MOFs-co induced derivative co-doped c3n5 photocatalyst and preparation method and application thereof

Abstract

The application discloses a preparation method of MOFs-Co induced derivative Co-doped C3N5 photocatalytic material and application of the material in photocatalytic degradation of antibiotics in cooperation with persulfate. The material is synthesized by a solvothermal method and a calcination method, a double-layer nitrogen body of MOFs-Co ligand skeleton and C3N5 nitrogen-rich precursor is co-derived to form a MOFs-Co-C3N5 photocatalyst with good Co dispersity, active sites are provided for PMS activation, and the double-layer nitrogen structure can improve the stability of the catalyst. The band gap of the MOFs-Co induced derivative Co-doped C3N5 is as low as 1.22 eV, and the recombination rate of photo-generated electrons and holes is significantly reduced. Under the condition of a 50 W LED white light source with a wavelength range of 400 nm to 830 nm and light intensity controlled at 10000 Lux, when the material dosage is 0.6 g / L and the PMS dosage is 0.5 mM, 30 mg / L of antibiotics can be completely degraded in 6 min. Therefore, the photocatalyst can effectively activate PMS under visible light irradiation, rapidly degrade organic pollutants, and has a wide application prospect.

Description

Technical fields:

[0001] This invention belongs to the field of photocatalysis technology, and relates to a method for preparing a MOFs-Co-induced Co-doped C3N5 photocatalyst and its application in the degradation of antibiotics in wastewater. Technical background:

[0002] Due to the widespread use of antibiotics by humans, residual antibiotics are continuously released into ecosystems and gradually accumulate, posing serious threats to human health and ecosystems. Currently, most mainstream treatment methods for novel antibiotic-based organic pollutants are complex and have limited effectiveness. Therefore, there is a need to develop green and efficient processes to remove antibiotics from water.

[0003] Currently, advanced oxidation processes based on photocatalytic activation of persulfate (PMS) have attracted much attention and are considered a rapid and effective water treatment technology capable of quickly removing recalcitrant organic pollutants from water. Compared with traditional hydroxyl radical-based advanced oxidation technologies, PMS exhibits higher reaction stability and wider applicability. However, to fully utilize its strong oxidizing power, a photocatalyst with high photocatalytic activity is required to activate the persulfate. However, most semiconductor photocatalysts are limited by their own characteristics, such as high photo-generated electron-hole recombination rates, resulting in photocatalytic effects that fail to meet practical requirements. Therefore, there is an urgent need for a photocatalyst with high photocatalytic activity and good photocatalytic stability for use in PMS advanced oxidation technology.

[0004] C3N5, as an emerging semiconductor photocatalyst, possesses a strong conjugated structure, semiconductor properties, and photocatalytic performance. It can absorb visible light to generate photogenerated electrons to activate persulfate. To further enhance its photocatalytic performance, the electronic structure can be adjusted by doping with metal ions to reduce the electronic band gap and promote the separation of photogenerated charges.

[0005] Cobalt ions (Co) are the most effective catalyst for activating PMS, enabling efficient degradation of a variety of pollutants. Co-doped C3N5, as a heterogeneous catalyst, has attracted widespread attention due to its abundant sources, low cost, good stability, ease of synthesis and separation, and low leaching rate of metal ions.

[0006] He P, Gu C, Tang B, et al. Expeditious degradation of SMX by high-valent cobalt-oxo species derived from cobalt-doped C3N5-activated peroxymonosulfate with the assistance of visible light[J]. Separation and Purification Technology, 2022, 301. This paper discloses a method for preparing cobalt acetate-doped C3N5. Specifically, cobalt acetate and 1,10-o-phenanthroline monohydrate are added to pre-prepared C3N5 in a certain proportion and mixed thoroughly. The mixture is then transferred to a tube furnace for calcination and cooling to obtain Co-doped C3N5 photocatalytic material with a band gap of 1.63 eV. Under the conditions of a 500W xenon lamp with a 420nm filter, the degradation rate of sulfamethoxazole by activated PMS reaches 99.57% within 20 minutes.

[0007] Tong Y, Gao P, Xu J, et al. Cobalt doped nitrogen-vacancies-rich C3N5 with optimizing local electron distribution boosts peroxymonsulfate activation for tetracycline degradation: Multiple electron transfer mechanisms[J]. Chemosphere, 2023:139549-139549. This paper discloses a method for preparing cobalt chloride-doped C3N5. The method involves a one-step calcination process where cobalt chloride is used as the cobalt source and 3-amino-1,2,4-triazole are mixed and stirred in an aqueous solution for 6 h. The mixture is then dried in a vacuum oven at 60 °C for 12 h to remove the solvent, and finally calcined to prepare a Co-C3N5 photocatalyst with nitrogen vacancies and a band gap of 1.85 eV. The photocatalyst exhibits a band gap of 120 mW / cm² under a 500 W xenon lamp. 2 Under these conditions, PMS can be activated to achieve a 100% degradation rate of tetracycline within 40 minutes.

