A high-flux super-hydrophobic composite membrane and a preparation method thereof

Abstract

The application discloses a high-flux strong-hydrophobic composite membrane and a preparation method thereof, and belongs to the field of membrane separation and technology.The method comprises the following steps: formulating a casting solution and a preparation method, wherein the casting solution comprises a binder and a certain graphite-based carbon material; the casting solution is prepared into a film through a vacuum-assisted solvent evaporation method; and the volatilization of a solvent in the binder and the adhesion between the binder and the graphite-based carbon material are promoted at 50-100 DEG C, so that a high-flux strong-hydrophobic microporous composite membrane is obtained.The method is simple, fast and green, and lays a foundation for industrial application of the high-flux strong-hydrophobic microporous composite membrane.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation and technology, specifically relating to a high-flux superhydrophobic composite membrane and its preparation method. Background Technology

[0002] The membrane industry has made a greater contribution to improving the efficiency of water resource utilization, and membrane separation has been a key focus of development due to its energy-saving and high-efficiency characteristics. At present, seawater desalination technology has transitioned from the traditional high-energy-consuming thermal method to the low-energy-consuming membrane method, and membrane distillation (MD, also known as pervaporation) is a high-efficiency, low-energy-consuming thermal membrane coupling method. Membranes used in membrane distillation should meet the following requirements: (1) low mass transfer resistance to increase flux; (2) low thermal conductivity to reduce heat loss; (3) hydrophobic microporous membrane. Common materials for membranes used in membrane distillation include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polypropylene (PP), which rely on the principle of "air permeability but water impermeability" of hydrophobic porous membranes to achieve seawater desalination. Developing high-flux, fouling-resistant microporous hydrophobic membranes is an important step in the industrialization of membrane distillation.

[0003] Polytetrafluoroethylene (PTFE) is an ideal material for superhydrophobic membranes (MD) due to its outstanding hydrophobicity, excellent heat resistance, and chemical resistance. However, because of its non-polar nature, it cannot be dissolved by common polar solvents. Therefore, commercial PTFE is often mixed with lubricants and then fabricated using mechanical stretching and sintering methods, causing environmental pollution. In contrast, PTFE in PTFE emulsions exists stably as submicron rod-shaped particles and exhibits bonding properties after simple drying. However, ensuring the antifouling performance of the membrane is also a key factor for the industrial application of MD membranes. Membranes prepared from dried PTFE emulsion particles have low porosity and are easily wetted when used in vacuum membrane distillation (VMD). In the construction of superhydrophobic materials, the materials used must have low surface energy and highly ordered roughness in terms of surface morphology. Therefore, constructing micro-nano hierarchical structures is an important step in realizing the "lotus effect." A three-dimensional wrinkled spherical nanomaterial is assembled from two-dimensional nanosheets through high-temperature reduction. This nanomaterial is then micro-doped into a PTFE emulsion and loaded onto a commercial base membrane. This process enhances the hydrophobicity while maintaining the micropore structure, resulting in superior membrane distillation performance. This invention prepares a microporous composite membrane with a micro-nano hierarchical structure using submicron PTFE particles and three-dimensional nanomaterials, which is then used for vacuum membrane distillation to remove salt from water. This improves the separation performance and stability during membrane distillation, further advancing the industrial application of membrane distillation. Summary of the Invention

[0004] The key technical problem to be solved by this invention is to provide a method for preparing a high-flux superhydrophobic composite membrane, so that the prepared membrane has a good effect of high flux and high retention rate for salt removal from water. The specific technical solution is as follows:

[0005] In a first aspect, the present invention provides a high-flux superhydrophobic PTFE membrane, comprising a porous base membrane as a support layer, and three-dimensional micro-nano wrinkled material and PTFE submicron particles co-loaded as a selective separation layer.

[0006] Specifically, the porous base membrane has an average pore size of 0.45 μm;

[0007] The aforementioned three-dimensional micro-nano wrinkled material is a spherical structure self-assembled from two-dimensional nanosheet carbon-based materials. It has extremely strong stability in water and organic solvents, and has a stable and uniform morphology and size, just like PTFE submicron particles.

[0008] Preferably, the two-dimensional nanosheet carbon-based material is one or more of graphene oxide nanosheets, single-crystal diamond nanosheets, sheet-like exfoliated fluorinated graphite, reduced graphene oxide nanosheets, and graphene nanosheets; the three-dimensional micro-nano wrinkled material is spherical with an average particle size of 0.5–5.0 μm.

