Composite photocatalyst based on pyrenyl-heptazine ring electron donor-acceptor structure as well as preparation method and application of composite photocatalyst

Abstract

The invention provides a composite photocatalyst based on a pyrenyl-heptazine ring electron donor-acceptor structure as well as a preparation method and application of the composite photocatalyst, and belongs to the technical field of catalysts. The preparation method of the composite photocatalyst comprises the following steps: uniformly mixing a pyrenyl precursor and urea, and calcining to obtain the composite photocatalyst, the mass ratio of the pyrenyl precursor to the urea is (0.001-0.005): 1. A molecular modification strategy is innovatively adopted, a pyrenyl (Py) unit with a strong electron donating characteristic is grafted to the edge of a heptazine ring group, and an electron D-A structure with a strong built-in electric field is constructed by accurately regulating and controlling molecular orbital energy level matching. The light absorption range and the carrier separation efficiency are obviously enhanced, and the organic pesticide pollutant degradation performance is excellent. The method is simple in process and low in cost, and the obtained photocatalyst is good in stability and high in repeatability.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a composite photocatalyst based on a pyrene-based - heptazine ring electron donor - acceptor structure, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, photocatalytic technology has received extensive attention due to its environmental protection and high efficiency characteristics. Photocatalytic technology mainly adds a photocatalyst on the basis of photocatalysis to promote the rapid generation of a large number of reactive oxygen species (·OH, 1 O2, ·O2 - etc.), photogenerated charges (e - ) and holes (h + ) to participate in the pollutant degradation reaction under light illumination. The reactive substances mainly attack special sites on the pollutant molecules, destroy their molecular structures, and make them lose their toxic characteristics. The photocatalyst plays a major role in the photocatalytic degradation process. To enable the degradation process to proceed rapidly and fully, the targeted selection of the photocatalyst is essential. From the perspective of practical applications, the photocatalyst should have characteristics such as stable structure, strong light response ability, and safety and environmental protection to ensure the stable and efficient progress of the process of photocatalytic degradation of pollutants in water. Therefore, polymeric carbon nitride (PCN) with a stable framework has attracted people's research interest. However, the localization of excitons, the incomplete conversion to the charge separation state, and the recombination of carriers limit the photocatalytic performance of single-component polymeric carbon nitride. Summary of the Invention

[0003] Aiming at the problems of high charge recombination rate and narrow light response range of traditional PCN as a photocatalytic material, the purpose of the present invention is to provide a composite photocatalyst based on a pyrene-based - heptazine ring electron donor - acceptor structure, a preparation method thereof, and an application thereof. The present invention innovatively adopts a molecular modification strategy to graft a pyrene (Py) unit with strong electron-donating characteristics to the edge of the heptazine ring group, and constructs an electron D - A structure with a strong built-in electric field by precisely regulating the molecular orbital energy level matching. The light absorption range and the carrier separation efficiency are significantly enhanced, and it has excellent performance in degrading organic pesticide pollutants. The process of the present invention is simple, the cost is low, and the obtained photocatalyst has good stability and high repeatability.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] One of the technical solutions of the present invention is a preparation method of a composite photocatalyst based on a pyrene-based - heptazine ring electron donor - acceptor structure. The pyrene precursor and urea are mixed evenly and then calcined to obtain the composite photocatalyst;

[0006] The mass ratio of the pyrene precursor to urea is 0.001 - 0.005:1.

[0007] The second technical solution of the present invention is a composite photocatalyst based on a pyrene-heptazine ring electron donor-acceptor structure prepared by the above preparation method.

[0008] The third technical solution of the present invention is an application of the above composite photocatalyst based on a pyrene-heptazine ring electron donor-acceptor structure in the photocatalytic degradation of organic pollutants.

[0009] The fourth technical solution of the present invention is a method for degrading pesticide-containing wastewater. The above composite photocatalyst and the pesticide-containing wastewater are mixed for pesticide adsorption, and then the reaction system is subjected to a catalytic reaction under visible light conditions.

