Preparation method of modified graphite phase carbon nitride photocatalyst and application of modified graphite phase carbon nitride photocatalyst in degradation of tetracycline

Abstract

This invention discloses a method for preparing a graphitic carbon nitride photocatalytic material co-modified with sodium ions, cyano groups, and pyrimidine groups, and its application in the degradation of tetracycline. The material uses graphitic carbon nitride as the main framework, and the modified material simultaneously contains sodium ions, cyano groups, and pyrimidine groups. The preparation method employs a two-step calcination process: first, melamine is calcined to obtain a melamine intermediate, which is then mixed with 2-aminopyrimidine and sodium chloride, ground, and subjected to a second high-temperature calcination. By optimizing its internal structure, this material significantly expands the light absorption range, reduces the recombination rate of photogenerated carriers, and achieves efficient generation of hydroxyl radicals under illumination. The preparation process of this material is simple, and it exhibits extremely excellent photocatalytic degradation efficiency for the antibiotic pollutant tetracycline, showing broad application prospects in the field of environmental remediation.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis and environmental pollution control technology, and discloses a graphitic carbon nitride photocatalytic material co-modified with sodium ions, cyano groups, and pyrimidine groups, and its application in the degradation of tetracycline. Background Technology

[0002] Since the beginning of the 21st century, the widespread use of antibiotics has led to their extensive residues in the aquatic environment. Tetracycline, as a widely used broad-spectrum antibiotic, is continuously introduced into the environment through medical treatment, animal husbandry, and aquaculture, accumulating there. Due to its stable structure and poor biodegradability, traditional wastewater treatment technologies struggle to remove it effectively. Photocatalysis, which can directly utilize solar energy to drive a catalyst to generate reactive oxygen species under mild conditions, efficiently degrading pollutants, has become one of the most promising technologies in the field of wastewater treatment.

[0003] Graphitic carbon nitride, as a non-metallic polymer semiconductor photocatalyst, has attracted widespread attention due to its ease of synthesis, low cost, and good stability. However, the photocatalytic performance of existing graphitic carbon nitride is still greatly limited, mainly due to its wide band gap (~2.7 eV), limited specific surface area, and low carrier utilization efficiency caused by the rapid recombination of photogenerated electron-hole pairs. To overcome these limitations, this invention employs multiple synthesis strategies to effectively modulate its band structure by synergistically introducing ions and functional groups into the graphitic carbon nitride framework. This improves charge separation efficiency and efficiently generates highly oxidizing reactive oxygen species (such as •OH), which is of great significance for the degradation of pollutants in the environment. Summary of the Invention

[0004] To address the shortcomings of existing graphitic carbon nitride photocatalytic materials, such as wide band gaps, easy recombination of photogenerated carriers, and weak ability to directionally generate highly oxidizing reactive oxygen species, this invention aims to provide a graphitic carbon nitride photocatalytic material (CN-AP-Na) co-modified with sodium ions, cyano groups, and pyrimidine groups, and its preparation method. This modification strategy can effectively change the band structure of the material, improve charge separation efficiency, and efficiently generate highly oxidizing hydroxyl radicals (•OH), thereby achieving efficient degradation of stubborn antibiotics such as tetracycline.

[0005] The technical problem to be solved by this invention is achieved by the following technical solution:

[0006] The first objective of this invention is to provide a method for preparing a modified graphitic carbon nitride photocatalyst, comprising the following steps:

[0007] (1) Melamine was subjected to a two-step calcination process to obtain the precursor melamine;

[0008] (2) The precursor melamine obtained in step (1) is uniformly mixed with sodium chloride and 2-aminopyrimidine, and then calcined under high temperature to obtain the modified graphite phase carbon nitride photocatalyst.

