Sandwich-structured atmospheric water harvesting nanofiber membrane and method of making same

Abstract

The application discloses a sandwich-structured atmospheric water collection nanofiber membrane and a preparation method thereof, and belongs to the field of textile science and technology. The application first prepares hydrophilic and hydrophobic nanofiber membranes with controllable internal diameters by electrospinning, wherein the fiber diameters are between 50-200nm, and the pore diameters are between 57nm-1.8mm; then, the hydrophobic-hydrophilic-hydrophobic sandwich-structured atmospheric water collection nanofiber membrane is prepared by wrapping a layer of hydrophilic nanofiber membrane loaded with hygroscopic metal salt with two layers of hydrophobic nanofiber membrane. The atmospheric water collection nanofiber membrane prepared by the application can confine the captured water in the hydrophilic layer, effectively prevent the leakage of the collected liquid water and metal salt, and release the captured water in the form of water vapor under sunlight, so that the continuous circulation of atmospheric water is realized, and the service life of the atmospheric water collection device is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to an atmospheric water collection nanofiber membrane with a sandwich structure and a preparation method thereof, and belongs to the field of textile science and technology. BACKGROUND

[0002] Due to global warming, rapid population growth and increasing water pollution, billions of people around the world are facing a severe lack of available fresh water resources. At present, about 97% of the water on earth is salt water in the ocean, in order to meet the demand for fresh water, seawater desalination is one of the common methods to solve the lack of water resources. However, the process of desalinating seawater often requires a large amount of energy consumption, and seawater desalination plants are generally distributed in coastal areas, and it is difficult to apply seawater desalination in inland areas far from the sea. Atmospheric water collection can directly obtain fresh water from the air at any location and in any environment, which is an effective way to solve the lack of water resources.

[0003] The atmospheric water collection method can be mainly divided into physical adsorption and chemical adsorption. Among them, the chemical adsorption method generally has the characteristics of high adsorption rate and low desorption temperature, and is considered to be the main means of atmospheric water collection. Recently, some studies have shown that the atmospheric water collection device prepared by loading hygroscopic metal salt in the porous substrate with photothermal conversion effect can more efficiently utilize sunlight and reduce the desorption temperature. However, due to the fast water absorption rate and high water absorption capacity of the metal salt, the traditional porous substrate is difficult to accommodate the excess salt solution, resulting in leakage of the salt solution from the porous substrate, which gradually reduces the water collection efficiency of the atmospheric water collection device and reduces the sustainability. SUMMARY

[0004] [Technical problem]

[0005] At present, the adsorption type atmospheric water collection device has the problem of easy leakage of hygroscopic metal salt, which reduces the reusability of the device.

[0006] [Technical scheme]

[0007] In order to solve the above problems, the application provides a sandwich structure atmospheric water collection nanofiber membrane (San-PAN) and a preparation method thereof; specifically, first, hydrophilic and hydrophobic nanofiber membranes with controllable internal pore diameters of 50-200 nm and pore diameters of 57 nm-1.8 mm are prepared by electrospinning technology, then a hydrophilic nanofiber membrane loaded with hygroscopic metal salt is wrapped by two layers of hydrophobic nanofiber membranes, and a hydrophobic-hydrophilic-hydrophobic sandwich structure atmospheric water collection nanofiber membrane is prepared. The outer two layers of hydrophobic nanofiber membranes of the atmospheric water collection nanofiber membrane prepared by the application can confine the captured water in the hydrophilic layer, effectively prevent the leakage of the collected liquid water and metal salt (such as lithium chloride), and release the captured water in the form of water vapor under sunlight, realize the continuous cycle of atmospheric water collection / desorption, and improve the service life of the atmospheric water collection device.

