Simultaneous desalination and thermal localization through capillary structure and large channel design in 3D evaporator and method of manufacture thereof

Abstract

The invention provides an efficient buoyancy-driven convection type 3D solar evaporator which is used for removing salt and efficiently evaporating high-salinity water when the high-salinity water is stable at the same time. The invention combines different strategies, including capillary structures, low tortuosity large channels, and edge-first salt crystallization. With synergy of these strategies, the evaporator of the present invention exhibits a stable evaporation rate of at least 2.5 kgm <-2 > h <-1 > for seawater or saline solutions having a salinity of more than 10% by weight under 1 kWm <-2 > solar radiation.

Description

Cross - Reference to Related Applications

[0001] This application claims the priority of U.S. Provisional Patent Application No. 18 / 525,917, filed on December 1, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] The present invention relates to an evaporator for desalination. More specifically, the evaporator has a specially designed 3D capillary structure and large channels, which can achieve desalination and heat localization simultaneously. Background Art

[0003] Fresh water has always been a necessity for human life. However, various factors such as population growth, urbanization, industrialization, and climate change have led to water shortages. Therefore, solar desalination is an increasingly popular and crucial solution in addressing global challenges related to water shortages and growing freshwater demand.

[0004] Compared with other desalination technologies, solar desalination has multiple advantages. First, it can extract a large amount of water resources from the ocean that are otherwise unusable for drinking water and agricultural irrigation, so it is particularly effective in alleviating freshwater shortages in areas with abundant seawater. In addition, some traditional freshwater resources (i.e., rivers and lakes) are vulnerable to environmental pressures, including over - extraction and pollution, while solar desalination allows regions to reduce their dependence on these traditional freshwater resources. Moreover, solar desalination systems can be operated even off - grid, which promotes their application in regions such as remote areas or disaster - affected areas with weak or no power infrastructure. Solar desalination is powered by sunlight, so this technology is inherently sustainable and environmentally friendly.

[0005] In desalination technology, interfacial solar water evaporation is considered one of the most sustainable options. Interfacial solar water evaporation technology uses solar energy to transform liquid water into steam, which is not only efficient and has a high recovery rate, but also sustainable and has a zero carbon footprint. In addition, this technology is scalable and adaptable, thus allowing off - grid applications. Interfacial solar water evaporation systems are generally relatively simple and have low implementation costs, without relying on complex infrastructure. In solar evaporators, 3D evaporators are becoming a promising design because they can capture additional energy from the surrounding environment and greatly promote evaporation.

[0006] However, in addition to the evaporation rate, the problem of salt scaling has also received increasing attention. Since the diffusion rate of salt in water is slow (~10 -9 m 2 s -1) During continuous operation, serious salt accumulation will occur. The accumulated salt not only seriously affects sunlight absorption but also blocks the water transportation channels, reducing the evaporation performance and ultimately leading to system failure.

[0007] Currently, innovative strategies for long-term solar desalination can be divided into three categories.

[0008] The first category is designs that separate the solar absorber from the brine (such as non-contact evaporation and Janus structures). These designs prevent the brine from reaching the light-absorbing layer, thus avoiding surface salt accumulation. However, the rapid heat dissipation of the photothermal layer to the environment or the bulk water will hinder the evaporation performance, resulting in low energy convection efficiency.

[0009] The second category is designs aimed at localizing salt crystallization. A two-dimensional evaporator with edge-priority crystallization achieved by adjusting the brine delivery path has been reported. Although it has excellent desalination ability, its evaporation rate is relatively low.

[0010] The third category is designs that utilize enhanced convection for salt transfer. Designing high-throughput large channels in the capillary structure to enhance fluid convection is considered the simplest method to achieve desalination. By introducing low-tortuosity large channels in the capillary structure to bridge the high-salt region and the bulk water, stronger water supply and faster salt ion transport can be achieved ( Figure 1A ). However, due to the coincidence of high temperature (T 1 ) and the high-salt region, the fluid exchange between the high-salt region and the bulk water will not only remove salt but also cause significant heat loss (ΔT 1 ) and low evaporation rate.

