A flexible solar evaporator with vertical pore structure and preparation method and application thereof

Abstract

This invention provides a flexible solar evaporator with a vertical perforation structure, its preparation method, and its application. The preparation method of the flexible solar evaporator includes constructing a polyurethane / carbon black composite system using polyurethane as a flexible matrix and carbon black as a photothermal conversion material. Ice crystals are directionally grown to form a vertical ice crystal structure through directional freezing. After drying, the ice crystals are removed to obtain a flexible solar evaporator with a vertical through-hole structure. The flexible solar evaporator provided by this invention utilizes the excellent elasticity and mechanical stability of the polyurethane matrix, making it less prone to damage. Combined with carbon black as a photothermal conversion material to construct a composite structure, the polyurethane matrix encapsulates the carbon black during construction, forming a tightly bonded continuous phase. This retains the flexible characteristics of the evaporator while enhancing its structural strength, preventing flaking and damage caused by external impacts or water erosion during use.

Description

Technical Field

[0001] This invention relates to the field of solar-driven interface water evaporation technology, specifically to a flexible solar evaporator with a vertical pore structure, its preparation method, and its application. Background Technology

[0002] With the increasing severity of global water scarcity and the environmental pressure from the consumption of traditional fossil fuels, developing clean, efficient, and low-cost water purification technologies has become a key direction for solving the water crisis. Solar energy, as an inexhaustible and renewable energy source, can achieve efficient evaporation and condensation recovery of various water bodies through solar-driven interfacial water evaporation technology, and has become a research hotspot in the field of water treatment in recent years.

[0003] The core of solar-driven interfacial water evaporation technology lies in the solar evaporator. Its working principle involves constructing a porous solar evaporator using photothermal materials to absorb solar energy and convert it into heat energy. This causes water on the evaporator surface to evaporate rapidly at the interface, and the water vapor is then converted into fresh water through a condensation device. Compared to traditional bulk heating evaporation technology, solar interfacial water evaporation technology has significant advantages such as low heat loss, high evaporation efficiency, and environmental friendliness, showing broad application prospects in the field of low-energy water treatment.

[0004] However, existing solar evaporators still face numerous technical bottlenecks, making it difficult to meet the diverse needs of practical applications. On one hand, the insufficient flexibility of evaporators is a key issue restricting their application expansion. Currently, most solar evaporators are rigid structures, such as carbonized wood and other carbonized plant derivatives, porous ceramics, porous carbon foam, and metal oxide-based evaporators. While these rigid evaporators possess good structural stability and mechanical strength, they are not easily bent or folded, making them unsuitable for flexible applications such as curved surfaces and portable devices. They also hinder large-scale roll-to-roll fabrication and application, significantly limiting their promotion in emergency rescue, field operations, and mobile water treatment. On the other hand, existing flexible evaporator designs (such as loading photothermal materials onto polymer sponges or fabric surfaces) often suffer from insufficient material bonding strength, leading to easy peeling under mechanical stresses such as bending and stretching, thus restricting practical applications. This issue urgently needs to be addressed through material and structural optimization.

[0005] On the other hand, the disordered pore structure of the evaporator also affects the water mass transfer efficiency and evaporation performance. Most existing evaporators have disordered pore structures, which are prone to problems such as excessive capillary resistance and uneven water distribution during water transport, leading to insufficient water supply to the evaporator surface and thus reducing evaporation efficiency. Furthermore, while evaporators with vertical pore structures in existing technologies can improve water mass transfer efficiency, they typically rely on complex fabrication processes such as template methods and photolithography, resulting in high production costs, long fabrication cycles, and the substrates are mostly rigid materials, failing to combine the advantages of both flexibility and vertical pore structures.

[0006] Therefore, developing a solar evaporator with a simple manufacturing process, low cost, good flexibility, and stable vertical hole structure is of great significance for the practical application of solar water treatment technology and is also one of the technical problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0007] To achieve the above objectives, the present invention provides a solar evaporator with good flexibility and a stable vertical hole structure, as well as its preparation method and application, to solve the technical problems existing in the current process of solar evaporators.

[0008] As one of the objectives of this invention, this invention provides a method for preparing a flexible solar evaporator with a vertical pore structure, comprising constructing a polyurethane / carbon black composite system using polyurethane as a flexible matrix and carbon black as a photothermal conversion material, wherein the polyurethane matrix encapsulates the carbon black to form a tightly bonded continuous phase, and ice crystals are directionally grown to form a vertical ice crystal structure by directional freezing, and the ice crystals are removed after drying to obtain a flexible solar evaporator with a vertical through-hole structure.

