Efficient and stable flexible solar interface evaporation film with self-cleaning property and preparation method and application thereof

Abstract

The invention discloses an efficient, stable and self-cleaning flexible solar interface evaporation film as well as a preparation method and application thereof. The solar interface evaporation film comprises a photo-thermal material rGCW and a hydrophilic porous PVP-PVDF flexible base film. The rGCW is uniformly embedded on the surface of the flexible base membrane and in an internal polymer network, and the rGCW comprises one-dimensional MWCNTs-NH2, a substrate rGO sheet and a W18O49 nanowire loaded on rGO. GO is used as a precursor, MWCNTs-NH2 and WCl3 are added, rGCW is synthesized through high-temperature hydrothermal one-step synthesis, and rGCW is dispersed in a PVDF base membrane containing PVP by using a phase inversion method to obtain the PVDF / rGCW composite membrane. According to the interface evaporation film designed by the invention, the synergistic absorption and conversion capability of the rGCW on sunlight is efficient and stable, the PVDF base film has flexibility, so that the film has reusability, the PVP is added, so that the PVDF base film has abundant pore channels and can quickly transport water, the preparation process is relatively simple, and the film is flexible and convenient to carry and wash repeatedly; and the material has certain self-cleaning capability and good repeatability, can be used under relatively harsh environmental conditions, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of fresh water collection, and particularly relates to a flexible solar interface evaporation film with high efficiency, stability and self-cleaning property, a preparation method thereof and an application thereof. Background Art

[0002] The shortage of fresh water resources is an issue that cannot be ignored in the process of human development. Although the earth has abundant water resources, most of them are seawater that cannot be directly used, and the fresh water resources that are crucial for human survival and social development only account for 3% of the total global water resources. However, with the increase in population and continuous environmental pollution, the shortage of fresh water has become a key global problem. Early seawater desalination technologies such as multi-stage flash evaporation are not suitable for large-scale implementation due to factors such as large scale, large floor area, high energy consumption and greenhouse gas emissions. Therefore, a clean and renewable energy-driven seawater desalination method is needed.

[0003] Interface water evaporation films generally adopt a 2D structure, which confines heat at the gas-liquid interface and only heats the water at the interface, thus greatly improving the utilization rate of heat and the evaporation rate of water. However, the problem is that for common carbon films and vacuum filtration membranes, the poor adhesion and uneven distribution of photothermal materials in the vacuum filtration interface evaporation film have always restricted its performance, and although the carbon film has a good internal pore structure as an interface evaporation film, its easy-to-damage property restricts its long-term and efficient utilization. Therefore, it is particularly important to prepare an efficient solar-driven flexible interface evaporation film. Summary of the Invention

[0004] The purpose of the present invention is to provide a flexible solar interface evaporation film with high efficiency, stability and self-cleaning property, a preparation method thereof and an application thereof. The interface evaporation film comprises a composite of a photothermal conversion material rGCW and a PVDF-PVP flexible film. The photothermal conversion material rGCW comprises rGO, MWCNTs-NH2 and W 18 O 49 nanowires loaded on rGO, which are prepared by a hydrothermal method. The interface evaporation film is prepared by a phase inversion method. The synergistic absorption and conversion ability of rGO, MWCNTs-NH2 and linear W 18 O4 for sunlight effectively improves the efficiency of solar water evaporation; and the structure of the PVDF membrane is optimized by a hydrophilic additive PVP, which improves the hydrophilicity of the membrane, has good light absorption and is conducive to water conduction and transportation, thereby increasing the rate of solar water evaporation.

[0005] To achieve the above purposes, the present invention provides the following technical solutions:

[0006] A flexible solar interfacial evaporation film that is highly efficient, stable, and has self-cleaning properties, comprising a photothermal material rGCW and a hydrophilic porous PVP-PVDF (polyvinylidene fluoride-polyvinylpyrrolidone) flexible substrate film; the rGCW is uniformly embedded in the surface and internal polymer network of the flexible substrate film, and the rGCW includes one-dimensional MWCNTs-NH2 (aminated carbon nanotubes), a substrate rGO (reduced graphene oxide) sheet, and W 18 O 49 nanowires, the W 18 O 49 nanowires are uniformly loaded on the surface of the rGO sheet, and the rGO sheet is 2-6 μm; the mass percentage of the photothermal material in the flexible solar interfacial evaporation film is 15-25%, and the W 18 O 49 nanowires account for 11-64% of the mass percentage in the photothermal conversion material.

