Method for improving photo-thermal conversion efficiency of photo-thermal material under large-range light intensity, photo-thermal material and solar thermal collector

Abstract

The invention discloses a method for improving photo-thermal conversion efficiency of a photo-thermal material under large-range light intensity, the photo-thermal material and a solar heat collector, and belongs to the field of solar evaporation water treatment. According to the technical scheme, the method comprises the steps that polyaniline particle-loaded carbon aerogel is prepared, the light intensity range is greatly widened to 10 sunlight intensities or above through a Fresnel lens, the corresponding relation between the material surface water evaporation rate and the temperature change is established, and the energy loss is reduced to the maximum extent by adding a foam side heat insulation layer; and the water evaporation rate of the photo-thermal material is improved. The method is applied to the aspect of solar water evaporation, and the problem that the water evaporation rate is low in an existing solar evaporation method is solved.

Description

Technical Field

[0001] The present invention belongs to the field of solar evaporation water treatment, and particularly relates to a method for improving the photothermal conversion efficiency of a photothermal material under a wide range of light intensities, a photothermal material, and a solar collector. Background Art

[0002] Desalination of seawater has become a viable solution to meet the growing demand for clean water. Among emerging technologies, solar-driven interfacial evaporation shows great potential for obtaining fresh water by effectively evaporating brine or sewage. The efficiency of this process depends on effective energy management, including the management of light, heat, and water supply. Various strategies have been adopted to improve energy efficiency, including optimizing light absorption, minimizing energy loss, harvesting ambient energy, and reducing the enthalpy of evaporation, which are mainly achieved through advanced interfacial engineering and system design.

[0003] Carbon materials are one of the most promising light absorbers. Since they were first used in solar thermal evaporation in 2011, carbon-based materials have attracted extensive attention. Nowadays, three-dimensional (3D) porous graphene, especially free-floating graphene-based aerogels, have been developed. Due to the narrowing of the bandgap and the lightweight and porous internal structure, they exhibit broadband solar absorption and efficient water transport; however, their limited low photothermal conversion efficiency hinders their evaporation performance. Recently, various conjugated polymers, such as polypyrrole, polyaniline (PANI), and polydopamine, have also been studied for solar interfacial evaporation applications due to their broad light absorption, low cost, and effective heat localization at the interface. However, their utilization usually requires complex procedures to prepare the corresponding pervaporation films. Therefore, directly integrating PANI into 3D graphene-based aerogels through interfacial engineering can simplify the manufacturing process and improve the solar evaporation performance.

[0004] In addition, a novel solar-driven interfacial evaporation system has been developed, which improves the actual clean water productivity by integrating various processes such as membrane filtration, thermoelectric conversion, and bionic methods. However, there are few research reports on integrated solar collectors. High-intensity environments can be easily created using inexpensive Fresnel lenses, which can significantly increase the evaporation rate of water when applied to the evaporation process of solar evaporators. The Halas group reported this pioneering application, where they used a Fresnel lens to raise the surface temperature of plasmonic gold nanoparticles above the boiling point of water, resulting in the formation of vapor at the particle-liquid interface. Naldoni and co-authors further investigated the performance of plasmonic absorbers at different light intensities and showed a highly non-linear enhancement in performance at high light intensities (≥7 suns) compared to that at standard light concentrations. It seems that for carbon-based materials, higher energy input can also increase the evaporation rate. For example, Ma et al. observed that both the evaporation rate and surface temperature of graphene oxide (GO)-modified carbonized cotton materials continuously increased under solar light intensities of 1 to 4 suns. However, note that the above studies mainly focused on light intensities below 4 suns because standard solar simulators are limited to this intensity without the help of solar collectors. It is currently uncertain whether the water evaporation rate will continue to increase or even surge at high light intensities. Therefore, for carbon-based materials, the relationship between different light radiation intensities and the water evaporation process and its underlying mechanism are not clear. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to overcome the problem that the water evaporation rate of the photothermal material is nearly constant and does not increase with the increase of light intensity at high light intensities of 6 - 10 suns, and the problem of low photothermal conversion efficiency in the solar evaporation method. A method, a photothermal material, and a solar collector for improving the photothermal conversion efficiency of the photothermal material and significantly increasing the water evaporation rate by adding a side foam insulation layer around the photothermal material are proposed.

