Preparation and application of sunlight-responsive stirring-free carbon nitride nanosheet photocatalyst capable of efficiently degrading water and surface pollutants

Abstract

The invention discloses a sunlight-responsive stirring-free carbon nitride nanosheet photocatalyst capable of efficiently degrading water and surface pollutants. According to the method, melamine is taken as a precursor, KCl is taken as a dispersion medium, defect-state carbon nitride is obtained through high-temperature calcination, chemical shearing and surface carboxylation are carried out through concentrated nitric acid hydro-thermal treatment, and the ultra-dispersed carbon nitride nanosheet is obtained through centrifugal cleaning. The process is simple and low in cost. The size of the obtained nanosheet is dozens of nanometers, the surface of the nanosheet is rich in carboxyl, the dispersity in water is good, and the nanosheet has strong photochemical activity of sunlight response. Under real sunlight, only 50 mu g / mL of a catalyst is needed, stirring and aeration are not needed, and the degradation rate of rhodamine B (the concentration is 75 mu M) and typical mycotoxin aflatoxin B1 (the concentration is 1 ppm) in an aqueous solution exceeds 99% within one hour. And pollutants (including fungaltoxin and dye residues) on the surfaces of traditional Chinese medicinal materials and bulk foods (including peanuts and corns) can be effectively degraded in a spraying or immersing manner.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to the preparation of a solar-responsive, stir-free carbon nitride nanosheet photocatalyst that can efficiently degrade pollutants in water and on surfaces, and its application in the efficient degradation of various pollutants (including dyes, fungal toxins in aqueous solutions and organic pollutants on solid surfaces). Background Technology

[0002] Photocatalysis, as a green and efficient environmental remediation method, takes the redox ability of photogenerated charge carriers as its core and can degrade organic pollutants under mild conditions. It has advantages such as simple operation, no secondary pollution, and recyclable catalysts, and shows broad prospects in the removal of pollutants such as dyes, pesticides, antibiotics and fungal toxins.

[0003] Carbon nitride, as a novel non-metallic polymer semiconductor photocatalyst, has rapidly become a research hotspot in the field of environmental catalysis since its first report on photocatalytic water splitting in 2009. Its core advantages lie in its visible light response (band gap of approximately 2.7 eV), non-toxic and inexpensive synthesis process (prepared through thermal polycondensation of nitrogen-containing precursors such as urea and melamine), and excellent chemical stability (resistance to acids, alkalis, and photocorrosion). In the field of pollution control, carbon nitride utilizes photogenerated electron-hole pairs to generate reactive oxygen species (including ·OH and ·O2). - Photocatalysts are highly efficient at degrading organic pollutants (including but not limited to dyes, pesticides, and antibiotic residues), providing a sustainable technological pathway for solving water and air pollution, and are considered one of the ideal candidate materials for environmental photocatalysts. However, traditional bulk carbon nitride (P-C3N4) suffers from drawbacks such as easy recombination of photogenerated carriers and a limited specific surface area (typically less than 10 m²). 2 Problems such as poor surface hydrophilicity and poor dispersibility in aqueous systems (limited number of oxygen-containing groups on the surface) limit its actual catalytic performance and large-scale application.

[0004] Fungal toxin contamination is a significant challenge in the fields of environment and food safety. Aflatoxin, in particular, is a potent carcinogen (aflatoxin is the most potent known carcinogen, causing various cancers including liver and kidney cancer), and is extremely common in traditional Chinese medicine materials, bulk foods (such as peanuts, corn, soybeans, and nuts), and grain and oil products. Currently, mainstream degradation technologies include:

[0005] 1) Physical methods include gamma ray irradiation and pulsed intense light irradiation, but are limited by the need for expensive instruments and equipment, high energy consumption, and high operational difficulty (requiring professional personnel to operate).

[0006] 2) Chemical methods include the use of strong oxidants (such as ozone, peroxide, chlorine dioxide, etc.), but are limited by high cost and the risk of oxidant residue (which is extremely harmful to the human body).

[0007] 3) Biological methods include microbial degradation and enzymatic hydrolysis, but they are limited by the need for special culture and screening of strains, strict requirements for working conditions, and high operating costs.

