Hydrophobic-hydrophilic Janus water collection membrane and efficient preparation method thereof

Abstract

The invention discloses a hydrophobic-hydrophilic Janus water collecting film and an efficient preparation method thereof, and belongs to the field of water collecting materials. An electrostatic spinning process is adopted, and a hydrophobic polymer is accurately deposited on the surface of a hydrophilic substrate in the form of a nanofiber array, so that the Janus composite membrane with an asymmetric wetting gradient structure is successfully constructed. The unique double-sided wettability difference drives the liquid drops to realize directional transmission, and the core mechanism of the liquid drops is derived from capillary force regulation and control caused by interfacial wetting potential energy difference. The Janus membrane shows excellent performance in the aspect of air moisture trapping, the ultra-fast moisture absorption characteristic and the surface regeneration capacity are achieved, and compared with a traditional single-layer hydrophilic membrane, the water collecting efficiency is remarkably improved by 110%. A one-step forming process is adopted for preparation, the diameter of the nanofibers is controllable, complex post-treatment procedures are not needed, and energy consumption required by equipment is low. The high-performance water collecting film has important application value in the fields of atmospheric water taking in arid regions, dehumidification of precise instruments and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of water collection materials, and particularly relates to a hydrophobic-hydrophilic Janus water collection membrane and an efficient preparation method thereof. Background Art

[0002] The growth of the global population and the increase in water consumption have led to an increasingly severe problem of water resource shortage. According to research, about 78% of the global population (about 610 million people) do not have access to clean water for daily use, and the water shortage in some African countries has directly threatened human survival. Therefore, there is an urgent need to develop new technologies to alleviate the water resource crisis.

[0003] In arid and semi-arid foggy regions, fog water collection is an effective way to alleviate the water shortage problem. Current fog water collection technologies are mostly inspired by natural organisms: spider silk captures moisture in the air through a hydrophilic spindle knot structure; desert beetles use a hydrophilic / hydrophobic (Janus) heterogeneous texture on their backs to achieve water collection. These organisms mainly achieve water capture through the regulation of surface wettability. Based on this, researchers have systematically explored the influence of material wettability on fog droplet capture and transport, and developed a variety of efficient water collection materials. Liu Yufang et al. prepared biomimetic nanofiber raised fibers by combining electrospinning technology and fluid coating method. Its surface has a periodic protrusion composed of randomly intertwined nanofibers and an oriented node structure (mimicking the micro-nano structure of wet spider silk), showing excellent water collection performance. Ren Feifei et al. designed a single-layer hydrophilic-hydrophobic Janus aluminum membrane based on a double-gradient conical microporous array. Fog droplets can spontaneously penetrate the conical micropores, and the water collection efficiency is increased by 209% compared with that of a pure hydrophilic membrane. Yin Kai et al. used femtosecond laser direct writing technology to construct a microstructure covered with nanoparticles on the surface of copper foam, forming a hydrophilic-hydrophobic Janus property, and realizing the unidirectional penetration of fog droplets from the hydrophobic side to the hydrophilic side, with a maximum water collection efficiency of 3.7 g cm -2 h -1 。

[0004] However, the existing methods generally have problems of complex preparation processes and high material costs, and the surface microstructure size is relatively large (micrometer level), which is not conducive to capturing tiny droplets in the air. Summary of the Invention

[0005] To overcome the above-mentioned technical deficiencies, the present invention proposes a process-simple and low-cost nano-scale hydrophobic / hydrophilic Janus membrane and its preparation method. By combining hydrophobic polymer fibers with a hydrophilic membrane, the Janus membrane is prepared through electrospinning. This membrane consists of a hydrophobic nanofiber layer firmly bonded to the hydrophilic membrane, forming a wettability-asymmetric structure. Under the synergistic action of hydrostatic pressure and capillary force, the Janus membrane can achieve efficient fog water collection and keep the surface dry. Experiments show that its water collection efficiency is 2.1 times that of a pure hydrophilic membrane. By in-situ observing the dynamic water collection process, analyzing the forces acting on the droplets, and conducting numerical simulations, the essential mechanism of the efficient and rapid water collection of the Janus membrane is revealed. This research provides a new idea for the development of efficient fog water collection membranes and has potential application value for solving the water resource crisis.

