Homotype heterojunction g-c3n4 photocatalytic material and preparation method

Abstract

The application discloses a kind of homotype heterojunction g-C3N4 Photocatalytic material and preparation method, dicyandiamide is prepared by calcination to obtain pre-sintered body A, urea is prepared by calcination to obtain pre-sintered body B, then pre-sintered body A and pre-sintered body B are mixed evenly, then, calcination reaction is carried out, i.e. specific porous structure homotype heterojunction g-C3N4 Photocatalytic material can be prepared.In further calcination reaction process, pre-sintered body A is stripped from dense structure to porous structure, the porous structure of pre-sintered body B is further stripped to improve porosity, and a large number of reaction sites are provided for adsorption and photocatalysis by high specific surface area;In addition, in the calcination process, pre-sintered body A and pre-sintered body B are in full contact, form a good homotype heterojunction, improve the space charge separation efficiency and reduce the electron-hole pair recombination rate, thereby improve the photocatalytic activity and reaction rate of photocatalytic material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photocatalytic materials, in particular to a homotype heterojunction g-C3N4 photocatalytic material and a preparation method thereof. BACKGROUND

[0002] Graphitic carbon nitride (g-C3N4) as an inorganic non-metallic semiconductor, due to its excellent visible light response, thermal stability and chemical stability, is widely used in photocatalytic degradation of pollutants. In recent years, researchers mainly use nitrogen-rich precursors such as urea, melamine, dicyanediamine and thiourea, etc. to prepare g-C3N4 materials by calcination. However, the prepared g-C3N4 bulk has small specific surface area and the hole-electron pairs are easy to quickly recombine, which seriously limits the photocatalytic activity of g-C3N4.

[0003] In view of the above defects of g-C3N4 bulk photocatalytic material, researchers have improved the morphology of g-C3N4 to increase the specific surface area, doped with elements or combined with other photocatalytic materials to form a heterojunction to promote carrier separation and migration, etc. The photocatalytic activity of g-C3N4 is effectively improved. In addition, compared with conventional heterojunctions, the same type of heterojunction composed of two g-C3N4s derived from different precursors can more easily realize the combination due to the realization of lattice matching in the same material system, and has the advantages of relatively simple preparation, low cost, easy large-scale production, etc.

[0004] Gang Liao et al. ("Facile synthesis of porous isotype heterojunction g-C3N4 for enhanced photocatalytic degradation of RhB under visible light", Diamond & Related Materials) takes urea and melamine as precursors, first grinds urea and melamine in ethanol until ethanol is completely evaporated, then pours the mixture into an alumina crucible with a cover, calcines at 550°C for 120 min, and finally, the product is ground into powder to obtain g-C3N4 isotype heterojunction, which improves the separation and migration efficiency of photo-generated charge carriers, and significantly improves the photocatalytic efficiency of g-C3N4. The composite morphology of the isotype heterojunction prepared by this method is that the internal aggregates are tightly wrapped by the external nanosheets. Although a porous structure is formed in the external nanosheets, the internal aggregates still maintain a dense structure, which is not conducive to improving the specific surface area of the entire composite structure. CN108543544B discloses a honeycomb-shaped isotype heterojunction carbon nitride composite material, which is prepared by calcining urea and thiourea as precursors in the presence of water. However, the isotype heterojunction carbon nitride prepared by this method has a low doping amount of thiourea due to the low solubility of thiourea in water, which tends to precipitate and aggregate first during the calcination process, making it difficult for urea and thiourea to fully contact and form a well-combined isotype heterojunction structure. SUMMARY

[0005] In order to improve the specific surface area of g-C3N4 and form a well-combined isotype heterojunction structure, the present application provides an isotype heterojunction g-C3N4 photocatalytic material and a preparation method.

[0006] A preparation method of an isotype heterojunction g-C3N4 photocatalytic material, comprising the following steps:

[0007] S1. Calcining dicyandiamide to prepare a pre-sintered body A and calcining urea to prepare a pre-sintered body B;

[0008] S2. Mixing the pre-sintered body A and the pre-sintered body B to prepare a pre-sintered body mixture;

[0009] S3. Calcining the pre-sintered body mixture to prepare an isotype heterojunction g-C3N4 photocatalytic material.