[0011] Therefore, it is necessary to improve the interfacial solar desalination system to achieve the ability of simultaneous desalination and heat localization to maintain high evaporation performance and prevent salt pollution. The present invention meets this need. Summary of the Invention

[0012] Aiming at the above technical deficiencies, the present invention provides an efficient convective three-dimensional solar evaporator for simultaneously removing salts and stably evaporating high-salinity water. This product combines different strategies, including engineered capillary structures, low-tortuosity large channels, and edge-priority salt crystallization. Therefore, the system of the present invention achieves high evaporation efficiency and good salt removal rate.

[0013] In one aspect, the present invention provides an efficient convective three-dimensional solar evaporator for simultaneously achieving desalination and stable evaporation of high-salinity water. The evaporator includes a porous matrix and a photothermal material connected to each other. The three-dimensional structure of the evaporator includes a funnel-shaped structure and microchannels on the outer surface. The evaporator exhibits at least 2.5 kg m -2 under a solar irradiance of 1 kW m-2 h -1 The stable evaporation rate of

[0014] The connected porous structure of the evaporator includes polyurethane, cellulose, alginate, polyvinyl alcohol, polyacrylamide, or any mixture thereof.

[0015] The photothermal material of the evaporator can be selected from carbon nanotubes, carbon black, carbon nanodots, graphene, or any mixture thereof.

[0016] The large channels of the evaporator have a low tortuosity and a high throughput. In addition, the average size of these large channels is about 500 - 1200 μm.

[0017] The 3D solar evaporator exhibits high hydrophilicity and water transport ability. It can absorb 800 μL of water in less than 0.2 seconds and transport the water to a height of 20 mm in less than 50 seconds.

[0018] The 3D solar evaporator also has a high light absorption rate of at least 95%.

[0019] There is a temperature difference between the high - salt region and the bulk water in the 3D solar evaporator.

[0020] On the other hand, a method for manufacturing a 3D solar evaporator is provided. The method includes separately providing a first porous matrix and a second photothermal material, and mixing the two to form a third aqueous mixture. The method also includes pouring the third mixture into a 3D - printed silicone mold and freezing it at a temperature of - 20 °C to - 90 °C; and freeze - drying to remove ice crystals. In this way, an engineered core structure with large channels having an average size of 500 - 1200 μm is formed.

[0021] The first porous matrix can be selected from polyurethane, cellulose, alginate, polyvinyl alcohol, polyacrylamide, or a mixture thereof.

[0022] The second photothermal material can be selected from carbon nanotubes, carbon black, carbon nanodots, graphene, or a mixture thereof. Brief Description of the Drawings

[0023] In the following detailed description, with reference to the accompanying drawings, exemplary, non - limiting, and non - exhaustive embodiments of the present invention are described. For a detailed understanding of the above - mentioned features of the present invention, the present invention briefly summarized above can be described more specifically with reference to the embodiments, some of which are shown in the drawings. However, it should be noted that these figures only show typical embodiments of the present invention and should not be regarded as limiting its scope, since the present invention can permit other equally effective embodiments.

[0024] Figure 1ASchematic diagrams of heat localization and desalination in a conventional convective evaporator (left) and the evaporator of the present invention (middle) are respectively shown; and the temperature difference between the high-salt region and the bulk water (T 1 ) in the convective evaporator (ΔT 2 ) and the evaporator of the present invention (ΔT 0 ) is compared (right). T 1 and T 2 respectively refer to the temperatures of the high-salt regions of the two evaporators. It is observed that in the convective evaporator, the high-temperature and high-salt concentration regions always overlap, resulting in significant heat loss during the convection of salt through the microchannels. However, in the evaporator of the present invention, the high-temperature and high-salt regions are isolated, where the inner surface is hot while the outer surface and the edges are cold. Salt crystallization is confined to the edges; while the microchannels on the cold side convect salt from the high-salt region with high efficiency and minimal heat loss. Figure 1B An SEM image is shown, where the inset is an optical image of the evaporator of the present invention; the right figure is the polyurethane skeleton. Figure 1C Water transport in 3D transport is shown (height = 2 cm).

