A n-hexane modified zif-95 composite nanofiber membrane and a preparation method thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING TECH UNIV
- Filing Date
- 2025-06-10
- Publication Date
- 2026-06-19
AI Technical Summary
In existing membrane distillation technologies, membranes prepared by the traditional phase inversion method have low porosity, high mass transfer resistance, and insufficient permeate flux. Furthermore, pollutants tend to deposit on the membrane surface during long-term operation, leading to a significant decrease in membrane flux.
ZIF-95 was synthesized with the aid of n-hexane. The modified ZIF-95 was then combined with PVDF by electrospinning to construct a multi-level porous nanofiber membrane. The CH-π interaction of n-hexane was used to form a molecular-level hydrophobic barrier, which improved the hydrophobicity and dispersibility of the membrane.
It significantly improves the membrane's permeation flux and long-term stability, reduces mass transfer resistance, and ensures the membrane's anti-wetting ability and separation efficiency during long-term operation.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of membrane separation technology, specifically relating to a high-performance superhydrophobic membrane for membrane distillation and its preparation method. The membrane is prepared by modification with a metal-organic framework material (ZIF-95) and electrospinning technology, exhibiting excellent hydrophobicity and permeability, and is suitable for seawater desalination, high-salinity wastewater treatment, and other fields. Background Technology
[0002] Freshwater scarcity has become a global challenge, and traditional seawater desalination technologies such as reverse osmosis (RO) have inherent drawbacks such as high energy consumption and poor adaptability to high-salinity wastewater. Membrane distillation (MD) technology, as a novel heat-driven separation process, is considered a highly promising alternative due to its theoretical 100% non-volatile substance rejection rate, ability to utilize low-grade heat sources (such as industrial waste heat), and excellent high-salinity wastewater treatment capabilities. However, existing MD membranes still face two major technical bottlenecks: firstly, membranes prepared by traditional phase inversion methods have low porosity, resulting in high mass transfer resistance and insufficient permeate flux; secondly, pollutants easily deposit on the membrane surface during long-term operation, causing scaling problems and resulting in a significant decrease in membrane flux.
[0003] In recent years, zeolite imidazole framework materials (ZIFs) have attracted widespread attention in the field of membrane separation due to their high porosity, large specific surface area, and excellent chemical stability. Among them, ZIF-95, composed of zinc ions coordinated with 2-methylimidazolium, possesses both hydrophobicity and structural stability, and is expected to enhance the permeation performance of MD membranes by improving membrane porosity and hydrophobicity. However, ZIF-95 powder prepared by traditional room-temperature synthesis methods generally suffers from problems such as uneven crystal structure and severe particle agglomeration. When used directly for membrane formation, it easily leads to uneven material distribution, thereby reducing membrane separation efficiency. For example, patent CN120079263A discloses a self-supporting MOF mixed matrix membrane prepared by a high-temperature roller-to-roll hot pressing process. Although it has anti-wetting ability, its preparation process is complex, and MOF particles still exhibit agglomeration, affecting the long-term stability of the membrane.
[0004] To overcome the aforementioned shortcomings, this invention proposes an improved method for ZIF-95 synthesis and composite membrane preparation: ZIF-95 is synthesized using a one-step method assisted by n-hexane. The ligand-directed effect of the co-solvent promotes the ordered expansion of the three-dimensional lattice, resulting in well-structured, low-agglomeration ZIF-95 crystals. Simultaneously, n-hexane forms a molecular-level hydrophobic barrier on the ZIF-95 surface through CH-π interactions, further enhancing the material's hydrophobicity. Furthermore, ZIF-95 is in-situ composited into a PVDF matrix using electrospinning technology to construct a nanofiber membrane with a hierarchical porous structure—large pores between fibers promote water vapor transport, while ZIF-95 micropores enhance the membrane's hydrophobicity. This composite membrane possesses superhydrophobicity, high flux, and long-term operational stability, effectively solving the technical bottlenecks of existing MD membranes. Summary of the Invention
[0005] This invention provides a method for preparing a hexane-modified ZIF-95 composite nanofiber membrane. ZIF-95 is synthesized with the aid of hexane, resulting in a more regular structure and reduced material agglomeration. A highly hydrophobic material, ZIF-95, is prepared by forming a molecular-level hydrophobic barrier through CH-π interactions. The modified hydrophobic material is then combined with PVDF using electrospinning technology to construct a hierarchical porous structure, giving the prepared membrane superhydrophobicity and high porosity, thereby improving the membrane's permeate flux and stability in membrane distillation.
