Hydrophilic molecularly imprinted carbon nitride photocatalyst, preparation method and application of hydrophilic molecularly imprinted carbon nitride photocatalyst in selective removal of ofloxacin

Abstract

The invention discloses a hydrophilic molecularly imprinted carbon nitride photocatalyst, a preparation method and application of the hydrophilic molecularly imprinted carbon nitride photocatalyst to selective removal of ofloxacin (OFL), and belongs to the technical field of environmental pollution removal. Resorcinol and melamine are used as double hydrophilic monomers, formaldehyde is used as a hydrophilic cross-linking agent, and the hydrophilic molecularly imprinted carbon nitride photocatalyst is prepared. The hydrophilic molecularly imprinted carbon nitride photocatalyst with high selectivity and high activity is prepared by taking carbon nitride prepared by doping p-aminopyridine borate hydrochloride and combining with auxiliary calcination of molten salt as a matrix and OFL as a template and adopting a strategy of cooperation of surface imprinting and a two-step template immobilization method. The OFL in the water environment is stably, efficiently and selectively removed at low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalyst preparation and environmental pollution remediation, and particularly relates to a hydrophilic molecularly imprinted carbon nitride photocatalyst, a preparation method and an application thereof in selectively removing ofloxacin. Background Art

[0002] Ofloxacin (OFL) is a representative second-generation fluoroquinolone drug. Due to its broad-spectrum activity against bacteria, it is widely used to treat bacterial infections in humans and animals. In recent years, it has been widely detected in environmental water. Due to its recalcitrant nature, widespread distribution, and high toxicity, OFL can exhibit significant ecotoxicity, such as teratogenicity and carcinogenicity, even at very low levels. Currently, there is a lack of processes specifically designed to remove OFL from environmental water. Developing technologies for its deep removal is crucial for the health of humans and even the entire ecosystem.

[0003] Photocatalytic technology has the advantages of being environmentally friendly, efficient, low-cost and sustainable, and has attracted much attention in the field of environmental water remediation. The key to implementing this technology lies in the development of photocatalysts. Among the many photocatalysts, graphitic carbon nitride (g-C3N4 or CN) is widely used in environmental water remediation due to its non-toxicity, stable physical and chemical properties and suitable band gap. Although CN has many advantages, its defects such as narrow visible light response range, slow migration of photogenerated charges and easy recombination, and insufficient exposure of active sites limit its photocatalytic activity. More importantly, like most common photocatalytic materials, CN has a broad spectrum and lacks selectivity. It will degrade beneficial, non-toxic or low-toxic components in water, making it difficult to efficiently and targetedly remove target pollutants (OFL) from numerous interferences. This has seriously restricted the application and development of CN photocatalytic materials in the field of water pollution control.

[0004] Molecularly imprinted polymers (MIPs) are artificially constructed selective adsorption materials that mimic the antigen-antibody recognition mechanism and possess specific recognition for their target. They achieve specific recognition of template molecules by customizing imprinted sites with complementary shapes, sizes, and functional groups to those of the template molecules. Despite their strong selectivity, MIPs still face the critical scientific challenge of difficulty recognizing them in aqueous phases. Combining hydrophilic MIPs with CN yields a highly selective and active hydrophilic MIP carbon nitride photocatalytic material for OFL in environmental water, which holds great significance for the management of OFL in environmental water, as well as the development of CN and MIPs. Summary of the Invention

[0005] In response to the shortcomings of the above-mentioned prior art technologies, namely (1) insufficient photocatalytic activity and low selectivity of CN; (2) a lack of methods for selectively removing OFL from environmental water; and (3) difficulty in water phase recognition of molecularly imprinted polymers, the present invention aims to provide a hydrophilic molecularly imprinted carbon nitride photocatalyst, a preparation method, and its application in the selective removal of ofloxacin. The hydrophilic molecularly imprinted carbon nitride photocatalyst prepared by the present invention has high hydrophilicity, high selectivity, and high catalytic activity, a method that has not yet been reported.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst comprises the following steps:

