MnTiO2atC3N4NPs-based carbaryl three-mode detection method and photocatalytic degradation method

Abstract

The invention relates to a method based on Mnamp; the invention discloses a carbaryl three-mode detection method and a photocatalytic degradation method of TiO2 (at) C3N4NPs, and belongs to the technical field of environment and food pollution detection and treatment. The invention discloses a preparation method of Mnamp with peroxidase-like activity and photocatalytic activity. According to the preparation method of the TiO2-coated C3N4 fluorescent nano-enzyme, the TiO2-coated C3N4 fluorescent nano-enzyme has the capabilities of detecting and degrading pesticides in multiple modes. A colorimetric-photo-thermal-fluorescence three-mode combined strategy is adopted, the detection accuracy is high, and matrix interference is resisted; the detection sensitivity is high, the detection limit of a colorimetric mode reaches 0.047 [mu] mol / L, the detection limit of a photo-thermal mode reaches 0.159 [mu] mol / L, and the detection limit of a fluorescence mode reaches 0.185 [mu] mol / L; on-site and real-time rapid semi-quantitative and even quantitative analysis can be realized; mn < amp >; after the detection of the TiO2 (at) C3N4NPs is completed, the TiO2 (at) C3N4NPs can also be used for carrying out photocatalytic degradation on carbaryl.

Description

Technical Field

[0001] This invention relates to the field of environmental and food pollution detection and control technology, and in particular to a three-modal detection method for Sevin based on Mn&TiO2@C3N4NPs and a photocatalytic degradation method. Background Technology

[0002] Carbaryl is a broad-spectrum carbamate insecticide widely used in agricultural production due to its high efficiency and low cost. It is particularly used in rice cultivation to control pests such as the rice leaf roller and rice stem borer; in soybean cultivation to control pod borers, aphids, and thrips; and in tea cultivation to control tea green leafhoppers and tea geometrid moths, as well as in grape cultivation to control thrips and leafhoppers. Soybeans have a high fat content, and as a fat-soluble pesticide, carbaryl is more likely to accumulate in soybean grains and enter the human body through the food chain, such as soybean oil and soy products, posing potential health risks. Rice, as a staple food, has pesticide residues that directly affect the safety of daily intake, and countries have extremely strict residue limits (MRLs) for it. For tea and grapes, the brewing method of tea increases the risk of pesticide residues directly entering the human body, and grapes, as fresh fruits, may have pesticide residues directly on their skin, which is difficult to wash off. Therefore, carbaryl residues in these two types of agricultural products are also a major concern.

[0003] Currently, there is a lack of detection methods on the market that simultaneously meet the requirements of high sensitivity (below the national standard limit), strong resistance to interference (to cope with complex matrices), and the ability to conduct rapid on-site screening to ensure the safety of these agricultural products entering the market. The detection of carbaryl residues in matrices of these agricultural products is often affected by complex matrix interference (such as oil in soybeans and starch in rice), leading to cumbersome pretreatment, decreased detection accuracy, and high false positive rates in traditional methods. At the same time, there is a lack of efficient and rapid degradation methods for carbaryl-containing wastewater generated during storage and processing, posing a risk of secondary pollution. Therefore, developing a treatment method that is resistant to matrix interference, allows for rapid and accurate detection, and simultaneously enables efficient degradation of carbaryl is of great practical significance for ensuring the safety of staple grains and oil crops and meeting national regulatory requirements.

[0004] Given the limitations of existing methods, researchers have been exploring new approaches, and nanozymes and photocatalytic degradation technologies have gradually gained attention due to their unique advantages. Nanozymes, with their high stability, ease of synthesis, and low cost, have become a promising alternative to natural enzymes. These properties make nanozymes suitable for a wide range of applications, including biosensing, environmental monitoring, and food safety analysis. Furthermore, photocatalytic degradation is noteworthy as a promising method due to its high efficiency, non-selectivity, and environmental friendliness. Photocatalytic degradation of pesticides involves the use of semiconductor materials that absorb light and generate electron-hole pairs. These electron-hole pairs can react with water and oxygen molecules to produce reactive oxygen species (ROS), such as hydroxyl radicals (·OH) and superoxide anions (O2). - These reactive oxygen species can mineralize pesticides into harmless CO2 and H2O. However, despite the significant advantages of both nanozymes and photocatalysis, their individual applications still have obvious limitations. Nanozymes exhibit high sensitivity and specificity in sensing and detection, but their functions are mainly focused on recognition and signal conversion, making it difficult to directly achieve deep degradation and removal of pollutants. While photocatalysis can efficiently mineralize organic pollutants, it lacks the ability to recognize and sense specific targets, making it difficult to achieve coordinated detection and treatment. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a three-mode detection method for Sevin based on Mn&TiO2@C3N4NPs and a photocatalytic degradation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing Mn&TiO2@C3N4 fluorescent nanozymes with peroxidase-like activity and photocatalytic activity, comprising the following steps: S11: Melamine was heated at 550.0~600.0℃ for 2.0~3.0h and sonicated for 10.0~14.0h to obtain g-C3N4NPs; S12: Mix the g-C3N4NPs from step S1 with an ethanol aqueous solution, disperse evenly, adjust the pH to neutral, add Ti(OC4H9)4 and MnSO4·H2O, mix evenly, and react at 160.0~180.0℃ for 8.0~10.0h to obtain the reaction product; S13: Wash the reaction product of step S2 with ethanol and water to obtain the Mn&TiO2@C3N4 fluorescent nanozyme.

[0007] This invention prepares a novel fluorescent nanozyme Mn&TiO2@C3N4NPs, which simultaneously possesses peroxidase-like activity and photocatalytic activity, enabling it to perform multi-mode pesticide detection and degradation. It effectively overcomes matrix interference, achieving highly accurate and reliable detection, and simultaneously and efficiently degrading pesticides. This provides an integrated solution that combines detection and removal functions, offering a new strategy for pesticide residue management in complex real-world scenarios.

[0008] Preferably, in step S11, melamine is heated at 600°C for 2.0 h and then sonicated for 12.0 h. The g-C3N4 nanosheets obtained by sonication in deionized water for 12 h have the thinnest thickness and the best dispersibility, which is beneficial to the subsequent formation and performance improvement of composite materials.

[0009] Further, in step S12, the mass ratio of g-C3N4NPs to MnSO4·H2O is (0.01~0.03):(0.0042~0.0168).