[0006] To achieve the above objectives, the technical solution adopted by this invention is: a method for preparing a hexane-modified ZIF-95 composite nanofiber membrane, the specific steps of which are as follows:
[0007] (1) Preparation of ZIF-95 hydrophobic material
[0008] Zinc nitrate hexahydrate (3.3-3.5 wt%) was dissolved in methanol and stirred for 10-15 min to obtain solution 1; 2-methylimidazole (3.7-3.9 wt%) was dissolved in a methanol mixture containing a nonpolar solvent (0-14.3 wt%) and sonicated for 2-3 h to obtain solution 2; solution 1 was added dropwise to solution 2, stirred for 24 h, centrifuged (8000-10000 rpm, 15-20 min), and vacuum dried at 60°C to obtain ZIF-95 powder;
[0009] (2) Preparation of spinning solution
[0010] ZIF-95 (0.1-1wt%), film-forming material (10-13wt%), and TPU (5-6wt%) were dissolved in an organic solvent and stirred at 80°C for 12 hours.
[0011] (3) Electrospinning to form film
[0012] Spinning solution of 4-6 mL is prepared under the conditions of 14-18 kV voltage, 0.5-0.8 mL / h flow rate, 25±5℃ and 30±10% humidity.
[0013] The preferred nonpolar solvent in step (1) is selected from one of n-hexane, n-pentane, and cyclohexane.
[0014] The preferred step (2) is to select one of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, and polypropylene.
[0015] The solvent in step (2) is preferably selected from one of dimethyl sulfoxide, N,N-dimethylformamide, methanol, and acetone.
[0016] This invention prepares a structurally regular, highly hydrophobic material ZIF-95 by adding different amounts of the co-solvent n-hexane, and combines ZIF-95 with PVDF using electrospinning technology. By changing the content of modified ZIF-95 and the electrospinning parameters, a superhydrophobic, high-flux membrane for membrane distillation is prepared.
[0017] Beneficial effects:
[0018] This invention synthesizes ZIF-95 by introducing n-hexane as a co-solvent, and then uses electrospinning technology to in-situ composite ZIF-95 with PVDF to construct a nanofiber membrane with a hierarchical porous structure, which has the following significant advantages:
[0019] (1) Improve the crystal structure of ZIF-95
[0020] The ligand-directing effect of n-hexane promotes the ordered expansion of the three-dimensional lattice, making the ZIF-95 crystal structure more regular, effectively reducing the material's own agglomeration, and improving its dispersibility in the polymer matrix.
[0021] (2) Enhance hydrophobic stability
[0022] As a nonpolar solvent, n-hexane forms CH-π interactions with ligand molecules, creating a molecular-level hydrophobic barrier on the ZIF-95 crystal surface. This significantly enhances the hydrophobicity of the ZIF-95 material and the anti-wetting ability of the composite membrane. Its uniform distribution avoids the aggregation problem of traditional mixed matrix membranes, ensuring the stability of the membrane during long-term operation.
[0023] (3) Optimize mass transfer efficiency
[0024] The macroporous structure between fibers effectively reduces mass transfer resistance, promotes rapid water vapor transport, and increases membrane permeation flux. Attached Figure Description
[0025] Figure 1 Surface electron micrograph of the composite film prepared in Example 7
[0026] Figure 2 The contact angle of the composite membrane prepared in Example 7 Detailed Implementation
[0027] 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.
[0028] The superhydrophobic high-flux membrane prepared by this invention can be used for membrane distillation. Therefore, water contact angle, permeate flux, salt rejection rate, and long-term performance testing are four important parameters for evaluating this membrane.