[0009] As a preferred embodiment, the method for preparing a flexible solar evaporator with a vertical hole structure includes the following steps: S1. Carbon black powder, waterborne polyurethane and dispersant sodium dodecyl sulfate are added to deionized water and stirred until uniform to form a black suspension, which is used as a cryogenic slurry; S2. The frozen slurry is poured into a mold with copper as the base and polycarbonate as the wall, and directional freeze casting is performed at low temperature. During the freezing process, ice crystals grow in a direction perpendicular to the base, and through-type vertical ice crystals are constructed in the composite system of waterborne polyurethane and carbon black. Waterborne polyurethane and carbon black separate from the aqueous phase during the ice crystal condensation process to form a polyurethane / carbon black composite wall layer, thereby obtaining a solar evaporator blank with a vertical structure. S3. The evaporator blank is freeze-dried in a freeze dryer to remove ice crystals and form a vertical through-hole structure; then it is heated and cured to coat the polyurethane matrix with carbon black to form a tightly bonded continuous phase, thus obtaining the flexible solar evaporator with a vertical hole structure.

[0010] In a preferred embodiment, in S1, carbon black powder, aqueous polyurethane, and dispersant sodium dodecyl sulfate form a stable black suspension.

[0011] In a preferred embodiment, the amount of sodium dodecyl sulfate dispersant added is 0.5% to 1% of the total mass of the cryogenic slurry.

[0012] In a preferred embodiment, the amount of carbon black powder and waterborne polyurethane added is 20% of the total mass of the cryogenic slurry, based on the total mass of the carbon black powder and waterborne polyurethane. Specifically, the amount of carbon black powder added is 0.1-10% of the total mass of the cryogenic slurry, and the amount of waterborne polyurethane added is 10%-19.9% ​​of the total mass of the cryogenic slurry.

[0013] In a preferred embodiment, in S2, the temperature of the low-temperature freezing is -50 ℃ to -60 ℃, and the directional freezing casting time is 5 to 10 min.

[0014] In a preferred embodiment, in S3, the freeze-drying temperature is -50 ℃ to -60 ℃, and the freeze-drying time is 48 to 72 h.

[0015] In a preferred embodiment, in S3, the curing temperature is 120~140 ℃ and the curing time is 2~3 h.

[0016] As one of the objectives of this invention, this invention also provides a flexible solar evaporator with a vertical hole structure, which is prepared using the preparation method described above.

[0017] As a preferred embodiment, the flexible solar evaporator has an interior vertical structure formed by vertically arranged polyurethane / carbon black composite wall layers; the vertical structure has vertically permeable channels.

[0018] In a preferred embodiment, the light absorption rate of the flexible solar evaporator is ≥80%.

[0019] As a preferred embodiment, the flexible solar evaporator operates at 1 kW m -2 Under solar irradiation, the evaporation rate of the flexible solar evaporator is 1.2~1.3 kg m³. -2 h -1 The surface temperature is 42~45℃.

[0020] As one of the objectives of this invention, it also provides an application of the flexible solar evaporator described above in seawater desalination, wastewater treatment, and other fields. The flexible solar evaporator provided by this invention, used in seawater desalination and other fields, utilizes the property of solar-driven interface evaporators to remove water and precipitate salt, thus not only obtaining pure water but also valuable mineral resources. Similarly, it can also be used in wastewater treatment and other fields.

[0021] The beneficial effects of the technical solution provided by this invention compared with the prior art are as follows: 1. The flexible solar evaporator provided by this invention selects polyurethane as the flexible matrix to construct a flexible solar evaporator with high structural strength and not easily damaged. It utilizes the excellent elasticity and mechanical stability of the flexible matrix and combines it with carbon black as a photothermal conversion material to construct a composite structure. During the construction process, the polyurethane matrix encapsulates the carbon black to form a tightly bonded continuous phase, which not only retains the flexible characteristics of the evaporator, but also improves its structural strength, avoiding slagging and damage caused by external impacts, water flow erosion, etc. during use.

[0022] 2. The flexible solar evaporator provided by the present invention uses a directional cryogenic casting method to construct a stable vertical pore structure. By utilizing the characteristic of ice crystal directional growth during the freezing process, a through-type vertical channel is constructed in the polyurethane / carbon black composite system to reduce capillary resistance, realize rapid and uniform water transport, and optimize the water mass transfer process.

[0023] 3. This invention addresses the problem that existing vertical hole structure evaporators rely on complex processes such as template methods and photolithography. The cryogenic casting method used in this invention has simple process steps, does not require complex molds and precision equipment, and the polyurethane and carbon black raw materials used are widely available and inexpensive, effectively reducing production costs. This provides support for the practical application of solar-driven interface water evaporation technology in seawater desalination, brackish water desalination, and sewage purification, and enables the simple and low-cost preparation of evaporators. Attached Figure Description

[0024] Figure 1 This is a photograph of the flexible solar evaporator with a vertical hole structure prepared in Example 1 of the present invention.

[0025] Figure 2 This is a scanning electron microscope (SEM) image of the cross-section of the flexible solar evaporator with a vertical hole structure prepared in Example 1 of the present invention.

[0026] Figure 3 This is a photograph of the flexible solar evaporator with a vertical hole structure prepared in Example 2 of the present invention.

