MOF (Metal Organic Framework) modified zeolite fluorine removal agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of fluorine-containing wastewater treatment, and discloses an MOF modified zeolite fluorine removal agent and a preparation method and application thereof, and the preparation method comprises the following steps: carrying out carboxylation or roasting pretreatment on natural zeolite; preparing an MOF precursor; the MOF precursor is prepared from at least two rare earth metal ions of La < 3 + >, Ce < 3 + > or Zr < 4 + > and an organic ligand; adding the MOF precursor into a DMF (Dimethyl Formamide) solvent, then adding the pretreated natural zeolite, and carrying out ultrasonic treatment for 5-10 minutes; adding the obtained mixed solution into a high-pressure reaction kettle, and reacting at 160 DEG C for 24 hours; after the high-pressure reaction kettle is naturally cooled, a mixed solution in the high-pressure reaction kettle is centrifuged, precipitates are washed 3-5 times with DMF, then drying is conducted for 18-24 h at the temperature of 65-90 DEG C, and finally the MOF modified zeolite fluorine removal agent is obtained. The fluorine removal agent disclosed by the invention has larger pore volume and specific surface area and good fluorine removal effect.

Description

Technical Field

[0001] The invention relates to the technical field of fluorine-containing wastewater treatment, and in particular to a MOF-modified zeolite defluorinating agent and a preparation method and application thereof. Background Art

[0002] In the natural environment, fluorine is relatively widely distributed, and the natural fluorine content in groundwater in some areas is relatively high. In the process of industrial production, industries such as new energy, batteries, semiconductors and new pesticides will produce fluorine-containing waste or waste liquid, which is also an important source of fluorine pollution. An appropriate amount of fluorine promotes the formation of teeth and bones, but excessive intake may damage human health. Long-term drinking of high-fluoride water can lead to fluorosis, and in severe cases, bone deformation, pain, joint stiffness, tendon calcification, difficulty walking, and even paralysis may occur. Therefore, it is particularly important to effectively remove excess fluoride in the water.

[0003] At present, the methods for treating fluoride-containing wastewater mainly include adsorption, electrocoagulation, reverse osmosis, ion exchange, chemical precipitation and coagulation sedimentation, etc. Each method has its own advantages and disadvantages. The ion exchange method removes fluoride ions by using materials such as ion exchange resins, but its selectivity is relatively low, the regeneration process is complicated and the cost is high, so it is limited in practical applications. The reverse osmosis method can effectively remove fluoride ions, but this method requires high operating pressure and equipment investment, and the operating cost is also high, which is not suitable for large-scale application. Chemical precipitation and coagulation sedimentation methods are prone to produce a large amount of residual sludge, causing secondary pollution. The adsorption method has the advantages of low cost, simple design, easy operation and high removal efficiency. It is a well-studied and widely used fluoride ion removal technology, and has broad application prospects in the problem of fluoride pollution.

[0004] Zeolite is an aluminum silicate mineral with a skeleton-like crystal structure and a large number of holes and channels inside the crystal, which gives it a large specific surface area and a rich pore structure, providing basic support for its adsorption performance. Due to the diverse connection methods of silicon (aluminum) oxygen tetrahedrons, zeolite exhibits characteristics such as adsorption separation, ion exchange and catalysis. Natural zeolite is a commonly used adsorbent. Although natural zeolite itself has a certain degree of fluoride removal ability, its fluoride removal effect is not ideal due to its surface properties and structural limitations, and the adsorption capacity and selectivity for fluoride ions still need to be improved.

[0005] The surface properties, pore structure and chemical composition of zeolite can be changed by modification, thus improving the defluorination performance of zeolite materials. However, the adsorption capacity of existing modified zeolites for defluorination is relatively low and cannot meet the increasingly stringent requirements for the treatment of fluoride-containing wastewater. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a MOF-modified zeolite defluorinating agent and a preparation method and application thereof, so as to achieve the purpose of making the modified zeolite have a larger pore volume and specific surface area and improving the defluorinating effect of the modified zeolite.

