A horizontally oriented zif-l composite membrane and a method of making the same
By using PEI to regulate the horizontal orientation of ZIF-L crystals and employing an "in-situ seed growth + secondary growth" process, the problems of disordered ZIF-L membrane growth and insufficient hydrophilicity were solved, achieving high-performance alcohol-water separation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING TECH UNIV
- Filing Date
- 2025-05-13
- Publication Date
- 2026-06-19
AI Technical Summary
In the existing technology, the preparation of ZIF-L membranes suffers from disordered crystal growth, making it impossible to achieve directional horizontal growth, and the material lacks sufficient hydrophilicity, resulting in poor alcohol-water separation performance.
Polyethyleneimine (PEI) was used as a regulator to achieve horizontal orientation of ZIF-L crystals through multiple interactions with the surface of ZIF-L crystals. Combined with the "in-situ seed growth + secondary growth" process, a continuously oriented ZIF-L layer was formed.
The molecular sieving effect and hydrophilicity of the ZIF-L membrane were significantly improved, enhancing the alcohol-water separation performance. The pure water flux and separation factor were significantly increased, achieving high-performance alcohol-water separation.
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Abstract
Description
Technical Field
[0001] This invention relates to a high-performance membrane for alcohol-water separation, belonging to the field of separation membrane preparation technology. This modified membrane has high pure water flux and good ethanol separation effect, and is suitable for alcohol-water separation and other fields. Background Technology
[0002] Pervaporation membrane separation technology, as a novel membrane separation process, has demonstrated significant application value in the field of liquid mixture separation due to its advantages such as low energy consumption, environmental friendliness, and high separation efficiency. This technology achieves molecular-level separation through the selective permeation and vaporization of membrane materials, and is particularly suitable for systems that are difficult to handle using traditional distillation processes, such as azeotropics, near-boiling substances, and heat-sensitive materials.
[0003] In the field of alcohol-water separation, metal-organic frameworks (MOFs) have attracted much attention due to their tunable pore structure and surface properties. Among them, ZIF-L materials have the following characteristics: (1) unique two-dimensional leaf-like morphology and semi-SOD topology; (2) regular pore size of 3.4 Å, which is between the dynamic diameter of water molecules (2.68 Å) and ethanol molecules (4.5 Å), and can produce a precise molecular sieving effect; (3) the anisotropic structure provides a fast transport channel for water molecules.
[0004] However, the preparation of ZIF-L films in the prior art has the following technical bottlenecks: the crystal growth is disordered and uncontrollable, easily forming a disordered structure, and it is impossible to achieve directional horizontal growth; the material has insufficient hydrophilicity, affecting the water molecule transport efficiency. Studies have shown that the natural growth of ZIF-L crystals tends to be vertically oriented, which is because: (1) the growth rate of crystals in the vertical direction is significantly higher than that in the horizontal direction; (2) the aspect ratio of vertically oriented crystals is more conducive to reducing the surface energy of the system. This growth characteristic makes it difficult to obtain a horizontally oriented continuous ZIF-L separation layer by traditional methods. For example, the ZIF-L layer prepared in the prior art CN202310934028.1, although it satisfies the directional growth, has a vertical orientation, and the vertical ZIF-L has a poor sieving effect on ethanol and water. Because ZIF-L has a crystal structure similar to ZIF-8, Figure 2 The hexagonal window-like pore size (∼0.34 nm) and very small quaternary windows on the horizontally oriented plane are shown, located between the kinetic diameters of water (2.68 Å) and ethanol (4.5 Å). Therefore, dispersing ZIF-L parallel to the membrane surface will show a significant sieving effect on water / ethanol mixtures. Figure 3 The diagram shows the principle of how PEI solution causes ZIF-L to be horizontally oriented.
