Preparation method of double-defect type flaky carbon nitride with increased specific surface area

Abstract

The invention relates to a preparation method of double-defect type flaky carbon nitride with an increased specific surface area, which comprises the following steps: grinding and uniformly mixing strip-shaped melamine and ammonium salt, and roasting in an air atmosphere to obtain a strip-shaped carbon nitride intermediate; and roasting the strip-shaped carbon nitride intermediate in a semi-closed tubular furnace to obtain the target product high-specific-surface-area double-defect type flaky carbon nitride. The double-defect type flaky carbon nitride product prepared by the preparation method of the double-defect type flaky carbon nitride with the increased specific surface area has weaker (210) and (002) diffraction peak intensities; the microstructure of the product is of a sheet structure; the specific surface area of the product reaches 226.9 m < 2 > / g. A bottom-to-top two-step roasting method is adopted, the specific surface area of carbon nitride is increased, meanwhile, double defects are introduced, visible light absorption is increased, photo-generated charge separation is promoted, the whole operation process is simple, cost is low, and industrial batch production is easy to achieve.

Description

Technical Field

[0001] The present invention relates to a method for preparing double-defect flaky carbon nitride with increased specific surface area, and specifically to a method for preparing double-defect flaky carbon nitride with high specific surface area by a bottom-up two-step calcination method, belonging to the technical field of two-dimensional nanomaterial preparation and photocatalysis. Background Art

[0002] As a non-metallic organic semiconductor material, carbon nitride has excellent thermal and chemical stability and suitable energy band structure, and has great application prospects in photocatalytic antibacterial, hydrogen peroxide preparation, water decomposition hydrogen production, carbon dioxide reduction and nitrogen fixation. However, traditional bulk carbon nitride has a narrow visible light absorption range and a small specific surface area (less than 10m 2 / g) and rapid recombination of photogenerated charge carriers limit its photocatalytic activity, making it difficult to meet the requirements of industrial applications.

[0003] Increasing the specific surface area of ​​carbon nitride and introducing defects are important methods to improve the photocatalytic performance of carbon nitride. At present, many researchers use a top-down thermal oxidation method to peel off bulk carbon nitride into ultrathin porous nanosheets, thereby increasing the specific surface area, exposing more active sites, and shortening the distance for photogenerated charges to migrate from the inside of carbon nitride to the surface. However, this leads to a significant increase in the band gap of carbon nitride, which is not conducive to the absorption of visible light. Therefore, in order to increase the light absorption characteristics, nitrogen vacancies, carbon vacancies and heteroatoms are usually further introduced into carbon nitride ultrathin nanosheets. The introduction of vacancies and heteroatoms can increase additional active sites and generate impurity energy levels, thereby enhancing the capture ability and migration kinetics of photogenerated charge carriers. Although this type of synthesis method improves the photocatalytic performance of carbon nitride, the preparation process is complicated, the yield is low, and the reproducibility of material synthesis is poor.

[0004] Therefore, there is an urgent need to find a method for synthesizing high specific surface area double-defect flake carbon nitride that is simple to operate, low cost, high yield, and easy to industrialize, so as to improve the photocatalytic performance of carbon nitride. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing a high specific surface area double-defect flaky carbon nitride. The method prepares a high specific surface area double-defect flaky carbon nitride by a bottom-up two-step calcination method. The method is simple to operate, low in cost, easy to realize industrial mass production, and can significantly improve the photocatalytic hydrogen peroxide production and antibacterial efficiency of the material.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing double-defect flaky carbon nitride with increased specific surface area comprises grinding and mixing ribbon-shaped melamine (C3H6N6) and ammonium salt evenly, and then calcining them in an air atmosphere to obtain a ribbon-shaped carbon nitride intermediate. The ribbon-shaped carbon nitride intermediate is then placed in a semi-enclosed tubular furnace and calcined to obtain the target product, high specific surface area double-defect flaky carbon nitride (C6N7(NH2)(NH)] n ).

