Solar evaporator with gradient pores and method of making the same

Abstract

The application provides a solar evaporator with gradient pores and a preparation method thereof. First, a two-dimensional nanometer material dispersion liquid, magnetic nano particles and sodium alginate are mixed to obtain a mixed solution, the mixed solution is placed in a mold, an external parallel electric field or a vertical magnetic field is constructed, and the mixed solution is immediately frozen in liquid nitrogen after treatment, and then freeze-drying is performed to obtain the solar evaporator with gradient pores. The application utilizes the lamellar structure of the two-dimensional nanometer material to move to the positive electrode under the electric field effect, or utilizes the magnetic attraction effect of the magnetic nano particles in the magnetic field to drive the two-dimensional nanometer material to move, constructs the two-dimensional nanometer material with different spatial concentration distribution in the base body, realizes the adjustment of the evaporator pore diameter, forms the gradient pore structure, becomes the ideal channel for water transmission, and obtains the solar evaporator with high water transmission rate, good light-heat performance and small heat loss. The preparation process is simple, the conditions are easy to control, the energy consumption is small, and the solar evaporator has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of evaporator technology, and more particularly to a solar evaporator with gradient holes and its preparation method. Background Technology

[0002] With the continuous increase in population, the shortage of freshwater resources has received widespread attention. Freshwater is an indispensable resource for human survival, but currently, usable groundwater and freshwater from lakes and rivers account for only 0.77% of the Earth's total water resources. Furthermore, with industrial development, water pollution caused by industrial emissions exacerbates the freshwater shortage problem. Seawater desalination is one of the important ways to solve the water shortage problem. Among all renewable energy sources, solar energy is considered the most abundant. Therefore, solar-driven interfacial evaporators have stood out among many freshwater production technologies and are considered the most promising and environmentally friendly strategy for alleviating the water crisis. In recent years, due to the advantages of energy saving and low cost, solar evaporators have become a focus of research in the field. The biggest advantage of solar evaporators is that their porous structure provides a large surface area. Under sunlight, the surface absorbs sufficient light, the surface temperature rises, causing vapor to escape and generate enough water vapor to collect water.

[0003] To date, many solar evaporators with porous structures have been designed and developed in the industry. For example, an invention patent (application number 202110126848.9) discloses the preparation of a corn starch / sodium alginate / MXene composite hydrogel and its application in seawater desalination. The method involves dissolving corn starch, sodium alginate, and MXene in deionized water to obtain a mixed solution. The solution is stirred to gelatinize the corn starch, and then a crosslinking agent is added for crosslinking to obtain the corn starch / sodium alginate / MXene composite hydrogel. This method combines biomass materials with light-absorbing materials, offering advantages such as being green, pollution-free, and low-cost. However, although this composite hydrogel has good hydrophilicity and light absorption, its pore structure is relatively simple. This simple hollow pore structure results in low water transport efficiency and evaporation rate, which is not advantageous in practical applications.

[0004] Furthermore, most reported methods for manufacturing high-quality evaporators are complex, with unfavorable water transport channels and poor water transfer rates. This limits vapor diffusion within the evaporator's porous structure, considered the biggest obstacle to further improving the water production capacity of solar evaporators. Additionally, most current evaporators have poor insulation, resulting in low evaporation rates. These processes typically require multiple steps and are carried out under special conditions such as high temperature or high vacuum, involving significant time and effort, leading to high costs and making them unsuitable for large-scale industrial production.

[0005] In view of this, it is necessary to design an improved solar evaporator with gradient holes and its preparation method to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a solar evaporator with gradient pores and its preparation method. Two-dimensional nanomaterials with a layered structure are selected as raw materials. They move towards the positive electrode under the effect of an electric field, or are driven to move by the magnetic attraction effect of magnetic nanoparticles in a magnetic field. Then, the pore size of the evaporator is adjusted by utilizing the layered structure of the two-dimensional material itself and a large number of nanoscale capillary channels to form a gradient pore structure, so as to become an ideal channel for water transmission, resulting in a solar evaporator with high water transmission rate, good photothermal performance and low heat loss.

