Preparation method of carbon nitride nanosheet and application thereof in dye wastewater treatment

Abstract

The application discloses a preparation method of carbon nitride nanosheet for realizing efficient activation of molecular oxygen through exciton effect regulation, and application of the carbon nitride nanosheet in deep degradation treatment of organic dye wastewater, and belongs to the technical field of photocatalytic material preparation and water pollution control. The preparation method of the carbon nitride nanosheet comprises the following steps: taking melamine as raw material, calcining at a constant heating rate in an air atmosphere to obtain a calcination product; and performing water washing and drying on the calcination product to obtain the carbon nitride nanosheet containing oxygen substances. The innovative regulation method not only overcomes the defect of electron-hole recombination, but also realizes efficient activation of molecular oxygen, so that the practical application value of the carbon nitride in printing and dyeing wastewater treatment is improved. The technology not only improves the photocatalytic performance of the carbon nitride and reduces energy consumption, but also provides a more efficient, economical and environmentally-friendly solution for wastewater treatment.

Description

Technical Field

[0001] This invention relates to the fields of photocatalytic material preparation and water pollution control technology, and in particular to a method for preparing carbon nitride nanosheets that achieve efficient activation of molecular oxygen through exciton effect regulation, and its application in the deep degradation treatment of organic dye wastewater. Background Technology

[0002] With increasing environmental awareness and accelerated industrialization, wastewater treatment, especially from the dyeing and printing industry, has become a significant global issue. Dyeing and printing wastewater contains large amounts of toxic organic dyes and chemical pollutants, which are not only difficult to degrade but also severely impact aquatic bodies and the ecological environment. Traditional wastewater treatment methods, such as chemical precipitation, adsorption, and membrane separation, while capable of removing some pollutants, typically suffer from drawbacks such as high cost, complex operation, low efficiency, and secondary pollution. Therefore, developing an efficient, economical, and environmentally friendly wastewater treatment technology, particularly for degrading organic dyes, has become an urgent technical challenge.

[0003] Photocatalysis, as an emerging environmental protection technology, has attracted widespread attention due to its ability to degrade pollutants using light energy at ambient temperature and pressure. Among these materials, carbon nitride (g-C3N4), with its excellent photocatalytic performance, has become a research hotspot due to its good stability and low cost. However, carbon nitride still faces some challenges in practical applications, such as weak light absorption and rapid electron-hole recombination, which limit its photocatalytic efficiency. How to further improve the photocatalytic performance of carbon nitride materials, especially in its application in dyeing and printing wastewater, remains an urgent problem to be solved.

[0004] The exciton effect, as the physical process by which photogenerated electron-hole pairs in semiconductor materials combine through Coulomb forces to form excitons, provides a new pathway for the efficient activation of molecular oxygen—molecular oxygen can be directly activated through exciton energy transfer. 3 O2) is activated into highly reactive singlet oxygen ( 1 O2), avoiding the bottleneck of low efficiency in traditional electron-hole separation. The exciton effect of existing carbon nitride materials is not fully utilized, and the regulation of its surface defects and electronic structure lacks targeted design, resulting in low singlet oxygen generation efficiency. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing carbon nitride nanosheets based on exciton effect regulation, and its application in dye wastewater treatment. The method proposed in this invention can achieve efficient activation of molecular oxygen to generate singlet oxygen from carbon nitride nanosheets. When used as a carbon nitride photocatalytic material in dyeing wastewater treatment, it can significantly improve the degradation efficiency of organic dyes, providing a new high-efficiency material and technical solution for dyeing wastewater treatment.

[0006] This invention provides a method for preparing carbon nitride nanosheets, comprising the following steps:

[0007] Melamine is used as a raw material and calcined in air at a constant heating rate of 1~6℃ / min and a calcination temperature of 600~700℃ to obtain the calcined product.

[0008] The calcined product was washed with water and dried to obtain carbon nitride nanosheets containing oxygen.

[0009] Preferably, the melamine is placed in a crucible and then placed in a tube furnace for calcination in an air atmosphere.

[0010] Preferably, the amount of melamine added is 2-4 g.

[0011] Preferably, the heating rate is 2~5 °C / min, and the calcination temperature is 610~650 °C.