[0006] The hydrophobic-hydrophilic Janus water collection membrane described in the present invention consists of an electrospun nanofiber hydrophobic layer and a hydrophilic membrane layer.

[0007] Further, in the above technical solution, the fiber diameter of the hydrophobic nanofiber layer is 100 - 900 nm, and the grammage of the nanofiber layer is 0.01 - 5 g / m 2 , the porosity ≥ 80%, and the contact angle is 100 - 149 o .

[0008] Further, in the above technical solution, the fiber diameter of the hydrophilic membrane layer is 1 - 500 μm, and the grammage of the fiber layer is 100 - 200 g / m 2 , and the contact angle is 0 - 50 o . Based on this, a large contact angle difference is formed, increasing the wettability gradient, which is beneficial to the directional and rapid transmission of small water droplets and improves the water collection efficiency.

[0009] The present invention also provides a preparation method for the aforementioned hydrophobic-hydrophilic Janus water collection membrane, including the following steps:

[0010] (1) Prepare the spinning solution: Add 5 - 25 wt.% of hydrophobic polymer into the solvent, and keep it under constant temperature and shake until the solute is dissolved evenly to obtain the hydrophobic polymer spinning solution;

[0011] (2) Electrospinning: Prepare the hydrophobic polymer spinning solution onto the hydrophilic layer substrate through electrospinning technology to obtain the hydrophobic-hydrophilic Janus water collection membrane.

[0012] Further, in the above technical solution, the hydrophobic polymer includes: hydrophobic polymers such as polyvinyl chloride, polyvinylidene fluoride, polyethylene, polystyrene, polytetrafluoroethylene, chlorinated polyvinyl chloride, polypropylene, polycarbonate, polyether ketone, polyarylsulfone, polybutylene terephthalate, etc.

[0013] Further, in the above technical solution, the hydrophilic layer includes hydrophilic membranes such as hydrophilic nylon membranes, hydrophilic polyethersulfone (PES) membranes, hydrophilic mixed cellulose ester (MCE) membranes, and hydrophilic polyvinylidene fluoride (PVDF) membranes.

[0014] Further, in the above technical solution, the solvent includes one or a mixture of two of N,N-dimethylformamide, tetrahydrofuran, p-xylene, acetone, polyvinyl alcohol, dimethylacetamide, trifluoroacetic acid, and dichloromethane.

[0015] Further, in the above technical solution, the polymers and solvents correspond as follows:

[0016] Polyvinyl chloride: A mixture of N,N-dimethylformamide and tetrahydrofuran in equal mass ratio;

[0017] Polyvinylidene fluoride, polypropylene, and polycarbonate: N,N-dimethylformamide;

[0018] Polyethylene: p-xylene; Polystyrene: Acetone;

[0019] Polytetrafluoroethylene: Aqueous solution of polyvinyl alcohol;

[0020] Chlorinated polyvinyl chloride: A mixture of N,N-dimethylformamide and tetrahydrofuran in equal weight ratio;

[0021] Polyarylsulfone: Dimethylacetamide;

[0022] Polyethersulfone: A mixture of dimethylformamide and acetone in a mass ratio of 85 / 15;

[0023] Polyethylene terephthalate: A mixture of trifluoroacetic acid and dichloromethane in a volume ratio of 4 / 1.

[0024] Further, in the above technical solution, the electrospinning process conditions are: voltage 10 - 30 kV, receiving distance 5 - 25 cm, injection speed 1 - 5 mL / h, temperature 0 - 35 °C, relative humidity 0 - 70%, and spinning time 5 - 30 min.

[0025] Further, in the above technical solution, the hydrophilic layer substrate is a microfiber hydrophilic membrane.

[0026] The present invention has the following advantages and beneficial effects:

[0027] A. The present invention firmly attaches hydrophobic nanofibers to a hydrophilic fiber membrane to form a hydrophobic / hydrophilic Janus membrane with a large wetting gradient.

[0028] B. The method for fabricating the Janus water collection membrane of the present invention is simple, does not require special devices and equipment, and can be applied to the preparation of a wide range of water collection materials.