[0025] Figure 2A Salt crystallization on a flat sample (left), local salt crystallization on a 3D evaporator without large channels (middle), and local salt crystallization on a 3D evaporator with microchannels (right) are respectively shown. Figure 2B The structures of the flat and 3D evaporators are shown. Figure 2C and 2D The experimental and simulation results of salt crystallization on the flat sample and the 3D evaporator are shown. Figure 2E The structures of 3D evaporators with 2, 3, 4, and 8 large channels respectively are shown. Figure 2F and 2G show Figure 2E the experimental and simulation results of salt crystallization on the evaporator in Figure 2H The simulated salt transport path of a 3D evaporator with 2 large channels is shown. 2I shows the crystals harvested from 3D evaporators with different numbers of large channels after evaporation in a 10 wt% sodium chloride solution for 24 hours.

[0026] Figure 3A The enhanced light trapping and evaporation surface of the 3D evaporator are shown. Figure 3B The light absorption of 3D evaporators with different heights is shown. Figure 3C The evaporation surface areas of different evaporators are shown. Figure 3D The evaporation rate of the evaporator is shown. Figure 3E The infrared images of different evaporators under 1 unit of solar illumination (1 kW m -2 ) are shown. Figure 3F shows Figure 3E the outer and inner surface temperatures of the evaporator inFigure 3G The infrared images of the 3D evaporator without large channels and with 8 large channels after 4 hours under 1 unit of solar illumination are shown respectively. Figure 3H The temperature changes at different positions during the 4-hour evaporation process of the evaporation system are shown.

[0027] Figure 4A and 4B The optical images and evaporation rates of the flat evaporator, 3D evaporator, and 3D evaporator with 4 large channels during 24 hours of continuous operation are shown respectively. Figure 4C The change in evaporation rate during the 7-day cyclic evaporation test is shown, where the inset is the optical image of the 3D evaporator with 12 large channels during the cyclic test. Figure 4D The change in salinity of the bulk water below the evaporator during the cyclic experiment is shown.

[0028] Figure 5A The optical images of the 3D evaporator and the 3D evaporator with 12 large channels operating in real high-concentration seawater (10.4 wt% salinity) for 24 hours are shown. Figure 5B The detailed optical image of the 3D evaporator with 12 large channels is shown. Figure 5C The evaporation rates of the 3D evaporator and the 3D evaporator with 12 large channels are shown correspondingly. Figure 5D and 5E The schematic diagram and SEM image of the salt crystals accumulated in pure sodium chloride solution and concentrated seawater are shown respectively. Figure 5F The SEM image of the salt crystals in concentrated seawater and the corresponding ion distribution (sodium chloride crystals, calcium sulfate crystals, and magnesium sulfate) are shown.

[0029] Figure 6A The schematic diagram of the water collection device for outdoor testing is shown. Figure 6B The optical images of the device at different time points during outdoor testing are shown. Figure 6C The real-time changes in solar radiation flux, outdoor temperature, and humidity during outdoor testing are shown. Figure 6D The ion concentration comparison chart of seawater and collected water is shown.

[0030] Figure 7 The schematic diagram of the preparation process of the evaporator of the present invention is shown.

[0031] Figure 8 The contact angle of the prepared polyurethane / carbon black evaporator is shown, the contact angle is about 0°, and the droplet volume is 800 μL.

[0032] Figure 9 The mechanical properties of the evaporator are shown, and the optical images of the material before and after 100 cycles of compression are shown on the right.

[0033] Figure 10Are schematic diagrams and photographic images depicting the introduction of evaporation into EPS foam. In this configuration, water can be pumped out of the pores in the foam by capillary forces. The foam is cut with a custom cutter to the same diameter as the container to minimize evaporation from the gap between the foam and the container.

[0034] Figure 11 Show the detailed structures of a flat evaporator (left), a 3D evaporator (middle), and a 3D evaporator with large channels (right), respectively. The units in the figures are in millimeters.

[0036] Figure 12 Shows a comparison of the material consumption of a flat evaporator and a 3D evaporator of the same height.

[0037] Figure 13 Shows the evaporation-induced cooling effect at the edge and outer surface of the evaporator.

[0038] Figure 14 Shows the evaporation rates of 3D evaporators with different numbers of large channels.