[0008] The first object of the application is to provide a method for preparing a sandwich structure atmospheric water collection nanofiber membrane, comprising the following steps:

[0009] (1) Preparation of nanofiber membrane:

[0010] Light-heat nanoparticles are added to a polymer solution and mixed uniformly to obtain a spinning solution; then the spinning solution is prepared into a nanofiber membrane by electrospinning; wherein the fiber diameter of the nanofiber membrane ranges from 50 nm to 200 nm, and the pore diameter ranges from 57 nm to 1.8 mm;

[0011] (2) Preparation of hydrophilic nanofiber membrane:

[0012] The nanofiber membrane is immersed in a metal salt solution, taken out and dried to obtain a hydrophilic nanofiber membrane;

[0013] (3) Preparation of hydrophobic nanofiber membrane:

[0014] The nanofiber membrane is immersed in a hydrophobic agent solution, taken out and dried to obtain a hydrophobic nanofiber membrane;

[0015] (4) Preparation of sandwich structure atmospheric water collection nanofiber membrane:

[0016] The hydrophilic nanofiber membrane is wrapped in the middle by the hydrophobic nanofiber membrane to form a hydrophobic-hydrophilic-hydrophobic sandwich structure atmospheric water collection nanofiber membrane.

[0017] In one embodiment of the present application, the high molecular polymer in the high molecular polymer solution of step (1) comprises one or more of polyacrylonitrile, polyurethane, polycarbonate, nylon 66, polylactic acid, polymethyl methacrylate, polycaprolactone, polyethylene terephthalate, cellulose acetate, cellulose, ethyl cellulose, chitin, chitosan, dextran, fibrin, silk fibroin and gelatin.

[0018] In one embodiment of the present application, the solvent in the high molecular solution of step (1) comprises one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetone, dichloromethane, ethanol, formic acid, acetic acid, diethyl ether, carbon tetrachloride, 1,2-dichloroethane, trichloroethane, 1,1,2-trichloroethylene, 1,2-dimethoxyethane, pyrimidine, formamide, n-hexane, acetonitrile, vinyl glycol, methylcyclohexane, 1,2-dichloroethylene, cyclohexane, butyl acetate, trichloroacetic acid and pyridine.

[0019] In one embodiment of the present application, the photo-thermal nanoparticles in step (1) comprise one or more of carbon black, black phosphorus, carbon nanotube, polypyrrole, graphene and graphene oxide.

[0020] In one embodiment of the present application, the mass ratio of the high molecular polymer, the solvent and the photo-thermal nanoparticles in the spinning solution of step (1) is 10-20:65-88:2-8.

[0021] In one embodiment of the present application, the electrospinning parameters of step (1) are set as follows: the electrospinning speed is 1-2 mL h -1 , the applied voltage is 15-25 kV, and the distance between the injector and the electrode is 15-25 cm.

[0022] In one embodiment of the present application, the metal salt in the metal salt solution of step (2) comprises one or more of lithium chloride, calcium chloride and magnesium chloride.

[0023] In one embodiment of the present application, the concentration of the metal salt solution of step (2) is 10-50 wt%, and the solvent is water.

[0024] In one embodiment of the present application, the immersion of step (2) is performed at room temperature (20-30 °C) for 0.5-3 h at a bath ratio of 1:10-50.

[0025] In one embodiment of the present application, the concentration of the hydrophobic agent in the hydrophobic agent solution of step (3) is 1-5 wt%.

[0026] In an embodiment of the present application, the hydrophobic agent solution in step (3) comprises a hydrophobic agent, a curing agent, and a solvent; wherein the hydrophobic agent comprises one or more of polysiloxane, polyolefin, silicone resin, and fluorocarbon polymer; the curing agent corresponds to the hydrophobic agent; the mass ratio of the hydrophobic agent to the curing agent is 5-15:1; and the solvent is one or more of water, ethanol, and n-hexane.

[0027] In an embodiment of the present application, the dipping in step (3) is performed at room temperature (20-30℃) for 0.5-3h at a bath ratio of 1:10-50.

[0028] In an embodiment of the present application, the area of the hydrophobic nanofiber membrane in step (4) is larger than that of the hydrophilic nanofiber membrane, and the hydrophobic agent solution is added dropwise to the edge of the hydrophilic nanofiber membrane so that the hydrophilic nanofiber membrane is completely wrapped.

[0029] A second object of the present application is the sandwich structure atmospheric water collection nanofiber membrane prepared by the method of the present application.

[0030] In an embodiment of the present application, the sandwich structure atmospheric water collection nanofiber membrane can be circular, rectangular, triangular, or the like.

[0031] In an embodiment of the present application, the sandwich structure of the sandwich structure atmospheric water collection nanofiber membrane can wrap the hydrophilic cellulose membrane inside to prevent the loss of LiCl particles and increase the service life of the sandwich structure atmospheric water collection nanofiber membrane.