[0008] The ammonium salt is one or a combination of two or more of ammonium chloride, ammonium bromide, ammonium sulfate, ammonium nitrate or ammonium bicarbonate.

[0009] The ammonium salt is ammonium bromide or ammonium chloride.

[0010] The mass ratio of the strip-shaped melamine to the ammonium salt is 1:0.5-5.

[0011] The roasting temperature of the strip-shaped melamine and ammonium salt mixture is 350-520°C.

[0012] The roasting time of the strip-shaped melamine and ammonium salt mixture is 2 to 8 hours.

[0013] The heating rate of the strip-shaped melamine and ammonium salt mixture is 1-10°C / min.

[0014] The calcination temperature of the ribbon-shaped carbon nitride intermediate is 520-600° C. and the calcination time is 1-8 hours.

[0015] The double-defect flaky carbon nitride product prepared by the method for preparing the double-defect flaky carbon nitride with increased specific surface area has weaker (210) and (002) diffraction peak intensities; the microscopic morphology of the product is a flaky structure; the specific surface area of ​​the product reaches 226.9 m 2 / g.

[0016] In the method for preparing double-defect flaky carbon nitride with increased specific surface area of ​​the present invention, it is further preferred that the ammonium salt is ammonium bromide;

[0017] A further preferred mass ratio of the strip-shaped melamine to the ammonium salt is 1:1.

[0018] According to the present invention, the grinding is to fully mix the raw materials, so there is no special requirement for the grinding time, preferably 5 minutes.

[0019] The calcination temperature of the ribbon-shaped melamine and ammonium salt mixture is more preferably 500°C.

[0020] The roasting time of the strip-shaped melamine and ammonium salt mixture is more preferably 3 hours.

[0021] The heating rate of the strip-shaped melamine and ammonium salt mixture is more preferably 2° C. / min.

[0022] The calcination temperature of the ribbon-shaped carbon nitride intermediate is more preferably 550°C.

[0023] The calcination time of the ribbon-shaped carbon nitride intermediate is more preferably 3 hours.

[0024] The product obtained by the present invention is tested by X-ray diffraction spectrum, scanning electron microscope photos and N2 adsorption-desorption isotherm curve, which proves that high specific surface area double-defect flake carbon nitride is obtained. Figure 1 The (210) and (002) diffraction peak intensities of the obtained product are weaker than those of conventional bulk carbon nitride and conventional ultra-thin carbon nitride, indicating that a large number of defects have been generated; Figure 3 It can be seen that the microstructure of the obtained product is a flake structure, while the traditional bulk carbon nitride and traditional ultra-thin carbon nitride are bulk and porous structures respectively; Figure 4 It can be seen that the specific surface area of ​​the obtained product (226.9m 2 / g) compared with bulk carbon nitride (9.6m 2 / g) and ultrathin carbon nitride (159.7m 2 / g) were increased by about 23.6 and 1.4 times respectively, so the present invention provides a method for preparing double-defect flaky carbon nitride with increased specific surface area.

[0025] The technical features of the present invention are as follows:

[0026] 1. The present invention finds that the mixing ratio of the strip melamine and the ammonium salt described in the step is critical. When the amount of ammonium salt used is small, the fusion of the strip melamine in the subsequent roasting process cannot be suppressed; when the amount of ammonium salt is too much, it is wasted. Therefore, the mass ratio of the strip melamine and the ammonium salt needs to be strictly controlled.

[0027] 2. The present invention finds that the heating rate of the precursor mixture described in the step is particularly important. When the heating rate is too high, the band-shaped melamine will fuse quickly, and the intermediate structure obtained will be difficult to obtain a band-shaped structure, which is not conducive to obtaining carbon nitride with a high specific surface area; when the heating rate is too low, the heating time is too long, which will increase energy consumption. Therefore, it is necessary to strictly control the heating rate of the precursor mixture.

