A dopamine in-situ growth ZIF-8 dye / salt separation loose nanofiltration membrane and a preparation method thereof
By anchoring ZIF-8 particles to dopamine-polyethyleneimine covalent crosslinking and growing them in situ on the surface of polysulfone ultrafiltration membranes, the problems of insufficient selectivity and stability of nanofiltration membranes were solved, and a high-performance loose nanofiltration membrane for dye/salt separation was prepared, which improved the dye desalination effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV OF TECH
- Filing Date
- 2023-09-05
- Publication Date
- 2026-05-29
AI Technical Summary
Existing nanofiltration membranes suffer from poor selectivity and insufficient stability during dye desalination. In particular, MOF materials tend to agglomerate on the membrane surface and have weak interaction with the substrate, leading to easy detachment during operation.
A loose nanofiltration membrane was prepared by in-situ growth of ZIF-8 anchored by dopamine-polyethyleneimine covalent crosslinking. ZIF-8 particles were uniformly dispersed on the surface of the polysulfone ultrafiltration membrane to form nanopores by utilizing the Schiff base and Michael addition reaction of PDA with PEI and the complexation reaction of PEI with zinc ions.
It achieves highly selective and stable dye desalination performance, improves membrane flux and separation ratio, and has a simple process and easy operation.
Smart Images
Figure CN117018867B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of filter membranes, specifically to a loose nanofiltration membrane for dye / salt separation with dopamine in situ grown ZIF-8 and its preparation method. Background Technology
[0002] With increasingly stringent environmental policies in my country and the growing acceptance of sustainable development, the treatment of high-salt dye wastewater is no longer limited to mere removal. Effective separation of "waste" and the conversion of dyes and salts in wastewater into recyclable resources are currently key research areas in wastewater treatment. The addition of inorganic salts makes conventional treatment methods such as flocculation, oxidation, adsorption, and degradation more difficult. Membrane separation technology, due to its advantages of low energy consumption, high efficiency, and simple operation, is widely used in the separation field. For dye desalination, while ultrafiltration has a large flux, it suffers from low rejection rates and poor selectivity for both dyes and salts. Nanofiltration, as a membrane technology, can effectively separate small molecules in solution under low pressure. It has a higher removal rate for low molecular weight organic matter than ultrafiltration and higher permeability than reverse osmosis, leading to its widespread application. However, to achieve high rejection performance, traditional nanofiltration membranes are designed with dense selective layers, resulting in high rejection rates for dyes and salts, but still unsatisfactory selectivity for both. Therefore, developing a loose nanofiltration membrane with high selectivity and high throughput suitable for dye / salt separation is of great practical significance.
[0003] Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials with intramolecular pores, formed by the self-assembly of organic ligands and metal ions or clusters through coordination bonds. Zinc-imidazolium frameworks (ZIFs), as a type of MOF, possess characteristics such as large specific surface area, high porosity, and tunable pore size, and are widely used in gas adsorption, separation, catalysis, and drug delivery. Currently, an increasing number of researchers are combining ZIFs with polymer membrane materials to prepare high-performance membranes. Based on the high porosity of ZIFs, additional permeate channels are created, hoping to overcome the trade-off between retention and permeate flux. However, due to the tendency of MOF materials to aggregate on the membrane surface and their weak interaction with the substrate, they are prone to detachment during operation, which affects the selectivity and stability of the membrane. Therefore, developing high-selectivity and high-stability high-performance MOF membrane materials faces significant challenges. Summary of the Invention
[0004] To address the above problems, this invention provides a loose nanofiltration membrane for dye / salt separation with in-situ growth of ZIF-8 using dopamine and its preparation method. The loose nanofiltration membrane for dye desalination is prepared by covalently crosslinking and anchoring in-situ grown ZIF-8 with dopamine-polyethyleneimine. Through this method, ZIF-8 particles are formed in-situ on the membrane surface. The ZIF-8 particles are uniformly dispersed and anchored on the polysulfone ultrafiltration membrane surface through the self-polymerization of dopamine (PDA) and its Schiff base and Michael addition reactions with polyethyleneimine (PEI) molecules, as well as the complexation reaction of PEI with zinc ions. Nanopores are formed through the stacking of ZIF particles. The prepared dye desalination membrane exhibits high dye flux and retention, excellent stability, high separation ratio, and simple process characteristics.