[0010] Preferably, in step S12, the mass ratio of g-C3N4NPs to MnSO4·H2O is 0.03:0.0084. The synthesized Mn&TiO2@C3N4NPs exhibits the strongest peroxidase-like activity and the highest fluorescence intensity. Further increasing the amount of MnSO4·H2O leads to fluorescence quenching, while decreasing its amount significantly reduces enzyme activity; both excessively high and low amounts of g-C3N4NPs affect the fluorescence properties and photocatalytic activity of the composite material.

[0011] Further, in step S12, the volume ratio of ethanol to water in the ethanol-water solution is 1:(2-3), preferably 1:2.

[0012] Further, in step S12, the ratio of g-C3N4NPs to the ethanol aqueous solution is 0.01g:(10-15)mL, preferably 0.01g:10mL.

[0013] Further, in step S12, the ultrasonic treatment lasts for 20–40 minutes to achieve uniform dispersion; preferably, it lasts for 30.0 minutes.

[0014] Further, in step S12, the pH is adjusted to 8.0–9.0.

[0015] Further, in step S12, the ratio of g-C3N4NPs to Ti(OC4H9)4 is 0.03g:(200~1000)μL, preferably 0.03g:500.0μL.

[0016] Furthermore, in step S12, the mixture is stirred for 20 to 40 minutes to achieve uniform mixing, preferably 30.0 minutes.

[0017] Preferably, in step S12, the reaction is carried out at 180°C for 8.0 h.

[0018] Further, in step S13, ethanol and water are centrifuged and washed separately, with centrifugation parameters of 8000-12000 rpm for 8-12 min each time, preferably 10000.0 rpm for 10 min.

[0019] Secondly, the present invention provides a Mn&TiO2@C3N4 fluorescent nanozyme, which is prepared by the aforementioned preparation method.

[0020] Thirdly, the present invention provides the application of the Mn&TiO2@C3N4 fluorescent nanozyme in the detection and / or degradation of carbamate pesticides.

[0021] Furthermore, the carbamate pesticides include at least one of carbaryl, pirimicarb, and isoprocarb.

[0022] Furthermore, the pesticide is a pesticide in agricultural products or water, and the agricultural products include at least one of rice, soybeans, tea, grapes, and winter jujubes.

[0023] Fourthly, the present invention provides a method for detecting sevin, comprising the following steps: S21: Extract carbaryl from the agricultural product to be tested using water, then filter, or filter the water sample to be tested to obtain the solution to be tested; S22: Mix the test solution with acetylcholinesterase solution, acetylcholine solution and choline oxidase solution, incubate at 30-40℃ for 10-15 min, add Mn&TiO2@C3N4NPs solution, 3,3',5,5'-tetramethylbenzidine solution and HAc-NaAc buffer, and incubate at 30-40℃ for 20-25 min to obtain the nanozyme reaction product; S23: Measure the absorbance of the nanozyme reaction product at 652 nm; And / or, measure the temperature of the nanozyme reaction products under 660 nm laser irradiation; And / or, measure the fluorescence intensity of the nanozyme reaction product at 445 nm.

[0024] The fluorescence, colorimetric, and photothermal three-modal detection method established in this invention exhibits good consistency and complementarity in most cases. In practical applications, the detection results of the three modes show little difference and can all be used for the quantitative analysis of Sevin. However, different sample matrices may interfere with one of the detection modes; therefore, the appropriate detection mode can be flexibly selected according to the actual scenario. Colorimetric mode is suitable for colorless or light-colored samples. If the sample itself is dark in color or contains pigments, it may interfere with absorbance measurement. In this case, it is not recommended to use this mode alone. Fluorescence mode is more sensitive to certain fluorescent substances (such as some amino acids, pigments, etc.). If the sample contains such interfering substances, it may affect the accuracy of detection. Photothermal mode depends on the absorption characteristics of the sample to 660nm laser. If the sample contains components that have strong absorption of this wavelength, it may interfere with the acquisition of temperature signals.

[0025] Therefore, this invention recommends selecting one or more modes for cross-validation based on sample characteristics during actual testing. If all three modes are available, fluorescence or photothermal modes are preferred due to their stronger resistance to matrix interference. If signal conflicts occur, data can be processed using the majority consensus principle or weighted averaging to ensure the reliability of the results.

[0026] Furthermore, before testing the actual sample, linear equations were established for the absorbance at 652 nm, the temperature under 660 nm laser irradiation, and the fluorescence intensity at 445 nm using carbaryl solutions of 0.0, 50.0, 100.0, 150.0, 200.0, 250.0, 300.0, 350.0, 400.0, and 450.0 μmol / L. The absorbance at 652 nm, the temperature under 660 nm laser irradiation, and the fluorescence intensity at 445 nm of the actual sample were then substituted into these linear equations to calculate the concentration of carbaryl in the actual sample.

[0027] Further, in step S21, the agricultural product to be tested is soaked in water for 20.0 to 30.0 minutes, preferably 30.0 minutes.

[0028] Furthermore, in step S21, the ratio of the agricultural product to be tested to water is 1g:(10-20)mL, preferably 1g:10mL.

[0029] Furthermore, in step S21, the centrifugation parameters are 8000-12000 rpm for 8-12 min, preferably 10000 rpm for 10 min.

[0030] Furthermore, in step S21, filtration is performed using a conventional 0.22μm filter membrane.

[0031] Furthermore, in step S22, the pH of the HAc-NaAc buffer solution is 3.5–4.5.

[0032] Preferably, in step S22, the pH of the HAc-NaAc buffer solution is 4.5.

[0033] Further, in step S22, the concentration of the 3,3',5,5'-tetramethylbenzidine solution is 20.0–30.0 mmol / L.

[0034] Preferably, in step S22, the concentration of the 3,3',5,5'-tetramethylbenzidine solution is 20.0 mmol / L.

[0035] Further, in step S22, the concentration of acetylcholinesterase solution is 50.0–150.0 U / mL, the concentration of acetylcholine solution is 100.0–250.0 mmol / L, the concentration of choline oxidase solution is 20.0–80.0 U / mL, and the concentration of Mn&TiO2@C3N4NPs solution is 0.5–1.5 mg / mL.

[0036] Preferably, in step S22, the concentration of acetylcholinesterase solution is 100.0 U / mL, the concentration of acetylcholine solution is 200.0 mmol / L, the concentration of choline oxidase solution is 50.0 U / mL, and the concentration of Mn&TiO2@C3N4NPs solution is 1.0 mg / mL.