[0007] To achieve the above object, the technical solution of the present invention is as follows: A method for preparing a MOF-modified zeolite defluorinating agent comprises the following steps: Step 1, pre-treating the natural zeolite by carboxylation or calcination; Step 2, preparing a MOF precursor; the MOF precursor is La 3+ 、Ce 3+ or Zr 4+ At least two rare earth metal ions and organic ligands are prepared; Step 3, adding the pretreated natural zeolite and MOF precursor into DMF solvent and ultrasonically treating for 5-10 min; Step 4, adding the obtained mixed solution into a high-pressure reactor and reacting at 160° C. for 24 h; after the high-pressure reactor is naturally cooled, the mixed solution in the high-pressure reactor is centrifuged, and the precipitate is washed with DMF for 3 to 5 times, and then dried at 65 to 90° C. for 18 to 24 h, and finally a MOF-modified zeolite defluorinator is obtained.

[0008] In the above scheme, in step 1, the process of carboxylating the natural zeolite is as follows: (1) Place natural zeolite powder in a beaker, add hydrochloric acid solution at a solid-liquid ratio of 1:10, and then place the beaker in a shaker and shake continuously at room temperature for 12 h; (2) Filter the zeolite sample and wash it with distilled water until it is neutral, then heat it in a muffle furnace at 350-400 °C for 3-6 h; (3) adding the treated zeolite sample and succinic anhydride in a mass ratio of 1 to 1.5:3 into a mixed solution of 3-aminopropyltriethoxysilane and DMF in a volume ratio of 1:6 to 8; (4) The resulting mixed solution was ultrasonically treated for 30 min and then stirred with a stirrer for 24 h. It was then filtered, washed with ethanol several times and dried to obtain a carboxylated natural zeolite.

[0009] In the above scheme, in step 1, the process of calcining the natural zeolite is as follows: placing the natural zeolite powder in a muffle furnace and heating it at 400° C. for 5 h to obtain the calcined natural zeolite.

[0010] In the above scheme, in step 2, the organic ligand is 2-aminoterephthalic acid or terephthalic acid.

[0011] In the above scheme, in step 2, La 3+ 、Ce 3+ or Zr 4+ The molar ratio of the total amount of any two rare earth metal ions to the organic ligand is 2~4:1~4.

[0012] In the above scheme, in step 2, La 3+ 、Ce 3+ 、Zr 4+ The molar ratio to the organic ligand is 1~2:1:1:2~5.

[0013] In the above scheme, in step 3, the mass ratio of the pretreated natural zeolite, MOF precursor and DMF solvent is 1:1~5:60~80.

[0014] A MOF-modified zeolite defluorinating agent prepared by the preparation method as described above.

[0015] An application of the MOF modified zeolite defluorinating agent as described above in the treatment of fluoride-containing wastewater.

[0016] In a further technical solution, the application comprises the following steps: (S1) adjusting the pH of fluoride-containing wastewater to 3.5-6.5; (S2) adding a MOF-modified zeolite defluorinating agent to the fluorine-containing wastewater, wherein 1.5 to 3 g of the MOF-modified zeolite defluorinating agent is added to every 1 L of the fluorine-containing wastewater; (S3) Stir for 15-40 min; (S4) After standing and settling for 2 to 5 minutes, filter.

