Solar interface evaporator inducing directional crystallization and preparation method and application thereof

Abstract

The application belongs to the technical field of seawater desalination, and discloses a solar interfacial evaporator for inducing directional crystallization and a preparation method and application thereof. The preparation method comprises the following steps: mixing salt particles with different particle sizes and a solvent to form a salt slurry; using a multilayer annular mold, filling each level of the salt slurry from large to small in particle size and from inside to outside, and compacting and drying to obtain a radial gradient salt template; preparing a prepolymer by mixing a siloxane polymer, a light-heat conversion filler and a curing agent, pouring the prepolymer into the salt template, and removing the salt template through vacuum degassing, curing and dissolution to obtain a light-heat conversion material. The radial gradient pores with a large center and a small edge are formed in the material, the radial capillary driving force and the Marangoni effect are used in cooperation to guide the directional transport of salt to the edge and crystallize and precipitate, and the core evaporation surface is ensured to be clean, so that the unification of high evaporation rate and long-term salt resistance is realized in the evaporation process of high-salinity water.

Description

Technical Field

[0001] This invention relates to the field of solar-powered seawater desalination, specifically to a solar-powered interfacial evaporator for induced directional crystallization, its preparation method, and its application. Background Technology

[0002] Seawater desalination technology is an effective way to obtain freshwater resources and alleviate freshwater shortages. Traditional seawater desalination methods mainly include multi-stage flash distillation, multi-effect distillation, reverse osmosis, and electrodialysis. However, these methods usually rely heavily on the continuous input of fossil fuels and generally have limitations such as high energy consumption, complex equipment, and high operating costs. In addition, they inevitably cause environmental pollution problems during operation.

[0003] In recent years, solar-driven interfacial evaporation technology has attracted widespread attention as a green and low-carbon new method for freshwater acquisition. This technology utilizes photothermal conversion materials to capture solar energy and convert it into heat energy, achieving localized heat concentration to drive the vaporization of interfacial water. However, existing porous photothermal conversion materials are mostly integrally molded, making it difficult to precisely control the internal pore size and distribution. On the one hand, the uniform or uncontrollable pore structure makes it difficult to achieve a balance between the capillary suction force of water and fluid resistance, resulting in the inability of interfacial water transport and replenishment to effectively match the evaporation rate. On the other hand, when treating high-salinity water, as the evaporation process continues, salt ions tend to rapidly accumulate on the evaporation surface and precipitate solid salt crystals. The salt crystals covering the surface not only hinder the incidence of sunlight and reduce photothermal conversion efficiency, but also block the internal water transport and vapor diffusion channels, leading to a severe decline in evaporation performance and greatly limiting the long-term stable application of interfacial evaporators in practical high-salinity water desalination projects. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a solar interface evaporator with induced directional crystallization, its preparation method, and its application.

[0005] The technical solution of this invention is as follows: A method for preparing a solar interfacial evaporator with induced directional crystallization includes the following steps: S1. Constructing a radial gradient salt template: Sodium citrate particles are ground and sieved to obtain salt particles with different particle sizes; the salt particles of different particle sizes are mixed with solvents to form salt slurries; a multi-layer concentric annular mold is provided, and the salt slurries of different particle sizes are filled into the annular cavities of the mold in descending order of particle size, and compacted. After heating and drying to remove moisture and the mold, a radial gradient salt template is obtained. S2. Preparation of photothermal prepolymer: Mix siloxane polymer and photothermal conversion filler to obtain a mixture, add curing agent and stir to obtain photothermal prepolymer; S3. Prepolymer curing: The photothermal prepolymer prepared in step S2 is cast onto the radial gradient salt template prepared in step S1, and placed in a vacuum environment for degassing treatment, so that the photothermal prepolymer fills the pores inside the radial gradient salt template, and then is heated and cured. S4. Detemplating treatment: Immerse the solidified product in deionized water to dissolve and remove the internal salt particles. After drying, the solar interface evaporator with induced directional crystallization is obtained.

[0006] Further, in step S1, the salt particles with different particle sizes include salt particles with a first particle size, salt particles with a second particle size, and salt particles with a third particle size; the first particle size salt particles have a particle size range of 30-80 μm, the second particle size salt particles have a particle size range of 100-200 μm, and the third particle size salt particles have a particle size range of 250-400 μm.

[0007] Further, in step S1, the solvent is deionized water, and the mass ratio of the salt particles to the deionized water is (15-25):1; the heating and drying temperature is 50-80℃, and the time is 0.5-3 h.

[0008] Further, in step S2, the siloxane polymer is polydimethylsiloxane, and the photothermal conversion filler is nano-carbon powder; the mass ratio of the siloxane polymer to the photothermal conversion filler is (8-15):1; and the mass ratio of the mixture to the curing agent is (15-25):1.

[0009] Further, in step S3, the degassing treatment time is 1-3 h; the heating and curing temperature is 50-80℃, and the curing time is 1-3 h; in step S4, the dissolution process is carried out under ultrasonic conditions, the temperature of the deionized water is 40-80℃, and the ultrasonic treatment time is 2-6 h.

[0010] Furthermore, the preparation method also includes: S5, surface hydrophobic modification treatment: spraying a hydrophobic modification liquid onto the top evaporation surface of the solar interface evaporator obtained in step S4 to form a hydrophobic coating.

[0011] A solar interface evaporator with induced directional crystallization is prepared by the aforementioned preparation method.

[0012] Furthermore, the interior of the photothermal conversion material has a radial gradient pore structure in which the pore size gradually decreases from the center to the edge.

