Material for removing organic pollutants in water, preparation method of material and method for treating water

Abstract

The invention discloses a material for removing organic pollutants in water, a preparation method of the material and a method for treating water. The water treatment material is prepared by organically combining a precursor and an active catalytic component and optimizing and modifying the precursor and the active catalytic component, the preparation method comprises the following steps: pretreating a precursor metal organic framework, etching surface active sites by acid, doping sulfur to improve charge / spin redistribution of a carbon skeleton to regulate and control a coordination environment, and optimizing a material structure by optimizing a coordination structure and material morphology of the treated precursor through thermal derivation. The prepared material is cross-linked and doped to construct an active filter membrane; the method for treating water comprises the steps of heterogeneous activation persulfate water treatment as a catalyst, and coupling filtration and persulfate oxidation as a catalytic filter membrane for water treatment. The material for removing the organic pollutants in the water and the method for treating the water, disclosed by the invention, are excellent in performance and efficient in treatment, integrate various effects of adsorption, catalysis, membrane filtration and the like, and are suitable for water purification treatment.

Description

Technical Field

[0001] The invention relates to a water treatment material and a preparation method thereof and a method for treating water, and in particular to a material for removing organic pollutants in water and a preparation method thereof and a method for treating water, belonging to the field of water treatment materials and methods. Background Art

[0002] Organic pollutants are widely present in various water bodies and can be introduced into the water environment through various pathways such as wastewater discharge, sewer leakage / overflow and field runoff. Organic pollutants have varying degrees of toxicity, threatening the safety of aquatic ecosystems. Accumulation in the human body will also cause the occurrence of various acute and chronic diseases, affecting human health, and pollution control is becoming increasingly urgent. Persulfate advanced oxidation is considered to be an effective technology for degrading organic pollutants in water. Some methods have been used to activate persulfate, such as by directly applying additional energy (light, heat, ultrasound, radiation), transition metal ions, metal materials, and non-metallic materials (carbon-based, boron-based). Compared with metal materials, carbon-based materials are often safer and more environmentally friendly, but conventional carbon-based materials encounter a series of problems in practical applications, such as limited mass transfer, surface contamination, poor stability, and easy aggregation.

[0003] Metal-organic frameworks may be used as precursors for the preparation of high-performance carbon-based materials, which have the advantages of high porosity, high metal dispersion and controllable pore size. The generation of efficient active sites and the optimization of their coordination environment are the keys to improving their catalytic performance, such as the regulation of coordination number, the introduction of heteroatoms as coordinating atoms, and the synergistic effect of different catalytic sites. However, how to select suitable heteroatom doping to perturb the electronic structure to control the generation of free radicals requires further research breakthroughs. In addition, in the traditional persulfate oxygen advanced oxidation water treatment system, the mass transfer efficiency of the reactants is low, the recovery of the catalyst after use is difficult, and the effectiveness and economy of water treatment need to be further improved. Summary of the invention

[0004] Purpose of the invention: In order to solve the problems existing in the prior art, the first purpose of the present invention is to provide a material for removing organic pollutants in water that has efficient adsorption, catalysis and separation properties. The second purpose of the present invention is to provide a method for preparing the material for removing organic pollutants in water. The third purpose of the present invention is to provide a catalytic filter membrane prepared using the material for removing organic pollutants in water. The fourth purpose of the present invention is to provide a method for removing organic pollutants in water using the material for removing organic pollutants in water or the catalytic filter membrane, which solves the problems of low system treatment efficiency, relatively single material applicability, and inability to recycle and reuse materials after use in the prior art.

[0005] Technical solution: The material for removing organic pollutants in water described in the present invention includes a precursor and an active catalytic component. The precursor is an acid-etched metal organic framework material, and the active catalytic component is a carbonized material that is formed by high-temperature pyrolysis under inert gas conditions after sulfur coordination atoms doped on the precursor form thiophene groups.

[0006] Furthermore, the metal organic framework material is a cobalt-based zeolite imidazolate framework structure material.

[0007] Furthermore, the metal organic framework material is ZIF-67.

[0008] Further, the acid etching uses one of acid xylenol orange, gallic acid or tannic acid.