[0027] Figure 4This is a scanning electron microscope (SEM) image of the cross-section of the flexible solar evaporator with a vertical hole structure prepared in Example 2 of the present invention.

[0028] Figure 5 This is a photograph of the flexible solar evaporator with a vertical hole structure prepared in Example 3 of the present invention.

[0029] Figure 6 This is a scanning electron microscope (SEM) image of the cross-section of the flexible solar evaporator with a vertical hole structure prepared in Example 3 of the present invention.

[0030] Figure 7 This is a photograph of the flexible solar evaporator with a vertical hole structure prepared in Example 4 of the present invention.

[0031] Figure 8 This is a scanning electron microscope (SEM) image of the cross-section of the flexible solar evaporator with a vertical hole structure prepared in Example 4 of the present invention.

[0032] Figure 9 This is a photograph of the flexible solar evaporator with a vertical hole structure prepared in Example 5 of the present invention.

[0033] Figure 10 This is a scanning electron microscope (SEM) image of the cross-section of the flexible solar evaporator with a vertical hole structure prepared in Example 5 of the present invention.

[0034] Figure 11 The diffuse reflectance absorption spectra of the ultraviolet-visible-near infrared components of Examples 1-5 and Comparative Example 1 of this invention are shown.

[0035] Figure 12 These are the compressive stress-strain diagrams for Embodiments 1-5 of the present invention.

[0036] Figure 13 This is a physical flexible display diagram of the flexible solar evaporator of Embodiment 3 of the present invention.

[0037] Figure 14 The flexible solar evaporators prepared for Examples 1-5 and Comparative Example 1 of this invention are used at a power output of 1 kW m³. -2 A diagram showing the evaporation rate under simulated solar radiation.

[0038] Figure 15 The flexible solar evaporators prepared for Examples 1-5 and Comparative Example 1 of this invention are used at a power output of 1 kW m³. -2 Simulates surface temperature changes during evaporation under solar radiation. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0040] This invention provides a method for preparing a solar evaporator with a vertical hole structure, the specific steps of which include: (1) Add carbon black powder, waterborne polyurethane and dispersant sodium dodecyl sulfate to deionized water and stir to mix evenly to form a black suspension, which is used as a cryogenic slurry; (2) Pour the frozen slurry obtained in step 1 into a mold with copper as the base and polycarbonate as the wall, and perform directional freeze casting at low temperature. During the freezing process, ice crystals grow in a direction perpendicular to the base, and through vertical ice crystals are constructed in the composite system of waterborne polyurethane and carbon black. Waterborne polyurethane and carbon black separate from the aqueous phase during the ice crystal condensation process to form a polyurethane / carbon black composite wall layer, and obtain a solar evaporator blank with a vertical structure. (3) The evaporator blank in step 2 is freeze-dried in a freeze dryer to remove ice crystals and form a vertical through-hole structure; then it is heated and cured to coat the polyurethane matrix with carbon black to form a tightly bonded continuous phase, thus obtaining the flexible solar evaporator with vertical hole structure.

[0041] In some specific embodiments, the amount of sodium dodecyl sulfate dispersant added in step 1 is 0.5% to 1% of the total mass of the cryogenic slurry.

[0042] In some specific embodiments, in step 1, the amount of carbon black powder and waterborne polyurethane added is 20% of the total mass of the cryogenic slurry, based on the total mass of the carbon black powder and waterborne polyurethane. Specifically, the amount of carbon black powder added is 0.1% to 10% of the total mass of the cryogenic slurry, and the amount of waterborne polyurethane added is 10% to 19.9% ​​of the total mass of the cryogenic slurry.

[0043] In some specific embodiments, the cryogenic freezing platform described in step 2 is a freezing plane constructed by operating a compressor, with a temperature range of -50℃ to -60℃ and a directional cryogenic casting time of 5 to 10 minutes.

[0044] In some specific embodiments, the temperature of the freeze-drying process in step 3 is -50 ℃ to -60 ℃, and the freeze-drying time is 48 to 72 h.

[0045] In some specific embodiments, the curing temperature in step 3 is 120~140 ℃, and the curing time is 2~3 h.

[0046] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0047] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0048] Example 1 This embodiment provides a method for preparing a flexible solar evaporator with a vertical hole structure, the specific steps of which include: 1. Carbon black powder, waterborne polyurethane, and sodium dodecyl sulfate are added to deionized water and mixed evenly with magnetic stirring for 2 hours to form a black suspension, which is used as a cryogenic slurry. The mass of carbon black powder added is 0.1% of the total mass of the cryogenic slurry, the mass of waterborne polyurethane added is 19.9% ​​of the total mass of the cryogenic slurry, and the mass of sodium dodecyl sulfate added is 0.5% of the total mass of the cryogenic slurry.