[0008] These mainstream physical, chemical, and biological degradation methods each have limitations, such as expensive equipment, high residue risks, or demanding conditions. Therefore, developing an efficient, safe, low-cost, and easy-to-operate mycotoxin degradation technology is of significant practical importance. Photocatalysis technology, due to its mild conditions, lack of harmful residues, and wide applicability (capable of simultaneously degrading and removing multiple mycotoxins), offers a promising solution to this problem. Summary of the Invention

[0009] One objective of this invention is to provide a sunlight-responsive, stir-free, easily synthesized, and low-cost ultradispersed carbon nitride nanosheet photocatalyst and its preparation method. A second objective is to provide the application of this catalyst in the degradation of pollutants in water and on solid surfaces, particularly for the highly efficient photocatalytic degradation of organic dyes (including but not limited to Rhodamine B) and mycotoxins (including but not limited to aflatoxin B1). Under real sunlight, only 50 μg / mL of catalyst is required, without stirring or aeration, achieving a degradation rate of over 99% for Rhodamine B (75 μM) and the typical mycotoxin aflatoxin B1 (1 ppm) in aqueous solution within 1 hour. It can also effectively degrade pollutants (including mycotoxins and dye residues) on the surface of traditional Chinese medicine and bulk foods (including peanuts and corn) through spraying or immersion.

[0010] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a method for preparing a solar-responsive ultradispersed carbon nitride photocatalyst, comprising the following steps:

[0011] S1. Preparation of bulky defective carbon nitride (K-C3N4): Melamine, a nitrogen-rich organic precursor, is mixed with potassium chloride, an inorganic salt, and ground into a fine powder. The powder is then calcined at high temperature in a tube furnace, cooled to room temperature, and then transferred to a mortar and ground into a powder. After washing with water and drying, bulky defective carbon nitride is finally obtained.

[0012] S2. Preparation of ultradispersed carbon nitride (U-C3N4): The defective carbon nitride obtained in step S1 above was added to 15M concentrated nitric acid, hydrothermally treated at 180℃ for 24h, cooled to room temperature, washed with water and centrifuged until the pH of the supernatant was close to neutral, and then freeze-dried to obtain ultradispersed carbon nitride nanosheets.

[0013] Preferably, in step S1, the melamine content after mixing is 47 mmol and the potassium chloride content is 320 mmol.

[0014] Preferably, in step S1, the temperature in the tube furnace is increased from room temperature to 550°C at a rate of 5°C / min, maintained at 550°C for 4 hours, and then decreased to room temperature at a rate of 2.5°C / min.

[0015] Preferably, in step S1, the product is washed three times with ultrapure water, centrifuged at 14800 rpm for ten minutes each time, and then dried in a vacuum drying oven for 12 hours.

[0016] Preferably, in step S2, 15M nitric acid is used, and the mixture is hydrothermally treated at 180°C for 24 hours.

[0017] Preferably, in step S2, the supernatant is washed five to eight times with ultrapure water, centrifuged at 14,800 rpm for 10 minutes each time, until the pH of the supernatant is close to neutral, and finally freeze-dried to prepare ultradispersed carbon nitride nanosheet powder.

[0018] To address the aforementioned technical problems, another technical solution proposed in this invention is to prepare a solar-responsive ultradispersed carbon nitride photocatalyst for photocatalytic degradation of dyes (including but not limited to Rhodamine B) and fungal toxins (including but not limited to aflatoxin B1).

[0019] Preferably, the light source used in the photocatalytic degradation is real sunlight.

[0020] Preferably, the application specifically involves: the photocatalytic degradation of Rhodamine B by ultradispersed carbon nitride nanosheets in response to sunlight needs to be carried out in an aqueous solution; the concentration of the photocatalyst in the solution is 50 μg / ml, and the concentration of Rhodamine B is 75 μM; the photocatalytic reaction can be carried out under real sunlight (60 min) without stirring or aeration.

[0021] Preferably, the application specifically involves the following: the photocatalytic degradation of fungal toxins (including but not limited to aflatoxin B1) by the sunlight-responsive ultradispersed carbon nitride photocatalyst needs to be carried out in solution; the concentration of the photocatalyst in the solution is 50 μg / ml, and the concentration of aflatoxin B1 is 1 ppm; the photocatalytic reaction can be carried out under real sunlight (60 min) without stirring or aeration.

