A catalyst for degrading organic pollutants, its preparation method and application

Abstract

The present invention relates to the field of energy conservation and environmental protection, and more particularly to a catalyst for degrading organic pollutants, a preparation method thereof, and an application thereof. Double-modified MCM-49 zeolite nanocrystals are prepared in a one-step method by hexamethylimine and quaternary ammonium salt as a dual-template agent. This makes the prepared MCM-49 zeolite nanocrystals amphiphilic, i.e., having both hydrophilic and lipophilic properties and synergistic effects with peroxymonosulfate or peroxydisulfate, and can efficiently degrade organic pollutants such as antibiotics, dyes, and endocrine disruptors within a wide pH range, and is suitable for treating wastewater containing organic pollutants. The number of reuses is ≥10 times, and the activity retention rate of the catalyst reaches more than 95%. The catalyst preparation process of the present invention is simple, low cost, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of energy conservation and environmental protection, and in particular to a catalyst for degrading organic pollutants, a preparation method thereof and an application thereof. Background Art

[0002] With the acceleration of global industrialization, industrial production processes have discharged large amounts of wastewater containing organic pollutants into natural water bodies. These organic pollutants come from a wide range of sources and are diverse in type. For example, the chemical industry produces wastewater containing complex organic compounds such as aromatic compounds, halogenated hydrocarbons, and amine compounds during organic synthesis reactions. These substances are often highly toxic, difficult to degrade, and bioaccumulative. The textile printing and dyeing industry uses a large number of dyes and auxiliaries, resulting in wastewater with high chromaticity and containing difficult-to-degrade organic pollutants such as azo dyes and anthraquinone dyes. The papermaking industry produces wastewater from pulping and papermaking processes containing lignin, cellulose derivatives, and various chemical additives, with high chemical oxygen demand (COD) and biochemical oxygen demand (BOD), and some contain toxic and harmful organic chlorides. The electronics industry, such as circuit board production and semiconductor manufacturing, produces wastewater containing heavy metal ions, organic solvents, photoresists, and other organic pollutants. These organic pollutants are chemically stable, highly biotoxic, and difficult to degrade through conventional methods. Domestic sewage also cannot be ignored. With the population growth and accelerated urbanization, its discharge volume continues to increase. In addition to conventional organic matter, it also contains various emerging organic pollutants, such as ingredients in personal care products, drug residues, and endocrine disruptors. These emerging organic pollutants have potential ecotoxicological risks and pose a threat to aquatic organisms and human health.

[0003] Faced with the dire situation of wastewater containing organic pollutants, traditional wastewater treatment technologies face numerous limitations. Biological treatment methods utilize microbial metabolism to degrade organic pollutants. However, many organic pollutants are biotoxic, inhibiting microbial growth and metabolic activity, reducing biological treatment efficiency or even rendering them ineffective. Furthermore, some organic pollutants are complex in structure and chemically stable, making them difficult for microorganisms to completely degrade. Physical treatment methods remove organic pollutants from wastewater through physical action, but they can only transfer organic pollutants from one phase to another, failing to achieve true degradation. For example, adsorbent regeneration after adsorption can cause secondary pollution, and precipitation and filtration methods are limited in their removal of dissolved organic pollutants. Chemical treatment methods convert organic pollutants into harmless substances through chemical reactions, but traditional chemical redox and chemical precipitation methods have limited effectiveness and can generate secondary pollution. Advanced oxidation processes, while efficient and rapid, are costly and require stringent equipment and operating conditions, limiting their large-scale application. Combined physical and chemical processes and biological-physical and chemical processes have improved wastewater treatment efficiency to some extent, but they are complex, costly, require large floor space, and are less adaptable to varying types and concentrations of organic pollutants.

[0004] Among the many emerging advanced oxidation technologies, the oxidation system based on peroxymonosulfate (PMS) and peroxydisulfate (PDS) has attracted attention due to its strong oxidation ability, wide application range, and environmental friendliness. The sulfate radicals (SO4 - ·) has an oxidation capacity close to that of hydroxyl radicals, effectively oxidizing a wide range of organic pollutants. However, the decomposition of PMS and PDS is susceptible to environmental influences, and their activation efficiency is low and their cost is high when used alone. Therefore, developing an efficient, stable, and low-cost catalyst to synergize with these catalysts to enhance the generation and utilization of sulfate radicals and achieve efficient degradation of organic pollutants is crucial for addressing the challenges of treating wastewater containing organic pollutants. Dually modified MCM-49 catalysts have emerged as a promising candidate. MCM-49 molecular sieves, with their large surface area, regular pore structure, and excellent thermal stability, provide a support for the adsorption and catalytic reactions of organic pollutants. Dual modification enhances adsorption selectivity and catalytic activity for organic pollutants, improving their synergistic effects with PMS or PDS, and is expected to play a significant role in wastewater treatment. Summary of the Invention