[0010] The present invention discloses the following technical effects:

[0011] (1) The preparation method of the composite photocatalyst provided by the present invention can achieve the purpose through sufficient grinding and mixing and one-step high-temperature thermal polycondensation, and the preparation method is simple.

[0012] (2) The present invention successfully realizes the modification of the heptazine unit of pure PCN at the molecular level to form an intramolecular electron D-A structure. The covalent grafting strategy effectively inhibits phase separation and enhances the structural stability. The D-A pair of pyrene (Py) and the heptazine group forms a strong built-in electric field inside the photocatalyst, constructs a fast intermolecular electron transfer pathway, and realizes the directional transfer of intramolecular charges. In addition, the addition of Py also causes obvious changes in the nanosheet morphology of the original PCN, and the entire reaction system has excellent light response ability. Under the synergistic action of each component, e- and h+ are quickly separated and aggregated in the A unit and D unit respectively during the photocatalytic reaction of PyCN, forming strong reactive sites to participate in the reaction. It has important application value in the fields of solar energy conversion, environmental remediation, etc.

[0013] (3) The photocatalyst prepared by the present invention has good stability and high reproducibility, showing a curled edge morphology of a round rod different from the original polymeric carbon nitride.

[0014] (4) The method for treating pesticide-containing wastewater provided by the present invention only needs to add the photocatalyst prepared by the present invention to the reaction system, and can quickly and efficiently degrade the pollutants in the agricultural wastewater under visible light irradiation without adding any other substances. The method is simple and easy to operate, and the cost is low. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1 Local scanning electron microscope image (a) and high-resolution transmission electron microscope image (b) of PyCN-30 obtained in Example 1, and local scanning electron microscope image (c) of PCN obtained in Comparative Example 1;

[0017] Figure 2 X-ray diffraction analysis diagrams of PyCN-30 obtained in Example 1 and PCN obtained in Comparative Example 1;

[0018] Figure 3 Diffuse reflectance ultraviolet-visible spectroscopy analysis diagrams of PyCN-30 obtained in Example 1 and PCN obtained in Comparative Example 1;

[0019] Figure 4 Schematic diagram showing the relationship between the concentration change of imidacloprid degraded by PyCN-30 obtained in Example 1 and PCN obtained in Comparative Example 1 with time under visible light;

[0020] Figure 5 Cyclic effect diagram of the degradation of imidacloprid by PyCN-30 obtained in Example 1;

[0021] Figure 6 Effect diagrams of the photocatalytic degradation of imidacloprid by the D-A type polymeric photocatalyst (PyCN) formed by 1-PBA and urea in different mass ratios and PCN obtained in Comparative Example 1;

[0022] Figure 7 Effect diagrams of the degradation of imidacloprid by PyCN-30 obtained in Example 1 under different imidacloprid concentration conditions;

[0023] Figure 8 Effect diagrams of the degradation of imidacloprid by PyCN-30 obtained in Example 1 under different pH conditions. Detailed implementation manners

[0024] Now, various exemplary implementation manners of the present invention will 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, characteristics, and implementation schemes of the present invention.

[0025] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0027] Without departing from the scope or spirit of the present invention, various modifications and variations to the specific embodiments of the description of the present invention will be apparent to those skilled in the art. Other embodiments derived from the description of the present invention will be apparent to those skilled in the art. The description and examples of the present invention are merely exemplary.

[0028] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0029] The pyrenyl group (Py) itself has the ability to absorb and transfer the energy of laser radiation and can interact with neighboring functional groups under mild conditions as a derivatizing reagent to form covalent adducts. Moreover, Py in the organic polymer structure has a high ultraviolet laser quantum absorption ability and a very strong electron-withdrawing ability. Py can react with distal ·OH groups to promote the photocatalytic reaction. The small molecule Py with a π-conjugated fused ring structure is considered a typical ladder-conjugated small molecule group. Ladder-conjugated polymers are considered a class of organic polymers with good thermal, chemical, and mechanical stabilities because the π-π ring units in their structures are connected in a form of sharing at least two atoms, having a rigid planar structure and strong conjugation. At the same time, due to the larger conjugation degree inside the conjugated ladder polymers compared with other organic polymers, their intramolecular charge transfer rate and fluorescence quantum efficiency are also higher.

