconductor is a non-metal organic semiconductor, has a proper forbidden band width (2.7 eV) excited by visible light, and is widely concerned due to the advantages of simple preparation method, stable physicochemical properties and the like.
g-C3N4The material can be obtained by thermal polymerization of a precursor rich in nitrogen, but the obtained material has a blocky structure, small specific surface area and poor photocatalytic performance. Therefore, it is of interest to researchers how to overcome these inherent drawbacks. The method for stripping blocky carbon nitride into thin slices by adopting a technical means is a method for effectively improving the photocatalytic performance, and the conventional methods mainly comprise a chemical stripping method, a thermal etching method, an ultrasonic stripping method and the like, but the methods have some defects such as introduction of new chemical substances and treatmentToo long a time, etc., thereby affecting further applications in the industry.
Based on the above discussion, the invention mainly provides a method for preparing carbon nitride nanosheets by a microwave hydrothermal method, and applies the nanomaterial to a photocatalytic hydrogen production experiment.
Disclosure of Invention
Aiming at the defects of long process, low yield, environmental pollution and the like in the prior art, the invention provides a novel method for preparing carbon nitride nanosheets by using a microwave hydrothermal method, only green solvent water is used in the process of the method, and the method is green and efficient in process.
The invention is realized by adopting the following technical scheme:
preparation of rod-like g-C by microwave hydrothermal method3N4According to the method for preparing the carbon nitride nanosheet, a nitrogen-rich compound is roasted and cooled to obtain bulk-phase carbon nitride, and then the carbon nitride nanosheet is prepared through a microwave hydrothermal method.
Preferably, the nitrogen-rich compound comprises one or more of dicyandiamide, melamine or thiourea.
Preferably, the roasting temperature is 500-580 ℃, the heating rate is 2-10 ℃/min, and the roasting time is 2-6 h.
Preferably, the microwave hydrothermal temperature is 150-200 ℃, the microwave power is 80-150W, and the microwave hydrothermal time is 0.5-2 h.
Rod-like g-C prepared by microwave hydrothermal method3N4The nano-sheet is applied to the aspect of being used as a hydrogen production catalyst.
Hydrogen production catalyst, rod-like g-C prepared by the method and microwave hydrothermal method3N4Precious metals are deposited on the nano-sheets in a photoreduction mode, and the precious metals are one or more of Au, Ag and Pt.
Preferably, the noble metal is deposited in a rod-like g-C3N40.5-5% of the weight of the nanosheet.
The invention adopts a microwave hydrothermal method for constructing g-C3N4Compared with bulk-phase carbon nitride, the specific surface area of the photocatalyst treated by the scheme of the invention is obviously increasedIs large. Meanwhile, the technical scheme can reduce g-C3N4The recombination rate of electron holes and the accelerated interface charge transport. G to C3N4The nano-sheet is applied to the photocatalytic hydrogen production reaction to obtain excellent results, and the hydrogen production rate is more than 10 times higher than that of bulk phase carbon nitride. In addition, the semiconductor nano-catalyst obtained by the technical scheme shows excellent stability in hydrogen evolution reaction.
The invention has reasonable design and good practical application value.
Drawings
Fig. 1 shows the XRD pattern of the nano-catalyst prepared in example 4.
Fig. 2 shows a specific surface area and pore size diagram of the nanocatalyst prepared in example 4.
Fig. 3 shows a pore size diagram of the nanocatalyst prepared in example 4.
Fig. 4 shows a transmission electron micrograph of the nano-catalyst prepared in example 4.
Figure 5a shows an XPS plot (C1 s spectrum) of the nanocatalyst prepared in example 4.
Figure 5b shows an XPS plot (N1 s spectrum) of the nanocatalyst prepared in example 4.
Fig. 6 shows the solid uv-vis absorption profile of the nanocatalyst prepared in example 4.
Detailed Description
The following provides a detailed description of specific embodiments of the present invention.
The microwave hydrothermal technology provided by the invention is used for constructing g-C3N4The nano sheet is prepared by firstly roasting raw materials with rich nitrogen content such as dicyandiamide (dicyanodiamide), melamine or thiourea for 2-6 h in air atmosphere to obtain original bulk-phase carbon nitride. And then treating the bulk-phase carbon nitride for 0.5-2 hours at 150-220 ℃ and 80-150W by using a microwave hydrothermal synthesizer, washing and drying the obtained product to obtain the carbon nitride nanosheet with the thickness of about 3 microns. The specific embodiment is as follows:
example 1
Preparation of a bulk-phase carbon nitride: 10g of melamine is adopted as a precursor, the temperature is raised to 550 ℃ at the heating rate of 5 ℃/min, the mixture is roasted for 4h, the mixture is naturally cooled to the room temperature, and the obtained solid particles are ground by an agate mortar.
Example 2
Rod-like g-C3N4The nano-sheet is prepared by a microwave hydrothermal method, and comprises the following steps:
and (3) taking 100mg of the solid powder in the example 1, adding 25ml of deionized water, stirring for 10min, placing in a microwave hydrothermal synthesizer, treating at 170 ℃ for 1h at 110W, naturally cooling, washing and drying to obtain a sample.
Example 3
Rod-like g-C3N4The nano-sheet is prepared by a microwave hydrothermal method, and comprises the following steps:
and (3) taking 100mg of the solid powder in the example 1, adding 25ml of deionized water, stirring for 10min, placing in a microwave hydrothermal synthesizer, treating at 180 ℃ for 1h at 110W, naturally cooling, washing and drying to obtain a sample.