[0005] A loose nanofiltration membrane for dye / salt separation with in-situ growth of ZIF-8 by dopamine and its preparation method. The loose nanofiltration membrane is divided into a polymer support layer and a functional layer. Polysulfone is the polymer support layer, and PDA-PEI-ZIFs, which are ZIFs grown in situ after co-deposition of dopamine (PDA), polyethyleneimine (PEI), and zinc ions, is the functional layer.
[0006] The polymer support layer is composed of a nonwoven or textile material made of one or more polymers such as polyester, polyolefin, polytetrafluoroethylene, polyvinylidene fluoride, nylon, polysulfone, polyethersulfone, and polyacrylonitrile, with a thickness of 30-300 micrometers.
[0007] The polymer support layer includes a flat sheet membrane, a hollow fiber homogeneous membrane, or a hollow composite membrane and a tubular membrane;
[0008] The PDA-PEI-ZIFs functional layer is made by cross-linking dopamine, polyethyleneimine, and zinc ions, and then adding imidazole to grow ZIFs nanoparticles in situ. The prepared functional layer forms nanoscale channels through the accumulation of in-situ grown ZIFs nanoparticles. The membrane surface is uniform and has high porosity.
[0009] A loose nanofiltration membrane for dye / salt separation with dopamine in situ grown ZIF-8 and its preparation method includes the following steps;
[0010] 1) Dissolve tris(hydroxymethyl)aminomethane (Tris) in an alcohol / water mixture with a volume fraction of 0.1-50% v / v (preferably 10-30% v / v), then adjust the pH of the Tris solution to 8.5 with 0.1 mol / L HCl, and divide it into two equal portions for later use, which are designated as Tris buffer A and B respectively.
[0011] 2) The precursor solution is composed of PDA, PEI, and a metal ion compound added to solution A;
[0012] 3) Fix the support layer to the base plate with a square plate frame, and add the precursor solution from step 2) onto the support layer pressed on the base plate frame and let it stand and deposit for a period of time.
[0013] 4) Using solution B as a solvent, prepare a solution of imidazole ligands and add it to the precursor solution in the above plate frame, and deposit it at a certain temperature for a period of time.
[0014] 5) After pouring out the solution from the plate frame, put it in an oven to dry for a certain period of time, and then store it in deionized water.
[0015] The alcohol / aqueous solution used in step 1) includes one or more of the following: aqueous methanol solution, aqueous ethanol solution, aqueous propanol solution, aqueous butanol solution, aqueous ethylene glycol solution, glycerol solution, and aqueous isopropanol solution;
[0016] In step 1), the volume fraction of the alcohol-water solution is 0.1–50% v / v;
[0017] In step 2), the mass-to-volume ratio of the PDA is 0.01–2% wt / v;
[0018] In step 2), the mass-to-volume ratio of PEI is 0.01–2% wt / v;
[0019] In step 2), the mass-to-volume ratio of the metal ion compound is 0.01–3% wt / v;
[0020] The metal ion compound in step 2) includes one or more of zinc nitrate, zinc chloride, zinc sulfate, zinc acetate, cobalt nitrate, cobalt oxide, and cobalt acetate.
[0021] In step 3), the settling time is 0.01 to 6 hours;
[0022] In step 4), the imidazole ligands include one or more other compounds containing imidazoles, such as 2-methylimidazolium, benzimidazole, 2-aminobenzimidazole, 2-aminoimidazolium, imidazole-2-carboxaldehyde, and 2-ethylimidazolium.
[0023] In step 4), the mass-to-volume ratio of imidazole ligands is 0.01-10% wt / v; the reaction temperature is 2-90℃; and the reaction time is 0.1-24 hours.
[0024] The drying time in step 5) is 0.01 to 2 hours.
[0025] Furthermore, the technical solution of the present invention is carried out according to the following steps:
[0026] (1) Dissolve tris(hydroxymethyl)aminomethane (Tris) in an alcohol / water mixture with a volume fraction of 0.1-50% v / v (preferably 10-30% v / v), then adjust the pH of the Tris solution to 8.5 with 0.1 mol / L HCl, and divide it into two portions for later use, which are denoted as Tris buffer A and B respectively.