[0030] In order to break through the limitations such as the localization of excitons in polymeric carbon nitride (PCN), incomplete conversion to the charge separation state, and the recombination of carriers, the present invention attempts to modify PCN from the molecular structure level by introducing specific functional molecular groups. Utilizing the stability of PCN as a substrate to carry the modification of the vast majority of functional molecules to enhance the photocatalytic performance of the original PCN. When there is a large difference in the electronegativity between the introduced small molecule group and the heptazine ring group of pure PCN, the molecular pair formed after their bonding will exhibit obvious electron donor-acceptor (D-A) characteristics under light illumination. The electron D-A structure can effectively promote the dissociation of exciton pairs and intramolecular charge transfer during the photoreaction, breaking through the limitations of the performance of pure PCN.

[0031] In the research of the present invention, it is found that by using a molecular modification strategy, a pyrene-based (Py) unit with strong electron-donating properties is grafted onto the edge of the heptazine ring group. By precisely regulating the molecular orbital energy level matching, a D-A structure with a strong built-in electric field is constructed. The covalent grafting strategy effectively inhibits phase separation and enhances the structural stability. The D-A pair of the pyrene-based (Py) and heptazine groups forms a strong built-in electric field inside the photocatalyst, constructs a rapid intermolecular electron transfer pathway, and realizes the directional transfer of intramolecular charges. The problems of high charge recombination rate and narrow light response range of the original polymeric carbon nitride material are successfully solved. The research proves that the electric field of the electron D-A structure has a very positive effect on exciton dissociation, highly inhibits electron recombination inactivation, and stimulates the ultra-high reactivity of the reaction system. In addition, the addition of Py also causes obvious changes in the nano-sheet morphology of the original PCN, and the entire reaction system has excellent light response ability. Under the synergistic effect of each component, e- and h+ are rapidly separated and aggregated in the A unit and D unit respectively during the photocatalytic reaction of PyCN, forming strong reactive sites to participate in the reaction. It has important application value in the fields of solar energy conversion, environmental remediation, etc.

[0032] In the first aspect of the present invention, a preparation method of a composite photocatalyst based on a pyrene-heptazine ring electron donor-acceptor structure is provided. The pyrene precursor and urea are mixed evenly and then calcined to obtain the composite photocatalyst;

[0033] The mass ratio of the pyrene precursor to urea is 0.001-0.005:1.

[0034] In a preferred embodiment of the present invention, the mass ratio of the pyrene precursor to urea is 0.001:1, 0.002:1, 0.003:1, 0.004:1 or 0.005:1.

[0035] In a preferred embodiment of the present invention, the pyrene precursor is 1-pyreneboronic acid.

[0036] In a preferred embodiment of the present invention, the way of mixing evenly is grinding. The present invention does not make special limitations on the specific parameters of grinding, and conventional parameters well-known to those skilled in the art can be selected. In this application, ordinary urea and 1-pyreneboronic acid are fully mixed and refined by grinding to improve the efficiency of subsequent calcination and facilitate the formation of the structure of the composite photocatalyst.

[0037] In a preferred embodiment of the present invention, the calcination temperature is 500 to 600 °C, specifically it can be 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, 600 °C, or any value between the aforementioned two values; the time is 3 to 5 h, specifically it can be 3 h, 3.5 h, 4 h, 4.5 h, 5 h, or any value between the aforementioned two values; the heating rate is 3 to 5 °C / min, specifically it can be 3 °C / min, 4 °C / min, 5 °C / min, or any value between the aforementioned two values.

