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

Abstract

The invention discloses a hydrophobic-hydrophilic Janus composite membrane with efficient fog collection and organic pollutant degradation performance and a preparation method and application thereof.The composite membrane is of a three-layer structure, a base membrane of the composite membrane is a PAN hydrophilic layer, the base membrane is sequentially covered with a photocatalytic middle layer and a plaque PVDF hydrophobic layer, and the photocatalytic middle layer and the plaque PVDF hydrophobic layer are sequentially arranged on the base membrane. The base membrane is a plaque-shaped PVDF hydrophobic layer, the photocatalytic middle layer is a PAN hydrophilic layer doped with a nano TiO2 photocatalyst, the base membrane and the photocatalytic middle layer form an integrated membrane, the coverage rate of the plaque-shaped PVDF hydrophobic layer on the integrated membrane is 60-75%, and nano TiO2 is nano titanium dioxide P25. According to the Janus two-side film, fog can be captured and purified at the same time, new fresh water increment is achieved without additional energy, the composite film Janus Ti-40 is optimal in property, the long-time fog collection rate can reach 51.7 + / -5.8 mg / (cm < 2 >. Min) at most, simulated sunlight is used as a light source, and the effect that the fresh water can be increased is achieved. The photocatalytic Janus composite membrane can stably achieve the degradation rate of 70% or above on bisphenol A while collecting fog, and the composite function of fog collection and water purification is successfully achieved.

Description

Technical Field

[0001] The invention relates to a hydrophobic-hydrophilic Janus composite membrane with high-efficiency mist collection and organic pollutant degradation performance, a preparation method and application thereof. Background Art

[0002] The hydrophobic-hydrophilic Janus membrane, with different hydrophilic and hydrophobic properties on both sides of the membrane material, can effectively reduce energy consumption during fog collection compared to traditional homogeneous membranes. The hydrophobic side is primarily a patchy structure, with the hydrophobic patches being independent of each other, allowing water to easily pass through the small pores between the patches. The hydrophilic layer, on the other hand, is a dense membrane-like structure, which maintains membrane stability and mechanical strength while better absorbing collected fog droplets.

[0003] When a water droplet lands on the hydrophobic side, the hydrophobic effect and the surface tension of water cause the droplet to form a sphere, squeezing the portion of the droplet in contact with the membrane into a small pore in the hydrophobic membrane. The other end of the pore is hydrophilic, quickly "pulling" the droplet to the opposite, hydrophilic side, achieving spontaneous transport across the membrane. The reverse process cannot occur automatically. This simple structure enables unidirectional liquid transport, similar to the directional conduction of current by a diode in an electrical circuit. Therefore, the hydrophobic-hydrophilic Janus membrane is also known as a "liquid diode." This spontaneous transport process, achieved by exploiting the hydrophobic-hydrophilic properties, reduces the additional energy required to move 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. Therefore, the collected water still needs to be further photocatalytically degraded before it can be used. However, this requires the adaptation of fog collection and photocatalysis. Without damaging the photocatalyst's own membrane structure, the photocatalytic efficiency and fog collection efficiency must be adjusted to achieve both efficient fog collection and photocatalysis. Summary of the Invention

[0005] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a hydrophobic-hydrophilic Janus composite membrane with high efficiency in mist collection and organic pollutant degradation, as well as a preparation method and application thereof.

[0006] The technical solution adopted in the present invention is as follows:

[0007] A hydrophobic-hydrophilic Janus composite membrane with high-efficiency fog collection and organic pollutant degradation properties. The composite membrane has a three-layer structure, wherein the base membrane is a hydrophilic layer of a hydrophilic polymer, which is sequentially covered with a photocatalytic intermediate layer and a hydrophobic layer of a patchy hydrophobic polymer. The photocatalytic intermediate layer material is a hydrophilic polymer doped with a nano-TiO2 photocatalyst. The base membrane and the photocatalytic intermediate layer constitute an aggregate membrane, and the coverage rate of the patchy hydrophobic polymer on the aggregate membrane 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] Furthermore, the coverage of the patchy PVDF hydrophobic layer on the collective membrane is 70-72%.

