CN (at) PDI-CS metal-free photocatalyst with biomass-based D-A structure as well as preparation method and application of CN (at) PDI-CS metal-free photocatalyst

Abstract

The invention provides a CN (at) PDI-CS metal-free photocatalyst with a biomass-based D-A structure as well as a preparation method and application of the CN (at) PDI-CS metal-free photocatalyst, and belongs to the technical field of photocatalytic materials and environmental remediation. The preparation method of the CN (at) PDI-CS metal-free photocatalyst comprises the following steps: (1) mixing PTCDA, CS and imidazole, and carrying out a reaction 1 under a protective atmosphere to obtain PDI-CS; and (2) mixing the PDI-CS, the g-C3N4 and imidazole, and carrying out a reaction 2 to obtain the CN (at) PDI-CS metal-free photocatalyst. According to the catalyst disclosed by the invention, the charge separation efficiency and the visible light absorption capacity are synergistically enhanced through a D-A structure and an electronic push-pull effect, and the recombination rate of photon-generated carriers is reduced, so that the CN (at) PDI-CS material has efficient photocatalytic degradation performance.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials and environmental remediation technology, and in particular to a biomass-based DA structure CN@PDI-CS metal-free photocatalyst, its preparation method and application. Background Technology

[0002] Due to industrialization, urbanization, and population growth, the demand for water is constantly increasing, especially as related industrial sectors produce large amounts of pollutants. For example, the generation and discharge of dyes, heavy metals, antibiotics, and pesticides have posed a serious threat to aquatic ecosystems. In recent years, with the increasing demands of agricultural practices, the use of pesticides has also increased significantly; pesticides can reach aquatic ecosystems through various means, exacerbating water pollution. Due to the toxicity and persistence of pesticides in the environment, even trace amounts can have a significant impact on ecosystems and human health. Currently, conventional technologies for pesticide wastewater treatment mainly include biodegradation, filtration, chemical oxidation, sedimentation, and adsorption, but these technologies are mostly inefficient, costly, or require strict conditions. Compared with these traditional pollutant treatment methods, photocatalysis technology is a highly efficient and environmentally friendly method that uses solar energy to convert target pollutants into non-toxic small molecule products, offering significant advantages.

[0003] Perylene tetracarboxylic dianhydride (PTCDA), as an organic semiconductor with a moderate band gap, high photoresponsiveness, and environmental friendliness, has attracted much attention in the field of photocatalysis due to its strong electron-withdrawing properties and the synergistic effect of its conjugated backbone. Among them, self-assembled PDI driven by π-π stacking possesses an extended π-electron conjugated system, which can enhance light harvesting and charge transport capabilities. For example, the amino groups on the biomass chitosan (CS) backbone can be combined with the anhydride in PTCDA through π-π stacking to construct self-assembled PDI-CS polymers. However, its high exciton binding energy, low charge transfer efficiency, and small specific surface area limit its redox capabilities, hindering its large-scale application as a low-cost photocatalyst. To address these challenges, constructing DA structures has proven to be an efficient design strategy: the asymmetric charge distribution of DA units can induce a built-in electric field (IEF), driving the reverse migration of photogenerated holes and electrons, thereby significantly suppressing photogenerated electron recombination and promoting the photocatalytic degradation process. Furthermore, the inherent ICT process of the DA structure generates a strong charge transfer absorption band; simultaneously, a twisted configuration can be introduced to suppress π-π stacking, reduce exciton self-quenching, and improve fluorescence quantum efficiency. Therefore, the development of novel DA-structured photocatalytic materials will not only contribute to the effective recycling of biomass and solve existing technical challenges, but will also bring new breakthroughs and progress to the field of pesticide wastewater treatment. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a biomass-based DA structure CN@PDI-CS metal-free photocatalyst, its preparation method and application. This invention effectively improves the separation efficiency of photogenerated holes and electrons and the visible light absorption capacity of the composite material by constructing a DA structure and combining the π-π push-pull effect, thereby enhancing the photocatalytic performance of the composite material.

[0005] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is a method for preparing a biomass-based DA-structured CN@PDI-CS metal-free photocatalyst, comprising the following steps: (1) PTCDA, CS and imidazole were mixed and reacted under a protective atmosphere to obtain PDI-CS; (2) After mixing the PDI-CS, g-C3N4 and imidazole, reaction 2 is carried out to obtain the CN@PDI-CS metal-free photocatalyst.

