An evaporator of boron-doped carbon foam for seawater desalination and a preparation method thereof

Abstract

The present application relates to the technical field of seawater desalination, and particularly relates to a boron-doped carbon foam evaporator for seawater desalination and a preparation method thereof, and the evaporator comprises a photothermal material and a heat insulation layer substrate for floating on the surface of seawater, the photothermal material is embedded on the heat insulation layer substrate, the upper end of the photothermal material penetrates through the upper surface of the heat insulation layer substrate, the lower end of the photothermal material penetrates through the lower surface of the heat insulation layer substrate, and the photothermal material is prepared by the following preparation method, which comprises the following steps: S1, soaking melamine foam in boric acid, and then placing the melamine foam in an oven for drying to obtain a BMF precursor; S2, placing the BMF precursor obtained in step S1 in a tube furnace for calcination under a N2 atmosphere to obtain the photothermal material.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination technology, and in particular to an evaporator for seawater desalination using boron-doped carbon foam and its preparation method. Background Technology

[0002] Freshwater resources are essential for human life, agriculture, industry, and ecosystems. However, due to factors such as global population growth, industrialization, and climate change, freshwater resources are rapidly depleting. Global demand for water is constantly increasing; water and energy are indispensable commodities for life on Earth. With 70% of the Earth's surface covered by seawater, seawater desalination has become one of the most critical water treatment solutions globally to meet the increasing water demands brought about by rapid population growth, economic expansion, and agricultural development. Traditional seawater desalination technologies typically employ multi-effect flash distillation (MED), multi-stage flash distillation (MSF), vapor compression (MVR), and reverse osmosis (RO), but these technologies suffer from environmental pollution, high costs, or excessive energy consumption. Compared to traditional seawater desalination technologies, solar-driven seawater desalination technology utilizes sunlight as a renewable energy source to address the shortage of clean water resources, has a smaller environmental impact, and is a sustainable and environmentally friendly method. Furthermore, solar desalination technology can be implemented using low-cost materials. Therefore, solar-powered seawater desalination has enormous application potential and has received widespread attention from researchers in recent years. To date, solar-driven seawater desalination systems have mainly undergone three heating methods: (1) the photothermal material is fixed at the bottom of the water body for heating, i.e., bottom heating; (2) the photothermal material is dispersed in the water body to achieve overall heating and evaporation of the water body, i.e., volume heating; and (3) the photothermal material is fixed on the surface of the water body through self-floating or self-assembly to achieve local interface heating of the water body, i.e., interface heating evaporation. The current mainstream interface heating method effectively improves the problems of heat conduction and heat convection loss in the water body. Due to the presence of an isolation layer, the photothermal material at the top does not directly contact the water body, and the heat can be confined to the interface between the gas phase and the liquid phase. Only the water at the interface is heated, thereby achieving excellent evaporation performance and efficient photothermal conversion.

[0003] In recent years, devices based on interfacial evaporation have gained widespread attention and in-depth research. To improve evaporation rates and efficiency, researchers have focused on optimizing evaporator structures and synthesizing highly efficient photothermal conversion materials. Shen et al. used modified carbon nanotubes as the photothermal evaporation layer, loaded onto a substrate with EPE foam as the insulation layer and cotton swabs as the absorbent layer, and obtained 1.41 kg m³ of [material name missing] under sunlight irradiation. -2 h -1The high evaporation rate and 91.1% energy utilization efficiency demonstrate the usability of the interfacial evaporation system. However, due to the theoretical limits of the evaporation process in 2D interfacial evaporators, further improvements to the interfacial evaporator structure are needed. Therefore, integrated 2.5D and 3D interfacial evaporators have also received widespread attention in recent years. Liu et al. reported an interconnected, open-cell 2.5D Cu / CuO foam-based photothermal evaporator, which adds a vertical dimension to the traditional 2D structure by exposing one end of the planar structure to air, thus expanding the exposure area and achieving a evaporation rate of 4.1 kg m³ under a single solar irradiation. -2 h -1 The ultra-high evaporation rate was achieved. Zhang et al. designed a neatly arranged 3D array of freeze-dried graphene foam using lasers, and by achieving multiple reflections of light within the array, they achieved a evaporation rate of 2.01 kg / m³ under sunlight. -2 h -1 The evaporation rate was improved. Luo et al. introduced an arch-shaped structure, which, by adjusting the curvature, could expand the evaporation area and accelerate steam overflow. Under one solar irradiation, the evaporation efficiency reached 125.6%, exceeding the theoretical limit. In addition, conical, spherical, cup-shaped, bowl-shaped, tree-shaped, and wavy structures were widely used in the structural design of multidimensional interface evaporators, significantly improving the evaporation performance of interface evaporators.