[0022] Preferably, the application specifically involves a sunlight-responsive ultradispersed carbon nitride photocatalyst that can effectively degrade contaminants (including aflatoxin and dyes) on the surface of medicinal herbs and bulk foods (including peanuts, corn, soybeans, and nuts). This is achieved by preparing the ultradispersed carbon nitride photocatalyst into an aqueous dispersion and spraying it onto the contaminated surface, or by directly immersing the surface-contaminated bulk foods (medicines) in the aqueous dispersion of the ultradispersed carbon nitride.

[0023] Beneficial effects:

[0024] This invention provides a method for preparing and applying a highly efficient, sun-responsive, stir-free, and water- and surface-polluting ultradispersed carbon nitride nanosheet photocatalyst. The preparation process is simple and low-cost. Chemical thinning is achieved through KCl-assisted solid-state calcination of a melamine precursor followed by hydrothermal treatment with concentrated nitric acid, resulting in highly efficient preparation of carbon nitride nanosheets (U-C3N4) with a surface rich in carboxyl groups and a size of tens of nanometers. These nanosheets exhibit good dispersibility in aqueous phases.

[0025] Under sunlight irradiation, the prepared carbon nitride nanosheets undergo efficient charge separation, generating highly oxidizing holes and highly reducing electrons (which in turn generate oxidizing superoxide anions and a suitable amount of hydroxyl radicals). Thanks to its ultradispersed properties, this catalyst can achieve sufficient mass transfer and efficient photocatalytic reaction without additional mechanical stirring and aeration, significantly reducing energy consumption and showing broad application prospects.

[0026] Under real sunlight irradiation conditions, the ultradispersed carbon nitride nanosheets U-C3N4 exhibit excellent photocatalytic degradation performance for various pollutants. For example, the degradation efficiency for Rhodamine B dye and the fungal toxin aflatoxin B1 can reach over 99% within 1 hour. Comparative experiments show that: without a catalyst, the degradation rate of Rhodamine B under sunlight is less than 1%; using traditional bulk carbon nitride, the degradation rate is less than 1%; carbon nitride nanosheets prepared by the 12M concentrated hydrochloric acid hydrothermal treatment method have a degradation rate of approximately 50% within 1 hour; while the ultradispersed carbon nitride nanosheets obtained by the 15M nitric acid hydrothermal treatment process of this invention have a degradation rate exceeding 99% within 1 hour under the same conditions, demonstrating significantly superior catalytic performance. Furthermore, without a catalyst, the degradation rate of aflatoxin B1 under sunlight is less than 1%; while under the combined action of ultradispersed carbon nitride nanosheets U-C3N4 and sunlight, the degradation rate of aflatoxin B1 exceeds 99% within 1 hour (corresponding to the reactivity, 40 mg AFB1 g). -1 h -1 This is superior to most existing photocatalytic systems. Furthermore, the U-C3N4 exhibits a certain adsorption capacity for aflatoxin (50 μg / ml of U-C3N4 can adsorb approximately 0.2 ppm of aflatoxin), which helps it to efficiently remove aflatoxin.

[0027] The invention offers flexible applications and a wide range of applicability. The ultradispersed carbon nitride nanosheets U-C3N4 can not only degrade pollutants in aqueous phases, but can also be formulated into aqueous dispersions to effectively remove fungal toxins and dye residues from the surfaces of traditional Chinese medicine materials and bulk foods (including peanuts, corn, soybeans, and nuts) through spraying or immersion. This provides a feasible solution for the treatment of pollutants from traditional Chinese medicine materials and food in real-world environments. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 (a, b) Water dispersibility test diagrams of P-C3N4 and U-C3N4; (c, d) Nitrogen adsorption-desorption isotherms and BET specific surface areas of P-C3N4 and U-C3N4.

[0030] Figure 2 (a) Scanning electron microscope image of P-C3N4; (b) Scanning electron microscope image of U-C3N4; (c, d) Transmission electron microscope image of U-C3N4.

