Self-assembled COF membrane for treating ardealite leachate and preparation method of self-assembled COF membrane

Abstract

The invention belongs to the technical field of membrane separation treatment of ardealite leachate, and particularly relates to a self-assembled COF membrane for treating ardealite leachate and a preparation method of the self-assembled COF membrane. A beta-cyclodextrin aqueous solution is loaded on a base membrane to obtain a composite membrane with beta-cyclodextrin as an active layer, then TPB-DMTP-COF is grown and loaded on the composite membrane in situ, and the self-assembled COF membrane is constructed. The preparation method is simple and easy to operate, the prepared self-assembled COF membrane has a large specific surface area and good permeability, the characteristic of removing phosphate ions and multivalent ions in the ardealite leachate is reserved, and then removal of trace ions in the ardealite leachate and water softening are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane separation treatment of phosphogypsum leachate, and particularly relates to a self-assembled COF membrane for treating phosphogypsum leachate and a preparation method thereof. Background Art

[0002] Phosphogypsum leachate is a liquid formed during the storage process of phosphogypsum, which mainly comes from phosphogypsum, a by-product of the wet phosphoric acid production process. After phosphogypsum is produced, it is usually transported to a specific storage yard for storage, and the storage methods include wet stacking and dry stacking. The phosphogypsum leachate produced by the storage method is usually characterized by a high salt content, and contains a large amount of phosphorus and harmful substances such as heavy metal elements. If these harmful substances enter natural water bodies through leakage, they will pollute groundwater and surface water, and then pose a threat to the natural environment and the health of humans, animals and plants. According to statistics, the cumulative stockpile of waste residues in my country's phosphogypsum storage yards has exceeded 200 million tons, and the phosphogypsum leachate produced poses a serious threat to water quality safety.

[0003] Compared with physical methods, chemical precipitation methods and biological methods, membrane separation technology has been widely used in the treatment of phosphorus-containing wastewater due to its low energy consumption, high efficiency and environmental friendliness. When treating phosphogypsum leachate, the separation membrane is the core of membrane technology, and its performance is directly related to the effect and cost of the treatment process. Therefore, there is great potential for the development of high-performance separation membranes and their application in the treatment of phosphogypsum leachate to achieve water resource purification and phosphorus resource recovery. However, the design and preparation of high-performance membranes suitable for the treatment of phosphogypsum leachate is still insufficient. Summary of the invention

[0004] The purpose of the present invention is to provide a self-assembled COF membrane for treating phosphogypsum leachate and a preparation method thereof, which can effectively remove phosphorus elements and multivalent cations in the phosphogypsum leachate.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A self-assembled COF membrane for treating phosphogypsum leachate is obtained by the following preparation method: a β-cyclodextrin aqueous solution is loaded on a base membrane to obtain a composite membrane with β-cyclodextrin as an active layer, and then TPB-DMTP-COF is loaded on the composite membrane in situ to construct the self-assembled COF membrane.

[0007] The base film is a hydrophilic base film; for example, a polypropylene film or a hydrophilic polytetrafluoroethylene film may be selected.

[0008] The mass percentage concentration of the β-cyclodextrin aqueous solution is 0.02-0.1%.

[0009] The thickness of the obtained β-cyclodextrin active layer is 20-100 nm.

[0010] The in-situ growth time for constructing the self-assembled COF film is 6-24h, and the secondary growth time is 6-18h.

[0011] The TPB-DMTP-COF monomers are 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5-dimethoxyterephthalaldehyde (DMTA), and the molar ratio of TAPB:DMTA is 1:1-2:1.

[0012] During the preparation, TAPB is placed in 1,4-dioxane solvent with a mass fraction of 0.02-0.08 wt %; DMTA is placed in mesitylene solvent with a mass fraction of 0.02-0.08 wt %.

[0013] Specifically, the preparation method of the self-assembled COF membrane for treating phosphogypsum leachate comprises the following steps:

[0014] 1) Fixing the basement membrane in the membrane assembly, applying a β-cyclodextrin aqueous solution on the surface of the basement membrane to obtain a composite membrane;

[0015] 2) Dissolve DMTA in mesitylene solution and immerse the composite membrane for 6-12 hours; then dissolve TAPB in 1,4-dioxane solution and immerse the membrane for 6-12 hours;

[0016] 3) Repeat step 2) to add the two solutions to the membrane surface in sequence, and the reaction time of the two monomers is 6-18h respectively;

[0017] 4) After the reaction is completed, the film is dried to obtain a self-assembled COF film.

[0018] The method of the present invention uses β-cyclodextrin (β-CD) as an active layer to prepare a composite membrane, and then in-situ grows a COF (TPB-DMTP-COF) membrane on the β-cyclodextrin-based composite membrane to construct the self-assembled COF membrane.