[0006] To solve the above technical problem, the technical solution adopted by the present invention is as follows:

[0007] On the one hand, the present invention provides a method for improving the photothermal conversion efficiency of a photothermal material under a wide range of light intensities, including: loading polyaniline particles in a carbon aerogel, controlling the proportion of the polyaniline loading, using a Fresnel lens to broaden the light intensity range to more than 10 sun light intensities, establishing the corresponding relationship between the water evaporation rate on the material surface and the temperature change, and adding a foam side heat insulation layer around the photothermal material to significantly improve the problem that the water evaporation rate on the material surface of the photothermal material is inhibited under the high light intensity of 6-10 suns. This method uses a Fresnel lens to enhance the sunlight intensity incident on the evaporation surface of the photothermal material, and adds a side foam heat insulation layer to reduce the heat loss under the high light intensity of 6-10 suns, thereby improving the photothermal conversion ability of the photothermal material. Among them, the photothermal material is selected from carbon aerogels doped with dark green polyaniline.

[0008] Preferably, a Fresnel lens is used to enhance the sunlight intensity received on the surface of the photothermal material, and the correlation between the water evaporation rate on the surface of the photothermal material and the change in the evaporation interface temperature of the photothermal material is established within the range of sunlight intensity of 1-10 suns, and a water evaporation rate-temperature curve is made. It is found that the water evaporation process of the carbon-based photothermal material is in a "plateau period" under the condensing intensity of 6-10 suns. Furthermore, the conclusion that the evaporation rate is significantly increased is obtained by adding a foam side heat insulation layer.

[0009] Preferably, the Fresnel lens is placed parallel between the sunlight source and the carbon aerogel. The light rays are converged by the Fresnel lens, and the sunlight intensity irradiated on the surface of the photothermal material is enhanced. Polystyrene foam is used to make the heat insulation layer and is placed around the carbon aerogel.

[0010] Preferably, by adjusting the power of the xenon lamp and changing the distance between the Fresnel lens and the surface of the photothermal material, the light intensity obtained on the surface of the photothermal material is changed.

[0011] Preferably, an infrared thermal imager is used to record the change in the highest temperature of the evaporation interface of the photothermal material with the increase in sunlight intensity.

[0012] Preferably, under the high light intensity environment of 6-10 suns, the heat insulation layer material around the carbon aerogel is selected as polystyrene foam; the carbon aerogel is selected from one or more of graphene aerogel, carbon nanotube aerogel, porous carbon aerogel, and activated carbon fiber aerogel.

[0013] On the other hand, the present invention provides a photothermal material for use in the method for improving the photothermal conversion efficiency of a photothermal material described in any of the above technical solutions; the dark green polyaniline is prepared by the following method: under an ice bath, aniline monomer is dissolved in an HCl aqueous solution to obtain solution A, and ammonium persulfate is dissolved in an HCl aqueous solution to obtain solution B. Then, solution A and solution B are mixed, and the solution gradually turns dark green. After reacting at 0 °C, the precipitate is obtained by centrifugation, and the dark green polyaniline is obtained by washing.

[0014] Preferably, the carbon aerogel loaded with dark green polyaniline is prepared by the following method: doping dark green polyaniline into the graphene oxide solution, and obtaining the carbon aerogel loaded with dark green polyaniline after reduction, freeze-drying and heat baking treatments.

[0015] Preferably, the carbon aerogel loaded with dark green polyaniline is prepared by the following method: mixing and stirring the graphene oxide solution, ascorbic acid, and dark green polyaniline, drying at 90 °C to obtain a hydrogel, and subjecting the hydrogel to freeze-drying treatment and drying at 70 °C to convert it into an aerogel, thereby obtaining the carbon aerogel loaded with dark green polyaniline.

[0016] The present invention also provides a solar collector, which uses the Fresnel lens to enhance the intensity of incident sunlight, uses polymer foam as a waterproof and heat-insulating boundary material, places the photothermal material described in any of the above technical solutions around the polymer foam, so that the water evaporation rate is significantly increased, and obtains the solar collector floating on the water surface.