[0009] The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in mist collection and organic pollutant degradation comprises the following steps:

[0010] Step 1: dissolving hydrophilic polymer powder in solvent A to prepare hydrophilic casting solution A, dissolving hydrophobic polymer powder in solvent B to prepare hydrophobic casting solution B, adding nano-TiO2 to casting solution A and stirring thoroughly to obtain casting solution C;

[0011] Step 2: Electrospinning is performed using casting solution A as the spinning solution to obtain the first base layer of the hydrophilic polymer membrane; then electrospinning is performed using casting solution C as the spinning solution on the basis of the hydrophilic polymer membrane base layer to obtain the second intermediate layer of the TiO2-hydrophilic polymer membrane with photocatalytic function; finally, electrospinning is performed using casting solution B as the spinning solution to obtain the third outer layer of the hydrophobic polymer membrane, that is, the composite membrane.

[0012] Furthermore, in step 1, solvent A is DMF, and the mass concentration of the hydrophilic polymer in the casting solution A is 10-15%; 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 mg / mL.

[0013] Furthermore, when performing electrospinning of the first and second layers in step 2, the electrospinning process parameters include at least one of the following parameters:

[0014] 1) The spinning distance is 6-10 cm;

[0015] 2) Pushing speed is 0.002-0.003mm / s;

[0016] 3) The positive voltage of electrospinning is 12-16kV, and the negative voltage is -4kV to -6kV;

[0017] 4) The ambient temperature is room temperature and the relative humidity is 30%-50%;

[0018] The electrospinning time of the first layer is 2-4 h, and the electrospinning time of the second layer is 0.5-1.2 h.

[0019] Furthermore, when the third layer of electrospinning is performed in step 2), the electrospinning process parameters include at least one of the following parameters:

[0020] 1) The spinning distance is 6-10 cm;

[0021] 2) Pushing speed is 0.002-0.003mm / s;

[0022] 3) The positive voltage of electrospinning is 16-20kV, and the negative voltage is -2kV to -4kV;

[0023] 4) The ambient temperature is room temperature and the relative humidity is 30%-50%;

[0024] 5) The electrospinning time is 20-60 min, preferably 40 min.

[0025] Furthermore, the hydrophilic polymer is PAN, and its molecular weight is 100-200 kDa; the hydrophobic polymer is PVDF, and its molecular weight is 400-700 kDa, preferably 500-600 kDa.

[0026] The present invention also discloses the application of the hydrophobic-hydrophilic Janus composite membrane with high-efficiency mist collection and organic pollutant degradation performance in simultaneous mist collection and photocatalytic degradation of organic pollutants, wherein the photocatalytic process is carried out under ultraviolet light or sunlight.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) This application utilizes a photocatalytic Janus composite membrane with efficient fog collection capabilities to extract clean fresh water from the atmosphere without the need for external power. This fog-derived water resource can be used as a new source of fresh water, further addressing the water shortages and limited freshwater resources in remote mountainous areas and islands. As a passive water treatment technology, the photocatalytic Janus composite membrane prepared in this application does not require significant energy consumption, aligns with the concept of green and environmentally friendly development, contributes to the development of an environmentally friendly society, and provides new ideas and methods for addressing water shortages.

[0029] 2) This study aims to prepare a Janus two-sided membrane with high efficiency in fog collection and degradation of organic pollutants. By simulating the heterogeneous structure of the back of the desert beetle, the electrospinning fine-tuning technology is used to compound PAN and PVDF with different wettabilities and perform structural regulation to prepare a Janus membrane with opposite wettability; by loading an efficient TiO2 nanophotocatalyst in the Janus membrane, a composite photocatalytic Janus membrane with high efficiency in degradation of organic pollutants is prepared. According to the fog collection data, the composite membrane Janus-Ti-40 of the present invention has the best properties, and the long-term fog collection rate can reach up to 51.7±5.8mg / (cm 2 ·min), using simulated sunlight as the light source, the photocatalytic Janus composite membrane can stably achieve a degradation rate of more than 70% for bisphenol A while collecting fog, successfully realizing the combined functions of fog collection and water purification.

