Preparation method and application of reproducible compound catalyst for activating persulfate

Abstract

The invention discloses a preparation method of a reproducible compound catalyst for activating persulfate. The preparation method comprises the following steps: (1) preparing a solution A: dissolving a certain amount of cobalt salt and a surfactant in a solvent to obtain the solution A; (2) preparing a solution B: uniformly dispersing a certain amount of 2-methylimidazole and a carbon nitrogen compound precursor into water to obtain the solution B; and (3) pouring the solution A into the solution B, stirring, centrifuging and drying the generated precipitate, and calcining the obtained powder in a muffle furnace to prepare the reproducible compound catalyst for activating persulfate. The invention also comprises the renewable composite catalyst prepared by the method and application of the renewable composite catalyst in degrading organic pollutants in water by catalyzing and activating persulfate. By optimizing the preparation conditions of the catalyst, the persulfate activation efficiency of the catalyst is remarkably improved, the catalyst has a remarkable degradation effect on organic pollutants, the effect is enhanced under the illumination condition, active sites are subjected to light regeneration, and the catalyst has good stability and reusability; and an efficient and environment-friendly solution is provided for water pollution treatment.

Description

Technical Field

[0001] This invention relates to the fields of catalytic materials and wastewater treatment technology, and in particular to the preparation of a renewable composite catalyst and its application in the degradation of organic pollutants in water by activated persulfate. Background Art

[0002] With rapid economic development and continuous population growth, water pollution has become a global environmental problem, seriously threatening human health and the balance of ecosystems. The large-scale discharge of industrial wastewater, agricultural wastewater, and domestic sewage has led to a continuous increase in the types and quantities of organic pollutants in water bodies. These organic pollutants include antibiotics and endocrine disruptors, which are characterized by high toxicity, strong stability, and difficulty in natural degradation. Once they enter water bodies, they can persist for a long time and harm aquatic life and human health.

[0003] Traditional water treatment technologies, such as physical adsorption, flocculation and sedimentation, and biodegradation, have certain limitations in treating organic pollutants. While physical adsorption can remove some pollutants, its adsorption capacity is limited, and the adsorbent is difficult to regenerate. Flocculation and sedimentation mainly target suspended and colloidal particles, and are less effective at removing dissolved organic pollutants. Biodegradation requires a long time and has certain requirements regarding the type and concentration of pollutants, making it difficult to cope with complex and ever-changing water pollution conditions.

[0004] To address this challenge, researchers have begun exploring more efficient and environmentally friendly water treatment technologies, among which persulfate advanced oxidation technology has attracted widespread attention due to its unique advantages. Persulfate, as a commonly used oxidant, possesses a certain oxidizing capacity, but its redox potential is relatively low, making it difficult to effectively degrade certain recalcitrant organic pollutants. However, by activating persulfate, it is possible to generate sulfate free radicals (·SO4) with stronger oxidizing power. - This improves the degradation efficiency of organic pollutants. Commonly used persulfate activation methods include thermal activation, photoactivation, and transition metal ion activation. Among these, photocatalytic activation of persulfate has become a research hotspot due to its advantages such as high efficiency, environmental friendliness, and ease of operation.

[0005] However, existing photocatalysts still face some challenges in activating persulfate. For example, some metal-based catalysts may experience metal ion leaching during use, leading to secondary pollution. While non-metallic photocatalysts such as graphitic carbon nitride (g-C3N4) possess advantages such as non-toxicity and good stability, their persulfate activation capacity is relatively low, making it difficult to meet the needs of practical applications. Catalyst stability and sustainable utilization are also significant issues. Therefore, developing novel, highly efficient catalysts to improve their persulfate activation performance is of great importance for solving water pollution problems. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a regenerable composite catalyst for activating persulfate and its preparation method. This catalyst exhibits good catalytic activity in the application of activated persulfate to degrade wastewater, and has photocatalytic enhanced activation and photoregeneration function of active sites, thus solving the technical problems of poor stability and easy deactivation of existing catalytic materials.

[0007] A method for preparing a regenerable composite catalyst for activating persulfate includes the following steps:

[0008] (1) Prepare solution A: Dissolve a certain amount of cobalt salt and surfactant in a solvent to obtain solution A;

[0009] (2) Preparation of solution B: A certain amount of 2-methylimidazole and carbon-nitrogen compound precursor are uniformly dispersed in water to obtain solution B;

[0010] (3) Pour solution A into solution B, stir, centrifuge and dry the precipitate, and calcine the obtained powder in a muffle furnace to obtain a regenerable composite catalyst for activating persulfate.