[0017] Through the above technical scheme, the MOF modified zeolite defluorinating agent provided by the present invention and its preparation method and application have the following beneficial effects: 1. In the present invention, a MOF-modified zeolite defluoridation agent was successfully prepared by screening specific components and optimizing the distribution ratio of each component. When the defluoridation agent is used to treat low-concentration fluoride-containing wastewater (fluoride ion concentration ≤ 15 mg / L), the fluoride ion removal rate can be as high as 90% or more under the condition of pH 3.5-6.5 and stirred for 15 to 40 minutes, showing good defluoridation performance; 2. When the MOF modified zeolite defluoridation agent of the present invention comes into contact with fluoride-containing wastewater, the surface of the modified zeolite will simultaneously start the two reaction mechanisms of adsorption and ion exchange. Specifically, the fluoride ions in the wastewater can not only adhere to the surface of the modified zeolite, but also react with the OH groups on the surface of the modified zeolite. -Ions are exchanged with each other. It is by virtue of the synergistic effect of adsorption and ion exchange that the fluoride ions are efficiently removed, which greatly improves the treatment efficiency of fluoride-containing wastewater and provides an effective solution for the purification of fluoride-containing wastewater. 3. The MOF-modified zeolite defluoridation agent of the present invention has a stable crystal structure and good adsorption performance. After repeated use, the adsorption effect is still highly effective. The adsorbent will not produce irreversible structural changes after adsorbing fluoride ions. It has a stable pore structure and strong plasticity. 4. The mesh porous structure of the MOF-modified zeolite defluoridant of the present invention and the complex active groups on its surface enable it to strongly adsorb fluoride ions. At the same time, its huge specific surface area provides sufficient adsorption sites for fluoride ions, thereby improving the removal effect of the adsorbent on fluoride ions; 5. The present invention composites the natural zeolite after carboxylation or calcination pretreatment with the MOF precursor. Compared with the natural zeolite without pretreatment, the surface of the carboxylated natural zeolite has abundant carboxylic acid groups, which is more conducive to its composite with the MOF precursor to form a more stable crystal structure; the surface of the calcined natural zeolite has a richer pore structure, thereby increasing the specific surface area of ​​the composite material and improving the defluorination performance of the MOF modified zeolite; 6. The MOF-modified zeolite defluoridation agent prepared by the present invention introduces bimetallic or multimetallic MOF precursors to utilize the synergistic effect between metals. The presence of multiple metals can provide more active sites and reaction pathways for the reaction, improve the reaction efficiency, and enhance the adsorption capacity for fluoride ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0019] Figure 1 This is the FTIR spectrum of the MOF-modified zeolite defluorinating agent prepared in Example 1 of the present invention.

[0020] Figure 2 This is a SEM image of the MOF-modified zeolite defluorinating agent prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] Embodiment 1: This embodiment provides a method for preparing a MOF-modified zeolite defluorinating agent, comprising the following steps: (1) Take natural zeolite powder with a particle size of 200 mesh and put it into a beaker. Add a 4% hydrochloric acid solution at a solid-liquid ratio of 1:10. Then place the beaker in a shaker and shake it continuously at room temperature for 12 hours. (2) The zeolite sample was filtered and washed with deionized water until neutral, and then heated in a muffle furnace at 380 °C for 6 h. (3) adding the treated zeolite sample and succinic anhydride in a mass ratio of 1:3 to a mixed solution of APTES (3-aminopropyltriethoxysilane) and DMF in a volume ratio of 1:7; (4) subjecting the mixed solution obtained in step (3) to ultrasonic treatment for 30 min, and then stirring with a stirrer for 24 h, and then filtering, washing with ethanol several times and drying to obtain a carboxylated natural zeolite; (5) Cerium nitrate hexahydrate, zirconium nitrate pentahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1:2 were added to DMF as MOF precursors and ultrasonically treated for 5 min; (6) adding the carboxylated natural zeolite to the solution obtained in step (5) in a mass ratio of MOF precursor, carboxylated natural zeolite and DMF solvent of 1:1:60; (7) The mixed turbid liquid obtained in step (6) was transferred to a polytetrafluoroethylene-lined autoclave and reacted at 160 °C for 24 h; (8) After the autoclave was cooled naturally, the mixed liquid in the autoclave was centrifuged and washed with DMF four times, and then dried at 70 °C for 24 h to finally obtain the MOF-modified zeolite defluorinating agent.