[0005] The purpose of the present invention is to provide a catalyst for degrading organic pollutants and a preparation method thereof. By using hexamethylimine and quaternary ammonium salt as dual templates, a double-modified MCM-49 zeolite nanocrystal is prepared in a one-step method. This makes the prepared MCM-49 zeolite nanocrystal amphiphilic, that is, it has both hydrophilic and lipophilic properties. This plays an extremely important role in the treatment of wastewater containing organic pollutants. It can significantly improve the activation efficiency of peroxymonosulfate (PMS) and peroxydisulfate (PDS), accelerate the generation of sulfate radicals (SO4 - ), thereby achieving efficient degradation of organic pollutants. In practical applications, this catalyst can effectively treat a variety of organic pollutants, including antibiotics, dyes, and endocrine disruptors, breaking them down into harmless carbon dioxide, water, and inorganic ions. This significantly reduces the chemical oxygen demand (COD) and toxicity of wastewater, ensuring that treated wastewater meets strict environmental emission standards. This is of great significance for protecting the ecological environment and human health.

[0006] In order to solve the above technical problems, the present invention provides a catalyst for degrading organic pollutants, a preparation method and an application thereof.

[0007] To achieve the above object, the present invention provides the following technical solution: a catalyst for degrading organic pollutants and a preparation method thereof, comprising the following steps:

[0008] S1: Sodium metaaluminate and sodium hydroxide are dissolved in deionized water, and then silica sol is added, and the mixture is stirred at 800 r / min for 1 hour. After the solution is dissolved until clear, hexamethyleneimine is added and the stirring is continued for 15 minutes. The quaternary ammonium salt is added and the stirring is continued for 30 minutes. The above mixture is placed in a polytetrafluoroethylene-lined reactor and aged at 40-50° C. for 24 hours to obtain a mixture, wherein the above raw materials are calculated by mass ratio of silica sol: sodium metaaluminate: sodium hydroxide: hexamethyleneimine: quaternary ammonium salt: deionized water = 1:0.01-0.03:0.15-0.35:0.2-0.45:0.15-0.35:5-25;

[0009] S2, drying the mixture at 40°C for 0.5 to 4 h, until the mass is reduced to 35% to 70% of the original mass of the mixture and the sample appears as a dry gel;

[0010] S3: Place the dry gel-like mixture in an open glass container, place the glass container in the reactor liner, add deionized water to the outside of the glass container, and add an amount of 1 / 3 to 2 / 3 of the volume between the glass container and the reactor liner to prevent the deionized water from entering the glass container, thereby providing a water vapor environment for the reaction. Crystallize at 150°C for 1 to 3 days under steam-assisted conditions, wash and dry to obtain a crystalline product; S4: Calcine the crystalline product at 300 to 400°C for 4 to 8 hours to obtain a dual-modified MCM-49 nanocrystalline catalyst for degrading organic pollutant D.

[0011] Furthermore, the preparation method of the quaternary ammonium salt comprises the following steps:

[0012] In a nitrogen atmosphere, a mixed solution of methyl acrylate and methanol is added dropwise to diethylenetriamine. After the reaction, a light yellow transparent liquid is obtained. After removing the methanol, the temperature is raised to 150°C and the reaction is continued under reduced pressure to generate a viscous, light yellow compound. The compound is dissolved in water, and an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride is added dropwise at a mass of 1 to 10 times that of the compound. After the reaction is completed, the product is separated and purified to obtain a light yellow solid quaternary ammonium salt. The above raw materials are calculated in a mass ratio of methyl acrylate: methanol: diethylenetriamine = 1:3 to 15:2 to 10, and the mass fraction of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride is 40% to 80%.

[0013] Furthermore, the method for removing the methanol is distillation.

[0014] Furthermore, the degradation method of the double-modified MCM-49 nanocrystalline catalyst for degrading organic pollutants D comprises the following steps:

[0015] The catalyst is dispersed in wastewater containing organic pollutants at a concentration of 0.2-1.5 g / L, the pH is adjusted to 3.0-9.0, 0.5-5 mmol / L of peroxymonosulfate PMS or peroxydisulfate PDS is added, and the reaction is carried out at 20-50°C for 10-120 minutes to achieve efficient degradation of organic pollutants.

