Hydrophobic-hydrophilic Janus composite membrane with efficient fog collection and organic pollutant degradation performance as well as preparation method and application of hydrophobic-hydrophilic Janus composite membrane
By preparing a three-layer hydrophobic-hydrophilic Janus composite membrane and combining it with electrospinning technology and nano-TiO2 photocatalyst, a combined function of efficient fog collection and organic pollutant degradation was achieved. This solved the problems of high energy consumption and low pollutant degradation efficiency during fog collection and provided a freshwater increment and environmentally friendly solution.
Patent Information
- Application Number
- CN202511511061.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2025-06-04
- Filing Date
- 2025-12-29
- Publication Date
- 2026-02-27
AI Technical Summary
Existing technologies struggle to efficiently degrade organic pollutants in fog droplets during fog collection while maintaining low-energy water collection efficiency, and photocatalysts may damage membrane structures.
A three-layer hydrophobic-hydrophilic Janus composite membrane was prepared by electrospinning, with a photocatalytic intermediate layer and a hydrophobic layer covering the base membrane. The hydrophobic layer coverage was 60-75%, and the intermediate layer contained nano-TiO2 photocatalyst. By optimizing the electrospinning process parameters, a composite membrane with high efficiency in fog collection and organic pollutant degradation was prepared.
It achieves efficient freshwater collection without external power and stable degradation of organic pollutants under ultraviolet or sunlight irradiation, with a degradation rate of over 70%. This solves the problem of freshwater shortage in remote mountainous areas and islands and is in line with the concept of green and environmentally friendly development.
Smart Images
Figure CN121571005A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a hydrophobic-hydrophilic Janus composite membrane with high-efficiency fog collection and organic pollutant degradation performance, and a preparation method and application thereof. BACKGROUND
[0002] The hydrophobic-hydrophilic Janus membrane, i.e., the two sides of the membrane material have different hydrophilic and hydrophobic properties, can effectively reduce the energy consumption in the fog collection process compared to the traditional homogeneous phase membrane. The hydrophobic side is mainly a patchy structure, and the hydrophobic patches are not independent of each other, so that water can pass through the small pores between the patches more easily, and the hydrophilic layer is a dense membrane structure, which can better collect fog droplets while maintaining the stability and mechanical strength of the membrane.
[0003] When water droplets are dropped on the hydrophobic side, due to the hydrophobic effect and the surface tension of water itself, the water droplets will form a spherical ball, so that the contact part of the water droplets is squeezed into the small pores on the hydrophobic membrane. The other end of the small pores is hydrophilic, so that the water droplets can be quickly "pulled" to the hydrophilic side, realizing spontaneous transport across the membrane. The reverse process of this process cannot be automatically performed. Through this simple structure, unidirectional transport of liquid can be realized. Since this process is similar to the directional conduction of a diode in an electrical circuit, the hydrophobic-hydrophilic Janus membrane is also called a "liquid diode". This spontaneous transport process realized by using the hydrophobic-hydrophilic property reduces the additional energy required to pass the liquid through the membrane, thereby reducing external energy input.
[0004] Fog droplets often contain organic pollutants with concentrations ranging from 0.3 to 25 ppm, so the collected water still needs to be further photocatalytically degraded before use. However, the adaptation of fog collection and photocatalysis needs to be completed, and the photocatalyst does not destroy the structure of the membrane itself, and the photocatalytic efficiency and fog collection efficiency are adjusted, so that the photocatalysis is completed while the fog is collected efficiently. SUMMARY
[0005] In view of the above technical problems existing in the prior art, the purpose of the present application is to provide a hydrophobic-hydrophilic Janus composite membrane with high-efficiency fog collection and organic pollutant degradation performance, and a preparation method and application thereof.
[0006] The technical solution adopted by the present application is as follows:
[0007] A hydrophobic-hydrophilic Janus composite membrane with high-efficiency fog and organic pollutant degradation performance, the composite membrane is divided into a three-layer structure, the base film is a hydrophilic layer of a hydrophilic polymer, a photocatalytic intermediate layer and a hydrophobic layer of patchy hydrophobic polymer are sequentially covered on the base film, the photocatalytic intermediate layer material is a hydrophilic polymer doped with a nano-TiO2 photocatalyst, the base film and the photocatalytic intermediate layer constitute a collection film, the coverage of the patchy hydrophobic polymer on the collection film is 60-75%, the nano-TiO2 is nano-titanium dioxide P25, the hydrophobic polymer is at least one of polybutyl methacrylate PBMA, polypropylene PP, polyethylene PE, and polyvinylidene fluoride PVDF, and the hydrophilic polymer is at least one of polyacrylonitrile PAN and cellulose acetate CA.