[0032] A third object of the present application is the application of the sandwich structure atmospheric water collection nanofiber membrane of the present application in the field of atmospheric water collection.

[0033] A fourth object of the present application is to provide a method for improving the recycling performance of an atmospheric water collection device, which uses the sandwich structure atmospheric water collection nanofiber membrane of the present application.

[0034] [Advantages]

[0035] (1) The method of the present application is simple to operate, and the sandwich structure atmospheric water collection nanofiber membrane prepared by the method has high water collection efficiency and low loss, solving the problems of complex preparation process, low water collection efficiency, and poor storage of many traditional methods.

[0036] (2) The sandwich structure atmospheric water collection nanofiber membrane prepared by the present application has light texture and good water storage property.

[0037] (3) The sandwich structure atmospheric water collection nanofiber membrane prepared by the present application has long service life and can be applied in the field of atmospheric water collection to collect drinkable water for people going out and residents in drought areas. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Flow chart of the method for preparing sandwich structure atmospheric water harvesting nanofiber membrane according to the present application.

[0039] Figure 2 Test results of moisture permeability of PAN membrane, CB@PAN membrane and CB-PDMS@PAN membrane at different time lengths.

[0040] Figure 3 Pore size distribution graph and corresponding electron microscope graph of CB@PAN and CB-PDMS@PAN.

[0041] Figure 4 Water absorption rate of dried San@PAN membrane under different humidity: 30% semi-arid, 60% mild, 90% humid state.

[0042] Figure 5 Internal ion concentration graph of collected water of CB-LiCl@PAN membrane and CB-PDMS@PAN membrane.

[0043] Figure 6 Surface temperature of outer layer nanofiber membrane (CB-PDMS@PAN) with different carbon black loadings under sunlight. DETAILED DESCRIPTION

[0044] The preferred embodiments of the present application are described below, and it should be understood that the embodiments are for better explaining the present application, and are not used to limit the present application.

[0045] Test method:

[0046] 1. Water harvesting performance:

[0047] On June 24, 2022, the test was carried out in the actual outdoor environment in Wuxi, China, using self-made equipment, and the outdoor temperature varied in the range of 23.1℃-46.2℃, and the relative humidity varied in the range of 40.6% RH-95.7% RH. During the period, the sandwich structure atmospheric water harvesting nanofiber membrane was placed in a transparent acrylic box, and the box was placed on an electronic balance, and the water harvesting performance of the sandwich structure atmospheric water harvesting nanofiber membrane was measured by recording the mass change of the sandwich structure atmospheric water harvesting nanofiber membrane.

[0048] 2. Water evaporation performance:

[0049] The sandwich structure atmospheric water harvesting nanofiber membrane saturated with water was placed under 1kW m -2 of simulated light, and the mass of the sandwich structure atmospheric water harvesting nanofiber membrane was measured every 1 min, and the surface temperature change was measured by using an infrared thermal imager during the period, and the water evaporation performance of the sandwich structure atmospheric water harvesting nanofiber membrane was reflected by the mass change and surface temperature change of the sandwich structure atmospheric water harvesting nanofiber membrane.

[0050] 3. Cycling performance:

[0051] The prepared sandwich structure atmospheric water harvesting nanofiber membrane was placed in a constant temperature and humidity chamber at 25℃, 60% RH for 4h to absorb water, and its water harvesting efficiency was measured, then it was completely dried in an oven at 100℃, after that the sandwich structure atmospheric water harvesting nanofiber membrane was again placed in a constant temperature and humidity chamber at 25℃, 60% RH for 4h to absorb water, its water harvesting efficiency was calculated again, and then it was dried again; after such repeated measurement for 10 times, the change of its water harvesting efficiency was observed.

[0052] Raw materials used in the examples:

[0053] Carbon black (CB): particle size 24nm;

[0054] Polyacrylonitrile (PAN), carbon black nanoparticles, nylon 66 (PA), cellulose acetate (CA) and polyurethane (PU) can be bought in the local market;

[0055] Lithium chloride (LiCl), calcium chloride (CaCl2), N,N-dimethylformamide (DMF), m-cresol, n-hexane, octamethylcyclotetrasiloxane (D4), tetrahydrofuran and magnesium chloride (MgCl2) were purchased from Shanghai Roder Scientific Co., Ltd.

[0056] PDMS and curing agent diphenylbutyl carbamate DBP were purchased from Dow Corning.