[0010] Optionally, in step S1, the reaction temperature for calcining dicyandiamide is 500-600°C, and the reaction time is 2-6h.

[0011] Optionally, in step S1, the reaction temperature for calcining urea is 500-600 DEG C, and the reaction time is 2-6 h.

[0012] Optionally, in step S2, the mass ratio of pre-sintered body A to pre-sintered body B is 0.5-5:1.

[0013] Optionally, in step S3, the reaction temperature for calcining the pre-sintered body mixture is 380-520 DEG C, and the reaction time is 1-3 h.

[0014] Optionally, in step S1, the prepared pre-sintered body A is of dense structure, and the specific surface area of pre-sintered body A is 10-20 m 2 / g as measured by BET method.

[0015] Optionally, in step S1, the prepared pre-sintered body B is of porous structure, and the specific surface area of pre-sintered body B is 40-80 m 2 / g as measured by BET method.

[0016] Optionally, in step S3, the prepared same-type heterojunction g-C3N4 photocatalytic material is of porous structure, and the specific surface area is 120-180 m 2 / g as measured by BET method.

[0017] Optionally, in step S3, the prepared same-type heterojunction g-C3N4 photocatalytic material is used for photocatalytic degradation of tetracycline solution with a concentration of 10 mg / L at an addition amount of 0.04 g / 100 mL, and the degradation rate of tetracycline is 65.7%-82.1% after 60 min of illumination.

[0018] A same-type heterojunction g-C3N4 photocatalytic material is prepared by the method for preparing same-type heterojunction g-C3N4 photocatalytic material.

[0019] In summary, the present application has at least one of the following beneficial technical effects:

[0020] 1. The method for preparing same-type heterojunction g-C3N4 photocatalytic material provided by the present application, which comprises the following steps: calcining dicyandiamide to prepare pre-sintered body A, calcining urea to prepare pre-sintered body B, mixing pre-sintered body A and pre-sintered body B uniformly to obtain a pre-sintered body mixture, and further calcining the pre-sintered body mixture, wherein, during the calcination, the pre-sintered body A is peeled off from dense structure to porous structure, and the porous structure of pre-sintered body B is further peeled off to increase the porosity, thereby obtaining a high specific surface area to provide a large number of reaction sites for adsorption and photocatalysis; in addition, during the calcination, pre-sintered body A and pre-sintered body B are in full contact to form a same-type heterojunction with good combination, thereby improving the space charge separation efficiency and reducing the recombination rate of electron-hole pairs, and thus improving the photocatalytic activity and reaction rate of the photocatalytic material.

[0021] 2. The preparation method of the homotype heterojunction g-C3N4 photocatalytic material provided by the application is simple, has strong controllability, and can control the morphology, structure and ratio of the pre-sintered body A and the pre-sintered body B, further, through calcination, the composite morphology, structure, photocatalytic activity and reaction rate of the homotype heterojunction are controlled.

[0022] 3. The homotype heterojunction g-C3N4 photocatalytic material provided by the application has excellent photocatalytic activity and reaction rate, and when the addition amount is 0.04 g / 100 mL, the degradation rate of tetracycline solution with a concentration of 10 mg / L is more than 65.7% after 60 min of irradiation, preferably more than 69.1%, more preferably more than 75.7%, and most preferably 82.1%. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is an XRD diagram of the DCN, the UCN and the SDUCN prepared in Example 1, the SDCN prepared in Comparative Example 1 and the SUCN prepared in Comparative Example 2;

[0024] Figure 2 is a specific surface area performance curve of the DCN, the UCN and the SDUCN of Example 1, the SDCN of Comparative Example 1 and the SUCN of Comparative Example 2;

[0025] Figure 3 is a SEM diagram of the DCN, the UCN and the SDUCN prepared in Example 1, the SDCN prepared in Comparative Example 1 and the SUCN prepared in Comparative Example 2;