[0008] Further, the coverage of the patchy PVDF hydrophobic layer on the collection film is 70-72%.
[0009] The preparation method of the hydrophobic-hydrophilic Janus composite membrane with high-efficiency fog and organic pollutant degradation performance comprises the following steps:
[0010] Step 1: Dissolve the hydrophilic polymer powder in solvent A to prepare a hydrophilic casting solution A, dissolve the hydrophobic polymer powder in solvent B to prepare a hydrophobic casting solution B, add nano-TiO2 to the casting solution A and stir thoroughly to obtain a casting solution C;
[0011] Step 2: Perform electrospinning with the casting solution A as the spinning solution to obtain a hydrophilic polymer film first layer base layer; then perform electrospinning with the casting solution C as the spinning solution on the basis of the hydrophilic polymer film base layer to obtain a TiO2-hydrophilic polymer film second layer intermediate layer with photocatalytic function; finally, perform electrospinning with the casting solution B as the spinning solution to obtain a hydrophobic polymer film third layer outer layer, thereby obtaining the composite membrane.
[0012] Further, in step 1, the solvent A is DMF, the mass concentration of the hydrophilic polymer in the casting solution A is 10-15%, the solvent B is DMAc-acetone with a volume ratio of 3-5:1, the mass concentration of the hydrophobic polymer film in the casting solution B is 18-25%, and the concentration of nano-TiO2 in the casting solution C is 0.08-0.15 g / mL.
[0013] Further, in step 2, when performing the first and second layer electrospinning, the process parameters of the electrospinning include at least one of the following parameters:
[0014] 1) The spinning distance is 6-10 cm;
[0015] 2) The pushing speed is 0.002-0.003 mm / s;
[0016] 3) the positive voltage of electrospinning is 12-16 kV, and the negative voltage is -4 kV to -6 kV;
[0017] 4) the ambient temperature is room temperature, and the relative humidity is 30%-50%;
[0018] Further, the time of electrospinning of the third layer in step 2) is 2-4 h.
[0019] Further, the process parameters of electrospinning when electrospinning the third layer in step 2) include at least one of the following parameters:
[0020] 1) the spinning distance is 6-10 cm;
[0021] 2) the pushing speed is 0.002-0.003 mm / s;
[0022] 3) the positive voltage of electrospinning is 16-20 kV, and the negative voltage is -2 kV to -4 kV;
[0023] 4) the ambient temperature is room temperature, and the relative humidity is 30%-50%;
[0024] 5) the time of electrospinning is 20-60 min, preferably 40 min.
[0025] Further, the hydrophilic polymer is PAN with a molecular weight of 100-200 kDa, and the hydrophobic polymer is PVDF with a molecular weight of 400-700 kDa, preferably 500-600 kDa.
[0026] The application further discloses an application of the hydrophobic-hydrophilic Janus composite membrane with high fog collection and organic pollutant degradation performance in synchronous fog collection and photocatalytic degradation of organic pollutants.
[0027] Compared with the prior art, the application has the following beneficial effects:
[0028] 1) The application prepares a photocatalytic Janus composite membrane with high fog collection capacity, obtains clean fresh water from the atmosphere without external power, and uses fog water resources as a new fresh water increment to further solve the water shortage and poor fresh water resource problem in remote mountainous areas and islands.
[0029] 2) The present research intends to prepare Janus two-sided film with high efficient fog collection and organic pollutant degradation performance. By simulating the heterogeneous structure on the back of desert beetle, using electrospinning fine tuning technology to composite PAN and PVDF with different wettability and structure regulation, Janus film with opposite wettability is prepared; by loading high efficient TiO2 nano photocatalyst in Janus film, composite photocatalytic Janus film with high efficient organic pollutant degradation capacity is prepared. According to the fog collection data, the property of the composite film Janus-Ti-40 of the present application is the best, and the long-time fog collection rate can reach 51.7±5.8mg / (cm 2 ·min) at most. With simulated sunlight as light source, the photocatalytic Janus composite film can stably achieve more than 70% degradation rate of bisphenol A while collecting fog, and successfully realizes the composite function of fog collection and water purification.