[0037] Furthermore, in step S22, the test solution, acetylcholinesterase solution, acetylcholine solution, choline oxidase solution, Mn&TiO2@C3N4NPs solution, and 3,3',5,5'-tetramethylbenzidine solution have the same volume, and the total reaction system is 20 times the volume of the test solution.

[0038] Preferably, in step S22, the first incubation is carried out at 37°C for 10 minutes; the second incubation is carried out at 35°C for 20 minutes.

[0039] Fifthly, the present invention provides a method for degrading carbaryl, wherein the sample solution to be degraded is mixed with the Mn&TiO2@C3N4 fluorescent nanozyme, the pH is adjusted to 3.0-5.0, the reaction is stirred in the dark for 0.5-1.0 h, and the photocatalytic reaction is carried out under ultraviolet light or sunlight irradiation.

[0040] Furthermore, the concentration of the Mn&TiO2@C3N4 fluorescent nanozyme is 0.150–0.300 mg / mL.

[0041] Preferably, the concentration of the Mn&TiO2@C3N4 fluorescent nanozyme is 0.200 mg / mL.

[0042] Preferably, the pH is adjusted to 5.0.

[0043] Preferably, the reaction is stirred in the dark for 0.5 h.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High detection accuracy and resistance to matrix interference: Extracts from soybeans, rice, and tea have complex compositions, which can interfere with the results of single-mode detection. This invention employs a colorimetric-photothermal-fluorescence three-mode combined strategy. Through mutual confirmation between different modes, the three modes provide built-in cross-reference correction, significantly improving the reliability and accuracy of carbaryl detection in complex environmental samples and avoiding false positives. When one mode experiences signal abnormalities due to matrix interference, the other two modes can provide cross-validation, effectively avoiding false positives or false negatives, greatly improving the reliability and accuracy of detection in complex agricultural product matrices. This is an advantage that single-mode detection cannot match.

[0045] 2. High detection sensitivity: Conventional detection methods lack sufficient sensitivity, making reliable detection near the maximum residue limit (MRL) of carbaryl as specified in national standards difficult, potentially leading to inaccurate determination of the quality of agricultural products such as rice and soybeans. This invention employs a colorimetric-photothermal-fluorescence three-modal detection method. The limit of detection (LOD) of this method is significantly better than the requirements of the national standard GB 2763-2021, which has an MRL of 1 mg / kg for carbaryl in rice and 1 mg / kg for carbaryl in soybeans. The LOD of this method is far lower than these standards; the colorimetric mode LOD reaches 0.047 μmol / L (approximately 0.009 mg / kg), the photothermal mode LOD reaches 0.159 μmol / L (approximately 0.032 mg / kg), and the fluorescence mode LOD reaches 0.185 μmol / L (approximately 0.037 mg / kg). With its high-sensitivity detection capability, it ensures high reliability and accuracy when testing near the legal limit level. It can accurately determine whether there is excessive levels of carbaryl in agricultural products, and its high detection sensitivity provides strong support for product qualification assessment.

[0046] 3. Rapid on-site screening: Laboratory methods such as chromatography are too time-consuming and cannot meet the needs of rapid screening in agricultural product acquisition and processing lines. This invention utilizes a photothermal mode with the aid of a portable imager, eliminating the need for large instruments, and enables rapid, real-time, on-site semi-quantitative or even quantitative analysis. The colorimetric mode allows for visual identification and on-site qualitative analysis, making it ideal for rapid initial screening in settings such as soybean warehouses, rice mills, and sesame processing workshops.

[0047] 4. Degradation treatment of Sevin: Wastewater generated during cleaning and processing contains pesticide residues such as carbaryl. Traditional treatment methods are inefficient or cause secondary pollution. The Mn&TiO2@C3N4NPs of this invention, after detection, can also be used for photocatalytic degradation of carbaryl in positive samples or wastewater. It efficiently degrades carbaryl (88.4%) within 30 minutes, mineralizing it into harmless CO2 and H2O, achieving a closed-loop treatment from detection to remediation. The photocatalytic degradation process utilizes light energy as an energy source, eliminating the need for additional chemical oxidants and avoiding secondary pollution. Attached Figure Description

[0048] Figure 1 The image shows the synthesis of Mn&TiO2@C3N4NPs.

[0049] Figure 2 The images show the transmission electron microscope (TEM) images and elemental distribution maps of Mn&TiO2@C3N4NPs. In the images, A is the TEM image of Mn&TiO2@C3N4NPs; B is the Ti elemental mapping of Mn&TiO2@C3N4NPs; C is the Mn elemental mapping of Mn&TiO2@C3N4NPs; D is the C elemental mapping of Mn&TiO2@C3N4NPs; E is the N elemental mapping of Mn&TiO2@C3N4NPs; F is the O elemental mapping of Mn&TiO2@C3N4NPs; and G is the EDX spectrum of Mn&TiO2@C3N4NPs.

[0050] Figure 3 Transmission electron microscopy (TEM) images of g-C3N4NPs synthesized by ultrasound at different times. A represents ultrasound for 10.0 h; B represents ultrasound for 12.0 h; and C represents ultrasound for 14.0 h.

[0051] Figure 4 The absorbance and fluorescence intensity of Mn&TiO2@C3N4NPs are shown in Figure 1. A represents the effect of the amount of MnSO4·H2O added on the absorbance of synthesized Mn&TiO2@C3N4NPs+TMB+H2O2 at 652 nm; 1, 2, and 3 represent the amounts of MnSO4·H2O added as 0.0042 g, 0.0084 g, and 0.0168 g, respectively. B represents the effect of the amount of g-C3N4NPs added on the fluorescence intensity of synthesized Mn&TiO2@C3N4NPs excited at 445 nm using 365 nm excitation; 1, 2, and 3 represent the amounts of g-C3N4NPs added as 0.01 g, 0.02 g, and 0.03 g, respectively.

[0052] Figure 5 To verify the peroxidase-like activity of Mn&TiO2@C3N4NPs by external visible absorption spectroscopy.

[0053] Figure 6To verify the peroxidase-like activity of Mn&TiO2@C3N4NPs using electron paramagnetic resonance spectroscopy.

[0054] Figure 7 To verify the feasibility of detecting carbaryl in the Mn&TiO2@C3N4+ACh+AChE+ChOx+TMB system using a UV-Vis spectrophotometer, the obtained UV-Vis absorption spectrum was obtained.

[0055] Figure 8 To verify the feasibility of detecting carbaryl in the Mn&TiO2@C3N4+ACh+AChE+ChOx+TMB system using a portable photothermal imager, the resulting photothermal signal response diagram was obtained.