[0013] The solar interface evaporator is used in solar interface evaporation, seawater desalination, or brine separation systems.

[0014] Compared with the prior art, the present invention has at least the following advantages: 1. This invention relates to a solar interface evaporator with induced directional crystallization and its preparation method. By combining a multi-layered annular mold and pore-forming agents of different particle sizes, a structure with a continuously decreasing pore size from the center to the edge is achieved. The resulting material can rapidly raise its surface temperature to approximately 80°C under one solar-irradiated, waterless condition, exhibiting excellent photothermal conversion performance. Simultaneously, the large pores in the central region of this structure reduce the resistance to liquid flow, while the dense small pores in the edge region provide strong capillary suction. This radial gradient pore size forms a radial capillary driving force from the center to the edge within the material, effectively guiding the radial directional transport of water within the material, overcoming the physical bottleneck of water supply mismatch in traditional uniform porous materials.

[0015] 2. This invention also relates to the application of a solar interfacial evaporator with induced directional crystallization in solar interfacial evaporation, seawater desalination, or brine separation systems. When treating high-salinity water, rapid evaporation at the edges leads to a localized increase in salt concentration, creating a salt concentration gradient from the edge to the center. This gradient alters the interfacial tension and induces Marangoni convection, where fluid shear force and radial capillary action work synergistically to drive salt ions to migrate directionally towards the edge region and preferentially precipitate. Experiments show that after continuous evaporation in a 10 wt% NaCl solution for 240 minutes, surface salt crystallization of the material of this invention is concentrated only in the edge region, with a surface crystallization rate of only 35.20%, while the core main evaporation surface remains clean throughout; its evaporation rate remains stably maintained at 1.25 kg / m³ throughout the entire process. 2 The cumulative evaporation rate is approximately 5.38 kg / m³ over 4 hours. 2 This solves the problem of photothermal performance degradation caused by surface salt deposition at its root, and achieves a dynamic balance between high evaporation rate and long-term salt resistance stability. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0017] Figure 1The flowchart for the preparation of the radial gradient pore size porous photothermal conversion material in Example 1 is shown below (Saltparticles; DI water; PDMS & CNPs; Salt-water mixing; Water removal; Vacuum degassing; Curing & Salt dissolution; Grain sieving; Salt slurry; Salt template; Infiltration molding; PDMS CNPs sponge).

[0018] Figure 2 The diagram shows the solar interface evaporation test system of Example 2 (Xenon lamp: xenon lamp light source; AM 1.5 G filter: AM 1.5 G filter; IR camera: infrared thermal imager; Solar evaporator: solar interface evaporator; Digital balance: electronic balance; Polystyrene floater: polystyrene foam float; Non-woven fabric: non-woven fabric).

[0019] Figure 3 This is a schematic diagram of the radial gradient salt template prepared using a multi-ring mold in Example 1 (Ring-shaped molds: ring molds; Large: large size; Middle: medium size; Small: small size).

[0020] Figure 4 The surface infrared temperature distribution of porous photothermal conversion materials with different pore sizes in Example 2 is shown in the figure. (Small pore structure; Large pore structure)

[0021] Figure 5 The graph shows the surface temperature of the porous photothermal conversion materials with different pore sizes in Example 2 as a function of time (Temperature: temperature; Time: time).

[0022] Figure 6The images show the microstructure and pore size distribution of the porous photothermal conversion material with a radial gradient structure in Example 3. A is a scanning electron microscope image of the microstructure in the longitudinal section; B is a pore size distribution diagram obtained by mercury intrusion porosimetry (Radial direction; Pore size proportion; Pore diameter; μm).

[0023] Figure 7 This is a diagram showing the surface salt crystal distribution and crystallization area percentage of the evaporator with different pore sizes in Example 4. A is a salt crystal distribution diagram; B is a crystallization area percentage curve (L: uniform macropores; S: uniform micropores; RG: radial gradient pores; Percentage of salt crystal: percentage of salt crystal area).

[0024] Figure 8 This is a schematic diagram of water transport inside the porous photothermal conversion material with radial gradient pore structure in Example 4.

[0025] Figure 9 The graph shows the evaporation performance of porous photothermal conversion materials with different pore sizes in Example 4 under a solar irradiation condition. A is a graph showing the change in evaporation rate over time; B is a graph showing the evaporation rate per hour (mass loss: mass loss, i.e., evaporation rate; h: hour).

[0026] Figure 10 The diagram and physical image show the evaporation system with a reflective device introduced in Example 5. A is a schematic diagram of the evaporation system with a reflective device introduced; B is a physical image (Sunlight: sunlight; Reflector: reflective device; Bulk: water body).

[0027] Figure 11 Evaporation performance and infrared temperature distribution of the interface evaporator with radial gradient structure in Example 5 after introducing a reflective device.

[0028] Figure 12 The diagram shows the contact angle of the photothermal conversion material with the radial gradient structure in Example 6. A is the contact angle diagram at the bottom of the evaporator; B is the contact angle diagram of the modified region at the top of the evaporator.

[0029] Figure 13 The image shows the evaporation performance and infrared temperature distribution of the radial gradient structure evaporator with a reflective device and a hydrophobic top surface, as described in Example 6.

[0030] Figure 14The diagram shows the evaporation performance of the radial gradient structure evaporator with a reflective device and hydrophobic top surface modification in Example 6 under different light intensities. A is the evaporation curve under different light intensities; B is the evaporation rate diagram (sun: solar light intensity; Evaporation rate: evaporation rate; Light intensity: light intensity).