[0007] To achieve the above-mentioned objective, this invention provides a method for preparing a solar evaporator with gradient holes, comprising the following steps:

[0008] S1. A two-dimensional nanomaterial dispersion, magnetic nanoparticles, and sodium alginate are mixed and mechanically stirred to obtain a mixed solution; the mass percentage concentration of sodium alginate in the mixed solution is 0.5% to 1%; the two-dimensional nanomaterial has a layered structure with a thickness of 1 to 5 nm;

[0009] S2. Place the mixed solution from step S1 into a mold, construct a parallel electric field outside the mold or place a magnet directly above the mold to construct a magnetic field, process for 2 to 6 minutes, and then immediately place it in liquid nitrogen to freeze for 20 to 40 minutes.

[0010] S3. Freeze-dry the material frozen in step S2 to obtain a solar evaporator with gradient holes.

[0011] As a further improvement of the present invention, in step S1, the mass percentage concentration of the two-dimensional nanomaterial in the mixed solution is 10% to 60%, and the mass percentage concentration of the magnetic nanoparticles is 0.5% to 1%.

[0012] As a further improvement of the present invention, in step S2, the voltage of the parallel electric field is controlled to be 10-20V.

[0013] As a further improvement of the present invention, in step S2, the magnetic field strength of the magnet is 3000GS; the distance between the lower surface of the magnet and the upper surface of the mold is 2-6cm.

[0014] As a further improvement of the present invention, in step S1, the two-dimensional nanomaterial includes one or more of Mxene, graphene, and black phosphorus, and the two-dimensional nanomaterial is preferably Mxene.

[0015] As a further improvement of the present invention, in step S1, the magnetic nanoparticles are magnetic iron oxide nanoparticles, preferably iron(II,III) oxide particles.

[0016] As a further improvement of the present invention, in step S3, the freeze-drying process involves freezing the material at -40 to -50°C for 24 hours, and then freeze-drying it at -50 to -60°C for 36 to 72 hours.

[0017] As a further improvement of the present invention, in step S1, the mechanical stirring time is 20 to 28 hours; the solvent in the mixed solution is water.

[0018] The present invention also provides a solar evaporator with gradient pores prepared by the preparation method described in any one of the above-mentioned methods. The solar evaporator is an aerogel composed of two-dimensional nanomaterials with a layered structure, magnetic nanoparticles and sodium alginate, and the solar evaporator has a micron-scale gradient pore structure.

[0019] As a further improvement of the present invention, the gradient hole structure has a three-dimensional interconnected integral channel structure, and the aperture of the gradient hole structure gradually increases from top to bottom in the vertical dimension, providing an ultra-fast water transmission channel for the solar evaporator.

[0020] As a further improvement of the present invention, the surface solar energy absorption rate of the solar evaporator reaches more than 97%.

[0021] The beneficial effects of this invention are:

[0022] 1. The present invention relates to a solar evaporator with gradient pores and its preparation method. First, a two-dimensional nanomaterial dispersion, magnetic nanoparticles, and sodium alginate are mixed to obtain a mixed solution. The mixed solution is placed in a mold, and a parallel electric field or a vertical magnetic field is constructed outside the mold. After processing for a certain period, the solution is immediately placed in liquid nitrogen for freezing. Finally, the frozen material is freeze-dried to obtain the solar evaporator with gradient pores. This invention uses layered two-dimensional nanomaterials as raw materials. After constructing an electric field, the electric field effect causes the two-dimensional nanomaterials to move towards the positive electrode. Alternatively, after constructing a magnetic field, the magnetic attraction effect of the magnetic nanoparticles drives the two-dimensional nanomaterials to move. Furthermore, the layered structure and numerous nanoscale capillary channels of the two-dimensional nanomaterials themselves are used to adjust the pore size of the evaporator, forming a gradient pore structure. This becomes an ideal channel for water transport, resulting in a solar evaporator with high water transport rate, good photothermal performance, and low heat loss. This is of great significance in broadening the structural characteristics of solar evaporators. Moreover, the preparation process of this invention is simple, the conditions are easy to control, the cost is low, and the energy consumption is low, showing broad application prospects in seawater desalination, steam power generation, and wastewater purification.