[0039] Figure 15A Shows a 3D evaporator, where one part contains 6 large channels and the other part has no large channels. Figure 15B Shows the height of seawater before and after 150 hours of continuous evaporation. Figure 15C Is an optical image after the evaporator operation.

[0040] Figure 16 Shows detailed optical images of the evaporator and the system during 150 hours of operation. 110 ml of seawater is almost completely evaporated after continuous irradiation. The part without large channels (right view) is completely covered by a dense salt crust, which prevents light absorption and steam generation. However, the part with large channels (left view) shows local salt crystallization. The rapid convection in the large channels enables the salt to quickly flow back to the bulk water, avoiding salt precipitation on the main surface. Detailed Description of the Invention

[0041] The present invention discloses an efficient convective three-dimensional solar evaporator for simultaneously removing salts and stably evaporating high-salinity water. The evaporator includes a porous matrix and a photothermal material connected to each other, having a unique funnel-shaped structure with large channels on the outer surface. The large channels act as a bridge between the bulk water and the high-salt region, triggering buoyancy flow due to the salt gradient, thereby enabling the salt to quickly flow back to the bulk water.

[0042] With the above unique features, the 3D solar evaporator of the present invention exhibits at least 2.5 kg m -2 under a solar irradiance of 1 kW m -2 h -1Significant evaporation rate. Importantly, the evaporator exhibits good evaporation stability when treating salt solutions or natural seawater with a salt concentration of at least 10 wt%, demonstrating its great application potential in practical desalination.

[0043] Examples:

[0044] Example 1

[0045] Design and characteristics of the evaporator

[0046] To fabricate the evaporator, readily available freeze-dried polyurethane (PU) and carbon black were selected as the porous matrix and photothermal material, respectively. The self-made PU sponge features excellent water absorption speed, mechanical durability, and low cost, which are crucial for practical applications. The preparation process is as Figure 7 shown. First, the PU emulsion and crosslinker were mixed with deionized (DI) water at a volume ratio of 1:0.05:1.5. Then, 1 wt% of carbon black was added to the mixture, and the prepared solution was poured into a customized 3D-printed silica mold, frozen at -80 °C for 24 h, and then freeze-dried at -50 °C for 48 h to obtain a highly interconnected evaporator.

[0047] After freeze-drying to remove ice crystals, a porous three-dimensional evaporator with large channels of 800 μm on the outer surface was obtained ( Figure 1B ). The evaporator has a highly interconnected porous structure, which is beneficial for light trapping and water transportation.

[0048] The mixed PU skeleton was observed, providing mechanical durability for the evaporator. Due to its high affinity for water, the prepared evaporator can rapidly absorb 800 μL of water droplets within 0.1 s ( Figure 8 ). In addition, it can pump water to a height of 20 mm and fully wet the top paper within 45 s, demonstrating its strong capillary force for water transportation ( Figure 1C ).

[0049] Mechanical durability was demonstrated by a cyclic compression test. A cuboid evaporator with a length of 20 mm and a height of 8 mm was prepared. The strain rate was set to 1 mm s -1 , and the compression / recovery process was carried out 100 times. After 100 compressions at 80% strain, the PU / carbon black sponge can recover to its original size without deterioration ( Figure 9 ).

[0050] To measure the desalination rate and evaporation performance of the evaporator, the evaporator was inserted into EPS foam for floating ( Figure 10 ).

[0051] Desalination caused by local salt crystallization and convection

[0052] To clarify the controllable salt crystallization of this design, three types of samples were prepared, including a flat evaporator, a 3D evaporator, and a 3D evaporator with different numbers of large channels. The detailed designs of the three different types of samples are as Figure 11 shown.