[0008] Step 1: Preparation of p-aminopyridinium boronate hydrochloride-doped carbon nitride;

[0009] Urea and p-aminopyridine borate are uniformly dispersed in a mixed solution of anhydrous ethanol and water in a certain proportion. After the mixture is heated and dried at a certain temperature, it is heated in a muffle furnace at a fixed heating rate and maintained at a certain temperature for a period of time. After naturally cooling to room temperature, the obtained powder sample is thoroughly ground with a certain mass and fixed proportion of molten salt. The mixture is placed in a tube furnace and heated at a fixed heating rate under an inert gas atmosphere and maintained at a certain temperature for a period of time. After cooling to room temperature, the product is washed, freeze-dried, and ground into a powder.

[0010] Step 2: Preparation of hydrophilic molecularly imprinted carbon nitride photocatalyst, specifically including the following:

[0011] A1. Dissolving a certain amount of melamine and formaldehyde in water at a certain temperature, then adding a certain amount of carbon nitride doped with p-aminopyridinium boron hydrochloride prepared in step 1 and a certain amount of formaldehyde, and uniformly dispersing them by ultrasonication. Subsequently, adding a certain amount of a mixed solution of a template molecule and a porogen, and self-assembling to obtain a mixture I;

[0012] A2. dissolving a certain amount of resorcinol in water and stirring at a certain temperature for a period of time to obtain a mixture II;

[0013] A3, transferring mixture I into mixture II, and performing a second self-assembly at a certain temperature and rotation speed;

[0014] A4. The mixture obtained in step A3 is heated at a constant temperature for a period of time. The product is collected using an external magnetic field and repeatedly eluted with the aid of light and an eluent until no template molecules can be detected by HPLC-UV. The product is washed and dried to obtain a hydrophilic molecularly imprinted carbon nitride photocatalyst.

[0015] Preferably, in step 1, the mass ratio of urea to p-aminopyridine borate hydrochloride is 1 g:2.5-3.5 mg; the volume ratio of anhydrous ethanol to water is 2-3 mL:1 mL;

[0016] The heating temperature of the p-aminopyridine borate-urea mixed solution is 60-80°C; the heating rate of the p-aminopyridine borate-urea mixture in the muffle furnace is 4-6°C min -1 , maintaining the temperature at 545-560°C for 2.8-3.2h; the mass ratio of the sample obtained in the muffle furnace to the mass ratio of the molten salt is 1mg:4.5-5.5mg;

[0017] The molten salt is lithium chloride and potassium chloride, and the molar ratio of the two is 41:59; the gas environment in which the mixture after grinding with the molten salt is heated in a tube furnace is one of argon or nitrogen; the heating rate of the mixture after grinding with the molten salt in the tube furnace is 4-6 ° C min -1 , maintain the temperature at 545-560°C and the holding time at 2.8-3.2h.

[0018] Preferably, in step A1, the mass volume ratio of melamine to the first added formaldehyde is 1 g: 2.0-2.8 mL; the mass volume ratio of melamine to water is 1 g: 150-200 mL; and the dissolution temperature in water is 80-90° C.;

[0019] In step A1, the mass volume ratio of melamine to the second added formaldehyde is 1 g:1.2-1.7 mL; the mass ratio of melamine to p-aminopyridinium boronate-doped carbon nitride is 1 mg:14.2-17.4 mg;

[0020] The molar mass ratio of the template molecule to melamine is 1 mol: 105-320 g; the molar volume ratio of the template molecule to the porogen is 1 mol: 30-100 L;

[0021] The template molecule is OFL; the porogen is acetonitrile; and the self-assembly time is 30 to 60 minutes.

[0022] Preferably, in step A2, the mass ratio of resorcinol to water is 1 g: 180-190 mL; the dissolution temperature in water is 30-45° C., and the stirring time is 1 h.