[0038] The second aspect of the present invention provides a composite photocatalyst based on a pyrene-based heptazine ring electron donor-acceptor structure prepared by the above preparation method. Since the pyrene group is grafted on the edge of the heptazine ring group in the composite catalyst provided by the present invention, a strong built-in electric field is built inside the catalyst, and at the same time, the key charge activity and migration rate in the photocatalytic reaction are improved. Its morphology is different from that of the original polymeric carbon nitride, showing a circular rod shape with edge curling and being porous.

[0039] The third aspect of the present invention provides an application of the above composite photocatalyst based on a pyrene-based heptazine ring electron donor-acceptor structure in the photocatalytic degradation of organic pollutants.

[0040] In a preferred embodiment of the present invention, the organic pollutant is imidacloprid. In addition, through experimental verification, the present invention also has strong degradation performance for pollutants such as antibiotics represented by ciprofloxacin, pesticides represented by atrazine, and antibacterial drugs represented by sulfamethazine.

[0041] The fourth aspect of the present invention provides a method for degrading pesticide-containing wastewater. After mixing the above composite photocatalyst and the pesticide-containing wastewater for pesticide adsorption, the reaction system is then subjected to a catalytic reaction under visible light conditions.

[0042] In a preferred embodiment of the present invention, the pesticide-containing wastewater is imidacloprid-containing wastewater, ciprofloxacin-containing wastewater, atrazine-containing wastewater, or sulfamethazine-containing wastewater; the visible light wavelength is λ > 420 nm; the pH value of the reaction system is 3 to 11, specifically it can be 3, 5, 7, 9, 11, or any value between the aforementioned two values; the temperature of the catalytic reaction is 10 to 35 °C, specifically it can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, or any value between the aforementioned two values, and the time is 1 to 2 h, specifically it can be 1 h, 1.5 h, 2 h, or any value between the aforementioned two values.

[0043] In a preferred embodiment of the present invention, the concentration of the pesticide in the pesticide-containing wastewater is 1-10 mg / L; the mass-volume ratio of the composite photocatalyst to the pesticide-containing wastewater is 20 mg:50 mL; the adsorption time is 10-20 min, specifically it can be 10 min, 15 min, 20 min, 25 min, or any value between the aforementioned two values.

[0044] The technical solutions of the present invention are all conventional solutions in the art unless otherwise specified.

[0045] In the following examples, the concentration of imidacloprid was analyzed and determined by a high-performance liquid chromatograph; unless otherwise specified, the raw materials and instruments used were all conventional commercially available products. Among them, urea and 1-pyreneboronic acid were both purchased from Shanghai Macklin Biochemical Technology Co., Ltd., the pesticide-containing wastewater was a self-prepared imidacloprid solution as a simulated pesticide wastewater, and imidacloprid was purchased from Shanghai Macklin Biochemical Technology Co., Ltd.

[0046] In the following examples, unless otherwise specified, the obtained data are all the averages of more than three repeated experiments, and the room temperature is 30±10 °C.

[0047] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with examples, but the content of the present invention is not limited to the following examples.

[0048] Example 1

[0049] Using urea and 1-pyreneboronic acid as precursors, PyCN was prepared by a one-step thermal polycondensation method:

[0050] First, 10 g of urea and 30 mg of 1-pyreneboronic acid were weighed, ground and mixed thoroughly, and then placed in a 100 mL ceramic crucible. After covering it with tin foil and covering the lid, it was then placed in a muffle furnace and heated to 550 °C at a heating rate of 5 °C / min and maintained for 3 h. After cooling, the synthesized bulk solid was ground into powder and loaded into a centrifuge tube labeled as PyCN-30. (In this example, the mass ratio of 1-pyreneboronic acid to urea is 0.003:1)

[0051] Example 2

[0052] Using urea and 1-pyreneboronic acid as precursors, PyCN was prepared by a one-step thermal polycondensation method:

[0053] First, weigh 10 g of urea and 10 mg of 1-pyreneboronic acid, grind and mix them thoroughly, then place them in a 100 mL ceramic crucible. Cover it with tin foil and then put on the lid. After that, place it in a muffle furnace and heat it at a heating rate of 5 °C / min to 550 °C, and hold for 3 h. After cooling, grind the synthesized bulk solid into powder and put it into a centrifuge tube labeled as PyCN-10. (That is: different from Example 1, the mass ratio of 1-pyreneboronic acid to urea is 0.001:1)