[0053] Figure 2A The salt crystallization mechanism of the prepared evaporators is shown. The highly interconnected porous medium drives the brine transport through capillary infiltration, where the core structure significantly affects the capillary flow pattern. For example, the flat evaporator passively absorbs the brine from the bulk reservoir and transports it to the evaporation surface. On the surface, continuous evaporation increases the salt concentration, resulting in salt crystallization and accumulation ( Figure 2A ). In contrast, the structural design of the 3D evaporator enables the salt to be preferentially transported from the center to the edge. As evaporation proceeds, the concentration steadily increases at the edge, leading to edge-prior salt crystallization ( Figure 2A ). The large channels on the outer surface of the 3D evaporator are then designed to connect the high-salt region to the bulk water ( Figure 2A ). The salinity gradient between the high-salt region and the bulk water can passively trigger natural convection in the large channels, resulting in the reflux and splitting of the precipitated salt crystals. In addition, the sufficient water supply caused by the large channels weakens the binding force between the split salt crystals and the evaporator. Therefore, the salt particles suspended at the edge will spontaneously fall off due to gravity, providing an opportunity to obtain valuable mineral resources from the desalination process.

[0054] Figure 2B , 2C and 2D respectively show the experimental results and simulation results of the flat evaporator and the three-dimensional evaporator after evaporating for 4 h under 1 unit of solar illumination in a 10 wt% sodium chloride solution. Salt precipitated on the entire evaporation surface of the flat evaporator sample, and the evaporation surface changed from black to white. In contrast, salt only precipitated at the edge in the three-dimensional evaporator, indicating that local salt crystallization was successfully achieved. Although the salt ions convectively moved with the passive fluid flow in both evaporators, the engineered shape of the 3D evaporator caused capillary flow preferential to the edge, resulting in local salt accumulation at the structural edge.

[0055] To demonstrate the effect of the large channels on fluid splitting and convection, four 3D evaporators were prepared with 2, 3, 4, and 8 large channels arranged in a circular array on their outer surfaces ( Figure 2E ). Figure 2F and 2G show the precipitated salt crystals obtained from the experimental and simulated evaporation processes. Compared with the 3D evaporator without large channels in Figure 2B , due to the presence of the large channels, the circular salt crystal region was divided into several parts. As the number of large channels increased from 2 to 8, the simulated region reaching the surface salt saturation point decreased, demonstrating the local repulsion of salt by the large channels. Figure 2Hshows the salt transport path under the influence of large channels, revealing that convection causes the salt to rapidly return from the region with a higher salt concentration to the bulk water. In addition, the sufficient water provided by the channels weakens the binding force between the salt crystals and the evaporator, which causes the salt crystals to fall off from the edge of the evaporator. The salt crystals collected after 24 hours of continuous evaporation further prove the splitting and repulsion phenomena caused by the large channels. It was observed that as the number of large channels increases, the size and weight of the collected salt crystals both decrease( Figure 2I ).

[0056] Thermal localization and evaporation performance

[0057] Flat evaporators with a height of 7 mm and 3D evaporators with heights of 7, 10, 15, and 20 mm were prepared to evaluate the influence of the 3D structure on evaporation performance and thermal localization. Compared with the flat samples, the 3D structure exhibits better light-trapping ability by absorbing multiply reflected light( Figure 3A ). At the same time, the 3D evaporators exhibit a larger air-evaporator interface to generate steam while using less material( Figure 12 ), which will be beneficial for practical applications. The light absorption characteristics were evaluated by UV-Vis-NIR absorption spectra in the range of 250 - 2500 nm( Figure 3B ). The light absorption rate of the 3D evaporator with a height of 7 mm is 97.4%, slightly higher than that of the flat evaporator with the same height. As the height of the 3D evaporator further increases, the light absorption rate significantly increases to 99.6%, which strongly proves the superiority of the designed 3D structure in light trapping. In addition, the absorbance of the 3D evaporator is also outstanding among the recently reported structured light-absorbing materials. Subsequently, the evaporation surfaces of different evaporators were calculated( Figure 3C ). The evaporation surfaces of the flat and 3D samples with the same height (7 mm) are 753.6 mm 2 to 972.9 mm 2 , an increase of nearly 30%. The enlarged surface area is conducive to the water molecules at the interface obtaining energy and escaping into the air, resulting in a high evaporation rate. The evaporation performance of the prepared evaporators was measured under 1 unit of solar illumination( Figure 3D ). The evaporation performance of the 20-mm-high 3D sample is much higher than that of the 7-mm sample. This enhancement is due to the engineered 3D structure, which endows higher light absorption and evaporation surface area.