[0007] The mass ratio of the rGO, CNTs, and W 18 O 49 is 0.35-0.4:0.35-0.4:1.

[0008] The present invention provides a method for preparing a flexible solar interfacial evaporation film that is highly efficient, stable, and has self-cleaning properties, including forming a uniform casting solution by mixing rGCW, a solvent, a polymer PVDF, and a pore-forming agent PVP, then scraping to form a film, and then obtaining it by a phase inversion method.

[0009] The photothermal material rGCW is prepared by a hydrothermal method.

[0010] Specifically, it includes the following steps:

[0011] S1. Preparation of rGCW

[0012] Disperse GO (graphene oxide) and MWCNTs-NH2 powders in absolute ethanol to obtain a uniform solution. Then, add WCl6 to this system. After the solution is stirred evenly, quickly place the solution in a hydrothermal autoclave and react in an oven. Then, collect the reaction product by vacuum filtration and wash it multiple times with an ethanol solution to obtain the rGCW composite material;

[0013] S2. Preparation of the phase inversion film

[0014] Add rGCW, PVDF, PVP, and DMF to a reagent bottle, stir on a heating and stirring platform to obtain a casting solution. After ensuring relatively uniform dispersion, use an automatic film scraping machine to scrape the film. Then, quickly transfer the glass plate coated with the casting solution to deionized water, let it stand for one day, and then take it out to obtain the phase inversion film - flexible solar interfacial evaporation film.

[0015] The GO is prepared by the Hummers method. Scaly graphite is put into the mixed acid and stirred evenly. Then, potassium permanganate crystals are slowly added under an ice bath. Subsequently, the solution is stirred at room temperature for 30 min and then stirred in an oil bath. The reacted substance is quickly stirred in ice water, and hydrogen peroxide is added during this process. Then, the powder obtained by centrifuging the solution is washed 3 times with 5 wt% hydrochloric acid and then centrifuged and washed with water multiple times until the pH = 7. The precipitate is freeze-dried under vacuum for 48 h to obtain a fluffy GO powder.

[0016] In the GO preparation process, the addition amounts of various substances are as follows: the mass ratio of scaly graphite to potassium permanganate is 1:6, the volume ratio of concentrated sulfuric acid to concentrated phosphoric acid in the mixed acid is 9:1; the mass-volume ratio (g / ml) of graphite to the mixed acid solution is 1:100 - 134; the mass-volume ratio (g / ml) of graphite to hydrogen peroxide is

[0017] The set oil bath temperature is 50 ± 2 °C, and the stirring time is 12 - 15 h.

[0018] In step S1, the addition amount of WCl6 is 1 - 8 mg ml-1.

[0019] In step S1, the hydrothermal temperature is 180 °C, and the hydrothermal time is 12 h.

[0020] In step S1, the stirring duration is 15 - 20 min.

[0021] In step S2, the mass ratio of rGCW, PVDF, PVP to DMF is 0.2 - 0.3:1:0.1:10.

[0022] In step S2, first, rGCW and DMF are added to a reagent bottle and mixed evenly. Subsequently, PVP and PVDF are added to the system.

[0023] In step S2, the operating conditions are: heating temperature 65 ± 3 °C, stirring duration 12 - 15 h.

[0024] In step S2, the scraping film thickness is 375 - 425 μm.

