Flexible polydopamine / enteromorpha photothermal film, preparation method and application thereof

Abstract

The present application relates to a flexible polydopamine / enteromorpha thermophotovoltaic film and a preparation method and application thereof, the flexible polydopamine / enteromorpha thermophotovoltaic film is prepared by using enteromorpha and dopamine as raw materials, and adopting polymerization to make polydopamine and enteromorpha interface polymerization reaction.The flexible polydopamine / enteromorpha thermophotovoltaic film material prepared by the present application has a rough black polymer texture structure on the surface, forms a hydrophilic interface of photothermal conversion, and the evaporation rate in deionized water under the irradiation of one sunlight can reach 2.7334 kg m ‑2 h ‑1 ; in actual seawater evaporation, the film can be used repeatedly, and after 5 cycles of cleaning and drying, the evaporation rate does not decrease obviously, the polymer on the film surface does not fall off obviously, and the film shape remains stable.The present application has the advantages of low cost, environmental friendliness, high flexibility, high stability, good recycling effect and the like, and has a wide application prospect in actual production.

Description

TECHNICAL FIELD

[0001] The present application relates to a flexible polydopamine / enteromorpha light-heat film for solar-driven seawater desalination and a preparation method and application thereof, belonging to the field of chemistry and environment technology. BACKGROUND

[0002] Water is the source of life and an important factor for social development and human progress. With the continuous growth of population and the expansion of production in various fields, the shortage of fresh water resources has become a major challenge to development. As the largest reservoir on earth, seawater desalination is considered the most promising technology to solve the problem of lack of fresh water resources. Currently, common seawater desalination treatment technologies mainly include distillation, electrodialysis, reverse osmosis and ion exchange methods. However, the above technologies often consume a large amount of energy during use, not only increasing the cost of seawater desalination treatment, but also possibly causing secondary pollution in the process, hindering its large-scale and continuous application. Therefore, it is urgent to develop new technologies that aim at low energy consumption, high separation efficiency, environmentally friendly materials and the use of green energy.

[0003] Solar energy is a green and clean renewable energy. If the received sunlight is converted into heat energy by using light-heat conversion materials, the air-water interface can be heated to evaporate water, achieving the separation and recovery of salt and fresh water in seawater. The efficiency of light-heat conversion is closely related to the light-heat conversion material, and it is crucial to explore materials with excellent optical, thermal and mechanical properties. Currently, there are many studies on metal-based materials, semiconductor materials, carbon-based materials and organic polymer materials. These materials have high light absorption and light-heat conversion capabilities, and solar evaporators made of them can greatly improve the evaporation efficiency of seawater. For example: CN117306261A discloses a light-heat conversion material, a preparation method, an evaporator and an application thereof. The preparation method comprises: providing a substrate with a porous structure; forming a polydopamine layer or a polypyrrole layer on the surface of the substrate; and attaching carbon nanotubes and a light-heat enhancer to the polydopamine layer or the polypyrrole layer to obtain a light-heat conversion material. However, the preparation of these materials generally has a complex process and high cost, making it difficult to achieve large-scale production of the materials. On the other hand, the mechanical strength and flexibility of the materials are low, making it difficult to achieve sustainable and durable use of the materials. Therefore, it is of great practical significance to study new green technologies and methods to achieve low-cost preparation of high-efficiency light-heat materials for seawater desalination.