[0030] 3) The Janus two-face mask of the present invention can simultaneously capture and purify fog, and achieve new fresh water increment without the need for external energy. The base structure is PAN, which mainly serves as a hydrophilic layer and a supporting layer, mainly to provide hydrophilic properties and enhance mechanical strength; the middle layer is a mixed layer of PAN doped with nano-TiO2. Since PVDF is a transparent substance, it will not absorb much light, but the multi-layer coverage of PAN may result in limited light energy entering, so nano-TiO2 is only inserted in the middle layer, which can better contact the light source and mainly complete photocatalytic degradation in this layer; the outer PVDF hydrophobic layer provides a surface hydrophobic environment, which is convenient for the realization of one-way water transmission performance. At the same time, PVDF has good mechanical properties and can further improve mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a photo of the Janus-Ti-40 membrane prepared in Example 1;

[0032] Figure 2 are the SEM images of different membranes;

[0033] Figure 3 is a comparison of FTIR spectra results of different films;

[0034] Figure 4 The comparison results of UV-Vis DRS diagram and Tauc transformation diagram of Janus-40 film and Janus-Ti-40 film are shown in Figure 2.

[0035] Figure 5 This is a comparison of the contact angle and dynamic contact angle of the hydrophobic surface of the photocatalytic Janus composite membrane, pure PAN membrane and pure PVDF membrane;

[0036] Figure 6 It is the detection result of droplets produced by the aerosol generator;

[0037] Figure 7 The results are the comparison of the amount of fog collected by the photocatalytic Janus composite film in 20 minutes, the fog collection rate within 20 minutes, and the average fog collection rate of 40 minutes;

[0038] Figure 8 This is the degradation ability of photocatalytic Janus composite film on bisphenol A under ultraviolet and simulated sunlight conditions. Figure 8 UV stands for ultraviolet conditions, and SUN stands for simulated sunlight conditions;

[0039] Figure 9a is a SEM image of the PVDF-180k membrane of Control Example 1 at 10 μm;

[0040] Figure 9b is a SEM image of the PVDF-180k membrane of Control Example 1 at 40 μm;

[0041] Figure 10 This is a comparison of the dynamic contact angles of Janus membranes loaded with PVDF of different molecular weights. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0043] The experimental reagents used in the examples of the present invention are shown in Table 1.

[0044] Table 1

[0045]

[0046] Example 1: Preparation of photocatalytic Janus composite film

[0047] 1.1 Preparation of casting solution

[0048] Preparation of casting solution A: PAN powder was dissolved in DMF solvent to prepare a casting solution with a mass concentration of 12 wt % PAN, and the solution was stirred continuously at 70° C. and 300 rpm overnight to obtain casting solution A.

[0049] Preparation of casting solution B: PVDF powder (molecular weight is 534kDa) was dissolved in a mixed solvent (DMAc / acetone = 4:1, v / v) to prepare a casting solution with a mass concentration of 20wt% PVDF. The solution was stirred continuously at 70°C and 300rpm overnight to obtain casting solution B.

[0050] Preparation of casting liquid C: Nano-TiO2 was loaded by in-situ doping method. Nano-TiO2 was weighed into casting liquid A to prepare a dispersion with a TiO2 concentration of 0.1 mg / mL. In a dark environment, the dispersion was continuously stirred at 70°C and 300 rpm for 4 hours to fully disperse the nano-TiO2 in the casting liquid to obtain casting liquid C.

[0051] 1.2 Preparation of photocatalytic Janus composite membrane by electrospinning

[0052] The preparation of Janus composite membrane by electrospinning method includes the following steps:

[0053] Step 1: Electrospinning was performed using a 5 mL syringe with a flat-tipped 18-gauge needle. The syringe was mounted on a reciprocating platform with a center position of 60 mm, a 60 mm swing, and a speed of 20 mm / s. The spun fibers were collected on a rolling collector at 200 rpm and covered with aluminum foil.

[0054] Step 2: electrospinning is performed using the casting solution A as the spinning solution to obtain the first layer of the hydrophilic PAN membrane base;

[0055] Step 3: Then, electrospinning is performed on the PAN membrane base layer using the casting solution C as the spinning solution to obtain the second intermediate layer of the TiO2-PAN membrane with photocatalytic function;

[0056] Step 4: Finally, the casting solution B is used as the spinning solution to perform electrostatic spinning on the surface of the PAN membrane base layer and the TiO2-PAN membrane intermediate layer to obtain the hydrophobic PVDF membrane third outer layer, that is, the composite membrane.