[0027] (2) The precursor solution is composed of PDA, PEI and metal ion compound added to solution A in sequence;
[0028] The solution contains PDA at a mass-to-volume ratio of 0.01-2% wt / v (preferably 0.1-1% wt / v), PEI at a mass-to-volume ratio of 0.01-2% wt / v (preferably 0.3-0.9% wt / v), and metal ion compounds at a mass-to-volume ratio of 0.01-3% wt / v.
[0029] (3) Using a polysulfone ultrafiltration membrane as a support layer, fix it on a base plate with a square frame, and cover the membrane surface with the above mixed solution for 0.01-6 hours (preferably 2-4 hours);
[0030] (4) Take Tris buffer B, prepare a solution of 2-methylimidazole with a mass-to-volume ratio of 0.01-10 wt / v, add it to the solution in the plate frame above, and react for 0.01-24 hours (preferably 4-10 hours).
[0031] (5) Pour out the supernatant in the plate frame, put the membrane in an oven at 20-90℃ (preferably 30-60℃) and dry for 0.01-2 hours (preferably 10-30 minutes), then store it in deionized water;
[0032] The alcohol-water mixed solution is one of methanol aqueous solution, ethanol aqueous solution, propanol aqueous solution, butanol aqueous solution, ethylene glycol aqueous solution, glycerol, and isopropanol aqueous solution (preferably methanol aqueous solution);
[0033] The metal ion compound is one of zinc nitrate, zinc chloride, zinc acetate, zinc oxide, zinc sulfide, cobalt nitrate, cobalt oxide, and cobalt acetate (preferably zinc nitrate hexahydrate);
[0034] The loose nanofiltration membrane has ZIF nanoparticles uniformly covering the support layer on its surface. The loose nanofiltration membrane has a uniform and smooth surface and consists of a functional separation layer and a support layer. It is stored by immersion in deionized water.
[0035] The technical advantages of this invention are:
[0036] 1) The process is simple, the operation is straightforward, and the synthesis method and preparation conditions are easy;
[0037] 2) By using an alcohol-water mixture as a solvent, the surface tension between the precursor solution and the base film can be reduced, which to some extent solves the problems of nanoparticles being difficult to deposit and uneven deposition, making the film smoother.
[0038] 3) The coating has excellent chemical stability, which provides a good anchoring effect between the base film and the nanoparticles;
[0039] 4) The nanoscale pores generated by the accumulation of ZIFs particles are beneficial for obtaining excellent separation performance and selectivity at the same time. Attached Figure Description
[0040] Figure 1 This is a planar scanning electron microscope image of Example 13;
[0041] Figure 2 This is a cross-sectional scanning electron microscope image of Example 13;
[0042] Figure 3 This is a planar scanning electron microscope image of Comparative Example 1;
[0043] Figure 4 These are the infrared spectra of Comparative Example 1, Comparative Example 2, Example 3, Example 7, Example 11, and Example 15;
[0044] Figure 5 This is a flowchart of the fabrication process for the loose nanofiltration membrane. Detailed Implementation
[0045] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0046] In the examples, the preparation environment for all nanofiltration membranes was 30°C, humidity 40-45%, and atmospheric pressure.
[0047] The polysulfone ultrafiltration membrane support layer used in the examples was purchased from Hangzhou Water Treatment Center.
[0048] Comparative Example 1:
[0049] Unmodified commercial polysulfone ultrafiltration membrane support layer (Hangzhou Water Treatment Center)
[0050] Comparative Example 2:
[0051] Dissolve Tris in a 10% v / v methanol-water mixture, then adjust the pH of the Tris solution to 8.5 with 0.1 mol / L HCl before use. Divide the solution into two equal portions, labeled as solution A and solution B.
[0052] Dissolve 0.15g of PDA in solution A and denote it as solution C. Add 0.3g of PEI to solution C.