[0029] C. When the hydrophobic / hydrophilic Janus water collection membrane prepared by the present invention is used as a water collection material, it can achieve a very good high-efficiency water collection effect. Small droplets can be absorbed on its surface within 2 ms, and the membrane surface remains dry, which is conducive to further collecting small droplets in the air and doubling the water collection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the hydrophobic / hydrophilic Janus membrane prepared in Example 1 of the present invention;

[0031] Figure 2 SEM image of the hydrophobic / hydrophilic Janus membrane prepared in Example 1 of the present invention;

[0032] Figure 3 Comparison chart of water collection efficiency of hydrophilic membrane (L0), hydrophobic / hydrophilic Janus membranes (J1, J2, J3, J4) and hydrophobic membrane (B0);

[0033] Figure 4 Motion states of water droplets on the surfaces of hydrophilic membrane (a), hydrophobic membrane (b) and Janus membrane (c). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0035] Example 1

[0036] The preparation method and sample of a hydrophobic-hydrophilic Janus water collection membrane in this example are as follows:

[0037] (1) Place the polyvinyl chloride powder in a vacuum oven at 60 °C and dry for 2 h.

[0038] (2) Accurately weigh 10.9875 g of N,N-dimethylformamide and 10.9875 g of tetrahydrofuran with an electronic balance and place them in a 50 mL beaker. Oscillate with an ultrasonic oscillator for 1.5 h. Take out the beaker, accurately weigh 3 g of the dried polyvinyl chloride powder and place it in the beaker. Place the beaker on a water bath constant temperature oscillator and oscillate for 4 h at a constant temperature of 40 °C to prepare a uniform and stable polyvinyl chloride spinning solution.

[0039] (3) Electrospinning was carried out using an SS-2535H type electrospinning machine (Beijing Yongkang Leye Technology Development Co., Ltd.). The cut superhydrophilic experimental filter paper was used as the substrate and adhered to the rotating drum receiver. The above-mentioned electrospinning solution was added to the syringe and placed on the rack. The electrospinning parameters were set as follows: the translation speed of the injection system was 80 mm / min, the receiving distance was 15 cm, the electrostatic high voltage was 10 kV, the injection speed was 1 mL / h, and the electrospinning time was 5 min. A hydrophobic / hydrophilic Janus membrane (J1) was obtained. Electrospinning times of 10 min, 15 min, and 20 min were used as comparative samples (J2, J3, J4).

[0040] The water collection efficiency of the hydrophobic / hydrophilic Janus membrane (J1) prepared in this example was about 4 g / h (as Figure 3 shown).

[0041] It had significant advantages compared with the hydrophilic membrane ( Figure 4 ):

[0042] (i) The time (2 ms) for a water droplet to be completely absorbed by the Janus membrane was much less than the time (5 ms) for the water droplet to completely spread on the surface of the hydrophilic membrane;

[0043] (ii) After the water droplet was completely absorbed on the surface of the Janus membrane, the surface of the Janus membrane remained dry, which was beneficial for the next droplet to enter the membrane surface and be quickly absorbed by the underlying hydrophilic membrane. After the water droplet completely spread on the surface of the hydrophilic membrane, the membrane surface was wet, preventing the next water droplet from entering the membrane;

[0044] (iii) After the water droplet entered the interior of the Janus membrane, due to the hydrophobic repulsive force of the upper hydrophobic membrane on the underlying water droplet and the gravity of the water droplet itself, it was relatively easy to drip into the collection measuring cylinder. For the water droplet inside the hydrophilic membrane, the water droplet would only break away from the hydrophilic membrane and be collected in the measuring cylinder when its own gravity was large enough. The above three points were the reasons why the Janus membrane had a higher water collection rate than the hydrophilic membrane.

[0045] Example 2

[0046] A hydrophobic-hydrophilic Janus water collection membrane, its efficient preparation method and sample in this example are as follows:

[0047] (1) The polyvinylidene fluoride powder was placed in a vacuum oven at 60 °C and dried for 2 h.

[0048] (2) Accurately weigh 21.975 g of N,N-dimethylformamide with an electronic balance and place it in a 50 mL beaker. Accurately weigh 3 g of the dried polyvinylidene fluoride powder with an electronic balance and place it in the beaker. The beaker was placed on a water bath thermostatic shaker and shaken for 6 h at a constant temperature of 40 °C to prepare a uniform and stable polyvinylidene fluoride electrospinning solution.