[0054] Example 3

[0055] Using urea and 1-pyreneboronic acid as precursors, PyCN was prepared by one-step thermal polycondensation method:

[0056] First, weigh 10 g of urea and 20 mg of 1-pyreneboronic acid, grind and mix them thoroughly, then place them in a 100 mL ceramic crucible. Cover it with tin foil and then put on the lid. After that, place it in a muffle furnace and heat it at a heating rate of 5 °C / min to 550 °C, and hold for 3 h. After cooling, grind the synthesized bulk solid into powder and put it into a centrifuge tube labeled as PyCN-20. (That is: different from Example 1, the mass ratio of 1-pyreneboronic acid to urea is 0.002:1)

[0057] Example 4

[0058] Using urea and 1-pyreneboronic acid as precursors, PyCN was prepared by one-step thermal polycondensation method:

[0059] First, weigh 10 g of urea and 50 mg of 1-pyreneboronic acid, grind and mix them thoroughly, then place them in a 100 mL ceramic crucible. Cover it with tin foil and then put on the lid. After that, place it in a muffle furnace and heat it at a heating rate of 5 °C / min to 550 °C, and hold for 3 h. After cooling, grind the synthesized bulk solid into powder and put it into a centrifuge tube labeled as PyCN-50. (That is: different from Example 1, the mass ratio of 1-pyreneboronic acid to urea is 0.005:1)

[0060] Comparative Example 1

[0061] Weigh 10 g of urea, grind and mix it thoroughly, then place it in a 100 mL ceramic crucible. Cover it with tin foil and then put on the lid. Place it in a muffle furnace and heat it at a heating rate of 5 °C / min to 550 °C, and hold for 3 h. After cooling, ordinary polymeric carbon nitride (PCN) is obtained.

[0062] Effect verification

[0063] Test Example 1

[0064] The PyCN-30 obtained in Example 1 and the PCN obtained in Comparative Example 1 were respectively subjected to scanning electron microscope images (SEM) comparison, and at the same time, TEM analysis was carried out on PyCN-30. The results are as Figure 1As shown in the figure, where (a) is the SEM image of PyCN-30, (b) is the TEM image of PyCN-30, and (c) is the SEM image of PCN. Ordinary PCN presents a nanosheet structure, while PyCN has a rod-like structure with holes. At the same time, more obvious and dense holes and edge curling traits appear between the nanolayers of PyCN compared with the nanosheet structure of PCN. This indicates that after the graft modification with pyrene groups, the morphology of the catalyst has changed, and a new type of D-A polymeric carbon nitride photocatalyst has been successfully prepared.

[0065] The PyCN-30 obtained in Example 1 and the PCN obtained in Comparative Example 1 were respectively subjected to XRD analysis, and the results are as Figure 2 shown (PyCN in the figure represents PyCN-30 obtained in Example 1). Typical diffraction peaks (001) of the heptazine ring group of carbon nitride and the interlayer stacking peak (002) of the molecular layer appeared in both the modified PyCN and PCN. At the same time, it is not difficult to find that the peak intensity at the position of 12.7° shifted significantly to the left after the introduction of the small molecule group pyrene group. This indicates that the small molecule group has been successfully grafted to the edge of the heptazine group to form an electronic D-A structure, and the intermolecular electrons begin to migrate actively, resulting in a deviation. The weakening of the peak intensity indicates that the stacking of the sample material along the (002) direction between the layers decreases and the amorphous characteristics become more obvious, which is related to the increase in the aromatic conjugate structure in the material due to the introduction of pyrene groups. This also provides favorable interlayer conditions for the photocatalytic degradation reaction process.