[0005] To address the aforementioned problems, this invention innovatively employs polyethyleneimine (PEI) as a regulating agent. Through multiple interactions (including hydrogen bonds and Zn-N coordination bonds) between PEI and the ZIF-L crystal surface, a horizontally oriented arrangement of the ZIF-L crystals is achieved, opening up the internal pores and significantly enhancing the material's hydrophilicity. This horizontally oriented ZIF-L layer can fully utilize its 3.4 Å pore size for molecular sieving, providing a new technical solution for developing high-performance alcohol-water separation membranes. Summary of the Invention
[0006] The purpose of this invention is to address the current situation where membrane flux and separation factor are not balanced, thus failing to adequately meet membrane separation requirements. This invention provides a high-performance pervaporation membrane for alcohol-water separation. The high-performance pervaporation membrane prepared by this method has advantages such as high flux and good separation factor, is suitable for membrane separation processes, and can ensure excellent separation performance and long-term stable operation. To achieve the above objective, the technical solution adopted in this invention is: a horizontally oriented ZIF-L composite membrane and its preparation method, the specific steps of which are as follows:
[0007] (1) Synthesis of leaf-shaped ZIF-L: metal nitrate hexahydrate and dimethylimidazole were dissolved in water at a mass ratio of 20-50% at room temperature. The dimethylimidazole solution was quickly poured into the nitrate hexahydrate and stirred for 2-4 hours. After centrifugation three times (6000-8000r / 20min), the mixture was washed and dried at 60°C for 5-8 hours. The ZIF-L powder was then obtained by grinding.
[0008] (2) Preparation of oriented ZIF-L seed layer: Dissolve the ZIF-L powder prepared in (1) in 0.01~1wt% PEI solution, disperse it by ultrasonication and filter it onto PAN base film, then immerse it in ZIF-L synthesis solution, grow it at a suitable temperature for 20-40 min, wash it and dry it at 60℃ for 4-6 h;
[0009] (3) Secondary growth of the separation layer: The membrane obtained in (2) is immersed again in the ZIF-L synthesis solution with different metal sources and grown at a suitable temperature for 10-30 min. After washing and drying, the final composite membrane is obtained.
[0010] The preferred metal source for synthesizing ZIF-L in step (1) is one of cobalt nitrate hexahydrate, zinc nitrate hexahydrate, or a mixture of cobalt and zinc crystals.
[0011] In preferred step (2), the amount of ZIF-L powder added is 0.1~4 wt% of the water mass.
[0012] The preferred step (3) is the secondary growth of the separation layer: the metal ions in the ZIF-L synthesis solution are either Zn ions or Co ions.
[0013] This invention improves upon the irregular and disordered ZIF-L structures prepared in previous experiments by using a secondary growth method to prepare continuously oriented ZIF-L layers. This study uses a PEI solution as a binder. By controlling the orientation of the seed layer, micron-sized ZIF-L nanosheets with PEI as the binder are deposited, followed by a short secondary growth process to form a horizontally oriented layer. When the ZIF-L crystal suspension is vacuum filtered, a normal force acts on the ZIF-L crystals near the support, i.e., resistance under vacuum. This resistance causes the solution to transport to the support and deposit the ZIF-L crystals on the surface. A large number of ZIF-L particles are well dispersed in the PEI matrix. PEI can form hydrogen bonds with the free hydroxyl groups on the ZIF-L crystals and support surface, and can also form Zn-N coordination bonds with zinc cations on the crystal surface. Therefore, adding PEI to the seed solution is crucial for ensuring the seed crystals adhere firmly to the support surface, improving the distribution of ZIF-L materials in the membrane, enabling them to align horizontally, resulting in excellent targeted separation, and greatly enhancing the membrane's selectivity. This is key to ensuring the horizontal growth of the seed crystals. Furthermore, by changing the metal source in the growth solution, a heterogeneous ZIF-L membrane (Zn / Co) was prepared, significantly increasing the membrane permeation flux.