[0023] 2. In the preparation method of this invention, the ultra-high electrical conductivity of two-dimensional nanomaterials is utilized under an electric field. After mixing the two-dimensional nanomaterials with magnetic nanoparticles in a magnetic field, the magnetic attraction effect of the magnetic nanoparticles is utilized, causing the two-dimensional nanomaterials uniformly distributed in the sodium alginate matrix to move in a specific direction (towards the positive pole or the magnet). This causes them to aggregate in the region near the positive pole or magnet, resulting in a smaller spatial concentration distribution of the two-dimensional nanomaterials. This leads to smaller pore sizes in this region after freeze-drying. Conversely, the spatial concentration distribution of the two-dimensional nanomaterials increases further away from the positive pole or magnet, resulting in larger pore sizes in the aerogel. This process creates a solar evaporator with gradient pores. Furthermore, the gradient distribution of the two-dimensional nanomaterials and magnetic nanoparticles in the sodium alginate matrix also results in a small pore size on the surface of the evaporator during application. This allows for multiple light reflections, leading to excellent light absorption and photothermal performance, thus improving the photothermal conversion efficiency of the solar evaporator and consequently increasing its evaporation rate.

[0024] 3. This invention utilizes a two-dimensional layered structure of Mxene, which possesses high electrical conductivity and contains numerous nanocapillary channels, exhibiting a strong response under an electric field. Furthermore, the uniform mixing of the two-dimensional layered Mxene with magnetic iron oxide nanoparticles facilitates the control of Mxene movement when the magnetic iron oxide nanoparticles move under a magnetic field, thereby constructing Mxene with varying spatial concentrations within a sodium alginate matrix, resulting in a gradient pore structure. The presence of hydrophilic groups on the Mxene surface facilitates the construction of hydrophilic channels for rapid water transport, enabling ultrafast water transfer. Additionally, Mxene exhibits excellent photothermal conversion efficiency, demonstrating good light absorption in solar evaporators. This invention also introduces a sodium alginate-Mxene composite into the evaporator, improving its mechanical properties and elasticity, thereby enhancing the practical performance of the solar evaporator.

[0025] 4. The solar evaporator with gradient pores of this invention features a densely distributed, small-diameter pore layer on the surface, with the pore size increasing vertically throughout the structure. This structure offers the advantage of rapid water transport during evaporation, facilitating steam escape. Furthermore, the pore size remains within the micrometer range, resulting in a large specific surface area. This promotes rapid water transport and evaporation while also providing excellent thermal insulation. The gradient pore structure allows for different thermal insulation properties between different gradient layers, further reducing heat loss and thus increasing the evaporation rate of the evaporator. The solar evaporator prepared by this invention achieves a surface light absorption rate of over 97%, exhibiting excellent photothermal performance. Attached Figure Description

[0026] Figure 1The cross-sectional microstructure diagram of the solar evaporator with gradient holes prepared in Example 1 is shown.

[0027] Figure 2 The cross-sectional microstructure diagram of the solar evaporator with gradient holes prepared in Example 2 is shown. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0030] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0031] A method for preparing a solar evaporator with gradient holes includes the following steps:

[0032] S1. A two-dimensional nanomaterial dispersion, magnetic nanoparticles, and sodium alginate are mixed and mechanically stirred to obtain a mixed solution. The mass percentage concentration of sodium alginate in the mixed solution is 0.5% to 1%. The two-dimensional nanomaterial has a layered structure with a thickness of 1 to 5 nm.

[0033] By introducing sodium alginate into composites with two-dimensional nanomaterials and magnetic nanoparticles, the mechanical properties and elasticity of the evaporator are improved, thus enhancing the practical performance of the solar evaporator. Furthermore, the concentration of sodium alginate should not be too high. If the concentration is too high, it will cause significant resistance to the electric field effect of the two-dimensional nanomaterials and the magnetic effect of the two-dimensional nanomaterials and magnetic nanoparticles, i.e., the movement of the two-dimensional nanomaterials driven by the magnetic nanoparticles in the matrix, which is not conducive to the preparation of solar evaporators with gradient pores.