[0011] The specific process conditions for each step in the above preparation route are as follows:

[0012] (a) In step (1):

[0013] The cobalt salt may be one of cobalt nitrate, cobalt chloride, cobalt sulfate, or cobalt acetate. The surfactant may be cetyl ammonium bromide, sodium citrate, polyvinylpyrrolidone, or none. The solvent may be water, methanol, or an aqueous methanol solution of any proportion.

[0014] Preferably, the cobalt salt is cobalt nitrate hexahydrate, the surfactant is hexadecyl ammonium bromide, and the solvent is water.

[0015] Further optimization involves dissolving 2 mmol of cobalt nitrate and 10 mg of cetyl ammonium bromide in 20 mL of water.

[0016] (ii) In step (2):

[0017] The carbon and nitrogen compound precursor can be one of melamine, urea, cyanamide, or dicyandiamide.

[0018] Preferably, 0.1 mol of 2-methylimidazole and 3 g of melamine are added to 140 mL of water and stirred to disperse them evenly.

[0019] (iii) In step (3):

[0020] The calcination heating rate is 3-6℃ / min, the calcination temperature is 350-600℃, and the calcination time is 1-5h.

[0021] Preferably, the calcination heating rate is 5℃ / min, the calcination temperature is 500℃, and the calcination time is 2h.

[0022] This invention also includes an application of the prepared renewable composite catalyst to efficiently activate persulfate, thereby effectively degrading organic pollutants in water. Specifically, it includes the following steps: adding the renewable composite catalyst to wastewater containing organic pollutants, adding persulfate, and continuously stirring; the catalyst activates the persulfate under visible light or no light conditions to produce active substances, thereby degrading the organic matter in the water. Preferably, the visible light source is a xenon lamp with a light intensity of 100–600 mW·cm⁻¹. -2 The persulfate is permonosulfate or perdisulfate, with a concentration of 5–80 mg / L; the organic pollutants include, but are not limited to, antibiotics such as phenol, bisphenol A, ofloxacin, and tetracycline, and endocrine disruptors; the pH of the wastewater is 3–9, and the concentration is 1–100 mg / L.

[0023] Compared with existing technologies, the beneficial effects of this invention are as follows:

[0024] (1) The present invention prepares a highly efficient regenerable composite catalyst for the degradation of pollutants by persulfate. Due to the formation of an electric field inside the composite material, the regenerable composite catalyst exhibits a very good charge transfer ability and provides more active sites.

[0025] (2) The preparation process of the regenerable composite catalyst of this invention is simple, has high stability, and can be prepared in batches. The activity of the catalyst is restored by replenishing it with a photogenerated support, making it suitable for large-scale long-term operation and solving the problems of poor stability and easy deactivation of existing catalytic materials. Attached Figure Description

[0026] Figure 1 Images of the morphology of (a) Co3O4, (b) g-C3N4, and (c) Co3O4 / g-C3N4-3 under a scanning electron microscope;

[0027] Figure 2 XRD spectra of (a) Co3O4, (b) g-C3N4, and (c) Co3O4 / g-C3N4-3;

[0028] Figure 3 XPS full spectra of (a) Co3O4, (b) g-C3N4, and (c) Co3O4 / g-C3N4-3;

[0029] Figure 4Degradation curves of ofloxacin by Co3O4 / g-C3N4-3 under (a) light and (b) dark conditions;

[0030] Figure 5 The effects of (a) persulfate (PMS) dosage and (b) pH on the degradation of ofloxacin under light-free conditions on Co3O4 / g-C3N4-3;

[0031] Figure 6 The effect of PMS dosage on the degradation of ofloxacin under light conditions was investigated.

[0032] Figure 7 The graphs show the degradation of ofloxacin by different ion interferences of Co3O4 / g-C3N4-3 under (a) dark and (b) light conditions;

[0033] Figure 8 A cyclic experimental diagram of the degradation of ofloxacin in the Co3O4 / g-C3N4-3 system. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific examples.

[0035] Example 1

[0036] The preparation method of the regenerable composite catalyst in this embodiment includes the following steps:

[0037] (1) Prepare solution A: Add 0.58g of cobalt nitrate hexahydrate and 10mg of cetyl ammonium bromide to 20mL of water and stir to dissolve.