[0008] Li T, Cui P, Wang X, et al. Efficient activation of peroxymonosulfate by C3N5 doped with cobalt for organic contaminant degradation[J].Environmental Science-Nano,2022,9(7):2534-2547. A method for preparing cobalt chloride-doped C3N5 is also disclosed. Unlike the above method, this method involves mixing synthesized C3N5 with KCl and LiCl, and then adding a certain amount of CoCl2·6H2O. The resulting mixture is placed in a tube furnace for calcination, finally obtaining a Co-C3N5 photocatalyst. This catalyst can degrade 96% of 5 mg / L 2,4,4′-trichlorobiphenyl within 30 min.

[0009] Publication No. CN 202211583359.7 discloses a cobalt-doped carbon nitride photocatalyst, its preparation method, and its application: Using cobalt nitrate as the cobalt source, the cobalt source is first calcined at low temperature to coordinate with urea, the precursor of carbon nitride. Then, during high-temperature calcination, the cobalt-catalyzed decomposition of carbon nitride at high temperatures is suppressed, thus preparing a carbon nitride photocatalyst with a high cobalt doping content in an air atmosphere. This catalyst exhibits a phenol degradation rate of approximately 75% within 60 minutes, which is 5.5 times that of pure carbon nitride.

[0010] Publication No. CN 202110159945.8 discloses an activated persulfate catalyst, its preparation method, and its application: A 1 mmol / mL solution of cobalt nitrate was prepared and added dropwise to 0.08 g / mL (20 mL) of 3-amino-1,2,4-triazole to obtain a mixture. The mixture was then vacuum dried at 90 °C until a solid product was obtained. The obtained solid product was calcined in a muffle furnace (heating rate: 5 °C / min, target temperature: 500 °C, holding time: 3 h) to obtain Co3O4@Co1 / C3N5. When the catalyst concentration was 0.5 g / L, the PMS concentration was 0.125 g / L, the diclofenac concentration was 50 ppm, and the reaction time was 20 min, diclofenac was completely degraded under visible light.

[0011] However, currently prepared Co-doped C3N5 photocatalysts are produced by doping the C3N5 structure with cobalt salts as the cobalt source. These catalysts generally suffer from defects such as low visible light utilization, high photoluminescence intensity, high electron-hole recombination rate, undispersed active sites, low degradation efficiency, unstable catalyst structure, and poor Co dispersion. Therefore, this invention proposes to utilize MOFs to derive Co in situ to form nitrogen-rich Co-doped C3N5 materials. Due to their highly dispersed metal sites, these materials are beneficial for activating PMS and improving their photocatalytic degradation efficiency of organic pollutants. The Co-doped C3N5 materials prepared by this method can significantly reduce the band gap and the photogenerated electron-hole recombination rate, improve the actual visible light utilization efficiency, and the suitable specific surface area and microstructure facilitate shorter photocatalytic time. Summary of the Invention:

[0012] The purpose of this invention is to provide a MOFs-Co induced derivatized Co-doped C3N5 photocatalyst and its preparation method, as well as the application of this material in the photocatalytic degradation of organic pollutants in water.

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] 1. At least one of different series of MOFs-Co (ZIF-Co, BTC-Co, PDA-Co) is mixed with a mixture of nitrogen-rich compound and six-membered nitrogen heterocycle under heating, dried, and the resulting solid material is ground into powder and calcined at high temperature to obtain MOFs-Co-C3N5 photocatalyst.

[0015] a. The mixture mainly includes a nitrogen-rich compound: 3-amino-1,2,4-triazole, wherein the six-membered nitrogen heterocycle is at least one of cyanuric acid and barbituric acid;

[0016] b. Mix MOFs-Co with the mixture: First, sonicate the MOFs-Co solution, then add it dropwise to the mixture under heating conditions and stir thoroughly until the water is completely evaporated. Grind it into powder in an agate mortar.

[0017] c. The mixed powder is heated to 500℃~550℃ at a maximum heating rate of 5℃ / min and held for at least 1.5h. After cooling to room temperature, it is removed, washed, and dried to obtain the MOFs-Co-C3N5 photocatalyst. The calcination is carried out under an argon or nitrogen atmosphere.

