A photothermal conversion material, its preparation method and application

Abstract

The present invention discloses a photothermal conversion material, a preparation method thereof and an application. The preparation method includes the steps of: soaking a fabric substrate in an alkaline metal hydroxide solution for a preset time to obtain an alkali-treated fabric substrate; soaking the alkali-treated fabric substrate in a silver salt solution, adding a reducing agent to carry out a reduction reaction, soaking the obtained fabric substrate loaded with silver nanoparticles in an acidic solution containing pyrrole, and then adding an oxidative polymerization agent to carry out an oxidative polymerization reaction to form polypyrrole on the fabric substrate loaded with silver nanoparticles, thereby obtaining the photothermal conversion material. The silver nanoparticles in the photothermal conversion material have a solar photothermal effect, and cooperate with polypyrrole to enhance the absorption and thermal conversion of sunlight, improving the photothermal conversion ability of the photothermal conversion material; meanwhile, the silver nanoparticles have an antibacterial effect, so that the photothermal conversion material has a good antibacterial effect on Escherichia coli and Staphylococcus aureus.

Description

Technical Field

[0001] The present invention relates to the technical field of photothermal conversion materials, and in particular, to a photothermal conversion material, a preparation method thereof, and an application thereof. Background Art

[0002] The rapid economic and social development, as well as serious energy consumption and shortages, have made the research on alternative new energy a subject that people constantly challenge. At present, the application of solar thermal conversion is already very extensive. Compared with fields such as photoelectricity and photocatalysis, solar thermal application is the most effective way to utilize solar energy. It is of great significance to apply green and sustainable solar energy to develop efficient and large-scale seawater desalination and wastewater treatment technologies. Many existing seawater desalination technologies, such as low-temperature multi-effect distillation (MED) and reverse osmosis (RO), etc., are achieved with huge investment costs and high energy consumption, which is not feasible for remote areas. Therefore, solving the contradiction between water purification and energy consumption has become a key issue for sustainable fresh water production.

[0003] In recent years, people have developed an efficient solar-driven interfacial evaporation (SDIE) system, which is quite different from ordinary volume evaporation strategies. The solar absorber is located at the water-air interface, connected to the water body by a path, and the absorber is thermally isolated from the bulk water, so that the heat is restricted to the evaporation interface, where only a small volume of water is heated, and the overall water temperature below remains basically unchanged, close to the ambient temperature. Therefore, most unnecessary heat dissipation is suppressed, the temperature of the light absorber is greatly increased, and the evaporation efficiency can be increased to more than 90%. However, there are still some problems with the existing SDIE systems in purifying seawater, mainly that the desalination efficiency of the photothermal conversion material for seawater is still relatively low. Therefore, there is an urgent need to design an efficient photothermal conversion material for seawater desalination. Summary of the Invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a photothermal conversion material, a preparation method thereof, and an application thereof, aiming to solve the problem that the desalination efficiency of the existing photothermal conversion material for seawater is still relatively low.

[0005] The technical solution of the present invention is as follows:

[0006] In the first aspect of the present invention, a preparation method of a photothermal conversion material is provided, which includes the steps of:

[0007] Providing a fabric substrate;

[0008] Immersing the fabric substrate in an alkaline metal hydroxide solution for a preset time to obtain an alkali-treated fabric substrate;

[0009] Immerse the alkali-treated fabric substrate in a silver salt solution, then add a reducing agent to carry out a reduction reaction to obtain a fabric substrate loaded with silver nanoparticles;

[0010] Immerse the fabric substrate loaded with silver nanoparticles in an acidic solution containing pyrrole, then add an oxidative polymerization agent to carry out an oxidative polymerization reaction, and polypyrrole is formed on the fabric substrate loaded with silver nanoparticles to obtain the photothermal conversion material.

[0011] Optionally, the alkaline metal hydroxide solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, and barium hydroxide solution.

[0012] Optionally, the silver salt solution includes silver ammonia solution.

[0013] Optionally, the reducing agent includes at least one of glucose, formaldehyde, and acetaldehyde.

[0014] Optionally, the acidic solution includes hydrochloric acid.

[0015] Optionally, the oxidative polymerization agent includes at least one of ferric salts and ammonium persulfate.

[0016] Optionally, the fabric substrate includes at least one of cotton fabric and non-woven fabric.

[0017] In the second aspect of the present invention, a photothermal conversion material is provided, wherein it is prepared by using the preparation method as described above in the present invention.