[0030] 3) The Janus two-sided film of the present application can realize fog collection and purification at the same time, and realize new fresh water increment without additional energy. The base structure is PAN, which mainly serves as a hydrophilic layer and a support layer, mainly giving hydrophilic properties and enhancing mechanical strength. The middle layer is a mixed layer of PAN doped with nano TiO2. Since PVDF is a transparent material, it will not absorb much light, but the multiple layers of PAN layer may limit the entry of light energy, so only nano TiO2 is inserted in the middle layer, which can better contact the light source and mainly complete photocatalytic degradation in this layer. The outer layer PVDF hydrophobic layer provides a hydrophobic surface environment, facilitating one-way water transmission performance. At the same time, the mechanical properties of PVDF are good, which can also further improve the mechanical strength. BRIEF DESCRIPTION OF DRAWINGS
[0031] Figure 1 is a real photo of Janus-Ti-40 film prepared in Example 1;
[0032] Figure 2 is a SEM image of different films;
[0033] Figure 3 is a comparison of FTIR spectrum results of different films;
[0034] Figure 4 is a comparison of UV-Vis DRS and Tauc transformation of Janus-40 film and Janus-Ti-40 film;
[0035] Figure 5 is a comparison of contact angle and dynamic contact angle of hydrophobic surface of photocatalytic Janus composite film, pure PAN film and pure PVDF film;
[0036] Figure 6 is the detection result of droplets generated by aerosol generator;
[0037] Figure 7 is the comparison results of the fog collection amount of the photocatalytic Janus composite membrane 20 min, the fog collection rate within 20 min, and the average fog collection rate of the fog collection 40 min;
[0038] Figure 8 is a diagram of the degradation ability of bisphenol A of the photocatalytic Janus composite membrane under ultraviolet and simulated sunlight conditions, Figure 8 UV represents ultraviolet conditions, and SUN represents simulated sunlight conditions;
[0039] Figure 9a is a SEM diagram of the PVDF-180k membrane of Comparative Example 1 under 1k magnification;
[0040] Figure 9b is a SEM diagram of the PVDF-180k membrane of Comparative Example 1 under 200 times magnification;
[0041] Figure 10 is a comparison diagram of the dynamic contact angle of the Janus membrane loaded with different molecular weight PVDF. DETAILED DESCRIPTION
[0042] The application will be further described below in conjunction with specific examples, but the scope of protection of the application is not limited thereto.
[0043] The experimental reagents used in the embodiments of the application are shown in Table 1.
[0044] Table 1
[0045]
[0046] Example 1: Preparation of photocatalytic Janus composite membrane
[0047] 1.1, Preparation of casting solution
[0048] Preparation of casting solution A: dissolve PAN powder in DMF solvent to prepare a casting solution with a mass concentration of 12wt% PAN, continuously stir at 70°C and 300rpm overnight to obtain casting solution A.
[0049] Preparation of casting solution B: dissolve PVDF powder (molecular weight is 534kDa) in mixed solvent (DMAc / acetone = 4:1, v / v) to prepare a casting solution with a mass concentration of 20wt% PVDF, continuously stir at 70°C and 300rpm overnight to obtain casting solution B.
[0050] Preparation of casting solution C: load nano-TiO2 by doping method, weigh nano-TiO2 in casting solution A, prepare a dispersion liquid with TiO2 concentration of 0.1 g / mL, continuously stir at 70°C and 300 rpm for 4 h in the dark to make nano-TiO2 fully dispersed in the casting solution, and obtain casting solution C.
[0051] 1.2. Preparation of photocatalytic Janus composite membrane by electrospinning method
[0052] The preparation of Janus composite membrane by electrospinning method includes the following steps:
[0053] Step 1: Use a 5 mL syringe with a flat 18 gauge needle for spinning in the electrospinning machine, fix the syringe on the reciprocating moving platform, set the center position of the moving platform to 60 mm, the movement swing to 60 mm, and the moving speed to 20 mm / s. The rotating collector rotates at 200 rpm and is covered with an aluminum foil to collect the spun fibers.
[0054] Step 2: Electrospinning with casting solution A as the spinning solution to obtain a hydrophilic PAN membrane first layer;
[0055] Step 3: Then electrospinning with casting solution C as the spinning solution on the basis of the PAN membrane base layer to obtain a TiO2-PAN membrane second layer intermediate layer with photocatalytic function;
[0056] Step 4: Finally, electrospinning with casting solution B as the spinning solution on the basis of the PAN membrane base layer and the TiO2-PAN membrane intermediate layer surface to obtain a hydrophobic PVDF membrane third layer outer layer, i.e. the composite membrane.