[0018] In one specific embodiment, the method further includes adding the fully mixed powder from step a to the auxiliary agent solution, stirring, then drying, and then performing step b on the dried powder; the auxiliary agent is a potassium salt, preferably at least one of potassium bromide, potassium chloride, or potassium iodide, and the mass ratio of the auxiliary agent to the mixed powder is preferably 0-4%.

[0019] In one specific embodiment, the method further includes step b, wherein the stirring is performed at 80°C for a time greater than 1 hour.

[0020] In one specific embodiment, the method further includes step b, wherein the MOFs-Co mainly comprises one or more of the following: the organic ligand is 2-methylimidazole, 1,3,5-benzenetricarboxylic acid, pyridine-2,6-dicarboxylic acid, methanol, ethanol, and PVP; and the cobalt salt is cobalt nitrate hexahydrate. MOFs-Co is synthesized by centrifugal auto-assembly or by hydrothermal method, and more preferably by auto-assembly of 2-methylimidazole and methanol to synthesize ZIF-Co.

[0021] In one specific embodiment, the MOFs-Co mainly includes: PDA-Co, ZIF-Co, and BTC-Co. The ligand for PDA-Co is preferably an ethanol solution of pyridine-2,6-dicarboxylic acid, with a metal ligand to organic ligand mass ratio of 1:(0.1–0.5), further optimized to 1:0.3; the organic ligand for ZIF-Co is preferably 2-methylimidazole in methanol solution, with a metal ligand to organic ligand mass ratio of 1:(0.5–2.5), further optimized to 1:2; the organic ligand for BTC-Co is preferably 1,3,5-benzenetricarboxylic acid dissolved in a water:ethanol:N,N-dimethylformamide (DMF) mixture of 1:1:1, with a metal ligand to organic ligand mass ratio of 1:(0.1–0.8), further optimized to 1:0.4.

[0022] In one specific embodiment, the MOFs-derived Co is at least one of ZIF-Co, BTC-Co, and PDA-Co; ZIF-Co is preferred among the MOFs-derived Co.

[0023] In one specific embodiment, the mass ratio of MOFs-Co to the mixture is 0.001 to 0.01:1; preferably 0.025 to 0.075:1.

[0024] Applications of the above MOF-derived Co-doped C3N5 photocatalytic materials in the degradation of organic pollutants:

[0025] Step 1: Add MOFs-Co-C3N5 to wastewater containing organic matter to obtain a mixed solution;

[0026] Step 2: Add persulfate to the mixture obtained in Step 1 to obtain a mixed solution containing catalyst and oxidant;

[0027] Step 3: React the mixed solution obtained in Step 2 under visible light for 2-30 minutes.

[0028] The amount of ZIF-Co-C3N5 added was 0.8 g / L.

[0029] The target organic pollutant mentioned above is the antibiotic chlortetracycline.

[0030] The pH of the above reaction system is 3-10, and the reaction system is suitable for the treatment of organic pollutants in wastewater with concentrations of chloride ions, carbonates, nitrates, and bicarbonates below 5 mM.

[0031] The present invention has the following advantages and effects compared with the prior art:

[0032] (1) The material described in this patent is formed by co-derived MOFs-Co ligand framework and C3N5 nitrogen-rich precursor to form a double nitrogen structure, which can improve the stability of the catalyst, effectively solve the problem of Co dispersion, and avoid the problem of Co ion leaching, thus avoiding secondary pollution to the environment.

[0033] (2) Compared with traditional C3N5 photocatalysts, the MOFs-Co-C3N5 prepared in this invention has higher separation efficiency of photogenerated carriers, more reactive sites, and stronger photocatalytic activity.

[0034] (3) The activated persulfate treatment of organic pollutants using MOFs-Co-C3N5 prepared in this invention can react rapidly at room temperature and pressure, consumes little energy, and is simple to operate. Compared with other catalysts, it has the characteristics of fast free radical generation rate, reaction time shortened to less than 6 minutes, and high pollutant degradation efficiency.

[0035] (4) The MOFs-Co-C3N5 activated persulfate prepared in this invention is less affected by the environment when treating organic pollutants and can degrade pollutants in the pH range of 3 to 10. The reaction system is suitable for the treatment of various complex water pollutants. Attached Figure Description

[0036] Figure 1 The images shown are XRD patterns of embodiments 1, 2, 3, 4, and 5 of the present invention.

[0037] Figure 2 These are the FTIR images of embodiments 1, 2, 3, 4, and 5 of the present invention;

[0038] Figure 3 The images shown are SEM images of embodiments 3, 4, and 5 of the present invention; image a shows the original C3N5 without cobalt doping, image b shows ZIF-Co-C3N5 (5%), image c shows ZIF-Co-C3N5 (10%), and image d shows ZIF-Co-C3N5 (15%).

