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CN111186824B - Preparation method of high-specific-surface-area defective carbon nitride - Google Patents

Preparation method of high-specific-surface-area defective carbon nitride Download PDF

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CN111186824B
CN111186824B CN202010026656.6A CN202010026656A CN111186824B CN 111186824 B CN111186824 B CN 111186824B CN 202010026656 A CN202010026656 A CN 202010026656A CN 111186824 B CN111186824 B CN 111186824B
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carbon nitride
ball milling
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roasting
precursor
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CN111186824A (en
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邓全花
巴贵明
李海平
侯万国
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Shandong University
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Abstract

The invention provides a preparation method of high specific surface area defective carbon nitride, which comprises the following steps: roasting the carbon nitride precursor at 200-500 ℃ to obtain a carbon nitride intermediate; performing ball milling on the obtained carbon nitride intermediate to obtain a ball-milled carbon nitride intermediate; and roasting the obtained carbon nitride intermediate subjected to ball milling at 520-650 ℃ to obtain the high-specific-surface-area defective carbon nitride. The invention ball-mills the carbon nitride intermediate, then bakes, and then prepares the high specific surface area defective carbon nitride. The generation of defects and mesopores obviously enhances the light absorption performance of the carbon nitride, accelerates the separation of photo-generated charges, and obviously improves the hydrogen production rate of the photocatalytic water decomposition compared with the traditional massive carbon nitride. The method has low requirement on equipment, is simple to operate, is easy to realize industrial mass production, and can be widely applied to the field of defective carbon nitride production.

Description

Preparation method of high-specific-surface-area defective carbon nitride
Technical Field
The invention relates to a preparation method of high specific surface area defective carbon nitride, in particular to a method for preparing high specific surface area defective carbon nitride by a ball milling method, and belongs to the technical field of nano materials and photocatalysis.
Background
In the face of the problems of energy crisis, greenhouse effect, environmental pollution and the like which are urgently to be solved at present, the photocatalytic technology can convert low-density solar energy into high-density chemical energy through processes of hydrogen production by splitting water, carbon dioxide reduction and the like, and represents great application potential. Carbon Nitride (CN) as an organic semiconductor photocatalyst has the advantages of no toxicity, high chemical stability, low cost and the like, and has wide application prospect in the technical field of photocatalysis. However, CN has its own defects of small specific surface area, poor crystallinity, narrow spectral absorption range, poor conductivity, low photo-generated charge separation efficiency, etc., and its photocatalytic activity is low, and thus it cannot meet the requirements of industrial application.
At present, methods for enhancing the CN photocatalysis performance mainly comprise appearance regulation (template method, stripping and the like), heterojunction construction, heteroatom modification and the like. However, these methods are mainly chemical methods, the preparation process is complicated, additional toxic or expensive chemical reagents are required to be added, and industrial mass production is generally difficult. Physical methods meeting the requirements of green chemistry and atom economy, such as the ball milling method which is most widely applied in the field of nanochemistry, have few reports on CN structure modification, but still have technical or technological defects. For example: chinese patent document CN109205580A provides a method for ball milling to strip carbon nitride, which comprises the following steps: 1) mixing the nitrogen-rich precursor with salt, and then calcining to obtain a carbon nitride-salt compound; 2) performing ball milling treatment on the obtained compound; 3) centrifuging to remove salt in the compound, and drying to obtain the final product. However, the method has complex process, needs to add extra salt and adopts solvent to dissolve and remove, generates extra waste liquid, and has longer ball milling time and higher production cost. In addition, the method can only thin the carbon nitride nanosheet, and no defects are introduced, so that the capability of the method for increasing the light absorption and photocatalytic activity of the material is limited. Chinese patent document CN109046422A relates to a lamellar carbon nitride material and a preparation method thereof, comprising the steps of: (1) adding an organic matter precursor containing amino into a ball mill, and fully ball-milling; (2) roasting the ball-milled precursor at a certain temperature; (3) washing and drying the solid obtained in the step (2); (4) and (4) raising the temperature of the dried solid obtained in the step (3) and roasting again to obtain the lamellar carbon nitride material. However, the intermediate in the method needs to be washed by ethanol, additional waste liquid is generated, and defects cannot be introduced into carbon nitride, so that the light absorption and photocatalytic activity of the material cannot be obviously improved.