[0017] Preferably, when the solar collector works: floating melamine foam on the water surface, placing the cylindrical carbon aerogel on the melamine foam, placing the container on an electronic balance connected to a computer for real-time data recording, placing the Fresnel lens parallel between the xenon lamp and the carbon aerogel, converging the light through the Fresnel lens and irradiating on the surface of the cylindrical carbon aerogel, using polystyrene foam to make a heat-insulating layer and placing it around the carbon aerogel, with an irradiation time of 1 h, an environmental temperature of 25 °C, a humidity maintained at 50 - 55%, and a water temperature of 25 °C.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention provides a method for improving the photothermal conversion efficiency of a photothermal material. By optimizing the photothermal material and introducing a Fresnel lens to enhance the intensity of sunlight incident on the evaporation surface of the photothermal material, the problem that the evaporation rate of the photothermal material is nearly the same under the light intensity of 6 - 10 suns is discovered. By adding a foam side heat-insulating layer around the photothermal material, the limitation is effectively overcome, the heat loss of the photothermal material to the air is reduced, and thus the conclusion that adding a side foam heat-insulating layer to the photothermal material under the light intensity of 6 - 10 suns makes the evaporation rate increase significantly is obtained, thereby effectively improving the photothermal conversion ability of the photothermal material;

[0020] The present invention provides a photothermal material, which combines graphene aerogel with polyaniline to prepare a carbon aerogel material with excellent photothermal conversion ability. Description of the Drawings

[0021] Figure 1 It is a physical picture of the carbon aerogel material;

[0022] Figure 2 Schematic diagram of the preparation process of carbon aerogel material;

[0023] Figure 3 Variation curve of the water evaporation rate of carbon aerogel material showing a plateau with different light intensities;

[0024] Figure 4 Variation curves of the evaporation interface temperature and water evaporation rate of four carbon aerogel materials with different light intensities;

[0025] Figure 5 Relationship curves of the evaporation interface temperature and water evaporation rate of three carbon aerogel materials;

[0026] Figure 6 Relationship between the evaporation rate of carbon fiber cloth and the highest surface temperature. The inset shows the evaporation rate (left axis) and the highest surface temperature (right axis) obtained at different light intensities;

[0027] Figure 7 Histogram of the photothermal conversion efficiency corresponding to the concentrated light intensity experienced by the carbon aerogel material;

[0028] Figure 8 Schematic diagram of adding a foam side heat insulation layer around the carbon aerogel material.

[0029] Figure 9 Variation curve of the water evaporation rate of the carbon aerogel material with a foam side heat insulation layer added with different light intensities. Specific implementation manner

[0030] The technical solutions in the specific embodiments of the present invention will be described in detail and completely below with reference to the accompanying drawings. Obviously, the described embodiments are only partial specific implementation manners of the overall technical solution of the present invention, rather than all implementation manners. Based on the overall concept of the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the protection scope of the present invention.

[0031] On the one hand, the present invention provides a method for improving the water evaporation rate around a photothermal material by adding a side foam heat insulation layer to improve the photothermal conversion efficiency of the photothermal material, including: loading polyaniline particles in the carbon aerogel, controlling the proportion of the polyaniline loading amount, and using a Fresnel lens to broaden the light intensity range to more than 10 sun light intensities, establishing the corresponding relationship between the water evaporation rate on the material surface and the temperature change, and adding a foam side heat insulation layer around the photothermal material to significantly improve the problem that the water evaporation rate on the material surface is inhibited under high light intensities of 6 - 10 suns of the photothermal material.

[0032] The above method uses a Fresnel lens to enhance the intensity of sunlight incident on the evaporation surface of the photothermal material, thereby obtaining the change curves of the water evaporation rate and temperature of the photothermal material under different light concentration intensities, and adding a foam insulation layer to reduce the heat loss of the photothermal material to the surrounding environment, thereby improving the photothermal conversion ability of the photothermal material; the photothermal material is selected from carbon aerogel doped with dark green polyaniline. This method optimizes the photothermal material, introduces a Fresnel lens to enhance the intensity of sunlight incident on the evaporation surface of the photothermal material, studies the water evaporation performance under different light intensities, measures the performance of the photothermal material under higher light intensities through the changes in the water evaporation rate and temperature, and adds a foam insulation layer to effectively improve the photothermal conversion ability of the photothermal material.