[0039] Figure 4The N2 adsorption-desorption isotherms for Example 3 and undoped pristine C3N5 are shown.

[0040] Figure 5 The ultraviolet-visible diffuse reflectance absorption spectra of Examples 1, 2, 3, 4, and 5 of this invention are shown.

[0041] Figure 6 These are bandgap width diagrams for embodiments 1, 2, 3, 4, and 5 of the present invention;

[0042] Figure 7 Comparison of electrochemical impedance spectroscopy (EIS) spectra of Examples 3, 4, 5 and the original C3N5 without cobalt doping;

[0043] Figure 8 Comparison of transient photocurrent responses of Examples 3, 4, 5 and undoped cobalt C3N5;

[0044] Figure 9 The graph shows the efficiency of activated persulfate in degrading chlortetracycline (CTC) in the test examples and comparative examples of the present invention.

[0045] Figure 10 This is a comparison chart showing the effect of ZIF-Co-C3N5 (10%) on the degradation efficiency of CTC under different pH conditions in the test examples;

[0046] Figure 11 This is a comparison chart showing the effect of ZIF-Co-C3N5 (10%) on the degradation efficiency of CTC under different PMS concentrations in the test examples;

[0047] Figure 12 This is a comparison chart showing the effect of ZIF-Co-C3N5 (10%) on the degradation efficiency of CTC under different interfering ions in the test examples;

[0048] Figure 13 This is a comparison chart showing the degradation effects of ZIF-Co-C3N5 (10%) on different pollutants in the test example.

[0049] Figure 14 This is a comparison chart of the degradation efficiency and Co ion leaching concentration of ZIF-Co-C3N5 (10%) after being cycled four times under the same conditions in the test example;

[0050] Figure 15 FTIR comparison charts before and after using ZIF-Co-C3N5 (10%) in the test example;

[0051] Figure 16 The graph shows the results of ZIF-Co-C3N5 (10%) activation of persulfate in different water bodies during the test example.

[0052] Figure 17The image shows the results of ZIF-Co-C3N5 (10%) activation of CTC degradation by persulfate under different light source conditions in the test example.

[0053] The present invention will be described in more detail below through specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0054] Example 1

[0055] This example provides a method for preparing a PDA-Co-C3N5 (10%) induced derivatized Co-doped C3N5 photocatalyst, the specific steps of which are as follows:

[0056] 1) Synthesis of C3N5 precursor: 4.5g of 3-amino-1,2,4-triazole, 4.5g of cyanuric acid, 0.45g of barbituric acid, and 0.8g of potassium bromide were dissolved in 100mL of deionized water, stirred for 2h, sonicated for 1h, mixed well, dried and ground to obtain C3N5 precursor.

[0057] 2) Preparation of PDA-Co-C3N5 (10%) precursor: First, dissolve 0.1g PDA-Co in 40mL of deionized water, then sonicate at room temperature for 30min. Finally, slowly add the above solution to a 40mL solution containing 2g C3N5 precursor, stir at 80℃ until the water is completely evaporated, and grind into powder in an agate mortar.

[0058] 3) Calcination of PDA-Co-C3N5 (10%): The powder obtained above was transferred to a 5 mL alumina crucible and then to a tube furnace. The temperature was increased to 500 °C at a rate of 5 min / °C and held for 3 h. After cooling to room temperature, the powder was removed and ground into powder with an agate mortar. Impurities were washed away with deionized water and dried at 80 °C to obtain black powder PDA-Co-C3N5 (10%).

[0059] Example 2

[0060] This example provides a method for preparing a BTC-Co-C3N5 (10%) induced derivative Co-doped C3N5 photocatalyst, the specific steps of which are as follows:

[0061] 1) Synthesis of C3N5 precursor: 4.5g of 3-amino-1,2,4-triazole, 4.5g of cyanuric acid, 0.45g of barbituric acid, and 0.8g of potassium bromide were dissolved in 100mL of deionized water, stirred for 2h, sonicated for 1h, mixed well, dried and ground to obtain C3N5 precursor.

[0062] 2) Preparation of BTC-Co-C3N5 (10%) precursor: First, 0.1g BTC-Co was dissolved in 40mL of deionized water, and then ultrasonically treated for 30min at room temperature. Finally, the above solution was slowly added to a 40mL solution containing 2g C3N5 precursor, and stirred at 80℃ until the water was completely evaporated. The mixture was then ground into powder in an agate mortar.