[0018] In the third aspect of the present invention, an application of the photothermal conversion material as described above in the present invention in solar seawater desalination is provided.

[0019] In the fourth aspect of the present invention, an evaporator is provided, which includes the photothermal conversion material as described above in the present invention.

[0020] Beneficial effects: In the present invention, the fabric substrate is first treated with an alkaline metal hydroxide solution so that the fabric substrate can better adsorb Ag + , and Ag is reduced by adding a reducing agent +Reduced to silver nanoparticles; then the fabric substrate loaded with silver nanoparticles was immersed in an acidic solution containing pyrrole, and an oxidative polymerization agent was added to oxidatively polymerize pyrrole monomers into polypyrrole, thereby preparing the photothermal conversion material. The photothermal conversion material provided by the embodiment of the present invention has good hydrophilicity, photothermal conversion ability and antibacterial effect, has a high seawater desalination efficiency, and does not produce salt crystallization. Specifically, the silver nanoparticles in the photothermal conversion material have a solar photothermal effect, synergistically enhance the absorption and thermal conversion of sunlight with polypyrrole, improve the photothermal conversion ability of the photothermal conversion material, and enable the photothermal conversion material to have a high seawater desalination effect; at the same time, the silver nanoparticles have an antibacterial effect, thereby enabling the photothermal conversion material to have a good antibacterial effect on Escherichia coli and Staphylococcus aureus. Description of the Drawings

[0021] Figure 1 It is a process flow chart of the preparation of the photothermal conversion material in the embodiment of the present invention.

[0022] Figure 2 It is a schematic diagram of the preparation of the photothermal conversion material in the embodiment of the present invention.

[0023] Figure 3 It is a test result diagram of the dynamic water contact angle of CF-Ag-PPy in Example 1 of the present invention, CF in Comparative Example 1 and CF-Ag in Comparative Example 2.

[0024] Figure 4 It is an ultraviolet-visible-near-infrared absorption spectrum diagram of CF-Ag-PPy in Example 1 of the present invention, CF in Comparative Example 1 and CF-Ag in Comparative Example 2.

[0025] Figure 5 It is a result diagram of the change of temperature with illumination time under sunlight irradiation of CF-Ag-PPy in Example 1 of the present invention, CF in Comparative Example 1, CF-Ag in Comparative Example 2 and CF-PPy in Comparative Example 3.

[0026] Figure 6a It is a physical diagram of CF-Ag-PPy in Example 1 of the present invention, CF in Comparative Example 1, CF-Ag in Comparative Example 2 and CF-PPy in Comparative Example 3. Figure 6b is Figure 6a The corresponding infrared thermal imaging diagram of CF-Ag-PPy in Example 1 of the present invention, CF in Comparative Example 1, CF-Ag in Comparative Example 2 and CF-PPy in Comparative Example 3.

[0027] Figure 7 It is a schematic structural diagram of the suspension bridge type floating evaporator in Example 1 of the present invention, where (a) is a front view and (b) is a top view.

[0028] Figure 8Evaporation rate result diagram of evaporators using different photothermal conversion materials.

[0029] Figure 9 Evaporation rate result diagram of evaporators with the ratio of the total area of different CF-Ag-PPy exposed to sunlight to the projected area of CF-Ag-PPy in the sunlight irradiation direction.

[0030] Figure 10 Ion concentration result diagram after desalination of 3.5 wt.% simulated seawater by an evaporator using CF-Ag-PPy.

[0031] Figure 11 Long-term stability test result diagram when an evaporator using CF-Ag-PPy is used for simulating seawater evaporation.

[0032] Figure 12 Surface salt crystallization diagram when an evaporator using CF-Ag-PPy is used for simulating seawater evaporation. Detailed implementation manners

[0033] The present invention provides a photothermal conversion material, a preparation method thereof and an application. To make the purpose, technical solution and effect of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific implementation manners and are not intended to limit the present invention.

[0035] An embodiment of the present invention provides a preparation method of a photothermal conversion material, wherein, as Figure 1 shown, it includes the steps:

[0036] S1. Provide a fabric substrate;

[0037] S2. Immerse the fabric substrate in an alkaline metal hydroxide solution for a preset time to obtain an alkali-treated fabric substrate;

[0038] S3. Immerse the alkali-treated fabric substrate in a silver salt solution, and then add a reducing agent to carry out a reduction reaction to obtain a fabric substrate loaded with silver nanoparticles;

[0039] S4. Immerse the fabric substrate loaded with silver nanoparticles in an acidic solution containing pyrrole, and then add an oxidative polymerization agent to carry out an oxidative polymerization reaction, and polypyrrole is formed on the fabric substrate loaded with silver nanoparticles to obtain the photothermal conversion material.