[0033] In view of the deficiencies of the prior art, the present invention introduces a Fresnel lens into the system of water evaporation of the photothermal material. By using the Fresnel lens to enhance the intensity of the incident sunlight, the high light intensity acts on the surface of the photothermal material, which can significantly increase the water evaporation rate. As the light intensity on the surface of the photothermal material increases, within 1 hour of continuous irradiation, the water evaporation rate and the evaporation interface temperature that the material can reach tend to a "plateau period", as shown in Figure 3 , Figure 4 , under low to medium light intensities of 1 to 6 suns, the water evaporation rate and the highest surface temperature almost linearly increase with the increase of the light intensity, reaching 6.4 kg m -2 h -1 and 71 °C respectively at 6 suns. However, under high light intensities of 6 to 10 suns, the water evaporation rate may enter a "steady period", remaining stable in the range of 6 - 7 kg m -2 h -1 , while the highest surface temperature only increases slightly, ranging from about 71 °C to nearly 79 °C. At the same time, the solar steam conversion efficiency decreases with the increase of the light intensity, as shown in Figure 7 , for carbon-based materials, during the process of using solar energy to evaporate water, internal electrons are excited by external photons and jump, and then relax back to the ground state from the excited state, releasing energy mainly in the form of heat. Therefore, the evaporation performance of specific carbon-based materials depends on the highest temperature of their material evaporation interface. However, the highest temperature observed here also seems to have a maximum value under strong light irradiation, indicating that most of the input energy is dissipated to the surrounding environment through heat convection and conduction. In order to find a reliable descriptor to describe the photothermal evaporation ability, in the linearly increasing region, that is, under low and medium light intensities, the evaporation rate is plotted against the corresponding highest surface temperature, because the evaporation performance depends on the surface temperature of the material ( Figure 5 ). A rather good linear relationship is observed between the evaporation rate and the highest surface temperature. Based on this performance, the evaporation performance of typical carbon fiber cloth under different light intensities is also measured to further confirm the reliability of the slope as a descriptor. When the relationship between the evaporation rate and the highest surface temperature is plotted in the linearly increasing region, a rather good linear relationship is also observed.Figure 6 , inspired by the design of the heat-insulating box, a side foam heat-insulating layer was added to solve the platform problem that occurs under high light intensity. A side foam heat-insulating layer was applied around the carbon aerogel evaporator to inhibit energy dissipation. As expected, the highest surface temperature and the corresponding evaporation rate continued to increase under high light intensity, reaching nearly 95 °C and 7.5 kg m - 2 h -1 , respectively, under 10 suns. Therefore, for carbon-based materials, the application of side foam heat-insulating materials is crucial for preventing energy dissipation, especially when operating at high evaporation rates, thus avoiding the energy loss caused by using too high light intensity in the practical application of solar water evaporation. This finding can better guide the design of actual devices.

[0034] In a preferred embodiment, a Fresnel lens was used to enhance the sunlight intensity received on the surface of the photothermal material. A correlation was established between the water evaporation rate on the surface of the photothermal material and the change in the evaporation interface temperature of the photothermal material within the range of sunlight intensity from 1 to 10 suns, and a water evaporation rate-temperature curve was plotted. Furthermore, the problem that the evaporation rate of the photothermal material was nearly consistent under the light intensity of 6 - 10 suns was discovered. By adding a foam side heat-insulating layer around the photothermal material, the limitation was effectively overcome, and the conclusion was obtained that adding a side foam heat-insulating layer to the photothermal material under the light intensity of 6 - 10 suns resulted in a significant increase in the evaporation rate. Through the water evaporation experiments of carbon-based materials (reduced graphene oxide aerogel, reduced graphene oxide aerogel loaded with polyaniline) under different light concentration intensities, with the water evaporation rate as the ordinate and the temperature as the abscissa, the magnitude of the slope of the fitting curve can reflect the strength of the photothermal conversion ability of the material, and can also intuitively show the evaporation performance of the photothermal material in the plateau period under high light intensity. Therefore, by comparing the slopes, the ability of different carbon-based materials to utilize sunlight under high light intensity can be measured, as Figure 5 shown. Furthermore, using a Fresnel lens to enhance the sunlight intensity incident on the evaporation surface of the photothermal material to 6 - 10 suns and adding a foam side heat-insulating layer can effectively improve the water evaporation effect.