[0063] 3) Calcination of BTC-Co-C3N5 (10%): The powder obtained above was transferred to a 5 mL alumina crucible and then to a tube furnace. The temperature was increased to 500 °C at a rate of 5 min / °C and held for 3 h. After cooling to room temperature, the powder was removed and ground into powder with an agate mortar. Impurities were washed away with deionized water and dried at 80 °C to obtain black powder BTC-Co-C3N5 (10%).

[0064] Example 3

[0065] This example provides a method for preparing a ZIF-Co-C3N5 (10%) induced derivatized Co-doped C3N5 photocatalyst, the specific steps of which are as follows:

[0066] 1) Synthesis of C3N5 precursor: 4.5g of 3-amino-1,2,4-triazole, 4.5g of cyanuric acid, 0.45g of barbituric acid, and 0.8g of potassium bromide were dissolved in 100mL of deionized water, stirred for 2h, sonicated for 1h, mixed well, dried and ground to obtain C3N5 precursor.

[0067] 2) Preparation of ZIF-Co-C3N5 (10%) precursor: First, dissolve 0.1g ZIF-Co in 40mL of deionized water, then sonicate at room temperature for 30min. Finally, slowly add the above solution to a 40mL solution containing 2g C3N5 precursor, stir at 80℃ until the water is completely evaporated, and grind into powder in an agate mortar.

[0068] 3) Calcination of ZIF-Co-C3N5 (10%): The powder obtained above was transferred to a 5 mL alumina crucible and then to a tube furnace. The temperature was increased to 500 °C at a rate of 5 min / °C and held for 3 h. After cooling to room temperature, the powder was removed and ground into powder with an agate mortar. Impurities were washed away with deionized water and dried at 80 °C to obtain black powder ZIF-Co-C3N5 (10%).

[0069] Example 4

[0070] This example provides a method for preparing ZIF-Co-C3N5 (5%) induced derivatized Co-doped C3N5 photocatalysts, the specific steps of which are as follows:

[0071] 1) Synthesis of C3N5 precursor: 4.5g of 3-amino-1,2,4-triazole, 4.5g of cyanuric acid, 0.45g of barbituric acid, and 0.8g of potassium bromide were dissolved in 100mL of deionized water, stirred for 2h, sonicated for 1h, mixed well, dried and ground to obtain C3N5 precursor.

[0072] 2) Preparation of ZIF-Co-C3N5 (5%) precursor: First, dissolve 0.05g ZIF-Co in 40mL of deionized water, then sonicate at room temperature for 30min. Finally, slowly add the above solution to a 40mL solution containing 2g C3N5 precursor, stir at 80℃ until the water is completely evaporated, and grind into powder in an agate mortar.

[0073] 3) Calcination of ZIF-Co-C3N5 (5%): The powder obtained above was transferred to a 5 mL alumina crucible and then to a tube furnace. The temperature was increased to 500 °C at a rate of 5 min / °C and held for 3 h. After cooling to room temperature, the powder was removed and ground into powder with an agate mortar. Impurities were washed away with deionized water and dried at 80 °C to obtain black powder ZIF-Co-C3N5 (5%).

[0074] Example 5

[0075] This example provides a method for preparing a ZIF-Co-C3N5 (15%) induced derivatized Co-doped C3N5 photocatalyst, the specific steps of which are as follows:

[0076] 1) Synthesis of C3N5 precursor: 4.5g of 3-amino-1,2,4-triazole, 4.5g of cyanuric acid, 0.45g of barbituric acid, and 0.8g of potassium bromide were dissolved in 100mL of deionized water, stirred for 2h, sonicated for 1h, mixed well, dried and ground to obtain C3N5 precursor.

[0077] 2) Preparation of ZIF-Co-C3N5 (15%) precursor: First, dissolve 0.15g ZIF-Co in 40mL of deionized water, then sonicate at room temperature for 30min. Finally, slowly add the above solution to a 40mL solution containing 2g C3N5 precursor, stir at 80℃ until the water is completely evaporated, and grind into powder in an agate mortar.

[0078] 3) Calcination of ZIF-Co-C3N5 (15%): The powder obtained above was transferred to a 5 mL alumina crucible and then to a tube furnace. The temperature was increased to 500 °C at a rate of 5 min / °C and held for 3 h. After cooling to room temperature, the powder was ground into powder with an agate mortar and washed with deionized water to remove impurities. The powder was then dried at 80 °C to obtain black powder ZIF-Co-C3N5 (15%).