[0026] Figure 4 is a TEM diagram of the DCN, the UCN and the SDUCN prepared in Example 1;

[0027] Figure 5 is a tetracycline degradation performance curve of the DCN, the UCN, the DUCN and the SDUCN prepared in Example 1, the SDCN prepared in Comparative Example 1 and the SUCN prepared in Comparative Example 2;

[0028] Figure 6 is a tetracycline degradation performance curve of the SDUCN-450 prepared in Example 2;

[0029] Figure 7 is a tetracycline degradation performance curve of the SDUCN-400 prepared in Example 3;

[0030] Figure 8 is a tetracycline degradation performance curve of the SDUCN' prepared in Example 4;

[0031] Figure 9 is the performance curve of SMUCN prepared from Comparative Example 3 degrading tetracycline;

[0032] Figure 10 is the performance curve of SDUCN-350 prepared from Comparative Example 4 degrading tetracycline;

[0033] Figure 11 is the performance curve of DUCN-S prepared from Comparative Example 5 degrading tetracycline. DETAILED DESCRIPTION

[0034] Graphitic carbon nitride (g-C3N4) is considered as a potential photocatalytic material due to its visible light response, non-toxicity and easy preparation. However, the bulk g-C3N4 prepared by traditional method usually has small specific surface area and the photo-generated electron-hole pairs are easy to recombine, which is considered to be not conducive to improve the photocatalytic activity. At present, researchers mainly increase the specific surface area of g-C3N4, element doping, construct heterojunction and other methods to improve the photocatalytic activity of g-C3N4. Among them, the homojunction has the advantages of low cost and simple preparation, and has become a research hotspot. The inventors propose an original homojunction g-C3N4 photocatalyst and a preparation method. First, dicyandiamide is calcined to prepare a pre-sintered body A, and urea is calcined to prepare a pre-sintered body B. Then, the pre-sintered body A and the pre-sintered body B are mixed to prepare a pre-sintered mixture. Finally, the pre-sintered mixture is calcined to prepare a homojunction g-C3N4 photocatalytic material. The homojunction g-C3N4 photocatalytic material prepared in the application can increase the specific surface area, shorten the charge diffusion distance and enhance the redox ability, while inhibiting the recombination of photo-generated carriers, promoting the separation and migration of carriers, thereby improving the catalytic activity and reaction rate of the photocatalytic material.

[0035] In some embodiments of the application, in step S1, the reaction temperature for calcining dicyandiamide is 500-600℃, and the reaction time is 2-6h. In step S1, the reaction temperature for calcining urea is 500-600℃, and the reaction time is 2-6h. In step S1, the pre-sintered body A prepared has a dense structure, and the specific surface area of the pre-sintered body A is 10-20m 2 / g measured by BET method. In step S1, the pre-sintered body B prepared has a porous structure, and the specific surface area of the pre-sintered body B is 40-80m 2 / g measured by BET method, preferably 45-65m 2 / g, and more preferably 50-60m 2 / g.

[0036] In some embodiments of the present application, in step S2, the mass ratio of the pre-sintered body A to the pre-sintered body B is 0.5-5:1; preferably 1-4:1, more preferably 1-2:1.

[0037] In some embodiments of the present application, in step S3, the temperature for the calcination reaction of the pre-sintered body mixture is 380-520℃, and the reaction time is 1-3h; the temperature for the calcination reaction is preferably 400-510℃, further preferably 450-510℃, more preferably 480-510℃. In step S3, the prepared homotype heterojunction g-C3N4 photocatalytic material is of a porous structure, and the specific surface area measured by the BET method is 120-180m 2 / g, preferably 130-165m 2 / g, more preferably 140-160m 2 / g. In step S3, the prepared homotype heterojunction g-C3N4 photocatalytic material, with an addition amount of 0.04g / 100mL, photocatalytically degrades a tetracycline solution with a concentration of 10mg / L, and after 60min of illumination, the degradation rate of tetracycline is 65.7%-82.1%, preferably 69.1%-82.1%, more preferably 75.7%-82.1%.

[0038] The present application is further described in detail below in combination with embodiments.