[0034] S2. Place the mixed solution from step S1 into a mold, construct a parallel electric field outside the mold or place a magnet directly above the mold to construct a magnetic field, process for 2 to 6 minutes, and then immediately place it in liquid nitrogen to freeze for 20 to 40 minutes.

[0035] S3. Freeze-dry the material frozen in step S2 to obtain a solar evaporator with gradient holes.

[0036] Specifically, this preparation method utilizes the ultra-high electrical conductivity of two-dimensional nanomaterials with a layered structure under an electric field. After mixing the two-dimensional nanomaterials with magnetic nanoparticles in a magnetic field, the magnetic attraction effect of the nanoparticles causes the uniformly distributed two-dimensional nanomaterials in the sodium alginate matrix to move in a specific direction (towards the positive pole or the magnet). This causes them to aggregate in the region near the positive pole or magnet, resulting in a smaller spatial concentration distribution of the two-dimensional nanomaterials. This leads to smaller pore sizes in this region after freeze-drying. Conversely, the spatial concentration distribution increases further away from the positive pole or magnet, resulting in larger pore sizes in the resulting aerogel. This creates a solar evaporator with gradient pores. Furthermore, the gradient distribution of the two-dimensional nanomaterials and magnetic nanoparticles within the sodium alginate matrix in this solar evaporator results in a smaller surface pore size due to the combined effects of the two-dimensional nanomaterials and magnetic nanoparticles. This allows for multiple light reflections, leading to excellent light absorption and photothermal performance, thus improving the photothermal conversion efficiency and evaporation rate of the solar evaporator.

[0037] Specifically, in step S1, the mass percentage concentration of two-dimensional nanomaterials in the mixed solution is 10%–60%. These two-dimensional nanomaterials not only possess excellent electrical conductivity but also good photothermal conversion properties. They include one or more of Mxene, graphene, and black phosphorus, with Mxene being the preferred material. The raw material size used to prepare Mxene is 100–500 nm. The use of a two-dimensional layered structure of Mxene provides high electrical conductivity and contains numerous nanocapillary channels, exhibiting a strong response under an electric field. Furthermore, the uniform mixing of the two-dimensional layered structure of Mxene with magnetic nanoparticles facilitates the control of Mxene movement when the magnetic nanoparticles move under a magnetic field, thereby constructing Mxene with different spatial concentration distributions within the sodium alginate matrix, resulting in a gradient pore structure. The surface of Mxene contains hydrophilic groups, which facilitates the construction of hydrophilic channels for rapid water transport, enabling ultrafast water transport. Additionally, Mxene exhibits excellent photothermal conversion efficiency and can play a significant role in light absorption in solar evaporators.

[0038] The magnetic nanoparticles are magnetic iron oxide nanoparticles, preferably iron(III) oxide particles.

[0039] In step S2, the voltage of the parallel electric field is controlled to be 10-20V. By controlling the energizing time and voltage of the parallel electric field, the size of the gradient aperture in the solar evaporator is adjusted. If the energizing time is too long or the voltage is too high, the aperture on the evaporator surface will be too small, and salt deposition will easily occur on the surface. If the energizing time is too short or the voltage is too low, the aperture change of the evaporator will not be obvious, and it will be difficult to form a gradient aperture structure.

[0040] Alternatively, the magnetic field strength of the magnet can be 3000GS; the distance between the lower surface of the magnet and the upper surface of the mold (magnetic attraction height) can be 2-6cm. The size of the gradient aperture in the solar evaporator can be adjusted by controlling the magnetic attraction height; if the magnetic attraction height is too small or 0, the aperture on the evaporator surface will be small, and salt deposition will easily occur on the surface; if the magnetic attraction height is too large, the aperture change of the evaporator will not be obvious, and it will be difficult to form a gradient aperture structure.

[0041] In some specific embodiments, in step S3, the freeze-drying process involves freezing the material at -40 to -50°C for 24 hours, and then freeze-drying it at -50 to -60°C for 36 to 72 hours.

[0042] In some specific embodiments, in step S1, the mechanical stirring time is 20 to 28 hours; the solvent in the mixed solution is water.