[0040] As Figure 2 shown, in the present invention, the fabric substrate is first treated with an alkaline metal hydroxide solution so that the fabric substrate can better adsorb Ag + , and Ag + is reduced to silver nanoparticles by adding a reducing agent; then the fabric substrate loaded with silver nanoparticles is immersed in an acidic solution containing pyrrole, the fabric substrate loaded with silver nanoparticles adsorbs pyrrole monomers, and after adding an oxidative polymerization agent, the pyrrole monomers are oxidatively polymerized into polypyrrole, and the photothermal conversion material is prepared. The photothermal conversion material provided by the embodiment of the present invention has good hydrophilicity, photothermal conversion ability and antibacterial effect, has a high seawater desalination efficiency, and does not produce salt crystallization. Specifically, the silver nanoparticles in the photothermal conversion material have a solar photothermal effect, and cooperate with polypyrrole (which has a solar photothermal effect) to enhance the absorption and thermal conversion of sunlight, improve the photothermal conversion ability of the photothermal conversion material, and enable the photothermal conversion material to have a high seawater desalination effect; at the same time, the silver nanoparticles have an antibacterial effect, and thus the photothermal conversion material has a good antibacterial effect on Escherichia coli and Staphylococcus aureus.

[0041] In step S1, in some embodiments, the fabric substrate is at least one of cotton fabric and non-woven fabric, but is not limited thereto. In some specific embodiments, the cotton fabric is cotton cloth.

[0042] In step S2, in some embodiments, the alkaline metal hydroxide solution includes but is not limited to at least one of sodium hydroxide solution, potassium hydroxide solution, and barium hydroxide solution. As Figure 2 shown, a large number of -OH exist on the surface of the fabric substrate (such as cotton fabric, etc.), and the -OH reacts with the alkaline metal hydroxide solution (such as sodium hydroxide solution) to obtain -O - , so that the fabric substrate can adsorb silver ions during the subsequent reaction process, which is beneficial to the deposition of silver nanoparticles on the fabric substrate.

[0043] In step S3, in some embodiments, the silver salt solution includes but is not limited to silver ammonia solution.

[0044] In some embodiments, the reducing agent includes but is not limited to at least one of glucose, formaldehyde, and acetaldehyde.

[0045] When the silver salt solution is silver ammonia solution and the reducing agent is glucose, the fabric substrate after alkali treatment is immersed in the silver ammonia solution, and then glucose is added for a silver mirror reaction to reduce the silver ions on the surface of the fabric substrate to silver nanoparticles, and a fabric substrate loaded with silver nanoparticles is obtained.

[0046] In step S4, in an acidic solution, pyrrole is oxidized and polymerized into polypyrrole, and the polypyrrole is formed in situ on the fabric substrate loaded with silver nanoparticles.

[0047] In some embodiments, the acidic solution includes but is not limited to hydrochloric acid.

[0048] In some embodiments, the oxidation polymerization agent includes but is not limited to at least one of ferric salts (such as ferric chloride, ferric nitrate, etc.) and ammonium persulfate.

[0049] In some embodiments, in the photothermal conversion material, the mass of silver nanoparticles and the mass of polypyrrole contained in the fabric substrate per unit volume (per mm 3 ) can be set according to actual needs. As an example, the mass of silver nanoparticles and the mass of polypyrrole contained in the fabric substrate per mm 3 are 0.0113 mg and 0.0155 mg respectively.

[0050] The embodiment of the present invention also provides a photothermal conversion material, which is prepared by using the preparation method as described above in the present invention. The photothermal conversion material is a fabric substrate loaded with silver nanoparticles and polypyrrole at the same time, and the silver nanoparticles and polypyrrole are loaded on the surface and internal gaps of the fabric substrate. The photothermal conversion material provided by the embodiment of the present invention has good hydrophilicity, photothermal conversion ability and antibacterial effect.

[0051] The embodiment of the present invention also provides an application of the photothermal conversion material as described above in the present invention in solar desalination of seawater. The photothermal conversion material has good hydrophilicity and excellent photothermal conversion ability, is very suitable for solar desalination of seawater, and has a high seawater desalination efficiency.

[0052] The embodiment of the present invention also provides an evaporator, which includes the photothermal conversion material as described above in the embodiment of the present invention. The evaporator can achieve efficient solar desalination of seawater, and due to the presence of silver nanoparticles, the evaporator has a good antibacterial effect on Escherichia coli and Staphylococcus aureus.