[0066] The PyCN-30 obtained in Example 1 and the PCN obtained in Comparative Example 1 were respectively subjected to ultraviolet-visible spectroscopy diffuse reflectance analysis (UV-vis), and the results are as Figure 3 shown (PyCN in the figure represents PyCN-30 obtained in Example 1). It can be clearly seen that both PyCN and PCN exhibit obvious light response characteristics, and with the addition of pyrene groups, the light absorption intensity increases significantly, which benefits from the strong ultraviolet light absorption ability of Py itself. Obvious π-π* electron delocalization appears in the wavelength region of 236.2 - 395.8 nm and obvious n-π* electron transition phenomenon appears in the wavelength region of 428.1 - 545.2 nm for PyCN, which fully demonstrates the positive impact of the intermolecular D-A structure on the internal photo-generated charge transfer of the material.

[0067] Test Example 2

[0068] (1) Under dark conditions, 20 mg of PyCN-30 obtained in Example 1 and 20 mg of PCN obtained in Comparative Example 1 were respectively weighed and mixed with 50 mL of imidacloprid solution with an initial concentration of 10 mg / L, and the mixture was adsorbed for 20 min to obtain a mixed solution; during this period, about 2 mL of the sample solution was taken every 10 min and filtered through a 0.22 μm water-based filter membrane into a 2 mL sampling bottle and labeled as 1 and 2 respectively. The original solution was labeled as 0.

[0069] (2) After adsorption equilibrium, the mixed solution was placed on a magnetic stirrer and stirred at a speed of 600 rpm while the photoreaction was carried out. A 300 W xenon lamp (PLS-SXE 300D, Beijing Perfectlight, China) was used as the light source, and the filter was λ > 420 nm. Timing started from when it was placed under the xenon lamp. About 2 mL of the sampling solution was taken at 20 min, 40 min, and 60 min respectively, filtered through a 0.22 μm aqueous filter membrane into a 2 mL sampling bottle and labeled as 3, 4, and 5 respectively. Finally, the concentration of imidacloprid was determined by high performance liquid chromatography. The detection wavelength was 270 nm, the mobile phase was 55% methanol and 45% ultrapure water, and the flow rate was 1 mL / min. According to the formula (concentration ratio = C / C0×100%, where C0 is the initial concentration of imidacloprid), the residual amount of imidacloprid in the reaction solution was calculated to represent the degradation effect on imidacloprid, and the results obtained were as Figure 4 shown (PyCN in the figure represents PyCN-30 obtained in Example 1). The degradation rate D of imidacloprid was calculated according to the formula (D = (C0 - C) / C0×100%, where C0 is the initial concentration of imidacloprid).

[0070] From Figure 4 it can be seen that PyCN-30 obtained in Example 1 showed outstanding imidacloprid degradation performance. The degradation efficiency was as high as 70% after 60 min of illumination, and the reaction rate constant (k) was 18.97×10 -3 min -1 , which was 3.18 times that of PCN (D = 22%) obtained in Comparative Example 1. This was due to the strong ladder conjugation performance of the Py group, which improved the overall conjugated structure of the PyCN reaction system and further enhanced the D-A electric field. Moreover, PyCN had denser and larger pores and curled edges compared to other samples, providing more active sites for the reaction.

[0071] Test Example 3

[0072] (1) Under dark conditions, 20 mg of PyCN-30 obtained in Example 1 was weighed and mixed with 50 mL of an imidacloprid solution with an initial concentration of 10 mg / L, and the mixture was adsorbed for 20 min to obtain a mixed solution; during this period, about 2 mL of the sampling solution was taken every 10 min, filtered through a 0.22 μm aqueous filter membrane into a 2 mL sampling bottle and labeled as 1 and 2 respectively. The stock solution was labeled as 0.

[0073] (2) After adsorption equilibrium, place the mixed solution on a magnetic stirrer and stir at a speed of 600 rpm while performing the photoreaction. The light source is a 300 W xenon lamp (PLS-SXE 300D, Beijing Perfectlight, China), and the filter is λ > 420 nm. Start timing from when it is placed under the xenon lamp. Take about 2 mL of the sample solution at 20 min, 40 min, and 60 min respectively, and filter it through a 0.22 μm aqueous filter membrane into a 2 mL sampling bottle and label them as 3, 4, and 5 respectively.