[0039] Embodiment 1

[0040] A preparation method of a homotype heterojunction g-C3N4 photocatalytic material, comprising the following steps:

[0041] S1. Calcining dicyandiamide to prepare a pre-sintered body A and calcining urea to prepare a pre-sintered body B, specifically:

[0042] 10g of dicyandiamide is weighed into an alumina crucible (100x40x20mm) with a cover, then it is placed into a muffle furnace to be heated to 550℃ at a heating rate of 5℃ / min and kept for 4h, after the reaction is completed, the furnace is allowed to cool to room temperature, the sample is ground, then washed with deionized water and anhydrous ethanol in sequence, repeated for three times, dried, to prepare the pre-sintered body A, marked as DCN;

[0043] 10g of urea is weighed into an alumina crucible (100x40x20mm) with a cover, then it is placed into a muffle furnace to be heated to 550℃ at a heating rate of 5℃ / min and kept for 4h, after the reaction is completed, the furnace is allowed to cool to room temperature, the sample is ground, then washed with deionized water and anhydrous ethanol in sequence, repeated for three times, dried, to prepare the pre-sintered body B, marked as UCN.

[0044] S2. Mixing the pre-sintered body A and the pre-sintered body B to prepare a pre-sintered body mixture, specifically:

[0045] Weigh 0.5 g of DCN prepared in step S1 and 0.5 g of UCN prepared in step S1, and put them into 50 mL of anhydrous ethanol, and then put them into a constant-temperature water bath at 80℃ and stir at 150 rpm for 30 min. After mixing uniformly, dry to prepare a pre-sintered body mixture, marked as DUCN.

[0046] S3. The pre-sintered body mixture is subjected to a calcination reaction to prepare a homojunction g-C3N4 photocatalytic material, specifically:

[0047] Put all the DUCN prepared in step S2 into an alumina porcelain boat (85x60x15mm), and then heat it to 500℃ at a heating rate of 5℃ / min in a muffle furnace and keep it for 2h. After the reaction is completed, the furnace is cooled to room temperature. The sample is ground and washed with deionized water and anhydrous ethanol in turn, and the process is repeated three times. Dry to prepare a homojunction g-C3N4 photocatalytic material, marked as SDUCN.

[0048] Comparative Example 1

[0049] A method for preparing a g-C3N4 photocatalytic material, comprising the following steps:

[0050] S1. Weigh 10 g of dicyandiamide into an alumina crucible (100x40x20mm) with a cover, and then put it into a muffle furnace and heat it to 550℃ at a heating rate of 5℃ / min and keep it for 4h. After the reaction is completed, the furnace is cooled to room temperature. The sample is ground and washed with deionized water and anhydrous ethanol in turn, and the process is repeated three times. Dry to prepare a pre-sintered body A, marked as DCN.

[0051] S2. Weigh 1 g of DCN prepared in step S1 into an alumina porcelain boat (85x60x15mm), and then heat it to 500℃ at a heating rate of 5℃ / min in a muffle furnace and keep it for 2h. After the reaction is completed, the furnace is cooled to room temperature. The sample is ground and washed with deionized water and anhydrous ethanol in turn, and the process is repeated three times. Dry to prepare a g-C3N4 photocatalytic material, marked as SDCN.

[0052] Comparative Example 2

[0053] A method for preparing a g-C3N4 photocatalytic material, comprising the following steps:

[0054] S1. 10 g of urea was weighed into an alumina crucible (100 x 40 x 20 mm) with a cover, and then it was placed in a muffle furnace to be heated to 550°C at a heating rate of 5°C / min and kept for 4 h, after the reaction was completed, the furnace was cooled to room temperature, the sample was ground, and then washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare a pre-sintered body B, labeled as UCN;

[0055] S2. 1 g of UCN prepared in step S1 was weighed into an alumina crucible (85 x 60 x 15 mm), and then it was heated to 500°C at a heating rate of 5°C / min in a muffle furnace and kept for 2 h, after the reaction was completed, the furnace was cooled to room temperature, the sample was ground, and then washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare a g-C3N4 photocatalyst material, labeled as SUCN.