[0012] Preferably, the calcination time is 1-2 hours, and the calcined product is obtained by natural cooling.

[0013] Preferably, the number of water washings is 1 to 3, and the drying is vacuum drying at 40 to 60 ℃.

[0014] Preferably, the oxygen-containing carbon nitride nanosheets have exciton-related defect sites.

[0015] This invention provides an application of a photocatalyst in the treatment of dye wastewater, wherein the photocatalyst is carbon nitride nanosheets containing oxygen obtained by the preparation method.

[0016] Preferably, the temperature for treating the dye wastewater is 20~30 ℃; and the pH for treating the dye wastewater is 3~11.

[0017] Preferably, the dye wastewater treatment is carried out under oxygen aeration.

[0018] This invention uses melamine as a raw material and optimizes the structure and properties of carbon nitride materials by adjusting the calcination process to an air atmosphere, resulting in oxygen-containing carbon nitride nanosheets. This invention enhances the catalytic activity of carbon nitride under visible light, significantly improving the degradation efficiency of organic dyes. Simultaneously, the carbon nitride material effectively activates molecular oxygen to generate singlet oxygen through the exciton effect. Singlet oxygen, as a highly reactive oxide species, can efficiently degrade dye molecules in wastewater. This innovative control method not only overcomes the defects of electron-hole recombination but also achieves efficient activation of molecular oxygen, thereby enhancing the practical application value of carbon nitride in dyeing and printing wastewater treatment. This technology not only improves the photocatalytic performance of carbon nitride and reduces energy consumption but also provides a more efficient, economical, and environmentally friendly solution for wastewater treatment. Attached Figure Description

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0020] Figure 1 The image shown is a scanning electron microscope (SEM) image of the sample obtained in Example 1 of this invention.

[0021] Figure 2 This is a SEM image of the comparative sample in Example 1 of the present invention;

[0022] Figure 3 This is a comparison of X-ray diffraction (XRD) images of carbon nitride in Example 1 of the present invention;

[0023] Figure 4 This is a comparison chart of the Fourier transform infrared (FT-IR) spectra of carbon nitride in Example 1 of the present invention;

[0024] Figure 5 This is a comparative total X-ray photoelectron spectroscopy (XPS) spectrum of carbon nitride in Example 1 of the present invention;

[0025] Figure 6 This is a comparison of the XPS C 1s peak fitting spectra of carbon nitride in Example 1 of the present invention;

[0026] Figure 7 This is a comparison of the XPS N 1s peak fitting spectra of carbon nitride in Example 1 of the present invention;

[0027] Figure 8 The degradation curve of Rhodamine B by the catalyst obtained in Example 1 of this invention is shown.

[0028] Figure 9 The kinetic curve of the photocatalytic degradation of Rhodamine B by the catalyst obtained in Example 1 of this invention is shown.

[0029] Figure 10 The catalyst obtained in Example 1 of this invention degrades RhB solutions at different pH values;

[0030] Figure 11 The catalyst obtained in Example 1 of this invention and the RhB degradation solution with different anions added to the solution;

[0031] Figure 12 Cyclic experiments were conducted to degrade RhB using the catalyst obtained in Example 1 of this invention;

[0032] Figure 13 This is an experiment on the photocatalytic degradation of printing and dyeing ink wastewater by the catalyst obtained in Example 1 of the present invention;

[0033] Figure 14 The degradation curves of Rhodamine B by photocatalytic degradation after adding different quenchers to the catalyst obtained in Example 1 of this invention are shown.

[0034] Figure 15 This is an aeration experiment of the photocatalytic degradation of Rhodamine B by the catalyst obtained in Example 1 of the present invention. Detailed Implementation

[0035] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0036] This invention provides a method for preparing carbon nitride nanosheets, comprising the following steps:

[0037] Melamine is used as a raw material and calcined in air at a constant heating rate of 1~6℃ / min and a calcination temperature of 600~700℃ to obtain the calcined product.

[0038] The calcined product was washed with water and dried to obtain carbon nitride nanosheets containing oxygen.

[0039] This invention enables the efficient activation of molecular oxygen in carbon nitride nanosheets to generate singlet oxygen. When used as a carbon nitride photocatalytic material in the treatment of dyeing and printing wastewater, it can significantly improve the degradation efficiency of organic dyes and is therefore applicable.