[0053] In some specific embodiments, the evaporator is a suspension evaporator of suspension bridge type. When the total area of the photothermal conversion material exposed to sunlight in this suspension evaporator of suspension bridge type is greater than the projected area of the photothermal conversion material in the sunlight irradiation direction (vertical direction), compared with the case where the total area of the photothermal conversion material exposed to sunlight is equal to the projected area of the photothermal conversion material in the vertical direction, the evaporation rate of water is high, and the photothermal conversion material is fully utilized. The suspension evaporator of suspension bridge type can achieve efficient solar desalination of seawater, and the evaporation rate of water can reach 1.55 kg·m -2 ·h -1 , and has good thermal management ability.

[0054] In the prior art, due to insufficient water supply during continuous SDIE, a large amount of deposited salts are generated, resulting in serious salt pollution. The deposited salts will gradually block the pathways of light absorption, water transportation, and steam escape, ultimately reducing the evaporation rate and long-term stability. However, the suspension evaporator of the suspension bridge type provided by the present invention has long-term stability and can effectively inhibit salt crystallization in high-concentration seawater.

[0055] The following is a detailed description through specific examples.

[0056] Unless otherwise specified, the solutions in the following examples are all aqueous solutions.

[0057] Example 1

[0058] A 150 mm × 50 mm × 1 mm cotton cloth was immersed in ethanol, taken out after ultrasonic cleaning for 30 min, placed in a drying oven for drying. After the dried cotton fabric was immersed in 200 mL of an aqueous NaOH solution (NaOH mass content was 10%) for 30 min, it was rinsed with a large amount of deionized water and then placed in an oven for drying to obtain the alkali-treated cotton cloth, denoted as CF-NaOH.

[0059] CF-NaOH was immersed in 250 mL of 0.1 M silver ammonia solution for 1 h and then taken out and dried to obtain the cotton cloth with silver ions adsorbed on its surface, denoted as CF-Ag + ;

[0060] CF-Ag + was placed in 250 mL of 0.01 M glucose (C6H 12 O6) solution, heated and stirred at 60 °C for 40 min to obtain the cotton cloth loaded with silver nanoparticles, denoted as CF-Ag.

[0061] Under an ice bath at 0 °C, 60 μL of pyrrole (py) was added to 90 mL of 1 M hydrochloric acid, stirred evenly, then CF-Ag was immersed therein, and then 20 mL of 1 g / L FeCl3 solution was added dropwise. After 2 h, the cotton cloth was taken out, washed with deionized water, and placed in the environment to dry naturally. Polypyrrole was formed on CF-Ag to obtain the photothermal conversion material, denoted as CF-Ag-PPy.

[0062] Comparative Example 1

[0063] The same cotton cloth as in Example 1 was used as the photothermal conversion material, denoted as CF.

[0064] Comparative Example 2

[0065] The same CF-Ag as in Example 1 was used as the photothermal conversion material.

[0066] Comparative Example 3

[0067] Under an ice bath at 0 °C, 60 μL of pyrrole (py) was added to 90 mL of 1 M hydrochloric acid. After stirring evenly, CF (the same CF as in Example 1) was immersed therein, and then 20 mL of 1 g / L FeCl3 solution was added dropwise. After 2 h, the cotton cloth was taken out, washed with deionized water, and placed in the environment to dry naturally. Polypyrrole was formed on the CF, and the obtained photothermal conversion material was denoted as CF-PPy.

[0068] Test:

[0069] (1) The dynamic water contact angles of CF-Ag-PPy in Example 1 and CF and CF-Ag in Comparative Examples 1-2 were tested. The results are as Figure 3 shown. It can be seen that water can be completely spread on the surface of CF-Ag-PPy, and CF-Ag-PPy has good hydrophilicity.

[0070] (2) The ultraviolet-visible-near-infrared light absorption rates of CF-Ag-PPy in Example 1 and CF and CF-Ag in Comparative Examples 1-2 were tested. The calculation formula of the light absorption rate is , where R represents the light reflectance, T represents the light transmittance. The results are as Figure 4 shown. It can be seen that in the entire ultraviolet-visible-near-infrared light region, the absorption rate of CF-Ag-PPy reaches 90% (up to 95% at most), which is much higher than that of CF and CF-Ag.