[0038] (2) Prepare solution B: Add 9.08g of 2-methylimidazole and 3g of melamine to 140mL of water and stir to disperse them evenly.

[0039] (3) Pour liquid A into liquid B and stir for 10 min. Centrifuge and dry the precipitate. Calcine the powder obtained in a muffle furnace at 500 °C for 2 h to obtain a regenerable composite catalyst for activated persulfate, denoted as Co3O4 / g-C3N4-3 catalyst.

[0040] Comparative Example 1

[0041] To facilitate performance comparison, 3g of melamine powder was calcined in a muffle furnace at 500℃ for 2h to prepare g-C3N4 catalyst.

[0042] Comparative Example 2

[0043] To facilitate performance comparison, the operation steps of Example 1 were repeated, except that in step (2), the amount of melamine added was 0g, and other experimental conditions were the same, thus obtaining the Co3O4 catalyst.

[0044] Example 2

[0045] To facilitate performance comparison, the operation steps of Example 1 were repeated, except that in step (2), the amount of melamine added was 2g, and other experimental conditions were the same, thus the Co3O4 / g-C3N4-2 catalyst was prepared.

[0046] Example 3

[0047] To facilitate performance comparison, the operation steps of Example 1 were repeated, except that in step (2), the amount of melamine added was 4g, and other experimental conditions were the same, thus the Co3O4 / g-C3N4-4 catalyst was prepared.

[0048] Figure 1 Images of the morphology of Co3O4 / g-C3N4-3 (c, d), g-C3N4 (b), and Co3O4 (a) prepared in Examples 1 and Comparative Examples 1-2 under a scanning electron microscope. Figure 1 It can be seen that g-C3N4 exhibits a 2D layered morphology, while Co3O4 consists of irregular particles. From Figure 1 As can be observed in (c, d), Co3O4 adheres well to the surface of g-C3N4.

[0049] Figure 2 The images show the XRD patterns of Co3O4 / g-C3N4-3, g-C3N4, and Co3O4 obtained in Example 1 and Comparative Examples 1-2. Figure 2 It can be seen that the characteristic peak at 27.36° corresponds to the (002) plane of g-C3N4, and the characteristic peaks at 31.06°, 36.92°, 44.82°, 59.20°, and 69.08° correspond to the (220), (222), (400), (511), and (442) planes of Co3O4. The simultaneous detection of characteristic peaks corresponding to both g-C3N4 and Co3O4 in the XRD pattern of the Co3O4 / g-C3N4-3 composite material confirms the successful synthesis of Co3O4 / g-C3N4-3.

[0050] Figure 3 The images show the XPS full spectra of Co3O4 / g-C3N4-3, g-C3N4, and Co3O4 prepared in Example 1 and Comparative Examples 1-2. Figure 3 It can be seen that Co3O4 / g-C3N4-3 is composed of C, N, O and Co elements, which proves the successful combination of g-C3N4 and Co3O4.

[0051] Application Example 1

[0052] The Co3O4 / g-C3N4-3 from Example 1, g-C3N4 from Comparative Example 1, Co3O4 from Comparative Example 2, Co3O4 / g-C3N4-2 from Example 2, and Co3O4 / g-C3N4-4 from Example 3 were used as heterogeneous catalysts for activating persulfate treatment. Specifically, 10 mg of each catalyst was weighed and uniformly dispersed together with 10 mg of potassium peroxymonosulfate (PMS) in an aqueous solution containing 50 mL of ofloxacin at a concentration of 10 mg / L. The reaction was carried out under magnetic stirring at a speed of 500 rpm for 10 minutes. A 0.5 mL sample was taken every 0.5–1 minute to determine the concentration of pollutants.

[0053] The experimental results of this application example are as follows: Figure 4 As shown in (a). By Figure 4 (a) It is evident that g-C3N4 is almost incapable of degrading ofloxacin. After combining g-C3N4 with Co3O4, the Co3O4 / g-C3N4 composite material exhibits significantly enhanced performance in PMS activation for ofloxacin degradation. Among them, Co3O4 / g-C3N4-3 shows the best performance in PMS activation, achieving approximately 99.7% ofloxacin removal efficiency within 3 minutes. The rate constant (k value) of Co3O4 / g-C3N4-3 is as high as 1.6813 min. -1 .

[0054] Application Example 2

[0055] The procedure of Example 1 was repeated, except that the reaction was carried out under a xenon lamp as a simulated visible light source (500W, λ>400nm) to study the effect of light irradiation on PMS activation.