[0057] During the first and second electrospinning layers, the electrospinning process parameters were as follows: spinning distance was 8 cm, pushing speed was 0.0023 mm / s, positive voltage was 15 kV, negative voltage was -5 kV, and the temperature and humidity in the electrospinning chamber were controlled at 25°C and 35%, respectively.

[0058] When performing the third layer of electrospinning, the electrospinning process parameters were as follows: the spinning distance was 8 cm, the pushing speed was 0.0023 mm / s, the positive voltage of the electrospinning was 17 kV, the negative voltage was -3 kV, and the temperature and humidity in the electrospinning chamber were controlled at 25° C. and 35%, respectively.

[0059] After completing all the electrospinning steps, the membranes were dried in an oven at 60°C overnight to evaporate any residual solvent. Finally, the membranes were peeled from the aluminum foil in a 75% ethanol solution and left to dry at room temperature for further use. The composition of the membranes in the different groups and the spinning times for each layer are shown in Table 2.

[0060] The above steps 3-4 are omitted when spinning PAN membranes, and the above steps 2-3 are omitted when spinning PVDF membranes.

[0061] When spinning Janus-10, Janus-20, Janus-30, Janus-40, Janus-50, and Janus-60 membranes, the above step 3 is omitted.

[0062] Table 2 Janus membrane composition and spinning time

[0063]

[0064] The actual picture of the Janus-Ti-40 film prepared in Table 2 of Example 1 is as follows Figure 1 As shown, it is a titanium white fiber membrane with a relatively smooth surface.

[0065] Figure 2 The middle figures (a)-(b) are SEM images of Janus-40 membrane and Janus-Ti-40 membrane at 5k times magnification, respectively. They can compare the difference between electrospun fibers with and without TiO2 loading conditions, as well as the different morphologies of PAN and PVDF under the electron microscope.

[0066] Figure 2 The middle figures (c)-(h) are SEM images of Janus-Ti-10 membrane, Janus-Ti-20 membrane, Janus-Ti-30 membrane, Janus-Ti-40 membrane, Janus-Ti-50 membrane and Janus-Ti-60 membrane at 200 times magnification, respectively. It can be seen that the loading amount of PVDF on the membrane surface and the surface morphology change at different spinning times are different. Figure 2 Figures (c)-(h) are images of PVDF after spinning time of 10 min, 20 min, 30 min, 40 min, 50 min and 60 min respectively. By processing the obtained images with ImageJ software, it can be seen that the PVDF coverage is 23.01%, 46.70%, 62.73%, 71.27%, 74.28% and 84.42% respectively. With the increase of spinning time, the coverage of PVDF gradually increases. Figure 2 The spots in the images (c)-(h) are PVDF. The PVDF coverage can be calculated by analyzing the area ratio of the black spots on the entire screen.

[0067] The FTIR spectra of the hydrophilic side of Janus-40 membrane and Janus-Ti-40 membrane and their comparison with pure PAN and pure PVDF membranes can be found in Figure 3 Figure a, hydrophobic side FTIR spectra of Janus-40 and Janus-Ti-40 and their comparison with pure PAN and pure PVDF membranes. Figure 3 Component b of .

[0068] according to Figure 3 The results were obtained on the hydrophobic surface of Janus-40 at 2240 cm -1 、830cm -1 -880cm -1 There is an obvious characteristic peak at 2240cm -1 、830cm -1 -880cm -1 , 440cm -1 The hydrophilic surface of Janus-40 and Janus-Ti-40 is only at 2240 cm -1 There is an obvious characteristic peak. 2240cm -1 The peak at 830cm represents the cyano (C≡N) stretching vibration peak, which is the most obvious characteristic peak of PAN and is detected on both the hydrophobic and hydrophilic sides. It is worth noting that on the hydrophilic side, the cyano (C≡N) stretching vibration peak intensity is basically consistent with that of the pure PAN membrane, proving that the composition of the hydrophilic side is similar to that of the pure PAN membrane. On the hydrophobic side, the cyano (C≡N) stretching vibration peak intensity is significantly lower, but still exists, indicating that the PVDF layer does not completely cover the PAN layer. -1 -880cm -1 The peak at 440cm represents the stretching vibration of the C-F bond, which is the characteristic peak of β-type PVDF. It is not difficult to see that this peak only appears on the hydrophobic side, proving that PVDF only exists on the hydrophobic side. -1 The peak represents the stretching vibration of the Ti-O-Ti skeleton, primarily found in anatase TiO2. This peak appears on the hydrophobic side of Janus-Ti-40, demonstrating that the nano-TiO2 is well exposed to light and meets the requirements for photocatalysis. The above FTIR spectra demonstrate the successful synthesis of the photocatalytic Janus composite film.