[0058] Figure 3E shows the temperature distribution of the prepared evaporators. The flat evaporator exhibits a high-temperature region on its top surface, which is consistent with Figure 2Dcoincides with the high-salt concentration region shown in the figure. In contrast, the 3D evaporator exhibits an obvious temperature distribution, with a concentrated heat zone on its inner surface, while the edges and outer surface exhibit lower temperatures. This temperature distribution results in the separation of the high-temperature zone and the salt zone within the 3D evaporator. The low temperature at the edges generates a large tension, accelerating the transport of brine towards the edges. According to classical nucleation theory, heterogeneous nucleation tends to occur in places with lower temperatures, which also promotes edge-preferred salt crystallization. The temperature of the high-salt zone of the flat evaporator is 35.4 °C, 7.7 °C higher than that of the 3D evaporator at the same height. When the height of the 3D evaporator increases to 20 mm, the temperatures of the edges and outer surface drop to 24 °C and 26.4 °C respectively( Figure 3F ). The lower temperatures observed at the edges and outer surface are mainly attributed to the absence of direct sunlight, and the cooling effect caused by evaporation further enhances the cooling( Figure 13 ). The large interfacial surface at the edges of the 3D evaporator is conducive to the escape of steam, thereby cooling the edges and outer surface through latent heat and radiation. Simulating the temperature distribution of the 3D evaporator also yields the same result. Therefore, by reducing the temperature difference between the high-salt zone and the bulk water from 10.4 °C (ΔT1) to 1.4 °C (ΔT2), the heat loss caused by fluid convection through the large channels can be significantly reduced. By separately monitoring the temperatures of the bulk water below the 3D evaporator and the 3D evaporator with 8 large channels( Figure 3G and 3H ), the effectiveness of the minimum heat loss is confirmed. After continuous evaporation for 4 hours under 1 unit of sunlight, the temperatures of the bulk water in both groups are almost the same as the ambient temperature. This indicates that the conductive heat is restricted and only a small amount is transferred to the bulk water, and the influence of the large channels on the heat dissipation into the bulk water can be ignored. In addition, the evaporation rates of the 3D evaporator are compared with different numbers of large channels (0, 4, 8, and 12). The increase in the number of large channels does not lead to a decrease in the evaporation rate, which further proves the minimum heat loss caused by the large channels( Figure 14 ).

[0059] Long-term stability

[0060] To evaluate the effects of the designed 3D capillary structure and large channels on the desalination and evaporation performance, long-term evaporation tests are conducted in a 10 wt% sodium chloride solution. After continuous operation for 24 hours under 1 unit of sunlight, the flat evaporator is completely covered with salt crystals( Figure 4A ). This results in a significant decrease in the evaporation rate, from 3.15 kg m -2 h -1 to 1.7 kg m -2 h -1 ( Figure 4B ). For the 3D evaporator, salt precipitates at the edges of the evaporator, resulting in an evaporation rate decrease from 3.23 kg m -2 h -1Slightly reduced to 2.52 kg m - 2 h -1 This indicates that edge - preferential salt crystallization can isolate the salt from most of the evaporation surface, thus avoiding evaporation cessation. In contrast, in a 3D evaporator with 4 large channels, the salt crystals split into 4 parts and automatically fall under the action of gravity. During long - term operation, the evaporation rate remains stable at 3.1 kg m -2 h -1 . These results show that the 3D structure is conducive to local salt crystallization, and the large channels split and convect the salt into the bulk water without causing heat loss. A 7 - day cycling experiment was conducted to further confirm the long - term stability of the evaporator. In each cycle, the evaporator operates for 9 hours under 1 unit of solar illumination. A 10 wt% sodium chloride solution is regularly replenished to maintain a constant distance between the evaporator and the light source. During the 7 - day cycling test, the evaporator rate stabilizes at about 3 kg m -2 h -1 and shows no decrease ( Figure 4C ). This stability is attributed to the 3D structure and large channels, which are conducive to the rapid transport of salt ions and prevent salt crystals from clogging the evaporation surface. Figure 4C The inset in shows the salt crystallization and reflux process. After operating under 1 unit of solar illumination radiation, the salt precipitates locally at the edge of the evaporator, splits into several small parts, and some salt crystals fall on the floating foam due to gravity. After turning off the light, driven by the strong water supply of the highly interconnected porous structure and large channels, the precipitated salt can reflux into the bulk water. Due to the reflux of salt ions, the salinity of the sodium chloride solution increases from 10.3 wt% to 13.9 wt% ( Figure 4D ).