[0043] A solar evaporator with gradient pores is an aerogel composed of layered two-dimensional nanomaterials, magnetic nanoparticles, and sodium alginate. The evaporator features a micron-scale gradient pore structure, with the pore size gradually increasing in the vertical dimension. This gradient pore structure has a three-dimensional interconnected channel structure, providing ultrafast water transport channels for the solar evaporator. The surface solar energy absorption rate of the solar evaporator reaches over 97%.

[0044] In particular, the solar evaporator uses two-dimensional nanomaterials with a layered structure as raw materials. After an electric field is constructed, the electric field effect causes the two-dimensional nanomaterials to move towards the positive electrode, or the magnetic attraction effect of magnetic nanoparticles drives the two-dimensional nanomaterials to move. Then, by utilizing the layered structure of the two-dimensional nanomaterials and a large number of nanoscale capillary channels, a gradient pore structure is formed, which becomes an ideal channel for water transmission. This results in a solar evaporator with high water transmission rate, good photothermal performance, and low heat loss, which is of great significance in broadening the structural characteristics of solar evaporators.

[0045] Specifically, the pore size of the gradient pores in the solar evaporator gradually increases in the vertical dimension, with the bottom containing the larger pores contacting the water surface during application. The surface layer of the solar evaporator has small, densely distributed pores, and the pore size increases progressively downwards from the surface. The advantage of this structure is that it allows for rapid water transport during evaporation, facilitating steam escape. Furthermore, the pore size remains within the micrometer range, resulting in a large specific surface area. While promoting rapid water transport and evaporation, it also exhibits excellent thermal insulation performance. The different thermal insulation properties between the different layers of the gradient pore structure further reduce heat loss, thereby increasing the evaporation rate of the evaporator.

[0046] Example 1

[0047] This embodiment provides a solar evaporator with gradient holes and its preparation method, which includes the following steps:

[0048] S1. Mix Mxene dispersion, iron oxide particles and sodium alginate, and stir mechanically to obtain a mixed solution; in the mixed solution, the mass percentage concentration of Mxene is 60%, the mass percentage concentration of sodium alginate is 0.5%, and the mass percentage concentration of iron oxide particles is 0.5%.

[0049] S2. Place the mixed solution from step S1 into a mold and construct a parallel electric field outside the mold. Due to the electronegativity of Mxene, the parallel electric field is constructed by using copper sheets. Place two copper sheets of the same size on the top and bottom of the mold, respectively, with the top of the mold as the positive electrode and the bottom as the negative electrode. Connect them with wires to form a circuit and apply a voltage to form a parallel electric field. The voltage is controlled at 15V. After energizing for 5 minutes, immediately place it in liquid nitrogen to freeze for 30 minutes.

[0050] S3. The material frozen in step S2 is freeze-dried. The freeze-drying process is to freeze at -45℃ for 24 hours and freeze-dry at -51.5℃ for 48 hours to obtain a solar evaporator with gradient holes.

[0051] The surface pore diameter, middle pore diameter, and bottom pore diameter of the solar evaporator with gradient pores prepared in Example 1 were measured and statistically analyzed using a mercury porosimeter test method. The results showed that the average pore diameter on the surface was 8.24 μm, the average pore diameter in the middle was 10.60 μm, and the average pore diameter at the bottom was 17.23 μm.

[0052] Please see Figure 1 The figure shows a cross-sectional microstructure of the solar evaporator with gradient holes prepared in Example 1, where (a) is the surface, (b) is the middle, and (c) is the bottom. As can be seen from the figure, the pore size of each layer of the solar evaporator is different in the vertical direction, indicating that the solar evaporator with gradient holes was successfully prepared in this example, and the pore size gradually increases from the surface layer to the bottom layer.

[0053] The light absorption performance and heat insulation performance of different layers of the solar evaporator prepared in Example 1 were tested individually, and the results are shown in Table 1.

[0054] Table 1. Performance test results of different layers of the solar evaporator in Example 1.