[0023] Preferably, in step A3, the second self-assembly temperature is 30-50° C., the rotation speed is 350-450 rpm, and the time is 30-60 min.

[0024] Preferably, in step A4, the mixture is heated at 80° C. for 16 to 24 hours; and the eluent is a mixed solution of one of methanol, ethanol or acetonitrile, acetic acid and water in a volume ratio of 3:1:1.

[0025] Another object of the present invention is to provide an application of a hydrophilic molecularly imprinted carbon nitride photocatalyst in the selective removal of OFL, which specifically includes the following steps: using a xenon lamp of a certain wattage and a cutoff filter of a certain wavelength to filter out ultraviolet light as a visible light source, dispersing a certain mass of photocatalyst in an OFL aqueous solution of a certain concentration, stirring the mixture in the dark for a certain time, turning on the light, taking a certain volume of the liquid and filtering it at regular intervals, and measuring the OFL concentration of the filtrate using HPLC-UV at a certain wavelength.

[0026] Preferably, the wattage of the xenon lamp is 300W; the wavelength of the cutoff filter is 420nm; the ratio of the photocatalyst mass to the OFL concentration is 1mg:0.5-10mg L -1 The volume of OFL aqueous solution is 40-50 mL; the mixture is stirred in the dark for 30-50 min; the sampling time interval after turning on the light is 10 min; the amount of each sample after turning on the light is 2 mL; the detection wavelength of HPLC-UV is 285-305 nm.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] 1. The raw materials used are cheap and easily available;

[0029] 2. The preparation method of the present invention is simple and efficient, and avoids the deoxygenation operations required for free radical polymerization;

[0030] 3. This method is prepared in aqueous solution, resulting in minimal swelling of the MMIR in water, effectively protecting the imprinted cavities and the aqueous phase recognition function of the imprinted material. 4. A two-step template immobilization strategy combined with surface imprinting provides high selectivity for the MMIR. The use of a highly active carbon nitride photocatalyst prepared by doping aminopyridinium borate with molten salt-assisted calcination as a matrix gives the MMIR high catalytic activity.

[0031] 5. The MMIR has good reusability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the specific embodiments of the present invention, the following briefly describes the drawings required for use in the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0033] Figure 1These are the X-ray diffraction patterns of x-MMIR, MNIR, MACN and CN prepared in Examples 1-3 and Comparative Examples 1-3.

[0034] It is obvious that all samples show two obvious carbon nitride characteristic peaks at around 13.1°(100) and 27.5°(002), indicating that the catalysts were successfully prepared and the coating of the imprinted layer did not change the crystal structure of CN.

[0035] Figure 2 FT-IR spectra of x-MMIR, MNIR, MACN and CN prepared in Examples 1-3 and Comparative Examples 1-3.

[0036] Functional group analysis of all samples was performed by FT-IR, and all samples were characterized by spectral analysis at 3100-3700, 1200-1700 and 810 cm -1 The typical peaks at 1624 and 1471 cm correspond to the stretching vibration peaks of -NH2, heptazine unit and triazine unit respectively. -1 (C=C stretching vibration of the aromatic ring in resorcinol), 1385 and 1544 cm -1 The two characteristic peaks near (melamine's "breathing" mode and aromatic CN stretching vibration) indicate that resorcinol and melamine successfully participated in the imprinting process. -1 The -OH stretching vibration peak intensity at the position is significantly enhanced, indicating that the coating of the imprinted layer enhances the hydrophilicity of the material.

[0037] Figure 3 These are the water contact angle images of the 0.02-MMIR prepared in Example 2 and the MNIR, MACN, and CN prepared in Comparative Examples 1-3.

[0038] As can be seen from the figure, the water droplet quickly immersed into 0.02-MMIR within 0.5s and left a contact angle of 0°, while MNIR, MACN and CN did not achieve this effect, further indicating that the coating of the imprinting layer enhanced the hydrophilicity of the material.