[0035] In a preferred embodiment, the Fresnel lens was placed parallel between the sunlight source and the carbon aerogel. The light rays converged after passing through the Fresnel lens, and the sunlight intensity irradiated on the surface of the photothermal material was enhanced. In the system of water evaporation of the photothermal material in the present invention, a Fresnel lens was introduced. By using the Fresnel lens, the water evaporation performance of carbon-based materials under different sunlight intensities was studied. The magnitude of the photothermal conversion ability of the photothermal material was measured through the slope change of the water evaporation rate and the temperature. At the same time, the reliability of using the slope as a comparison of the photothermal conversion ability was confirmed through the experiment of carbon fiber cloth, as shown in Figure 6, the curve of the evaporation rate and the highest surface temperature of the photothermal material with the increase of light intensity is obtained by the method of the present invention, and the slope of the fitting curve is determined as a reliable descriptor for describing the photothermal evaporation ability.

[0036] In a preferred embodiment, the light intensity obtained on the surface of the photothermal material is changed by adjusting the power of the xenon lamp and changing the distance between the Fresnel lens and the surface of the photothermal material. Further, an infrared thermal imager is used to record the change of the highest temperature of the evaporation interface of the photothermal material with the increase of sunlight intensity.

[0037] In a preferred embodiment, in a high light intensity environment of 6-10 suns, the thermal insulation layer material around the carbon aerogel is selected as polystyrene foam; the carbon aerogel is selected from one or more of graphene aerogel, carbon nanotube aerogel, porous carbon aerogel, and activated carbon fiber aerogel.

[0038] On the other hand, the present invention provides a photothermal material for use in the method for improving the photothermal conversion ability of the photothermal material in any of the above technical solutions; dark green polyaniline is prepared by the following method: under an ice bath, aniline monomer is dissolved in an HCl aqueous solution to obtain solution A, and ammonium persulfate is dissolved in an HCl aqueous solution to obtain solution B. Then, solution A and solution B are mixed, and the solution gradually turns dark green. After reacting at 0 °C, the precipitate is obtained by centrifugation, and the dark green polyaniline powder is obtained after washing and grinding. Specifically, under an ice bath, 5 mL of aniline monomer is completely dissolved in 1 M HCl aqueous solution (80 mL), and 15 g of ammonium persulfate (APS) is completely dissolved in 1 M HCl aqueous solution (20 mL). Then, the two solutions are mixed, and the solution gradually turns dark green. The reaction is carried out at 0 °C for 6 h, and the solution is centrifuged. The precipitate is washed 3 times with deionized water to obtain dark green polyaniline (PANI) powder. This technical solution specifically defines the preparation method of dark green polyaniline, and specifically defines the preparation of dark green polyaniline under acidic conditions. The reason is that polyaniline synthesized under acidic conditions has better light absorption ability and hydrophilicity than under basic synthesis conditions, making it have better performance in terms of the total photothermal efficiency in water evaporation.