[0079] The XRD patterns of the materials obtained in Examples 1, 2, 3, 4, and 5 are as follows: Figure 1 As shown. The examples did not exhibit new peak shapes and showed typical carbon nitride diffraction peaks, indicating that MOF-derived Co did not disrupt the original structure of C3N5. The peak intensity of the doped samples was weaker compared to C3N5, indicating that the combination of the framework structure and triazole ring structure of MOF materials can lead to a decrease in crystallinity and grain size. With increasing ZIF-Co doping concentration, the characteristic peaks shifted to higher angles and gradually weakened, indicating a decrease in graphitization, reduced conductivity, and reduced charge separation efficiency.

[0080] The FTIR of the materials obtained in Examples 1, 2, 3, 4, and 5 are as follows: Figure 2 As shown, there is no significant difference between the FTIR spectra of the doped and undoped samples, indicating that trace Co ion doping did not alter the chemical structure of C3N5. At 811 cm⁻¹ -1 The intensity of the reaction weakens with further increase of Co doping, indicating that the -NH groups on the catalyst surface may be important sites for bonding with Co, which is beneficial to improving catalyst performance.

[0081] SEM images of ZIF-Co-C3N5 with different Co doping levels in the ZIF-Co series are shown below. Figure 3 As shown in the figure, it is clear that C3N5 forms an irregular blocky structure by stacking layers together, with relatively few pores. With the introduction of cobalt, the pore structure gradually increases. When the doping amount reaches 15%, excessive Co leads to poor material crystallization, structural damage, and performance degradation.

[0082] The N2 adsorption-desorption curves of the materials obtained in Examples 1, 2, 3, 4, and 5 are as follows: Figure 4 As shown, the results indicate that ZIF-Co-C3N5 has a larger specific surface area compared to other materials, with ZIF-Co-C3N5 (10%) having a specific surface area of ​​2.24 m². 2 / g. This result further demonstrates that Co doping improves the specific surface area and porosity of the catalyst to some extent, providing a large number of surface adsorption sites and photocatalytic active sites, which is beneficial to the activation of PMS.

[0083] The UV-Vis diffuse reflectance absorption spectra and band gap widths of the materials obtained in Examples 1, 2, 3, 4, and 5 are as follows: Figure 5 , 6 As shown. Figure 5 The study showed that the material has light absorption capabilities in the range of 300–800 nm. The absorption wavelength threshold of all samples can be extended into the visible light region. When the absorption wavelength is in the range of 400–800 nm, all samples have strong absorption. Figure 6Calculations using the Kubellka-Munk function showed that ZIF-Co-C3N5 (10%) and PDA-Co-C3N5 (10%) had the lowest bandgap value of 1.22 eV, while BTC-Co-C3N5 (10%) had a bandgap value of 1.30 eV. The bandgap values ​​for ZIF-Co-C3N5 (5%) and ZIF-Co-C3N5 (15%) with different doping amounts were 1.20 eV and 1.24 eV, respectively. These results indicate that MOF-Co doping can modulate the band structure of C3N5, resulting in a stronger visible light response and thus better photocatalytic performance.

[0084] Figure 7 EIS analysis was performed on undoped samples and ZIF-Co series samples with different cobalt doping levels under dark conditions. The arc radius of the Co-doped samples was significantly smaller than that of the undoped C3N5 samples, with ZIF-Co-C3N5 (10%) showing the lowest resistivity, indicating enhanced photoelectrochemical performance of this sample; similarly, Figure 8 The transient photocurrent response of the above samples under visible light irradiation was shown. Among the tested samples, ZIF-Co-C3N5 (10%) showed the highest photocurrent, indicating that this sample had a higher photogenerated electron-hole separation rate, which is consistent with the EIS results. The above electrochemical tests show that the introduction of Co under photo-induced conditions can exert a certain resistance to charge separation and photogenerated electron transfer, thereby enhancing charge separation and transfer, which is beneficial to improving photocatalytic activity.

[0085] Tests and Results: The method for evaluating the photocatalytic activity of the material provided in this invention is as follows:

[0086] Take 0.01–0.05 g of the above catalyst and add it to 50 mL of a 30 mg / L chlortetracycline solution. Stir the solution at 450 rpm / min in the dark for 50 min until the photocatalytic material reaches adsorption equilibrium. After adding PMS, place the solution under a 50 W LED white light source at 10000 Lux (with a 50 W xenon lamp source as a control light source under the same conditions) to conduct a photocatalytic degradation experiment of pollutants. Samples were periodically filtered (using a 0.22 μm pore size filter membrane) and the chlortetracycline concentration was measured at 366 nm using a UV-Vis spectrophotometer.