[0061] Desalination of actual concentrated seawater

[0062] The evaporation performance in real - world concentrated seawater brine is of great significance for the field of solar desalination, but it has rarely been proposed. The salt removal rate in highly concentrated seawater is challenging because the crystallization behavior of salt in natural seawater is complex and it has more types of constituent elements than pure sodium chloride solution. When tested in pure sodium chloride solution, water evaporation remains stable for a long time. However, when operating in real concentrated seawater brine, water evaporation drops rapidly. This difference can be attributed to the significant difference in the salt - crust structure between pure sodium chloride solution and real seawater.

[0063] To demonstrate the practicality of this design, continuous operations were carried out to measure the evaporation performance of the 3D evaporator and the 3D evaporator with 12 large channels in highly concentrated seawater (salinity of 10.4%). Different from the annular salt crust formed by the evaporation of 10 wt% pure sodium chloride solution, the 3D evaporator presents a dense salt film in concentrated seawater, which finally covers the entire 3D evaporator ( Figure 5AThe resulting precipitation of salt crystals caused the evaporation rate to drop sharply by 1.67 kg m -2 h -1 ( Figure 5C ), which is better than Figure 4B Pure sodium chloride solution (0.71 kg m -2 h -1 ) is more than 2.3 times higher. In contrast, in the 3D evaporator with large channels, the salt only precipitates at the edges and presents a jagged shape ( Figure 5B ). The macrochannels enable the rapid influx of salt ions into the underlying seawater, thereby reducing salt crystallization near the macrochannels. As a result, the evaporation rate of the 3D evaporator with 12 macrochannels remains stable during continuous operation. This suggests that convection-induced salt rejection is also applicable to real concentrated seawater.

[0064] To illustrate the difference in evaporation performance when treating pure sodium chloride solution versus natural seawater, salt crystals formed from the two solutions at the same concentration (~10 wt%) were studied. Figure 5D The salt crust obtained by evaporation of pure sodium chloride solution is shown, where the cubic salt crystals have clean surfaces and the loosely packed salt allows water transport and steam escape. However, the salt crust in concentrated seawater shows a more compact structure. In addition to the cubic sodium chloride crystals, some rod-like crystals are observed, and the interstitial spaces between the crystals are filled with a waxy matrix ( Figure 5E and 5F ). EDS analysis showed that the rod-shaped crystals were calcium sulfate, sparsely decorated between the sodium chloride crystals ( Figure 5F ). Magnesium is found in the waxy substance, which fills the entire pore space around the sodium chloride and CaSO4 crystals, forming a dense salt crust. Therefore, a three-dimensional evaporator operating in concentrated seawater stops operating due to the formation of a dense salt crust. However, for a three-dimensional evaporator with large channels, the strong convection in the large channels allows not only sodium chloride but also calcium and magnesium ions to flow back, thereby preventing the precipitation of a dense salt crust on the main evaporation surface.

[0065] To further demonstrate the desalination capability of the evaporator in real seawater, a continuous evaporation of 108 mL of seawater was performed. Figure 15A As shown in the figure, a 3D evaporator was fabricated, one part of which contained six macrochannels and the other part did not have any macrochannels. -2 ) for 150 hours, the bottom seawater was almost completely evaporated. The evaporator showed an asymmetric distribution of salt crystals, where the part containing large channels showed localized and fragmented salt crystals. In contrast, the part without large channels was completely covered with salt crystals ( Figure 15C ).