[0004] Currently, flexible polymer composite photothermal film materials as photothermal materials for seawater desalination have attracted widespread attention. Flexible polymer composite photothermal film is a combination of materials with photothermal conversion capability and polymer, cellulose fiber, etc. Its preparation method is simple, which can greatly improve the flexibility and mechanical stability of the original photothermal material while maintaining good photothermal conversion efficiency, and has broad application prospects in seawater desalination. The development direction of environmentally friendly materials is to use abundant, renewable and low-cost biomass to prepare composite film materials. Polydopamine (PDA) is an environmentally friendly organic material, which is self-polymerized from dopamine molecules under alkaline conditions with oxygen. Due to its ordered and disordered structure and rich functional groups such as catechol, amine, and imine, polydopamine has high light absorption capacity, wide spectral absorption band, and strong adhesion. In recent years, polydopamine has been developed for seawater desalination, and there are many patent literatures reported. For example: CN114106409A discloses a photothermal conversion material for seawater desalination and a preparation method thereof, which uses ZIF-L to induce in-situ polymerization of dopamine into polydopamine to obtain ZIF-L / PDA, mixes the obtained ZIFL / PDA with sodium alginate to obtain a sol; the sol is spin-coated on the surface of melamine sponge to form a film, and the photothermal conversion material is obtained after drying. CN119570106A discloses a preparation method and application of high-efficiency polydopamine photothermal evaporation modified film, which proposes a method of co-deposition of polydopamine (PDA) photothermal material inside nanogel, which greatly improves the loading density of polydopamine in unit volume, thereby preparing a high-efficiency PDA photothermal evaporation modified film.

[0005] Enteromorpha as a kind of biomass is rich in various oxygen-containing functional groups, proteins, polysaccharides and cellulose, and shows excellent flexibility, which is an excellent precursor for preparing photothermal materials. Enteromorpha, as a seasonal marine pollution alga, has seriously damaged the stability of the ecosystem. There are many prior art reports on the resource utilization of Enteromorpha in photothermal materials, for example: CN117585751A discloses an Enteromorpha-derived carbon-based photothermal film and its application in seawater desalination. The Enteromorpha is dried and then carbonized at high temperature to obtain biochar, the biochar is dispersed in distilled water to obtain a suspension, and the suspension is filtered through a polyvinylidene fluoride membrane to obtain a photothermal film. CN115448401A discloses a solar seawater evaporator with self-floating jellyfish-like structure, preparation method and application, which collects Enteromorpha cellulose by freeze-drying to prepare Enteromorpha aerogel, and then carbonizes the surface of the Enteromorpha aerogel to obtain an integrated structure. However, in the prior art, Enteromorpha is often carbonized, which not only reduces the mechanical strength, but also destroys the flexibility.

[0006] Therefore, how to make full use of the biological performance of Enteromorpha prolifera to prepare flexible photothermal film, realize the resource utilization of Enteromorpha prolifera, and improve the flexibility, mechanical property and photothermal performance of the photothermal film are key problems. SUMMARY

[0007] In view of the status of the prior art, especially in view of the high cost, low stability and insufficient flexibility of the existing photothermal conversion material, the present application is based on the finding that the interfacial polymerization reaction of dopamine hydrochloride and uncarbonized Enteromorpha prolifera powder can not only enhance the bonding strength and maintain good flexibility, but also realize ecological management and resource utilization simultaneously, and the photothermal conversion performance is excellent.

[0008] Therefore, an object of the present application is to provide a flexible polydopamine / Enteromorpha prolifera photothermal film obtained by the interfacial polymerization reaction of dopamine hydrochloride and uncarbonized Enteromorpha prolifera powder.

[0009] A second object of the present application is to provide a preparation method of the flexible polydopamine / Enteromorpha prolifera photothermal film.

[0010] A third object of the present application is to provide an application of the flexible polydopamine / Enteromorpha prolifera photothermal film. The flexible polydopamine / Enteromorpha prolifera photothermal film has good effect especially in the field of solar-driven seawater desalination.

[0011] The technical solutions for achieving the above-mentioned objects of the application can be summarized as follows:

[0012] The flexible polydopamine / Enteromorpha prolifera photothermal film has a polydopamine particle layer polymerized in situ on the surface of an Enteromorpha prolifera matrix.

[0013] According to the present application, preferably, the surface of the flexible polydopamine / Enteromorpha prolifera photothermal film is a rough black polymer texture structure, forming a hydrophilic interface for photothermal conversion, and the contact angle with water is 0°.

[0014] According to the present application, preferably, the flexible polydopamine / Enteromorpha prolifera photothermal film further comprises a substrate and a photothermal layer loaded on the surface of the substrate, and the photothermal layer is an Enteromorpha prolifera matrix with a polydopamine particle layer polymerized in situ.

[0015] According to the present application, preferably, the thickness of the photothermal layer is 100-200 μm, and further preferably 126.73 μm.