[0087] Test Implementation Examples

[0088] Take 30 mg of ZIF-Co-C3N5 (10%) or (ZIF-Co-C3N5 (5%), ZIF-Co-C3N5 (15%)) and add it to 50 mL of a 30 mg / L chlortetracycline solution. Stir at 450 rpm / min in the dark for 50 min until the photocatalytic material reaches adsorption equilibrium. After adding PMS, place the solution under a 50 W LED white light source (10000 Lux) for photocatalytic degradation experiments of pollutants. Samples are taken periodically, filtered (using a 0.22 μm pore size filter membrane), and the concentration of chlortetracycline is determined by UV-Vis spectrophotometer.

[0089] Test comparison

[0090] 30 mg of undoped cobalt C3N5, PDA-Co-C3N5 (10%), and BTC-Co-C3N5 (10%) were added to 50 mL of a 30 mg / L chlortetracycline solution. The solution was stirred at 450 rpm / min in the dark for 50 min until the photocatalytic material reached adsorption equilibrium. After adding PMS, the solution was placed under a 50 W LED white light source (10000 Lux) for photocatalytic degradation experiments of pollutants. Samples were periodically filtered (using a 0.22 μm pore size filter membrane) and the chlortetracycline concentration was determined using a UV-Vis spectrophotometer.

[0091] Table 1 shows the experimental conditions and parameters in the test examples and comparative examples.

[0092]

[0093] Figure 9 The photocatalytic activity of the materials synthesized in the test examples and the comparative examples was compared. It is evident that the photocatalytic performance of the C3N5 doped sample is significantly better than that of the unmodified sample. The ZIF-Co series achieved a maximum CTC degradation rate of 77% within 30 minutes. MOF-derived Co forms highly dispersed metal sites (Co-Nx) on C3N5, which can rapidly activate PMS to generate active substances, serving as the main driving force for PMS activation and promoting CTC degradation. The degradation effects of 5%, 10%, and 15% ZIF-Co doped samples on pollutants were 74.8%, 77%, and 77.2%, respectively. The 15% doped sample showed only a 0.2% improvement in degradation compared to the 10% doped sample; therefore, ZIF-Co-C3N5 (10%) will be used in subsequent experiments. (Unless otherwise specified, all test examples below use ZIF-Co-C3N5 (10%).)

[0094] Table 2 shows the degradation of chlortetracycline by ZIF-Co-C3N5 (10%) under different pH and different PMS dosages.

[0095]

[0096]

[0097] Figure 10 The photocatalytic activity of the test examples under different pH conditions was compared. The results showed that ZIF-Co-C3N5 (10%) exhibited high degradation efficiency for CTC within the studied pH range and had a wide adaptability to different pH values. In particular, the degradation efficiency for CTC was significantly improved under neutral and weakly alkaline conditions. Since most water in nature is weakly alkaline, this material has broad practical applications. Figure 11 The degradation effects of potassium persulfate at pH 9 on chlortetracycline hydrochloride were compared in Test Example 2. The results showed that the ZIF-Co-C3N5 (10%) photocatalyst achieved 100% degradation of chlortetracycline hydrochloride within 6 minutes at pH 9 and a potassium persulfate dosage of 0.5 mM. Figure 12 The effects of different interfering ions on the degradation of chlortetracycline were compared under the conditions of pH 9, potassium persulfate dosage of 0.5 mM, and the presence of different ions. Sodium chloride, sodium bicarbonate, sodium dihydrogen phosphate, and sodium nitrate were added to simulate Cl-. - HCO3 - HPO4 2- and NO3 - Regarding the effect on CTC degradation efficiency, when the amount of coexisting ions added was set to 5 mM, the results showed that hydrogen phosphate could significantly promote the degradation of CTC, while the other coexisting ions had no significant inhibitory effect on CTC, indicating that the system has strong anti-interference ability.

[0098] Figure 13 The photocatalytic performance and selectivity of the ZIF-Co-C3N5(10%) / PMS / Vis system were compared with those of Example 2 at pH 9 with a potassium persulfate dosage of 0.5 mM. Five other antibiotics (TC, OTC, SD, CIP, and LEV) were also tested, with all antibiotic concentrations set at 30 mg / L. The results showed that although the degradation rate of SD was lower than the other four pollutants, the degradation rates of TC, LEV, and OTC all reached over 85% within 30 minutes. These results indicate that the ZIF-Co-C3N5(10%) / PMS / Vis system exhibits highly efficient photocatalytic performance and non-selectivity for the degradation of various antibiotics, demonstrating broad applicability in antibiotic degradation and potential for application in practical wastewater treatment.