[0014] Beneficial effects:
[0015] 1. Structural innovation
[0016] The horizontal oriented alignment of ZIF-L crystals was achieved through PEI induction, solving the technical challenge of disordered crystal growth (vertical orientation) in traditional methods. This constructed a continuous and ordered molecular transport channel, maximizing the sieving effect of the 3.4 Å pore size and significantly improving separation performance. The preparation of a ZIF-L heterostructure membrane also substantially improved the poor hydrophilicity of pure ZIF-L (Zn) membranes and the poor stability of pure ZIF-L (Co) membranes. The alcohol-water separation performance was: pure water flux ≥ 4000 g·m⁻²·h⁻¹, separation factor ≥ 2100.
[0017] 2. Functionality of processes and materials
[0018] The innovative "in-situ seed growth + secondary growth" process: the first growth ensures the horizontal orientation of the crystal, and the second growth optimizes the integrity of the separation layer; crystal orientation is achieved through the synergistic effect of PEI hydrogen bonding and Zn-N coordination, Zn 2+ With Co 2+ The heterogeneous interaction enhances the hydrophilicity of the membrane surface and improves structural stability. Attached Figure Description
[0019] Figure 1 The image shows a scanning electron microscope (SEM) image of the pervaporation membrane in Example 2.
[0020] Figure 2 ZIF-L horizontal aperture structure
[0021] Figure 3 Schematic diagram of the principle of horizontal orientation of ZIF-L in PEI solution. Detailed Implementation
[0022] The present invention will be further described in detail below through specific embodiments. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention.
[0023] The continuously oriented ZIF-L membrane prepared by this invention can be used to separate ethanol and water. Therefore, membrane permeation flux, alcohol-water separation factor, and stability are three important parameters for evaluating this pervaporation.
[0024] The test conditions for membrane permeation flux and alcohol-water separation factor are: pervaporation device, ethanol concentration of 80-90%, test temperature of 75℃, and test pressure of 300Pa.
[0025] Membrane permeation flux (J) is defined as:
[0026] In the formula, Q represents the total mass of the permeate, in g; A represents the effective membrane area, in m². 2 t represents the duration of the collection, h.
[0027] The alcohol-water separation coefficient (α) is defined as:
[0028] In the formula, X A and X B represent the concentrations of ethanol and water in the feed solution, respectively, in wt%; Y A and Y B , representing the concentrations of ethanol and water in the permeate, respectively, in wt%.
[0029] Comparative Example 1:
[0030] (1) Dissolve 0.59 g of Zn(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into zinc nitrate hexahydrate solution and stir at room temperature for 4 h. Collect two-dimensional ZIF-L crystals by centrifugation three times (8000 rpm, 20 min), wash three times with deionized water, dry under vacuum at 60 °C and grind to obtain ZIF-L powder.
[0031] (2) Dissolve 0.25g of the ZIF-L powder prepared in (1) in water and sonicate it for a period of time until it is completely dissolved. Filter the solution onto a PAN-based membrane using a vacuum filter. Immerse the filtered PAN-based membrane in the ZIF-L synthesis solution and grow it in a water bath at 30℃ for 30min. Remove the membrane, rinse it with deionized water, and dry it in an oven at 60℃ for 4-6h.
[0032] (3) Dissolve 0.59 g of Zn(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the zinc nitrate hexahydrate solution. Immerse the ZIF-L membrane prepared in (2) again in the above ZIF-L synthesis stock solution and grow it in a water bath at 30℃ for 10 min. Place the grown membrane on a drying rack to air dry naturally to obtain a high-performance membrane for alcohol-water separation and purification.
[0033] The ZIF-L layer structure prepared in Comparative Example 1 was randomly arranged. The pervaporation membrane prepared in Comparative Example 1 was tested, and the membrane permeation flux was 1100 g / m³. 2 *h, the alcohol-water separation coefficient is 620.
[0034] Example 1:
[0035] (1) Dissolve 0.59 g of Zn(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into zinc nitrate hexahydrate solution and stir at room temperature for 4 h. Collect two-dimensional ZIF-L crystals by centrifugation three times (8000 rpm, 20 min), wash three times with deionized water, dry under vacuum at 60 °C and grind to obtain ZIF-L powder.