[0016] According to the present application, preferably, the substrate is filter paper, non-woven fabric or polyurethane sponge.

[0017] According to the present application, the preparation method of the above-mentioned flexible polydopamine / Enteromorpha prolifera photothermal film comprises the following steps:

[0018] Dopamine hydrochloride is added to an alkaline buffer solution, and Enteromorpha powder is added and stirred to disperse the reaction to obtain a film forming solution, and the film forming solution is formed into a film to obtain a flexible polydopamine / Enteromorpha photothermal film.

[0019] According to the application, preferably, the alkaline buffer solution is a Tris alkaline buffer solution with a pH of 8-9.

[0020] According to the application, preferably, the particle size of the Enteromorpha powder is 150-300 mesh.

[0021] According to the application, preferably, the mass ratio of Enteromorpha to dopamine hydrochloride is 4-15:1.

[0022] According to the application, preferably, the preparation method of the flexible polydopamine / Enteromorpha photothermal film further comprises a substrate loading step, the film forming solution is loaded on the substrate, and vacuum drying is performed to obtain the flexible polydopamine / Enteromorpha photothermal film.

[0023] According to the application, preferably, the vacuum drying conditions are: a temperature of 50-60 DEG C, a vacuum degree of -15 Pa, and a drying time of 24 h.

[0024] According to the application, the flexible polydopamine / Enteromorpha photothermal film is used for seawater desalination or high-salinity wastewater desalination treatment.

[0025] The application has the following advantages:

[0026] 1. The application uses marine biological source Enteromorpha and dopamine as raw materials, and adopts a high polymer polymerization method to construct a high polymer / Enteromorpha-based photothermal fiber film for seawater desalination driven by solar energy.

[0027] 2. The flexible polydopamine / Enteromorpha photothermal film obtained by the application has a rough black polymer texture structure on the surface, forms a hydrophilic interface for light-heat conversion, and uses a simple interface evaporation device. -2 h -1 .

[0028] 3. The flexible polydopamine / Enteromorpha photothermal film obtained by the application is used for photothermal reaction of seawater desalination, and the concentration of main cations in the desalinated seawater is significantly reduced, and the water quality meets the WHO health standards and the requirements of the drinking water health standards.

[0029] 4、The flexible polydopamine / enteromorpha thermophotocatalytic film obtained by the method can be repeatedly used: after 5 cycles of evaporation for 5 hours in actual seawater, no salt deposition occurs on the polymer surface, the evaporation rate does not decrease obviously, no polymer on the film surface falls off obviously, and the film shape remains stable.

[0030] 5、The flexible polydopamine / enteromorpha thermophotocatalytic film is environment-friendly, non-toxic and harmless, and low in price, and a new way of resource utilization of enteromorpha is opened up. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The contact angle test result of the flexible polydopamine / enteromorpha thermophotocatalytic film prepared in Example 1 in air on water;

[0032] Figure 2 The micro-morphology electron microscope (SEM) of the flexible polydopamine / enteromorpha thermophotocatalytic film prepared in Example 1 and the qualitative filter paper without loading;

[0033] Figure 3 The infrared spectrum (FT-IR) of the flexible polydopamine / enteromorpha thermophotocatalytic film prepared in Examples 1-4;

[0034] Figure 4 The spectrum absorption diagram (UV-Vis-NIR) of the flexible polydopamine / enteromorpha thermophotocatalytic film prepared in Examples 1-4 and the filter paper base film without loading;

[0035] Figure 5 The thermogravimetric analysis curve of Example 1 of the application;

[0036] Figure 6 The pure water evaporation rate experimental device and effect diagram of the flexible polydopamine / enteromorpha thermophotocatalytic film prepared in Examples 1-4, and the experiment is continuously evaporated for 5 hours under 1 sunlight;

[0037] Figure 7 The water evaporation rate change curve of the flexible polydopamine / enteromorpha thermophotocatalytic film prepared in Example 1 of the application and the polydopamine / carbonized enteromorpha thermophotocatalytic film prepared in the comparative example after 5 cycles in actual seawater, and the polymer loading diagram on the film surface after repeated use for 5 days;

[0038] Figure 8 The main cation concentration change diagram of the polydopamine / enteromorpha thermophotocatalytic film prepared in Example 1 of the application before and after actual seawater desalination. DETAILED DESCRIPTION

[0039] In the application, hydrochloric acid dopamine is directly subjected to interfacial polymerization with uncarbonized enteromorpha powder, so that the combination strength is enhanced, good flexibility is maintained, ecological management and resource utilization are simultaneously realized, and excellent thermophotocatalytic conversion performance is achieved.