[0099] Figure 14The test examples were compared under the same experimental conditions for four degradation cycles to examine the reusability and stability of the catalyst in practical applications. As shown in the figure, the degradation efficiency of CTC decreased from 100% to 66% after the fourth cycle. However, after heating the catalyst (400℃), the degradation efficiency was basically restored. This is because heating removes the intermediates covering the material surface during the reaction, thus restoring the degradation performance, rather than the loss of active sites causing the performance decline. The infrared spectrum of the used ZIF-Co-C3N5 matched well with that of the unused ZIF-Co-C3N5. Figure 15 The results indicate that the functional groups on the material surface did not change significantly, demonstrating good structural and compositional stability. Furthermore, the concentration of leached Co ions in the treatment solution was less than 1 mg / L during each operation (Surface Water Environmental Quality Standard (GB3838-2002)). These results indicate that ZIF-Co-C3N5 exhibits good stability and reusability.

[0100] Table 3. Degradation of ZIF-Co-C3N5 (10%) under different water quality conditions and different light sources.

[0101]

[0102] Figure 16 The removal efficiency of CTC over time in different aqueous solutions was shown, revealing the stability of the ZIF-Co-C3N5 (10%) catalyst in degrading pollutants under different aqueous environments. Figure 16 As shown, regardless of whether it is ultrapure water, tap water, or the campus Yanhu Lake water, the photocatalytic efficiency of ZIF-Co-C3N5(10%) catalyst for CTC can reach 100% within 6 minutes under PMS activation. Furthermore, based on the dark reaction adsorption stage, it can be concluded that the ZIF-Co-C3N5(10%) / PMS / CTC system has better performance in water bodies with more complex compositions. Figure 17 The degradation of CTC by ZIF-Co-C3N5 (10%) catalyst under different light source conditions was shown. Under both LED and xenon lamp light source conditions, the degradation effect of CTC could reach 100% within 6 minutes. This indicates that the in-situ formation of nitrogen-rich Co-doped C3N5 material derived from MOFs can improve the efficiency of photocatalytic degradation of organic pollutants due to its highly dispersed metal sites, which is conducive to the activation of PMS. This has important application value for the treatment of pollutants in complex water bodies.

Claims

1. The application of MOFs-Co-induced Co-doped C3N5 photocatalytic materials in the degradation of organic pollutants, characterized in that... The organic pollutants are oxytetracycline hydrochloride, tetracycline, sulfadiazine, levofloxacin, ciprofloxacin, or chlortetracycline. The preparation method of the MOFs-Co-induced Co-doped C3N5 photocatalytic material includes the following steps: a. A mixture is obtained by thoroughly mixing a powder composed of a nitrogen-rich compound and a six-membered nitrogen heterocycle, adding the powder to an auxiliary agent solution, stirring, and drying; wherein the nitrogen-rich compound is 3-amino-1,2,4-triazole, the six-membered nitrogen heterocycle is at least one of cyanuric acid or barbituric acid, and the auxiliary agent is a potassium salt, wherein the potassium salt is at least one of potassium bromide, potassium chloride, or potassium iodide; b. First, the MOFs-Co solution is ultrasonically treated, and then added dropwise to the solution of the mixture obtained in step a under heating conditions. The mixture is stirred thoroughly until the water is completely evaporated, and then ground into powder in an agate mortar. The MOFs-Co is at least one of ZIF-Co, BTC-Co, and PDA-Co. c. Transfer the powder obtained in step b to a crucible, place it in a tube furnace, and use a programmed temperature rise to keep it at 500℃~550℃ for more than 1 hour. After cooling, take it out, wash it, and dry it to obtain MOFs-Co induced derivatized Co-doped C3N5 photocatalytic material, namely MOFs-Co-C3N5 photocatalyst.

2. The application according to claim 1, characterized in that, The MOFs-Co is ZIF-Co.

3. The application according to claim 1, characterized in that, Step 1: Add MOFs-Co-C3N5 photocatalyst to wastewater containing organic matter to obtain a mixed solution; Step 2: Add persulfate to the mixture obtained in Step 1 to obtain a mixed solution containing MOFs-Co-C3N5 photocatalyst and oxidant; Step 3: React the mixed solution obtained in Step 2 under visible light for 2-30 minutes.

4. The application according to claim 3, characterized in that, The MOFs-Co is ZIF-Co, and the amount of MOFs-Co-C3N5 photocatalyst added is 0.2-0.8 g / L.

5. The application according to claim 4, characterized in that, The pH of the reaction system is 2 to 10, and the reaction system is suitable for the treatment of organic pollutants in wastewater with a concentration of chloride ions, carbonates, nitrates, or bicarbonates of less than 5 mM.

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