[0025] The present invention provides a solar interface water evaporation film, and the photothermal conversion material and hydrophilic film of the evaporation film adopt the highly efficient, stable and self-cleaning flexible solar interface evaporation film.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention provides a flexible interface evaporation film, in which the linear W in the photothermal conversion material 18 O 49It is uniformly and efficiently loaded on the surface of flaky reduced graphene oxide by a hydrothermal method and doped into the surface and interior of the PVDF-PVP membrane by a phase inversion method, which provides a new method for the design of interfacial evaporation membranes. In this patent, a carbon-based material rGO is used as the substrate by the hydrothermal method, and W 18 O 49 nanowires are loaded on rGO. The photothermal material rGCW in which MWCNTs-NH2 is highly mixed with the loaded rGO is obtained. Through phase inversion, rGCW is uniformly embedded in the surface and interior polymer networks of the flexible base membrane to obtain an interfacial evaporation membrane. rGO and MWCNTs-NH2 are used to convert light energy into heat energy, and a semiconductor W 18 O 49 with high absorption activity in the visible-near infrared light region (Vis-NIR) is loaded by a one-step hydrothermal method. Through the uniform dispersion of the casting solution, the two carbon-based materials in the prepared phase inversion membrane are dispersed in each other to achieve the effect of synergistically enhancing the photothermal performance. The rich network pore structure inside the phase inversion membrane can better transport water and transfer heat; the rGCW material doped into the surface and interior of the phase inversion membrane can enhance the absorption of sunlight by the membrane and convert it into heat energy, which is uniformly transmitted through the membrane structure, resulting in a macroscopic increase in the temperature of the interfacial evaporation membrane, thereby strengthening water evaporation. The synergistic absorption and conversion ability of rGO, MWCNTs-NH2 and linear W 18 O 49 for sunlight effectively improves the efficiency of solar water evaporation. The water evaporation efficiency is 1.9 - 2.1 kg m -2 h -1 , and the solar conversion efficiency (η) reaches 90.7%. In the field of solar water evaporation, rGO, CNTs, and W 18 O 49 have been proven to be materials with relatively high photothermal efficiency. However, how to form a stable overall structure with hydrophilic and heat-conducting properties is still a problem worthy of exploration. Therefore, in this invention, a PVDF-PVP membrane that is hydrophilic, porous, acid and alkali resistant, has good salt resistance and self-cleaning ability, and can be applied in most environments is designed to support the highly efficient light-absorbing and heat-conducting composite material rGCW, and a highly efficient and stable interfacial water evaporation material is generated by the coupling and synergistic effect between the two. Description of the Drawings

[0028] Figure 1 It is a scanning electron microscope image of the surface of the solar interfacial evaporation membrane - rGCW@PVDF-PVP membrane prepared in Example 1.

[0029] Figure 2 It is a scanning electron microscope image of the cross-section of the solar interfacial evaporation membrane - rGCW@PVDF-PVP membrane prepared in Example 1.

[0030] Figure 3Absorption and transmission spectra of the interfacial evaporation film - rGCW@PVDF - PVP film prepared by the method of Example 1.

[0031] Figure 4 For 1 kW m -2 Comparison chart of the water evaporation rate of the interfacial evaporation film - rGCW@PVDF - PVP film prepared by the method of Example 1 with pure water and PVDF - PVP film under the illumination of 1 kW m

[0032] Figure 5 Comparison chart of the water evaporation rate of pure water and the interfacial evaporation film - rGCW@PVDF - PVP film prepared by the method of Example 1 under dark conditions.

[0033] Figure 6 Cyclic stability test chart of the interfacial evaporation film - rGCW@PVDF - PVP film prepared by the method of Example 1.

[0034] Figure 7 For 1 kW m -2 Comparison chart of the water evaporation rate of the interfacial evaporation film - rGCW@PVDF - PVP films prepared by the methods of Examples 1, 2, 3, and 4 under the illumination of 1 kW m

[0035] Figure 8 For 1 kW m -2 Comparison chart of the water evaporation rate of the interfacial evaporation film - rGCW@PVDF - PVP film prepared by the method of Example 1 under water conditions 1, 2, 3, 4, and 5 under the illumination of 1 kW m

[0036] Figure 9 Schematic diagram of the salt precipitation resistance and salt self - cleaning phenomena of the interfacial evaporation film - rGCW@PVDF - PVP film prepared by the method of Example 1 under water conditions 3, 4, and 5. Detailed implementation mode

[0037] The experimental scheme of the present invention will be further elaborated below in combination with specific examples, but the present invention is not limited to the following examples. The methods are all conventional methods unless otherwise specified. The raw materials or instruments can be obtained through commercial purchase unless otherwise specified.