[0039] Figure 4 The OFL removal performance of x-MMIR, MNIR, MACN and CN prepared in Examples 1-3 and Comparative Examples 1-3 was evaluated.

[0040] As shown in the figure, CN achieved an OFL removal rate of 68.5% within 90 minutes, while MACN and MNIR completely removed OFL within 70 minutes and 50 minutes, respectively. All x-MMIRs exhibited superior OFL removal performance, with 0.02-MMIR achieving complete OFL removal within 40 minutes. This demonstrates that the molecularly imprinted layer significantly enhances the OFL removal performance of carbon nitride materials.

[0041] Figure 5 The removal performance of the 0.02-MMIR prepared in Example 2 and the MNIR prepared in Comparative Example 1 on different pollutants (Examples 4-6) was evaluated.

[0042] It is obvious that the removal effect of 0.02-MMIR on OFL is significantly better than that of MNIR, and OFL can be completely removed in 40 minutes. In addition, the removal rate of 0.02-MMIR on OFL is significantly higher than that of other pollutants with different structures (TC and SMX), indicating that 0.02-MMIR has the ability to remove OFL with high selectivity and high activity.

[0043] Figure 6 This is the cyclic stability diagram of 0.02-MMIR prepared in Example 2.

[0044] After five consecutive photocatalytic cycle experiments, MMIR can still completely remove OFL, indicating that it has good reusability. DETAILED DESCRIPTION

[0045] In order to clearly and completely describe the technical solution and specific working process of the present invention, the specific implementation methods of the present invention are as follows in conjunction with the accompanying drawings:

[0046] Example 1

[0047] A method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst comprises the following steps:

[0048] Step 1: Preparation of p-aminopyridinium borate hydrochloride-doped carbon nitride (MACN) 20 g of urea and 60 mg of p-aminopyridinium borate hydrochloride were uniformly dispersed in a mixed solution of 10 mL of anhydrous ethanol and 5 mL of deionized water. The mixture was heated at 80 °C until dry and then heated in a muffle furnace at a heating rate of 5 °C min -1 Heat to 550 ° C and maintain for 3 hours. After cooling naturally to room temperature, 500 mg of the obtained powder sample was thoroughly ground with 2.5 g of molten salt (KCl: LiCl, molar ratio 41:59). The mixture was placed in a tube furnace and heated at a rate of 5 ° C min under an argon atmosphere. -1 The mixture was heated to 550°C and maintained for 3 h. After cooling to room temperature, the product was washed, freeze-dried, ground into powder and labeled as MACN.

[0049] Step 2: Preparation of hydrophilic molecularly imprinted carbon nitride photocatalyst (MMIR)

[0050] (1) Melamine (31.55 mg) and formaldehyde (0.075 mL) were dissolved in 80°C water (5 mL), and then MACN (0.5 g) and formaldehyde (0.05 mL) prepared in step 1 were added and dispersed uniformly by ultrasonication. Subsequently, 10 mL of OFL acetonitrile solution (0.01 mol L -1 ), self-assembled for 30 min to obtain mixture I.

[0051] (2) Resorcinol (0.08255 g) was dissolved in water (15 mL) and stirred at 40°C for 1 h to obtain mixture II.

[0052] (3) Transfer mixture I to mixture II and perform a second self-assembly at 40°C and 450 rpm for 30 min.

[0053] (4) The mixture was heated at 80°C for 16 h. The product was collected using an external magnetic field and eluted repeatedly with methanol / acetic acid / water (3:1:1, v / v) under light-assisted elution until OFL could no longer be detected by HPLC-UV. The product was washed and dried to obtain 0.01-MMIR.

[0054] Example 2

[0055] A method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst comprises the following steps:

[0056] Step 1: Preparation of aminopyridinium borate hydrochloride-doped carbon nitride (MACN), same as in Example 1.