[0031] Figure 3 , six The solid ultraviolet absorption spectrum (a), energy level diagram (b), XRD pattern (c), and infrared spectrum (d) of C3N4.

[0032] Figure 4 Real experimental diagrams (a) and kinetics of dye degradation (b, taking Rhodamine B dye as an example) of six C3N4 photocatalysts under sunlight irradiation.

[0033] Figure 5 Fluorescence images of real samples of U-C3N4 photocatalytic degradation of mycotoxins in response to sunlight (a) and kinetics of photocatalytic degradation of mycotoxins (b, taking aflatoxin B1 as an example).

[0034] Figure 6 U-C3N4 photocatalytically degrades surface contaminants on Chinese medicinal herbs and bulk foods (including peanuts, corn, soybeans, and nuts) (taking the Chinese medicinal herb *Polyporus umbellatus* and Rhodamine B dye as examples).

[0035] Figure 7 U-C3N4 photocatalytically degrades fungal toxins on the surface of Chinese medicinal herbs and bulk foods (including peanuts, corn, soybeans, and nuts) (taking the Chinese medicinal herb Coix seed and aflatoxin B1 as examples).

[0036] Figure 8 A schematic diagram illustrating the preparation of U-C3N4 nanosheets for stirless, sunlight-responsive dye degradation and aflatoxin detoxification. Detailed Implementation

[0037] Example 1: Preparation of bulk carbon nitride

[0038] 47 mmol of melamine and 320 mmol of KCl were thoroughly ground in a mortar, then transferred to a crucible and placed in a tube furnace for high-temperature calcination. The temperature was increased from room temperature to 550 °C at a rate of 5 °C / min, maintained at 550 °C for 4 hours, and then decreased to room temperature at a rate of 2.5 °C / min. After cooling to room temperature, the mixture was transferred back to a mortar and thoroughly ground into powder. The powder was washed three times with ultrapure water and centrifuged at 14800 rpm for 10 minutes each time. The powder was then dried in a vacuum drying oven for 12 hours to obtain yellow, blocky, defective carbon nitride.

[0039] Example 2 Preparation of ultradispersed carbon nitride nanosheets

[0040] The defective carbon nitride from Example 1 was subjected to deep chemical exfoliation using concentrated nitric acid. Specifically, 250 mg of yellow defective carbon nitride was dispersed in 15 M nitric acid and hydrothermally treated at 180°C for 24 hours. After cooling to room temperature, a milky white solution was obtained. This solution was then washed five to eight times with ultrapure water at 14800 rpm for 10 minutes each time, until the pH reached near neutral. After freeze-drying, white, ultradispersed carbon nitride nanosheet powder was obtained, with a yield of approximately 20%.

[0041] like Figure 1 As shown, significant differences were observed in the sedimentation of the materials in water before and after acid treatment. The figure shows the states of four groups of samples before and after standing: 500 μg / mL blocky carbon nitride (P-C3N4) after 0 hours and 12 hours of standing, and 500 μg / mL ultradispersed carbon nitride nanosheets (U-C3N4) after 0 hours and 12 hours of standing. The results show that U-C3N4 obtained by oxidative exfoliation with 15M concentrated nitric acid maintained good dispersion after 12 hours of standing, with a precipitation of approximately 30%; while under the same conditions, P-C3N4 showed a precipitation of up to 90% after 12 hours of standing, indicating that U-C3N4 has better water dispersibility. Secondly, according to Figure 1 The nitrogen adsorption-desorption isotherm test results shown indicate that the BET specific surface area of ​​U-C3N4 is 6 times larger than that of P-C3N4.

[0042] from Figure 2 Scanning electron microscopy images of U-C3N4 show that, significantly different from the aggregated, massive structure of P-C3N4, U-C3N4 possesses a coiled, scaly structure. From... Figure 2 Transmission electron microscopy (TEM) images of U-C3N4 show that its size is mainly distributed between 50-150 nm, with a clearly visible multilayered stacked structure, and nanopores are visible in some parts of the U-C3N4. These test results are consistent with the fact that U-C3N4 has a larger specific surface area. The significantly thinner layered structure of U-C3N4 is beneficial for exposing more active sites and promoting the transport of reactants.