[0066] Outdoor testing of water collection devices

[0067] In practical applications, water collection performance is also an important evaluation criterion, but it has been greatly overlooked in many previous studies on desalination evaporators. In this study, a portable solar water purification prototype was prepared to demonstrate its potential in practical seawater desalination.( Figure 6A ) Eleven 3D evaporators (each containing eight large channels) were inserted into insulating foam and floated on the water. The evaluation time was from 8:00 to 18:00. Under natural solar irradiation, steam was generated and condensed on the transparent cover to form droplets, which were finally collected at the bottom of the device.( Figure 6B ) The average solar flux was ~0.68 kW m -2 , and the highest recorded outdoor temperature was 93 °C.( Figure 6C ) After a one-day test, a total of 25.69 grams of water was collected. Calculated based on the evaporator area of 34.54 cm 2 , the daily water collection was 7.44 L m -2 . This fresh water production was better than the previous records of desalination solar evaporators (~2.5 L m -2 , ~5 L m -2 ). In addition, more than 99.9% of the ions were removed during the solar evaporation process, and the ion concentration of the purified water was lower than the requirements of WHO and EPA.( Figure 6D )

[0068] The terms "about", "substantially", "essentially" and "approximately" used in this document are used to describe and explain minor variations. When used in conjunction with an event or situation, the term can refer to the situation where the event or situation occurs precisely, as well as the situation where the event or situation occurs approximately. The term "about" used in this document with respect to a given value or range generally means within ±10%, ±5%, ±1% or ±0.5% of the given value or range. A range can be expressed as from one endpoint to another endpoint or between two endpoints. Unless otherwise stated, all ranges disclosed in this disclosure include the endpoints. The term "substantially coplanar" can refer to two surfaces located within a few micrometers (μm) of the same plane, such as within 10 μm, 5 μm, 1 μm or 0.5 μm of the same plane. When referring to "substantially" the same numerical value or characteristic, the term may refer to a value within the range of the average value ±10%, ±5%, ±1% or ±0.5%.

[0069] The above description of the present invention is for illustrative and descriptive purposes only. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed. Many modifications and variations will be obvious to those skilled in the art.

[0070] These embodiments are selected and described in order to best explain the principles of the present invention and its practical applications, so that those skilled in the art can understand the various embodiments of the present invention and the various modifications suitable for a particular purpose.

Claims

1. A highly efficient buoyancy-driven convection-type 3D solar evaporator for simultaneous desalination and stable evaporation of high-salinity water, characterized in that: include: an interconnected porous matrix; and Photothermal materials; wherein the 3D solar evaporator comprises a funnel-shaped structure and large channels on the outer surface; The evaporation rate of the 3D solar evaporator is 1 kW m -2 At least 2.5 kg m -2 h -1 ;as well as The evaporator is capable of stably evaporating a salt solution or natural seawater having a salt concentration of at least 10% by weight.

2. The high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1 is characterized in that: The interconnected porous structure is selected from polyurethane, cellulose, alginate, polyvinyl alcohol, polyacrylamide or a combination thereof.

3. The high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1 is characterized in that: The photothermal material is selected from carbon nanotubes, carbon black, carbon nanodots, graphene or a combination thereof.

4. The high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1 is characterized in that: Its light absorption rate is at least 95%.

5. The high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1 is characterized in that: There is a temperature difference between the high-salt area and the main water.

6. The high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1 is characterized in that: The average size of the macrochannels is 500-1200 μm.

7. The high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1 is characterized in that: It can absorb 800μL of water in less than 0.2 seconds.

8. The high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1 is characterized in that: It can transport water to a height of 20mm in less than 50 seconds.

9. A manufacturing method for manufacturing a high-efficiency buoyancy-driven convection-type 3D solar evaporator according to claim 1, comprising: providing a first porous substrate; providing a second photothermal material; mixing the first porous matrix with the second photothermal material to form a third aqueous mixture; pouring the third aqueous mixture into a 3D printed silicon mold and freezing it at a temperature between -20°C and -90°C; and Freeze-dry to remove ice crystals.

10. The method according to claim 9, characterized in that The first porous matrix is ​​selected from polyurethane, cellulose, alginate, polyvinyl alcohol, polyacrylamide or a combination thereof.

11. The method according to claim 9, characterized in that The second photothermal material is selected from carbon nanotubes, carbon black, carbon nanodots, graphene or a combination thereof.

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