[0049] 2. Take 5 mL of the above-mentioned well-stirred black cryogenic slurry and pour it into a cylindrical mold (50 mm in diameter and 50 mm in height) with copper as the base and polycarbonate as the wall. Wrap the mold wall with polyethylene foam and place it on a low-temperature freezing platform at -50 ℃ for directional cryogenic casting. The freezing time is 5 min. Through the vertical growth of ice crystals and the phase separation process of carbon black and polyurethane, a circular solar evaporator blank with a vertical pore structure is obtained.

[0050] 3. Remove the evaporator preform from the mold and transfer it to a freeze dryer. Freeze-dry the preform to remove ice crystals while preserving the porous structure. The freeze-drying temperature is -50 °C, and the freeze-drying time is 48 h. After the evaporator preform is completely dry, transfer it to an oven for heating and curing. The oven temperature is 140 °C, and the curing time is 3 h, ultimately yielding a flexible solar evaporator with a vertical pore structure.

[0051] See Figure 1 The solar evaporator obtained in this embodiment is a black circular disc.

[0052] See Figure 2The microstructure of the solar evaporator prepared in this embodiment was characterized by scanning electron microscopy (SEM). It can be seen that the internal structure of the solar evaporator constructed in Example 1 consists of vertically arranged polyurethane / carbon black composite wall layers forming a vertical pore structure. This vertical pore structure can create a light-trapping effect, improving the evaporator's absorption efficiency of sunlight and thus enhancing its photothermal conversion performance. Simultaneously, the vertically permeable channels reduce the upward transport resistance of water during evaporation, allowing water to quickly reach the evaporation surface and improving evaporation efficiency. Furthermore, the vertical pore structure can accelerate the downward migration of salt ions from the upper surface, reducing salt accumulation on the evaporator surface.

[0053] See Figure 11 The image shows the diffuse reflectance absorption spectrum of the evaporator constructed in this embodiment, which is the ultraviolet-visible-near infrared spectrum. The light absorption rate of the solar evaporator constructed in Example 1 is 80.01%, which shows that the addition of a small amount of carbon black (0.1%) can improve the absorption performance of the evaporator for sunlight.

[0054] See Figure 12 The figure shows the compressive stress-strain diagram of the evaporator constructed in this embodiment. The elastic modulus of the solar evaporator constructed through the steps of Example 1 is 29.52 MPa, which is low and exhibits the characteristics of a flexible material.

[0055] See Figure 14 The solar evaporator constructed according to the steps of Example 1 was placed in a 1 kW m -2 Photothermal evaporation tests were conducted under simulated solar irradiation. The solar evaporator was placed on polyethylene foam to separate it from the water to be purified below, reducing heat transfer loss. Simultaneously, a layer of non-woven fabric was placed between the evaporator and the polyethylene foam to utilize capillary action to transfer moisture from the lower layer to the upper layer of the evaporator for continuous evaporation. Test results showed that the solar evaporator constructed according to the steps of Example 1 achieved an evaporation rate of 1.16 kg m³ under these conditions. -2 h -1 It has a surface temperature of 42.0 ℃ and good water evaporation performance.

[0056] See Figure 15 The flexible solar evaporator prepared in this embodiment operates at 1 kW m -2 The surface temperature change during evaporation under simulated solar irradiation was shown in the figure. As can be seen from the figure, after about 8 minutes of irradiation, the surface temperature of the evaporator rapidly rises to above 42°C, and then stabilizes at 42°C, demonstrating excellent water evaporation performance.

[0057] Example 2 This embodiment provides a method for preparing a flexible solar evaporator with a vertical hole structure, the specific steps of which include: 1. Carbon black powder, waterborne polyurethane, and sodium dodecyl sulfate are added to deionized water and mixed evenly with magnetic stirring for 2 hours to form a black suspension, which is used as a cryogenic slurry. The mass of carbon black powder added is 0.5% of the total mass of the cryogenic slurry, the mass of waterborne polyurethane added is 19.5% of the total mass of the cryogenic slurry, and the mass of sodium dodecyl sulfate added is 0.5% of the total mass of the cryogenic slurry.

[0058] 2. Take 5 mL of the above-mentioned well-stirred black cryogenic slurry and pour it into a cylindrical mold (50 mm in diameter and 50 mm in height) with copper as the base and polycarbonate as the wall. Wrap the mold wall with polyethylene foam and place it on a low-temperature freezing platform at -50 ℃ for directional cryogenic casting. The freezing time is 10 min. Through the vertical growth of ice crystals and the phase separation process of carbon black and polyurethane, a circular solar evaporator blank with a vertical pore structure is obtained.

[0059] 3. Remove the evaporator preform from the mold and transfer it to a freeze dryer. Freeze-dry the preform to remove ice crystals while preserving the porous structure. The freeze-drying temperature is -60 °C, and the freeze-drying time is 72 h. After the evaporator preform is completely dry, transfer it to an oven for heat curing at 140 °C for 2 h, ultimately obtaining a flexible solar evaporator with a vertical pore structure.