[0036] (2) Take 0.04 g of the ZIF-L powder prepared in (1) and redissolve it in 0.025 wt% PEI solution. Sonicate the solution for a period of time until it is completely dissolved. Filter the solution onto a PAN base membrane using a vacuum filter. Immerse the filtered PAN base membrane in the ZIF-L synthesis stock solution and grow it in a water bath at 30°C for 30 min. Remove the membrane, rinse it with deionized water, and dry it in an oven at 60°C for 4-6 h.
[0037] (3) Dissolve 0.59 g of Zn(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the zinc nitrate hexahydrate solution. Immerse the ZIF-L membrane prepared in (2) again in the above ZIF-L synthesis stock solution and grow it in a water bath at 30℃ for 10 min. Place the grown membrane on a drying rack to air dry naturally to obtain a high-performance membrane for alcohol-water separation and purification.
[0038] The ZIF-L prepared in Example 1 exhibited better dispersion, with superior horizontal orientation and ZIF-L morphology. The pervaporation membrane prepared in Example 1 was tested, and its permeation flux was 2500 g / m³. 2 *h, the alcohol-water separation coefficient is 1800, and after a 12-hour stability test, the membrane permeation flux still reaches 2300 g / m³. 2 *h, the separation coefficient can also reach 1700.
[0039] Comparative Example 2:
[0040] (1) Dissolve 0.59 g of Co(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into cobalt nitrate hexahydrate solution and stir at room temperature for 4 h. Collect two-dimensional ZIF-L crystals by centrifugation three times (8000 rpm, 20 min), wash three times with deionized water, dry under vacuum at 60 °C and grind to obtain ZIF-L powder.
[0041] (2) Take 0.04 g of the ZIF-L powder prepared in (1) and redissolve it in 0.025 wt% PEI solution. Sonicate the solution for a period of time until it is completely dissolved. Filter the solution onto a PAN base membrane using a vacuum filter. Immerse the filtered PAN base membrane in the ZIF-L synthesis stock solution and grow it in a water bath at 30°C for 30 min. Remove the membrane, rinse it with deionized water, and dry it in an oven at 60°C for 4-6 h.
[0042] (3) Dissolve 0.59 g of Co(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the cobalt nitrate hexahydrate solution. Immerse the ZIF-L membrane prepared in (2) again in the above ZIF-L synthesis stock solution and grow it in a water bath at 30 °C for 10 min. Place the grown membrane on a drying rack to air dry naturally to obtain a high-performance membrane for alcohol-water separation and purification.
[0043] The ZIF-L prepared in Comparative Example 2 was compared with that prepared with Zn 2+ Although it has better hydrophilicity as the central ion, the material is not as good as that with Zn. 2+
[0044] The ZIF-L layer prepared with the central ion intact exhibited a horizontal orientation of 60%, possibly due to its poor stability. The pervaporation membrane prepared in Comparative Example 2 was tested, and its permeation flux was 2800 g / m³. 2 *h, the alcohol-water separation coefficient is 900.
[0045] Comparative Example 3:
[0046] (1) Dissolve 0.59 g of Co(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into cobalt nitrate hexahydrate solution and stir at room temperature for 4 h. Collect two-dimensional ZIF-L crystals by centrifugation three times (8000 rpm, 20 min), wash three times with deionized water, dry under vacuum at 60 °C and grind to obtain ZIF-L powder.
[0047] (2) Take 0.04 g of the ZIF-L powder prepared in (1) and redissolve it in 0.025 wt% PEI solution. Sonicate the solution for a period of time until it is completely dissolved. Filter the solution onto a PAN base membrane using a vacuum filter. Immerse the filtered PAN base membrane in the ZIF-L synthesis stock solution and grow it in a water bath at 30°C for 30 min. Remove the membrane, rinse it with deionized water, and dry it in an oven at 60°C for 4-6 h.