[0031] Figure 15 The diagram and physical image show the solar interface evaporation-freshwater collection device of Example 7. A is a schematic diagram of the solar interface evaporation-freshwater collection device; B is a physical image (Inlet: inlet; Outlet: outlet; Brine: brine; Fresh water: freshwater).

[0032] Figure 16 The diagram shows the droplet distribution on the acrylic sheet surface before and after hydrophilic treatment in Example 7. A represents the area before hydrophilic treatment; B represents the area after hydrophilic treatment.

[0033] Figure 17 The graphs show the long-term evaporation performance and salt crystallization distribution of the photothermal conversion material with a radial gradient structure in Example 7 under different light intensities. A is the evaporation curve; B is the hourly evaporation rate; and C is the salt crystallization and temperature distribution.

[0034] Figure 18 The graph shows the freshwater collection performance of the photothermal conversion material with a radial gradient structure under different light intensities in Example 7. A is the evaporation rate curve; B is the freshwater collection rate; C is the evaporation or collection rate per unit time; D is the collection efficiency (Collection mass: freshwater collection mass; Collection rate: collection rate; Collection efficiency: collection efficiency).

[0035] Figure 19 This is a diagram showing the salt crystallization of the photothermal conversion material with a radial gradient pore structure in Example 7 after running for 8 hours in a collection device under different light intensities. Detailed Implementation

[0036] The present invention will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above application content.

[0037] This invention provides a general and / or specific description of the materials and experimental methods used in the experiments. Unless otherwise specified, all experimental or testing methods are conventional methods; all reagents or instruments used, unless otherwise specified, are commercially available conventional products prepared or used using conventional methods.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art.

[0039] The materials and instruments involved in this invention are shown in Tables 1 and 2.

[0040] Table 1. Models, specifications, and supplier information of experimental materials and chemical reagents.

[0041] Table 2 Specifications and Manufacturers of Experimental Instruments

[0042] The experimental method involved in this invention is shown below.

[0043] Surface microstructure: A scanning electron microscope (SU8020, Hitachi, Japan) uses a high-energy electron beam to scan the surface of a test sample. By detecting the signals generated by the interaction between the test sample and secondary electrons, the microstructure of the test sample surface can be analyzed. In addition, the interaction between the high-energy electron beam and the test sample also produces back-reflected electrons, X-rays, and other signals, which can then be used to analyze the surface composition of the test sample.

[0044] Pore ​​size distribution within materials: The Auto Pore IV9600 (McMed Instruments, USA) mercury porosimeter utilizes the non-wetting behavior of liquid mercury on solid surfaces and its adsorption within capillary pores. Specifically, under constant θ and γ, as pressure gradually increases, liquid mercury is forced into smaller pores within the porous structure. Based on the volume of liquid mercury flowing in and the corresponding pressure, a relationship between pressure and pore size is established. The pore size can be calculated using the following formula: where P is the applied external pressure, r is the pore size, γ is the surface tension of the liquid mercury, and θ is the contact angle between the liquid mercury and the object being measured.

[0045]

[0046] Optical absorption characteristics: A UV / Vis / NIR spectrophotometer (Hitachi, Japan) can measure the transmittance (T) and reflectance (R) spectra of the sample in an atmosphere with wavelengths of 250-2500 nm. Since the prepared porous photothermal conversion material is sufficiently thick, its light transmission is considered to be zero. Therefore, in the laboratory, only the reflectance needs to be measured to obtain the absorptivity (A), and the light absorption characteristics of the material can be calculated using Equation 2.2.

[0047]

[0048] Wetting characteristics: The contact angle is an important parameter for evaluating the degree of wettability of a liquid on a solid surface. In this paper, the contact angle of different materials was measured using a contact angle meter (SZ-CAMC33) at room temperature (25℃). Specifically, a 5 µL droplet was dropped onto a horizontally placed sample surface using a pipette. The contact image of the droplet on the test sample surface was then recorded using a camera. The contact angle of the droplet on the material surface was acquired and analyzed using the built-in image processing software.

[0049] Solar Interfacial Evaporation Testing System: To test the photothermal conversion characteristics, interfacial evaporation characteristics, and salt resistance of the prepared materials in saline solutions, this invention constructs a solar interfacial evaporation testing system as follows: Figure 2 The visualization experimental system shown is comprised of the following components: a xenon lamp light source (PLS-FX300HU) with an AM1.5 filter to provide a simulated natural light source; the output light intensity of the xenon lamp can be controlled by adjusting the input current; and a radiometer (CEL-FZ-A) can be used to detect the output light intensity of the xenon lamp. During the experiment, the xenon lamp power output was set to 100 mW / cm². 2 The intensity is marked as one sun. An infrared thermal imager (FLIR A615) is used to capture the surface temperature distribution in real time; post-processing software can then be used to obtain the temperature changes of the material under illumination. An electronic balance (HC313) is used to record the mass change of water in the beaker in real time, which can be used to measure the interfacial evaporation performance of the porous photothermal conversion material. The entire interfacial evaporator is constructed as follows... Figure 2 As shown in the enlarged view on the right, the prepared porous photothermal conversion material is placed on polystyrene foam to minimize heat loss to the subcooled water. To maintain excellent water supply, a non-woven fabric with excellent water absorption properties is wrapped around the polystyrene foam, thereby continuously supplying water from the beaker to the bottom of the evaporator.

[0050] Example 1: Preparation of porous photothermal conversion material with radial gradient aperture structure This embodiment provides a method for preparing a porous photothermal conversion material with a radially gradient pore size structure, specifically including the following steps, the preparation process of which is illustrated in the schematic diagram below. Figure 1 As shown.