[0009] Furthermore, the method for preparing the cobalt-based zeolite imidazolate framework structure material comprises the following steps:

[0010] Dissolve 2-methylimidazole in methanol to obtain solution A, add cobalt nitrate hexahydrate into methanol, stir until completely dissolved to obtain solution B, pour solution A into solution B, stir vigorously, age at room temperature, wash several times by centrifugation with methanol, and dry in vacuum to obtain the solution.

[0011] Furthermore, the mass ratio of the 2-methylimidazole to the cobalt nitrate hexahydrate is 1:1 to 2:1.

[0012] Furthermore, the concentration of 2-methylimidazole in solution A is 80-100 mg / mL.

[0013] Furthermore, the concentration of cobalt nitrate hexahydrate in solution B is 20-30 mg / mL.

[0014] Furthermore, the vigorous stirring time is 10-20 minutes.

[0015] Furthermore, the aging time is more than 24 hours.

[0016] Furthermore, the vacuum drying temperature is 60-70° C., and the vacuum drying time is 10-24 hours.

[0017] Furthermore, the washing is performed more than 3 times.

[0018] Further, the preparation of the acid-etched metal organic framework material comprises the following steps:

[0019] The cobalt-based zeolite imidazolate framework structure material is ultrasonically treated, poured into an acid solution, stirred, washed with deionized water and anhydrous ethanol for multiple times, collected by centrifugation to obtain powder, and vacuum dried to obtain an acid-etched precursor material.

[0020] Furthermore, the solid-liquid ratio of the cobalt-based zeolite imidazolate framework structure material to the acid solution is 1:1 to 3:1 mg / mL.

[0021] Furthermore, the concentration of the acid solution is 3 to 8 mg / mL.

[0022] Furthermore, the stirring time is 30-60 min.

[0023] Furthermore, washing multiple times means washing 5 times or more.

[0024] Furthermore, the vacuum drying temperature is 60-70° C., and the vacuum drying time is 10-24 h.

[0025] The method for preparing the material for removing organic pollutants in water according to the present invention comprises the following steps:

[0026] (1) Coordination environment regulation: the precursor acid-etched metal organic framework material is mixed with thiourea, stirred, the product is collected by centrifugation, washed with methanol for multiple times, and vacuum dried to obtain sulfur-doped powder;

[0027] (2) Active site construction and material structure optimization: The sulfur-doped powder obtained in step (1) is pyrolyzed, cooled, and ground in a continuously flowing inert gas atmosphere.

[0028] Furthermore, in step (1), the mass ratio of thiourea to the acid-etched metal organic framework material is 1:1 to 1:2.

[0029] Furthermore, in step (1), the stirring time is 12 to 24 hours.

[0030] Furthermore, in step (1), washing multiple times is washing more than 3 times.

[0031] Furthermore, in step (1), the vacuum drying temperature is 60-70° C., and the vacuum drying time is 10-24 h.

[0032] Furthermore, in step (1), the inert gas is argon, nitrogen or helium.

[0033] Furthermore, in step (2), the heating rate of the pyrolysis is 2 to 5°C / min, the pyrolysis temperature is 700 to 900°C, and the pyrolysis time is 3 to 6 hours.

[0034] A catalytic filter membrane comprises the material for removing organic pollutants in water of the present invention, polyvinylidene fluoride (PVDF) and polyvinyl pyrrolidone (PVP) as raw materials, which are coupled in the membrane, coated on a glass plate, and immersed in a mixture of water and ethanol to undergo phase change to form a catalytic filter membrane.

[0035] Furthermore, the method includes dispersing the material for removing organic pollutants in water of the present invention into a dimethylacetamide solution (DMAc), ultrasonicating, adding PVDF and PVP, stirring in a water bath to obtain a solution, applying the solution on a glass plate with a scraper, and then immersing the solution in a mixture of water and ethanol to perform phase change to form a catalytic filter membrane.

[0036] Furthermore, the weight ratio of DMAc, PVDF and PVP is 82:15:3 to 84:15:1.

[0037] Furthermore, the material for removing organic pollutants in water according to the present invention is 1 to 7 wt % of the weight of PVDF.

[0038] Furthermore, the ultrasonic treatment time is 1 to 3 hours.

[0039] Furthermore, the stirring temperature in the water bath is 60-70° C., and the stirring time in the water bath is 6-12 h.

[0040] Furthermore, the thickness of the catalytic filter membrane is 200-600 μm.

[0041] Furthermore, the phase change solution is a mixture of water and ethanol, and the weight ratio of the two is 1:1 to 1:4.