[0056] Figure 9 To verify the feasibility of detecting carbaryl in the Mn&TiO2@C3N4+ACh+AChE+ChOx+TMB system using a fluorescence spectrophotometer, the obtained fluorescence spectrum was obtained.

[0057] Figure 10 The optimal reaction conditions for the Mn&TiO2@C3N4NPs+ACh+AChE+ChOx+TMB system, measured by a UV-Vis spectrophotometer, are given. Where A is pH, B is reaction temperature, and C is TMB concentration.

[0058] Figure 11 This is a schematic diagram illustrating the three-mode detection and photocatalytic degradation principle of cevin based on Mn&TiO2@C3N4NPs.

[0059] Figure 12 The absorption spectra and standard curves of reaction solutions with different concentrations of carbaryl are shown. Where A is the absorption spectrum and B is the standard curve.

[0060] Figure 13 Photothermal signals and standard curves for reaction solutions of different concentrations of carbaryl. Figure 14 The fluorescence spectra and standard curves of reaction solutions with different concentrations of carbaryl are shown. In the figure, A represents the fluorescence spectrum; B represents the standard curve.

[0061] Figure 15 This is a bar chart for the detection of interfering substances in complex environments using three modes. A represents absorbance (colorimetric mode); B represents fluorescence intensity (fluorescence mode); and C represents temperature (photothermal mode). 1 represents Mg. 2+ ;2 is NH 4+ ;3 is Na + ;4 is Ca 2+ ;5 is K + 6 represents SO4 2- 7 represents PO4 2-; 8 is sucrose; 9 is glucose; 10 is maltose; 11 is imidacloprid; 12 is dinotefuran; 13 is acetamiprid; 14 is carbaryl; 15 is pirimicarb; 16 is isoprocarb.

[0062] Figure 16 This is a graph showing the degradation of cibarin in a water sample as measured by a UV-Vis spectrophotometer.

[0063] Figure 17 The optimal conditions for the degradation of carbaryl in water samples, measured by a UV-Vis spectrophotometer, are given. Where A represents the concentration of Mn & TiO2@C3N4; B represents the carbaryl concentration; and C represents the pH.

[0064] Figure 18 This is a comparison chart of the degradation efficiency of different photocatalysts.

[0065] Figure 19 The degradation diagram of cibarin in water samples under different light sources was measured by a UV-Vis spectrophotometer. Detailed Implementation

[0066] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Unless otherwise specified, other materials and reagents used in the embodiments are commercially available.

[0067] The raw materials used in this invention—manganese sulfate monohydrate (99.0%), tetrabutyl titanate (99.0%), melamine (99.0%), acetylcholine chloride (ACh, 99.0%), acetylcholinesterase (AChE, 220.0 U / mg), choline oxidase (ChOx, 8.0–20.0 U / mg), and TMB (3,3',5,5'-tetramethylbenzidine, 99.5%)—were purchased from Shanghai Maclean Biotechnology Co., Ltd.; the acetate-sodium acetate buffer was purchased from Shanghai Yuanye Biotechnology Co., Ltd. All chemicals were purchased directly from the supplier without further purification; ultrapure water was used in the experiments.

[0068] The preparation method of acetate-sodium acetate buffer (pH 4.5) is as follows: take 50.0 mL of acetate-sodium acetate buffer with pH = 5.5, and adjust the pH of the acetate-sodium acetate buffer with pH = 5.5 to 4.5 using a pH meter and with the help of hydrochloric acid solution and sodium hydroxide solution.

[0069] Example 1: Preparation of Mn&TiO2@C3N4NPs fluorescent nanozymes with peroxidase-like and photocatalytic activities. I. Preparation method ( Figure 1 ) 1. Synthesis of ultrathin g-C3N4NPs: 5.0 g of melamine was placed in a muffle furnace and heated at 600 °C for 2.0 h. After the reaction was completed, the reactants were naturally cooled to room temperature, then sonicated in deionized water for 12.0 h, and finally frozen into powder using a freeze dryer to obtain ultrathin g-C3N4 nanosheets.

[0070] 2. Synthesis of Mn&TiO2@C3N4NPs: 0.03 g g-C3N4 was dispersed in a mixture of 10.0 mL ethanol and 20.0 mL deionized water. The dispersion was sonicated for 30.0 min to ensure uniform dispersion. Ammonia was added to adjust the pH to 8.0–9.0. Then, 500.0 μL Ti(OC4H9)4 was slowly added dropwise. Under magnetic stirring, 0.0084 g MnSO4·H2O was gradually added and stirred for 30.0 min to obtain a mixture. The mixture was transferred to a reaction vessel and reacted at 180℃ for 8.0 h. After the reaction was completed, it was cooled to room temperature to obtain the reaction product. The obtained reaction product was washed with anhydrous ethanol and deionized water at 10000.0 rpm for 10.0 min, respectively. The product was washed three times with each of the two reagents, and then dried in a 60℃ oven for 6.0 h to obtain the Mn&TiO2@C3N4NPs fluorescent nanozyme, which was stored in a refrigerator protected from light.

[0071] like Figure 2 A to Figure 2 Figure G shows the transmission electron microscope image and elemental distribution diagram of Mn&TiO2@C3N4NPs.

[0072] II. Effects of different ultrasonic times on the thickness and dispersibility of g-C3N4 nanosheets In the method for synthesizing ultrathin g-C3N4NPs, the ultrasonication time was set to 10.0 h, 12.0 h and 14.0 h, respectively, and g-C3N4NPs were prepared.

[0073] The results are as follows Figure 3 A to Figure 3 As shown in Figure C, the g-C3N4 nanosheets obtained by sonication in deionized water for 12 hours have the thinnest thickness and the best dispersibility, which is beneficial to the formation and performance improvement of subsequent composite materials.

[0074] III. Effects of the addition amounts of g-C3N4NPs and MnSO4·H2O on the activity and fluorescence intensity of Mn&TiO2@C3N4NPs In the method for synthesizing Mn&TiO2@C3N4NPs, the amount of g-C3N4NPs added was set to 0.01 g, 0.02 g, and 0.03 g, respectively; the amount of MnSO4·H2O added was set to 0.0042 g, 0.0084 g, and 0.0168 g, respectively; and Mn&TiO2@C3N4NPs were prepared.