[0040] The excellent properties of Enteromorpha can compensate for the limitations of current photothermal materials, such as poor mechanical stability, flexibility, and weak combination ability of polymers and cellulose. Using it as a raw material can save the production cost of materials, realize large-scale production of environmentally friendly materials, and has a wide application prospect.

[0041] Therefore, the present application uses marine biological source Enteromorpha and dopamine as raw materials, and uses a polymer polymerization method to construct a polymer / Enteromorpha-based photothermal fiber membrane for solar-driven seawater desalination. The method is simple, low-cost and environmentally friendly. The prepared flexible polydopamine / Enteromorpha photothermal membrane has excellent photothermal performance, high separation efficiency and can be reused.

[0042] The flexible polydopamine / Enteromorpha photothermal membrane of the present application has a polydopamine particle layer polymerized in situ on the surface of the Enteromorpha matrix.

[0043] The Enteromorpha used in the present application does not undergo carbonization and is directly subjected to reaction. The Enteromorpha has good flexibility, and hydrochloric acid dopamine is directly subjected to interfacial polymerization with Enteromorpha to produce a flexible photothermal membrane. The interfacial polymerization reaction includes polymerization of hydrochloric acid dopamine itself, and copolymerization of hydrochloric acid dopamine monomers and hydroxyl groups and cellulose in Enteromorpha. The polydopamine is combined with the Enteromorpha matrix through hydrogen bonding and hydroxyl group interaction.

[0044] In one or more preferred embodiments, the flexible polydopamine / Enteromorpha photothermal membrane further comprises a substrate and a photothermal layer loaded on the surface of the substrate, and the photothermal layer is an Enteromorpha matrix with a polydopamine particle layer polymerized in situ.

[0045] In one or more preferred embodiments, the thickness of the photothermal layer is 100-200 μm, and further preferably 126.73 μm.

[0046] In one or more preferred embodiments, the substrate is filter paper, non-woven fabric or polyurethane sponge.

[0047] According to the present application, the preparation method of the above-mentioned flexible polydopamine / Enteromorpha photothermal membrane comprises the following steps:

[0048] The hydrochloric acid dopamine is added to an alkaline buffer solution, Enteromorpha powder is added and stirred to disperse and react, a film-forming solution is obtained, and the film-forming solution is formed into a film to obtain the flexible polydopamine / Enteromorpha photothermal membrane.

[0049] In one or more preferred embodiments, the alkaline buffer solution is a trimethyl aminomethane (Tris) alkaline buffer solution with a pH of 8-9.

[0050] In one or more preferred embodiments, the particle size of the Enteromorpha powder is 150-300 mesh.

[0051] In one or more preferred embodiments, the mass ratio of Enteromorpha to dopamine hydrochloride is 4-15:1.

[0052] In one or more preferred embodiments, the preparation method of the flexible polydopamine / Enteromorpha photothermal film further comprises a step of loading a substrate, loading the film-forming solution on the substrate, vacuum drying, and obtaining the flexible polydopamine / Enteromorpha photothermal film.

[0053] In one or more preferred embodiments, the vacuum drying conditions are: temperature 50-60℃, vacuum degree -15Pa, and drying time 24h.

[0054] According to the present application, the flexible polydopamine / Enteromorpha photothermal film is used for seawater desalination or high-salinity wastewater desalination treatment.

[0055] In one or more preferred embodiments, the specific method of photothermal evaporation is as follows: the photothermal film is placed on a simple evaporation collection device, and continuously evaporated at room temperature under the irradiation of 1 sun intensity for 5 hours; a simple condensation device is used to collect the condensed water after seawater desalination; the concentration of main cations in seawater is significantly reduced, and the water quality meets the requirements of WHO health standards and drinking water health standards.