[0060] See Figure 3 The solar evaporator obtained in this embodiment is a black disc, which is darker than that in Example 1.

[0061] See Figure 4 The microstructure of the solar evaporator prepared in this embodiment was characterized by scanning electron microscopy (SEM). It can be seen that the internal structure of the solar evaporator constructed in this embodiment is similar to that in Example 1, and is a vertical pore structure formed by vertically arranged polyurethane / carbon black composite wall layers.

[0062] See Figure 11 The image shows the diffuse reflectance absorption spectrum of the evaporator constructed in this embodiment (UV-Vis-NIR). The light absorptivity of the solar evaporator constructed in Example 2 is 84.67%, which is 4.66% higher than that in Example 1. This result indicates that increasing the amount of carbon black can further improve the evaporator's absorption performance of sunlight.

[0063] See Figure 12 The figure shows the compressive stress-strain diagram of the evaporator constructed in this embodiment. The elastic modulus of the solar evaporator constructed through the steps of Example 2 is 30.44 MPa, which is low and exhibits the characteristics of a flexible material.

[0064] See Figure 14 The solar evaporator constructed according to the steps of Example 2 was placed in a 1 kW m -2 Photothermal evaporation tests were conducted under simulated solar irradiation. The results showed that the evaporation rate of the solar evaporator in Example 2 under these conditions was 1.18 kg m³. -2 h -1 It has good water evaporation performance.

[0065] See Figure 15 The flexible solar evaporator prepared in this embodiment operates at 1 kW m -2 The surface temperature change during evaporation under simulated solar irradiation was shown in the figure. As can be seen from the figure, after about 8 minutes of irradiation, the surface temperature of the evaporator rapidly increased to above 42℃, and then stabilized at 42.9℃, demonstrating excellent water evaporation performance.

[0066] Example 3 This embodiment provides a method for preparing a flexible solar evaporator with a vertical hole structure, the specific steps of which include: 1. Carbon black powder, waterborne polyurethane and sodium dodecyl sulfate are added to deionized water and mixed evenly with magnetic stirring for 2 hours to form a black suspension, which is used as a cryogenic slurry. The mass of carbon black powder added is 1% of the total mass of the cryogenic slurry, the mass of waterborne polyurethane added is 19% of the total mass of the cryogenic slurry, and the mass of sodium dodecyl sulfate added is 0.5% of the total mass of the cryogenic slurry.

[0067] 2. Take 5 mL of the above-mentioned well-stirred black cryogenic slurry and pour it into a cylindrical mold (50 mm in diameter and 50 mm in height) with copper as the base and polycarbonate as the wall. Wrap the mold wall with polyethylene foam and place it on a low-temperature freezing platform at -60 ℃ for directional cryogenic casting. The freezing time is 5 min. Through the vertical growth of ice crystals and the phase separation process of carbon black and polyurethane, a circular solar evaporator blank with a vertical pore structure is obtained.

[0068] 3. Remove the evaporator preform from the mold and transfer it to a freeze dryer. Freeze-dry the preform to remove ice crystals while preserving the porous structure. The freeze-drying temperature is -50 °C, and the freeze-drying time is 48 h. After the evaporator preform is completely dry, transfer it to an oven for heat curing. The oven temperature is 120 °C, and the curing time is 3 h, ultimately yielding a flexible solar evaporator with a vertical pore structure.

[0069] See Figure 5 The solar evaporator obtained in this embodiment is a black circular disc, and the black color is further deepened compared with the above embodiment.

[0070] See Figure 6 The microstructure of the solar evaporator prepared in this embodiment was characterized by scanning electron microscopy (SEM). It can be seen that the internal structure of the solar evaporator constructed in this embodiment is similar to that of the above embodiments, and is a vertical pore structure formed by vertically arranged polyurethane / carbon black composite wall layers.

[0071] See Figure 11 The image shows the diffuse reflectance absorption spectrum of the evaporator constructed in this embodiment (UV-Vis-NIR). The light absorption rate of the solar evaporator constructed in Example 3 is 91.94%. This result indicates that when the carbon black content is 1%, the evaporator achieves a high level of solar light absorption performance.

[0072] See Figure 12 The figure shows the compressive stress-strain diagram of the evaporator constructed in this embodiment. The elastic modulus of the solar evaporator constructed through the steps of Example 3 is 29.30 MPa, which is low and exhibits the characteristics of a flexible material.

[0073] See Figure 13 The figure shows a physical image of the flexible solar evaporator prepared in this embodiment. As can be seen from the figure, the flexible solar evaporator prepared using the technical solution of this invention exhibits the characteristics of a flexible material.

[0074] See Figure 14 The solar evaporator constructed according to the steps of Example 3 was placed in a 1 kW m -2 Photothermal evaporation tests were conducted under simulated solar irradiation. The results showed that the solar evaporator in Example 3 had an evaporation rate of 1.22 kg m³ under these conditions. -2 h -1 It has good water evaporation performance.