[0057] Example 1

[0058] A method for preparing a sandwich structure atmospheric water harvesting nanofiber membrane, comprising the following steps:

[0059] (1) Preparation of nanofiber membrane:

[0060] Polyacrylonitrile (PAN) was dissolved in N,N-dimethylformamide (DMF) and stirred for 12h to obtain a polyacrylonitrile (PAN) solution; then carbon black (CB) was added to the polyacrylonitrile (PAN) solution, which was dispersed in an ultrasonic disperser for 6h to obtain a spinning solution, the mass ratio of polyacrylonitrile (PAN), N,N-dimethylformamide (DMF) and carbon black (CB) in the spinning solution was 10:82:8;

[0061] The spinning solution was then electrospun, with the electrospinning speed set at 1.5mL h -1 , the applied voltage set at 20kV, and the distance between the injector and the electrode set at 20cm, to obtain a nanofiber membrane (CB@PAN membrane); wherein the fiber diameter of the nanofiber membrane was 50-200nm, and the pore size range was 9-11μm;

[0062] (2) Preparation of hydrophilic nanofiber membrane:

[0063] The nanofiber membrane (CB@PAN membrane) was immersed in a 30wt% lithium chloride (LiCl) aqueous solution at room temperature for 24h at a bath ratio of 1:20, taken out, and dried in a vacuum oven at 90°C for 2h to obtain a hydrophilic nanofiber membrane (CB-LiCl@PAN membrane).

[0064] (3) Preparation of a hydrophobic nanofiber membrane:

[0065] The hydrophobic agent polydimethylsiloxane PDMS was mixed with the curing agent butyl diphenyl urea DBP at a mass ratio of 10:1 to obtain a PDMS solution; then the PDMS solution was dissolved in n-hexane, and a magnetic stirrer was used for continuous stirring for 6h to obtain a hydrophobic agent solution; wherein the concentration of polydimethylsiloxane PDMS in the hydrophobic agent solution was 2wt%.

[0066] The nanofiber membrane (CB@PAN membrane) was immersed in the hydrophobic agent solution at room temperature for 0.5h at a bath ratio of 1:20, taken out, and dried in a vacuum oven at 90°C for 2h to obtain a hydrophobic nanofiber membrane (CB-PDMS@PAN membrane).

[0067] (4) Preparation of a sandwich structure atmospheric water collection nanofiber membrane:

[0068] The hydrophobic nanofiber membrane (CB-PDMS@PAN membrane) was cut into a circle with a diameter of 5.5cm; the hydrophilic nanofiber membrane (CB-LiCl@PAN membrane) was cut into a circle with a diameter of 5cm; then the hydrophobic nanofiber membrane (CB-PDMS@PAN membrane) was used to wrap the hydrophilic nanofiber membrane (CB-LiCl@PAN membrane) in the middle, and an appropriate amount of PDMS solution was added at the edge to make the hydrophobic nanofiber membrane wrap the hydrophilic nanofiber membrane completely, thereby forming a hydrophobic-hydrophilic-hydrophobic sandwich structure atmospheric water collection nanofiber membrane San@PAN.

[0069] Comparative Example 1

[0070] Polyacrylonitrile (PAN) was dissolved in N,N-dimethylformamide (DMF) and stirred for 12h to obtain a polyacrylonitrile (PAN) solution; the polyacrylonitrile (PAN) solution was used as a spinning solution, and a nanofiber membrane (PAN membrane) was prepared by electrospinning at an electrospinning speed of 1.5mL h -1 , an applied voltage of 20kV, and an injector-electrode distance of 20cm; wherein the fiber diameter of the nanofiber membrane was 50-200nm, and the pore size range was 9-11μm.

[0071] The fiber membranes prepared in Example 1 and Comparative Example 1 were subjected to performance testing, and the test results are as follows:

[0072] Figure 2 The test results of the moisture permeability of the PAN membrane, CB@PAN membrane and CB-PDMS@PAN membrane at different times. From Figure 2 It can be seen that the moisture permeability of CB-PDMS@PAN is 6.3192 kg day - 1 m -2 , which is slightly lower than that of PAN (7.3440 kg day -1 m -2 ) and CB@PAN (6.9720 kg day -1 m -2 ), indicating that CB and PDMS coating has little effect on the moisture permeability.