[0038] The drugs and their purities used are as follows: concentrated sulfuric acid (98 wt%), concentrated phosphoric acid solution (85 wt%), concentrated hydrochloric acid (30 - 36 wt%) with a purity of guaranteed reagent grade, potassium permanganate crystals, flake graphite (100 mesh), hydrogen peroxide (30 wt%) are of analytical grade; PVDF (5130), PVP (K30), N,N - dimethylformamide solution (DMF) are all of analytical grade.

[0039] Example 1

[0040] 1) Weigh 1.5 g of flake graphite (100 mesh) and put it into a mixed acid solution of concentrated sulfuric acid: concentrated phosphoric acid = 9:1, stir evenly, then slowly add 9.0 g of potassium permanganate crystals under an ice bath. Then, stir the solution at room temperature for 30 min. After no abnormality, place it in an oil bath at 50 °C and stir for at least 12 h. Then, quickly put the reacted substance into 700 ml of ice water and stir rapidly. During the cooling and stirring of the hot solution, add 10 ml of hydrogen peroxide. Then, separate the product at a centrifugal speed of 5000 r / min. Wash the obtained powder 3 times with 5 wt% hydrochloric acid and then wash it with water by centrifugation multiple times until the pH = 7. Then, freeze-dry the precipitate under vacuum for 48 h to obtain a fluffy rGO powder.

[0041] 2) Weigh 120 mg of GO and 60 mg of MWCNTs-NH2 powder and disperse them in 60 ml of absolute ethanol. Ultrasonicate this system at a frequency of 30 kHz for 1 h to obtain a uniformly dispersed solution. Then, add 360 mg of WCl6 to this system. After stirring for about 15 min to make the solution uniform, quickly put the solution into a 100 ml hydrothermal reactor. Place the hydrothermal reactor in an oven at 180 °C and react for 12 h. Then, collect the reaction product by vacuum filtration and wash it multiple times with an ethanol solution to obtain the rGCW composite material.

[0042] 3) Weigh 200 mg of the rGCW composite material obtained in step (2) and add it to a 40 ml glass bottle, and then add 10 ml of DMF solution. Then, heat and stir the system at 65 °C for 30 min, and add 1 g of PVDF and 100 mg of PVP. After continuing to heat and stir for 12 h, a uniform and viscous black casting solution will be formed. Use an automatic coater to coat the hot casting solution on a dry and clean glass plate, and use a controllable-thickness scraper to ensure the formation of a 400 μm liquid film. After scraping, quickly transfer the glass plate to deionized water. The liquid film forms a PVDF-PVP-based membrane doped with rGCW through a phase inversion process. After the phase inversion process lasts for 24 h, take out the membrane and dry it at room temperature to obtain the required highly efficient and stable interfacial evaporation membrane - rGCW@PVDF-PVP membrane.

[0043] Figure 1 and Figure 2 is the scanning electron microscope image of the prepared rGCW@PVDF-PVP membrane. It can be seen from the figure that the rGCW powder is relatively evenly distributed on the surface of the PVDF-PVP membrane, and a single rGCW material is composed of rGO nanosheets and W 18 O 49 nanowires combined. It can be seen from the cross-section that the prepared photothermal material rGCW powder is also embedded inside the membrane;

[0044] Figure 3Absorption spectrum of the rGCW@PVDF-PVP membrane prepared by the method of Example 1 for sunlight in the wavelength range of 200 - 2500 mn. It can be seen that this photothermal material has a strong absorption capacity for sunlight and is suitable as a photothermal conversion material.