[0040] The preparation method of carbon nitride nanosheets provided by this invention is as follows: First, an appropriate amount of melamine is weighed as a raw material, placed in a crucible, and then placed in a tube furnace. Melamine, commonly known as melamine, is a triazine-based nitrogen-containing heterocyclic organic compound with a molecular weight of 126.12. Specifically, the amount of melamine added is 2-4 g, more specifically 3 g.

[0041] Subsequently, in this embodiment of the invention, the temperature is raised to a specific temperature at a constant heating rate and maintained at that temperature in an air atmosphere in a tube furnace for calcination. After natural cooling, the calcined product is taken out and then subjected to water washing and drying steps to obtain carbon nitride nanosheet material containing oxygen.

[0042] In embodiments of the present invention, the ambient gas is air; the heating rate is 1~6 °C / min, more preferably 2~5 °C / min, for example, heating to the corresponding temperature at a constant heating rate of 5 °C / min. The calcination temperature is 600~700 °C, more preferably 610~650 °C, for example, maintaining the temperature at 650 °C for calcination. The calcination time can be 1~2 h, more preferably 2 h; after the reaction is completed, the calcined product is obtained by natural cooling.

[0043] In this embodiment of the invention, the calcined product is washed with pure water 1-3 times, and preferably placed in a vacuum drying oven at 40-60 °C for overnight drying (12 h) to obtain the final carbon nitride product. In some embodiments, after the reaction is completed, the calcined material is washed with pure water 3 times, and finally dried overnight in a vacuum drying oven at 60 °C.

[0044] The carbon nitride product described in this embodiment of the invention has a nanoscale sheet-like structure, i.e., it is a carbon nitride nanomaterial, and its surface is adsorbed with oxygen-containing substances. Furthermore, the obtained oxygen-containing carbon nitride nanosheets have exciton-related defect sites.

[0045] This invention provides an application of a photocatalyst in the treatment of dye wastewater, wherein the photocatalyst is carbon nitride nanosheets containing oxygen obtained by the preparation method.

[0046] The dye wastewater described in this embodiment of the invention contains common organic dyes (such as Rhodamine B) and some inorganic anions, and can be dyeing and printing wastewater; during treatment, the carbon nitride nanosheet photocatalyst is added, which can photocatalytically degrade the dyes at room temperature and under visible light irradiation.

[0047] In some embodiments, the treatment temperature of the dye wastewater is 20-30 °C. In some embodiments, the pH of the treated dye wastewater is 3-11. In other embodiments, the dye wastewater treatment is carried out under oxygen aeration, which is beneficial to improving the treatment effect.

[0048] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention. The substances used in these embodiments can be purchased commercially or prepared.

[0049] Example 1

[0050] A method for preparing carbon nitride nanosheets for the effective treatment of dye wastewater, and the basic morphology and material characterization.

[0051] 3g of melamine was placed in a crucible and calcined in a tube furnace under air atmosphere at a heating rate of 5℃ / min to 650℃, maintaining this temperature for 2 hours. After the reaction was complete, the calcined product was removed after natural cooling, washed three times with pure water, and dried overnight in a vacuum drying oven at 60℃. The final product was denoted as CNO.

[0052] Furthermore, compared with calcination under an argon atmosphere, the product obtained was designated CN-650.

[0053] To investigate the morphological characteristics of carbon nitride calcined in different atmospheres, the above photocatalyst materials were characterized using SEM. Figure 1 , Figure 2 These are SEM images of carbon nitride nanosheets calcined in different atmospheres. Figure 1 Characterize the CNO morphology of the sample; Figure 2 It is the comparison sample CN-650. According to Figure 1 and Figure 2 As can be seen, they all exhibit a distinct sheet-like structure. This sheet-like structure provides ample surface sites for exciton migration and molecular oxygen adsorption, which is beneficial for the exciton-driven molecular oxygen activation process.