[0051] S1. Preparation of salt template pore-forming agents with different particle sizes: Commercially available sodium citrate salt particles were thoroughly ground in a planetary ball mill. After grinding, the salt particles were screened in batches using sieves of different mesh sizes to obtain salt particles with different particle sizes. In this embodiment, the salt particles obtained by screening included small-diameter salt particles (approximately 50 μm), medium-diameter salt particles (approximately 150 μm), and large-diameter salt particles (approximately 300 μm). The screened salt particles of different particle sizes were sealed and stored separately to avoid moisture absorption.

[0052] S2. Constructing a radial gradient salt template: Salt particles of different sizes obtained in step S1 are mixed with deionized water at a mass ratio of 20:1, and thoroughly stirred to obtain wetted salt slurries of different particle sizes. Figure 3 As shown, a multi-layered annular mold is provided. Salt slurry of different particle sizes is filled into the annular cavities of the multi-layered annular mold in descending order of particle size, and then compacted to avoid discontinuities between salt particles of different sizes. Specifically, large-diameter salt particles are filled in the innermost layer of the cylindrical mold, medium-diameter salt particles in the middle layer, and small-diameter salt particles in the outermost layer. After filling and compaction, the mold containing the salt particles is placed in an oven at 65°C for 1 hour to dry. During the heating process, moisture evaporates from the salt block. After removing the mold, a radial gradient salt template is obtained, in which the internal salt particles are bonded together and the pore structure gradually decreases radially from the inside out.

[0053] S3. Preparation of photothermal prepolymer: Polydimethylsiloxane (PDMS) and carbon nanopowder (CNPs) are mixed at a mass ratio of 10:1 and stirred evenly; then, the mixture is mixed again with PDMS curing agent at a mass ratio of 20:1 and stirred evenly to obtain photothermal prepolymer.

[0054] S4. Prepolymer Infiltration and Crosslinking Curing: The photothermal prepolymer prepared in step S3 is cast into the radial gradient salt template prepared in step S2, and then placed in a vacuum chamber for degassing for 2 hours, allowing the photothermal prepolymer to completely fill the pores of the radial gradient salt template under negative pressure. After degassing, the salt template completely filled with prepolymer is transferred to an oven at 65°C for heating and curing for 1 hour, until the mixture is completely crosslinked and cured, resulting in a cured block containing salt particles inside.

[0055] S5. Detemplating and Post-processing: The cross-linked and cured block is cut into cylinders of a predetermined size (in this embodiment, cylinders with a radius of 2 cm and a height of 1.2 cm). The cut cylinders are then immersed in deionized water at 60°C and subjected to ultrasonic treatment for 4 hours until the salt particles inside the block are completely dissolved and removed. After removal and drying, a porous photothermal conversion material with a radial gradient structure is obtained. The internal pore size of this material exhibits a continuous gradient decrease from the center to the edge, with large open pores in the central region and dense small pores distributed in the edge region, forming a multi-level interconnected channel extending in both radial and axial directions internally.

[0056] As a control, porous photothermal conversion materials with uniform macropores (300 μm) and uniform micropores (50 μm) were prepared simultaneously.

[0057] Example 2 Photothermal conversion performance In solar interfacial evaporation systems, the photothermal conversion performance of the interfacial evaporator is one of the core factors affecting evaporation efficiency. Under solar irradiation, the interfacial evaporator possesses the ability to rapidly and significantly raise its surface temperature, which is a crucial prerequisite for ensuring excellent interfacial evaporation performance of the material. This embodiment operates at room temperature (25°C) and a standard solar irradiance (1 mW / cm²). 2 The photothermal conversion performance of the porous photothermal conversion material was tested under irradiation conditions, and the results are as follows: Figure 4 As shown. Among them, Figure 4 The image shows the surface temperature distribution of a porous photothermal conversion material recorded in real time using an infrared thermal imaging camera. It can be clearly observed from the image that the surface temperature distribution of the porous photothermal conversion material is uniform, regardless of whether it has a large pore size (300 μm) or a small pore size (50 μm) structure.

[0058] At the same time, the curve of the average temperature change of the material surface over time was extracted, such as... Figure 5 As shown in the figure. The results indicate that the surface temperature of the photothermal material rises rapidly at the moment the xenon lamp is turned on, and reaches approximately 80°C after 10 minutes of illumination before stabilizing. This demonstrates that the prepared porous photothermal conversion material possesses excellent photothermal conversion performance. Furthermore, from... Figure 5 The study also found that after 60 minutes of continuous illumination, the surface temperatures of porous photothermal conversion materials with larger and smaller pore sizes remained stable at around 79.36℃ and 79.69℃, respectively. This result indicates that the pore size structure has little impact on the differences in photothermal conversion performance of the materials.

[0059] Example 3: Microstructure and Pore Size Distribution Figure 6Figure a shows the microstructure characterization results of a longitudinal section of the porous photothermal conversion material with a radial gradient pore structure prepared in Example 1. Specifically, the longitudinal section is a vertical cut downwards along the diameter of the bottom surface of the cylinder, exposing the internal cross-section from the central axis to the outer edge of the cylinder to facilitate observation of the radial pore size distribution. The figure clearly shows a significant radial gradient pore distribution characteristic within the material. The edge region contains dense pores with an average pore size of approximately 50 μm, while the central region contains large open pores with an average pore size of approximately 300 μm. The pore size exhibits a continuous and smooth gradient decrease from the center to the edge. Furthermore, a multi-level interconnected pore network extending in both the radial and axial directions is formed within the material, providing a continuous water supply channel for water transport during the solar interface evaporation process.