[0006] The second technical solution of the present invention is a biomass-based DA structure CN@PDI-CS metal-free photocatalyst prepared by the above preparation method.

[0007] The third technical solution of the present invention is the application of a CN@PDI-CS metal-free photocatalyst with the above-mentioned biomass-based DA structure in the photocatalytic degradation of pesticides.

[0008] The fourth technical solution of the present invention is a method for degrading pesticide-containing wastewater, wherein the above-mentioned biomass-based DA structure CN@PDI-CS metal-free photocatalyst is added to the pesticide-containing wastewater to carry out a photocatalytic reaction.

[0009] The present invention discloses the following technical effects: The preparation method of the CN@PDI-CS material of the present invention is simple, the raw materials are non-toxic and harmless, the preparation process is pollution-free and environmentally friendly, and it has the advantages of high efficiency, convenience and controllability.

[0010] The CN@PDI-CS material prepared by this invention enhances charge separation efficiency and visible light absorption capacity through the synergistic effect of DA structure and electronic push-pull effect, and reduces the recombination rate of photogenerated carriers, thereby enabling the CN@PDI-CS material to have efficient photocatalytic degradation performance.

[0011] The CN@PDI-CS material of this invention has excellent photocatalytic degradation performance and good stability, and can effectively remove pesticide pollutants in the aquatic environment, showing promising prospects for practical application. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 The XRD patterns of different catalyst samples in Examples 1-4 and Comparative Examples 1-2 of this invention are shown. Figure 2 The different catalyst samples in Example 2 and Comparative Examples 1-2 of this invention 13 C SSNMR spectrum; Figure 3 The FT-IR spectra of different catalyst samples in Examples 1-4 and Comparative Examples 1-2 of this invention are shown. Figure 4 XPS full spectrum (A), elemental composition (B), and high-resolution spectrum (CO 1) of CN, PDI-CS, CN@PDI-CS-1%, CN@PDI-CS-3%, CN@PDI-CS-5%, and CN@PDI-CS-7% in this invention. s and high-resolution spectrum DN 1 s ; Figure 5 The UV-Vis diffuse reflectance spectra A and Tauc diagram B of different catalyst samples in Examples 1-4 and Comparative Examples 1-2 of this invention are shown. Figure 6 The transient photocurrent response spectra of different catalyst samples in Examples 1-4 and Comparative Examples 1-2 of this invention are shown. Figure 7 The figures show the photocatalytic degradation performance and reaction condition optimization of different catalyst samples in Examples 1-4 and Comparative Examples 1-2 of this invention; where A and B represent the photocatalytic degradation performance of different catalyst samples on imidacloprid and the corresponding K values; the effects of different operating parameters on the CN@PDI-CS-3% photocatalytic degradation system are: catalyst dosage C; initial imidacloprid concentration D; pH value E; different pesticide pollutants F; Figure 8 Experiments on the recycling of imidacloprid by photocatalytic degradation of CN@PDI-CS-3%. Detailed Implementation

[0014] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0015] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0016] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0017] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0018] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0019] The first aspect of this invention provides a method for preparing a biomass-based DA-structured CN@PDI-CS metal-free photocatalyst, comprising the following steps: (1) PTCDA, CS and imidazole were mixed and reacted under a protective atmosphere to obtain PDI-CS; (2) After mixing the PDI-CS, g-C3N4 and imidazole, reaction 2 is carried out to obtain the CN@PDI-CS metal-free photocatalyst.

[0020] In a preferred embodiment of the present invention, in step (1), the molar ratio of PTCDA to CS is (1~8):4 (more preferably, 1:2); the reaction temperature of reaction 1 is 135~140 °C, and the reaction time is 46~48 h. The present invention does not impose any special limitation on the amount of imidazole used; the amount used is sufficient to fully dissolve PTCDA and CS and to meet the requirements for reaction 1. For example, after mixing PTCDA, CS, and imidazole, the concentration of PTCDA is 97~99 g / L.