[0039] In a preferred embodiment, the carbon aerogel doped with dark green polyaniline is prepared by the following method: dark green polyaniline is doped into the graphene oxide solution, and after reduction, freeze-drying, and heat drying treatments, the carbon aerogel doped with dark green polyaniline is obtained. Specifically, the graphene oxide solution, ascorbic acid, and dark green polyaniline are mixed and stirred, and dried at 90 °C to obtain a hydrogel. The hydrogel is freeze-dried and then dried at 70 °C to be converted into an aerogel, obtaining the carbon aerogel doped with dark green polyaniline. Among them, the graphene oxide solution is 5 mg / mL; 800 mg of ascorbic acid is used as a reducing agent, and dark green polyaniline (PANI) powder is added to 100 mL of a 5 mg / mL GO aqueous solution, mechanically stirred for 30 min, placed in an oven and dried at 90 °C for 8 h to be converted into an rGO hydrogel, and then after freeze-drying treatment and kept in the oven at 70 °C for 24 h to be converted into an rGO aerogel, and the weight ratios of polyaniline are 33%, 50%, and 67% respectively. The surface area of the prepared carbon aerogel material is 13 cm 2 , and the thickness is 1.5 cm. This technical solution specifically defines the preparation method of the carbon aerogel doped with dark green polyaniline, especially the weight ratio of dark green polyaniline (preferably 67%). The reason is that in the solar-driven water evaporation experiment, the evaporation performance of different polyaniline loadings under different light concentration intensities was compared. When the polyaniline loading is 67%, with the increase of the light intensity experienced by the material surface, both the water evaporation rate and the temperature growth performance are more excellent than the other three materials, and there is still a small growth space when compared at higher light intensities. See Figure 4 , which proves that loading polyaniline on the reduced graphene oxide aerogel can significantly improve the photothermal performance of the PANI-rGO composite aerogel, and with the increase of the polyaniline loading, the photothermal performance will be further improved, while a higher ratio will inhibit the material forming.

[0040] The present invention also provides a solar collector, which uses a Fresnel lens to enhance the intensity of incident sunlight, uses a polymer foam as a waterproof and heat-insulating boundary material, places the photothermal material of any of the above technical solutions around the polymer foam, so that the water evaporation rate is significantly increased, obtaining a solar collector floating on the water surface.

[0041] In a preferred embodiment, when the solar collector operates: Melamine foam is floated on the water surface, cylindrical carbon aerogel is placed on the melamine foam, the container is placed on an electronic balance connected to a computer for real-time data recording, a Fresnel lens is placed parallel between the xenon lamp and the carbon aerogel, the light is converged by the Fresnel lens and irradiates on the surface of the cylindrical carbon aerogel, polystyrene foam is used to make a heat insulation layer and is placed around the carbon aerogel, the irradiation time is 1 h, the ambient temperature is 25 °C, the humidity is maintained at 50 - 55%, and the water temperature is 25 °C. Specifically, melamine foam with a diameter of 3 cm and a thickness of 1 cm is floated on the water surface of a 60 mL container filled with tap water, cylindrical carbon aerogel with a diameter of 3 cm and a thickness of 1.5 cm is placed on the melamine foam, the container is placed on an electronic balance connected to a computer for real-time data recording, a Fresnel lens is placed parallel between the xenon lamp and the carbon aerogel material, the light is converged by the lens and irradiates on the material surface, a cylindrical hollow polystyrene foam with a diameter of 6 cm and a thickness of 1.5 cm is used to make a heat insulation layer and is placed around the carbon aerogel, the time is 1 h, the ambient temperature is 25 °C, the humidity is maintained between 50 - 55%, the tap water temperature is 25 °C, and the water evaporation rate is 1.99 kg m -2 h -1 。

[0042] In order to introduce the method for improving the photothermal conversion efficiency of photothermal materials, the photothermal materials and the solar collector provided by the embodiments of the present invention more clearly and in detail, the following will be described in combination with specific embodiments.

[0043] Example 1

[0044] (1) Under an ice bath, 5 mL of aniline monomer is completely dissolved in 1 M HCl aqueous solution (80 mL), and then 15 g of ammonium persulfate (APS) is completely dissolved in 1 M HCl aqueous solution (20 mL). Then, the two solutions are mixed, and the solution gradually turns dark green. The reaction is carried out at 0 °C for 6 h. The solution is centrifuged, and the precipitate is washed 3 times with deionized water to obtain dark green PANI powder.