[0053] Using a polysulfone ultrafiltration membrane as a support layer, it is fixed on a base plate with a square plate frame. The above solution is added to the support layer pressed on the base plate by the plate frame and deposited for 2 hours. Then, solution B is poured in and the deposition reaction is carried out for 10 hours.
[0054] After deposition, the solution in the plate frame was poured out and dried in an oven at 60°C for 20 minutes. Then it was stored in deionized water to obtain a ZIF-free PDA-PEI membrane.
[0055] Comparative Example 3:
[0056] Commercial nanofiltration membrane NF-270 (Dow nanofiltration membrane)
[0057] Example 1:
[0058] The specific steps for preparing a loose nanofiltration membrane material for ZIF-8 dye / salt separation coated with PDA-PEI anchoring are as follows:
[0059] Dissolve Tris in a 10% v / v methanol-water mixture, then adjust the pH of the Tris solution to 8.5 with 0.1 mol / L HCl before use. Divide the solution into two equal portions, labeled as solution A and solution B.
[0060] Dissolve 0.15g of PDA in solution A and label it solution C. Then add 0.15g of PEI to solution C and label it solution D.
[0061] Take 0.475g of zinc nitrate hexahydrate and dissolve it in the above solution D, then record it as solution E;
[0062] The mass-to-volume ratio of dopamine in solution E is 0.3% wt / v;
[0063] The mass-to-volume ratio of polyethyleneimine in solution E is 0.3% wt / v;
[0064] The mass-to-volume ratio of the metal ion compound in solution E is 0.95% wt / v.
[0065] Using a polysulfone ultrafiltration membrane (Hangzhou Water Treatment Center) as the support layer, it was fixed to the base plate with a square plate frame. The above-mentioned E solution was added to the support layer pressed on the base plate and deposited for 2 hours.
[0066] Using solution B as solvent, 1.97 g of 2-methylimidazole was prepared into a solution named solution F, and added to solution E in the above plate frame. The mixture was allowed to fully deposit and react at 30°C for 10 hours.
[0067] The mass-to-volume ratio of 2-methylimidazole in solution F is 3.94% wt / v.
[0068] After deposition, the solution in the plate frame is poured out and dried for 20 minutes before being stored in deionized water.
[0069] Examples 2-6
[0070] Examples 2-6 follow the same method as Example 1, except for the preparation of the Tris buffer solution. Tris is dissolved in a methanol-water mixture with volume fractions of 5 v / v%, 10 v / v%, 15 v / v%, 20 v / v%, and 30 v / v%, respectively. The pH of the Tris solution is then adjusted to 8.5 with 0.1 mol / L HCl before use.
[0071] Examples 7-10
[0072] Examples 7-10 follow the same method as Example 1, except that the mass of PEI added is 0.3g, 0.45g, 0.6g, and 1.0g, respectively. By changing the amount of PEI added, the degree of crosslinking with PDA and the complexation reaction with zinc ions are controlled, thereby regulating the performance of the membrane.
[0073] Examples 11-13
[0074] Examples 11-13 are the same as those in Example 1, except that the amount of PDA added is 0.3g, 0.45g, and 0.6g, and the amount of PEI added is 0.3g. By changing the amount of PDA added, the addition reaction and self-polymerization of PDA with PEI are affected, thereby controlling the performance of the membrane.
[0075] Examples 14-15
[0076] Examples 14-15 follow the same method as Example 1, except that the amount of PEI added is 0.3g, and the mass of zinc nitrate hexahydrate added is 0.2375g and 0.7125g, respectively, with corresponding mass amounts of dimethylimidazole added of 0.985g and 2.955g. By maintaining a molar ratio of zinc nitrate hexahydrate to dimethylimidazole of 1:15, the amount of zinc ions added is varied to control the loading of ZIF-8 on the membrane, thereby regulating membrane performance.
[0077] like Figure 1 As shown, the ZIF-8 particles on the membrane surface have a cross-shaped morphology, and the pores formed by the accumulation of particles can be seen.
[0078] like Figure 2 As shown, this indicates that ZIF-8 particles formed a deposited layer on the membrane surface.
[0079] like Figure 3 As shown, the surface of the unmodified ultrafiltration membrane is smooth and has obvious pores.