[0056] The experimental results of this application example are as follows: Figure 4 As shown in (b). Figure 4 (b) It can be seen that under visible light irradiation, the activation of PMS in the g-C3N4 system is enhanced, and the degradation rate of ofloxacin increases, which implies the positive effect of photogenerated carriers. After the introduction of visible light irradiation, the k value of Co3O4 / g-C3N4-3 increases to 2.1705 min. -1 .

[0057] Application Example 3

[0058] The Co3O4 / g-C3N4-3 from Example 1 was used as a heterogeneous catalyst to activate persulfate treatment. The procedures of Example 1 were repeated, except that the PMS dosage and solution pH were replaced accordingly: (a) PMS dosage was set to 5, 10, 20, and 30 mg; (b) pH was set to 4, 5, 6, 7, 8, and 9. The concentration of pollutants was measured at each time point.

[0059] The experimental results of this application example are as follows: Figure 5 As shown. By Figure 5 (a) It can be seen that the degradation rate of ofloxacin in the Co3O4 / g-C3N4-3 system increases with increasing PMS concentration. Figure 5 (b) It can be seen that the change of pH value from 4 to 9 has almost no effect on the degradation of ofloxacin in the reaction system, which proves that the Co3O4 / g-C3N4-3 system has high reaction stability and a wide range of pH values, which is also conducive to its application in practical engineering.

[0060] Application Example 4

[0061] The Co3O4 / g-C3N4-3 from Example 1 was used as a heterogeneous catalyst to activate persulfate treatment. The procedures of Example 2 were repeated, except that the reaction was carried out in a xenon lamp used as a simulated visible light source (100 mW·cm⁻¹). -2 The study was conducted under the following conditions, with the PMS dosage in case 2 replaced by 5, 10, 20, and 30 mg, to investigate the effect of visible light irradiation on PMS activation.

[0062] The experimental results of this application example are as follows: Figure 6 As shown. By Figure 6 It is evident that the degradation rate of ofloxacin in the Co3O4 / g-C3N4-3 system increases with increasing PMS concentration, and the reaction rate is faster under light irradiation compared to the dark conditions. Therefore, introducing visible light irradiation can reduce PMS consumption, which helps to reduce process costs.

[0063] Application Example 5

[0064] The Co3O4 / g-C3N4-3 from Example 1 was used as a heterogeneous catalyst for the activation of persulfate brine treatment. The operating steps of Example 1 were repeated, except that a certain amount of Cl was added. - HCO3 - SO4 2- NO3 - The concentration of each ion in the solution was made to be 10 mM. The concentration of pollutants was measured at each time point.

[0065] The experimental results of this application example are as follows: Figure 7 As shown in (a). By Figure 7 (a) It can be seen that Cl - The inhibitory effect on the degradation of ofloxacin is the greatest, followed by SO4. 2- HCO3 - and NO3 - It has almost no inhibitory effect.

[0066] Application Example 6

[0067] The Co3O4 / g-C3N4-3 from Example 1 was used as a heterogeneous catalyst to activate persulfate treatment. The procedures of Example 2 were repeated, except that the reaction was carried out in a xenon lamp used as a simulated visible light source (100 mW·cm⁻¹). -2 The process was carried out under the following conditions, with a certain amount of Cl added respectively. - HCO3 - SO4 2- NO3 - This ensures that the concentration of each ion in the solution is 10 mM.

[0068] The experimental results of this application example are as follows: Figure 7 As shown in (b). Figure 7 (b) It can be seen that when visible light irradiation is turned on, the inhibitory effect of inorganic ions on the degradation of ofloxacin is significantly reduced.

[0069] Application Example 7

[0070] The reusability test was conducted on the Co3O4 / g-C3N4-3 catalyst from Application Example 1 after treating water with ofloxacin. Specifically, 10 mg of the Co3O4 / g-C3N4-3 catalyst from Application Example 1 was weighed and uniformly dispersed with 10 mg of potassium persulfate in a 50 mL aqueous solution containing 10 mg / L of ofloxacin. The reaction was carried out under magnetic stirring at 500 rpm for 10 minutes. A 0.5 mL sample was taken every 0.5–1 minute to determine the pollutant concentration. The reacted catalyst was then centrifuged, washed, and dried. This process was repeated three times.