[0029] The test conditions for water contact angle, permeate flux, salt rejection rate, and long-term performance were as follows: optical contact angle meter, membrane distillation apparatus, NaCl solution as the brine solution, brine concentration of 3.5%, and temperature controlled at 60℃. Water samples were collected and weighed every hour, and the long-term stability was evaluated after 100 hours of continuous operation.
[0030] Permeation flux is defined as:
[0031] In the formula, J represents the permeation flux (kg·m³). -2 ·h -1 ), Δm (kg) is the total mass increment on the cold side, A (m 2 ) is the effective membrane area, and t(h) is the operating time.
[0032] Salt rejection rate is defined as:
[0033] In the formula, R is the salt rejection rate, and C p and C f These are the concentrations of the permeate and the feed, respectively.
[0034] Comparative Example 1
[0035] (1) Dissolve 3.5 wt% zinc nitrate hexahydrate in methanol and stir for 10 min to obtain solution 1; dissolve 3.8 wt% 2-methylimidazole in methanol solution without non-polar solvent and sonicate for 2 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 8000 rpm for 15 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0036] (2) Dissolve 0.1 wt% ZIF-95, 10 wt% PVDF powder and 5 wt% TPU in N,N-dimethylformamide solvent and stir at 80°C for 12 h.
[0037] (3) Spinning solution of 4 mL was prepared under the conditions of 14 kV voltage, 0.5 mL / h flow rate, 25℃ and 30% humidity.
[0038] Performance tests were conducted on the membrane distillation membrane prepared in a comparative manner. The superhydrophobic membrane exhibited a water contact angle of 132.5° and a permeate flow rate of 7.5 kg·m³. -2 ·h -1 After 100 hours of continuous use, its water contact angle was 115.4°, with a decrease rate of 12.9%, and its permeability was 4.5 kg·m³. -2 ·h -1 The decline rate was 40.0%.
[0039] Example 1
[0040] (1) Dissolve 3.5 wt% zinc nitrate hexahydrate in methanol and stir for 15 min to obtain solution 1; dissolve 3.9 wt% 2-methylimidazole in a methanol mixture containing 5.9 wt% n-pentane and sonicate for 3 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 8000 rpm for 15 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0041] (2) Dissolve 1 wt% ZIF-95, 13 wt% polytetrafluoroethylene powder and 6 wt% TPU in dimethyl sulfoxide solvent and stir at 80°C for 12 h.
[0042] (3) Take 6 mL of spinning solution and the spinning parameters are voltage 18 KV, flow rate 0.8 mL / h, temperature 30℃ and humidity 40% to form a nanofiber membrane by electrospinning.
[0043] The membrane distillation membrane prepared in Example 1 was subjected to performance testing. The superhydrophobic membrane had a water contact angle of 141.5° and a permeate flow rate of 10.4 kg·m³. -2 ·h -1 After 100 hours of continuous use, its water contact angle was 137.5°, with a decrease rate of 2.8%, and its permeability was 10.1 kg·m³. -2 ·h -1 The decline rate was 2.9%.
[0044] Example 2
[0045] (1) Dissolve 3.5 wt% zinc nitrate hexahydrate in methanol and stir for 15 min to obtain solution 1; dissolve 3.8 wt% 2-methylimidazole in a methanol mixture containing 7.3 wt% cyclohexane and sonicate for 2 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 10000 rpm for 20 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0046] (2) Dissolve 0.1 wt% ZIF-95, 12 wt% polyethylene powder and 6 wt% TPU in methanol solvent and stir at 80°C for 12 h.
[0047] (3) Take 6 mL of spinning solution and the spinning parameters are voltage 18KV, flow rate 0.8 mL / h, temperature 30℃ and humidity 40% to form a nanofiber membrane by electrospinning.
[0048] The membrane distillation membrane prepared in Example 2 was subjected to performance testing. The superhydrophobic membrane had a water contact angle of 140.3° and a permeate flow rate of 9.2 kg·m³. -2 ·h -1 After 100 hours of continuous use, its water contact angle was 137.6°, with a decrease rate of 1.9%, and its permeability was 9.0 kg·m³. -2 ·h -1 The decline rate was 2.2%.