[0057] When electrospinning the first and second layers, the electrospinning process parameters are as follows: the spinning distance is 8 cm, the pushing speed is 0.0023 mm / s, the positive voltage of electrospinning is 15 kV, the negative voltage is -5 kV, and the temperature and humidity in the electrospinning chamber are controlled at 25°C and 35%, respectively.
[0058] When electrospinning the third layer, the electrospinning process parameters are as follows: the spinning distance is 8 cm, the pushing speed is 0.0023 mm / s, the positive voltage of electrospinning is 17 kV, the negative voltage is -3 kV, and the temperature and humidity in the electrospinning chamber are controlled at 25°C and 35%, respectively.
[0059] After the electrospinning of all the above steps is completed, the spun membrane is dried in an oven at 60°C overnight to volatilize the residual solvent. Finally, the membrane is peeled off from the aluminum foil in a 75% ethanol solution and dried at room temperature for further use. The composition of the membranes in different groups and the spinning time of each layer are shown in Table 2.
[0060] The operations of steps 3-4 above are omitted when spinning the PAN film, and the operations of steps 2-3 above are omitted when spinning the PVDF film.
[0061] The operation of step 3 above is omitted when spinning the Janus-10, Janus-20, Janus-30, Janus-40, Janus-50, and Janus-60 films.
[0062] Table 2: Composition of Janus films and spinning time
[0063]
[0064] The actual image of the Janus-Ti-40 film prepared in Table 2 of Example 1 is shown in Figure 1 , which is a titanium white fiber film, and the surface is relatively smooth.
[0065] Figure 2 The middle sub-figures (a)-(b) are SEM images of the Janus-40 film and the Janus-Ti-40 film at a magnification of 5k, which can be compared to see the difference between the electrospun fibers under the conditions of loading and non-loading of TiO2, and the different morphologies of PAN and PVDF under the electron microscope.
[0066] Figure 2 The middle sub-figures (c)-(h) are SEM images of the Janus-Ti-10 film, the Janus-Ti-20 film, the Janus-Ti-30 film, the Janus-Ti-40 film, the Janus-Ti-50 film, and the Janus-Ti-60 film at a magnification of 200, which can be seen that the loading amount of PVDF on the film surface and the surface morphology change with different spinning times. Figure 2 The sub-figures (c)-(h) of FIG. 4 are images after the PVDF spinning time is 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min. It can be known from the processing of the obtained images by the ImageJ software that the PVDF coverage rates are 23.01%, 46.70%, 62.73%, 71.27%, 74.28%, and 84.42%, respectively, and the PVDF coverage rate gradually increases with the increase of the spinning time. Figure 2 The spots in the sub-figures (c)-(h) of FIG. 4 are PVDF, and the PVDF coverage rate can be calculated by analyzing the area ratio of the black spots in the entire image.
[0067] The FTIR spectra of the hydrophilic side of the Janus-40 film and the Janus-Ti-40 film and the comparison results with the pure PAN and pure PVDF films are shown in Figure 3 The FTIR spectra of the hydrophobic side of the Janus-40 and Janus-Ti-40 and the comparison results with the pure PAN and pure PVDF films are shown inFigure 3 Sub-image b.
[0068] according to Figure 3 The results showed that the hydrophobic surface of Janus-40 was at 2240 cm⁻¹. -1 830cm -1 -880cm -1 A distinct characteristic peak appears at 2240 cm⁻¹, with the hydrophobic surface of Janus-Ti-40 at this point. -1 830cm -1 -880cm -1 440cm -1 A distinct characteristic peak appears at this point. The hydrophilic surfaces of both Janus-40 and Janus-Ti-40 are only at 2240 cm⁻¹. -1 A distinct characteristic peak appears. 2240cm -1 The peak at 830 cm⁻¹ represents the cyano (C≡N) stretching vibration peak, the most prominent characteristic peak of PAN. It is detected on both the hydrophobic and hydrophilic sides. Notably, on the hydrophilic side, the intensity of the cyano (C≡N) stretching vibration peak is basically consistent with that of the pure PAN film, indicating that the hydrophilic side composition is quite similar to that of the pure PAN film. On the hydrophobic side, the intensity of the cyano (C≡N) stretching vibration peak is significantly lower, but it still exists, indicating that the PVDF layer does not completely cover the PAN layer. -1 -880cm -1 The peak at 440 cm⁻¹ represents the stretching vibration of the CF bond, a characteristic peak of β-type PVDF. It is evident that this peak appears only on the hydrophobic side, proving that PVDF exists only on the hydrophobic side. -1 The peak represents the stretching vibration of the Ti-O-Ti framework, which is mainly present in anatase TiO2. The appearance of this peak on the hydrophobic side of Janus-Ti-40 indicates that nano-TiO2 can be well exposed to light and meets the relevant requirements for photocatalysis. The combined FTIR spectra demonstrate that the photocatalytic Janus composite film has been successfully synthesized.
