A positively charged mixed matrix membrane doped with etched zinc oxide nanoparticles and a method of making the same
By preparing porous zinc oxide nanoparticles through alkaline etching and doping them into a polyamide layer, the problem of low permeability of traditional positively charged nanofiltration membranes was solved, achieving high permeability and high selectivity for heavy metal ion retention, and reducing preparation costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- EAST CHINA UNIV OF SCI & TECH
- Filing Date
- 2023-11-28
- Publication Date
- 2026-06-19
AI Technical Summary
Traditional positively charged nanofiltration membranes have low permeability, making it difficult to simultaneously improve permeability and selectivity. Existing methods are costly and produce toxic byproducts.
Zinc oxide nanoparticles were prepared into a porous structure using an alkaline etching method and then doped into a polyamide layer. A novel positively charged hybrid matrix film with doped and etched zinc oxide nanoparticles was prepared by interfacial polymerization.
It significantly improves membrane permeability and heavy metal ion rejection performance, reduces costs, and maintains high selectivity.
Smart Images
Figure CN117654304B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of membrane separation technology, specifically relating to a novel positively charged hybrid matrix membrane doped with etched zinc oxide nanoparticles and its preparation method. Background Technology
[0002] Heavy metal ions originate from various natural and anthropogenic sources, such as mining, metallurgy, electroplating, leather tanning, textiles, papermaking, and the pesticide industry. These ions can have various adverse effects on human health and ecosystems. Therefore, developing effective and economical methods for removing heavy metal ions from wastewater is crucial. Conventional treatment methods include chemical precipitation, oxidation, ion exchange, and electrodialysis. However, these methods have some drawbacks, such as high cost, low selectivity, and the generation of toxic sludge or byproducts. Therefore, alternative methods based on membrane technology have been explored in recent years. Membrane technology has shown great potential in the removal of heavy metal ions because it offers a wide range of membrane properties and separation mechanisms.
[0003] Traditional non-metallic fluid (NF) membranes are a type of thin-film composite (TFC) membrane, consisting of a thin selective layer of polyamide (PA) on a porous support layer. However, TFC membranes typically have negatively charged surfaces, which limits their repulsion performance for heavy metal ions. To achieve better separation performance, two aspects are usually explored: particle size sieving and the Donnan effect. The radius of the hydrated cations of heavy metal ions is... However, nanofiltration membranes have a pore size range of 0.5 nm to 2 nm, making particle size separation an ineffective method for separating heavy metal ions. Therefore, the Donnan effect plays a crucial role, and developing positively charged nanofiltration membranes is an important way to improve water treatment efficiency and selectivity. Polyethyleneimine (PEI) is a hydrophilic cationic polyelectrolyte and the preferred amine monomer for producing positively charged nanofiltration (NF) membranes. However, PEI / TMC membranes have relatively weak treatment capabilities for heavy metal ion wastewater due to their denser selective layer, resulting in lower membrane permeability.
[0004] A persistent "trade-off" effect exists between permeability and selectivity, meaning that it is difficult to simultaneously improve selectivity for macromolecules and permeability to water. Therefore, numerous studies have incorporated porous materials such as molecular sieves, metal-organic frameworks, covalent organic frameworks, and graphene into polymers to prepare hybrid matrix membranes (MMMs), aiming to enhance membrane separation performance. The particle size of the dopant particles significantly impacts the performance of MMMs. Smaller dopant particles can increase the specific surface area of the MMM, thereby improving permeability and selectivity. Furthermore, the morphology of the filling particles also affects the performance of the MMM. Therefore, this invention employs alkaline etching to etch zinc oxide nanoparticles into a porous structure and dope them into a polyamide layer. By providing water channels within the pores of the nanoparticles or around the hydrophilic surface, the trade-off between permeability and selectivity is overcome, significantly improving the permeability and heavy metal ion retention of the TFN membrane, resulting in a novel positively charged MMM with doped and etched zinc oxide nanoparticles. Summary of the Invention
[0005] To address the problem of low permeability in traditional positively charged nanofiltration membranes, this invention provides a novel membrane preparation method. The novel positively charged hybrid matrix membrane with doped and etched zinc oxide nanoparticles prepared by this method can effectively improve the membrane flux and the retention performance of heavy metal ions.