[0021] In a preferred embodiment of the present invention, after reaction 1 is completed, the reaction system is further cooled to room temperature, then ethanol and hydrochloric acid are added, stirred, and then filtered, washed, centrifuged, and freeze-dried in sequence; the concentration of hydrochloric acid is 2 mol / L, the volume ratio of ethanol to hydrochloric acid is 2:1, the volume ratio of the reaction system to hydrochloric acid is 1:5; and the stirring time is 24 h.

[0022] In a preferred embodiment of the present invention, the preparation method of the g-C3N4 is as follows: calcining melamine at 500-550 °C for 2-4 h and grinding it.

[0023] In a preferred embodiment of the present invention, in step (2), the mass ratio of PDI-CS to g-C3N4 is (1~7):100; the reaction temperature of reaction 2 is 135~140 ℃, and the reaction time is 4~8 h.

[0024] In this invention, when the PDI-CS content is low, the activity is insufficient, and continuous charge transfer channels cannot be effectively formed, limiting the interfacial charge separation efficiency. When the PDI-CS content is high, aggregation easily occurs, forming larger particles, which hinders internal electron transfer, reduces the effective specific surface area and the exposure of active sites; furthermore, there are negative effects such as shielding and the formation of new recombination centers, leading to performance degradation. Therefore, the degradation effect of the prepared photocatalyst is best only when the parameters are within the range described in this invention.

[0025] More preferably, the mass ratio of PDI-CS to g-C3N4 is 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, or 7:100.

[0026] In a preferred embodiment of the present invention, after reaction 2 is completed, the reaction system is further cooled to room temperature, then hydrochloric acid is added, the mixture is stirred until the precipitate is dispersed, and then centrifuged, washed, and freeze-dried; the concentration of the hydrochloric acid is 4 mol / L.

[0027] A second aspect of the present invention provides a biomass-based DA-structured CN@PDI-CS metal-free photocatalyst prepared by the above preparation method.

[0028] The third aspect of this invention provides the application of the above-mentioned biomass-based DA structure CN@PDI-CS metal-free photocatalyst in the photocatalytic degradation of pesticides.

[0029] The fourth aspect of the present invention provides a method for degrading pesticide-containing wastewater, wherein the above-mentioned biomass-based DA structure CN@PDI-CS metal-free photocatalyst is added to the pesticide-containing wastewater to carry out a photocatalytic reaction.

[0030] In a preferred embodiment of the present invention, the pesticide in the pesticide-containing wastewater is at least one of imidacloprid, glyphosate, 2,4-D or atrazine; The concentration of pesticides in the pesticide-containing wastewater is 10~50 mg / L; The pH value of the pesticide-containing wastewater is 3-9; The amount of the biomass-based DA-structured CN@PDI-CS metal-free photocatalyst added is 0.02~0.50 mg / mL; The reaction time of the photocatalyst is 5~30 min.

[0031] More preferably, the concentration of pesticides in the pesticide-containing wastewater is 10-20 mg / L; The pH value of the pesticide-containing wastewater is 5-7; The amount of the biomass-based DA-structured CN@PDI-CS metal-free photocatalyst added is 0.02~0.05 mg / mL; The reaction time of the photocatalyst is 20-30 min.

[0032] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0033] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0034] Example 1 1. Preparation of DA-structured CN@PDI-CS-1% material, the steps are as follows: (1) Preparation of CN: First, 10 g of melamine was placed in a semi-closed alumina crucible with a lid. Then, it was heated to 500 °C in a muffle furnace at a heating rate of 10 °C / min and held for 2 h. Next, the temperature was raised to 520 °C (heating rate of 2 °C / min) and held for another 2 h to achieve further deammoniation. Finally, g-C3N4, abbreviated as CN, was obtained by grinding in an agate mortar.

[0035] (2) Preparation of PDI-CS: First, 1.96 g (0.005 mol) PTCDA, 1.61 g CS (0.01 mol), and 20 g imidazole were mixed in a 100 mL three-necked flask. The flask was then heated and stirred at 140 °C for 48 h under a N2 atmosphere. After cooling to room temperature, 200 mL of ethanol and 100 mL of 2 M hydrochloric acid were added to the mixture, and the mixture was stirred for another 24 h. Subsequently, the reaction mixture was filtered through a 0.45 μm membrane to collect the reactants, which were then washed with an aqueous solution (600 mL) containing 60 g KOH and 48 g KCl to remove unreacted PTCDA. To neutralize the remaining alkaline solution, 100 mL of 10% hydrochloric acid was added and stirred for 24 h, and the resulting mixture was centrifuged. After vacuum freeze-drying, a brown PDI-CS powder product was obtained.