[0009] In this invention, melamine is used as the initial raw material. The first stage calcination temperature is 200-300 °C, held for 4-12 h; the second stage calcination temperature is 300-450 °C, held for 10-24 h; the heating rate for both stages is 5-25 °C / min. The obtained melamine is uniformly mixed with 2-aminopyrimidine and sodium chloride in a molar ratio of 1:5:10-30, placed in a covered alumina crucible, and heated to 500-600 °C at a programmed heating rate of 4-20 °C / min under air atmosphere, and held for 3-12 h for high-temperature thermal polymerization. During this high-temperature process, various ions and groups are successfully embedded into the graphitic carbon nitride framework, resulting in graphitic carbon nitride co-modified with sodium ions, cyano groups, and pyrimidine groups.

[0010] Based on the above preparation method, one of the objectives of this invention is to provide a photocatalyst prepared by this method. This material can efficiently generate •OH under photoexcitation conditions, thereby effectively degrading antibiotic pollutants such as tetracycline, achieving efficient and green degradation of persistent organic pollutants in water.

[0011] The beneficial effects of this invention are reflected in its simple and controllable preparation process: a solid-phase synthesis method is used, employing low-cost inorganic salts and small organic molecules as raw materials. The material exhibits high crystallinity, good reproducibility, and is easily mass-produced. When applied to the photocatalytic degradation of a typical antibiotic (tetracycline), it demonstrates an extremely high degradation rate. The entire process is directly driven by solar energy, operating under mild conditions with no secondary pollution, and possesses significant practical application value and commercial prospects in the field of water environment remediation. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of CN-AP-Na prepared in Example 1;

[0013] Figure 2 X-ray diffraction patterns of CN prepared in Comparative Example 1, CN-AP prepared in Comparative Example 2, CN-Na prepared in Comparative Example 3, and CN-AP-Na prepared in Example 1;

[0014] Figure 3 Fourier transform infrared spectra of CN prepared for Comparative Example 1, CN-AP prepared for Comparative Example 2, CN-Na prepared for Comparative Example 3, and CN-AP-Na prepared for Example 1;

[0015] Figure 4(a) UV-Vis diffuse reflectance spectrum, (b) Tauc plot, (c) periodic on / off photocurrent response (relative to Ag / AgCl, pH=7) for CN prepared in Comparative Example 1, CN-AP prepared in Comparative Example 2, CN-Na prepared in Comparative Example 3, and CN-AP-Na prepared in Example 1; (d) electrochemical impedance spectroscopy.

[0016] Figure 5 Using DCFH-DA as a fluorescent probe, the photoactive oxygen species of (a) CN prepared in Control Example 1, (b) CN-AP prepared in Control Example 2, (c) CN-Na prepared in Control Example 3, and (d) CN-AP-Na prepared in Example 1 were measured every 5 seconds.

[0017] Figure 6 The fluorescence spectra of (a) control group, (b) CN prepared in control example 1, (c) CN-AP prepared in control example 2, (d) CN-Na prepared in control example 3, and (e) CN-AP-Na prepared in example 1 were measured every 20 seconds using the commercial indicator HPF of •OH.

[0018] Figure 7 The graphs show the photocatalytic degradation performance of tetracycline by (a) the control group, (b) CN prepared in Example 1, (c) CN-AP prepared in Example 2, (d) CN-Na prepared in Example 3, and (e) CN-AP-Na prepared in Example 1. Detailed Implementation

[0019] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments and illustrations.

[0020] Example 1

[0021] (1) Melamine (10 g) was placed in a muffle furnace and heated to 250 °C at 5 °C / min and held for 9 h. Then the temperature was increased to 385 °C and held for 12 h to form melamine intermediate.

[0022] (2) Melamine (1.57 g), 2-aminopyrimidine (3.43 g), and sodium chloride (10.10 g) were thoroughly ground and mixed in an agate mortar (molar ratio 1:5:24). The mixture was then transferred to a covered alumina crucible and heated to 550 °C at a rate of 5 °C / min in a muffle furnace and held for 4 h. The product was washed several times with deionized water and ethanol, dried at 60 °C for 12 h, and then ground into a fine powder to obtain CN-AP-Na. The structural schematic diagram is shown below. Figure 1 As shown.