[0023] like Figure 1 As shown in the figure, the FTIR spectrum of the MOF modified zeolite defluorinator prepared in this embodiment shows the asymmetric internal TO stretching vibration of the TO4 tetrahedron (T=Si or Al) of the zeolite framework structure and the stretching vibration of -COOH, as well as the characteristic peaks of Ce-O and Zr-O bonds and the C=C skeleton stretching vibration of the benzene ring. Figure 2 As shown, it can be observed by SEM electron microscopy that the surface of the MOF-modified zeolite defluorinating agent prepared in this example has abundant wrinkles and microporous structures. This morphological structure increases the possibility of contact between the adsorbent and fluoride, making it more potential for defluorination.

[0024] Embodiment 2: Compared with Example 1, in step (5), lanthanum nitrate hexahydrate, cerium nitrate hexahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1:1 are added to DMF as MOF precursors, and the other steps are the same as those in Example 1.

[0025] Embodiment 3: Compared with Example 1, in step (5), lanthanum nitrate hexahydrate, zirconium nitrate pentahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1:2 are added to DMF as MOF precursors, and the other steps are the same as those in Example 1.

[0026] Embodiment 4: Compared with Example 1, in step (5), lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, zirconium nitrate pentahydrate and 2-aminoterephthalic acid in a molar ratio of 2:1:1:4 are added to DMF as MOF precursors, and the other steps are the same as those in Example 1.

[0027] Embodiment 5: This embodiment provides a method for preparing a MOF-modified zeolite defluorinating agent, comprising the following steps: (1) placing natural zeolite powder with a particle size of 200 mesh in a muffle furnace and heating it at 400 °C for 5 h to obtain calcined natural zeolite; (2) Lanthanum nitrate hexahydrate, cerium nitrate hexahydrate and terephthalic acid in a molar ratio of 1:1:1 were added to DMF as MOF precursors and ultrasonically treated for 5 min; (3) adding the calcined natural zeolite powder to the solution obtained in step (2) in a mass ratio of MOF precursor, calcined natural zeolite powder and DMF solvent of 1:1:60; (4) transferring the mixed turbid liquid obtained in step (3) into a polytetrafluoroethylene-lined autoclave and reacting at 160° C. for 24 h; (5) After the reactor was cooled naturally, the mixed liquid in the reactor was centrifuged and washed with DMF four times, and then dried at 70 °C for 24 h to finally obtain the MOF-modified zeolite defluorinating agent.

[0028] Comparative Example 1: Compared with Example 1, in step (5), aluminum nitrate nonahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1 are added to DMF as MOF precursors, and the other steps are the same as those in Example 1.

[0029] Comparative Example 2: Compared with Example 1, in step (5), lanthanum nitrate hexahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1 are added to DMF as MOF precursors, and the other steps are the same as those in Example 1.

[0030] Comparative Example 3: Compared with Example 1, in step (5), lanthanum nitrate hexahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1 are added to DMF as MOF precursors, and the other steps are the same as those in Example 1.

[0031] Comparative Example 4: Compared with Example 5, in step (3), the calcined natural zeolite powder is added to the solution obtained in step (2) in a mass ratio of MOF precursor, calcined natural zeolite powder and DMF solvent of 9:1:300, and the heating temperature in step (4) is 120°C. The other steps are the same as those in Example 5.

[0032] Sodium fluoride solution was prepared with deionized water as the fluoride-containing water to be treated, the fluoride ion concentration C0 was 15 mg / L, and the pH was adjusted to 4 with dilute hydrochloric acid. 1 L of the fluoride-containing water to be treated was added to a beaker, and then 2 g of the defluoridation agent prepared in the embodiment of the present invention and the comparative example was added to the beaker, stirred for 20 min, and then allowed to settle for 2 min. The supernatant was filtered and the fluoride ion concentration C1 after treatment was detected by a PXSJ-216F ion meter, and the defluorination rate η=(C0-C1) / C0 was calculated. The results are shown in Table 1.