[0009] The PTFE submicron particles have a particle size of 100-500 nm (preferably long rod structure, with a diameter and axial length ranging from 100-500 nm);

[0010] Specifically, the porous base membrane support layer is a PTFE membrane with an average thickness of about 200 μm, and the selective separation layer, composed of three-dimensional micro-nano wrinkled materials and PTFE submicron particles, has an average thickness of about 10 to 50 μm.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned microporous hydrophobic composite membrane, comprising:

[0012] Step a, Preparation of three-dimensional micro-nano wrinkled materials: Two-dimensional nanosheets are prepared into an aqueous dispersion, and an appropriate amount of reducing agent is added as needed. After being mixed evenly with ultrasonic assistance, the dispersion is injected into the receiving phase at a certain injection rate using an ultrasonic nozzle to achieve the self-assembly of two-dimensional nanosheets.

[0013] Step b: A certain amount of PTFE emulsion (aqueous dispersion of PTFE submicron particles) and the three-dimensional micro-nano wrinkled material prepared in step a are dispersed in a certain amount and proportion of ethanol and water, and ultrasonically dispersed to obtain a casting solution. Then, a commercial PTFE porous base membrane is fixed on a vacuum filter cup, and the casting solution is loaded onto the membrane using a vacuum-assisted method, i.e., vacuum forming. The membrane is then dried at a certain temperature for 4 hours to allow the PTFE emulsion to be fully dried and fully combined with the three-dimensional wrinkled microspheres, thus obtaining a microporous composite membrane with superhydrophobicity.

[0014] Specifically, the process of assembling two-dimensional nanosheets into three-dimensional wrinkled microspheres in step a is optimized for performance: the concentration of the aqueous dispersion of the two-dimensional nanosheets is 0.1–10.0 mg / mL; if a reducing agent is added, the mass ratio of the reducing agent to the two-dimensional nanosheets is 1:1. The ultrasonic nozzle injection rate is set to 0.1–10.0 mL / min, wherein the reducing agent is one or more of ascorbic acid, sodium triacetoxyborohydride, oxalic acid, and ethanol; the high-temperature receiving phase is one or more of air, nitrogen, and polydimethylsiloxane, and the receiving phase temperature is 100℃–500℃.

[0015] Specifically, in step b, the performance of the superhydrophobic microporous composite membrane is optimized as follows: 10-60 wt.% PTFE emulsion and 1-10 mg of three-dimensional wrinkled microspheres are dissolved in 3-10 mL of anhydrous ethanol, and the mixture is dispersed and mixed evenly by ultrasonication. The negative pressure during membrane preparation is 0.1 MPa, and the drying temperature is 60 °C to construct a superhydrophobic microporous coating. The ratio of the amount of three-dimensional wrinkled microspheres to PTFE emulsion is 30-300 μL of PTFE emulsion for every 1 mg of three-dimensional wrinkled microspheres.

[0016] The composite membrane obtained by this invention can be used as a pervaporation membrane for the removal of salt from water.

[0017] The beneficial effects of the technical solution provided by this invention are as follows: This invention loads a microporous hydrophobic layer with selective separation function onto a commercial PTFE microporous membrane, and uses membrane distillation to remove salt from water. Furthermore, within the separation layer constructed by PTFE submicron particles and three-dimensional wrinkled microspheres, the three-dimensional wrinkled microspheres with an average particle size of 3μm enhance surface hydrophobicity. The water contact angle of this material powder tablet can reach 150°, effectively preventing the membrane surface from being wetted by water and constructing an antifouling layer that maintains the stability of membrane operation. The PTFE submicron particles have an average particle size of 150nm, which can form a micro-nano hierarchical structure with the three-dimensional wrinkled microspheres. The uniform morphology of the PTFE particles allows them to accumulate on the base membrane surface to form a relatively dense microporous separation layer. The separation layer formed by the combination of these two components has uniform pore size, achieving salt retention by blocking saline water and allowing water vapor to pass through. Moreover, the membrane's permeation flux is 2-3 times higher than that of common vacuum membrane distillation membranes. Furthermore, the method of this invention is simple and easy to implement, does not involve hazardous solvents, complex lubricants, binders, or other substances during the preparation process, has low raw material costs, and can be industrialized. Attached Figure Description

[0018] Figure 1 Contact angle test diagram of the three-dimensional wrinkled material and high-flux superhydrophobic microporous composite membrane prepared in Example 1 of this invention.