[0054] Figure 3 , Figure 4 The images show the X-ray diffraction (XRD) patterns and Fourier transform infrared (FT-IR) spectra of carbon nitride calcined in different atmospheres. The crystal structure of the graphene-like carbon nitride samples was analyzed using XRD, and the results are as follows: Figure 3As shown. Carbon nitride samples prepared by calcination under different atmospheres (argon, air) all exhibited characteristic diffraction peaks at 13.1° and 27.3°, respectively related to hydrogen bonds used to maintain long-range atomic order within the layers and van der Waals forces used to control the periodic stacking of graphitic carbon nitrides along the c-axis, indicating that their crystal structures share common characteristics. The strong characteristic peak at 27.3° is attributed to the (002) plane, reflecting the graphene-like π-π interlayer stacking of conjugated aromatic units; while the weak peak at 13.1° corresponds to the (100) plane, attributed to the in-plane stacking of the aromatic system. The (002) and (100) diffraction peak positions of each sample did not show significant shifts or disappearances, indicating that calcination under different atmospheres did not alter the chemical structure of carbon nitride. Furthermore, the 13.1° peak of CNO calcined in an air atmosphere is somewhat weakened compared to CN-650 calcined in an argon atmosphere, indicating the breaking of hydrogen bonds in the intralayer framework. This breaking of intralayer hydrogen bonds also leads to a weakening of the (002) peak compared to CN-650, possibly due to structural fluctuations in the hydrogen-bonded layers interfering with the periodic stacking of the layers. This structural feature makes CNO more prone to generating singlet oxygen through energy transfer and interaction with molecular oxygen, providing a structural basis for the enhancement of the exciton effect.

[0055] Simultaneously, the chemical functional groups and structure of the samples were analyzed using FT-IR. For example... Figure 4 As shown, FT-IR spectroscopy analysis reveals that the carbon nitride samples prepared by calcination under different atmospheres maintain high structural consistency, with no significant changes in the positions of the main characteristic absorption peaks, indicating strong stability of the material's functional group structure. Among all samples, the 810 cm⁻¹ peak... -1 1200-1750 cm -1 and 3000-3650 cm -1 Obvious absorption peaks can be observed at all locations. Among them, the 810 cm⁻¹ peak is the most prominent. -1 The sharp peak at 1200-1750 cm⁻¹ is attributed to the out-of-plane bending vibration of the triazine units, indicating that the triazine framework was preserved during calcination; -1 The absorption peaks in the range of 3000-3650 cm⁻¹ are related to the stretching vibrations of CN and C=N, originating from the heterocyclic structure of bridging or terminal amine groups in carbon nitride; while the absorption peaks in the range of 3000-3650 cm⁻¹ are related to the stretching vibrations of CN and C=N, originating from the heterocyclic structure of bridging or terminal amine groups in carbon nitride; -1 The broad absorption peaks within the range are mainly caused by the NH stretching vibration of amino groups and the overlapping absorption of -OH groups of water molecules adsorbed on the sample surface. These characteristics indicate that the basic framework and functional group structure of the carbon nitride sample are relatively stable under different calcination atmospheres, ensuring the consistency of reaction sites for exciton effect activation of molecular oxygen and providing structural assurance for the efficient generation of singlet oxygen.

[0056] XPS spectra revealed the surface elemental composition and chemical state of the prepared carbon nitride samples. For example... Figure 5A comparison of the XPS full spectra of carbon nitride calcined under different atmospheres shows that the carbon nitride samples calcined under different atmospheres exhibit similar peak structures, and the main components of the samples are carbon and nitrogen. In addition to the C and N peaks, a weak oxygen peak was observed, which may be attributed to the adsorption of oxygen-containing substances (such as moisture) on the sample surface during the measurement process. In the high-resolution spectral comparison of C 1s, as shown... Figure 6 As shown, both exhibit two main peaks: CN-650 at 288.12 eV and 284.8 eV, respectively. These peaks correspond to the C=NC group in the aromatic heterocycle of the carbon nitride structure and the sp group, which may originate from the CC or C=C structure. 2 Hybridized carbon atoms. The CNO peak shows a difference at 288.34 eV.