[0045] (2) 800 mg of ascorbic acid is added as a reducing agent to 100 mL of 5 mg / mL GO aqueous solution, and dark green PANI powder with a weight ratio of 33% is incorporated into the GO aqueous solution. It is mechanically stirred for 30 min, dried in an oven at 90 °C for 8 h to turn into PANI-rGO hydrogel, and then after freeze-drying treatment and kept in an oven at 70 °C for 24 h to turn into PANI-rGO aerogel. The physical picture of the PANI-rGO aerogel is shown in Figure 1 ,and the preparation schematic diagram is shown in Figure 2 。

[0046] (3) Float a melamine foam with a diameter of 3 cm and a thickness of 1 cm on the water surface of a 60 mL container filled with tap water. Place a cylindrical carbon aerogel with a diameter of 3 cm and a thickness of 1.5 cm on top of the melamine foam. Place the container on an electronic balance connected to a computer for real-time data recording. Use a xenon lamp to simulate sunlight, and irradiate the carbon aerogel material vertically with light intensities of 1, 2, 4, 6, 8, 10 kW / m 2 for 1 h at an ambient temperature of 25 °C, a humidity maintained between 50 - 55%, and a tap water temperature of 25 °C.

[0047] Comparative Example 1

[0048] (1) Under an ice bath, completely dissolve 5 mL of aniline monomer in 1 M HCl aqueous solution (80 mL), and then completely dissolve 15 g of ammonium persulfate (APS) in 1 M HCl aqueous solution (20 mL). Then, mix the two solutions, and the solution gradually turns dark green. The reaction proceeds at 0 °C for 6 h. Centrifuge the solution, and wash the precipitate 3 times with deionized water to obtain dark green PANI powder.

[0049] (2) Add 800 mg of ascorbic acid as a reducing agent to 100 mL of a 5 mg / mL GO aqueous solution, and incorporate dark green PANI powder with a weight ratio of 33% into the GO aqueous solution. Stir mechanically for 30 min, dry in an oven at 90 °C for 8 h to convert to PANI-rGO hydrogel, and then after freeze-drying and maintaining at 70 °C in an oven for 24 h to convert to PANI-rGO aerogel. The physical picture of the PANI-rGO aerogel is shown in Figure 1 , and the preparation schematic diagram is shown in Figure 2 .

[0050] (3) Float a melamine foam with a diameter of 3 cm and a thickness of 1 cm on the water surface of a 60 mL container filled with tap water. Place a cylindrical carbon aerogel with a diameter of 3 cm and a thickness of 1.5 cm on top of the melamine foam. Place the container on an electronic balance connected to a computer for real-time data recording. Use a xenon lamp to simulate sunlight, and irradiate the carbon aerogel material vertically with light intensities of 1, 2, 4, 6, 8, 10 kW / m 2 for 1 h at an ambient temperature of 25 °C, a humidity maintained between 50 - 55%, and a tap water temperature of 25 °C. A cylindrical hollow polystyrene foam with a diameter of 6 cm and a thickness of 1.5 cm is used to make a heat insulation layer and placed around the carbon aerogel.

[0051] Performance Test

[0052] At light intensities of 1, 2, 4, 6, 8, 10 kW / m 2When irradiated under a light source for 1 h, the water evaporation rates of the PANI-rGO aerogel prepared in Example 1 were 1.99, 3.48, 4.68, 6.45, 6.5, and 6.8 kg m -2 h -1 ( Figure 3 ). The experimental data show that the evaporation amount of pure water per unit area and time is very small. The addition of the PANI-rGO aerogel can significantly increase the evaporation amount. As the light intensity irradiated on the material surface gradually increases, the growth trend of the water evaporation rate slows down, and the water evaporation rate is in a "plateau period" between 6 and 10 light intensities.

[0053] When irradiated under a light source with intensities of 1, 2, 4, 6, 8, and 10 kW / m 2 for 1 h, the water evaporation rates of the PANI-rGO aerogel with a side foam insulation layer added in Comparative Example 1 were 2.69, 3.63, 4.68, 5.53, 6.02, and 7.42 kg m -2 h -1 ( Figure 9 ). The experimental data show that the evaporation amount of pure water per unit area and time is very small. The addition of the PANI-rGO aerogel can significantly increase the evaporation amount. As the light intensity irradiated on the material surface gradually increases, the surface maximum temperature and the corresponding evaporation rate continue to increase at high light intensities, reaching nearly 95 °C and 7.42 kg m -2 h -1 .