[0073] Figure 3 The pore size distribution diagram and the corresponding electron microscope diagram of CB@PAN and CB-PDMS@PAN. From Figure 3 It can be seen that the pore size of CB-PDMS@PAN (about 9-11 μm) is slightly smaller than that of CB@PAN (about 10-11 μm), indicating that the addition of PDMS has little effect on the pore size of the nanofiber membrane, and does not hinder the free transmission of water molecules (~0.4 nm) in CB-PDMS@PAN.

[0074] Figure 4 The water absorption rate of the dried San@PAN membrane under different humidity: 30% semi-arid, 60% moderate, and 90% humid state. From Figure 4 It can be seen that the water absorption rate of the dried San@PAN membrane can reach 1.66, 2.68 and 4.08 g g -1 respectively under 30%, 60% and 90% RH. Moreover, San@PAN membrane reaches moisture saturation only needs 120 minutes, and the water absorption amount is positively correlated with the increase of RH.

[0075] Figure 5 The collected water internal ion concentration diagram of CB-LiCl@PAN membrane and CB-PDMS@PAN membrane. From Figure 5 It can be seen that the collected water of CB-LiCl@PAN membrane and CB-PDMS@PAN membrane is lower than the standard of World Health Organization (WHO) and U.S. Environmental Protection Agency (EPA), indicating that the collected water of sandwich structure atmospheric water harvesting nanofiber membrane is drinkable, and has high safety and reliability.

[0076] The cycle test results of CB-PDMS@PAN membrane are as follows:

[0077] After repeated measurement for 10 times, the water absorption rate of sandwich structure atmospheric water harvesting nanofiber membrane is maintained at about 3.88 g g-1 At the same time, the LiCl nanoparticle content in the interior is basically unchanged, and the high water absorption of the sandwich structure atmospheric water collection nanofiber membrane is always maintained, proving that the sandwich structure atmospheric water collection nanofiber membrane has good recycling performance and can be reused.

[0078] Example 2

[0079] A method for preparing a sandwich structure atmospheric water collection nanofiber membrane, comprising the following steps:

[0080] (1) Preparation of a nanofiber membrane:

[0081] Nylon 66 (PA) was dissolved in m-cresol and stirred for 12 h to obtain a nylon 66 (PA) solution; then carbon black (CB) was added to the nylon 66 (PA) solution, and dispersed in an ultrasonic dispersing machine for 7 h to obtain a spinning solution, wherein the mass ratio of nylon 66 (PA), m-cresol and carbon black (CB) in the spinning solution was 10:82:8;

[0082] The spinning solution was then electrospun, and the electrospinning speed was set to 1.5 mL h -1 , the applied voltage was 20 kV, and the distance between the injector and the electrode was 20 cm to prepare a nanofiber membrane (CB@PA membrane); wherein the fiber diameter of the nanofiber membrane was 50-200 nm, and the pore size range was 9-11 μm;

[0083] (2) Preparation of a hydrophilic nanofiber membrane:

[0084] The nanofiber membrane (CB@PA membrane) was immersed in a 30wt% calcium chloride (CaCl2) solution at room temperature according to a bath ratio of 1:20 for 24 h, and then taken out and dried in a vacuum oven at 90°C for 2 h to obtain a hydrophilic nanofiber membrane (CB-CaCl2@PA membrane);

[0085] (3) Preparation of a hydrophobic nanofiber membrane:

[0086] The hydrophobic agent octamethylcyclotetrasiloxane D4 was dissolved in tetrahydrofuran, and a magnetic stirrer was used for continuous stirring for 7 h to obtain a hydrophobic agent solution; wherein the concentration of octamethylcyclotetrasiloxane D4 in the hydrophobic agent solution was 2wt%;

[0087] The nanofiber membrane (CB@PA membrane) was immersed in the hydrophobic agent solution at room temperature according to a bath ratio of 1:20 for 0.5 h, and then taken out and dried in a vacuum oven at 90°C for 2 h to obtain a hydrophobic nanofiber membrane (CB-D4@PA membrane);

[0088] (4) Preparation of a sandwich structure atmospheric water collection nanofiber membrane:

[0089] The hydrophobic nanofiber membrane (CB-D4@PA membrane) is cut into a circle with a diameter of 5.5 cm; the hydrophilic nanofiber membrane (CB-CaCl2@PA membrane) is cut into a circle with a diameter of 5 cm; then the hydrophobic nanofiber membrane (CB-D4@PA membrane) is wrapped in the middle of the hydrophilic nanofiber membrane (CB-CaCl2@PA membrane), and an appropriate amount of hydrophobic agent solution is added at the edge, so that the hydrophobic nanofiber membrane can completely wrap the hydrophilic nanofiber membrane, forming a hydrophobic-hydrophilic-hydrophobic sandwich structure of the atmospheric water collection nanofiber membrane San@PA.