[0004] Patent CN 111072087 A discloses a three-dimensional seawater evaporator and its application. The three-dimensional seawater evaporator includes a channel structure for water absorption and transport, and a reactor unit for photothermal conversion. The reactor unit is located at one end of the channel structure, and the channel structure and reactor unit together form a three-dimensional structure. The reactor unit includes polymer functionalized paper. The evaporation capacity of this three-dimensional seawater evaporator is 2.6 kg m³. -2 h -1 The above results show that the rejection rate of ions in seawater is over 99.98%, with relatively low evaporation.

[0005] In summary, interfacial evaporators can generate heat through photothermal conversion on their surface to fully heat the localized water on the surface of the photothermal material, causing it to evaporate. However, the surface of the interfacial evaporator experiences convective dissipation with the cooler air, and due to the limitations of its 2D surface structure, it cannot fully utilize the scattered irradiance energy from the surrounding environment, thus limiting its photothermal utilization rate. Currently, effectively enhancing the efficiency of light irradiation utilization through methods such as controlling the microstructure of the irradiated surface, changing its shape, or increasing the irradiated area under equal projected areas has become a key issue. Therefore, developing an evaporator with simple photothermal material fabrication processes, high photothermal conversion efficiency, efficient and stable water evaporation rate, excellent desalination performance, and practical application capabilities is an urgent problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide an evaporator for boron-doped carbon foam used in seawater desalination and its preparation method, which can solve the above-mentioned technical problems.

[0007] This invention provides an evaporator for boron-doped carbon foam used in seawater desalination, comprising a photothermal material and a heat-insulating layer substrate for floating on the seawater surface. The photothermal material is embedded in the heat-insulating layer substrate, with its upper end penetrating the upper surface of the heat-insulating layer substrate and its lower end penetrating the lower surface of the heat-insulating layer substrate. The photothermal material is prepared by the following method, which includes:

[0008] Step S1: Soak melamine foam in boric acid, and then place it in an oven to dry to obtain BMF precursor;

[0009] Step S2: The BMF precursor obtained in step S1 is placed in a tube furnace and calcined under N2 atmosphere to prepare the photothermal material.

[0010] Preferably, the base of the insulation layer is made of polyethylene foam board.

[0011] Preferably, the photothermal material has a cuboid structure.

[0012] Preferably, the concentration of boric acid in step S1 is 0.05-0.5 mol / L.

[0013] Preferably, the concentration of boric acid in step S1 is 0.2 mol / L.

[0014] Preferably, the calcination temperature in step S2 is 500°C and the calcination time is 10 min.

[0015] The present invention also provides a method for preparing the above-mentioned evaporator, comprising the following steps:

[0016] Using a 5cm diameter polyethylene foam board as the insulation layer base, the photothermal material is embedded in the insulation layer base. The evaporator surface is kept under standard sunlight. The lower end of the photothermal material protrudes 0.5cm from the lower surface of the insulation layer base, and the upper end of the photothermal material penetrates the upper surface of the insulation layer base.

[0017] Preferably, the upper end of the photothermal material penetrates through the upper surface of the heat insulation layer substrate and is flush with the upper surface of the heat insulation layer substrate.

[0018] Preferably, the upper end of the photothermal material penetrates the upper surface of the heat insulation layer substrate and extends 2.5 cm above the upper surface of the heat insulation layer substrate.

[0019] Preferably, multiple photothermal materials are embedded in the heat insulation layer substrate in the same manner, wherein the upper end of the photothermal material penetrates through the upper surface of the heat insulation layer substrate and is 2.5 cm higher than the upper surface of the heat insulation layer substrate, and adjacent photothermal materials are spaced apart and maintain a certain distance from each other to obtain an array-type photothermal evaporator.