[0071] (3) The temperature change of CF-Ag-PPy in Example 1 and CF, CF-Ag, and CF-PPy in Comparative Examples 1-3 was tested under 1 sun illumination (light intensity is 1 kW / m 2 ). The temperature change curve with the illumination time is as Figure 5 shown. It can be seen that as the illumination progresses, the temperature of CF rises to about 40 °C and then basically remains unchanged; as the illumination progresses, the temperature of CF-Ag rises to about 60 °C and then basically remains unchanged; as the illumination progresses, the temperature of CF-PPy rises to about 62 °C and then basically remains unchanged; while as the illumination progresses, the temperature of CF-Ag-PPy can rise to about 72 °C and then basically remains unchanged. It shows that CF-Ag-PPy has more excellent photothermal conversion effect compared with CF, CF-Ag, and CF-PPy. The silver nanoparticles and polypyrrole in CF-Ag-PPy synergistically enhance the photothermal conversion ability of CF-Ag-PPy.

[0072] For CF-Ag-PPy in Example 1 and CF, CF-Ag, and CF-PPy in Comparative Examples 1-3 as shown in Figure 6a under 1 sun (light intensity is 1 kW / m 2) Irradiate from below for 15 min. The infrared thermal imaging results are as Figure 6b shown. It can be seen that the CF-Ag-PPy in the lower right corner has the highest temperature.

[0073] (4) Fabricate the CF-Ag-PPy in Example 1 and CF, CF-Ag, and CF-PPy in Comparative Examples 1-3 into the suspension evaporators in the form of a suspension bridge as shown in Figure 7 (a) and (b) in the figure to evaporate the water in two glass cylinders. Among them, the ratio of the total area of CF-Ag-PPy, CF, CF-Ag, and CF-PPy exposed to sunlight to their projected area in the sunlight irradiation direction (vertical direction) is 1:1. Taking CF-Ag-PPy as an example, that is, the ratio of the actual area of CF-Ag-PPy exposed to sunlight to its projected area in the sunlight irradiation direction is 1:1). Simulate sunlight with a xenon lamp, and the light intensity is 1 kW / m 2 (1 sun), and perform solar evaporation on water. Specifically, as Figure 7 shown, the water in the two side glass cylinders is transferred to the middle suspension bridge structure part through the photothermal conversion material. The photothermal conversion material in the middle suspension bridge structure part is heated by sunlight irradiation, and then the water in the photothermal conversion material of the middle suspension bridge structure part is heated and evaporated.

[0074] The evaporation rate is calculated by the formula (Δm (kg) represents the mass change of the evaporation system, t (h) represents the evaporation time, S (m 2 ) is the effective evaporation area of the evaporator).

[0075] The evaporation rate results are as Figure 8 shown. The evaporation rate of water by the evaporator using CF is 0.71 kg·m -2 ·h -1 , while the evaporation rates of water by the evaporators using CF-PPy and CF-Ag are higher than that of the evaporator using CF. The evaporation rate of water by the evaporator using CF-Ag-PPy can reach 1.2 kg·m -2 ·h -1 .

[0076] Fabricate three evaporators using CF-Ag-PPy, in which the ratios of the total area of CF-Ag-PPy exposed to sunlight to its projected area in the sunlight irradiation direction (vertical direction) are 1:1, 3:2, and 2:1 respectively. Measure the evaporation rates of water by the three evaporators using CF-Ag-PPy respectively. The results are as Figure 9As shown, when the ratio of the total area of CF-Ag-PPy exposed to sunlight to the projected area of CF-Ag-PPy in the sunlight irradiation direction (vertical direction) is 2:1, the evaporation rate of water by the evaporator using CF-Ag-PPy can reach 1.55 kg·m -2 ·h -1 .

[0077] (7) Fabricate the CF-Ag-PPy in Example 1 and CF, CF-Ag, and CF-PPy in Comparative Examples 1-3 into the suspension evaporator in the form of a suspension bridge as Figure 7 shown. The ratio of the total area of CF-Ag-PPy, CF, CF-Ag, and CF-PPy exposed to sunlight to the projected area of each in the sunlight irradiation direction (vertical direction) is 2:1. Use a xenon lamp to simulate sunlight with a light intensity of 1 kW / m 2 (1 sun), and perform solar evaporation on 3.5 wt.% simulated seawater. The concentration of Na + in the simulated seawater is 11000 mg / L, the concentration of Mg 2+ is 1500 mg / L, the concentration of Ca 2+ is 800 mg / L, the concentration of K + is 500 mg / L. The ion concentrations of the distilled water obtained after evaporation and condensation are as Figure 10 shown. It can be seen that the ion concentrations in the distilled water obtained after evaporation and condensation all decrease exponentially compared to the simulated seawater, proving that the evaporator has excellent desalination performance.