Therefore, it is urgently needed to develop a method for preparing high specific surface area defective carbon nitride by a ball milling method, which has simple preparation process, low cost and easy industrial production, so as to improve the photocatalytic performance of CN and realize large-scale production, thereby solving the current increasingly serious energy and environmental problems.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method of high specific surface area defective carbon nitride, the method prepares the high specific surface area defective carbon nitride by ball milling, the operation is simple, the cost is low, the industrial batch production is easy to realize, and the photocatalytic activity of the material can be obviously improved.
The technical scheme of the invention is as follows:
a preparation method of high specific surface area defective carbon nitride comprises the following steps:
(1) roasting the carbon nitride precursor at 200-500 ℃ to obtain a carbon nitride intermediate; performing ball milling on the obtained carbon nitride intermediate to obtain a ball-milled carbon nitride intermediate;
(2) and (2) roasting the carbon nitride intermediate subjected to ball milling in the step (1) at 520-650 ℃, so as to obtain the high-specific-surface-area defective carbon nitride.
According to the invention, preferably, the carbon nitride precursor in step (1) is one or a combination of more than two of melamine, cyanamide, dicyandiamide, ammonium thiocyanate, urea and thiourea; further preferably, the carbon nitride precursor is melamine, cyanamide or dicyandiamide.
According to the invention, preferably, the roasting temperature in the step (1) is 300-400 ℃; further preferably, the roasting temperature is 400 ℃ when the carbon nitride precursor is melamine, and the roasting temperature is 350 ℃ when the carbon nitride precursor is cyanamide or dicyandiamide.
According to the invention, the roasting time in the step (1) is preferably 1-6 h, and more preferably 3 h.
According to the present invention, in the ball milling step described in step (1), the mass ratio of the ball milling balls to the carbon nitride intermediate is preferably (10 to 100):1, more preferably (50 to 70):1, and even more preferably 50: 1.
According to the invention, the rotation speed of the ball mill in the step (1) is preferably 500-3000 rpm, more preferably 1500-2500 rpm, and even more preferably 1500 rpm; the ball milling time is 1-24 h, preferably 6-10 h, and more preferably 6 h.
According to the present invention, it is preferable that the calcination temperature in the step (2) is 550 ℃; the roasting time is 2-6 h, and preferably 4 h.
According to the present invention, the calcination described in the steps (1) and (2) is preferably carried out in a muffle furnace or a tube furnace, and more preferably in a muffle furnace.
The invention has the technical characteristics that:
the invention discovers that in the process of roasting the carbon nitride intermediate by the carbon nitride precursor at different temperatures, the roasting temperature is particularly important, when the temperature is too high, the structure of the obtained intermediate is close to that of carbon nitride, the damage degree of ball milling on the intermediate is low, and the defects are few; when the temperature is too low, the crystallinity of the intermediate is poor, the structural rigidity is not strong, and the ball milling effect can not cause a large number of defects to be formed, so that the roasting temperature of the carbon nitride precursor needs to be strictly controlled.
Secondly, the invention discovers that the ball milling rotating speed and the ball milling time are equally important in the ball milling process of the carbon nitride intermediate, and when the ball milling rotating speed is too high and the ball milling time is too long, defects are introduced into the carbon nitride too much to form a photo-generated charge composite center, so that the catalytic activity of the carbon nitride intermediate is reduced; when the ball milling speed is too low and the ball milling time is too short, the damage degree of the carbon nitride intermediate is weak, so that the defect formation is too little, and the photocatalytic activity is not improved. Therefore, the ball milling speed and the ball milling time of the carbon nitride intermediate need to be strictly controlled.
The invention has the following beneficial effects:
1. compared with the traditional chemical method for modifying the carbon nitride structure, the mechanical ball milling method for preparing the high-specific-surface-area defective carbon nitride only needs to ball mill the carbon nitride intermediate and roast, has simple operation process and low cost, and is easy to realize industrialized mass production.
2. The high specific surface area defect type carbon nitride prepared by the invention has high photocatalytic activity and great application value in the fields of energy, environment and the like.