[0074] (3) Vacuum filter the reaction solution obtained in step (2), collect the PyCN-30 catalyst powder, wash it with a large amount of ultrapure water and absolute ethanol, and then dry it in an oven at 60 °C for 12 h to obtain the regenerated D-A type polymeric carbon nitride material.

[0075] (4) Repeat steps (1) to (3) for the regenerated D-A type polymeric carbon nitride material 4 times. Take the reaction solution samples obtained each time, filter them through a 0.22 μm filter membrane, and then detect the imidacloprid concentration C in the sample solution; calculate the removal rate D of imidacloprid according to the formula (D = (C0 - C) / C0 × 100%, where C0 is the initial concentration of imidacloprid) to obtain the cyclic degradation effect. The results are as Figure 5 shown.

[0076] As Figure 5 can be seen, after 4 cycles of use, the removal rate of imidacloprid by the D-A type polymeric carbon nitride material obtained in Example 1 within 1 h is still as high as 65%. This shows that the D-A type polymeric carbon nitride material provided by the present invention has good stability and reusability.

[0077] Test Example 4

[0078] According to the method of Test Example 2, experiments on the photocatalytic degradation of imidacloprid in agricultural wastewater were carried out on PyCN-30 obtained in Example 1 and PCN obtained in Comparative Example 1 respectively. At the same time, the degradation performance of imidacloprid by PyCN with different mass ratios of 1-pyreneboronic acid and urea (Examples 1 - 4) was compared under the same reaction conditions. As Figure 6 shown, when the mass ratio of 1-pyreneboronic acid and urea is 0.001:1, 0.002:1, 0.003:1, and 0.005:1, the degradation rates D of imidacloprid are 57%, 60%, 70%, and 50% respectively, while the imidacloprid removal rate of PCN is only 25%. Obviously, the strong ladder conjugation performance of the Py group improves the overall conjugated structure of the PyCN reaction system, further enhances the D-A electric field, and enables the PyCN reaction system to have excellent photocatalytic degradation performance of imidacloprid.

[0079] Test Example 5

[0080] (1) Under light - avoiding conditions, weigh 20 mg of PyCN - 30 obtained in Example 1 and mix it with 50 mL of imidacloprid solutions with initial concentrations of 0.2, 0.4, 0.6, and 0.8 mg / L. Adsorb for 20 min to obtain a mixed solution. During this period, take about 2 mL of the sample solution every 10 min, filter it through a 0.22 - μm aqueous filter membrane into 2 - mL sampling bottles and label them as 1, 2 respectively. The original solution is labeled as 0.

[0081] (2) After adsorption equilibrium, place the mixed solution on a magnetic stirrer and stir at a speed of 600 rpm while performing a photoreaction. The light source is a 300 - W xenon lamp (PLS - SXE 300D, Beijing Perfectlight, China), and the filter is λ>420 nm. Start timing from when it is placed under the xenon lamp. Take about 2 mL of the sample solution at 20 min, 40 min, and 60 min respectively, filter it through a 0.22 - μm aqueous filter membrane into 2 - mL sampling bottles and label them as 3, 4, 5 respectively. Detect the concentration C of imidacloprid in the sample solution. According to the formula (concentration ratio = C / C0×100%, where C0 is the initial concentration of imidacloprid), calculate the remaining concentration of imidacloprid in the reaction solution and the reaction removal effect. The results are shown in Figure 7 .

[0082] Figure 7 It can be seen that PyCN - 30 has excellent degradation performance for imidacloprid solutions with different concentrations. Especially when the concentration of imidacloprid in the solution is small, the degradation rate of PyCN - 30 can reach up to 100% within 60 min of the photoreaction. Thus, it can be seen that the PyCN photocatalytic reaction system has extremely high application prospects in the photocatalytic degradation of imidacloprid in agricultural wastewater.