[0042] A method for removing organic pollutants from water, using the material for removing organic pollutants from water or the catalytic filter membrane of the present invention as a heterogeneous catalyst to perform persulfate activated water treatment.

[0043] Furthermore, persulfate and the material for removing organic pollutants in water of the present invention are added to the water to be treated, stirred, and after the water is purified, the material is recycled and reused by magnetic separation or filtration;

[0044] Alternatively, the water to be treated containing persulfate can be driven by pressure to penetrate through the catalytic filter membrane of the present invention.

[0045] The preparation process of the material for removing organic pollutants in water of the present invention includes the steps of in-situ generation of catalytic components, optimization of material structure, etc., wherein the catalytic component is a thiophene group derived from a cobalt-based zeolite imidazolate skeleton structure material, and the structure optimization is to derive the active sites and confined spaces of the coordination structure optimization through high-temperature pyrolysis, that is, by acid etching the surface active sites, doping sulfur to improve the charge / spin redistribution of the carbon skeleton to regulate the coordination environment, and then optimizing the material structure by thermal derivatization to optimize the coordination structure and material morphology of the treated precursor. The synthesis of the filter membrane is to further organically cross-link the material and form pores in situ to generate a highly active filter membrane.

[0046] The material for removing organic pollutants from water has excellent mechanical properties, large specific surface area and stability, simple synthesis of metal organic framework materials, metal and carbon properties, periodic replacement of metal ions and organic ligands to prevent the aggregation of metal / metal oxide nanostructures generated by pyrolysis; orderly structure, rich pore structure, convenient for highly dispersed heteroatom doping and modulation of the local electronic structure of the catalyst, expanding its application scope and improving degradation efficiency. The present invention constructs a functionalized metal organic framework material by acid etching, which selectively occurs at a specific position or crystal surface to form large mesopores or a desired morphology. A small amount of protons is provided, and its phenolic hydroxyl group can chelate metal ions and release protons to accelerate etching, thereby exposing more active sites, improving the adsorption performance of the material, promoting mass transfer of the reaction system, and enhancing the water treatment effect. The present invention introduces heteroatoms as coordinating atoms, and the introduction of S atoms in the carbon skeleton can improve the charge / spin redistribution of the carbon skeleton and form more catalytic centers. The S atoms synergistically promote highly selective and active Co centers, while the hollow structure is conducive to exposing unique cobalt sites and allowing rapid mass transfer near these sites. It is beneficial for materials to activate persulfate and synergistically decompose pollutants through free radical and non-free radical pathways, thereby improving the efficiency of water treatment.

[0047] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0048] (1) The present invention improves the activation performance of the prepared material for persulfate by optimizing appropriate precursor material selection, atomic doping, catalytic active sites and their coordination structures, thereby having excellent water treatment efficiency and significantly improving the removal rate of pollutants compared to unmodified materials.

[0049] (2) The water treatment material of the present invention has good magnetic properties and can be recovered by magnetic adsorption in a heterogeneous treatment system, thereby solving the problem of separation and recycling of the material after use and avoiding the risk of secondary pollution caused by leakage of the material in the treated water.

[0050] (3) The present invention couples membrane filtration and persulfate oxidation, and utilizes flow field drive to greatly enhance the mass transfer of the reaction system, thereby improving the reaction efficiency. The simultaneous use of adsorption, membrane retention and catalytic oxidation can effectively and synergistically remove organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a scanning electron microscope image of the water treatment material prepared in Example 1;

[0052] Figure 2 is the XRD diagram of the water treatment materials prepared in Example 1 and Comparative Examples 1-2;

[0053] Figure 3This is a diagram showing the effect of magnetic separation of the water treatment material prepared in Example 1;

[0054] Figure 4 This is a photo of the catalytic filter membrane of Example 2. DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0056] Example 1

[0057] (1) Preparation of the precursor MOF, namely ZIF-67: Dissolve 4 g of 2-methylimidazole in a beaker containing 40 mL of methanol to obtain solution A. Pour 120 mL of methanol into another 250 mL beaker, add 3.5 g of cobalt nitrate hexahydrate, and stir until it is completely dissolved to form a pink solution to obtain solution B. Pour solution A into solution B and stir vigorously for 10 min until the solution turns dark purple. The resulting suspension is aged at room temperature for 24 h. Finally, the purple product is collected by centrifugation (8000 rpm, 5 min), washed 3 times with methanol, and vacuum dried at 60 ° C for 12 h to obtain purple powder of ZIF-67.