[0069] To investigate the optical properties of the composite film after loading nano-titanium dioxide P25 onto the Janus film surface, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) was used to measure the Janus-40 and Janus-Ti-40 films, respectively. The test results are as follows: Figure 4 .Depend on Figure 4 As shown in Figure (a), the film containing nano-titanium dioxide P25 exhibits a redshift, demonstrating significant light absorption in the wavelength range below 400 nm, while the film without nano-TiO2 loading shows no significant light absorption. Figure 4As can be seen from the subgraph (b) of Figure 1, the band gap of Janus-Ti-40 is 2.79 eV, which is smaller than that of anatase (3.2 eV) and rutile (3.0 eV), and conforms to the intrinsic characteristics of nano-titanium dioxide P25. The smaller band gap can prove that the photocatalytic Janus composite film can absorb a larger range of light, and the photocatalytic Janus composite film can utilize part of the visible light to some extent, which also makes it play a better role in actual application scenarios.
[0070] In addition, for the Janus-Ti-40 film, the tensile mechanical strength of the film was measured by an electronic universal testing machine, and the experimental results were as follows: the mechanical strength of Janus-Ti-40 was large, and the tensile strength reached 3.04 Mpa, which could well meet the use requirements.
[0071] The water contact angle of the hydrophobic surface of the photocatalytic Janus composite film with different PVDF loadings, the pure PAN film and the pure PVDF film was tested by using a contact angle instrument, and the results were as shown in Figure 2 (a). Figure 5 As can be seen from Figure 2 (a), with the increase of the PVDF loading, the water contact angle of the hydrophobic surface of the photocatalytic Janus composite film is larger, and the property is more hydrophobic. Figure 5 As can be seen from Figure 2 (a), with the increase of the PVDF loading, the water contact angle of the hydrophobic surface of the photocatalytic Janus composite film is larger, and the property is more hydrophobic. Figure 5 As can be seen from Figure 2 (b), the through time of the water droplets on the surfaces of different films is different, when the PVDF spinning time is greater than 30 min, the water droplets usually pass through the composite film in a more hydrophobic state, which means that it mainly relies on the Young-Laplace capillary pressure (P) and Laplace pressure (P L ) for one-way water conduction, rather than hydrophilic diffusion, and the through time of Janus-Ti-40 is the shortest, which proves that it is the best film in one-way water conduction performance.
[0072] Comparative Example 1:
[0073] The preparation process of the comparative example 1 composite film was repeated with the preparation process of Janus-Ti-40 film in Example 1, the only difference was that "in the preparation process of the casting solution B, the PVDF powder (molecular weight is 534 kDa) was replaced by the same mass of PVDF powder (molecular weight is 180 kDa)", and the rest of the conditions were unchanged, and finally the composite film was marked as PVDF-180k film.
[0074] The SEM images of PVDF-180k film under 1k times and 200 times magnification are shown in Figures 3 (a) and 3 (b) respectively. Figure 9a Figure 9b As shown, it is not difficult to find from the SEM images that when PVDF with a molecular weight of 180 kDa is used for spinning, the Janus membrane surface obtained does not have PVDF hydrophobic patches, but has PVDF fibers distributed in filaments, which is quite different from the image we expected to obtain.
[0075] The Janus-Ti-40 membrane of Example 1 is marked as PVDF-534k membrane.
[0076] The surfaces of the PVDF-180k membrane of Comparative Example 1 and the PVDF-534k membrane of Example 1 are respectively tested for dynamic contact angle using a contact angle meter, and the test results are as shown in Figure 10 As shown, the dynamic contact angles of the Janus membranes loaded with PVDF of different molecular weights are measured, and it is not difficult to find that when the PVDF spinning is performed for 40 min, the molecular weight of PVDF has a great influence on the performance of the composite membrane. The Janus membrane loaded with PVDF with a molecular weight of 534 kDa has a one-way water transmission property, and the water droplets can pass through the membrane at a faster speed, while the Janus membrane loaded with PVDF with a molecular weight of 180 k cannot achieve these effects.