[0075] See Figure 15 The flexible solar evaporator prepared in this embodiment operates at 1 kW m -2 The surface temperature change during evaporation under simulated solar irradiation was shown in the figure. As can be seen from the figure, after about 8 minutes of irradiation, the surface temperature of the evaporator rapidly increased to above 42℃, and then stabilized at 43.7℃, demonstrating excellent water evaporation performance.

[0076] Example 4 This embodiment provides a method for preparing a flexible solar evaporator with a vertical hole structure, the specific steps of which include: 1. Carbon black powder, waterborne polyurethane, and sodium dodecyl sulfate are added to deionized water and mixed evenly with magnetic stirring for 2 hours to form a black suspension, which is used as a cryogenic slurry. The mass of carbon black powder added is 5% of the total mass of the cryogenic slurry, the mass of waterborne polyurethane added is 15% of the total mass of the cryogenic slurry, and the mass of sodium dodecyl sulfate added is 1% of the total mass of the cryogenic slurry.

[0077] 2. Take 5 mL of the above-mentioned well-stirred black cryogenic slurry and pour it into a cylindrical mold (50 mm in diameter and 50 mm in height) with copper as the base and polycarbonate as the wall. Wrap the mold wall with polyethylene foam and place it on a low-temperature freezing platform at -60 ℃ for directional cryogenic casting. The freezing time is 10 min. Through the vertical growth of ice crystals and the phase separation process of carbon black and polyurethane, a circular solar evaporator blank with a vertical pore structure is obtained.

[0078] 3. Remove the evaporator preform from the mold and transfer it to a freeze dryer. Freeze-dry the preform to remove ice crystals while preserving the porous structure. The freeze-drying temperature is -60 ℃, and the freeze-drying time is 72 h. After the evaporator preform is completely dry, transfer it to an oven for heating and curing. The oven temperature is 120 ℃, and the curing time is 3 h, ultimately yielding a flexible solar evaporator with a vertical pore structure.

[0079] See Figure 7 The solar evaporator obtained in this embodiment is a black circular disc, and the black color is further deepened compared with the above embodiment.

[0080] See Figure 8 The microstructure of the solar evaporator prepared in this embodiment was characterized by scanning electron microscopy (SEM). It can be seen that the internal structure of the solar evaporator constructed in this embodiment is similar to that of the above embodiments, and is a vertical pore structure formed by vertically arranged polyurethane / carbon black composite wall layers.

[0081] See Figure 11 The image shows the diffuse reflectance absorption spectrum of the evaporator constructed in this embodiment (UV-Vis-NIR). The light absorption rate of the solar evaporator constructed in Example 4 is 94.30%. This result indicates that the absorption performance of the evaporator for sunlight can be further improved by increasing the amount of carbon black used.

[0082] See Figure 12 The figure shows the compressive stress-strain diagram of the evaporator constructed in this embodiment. The elastic modulus of the solar evaporator constructed through the steps of Example 4 is 28.87 MPa, which is low and exhibits the characteristics of a flexible material.

[0083] See Figure 14The solar evaporator constructed according to the steps of Example 4 was placed in a 1 kW m -2 Photothermal evaporation tests were conducted under simulated solar irradiation. The results showed that the solar evaporator in Example 4 had an evaporation rate of 1.23 kg m³ under these conditions. -2 h -1 It has good water evaporation performance.

[0084] See Figure 15 The flexible solar evaporator prepared in this embodiment operates at 1 kW m -2 The surface temperature change during evaporation under simulated solar irradiation was shown in the figure. As can be seen from the figure, after about 8 minutes of irradiation, the surface temperature of the evaporator rapidly increased to above 42℃, and then stabilized at 44.3℃, demonstrating excellent water evaporation performance.

[0085] Example 5 This embodiment provides a method for preparing a flexible solar evaporator with a vertical hole structure, the specific steps of which include: 1. Carbon black powder, waterborne polyurethane, and sodium dodecyl sulfate are added to deionized water and mixed evenly with magnetic stirring for 2 hours to form a black suspension, which is used as a cryogenic slurry. The mass of carbon black powder added is 10% of the total mass of the cryogenic slurry, the mass of waterborne polyurethane added is 10% of the total mass of the cryogenic slurry, and the mass of sodium dodecyl sulfate added is 1% of the total mass of the cryogenic slurry.

[0086] 2. Take 5 mL of the above-mentioned well-stirred black cryogenic slurry and pour it into a cylindrical mold (50 mm in diameter and 50 mm in height) with copper as the base and polycarbonate as the wall. Wrap the mold wall with polyethylene foam and place it on a low-temperature freezing platform at -60 ℃ for directional cryogenic casting. The freezing time is 10 min. Through the vertical growth of ice crystals and the phase separation process of carbon black and polyurethane, a circular solar evaporator blank with a vertical pore structure is obtained.