[0090] Through outdoor testing, the San@PA has a high water absorption rate and evaporation rate, and has good water collection performance.

[0091] Example 3

[0092] A method for preparing a sandwich structure atmospheric water collection nanofiber membrane, comprising the following steps:

[0093] (1) Preparation of nanofiber membrane:

[0094] Cellulose acetate (CA) is dissolved in DMF and stirred for 10 h to obtain a cellulose acetate (CA) solution; then carbon black (CB) is added to the cellulose acetate (CA) solution, and dispersed in an ultrasonic disperser for 8 h to obtain a spinning solution, the mass ratio of cellulose acetate (CA), DMF and carbon black (CB) in the spinning solution is 10:82:8;

[0095] The spinning solution is electrospun, the electrospinning speed is set to 1.5 mL h -1 , the applied voltage is 20 kV, and the distance between the injector and the electrode is 20 cm, to obtain a nanofiber membrane (CB@CA membrane); wherein the fiber diameter of the nanofiber membrane is 50-200 nm, and the pore size range is 9-11 μm;

[0096] (2) Preparation of hydrophilic nanofiber membrane:

[0097] The nanofiber membrane (CB@CA membrane) is immersed in a 30wt% magnesium chloride (MgCl2) aqueous solution at room temperature according to a bath ratio of 1:20 for 24 h, and then taken out and dried in a vacuum oven at 90°C for 2 h to obtain a hydrophilic nanofiber membrane (CB-MgCl2@CA membrane);

[0098] (3) Preparation of hydrophobic nanofiber membrane:

[0099] The hydrophobic agent polydimethylsiloxane PDMS and the curing agent butyl diphenyl carbamate DBP are mixed in a mass ratio of 10:1 to obtain a PDMS solution; then the PDMS solution is dissolved in n-hexane, and a magnetic stirrer is used for continuous stirring for 6 h to obtain a hydrophobic agent solution; wherein the concentration of polydimethylsiloxane PDMS in the hydrophobic agent solution is 3wt%;

[0100] The nanofiber membrane (CB@CA membrane) is immersed in the hydrophobic agent solution at room temperature for 0.5 h at a bath ratio of 1:20, and then taken out and dried in a vacuum oven at 90℃ for 2 h to obtain a hydrophobic nanofiber membrane (CB-PDMS@CA membrane);

[0101] (4) Preparation of sandwich structure atmospheric water collection nanofiber membrane:

[0102] The hydrophobic nanofiber membrane (CB-PDMS@CA membrane) is cut into a circle with a diameter of 5.5 cm; the hydrophilic nanofiber membrane (CB-MgCl2@CA membrane) is cut into a circle with a diameter of 5 cm; then the hydrophobic nanofiber membrane is used to wrap the hydrophilic nanofiber membrane in the middle, and an appropriate amount of hydrophobic agent solution is added at the edge to make the hydrophobic nanofiber membrane completely wrap the hydrophilic nanofiber membrane, forming a hydrophobic-hydrophilic-hydrophobic sandwich structure atmospheric water collection nanofiber membrane San@CA.

[0103] After outdoor testing, San@CA has a high water absorption rate and evaporation rate, and has good water collection performance.