[0006] The technical solution of this invention is as follows:
[0007] A method for preparing a positively charged hybrid matrix film doped with etched zinc oxide nanoparticles, the specific steps of which are as follows:
[0008] (1) Preparation of etched zinc oxide nanoparticles: Zinc oxide nanoparticles were added to an Erlenmeyer flask containing deionized water and ultrasonically dispersed to ensure uniform particle dispersion. KOH was then added, and the flask was quickly transferred to a water bath for heating. The white solid was then washed with deionized water by centrifugation. Finally, it was dried overnight in a vacuum oven to obtain powder.
[0009] (2) Aqueous coating of the membrane: The aqueous solution is poured onto the surface of the base membrane and excess water is blown away by an air knife to obtain a first-stage surface-treated membrane.
[0010] (3) Interfacial polymerization of the membrane: The oil phase solution is poured onto the surface of the primary surface-treated membrane to carry out an interfacial polymerization reaction, thereby obtaining a secondary surface-treated membrane.
[0011] (4) Heat treatment of the film: The secondary surface-treated film is placed in an oven for heat treatment, and the interfacial polymerization is further enhanced to increase the degree of crosslinking, so as to obtain a positively charged mixed matrix film doped with etched zinc oxide nanoparticles.
[0012] Furthermore, in step (1), the molar concentration of KOH used for etching is 0.05-0.2M, preferably 0.1M, the water bath temperature is 25-85℃, preferably 85℃, and the water bath time is 0.5-2h, preferably 1h.
[0013] Furthermore, the zinc oxide used in step (1) has a particle size of 30-50 nm.
[0014] Furthermore, the bottom membrane needs to be soaked in deionized water for 12 hours before use.
[0015] Furthermore, the aqueous solution comprises 10-20 ml, preferably 10 ml of a polyethyleneimine solution with a mass concentration of 0.05-0.2 wt.%, preferably 0.1 wt%, and 0.005-0.02 wt.%, preferably 0.01 wt%, of etched zinc oxide nanoparticles, with the remainder being deionized water.
[0016] Furthermore, the oil phase solution contains 10-20 ml, preferably 10 ml of a molar concentration of 0.05-0.1 wt.%, preferably 0.1 wt% of trimesoyl chloride, and the remainder is n-hexane.
[0017] Furthermore, in step (2), the aqueous solution is poured onto the surface of the bottom film and left to stand for 1 to 2 minutes, preferably 2 minutes.
[0018] Further, in step (3), the oil phase solution is poured onto the surface of the primary surface treatment film and left to stand for 10 to 30 seconds, preferably 30 seconds, after which the excess oil phase solution is poured off.
[0019] Furthermore, in step (4), the heat treatment temperature is 60-80℃, preferably 60℃, and the heat treatment time is 2-5min, preferably 5min.
[0020] Furthermore, the positively charged mixed matrix film doped with etched zinc oxide nanoparticles described in step (4) needs to be soaked in deionized water for 12 hours before testing.
[0021] Furthermore, the aqueous solution needs to be ultrasonically treated for 1 hour to ensure that the particles are fully dispersed.
[0022] Furthermore, the substrate membrane is a polysulfone ultrafiltration membrane.
[0023] Based on the same inventive concept, this invention also protects a novel positively charged mixed matrix membrane of doped and etched zinc oxide nanoparticles prepared by the above-mentioned method for preparing a positively charged mixed matrix membrane of doped and etched zinc oxide nanoparticles. The novel positively charged mixed matrix membrane of doped and etched zinc oxide nanoparticles is used in heavy metal ion removal experiments of 1000ppm CuSO4, ZnSO4 and NiSO4 solutions. Under the test pressure of 4 bar, its flux is 8 L h-1m-2bar-1 and the heavy metal ion rejection rate is 95% to 96%.
[0024] The inventive step of this invention is step (1). Conventional nanoparticle fillers such as alumina and titanium dioxide are nanoparticles without obvious pore structure. This invention transforms nanoparticles into a porous structure by alkaline etching and adds them to the polyamide layer to improve the hydrophilicity and positive charge of the membrane, thereby improving the flux and heavy metal ion rejection rate of the mixed matrix membrane.