[0036] (3) Preparation of CN@PDI-CS material: 0.5 g CN and 0.005 g PDI-CS were added to a flask containing 5 g imidazole. The mixture was then heated and stirred at 140 °C for 4 h. After cooling to room temperature, 100 mL HCl (4 mol / L) was added, and the mixture was stirred for 5 h until all precipitates were dispersed. After washing, centrifugation, and freeze-drying, the composite photocatalyst CN@PDI-CS-1% was obtained.

[0037] 2. Photocatalytic activity test Photocatalytic activity was tested at room temperature using a 300 W xenon lamp as the light source. 5 mg of catalyst CN@PDI-CS-1% and 100 mL of imidacloprid solution (20 mg / L) (pH=7) were added sequentially to a 100 mL quartz glass reactor. After reaching adsorption-desorption equilibrium with dark stirring for 30 min, the suspension was allowed to react under xenon lamp irradiation for another 30 min. During this period, 3 mL of the suspension was filtered through a 0.22 µm filter every 5 min, and the absorbance at the maximum absorption wavelength of 270 nm was recorded using a UV-Vis spectrophotometer. The calculated degradation efficiency was 88.34% after 30 min of reaction.

[0038] Comparative Example 1 1. The preparation of CN follows these steps: First, 10 g of melamine was placed in a covered, semi-enclosed alumina crucible. Then, it was heated to 500 °C in a muffle furnace at a heating rate of 10 °C / min and held for 2 h. Next, the temperature was increased to 520 °C (heating rate of 2 °C / min) and held for another 2 h to achieve further deammoniation. Finally, g-C3N4, abbreviated as CN, was obtained by grinding in an agate mortar.

[0039] 2. Photocatalytic activity test CN was subjected to the same photocatalytic activity test as in Example 1. When the reaction proceeded for 30 min, the degradation efficiency was 69.33%.

[0040] Comparative Example 2 The preparation steps of PDI-CS are as follows: 1.96 g (0.005 mol) PDI-CS, 1.61 g (0.01 mol) CS, and 20 g imidazole were mixed in a 100 mL three-necked flask. The flask was then heated and stirred at 140 °C for 48 h under a nitrogen atmosphere. After cooling to room temperature, 200 mL of ethanol and 100 mL of 2 M hydrochloric acid were added to the mixture, and stirring was continued for another 24 h. Subsequently, the reaction mixture was filtered through a 0.45 μm membrane to collect the reactants, which were then washed with 600 mL of an aqueous solution containing 60 g KOH and 48 g KCl to remove unreacted PDI-CS. To neutralize the remaining alkaline solution, 100 mL of 10% hydrochloric acid was added and stirred for 24 h, and the resulting mixture was centrifuged. After vacuum freeze-drying, a brown PDI-CS powder product was obtained.

[0041] The PDI-CS was subjected to the same photocatalytic activity test as in Example 1. When the reaction proceeded for 30 min, the degradation efficiency was 63.25%.

[0042] Example 2 1. Preparation of CN@PDI-CS-3% material: The only difference from the preparation of CN@PDI-CS-1% in Example 1 is that 0.005 g of PDI-CS is adjusted to 0.015 g. All other steps and parameters are the same as in Example 1, and the product obtained is CN@PDI-CS-3%.

[0043] 2. Adsorption-photocatalytic activity test The CN@PDI-CS-3% was subjected to the same photocatalytic activity test as in Example 1. When the reaction proceeded for 30 min, the degradation efficiency was 96.23%.

[0044] 3. Reuse The filtered and recovered catalyst sample was dried in a 60 °C oven for 12 h, then ground and stored for reuse. Figure 8 It can be seen that after six cycles of repeated use, the photocatalytic degradation efficiency of CN@PDI-CS-3% is still higher than 90%.