[0057] Step 2: Preparation of hydrophilic molecularly imprinted carbon nitride photocatalyst (MMIR)

[0058] (1) Melamine (31.55 mg) and formaldehyde (0.075 mL) were dissolved in 80°C water (5 mL), and then MACN (0.5 g) and formaldehyde (0.05 mL) prepared in step 1 were added and dispersed uniformly by ultrasonication. Subsequently, 10 mL of OFL acetonitrile solution (0.02 mol L -1 ), self-assembled for 30 min to obtain mixture I.

[0059] (2) Resorcinol (0.08255 g) was dissolved in water (15 mL) and stirred at 40°C for 1 h to obtain mixture II.

[0060] (3) Transfer mixture I to mixture II and perform a second self-assembly at 40°C and 450 rpm for 30 min.

[0061] (4) The mixture was heated at 80°C for 16 h. The product was collected using an external magnetic field and eluted repeatedly with methanol / acetic acid / water (3:1:1, v / v) under light-assisted elution until OFL could no longer be detected by HPLC-UV. The product was washed and dried to obtain 0.02-MMIR.

[0062] Example 3

[0063] A method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst comprises the following steps:

[0064] Step 1: Preparation of aminopyridinium borate hydrochloride-doped carbon nitride (MACN), same as in Example 1.

[0065] Step 2: Preparation of hydrophilic molecularly imprinted carbon nitride photocatalyst (MMIR)

[0066] (1) Melamine (31.55 mg) and formaldehyde (0.075 mL) were dissolved in 80°C water (5 mL), and then MACN (0.5 g) and formaldehyde (0.05 mL) prepared in step 1 were added and dispersed uniformly by ultrasonication. Subsequently, 10 mL of OFL acetonitrile solution (0.03 mol L -1 ), self-assembled for 30 min to obtain mixture I.

[0067] (2) Resorcinol (0.08255 g) was dissolved in water (15 mL) and stirred at 40°C for 1 h to obtain mixture II.

[0068] (3) Transfer mixture I to mixture II and perform a second self-assembly at 40°C and 450 rpm for 30 min.

[0069] (4) The mixture was heated at 80°C for 16 h. The product was collected using an external magnetic field and eluted repeatedly with methanol / acetic acid / water (3:1:1, v / v) under light-assisted elution until OFL could no longer be detected by HPLC-UV. The product was washed and dried to obtain 0.03-MMIR.

[0070] Comparative Example 1

[0071] A method for preparing a hydrophilic molecular non-imprinted carbon nitride photocatalyst (MNIR) comprises the following steps:

[0072] Step 1: Preparation of aminopyridinium borate hydrochloride-doped carbon nitride (MACN), same as in Example 1.

[0073] Step 2: Preparation of hydrophilic non-molecularly imprinted carbon nitride photocatalyst (MNIR)

[0074] (1) Melamine (31.55 mg) and formaldehyde (0.075 mL) were dissolved in 80°C water (5 mL), and then MACN (0.5 g) and formaldehyde (0.05 mL) prepared in step 1 were added and dispersed uniformly by ultrasonication. Subsequently, 10 mL of acetonitrile solution was added and self-assembled for 30 min to obtain mixture I.

[0075] (2) Resorcinol (0.08255 g) was dissolved in water (15 mL) and stirred at 40°C for 1 h to obtain mixture II.

[0076] (3) Transfer mixture I to mixture II and perform a second self-assembly at 40°C and 450 rpm for 30 min.

[0077] (4) The mixture was heated at 80°C for 16 h. The product was collected using an external magnetic field, washed, and dried to obtain MNIR.

[0078] Comparative Example 2

[0079] 20 g of urea and 60 mg of p-aminopyridine borate hydrochloride were uniformly dispersed in a mixture of 10 mL of anhydrous ethanol and 5 mL of deionized water. The mixture was heated at 80 °C until dry and then heated in a muffle furnace at a heating rate of 5 °C min -1 Heat to 550 ° C and maintain for 3 hours. After cooling naturally to room temperature, 500 mg of the obtained powder sample was thoroughly ground with 2.5 g of molten salt (KCl: LiCl, molar ratio 41:59). The mixture was placed in a tube furnace and heated at a rate of 5 ° C min under an argon atmosphere. -1 The mixture was heated to 550°C and maintained for 3 h. After cooling to room temperature, the product was washed, freeze-dried, ground into powder and labeled as MACN.