[0078] (8) Test on the long-term operation stability and surface salt crystallization of the evaporator in 3.5 wt.% simulated seawater

[0079] Fabricate the CF-Ag-PPy in Example 1 and CF, CF-Ag, and CF-PPy in Comparative Examples 1-3 into the suspension evaporator in the form of a suspension bridge as Figure 7 shown. The ratio of the total area of CF-Ag-PPy, CF, CF-Ag, and CF-PPy exposed to sunlight to the projected area of each in the sunlight irradiation direction (vertical direction) is 2:1. Use a xenon lamp to simulate sunlight with a light intensity of 1 kW / m 2 (1 sun), perform a solar evaporation test on 3.5 wt.% simulated seawater for 6 cycles, with one cycle per day, 8 hours per day, and measure the evaporation rate once per hour. The results are as Figure 11 and 12 shown. It can be seen that the evaporator is stable during long-term operation, and no salt crystallization occurs on the surface of the evaporator during long-term operation, proving that the evaporator can effectively inhibit salt crystallization.

[0080] In summary, the present invention provides a photothermal conversion material, a preparation method thereof, and an application thereof. In the present invention, a fabric substrate is first treated with an alkaline metal hydroxide solution so that the fabric substrate can better adsorb Ag + , and Ag + is reduced to silver nanoparticles by adding a reducing agent; then the fabric substrate loaded with silver nanoparticles is immersed in an acidic solution containing pyrrole, and an oxidative polymerization agent is added to oxidize and polymerize pyrrole monomers into polypyrrole to prepare the photothermal conversion material. The photothermal conversion material provided by the embodiment of the present invention has good hydrophilicity, photothermal conversion ability and antibacterial effect, has a high seawater desalination efficiency, and can effectively inhibit salt crystallization. Specifically, the silver nanoparticles in the photothermal conversion material have a solar photothermal effect, synergistically enhance the absorption and thermal conversion of sunlight with polypyrrole, improve the photothermal conversion ability of the photothermal conversion material, and enable the photothermal conversion material to have a high seawater desalination effect; at the same time, the silver nanoparticles have an antibacterial effect, and thus the photothermal conversion material has a good antibacterial effect on Escherichia coli and Staphylococcus aureus. It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A suspension-type evaporator of drawbridge type, characterized in that, It includes a photothermal conversion material, the total area of the photothermal conversion material exposed to sunlight being greater than the projected area of the photothermal conversion material in the sunlight irradiation direction, and both ends of the photothermal conversion material being used for water absorption; The preparation method of the photothermal conversion material includes the steps of: providing a fabric substrate; immersing the fabric substrate in an alkaline metal hydroxide solution for a preset time to obtain an alkali-treated fabric substrate; immersing the alkali-treated fabric substrate in a silver salt solution, and then adding a reducing agent to carry out a reduction reaction to obtain a fabric substrate loaded with silver nanoparticles; immersing the fabric substrate loaded with silver nanoparticles in an acidic solution containing pyrrole, and then adding an oxidation polymerization agent to carry out an oxidation polymerization reaction to form polypyrrole on the fabric substrate loaded with silver nanoparticles, thereby obtaining the photothermal conversion material.

2. The suspension evaporator of the drawbridge type according to claim 1, wherein The alkaline metal hydroxide solution includes at least one of a sodium hydroxide solution, a potassium hydroxide solution, and a barium hydroxide solution.

3. The suspension evaporator of the drawbridge type according to claim 1, characterized in that The silver salt solution includes a silver ammonia solution.

4. The suspension evaporator of the drawbridge type according to claim 1, wherein The reducing agent includes at least one of glucose, formaldehyde, and acetaldehyde.

5. The suspension evaporator of the drawbridge type according to claim 1, wherein The acidic solution includes hydrochloric acid.

6. The suspension evaporator of the drawbridge type according to claim 1, wherein The oxidation polymerization agent includes at least one of a ferric salt and ammonium persulfate.

7. The suspension evaporator of the drawbridge type according to claim 1, wherein, The fabric substrate includes at least one of a cotton fabric and a non-woven fabric.

8. The suspension evaporator of the drawbridge type according to claim 1, wherein, The ratio of the total area of the photothermal conversion material exposed to sunlight to the projected area of the photothermal conversion material in the sunlight irradiation direction is 2:1 or 3:2.

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