[0069] In order to study the optical properties of the composite film after nano-titanium dioxide P25 was loaded on the surface of the Janus film, the Janus-40 film and the Janus-Ti-40 film were measured by ultraviolet visible diffuse reflectance spectroscopy (UV-Vis DRS). The test results are shown in Figure 2. Figure 4 .Depend on Figure 4 As shown in the figure (a), the film containing nano-titanium dioxide P25 has a red shift and has significant light absorption ability in the wavelength range less than 400nm, while the film without nano-TiO2 has no significant light absorption effect. Figure 4As shown in Figure (b), 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), consistent with the inherent characteristics of nano-titanium dioxide P25. This smaller band gap demonstrates that the photocatalytic Janus composite film can absorb a wider range of light. To a certain extent, the photocatalytic Janus composite film can utilize some visible light, which also makes it more effective in practical applications.

[0070] In addition, for the Janus-Ti-40 membrane, an electronic universal testing machine was used to measure the tensile mechanical strength of the membrane. The experimental results showed that the mechanical strength of Janus-Ti-40 was relatively large, with a tensile strength of 3.04 MPa, which could well meet the use requirements.

[0071] The water contact angle of the hydrophobic surface of the photocatalytic Janus composite membrane with different PVDF loadings, pure PAN membrane and pure PVDF membrane was tested using a contact angle meter. The results are as follows: Figure 5 (a) is shown. Figure 5 (a) It can be found that with the increase of PVDF loading, the contact angle of water on the hydrophobic surface of the photocatalytic Janus composite membrane becomes larger, and the property is more hydrophobic. At the same time, the dynamic contact angle of each surface is tested, and the results are as follows Figure 5 As shown in (b), it can be found that the time it takes for water droplets to pass through different membrane surfaces is different. When the PVDF spinning time is greater than 30 min, water droplets can usually pass through the composite membrane in a relatively hydrophobic state, which means that it mainly relies on the Young-Laplace capillary pressure (P) and the Laplace pressure (P L ) for unidirectional water conduction rather than hydrophilic diffusion, and Janus-Ti-40 has the shortest permeation time, proving that it is the membrane with the best unidirectional water conduction performance.

[0072] Comparative Example 1:

[0073] The preparation process of the composite membrane of Control Example 1 repeated the preparation process of the Janus-Ti-40 membrane in Example 1, with the only difference being that "in the preparation process of the casting solution B, the PVDF powder (molecular weight is 534 kDa) is replaced with the PVDF powder of the same mass (molecular weight is 180 kDa)", and the other conditions remain unchanged. The final composite membrane is marked as PVDF-180k membrane.

[0074] The SEM images of PVDF-180k membrane at 1k times and 200 times magnification are shown in Figure 2. Figure 9a and Figure 9bAs shown in the figure, it is not difficult to find from the SEM image that when PVDF with a molecular weight of 180kDa is used for spinning, the surface of the Janus membrane obtained does not have PVDF hydrophobic patches, but filamentous PVDF fibers appear, which is quite different from the image we expected.

[0075] The Janus-Ti-40 membrane of Example 1 was labeled as PVDF-534k membrane.

[0076] The dynamic contact angles of the PVDF-180k membrane of Control Example 1 and the PVDF-534k membrane of Example 1 were tested using a contact angle meter. The test results are shown in FIG. Figure 10 As shown in the figure, the dynamic contact angles of Janus membranes loaded with PVDF of different molecular weights were measured. It is not difficult to find that, even with the same 40-minute PVDF spinning process, the molecular weight of PVDF has a significant impact on the performance of the composite membranes. The Janus membrane loaded with PVDF of 534 kDa exhibits unidirectional water transport properties, and water droplets can pass through the membrane at a relatively fast rate, while the Janus membrane loaded with PVDF of 180 kDa cannot achieve these effects.