[0023] Example 2

[0024] (1) Melamine (10 g) was placed in a muffle furnace and heated to 250 °C at 10 °C / min and held for 9 h. Then the temperature was increased to 385 °C and held for 12 h to form melamine intermediate.

[0025] (2) Melamine (1.57 g), 2-aminopyrimidine (3.43 g), and sodium chloride (12.60 g) were thoroughly ground and mixed in an agate mortar (molar ratio of 1:5:30), transferred to a covered alumina crucible, and heated to 550 °C at a rate of 5 °C / min in a muffle furnace and held for 4 h. The product was washed several times with deionized water and ethanol, dried at 60 °C for 12 h, and then ground into a fine powder for later use.

[0026] Compare with Example 1

[0027] Following the method of Example 1, except that 2-aminopyrimidine and sodium chloride are not added, graphitic carbon nitride CN is obtained through step (2).

[0028] Compare with Example 2

[0029] The method of Example 1 is followed, except that sodium chloride is not added, and CN-AP is obtained through step (2).

[0030] Compare with Example 3

[0031] The method of Example 1 is followed, except that 2-aminopyrimidine is not added, and CN-Na is obtained by step (2).

[0032] Figure 2 The X-ray diffraction (XRD) patterns of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3 are shown. The XRD pattern of the original carbon nitride (CN) material exhibits two characteristic diffraction peaks at 12.82° and 27.16°, which belong to the (100) crystal plane of the heptaazine planar repeating unit and the (002) crystal plane of the interlayer stack, respectively, which is consistent with the crystal structure of typical graphitic carbon nitride. In contrast, the diffraction peaks of CN-AP are weaker and broader, and the (002) peak is slightly shifted to a lower angle, indicating that the introduction of pyrimidine groups disrupts the in-plane periodicity and expands the interlayer spacing. The elemental composition of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3 was further analyzed by X-ray photoelectron spectroscopy, and the results are shown in Table 1.

[0033] Table 1

[0034] sample C(%) N(%) O(%) Na(%) Cl(%) C / N element ratio CN 41.5 56.81 1.58 / / 73.05 CN-AP 41.94 56.36 1.6 / / 74.41 CN-Na 43.78 48.18 3.19 4.78 / 90.97 CN-AP-Na 45.71 46.81 2.82 4.57 / 97.65

[0035] As can be seen from Table 1, the percentage of N element in CN-Na compared to CN and CN-AP-Na compared to CN-AP, as determined by XPS, is lower. This indirectly indicates that the pyrimidine group rich in carbon rings has been successfully doped into the carbon nitride framework.

[0036] Figure 3 The Fourier transform infrared spectra of the samples obtained in Example 1 and Comparative Examples 1, 2, and 3 are shown. All samples are at 810 cm⁻¹. −1 The characteristic absorption peak appears at 1200–1700 cm⁻¹, which is attributed to the out-of-plane bending vibration mode of the heptamethrin ring framework. −1 The multiple absorption peaks in the region correspond to the stretching vibrations of the C−N bonds in the aromatic heterocyclic structure, 2900–3300 cm⁻¹. −1 The broad peaks within the range are attributed to the N−H stretching vibrations of the −NH / NH2 group. Furthermore, compared to CN and CN-AP, the CN-Na and CN-AP-Na samples exhibit peaks in the 2900–3300 cm⁻¹ range. −1 The intensity of the broad peak in the region changes, and the peak position shifts to 3300–3600 cm. −1 The region (O−H stretching vibration). Furthermore, three new characteristic peaks appeared in the spectra of CN-Na and CN-AP-Na, at 998 cm⁻¹. −1 The characteristic peak at 1146 cm⁻¹ can be attributed to the stretching vibration of the N−Na bond. −1 The characteristic peak at 2162 cm⁻¹ corresponds to the asymmetric stretching vibration of the Na−NC₂ group, indicating that sodium ions in the molten salt are incorporated into the carbon nitride framework. Furthermore, the peak at 2162 cm⁻¹... −1 The nearby new peaks are attributed to the characteristic stretching vibrations of the cyano group (−C≡N). Nevertheless, the CN-AP-Na sample retains the basic chemical framework structure of graphitic carbon nitride.