[0056] Meanwhile, after each evaporation is completed, the film sample is cleaned and dried, and the cycle of heating-cooling-cleaning-drying is repeated; after multiple photothermal cycles, the evaporation rate of the film does not decrease significantly, the polymer does not fall off significantly, the shape of the film remains stable, and the film can be used repeatedly.

[0057] The application will be further described below in conjunction with specific examples and drawings, which are merely a description of preferred embodiments of the application, but do not limit the following description. The raw materials and reagents in the examples are commercially available products.

[0058] In the examples, fresh Enteromorpha along the coast of Qingdao Binhe Park in Shandong Province is selected as the raw material. A self-assembled solar simple interfacial evaporation collection device is used to test the performance, and the device diagram is shown in Figure 6 (a). The evaporation performance test, salt deposition resistance performance test, and application experiment are all completed using this device to collect data. This device is only used to test the performance of the photothermal film and verify the seawater desalination effect. The photothermal film prepared in the present application can be equipped in a similar seawater desalination device.

[0059] The self-assembled solar simple interface evaporation device is composed of a sunlight simulator, an evaporation body, and a data collector. The simulated sunlight is provided by a xenon lamp with an AM1.5 filter, and the light power meter is used to regulate it to a certain sunlight intensity. The evaporation body uses a beaker as the container, tin paper as the heat insulation material to reduce heat loss, and a sponge strip is cut into a suitable shape to transport water and support the light-heat film. The data collection is recorded by an electronic analytical balance with an accuracy of 0.0001 g to record the mass change during the evaporation process, and the computer records the mass loss at the corresponding time node in real time. Before each experiment, the light-heat film is completely wetted to reduce the influence of the start-up stage on the measurement of water evaporation rate.

[0060] In the examples, one sunlight intensity refers to 1 kW·m⁻².

[0061] Example 1

[0062] A preparation method of a flexible polydopamine / enteromorpha light-heat film, the steps are as follows:

[0063] (1) The enteromorpha is washed thoroughly to remove impurities such as mud, and is placed in a 40℃ air drying oven for sufficient drying, then ground by a grinding machine and sieved to 200 mesh to obtain clean enteromorpha powder;

[0064] (2) 3.6342 g of trimethylaminomethane (Tris) powder is added to 60 mL of deionized water, and magnetically stirred until dissolved. The initial pH value of the solution is measured by a pH meter, and 0.1 M dilute hydrochloric acid solution is slowly added dropwise by a rubber bulb dropper under magnetic stirring until the pH value is 8.5. Then deionized water is added to make the solution to 100 mL, obtaining a Tris buffer solution with a concentration of 0.3 mol / L (pH=8.5);

[0065] (3) 20 mL of the solution obtained in step (2) is taken, and 0.2 g of dopamine hydrochloride powder is added, and magnetically stirred for 5 min;

[0066] (4) 0.8 g of enteromorpha powder obtained in step (1) is added to the solution obtained in step (3), and magnetically stirred at room temperature for 12 h to obtain a mixed solution;

[0067] (5) 2 mL of the mixed solution obtained in step (4) is taken and loaded on a qualitative filter paper by vacuum filtration;

[0068] (6) The loaded filter paper obtained in step (5) is placed in a vacuum electric heating constant temperature drying oven, and vacuum dried at 60℃ for 12 h to obtain a flexible polydopamine / enteromorpha light-heat film.

[0069] Example 2

[0070] The preparation method of the flexible polydopamine / Enteromorpha thermophotovoltaic film described in Example 1 is different in that:

[0071] In step (3), the dopamine hydrochloride powder is 0.06 g. The rest of the operation, amount and Example 1 are exactly the same.

[0072] Example 3

[0073] The preparation method of the flexible polydopamine / Enteromorpha thermophotovoltaic film described in Example 1 is different in that:

[0074] In step (3), the dopamine hydrochloride powder is 0.1 g. The rest of the operation, amount and Example 1 are exactly the same.

[0075] Example 4

[0076] The preparation method of the flexible polydopamine / Enteromorpha thermophotovoltaic film described in Example 1 is different in that:

[0077] In step (4), the magnetic stirring time is 24 h. The rest of the operation, amount and Example 1 are exactly the same.