[0019] Figure 2Scanning electron microscope images of the surfaces of the (2-1) three-dimensional wrinkled material, (2-2) PTFE submicroparticles, and (2-3, 2-4, 2-5) high-throughput superhydrophobic microporous composite membranes prepared in Example 1 of this invention.

[0020] Figure 3 It is a self-assembly of three-dimensional wrinkled microspheres and a hydrophobic membrane. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Scanning electron micrographs were observed and measured using a Czech TESCAN MIRALMS scanning electron microscope (SEM).

[0022] In a first aspect, embodiments of the present invention provide a high-flux superhydrophobic PTFE membrane, comprising a porous PTFE base membrane as a support layer, and three-dimensional micro-nano wrinkled material and PTFE submicron particles co-loaded as a selective separation layer;

[0023] The three-dimensional micro-nano wrinkled material is made of carbon-based material and has extremely strong stability in water and organic solvents. It has a stable and uniform morphology and size, just like PTFE submicron particles.

[0024] Preferably, the two-dimensional nanosheets that are the precursors of the three-dimensional micro-nano wrinkled material are one or more of graphene oxide nanosheets, reduced graphene oxide nanosheets, and graphene nanosheets.

[0025] Specifically, the PTFE porous base film has an average pore size of 0.45 μm, the three-dimensional micro-nano wrinkled material is spherical with an average particle size of 3.0 μm, and the PTFE submicron particles have a particle size of 150 ± 50 nm.

[0026] Specifically, in this embodiment of the invention, the average thickness of the PTFE porous base film support layer is about 200 μm, and the average thickness of the selective separation layer composed of three-dimensional micro-nano wrinkled material and PTFE submicron particles is about 11 μm.

[0027] Secondly, examples of the present invention provide a method for preparing the above-mentioned microporous hydrophobic composite membrane, comprising:

[0028] Step 101: Prepare a two-dimensional nanosheet into an aqueous dispersion, add an appropriate amount of reducing agent, mix evenly with ultrasonic assistance, and then spray it into the receiving phase at a certain injection rate using an ultrasonic nozzle to achieve the self-assembly of the two-dimensional nanosheet.

[0029] Step 102: Disperse 200 μL of PTFE emulsion and the three-dimensional wrinkled microspheres prepared in step 101 in a certain amount of anhydrous ethanol, and sonicate for a certain time to make them evenly dispersed to obtain a casting solution. Then, fix the commercial PTFE porous base membrane on the suction cup, load the casting solution onto the membrane using a vacuum-assisted method, and dry it at a certain temperature for 4 hours to fully dry the PTFE emulsion and make it fully combined with the three-dimensional wrinkled microspheres to obtain a microporous composite membrane with superhydrophobicity.

[0030] Specifically, the process of assembling two-dimensional nanosheets into three-dimensional wrinkled microspheres in step 101 is optimized for performance: the concentration of the aqueous dispersion of the two-dimensional nanosheets is 0.5 mg / mL, 1 mg / mL, 1.5 mg / mL, 2.0 mg / mL, 2.5 mg / mL, 3.0 mg / mL, 5.0 mg / mL, and 10 mg / mL; if a reducing agent is added, the mass ratio of the reducing agent to the two-dimensional nanosheets is 1:1; and the ultrasonic nozzle injection rate is set to 0.5 mL / min, 1.0 mL / min, and 2.0 mL / min. The flow rates are L / min, 5.0 mL / min, and 10.0 mL / min, where the reducing agent is one or more of ascorbic acid, sodium triacetoxyborohydride, oxalic acid, and ethanol; the two-dimensional nanosheets are one or more of graphene oxide nanosheets, sheet fluorinated graphene, reduced graphene oxide nanosheets, and graphene nanosheets; the high-temperature receiving phase is one or more of air, nitrogen, polydimethylsiloxane, and high-performance fluorinated liquid; and the receiving phase temperature can be 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃.

[0031] Specifically, in step 102, the performance of the superhydrophobic microporous composite membrane is optimized: the mass of the three-dimensional wrinkled microspheres can be 1 mg, 2 mg, 3 mg, 4 mg, or 5 mg; the mass fraction of the PTFE emulsion can be 10 wt.%, 15 wt.%, or 20 wt.%, dissolved in 3 mL, 5 mL, or 10 mL of anhydrous ethanol; the mixture is then ultrasonically dispersed and mixed uniformly for 15 min; the negative pressure during membrane preparation is 0.1 MPa; and the drying temperature is 60 °C, thus constructing a superhydrophobic microporous coating. The mass ratio of the three-dimensional wrinkled microspheres to the PTFE emulsion can be 1 / 10, 1 / 15, 1 / 20, 1 / 25, or 1 / 30. This configuration allows the synthesized microporous composite membrane to possess superhydrophobicity and achieve highly efficient water desalination in membrane distillation, exhibiting a higher flux compared to most commercially available vacuum membrane distillation membranes.