[0037] The samples obtained in Example 1 and Control Examples 1, 2, and 3 were analyzed using ultraviolet-visible diffuse reflectance spectroscopy, and the corresponding Tauc diagrams were plotted. Figure 4 a and Figure 4 (b) The CN-AP-Na prepared in Example 1 has the smallest band gap of 1.89 eV compared to other samples, indicating that its broadened visible light absorption range is beneficial to improving the utilization efficiency of sunlight.

[0038] Electrochemical tests were performed on the samples obtained in Example 1 and Control Examples 1, 2, and 3: 4 mg of photocatalyst was weighed and added to 200 µL of Nafion solution, and sonicated for 10 min to ensure thorough dispersion. Each time, 50 µL of the suspension was uniformly coated onto a 1 cm² area... 2The sample was coated onto indium tin oxide conductive glass and allowed to air dry until the suspension was completely dripped. A 0.5 mol / L anhydrous sodium sulfate solution was used as the electrolyte. The indium tin oxide conductive glass coated with the sample served as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode for electrochemical testing, including transient photocurrent response testing and electrochemical impedance spectroscopy. Figure 4 As shown in Figure c, the CN-AP-Na prepared in Example 1 exhibited the highest photocurrent density, confirming its excellent photogenerated charge separation efficiency. Furthermore, its electrochemical impedance spectroscopy showed the smallest radius of curvature, indicating the lowest interfacial charge transfer impedance. These results demonstrate that CN-AP-Na possesses superior photogenerated carrier separation efficiency and interfacial charge transport capability, thus holding promise for exhibiting higher catalytic activity in photocatalytic reactions.

[0039] To investigate the photoactive oxygen species generation capacity of the samples obtained in Example 1 and Control Examples 1, 2, and 3, the fluorescent indicator 2′,7′-dichlorofluorescein diacetate (DCFH-DA) was used for detection. The specific steps were as follows: Under light-protected conditions, 0.0024 g of DCFH-DA was dissolved in 2.5 mL of dimethyl sulfoxide to prepare a 2 mmol / L solution. 100 µL of this solution was mixed with 0.8 mL of NaOH solution (0.01 mol / L), and after activation for 30 min in the dark, 4.1 mL of deionized water and 50 µL of photocatalyst suspension (1 mg / L) were added sequentially. Subsequently, the sample was irradiated with a 300 W xenon lamp equipped with a 400 nm cutoff filter, and the fluorescence spectrum was recorded every 5 s (excitation wavelength 488 nm, emission wavelength 528 nm). Figure 5 As shown, under the same illumination conditions, the total reactive oxygen species signal intensity of all modified samples was significantly higher than that of the original CN, indicating that the samples synthesized by various modification strategies all have a stronger ability to generate reactive oxygen species during illumination.

[0040] To further clarify the formation of •OH, hydroxyphenylfluorescein (HPF) was used as a specific fluorescent probe for •OH. Its strong fluorescence after oxidation by corresponding reactive oxygen species was utilized to evaluate the •OH formation ability of different samples. The specific steps were as follows: 2 mL of deionized water, 20 µL of photocatalyst dispersion (1 mg / mL), and 2 µL of HPF solution were mixed thoroughly. The mixture was irradiated with a 300 W xenon lamp equipped with a 400 nm cutoff filter, and the fluorescence spectrum was recorded every 20 s. After the addition of HPF (… Figure 6The CN-AP-Na sample prepared in Example 1 exhibited the strongest fluorescence signal under visible light irradiation, confirming its excellent •OH generation ability. This result can be attributed to the synergistic effect of sodium ions co-modification with cyano and pyrimidine groups: on the one hand, the introduction of pyrimidine groups expands the conjugated system and optimizes the band structure; on the other hand, the introduction of sodium ions and cyano groups further promotes the separation and migration of photogenerated carriers. The synergistic effect of both satisfies the •OH generation conditions.