[0078] Comparative Example

[0079] The interface polymerization reaction of dopamine hydrochloride and carbonized Enteromorpha powder is carried out to prepare a polydopamine / carbonized Enteromorpha thermophotovoltaic film,

[0080] And the following properties are compared by experiment: (1) photothermal evaporation performance, (2) repeated use performance, see Test Example 7 for details.

[0081] The preparation steps of this comparative example are the same as the preparation method of the thermophotovoltaic film described in Example 1, except that:

[0082] In step (1), the Enteromorpha powder sieved to 200 mesh is placed in a tube furnace and subjected to low-temperature carbonization treatment under the protection of nitrogen at a constant temperature of 200°C for 2 h to obtain carbonized Enteromorpha powder.

[0083] In step (6), the loaded filter paper is simply dried to obtain a polydopamine / carbonized Enteromorpha thermophotovoltaic film.

[0084] The rest of the operation, amount and Example 1 are exactly the same.

[0085] Test Example 1, contact angle measurement

[0086] The contact angle of the thermophotovoltaic film prepared in Example 1 on water in air is as follows: Figure 1The water droplets on the surface of the photothermal film are completely absorbed within 1s, and the photothermal film has strong hydrophilicity. At this time, the photothermal film has good water transport capacity, and the hydrophilicity in the photothermal layer can make water quickly transported from the bulk water to the evaporation interface by capillary action, and quickly discharge the generated steam.

[0087] Test Example 2, electron microscope image

[0088] The electron microscope images of the flexible polydopamine / enteromorpha photothermal film prepared in Example 1 and the unloaded qualitative filter paper base film are as shown in Figure 2 The surface of the unloaded filter paper base film presents a porous network structure formed by cross-linking of cellulose, which is a good photothermal evaporation base. After loading, the surface of the filter paper forms a photothermal layer of 126.73 μm, and the surface fibers are covered with polymer, while part of the cavities are left, forming a porous structure. The micropores give the photothermal film more capillary action, which is beneficial to the transport of water during the evaporation process.

[0089] Test Example 3, infrared spectrum analysis

[0090] The infrared spectrum analysis graphs of the flexible polydopamine / enteromorpha photothermal film prepared in Examples 1-4 and the unloaded filter paper base film are as shown in Figure 3 According to the spectral curve, the characteristic peaks of enteromorpha are assigned: enteromorpha contains a large number of oxygen-containing groups, the peak at 3245 cm -1 corresponds to O-H on the enteromorpha polysaccharide chain, the peak at 2928 cm -1 is caused by the C-H stretching of CH2 group, and the C-O stretching vibration signal at 1025 cm -1 is a characteristic band of sugar ring. The characteristic peaks of polydopamine are assigned: the peak at 1595 cm -1 is the stretching vibration peak of dopamine ring C=C, the peak at 1222 cm -1 corresponds to the stretching vibration peak of C-N bond, and the peak at 838 cm -1 corresponds to the deformation vibration peak of C-H bond.

[0091] Compared with the blank base film, the O-H stretching vibration peak and the C-H stretching vibration peak in the photothermal film of Example 1 are slightly shifted, and the C-O peak intensity is weakened, which is presumably due to the hydrogen bond interaction between enteromorpha polydopamine and the base film, and the further strengthened binding ability, which proves the stability of the combination of the photothermal film and the polymer component. All the FT-IR curves correspond to the characteristic peaks of the enteromorpha polydopamine polymer product, and with the increase of polydopamine in Examples 2-3, part of the characteristic peaks show an increasing trend, and with the increase of the polymerization time in Example 4, part of the characteristic peaks show a decreasing trend. The polymerization components are relatively stable in Example 1.

[0092] Test Example 4, optical performance test

[0093] The spectral absorption rate analysis chart of the flexible polydopamine / enteromorpha thermophotovoltaic film prepared in Example 1 and the unloaded filter paper base film is shown in Figure 4 As shown in the figure, compared with the unloaded base film, the light absorption capacity of the thermophotovoltaic film of Example 1 is obviously improved, and the light absorption capacity in the visible light and invisible light regions is much higher than that of the blank base film.