[0043] from Figure 3 Solid-state UV absorption spectroscopy and XRD characterization show that U-C3N4 obtained by nitric acid treatment of K-C3N4 still has good solar response activity and maintains the main structure of carbon nitride. Figure 3 Infrared characterization confirmed that the synthesized U-C3N4 surface has a large number of oxygen-containing hydrophilic groups (such as carboxyl groups), which endows U-C3N4 with good water dispersibility.

[0044] In summary, the ultradispersed carbon nitride nanosheets U-C3N4 possess excellent water dispersion stability and a significantly increased specific surface area, which can fully expose catalytic active sites in the reaction system, facilitating contact with the reaction substrate and thus enhancing their activity in photocatalytic degradation reactions.

[0045] Example 3: Photocatalytic degradation of dyes (Rhodamine B) by ultradispersed carbon nitride nanosheets

[0046] The ultradispersed carbon nitride nanosheets obtained above were applied to the photocatalytic degradation of dyes, taking Rhodamine B as an example. The specific steps were as follows: 150 μM Rhodamine B and 100 μg / ml ultradispersed carbon nitride nanosheet photocatalyst were prepared with ultrapure water, and then the 150 μM Rhodamine B and 100 μg / ml ultradispersed carbon nitride photocatalyst were mixed at a volume ratio of 1:1 to obtain a final reaction concentration of 75 μM Rhodamine B and 50 μg / ml ultradispersed carbon nitride photocatalyst.

[0047] Before light exposure, the mixture was pre-adsorbed in the dark for 30 minutes to ensure adsorption-desorption equilibrium. Then, the reaction mixture was placed under real sunlight for light exposure without mechanical stirring or aeration. The reaction mixture was monitored every 15 minutes (a small amount of sample was taken, centrifuged, and the supernatant was taken. The absorbance at 520 nm was measured using a UV spectrophotometer to observe the change in absorbance of the supernatant before and after degradation).

[0048] Depend on Figure 4 It is possible to obtain conventional bulk carbon nitride (P-C3N4), bulk defective carbon nitride (K-C3N4), conventional bulk carbon nitride nanosheets treated with concentrated hydrochloric acid hydrothermally (Cl-C3N4), bulk defective carbon nitride nanosheets treated with concentrated hydrochloric acid hydrothermally (ClK-C3N4), conventional bulk carbon nitride nanosheets treated with concentrated nitric acid hydrothermally (N-C3N4), and bulk defective carbon nitride nanosheets treated with concentrated nitric acid hydrothermally (U-C3N4).

[0049] Without a catalyst, Rhodamine B degrades by less than 1% under sunlight. With a catalyst, conventional bulk carbon nitride (P-C3N4) degrades Rhodamine B dye by less than 1%, carbon nitride nanosheets (ClK-C3N4) obtained by heat treatment with concentrated hydrochloric acid have a degradation rate of about 50% in 1 hour, while ultradispersed carbon nitride nanosheets (U-C3N4) obtained by heat treatment with concentrated nitric acid have a degradation rate of over 99% in 1 hour.

[0050] Example 4: Photocatalytic degradation of fungal toxins by ultradispersed carbon nitride nanosheets (using aflatoxin B1 as an example)

[0051] The ultradispersed carbon nitride nanosheets obtained above were applied to the photocatalytic degradation of fungal toxins, taking aflatoxin B1 as an example. The specific steps were as follows: 2 ppm of aflatoxin B1 was prepared using a 10% methanol-water mixture; 100 μg / ml of ultradispersed carbon nitride nanosheet photocatalyst was prepared using ultrapure water; then, 2 ppm of aflatoxin B1 and 100 μg / ml of photocatalyst were mixed at a volume ratio of 1:1 to obtain a final reaction concentration of 1 ppm of aflatoxin B1 and 50 μg / ml of photocatalyst. Before light exposure, the sample was pre-adsorbed in the dark for 30 min to ensure adsorption-desorption equilibrium. Subsequently, it was placed under real sunlight, and monitoring was performed every 5 min (a small amount of sample was taken, centrifuged, and the supernatant was collected; the aflatoxin B1 content was detected using high-performance liquid chromatography with a fluorescence detector). Changes before and after photodegradation were observed.