[0057] Similarly, in Figure 7 In the high-resolution spectral comparison of N 1s, different samples all showed consistent peak structures and main peak positions. N 1s was divided into four types of characteristic peaks. For the CNO sample, the peak signals corresponded to approximately 404.32 eV, 401.44 eV, 400.35 eV, and 398.81 eV, respectively. The peak near 404.32 eV originated from the π-π* bond in the aromatic heterocycle; the peak near 401.44 eV was attributed to the free amino (-NH2) group; and the peak at 400.35 eV corresponded to the sp in N-(C)3. 3 Hybridized nitrogen atoms; while the peak near 398.81 eV points to the sp atom in the C=NC structure of the triazine ring. 2 Hybridized nitrogen atoms. This indicates a difference in calcination atmosphere. Although the surface elemental composition and chemical state of the carbon nitride samples are similar, the CNO samples have a higher content of exciton effect-related defect sites (such as N-(C)3), which provides a chemical environment advantage for the efficient activation of molecular oxygen to generate singlet oxygen.

[0058] Example 2

[0059] Carbon nitride photocatalysts degrade Rhodamine B under visible light irradiation.

[0060] To verify the potential of the sample in treating organic wastewater, Rhodamine B (RhB) solution was selected as a representative dye wastewater. Rhodamine B is a common organic dye in dyeing and printing wastewater; therefore, using it as a target pollutant in experiments can effectively reflect the sample's application potential in actual wastewater treatment.

[0061] The graphene-like carbon nitride photocatalyst prepared by the method in Example 1 was used to conduct experiments on the photocatalytic degradation of Rhodamine B. All RhB degradation experiments were carried out at room temperature and under visible light irradiation, using a 300 W xenon lamp with a 420 nm cutoff filter to obtain visible light.

[0062] Specifically, a condensate system was connected to maintain a constant temperature of 25 °C. During the photocatalytic reaction, 1.5 mL of solution sample was taken at regular intervals, filtered through a 0.22 μm filter membrane, and the characteristic absorption peak of RhB (maximum absorption wavelength of 554 nm) was measured using a UV-Vis spectrophotometer. The removal rate of the target pollutant RhB (C / C0×100%) was used to characterize the degradation effect, where C0 and C are the initial RhB concentration and the RhB concentration at a specific time point of the reaction, respectively; C0 is 10 mg / L.

[0063] The degradation curve of RhB under visible light obtained by the calcined graphene-like carbon nitride photocatalyst in Example 1 is shown below. Figure 8 As shown in the figure, the efficiency of the material prepared in Example 1 in catalytically degrading Rhodamine B after light irradiation can be seen, with CNO exhibiting superior degradation performance compared to CN-650. According to... Figure 9 Comparing the kinetic curves, the k value of CN-650 is 0.184 min. -1 The k-value for CNO is approximately 0.341 min. -1 The efficiency of CNO is approximately twice that of CN-650, exhibiting the superior catalytic activity. This difference stems from the fact that CNO activates molecular oxygen more efficiently to generate singlet oxygen through an enhanced exciton effect—excitons directly convert molecular oxygen into highly reactive singlet oxygen via energy transfer, avoiding the energy loss from electron-hole recombination, thereby significantly improving degradation efficiency.

[0064] Example 3

[0065] Degradation experiments of RhB by carbon nitride under different pH and different anion addition conditions.

[0066] The catalyst CNO from Example 1 was used for repeated experiments to verify its photocatalytic degradation performance under different pH conditions and environmental matrices. Except for the catalyst, all other experimental conditions were the same as those for the RhB degradation experiment in Example 2. The pH value was adjusted by adding 1 mol / L HCl and NaOH solutions to the RhB solution, setting pH values ​​to 3, 5, 7, 9, and 11, respectively, to investigate the photocatalytic degradation efficiency of the catalyst for RhB at different pH values.

[0067] Experimental results are as follows Figure 10As shown, the degradation efficiency of RhB is significantly improved under lower pH conditions (i.e., pH=3-5), while the degradation efficiency decreases under alkaline conditions (pH=9-11). This phenomenon is mainly because the alkaline environment inhibits the generation of active species in the photocatalytic reaction. However, even under strongly alkaline conditions (pH=11), the CNO catalyst still completely degrades RhB within 40 minutes, demonstrating its excellent pH adaptability and broad application potential. This is due to the stability of singlet oxygen generated by exciton effect activation over a wide pH range—unlike traditional systems that rely on hydroxyl radicals (which are easily affected by pH), singlet oxygen is less affected by acid-base fluctuations, thus CNO can maintain high degradation efficiency even in complex pH environments.