[0087] 3. Remove the evaporator preform from the mold and transfer it to a freeze dryer. Remove ice crystals by freeze-drying while preserving the porous structure. The freeze-drying temperature is -60 ℃ and the freeze-drying time is 48 h. After the evaporator preform is completely dry, transfer it to an oven for heating and curing. The oven temperature is 120 ℃ and the curing time is 2 h, finally obtaining a flexible solar evaporator with a vertical pore structure.

[0088] See Figure 9 The solar evaporator obtained in this embodiment is a black circular disc, and the black color is further deepened compared with the above embodiment.

[0089] See Figure 10The microstructure of the solar evaporator prepared in this embodiment was characterized by scanning electron microscopy (SEM). It can be seen that the internal structure of the solar evaporator constructed in this embodiment is similar to that of the above embodiments, and is a vertical pore structure formed by vertically arranged polyurethane / carbon black composite wall layers.

[0090] See Figure 11 The image shows the diffuse reflectance absorption spectrum of the evaporator constructed in this embodiment (UV-Vis-NIR). The light absorption rate of the solar evaporator constructed in Example 5 is 96.26%. This result indicates that when the carbon black content reaches 10%, the evaporator can achieve highly efficient absorption of most sunlight.

[0091] See Figure 12 The diagram shows the compressive stress-strain of the evaporator constructed in this embodiment. The elastic modulus of the solar evaporator constructed through the steps of Example 5 is 27.16 MPa, which is relatively low and exhibits the characteristics of a flexible material.

[0092] See Figure 14 The solar evaporator constructed according to the steps of Example 5 was placed in a 1 kW m -2 Photothermal evaporation tests were conducted under simulated solar irradiation. The results showed that the solar evaporator in Example 5 had an evaporation rate of 1.26 kg m³ under these conditions. -2 h -1 It has good water evaporation performance.

[0093] See Figure 15 The flexible solar evaporator prepared in this embodiment operates at 1 kW m -2 The surface temperature change during evaporation under simulated solar irradiation was shown in the figure. As can be seen from the figure, after about 8 minutes of irradiation, the surface temperature of the evaporator rapidly increased to above 42℃, and then stabilized at 44.7℃, demonstrating excellent water evaporation performance.

[0094] Comparative Example 1 This comparative example provides a method for preparing a carbon black-free solar evaporator, the specific steps of which include: 1. Add waterborne polyurethane and sodium dodecyl sulfate to deionized water, without adding carbon black powder. Mix evenly with magnetic stirring for 2 hours to form a semi-transparent solution, which is used as the cryogenic slurry. The mass of waterborne polyurethane added is 20% of the total mass of the cryogenic slurry, and the mass of sodium dodecyl sulfate added is 0.5% of the total mass of the cryogenic slurry.

[0095] 2. Take 5 mL of the above-mentioned uniformly stirred translucent cryogenic slurry and pour it into a cylindrical mold (50 mm in diameter and 50 mm in height) with copper as the base and polycarbonate as the wall. Wrap the mold wall with polyethylene foam and place it on a low-temperature freezing platform at -50 ℃ for directional cryogenic casting. The freezing time is 5 min to obtain a white, round solar evaporator blank.

[0096] 3. Remove the evaporator blank from the mold and transfer it to a freeze dryer. Remove ice crystals by freeze-drying while preserving the porous structure. The freeze-drying temperature is -50 ℃ and the freeze-drying time is 72 h. After the evaporator blank is completely dry, transfer it to an oven for heating and curing. The oven temperature is 140 ℃ and the curing time is 3 h, finally obtaining a white solar evaporator.

[0097] See Figure 11 The figure shows the diffuse reflectance absorption spectrum of the evaporator constructed in this comparative example (UV-Vis-NIR). The light absorption rate of the solar evaporator constructed via Comparative Example 1 is 20.74%. This result indicates that the evaporator cannot achieve efficient absorption of sunlight without the use of carbon black.

[0098] See Figure 14 The solar evaporator constructed according to the steps in this comparative example is placed in a 1 kW m² evaporator. -2 Photothermal evaporation tests were conducted under simulated solar irradiation. The results showed that the evaporation rate of the solar evaporator in Comparative Example 1 under these conditions was 0.37 kg m³. -2 h -1 However, since this comparative example does not have good photothermal conversion performance, its water evaporation performance is significantly worse than that of the example.

[0099] See Figure 15 The flexible solar evaporator prepared for this comparative example operates at 1 kW m³. -2 The surface temperature change during evaporation under simulated solar irradiation was shown in the figure. As can be seen from the figure, after about 10 minutes of irradiation, the surface temperature of the evaporator rose to 29°C and then stabilized at 29.1°C. Obviously, the water evaporation performance is far inferior to that of the example.