[0075] When the amount of g-C3N4NPs was 0.03 g and the amount of MnSO4·H2O was 0.0084 g, the synthesized Mn&TiO2@C3N4NPs exhibited the strongest peroxidase-like activity. Figure 4 A) and the highest fluorescence intensity ( Figure 4 B). Further increasing the amount of MnSO4·H2O will lead to fluorescence quenching, while decreasing its amount will significantly reduce enzyme activity; both excessively high and low amounts of g-C3N4NPs will affect the fluorescence properties and photocatalytic activity of the composite material.

[0076] The above experimental results show that Mn&TiO2@C3N4NPs are highly sensitive to key reaction parameters (such as feed ratio and reaction time), and precise control is required to obtain high-performance nanozymes, which also reflects the uniqueness of the preparation process of this invention.

[0077] Example 2: Verification of Mn&TiO2@C3N4NPs-type peroxidase activity 1. Using TMB as the colorimetric reagent and HAc-NaAc as the buffer, the following five reactions were performed: (1) H2O2 + TMB; (2) Mn & TiO2 @ C3N4NPs + H2O2; (3) Mn & TiO2 @ C3N4NPs + TMB; (4) Mn & TiO2 @ C3N4NPs + TMB + H2O2; (5) g-C3N4NPs + TMB + H2O2.

[0078] After each group of reagents had fully reacted, they were transferred to cuvettes, and the absorbance at 652 nm was measured using a UV-Vis spectrophotometer. The catalytic activity of different nanozymes was then compared. Figure 5 As shown, the Mn&TiO2@C3N4+TMB+H2O2 combination exhibits the highest absorbance value, indicating that the Mn&TiO2@C3N4NPs nanozyme prepared in this invention possesses strong peroxidase-like activity.

[0079] In the above verification steps, the final concentration of Mn&TiO2@C3N4NPs or g-C3N4NPs added was 50.0 μg / mL; the final concentration of TMB was 1.0 mmol / L; the final concentration of H2O2 was 1.0 mmol / L; the pH of the added HAc-NaAc buffer was 4.0; the total mixed solution was 200.0 μL; the reaction temperature was 37.0℃; and the time for thorough mixing and reaction was 20.0 min.

[0080] 2. Accurately weigh a certain mass of Mn&TiO2@C3N4NPs, disperse it in ultrapure water, and prepare a uniform dispersion with a concentration of 1.0 mg / mL. At the same time, freshly prepare a 20 mM H2O2 solution and a 100 mM DMPO aqueous solution, and set up the following two reaction systems for comparison: (1) Experimental group: Take 100 μL Mn&TiO2@C3N4NPs dispersion (1.0 mg / mL), 100 μL H2O2 solution (20 mM) and 100 μL DMPO solution (100 mM) and mix them thoroughly (Mn&TiO2@C3N4+DMPO+H2O2). (2) Control group: 100 μL of Mn&TiO2@C3N4NPs dispersion (1.0 mg / mL) was mixed with 100 μL of DMPO solution (100 mM), and 100 μL of ultrapure water was added to replace H2O2 (Mn&TiO2@C3N4+DMPO).

[0081] like Figure 6 As shown, the Mn&TiO2@C3N4+DMPO system showed no significant change, while the Mn&TiO2@C3N4+DMPO+H2O2 system exhibited a distinct 1:2:2:1 signal peak. This indicates that the Mn&TiO2@C3N4NPs nanozyme reacted with hydrogen peroxide to generate ·OH free radicals, which subsequently produced characteristic signal peaks in the EPR spectrum. This further verifies that the Mn&TiO2@C3N4NPs nanozyme possesses strong peroxidase-like activity.

[0082] Example 3 Feasibility verification of detecting carbaryl in Mn&TiO2@C3N4+ACh+AChE+ChOx+TMB system 1. The following six reactions were performed using TMB as the colorimetric reagent and HAc-NaAc as the buffer: (1) TMB (2) Mn&TiO2@C3N4NPs; (3) Mn&TiO2@C3N4NPs+ACh (acetylcholine)+AChE (acetylcholinesterase)+ChOx (choline oxidase); (4) Mn&TiO2@C3N4NPs+AChE+ChOx+TMB; (5) Mn&TiO2@C3N4NPs+ACh+AChE+ChOx+TMB; (6) Mn&TiO2@C3N4NPs+carbaryl+ACh+AChE+ChOx+TMB.

[0083] In the above verification steps, the final concentration of Mn&TiO2@C3N4NPs was 50.0 μg / mL; the final concentration of TMB was 1.0 mmol / L; the final concentration of ACh was 10.0 mmol / L; the final concentration of AChE was 5.0 U / mL; the final concentration of ChOx was 2.5 U / mL; the final concentration of carbaryl was 450.0 μmol / L; the pH of the added HAc-NaAc buffer was 4.0; the total volume of the mixed solution was 200.0 μL; the reaction temperature was 37.0℃; and the time for thorough mixing and reaction was 30.0 min.

[0084] Figure 7 The spectra measured using a UV-Vis spectrophotometer are shown. It is clear that group (5) showed significant formation of oxTMB, resulting in enhanced absorbance at 652 nm. Group (6) inhibited the oxidation of TMB, leading to a reduction in oxTMB and thus a decrease in absorbance.

[0085] 2. Using TMB as the colorimetric reagent and HAc-NaAc as the buffer, the following four sets of reactions were carried out: (1) Mn&TiO2@C3N4NPs+Sevin+ACh+AChE+ChOx+TMB; (2) Mn&TiO2@C3N4NPs+ACh+AChE+ChOx+TMB; (3) Mn&TiO2@C3N4NPs+Sevin+ACh+AChE+ChOx+TMB; (4) Mn&TiO2@C3N4NPs+ACh+AChE+ChOx+TMB.

[0086] After the reagents in each group reacted fully, the photothermal signal response of groups (1) and (2) was detected by a portable photothermal imager without irradiation by a 660nm infrared laser; the photothermal signal response of groups (3) and (4) was detected by a portable photothermal imager under irradiation by a 660nm infrared laser.

[0087] In the above verification steps, the final concentration of Mn&TiO2@C3N4NPs was 50.0 μg / mL; the final concentration of TMB was 1.0 mmol / L; the final concentration of ACh was 10.0 mmol / L; the final concentration of AChE was 5.0 U / mL; the final concentration of ChOx was 2.5 U / mL; the final concentration of carbaryl was 450.0 μmol / L; the pH of the added HAc-NaAc buffer was 4.0; the total volume of the mixed solution was 200.0 μL; the reaction temperature was 37.0℃; and the time for thorough mixing and reaction was 30.0 min.