[0068] Furthermore, to evaluate the anti-interference ability of the CNO catalyst in the presence of different anions, different anions (HA, Cl) were added to the RhB solution respectively. - SO4 2- H2PO4 - and NO3 - This was done to simulate the inorganic anion environment commonly found in actual wastewater. The experimental results are as follows: Figure 11 As shown, the photocatalytic performance of the CNO catalyst remained almost unaffected after the addition of different anions, indicating that CNO has good resistance to interference from various anionic environments, which is of great significance for practical applications in complex environments. The core reason is that the singlet oxygen generated by the exciton effect-activated molecular oxygen has extremely low reactivity with the aforementioned anions, avoiding the problem of traditional reactive species (such as hydroxyl radicals and holes) being quenched by anions, thus maintaining high-efficiency degradation performance in complex matrices.

[0069] In summary, CNO exhibits excellent photodegradation activity and stability under relatively complex environments, making it a promising candidate for practical wastewater treatment.

[0070] Example 4

[0071] Experiments on the reusability of carbon nitride photocatalysts.

[0072] In this experiment, the catalyst CNO from Example 1 was selected for the material reproducibility test. Other experimental conditions were the same as those for the photocatalytic degradation of RhB in Example 2. After each reaction, the RhB solution was treated by filtration, and the catalyst material was separated using a 0.22 μm filter membrane. This material was then added back into a fresh RhB solution for the next round of photocatalytic degradation. This process was repeated multiple times. Figure 12As shown, after 15 consecutive cycles, the removal rate of RhB by CNO remained above 90%, demonstrating excellent cycle stability. This indicates that CNO possesses good durability and reusability, and has potential practical application value in photocatalysis.

[0073] Example 5

[0074] Carbon nitride photocatalyst degrades water-soluble ink dyeing wastewater under visible light.

[0075] The CNO photocatalyst prepared according to the method in Example 1 was used to conduct degradation experiments on aqueous ink dyeing and printing wastewater to evaluate its application potential in treating actual dyeing and printing wastewater. All degradation experiments were conducted at room temperature using a 300W xenon lamp equipped with a 420 nm cutoff filter to provide visible light illumination.

[0076] Specifically, the collected ink printing and dyeing wastewater samples were filtered through a 0.45 μm filter membrane to remove larger particulate impurities, thereby reducing the impact of suspended particles on light effects. The wastewater samples had a pH of 8.02, and the main components included: 30-35% styrene-propyl polymer, 0.5-1.5% monoethanolamine, 10-15% Lysol, 10-15% benzidine yellow, 10-15% phthalocyanine blue, 10-15% phthalocyanine green, 1-3% polyethylene wax, 1-3% mineral oil, and 10-20% water (all by mass).

[0077] Subsequently, the pre-filtered wastewater sample was diluted 100-fold with commercially available purified water, and 50 mL of the diluted solution was placed under light for photocatalytic degradation. To monitor the degradation effect, 1.5 mL of sample solution was taken from the reaction system every 10 minutes, filtered again through a 0.22 μm filter membrane to remove catalyst particles, and then the sample was scanned across the entire wavelength range using a UV-Vis spectrophotometer to record the absorbance changes.

[0078] like Figure 13 As shown in the embodiments of the present invention, after 60 minutes of light irradiation on a dye wastewater sample solution, the maximum absorbance of the ultraviolet-visible spectrum of the sampled solution gradually decreased at intervals, demonstrating excellent degradation effect on actual dyeing and printing wastewater. This result is attributed to the broad-spectrum degradation capability of singlet oxygen generated by exciton-activated molecular oxygen—actual wastewater has a complex composition, but singlet oxygen can efficiently attack the unsaturated bonds of various organic dye molecules, thus CNO can effectively meet the degradation requirements of actual dyeing and printing wastewater.

[0079] Example 6

[0080] Characterization of enhanced exciton effect in carbon nitride photocatalysts.

[0081] The catalyst CNO from Example 1 was used for free radical capture and aeration experiments to verify its ability to generate singlet oxygen through energy transfer activation of molecular oxygen. Except for the catalyst, all other experimental conditions were the same as those for singlet oxygen detection in Example 2.