[0020] Beneficial effects:

[0021] This invention prepares an evaporator by embedding photothermal materials into a heat-insulating substrate. The boron-doped carbon foam photothermal material is prepared using a simple impregnation-calcination synthesis method. The raw materials are mixed and impregnated, then thoroughly dried in an oven to obtain a precursor. The precursor is then calcined to obtain the catalyst. The preparation process is characterized by mild reaction conditions, simple steps, suitability for large-scale production, and readily available and inexpensive raw materials. The preparation revealed that the numerous pores and network structure within the boron-doped carbon foam material allow for capillary action, transporting water from the bottom of the foam to the upper illuminated surface. The surface water is then heated and evaporated through photothermal conversion. The hydrophilic surface reduces the surface tension of the liquid, driving it into the capillary more quickly and ensuring free flow within the capillary, thus effectively enhancing capillary action. This allows the liquid to be transported to a higher height, ensuring continuous water transport and stable evaporation in the 3D photothermal evaporator. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 These are schematic diagrams of the evaporators prepared in Examples 1-3 of the present invention, wherein (a) is a schematic diagram of Example 1, (b) is a schematic diagram of Example 2, and (c) is a schematic diagram of Example 3;

[0024] Figure 2 These are schematic diagrams showing the parameter changes of different photothermal materials and evaporators made of different photothermal materials obtained in Experiment Examples 1-6 of this invention; (a) Water mass change curves of different BCFs during water evaporation within 1 hour; (b) Surface temperature changes of evaporators with different BCF interfaces within 1 hour; (c) Evaporation rate and evaporation efficiency of different BCF materials; (d) Equivalent enthalpy of vaporization of different BCF materials;

[0025] Figure 3These are schematic diagrams showing the results of continuous water evaporation tests in simulated seawater for each evaporator prepared in Examples 1-3; (a) 10-hour continuous water evaporation test results of the interface evaporator in Example 1 in simulated seawater; (b) 10-hour continuous water evaporation test results of the single 3D photothermal evaporator in Example 2 in simulated seawater; (c) 10-hour water evaporation test results of the array evaporator in Example 3 in simulated seawater; (d) Images of the continuous evaporation test process of the array evaporator in Example 3 in simulated seawater (from left to right, from top to bottom); (e) Na+ before and after seawater desalination. + Mg 2+ K + Ca 2+ ICP test results;

[0026] Figure 4 The following is a schematic diagram of the specific working data of the evaporator of the present invention: (a) A physical picture of the outdoor evaporation device, which adopts an array-type evaporator with multiple units set horizontally and vertically; (b) A schematic diagram of the water collection process of the outdoor evaporation device; (c) The actual amount of water collected by outdoor evaporation over 5 consecutive days; (d) The changes in outdoor light intensity and surface temperature corresponding to the first and third days. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Example 1

[0031] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.2 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.2 photothermal material.

[0032] The constructed evaporator uses a 5cm diameter polyethylene foam board (EPE foam) as the insulation layer base. The prepared photothermal material is embedded in the polyethylene foam board (EPE foam), ensuring the evaporator surface is exposed to standard sunlight. The portion of the lower end protruding from the EPE foam surface is maintained at 0.5cm. The prepared photothermal material is then inserted into the EPE foam until the upper end is just exposed and flush with the upper surface of the EPE foam, thus obtaining the interface-type evaporator.

[0033] Example 2

[0034] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.2 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.2 photothermal material.

[0035] The constructed evaporator uses a 5cm diameter polyethylene foam board (EPE foam) as the insulation layer base. The prepared photothermal material is embedded in the EPE foam board, ensuring the evaporator surface is exposed to standard sunlight. The lower portion protruding from the EPE foam surface is maintained at 0.5cm. When the upper end of the prepared photothermal material extends above the EPE foam surface, it forms a single 3D photothermal evaporator. The evaporator height is adjusted to 2.5cm, but can also be adjusted to 0.5, 1, 1.5, 2, or 3cm according to actual needs.

[0036] Example 3

[0037] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.2 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.2 photothermal material.

[0038] The constructed evaporator uses a 5cm diameter polyethylene foam board (EPE foam) as the insulation layer base. Four of the prepared photothermal materials are embedded in the EPE foam board, ensuring the evaporator surface is exposed to standard sunlight. The portion of the lower end protruding from the EPE foam surface is maintained at 0.5cm. The four prepared photothermal materials are inserted into the EPE foam in the same manner to construct an array-type evaporator with a height of 2.5cm. Maintaining a certain distance between them results in an array-type photothermal evaporator. The arrangement distance is adjusted to 5mm, but can also be adjusted to 2mm, 8mm, etc., according to actual needs to construct the array-type evaporator.