Drawings
Fig. 1 is an X-ray diffraction pattern of carbon nitride prepared in example 1 and comparative example 1, in which the ordinate is diffraction intensity and the abscissa is diffraction angle (2 θ).
FIG. 2 is SEM photographs of carbon nitride intermediates before and after ball milling in example 1, wherein a is the SEM photograph of the carbon nitride intermediate before ball milling; and b is an SEM picture of the carbon nitride intermediate after ball milling.
Fig. 3 is SEM photographs of carbon nitride prepared in example 1 and comparative example 1, wherein a is an SEM photograph of carbon nitride prepared in comparative example 1; b is an SEM photograph of the carbon nitride prepared in example 1.
Fig. 4 is an optical photograph of carbon nitride prepared in example 1 and comparative example 1, wherein a is an optical photograph of carbon nitride prepared in comparative example 1; b is an optical photograph of the carbon nitride prepared in example 1.
Fig. 5 is a graph of the solid uv-vis diffuse reflectance spectra of carbon nitride prepared in example 1 and comparative example 1.
FIG. 6 shows N of carbon nitride prepared in example 1 and comparative example 12Adsorption and desorption isotherms.
Fig. 7 is a plot of the pore size distribution of the carbon nitride prepared in example 1 and comparative example 1.
Fig. 8 is a graph showing hydrogen production curves by visible light catalyzed water decomposition of carbon nitride prepared in example 1 and comparative examples 1 to 2.
Detailed Description
The invention is further illustrated by the following examples, without restricting its scope.
The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.
Melamine powder was purchased from national pharmaceutical group chemical agents limited, cat # 30112528;
cyanamide powder was purchased from Shanghai Shao Yuan reagent, Inc., cat # SY 058151;
dicyandiamide powder was purchased from Shanghai Allantin Biotechnology Ltd, cat # D100425.
In the examples described below, SEM photographs were obtained by observation with a Hitachi SU8010 field emission scanning electron microscope; n is a radical of2The adsorption and desorption isothermal curve is measured by a Quadrasorb EVO type full-automatic specific surface area and pore size analyzer of Congta instruments, USA, the specific surface area is calculated by a BET method, and the pore size distribution curve is obtained by processing adsorption line branches by a BJH method.
The hydrogen production by splitting water with visible light is carried out in a medium and high education gold source CEL-SPH2N/PAEM type photocatalytic activity evaluation system, a CEL-PF300-T8E type xenon lamp (150W) and a CEL-UVIRCUT420 cutoff filter (the wavelength is more than 420nm) are used as visible light sources, a circulating cooling water system controls the reaction temperature to be 5 ℃, and the generated hydrogen is generatedThermal conductivity detector by GC-7920 gas chromatograph (
Figure BDA0002362715670000041
Molecular sieve with argon as carrier gas).
Example 1
A preparation method of high specific surface area defective carbon nitride comprises the following steps:
(1) placing melamine in a muffle furnace, and roasting for 3h at 400 ℃ to obtain a carbon nitride intermediate; and putting the carbon nitride intermediate and the ball milling balls into a ball milling tank of a planetary ball mill according to the mass ratio of the ball milling balls to the carbon nitride intermediate of 50:1, and performing ball milling for 6 hours at the rotating speed of 1500rpm to obtain the ball-milled carbon nitride intermediate.
(2) And (2) placing the carbon nitride intermediate obtained in the step (1) after ball milling into a muffle furnace, and roasting for 4 hours at 550 ℃ to obtain the high specific surface area defective carbon nitride.
Example 2
A preparation method of high specific surface area defective carbon nitride comprises the following steps:
(1) placing dicyandiamide in a muffle furnace, and roasting for 4 hours at 350 ℃ to obtain a carbon nitride intermediate; and putting the carbon nitride intermediate and the ball milling balls into a ball milling tank of a planetary ball mill according to the mass ratio of the ball milling balls to the carbon nitride intermediate of 60:1, and performing ball milling for 8 hours at the rotating speed of 2000rpm to obtain the ball-milled carbon nitride intermediate.