[0019] The inner cavity of β-CD has a significant promoting effect on ion transfer and has the characteristics of selective screening. The hydrogen bonding formed by the polar substituents on β-CD and the oxygen or nitrogen atoms in the TPB-DMTP-COF skeleton can enhance the binding ability between the two and increase the permeability of water molecules; the microporous COF material used has sub-nanometer pores with a pore size of less than 2 nanometers.

[0020] In general, the cyclodextrin molecules with a hydrophilic outer surface and an inner cavity of the present invention are grown in situ on the hydrophilic COF, and at the same time, a transfer channel is constructed for ions. TPB-DMTP-COF has a large specific surface area, provides abundant adsorption sites, and helps to enhance ion selectivity. In addition, the two-dimensional COF membrane material has the advantages of a regular and orderly pore structure, a shorter molecular transmission path, and a tunable pore size. Therefore, the COF membrane prepared by the present invention has the potential to separate phosphate and multivalent ions in phosphogypsum leachate with high stability at high flux.

[0021] In the method for preparing the self-assembled COF membrane of the present invention, β-CD and COF monomers do not need to be pretreated, and the preparation method is simple. By adjusting the reaction conditions and improving the growth environment of the active layer to control the inner size of the COF pores and change the stacking mode of the sheets, the confined preparation of the self-assembled COF membrane and the precise control of the pore structure in the active layer are achieved, and microchannels are constructed to strengthen the selective separation of phosphate ions and multivalent ions, thereby solving the basic problems in the application of phosphogypsum wastewater treatment.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The preparation method of the present invention is simple and easy to operate. The prepared self-assembled COF membrane has a large specific surface area and good permeability, and retains the characteristics of removing phosphate ions and multivalent ions in phosphogypsum leachate, thereby achieving the removal of trace ions and water softening in the phosphogypsum leachate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a physical picture of the self-assembled COF film prepared in Example 4;

[0025] Figure 2 This is the surface morphology of the self-assembled COF film prepared in Example 4. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described below with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0027] Example 1

[0028] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0029] 1) Fixing the PAN base film in the membrane assembly, taking a 0.04 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0030] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.02 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.02 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0031] 3) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-1 film.

[0032] Example 2

[0033] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0034] 1) Fixing the PAN base film in the membrane assembly, taking a 0.04 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0035] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.02 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.02 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0036] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0037] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-2 film.

[0038] Example 3

[0039] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0040] 1) Fixing the PAN base film in the membrane assembly, taking a 0.04 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0041] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of 0.04 wt% DMTA was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, then 10 mL of 0.04 wt% TAPB was dispersed in a solution of 1,4-dioxane, the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0042] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0043] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-3 film.

[0044] Example 4

[0045] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0046] 1) Fixing the PAN base film in the membrane assembly, taking a 0.04 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0047] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.06 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.06 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0048] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0049] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-4 film.

[0050] Example 5

[0051] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0052] 1) Fixing the PAN base film in the membrane assembly, taking a 0.04 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0053] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.08 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.08 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0054] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0055] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-5 film.

[0056] Example 6

[0057] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0058] 1) Fixing the PAN base film in the membrane assembly, taking a 0.08 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0059] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.02 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.02 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0060] 3) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-6 film.

[0061] Example 7

[0062] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0063] 1) Fixing the PAN base film in the membrane assembly, taking a 0.08 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0064] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.02 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.02 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0065] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0066] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-7 film.

[0067] Example 8

[0068] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0069] 1) Fixing the PAN base film in the membrane assembly, taking a 0.08 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0070] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of 0.04 wt% DMTA was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, then 10 mL of 0.04 wt% TAPB was dispersed in a solution of 1,4-dioxane, the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0071] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0072] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-8 film.

[0073] Example 9

[0074] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0075] 1) Fixing the PAN base film in the membrane assembly, taking a 0.08 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0076] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.06 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.06 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0077] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0078] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-9 film.

[0079] Example 10

[0080] A self-assembled COF membrane for treating phosphogypsum leachate, the preparation method comprising the following steps:

[0081] 1) Fixing the PAN base film in the membrane assembly, taking a 0.08 wt% β-CD aqueous solution, and coating it on the surface of the base film to prepare a β-CD@PAN composite substrate;

[0082] 2) Using the in-situ growth technique, two monomers were added to the composite membrane surface in sequence: 10 mL of DMTA with a mass fraction of 0.08 wt% was dispersed in a solution of mesitylene, the solution was immersed on the membrane for 12 h, and then the DMTA-mesitylene solution on the membrane surface was removed, and then 10 mL of TAPB with a mass fraction of 0.08 wt% was dispersed in a solution of 1,4-dioxane, and the solution was immersed on the membrane for 12 h, and then the solution on the membrane was removed;

[0083] 3) Using the secondary in-situ growth technique, two monomers are added to the membrane surface in sequence according to step 2), and the reaction time of the two monomers is 12 hours respectively;

[0084] 4) After the reaction is completed, the film is placed in an oven at 80°C for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD@COF-10 film.