[0082] Specifically, the reactive oxygen species in the system were investigated by adding different types of quenchers. L-histidine, tert-butanol (TBA), and disodium ethylenediaminetetraacetate (EDTA-2Na) were added to the reaction system at specific concentrations to capture singlet oxygen, hydroxyl radicals, and photogenerated holes. The reaction system was run under xenon lamp irradiation, and the degradation rate of RhB in the solution was monitored to analyze the contribution of each reactive species to the reaction. Experimental results are as follows: Figure 14 As shown, the degradation rate decreased significantly after the addition of L-histidine, indicating that singlet oxygen plays a major role in the reaction. The addition of tert-butanol and disodium ethylenediaminetetraacetate had relatively little effect on the degradation rate, further verifying that singlet oxygen is the main reactive oxygen species in the system. This demonstrates that CNO activates molecular oxygen through energy transfer via the exciton effect, rather than relying on reactive species generated by traditional electron-hole separation, thus avoiding the efficiency loss from electron-hole recombination.

[0083] To further verify the singlet oxygen generation mechanism, an aeration experiment was conducted to increase the oxygen concentration in the solution, and the RhB degradation efficiency of CNO under sufficient molecular oxygen conditions was analyzed. Specifically, oxygen (O2) was continuously introduced into the reaction system, and changes in the pollutant degradation rate were observed. The experimental results are as follows: Figure 15 As shown, the degradation rate of pollutants increases with increasing aeration time, indicating that singlet oxygen generation increases under sufficient oxygen conditions. Simultaneously, nitrogen (N2) was introduced into the system to reduce the oxygen content in the solution to verify the possibility of singlet oxygen generation via electron transfer. The results showed that the degradation rate decreased after nitrogen introduction, indicating that singlet oxygen generation was inhibited. The aeration experiment results verified that carbon nitride generates singlet oxygen through energy transfer by activating molecular oxygen, and this mechanism has high efficiency in utilizing molecular oxygen—excitons directly interact with molecular oxygen without the need for an electron transfer step. Therefore, the amount of singlet oxygen generated increases significantly with increasing oxygen concentration, further highlighting the high efficiency of the exciton effect in activating molecular oxygen.

[0084] In summary, the material prepared by this invention, under light irradiation, can effectively activate molecular oxygen to generate singlet oxygen through energy transfer, and enhance the exciton effect to activate molecular oxygen to generate singlet oxygen for efficient dye degradation. This mechanism has advantages such as strong anti-interference ability, wide environmental adaptability, and high energy utilization efficiency, providing a theoretical basis and practical value for its application in complex wastewater treatment.

[0085] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of various ranges, the endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing carbon nitride nanosheets, characterized in that, Includes the following steps: Melamine is used as a raw material and calcined in air at a constant heating rate of 1~6℃ / min and a calcination temperature of 600~700℃ to obtain the calcined product. The calcined product was washed with water and dried to obtain carbon nitride nanosheets containing oxygen.

2. The production method according to claim 1, characterized by, The melamine was placed in a crucible and then placed in a tube furnace for calcination in an air atmosphere.

3. The preparation method according to claim 1, characterized in that, The dosage of melamine is 2-4g.

4. The production method according to claim 3, characterized by, The heating rate is 2~5℃ / min, and the calcination temperature is 610~650℃.

5. The preparation method according to claim 4, characterized in that, The calcination time is 1-2 hours, and the calcined product is obtained after natural cooling.

6. The preparation method according to any one of claims 1-5, characterized in that, The washing is performed 1 to 3 times, and the drying is performed under vacuum at 40 to 60°C.

7. The method of any one of claims 1-5, wherein, The oxygen-containing carbon nitride nanosheets have exciton-related defect sites.

8. Use of a photocatalyst in the treatment of dye wastewater, characterized in that, The photocatalyst is carbon nitride nanosheets containing oxygen-containing substances obtained by the preparation method according to any one of claims 1-7.

9. Use according to claim 8, characterized in that, The temperature for treating the dye wastewater is 20~30℃; the pH for treating the dye wastewater is 3~11.

10. Use according to claim 8, characterized in that, The dye wastewater treatment is carried out under oxygen aeration.

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