[0077] Example 2: Testing the fog collection performance of the membrane in a simulated fog environment:

[0078] Experimental tests were performed using the different Janus membranes in Table 2 of Example 1:

[0079] 1) Photocatalytic Janus composite membrane fog collection performance test

[0080] The photocatalytic Janus composite films with different PVDF loading times were covered on a 50 mL graduated cylinder (cross-sectional area 3.75 cm 2 ) was placed with the hydrophobic side of the composite membrane facing outward and the hydrophilic side facing inward as a simple mist collection device. A commercial aerosol generator (average droplet size 7 μm, mist output rate 1 mL / min, mist flow rate 0.5 m / s, mist concentration 0.65 g / m) was used. 3 ) Spray at a distance of 30 cm from the mist collection device. Weigh the mist collection device with an electronic balance after 2 minutes, 4 minutes, 7 minutes, 10 minutes, 15 minutes and 20 minutes respectively, and calculate the mist collection efficiency.

[0081] The droplets generated by a commercial aerosol generator were collected using a hydrophobic glass slide and placed in a special sealed device to prevent the droplets from shrinking due to evaporation. The droplets were observed using an optical microscope and the average particle size of the droplets was measured.

[0082] 2) The aerosol generator used in this experiment has a mist output rate of 1 mL / min, a mist flow rate of 0.5 m / s, and a mist concentration of 0.65 g / m3 In order to make the experiment more accurate, the size of the droplets produced by the aerosol generator used in this experiment was measured. The results are shown in Figure 6 Because droplets collide when they contact the hydrophobic glass slide, larger droplets are generated. Therefore, relatively evenly distributed droplets were selected for measurement. The results showed that the average droplet size produced by the aerosol generator used in this experiment was approximately 7 μm, which is consistent with the size of fog droplets in natural conditions and can be used as a fog simulation device.

[0083] 3) The fog collection amount of the photocatalytic Janus composite membrane with different PVDF loading time within 20 minutes is summarized in Figure 7 In (a), the amount of fog collected is the mass of water collected in the measuring cylinder. The change of fog collection rate over time in 20 minutes of photocatalytic Janus composite film is summarized in Figure 7 (b) The average fog collection rates of Janus-Ti-20 membrane, Janus-Ti-40 membrane and Janus-Ti-60 membrane for 40 min are summarized in Figure 7 (c) Fog collection rate = amount of fog water collected ÷ collection time.

[0084] from Figure 7 The following results can be seen:

[0085] ① Within 20 minutes, Janus-Ti-40 collected the most fog, which was 568.9±45.4mg / cm 2 , followed by Janus-Ti-20, with a mist collection capacity of 524.4±72.8mg / cm 2 The fog collection amount of Janus-Ti-10, Janus-Ti-30, Janus-Ti-50 and Janus-Ti-60 were 424.0±36.1mg / cm 2 , 470.7±16.2mg / cm 2 , 460.4±12.6mg / cm 2 , 455.11±34.3mg / cm 2 , but were significantly higher than those of pure PAN film (125.3±23.2 mg / cm 2 ) and pure PVDF membrane (64.0±2.67mg / cm 2 ) of fog collection efficiency.

[0086] ②Through observation Figure 7(a) It is not difficult to find that the 20-min fog collection rate of the photocatalytic Janus composite membrane shows an "M"-shaped trend with different PVDF loading time, which is quite different from the expected trend of first increasing and then decreasing. Therefore, the three membranes of Janus-Ti-20, Janus-Ti-40 and Janus-Ti-60 were selected as representatives to further analyze their fog collection rate within 20 minutes. The results are shown in the figure. Figure 7 (b) shown.

[0087] ③Except for Janus-Ti-40, the fog collection efficiency of other photocatalytic Janus composite membranes tends to increase first and then decrease over time, while Janus-Ti-40 can always maintain a high efficiency. Moreover, during the fog collection process, Janus-Ti-40 can always maintain a relatively "dry" state, and the accumulated water droplets on the membrane surface are less than those of Janus-Ti-20 and Janus-Ti-60. Therefore, Janus-Ti-20, Janus-Ti-40, and Janus-Ti-60 were subjected to fog collection for 40 minutes to determine their long-term fog collection capabilities. Figure 7 As shown in (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±5.8mg / (cm 2 ·min)、21.1±4.6mg / (cm 2 ·min), there is no doubt that in a longer time dimension, the fog collection effect of Janus-Ti-40 has an incomparable advantage.