[0060] The internal pore structure of the material was further quantitatively characterized using mercury intrusion porosimetry, and the test results are as follows: Figure 6 As shown in b, the pore size distribution curve obtained from the test exhibits a multi-peak distribution characteristic, with the main peaks located near 50 μm, 150 μm, and 300 μm, respectively. This result is highly consistent with the pore size range observed in the SEM images of the dense edge region, intermediate transition region, and central open region, fully verifying the successful construction of the radial gradient pore structure of the material. The structural design of the pore size gradient decreasing from the center to the edge can drive the water to spontaneously achieve radial directional transport from the center to the edge; at the same time, the multi-level interconnected pore network can efficiently transport water to various areas of the evaporator, ensuring that the moisture at the evaporation interface can be rapidly and continuously replenished under sunlight irradiation, ultimately providing the core structural foundation for the material to achieve efficient and stable solar interface evaporation performance.

[0061] Example 4: Evaporation and Salt Resistance Performance of Evaporators with Different Aperture Distributions The interfacial evaporation performance and salt resistance of the prepared porous photothermal conversion material with radial gradient pore structure were tested here. To accelerate the evaluation of surface salt crystallization behavior, the mass fraction of NaCl in the simulated seawater solution was increased to 10 wt%. By increasing the concentration of simulated seawater, the effect of salt crystallization on the evaporation interface can be significantly amplified in a shorter time, thereby more effectively revealing the advantages of the radial gradient pore structure in suppressing salt accumulation at the upper interface and maintaining long-term stable evaporation. Figure 7 The figures show the surface salt crystallization distribution of porous photothermal conversion materials with uniform large pores (L), uniform small pores (S), and radial gradient pores (RG) during the evaporation process.

[0062] from Figure 7It can be observed that the photothermal conversion material with a large porous structure exhibits a small amount of salt crystallization on its surface after 30 minutes, and the surface salt crystallization gradually intensifies with increasing time. Combined with... Figure 7 The surface salt crystallization area ratio results showed that the ratio reached 42.41% at 60 min, rose to 78.19% at 120 min, and reached as high as 91.57% at 240 min, almost covering the entire evaporation surface. This is because the photothermal conversion material with a larger pore structure experienced insufficient water supply during continuous interfacial evaporation, leading to rapid accumulation of salt ions and reaching a supersaturated state, ultimately resulting in rapid nucleation of salt ions to form salt crystals. In contrast, the photothermal conversion material with a smaller pore structure only began to crystallize after 60 min of illumination, and then gradually diffused from the center outwards, eventually covering the entire upper surface. Its salt crystallization ratio was 35.97% at 120 min and reached 87.45% at 240 min, with a significantly slower crystallization rate than the large-pore structure. The reason for the later crystallization time is that the small pores have a strong capillary water supply capacity, thus providing sufficient water supply to the interface. However, once salt crystals precipitate on the surface, the salt particles will block the water supply channels, thereby weakening the interfacial evaporation performance. In stark contrast to photothermal conversion materials with uniform pore structures, photothermal conversion materials with radially gradient pore structures exhibit surface salt crystallization that gradually accumulates at the edges over time, resulting in salt rings at the evaporator edges. The surface salt crystallization area percentage results show that at 240 min, the percentage is only 35.20%, entirely concentrated in the edge region, while the central evaporation surface remains clean. This is because its unique structure regulates the horizontal transport of water within the material, creating a salt concentration gradient and thus facilitating side crystallization. Side crystallization ensures that the top surface remains salt-free, thereby preventing surface salt crystallization from weakening photothermal conversion performance and reducing interfacial evaporation performance.

[0063] Figure 8 The diagram illustrates water transport within a porous photothermal conversion material with a radially gradient pore structure. The radially gradient pore size, gradually decreasing from the center to the edge, provides radial capillary driving force. Under continuous illumination, the higher evaporation rate at the edge leads to a rapid increase in local salt concentration, creating a salt concentration gradient from the edge to the center. This salt concentration gradient results in a non-uniform distribution of interfacial tension; typically, higher-concentration salt solutions have higher surface tension, inducing Marangoni convection. This fluid shear force driven by the surface tension gradient, in conjunction with radial capillary action, further enhances the directional transport of salt towards the edge. When the salt accumulation at the edge exceeds saturation, it preferentially precipitates to form salt rings. Therefore, by constructing a radially gradient pore structure, salt crystallization can be achieved at the evaporator edge, thus avoiding the problem of decreased evaporation performance caused by surface crystallization.

[0064] Figure 9 Figure a shows the evaporation performance of porous photothermal conversion materials with uniform (L), small (S), and radially gradient (RG) pore structures under one solar irradiation condition. During the 4-hour experimental period, the cumulative evaporation of the porous photothermal conversion materials with large (L), small (S), and radially gradient (RG) pore structures was 4.38 kg / m³. 2 4.92 kg / m 2 and 5.38 kg / m 2 . Figure 9 Figure b shows the hourly evaporation rate. It was found that the hourly evaporation rate of each group of materials gradually decreased with increasing time, with the lowest evaporation rate in the last hour. Among them, the porous photothermal conversion material with a larger pore structure showed an evaporation rate that started at 1.24 kg / m³. 2 •h decreased to 0.96 kg / m 2 The high evaporation rate (·h) is mainly due to the inability of the interfacial moisture replenishment rate to match the evaporation rate, leading to severe surface crystallization and consequently reducing evaporation performance. In contrast, porous photothermal conversion materials with smaller pore structures have an evaporation rate that initially was 1.27 kg / m³. 2 •h decreased to 1.14 kg / m 2 While the pore size (·h) offers some improvement in water transport compared to larger pore sizes, it still fails to completely resolve the salt inhibition problem that worsens over time. In stark contrast, porous photothermal conversion materials with radially gradient pore structures exhibit relatively stable evaporation rates, maintaining a level of 1.25 kg / m³ throughout the entire timeframe. 2 The efficiency is approximately 100 h. The main reason is that there is not much salt crystallization covering the evaporator surface during the evaporation process, thus ensuring a highly efficient and sustainable photothermal conversion process, and thereby achieving a high interfacial evaporation efficiency.