[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows:
[0026] (1) This invention uses polysulfone ultrafiltration membrane as substrate, polyethyleneimine (PEI) and etched zinc oxide nanoparticles as aqueous monomers, and trimesoyl chloride (TMC) as oil solution to prepare a novel positively charged mixed matrix membrane doped with etched zinc oxide nanoparticles by interfacial polymerization method, which effectively improves water flux and heavy metal ion rejection performance under optimal loading.
[0027] (2) Polyethyleneimine (PEI) is a hydrophilic cationic polyelectrolyte monomer used to manufacture positively charged NF membranes. In this invention, porous zinc oxide nanoparticles are prepared by wet alkaline etching, and a novel positively charged hybrid matrix membrane doped with etched zinc oxide nanoparticles is prepared by interfacial polymerization, which further improves the positive charge and hydrophilicity of the membrane.
[0028] (3) The preparation method of the present invention is simple and low in cost, which can improve the specific surface area and porosity of zinc oxide nanoparticles that originally had no obvious structure, as well as the flux of the membrane and the heavy metal ion retention performance. Attached Figure Description
[0029] Figure 1 This is a scanning electron microscope image of the etched zinc oxide nanoparticles in Example 3;
[0030] Figure 2 This is a scanning electron microscope (SEM) image (surface view) of the novel positively charged hybrid matrix film doped with etched zinc oxide nanoparticles in Example 3.
[0031] Figure 3 This is a scanning electron microscope (SEM) image (cross-sectional view) of the novel positively charged hybrid matrix film doped with etched zinc oxide nanoparticles in Example 3. Detailed Implementation
[0032] The following provides a specific embodiment of the method for preparing a novel positively charged hybrid matrix film doped with etched zinc oxide nanoparticles according to the present invention.
[0033] Example 1
[0034] A novel method for preparing a positively charged hybrid matrix film doped with etched zinc oxide nanoparticles includes the following steps:
[0035] (1) Use polysulfone ultrafiltration membrane as the base membrane, soak it in deionized water for 12 hours, and then use it after drying until there are no obvious water droplets on the surface.
[0036] (2) Prepare an aqueous solution and an oil solution containing etching nanoparticles with a particle size of 30 nm. The aqueous solution contains 10 ml of polyethyleneimine solution with a mass concentration of 0.1 wt% and 0.005 wt% of 30-50 nm etching zinc oxide nanoparticles, with the remainder being deionized water. The oil solution contains 10 ml of trimesoyl chloride with a molar concentration of 0.1 wt%, with the remainder being n-hexane.
[0037] (3) Pour the aqueous solution onto the surface of the bottom film, let it stand for 2 minutes, and then remove excess water by air knife to obtain a first surface treatment film. Fix the film in a square polytetrafluoroethylene frame.
[0038] (4) Pour the oil phase solution onto the surface of the primary surface treatment film, let it stand for 30 seconds to carry out the interfacial polymerization reaction, remove the oil phase solution, and obtain the secondary surface treatment film.
[0039] (5) Place the secondary surface treatment film in an oven for heat treatment at a temperature of 60°C. O C, heating time of 5 min, further interfacial polymerization to enhance crosslinking degree, to obtain a novel positively charged hybrid matrix film doped with etched zinc oxide nanoparticles.
[0040] (6) The novel positively charged hybrid matrix film with doped and etched zinc oxide nanoparticles obtained in step (5) was immersed in deionized water and a heavy metal ion rejection test was performed.
[0041] Example 2
[0042] A novel method for preparing a positively charged hybrid matrix film doped with etched zinc oxide nanoparticles includes the following steps:
[0043] (1) Use polysulfone ultrafiltration membrane as the base membrane, soak it in deionized water for 12 hours, and then use it after drying until there are no obvious water droplets on the surface.
[0044] (2) Prepare an aqueous solution and an oil solution containing etching nanoparticles with a particle size of 30 nm. The aqueous solution contains 10 ml of polyethyleneimine solution with a mass concentration of 0.1 wt% and 0.01 wt% of 30-50 nm etching zinc oxide nanoparticles, with the remainder being deionized water. The oil solution contains 10 ml of trimesoyl chloride with a molar concentration of 0.1 wt%, with the remainder being n-hexane.