[0085] Comparative Example 1

[0086] Preparation of β-CD-1 nanofiltration membrane:

[0087] 1) Fix the PAN base membrane in the membrane assembly, take a 0.04wt% β-CD aqueous solution and apply it on the surface of the base membrane;

[0088] 2) After the reaction is completed, the film is placed in an oven at 80° C. for 10 min to obtain a self-assembled COF film, which is labeled as β-CD-1 film.

[0089] Comparative Example 2

[0090] Preparation of β-CD-2 nanofiltration membrane:

[0091] 1) Fix the PAN base membrane in the membrane assembly, take a 0.08 wt% β-CD aqueous solution, and apply it on the surface of the base membrane;

[0092] 2) After the reaction is completed, the film is placed in an oven at 80° C. for heat treatment for 10 min to obtain a self-assembled COF film, which is labeled as β-CD-2 film.

[0093] Table 1 shows the permeability of the self-assembled COF membranes of Examples 1-10 and the β-CD membranes prepared in Comparative Examples 1-2, as well as the retention rates of phosphate ions and multivalent ions in phosphogypsum leachate by nanofiltration membranes reported in the literature. The data errors are all within a reasonable error range.

[0094] The pH value of the phosphogypsum filtrate used in Table 1 is 10. If the phosphogypsum filtrate has other pH values, its pH value can be adjusted to 10 first, and then treated according to the method of the present invention, and the corresponding treatment effect can also be obtained.

[0095] Table 1

[0096]

[0097] It can be seen from the table that compared with the nanofiltration membrane reported in the literature and the comparative β-CD membrane, the β-CD@COF membrane of the present invention can effectively remove phosphorus and Ca in the phosphogypsum leachate. 2+ Mg 2+ 、Al 3+ The membrane has good permeability to these three divalent or trivalent ions. In addition, the secondary grown β-CD@COF membrane has better separation performance than the primary grown β-CD@COF membrane.

Claims

1. A method for preparing a self-assembled COF membrane for treating phosphogypsum leachate, characterized in that: A β-cyclodextrin aqueous solution is loaded on the base film to obtain a composite film with β-cyclodextrin as the active layer, and then TPB-DMTP-COF is in situ grown on the composite film to construct the self-assembled COF film.

2. The method for preparing a self-assembled COF membrane for treating phosphogypsum leachate according to claim 1, characterized in that: The mass percentage concentration of the β-cyclodextrin aqueous solution is 0.02-0.1%.

3. The method for preparing a self-assembled COF membrane for treating phosphogypsum leachate according to claim 1, characterized in that: The thickness of the obtained β-cyclodextrin active layer was 20-100 nm.

4. The method for preparing a self-assembled COF membrane for treating phosphogypsum leachate according to claim 1, characterized in that: The in situ growth time for constructing the self-assembled COF film is 6-24h.

5. The method for preparing a self-assembled COF membrane for treating phosphogypsum leachate according to claim 4, characterized in that: A self-assembled COF film was constructed for secondary growth, and the secondary growth time was 6-18h.

6. The method for preparing a self-assembled COF membrane for treating phosphogypsum leachate according to claim 1, characterized in that: The basement membrane is a hydrophilic basement membrane.

7. The method for preparing a self-assembled COF membrane for treating phosphogypsum leachate according to any one of claims 1 to 6, characterized in that: The TPB-DMTP-COF adopts monomers 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 2,5-dimethoxyterephthalaldehyde (DMTA), and the molar ratio of TAPB to DMTA is 1-2:

1.

8. The method for preparing a self-assembled COF membrane for treating phosphogypsum leachate according to claim 7, characterized in that: During the preparation, TAPB is placed in 1,4-dioxane solvent with a mass fraction of 0.02-0.08wt%, and DMTA is placed in mesitylene solvent with a mass fraction of 0.02-0.08wt%.

9. The method for preparing the self-assembled COF membrane for treating phosphogypsum leachate according to claim 1, characterized in that: Here are the steps: 1) Fix the basement membrane and apply the β-cyclodextrin aqueous solution on the surface of the basement membrane to obtain a composite membrane; 2) The composite membrane is immersed in a solution of DMTA dissolved in mesitylene for 6-12 hours; then, the membrane is immersed in a solution of TAPB dissolved in 1,4-dioxane for 6-12 hours; 3) Repeat step 2) to add the two solutions to the membrane surface in sequence, and the reaction time of the two monomers is 6-18h respectively; 4) After the reaction is completed, the film is dried to obtain a self-assembled COF film.

10. A self-assembled COF membrane for treating phosphogypsum leachate obtained by any preparation method according to any one of claims 1 to 9.

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