[0058] (2) Preparation of etched and treated materials: First, 0.4 g of ZIF-67 purple powder was ultrasonicated for 5 min, poured into 200 mL (5 g / L) tannic acid solution, and stirred at room temperature for 30 min. The gray-brown product was collected by centrifugation (7000 r.p., 5 min). The gray-brown product was washed with deionized water and anhydrous ethanol for 5 times, and vacuum dried at 60°C for 12 h to obtain acid-etched ZIF-67 powder.

[0059] (3) 0.2 g of acid-etched ZIF-67 powder was added to a 100 mL beaker containing 20 mL of methanol, and 0.2 g of thiourea was added. The mixture was stirred at room temperature for 24 h, and the product was collected by centrifugation (7000 rpm, 5 min), washed three times with methanol, and dried under vacuum at 60 °C for 12 h.

[0060] (4) The powder finally obtained in step (3) is loaded into a porcelain ark and placed in a horizontal tube furnace for pyrolysis at 900°C for 3 hours with a continuous flow of argon gas. The heating rate is controlled at 5°C / min, and the obtained black powder solid is the required water treatment material Co-NC-S.

[0061] The water treatment material prepared in this example was subjected to electron microscope scanning analysis. The results are as follows: Figure 1 shown. Figure 1 This is a scanning electron microscope image of the water treatment material prepared in Example 1, which is a rhombic dodecahedron with a hollow structure.

[0062] (5) The water treatment material prepared in this example is used as a heterogeneous catalyst for the treatment of activated persulfate water. Specifically, 5 mg of the water treatment material prepared in this example is weighed and uniformly dispersed in 100 mL of an aqueous solution of lomefloxacin with a concentration of 20 mg / L, and a pre-adsorption experiment is performed in a constant temperature oscillator. After adsorption for 75 minutes, potassium persulfate is added to a concentration of 0.2 g / L. After the reaction is completed, samples are taken to determine the concentration of pollutants in the water, and the water treatment material is recovered by magnetic separation. The results are shown in Tables 1 and Figure 3 shown.

[0063] Comparative Example 1

[0064] The preparation process of the water treatment material is the same as that of Example 1, except that only the metal organic framework material ZIF-67 is used for carbonization, and no acid etching or sulfur doping is performed, that is, steps (2) and (3) in Example 1 are not performed, and only steps (1) and (4) are performed to obtain a water treatment material, that is, a material directly carbonized from ZIF-67 powder, which is recorded as Co-NC. Water treatment is performed according to step (5) in Example 1, and the results are shown in Table 1.

[0065] Comparative Example 2

[0066] The preparation process of the water treatment material is the same as that of Example 1, except that only the ZIF-67 material etched with tannic acid is used for carbonization, that is, step (3) in Example 1 is not performed, and steps (1), (2) and (4) are performed to obtain the water treatment material Co-NC-H. Water treatment is performed according to step (5) in Example 1, and the results are shown in Table 1.

[0067] Table 1 Heterogeneous system treatment methods and effects

[0068]

[0069]

[0070] As can be seen from Table 1, the lomefloxacin removal efficiency of the material in Example 1 is as high as 85%, which is 26% higher than that of the unmodified material (Comparative Example 1), and 9% higher than that of the material not doped with sulfur (Comparative Example 2), indicating that both the etching of tannic acid and sulfur doping optimize the material structure and promote the activation of persulfate and the degradation of organic pollutants.

[0071] XRD analysis was performed on the water treatment materials prepared in Example 1 and Comparative Examples 1-2. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the sample forms Co nanoparticles after carbonization in an inert atmosphere, and sulfur doping further optimizes its crystal structure.

[0072] Example 2

[0073] 34 mg of the water treatment material prepared in Example 1 was ultrasonically dispersed in 6.5 g of DMAc solution for 2 h, 1.2 g of PVDF and 80 mg of PVP were added to the above solution after ultrasonication, heated in a 60°C water bath with stirring for 6 h, coated on a glass plate with a 300 μm scraper, and then immersed in water / ethanol (the mass ratio of water to ethanol was 1:4) for phase change, and dried at 60°C for 12 h to obtain a catalytic filter membrane.