[0065] Example 5: Reflective device enhances side crystallization The results of Example 4 show that constructing a radially gradient porous structure within the material can generate radial capillary driving force, thereby inducing significant radial transport characteristics of water. To further enhance the lateral evaporation effect of the evaporator and induce directional precipitation of salt crystals on the side, this example adds an additional reflective device to the periphery of the interface evaporator constructed from the radially gradient porous photothermal conversion material. The reflective device has an upward-opening funnel-shaped structure located on the outer periphery of the evaporator, and the angle between the generatrix of the reflective sidewall and the horizontal plane is 45°. Figure 10 As shown, the reflective device installed on the outer periphery of the evaporator can reflect the incident light to the side area of ​​the evaporator, significantly improving the photothermal conversion efficiency of the side, thereby enhancing the interfacial evaporation performance of the side and ultimately achieving directional and controllable precipitation of salt crystals on the side, thus avoiding salt deposition on the main surface of the evaporator from the root.

[0066] Further tests were conducted on the interfacial evaporation performance of the radially gradient porous photothermal conversion material equipped with a reflective device under one solar irradiation. The test results are as follows: Figure 11 As shown in the figure. The results indicate that the evaporation performance of the evaporator was significantly improved after the introduction of the reflector. After 4 hours of continuous steady-state testing, the cumulative evaporation rate of the evaporator reached 7.86 kg / m³. 2 The average evaporation rate remained stable at 1.96 kg / m³. 2 •h. Furthermore, throughout the entire continuous evaporation test, the real-time evaporation rate of the evaporator remained almost constant, demonstrating excellent operational stability. In addition, from Figure 11 As can be clearly observed in the illustration, there is slight salt crystallization on the main evaporation surface of the evaporator. The salt crystals are mainly deposited in the edge area of ​​the evaporator, which is highly consistent with the initial design expectations.

[0067] Example 6: Surface hydrophobic coating to enhance lateral crystallization Although the introduction of reflective devices can effectively enhance lateral directional salt deposition, salt deposition still inevitably occurs on the top surface of the main evaporator as the evaporation time increases, such as... Figure 11 As shown in the illustration, this can further weaken the long-term operational stability of the evaporator. To further suppress the problem of top surface salt deposition at its source, this embodiment modifies the top evaporation surface of the radially gradient porous photothermal conversion material by spraying a hydrophobic coating (XN-204L). The contact angle related to the hydrophobicity is as follows: Figure 12 As shown.

[0068] Figure 12 a represents the contact angle test at the bottom of the evaporator. The results show that the droplets can completely penetrate and wet the interior of the porous structure within 25 seconds, which fully ensures the efficient and continuous water supply from the main body water to the interface evaporator. Figure 12 b shows the contact angle test of the modified area at the top of the evaporator. After hydrophobic modification, the material surface exhibits significant hydrophobic properties, with a static water contact angle of up to 105° for droplets placed on the surface, forming a clear wetting gradient with the strong hydrophilic properties at the bottom. The modification strategy can weaken the water transport capacity and wetting properties of the top surface, inducing water to spontaneously transport towards the edge region of the evaporator along the radial gradient structure, thereby completely avoiding the precipitation of salt crystals on the top surface and ultimately achieving efficient and long-term stable interfacial evaporation performance.

[0069] Figure 13 This report characterizes the interfacial evaporation performance and surface infrared temperature distribution of a radial gradient pore structure evaporator that simultaneously incorporates a reflective device and undergoes top surface hydrophobic modification. The test results show that the cumulative evaporation mass of the evaporator exhibits an excellent linear increase with evaporation time, indicating that the evaporation process possesses excellent steady-state operating characteristics. After 4 hours of continuous steady-state testing, the cumulative evaporation capacity of the evaporator reached as high as 9.16 kg / m³. 2The corresponding average evaporation rate is 2.29 kg / m³. 2 The cumulative evaporation rate over 4 hours was significantly higher than that of the control group sample, which only had a reflective device but did not undergo hydrophobic modification of the top surface (7.86 kg / m³). 2 The average evaporation rate is 1.96 kg / m³. 2 •h). Simultaneously acquired infrared thermal imaging results show that the evaporator exhibits a uniform surface temperature distribution during steady-state evaporation, providing stable thermal field conditions for efficient photothermal conversion and interfacial evaporation throughout the entire region. The improved evaporation performance is attributed to the introduction of a hydrophobic coating on the top surface, which significantly inhibits the transport and wetting of brine to the main evaporation interface. Simultaneously, the lateral capillary pumping effect of the radial gradient pore structure further enhances the directional transport of the salt solution to the evaporator edge region. Driven synergistically by these two factors, salt ions migrate directionally with the water to the evaporator side region, and salt crystallization occurs only at the side sites. This fundamentally avoids salt deposition on the main evaporation surface, photothermal site obstruction, and water transport channel blockage, ultimately achieving a simultaneous improvement in evaporation rate and long-term operational stability.