[0055] Average pore size (μm) Light absorbance (%) <![CDATA[Thermal conductivity (wm -1 k -1 )]]> Surface layer 8.24 98.33 0.108 Intermediate layer 10.60 87.61 0.136 bottom layer 17.23 72.53 0.187

[0056] Table 1 shows that the light absorption performance of each layer in the solar evaporator with gradient apertures varies with different aperture sizes, with the light absorption value gradually decreasing from 98.33% to 72.53%, indicating that different aperture sizes have a certain impact on light absorption; the thermal conductivity also gradually decreases from 0.108 W / m² for the surface structure. -1 k -1 0.187wm to the bottom structure -1 k -1 This indicates that the thermal conductivity varies depending on the size of the pores.

[0057] Example 2

[0058] This embodiment provides a solar evaporator with gradient holes and its preparation method. Compared with Embodiment 1, the difference is that in step S2, a parallel electric field is not constructed. Instead, a magnet (3000GS) is placed directly above the mold. After 5 minutes of magnetic attraction, the magnetic attraction height is 5cm. The rest is roughly the same as Embodiment 1, and will not be described again here.

[0059] The surface pore diameter, middle pore diameter, and bottom pore diameter of the solar evaporator with gradient pores prepared in Example 2 were measured and statistically analyzed using a mercury porosimeter test method. The results showed that the average pore diameter on the surface was 7.75 μm, the average pore diameter in the middle was 10.64 μm, and the average pore diameter at the bottom was 16.74 μm.

[0060] Please see Figure 2 The figure shows a cross-sectional microstructure of the solar evaporator with a gradient pore structure prepared in Example 2, where (a) is the surface, (b) is the middle, and (c) is the bottom. As can be seen from the figure, the pore size of each layer of the solar evaporator is different in the vertical direction, indicating that a solar evaporator with gradient pores was successfully prepared under the action of a magnetic field, and the pore size gradually increases from the surface layer to the bottom layer.

[0061] The light absorption performance and heat insulation performance of different layers of the solar evaporator prepared in Example 2 were tested individually, and the results are shown in Table 2.

[0062] Table 2. Performance test results of different layers of the solar evaporator in Example 2.

[0063] Average pore size (μm) Light absorbance (%) <![CDATA[Thermal conductivity (wm -1 k -1 )]]> Surface layer 7.75 97.87 0.106 Intermediate layer 10.64 89.01 0.123 bottom layer 16.74 71.89 0.177

[0064] Table 2 shows that the light absorption performance of each layer in the solar evaporator with a gradient pore structure varies depending on the pore size. The light absorption value gradually decreases from 97.87% to 71.89%, indicating that different pore sizes have a certain impact on light absorption. The thermal conductivity also gradually decreases from 0.106 W / m² at the surface. -1 k -1 0.177wm at the bottom -1 k -1This indicates that the thermal conductivity varies depending on the size of the pores.

[0065] Comparative Example 1

[0066] Comparative Example 1 provides a solar evaporator and its preparation method. The difference from Example 1 is that in step S2, a parallel electric field is not constructed outside the mold. The rest is roughly the same as Example 1 and will not be repeated here.

[0067] Comparative Example 2

[0068] Comparative Example 2 provides a solar evaporator and its preparation method. The difference from Example 1 is that in step S1, the mass percentage concentration of sodium alginate (SA) in the mixed solution is 2%, and the rest is roughly the same as in Example 1, which will not be repeated here.

[0069] Comparative Example 3

[0070] Comparative Example 3 provides a solar evaporator and its preparation method. The difference from Example 2 is that in step S1, iron oxide particles were not added. The rest is roughly the same as Example 2, and will not be repeated here.

[0071] After characterizing the pore size of the solar evaporators prepared in Comparative Examples 1-3, it was found that in Comparative Example 1, without constructing either a parallel electric field or a magnetic field, the pore structure of the resulting solar evaporator exhibited a randomly distributed pore size, rather than a gradient pore structure. In Comparative Example 2, when the sodium alginate concentration was 2%, the entire pore structure was almost entirely formed by SA, and the MXene nanosheets could not move, ultimately failing to form a solar evaporator with a gradient pore structure. In Comparative Example 3, without the addition of iron oxide particles, the movement of the MXene nanosheets lacked momentum, and a solar evaporator with a distinct gradient pore structure was not formed.