[0077] Example 2, simulation of fog environment for testing the fog collecting performance of the membrane:
[0078] Experiments are tested using different Janus membranes in Table 2 of Example 1:
[0079] 1) Fog collecting performance test of photocatalytic Janus composite membrane
[0080] The photocatalytic Janus composite membranes with different PVDF loading times are covered on a 50 mL graduated cylinder (cross-sectional area 3.75 cm 2 ) with the hydrophobic side outward and the hydrophilic side inward, serving as a simple fog collecting device. A commercial aerosol generator (average droplet size 7 μm, fog output speed 1 mL / min, fog flow speed 0.5 m / s, fog concentration 0.65 g / m 3 ) is used to spray at a distance of 30 cm from the fog collecting device, and the fog collecting device is weighed with an electronic balance after 2 min, 4 min, 7 min, 10 min, 15 min, and 20 min, respectively, to calculate the fog collecting efficiency.
[0081] The fog droplets generated by the commercial aerosol generator are collected using a hydrophobic glass slide and placed in a special sealed device to prevent the droplets from shrinking due to evaporation, and an optical microscope is used for observation to measure the average droplet size.
[0082] 2) The aerosol generator used in this experiment has a fog output speed of 1 mL / min, a fog flow speed of 0.5 m / s, and a fog concentration of 0.65 g / m3 For further accuracy of the experiment, size measurement of the droplets generated by the aerosol generator used in this experiment was conducted, and the results are shown in Figure 6 Due to the collision of droplets with the hydrophobic glass sheet to generate larger droplets, droplets with relatively uniform distribution were selected for measurement, and it was found that the average size of the droplets generated by the aerosol generator used in this experiment was about 7 μm, which was consistent with the size of the droplets in natural conditions and could be used as a fog simulation device.
[0083] 3) The fog collection amounts of the photocatalytic Janus composite membranes with different PVDF loading times within 20 min are summarized in Figure 7 (a), and the fog collection rate of the photocatalytic Janus composite membranes within 20 min is summarized in Figure 7 (b), and the average fog collection rate of Janus-Ti-20, Janus-Ti-40 and Janus-Ti-60 membranes within 40 min is summarized in Figure 7 (c), and the fog collection rate = the amount of collected fog water ÷ collection time.
[0084] The following results can be seen from Figure 7 :
[0085] ① Within 20 min, the fog collection amount of Janus-Ti-40 was the largest, which was 568.9 ± 45.4 mg / cm 2 , followed by Janus-Ti-20, which was 524.4 ± 72.8 mg / cm 2 , and the fog collection amounts of Janus-Ti-10, Janus-Ti-30, Janus-Ti-50 and Janus-Ti-60 were 424.0 ± 36.1 mg / cm 2 , 470.7 ± 16.2 mg / cm 2 , 460.4 ± 12.6 mg / cm 2 , 455.11 ± 34.3 mg / cm 2 , respectively, but were significantly higher than the fog collection efficiency of pure PAN membrane (125.3 ± 23.2 mg / cm 2 ) and pure PVDF membrane (64.0 ± 2.67 mg / cm 2 ).
[0086] ② By observing Figure 7(a) It is not difficult to find that the 20 min fog collection amount of the photocatalytic Janus composite film presents an "M" type change trend with different PVDF loading times, which is quite different from the expected trend of first increasing and then decreasing. Therefore, three films, Janus-Ti-20, Janus-Ti-40 and Janus-Ti-60, were selected as representatives for further analysis of the 20 min fog collection rate, and the results are shown in Figure 7 (b).
[0087] ③ Except for Janus-Ti-40, the fog collection efficiency of the rest of the photocatalytic Janus composite films all presents a trend of first increasing and then decreasing, while Janus-Ti-40 can maintain a relatively high efficiency all the time. During the fog collection process, Janus-Ti-40 can always maintain a relatively "dry" state, and the water droplets on the surface of the film are less than those of Janus-Ti-20 and Janus-Ti-60. Therefore, the fog collection of Janus-Ti-20, Janus-Ti-40 and Janus-Ti-60 was continued for 40 min to determine their long-term fog collection ability. As shown in Figure 7 (c), the results show that the fog collection rates of Janus-Ti-20, Janus-Ti-40 and Janus-Ti-60 are 27.7 ± 4.7 mg / (cm 2 ·min), 51.7 ± 5.8 mg / (cm 2 ·min) and 21.1 ± 4.6 mg / (cm 2 ·min), respectively. Without doubt, the fog collection effect of Janus-Ti-40 has an incomparable advantage in a longer time dimension.