[0032] The present invention will be further described below through specific embodiments.

[0033] In the following specific embodiments, unless otherwise specified, all operations are performed under standard conditions or conditions recommended by the manufacturer. Raw materials whose manufacturers and specifications are not specified are all commercially available products.

[0034] Example 1

[0035] Commercial PTFE fiber membranes were used as the base membrane, with a pore size of 0.45 μm and a porosity of 23%.

[0036] Step a: Prepare a 1 mg / mL aqueous dispersion of graphene oxide nanosheets, add an equal mass of ascorbic acid as a reducing agent, mix evenly with ultrasonic assistance, and then spray it into the polydimethylsiloxane receiving phase at 160℃ using an ultrasonic nozzle at a injection rate of 0.5 mL / min. Wash with n-heptane as a post-treatment, and dry to complete the self-assembly of three-dimensional wrinkled microspheres.

[0037] Step b: Disperse 200 μL of 15 wt.% PTFE emulsion and 3 mg of three-dimensional wrinkled microspheres prepared in step a in 5 mL of anhydrous ethanol, and sonicate for 15 min to ensure uniform dispersion and obtain a casting solution. Then fix a commercial PTFE porous base membrane on a vacuum filter cup, load the casting solution onto the membrane using a vacuum-assisted method, and dry it at 60 °C for 4 h to fully dry the PTFE emulsion and allow it to fully combine with the three-dimensional wrinkled microspheres to obtain a microporous composite membrane with superhydrophobicity.

[0038] SEM results ( Figure 2 (2-3) shows a composite membrane assembled from three-dimensional micro / nano-wrinkled materials and PTFE submicron particles. Figure 2 Figure 2-4 shows that the three-dimensional folds of the microspheres contain embedded PTFE submicron particles, which constitute a multi-level nano-micro hierarchical structure. Figure 2 Figure 2-5 shows that the thickness of the selective separation layer in this embodiment is 11.33 μm.

[0039] The prepared composite membrane was placed in a membrane distillation apparatus for performance testing. The test conditions were: (1) the original solution was 3.5 wt.% NaCl solution with an inlet temperature of 60℃; (2) the operating pressure was 0.1 MPa.

[0040] The measured performance of the composite membrane was as follows: the rejection rate of 3.5 wt.% NaCl exceeded 99.99%, and the permeation flux exceeded 381.189 kg / (m²). 2 It can withstand pressures of 1000 MPa and can operate stably for more than 180 hours.

[0041] Example 2

[0042] Commercial PTFE fiber membranes were used as the base membrane, with a pore size of 0.45 μm and a porosity of 23%.

[0043] Step a) Prepare an 8 mg / mL aqueous dispersion of single-crystal diamond nanosheets (70 nm in diameter). After uniform mixing with ultrasonic assistance, spray the dispersion into a polydimethylsiloxane receiving phase at 160 °C using an ultrasonic nozzle at a injection rate of 1.0 mL / min. Wash with n-heptane as a post-treatment, and dry to complete the self-assembly of the three-dimensional wrinkled microspheres. Figure 3 (3-1, 3-2);

[0044] Step b: Disperse 200 μL of 15 wt.% PTFE emulsion and 3 mg of three-dimensional wrinkled microspheres prepared in step a in 5 mL of anhydrous ethanol, and sonicate for 15 min to ensure uniform dispersion and obtain a casting solution. Then, fix a commercial PTFE porous base membrane on a filtration cup, load the casting solution onto the membrane using a vacuum-assisted method, and dry at 60 °C for 4 h to fully dry the PTFE emulsion and allow it to fully combine with the three-dimensional wrinkled microspheres, thus obtaining a microporous composite membrane with superhydrophobic properties. Figure 3 (3-3)

[0045] The prepared composite membrane was placed in a membrane distillation apparatus for performance testing. The test conditions were: (1) the original solution was 3.5 wt.% NaCl solution with an inlet temperature of 60℃; (2) the operating pressure was 0.1 MPa.