[0045] Example 3 1. Preparation of CN@PDI-CS-5% material: The only difference from the preparation of CN@PDI-CS-1% in Example 1 is that 0.005 g of PDI-CS is adjusted to 0.025 g. All other steps and parameters are the same as in Example 1, and the product obtained is CN@PDI-CS-5%.

[0046] 2. Adsorption-photocatalytic activity test The CN@PDI-CS-5% was subjected to the same photocatalytic activity test as in Example 1. When the reaction proceeded for 30 min, the degradation efficiency was 90.44%.

[0047] Example 4 1. Preparation of CN@PDI-CS-7% material: The only difference from the preparation of CN@PDI-CS-1% in Example 1 is that 0.005 g of PDI-CS is adjusted to 0.035 g. All other steps and parameters are the same as in Example 1, and the product obtained is CN@PDI-CS-7%.

[0048] 2. Adsorption-photocatalytic activity test The CN@PDI-CS-7% was subjected to the same photocatalytic activity test as in Example 1. When the reaction proceeded for 30 min, the degradation efficiency was 87.63%.

[0049] Characterization results: The XRD patterns of different samples in this invention are as follows: Figure 1 As shown. In the CN and CN@PDI-CS samples, strong diffraction peaks were observed at 13.1˚ and 27.3˚, corresponding to the (100) and (002) planes of the in-plane and interlayer heptaazine in CN, respectively, and no new characteristic peaks appeared. This indicates that the low grafting content of the introduced acceptor PDI-CS ensures that the structure remains unchanged during synthesis. In addition, compared with CN, the peak intensity of the CN@PDI-CS series samples gradually decreases with increasing PDI-CS content, and further decreases with increasing PDI-CS content. θ The value increases and shifts in the positive direction. This may be because PDI-CS successfully introduced the CN framework, distorting the original layered structure of CN and causing the nanosheets to become thinner and smaller, with reduced interlayer stacking along the (100) and (002) directions. This indicates that a DA structure was formed between CN and PDI-CS through π-π interactions, thereby promoting intermolecular charge transfer.

[0050] Different samples in this invention 13 C SSNMR spectra such as Figure 2As shown, multiple peaks in the 120-140 ppm range of PDI-CS and CN@PDI-CS are attributed to the delocalization of conjugated electrons in the benzo[a]phenanthrene ring. The continuous peaks in the 50-120 ppm range correspond to the methylene C atom in CS; additionally, peaks around 155.8 and 164.5 ppm correspond to NC=N and C-NHx, respectively. These signals are observed in both CN and CN@PDI-CS samples. Notably, the NC=N and C-NHx peaks in CN@PDI-CS are shifted to a lower field by 1.2 ppm due to covalent bonding. This confirms that the CN molecule in CN@PDI-CS acts as an electron donor during DA modulation.

[0051] The FT-IR spectra of different samples in this invention are as follows: Figure 3 As shown, all samples were at 3000-3500 cm⁻¹ -1 All samples exhibited stretching vibrations of the NH group. Except for PDI-CS, all samples ranged from 1240 to 1640 cm⁻¹. -1 809 cm -1 All exhibited typical stretching vibrations of the aromatic CN ring and triazine ring in CN. With increasing PDI-CS content in the structure, the 3000-3500 cm⁻¹... -1 and 809 cm -1 The intensity of the characteristic peak gradually decreases.

[0052] Figure 4 In this invention, A represents the XPS full spectrum of CN, PDI-CS, and CN@PDI-CS; B represents the elemental content; and C represents the high-resolution spectrum. s D is a high-resolution spectrum N 1 s XPS full spectrum and elemental composition plots show that CN is mainly composed of carbon and nitrogen, with its 2.19% oxygen content likely due to adsorbed water and carbon dioxide. PDI-CS and CN@PDI-CS are mainly composed of carbon, nitrogen, and oxygen. The increased oxygen content in CN@PDI-CS is attributed to the introduction of PDI-CS. Furthermore, in O 1 s In the high-resolution XPS spectrum, characteristic peaks appearing at 531.38, 532.63, and 533.85 eV correspond to C=O bonds, CO functional groups, and O=C-NH bonds, respectively. sThe peaks at 398.61 eV, 400.18 eV, and 401.22 eV correspond to the C=NC, NC, and C-NH bonds in CN, respectively. The peak at 404.45 eV represents the π-excited state of the CN heterocycle. In the CN@PDI-CS-3% sample, the C=NC and NC peaks are shifted positively towards higher binding energies by 0.04 and 0.03 eV, respectively; compared to PDI-CS, the O=C-NH peak of the diamide group is significantly shifted towards lower binding energies by approximately 0.50 eV. This indicates that the electron delocalization effect caused by strong π-π interactions promotes electron migration along the π-π stacking direction.