[0088] ④ According to the analysis of the surface hydrophilic and hydrophobic data, when the PVDF spinning time is less than 40 min (the PVDF coverage rate is less than 71.27%), the amount of exposed PAN on the surface is still large. At this time, the PAN hydrophilic layer can quickly collect small water droplets in the air, but due to the small amount of PVDF loading, the hole-shaped water transmission channel between the PVDF patches is large, the Young-Laplace capillary pressure (P) of the water droplets is small, and the Laplace pressure (P L ) is also small, which all lead to the fact that the water droplets cannot be quickly transported in one direction. Therefore, although Janus-Ti-20 can quickly collect more fog at the early stage, the fog collection efficiency begins to decrease rapidly after reaching a relative saturation state as more and more fog is collected.
[0089] When the PVDF spinning time is greater than 40 min (the PVDF coverage is greater than 71.27%), the amount of exposed PAN on the surface is small, and the rate of capturing small water droplets in the air by the PAN hydrophilic layer is also low. At the same time, the number of hole-shaped water transport channels between the PVDF patches is reduced, the water transport speed is low, and the hydrophobic layer continuously forms larger water droplets, but cannot be transported to the lower surface of the membrane at a faster rate and desorbed.
[0090] When the PVDF spinning time is 40 min (the PVDF coverage is 71.27%), the number of pore diameters formed by the surface hydrophobic layer is appropriate, the Young-Laplace capillary pressure (P) on the surface water droplets is larger, the Laplace pressure (P L ) is also larger, and the comprehensive one-way water transport rate is the fastest. The membrane surface can always maintain a relatively "dry" state and can continuously obtain fog resources from the outside world. From the perspective of long-term fog collection, the membrane structure of Janus-Ti-40 is the best.
[0091] Example 3, photocatalytic performance test:
[0092] Different Janus membranes in Table 2 of Example 1 were used for experimental testing:
[0093] 1) Janus composite membrane photocatalytic performance test
[0094] 12.5 mg of bisphenol A was dissolved in 250 mL of deionized water to prepare a 50 ppm bisphenol A stock solution and stored in a blue cap bottle. In the experiment, the bisphenol A stock solution was diluted to 2.5 ppm to simulate the concentration of pollutants in the fog, and the fog collection device in Example 2 was used to collect the simulated pollutants. At the same time, a 300 W xenon lamp was used as a light source to simulate sunlight illumination, and the fog was continuously collected for 30 min. The collected liquid was passed through a 0.22 μm water membrane for subsequent liquid chromatography determination.
[0095] The concentration of bisphenol A in the fog water was determined by high performance liquid chromatography. The chromatographic parameters are as follows: the mobile phase is methanol: water = 75:25 (v / v), the column temperature is 30°C, the ultraviolet detection wavelength is 224 nm, the injection amount is 20 μL, the flow rate is 0.7 mL / min, the detection time is 9 min, and the peak time is 5.1 min.
[0096] 2) To investigate the photocatalytic effect of the Janus composite membrane in actual fog collection, a 20-minute fog collection simulation experiment was conducted using a bisphenol A solution with an initial concentration (C0) of 2.5 ppm as the fog simulation liquid under both ultraviolet (λ = 365 nm) and simulated sunlight (simulated sunlight wavelength, covering the entire wavelength range). The concentration of the collected fog water was denoted as C (the collected fog water is the water formed after fog capture by the Janus composite membrane, which is then collected in a graduated cylinder through the Janus composite membrane). The degradation rate of each membrane was expressed as (C0 - C / C0). The degradation rates of different photocatalytic Janus composite membranes under different light conditions are shown below. Figure 8 As shown.
[0097] according to Figure 8 The results showed that all types of photocatalytic Janus composite membranes exhibited good photocatalytic effects, with degradation rates exceeding 70%. Janus-Ti-20 demonstrated particularly good photocatalytic degradation performance under both UV and sunlight conditions, achieving degradation rates of 94.7±0.6% and 87.3±5.7%, respectively. Since the photocatalyst loading was the same for all types of Janus composite membranes, the difference in degradation rates between them may be related to the mist collection rate of the membrane. This explains why Janus-Ti-40 (UV: 81.0±12.2%; Sun: 80.3±10.3%) showed relatively lower degradation rates under both UV and sunlight conditions.