[0080] Comparative Example 3

[0081] 20g of urea was placed directly into the muffle furnace at a heating rate of 5℃min -1 Heated to 550 °C and maintained for 3 h to obtain sample CN.

[0082] Example 4

[0083] A hydrophilic molecularly imprinted carbon nitride photocatalyst was used to remove OFL, specifically as follows: a 300W xenon lamp and a 420nm cutoff filter were used to filter out ultraviolet light (λ<420nm) as a visible light source. 10mg of the photocatalyst was dispersed in 10mgL -1 , 50 mL of OFL aqueous solution, the mixture was stirred in the dark for 30 min, and after turning on the light, 2 mL of the liquid was taken out and filtered every 10 min. The concentration of OFL in the filtrate was determined by HPLC-UV at 295 nm.

[0084] Example 5

[0085] A hydrophilic molecularly imprinted carbon nitride photocatalyst is used to remove tetracycline (TC), specifically as follows: a 300W xenon lamp and a 420nm cutoff filter are used to filter out ultraviolet light (λ<420nm) as a visible light source. 10mg of the photocatalyst is dispersed in 10mg L -1 The mixture was stirred in 50 mL of TC in a dark place for 30 min. After turning on the light, 2 mL of the liquid was taken out and filtered every 10 min. The concentration of TC in the filtrate was determined by HPLC-UV at 358 nm.

[0086] Example 6

[0087] A hydrophilic molecularly imprinted carbon nitride photocatalyst was used to remove sulfamethoxazole (SMX), specifically as follows: a 300W xenon lamp and a 420nm cutoff filter were used to filter out ultraviolet light (λ < 420nm) as a visible light source. 10mg of the photocatalyst was dispersed in 10mg L -1 , the mixture was stirred in 50 mL of SMX in the dark for 30 min. After turning on the light, 2 mL of the liquid was taken out and filtered every 10 min. The concentration of SMX in the filtrate was determined by HPLC-UV at 275 nm.

[0088] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0089] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0090] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst, characterized in that: The specific steps include: Step 1: Preparation of p-aminopyridinium boronate hydrochloride-doped carbon nitride; Urea and p-aminopyridine borate are uniformly dispersed in a mixed solution of anhydrous ethanol and water in a certain proportion; the mixture is heated and dried at a certain temperature, then heated in a muffle furnace at a fixed heating rate and maintained at a certain temperature for a period of time; after naturally cooling to room temperature, the obtained powder sample is fully ground with a certain mass and fixed proportion of molten salt, and the mixture is placed in a tube furnace, heated at a fixed heating rate under an inert gas atmosphere and maintained at a certain temperature for a period of time; after cooling to room temperature, the product is washed, freeze-dried, and ground into powder; Step 2: Preparation of hydrophilic molecularly imprinted carbon nitride photocatalyst, specifically including the following: A1. Dissolving a certain amount of melamine and formaldehyde in water at a certain temperature, then adding a certain amount of carbon nitride doped with p-aminopyridinium boron hydrochloride prepared in step 1 and a certain amount of formaldehyde, and uniformly dispersing them by ultrasonication. Subsequently, adding a certain amount of a mixed solution of a template molecule and a porogen, and self-assembling to obtain a mixture I; A2. dissolving a certain amount of resorcinol in water and stirring at a certain temperature for a period of time to obtain a mixture II; A3, transferring mixture I into mixture II, and performing a second self-assembly at a certain temperature and rotation speed; A4, heating the mixture obtained in step A3 at a certain temperature for a period of time; The product was collected using an external magnetic field and eluted repeatedly with the assistance of light and eluent until no template molecules could be detected by HPLC-UV; The product is washed and dried to obtain a hydrophilic molecularly imprinted carbon nitride photocatalyst.