[0071] The experimental results of this application example are as follows: Figure 8 As shown. By Figure 8 As shown in ①, ②, and ③, the removal efficiency of ofloxacin decreased from 99.7% to 85.1% after three cycles. Although the removal efficiency of ofloxacin decreased, the removal rate was still above 85%, indicating that the Co3O4 / g-C3N4-3 system has excellent overall stability and good economic benefits.

[0072] Application Example 8

[0073] Repeat the steps of Example 7, except that the reaction is carried out in a xenon lamp used as a simulated visible light source (100 mW·cm). -2 Perform the operation under the light, repeat the cycle three times, then turn off the light and repeat the cycle once more.

[0074] The experimental results of this application example are as follows: Figure 8 As shown, after the introduction of light irradiation, the removal efficiency of ofloxacin showed a significant increase, consistent with the removal rate during the first use. This indicates that the catalytic activity of Co3O4 / g-C3N4-3 was restored, demonstrating that light irradiation can repair active sites and regenerate the catalytic activity of Co3O4 / g-C3N4-3. After the light irradiation was removed, Co3O4 / g-C3N4-3 still maintained good PMS activation performance for the degradation of ofloxacin.

[0075] As can be seen from the above examples and applications, the Co3O4 / g-C3N4 composite catalyst exhibits higher activation performance and stability. The Co3O4 / g-C3N4 composite catalyst prepared by this invention demonstrates excellent catalytic activity and stability under both light and dark conditions, and light can repair active sites, making the composite catalyst regenerable.

[0076] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a regenerable composite catalyst for activating persulfate, characterized in that, Includes the following steps: (1) Prepare solution A: Dissolve a certain amount of cobalt salt and surfactant in a solvent to obtain solution A; (2) Preparation of solution B: A certain amount of 2-methylimidazole and carbon-nitrogen compound precursor are uniformly dispersed in water to obtain solution B; (3) Pour solution A into solution B, stir, centrifuge and dry the precipitate, and calcine the obtained powder in a muffle furnace to obtain a regenerable composite catalyst for activating persulfate.

2. The method for preparing a regenerable composite catalyst for activating persulfate according to claim 1, characterized in that, In step (1), the cobalt salt can be one of cobalt nitrate, cobalt chloride, cobalt sulfate, and cobalt acetate. The surfactant can be cetyl ammonium bromide, sodium citrate, polyvinylpyrrolidone, or none. The solvent can be water, methanol, or an aqueous methanol solution of any proportion.

3. The method for preparing a regenerable composite catalyst for activating persulfate according to claim 1, characterized in that, In step (2), the carbon-nitrogen compound precursor can be one of melamine, urea, cyanamide, or dicyandiamide.

4. The method for preparing a regenerable composite catalyst for activating persulfate according to claim 1, characterized in that, In step (3), the calcination heating rate is 3-6℃ / min, the calcination temperature is 350-600℃, and the calcination time is 1-5h.

5. A regenerable composite catalyst prepared according to any one of claims 1 to 4, characterized in that, The catalyst has the ability to activate persulfate to degrade pollutants and has enhanced photocatalytic activity.

6. The application of the regenerable composite catalyst according to claim 5 to efficiently activate persulfate and thus effectively degrade organic pollutants in water, characterized in that, Includes the following steps: A renewable composite catalyst is added to wastewater containing organic pollutants, along with persulfate and continuous stirring. The catalyst activates the persulfate under visible light or no light conditions to produce active substances, thereby degrading the organic matter in the water.

7. The application of the regenerable composite catalyst according to claim 6 to efficiently activate persulfate and thus effectively degrade organic pollutants in water, wherein the visible light source is a xenon lamp with a light intensity of 100–600 mW·cm⁻¹. -2 .

8. The application of the regenerable composite catalyst according to claim 6 to efficiently activate persulfate and thus effectively degrade organic pollutants in water, characterized in that, The persulfate is permonosulfate or perdisulfate, with a concentration of 5–80 mg / L.

9. The application of the regenerable composite catalyst according to claim 6 to efficiently activate persulfate and thus effectively degrade organic pollutants in water, characterized in that, The organic pollutants include, but are not limited to, antibiotics such as phenol, bisphenol A, ofloxacin, and tetracycline, and endocrine disruptors; the pH of the wastewater is 3 to 9, and the concentration is 1 to 100 mg / L.

10. The application of the regenerable composite catalyst according to claim 6 to efficiently activate persulfate and thus effectively degrade organic pollutants in water, characterized in that, Light exposure can repair the active sites of catalysts, thereby regenerating the catalytic activity of composite catalysts.

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