[0045] (3) Pour the aqueous solution onto the surface of the bottom film, let it stand for 2 minutes, and then remove excess water by air knife to obtain a first surface treatment film. Fix the film in a square polytetrafluoroethylene frame.
[0046] (4) Pour the oil phase solution onto the surface of the primary surface treatment film, let it stand for 30 seconds to carry out the interfacial polymerization reaction, remove the oil phase solution, and obtain the secondary surface treatment film.
[0047] (5) Place the secondary surface treatment film in an oven for heat treatment at a temperature of 60°C. O C, heating time of 5 min, further interfacial polymerization to enhance crosslinking degree, to obtain a novel positively charged hybrid matrix film doped with etched zinc oxide nanoparticles.
[0048] (6) The novel positively charged hybrid matrix film with doped and etched zinc oxide nanoparticles obtained in step (5) was immersed in deionized water and a heavy metal ion rejection test was performed.
[0049] Example 3
[0050] A novel method for preparing a positively charged hybrid matrix film doped with etched zinc oxide nanoparticles includes the following steps:
[0051] (1) Use polysulfone ultrafiltration membrane as the base membrane, soak it in deionized water for 12 hours, and then use it after drying until there are no obvious water droplets on the surface.
[0052] (2) Prepare an aqueous solution and an oil solution containing etching nanoparticles with a particle size of 30 nm. The aqueous solution contains 10 ml of polyethyleneimine solution with a mass concentration of 0.1 wt% and 0.015 wt% of 30-50 nm etching zinc oxide nanoparticles, with the remainder being deionized water. The oil solution contains 10 ml of trimesoyl chloride with a molar concentration of 0.1 wt%, with the remainder being n-hexane.
[0053] (3) Pour the aqueous solution onto the surface of the bottom film, let it stand for 2 minutes, and then remove excess water by air knife to obtain a first surface treatment film. Fix the film in a square polytetrafluoroethylene frame.
[0054] (4) Pour the oil phase solution onto the surface of the primary surface treatment film, let it stand for 30 seconds to carry out the interfacial polymerization reaction, remove the oil phase solution, and obtain the secondary surface treatment film.
[0055] (5) Place the secondary surface treatment film in an oven for heat treatment at a temperature of 60°C. O C, heating time of 5 min, further interfacial polymerization to enhance crosslinking degree, to obtain a novel positively charged hybrid matrix film doped with etched zinc oxide nanoparticles.
[0056] (6) The novel positively charged hybrid matrix film with doped and etched zinc oxide nanoparticles obtained in step (5) was immersed in deionized water and a heavy metal ion rejection test was performed.
[0057] Example 4
[0058] A novel method for preparing a positively charged hybrid matrix film doped with etched zinc oxide nanoparticles includes the following steps:
[0059] (1) Use polysulfone ultrafiltration membrane as the base membrane, soak it in deionized water for 12 hours, and then use it after drying until there are no obvious water droplets on the surface.
[0060] (2) Prepare an aqueous solution and an oil solution containing etching nanoparticles with a particle size of 30 nm. The aqueous solution contains 10 ml of polyethyleneimine solution with a mass concentration of 0.1 wt% and 0.02 wt% of 30-50 nm etching zinc oxide nanoparticles, with the remainder being deionized water. The oil solution contains 10 ml of trimesoyl chloride with a molar concentration of 0.1 wt%, with the remainder being n-hexane.
[0061] (3) Pour the aqueous solution onto the surface of the bottom film, let it stand for 2 minutes, and then remove excess water by air knife to obtain a first surface treatment film. Fix the film in a square polytetrafluoroethylene frame.
[0062] (4) Pour the oil phase solution onto the surface of the primary surface treatment film, let it stand for 30 seconds to carry out the interfacial polymerization reaction, remove the oil phase solution, and obtain the secondary surface treatment film.
[0063] (5) Place the secondary surface treatment film in an oven for heat treatment at a temperature of 60°C. O C, heating time of 5 min, further interfacial polymerization to enhance crosslinking degree, to obtain a novel positively charged hybrid matrix film doped with etched zinc oxide nanoparticles.