[0094] Comparing the absorption rate fold lines of Comparative Examples 1-3, with the increase of dopamine dosage, the light absorption capacity of the thermophotovoltaic film to all wavelengths of light in the spectrum shows an upward trend, among which the light absorption rate of Example 1 to the visible light of 400 nm wavelength can reach 96.8%.

[0095] Comparing the absorption rate fold lines of Comparative Example 1, Example 4 and Figure 4 The local enlarged view of It can be found that with the increase of polymerization time of dopamine, the light absorption rate of the thermophotovoltaic film in the ultraviolet (300-400 nm) and visible light (400-780 nm) range is slightly improved, the light absorption rate of Example 1 before 546 nm wavelength is higher than that of Example 4, and then the light absorption rate of Example 4 gradually increases, which is about 1.2% higher than that of Example 1 at 780 nm wavelength, and the light absorption rate in the near infrared is higher than that of Example 1. It can be seen that with the increase of polymerization time, the light absorption capacity of the thermophotovoltaic film shows an upward trend, but the absorption rate of visible light is limited or even reduced.

[0096] Test Example 5, thermal stability test

[0097] The thermogravimetric analysis chart of the flexible polydopamine / enteromorpha thermophotovoltaic film prepared in Example 1 is shown in Figure 5 As shown in the figure, the mass of the thermophotovoltaic film does not change obviously below 210°C, and has high thermal stability; the mass rapidly decreases after the temperature rises to 210°C, and combined with the actual interface evaporation, the thermal stability of the thermophotovoltaic film of Example 1 can meet the working requirements of solar-driven interface evaporation.

[0098] Test Example 6, deionized water evaporation performance test

[0099] The thermophotovoltaic films prepared in Examples 1-4 and the unloaded filter paper base film were subjected to pure water evaporation rate experiment, as shown in Figure 6 The experimental conditions were: at room temperature, using Figure 6 (a) The device shown in the figure, the deionized water in the beaker was continuously evaporated under 1 solar light for 5 hours. Figure 6 (b) The surface temperature change chart of Example 1 thermophotovoltaic film and unloaded filter paper base film during pure water evaporation, the temperature of the unloaded base film remained at 25°C room temperature, and the temperature was 33.1°C after 5 hours, while the surface temperature of the Example 1 thermophotovoltaic film rapidly rose in the first minute, and then gradually stabilized at about 45°C, and the surface temperature measured after 5 hours was 50°C. Figure 6(c) the deionized water evaporation rate graph of the prepared photothermal film, wherein the slope of the broken line of Example 1 is the largest. It is calculated that the evaporation rate of Example 1 reaches 2.7334 kg m -2 h -1 . Examples 2-3 gradually increase the evaporation rate due to the increase of the dopamine dosage. The loading amount of the Enteromorpha polydopamine of Example 4 is higher, but the rate is lower than that of Example 1. It is speculated that due to the excessive polymer loading amount, the pore channel is blocked, which reduces the water transport performance, so the evaporation rate is slowed down. The dopamine concentration, Enteromorpha dosage and polymerization time of Example 1 are all within the suitable range of the base film bearing, which benefits from the suitable polymer thickness and the internal pores formed, so that the water vapor can be quickly conducted.

[0100] Test Example 7, photothermal evaporation performance, and repeated use performance test

[0101] Example 1, the evaporation rate of the photothermal film prepared in the actual seawater in 5 cycles of the comparative example is as shown in Figure 7 a. The experimental conditions are: under room temperature, 1 sunlight for 5 h of continuous evaporation each time, after each evaporation, the film sample is naturally dried, a total of 5 cycles, and the film surface loading after each cycle is recorded, as shown in Figure 7 b.