[0016] Furthermore, the organic pollutants include at least one of antibiotics, dyes or endocrine disruptors, including tetracycline, rhodamine B, bisphenol A, etc.

[0017] Furthermore, the catalyst can be reused ≥10 times, and the catalytic activity of the catalyst can still be maintained at more than 95% of the initial catalytic performance.

[0018] The present invention provides a catalyst for degrading organic pollutants and a preparation method thereof. The catalyst, through a unique dual-modified structure, synergizes with peroxymonosulfate (PMS) or peroxydisulfate (PDS) to achieve efficient degradation of organic pollutants. The stacked pore structure between MCM-49 nanocrystals provides it with abundant active sites and a large specific surface area, which is conducive to the adsorption and enrichment of organic pollutant molecules. When in contact with PMS or PDS, the active sites on the catalyst can reduce the activation energy, prompting the rapid decomposition of PMS or PDS to produce sulfate radicals (SO4 - These free radicals possess powerful oxidizing power, capable of indiscriminately attacking organic pollutant molecules, breaking their chemical bonds and decomposing them into small organic molecules, or even completely mineralizing them into carbon dioxide and water. Furthermore, the introduction of modifiers such as quaternary ammonium salts during the double modification process further enhances the catalyst's adsorption selectivity and catalytic activity for organic pollutants, increasing the generation and utilization efficiency of sulfate radicals and thus accelerating the degradation of organic pollutants.

[0019] In addition, the catalyst of the present invention has good stability and reusability, which has significant economic advantages in actual wastewater treatment applications. After repeated recycling, the structure and performance of the catalyst are relatively stable, and the catalytic activity of the catalyst can still maintain more than 95% of the initial catalytic performance. As shown in Example 1, tetracycline reaches a degradation rate of 92% when first degraded. After multiple regeneration cycles, its degradation rate only slightly drops to 89%, and can still maintain 96.7% of the initial catalytic activity. Its excellent catalytic activity retention rate reduces the replacement frequency and processing cost of the catalyst. This characteristic makes the catalyst very feasible in large-scale industrial wastewater treatment, and provides strong support for reducing wastewater treatment costs and improving treatment efficiency. At the same time, the preparation method of the catalyst is relatively simple, mild conditions, and is easy to industrial production, which further promotes its widespread application in the actual wastewater treatment field and provides a solid technical guarantee for achieving green and efficient wastewater purification goals. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of a catalyst for degrading organic pollutants prepared in Example 1 of the present invention and a catalyst of model NZ-HM49-001 purchased in Comparative Example 1. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] The following examples specifically illustrate the catalyst for degrading organic pollutants and its preparation method provided by the present invention.

[0023] Example 1:

[0024] Catalyst preparation:

[0025] Step S1: Weigh 10g of silica sol (30% by mass), 0.2g of sodium metaaluminate, and 2g of sodium hydroxide, add them to deionized water, and stir at 800 rpm for 1 hour until dissolved and clear. Add 2g of hexamethyleneimine and continue stirring for 15 minutes. Then, add 2g of a quaternary ammonium salt and stir for 30 minutes. The mixture is placed in a polytetrafluoroethylene-lined reactor and aged at 45°C for 24 hours. The quaternary ammonium salt is prepared by dropwise adding a mixed solution of 5g of methyl acrylate and 30g of methanol to 10g of diethylenetriamine under a nitrogen atmosphere. After the reaction, a light yellow transparent liquid is obtained. The methanol is removed by distillation, the temperature is raised to 150°C, and the reaction is continued under reduced pressure for 5 hours to produce a viscous, light yellow compound. The compound was dissolved in water, and 80 g of a 60% by mass aqueous solution of 2,3-epoxypropyltrimethylammonium chloride (whose mass is 8 times that of the compound) was added dropwise. After the reaction was completed, a light yellow solid quaternary ammonium salt was obtained through separation and purification.

[0026] S2: Dry the above mixture at 40°C for 2 h until the mass is reduced to 50% of the original mixture mass and the sample appears as a dry gel.

[0027] S3: The dried gel-like mixture was placed in an open glass container, which was placed in the lining of a reactor. 10 g of deionized water was added to the outside of the glass container. The mixture was crystallized at 150° C. for 2 days under steam-assisted conditions. After washing and drying, a crystalline product was obtained.

[0028] S4: The crystalline product was calcined at 350° C. for 6 h to obtain a dual-modified MCM-49 nanocrystalline catalyst for degrading organic pollutant D.