[0064] (6) The novel positively charged hybrid matrix film with doped and etched zinc oxide nanoparticles obtained in step (5) was immersed in deionized water and a heavy metal ion rejection test was performed.
[0065] Comparative Example 1
[0066] The difference between Comparative Example 1 and Example 1 above is that some operations in step 2 are omitted, that is, no etching zinc oxide nanoparticles are added to the aqueous solution.
[0067] The heavy metal ion retention performance of the novel positively charged hybrid matrix films doped with etched zinc oxide nanoparticles prepared in Examples 1-4 and Comparative Example 1 was tested, and the performance indicators are shown in Table 1.
[0068] Table 1. Performance indicators of novel positively charged hybrid matrix films doped with etched zinc oxide nanoparticles prepared in Examples 1-4 and Comparative Example 1
[0069]
[0070] The above tests show that the novel positively charged hybrid matrix film with doped and etched zinc oxide nanoparticles prepared in this invention has a rejection rate of over 95% for divalent heavy metal ions under the optimal loading, proving that the hybrid matrix film of this invention has a high rejection rate for divalent heavy metal ions.
[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit it. It should be noted that those skilled in the art can make modifications to the foregoing embodiments without departing from the concept of the present invention, and these modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing a positively charged mixed matrix membrane doped with etched zinc oxide nanoparticles, characterized in that, Includes the following steps: (1) Preparation of etched zinc oxide nanoparticles: Zinc oxide nanoparticles were added to a conical flask containing deionized water and ultrasonically dispersed to make the particles uniform; then KOH was added and the mixture was heated in a water bath; after that, the white powder was washed by centrifugation with deionized water; and dried overnight in a vacuum oven to obtain powder. (2) Aqueous phase coating of the membrane: Pour the aqueous solution onto the surface of the substrate membrane and blow away the excess water with an air knife to obtain a first-stage surface-treated membrane; (3) Interfacial polymerization of the membrane: The oil phase solution is poured onto the surface of the primary surface-treated membrane to carry out the interfacial polymerization reaction and obtain the secondary surface-treated membrane; (4) Heat treatment of the film: The secondary surface-treated film is placed in an oven for heat treatment, and the interfacial polymerization is further enhanced to increase the degree of crosslinking, so as to obtain a positively charged mixed matrix film doped with etched zinc oxide nanoparticles. In step (1), the KOH molar concentration used for etching is 0.05 ~ 0.2 M, the water bath temperature is 25 ~ 85℃, and the water bath time is 0.5 ~ 2 h; The aqueous solution contains 10-20 ml of a polyethyleneimine solution with a mass concentration of 0.05-0.2 wt.% and 0.005-0.02 wt.% of etched zinc oxide nanoparticles, with the remainder being deionized water; The oil phase solution contains 10 to 20 mL of pyromellitic trimethylol chloride with a mass concentration of 0.05 to 0.1 wt.%, and the remainder is n-hexane.
2. The method according to claim 1, wherein the method for preparing a positively charged mixed matrix membrane doped with etched zinc oxide nanoparticles is characterized by: The zinc oxide nanoparticles have a particle size of 30-50 nm.
3. The method according to claim 1, wherein the method is characterized by: In step (2), the aqueous solution is poured onto the surface of the bottom film and left to stand for 1 to 2 minutes.
4. The method of claim 1, wherein the method is characterized by: In step (3), the oil phase solution is poured onto the surface of the primary surface treatment film, and after standing for 10-30 seconds, the excess oil phase solution is poured off.
5. The method of claim 1, wherein the method is characterized by: In step (4), the heat treatment temperature is 60 ~ 80 ℃ and the heat treatment time is 2 ~ 5 min.
6. The method according to any one of claims 1-5, wherein the method is characterized by: The positively charged hybrid matrix membrane doped with etched zinc oxide nanoparticles was used in experiments to remove heavy metal ions from 1000 ppm CuSO4, ZnSO4, and NiSO4 solutions. Under a test pressure of 4 bar, its flux was 8 L / h. -1 m -2 bar -1 The rejection rate for heavy metal ions is 95% to 96%.
7. The application of a positively charged hybrid matrix film of doped and etched zinc oxide nanoparticles prepared by the preparation method according to any one of claims 1-6 in the field of heavy metal ion removal.