[0041] Based on the material's high •OH generation capacity, the photocatalytic degradation ability of the antibiotic contaminant tetracycline was tested on the samples obtained in Example 1 and Control Examples 1, 2, and 3. The specific steps are as follows: 20 mg of the catalyst sample was weighed and dispersed in 20 mL of a 10 mg / L tetracycline solution. To achieve adsorption-desorption equilibrium, the solution was magnetically stirred for 30 min under light-protected conditions. Subsequently, a 300 W xenon lamp equipped with a 400 nm cutoff filter was used for photocatalytic reaction. During the reaction, 2 mL of the suspension was collected every 1 min. After the reaction, the solution and solid were separated by centrifugation, and the supernatant was used to determine the remaining tetracycline concentration at a wavelength of 355 nm using a UV-Vis spectrophotometer to evaluate the photocatalytic activity of the catalyst. All experiments were conducted at room temperature to ensure the accuracy and reliability of the data. Figure 7 As shown, after 5 min of visible light irradiation, the removal rates of tetracycline by photocatalysts CN, CN-AP, CN-Na, and CN-AP-Na were 7.77%, 22.63%, 38.55%, and 79.86%, respectively. Among them, the CN-AP-Na sample prepared in Example 1 exhibited the best photocatalytic degradation performance, with a removal efficiency approximately 10 times that of the original CN sample.

[0042] In summary, this invention provides a graphitic carbon nitride photocatalytic material co-modified with sodium ions, cyano groups, and pyrimidine groups. This material can efficiently generate reactive oxygen species, primarily •OH, under visible light irradiation, demonstrating broad application potential in fields such as environmental remediation.

[0043] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a modified graphite-phase carbon nitride photocatalyst, characterized by, Includes the following steps: (1) Melamine was subjected to a two-step calcination process to obtain the precursor melamine; (2) The precursor melamine obtained in step (1) is uniformly mixed with sodium chloride and 2-aminopyrimidine, and then calcined under high temperature to obtain the modified graphitic carbon nitride photocatalyst.

2. The production method according to claim 1, characterized by, In step (1), the conditions for the two-step calcination are as follows: the calcination temperature of the first stage is 200~300 ℃, and the holding time is 4~12 h; the calcination temperature of the second stage is 300~450 ℃, and the holding time is 10~24 h; the heating rate of both steps is 5~25 ℃ / min.

3. The method of claim 1, wherein: In step (2), the high-temperature calcination temperature is 500~600 ℃, the holding time is 3~12 h, and the heating rate is 4~20 ℃ / min.

4. The method of claim 1, wherein: In step (2), the molar ratio of the precursor melleramine, 2-aminopyrimidine and sodium chloride is 1:5:10~30.

5. A modified graphite phase carbon nitride photocatalyst, characterized by: The polymer is prepared by the preparation method according to any one of claims 1 to 4.

6. The modified graphite-phase carbon nitride photocatalyst according to claim 5, characterized by: The material has a stacked nanosheet structure.

7. The modified graphite-phase carbon nitride photocatalyst according to claim 5, characterized by: The material's microstructure is based on graphitic carbon nitride as the main framework, which is modified by sodium ion doping and cyano and pyrimidine groups. Furthermore, its hydroxyl radical generation signal is significantly enhanced under light irradiation.

8. The application of the modified graphitic carbon nitride photocatalyst according to claim 5, 6 or 7 in the field of photocatalysis.

9. The application of the modified graphitic carbon nitride photocatalyst according to claim 5, 6 or 7 in the degradation of tetracycline.

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