[0088] ④Combined with the analysis of the hydrophilic and hydrophobic data of the membrane surface, it can be found that when the PVDF spinning time is less than 40 min (PVDF coverage is less than 71.27%), the amount of PAN exposed on the surface is still large. At this time, the PAN hydrophilic layer captures tiny water droplets in the air at a faster rate. However, due to the small amount of PVDF loading, the porous water transmission channels between the PVDF patches are larger, the Young-Laplace capillary pressure (P) of the water droplets is small, and the surface hydrophobicity is poor, and the Laplace pressure (P L ) is also small, which makes it impossible for water droplets to be quickly transported in one direction. Therefore, although Janus-Ti-20 can quickly collect more fog in the early stage, as more and more fog is collected, the fog collection efficiency begins to decline rapidly after reaching relative saturation.

[0089] However, when the PVDF spinning time is greater than 40 minutes (PVDF coverage is greater than 71.27%), the amount of PAN exposed on the surface is less, and the rate at which the PAN hydrophilic layer captures tiny water droplets in the air is also lower. At the same time, the number of porous water transmission channels between PVDF patches is reduced, the water transmission speed is low, and the hydrophobic layer continuously forms larger water droplets, but cannot be transported to the lower surface of the membrane and desorbed at a faster rate.

[0090] When the PVDF spinning time is 40 min (PVDF coverage is 71.27%), the number of pores formed in the surface hydrophobic layer is appropriate, the Young-Laplace capillary pressure (P) on the surface water droplets is large, and the Laplace pressure (P L ) is also large, and the comprehensive one-way water transmission rate is the fastest. The membrane surface can always be maintained in 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] Experimental tests were performed using the different Janus membranes in Table 2 of Example 1:

[0093] 1) Janus composite film photocatalytic performance test

[0094] Dissolve 12.5 mg of bisphenol A in 250 mL of deionized water to create a 50 ppm bisphenol A stock solution, which was then stored in a blue-capped bottle. During the experiment, the bisphenol A stock solution was diluted to 2.5 ppm to simulate the peak pollutant concentration in fog. The simulated pollutants were collected using the fog collection device described in Example 2. A 300W xenon lamp was used as a light source to simulate sunlight, and fog was collected continuously for 30 minutes. The collected liquid was passed through a 0.22 μm aqueous membrane for subsequent liquid chromatography analysis.

[0095] The concentration of bisphenol A in the mist water was determined using high-performance liquid chromatography. The chromatographic parameters were as follows: mobile phase: methanol:water = 75:25 (v / v), column temperature 30°C, UV detection wavelength 224 nm, injection volume 20 μL, flow rate 0.7 mL / min, detection time 9 minutes, and peak elution time 5.1 minutes.

[0096] 2) In order to study the photocatalytic effect of the photocatalytic Janus composite membrane in the actual fog collection process, a 20-min fog collection simulation experiment was carried out under ultraviolet (λ = 365 nm) and simulated sunlight (the wavelength of simulated sunlight is the full wavelength range). The initial concentration (C0) of bisphenol A solution was 2.5 ppm as the fog simulation liquid, and the fog collection simulation experiment was carried out. The collected fog water concentration was recorded as C (the collected fog water is the water formed after the Janus composite membrane captures the fog, and the water is collected in the measuring cylinder through the Janus composite membrane). The degradation rate of each membrane is expressed as (C0-C / C0). The degradation rates of different photocatalytic Janus composite membranes under different light conditions are shown in the figure. Figure 8 shown.