[0039] Experimental Example 1

[0040] CF photothermal material was prepared by calcining commercial melamine foam (MF) at 500°C for 10 minutes in a tube furnace under N2 atmosphere.

[0041] Experimental Example 2

[0042] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.01 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.01 photothermal material.

[0043] Experimental Example 3

[0044] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.05 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.05 photothermal material.

[0045] Test Example 4

[0046] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.1 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.1 photothermal material.

[0047] Experimental Example 5

[0048] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.2 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.2 photothermal material.

[0049] Experimental Example 6

[0050] Using boric acid as the boron source, commercial melamine foam (MF) was fully soaked in 0.5 mol / L boric acid, and then dried in an oven to obtain the precursor of BMF photothermal material. Subsequently, it was calcined in a tube furnace at 500℃ for 10 min under N2 atmosphere to prepare BCF-0.5 photothermal material.

[0051] The photothermal materials prepared in Examples 1-6, combined with the heat insulation layer substrate, can be used to manufacture various evaporators according to the preparation method of this invention, which will not be described in detail here.

[0052] The boron-doped carbon foam photothermal material prepared in this invention employs a simple impregnation-calcination synthesis method. The raw materials are mixed and impregnated, then thoroughly dried in an oven to obtain a precursor. The precursor is then calcined to obtain the photothermal material. The preparation process involves mild reaction conditions, simple steps, and is suitable for large-scale production. Furthermore, the raw materials used are inexpensive and readily available. The preparation process revealed that the numerous pores and network structure within the boron-doped carbon foam material allow for capillary action, transporting moisture from the bottom of the foam to the upper light-illuminated surface. The surface moisture is then heated and evaporated through photothermal conversion. The hydrophilic surface reduces the surface tension of the liquid, driving it to enter the capillary more quickly and ensuring free flow within the capillary, thus effectively enhancing capillary action. This allows the liquid to be transported to a higher height, ensuring continuous moisture transport and stable evaporation in the 3D photothermal evaporator. The water droplet contact angle can directly reflect the wetting properties of a material surface. Dynamic changes in the water droplet contact angle on CF and different BCF materials revealed that with boron doping, droplets on BCF-0.01 and BCF-0.05 surfaces reached a stable state within 1 second, with a contact angle of approximately 130°, significantly smaller than the steady-state contact angle of CF. However, with further increases in boron doping in the boron-doped carbon foam, the steady-state contact angles of BCF-0.1 to BCF-0.5 reached 0°, exhibiting superhydrophilic properties. Furthermore, the times to reach a stable state were 0.4 s, 0.3 s, and 0.01 s, respectively, decreasing with increasing boron doping concentration. These results indicate that superhydrophilic carbon materials have been successfully developed through boron doping. The photothermal evaporation rates and photothermal efficiencies of six different materials were calculated. The evaporation rates of the six materials from CF to BCF-0.5 were 1.12, 1.43, 1.56, 1.79, 1.90, and 1.22 kg m³, respectively. -2 h -1 The evaporation efficiencies were 68.1%, 80.3%, 86.1%, 87.1%, 89.7%, and 67.3%, respectively. Without boron doping, the CF surface exhibits hydrophobic properties but can maintain a relatively slow photothermal evaporation process. This indicates that the porous structure inside the CF can maintain capillary action for water transport, while interfacial evaporation occurs on the illuminated surface. After boron doping, the evaporation rate and efficiency of the BCF material significantly increased, reaching their highest values ​​at BCF-0.2. This is because boron doping significantly enhances the hydrophilicity of the BCF surface, effectively strengthening capillary action and maintaining a faster water transport process, thus exhibiting stronger photothermal evaporation performance. Therefore, controlling the boron doping amount to 0.2 mol / L is the optimal ratio for synthesizing ideal BCF photothermal materials.