(2) And (2) placing the carbon nitride intermediate obtained in the step (1) after ball milling into a muffle furnace, and roasting for 5 hours at 550 ℃ to obtain the high specific surface area defective carbon nitride.
Example 3
A preparation method of high specific surface area defective carbon nitride comprises the following steps:
(1) placing cyanamide in a muffle furnace, and roasting for 5 hours at 300 ℃ to obtain a carbon nitride intermediate; putting the carbon nitride intermediate and the ball milling balls into a ball milling tank of a planetary ball mill according to the mass ratio of the ball milling balls to the carbon nitride intermediate of 70:1, and performing ball milling for 10 hours at the rotating speed of 2500rpm to obtain the ball-milled carbon nitride intermediate.
(2) And (2) placing the carbon nitride intermediate obtained in the step (1) after ball milling into a muffle furnace, and roasting for 6 hours at 550 ℃ to obtain the high specific surface area defective carbon nitride.
Comparative example 1
A preparation method of traditional blocky carbon nitride comprises the following steps:
and (3) placing the melamine in a muffle furnace, and roasting for 4 hours at 550 ℃ to obtain the traditional blocky carbon nitride.
Comparative example 2
A method for preparing blocky carbon nitride comprises the following steps:
(1) and (3) placing the melamine in a muffle furnace, and roasting for 3h at 400 ℃ to obtain a carbon nitride intermediate.
(2) And (2) placing the carbon nitride intermediate obtained in the step (1) into a muffle furnace, and roasting for 4 hours at 550 ℃ to obtain the blocky carbon nitride.
The overall analysis was as follows:
the X-ray diffraction patterns of the carbon nitrides prepared in example 1 and comparative example 1 are shown in fig. 1, and it can be seen from fig. 1 that the products obtained in example 1 and comparative example 1 have (210) and (002) peaks typical of carbon nitrides. Indicating that the resulting product is carbon nitride. The (002) peak of the carbon nitride prepared in example 1 was significantly weakened, indicating that the introduction of mesopores resulted in the decrease of crystallinity thereof, and that it was shifted to a low-angle direction, indicating that the interlayer spacing thereof was increased.
SEM photographs of the carbon nitride intermediate before ball-milling and the carbon nitride intermediate after ball-milling prepared in example 1 are shown in fig. 2, and as can be seen from fig. 2a, the carbon nitride intermediate before ball-milling is composed of micro-sized bulk, and as can be seen from fig. 2b, the carbon nitride intermediate after ball-milling is increased in a large amount of nano-sized particles on the bulk.
SEM photographs of the carbon nitrides prepared in example 1 and comparative example 1 are shown in fig. 3, and the morphology of the conventional bulk carbon nitride prepared in comparative example 1 is shown in fig. 3a, and the presence of pores is hardly observed; the morphology of the high specific surface area deficient carbon nitride prepared in example 1 is shown in fig. 3b, and comparing fig. 3a and fig. 3b, it can be found that the carbon nitride intermediate forms a large number of pore structures after being ball-milled and calcined.
The optical photographs of the carbon nitride prepared in example 1 and comparative example 1 are shown in fig. 4, and it can be seen from fig. 4 that the color of the carbon nitride intermediate becomes remarkably dark after ball milling and firing, indicating the formation of a large number of defects.
The solid uv-vis diffuse reflectance spectra of carbon nitride prepared in example 1 and comparative example 1 are shown in fig. 5, and it can be seen from fig. 5 that the visible light absorption property of carbon nitride is significantly enhanced and the low-energy long-wavelength light after 600nm is also significantly absorbed, indicating that the formation of defects enhances the visible light absorption property thereof.
N of carbon nitride prepared in example 1 and comparative example 12The adsorption/desorption isotherms are shown in fig. 6, the pore size distribution is shown in fig. 7, and it can be seen from fig. 6 and 7 that the carbon nitride prepared in comparative example 1 and the carbon nitride prepared in example 1 both have the type IV isotherm and the type H3 hysteresis loop, i.e., a mesoporous structure is present. The specific surface area and the pore volume of the carbon nitride prepared in comparative example 1 were 6.8m, respectively2G and 0.054cm3In g, the specific surface area and pore volume of the carbon nitride prepared in example 1 were 16.1m2G and 0.068cm3The comparative pore size distribution curve indicates that a large number of mesopores having a pore size of 2 to 5nm are formed in the carbon nitride prepared in example 1.