[0049] Example 3
[0050] (1) Dissolve 3.3 wt% zinc nitrate hexahydrate in methanol and stir for 15 min to obtain solution 1; dissolve 3.7 wt% 2-methylimidazole in a methanol mixture containing 14.3 wt% n-hexane and sonicate for 2 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 8000 rpm for 15 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0051] (2) Dissolve 0.1 wt% ZIF-95, 13 wt% polypropylene powder and 6 wt% TPU in acetone solvent and stir at 80°C for 12 h.
[0052] (3) Take 6 mL of spinning solution and the spinning parameters are voltage 16KV, flow rate 0.6 mL / h, temperature 30℃ and humidity 30% to form a nanofiber membrane by electrospinning.
[0053] The membrane distillation membrane prepared in Example 3 was subjected to performance testing. The superhydrophobic membrane had a water contact angle of 142.1° and a permeate flow rate of 9.1 kg·m³. -2 ·h -1 After 100 hours of continuous use, its water contact angle was 138.6°, with a decrease rate of 2.4%, and its permeability was 8.9 kg·m³. -2 ·h -1 The decline rate was 2.2%.
[0054] Example 4
[0055] (1) Dissolve 3.5 wt% g zinc nitrate hexahydrate in methanol and stir for 10 min to obtain solution 1; dissolve 3.9 wt% 2-methylimidazole in a methanol mixture containing 6.3 wt% n-hexane and sonicate for 2 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 10000 rpm for 20 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0056] (2) Dissolve 0.4 wt% ZIF-95, 11 wt% PVDF powder and 6 wt% TPU in N,N-dimethylformamide solvent and stir at 80°C for 12 h.
[0057] (3) Take 6 mL of spinning solution and the spinning parameters are voltage 16KV, flow rate 0.6 mL / h, temperature 30℃ and humidity 30% to form a nanofiber membrane by electrospinning.
[0058] The membrane distillation membrane prepared in Example 4 was subjected to performance testing. The superhydrophobic membrane had a water contact angle of 144.6° and a permeate flow rate of 17.5 kg·m³. -2 ·h -1 After 100 hours of continuous use, its water contact angle was 141.7°, with a decrease rate of 2.0%, and its permeability was 17.2 kg·m³. -2 ·h -1 The decline rate was 1.7%.
[0059] Example 5
[0060] (1) Dissolve 3.3 wt% zinc nitrate hexahydrate in methanol and stir for 15 min to obtain solution 1; dissolve 3.7 wt% 2-methylimidazole in a methanol mixture containing 14.3 wt% n-hexane and sonicate for 2 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 8000 rpm for 15 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0061] (2) Dissolve 0.4 wt% ZIF-95, 11 wt% PVDF powder and 6 wt% TPU in N,N-dimethylformamide solvent and stir at 80°C for 12 h.
[0062] (3) Take 6 mL of spinning solution and the spinning parameters are voltage 15KV, flow rate 0.5 mL / h, temperature 25℃ and humidity 30% to form a nanofiber membrane by electrospinning.
[0063] The membrane distillation membrane prepared in Example 5 was subjected to performance testing. The superhydrophobic membrane had a water contact angle of 148.8° and a permeate flow rate of 18.4 kg·m³. -2 ·h -1After 100 hours of continuous use, its water contact angle was 146.2°, with a decrease rate of 1.7%, and its permeability was 18.1 kg·m³. -2 ·h -1 The decline rate was 1.6%.
[0064] Example 6
[0065] (1) Dissolve 3.3 wt% zinc nitrate hexahydrate in methanol and stir for 15 min to obtain solution 1; dissolve 3.7 wt% 2-methylimidazole in a methanol mixture containing 14.3 wt% n-hexane and sonicate for 2 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 8000 rpm for 15 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0066] (2) Dissolve 0.6 wt% ZIF-95, 11 wt% PVDF powder and 6 wt% TPU in N,N-dimethylformamide solvent and stir at 80°C for 12 h.