[0028] 3. The present invention finds that in the process of preparing high specific surface area double-defect flake carbon nitride in the step, the amount of ribbon carbon nitride intermediate added is very important. When the amount added is too low, the residual oxygen will completely oxidize and decompose the intermediate; when the amount added is too high, it is not conducive to producing a high specific surface area.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. Compared with the traditional method for preparing high specific surface area carbon nitride, the bottom-up two-step calcination method for preparing high specific surface area double-defect flaky carbon nitride adopted in the present invention increases the specific surface area of ​​carbon nitride while introducing double defects, thereby increasing visible light absorption and promoting photogenerated charge separation. The required raw materials are simple and easy to obtain, and only simple calcination is required. The entire operation process is simple, low-cost, and easy to achieve industrial mass production.

[0031] 2. The high specific surface area double-defect flaky carbon nitride prepared by the present invention has a high photocatalytic hydrogen peroxide production rate and bactericidal activity, and has great application value in the fields of energy and environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the X-ray diffraction spectrum of the carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2, wherein the ordinate is the diffraction intensity and the abscissa is the diffraction angle (2θ).

[0033] Figure 2 This is a scanning electron microscope (SEM) photograph of the ribbon-shaped carbon nitride intermediate prepared in Example 1.

[0034] Figure 3 The SEM photographs of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2, wherein a is the SEM photograph of carbon nitride prepared in Example 1; b is the SEM photograph of carbon nitride prepared in Comparative Example 1; and c is the SEM photograph of carbon nitride prepared in Comparative Example 2.

[0035] Figure 4 N2 adsorption-desorption isotherms of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0036] Figure 5 Solid UV-visible diffuse reflectance spectra of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0037] Figure 6 Visible light photocatalytic hydrogen peroxide production curve of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0038] Figure 7 These are photos of the photocatalytic activity of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 against methicillin-resistant Staphylococcus aureus. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0040] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0041] In the following embodiments, the semi-enclosed tube furnace is a quartz tube with one side sealed and the other side having a hole with a diameter of 4 mm.

[0042] Example 1

[0043] A method for preparing high specific surface area double defect flaky carbon nitride comprises the following steps: grinding ribbon melamine and ammonium bromide at a mass ratio of 1:1 for 5 minutes, placing in a muffle furnace, and roasting at 500°C for 3 hours at a heating rate of 2°C / min to obtain a ribbon carbon nitride intermediate. Taking 0.2g of the ribbon carbon nitride intermediate, placing in a semi-enclosed tubular furnace, and roasting at 550°C for 3 hours, a high specific surface area double defect flaky carbon nitride is obtained, and the yield reaches 65%.

[0044] Example 2

[0045] A method for preparing high specific surface area double defect flaky carbon nitride comprises the following steps: grinding ribbon melamine and ammonium chloride at a mass ratio of 1:5 for 5 minutes, placing in a muffle furnace, and roasting at 350°C for 8 hours at a heating rate of 1°C / min to obtain a ribbon carbon nitride intermediate. The ribbon carbon nitride intermediate is then placed in a semi-enclosed tubular furnace and roasted at 600°C for 1 hour to obtain high specific surface area double defect flaky carbon nitride.

[0046] Example 3

[0047] A method for preparing high specific surface area double defect flaky carbon nitride comprises the following steps: grinding ribbon melamine and ammonium bicarbonate at a mass ratio of 1:0.5 for 5 minutes, placing in a muffle furnace, and calcining at 520°C for 2 hours at a heating rate of 10°C / min to obtain a ribbon carbon nitride intermediate. The ribbon carbon nitride intermediate is then placed in a semi-enclosed tubular furnace and calcined at 520°C for 8 hours to obtain high specific surface area double defect flaky carbon nitride.

[0048] Comparative Example 1

[0049] According to the preparation method of Advanced Functional Materials, 2022, 32, 2205119, a conventional bulk carbon nitride is prepared. The steps are as follows:

[0050] Melamine is placed in a muffle furnace and calcined at 550°C for 4 hours to obtain traditional bulk carbon nitride.