[0080] like Figure 4As shown, 1640cm appears in Examples 7, 11, and 15. -1 996cm -1 430cm -1 The characteristic peaks of ZIF-8 particles prove that ZIF particles have been successfully introduced onto the membrane surface.
[0081] Test example:
[0082] The dye desalination loose nanofiltration membranes prepared in Examples 3, 7, 13, and Comparative Examples 1 and 2 were tested using a cross-flow filtration device at room temperature and a pressure of 2 bar. The test results are shown in Table 1. In the table, R(Na2SO4), R(CR), and R(MB) represent the rejection rates of sodium sulfate, Congo red, and methylene blue, respectively; PWP, S(Na2SO4 / CR), and S(Na2SO4 / MB) represent the pure water flux, the permeation separation ratio of sodium sulfate to Congo red, and the permeation separation ratio of sodium sulfate to methylene blue, respectively. The permeation separation ratio is s.
[0083] Table 1
[0084]
[0085] As can be seen from the data in the table above, compared with the absence of ZIF-8 nanoparticles, the addition of ZIF-8 nanoparticles significantly improves the throughput while maintaining high rejection for dyes and low rejection for sodium sulfate. It has excellent performance and can be applied to dye / salt separation systems.
[0086] Please note to all technical personnel: Although the present invention has been described according to the specific embodiments above, the inventive concept of the present invention is not limited to this invention. Any modifications that utilize the inventive concept will be included within the protection scope of the present invention.
Claims
1. A method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8, characterized in that, Includes the following steps; 1) Dissolve tris(hydroxymethyl)aminomethane in a 0.1-50% (v / v) alcohol / water mixture, then adjust the pH of the solution to 8-9 with HCl, and divide it into two portions, labeled Tris buffer A and Tris buffer B respectively. 2) The precursor solution is prepared by adding dopamine, polyethyleneimine, and metal ion compounds to Tris buffer A; 3) Fix the polymer support layer onto the base plate with a square plate frame, and add the precursor solution from step 2) onto the polymer support layer pressed onto the base plate by the plate frame and allow it to settle. 4) Prepare a mixed solution of imidazole ligands with Tris buffer B as solvent, and add the mixed solution to the plate frame after step 3) standing and depositing the precursor solution. After post-processing, obtain the dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8. The dopamine-grown ZIF-8 dye / salt separation loose nanofiltration membrane includes a polymer support layer and a PDA-PEI-ZIFs functional layer disposed on the polymer support layer. The PDA-PEI-ZIFs functional layer is a functional layer in which ZIFs are grown in situ after co-deposition of dopamine, polyethyleneimine, and zinc ions.
2. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, The polymer support layer is a nonwoven or textile material composed of one or more of polyester, polyolefin, polytetrafluoroethylene, polyvinylidene fluoride, nylon, polysulfone, polyethersulfone, and polyacrylonitrile, and the thickness of the polymer support layer is 30-300 micrometers.
3. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, In step 2), the metal ion compound is one or more of zinc nitrate, zinc chloride, zinc sulfate, and zinc acetate.
4. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, In step 2), the mass-to-volume ratio of dopamine in the precursor solution is 0.01~2% wt / v; The mass-to-volume ratio of polyethyleneimine in the precursor solution is 0.01–2% wt / v; The mass-to-volume ratio of the metal ion compound in the precursor solution is 0.01–3% wt / v.
5. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, In step 3), the settling time is 0.01 to 6 hours.
6. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, In step 4), the imidazole ligand is one or more of 2-methylimidazole, benzimidazole, 2-aminobenzimidazole, 2-aminoimidazole, imidazole-2-carboxaldehyde, and 2-ethylimidazole.
7. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, In step 4), the mass-to-volume ratio of imidazole ligands in the mixed solution is 0.01-10% wt / v.
8. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, In step 4), the deposition reaction conditions are: reaction temperature 2–90 °C, reaction time 0.1–24 hours.
9. The method for preparing a dye / salt separation loose nanofiltration membrane with dopamine in situ grown ZIF-8 according to claim 1, characterized in that, In step 4), the post-processing includes: pouring out the solution from the plate frame after the deposition reaction, then drying it in an oven, and finally storing it in deionized water.