[0056] Structural characterization and performance test:

[0057] Figure 1 The XRD patterns of DCN, UCN and SDUCN prepared in Example 1, SDCN prepared in Comparative Example 1, and SUCN prepared in Comparative Example 2. As can be seen from Figure 1 , the phase composition of DCN, UCN and SDUCN of Example 1, SDCN of Comparative Example 1, and SUCN of Comparative Example 2 are all graphite phase carbon nitride (g-C3N4), and diffraction characteristic peaks (100) and (002) are detected.

[0058] Figure 2 For the BET specific surface area detection method, the performance curves of DCN, UCN and SDUCN of Example 1, SDCN of Comparative Example 1, and SUCN of Comparative Example 2 were measured according to the standard method GB / T 19587-2017, from Figure 2 , it can be obtained that the specific surface area of DCN of Example 1 is 18 m 2 / g, the specific surface area of UCN is 55.2 m 2 / g, the specific surface area of SDUCN is 144.2 m 2 / g, the specific surface area of SDCN of Comparative Example 1 is 101.4 m 2 / g, and the specific surface area of SUCN of Comparative Example 2 is 173.3 m 2 / g.

[0059] Figure 3 The SEM images of DCN, UCN and SDUCN prepared in Example 1, SDCN prepared in Comparative Example 1, and SUCN prepared in Comparative Example 2. As can be seen from Figure 3 (a), the DCN of Example 1 is a dense structure, and the shape is irregular granular; from Figure 3As can be seen in (b), the UCN of Example 1 is a porous structure, and is irregularly granular in shape; from Figure 3 As can be seen in (c), the SDCN of Comparative Example 1 is a porous structure, and is irregularly granular in shape; from Figure 3 As can be seen in (d), the SUCN of Comparative Example 2 is a porous structure, and is irregularly granular in shape; from Figure 3 As can be seen in (e), the SDUCN of Example 1 is a porous structure, and is irregularly granular in shape.

[0060] Figure 4 TEM images of the DCN, UCN and SDUCN prepared in Example 1. As can be seen in (a), the DCN prepared in Example 1 is a dense bulk structure, and from Figure 4 As can be seen in (a), the DCN prepared in Example 1 is a dense bulk structure, and from Figure 4 As can be seen in (b), the UCN prepared in Example 1 is a porous structure, and is irregularly granular in shape; from Figure 4 As can be seen in (c), the SDUCN prepared in Example 1 is a composite of the UCN and DCN, the structure of the DCN has changed from a dense structure to a porous structure, and the porosity of the porous UCN has further significantly increased, and a large number of mesopores have appeared inside.

[0061] 0.04 g of the DCN, UCN, DUCN and SDUCN prepared in Example 1, the SDCN prepared in Comparative Example 1 and the SUCN prepared in Comparative Example 2 were respectively taken and added to 100 mL of a tetracycline solution with a concentration of 10 mg / L. After adsorption and desorption equilibrium in a dark room for 30 minutes, samples were taken every 10 min under xenon lamp (power 500 W, filter AM 1.5) simulated visible light irradiation, and the concentration change was analyzed by using a UV-visible spectrophotometer combined with a standard curve. The degradation curve of tetracycline is shown in Figure 5 As can be seen in (a), the DCN prepared in Example 1 is a dense bulk structure, and from Figure 5 As can be seen in (a), the DCN prepared in Example 1 is a dense bulk structure, and from

[0062] Example 2

[0063] Example 2 differs from Example 1 in that step S3. The calcination reaction is carried out on the pre-sintered body mixture to prepare the same type of heterojunction g-C3N4 photocatalytic material, specifically: all the DUCN prepared in step S2 are placed in an alumina porcelain boat (85x60x15mm), then heated to 450°C at a heating rate of 5°C / min in a muffle furnace and kept for 2h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground and washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the same type of heterojunction g-C3N4 photocatalytic material, marked as SDUCN-450. The rest of the preparation steps are the same as Example 1. Using the same test method as Example 1, the performance curve of SDUCN-450 prepared in Example 2 after 60min of irradiation is shown in Figure 6 , and the degradation rate of tetracycline is 75.7%.