[0088] Figure 8The temperature change graph is measured by a portable photothermal imager. Group (3) inhibits the oxidation of TMB and reduces the generation of oxTMB, resulting in a slow temperature change. Group (4) does not inhibit the generation of oxTMB, so oxTMB can rapidly increase the temperature under 660nm near-infrared laser irradiation.

[0089] 3. Using TMB as the colorimetric reagent and HAc-NaAc as the buffer, the following three sets of reactions were carried out: (1) Carbaryl; (2) Mn&TiO2@C3N4NPs+ACh+AChE+ChOx+TMB; (3) Mn&TiO2@C3N4NPs+Carbaryl+ACh+AChE+ChOx+TMB.

[0090] After the reagents in each group have reacted fully, the fluorescence spectra of each group are measured using a fluorescence spectrophotometer.

[0091] In the above verification steps, the final concentration of Mn&TiO2@C3N4NPs was 50.0 μg / mL; the final concentration of TMB was 1.0 mmol / L; the final concentration of ACh was 10.0 mmol / L; the final concentration of AChE was 5.0 U / mL; the final concentration of ChOx was 2.5 U / mL; the final concentration of carbaryl was 450.0 μmol / L; the pH of the added HAc-NaAc buffer was 4.0; the total volume of the mixed solution was 200.0 μL; the reaction temperature was 37.0℃; and the time for thorough mixing and reaction was 30.0 min.

[0092] Figure 9 The fluorescence spectra were measured using a fluorescence spectrophotometer. The generated oxTMB quenched the fluorescence of Mn&TiO2@C3N4NPs (Group 2), but the fluorescence of Mn&TiO2@C3N4NPs was restored in the presence of carbaryl (Group 3) because the oxidation of TMB was inhibited.

[0093] Example 4 Optimal reaction conditions for the TMB colorimetric reaction catalyzed by Mn&TiO2@C3N4NPs In order to study the optimal reaction conditions for the TMB colorimetric reaction catalyzed by Mn&TiO2@C3N4NPs, the optimal conditions for the detection system of group (5) in step 1 of Example 3 were determined by using the controlled variable method and testing the ultraviolet-visible absorption spectrum. The conditions are set as follows.

[0094] (1) Set the reaction pH (i.e. HAc-NaAc buffer pH) to 3.5, 4.0, 4.5, 5.0, 5.5 and 6.0 respectively.

[0095] (2) Set the reaction temperatures to 30℃, 35℃, 40℃, 45℃, 50℃ and 55℃ respectively.

[0096] (3) Set the TMB concentrations to 0.1mM, 0.2mM, 0.3mM, 0.4mM, 0.5mM, 0.7mM, 0.9mM, 1.0mM and 1.2mM respectively.

[0097] like Figure 10 As shown in Figure A, the optimal pH is 4.5; Figure 10 As shown in B, the optimal temperature is 35℃; Figure 10 As shown in C, the absorbance value gradually increases with the increase of TMB concentration until the absorbance no longer increases when the TMB concentration is 1.0 mmol / L. Therefore, the optimal concentration of TMB is 1.0 mmol / L.

[0098] Example 5: Standard Curve Establishment and Sample Detection Method like Figure 11 The diagram shown illustrates the principle of three-mode detection and photocatalytic degradation of cesine based on Mn&TiO2@C3N4NPs.

[0099] 1. Establish the linear equation for detection. First, mix 10.0 μL of different concentrations of carbaryl solution with 10.0 μL of AChE solution, then add 10.0 μL of ACh solution and 10.0 μL of ChOx solution in sequence, mix well, and incubate at 37 °C for 10 min. Then add 10.0 μL of Mn&TiO2@C3N4NPs solution, 10.0 μL of TMB solution and HAc-NaAc buffer, keeping the total volume at 200 μL, and incubate at 35 °C for 20.0 min.

[0100] The concentrations of the substances in the above steps are as follows: HAc-NaAc buffer (pH 4.5, 0.2 mol / L), different concentrations of carbaryl solution (0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 mmol / L), AChE solution (concentration 100.0 U / mL), ACh solution (concentration 200.0 mmol / L), ChOx solution (concentration 50.0 U / mL), Mn&TiO2@C3N4NPs solution (concentration 1.0 mg / mL), and TMB solution (concentration 20.0 mmol / L).

[0101] After each group of reagents has reacted fully, the fluorescence intensity value F1 at 445 nm was measured using a fluorescence spectrophotometer; the absorbance value A1 at 652 nm was measured using a UV-Vis spectrophotometer; and the temperature value under 660 nm laser irradiation was measured using a portable photothermal imager and recorded as T1. The measured fluorescence intensity, absorbance, and temperature values ​​are shown in Table 1.

[0102] Table 1 After fitting and calculating using Origin software, it was found that: ... Figure 12 A and Figure 12 As shown in Figure B, a good linear relationship exists between the change in absorption intensity at 652 nm and the concentration of carbaryl in the range of 0.249–450.0 μmol / L. The regression equation is A = -0.00184Ccarbaryl + 1.37089, with a correlation coefficient of 0.996 and a detection limit of 0.047 μmol / L. Figure 13 As shown, a good linear relationship exists between the temperature value under 660nm laser irradiation and the concentration of carbaryl in the range of 0.418–450.0 μmol / L. The regression equation is T = -0.02403Ccarbaryl + 41.2046, with a correlation coefficient of 0.995 and a detection limit of 0.159 μmol / L. Figure 14 A and Figure 14 As shown in Figure B, there is a good linear relationship between the fluorescence intensity at 445 nm and the concentration of carbaryl in the range of 0.537–450.0 μmol / L. The regression equation is F = 1.15216C carbaryl + 424.691, with a correlation coefficient of 0.995 and a detection limit of 0.185 μmol / L. The minimum detection limit was obtained using the formula (3σ / k, where σ is the standard deviation of 11 blank samples).

[0103] 2. Sample pretreatment The items to be tested are agricultural products or environmental water bodies containing residual Sivin.

[0104] For agricultural products, take 1.0g of the sample to be tested and immerse it in 10.0mL of ultrapure water for 30.0min. Then centrifuge at 8000.0rpm for 10.0min, retain the supernatant, remove the precipitate, filter the supernatant through a 0.22μm filter membrane, collect the filtrate, and obtain the sample solution to be tested.

[0105] For environmental water bodies, the water is filtered using filter paper or filter membrane with a pore size of 0.22 μm to collect the filtrate, and the pH is adjusted to 4.5 with acetate-sodium acetate buffer to obtain the sample solution to be tested.