[0049] (3) Electrospinning was carried out using an SS-2535H type electrospinning machine (Beijing Yongkang Leye Technology Development Co., Ltd.). The cut superhydrophilic filter paper for experiments was used as the substrate and adhered to the rotating drum receiver. The electrospinning parameters were adjusted. The translation speed of the injection system was 80 mm / min, the receiving distance was 10 cm, the electrostatic high voltage was 10 kV, and the injection speed was 1 mL / h. A hydrophobic / hydrophilic Janus membrane was obtained.

[0050] The water collection efficiency of the hydrophobic / hydrophilic Janus membrane prepared in this example was about 4.2 g / h, which had significant advantages compared with the hydrophilic membrane.

[0051] As described above, only the preferred specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. Hydrophobic-hydrophilic Janus water collection membrane, characterized in that: The Janus membrane consists of an electrostatically spun nanofiber hydrophobic layer and a hydrophilic membrane layer.

2. The hydrophobic-hydrophilic Janus water collection membrane according to claim 1, characterized in that: The fiber diameter of the hydrophobic nanofiber layer is 100-900nm, and the gram weight of the nanofiber layer is 0.01-5g / m 2 , porosity ≥ 80%, contact angle 100-149°.

3. The hydrophobic-hydrophilic Janus water collection membrane according to claim 1, characterized in that: The fiber diameter of the hydrophilic membrane layer is 1-500μm, and the fiber layer weight is 100-200g / m 2 , contact angle 0-50°.

4. The method for preparing the hydrophobic-hydrophilic Janus water-collecting membrane according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) preparing a spinning solution: adding 5-25 wt.% of a hydrophobic polymer to a solvent, and shaking the solvent at a constant temperature until the solute is uniformly dissolved to obtain a hydrophobic polymer spinning solution; (2) Electrospinning: The hydrophobic polymer spinning solution is prepared on the hydrophilic layer substrate by electrospinning technology to obtain a hydrophobic-hydrophilic Janus water collection membrane.

5. The method for preparing the hydrophobic-hydrophilic Janus water-collecting membrane according to claim 4, characterized in that: The hydrophobic polymer includes: polyvinyl chloride, polyvinylidene fluoride, polyethylene, polystyrene, polytetrafluoroethylene, chlorinated polyvinyl chloride, polypropylene, polycarbonate, polyether ketone, polyaryl sulfone, polybutylene terephthalate.

6. The method for preparing the hydrophobic-hydrophilic Janus water collection membrane according to claim 4, characterized in that: The hydrophilic layer includes: a hydrophilic nylon membrane, a hydrophilic polyethersulfone PES membrane, a hydrophilic mixed cellulose membrane MCE, and a hydrophilic polyvinylidene fluoride PVDF membrane.

7. The method for preparing the hydrophobic-hydrophilic Janus water-collecting membrane according to claim 4, characterized in that: The solvent includes: one or a mixture of two of N,N-dimethylformamide, tetrahydrofuran, p-xylene, acetone, polyvinyl alcohol, dimethylacetamide, trifluoroacetic acid, and dichloromethane.

8. The method for preparing the hydrophobic-hydrophilic Janus water-collecting membrane according to claim 5, characterized in that: The polymers and solvents correspond to the following: polyvinyl chloride: a mixture of NN dimethylformamide and tetrahydrofuran in equal mass ratios; polyvinylidene fluoride: NN dimethylformamide; polyethylene: p-xylene; polystyrene: acetone; polytetrafluoroethylene: polyvinyl alcohol aqueous solution; Chlorinated polyvinyl chloride: NN dimethylformamide and tetrahydrofuran mixed in equal weight ratio; polypropylene: NN dimethylformamide; polycarbonate: NN dimethylformamide; polyether sulfone: dimethylformamide and acetone mixed in 85 / 15 mass ratio; polyaryl sulfone: dimethylacetamide; polyethylene terephthalate: trifluoroacetic acid and dichloromethane mixed in 4 / 1 volume ratio.

9. The method for preparing the hydrophobic-hydrophilic Janus water-collecting membrane according to claim 4, characterized in that: The electrospinning process conditions are: voltage 10-30 kV, receiving distance 5-25 cm, injection speed 1-5 mL / h, temperature 0-35° C., relative humidity 0-70%, and spinning time 5-30 min.

10. The method for preparing the hydrophobic-hydrophilic Janus water-collecting membrane according to claim 4, characterized in that: The hydrophilic layer substrate is a micron fiber hydrophilic membrane.

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