[0064] Example 3

[0065] Example 3 differs from Example 1 in that step S3. The calcination reaction is carried out on the pre-sintered body mixture to prepare the same type of heterojunction g-C3N4 photocatalytic material, specifically: all the DUCN prepared in step S2 are placed in an alumina porcelain boat (85x60x15mm), then heated to 400°C at a heating rate of 5°C / min in a muffle furnace and kept for 2h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground and washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the same type of heterojunction g-C3N4 photocatalytic material, marked as SDUCN-400. The rest of the preparation steps are the same as Example 1. Using the same test method as Example 1, the performance curve of SDUCN-400 prepared in Example 3 after 60min of irradiation is shown in Figure 7 , and the degradation rate of tetracycline is 65.7%.

[0066] Example 4

[0067] Example 4 differs from Example 1 in that S2. The pre-sintered body A and the pre-sintered body B are mixed to prepare a pre-sintered body mixture, specifically: 0.8g of DCN prepared in step S1 and 0.2g of UCN prepared in step S1 are weighed and placed in 50mL of anhydrous ethanol, then placed in a constant temperature water bath at 80°C and stirred at 150rpm for 30min, after mixing evenly, dried, to prepare a pre-sintered body mixture, marked as DUCN'. The rest of the preparation steps are the same as Example 1. Using the same test method as Example 1, the performance curve of SDUCN' prepared in Example 4 after 60min of irradiation is shown in Figure 8 , and the degradation rate of tetracycline is 69.1%.

[0068] Comparative Example 3

[0069] A preparation method of a homotype heterojunction g-C3N4 photocatalytic material, comprising the following steps:

[0070] S1. Melamine is calcined to prepare a pre-sintered body A, and urea is calcined to prepare a pre-sintered body B, specifically:

[0071] 10 g of melamine is weighed into an alumina crucible (100 x 40 x 20 mm) with a cover, then it is placed in a muffle furnace and heated to 550℃ at a heating rate of 5℃ / min and kept for 4 h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground, then washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the pre-sintered body A, marked as MCN;

[0072] 10 g of urea is weighed into an alumina crucible (100 x 40 x 20 mm) with a cover, then it is placed in a muffle furnace and heated to 550℃ at a heating rate of 5℃ / min and kept for 4 h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground, then washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the pre-sintered body B, marked as UCN.

[0073] S2. The pre-sintered body A and the pre-sintered body B are mixed to prepare a pre-sintered body mixture, specifically:

[0074] 0.5 g of MCN prepared in step S1 and 0.5 g of UCN prepared in step S1 are weighed into 50 mL of anhydrous ethanol, then placed in a constant temperature water bath and stirred at 80℃ for 30 min at a stirring speed of 150 rpm, then mixed uniformly, dried, to prepare the pre-sintered body mixture, marked as MUCN.

[0075] S3. The pre-sintered body mixture is calcined to prepare a homotype heterojunction g-C3N4 photocatalytic material, specifically:

[0076] All MUCN prepared in step S2 is placed in an alumina boat (85 x 60 x 15 mm), then heated to 500℃ at a heating rate of 5℃ / min in a muffle furnace and kept for 2 h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground, then washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the homotype heterojunction g-C3N4 photocatalytic material, marked as SMUCN. The same test method as in Example 1 is used, and the performance curve of SMUCN prepared in Comparative Example 3 after 60 min of light is shown in Figure 9 , and the degradation rate of tetracycline is 54.2%.

[0077] Comparative Example 4

[0078] Comparative Example 4 differs from Example 1 in that step S3. The pre-sintered mixture is subjected to a calcination reaction to prepare the homojunction g-C3N4 photocatalytic material, specifically: all the DUCN prepared in step S2 are placed in an alumina crucible (85x60x15mm), then heated to 350°C at a heating rate of 5°C / min in a muffle furnace and kept for 2h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground and washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the homojunction g-C3N4 photocatalytic material, marked as SDUCN-350. The rest of the preparation steps are the same as Example 1. Using the same test method as Example 1, the performance curve of SDUCN-350 prepared in Comparative Example 4 after 60min of light irradiation is shown in Figure 10 , and the degradation rate of tetracycline is 56.5%.