[0052] Depend on Figure 5 It can be seen that aflatoxin B1 itself has a degradation rate of less than 1% under sunlight, but under the action of ultradispersed carbon nitride nanosheets (U-C3N4), the degradation rate can reach 90% in 30 minutes and exceed 99% in 1 hour (corresponding to the reactivity, 40 mg AFB1 g -1 h -1 Its performance surpasses that of most current photocatalytic research systems. Even without light, the ultradispersed carbon nitride nanosheets still exhibit some adsorption of aflatoxin (50 μg / ml U-C3N4 can adsorb approximately 0.2 ppm of aflatoxin), which is beneficial for its photocatalytic removal of aflatoxin.

[0053] Example 5: Photocatalytic removal of contaminants from the surface of traditional Chinese medicine materials and bulk foods (including peanuts, corn, soybeans, and nuts) using ultradispersed carbon nitride nanosheets.

[0054] Taking the traditional Chinese medicine *Polyporus umbellatus* and the typical dye contaminant Rhodamine B as examples, Rhodamine B contamination was performed on *Polyporus umbellatus* samples. A 10 mM Rhodamine B aqueous solution was uniformly sprayed onto the sample surface and dried at 60°C for 5 minutes. This spray-drying process was repeated five times to ensure uniform dye contamination on the sample surface.

[0055] The contaminated samples were randomly divided into three groups for simultaneous light exposure experiments. To prevent Rhodamine B from detaching from the sample surface, each group of samples was placed directly in a petri dish containing 40 mL of a 100 μM Rhodamine B aqueous solution to maintain adsorption-desorption equilibrium. The three groups of petri dishes were then treated as follows: control group (no catalyst added); P-C3N4 group (P-C3N4 aqueous dispersion added); U-C3N4 group (U-C3N4 aqueous dispersion added). The P-C3N4 and U-C3N4 groups had the same sample volume. After equilibration in the dark, all three groups of petri dishes were simultaneously placed outdoors for natural sunlight exposure. The samples were photographed before and after sunlight exposure under the same conditions. By directly comparing the visual differences in the images before and after treatment, the degradation efficiency and cleaning performance of the two carbon nitride catalysts on surface Rhodamine B contaminants were evaluated.

[0056] Figure 6 The results of irradiating a sample of *Polyporus umbellatus* contaminated with Rhodamine B dye under sunlight are presented. It can be seen that, compared with the conventionally prepared bulk carbon nitride photocatalyst (P-C3N4), U-C3N4 exhibits superior degradation ability for Rhodamine B on food (pharmaceutical) surfaces.

[0057] Example 6: Photocatalytic degradation of mycotoxins on the surface of traditional Chinese medicine and bulk foods (including peanuts, corn, soybeans, and nuts) by ultradispersed carbon nitride nanosheets (taking aflatoxin B1 as an example).

[0058] Taking the traditional Chinese medicine coix seed and the typical fungal toxin aflatoxin B1 as examples, the coix seed sample was soaked in 3 mL of a 1 ppm aflatoxin B1 solution for 30 minutes to allow aflatoxin B1 contamination to adhere to its surface. After soaking, the contaminated solution was removed. 1.5 mL of a 60% (v / v) methanol aqueous solution was added to the contaminated sample, and the mixture was vortexed for 10 minutes to extract the aflatoxin B1 adsorbed on its surface. 1.5 mL of a 40 μg / mL U-C3N4 dispersion was added to the extract obtained in the previous step and mixed thoroughly to obtain a mixed reaction solution containing approximately 20 μg / mL U-C3N4 and the extracted aflatoxin B1. The mixed reaction solution was divided into several equal portions and irradiated under real sunlight for 0, 10, 20, 30, and 60 minutes respectively. After the reaction at each time point was completed, the corresponding sample solution was filtered through a 0.22 μm nylon needle filter, and the concentration of residual aflatoxin B1 in the filtrate was then detected by high performance liquid chromatography (HPLC) to evaluate the degradation effect.