[0045] Figure 4 Comparison of the water evaporation efficiency of the rGCW@PVDF-PVP membrane prepared by the method of Example 1 under one standard sunlight intensity irradiation with that of pure water and the PVDF-PVP membrane. The preparation method of the PVDF-PVP membrane is the same as step 3) of Example 1 but without adding the rGCW composite material. It can be seen that the evaporation rate of the rGCW@PVDF-PVP membrane is about 3.12 times that of pure water. The water evaporation efficiency of the rGCW@PVDF-PVP membrane prepared by the method of Example 1 is 1.9 - 2.1 kg m -2 h -1 。

[0046] Figure 5 Schematic diagram of the natural evaporation rate under dark and lightless conditions. The difference in the evaporation rate of the membrane itself for the evaporation rate of water inside the membrane can be calculated, and then the equivalent evaporation enthalpy ΔH of the water inside the membrane can be obtained Veva,T 。DarkWater is the natural evaporation rate of pure water under dark conditions, and DarkFilm is the natural evaporation rate of the water inside the membrane in Example 1 under dark conditions.

[0047] Calculated using the existing formula (1) for the solar energy conversion efficiency, the solar energy conversion efficiency (η) of the photothermal water evaporation material prepared by the above steps exceeds 90%.

[0048]

[0049] In the formula, η represents the solar photothermal conversion efficiency, represents the water evaporation amount per unit time and unit area, C opt is the optical concentration, and its value is 1. q0 is one standard sunlight intensity (1 Kw m -2 ), ΔH Veva is the equivalent evaporation enthalpy of the water inside the membrane in the photothermal device under standard atmospheric pressure, and its result can be calculated by formula (2).

[0050]

[0051] In the formula is the natural evaporation rate of pure water under dark conditions, is the natural evaporation rate of the water inside the membrane under dark conditions, ΔH Veva,T is the equivalent evaporation enthalpy of the water inside the membrane at temperature T (K), ΔH VWater,Tis the enthalpy of evaporation of pure water at temperature T (K), and the result can be calculated by the calculation formula (3).

[0052]

[0053] In the formula, T is the evaporation temperature of the membrane surface under a standard light intensity, which is 45.3 °C, that is, 318.45 K. C is the specific heat capacity of pure water (4.2 KJ Kg -1 ), and T0 is the room temperature of 20 °C during the test, that is, 293.15 K.

[0054] Figure 6 is the cyclic stability test of the solar water evaporation photothermal conversion material prepared by the method of Example 1. After being reused 30 times, the material still maintains a relatively stable evaporation rate. It can be seen that this kind of photothermal conversion material has good cyclic stability.

[0055] Example 2

[0056] Same as Example 1, but the addition amount of WCl6 is 60 mg, and the rGCW@PVDF-PVP interfacial evaporation membrane prepared under this condition is tested under a standard sunlight intensity to obtain the relationship between the water evaporation amount and the illumination time.

[0057] Example 3

[0058] Same as Example 1, but the addition amount of WCl6 is 180 mg. And the rGCW@PVDF-PVP interfacial evaporation membrane prepared under this condition is tested under a standard sunlight intensity to obtain the relationship between the water evaporation amount and the illumination time.

[0059] Example 4

[0060] Same as Example 1, but the addition amount of WCl6 is 480 mg. And the rGCW@PVDF-PVP interfacial evaporation membrane prepared under this condition is tested under a standard sunlight intensity to obtain the relationship between the water evaporation amount and the illumination time.

[0061] Figure 7 is the relationship diagram of the evaporation rate and time of the rGCW@PVDF-PVP membrane with different addition amounts of WCl6 under one-fold sunlight intensity. By comparison, it can be seen that as the addition amount of WCl6 increases, the water evaporation rate shows a trend of first increasing and then decreasing.

[0062] Figure 8Schematic diagram of the evaporation rate of the rGCW@PVDF-PVP membrane prepared by the method of Example 1 under different water conditions. It can be seen that the photothermal material has good evaporation performance in different saline solutions. Water condition 1 is pure water, water condition 2 is 3.5 wt% NaCl solution, water condition 3 is real seawater, water condition 4 is 5 wt% NaCl solution, and water condition 5 is 10 wt% NaCl solution.