[0106] 3. Testing of the sample to be tested (1) Measure the absorbance value An of the sample to be tested at 652 nm. First, mix 10.0 μL of the sample solution to be tested with 10.0 μL of AChE solution, then add 10.0 μL of ACh solution and 10.0 μL of ChOx solution in sequence, mix well, and incubate at 37°C for 10 min. Then add 10.0 μL of Mn&TiO2@C3N4NPs solution, 10.0 μL of TMB solution and HAc-NaAc buffer, keeping the overall system at 200 μL (the concentrations of AChE solution, ACh solution, ChOx solution, Mn&TiO2@C3N4NPs solution, TMB solution and HAc-NaAc buffer are the same as in step 1 of Example 5), and incubate at 35°C for 20.0 min. Measure the absorbance value at 652 nm using a UV-Vis spectrophotometer and record it as An.

[0107] (2) Determine the photothermal response signal value Tn of the sample under 660nm laser irradiation. First, mix 10.0 μL of the sample solution to be tested with 10.0 μL of AChE solution. Then, add 10.0 μL of ACh solution and 10.0 μL of ChOx solution sequentially, mix well, and incubate at 37°C for 10 min. Next, add 10.0 μL of Mn&TiO2@C3N4NPs solution, 10.0 μL of TMB solution, and HAc-NaAc buffer, keeping the total volume at 200 μL (the concentrations of AChE solution, ACh solution, ChOx solution, Mn&TiO2@C3N4NPs solution, TMB solution, and HAc-NaAc buffer are the same as in step 1 of Example 5). Incubate at 35°C for 20.0 min and irradiate with a 660 nm near-infrared laser (0.75 W / cm²). 2 (5.0cm, 300.0s), and the temperature value Tn was observed using a portable temperature imager.

[0108] (3) Measure the fluorescence spectrum of the sample under excitation at 365 nm wavelength. First, mix 10.0 μL of the sample solution to be tested with 10.0 μL of AChE solution, then add 10.0 μL of ACh solution and 10.0 μL of ChOx solution in sequence, mix well, and incubate at 37 °C for 10 min. Then add 10.0 μL of Mn&TiO2@C3N4NPs solution, 10.0 μL of TMB solution and HAc-NaAc buffer, keeping the total system volume at 200 μL (the concentrations of AChE solution, ACh solution, ChOx solution, Mn&TiO2@C3N4NPs solution, TMB solution and HAc-NaAc buffer are the same as in step 1 of Example 5), and incubate at 35 °C for 20.0 min. Measure the fluorescence spectrum under excitation at 365 nm using a fluorescence spectrophotometer, and record the fluorescence intensity value Fn at 445 nm.

[0109] 4. Calculate the concentration of carbaryl in the sample to be tested. The linear equation for absorbance is A = -0.00184C-sevin + 1.37089; the linear equation for temperature is T = -0.02403C-sevin + 41.2046; the linear equation for fluorescence spectroscopy is F = 1.15216C-sevin + 424.691. Substituting the Fn, An, and Tn values ​​obtained in step 3 into the standard curve, the concentration C of sevin in the sample to be tested can be calculated. The value of sevin is the residual value of sevin.

[0110] Example 6: The Influence of Different Environmental Interference Substances on the Three-Modal Detection Method of Carbamate Pesticides Based on Mn&TiO2@C3N4NPs Following the method in Example 5, different environmental interfering substances were detected: Mg 2+ NH4 + Na + Ca 2+ K + SO4 2- PO4 2- Sucrose, glucose, maltose, imidacloprid, dinotefuran, acetamiprid, carbaryl, pirimicarb, and isoprocarb.

[0111] Only the absorbance value A of carbamate pesticides (carbaryl, imidacloprid, and isoprocarb) Figure 15 A) and temperature value T( Figure 15 C) showed a significant decrease, and the fluorescence intensity value F( Figure 15 B) A significant increase occurs. This indicates that the detection system has good selectivity for carbamate pesticides. The present invention can specifically detect carbamate pesticides, while other interfering substances have no effect on the method of the present invention, demonstrating the anti-interference and high sensitivity of the present invention.

[0112] Example 7: Detection of the sensing performance of Sevin in practical applications using the Mn&TiO2@C3N4+ACh+AChE+ChOx+TMB system. Rice, soybeans, tea, grapes, and jujubes were selected as actual samples for testing.

[0113] Weigh 1.0 g of each sample and immerse it in 10.0 mL of ultrapure water for 30.0 min. Then centrifuge at 8000.0 rpm for 10.0 min, retain the supernatant, remove the precipitate, and filter the supernatant through a 0.22 μm filter membrane. Collect the filtrate, and mix the five filtrates of different types of samples with different concentrations of carbaryl (20.0 μM, 50.0 μM, and 250.0 μM) to obtain spiked samples. Mix the spiked samples with 10.0 μL of AChE solution, then add 10.0 μL of ACh solution and 10.0 μL of ChOx solution sequentially, mix well, and incubate at 37 °C for 10 min. Add 10.0 μL of Mn&TiO2@C3N4NPs solution and 10.0 μL of... The TMB solution and HAc-NaAc buffer were kept at a total volume of 200 μL (the concentrations of AChE solution, ACh solution, ChOx solution, Mn&TiO2@C3N4NPs solution, TMB solution, and HAc-NaAc buffer were the same as in step 1 of Example 5). The mixture was incubated at 35°C for 20.0 min. The absorbance value A at 652 nm was measured using a UV-Vis spectrophotometer. The fluorescence spectrum under excitation at 365 nm was measured using a fluorescence spectrophotometer, and the fluorescence intensity value F at 445 nm was recorded. The mixture was then irradiated with a 660 nm near-infrared laser (0.75 W / cm²). 2 The absorbance value A, fluorescence intensity value F, and photothermal response signal value T were measured using a portable temperature imager. The obtained absorbance value A, fluorescence intensity value F, and photothermal response signal value T were substituted into the corresponding linear equation constructed in Example 5. The results of Sevin measured under the three detection modes are shown in Table 2.

[0114] Table 2 The results show that the established three-modal sensing system exhibits good applicability and reliability in actual sample detection. The recoveries of carbaryl in all tested samples ranged from 95.4% to 104.7%, with relative standard deviations (RSDs) all less than 5%. These results meet the general requirements for accuracy and precision in pesticide residue detection, indicating that this method possesses good anti-interference ability and repeatability in different types of actual sample matrices, and can meet the practical needs of rapid detection of carbaryl residues.