[0059] Depend on Figure 7As can be seen, under the action of ultra-dispersed carbon nitride nanosheets (U-C3N4), after irradiation with sunlight on a Job's tears sample contaminated with aflatoxin B1, more than 95% of the aflatoxin was removed. This result confirms that U-C3N4 has excellent removal and detoxification capabilities against mycotoxins on the surface of food (pharmaceuticals).

[0060] Comparative Example 1 (Comparison of ultrasound or other synthesis methods with the synthesis method of this invention)

[0061] To improve the dispersibility of carbon nitride in water and increase its specific surface area and active sites, there are reports on hydrothermal treatment of bulk carbon nitride (Ultra-thin carbon nitride nanosheets for efficient photocatalytic hydrogen evolution). In these reports, bulk carbon nitride is first synthesized and then hydrothermally treated to obtain carbon nitride nanosheets with a size of 150 nm to 300 nm. However, the nanosheets synthesized in this invention are even smaller, with a size concentrated in the range of 50 nm to 150 nm. This is because this invention uses defective carbon nitride as a reaction precursor, which creates conditions for deep chemical shearing of 15 M nitric acid. At the same time, a large number of carboxyl groups are derived on the surface, giving the carbon nitride ultra-high water dispersibility, thereby improving the catalytic reaction activity.

[0062] In addition, there are many methods for synthesizing carbon nitride nanosheets using ultrasonic technology (Exploring theremarkably high photocatalytic efficiency of ultra-thin porous graphiticcarbon nitride nanosheets). These reports first synthesize bulk carbon nitride, then perform a hydrothermal reaction to obtain porous carbon nitride, and finally obtain a small number of nanosheets with sizes exceeding 200 nm through prolonged ultrasonication in acid, but with low yields. In contrast, the nanosheets synthesized in this patent are smaller, concentrated in the 50 nm to 150 nm range, improving specific surface area and reactivity. More importantly, the yield of nanosheets obtained by ultrasonication is very low, only about 5%, while the concentrated nitric acid exfoliation method used in this invention achieves a yield of 20%, demonstrating a significant advantage and making it more suitable for large-scale production compared to ultrasonication.

[0063] Comparative Example 2: Comparison of different acids

[0064] To compare the shearing effects of different acids on defective carbon nitride, two inorganic acids (12M hydrochloric acid and 15M nitric acid) were tested simultaneously. It was found that 15M nitric acid, which has stronger oxidizing and corrosive properties, is more effective in chemically exfoliating carbon nitride and more easily produces ultradispersed carbon nitride nanosheets, and its photocatalytic degradation activity is also better.

[0065] Depend on Figure 4 It can be seen that without a catalyst, Rhodamine B degrades by less than 1% under sunlight; with a catalyst, traditional bulk carbon nitride (P-C3N4) degrades Rhodamine B dye by less than 1%, carbon nitride nanosheets (ClK-C3N4) obtained by hydrothermal treatment with 12M hydrochloric acid have a degradation rate of about 50% in 1 hour, while ultradispersed carbon nitride nanosheets (U-C3N4) obtained by hydrothermal treatment with 15M nitric acid have a degradation rate of over 99% in 1 hour.

[0066] Comparative Example 3: Comparison of different hydrothermal treatment temperatures

[0067] Yellow, blocky defective carbon nitride was dispersed in 15M nitric acid and hydrothermally treated for 24 hours. Temperatures were screened, including 70℃, 115℃, and 180℃. The study found that as temperature increased, the dispersibility of carbon nitride increased, and its photocatalytic activity also increased, with 180℃ showing the best performance.

[0068] Comparative Example 4: Selection of Nitrogen-Rich Precursors and Inorganic Salts

[0069] In step (1), 47 mmol of melamine and 320 mmol of KCl were ground thoroughly in a mortar and then calcined. Melamine was chosen as the precursor because it is a relatively stable, inexpensive, and widely used precursor for carbon nitride synthesis among nitrogen-rich compounds. The production of toxic gases during high-temperature calcination is relatively low and well-understood. KCl inorganic salt was used as the calcination matrix to reduce the degree of polymerization of carbon nitride and to generate nitrogen defects (including cyano and hydroxyl groups). The insertion of K ions into the interlayer gaps of carbon nitride also causes the carbon nitride lattice to expand, facilitating deep chemical shearing by concentrated nitric acid. Potassium fluoride calcination at high temperatures produces toxic hydrogen fluoride gas, while potassium iodide and potassium bromide calcination at high temperatures produce highly toxic iodine and bromine vapors, which are highly irritating to the respiratory tract. In contrast, potassium chloride is safer, with a high melting point (770℃), and does not significantly produce toxic gases when calcined at 550℃.