[0102] The experiment shows that the flexible polydopamine / Enteromorpha photothermal film (Example 1) always maintains a high evaporation rate in 5 cycles, and the polymer loading on the film surface is stable, and no obvious shedding occurs on the film surface after 5 cycles; the polydopamine / carbonized Enteromorpha photothermal film (comparative example) formed by the polymerization of the carbonized Enteromorpha powder and hydrochloric acid dopamine has a higher evaporation rate in the first day, but after 5 cycles, the polymer loading on the film surface is severely detached, and the photothermal evaporation rate is greatly reduced, which is specifically analyzed as follows:

[0103] The salt on the surface of the photothermal film of Example 1 is precipitated, but most of the salt is deposited on the edge of the blank filter paper. After 4 cycles, the evaporation rate does not obviously decrease, and is maintained at 2.2 kg m -2 h -1 . The highest can reach 2.3375 kg m -2 h -1 . After the 5th cycle, the rate decreases to 1.98 kg m -2 h -1 , and no obvious detachment occurs on the film surface; although the evaporation rate of the comparative example is higher than that of Example 1 in the initial cycle, reaching 2.3239 kg m -2 h -1 , but due to the poor adhesion of the polymer formed after the carbonization of the Enteromorpha powder, the loading layer starts to partially detach in the second cycle, and the evaporation rate is obviously decreased, and more than half of the loading layer is detached after 5 cycles.

[0104] By comparison, it can be obtained that in the carbonization process of the comparative example, the hydrophilic components (polysaccharides, proteins, etc.) of Enteromorpha powder are destroyed at high temperature, forming a hydrophobic structure, resulting in weakened adhesion; at the same time, the fiber structure of Enteromorpha collapses, the surface becomes smooth, the mechanical embedding effect between the film is weakened, the stability is poor, the material does not have the condition of repeated use, and cannot meet the requirements of large-scale production. While the flexible polydopamine / Enteromorpha photo-thermal film formed by the polymerization of Enteromorpha powder without carbonization and dopamine hydrochloride still has good repeated use performance while maintaining the evaporation rate.

[0105] Test Example 8, Ion Removal

[0106] The main cation concentration changes of the flexible polydopamine / Enteromorpha photo-thermal film prepared in Example 1 before and after actual seawater purification are shown in Figure 8 The results show that the concentrations of main cations (Na + , K + , Ca 2+ , Mg 2+ ) in seawater are significantly reduced, and the removal efficiency can reach more than 99.1%, among which the concentration of Na + ions also reaches a removal efficiency of 99.9%, and the quality of condensed water meets the requirements of WHO health standards and drinking water health standards.

Claims

1. A method for preparing a flexible polydopamine / Enteromorpha thermophotovoltaic film, comprising the following steps: adding dopamine hydrochloride into an alkaline buffer solution, adding Enteromorpha powder, stirring and dispersing to obtain a film-forming solution, loading the film-forming solution on a substrate, and vacuum drying at a temperature of 50-60℃ to obtain the flexible polydopamine / Enteromorpha thermophotovoltaic film. The substrate is filter paper, non-woven fabric or polyurethane sponge, the alkaline buffer solution is a Tris alkaline buffer solution with a pH of 8-9, and the particle size of the Enteromorpha powder is 150-300 mesh, and the mass ratio of Enteromorpha to dopamine hydrochloride is 4-15:

1.

2. The method for preparing the flexible polydopamine / Ulva prolifera photothermal film according to claim 1, characterized in that, The vacuum degree of the vacuum drying is -15 Pa, and the drying time is 24 h.

3. A flexible polydopamine / Enteromorpha photothermal film, the photothermal film comprising a substrate and a photothermal layer loaded on the surface of the substrate, the photothermal layer being an Enteromorpha matrix in which a layer of polydopamine particles is polymerized in situ, characterized in that, The thermophotovoltaic film is prepared according to the method of claim 1 or 2.

4. The flexible polydopamine / Enteromorpha photothermal film according to claim 3, characterized in that, The thickness of the thermophotovoltaic layer is 100-200 μm.

5. The flexible polydopamine / Enteromorpha photothermal film according to claim 3, characterized in that, The surface of the flexible polydopamine / Enteromorpha thermophotovoltaic film is a rough black polymeric texture structure, forming a hydrophilic interface for thermophotovoltaic conversion, and the contact angle with water is 0°.

6. Use of the flexible polydopamine / Enteromorpha thermophoto film according to any one of claims 3-5, characterized in that, The film is used for seawater desalination or high-salinity wastewater desalination treatment.

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