[0079] Comparative Example 5

[0080] A preparation method of a homojunction g-C3N4 photocatalytic material, comprising the following steps:

[0081] 5g of dicyandiamide and 5g of urea are weighed and mixed uniformly, then placed in an alumina crucible (100x40x20mm) with a cover, then placed in a muffle furnace and heated to 550°C at a heating rate of 5°C / min and kept for 4h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground and washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the pre-sintered body M.

[0082] 1g of the prepared pre-sintered body M is placed in an alumina crucible (85x60x15mm), then heated to 500°C at a heating rate of 5°C / min in a muffle furnace and kept for 2h, after the reaction is completed, the furnace is cooled to room temperature, the sample is ground and washed with deionized water and anhydrous ethanol in turn, repeated three times, dried, to prepare the homojunction g-C3N4 photocatalytic material, marked as DUCN-S. Using the same test method as Example 1, the performance curve of DUCN-S prepared in Comparative Example 5 after 60min of light irradiation is shown in Figure 11 , and the degradation rate of tetracycline is 60.5%.

[0083] Comparative Example 6

[0084] Comparative Example 6 differs from Example 1 in that step S3. The pre-sintered mixture is subjected to a calcination reaction to prepare the homojunction g-C3N4 photocatalytic material, specifically: all the DUCN prepared in step S2 are placed in an alumina crucible (85x60x15mm), then heated to 550°C at a heating rate of 5°C / min in a muffle furnace and kept for 2h, after the reaction is completed, the furnace is cooled to room temperature, the sample is taken out, and the sample yield is less than 1%.

[0085] The above are all preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, and thus: any equivalent changes made in the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing a homo-heterojunction g-C3N4 photocatalytic material, characterized in that, Includes the following steps: S1. Pre-calcined body A was prepared by calcining dicyandiamine, and pre-calcined body B was prepared by calcining urea. The reaction temperature for calcining dicyandiamine was 500-600℃, and the reaction time was 2-6 h. The reaction temperature for calcining urea was 500-600℃, and the reaction time was 2-6 h. The prepared pre-calcined body A had a dense structure, and the specific surface area of ​​pre-calcined body A was measured to be 10-20 m² / g by the BET method. 2 / g; The prepared pre-fired body B has a porous structure, and the specific surface area of ​​the pre-fired body B, measured by the BET method, is 40~80m². 2 / g; S2. Pre-fired body A and pre-fired body B are mixed to prepare a pre-fired body mixture; the mass ratio of pre-fired body A to pre-fired body B is 1~2:1; S3. A homo-heterojunction g-C3N4 photocatalyst material was prepared by calcining a pre-burned mixture. The calcination temperature of the pre-burned mixture was 480–510 °C, and the reaction time was 1–3 h. The homo-heterojunction g-C3N4 photocatalyst material was composed of pre-burned body A and pre-burned body B. The structure of pre-burned body A changed from a dense structure to a porous structure, while the porosity of the porous pre-burned body B increased significantly, with a large number of mesopores appearing inside. The prepared homo-heterojunction g-C3N4 photocatalyst material had a porous structure, and the specific surface area measured by the BET method was 120–180 m². 2 / g.

2. The method for preparing the isomorphic heterojunction g-C3N4 photocatalytic material according to claim 1, characterized in that, In step S3, the prepared homo-heterojunction g-C3N4 photocatalytic material was added at a rate of 0.04 g / 100 mL to photocatalytically degrade tetracycline at a concentration of 10 mg / L. After 60 min of illumination, the degradation rate of tetracycline was 82.1%.

3. A homo-heterojunction g-C3N4 photocatalytic material, obtained by the preparation method of the homo-heterojunction g-C3N4 photocatalytic material according to claim 1 or 2.

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