[0072] In summary, this invention provides a solar evaporator with gradient pores and its preparation method. Two-dimensional nanomaterials with a layered structure are selected as raw materials. After an electric field is constructed, the electric field effect causes the two-dimensional nanomaterials to move towards the positive electrode. Alternatively, after a magnetic field is constructed, the magnetic attraction effect of the magnetic nanoparticles drives the two-dimensional nanomaterials to move. Furthermore, the layered structure and numerous nanoscale capillary channels of the two-dimensional nanomaterials themselves are used to adjust the pore size of the evaporator, forming a gradient pore structure. This becomes an ideal channel for water transport, resulting in a solar evaporator with high water transport rate, good photothermal performance, and low heat loss. In the solar evaporator with gradient pores prepared by this invention, the two-dimensional nanomaterials and magnetic nanoparticles are also distributed in a gradient within the sodium alginate matrix. This results in smaller pores on the surface of the evaporator due to the two-dimensional nanomaterials and magnetic nanoparticles, leading to multiple reflections of light, excellent light absorption performance, and excellent photothermal performance. This improves the photothermal conversion efficiency of the solar evaporator, thereby increasing the evaporation rate. The solar evaporator and its preparation method of the present invention are of great significance in broadening the structural characteristics of solar evaporators. Moreover, the preparation process is simple, the conditions are easy to control, the cost is low, and the energy consumption is low. It has broad application prospects in the fields of seawater desalination, steam power generation, and wastewater purification.

[0073] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a solar evaporator with gradient holes, characterized in that, Includes the following steps: S1. A two-dimensional nanomaterial dispersion, magnetic nanoparticles, and sodium alginate are mixed and mechanically stirred to obtain a mixed solution; in the mixed solution, the mass percentage concentration of sodium alginate is 0.5%~1%; the two-dimensional nanomaterial has a layered structure with a thickness of 1~5nm; S2. Place the mixed solution from step S1 into a mold, construct a parallel electric field outside the mold or place a magnet directly above the mold to construct a magnetic field, process for 2-6 minutes, and then immediately place it in liquid nitrogen to freeze for 20-40 minutes. S3. Freeze-dry the material frozen in step S2 to obtain a solar evaporator with gradient holes.

2. The method for preparing a solar evaporator with gradient holes according to claim 1, characterized in that, In step S1, the mass percentage concentration of the two-dimensional nanomaterial in the mixed solution is 10% to 60%, and the mass percentage concentration of the magnetic nanoparticles is 0.5% to 1%.

3. The method for preparing a solar evaporator with gradient holes according to claim 1, characterized in that, In step S2, the voltage of the parallel electric field is controlled to be 10~20V.

4. The method for preparing a solar evaporator with gradient holes according to claim 1, characterized in that, In step S2, the magnetic field strength of the magnet is 3000GS; the distance between the lower surface of the magnet and the upper surface of the mold is 2~6cm.

5. The method for preparing a solar evaporator with gradient holes according to claim 1, characterized in that, In step S1, the two-dimensional nanomaterial includes one or more of Mxene, graphene, and black phosphorus.

6. The method for preparing a solar evaporator with gradient holes according to claim 5, characterized in that, The two-dimensional nanomaterial is Mxene.

7. The method for preparing a solar evaporator with gradient holes according to claim 1, characterized in that, In step S3, the freeze-drying process involves freezing the material at -40~-50℃ for 24 hours, and then freeze-drying it at -50~-60℃ for 36~72 hours.

8. The method for preparing a solar evaporator with gradient holes according to claim 1, characterized in that... The stirring time is 20-28 hours; the solvent in the mixed solution is water.

9. A solar evaporator with gradient holes prepared by the preparation method according to any one of claims 1-8, characterized in that, The solar evaporator is an aerogel composed of two-dimensional nanomaterials with a layered structure, magnetic nanoparticles, and sodium alginate, and has a micron-scale gradient pore structure.

10. The solar evaporator with gradient holes according to claim 9, characterized in that, The gradient hole structure has a three-dimensional interconnected integral channel structure, and the aperture of the gradient hole structure gradually increases from top to bottom in the vertical dimension, providing an ultra-fast water transport channel for the solar evaporator.

11. The solar evaporator with gradient holes according to claim 9, characterized in that, The surface solar energy absorption rate of the solar evaporator reaches over 97%.

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