[0046] The measured performance of the composite membrane was as follows: a rejection rate of 99.7006% for 3.5 wt.% NaCl, and a permeation flux of 271.964 kg / (m²). 2 (·h·MPa).

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-flux superhydrophobic composite membrane, characterized in that, It includes a porous base membrane as a support layer, and three-dimensional micro-nano wrinkled materials and PTFE submicron particles as a selective separation layer. The three-dimensional micro-nano wrinkled material is a spherical structure self-assembled from two-dimensional nanosheet graphite-based material. The two-dimensional nanosheet graphite-based material is one or more of the following: graphene oxide nanosheets, single-crystal diamond nanosheets, sheet-like exfoliated fluorinated graphite, reduced graphene oxide nanosheets, and graphene nanosheets. The three-dimensional micro-nano wrinkled material is spherical with an average particle size of 0.5~5.0μm; the PTFE submicron particles have a particle size of 100-500nm. The preparation of the three-dimensional micro-nano wrinkled material involves: configuring two-dimensional nanosheets into an aqueous dispersion, optionally adding a reducing agent, mixing them uniformly with ultrasonic assistance, and then spraying them into a high-temperature receiving phase at a certain injection rate using an ultrasonic nozzle to achieve the self-assembly of the two-dimensional nanosheets; the high-temperature receiving phase is one or more of polydimethylsiloxanes, and the temperature of the receiving phase is 100℃~500℃.

2. The high-flux superhydrophobic composite membrane according to claim 1, characterized in that, The porous base membrane has an average pore size of 0.45 μm.

3. The high-flux superhydrophobic composite membrane according to claim 1, characterized in that, PTFE submicron particles have a long rod structure with a diameter and axial length ranging from 100 to 500 nm.

4. The high-flux superhydrophobic composite membrane according to claim 1, characterized in that, The porous base membrane support layer is a PTFE membrane with an average thickness of 200 μm, and the selective separation layer, composed of three-dimensional micro-nano wrinkled materials and PTFE submicron particles, has an average thickness of 10~50 μm.

5. A method for preparing the high-flux superhydrophobic composite membrane according to any one of claims 1-4, characterized in that, Includes the following steps: Step a, Preparation of three-dimensional micro / nano wrinkled materials: Two-dimensional nanosheets are prepared into an aqueous dispersion, and a reducing agent is optionally added. After being mixed evenly with ultrasonic assistance, the dispersion is injected into a high-temperature receiving phase at a certain injection rate using an ultrasonic nozzle to achieve self-assembly of the two-dimensional nanosheets. The high-temperature receiving phase is one or more of polydimethylsiloxanes, and the temperature of the receiving phase is 100℃~500℃. Step b: Disperse a certain amount of PTFE emulsion and the three-dimensional micro-nano wrinkled material prepared in step a in a certain amount and proportion of ethanol and water, and sonicate to make them evenly dispersed to obtain a casting solution. Then fix the PTFE porous base membrane on the suction cup, load the casting solution onto the membrane using a vacuum-assisted method, i.e., vacuum film formation, and dry it at a certain temperature to fully dry the PTFE emulsion and fully combine it with the three-dimensional wrinkled microspheres to obtain a microporous composite membrane with superhydrophobicity.

6. The method according to claim 5, characterized in that, In step a, the concentration of the aqueous dispersion of the two-dimensional nanosheets is 0.1~10 mg / mL. If a reducing agent is required, the mass ratio of the reducing agent to the two-dimensional nanosheets is 1:

1. The injection rate of the ultrasonic nozzle is set to 0.5~1.0 mL / min. The reducing agent is one or more of ascorbic acid, sodium triacetoxyborohydride, oxalic acid, and ethanol.

7. The method according to claim 5, characterized in that, In step b, 10-60 wt.% PTFE emulsion and 1-10 mg of three-dimensional wrinkled microspheres are dissolved in 3-10 mL of anhydrous ethanol, and the mixture is dispersed and mixed evenly by ultrasonication. The negative pressure during the filtration membrane formation is 0.1 MPa, and the drying temperature is 60 °C to construct a superhydrophobic microporous coating. The ratio of the amount of three-dimensional wrinkled microspheres to PTFE emulsion is 30-300 μL of PTFE emulsion for every 1 mg of three-dimensional wrinkled microspheres.

8. The application of the high-flux superhydrophobic composite membrane according to any one of claims 1-4 as a pervaporation membrane.

9. The application according to claim 8, wherein the high-flux superhydrophobic composite membrane is used for salt removal from water.

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