[0029] Catalyst degradation wastewater test: Simulated wastewater containing tetracycline (100 mg / L) was prepared. To 500 ml of this simulated wastewater, the catalyst was added to a concentration of 0.5 g / L. The pH was adjusted to 7.0, and 2 mmol / L of peroxymonosulfate (PMS) was added. The reaction was allowed to proceed at 30°C for 60 minutes. The tetracycline degradation rate reached 92%. After the initial tetracycline degradation reaction, the catalyst was separated by filtration and washed with deionized water until the filtrate was free of significant impurities. The recovered catalyst was then dried in a vacuum oven at 240°C for 2 hours and redispersed in fresh simulated wastewater containing tetracycline (100 mg / L) at a catalyst concentration of 0.5 g / L. All other reaction conditions (pH = 7.0, PMS concentration 2 mmol / L, reaction time at 30°C for 60 minutes) remained the same as for the initial use. This process was repeated 10 times. After 10 consecutive cycles of use (i.e., the 11th tetracycline degradation test), the tetracycline degradation rate remained at 89%.

[0030] Example 2:

[0031] Catalyst preparation:

[0032] Step S1: Weigh 10g of silica sol (30% by mass), 0.1g of sodium metaaluminate, and 1.5g of sodium hydroxide, add them to deionized water, and stir at 800 rpm for 1 hour until dissolved and clear. Add 1g of hexamethyleneimine and continue stirring for 15 minutes. Then, add 1g of a quaternary ammonium salt and stir for 30 minutes. The mixture is placed in a polytetrafluoroethylene-lined reactor and aged at 40°C for 24 hours. The preparation method of the quaternary ammonium salt is the same as in Example 1, except that the raw material ratio is adjusted to 5g of methyl acrylate, 15g of methanol, and 5g of diethylenetriamine. The mass fraction of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride added dropwise is 40% and its mass is 5 times that of the compound.

[0033] Step S2: Dry the mixture at 40° C. for 3 h until the mass is reduced to 60% of the original mass of the mixture and the sample becomes a dry gel.

[0034] Step S3: The dried gel-like mixture was placed in an open glass container, which was placed in the lining of a reactor. 5 g of deionized water was added to the outside of the glass container. The mixture was crystallized at 150° C. for 1 day under steam-assisted conditions. After washing and drying, a crystalline product was obtained.

[0035] Step S4: calcining the crystalline product at 300° C. for 8 h to obtain a dual-modified MCM-49 nanocrystalline catalyst for degrading organic pollutants D.

[0036] Catalyst degradation wastewater test: Simulated wastewater containing rhodamine B (50 mg / L) was prepared. 500 ml of the simulated wastewater was added with the catalyst to a concentration of 1.0 g / L. The pH was adjusted to 5.0, and 3 mmol / L of peroxydisulfate (PDS) was added. The mixture was reacted at 25°C for 90 minutes. The degradation rate of rhodamine B reached 89%.

[0037] Example 3:

[0038] Catalyst preparation:

[0039] Step S1: Weigh 10g of silica sol (30% by mass), 0.3g of sodium metaaluminate, and 3g of sodium hydroxide, add them to deionized water, and stir at 800 rpm for 1 hour until dissolved and clear. Add 3g of hexamethyleneimine and continue stirring for 15 minutes. Then, add 3g of a quaternary ammonium salt and stir for 30 minutes. The mixture is placed in a polytetrafluoroethylene-lined reactor and aged at 50°C for 24 hours. The preparation method of the quaternary ammonium salt is the same as in Example 1, except that the raw material ratio is adjusted to 5g of methyl acrylate, 20g of methanol, and 8g of diethylenetriamine. The mass fraction of the 2,3-epoxypropyltrimethylammonium chloride aqueous solution added dropwise is 80% and its mass is 10 times that of the compound.

[0040] Step S2: Dry the mixture at 40° C. for 4 h until the mass is reduced to 70% of the original mass of the mixture and the sample is in a dry gel state.

[0041] Step 3: Place the dry gel-like mixture in an open glass container, place it in the lining of the reactor, add 6 g of deionized water outside the glass container, crystallize at 150° C. for 3 days under steam-assisted conditions, and obtain a crystalline product after washing and drying.

[0042] Step S4: calcining the crystalline product at 400° C. for 4 h to obtain a dual-modified MCM-49 nanocrystalline catalyst for degrading organic pollutants D.