[0054] In solar water evaporation, the spotlight technique provides a promising method to enhance the incident light intensity, thereby increasing the energy input and significantly promoting water evaporation. To achieve this, a lightweight, thin, and cost-effective Fresnel lens was integrated into the water evaporation experiment as a substitute for the traditional convex lens. The Fresnel lens was placed between the photothermal material and the xenon lamp to ensure that the generated light spot completely covered the evaporation material surface. The surface light intensity could be adjusted by vertically moving the lens, thereby precisely controlling the experimental conditions. To explore the performance of the carbon aerogel material under higher light intensities, in the presence of the Fresnel lens, several different light intensities of 1 sun, 2 sun, 4 sun, 6 sun, 8 sun, and 10 sun were selected for a 1-h water evaporation experiment, and the experiment for each light intensity was repeated 3 times.

Claims

1. A method for improving the photothermal conversion efficiency of a photothermal material under a wide range of light intensities, characterized in that: include: Polyaniline particles are loaded into carbon aerogel, the proportion of polyaniline loading is controlled, and a Fresnel lens is used to broaden the light intensity range to more than 10 suns. A corresponding relationship between the water evaporation rate on the material surface and the temperature change is established, and a foam side insulation layer is added around the photothermal material.

2. The method for improving the photothermal conversion efficiency of photothermal materials according to claim 1, characterized in that: Fresnel lens is used to enhance the intensity of sunlight received by the surface of photothermal material. The correlation between the water evaporation rate on the surface of photothermal material and the change of the evaporation interface temperature of photothermal material is established within the range of sunlight intensity of 1-10sun, and a water evaporation rate-temperature curve is drawn.

3. The method for improving the photothermal conversion efficiency of photothermal materials according to claim 1, characterized in that: The Fresnel lens is placed parallel to the sunlight source and the carbon aerogel. The light is converged by the Fresnel lens, and the intensity of the sunlight irradiated on the surface of the photothermal material is enhanced. The light intensity obtained on the surface of the photothermal material can be changed by adjusting the power of the light source and changing the distance between the Fresnel lens and the surface of the photothermal material.

4. The method for improving the photothermal conversion efficiency of photothermal materials according to claim 2, characterized in that: An infrared thermal imager is used to record the change of the maximum temperature of the evaporation interface of the photothermal material as the intensity of sunlight increases.

5. The method for improving the photothermal conversion efficiency of photothermal materials according to claim 1, characterized in that: In a high light intensity environment of 6-10 suns, polystyrene foam is used as the insulation material around the carbon aerogel.

6. The method for improving the photothermal conversion efficiency of photothermal materials according to claim 1, characterized in that: The carbon aerogel is selected from one or more of graphene aerogel, carbon nanotube aerogel, porous carbon aerogel and activated carbon fiber aerogel.

7. A photothermal material, characterized in that: Used in the method for improving the photothermal conversion efficiency of photothermal materials as described in any one of claims 1 to 6; polyaniline is prepared by the following method: in an ice bath, aniline monomer is dissolved in an aqueous HCl solution to obtain solution A, and then ammonium persulfate is dissolved in an aqueous HCl solution to obtain solution B, and then solution A and solution B are mixed, the solution gradually turns dark green, reacts at 0°C, centrifuges to obtain a precipitate, and washes and grinds to obtain dark green polyaniline powder particles.

8. The photothermal material according to claim 7, characterized in that: The carbon aerogel loaded with polyaniline is prepared by the following method: polyaniline particles are doped into a carbon oxide solution, and the carbon aerogel loaded with polyaniline is obtained after reduction, freeze-drying and heat-baking treatment.

9. The photothermal material according to claim 8, characterized in that: The carbon aerogel of composite polyaniline is prepared by the following method: carbon dioxide solution, ascorbic acid and polyaniline are mixed and stirred, and dried at 90°C to obtain a hydrogel, and the hydrogel is freeze-dried and dried at 70°C to convert into an aerogel, thereby obtaining a polyaniline composite carbon aerogel.

10. A solar thermal collector, characterized in that: The intensity of incident sunlight is enhanced by using a Fresnel lens, and a side foam insulation layer is added around the photothermal material described in any one of claims 7 to 9 to significantly increase the water evaporation rate at a higher light intensity of 6 to 10 sun, thereby obtaining a solar collector floating on the water surface.

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