[0051] Comparative Example 2

[0052] According to the preparation method of the literature Applied Catalysis B: Environmental, 2018, 239, 16–26, conventional ultra-thin carbon nitride was prepared. The steps included are as follows:

[0053] 0.5 g of the blocky carbon nitride in Comparative Example 1 was placed in a muffle furnace and calcined at 550° C. for 3 h to obtain conventional ultra-thin carbon nitride with a yield of 20%.

[0054] The comprehensive analysis is as follows:

[0055] Figure 1 The X-ray diffraction spectra of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown in Figure 1. As can be seen from the figure, the products obtained in Example 1, Comparative Example 1 and Comparative Example 2 have typical carbon nitride (210) and (002) peaks, indicating that the obtained products are carbon nitride. The peak intensities of (210) and (002) of carbon nitride obtained in Example 1 are significantly weakened, indicating that the introduction of defects leads to a decrease in its crystallinity.

[0056] Figure 2 is a scanning electron microscope (SEM) photograph of the ribbon-shaped carbon nitride intermediate prepared in Example 1. Figure 2 It can be seen that the ribbon-like carbon nitride intermediate is composed of smooth ribbon structures of varying sizes and several hundred nanometers thick.

[0057] Figure 3 is the SEM photograph of the carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2. Figure 3 As can be seen from a, the high specific surface area double defect flake carbon nitride is composed of a porous flake structure that is thinner than the ribbon-like carbon nitride intermediate. The morphology of the conventional bulk carbon nitride prepared in Comparative Example 1 is as follows: Figure 3 As shown in b, it is composed of a block structure with a thickness of tens of microns, and almost no pores are observed; the morphology of the conventional ultrathin carbon nitride prepared in Comparative Example 2 is as follows Figure 3 c shows a porous structure composed of tens of microns thick. Figure 3 a. Figure 3 b and Figure 3 c It can be found that the carbon nitride precursor mixture forms an ultra-thin porous structure of smaller size after secondary calcination.

[0058] Figure 4 The N2 adsorption-desorption isotherms of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 4 It can be seen that the carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 all have type IV isotherms and H3 type hysteresis loops, that is, they have mesoporous structures. The specific surface area of ​​the carbon nitride prepared in Comparative Example 1 is 9.6 m 2 / g, the specific surface area of ​​carbon nitride prepared in Comparative Example 2 is 226.9m2 / g, while the specific surface area of ​​the carbon nitride prepared in Example 1 is 159.7m 2 / g, indicating that this method can prepare carbon nitride with high specific surface area.

[0059] Figure 5 The solid ultraviolet-visible diffuse reflectance spectra of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 5 It can be seen that the light absorption intensity of the traditional ultrathin carbon nitride prepared in Comparative Example 2 is weaker than that of the traditional bulk carbon nitride prepared in Comparative Example 1, while the light absorption intensity of the carbon nitride prepared in Example 1 is significantly increased, indicating that the formation of double defects enhances its light absorption performance.

[0060] The carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 was applied to photocatalytic hydrogen peroxide production, and the specific steps were as follows:

[0061] 20 mg of carbon nitride powder was ultrasonically dispersed in 100 mL of an aqueous solution containing 10 vol% methanol, and then oxygen was introduced for 30 min to reach saturation. A 300 W xenon lamp (wavelength greater than 420 nm) was turned on to start the photocatalytic hydrogen peroxide reaction. 2 mL of the reaction solution was taken every 15 min, and the photocatalyst particles in the solution were removed with a syringe organic filter. Then, 2 mL of potassium iodide (0.1 M) and 50 μL of ammonium molybdate (0.01 M) were added to the mixed solution and stirred for 5 min to allow it to react fully. The concentration of the reaction solution was determined using a Shimadzu UV-2700 UV-visible spectrophotometer.

[0062] The visible light photocatalytic hydrogen peroxide production curves of carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 are as follows: Figure 6 As shown, from Figure 6 It can be seen that the hydrogen peroxide generation rate of the high specific surface area double-defect flaky carbon nitride prepared in Example 1 is 1030 μmol g -1 h -1 The hydrogen peroxide generation rate of the bulk carbon nitride prepared in Comparative Example 1 was 53 μmol g -1 h -1 The hydrogen peroxide generation rate of the ultrathin carbon nitride prepared in Comparative Example 2 is 329 μmol g -1 h -1 The hydrogen peroxide generation rate of the carbon nitride prepared in Example 1 is 19.5 and 3.1 times that of Comparative Example 1 and Comparative Example 2, respectively.