[0097] according to Figure 8 Analysis of the results showed that all photocatalytic Janus composite membranes exhibited good photocatalytic effects, with degradation rates exceeding 70%. Janus-Ti-20 exhibited excellent photocatalytic degradation performance under both UV and sunlight conditions, with degradation rates reaching 94.7±0.6% and 87.3±5.7%, respectively. Since the photocatalyst loadings of the various Janus composite membranes were the same, the differences in degradation rates among the different Janus composite membranes may be related to the membrane's mist collection rate, which explains the relatively low degradation rates of Janus-Ti-40 (UV: 81.0±12.2%; Sun: 80.3±10.3%) 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, its absorption of ultraviolet light is stronger. At the same time, ultraviolet light can provide greater energy. The ultraviolet intensity in sunlight is lower, so 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 protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A hydrophobic-hydrophilic Janus composite membrane with high efficiency in fog collection and organic pollutant degradation, characterized in that The composite membrane has a three-layer structure, wherein the base membrane is a hydrophilic layer of a hydrophilic polymer, and the base membrane is sequentially covered with a photocatalytic intermediate layer and a hydrophobic layer of a patchy hydrophobic polymer. The photocatalytic intermediate layer material is a hydrophilic polymer doped with a nano-TiO2 photocatalyst. The base membrane and the photocatalytic intermediate layer constitute an aggregate membrane, and the coverage rate of the patchy hydrophobic polymer on the aggregate membrane 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. A hydrophobic-hydrophilic Janus composite membrane with high efficiency fog collection and organic pollutant degradation performance as claimed in claim 1, characterized in that The coverage of the patchy PVDF hydrophobic layer on the collective membrane was 70-72%.

3. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in fog collection and organic pollutant degradation according to claim 1, characterized in that The following steps are involved: Step 1: dissolving hydrophilic polymer powder in solvent A to prepare hydrophilic casting solution A, dissolving hydrophobic polymer powder in solvent B to prepare hydrophobic casting solution B, adding nano-TiO2 to casting solution A and stirring thoroughly to obtain casting solution C; Step 2: Electrospinning is performed using casting solution A as the spinning solution to obtain the first base layer of the hydrophilic polymer membrane; then electrospinning is performed using casting solution C as the spinning solution on the basis of the hydrophilic polymer membrane base layer to obtain the second intermediate layer of the TiO2-hydrophilic polymer membrane with photocatalytic function; finally, electrospinning is performed using casting solution B as the spinning solution to obtain the third outer layer of the hydrophobic polymer membrane, that is, the composite membrane.

4. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in fog collection and organic pollutant degradation according to claim 3, characterized in that In step 1, solvent A is DMF, and the mass concentration of the hydrophilic polymer in the casting solution A is 10-15%; 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 mg / mL.

5. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in mist collection and organic pollutant degradation according to claim 3, characterized in that When performing electrospinning of the first and second layers in step 2, the electrospinning process parameters include at least one of the following parameters: 1) The spinning distance is 6-10 cm; 2) Pushing speed is 0.002-0.003mm / s; 3) The positive voltage of electrospinning is 12-16kV, and the negative voltage is -4kV to -6kV; 4) The ambient temperature is room temperature and the relative humidity is 30%-50%; The electrospinning time of the first layer is 2-4 h, and the electrospinning time of the second layer is 0.5-1.2 h.

6. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in mist collection and organic pollutant degradation according to claim 3, characterized in that When the third layer of electrospinning is performed in step 2), the electrospinning process parameters include at least one of the following parameters: 1) The spinning distance is 6-10 cm; 2) Pushing speed is 0.002-0.003mm / s; 3) The positive voltage of electrospinning is 16-20kV, and the negative voltage is -2kV to -4kV; 4) The ambient temperature is room temperature and the relative humidity is 30%-50%; 5) The electrospinning time is 20-60 min.

7. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in mist collection and organic pollutant degradation according to claim 6, characterized in that The electrospinning time of the third layer was 40 min.

8. The method for preparing a hydrophobic-hydrophilic Janus composite membrane with high efficiency in mist collection and organic pollutant degradation according to claim 3, characterized in that The hydrophilic polymer is PAN, and its molecular weight is 100-200 kDa; the hydrophobic polymer is PVDF, and its molecular weight is 400-700 kDa.

9. Use of the hydrophobic-hydrophilic Janus composite membrane with high efficiency mist collection and organic pollutant degradation performance as claimed in claim 1 in simultaneous mist collection and photocatalytic degradation of organic pollutants.

10. The use according to claim 9, characterized in that The photocatalytic process is carried out under the irradiation of ultraviolet light or sunlight.

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