[0053] Figure 5 These are the UV-Vis diffuse reflectance spectra of different samples in this invention. They show that the formation of the DA structure can broaden the light absorption range and effectively modulate the band gap of the photocatalytic material. Figure 6 The transient photocurrent response diagram further confirms this.

[0054] Figure 7 Figures show the optimized photocatalytic degradation performance and reaction conditions for different catalyst samples; where A and B represent the photodegradation performance of different catalyst samples on imidacloprid and the corresponding K values; the effects of different operating parameters on the CN@PDI-CS-3% photocatalytic degradation system are: catalyst dosage C; initial imidacloprid concentration D; pH value E; and different pesticide pollutants F. As shown in the figures, the DA-structured CN@PDI-CS prepared in this invention exhibits excellent photocatalytic performance, achieving a degradation efficiency of 96.23% for imidacloprid; it also shows good photocatalytic degradation performance for other pesticides.

[0055] In summary, the catalytic material prepared by the method described in this invention possesses a DA structure and an adjustable band structure, which effectively promotes the rapid separation of photogenerated carriers at the interface, thereby enhancing its high photocatalytic activity. When this catalyst is applied to the photocatalytic degradation of imidacloprid, a degradation efficiency of 96.23% can be achieved within 30 minutes. After six cycles of use, the photocatalytic degradation efficiency remains above 90%. Furthermore, this catalyst also exhibits good versatility for other pesticide pollutants. Therefore, this invention has broad application prospects.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a biomass-based CN@PDI-CS metal-free photocatalyst with D-A structure, characterized in that, The method comprises the following steps: (1) mixing PTCDA, CS and imidazole, and then performing reaction 1 under a protective atmosphere to obtain PDI-CS; (2) mixing the PDI-CS, g-C3N4 and imidazole, and then performing reaction 2 to obtain the CN@PDI-CS metal-free photocatalyst.

2. The production method according to claim 1, characterized by, In step (1), the molar ratio of PTCDA to CS is (1-8):4; the reaction temperature of the reaction 1 is 135-140 DEG C, and the reaction time is 46-48 h.

3. The preparation method according to claim 1, characterized in that, After the reaction 1 is completed, the reaction system is cooled to room temperature, then ethanol and hydrochloric acid are added, stirring is performed, and then the steps of filtration, washing, centrifugation and freeze-drying are performed in sequence.

4. The production method according to claim 1, characterized by, In step (2), the mass ratio of PDI-CS to g-C3N4 is (1-7):100; the reaction temperature of the reaction 2 is 135-140 DEG C, and the reaction time is 4-8 h.

5. The preparation method according to claim 1, characterized in that, After the reaction 2 is completed, the reaction system is cooled to room temperature, then hydrochloric acid is added, stirring is performed until the precipitate is dispersed, and then the steps of centrifugation, washing and freeze-drying are performed.

6. A biomass-based CN@PDI-CS metal-free photocatalyst with a D-A structure, which is prepared by the preparation method of any one of claims 1-5.

7. An application of the biomass-based CN@PDI-CS metal-free photocatalyst with a D-A structure of claim 6 in photocatalytic degradation of pesticides.

8. A method for degrading pesticide-containing wastewater, characterized by, The biomass-based CN@PDI-CS metal-free photocatalyst with a D-A structure of claim 6 is added to wastewater containing pesticides for photocatalytic reaction.

9. The method of claim 8, wherein, The pesticide in the wastewater containing pesticides is at least one of imidacloprid, glyphosate, 2,4-D or atrazine; The concentration of the pesticide in the wastewater containing pesticides is 10-50 mg / L; The pH value of the wastewater containing pesticides is 3-9; The addition amount of the biomass-based CN@PDI-CS metal-free photocatalyst with a D-A structure is 0.02-0.50 mg / mL; The reaction time of the photocatalyst is 5-30 min.

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