[0098] The degradation rate under ultraviolet light is generally greater than that under sunlight. Although nano-titanium dioxide P25 can absorb some visible light, it absorbs ultraviolet light more strongly. At the same time, ultraviolet light can provide more energy. The ultraviolet intensity in sunlight is low. Therefore, the degradation rate under ultraviolet conditions is relatively large.
[0099] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.
Claims
1. A hydrophobic-hydrophilic Janus composite membrane with high-efficiency fog and organic pollutant degradation performance, characterized in that The composite membrane is divided into three layers, the base film is a hydrophilic layer of a hydrophilic polymer, a photocatalytic intermediate layer and a patchy hydrophobic polymer hydrophobic layer are sequentially covered on the base film, the photocatalytic intermediate layer material is a hydrophilic polymer doped with nano TiO2 photocatalyst, the base film and the photocatalytic intermediate layer constitute a collection film, the coverage of the patchy hydrophobic polymer on the collection film is 60-75%, the nano TiO2 is nano titanium dioxide P25, the hydrophobic polymer is at least one of polybutyl methacrylate PBMA, polypropylene PP, polyethylene PE, and polyvinylidene fluoride PVDF, and the hydrophilic polymer is at least one of polyacrylonitrile PAN and cellulose acetate CA.
2. The hydrophobic-hydrophilic Janus composite membrane with high-efficiency mist and organic pollutant degradation performance according to claim 1, characterized in that The coverage of the patchy PVDF hydrophobic layer on the collection film is 70-72%.
3. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high-efficiency mist and organic pollutant degradation performance according to claim 1, characterized in that The method comprises the following steps: Step 1: Dissolve the hydrophilic polymer powder in solvent A to prepare a hydrophilic casting solution A, dissolve the hydrophobic polymer powder in solvent B to prepare a hydrophobic casting solution B, add nano TiO2 to the casting solution A and stir well to obtain a casting solution C; Step 2: Perform electrospinning with the casting solution A as the spinning solution to obtain a hydrophilic polymer film first layer base layer; then perform electrospinning with the casting solution C as the spinning solution on the basis of the hydrophilic polymer film base layer to obtain a TiO2-hydrophilic polymer film second layer intermediate layer with photocatalytic function; finally, perform electrospinning with the casting solution B as the spinning solution to obtain a hydrophobic polymer film third layer outer layer, thereby obtaining the composite membrane.
4. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high-efficiency mist and organic pollutant degradation performance according to claim 3, characterized in that In step 1, the solvent A is DMF, the mass concentration of the hydrophilic polymer in the casting solution A is 10-15%, the solvent B is DMAc-acetone with a volume ratio of 3-5:1, and the mass concentration of the hydrophobic polymer film in the casting solution B is 18-25%; the concentration of nano TiO2 in the casting solution C is 0.08-0.15 g / mL.
5. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in fog collection and organic pollutant degradation as described in claim 3, characterized in that... In step 2, when performing the first and second layer electrospinning, the process parameters of electrospinning include at least one of the following parameters: 1) The spinning distance is 6-10 cm; 2) The pushing speed is 0.002-0.003 mm / s; 3) The positive voltage of electrospinning is 12-16 kV, and the negative voltage is -4 kV to -6 kV; 4) The environmental temperature is room temperature, and the relative humidity is 30%-50%; Among them, the time of the first layer electrospinning is 2-4 h, and the time of the second layer electrospinning is 0.5-1.2 h.
6. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in fog collection and organic pollutant degradation as described in claim 3, characterized in that... In step 2), when performing the third layer electrospinning, the process parameters of electrospinning include at least one of the following parameters: 1) The spinning distance is 6-10 cm; 2) The pushing speed is 0.002-0.003 mm / s; 3) The positive voltage of electrospinning is 16-20 kV, and the negative voltage is -2 kV to -4 kV; 4) The environmental temperature is room temperature, and the relative humidity is 30%-50%; 5) The time of electrospinning is 20-60 min.
7. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in fog collection and organic pollutant degradation as described in claim 6, characterized in that... The time of the third layer electrospinning is 40 min.
8. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in fog collection and organic pollutant degradation as described in claim 3, characterized in that... The hydrophilic polymer is PAN with a molecular weight of 100-200 kDa, and the hydrophobic polymer is PVDF with a molecular weight of 400-700 kDa.
9. The use of a hydrophobic-hydrophilic Janus composite membrane with high efficiency of fog and organic pollutants degradation in the simultaneous fog collection-photocatalytic degradation of organic pollutants according to claim 1.
10. The use according to claim 9, wherein The process of photocatalysis is carried out under UV light or sunlight irradiation.