2. The method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst according to claim 1, wherein: In step 1, the mass ratio of urea to p-aminopyridine borate hydrochloride is 1 g:2.5-3.5 mg; the volume ratio of anhydrous ethanol to water is 2-3 mL:1 mL; The heating temperature of the p-aminopyridine borate-urea mixed solution is 60-80°C; the heating rate of the p-aminopyridine borate-urea mixture in the muffle furnace is 4-6°C min -1 , maintaining the temperature at 545-560°C for 2.8-3.2h; the mass ratio of the sample obtained in the muffle furnace to the mass ratio of the molten salt is 1mg:4.5-5.5mg; The molten salt is lithium chloride and potassium chloride, and the molar ratio of the two is 41:59; the gas environment in which the mixture after grinding with the molten salt is heated in a tube furnace is one of argon or nitrogen; the heating rate of the mixture after grinding with the molten salt in the tube furnace is 4-6 ° C min -1 , maintain the temperature at 545-560°C and the holding time at 2.8-3.2h.

3. The method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst according to claim 1, wherein: In step A1, the mass volume ratio of melamine to the first added formaldehyde is 1 g: 2.0-2.8 mL; the mass volume ratio of melamine to water is 1 g: 150-200 mL; and the dissolution temperature in water is 80-90° C.; In step A1, the mass volume ratio of melamine to the second added formaldehyde is 1 g:1.2-1.7 mL; the mass ratio of melamine to p-aminopyridinium boronate-doped carbon nitride is 1 mg:14.2-17.4 mg; The molar mass ratio of the template molecule to melamine is 1 mol: 105-320 g; the molar volume ratio of the template molecule to the porogen is 1 mol: 30-100 L; The template molecule is OFL; the porogen is acetonitrile; and the self-assembly time is 30 to 60 minutes.

4. The method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst according to claim 1, wherein: In step A2, the mass ratio of resorcinol to water is 1 g: 180-190 mL; the dissolution temperature in water is 30-45° C., and the stirring time is 1 h.

5. The method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst according to claim 1, wherein: In step A3, the second self-assembly temperature is 30-50° C., the rotation speed is 350-450 rpm, and the time is 30-60 min.

6. The method for preparing a hydrophilic molecularly imprinted carbon nitride photocatalyst according to claim 1, wherein: In step A4, the mixture is heated at 80° C. for 16 to 24 hours; the eluent is a mixed solution of one of methanol, ethanol or acetonitrile, acetic acid and water in a volume ratio of 3:1:

1.

7. A hydrophilic molecularly imprinted carbon nitride photocatalyst, characterized in that: The method is prepared by any one of claims 1 to 6.

8. Use of a hydrophilic molecularly imprinted carbon nitride photocatalyst for selectively removing OFL according to claim 7, characterized in that: Specifically, the method includes the following steps: using a xenon lamp of a certain wattage and a cutoff filter of a certain wavelength to filter out ultraviolet light as a visible light source, dispersing a certain mass of photocatalyst in an OFL aqueous solution of a certain concentration, stirring the mixture in the dark for a certain time, turning on the light, taking a certain volume of liquid and filtering it at regular intervals, and measuring the OFL concentration of the filtrate using HPLC-UV at a certain wavelength.

9. Use of a hydrophilic molecularly imprinted carbon nitride photocatalyst for selective removal of OFL according to claim 8, characterized in that: The wattage of the xenon lamp is 300W; the wavelength of the cutoff filter is 420nm; the ratio of the photocatalyst mass to the OFL concentration is 1mg:0.5-10mg L -1 The volume of OFL aqueous solution is 40-50 mL; the mixture is stirred in the dark for 30-50 min; the sampling time interval after turning on the light is 10 min; the amount of each sample after turning on the light is 2 mL; the detection wavelength of HPLC-UV is 285-305 nm.

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