Example 4
Rod-like g-C3N4The nano-sheet is prepared by a microwave hydrothermal method, and comprises the following steps:
and (3) taking 100mg of the solid powder in the example 1, adding 25ml of deionized water, stirring for 10min, placing in a microwave hydrothermal synthesizer, treating at 190 ℃ for 1h at 110W, naturally cooling, washing and drying to obtain a sample.
Example 5
Rod-like g-C3N4The nano-sheet is prepared by a microwave hydrothermal method, and comprises the following steps:
and (3) taking 100mg of the solid powder in the example 1, adding 25ml of deionized water, stirring for 10min, placing in a microwave hydrothermal synthesizer, treating at 200 ℃ for 1h at 110W, naturally cooling, washing and drying to obtain a sample.
Example 6
Preparation of a bulk-phase carbon nitride: adopting 10g of dicyandiamide as a precursor, heating to 550 ℃ at the heating rate of 5 ℃/min, roasting for 4h, naturally cooling to room temperature, and grinding the obtained solid particles by using an agate mortar.
Example 7
Rod-like g-C3N4The nano-sheet is prepared by a microwave hydrothermal method, and comprises the following steps:
and (3) taking 100mg of the solid powder in the example 6, adding 25ml of deionized water, stirring for 10min, placing in a microwave hydrothermal synthesizer, treating at 190 ℃ for 1h at 110W, naturally cooling, washing and drying to obtain a sample.
Example 8
Preparation of a bulk-phase carbon nitride: 10g of thiourea is adopted as a precursor, the temperature is raised to 550 ℃ at the heating rate of 5 ℃/min for roasting for 4h, the solid particles are naturally cooled to the room temperature, and the obtained solid particles are ground by an agate mortar.
Example 9
Rod-like g-C3N4The nano-sheet is prepared by a microwave hydrothermal method, and comprises the following steps:
and (3) taking 100mg of the solid powder in the example 8, adding 25ml of deionized water, stirring for 10min, placing in a microwave hydrothermal synthesizer, treating at 170 ℃ for 1h at 110W, naturally cooling, washing and drying to obtain a sample.
Example 10
The photocatalytic hydrogen production test experiments of the above examples 1 to 9 were carried out, and the specific test procedures were as follows: 50mg of photocatalyst is taken, 3% by weight of Pt is added as a cocatalyst, 90ml of deionized water and 10ml of triethanolamine are added as a sacrificial agent. Performing ultrasonic treatment for 30min, performing hydrogen production test by using Pofely on-line hydrogen production system, controlling the temperature of circulating condensed water at 6 deg.C, vacuumizing for 30min before test, and analyzing the product hydrogen by Agilent gas chromatography. Specific results of the hydrogen production experiment are shown in table 1.
TABLE 1 Hydrogen generation results for different catalysts of the examples
As can be seen from Table 1, the hydrogen production rates of the photocatalysts prepared from the original bulk-phase carbon nitride prepared in examples 1, 6 and 8 were 200. mu. mol. h-1·g-1While examples 2-5 and 7-9 employ micro-scale with bulk phase carbon nitridePreparing rod-like g-C by wave hydrothermal method3N4After the nano-sheets are prepared, the hydrogen production rate is obviously improved. Moreover, it can be seen from examples 2 to 5 that the hydrogen production rate gradually increases with the temperature gradually increasing in the microwave hydrothermal method, but the hydrogen production rate starts to decrease after the temperature increases from 190 ℃ to 200 ℃, which indicates that the hydrothermal temperature is not as high as possible, and should be preferably 170 to 190 ℃. Finally, rod-like g-C prepared in example 43N4The hydrogen production rate of the nano-sheet as the photocatalyst is the best.
FIG. 1 shows the XRD pattern of the material prepared in example 4, 27.5oAnd 13.1oThe diffraction peaks at the center are respectively assigned to the (002) plane and the (100) plane of the carbon nitride, and the nitrogen adsorption desorption pattern and the pore size distribution diagram of the carbon nitride material subjected to microwave hydrothermal treatment are shown in FIGS. 2 and 3, and the corresponding specific surface area is 89.4cm2·g-1Much higher than the specific surface area of bulk phase carbon nitride, and has an average pore diameter and pore volume of 20nm and 0.285cc g-1. The large specific surface area and pore volume can effectively increase the active sites for catalytic hydrogen production, thereby obtaining higher hydrogen production rate. Fig. 4 shows a transmission electron microscope image of the nano material, and it can be clearly seen that the material has a rod-like structure. FIG. 5a shows an XPS spectrum of a material with three distinct peaks centred at 288.2eV, 286.3eV and 284.8eV in the C1s spectrum assigned to N = C (-N)2N = CH-N and C-C bond; FIG. 5b shows an XPS spectrum of a material with major peaks distributed at 398.7eV, 400.1eV, 401.2eV and 404.5eV for the N1s spectrum assigned to C = N-C, N- (C), respectively3、C-NH2And charge effects. Fig. 6 shows the solid ultraviolet absorption spectrum of the carbon nitride material after microwave treatment, the absorption edge of the material is about 470nm, and the material has a good visible light absorption range, which also provides necessary conditions for the material to exhibit good hydrogen production performance.
The nano material prepared by the microwave hydrothermal method in the scheme of the invention obviously improves the specific surface area of the material, promotes the separation of electron holes, is applied to the photocatalytic hydrogen production reaction, effectively improves the photocatalytic hydrogen production performance, and is a photocatalyst with a very promising prospect.
The above embodiments are merely illustrative of the effects and principles of the present invention, and do not limit the present invention to the specific structures and applications described above, and therefore all similar and equivalent structures that may be used are within the scope of the invention as claimed.