[0070] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a carbon nitride nanosheet photocatalyst capable of efficiently degrading water and surface pollutants in response to sunlight without stirring, characterized in that, Comprising the following steps: S1. Preparation of defective carbon nitride (K-C3N4): The precursor melamine is mixed with inorganic salt KCl uniformly and ground thoroughly, then calcined at high temperature in a tube furnace, cooled to room temperature, ground into ultrafine powder, washed with water, dried, and finally obtained as a block of defective carbon nitride; S2. Preparation of ultra-dispersed carbon nitride nanosheets (U-C3N4): The defective carbon nitride obtained in step S1 above is mixed with concentrated nitric acid uniformly, then subjected to hydrothermal treatment, centrifuged and washed with water to neutral, freeze-dried to obtain ultra-dispersed carbon nitride nanosheets.

2. The preparation of a non-agitation sunlight-responsive, non-agitation, high-efficiency carbon nitride nanosheet photocatalyst for degrading water and surface pollutants according to claim 1, characterized in that, In step S2, 15M concentrated nitric acid is used, and the hydrothermal treatment is carried out at 180℃ for 24h.

3. The preparation method of the carbon nitride nanosheet photocatalyst for sunlight response without stirring, high efficiency and degradation of water and surface pollutants according to claim 1, characterized in that, In step S1, the amount of melamine is 47mmol, and the amount of potassium chloride is 320mmol.

4. The preparation method of the carbon nitride nanosheet photocatalyst for sunlight response without stirring, high efficiency and degradation of water and surface pollutants according to claim 1, characterized in that, In step S1, the temperature in the tube furnace is raised from room temperature to 550℃ at a rate of 5℃ / min, kept at 550℃ for 4h, and then reduced to room temperature at a rate of 2.5℃ / min.

5. The preparation of a carbon nitride nanosheet photocatalyst for sunlight response, free stirring, and efficient degradation of water and surface pollutants according to claim 1, characterized by, In step S1, the obtained precipitate is dried in a vacuum oven for 12h after washing with ultrapure water three times at a centrifugal speed of 14800rpm for 10 minutes each time; In step S2, the obtained precipitate is freeze-dried after washing with ultrapure water five to eight times at a centrifugal speed of 14800rpm for 10 minutes each time until the pH is close to neutral.

6. The application of the solar-responsive ultra-dispersed carbon nitride photocatalyst prepared by the method of any one of claims 1-5 in photocatalytic degradation of dyes (including rhodamine B) and mycotoxins (including aflatoxin B1).

7. Use according to claim 7, characterized in that, The light source used in the photocatalytic degradation is real sunlight.

8. Use according to claim 7, characterized in that, The application specifically refers to the photocatalytic degradation of rhodamine B dye by solar-responsive ultra-dispersed carbon nitride nanosheets, which is carried out in an aqueous solution, with a photocatalyst concentration of 50μg / ml and a rhodamine B concentration of 75μM; the photocatalytic reaction can be carried out under real sunlight (60min) without stirring and aeration.

9. Use according to claim 7, characterized in that, The application specifically refers to the photocatalytic degradation of mycotoxin aflatoxin B1 by solar-responsive ultra-dispersed carbon nitride nanosheets, which is carried out in an aqueous solution; the photocatalyst concentration in the solution is 50μg / ml, and the concentration of aflatoxin B1 is 1ppm; the photocatalytic reaction can be carried out under real sunlight (60min) without stirring and aeration.

10. Use according to claim 7, characterized in that, The application specifically refers to the solar-responsive ultra-dispersed carbon nitride nanosheets, which can effectively photocatalyze and degrade pollutants (including aflatoxins and dyes) on the surface of traditional Chinese medicinal materials and bulk foods (including peanuts, corn, soybeans, and nuts) through spraying or immersion.

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