[0063] The carbon nitride prepared in Example 1, Comparative Example 1 and Comparative Example 2 was applied to photocatalytic sterilization, and the specific steps were as follows:

[0064] 5 mg of carbon nitride powder was ultrasonically dispersed in 1 mL of aqueous solution for 5 min. Then 40 μL of catalyst suspension was taken and 160 μL of bacterial solution (1×10 7 CFU mL -1 ) and mixed evenly. Then the mixture was transferred to a 96-well plate and irradiated with a 300W xenon lamp (wavelength greater than 420nm) for 5 minutes. The mixed solution containing bacteria was diluted to 1×10 5 CFU mL -1 , take 10 μL and evenly spread it on the agar plate, and culture it in a 37℃ constant temperature incubator for 24 hours. Finally, take out the cultured bacteria, take pictures and count them. Use the formula, antibacterial rate = (control group colony number - experimental group colony number) / control group colony number × 100% to calculate the antibacterial rate of each group.

[0065] The photos of the photocatalytic activity of carbon nitride against methicillin-resistant Staphylococcus aureus prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 7 As shown, from Figure 7 It can be seen that the antibacterial efficiency of the block carbon nitride prepared in Comparative Example 1 is 21.39%, the antibacterial efficiency of the ultrathin carbon nitride prepared in Comparative Example 2 is 71.69%, and the antibacterial efficiency of the high specific surface area double-defect flake carbon nitride prepared in Example 1 is 99.78%, proving that the high specific surface area double-defect flake carbon nitride has more excellent photocatalytic antibacterial properties.

[0066] The above data show that the high specific surface area double-defect flake carbon nitride prepared by the bottom-up two-step calcination method has higher photocatalytic activity and higher value for industrial application.

[0067] Obviously, the above-mentioned embodiments of the present invention are only simple applications of high specific surface area double-defect flaky carbon nitride in many application fields. They are examples made to clearly illustrate the breadth of the present invention, but not to limit the application fields and implementation methods of the present invention. For specific applications in various fields, other different forms of changes should be made under specific circumstances. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing double-defect flaky carbon nitride with increased specific surface area, comprising the following steps: grinding and mixing ribbon-shaped melamine and ammonium salt evenly, and then calcining them in an air atmosphere to obtain a ribbon-shaped carbon nitride intermediate; and then calcining the ribbon-shaped carbon nitride intermediate in a semi-enclosed tubular furnace to obtain a double-defect flaky carbon nitride with high specific surface area.

2. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1, characterized in that: The ammonium salt is one or a combination of two or more of ammonium chloride, ammonium bromide, ammonium sulfate, ammonium nitrate or ammonium bicarbonate.

3. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1, characterized in that: The ammonium salt is ammonium bromide or ammonium chloride.

4. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1, characterized in that: The mass ratio of the strip melamine to the ammonium salt is 1:0.5-5.

5. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1, characterized in that: The calcination temperature of the strip-shaped melamine and ammonium salt mixture is 350-520°C.

6. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1, characterized in that: The roasting time of the strip-shaped melamine and ammonium salt mixture is 2 to 8 hours.

7. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1, characterized in that: The heating rate of the strip-shaped melamine and ammonium salt mixture is 1-10°C / min.

8. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1, characterized in that: The calcination temperature of the ribbon carbon nitride intermediate is 520-600°C; the calcination time is 1-8h.

9. The method for preparing double-defect flaky carbon nitride with increased specific surface area according to claim 1 has weaker (210) and (002) diffraction peak intensities of the double-defect flaky carbon nitride product; the microscopic morphology of the product is a flaky structure; the specific surface area of ​​the product reaches 226.9 m 2 / g.

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