[0048] (3) Dissolve 0.59 g of Zn(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the zinc nitrate hexahydrate solution. Immerse the ZIF-L membrane prepared in (2) again in the above ZIF-L synthesis stock solution and grow it in a water bath at 30℃ for 10 min. Place the grown membrane on a drying rack to air dry naturally to obtain a high-performance membrane for alcohol-water separation and purification.
[0049] The ZIF-L layer prepared in Comparative Example 3 had a horizontal orientation of 70%, but there was some overlap between the blades. The pervaporation membrane prepared in Comparative Example 3 was tested, and the membrane permeation flux was 2000 g / m³. 2 *h, the alcohol-water separation coefficient is 1400.
[0050] Example 2:
[0051] (1) Dissolve 0.59 g of Zn(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into zinc nitrate hexahydrate solution and stir at room temperature for 4 h. Collect two-dimensional ZIF-L crystals by centrifugation three times (8000 rpm, 20 min), wash three times with deionized water, dry under vacuum at 60 °C and grind to obtain ZIF-L powder.
[0052] (2) Take 0.04 g of the ZIF-L powder prepared in (1) and redissolve it in 0.025 wt% PEI solution. Sonicate the solution for a period of time until it is completely dissolved. Filter the solution onto a PAN base membrane using a vacuum filter. Immerse the filtered PAN base membrane in the ZIF-L synthesis stock solution and grow it in a water bath at 30°C for 30 min. Remove the membrane, rinse it with deionized water, and dry it in an oven at 60°C for 4-6 h.
[0053] (3) Dissolve 0.59 g of Co(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the cobalt nitrate hexahydrate solution. Immerse the ZIF-L membrane prepared in (2) again in the above ZIF-L synthesis stock solution and grow it in a water bath at 30 °C for 10 min. Place the grown membrane on a drying rack to air dry naturally to obtain a high-performance membrane for alcohol-water separation and purification.
[0054] The ZIF-L material prepared in Example 2 has a basically full blade-like structure with no obvious defects. The horizontal orientation of the prepared ZIF-L layer is 95% and it is well dispersed. The pervaporation membrane prepared in Example 2 was tested, and the membrane permeation flux was 4000 g / m³. 2 *h, the alcohol-water separation coefficient is 2100. After a 12-hour stability test, the membrane permeation flux still reaches 3800 g / m³. 2 *h, the separation coefficient can also reach 2000.
[0055] Comparative Example 4:
[0056] (1) Dissolve 0.59 g of Zn(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into zinc nitrate hexahydrate solution and stir at room temperature for 4 h. Collect two-dimensional ZIF-L crystals by centrifugation three times (8000 rpm, 20 min), wash three times with deionized water, dry under vacuum at 60 °C and grind to obtain ZIF-L powder.
[0057] (2) Dissolve 0.01g of the ZIF-L powder prepared in (1) in 0.025wt% PEI solution and sonicate for a period of time until completely dissolved. Filter the solution onto a PAN-based membrane using a vacuum filter. Immerse the filtered PAN-based membrane in the ZIF-L synthesis stock solution and grow it in a water bath at 30℃ for 30min. Remove the membrane, rinse it with deionized water, and dry it in an oven at 60℃ for 4-6h.
[0058] (3) Dissolve 0.59 g of Co(NO3)2·6H2O and 1.30 g of dimethylimidazole (Hmim) in 40 mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the cobalt nitrate hexahydrate solution. Immerse the ZIF-L membrane prepared in (2) again in the above ZIF-L synthesis stock solution and grow it in a water bath at 30 °C for 10 min. Place the grown membrane on a drying rack to air dry naturally to obtain a high-performance membrane for alcohol-water separation and purification.