The carbon nitride prepared in example 1 and comparative examples 1-2 is applied to visible light catalysis water decomposition hydrogen production, and the specific steps are as follows:
20mg of carbon nitride powder was ultrasonically dispersed in 80mL of an aqueous solution containing 10 vol% triethanolamine, and then 0.31mL of H having a concentration of 0.01mol/L was added2PtCl6And (4) solution, and transferring the suspension into a hydrogen production reaction vessel. Vacuumizing for 15min, and illuminating for 1h by using a 300W xenon lamp as a light source to finish Pt deposition. Then vacuumizing again, and starting the hydrogen production reaction by using a 300W xenon lamp (the wavelength is more than 420nm) as a light source. The hydrogen production was detected by gas chromatography every 30 min.
The visible light catalyzed water splitting hydrogen production curves of the carbon nitride prepared in example 1 and comparative examples 1-2 are shown in FIG. 8. As can be seen from FIG. 8, the hydrogen production rate of the carbon nitride prepared in example 1 is 529. mu. mol g-1h-1Comparison ofThe hydrogen production rate of carbon nitride prepared in example 1 was 72. mu. mol g-1h-1Comparative example 2 the hydrogen production rate of carbon nitride was 140. mu. mol g-1h-1The hydrogen production rates of the carbon nitride prepared in example 1 were 7.3 and 3.8 times as high as those of comparative example 1 and comparative example 2, respectively.
The data show that the high specific surface area defect type carbon nitride prepared by the ball milling method has higher photocatalytic activity and higher industrial application value.
It is obvious that the above examples of the present invention are only simple applications of the ball milling method to improve the activity of the photocatalyst, and are given by way of illustration to clearly illustrate the broad scope of the present invention, and are not intended to limit the application fields and embodiments of the present invention. Other variations should be made in specific cases for specific applications of each photocatalyst. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims (10)

1. A preparation method of high specific surface area defective carbon nitride comprises the following steps:
(1) roasting the carbon nitride precursor at 200-500 ℃ to obtain a carbon nitride intermediate; performing ball milling on the obtained carbon nitride intermediate to obtain a ball-milled carbon nitride intermediate; the carbon nitride precursor is one or the combination of more than two of melamine, cyanamide, dicyandiamide, ammonium thiocyanate, urea and thiourea; in the ball milling step, the mass ratio of the ball milling ball to the carbon nitride intermediate is (10-100): 1; the rotation speed of the ball mill is 500-3000 rpm; the ball milling time is 1-24 h;
(2) and (2) roasting the carbon nitride intermediate subjected to ball milling in the step (1) at 520-650 ℃, so as to obtain the high-specific-surface-area defective carbon nitride.
2. The method for preparing carbon nitride according to claim 1, wherein the carbon nitride precursor in step (1) is melamine, cyanamide or dicyandiamide.
3. The method for producing carbon nitride according to claim 1, wherein the baking temperature in the step (1) is 300 to 400 ℃.
4. The method for preparing carbon nitride according to claim 1, wherein the calcination temperature in the step (1) is 400 ℃ when the carbon nitride precursor is melamine and 350 ℃ when the carbon nitride precursor is cyanamide or dicyandiamide.
5. The method for preparing carbon nitride according to claim 1, wherein the calcination time in the step (1) is 1 to 6 hours.
6. The method for preparing carbon nitride according to claim 1, wherein the mass ratio of the ball milling balls to the carbon nitride intermediate in the ball milling step in the step (1) is (50-70): 1.
7. The method for preparing carbon nitride according to claim 1, wherein the rotation speed of the ball mill in the step (1) is 1500 to 2500 rpm.
8. The method for preparing carbon nitride according to claim 1, wherein the time of ball milling in step (1) is 6 to 10 hours.
9. The method for producing carbon nitride according to claim 1, wherein the baking temperature in the step (2) is 550 ℃; the roasting time is 2-6 h.
10. The method for producing carbon nitride according to claim 1, wherein the firing in steps (1) and (2) is performed in a muffle furnace or a tube furnace.
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