[0074] The catalytic filter membrane prepared in this example was used for activating persulfate water treatment, specifically: the prepared catalytic filter membrane was placed on a filtration device, and an adsorption saturation experiment was conducted in an aqueous solution containing 20 mg / L lomefloxacin. An aqueous solution containing 200 mg / L potassium persulfate and 20 mg / L lomefloxacin was pumped into the above catalytic filter membrane for a filtration water treatment experiment, and the pollutant concentration in the water after the filtration membrane was measured, and the removal rate was analyzed. The catalytic filter membrane photo is shown in FIG. Figure 4 The treatment methods and effects are shown in Table 2.

[0075] Table 2 Treatment methods and effects of membrane filtration system

[0076] Serial number Initial concentration of pollutants (mg / L) Pollutant removal rate (%) Example 2 ～20 ～98％

[0077] As can be seen from Table 2, the catalytic filter membrane exhibited a 98% removal rate for lomefloxacin, indicating that when the catalytic material is anchored in the membrane matrix and a reaction site is constructed on the membrane channel, the treatment system has an excellent removal performance for lomefloxacin.

Claims

1. A material for removing organic pollutants from water, characterized in that: The material comprises a precursor and an active catalytic component, wherein the precursor is an acid-etched metal organic framework material, and the active catalytic component is a carbonized material obtained by high-temperature pyrolysis under inert gas conditions after sulfur coordination atoms doped on the precursor form thiophene groups.

2. The material for removing organic pollutants in water according to claim 1, characterized in that: The metal organic framework material is a cobalt-based zeolite imidazolate framework material, and the acid etching uses one of acid xylenol orange, gallic acid or tannic acid.

3. The material for removing organic pollutants from water according to claim 2, characterized in that: The preparation of the acid-etched metal organic framework material includes the following steps: The cobalt-based zeolite imidazolate framework structure material is ultrasonically treated, poured into an acid solution, stirred, washed with deionized water and anhydrous ethanol for multiple times, collected by centrifugation to obtain powder, and vacuum dried to obtain an acid-etched precursor material.

4. The material for removing organic pollutants from water according to claim 3, characterized in that: The solid-liquid ratio of the cobalt-based zeolite imidazolate framework structure material to the acid solution is 1:1-3:1 mg / mL, the concentration of the acid solution is 3-8 mg / mL, the stirring time is 30-60 min, the washing multiple times is more than 5 times, the vacuum drying temperature is 60-70° C., and the vacuum drying time is 10-24 h.

5. The method for preparing the material for removing organic pollutants in water according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Coordination environment regulation: the precursor acid-etched metal organic framework material is mixed with thiourea, stirred, the product is collected by centrifugation, washed with methanol for multiple times, and vacuum dried to obtain sulfur-doped powder; (2) Active site construction and material structure optimization: The sulfur-doped powder obtained in step (1) is pyrolyzed, cooled, and ground in a continuously flowing inert gas atmosphere.

6. The preparation method according to claim 5, characterized in that: In step (1), the mass ratio of thiourea to acid-etched metal organic framework material is 1:1-1:2, the stirring time is 12-24 hours, the washing multiple times is more than 3 times, the vacuum drying temperature is 60-70°C, and the vacuum drying time is 10-24 hours.

7. The preparation method according to claim 5, characterized in that: In step (2), the heating rate of pyrolysis is 2-5°C / min, the pyrolysis temperature is 700-900°C, and the pyrolysis time is 3-6h.

8. A catalytic filter membrane, characterized in that: The method comprises using the material for removing organic pollutants in water as described in any one of items 1 to 4, polyvinylidene fluoride and polyvinyl pyrrolidone as raw materials, performing intra-membrane coupling, coating on a glass plate, and immersing in a mixture of water and ethanol to perform phase change to form a catalytic filter membrane.

9. A method for removing organic pollutants from water, characterized in that: The material for removing organic pollutants in water according to any one of items 1 to 4 or the catalytic filter membrane according to claim 8 is used as a heterogeneous catalyst for persulfate activated water treatment.

10. The method according to claim 9, characterized in that Adding persulfate and the material for removing organic pollutants in water described in any one of items 1 to 4 to the water to be treated, stirring and treating, and after the water is purified, using magnetic separation or filtration to recycle the material; Alternatively, the water to be treated containing persulfate is driven by pressure to penetrate through the catalytic filter membrane of claim 8.

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