[0115] Example 8: Photodegradation experiment of carbaryl pesticide under ultraviolet light. Take 50.0 mL of the reaction mixture containing 0.020 g / L carbaryl and 0.200 g / L Mn&TiO2@C3N4NPs, adjust the pH to 5.0, stir in the dark for 0.5 h, and then stir under direct irradiation with 310 nm ultraviolet light to carry out the photocatalytic reaction.

[0116] Every 5.0 min, 2.0 mL of the reaction mixture was collected, the supernatant was collected by centrifugation and analyzed by a UV-Vis spectrophotometer. The quantification of carbaryl was based on the absorption peak of carbaryl at 220 nm. The degradation efficiency was calculated as follows: Degradation efficiency (%) = [1 - Ct / Co] × 100, where Co is the initial concentration of carbaryl and Ct is the remaining concentration of carbaryl at time t.

[0117] The results are as follows Figure 16 As shown, with the increase of light exposure time, the absorption peak of carbaryl gradually decreases and tends to level off. It is calculated that 88.4% of carbaryl is degraded at 30.0 min.

[0118] Example 9: Optimal reaction conditions for the degradation of carbaryl by Mn & TiO2@C3N4NPs To investigate the optimal reaction conditions for the degradation of carbaryl by Mn&TiO2@C3N4NPs, the optimal conditions for the detection reagent were determined by measuring the UV-Vis absorption spectrum using the controlled variable method. The conditions are set as follows.

[0119] (1) The concentrations of Mn&TiO2@C3N4NPs were 0.025, 0.050, 0.100, 0.150, 0.200, 0.250 and 0.300 mg / mL, respectively.

[0120] (2) The concentrations of carbaryl were 0.005, 0.010, 0.015, 0.020, 0.025, 0.030 and 0.035 mg / mL, respectively.

[0121] (3) The reaction pH values ​​were 3.0, 5.0, 7.0, 9.0 and 11.0, respectively.

[0122] like Figure 17 As shown in Figure A, the optimal concentration of Mn&TiO2@C3N4 is 0.200 mg / mL; Figure 17 As shown in B, the optimal concentration of carbaryl is 0.020 mg / mL; Figure 17 As shown in C, the optimal pH is 5.0.

[0123] Example 10: Degradation of Sevin under different photocatalysts and light sources The degradation efficiency of three photocatalysts (TiO2, g-C3N4, and Mn&TiO2@C3N4) and the efficiency of Mn&TiO2@C3N4 in degrading carbaryl under different light sources (darkness, visible light, sunlight, and ultraviolet light) were compared by measuring ultraviolet-visible absorption spectra. The amounts of the three photocatalysts were the same.

[0124] like Figure 18As shown, at 30.0 min, the degradation rate of carbaryl under the catalysis of Mn&TiO2@C3N4 reached 88.4%, while that of TiO2 and g-C3N4 was only 59.6% and 54.0%, respectively. Compared with the original TiO2 and g-C3N4, Mn&TiO2@C3N4 greatly improved the degradation efficiency and can significantly degrade carbaryl.

[0125] like Figure 19 As shown, the degradation rate of carbaryl reached 27.0% under dark conditions, which is attributed to the adsorption of carbaryl by Mn&TiO2@C3N4. Unlike dark conditions, the degradation rate was 58.8% under visible light; the highest degradation rate of carbaryl was achieved under sunlight, reaching 92.6%; and under ultraviolet light, the degradation rate was 88.4%. The results indicate that the degradation rates under sunlight and ultraviolet light conditions are significantly higher than those under dark and visible light conditions, suggesting that Mn&TiO2@C3N4 is more effective at degrading carbaryl under these two light sources.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing Mn&TiO2@C3N4 fluorescent nanozymes with peroxidase-like activity and photocatalytic activity, characterized in that, Includes the following steps: S11: Melamine was heated at 550.0~600.0℃ for 2.0~3.0h and sonicated for 10.0~14.0h to obtain g-C3N4NPs; S12: Mix the g-C3N4NPs from step S1 with an ethanol aqueous solution, disperse evenly, adjust the pH to neutral, add Ti(OC4H9)4 and MnSO4·H2O, mix evenly, and react at 160.0~180.0℃ for 8.0~10.0h to obtain the reaction product; S13: Wash the reaction product of step S12 with ethanol and water to obtain the Mn&TiO2@C3N4 fluorescent nanozyme.

2. The preparation method according to claim 1, characterized in that, In step S12, the mass ratio of g-C3N4NPs to MnSO4·H2O is (0.01~0.03):(0.0042~0.0168).

3. A Mn&TiO2@C3N4 fluorescent nanozyme, characterized in that, It is prepared by the preparation method described in claim 1 or 2.

4. The application of the Mn&TiO2@C3N4 fluorescent nanozyme of claim 3 in the detection and / or degradation of carbamate pesticides.

5. The application as described in claim 4, characterized in that, The carbamate pesticides include at least one of carbaryl, pirimicarb, and isoprocarb.

6. A method for detecting sevin, characterized in that, Includes the following steps: S21: Extract carbaryl from the agricultural product to be tested using water, then filter, or filter the water sample to be tested to obtain the solution to be tested; S22: Mix the test solution with acetylcholinesterase solution, acetylcholine solution and choline oxidase solution, incubate at 30-40℃ for 10.0-15.0 min, add Mn&TiO2@C3N4NPs solution, 3,3',5,5'-tetramethylbenzidine solution and HAc-NaAc buffer, and incubate at 30-40℃ for 20.0-25.0 min to obtain the nanozyme reaction product; S23: Measure the absorbance of the nanozyme reaction product at 652 nm; And / or, measure the temperature of the nanozyme reaction products under 660 nm laser irradiation; And / or, measure the fluorescence intensity of the nanozyme reaction product at 445 nm.

7. The method as described in claim 6, characterized in that, In step S22, the pH of the HAc-NaAc buffer solution is 3.5–6.

0.

8. The method as described in claim 6, characterized in that, In step S22, the concentration of the 3,3',5,5'-tetramethylbenzidine solution is 20.0–30.0 mmol / L.

9. A method for degrading carbaryl, characterized in that, The sample to be degraded was mixed with the Mn&TiO2@C3N4 fluorescent nanozyme described in claim 3, the pH was adjusted to 3.0-5.0, and the reaction was stirred in the dark for 0.5-1.0 h. The photocatalytic reaction was carried out under ultraviolet light or sunlight irradiation.

10. The method as described in claim 9, characterized in that, The concentration of the Mn&TiO2@C3N4 fluorescent nanozyme is 0.150–0.300 mg / mL.

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