[0104] Example 4

[0105] A method for preparing a sandwich structure atmospheric water collection nanofiber membrane, comprising the following steps:

[0106] (1) Preparation of nanofiber membrane:

[0107] Polyurethane (PU) is dissolved in DMF for 12 h to obtain a polyurethane (PU) solution; then carbon black (CB) is added to the polyurethane (PU) solution, and dispersed in an ultrasonic dispersing machine for 6 h to obtain a spinning solution; the mass ratio of polyurethane (PU), DMF and carbon black (CB) in the spinning solution is 10:82:8;

[0108] The spinning solution is electrospun, and the electrospinning speed is set to 1.5mL h -1 , the applied voltage is 20kV, and the distance between the injector and the electrode is 20cm to prepare a nanofiber membrane (CB@PU membrane); wherein the fiber diameter of the nanofiber membrane is 50-200nm, and the pore size range is 9-11μm;

[0109] (2) Preparation of hydrophilic nanofiber membrane:

[0110] The nanofiber membrane (CB@PU membrane) was immersed in a 30wt% lithium chloride (LiCl) aqueous solution at room temperature for 24 hours at a bath ratio of 1:20. After immersion, it was dried in a vacuum oven at 90℃ for 2 hours to obtain a hydrophilic nanofiber membrane (CB-LiCl@PU membrane).

[0111] (3) Preparation of hydrophobic nanofiber membranes:

[0112] The hydrophobic agent polydimethylsiloxane PDMS and the curing agent diphenylcarbamate butyl diphenylcarbamate (DBP) were mixed evenly at a mass ratio of 10:1 to obtain a PDMS solution; then, the PDMS solution was dissolved in n-hexane and stirred continuously with a magnetic stir bar for 6 hours to obtain a hydrophobic agent solution; wherein, the concentration of polydimethylsiloxane PDMS in the hydrophobic agent solution was 2 wt%.

[0113] The nanofiber membrane (CB@PU membrane) was immersed in a hydrophobic agent solution at room temperature for 0.5 h at a bath ratio of 1:20, then removed and dried in a vacuum oven at 90 °C for 2 h to obtain a hydrophobic nanofiber membrane (CB-PDMS@PU membrane).

[0114] (4) Preparation of sandwich-structured atmospheric water-collecting nanofiber membranes:

[0115] The hydrophobic nanofiber membrane (CB-PDMS@PU membrane) was cut into circles with a diameter of 5.5 cm; the hydrophilic nanofiber membrane (CB-LiCl@PU membrane) was cut into circles with a diameter of 5 cm; then the hydrophobic nanofiber membrane was used to wrap the hydrophilic nanofiber membrane in the middle, and an appropriate amount of hydrophobic agent solution was dropped at the edge so that the hydrophobic nanofiber membrane could completely wrap the hydrophilic nanofiber membrane, forming an atmospheric water-collecting nanofiber membrane San@PU with a hydrophobic-hydrophilic-hydrophobic sandwich structure.

[0116] Outdoor testing showed that San@PU has a high water absorption rate and evaporation rate, and possesses good water collection performance.

[0117] Example 5

[0118] The mass ratios of polyacrylonitrile (PAN), N,N-dimethylformamide (DMF), and carbon black (CB) in step (1) of Example 1 were adjusted to 10:88:2, 10:86:4, 10:84:6, and no carbon black, while other aspects remained the same as in Example 1, to obtain atmospheric water-collecting nanofiber membranes with sandwich structures of different carbon contents.

[0119] The obtained sandwich-structured atmospheric water-collecting nanofiber membrane was subjected to a temperature-drying performance test. The test results are as follows: Figure 6 :

[0120] from Figure 6It can be seen that the surface temperature of the sandwich structure atmospheric water collection nanofiber membrane with a mass ratio of 10:82:8 can be increased to 77.2 DEG C within 50 min, and the surface temperature of the sandwich structure atmospheric water collection nanofiber membrane with a mass ratio of 10:88:2, 10:86:4 and 10:84:6 can be increased to 43.3 DEG C, 50.5 DEG C and 61.7 DEG C within 50 min respectively, and the surface temperature of the sandwich structure atmospheric water collection nanofiber membrane without carbon black can be increased to 37.2 DEG C. It can be seen that, with the increase of the carbon content, the surface temperature of the sandwich structure atmospheric water collection nanofiber membrane gradually increases within 50 min, and reaches the maximum when the mass ratio is 10:82:8.

[0121] Example 6

[0122] When the pore size of the prepared nanofiber membrane (CB-PDMS@PAN membrane) is greater than 57 nm, atmospheric water molecules cannot penetrate, and water collection cannot be achieved;

[0123] When the pore size of the prepared nanofiber membrane (CB-PDMS@PAN membrane) is greater than 1.8 mm, the solution will leak, and water collection cannot be achieved;

[0124] Therefore, the pore size of the nanofiber membrane is between 57 nm and 1.8 mm.