[0100] Comparative Example 2 This comparative example provides a method for preparing a solar evaporator containing a relatively high amount of carbon black, the specific steps of which include: 1. Carbon black powder, waterborne polyurethane, and sodium dodecyl sulfate are added to deionized water and mixed evenly with magnetic stirring for 2 hours to form a black suspension, which is used as a cryogenic slurry. The mass of carbon black powder added is 15% of the total mass of the cryogenic slurry, the mass of waterborne polyurethane added is 5% of the total mass of the cryogenic slurry, and the mass of sodium dodecyl sulfate added is 1% of the total mass of the cryogenic slurry.

[0101] 2. Take 5 mL of the above-mentioned well-stirred black cryogenic slurry and pour it into a cylindrical mold (50 mm in diameter and 50 mm in height) with copper as the base and polycarbonate as the wall. Wrap the mold wall with polyethylene foam and place it on a low-temperature freezing platform at -60 ℃ for directional cryogenic casting. The freezing time is 10 min. Through the vertical growth of ice crystals and the phase separation process of carbon black and polyurethane, a circular solar evaporator blank with a vertical pore structure is obtained.

[0102] 3. Remove the evaporator blank from the mold and transfer it to a freeze dryer. Remove ice crystals by freeze-drying while preserving the porous structure. The freeze-drying temperature is -60 ℃ and the freeze-drying time is 48 h. After the evaporator blank is completely dry, transfer it to an oven for heating and curing. The oven temperature is 120 ℃ and the curing time is 2 h, finally obtaining the solar evaporator.

[0103] The solar evaporator constructed in this comparative example had a high carbon black powder content, and the water-based polyurethane matrix used as a binder could not effectively fix the carbon black powder. As a result, the solar evaporator constructed in this comparative example experienced slagging and cracking during use.

[0104] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible solar evaporator with a vertical pore structure, comprising using polyurethane as a flexible matrix and carbon black as a photothermal conversion material to construct a polyurethane / carbon black composite system, wherein the polyurethane matrix encapsulates the carbon black to form a tightly bonded continuous phase, and ice crystals are directionally grown to form a vertical ice crystal structure by directional freezing, and the ice crystals are removed after drying to obtain a flexible solar evaporator with a vertical through-hole structure.

2. The preparation method according to claim 1, characterized in that, The specific steps include: S1. Carbon black powder, waterborne polyurethane and dispersant sodium dodecyl sulfate are added to deionized water and stirred until uniform to form a black suspension, which is used as a cryogenic slurry; S2. The frozen slurry is poured into a mold with copper as the base and polycarbonate as the wall, and directional freeze casting is performed at low temperature. During the freezing process, ice crystals grow in a direction perpendicular to the base, and through-type vertical ice crystals are constructed in the composite system of waterborne polyurethane and carbon black. Waterborne polyurethane and carbon black separate from the aqueous phase during the ice crystal condensation process to form a polyurethane / carbon black composite wall layer, thereby obtaining a solar evaporator blank with a vertical structure. S3. The evaporator blank is freeze-dried in a freeze dryer to remove ice crystals and form a vertical through-hole structure; then it is heated and cured to coat the polyurethane matrix with carbon black to form a tightly bonded continuous phase, thus obtaining the flexible solar evaporator with a vertical hole structure.

3. The preparation method according to claim 2, characterized in that, In S1, the amount of sodium dodecyl sulfate dispersant added is 0.5 to 1% of the total mass of the cryogenic slurry.

4. The preparation method according to claim 2, characterized in that, In S1, the amount of carbon black powder and waterborne polyurethane added is 20% of the total mass of the cryogenic slurry, based on the total mass of carbon black powder and waterborne polyurethane. Specifically, the amount of carbon black powder added is 0.1-10% of the total mass of the cryogenic slurry, and the amount of waterborne polyurethane added is 10-19.9% ​​of the total mass of the cryogenic slurry.

5. The preparation method according to claim 2, characterized in that, In S2, the temperature of the low-temperature freezing is -50 ~ -60 ℃, and the directional freezing casting time is 5 ~ 10 min.

6. The preparation method according to claim 2, characterized in that, In S3, the freeze-drying temperature is -50 ℃ to -60 ℃, and the freeze-drying time is 48 to 72 h; And / or, in S3, the curing temperature is 120~140 ℃, and the curing time is 2~3 h.

7. A flexible solar evaporator with a vertical hole structure, prepared by the preparation method described in any one of claims 1-6.

8. The flexible solar evaporator according to claim 7, characterized in that, include: The flexible solar evaporator has an internal vertical structure formed by vertically arranged polyurethane / carbon black composite wall layers; the vertical structure has vertically permeable channels.

9. The flexible solar evaporator according to claim 7, characterized in that, The light absorption rate of the flexible solar evaporator is ≥80%; at 1 kW m -2 Under solar irradiation, the evaporation rate of the flexible solar evaporator is 1.2~1.3 kg / m³. -2 h -1 The surface temperature is 42~45℃.

10. A flexible solar evaporator prepared by the preparation method according to any one of claims 1-6, or the application of the flexible solar evaporator according to any one of claims 7-9 in seawater desalination and wastewater treatment.

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