[0067] (3) Take 6 mL of spinning solution and the spinning parameters are voltage 15KV, flow rate 0.5 mL / h, temperature 25℃ and humidity 30% to form a nanofiber membrane by electrospinning.
[0068] The membrane distillation membrane prepared in Example 6 was subjected to performance testing. The superhydrophobic membrane had a water contact angle of 152.4° and a permeate flow rate of 21.9 kg·m³. -2 ·h -1 After 100 hours of continuous use, its water contact angle was 149.9°, with a decrease rate of 1.6%, and its permeability was 21.6 kg·m³. -2 ·h -1 The decline rate was 1.2%.
[0069] Example 7
[0070] (1) Dissolve 3.3 wt% zinc nitrate hexahydrate in methanol and stir for 15 min to obtain solution 1; dissolve 3.7 wt% 2-methylimidazole in a methanol mixture containing 14.3 wt% n-hexane and sonicate for 2 h to obtain solution 2; add solution 1 dropwise to solution 2, stir for 24 h, centrifuge at 8000 rpm for 15 min, and vacuum dry at 60℃ to obtain ZIF-95 powder.
[0071] (2) Dissolve 0.8 wt% ZIF-95, 11 wt% PVDF powder and 6 wt% TPU in N,N-dimethylformamide solvent and stir at 80°C for 12 h.
[0072] (3) Take 6 mL of spinning solution and the spinning parameters are voltage 15KV, flow rate 0.5 mL / h, temperature 25℃ and humidity 30% to form a nanofiber membrane by electrospinning.
[0073] The membrane distillation membrane prepared in Example 7 was subjected to performance testing. The superhydrophobic membrane had a water contact angle of 158.9° and a permeation rate of 25.0 kg·m³. -2 ·h -1 After 100 hours of continuous use, its water contact angle was 156.8°, with a decrease rate of 1.3%, and its permeability was 24.8 kg·m³. -2 ·h -1 The decline rate was 0.8%.
Claims
1. A method for preparing a hexane-modified ZIF-95 composite nanofiber membrane, characterized in that: Includes the following steps: (1) Preparation of ZIF-95 hydrophobic material Zinc nitrate hexahydrate was dissolved in methanol and stirred for 10-15 min to obtain solution 1, wherein the amount of zinc nitrate hexahydrate added in solution 1 was 3.3-3.5 wt%; 2-methylimidazole was dissolved in a methanol mixture containing a non-polar solvent and sonicated for 2-3 h to obtain solution 2, wherein the non-polar solvent was n-hexane, wherein the amount of 2-methylimidazole added in solution 2 was 3.7-3.9 wt%, and the amount of non-polar solvent added was 0-14.3 wt%; solution 1 was added dropwise to solution 2, stirred for 24 h, centrifuged at a speed of 8000-10000 rpm for 15-20 min, and vacuum dried at 60℃ to obtain ZIF-95 powder; (2) Preparation of spinning solution ZIF-95, film-forming material, and TPU were dissolved in an organic solvent and stirred at 80°C for 12 h. The addition amounts of ZIF-95 were 0.1-1 wt%, the film-forming material was 10-13 wt%, and the TPU was 5-6 wt%. (3) Electrospinning to form film Spinning solution of 4-6 mL is prepared under the conditions of 14-18 kV voltage, 0.5-0.8 mL / h flow rate, 25±5℃ and 30±10% humidity.
2. The production method according to claim 1, characterized by, The film-forming material in step (2) is selected from one of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, and polypropylene.
3. The preparation method according to claim 1, characterized in that, The organic solvent in step (2) is selected from one of dimethyl sulfoxide, N,N-dimethylformamide, methanol, and acetone.
4. The composite nanofiber membrane prepared according to the method of any one of claims 1-3, characterized by, Its permeation flux can reach 9-25 kg·m -2 ·h -1 The water contact angle is 141.5-158.9°, and the performance degradation is less than 3% after 100 hours of use.