[0070] This embodiment further systematically tested the interfacial evaporation performance of a radial gradient structure evaporator equipped with both a reflective device and a hydrophobically modified top surface in a 3.5 wt% NaCl simulated seawater solution under different incident light intensities (0 sun, 1 sun, 2 sun, 3 sun). The test results are as follows: Figure 14 As shown in the figure, the test results demonstrate that under different light conditions, the cumulative evaporation mass loss of the system exhibits an excellent linear relationship with evaporation time, indicating that the evaporator can maintain a stable steady-state evaporation process under different light intensities. Specifically, under one solar irradiation, the steady-state evaporation rate of the evaporator can reach 2.40 kg / m³. 2 •h; When the light intensity increases to 200 mW / cm 2 The hourly average evaporation rate increased to 4.09 kg / m³. 2 •h; When the light intensity is further increased to 300 mW / cm 2 The average evaporation rate can reach 5.54 kg / m³. 2 This is because as the intensity of incident light increases, the heat energy generated by the photothermal material conversion also increases, providing more energy for the interfacial water evaporation process and significantly accelerating it. The light intensity and evaporation rate exhibit a significant positive correlation, indicating that controlling the light intensity is an effective means to improve the water production efficiency of the evaporator. In practical seawater desalination engineering applications, the incident light intensity can be increased by combining it with a concentrator, thereby achieving higher water production efficiency and greater engineering application value.

[0071] Example 7 Integrated System for Interfacial Evaporation and Freshwater Collection In this embodiment, an evaporation and condensation collection system made of acrylic plates was independently constructed, and its structural schematic diagram is shown below. Figure 15 As shown. The main body is constructed of high-transparency acrylic panels, providing excellent light transmission and maximizing the incidence of sunlight onto the evaporator surface. The top of the cavity has a sloping roof structure similar to a house, its core function being to guide the condensed droplets to slide down the wall under gravity into the freshwater collection tank. The left side of the cavity is a brine storage tank, and the right side is a freshwater collection tank. Two inlets / outlets are provided on the left wall of the cavity to facilitate the introduction and discharge of brine: the upper one is the brine inlet for replacing the brine; the lower one is the high-concentration brine outlet for discharging the concentrated brine. A freshwater collection port is located at the bottom right side of the system. Condensed water collects along the sloping acrylic roof wall and eventually slides into the collection chamber. The freshwater collection port is connected to a collection device, thus realizing a complete freshwater collection process integrating evaporation, condensation, and final collection.

[0072] The condensation of water vapor generated during the interfacial evaporation process at the top severely hinders the transmission of sunlight, preventing incident light from reaching the evaporator surface and weakening the material's photothermal conversion performance. Figure 16 As shown. In this embodiment, a commercial hydrophilic coating (XN-534) is sprayed onto the inner surface of the acrylic plate above the solar interface evaporation area. This treatment allows water droplets to quickly spread on the acrylic glass to form a uniform water film, effectively reducing the loss of incident light and allowing sunlight to normally enter the solar interface evaporation area, such as... Figure 16 As shown in b. The results show that after hydrophilic treatment, there are no small water droplets adhering to the surface of the acrylic sheet, which significantly improves the light transmittance of the acrylic sheet during the evaporation process, allowing incident light to normally irradiate the internal evaporator and ensuring the continuous evaporation performance of the system.

[0073] Evaporation and Freshwater Recovery Performance of Radial Gradient Structure Materials: To further clarify the influence of pore size distribution on the interfacial evaporation process, the long-term evaporation performance of the radial gradient pore structure photothermal conversion material was investigated using the reflective device and hydrophobic coating introduced in Examples 5-6. The results are as follows: Figure 17 As shown. Figure 17 'a' represents the evaporation curve under a given solar radiation intensity over 8 hours. In the continuous 8-hour evaporation test, the cumulative evaporation increases linearly with time, reaching a total evaporation of 15.87 kg / m³. 2 Compared to the radial gradient pore structure, the overall evaporation performance is improved by approximately 28%. To investigate the reason for the increased evaporation, the evaporation rate per unit time of the photothermal conversion material with radial gradient pores was extracted, such as... Figure 17 As shown in b. During the first 4 hours of evaporation, the evaporation rate remained consistently at 2 kg / m³. 2The evaporation rate reaches a high level of over 1 hour. However, after 5 hours, the evaporation rate shows a significant decrease. Due to the gain brought by the photothermal evaporation on the side of the radial gradient hole structure and the synergistic effect of the hydrophobic interface treatment, salt crystals are preferentially precipitated on the side of the evaporator, thus not affecting the photothermal conversion process in the central region, thereby achieving further improvement in evaporation performance and long-term stability.

[0074] During water evaporation, the radial gradient structure guides water preferentially towards the sides of the evaporator. As evaporation continues, a radial salt concentration gradient forms inside the evaporator. Driven by both capillary force and the concentration gradient, salt ions migrate towards the edge region of the evaporator, ultimately resulting in edge-preferential crystallization. This characteristic of salt crystals preferentially precipitating in the side region of the evaporator ensures that the evaporator maintains high evaporation efficiency throughout the 8-hour continuous test. Figure 17 In the salt crystal distribution in section c, it can be observed that the growth of salt crystals exhibits a gradual encirclement of the interface from the sides towards the center. Throughout the entire 8-hour evaporation process, the core evaporation interface was never completely covered by salt crystals, thus maintaining efficient photothermal conversion. Simultaneously, the surface temperature distribution results show that the temperature is higher in the central region of the evaporator interface and decreases gradually towards the edges. This result confirms that the radial gradient pore structure can effectively guide moisture transport to the sides, causing salt crystals to mainly accumulate on the sides of the evaporator, ultimately achieving a synergistic balance between high evaporation rate and long-term salt resistance.