[0033] Table 1 Fluoride ion concentration C1 and fluoride removal rate η after treatment

[0034] As shown in Table 1, the MOF-modified zeolite defluoridants prepared in Examples 1 to 5 according to the technical scheme provided by the present invention have good defluoridation effects, and can reduce the fluoride ion concentration to below 1 mg / L, meeting the fluoride-containing wastewater discharge standard. However, the defluoridation effects of the defluoridants prepared in Comparative Examples 1-4 are obviously inferior to those of Examples 1-5 of the present invention.

[0035] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a MOF-modified zeolite defluorinating agent, characterized in that: The steps include: Step 1, pre-treating the natural zeolite by carboxylation or calcination; Step 2, preparing a MOF precursor; the MOF precursor is La 3+ 、Ce 3+ or Zr 4+ At least two rare earth metal ions and organic ligands are prepared; Step 3, adding the MOF precursor to DMF solvent, ultrasonically treating for 5 to 10 min, and then adding the pretreated natural zeolite thereto; Step 4, adding the obtained mixed solution into a high-pressure reactor and reacting at 160° C. for 24 h; after the high-pressure reactor is naturally cooled, the mixed solution in the high-pressure reactor is centrifuged, and the precipitate is washed with DMF for 3 to 5 times, and then dried at 65 to 90° C. for 18 to 24 h, and finally a MOF-modified zeolite defluorinator is obtained.

2. The method for preparing a MOF-modified zeolite defluorinating agent according to claim 1, characterized in that: In step 1, the process of carboxylating natural zeolite is as follows: (1) Place natural zeolite powder in a beaker, add hydrochloric acid solution at a solid-liquid ratio of 1:10, and then place the beaker in a shaker and shake continuously at room temperature for 12 h; (2) Filter the zeolite sample and wash it with distilled water until it is neutral, then heat it in a muffle furnace at 350-400 °C for 3-6 h; (3) adding the treated zeolite sample and succinic anhydride in a mass ratio of 1 to 1.5:3 into a mixed solution of 3-aminopropyltriethoxysilane and DMF in a volume ratio of 1:6 to 8; (4) The resulting mixed solution was ultrasonically treated for 30 min and then stirred with a stirrer for 24 h. It was then filtered, washed with ethanol several times and dried to obtain a carboxylated natural zeolite.

3. The method for preparing a MOF-modified zeolite defluorinating agent according to claim 1, characterized in that: In step 1, the process of calcining the natural zeolite is as follows: placing the natural zeolite powder in a muffle furnace and heating it at 400° C. for 5 h to obtain the calcined natural zeolite.

4. The method for preparing a MOF-modified zeolite defluorinating agent according to claim 1, characterized in that: In step 2, the organic ligand is 2-aminoterephthalic acid or terephthalic acid.

5. The method for preparing a MOF-modified zeolite defluorinating agent according to claim 1, characterized in that: In step 2, La 3+ 、Ce 3+ or Zr 4+ The molar ratio of the total amount of any two rare earth metal ions to the organic ligand is 2~4:1~4.

6. The method for preparing a MOF-modified zeolite defluorinating agent according to claim 1, characterized in that: In step 2, La 3+ 、Ce 3+ 、Zr 4+ The molar ratio to the organic ligand is 1~2:1:1:2~5.

7. The method for preparing a MOF-modified zeolite defluorinating agent according to claim 1, characterized in that: In step 3, the mass ratio of the pretreated natural zeolite, the MOF precursor and the DMF solvent is 1:1~5:60~80.

8. A MOF-modified zeolite defluorinating agent obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the MOF-modified zeolite defluorinating agent as claimed in claim 8 in the treatment of fluorine-containing wastewater.

10. The use according to claim 9, characterized in that: The steps include: (S1) adjusting the pH of fluoride-containing wastewater to 3.5-6.5; (S2) adding a MOF-modified zeolite defluorinating agent to the fluorine-containing wastewater, wherein 1.5 to 3 g of the MOF-modified zeolite defluorinating agent is added to every 1 L of the fluorine-containing wastewater; (S3) Stir for 15-40 min; (S4) After standing and settling for 2 to 5 minutes, filter.

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