[0043] Catalyst degradation wastewater test: Simulated wastewater containing bisphenol A (80 mg / L) was prepared. 500 ml of the simulated wastewater was added with the catalyst to a concentration of 1.5 g / L. The pH was adjusted to 9.0, and 5 mmol / L of peroxymonosulfate (PMS) was added. The mixture was reacted at 50°C for 120 minutes. The degradation rate of bisphenol A reached 95%.

[0044] Comparative Example 1:

[0045] To prepare simulated wastewater containing tetracycline (100 mg / L), 500 ml of the water was added with commercially available MCM-49 molecular sieve catalyst (model NZ-HM49-001) to a concentration of 0.5 g / L. The pH was adjusted to 7.0, and 2 mmol / L of peroxymonosulfate (PMS) was added. The mixture was reacted at 30°C for 60 minutes. The degradation rate of tetracycline was 72%.

[0046] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a catalyst for degrading organic pollutants, characterized in that: The following steps are involved: S1: Sodium metaaluminate and sodium hydroxide are dissolved in deionized water, and then silica sol is added, and the mixture is stirred at 800 r / min for 1 hour. After the solution is dissolved until clear, hexamethyleneimine is added and the stirring is continued for 15 minutes. The quaternary ammonium salt is added and the stirring is continued for 30 minutes. The above mixture is placed in a polytetrafluoroethylene-lined reactor and aged at 40-50° C. for 24 hours to obtain a mixture, wherein the above raw materials are calculated by mass ratio of silica sol: sodium metaaluminate: sodium hydroxide: hexamethyleneimine: quaternary ammonium salt: deionized water = 1:0.01-0.03:0.15-0.35:0.2-0.45:0.15-0.35:5-25; S2: drying the above mixture at 40°C for 0.5-4 h until the mass is reduced to 35%-70% of the original mixture mass and the sample appears as a dry gel; S3: placing the dry gel-like mixture in an open glass container, placing the glass container in the reactor liner, adding deionized water to the outside of the glass container in an amount of 1 / 3 to 2 / 3 of the volume between the glass container and the reactor liner, so that liquid deionized water cannot enter the glass container, providing a water vapor environment for the reaction, and crystallizing at 150° C. for 1 to 3 days under steam-assisted conditions, and washing and drying to obtain a crystalline product; S4: calcining the crystalline product at 300-400° C. for 4-8 hours to obtain a double-modified MCM-49 nanocrystalline catalyst for degrading organic pollutants; The preparation method of the quaternary ammonium salt comprises the following steps: In a nitrogen atmosphere, a mixed solution of methyl acrylate and methanol is added dropwise to diethylenetriamine. After the reaction, a light yellow transparent liquid is obtained. After removing the methanol, the temperature is raised to 150°C and the reaction is continued under reduced pressure to generate a viscous, light yellow compound. The compound is dissolved in water, and an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride is added dropwise at a mass of 1 to 10 times that of the compound. After the reaction is completed, the product is separated and purified to obtain a light yellow solid quaternary ammonium salt. The above raw materials are calculated in a mass ratio of methyl acrylate: methanol: diethylenetriamine = 1:3 to 15:2 to 10, and the mass fraction of the aqueous solution of 2,3-epoxypropyltrimethylammonium chloride is 40% to 80%.

2. The method for preparing a catalyst for degrading organic pollutants according to claim 1, wherein: The method for removing the methanol is distillation.

3. The method for preparing a catalyst for degrading organic pollutants according to claim 1, wherein: The organic pollutants include at least one of antibiotics, dyes or endocrine disruptors.

4. The method for preparing a catalyst for degrading organic pollutants according to claim 3, wherein: The organic pollutants include tetracycline, rhodamine B, and bisphenol A.

5. A catalyst for degrading organic pollutants, characterized in that: The invention is prepared by the method according to any one of claims 1 to 4.

6. Use of the catalyst according to claim 5 in degrading organic pollutants, characterized in that: The method for degrading organic pollutants using the catalyst comprises the following steps: dispersing the catalyst in wastewater containing organic pollutants at a concentration of 0.2 to 1.5 g / L, adjusting the pH to 3.0 to 9.0, adding 0.5 to 5 mmol / L of peroxymonosulfate (PMS) or peroxydisulfate (PDS), and reacting at 20 to 50° C. for 10 to 120 minutes to achieve efficient degradation of the organic pollutants.

7. Use of the catalyst according to claim 6 in degrading organic pollutants, characterized in that: The catalyst can be reused 10 times or more, and the catalytic activity of the catalyst can still be maintained at more than 95% of the initial catalytic performance.

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