[0059] Although the ZIF-L layer prepared in Comparative Example 4 has good horizontal orientation, it has obvious surface defects. The pervaporation membrane prepared in Comparative Example 4 was tested, and the membrane permeation flux was 3200 g / m³. 2 *h, the alcohol-water separation coefficient is 800.
[0060] Example 3:
[0061] (1) Dissolve 0.5g of Zn(NO3)2·6H2O, 0.3g of Co(NO3)2·6H2O, and 1.30g of dimethylimidazole (Hmim) in 40mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the nitrate hexahydrate solution and stir at room temperature for 4h. Collect two-dimensional ZIF-L crystals by centrifugation three times (8000 rpm, 20min), wash three times with deionized water, dry under vacuum at 60℃ and grind to obtain ZIF-L powder.
[0062] (2) Take 0.04 g of the ZIF-L powder prepared in (1) and redissolve it in 0.025 wt% PEI solution. Sonicate the solution for a period of time until it is completely dissolved. Filter the solution onto a PAN base membrane using a vacuum filter. Immerse the filtered PAN base membrane in the ZIF-L synthesis stock solution and grow it in a water bath at 30°C for 30 min. Remove the membrane, rinse it with deionized water, and dry it in an oven at 60°C for 4-6 h.
[0063] (3) Dissolve 0.5g of Zn(NO3)2·6H2O, 0.3g of Co(NO3)2·6H2O, and 1.30g of dimethylimidazole (Hmim) in 40mL of water respectively. After stirring and dissolving, quickly pour the dimethylimidazole solution into the nitrate hexahydrate solution. Immerse the ZIF-L membrane prepared in (2) again in the above ZIF-L synthesis stock solution and grow it in a water bath at 30℃ for 10min. Place the grown membrane on a drying rack to air dry naturally to obtain a high-performance membrane for alcohol-water separation and purification.
[0064] The ZIF-L material prepared in Example 3 still has certain structural defects, with some rod-like structures. The pervaporation membrane prepared in Example 3 was tested, and the membrane permeation flux was 2500 g / m³. 2*h, the alcohol-water separation coefficient is 1500. After a 12-hour stability test, the membrane permeation flux still reaches 2300 g / m³. 2 *h, the separation coefficient can also reach 1450.
Claims
1. A method for preparing a high-performance pervaporation membrane for alcohol-water separation, characterized in that... Includes the following steps: (1) Synthesis of leaf-shaped ZIF-L: The hexahydrate metal nitrate and dimethylimidazolium were dissolved in water at a mass ratio of 20-50% at room temperature. The dimethylimidazolium solution was quickly poured into the hexahydrate metal nitrate and stirred for 2-4 hours. The mixture was centrifuged at a speed of 6000-8000 r / min for 20 minutes and repeated three times. After washing, the mixture was dried at 60℃ for 5-8 hours and then ground to obtain ZIF-L powder. (2) Preparation of oriented ZIF-L seed layer: Dissolve the ZIF-L powder prepared in (1) in 0.01~1wt% PEI solution, disperse it by ultrasonication and filter it onto PAN base film, then immerse it in ZIF-L synthesis solution, grow it at a suitable temperature for 20-40 min, wash it and dry it at 60℃ for 4-6 h; (3) Secondary growth of the separation layer: The membrane obtained in (2) is immersed again in the ZIF-L synthesis solution with a different metal source than that in (1), and grown at a suitable temperature for 10-30 min. After washing and drying, the final composite membrane is obtained. The metal source in steps (1) and (3) is one of cobalt nitrate hexahydrate, zinc nitrate hexahydrate, or a mixture of cobalt and zinc crystals. The amount of ZIF-L powder added in step (2) is 0.1 to 4 wt% of the water mass.
2. A high-performance pervaporation membrane for alcohol-water separation, characterized in that, It was prepared by the preparation method described in claim 1.
3. The high-performance pervaporation membrane according to claim 2, characterized in that, This membrane is used in pervaporation technology to separate ethanol and water, and it exhibits good stability and antifouling properties during long-term use.