[0075] Subsequently, the evaporation rate of the photothermal conversion material with a radial gradient structure under different light intensities and the amount of freshwater collected in the collection device were tested. Figure 18 As shown in Figure a, during the 8-hour evaporation process, the evaporation rates under 1-3 solar irradiance intensities were 15.87 kg / m³. 2 23.68 kg / m 2 32.93 kg / m 2 As the light intensity increased, the evaporation rate increased dramatically. Subsequently, the collection performance within the device was further evaluated, such as... Figure 18 As shown in b. In an 8-hour freshwater collection experiment, 7.54 kg / m³ was achieved under 1 solar intensity. 2 The freshwater collection rate can be increased to 17.02 kg / m³ under three solar irradiance conditions by increasing light intensity. 2 . Figure 16 c represents the evaporation rate and collection rate per unit time, which is 1.98 kg / m³ under one solar irradiance. 2 The evaporation rate per hour (·h) increases with increasing light intensity; the average evaporation rate under three different solar light intensities can reach 4.12 kg / m³. 2The collection rate at 1 solar irradiance is only 0.94 kg / m³. 2 •h, by increasing the light intensity to 2 suns, the collection amount can reach 1.63 kg / m³. 2 •h, achieving 2.12 kg / m² under 3 solar irradiance levels 2 • h Collection rate. For example Figure 18 As shown in d, the evaporation collection efficiency of the evaporator was further calculated. The collection efficiency remained at around 50% when the solar irradiance was 47.49%, 54.72%, and 51.68% for 1-3 solar irradiances, respectively.

[0076] During the collection process, salt crystallization occurred to varying degrees in the evaporator, such as... Figure 19 As shown, salt crystals mainly concentrate on the sides of the evaporator, and with increasing light intensity, the growth of salt crystals exhibits a wrapping pattern from the outside in, which has a certain impact on evaporation. However, the central area of ​​the main interface remains uncovered by salt crystals and still maintains good photothermal conversion performance. The collection efficiency is limited to this level mainly due to two reasons. Firstly, the partial coverage by salt crystals leads to a certain degree of decrease in the evaporator's evaporation performance. Secondly, as the evaporation process continues, condensate generated during evaporation collects on the sides of the freshwater collection device. This condensate flows back into the brine storage tank and is not effectively collected, thus reducing the collection efficiency.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing a solar interface evaporator with induced directional crystallization, characterized in that, Includes the following steps: S1. Constructing a radial gradient salt template: Sodium citrate particles are ground and sieved to obtain salt particles with different particle sizes; the salt particles of different particle sizes are mixed with solvents to form salt slurries; a multi-layer concentric annular mold is provided, and the salt slurries of different particle sizes are filled into the annular cavities of the mold in descending order of particle size, and compacted. After heating and drying to remove moisture and the mold, a radial gradient salt template is obtained. S2. Preparation of photothermal prepolymer: Mix siloxane polymer and photothermal conversion filler to obtain a mixture, add curing agent and stir to obtain photothermal prepolymer; S3. Prepolymer curing: The photothermal prepolymer prepared in step S2 is cast onto the radial gradient salt template prepared in step S1, and placed in a vacuum environment for degassing treatment, so that the photothermal prepolymer fills the pores inside the radial gradient salt template, and then is heated and cured. S4. Detemplating treatment: Immerse the solidified product in deionized water to dissolve and remove the internal salt particles. After drying, the solar interface evaporator with induced directional crystallization is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the salt particles with different particle sizes include salt particles with a first particle size, salt particles with a second particle size, and salt particles with a third particle size; the first particle size salt particles have a particle size range of 30-80 μm, the second particle size salt particles have a particle size range of 100-200 μm, and the third particle size salt particles have a particle size range of 250-400 μm.

3. The preparation method according to claim 1, characterized in that, In step S1, the solvent is deionized water, and the mass ratio of the salt particles to the deionized water is (15-25):1; the heating and drying temperature is 50-80℃, and the time is 0.5-3h.

4. The preparation method according to claim 1, characterized in that, In step S2, the siloxane polymer is polydimethylsiloxane, and the photothermal conversion filler is nano-carbon powder; the mass ratio of the siloxane polymer to the photothermal conversion filler is (8-15):1; and the mass ratio of the mixture to the curing agent is (15-25):

1.

5. The preparation method according to claim 1, characterized in that, In step S3, the degassing treatment time is 1-3 hours; the heating and curing temperature is 50-80℃, and the curing time is 1-3 hours; in step S4, the dissolution process is carried out under ultrasonic conditions, the temperature of the deionized water is 40-80℃, and the ultrasonic treatment time is 2-6 hours.

6. The preparation method according to any one of claims 1-5, characterized in that, The preparation method further includes: S5. Surface hydrophobic modification treatment: A hydrophobic modification liquid is sprayed onto the top evaporation surface of the solar interface evaporator obtained in step S4 to form a hydrophobic coating.

7. A solar interface evaporator for induced directional crystallization, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The solar interface evaporator according to claim 7, characterized in that, The interior of the photothermal conversion material has a radial gradient pore structure in which the pore size gradually decreases from the center to the edge.

9. The application of the solar interface evaporator as described in any one of claims 7-8 in solar interface evaporation, seawater desalination, or brine separation systems.

Images