[0063] Figure 9 Salt precipitation diagram during long-term evaporation of the rGCW@PVDF-PVP membrane prepared by the method of Example 1 under different water conditions and self-cleaning schematic diagram of the material for salt crystals. It can be seen from the figure that the membrane has good salt tolerance and self-cleaning ability. (a) shows the salt precipitation phenomenon of real seawater, (b) shows the salt precipitation phenomenon of 5 wt% NaCl solution, (c) shows the salt precipitation phenomenon of 10 wt% NaCl solution, and (d) shows the self-cleaning phenomenon of the rGCW@PVDF-PVP membrane.

[0064] Finally, it should be noted that the above embodiments are only one of the specific implementation manners of the present invention. Although the description thereof is relatively detailed and specific, this should not be construed as a limitation on the scope of the present invention. Those skilled in the art should understand that any equivalent replacement or modification made to the present invention without departing from the technical scope of the present invention still belongs to the content of the technical solution of the present invention and is still within the protection scope of the present invention.

Claims

1. A highly efficient, stable and self-cleaning flexible solar interface evaporation film, characterized by: The invention comprises a photothermal material rGCW and a hydrophilic porous PVP-PVDF flexible base film; the rGCW is uniformly embedded on the surface of the flexible base film and in the internal polymer network, and the rGCW comprises a one-dimensional MWCNTs-NH2, a base rGO sheet and W 18 O 49 Nanowire, the W 18 O 49 The nanowires are uniformly loaded on the surface of the rGO sheet, wherein the rGO sheet is 2-6 μm; the mass percentage of the rGCW in the flexible solar interface evaporation film is 15-25%, and the W 18 O 49 The mass percentage of nanowires in rGCW ranged from 11 to 64%.

2. The highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 1, characterized in that: The rGO, MWCNTs-NH2 and W 18 O 49 The mass ratio is 0.35-0.4:0.35-0.4:

1.

3. A method for preparing the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 1, characterized in that: rGCW, solvent, high polymer PVDF and pore-forming agent PVP are formed into a uniform casting solution, which is then scraped into a film and then prepared by a phase inversion method.

4. The method for preparing the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 3, characterized in that: The photothermal material rGCW is prepared by a hydrothermal method.

5. The method for preparing the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 3 or 4, characterized in that: The specific steps include: S1. Preparation of rGCW GO and MWCNTs-NH2 powders were dispersed in anhydrous ethanol to obtain a uniform solution, and then WCl6 was added to the system. After the solution was stirred evenly, the solution was quickly placed in a hydrothermal kettle to react in an oven, and then the reaction product was collected by vacuum filtration and washed with ethanol solution for multiple times to obtain the rGCW composite material; S2. Preparation of Phase Transformation Membrane Add rGCW, PVDF, PVP and DMF into a reagent bottle, stir on a heated stirring table to obtain a casting solution, ensure that the dispersion is relatively uniform, and then use an automatic scraper to scrape the film. Then, quickly transfer the glass plate coated with the casting solution into deionized water, let it stand for one day, and then take it out to obtain a phase conversion film-flexible solar interface evaporation film.

6. The method for preparing the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 5, characterized in that: The amount of WCl6 added in step S1 is 1-8 mg ml -1 .

7. The method for preparing the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 5, characterized in that: In step S1, the hydrothermal temperature is 180° C. and the hydrothermal time is 12 h.

8. The method for preparing the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 5, characterized in that: In step S2, the mass ratio of rGCW, PVDF, PVP and DMF is 0.2-0.3:1:0.1:10; and / or, In step S2, rGCW and DMF are first added to a reagent bottle and mixed evenly, and then PVP and PVDF are added to the system.

9. The method for preparing the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 5, characterized in that: In step S2, the heating temperature is 65±3° C., and the stirring time is 12-15 hours; and / or, the scraping film thickness in step S2 is 375-425 μm.

10. A solar interface water evaporation film, wherein the photothermal conversion material and the hydrophilic film of the evaporation film are the highly efficient, stable and self-cleaning flexible solar interface evaporation film according to claim 1.

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