[0125] Comparative Example 2

[0126] The preparation of the hydrophobic nanofiber membrane in step (3) of Example 1 is omitted, and the nanofiber membrane (CB@PAN membrane) is directly used as the upper and lower two layers, and the other steps are the same as those of Example 1, to obtain a sandwich structure atmospheric water collection nanofiber membrane.

[0127] The obtained sandwich structure atmospheric water collection nanofiber membrane is subjected to performance test, and the test results are as follows:

[0128] With the increase of the water collection time of the sandwich structure atmospheric water collection nanofiber membrane, a large amount of water molecules in the air are captured, when the water absorption gradually increases, the excess water solution will leak from the nanofiber membrane, and the LiCl dissolved in the water solution will also leak out, resulting in the decrease of the LiCl particles in the sandwich structure atmospheric water collection nanofiber membrane, and the gradually reduced water collection efficiency.

[0129] In summary, the method of the present application fully utilizes the thermal conductivity of the photo-thermal nanoparticles on the basis of the existing electrospinning technology, can collect a large amount of atmospheric water, combines with light materials, adopts a sandwich structure of hydrophobic-hydrophilic-hydrophobic, so that the prepared sandwich structure atmospheric water collection nanofiber membrane has the advantages of light weight, portability, strong water absorption and storage capacity, high safety, good durability and long service life. In addition, it is pollution-free to the environment and has good application prospect.

[0130] While the application has been described by way of example and in terms of the preferred embodiment, it is to be understood that certain modifications can be made to the disclosed apparatus without departing from the scope of the application, and the scope of the application should be determined not by the embodiment but by the appended claims.

Claims

1. A method of making a sandwich structured atmospheric water harvesting nanofiber membrane, characterized by, The method comprises the following steps: (1) Preparation of nanofiber membrane: adding photo-thermal nanoparticles into a high polymer solution, mixing uniformly to obtain a spinning solution; then preparing a nanofiber membrane through electrospinning; wherein the fiber diameter of the nanofiber membrane ranges from 50 nm to 200 nm, and the pore size ranges from 57 nm to 1.8 mm; the mass ratio of the high polymer, the solvent and the photo-thermal nanoparticles in the spinning solution is 10-20:65-88:2-8; the photo-thermal nanoparticles are carbon black with a particle size of 24 nm; the high polymer in the high polymer solution is polyacrylonitrile, nylon 66, cellulose acetate or polyurethane; (2) Preparation of hydrophilic nanofiber membrane: immersing the nanofiber membrane in a metal salt solution, taking out and drying to obtain a hydrophilic nanofiber membrane; the metal salt in the metal salt solution comprises one or more of lithium chloride, calcium chloride and magnesium chloride; (3) Preparation of hydrophobic nanofiber membrane: immersing the nanofiber membrane in a hydrophobic agent solution, taking out and drying to obtain a hydrophobic nanofiber membrane; (4) Preparation of sandwich structure atmospheric water collection nanofiber membrane: wrapping the hydrophilic nanofiber membrane in the middle with the hydrophobic nanofiber membrane to form a sandwich structure atmospheric water collection nanofiber membrane with a hydrophobic-hydrophilic-hydrophobic structure.

2. The method of claim 1, wherein, The concentration of the metal salt solution in step (2) is 10-50 wt%, and the solvent is water.

3. The method of claim 1, wherein, The concentration of the hydrophobic agent in the hydrophobic agent solution in step (3) is 1-5 wt%.

4. The method of claim 1, wherein, The hydrophobic agent solution in step (3) comprises a hydrophobic agent, a curing agent and a solvent; wherein the hydrophobic agent comprises one or more of polysiloxane, polyolefin, silicone resin and fluorocarbon polymer; the curing agent corresponds to the hydrophobic agent; the mass ratio of the hydrophobic agent to the curing agent is 5-15:1; and the solvent is one or more of water, ethanol and n-hexane.

5. The sandwich structure atmospheric water collection nanofiber membrane prepared by the method of any one of claims 1-4.

6. The use of the sandwich structure atmospheric water collection nanofiber membrane of claim 5 in the field of atmospheric water collection.

7. A method of improving the recycling performance of an atmospheric water collector, characterized by, The method uses the sandwich structure atmospheric water collection nanofiber membrane of claim 5.

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