[0053] The method for constructing an array-type evaporator for seawater desalination in Embodiment 3 of this invention involves assembling and arranging individual evaporators to form an evaporation array. Due to the multi-level light reflection process and heat conduction between adjacent materials in the array, the light utilization efficiency of the array-type evaporator can be significantly enhanced, while also limiting heat convection losses and improving the overall heat utilization efficiency. Compared with interface-type and single-unit 3D evaporators, an array-type evaporator with a height of 2.5cm was constructed using four single evaporators of photothermal material with a projected area of ​​0.5cm*0.5cm and an arrangement distance of 5mm. The water evaporation rate of the array-type evaporator reached 5.72 kg / m³. -2 h -1 It reached 5.8 kg m under one sun. -2 h -1 The array-type water evaporator achieved the best water evaporation rate and light utilization efficiency in terms of evaporation flux. In simulated seawater, the water evaporation rate variation was tested over a continuous 10-hour evaporation process, and the evaporator maintained relatively stable evaporation throughout the 10-hour period. Furthermore, the properties of the prepared photothermal material itself were found to support the stable operation of the constructed photothermal evaporator during long-term seawater desalination. The Na+ concentration in the simulated seawater was measured using ICP. + Mg 2+ K + Ca 2+ The concentrations of the four ions in the simulated seawater were 10557, 1100, 529, and 283 mg / L, respectively. -1 After desalination, the concentrations of the four ions decreased to 5.9, 1.1, 15, and 0.3 mg / L, respectively. -1 The desalination rate can reach at least 98%, demonstrating the excellent seawater desalination capability of the BCF array evaporator and highlighting its significant practical value in seawater desalination. Furthermore, through a self-assembled outdoor evaporation water collection device, a collection capacity of 2-10 kgm³ can be achieved. -2 day -1 Freshwater collection volume.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these 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.

Claims

1. A vaporiser of boron-doped carbon foam for seawater desalination, characterised in that, The application relates to a heat insulation layer base for floating on the surface of seawater, wherein a photothermal material is embedded on the heat insulation layer base, the upper end of the photothermal material penetrates through the upper surface of the heat insulation layer base, the lower end of the photothermal material penetrates through the lower surface of the heat insulation layer base, and the photothermal material is prepared by the following preparation method. Step S1: melamine foam is soaked in boric acid, and then the melamine foam is placed in an oven for drying to obtain a BMF precursor; Step S2: the BMF precursor obtained in step S1 is placed in a tube furnace for calcination under an N2 atmosphere to prepare the photothermal material.

2. The evaporator of boron-doped carbon foam for seawater desalination according to claim 1, characterized in that, The heat insulation layer base is made of a polyethylene foam plate.

3. The evaporator of boron-doped carbon foam for seawater desalination according to claim 1, characterized in that, The photothermal material is in a cuboid structure.

4. The evaporator of boron-doped carbon foam for seawater desalination according to claim 1, characterized by, The concentration of the boric acid in step S1 is 0.05-0.5 mol / L.

5. The evaporator of boron-doped carbon foam for seawater desalination according to claim 4, characterized in that, The concentration of the boric acid in step S1 is 0.2 mol / L.

6. The evaporator of boron-doped carbon foam for seawater desalination according to claim 1, characterized in that, The calcination temperature in step S2 is 500 DEG C, and the calcination time is 10 min.

7. A method of producing an evaporator as claimed in any one of the claims 1-6, characterized in that The application relates to a heat insulation layer base for floating on the surface of seawater, wherein a photothermal material is embedded on the heat insulation layer base, the upper end of the photothermal material penetrates through the upper surface of the heat insulation layer base, the lower end of the photothermal material penetrates through the lower surface of the heat insulation layer base, and the photothermal material is prepared by the following preparation method. The upper end of the photothermal material penetrates through the upper surface of the heat insulation layer base and is flush with the upper surface of the heat insulation layer base.

8. The method of claim 7, wherein, The upper end of the photothermal material penetrates through the upper surface of the heat insulation layer base and is 2.5 cm higher than the upper surface of the heat insulation layer base.

9. The preparation method according to claim 7, characterized in that, A plurality of photothermal materials are embedded in the heat insulation layer base in the same way, wherein the upper end of the photothermal material penetrates through the upper surface of the heat insulation layer base and is 2.5 cm higher than the upper surface of the heat insulation layer base, and adjacent photothermal materials are arranged at intervals.

10. The method of claim 7, wherein, ​

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