[0083] Test Example 6

[0084] (1) Under light - avoiding conditions, weigh 20 mg of PyCN - 30 obtained in Example 1 and mix it with 50 mL of imidacloprid solution with an initial concentration of 10 mg / L. The pH values of the imidacloprid solutions are 3, 5, 7, 9, and 11 respectively. Adsorb for 20 min to obtain a mixed solution. During this period, take about 2 mL of the sample solution every 10 min, filter it through a 0.22 - μm aqueous filter membrane into 2 - mL sampling bottles and label them as 1, 2 respectively. The original solution is labeled as 0.

[0085] (2) After adsorption equilibrium, the mixed solution was placed on a magnetic stirrer and stirred at a speed of 600 rpm while the photoreaction was carried out. The light source was a 300 W xenon lamp (PLS-SXE 300D, Beijing Perfectlight, China), and the filter was λ > 420 nm. Starting from the time when it was placed under the xenon lamp, about 2 mL of the sampling solution was taken at 20 min, 40 min, and 60 min respectively, and filtered through a 0.22 μm aqueous filter membrane into a 2 mL sampling bottle and labeled as 3, 4, and 5 respectively. The concentration C of imidacloprid in the sample solution was detected, and according to the formula (concentration ratio = C / C0 × 100%, where C0 is the initial concentration of imidacloprid), the removal effect of the reacted imidacloprid was calculated.

[0086] The results are as Figure 8 shown. It was measured that the pH of the original imidacloprid solution with a concentration of 10 mg / L was about 7.5, which was significantly higher than the imidacloprid degradation rate and k value at pH = 7.0. The PyCN reaction system has a wide pH adaptation range, and both overly acidic and overly alkaline environments will inhibit the reaction system. However, it was found that when the pH of the reaction system was about 9, the imidacloprid degradation rate could be increased to 72% in 60 min and the optimal k value was 19.8 × 10 -3 min -1 . The weakly alkaline environment promotes the reaction system, which is related to the full utilization of electrons in the weakly alkaline environment of the electron D-A structure, resulting in the PyCN reaction system having super oxidation ability. This shows that the PyCN reaction system has excellent environmental adaptability.

[0087] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a composite photocatalyst based on a pyrene-heptazine ring electron donor-acceptor structure, characterized in that, Mix the pyrene-based precursor and urea evenly and then calcine them to obtain the composite photocatalyst; The mass ratio of the pyrene-based precursor to urea is 0.001 - 0.005:

1.

2. The preparation method according to claim 1, characterized in that, The pyrene-based precursor is 1-pyreneboronic acid.

3. The preparation method according to claim 1, wherein The way of mixing evenly is grinding.

4. The preparation method according to claim 1, characterized in that, The calcination temperature is 500 - 600 °C, the time is 3 - 5 h, and the heating rate is 3 - 5 °C / min.

5. A composite photocatalyst based on a pyrene-heptazine ring electron donor-acceptor structure prepared by the preparation method according to any one of claims 1 - 4.

6. Use of the composite photocatalyst based on a pyrene-heptazine ring electron donor-acceptor structure according to claim 5 in the photocatalytic degradation of organic pollutants.

7. The application according to claim 6, characterized in that, The organic pollutants are imidacloprid, ciprofloxacin, atrazine or sulfamethazine.

8. A method for degrading pesticide-containing wastewater, characterized in that, Mix the composite photocatalyst according to claim 5 and the pesticide-containing wastewater, then adsorb the pesticide, and then carry out a catalytic reaction on the reaction system under visible light conditions.

9. The method for degrading pesticide-containing wastewater according to claim 8, characterized in that, The pesticide-containing wastewater is imidacloprid-containing wastewater, ciprofloxacin-containing wastewater, atrazine-containing wastewater or sulfamethazine-containing wastewater; the visible light wavelength is λ > 420 nm; the pH value of the reaction system is 3 - 11; the temperature of the catalytic reaction is 10 - 35 °C, and the time is 1 - 2 h.

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