Directional hole structure cement-based interface solar evaporator and preparation method thereof

Abstract

The invention provides a directional hole structure cement-based interface solar evaporator and a preparation method thereof. The evaporator comprises a cement-based porous substrate and a composite photo-thermal coating laid on the surface of the cement-based porous substrate. The cement-based porous substrate is prepared by directionally freezing through an ice template method; the cement-based porous substrate is internally provided with a plurality of micron-sized directional pore channels which are through along the thickness direction. The preparation method comprises the following steps: preparing slurry, directionally freezing and forming, freezing and drying, and laying the composite photo-thermal coating on the surface of the cement-based porous substrate to obtain a finished product. According to the evaporator, mutually parallel directional hole channels are constructed in a cement base body, a water body below can be quickly conveyed to the surface without obstruction by utilizing capillary acting force, and the evaporation efficiency is improved. The preparation method is simple and easy to implement, can be implemented under laboratory conditions and in industrial production, and is easy to realize automatic and large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cement-based solar evaporator, in particular to a directional hole structure cement-based interface solar evaporator and a preparation method thereof. BACKGROUND

[0002] With the increasing scarcity of global freshwater resources and the intensification of environmental pollution problems, it has become a trend to develop efficient, low-cost and environmentally friendly water purification technologies. Interfacial solar steam generation (ISSG) technology limits the solar energy absorption and water evaporation process to a thin layer at the gas-liquid interface, thereby minimizing heat loss to the overall water body, achieving extremely high light-heat conversion efficiency. The core of this technology is a photothermal evaporator. An ideal photothermal evaporator should have the following characteristics: strong solar light absorption ability in a wide spectral range, high light-heat conversion efficiency, fast and continuous water transport capacity, excellent thermal insulation performance to achieve heat localization, good mechanical strength and long-term operation stability, and low manufacturing cost and potential for scalable production.

[0003] At present, researchers have developed a variety of photothermal evaporators based on different material systems. For example, evaporators based on carbon materials (such as graphene, carbon nanotubes, carbonized biomass) exhibit excellent light absorption performance, but their preparation cost is high, and the dispersion and long-term stability of the materials in water need to be improved. Evaporators based on noble metal plasmonic nanoparticles (such as gold and silver nanoparticles) have extremely high light-heat conversion efficiency, but their high cost and complex preparation process seriously restrict their large-scale application. Evaporators based on polymers (such as polypyrrole and polyaniline) or polymer aerogels have the advantages of low cost and easy functionalization, but they generally have poor mechanical strength and are prone to aging and degradation under long-term immersion and light.

[0004] In order to overcome the limitations of the above-mentioned materials, researchers have begun to explore the use of low-cost, high-strength inorganic materials as evaporator substrates. Cement, as the world's largest and most widely used building material, has a series of outstanding advantages such as extremely low cost, wide source, stable physical and chemical properties, and high mechanical strength, making it an ideal candidate material for building high-performance, scalable evaporators.

[0005] However, ideal photothermal evaporator needs to have continuous, directional and high connectivity of pore structure to achieve rapid water transport from water body to evaporation interface. The internal pore structure of traditional cement-based materials such as cement mortar or concrete is random, curved and poor in connectivity, which greatly hinders the rapid and effective transport of water. Therefore, how to accurately design and control the micro-pore structure of cement-based materials to build channels that can achieve efficient and rapid water transport is a key technical bottleneck for developing high-performance cement-based solar evaporator.

[0006] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies of the prior art. SUMMARY

[0007] The purpose of the present application is to provide a directional pore structure cement-based interface solar evaporator and a preparation method thereof to solve or alleviate the problems existing in the prior art.

[0008] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions: A directional pore structure cement-based interface solar evaporator, comprising a cement-based porous substrate and a composite photothermal coating layer laid on the surface of the cement-based porous substrate; the composite photothermal coating layer is at least located on the upper surface of the cement-based porous substrate, and can also be coated on the peripheral surface of the cement-based porous substrate. The cement-based porous substrate is made by directional freezing by ice template method; the cement-based porous substrate has a plurality of micron-level directional pores penetrating through the thickness direction inside.

[0009] Further, the cement-based porous substrate is prepared from a slurry containing cement, water and cellulose ether viscosity modifier; the amount of cellulose ether viscosity modifier is 0.1%-2% of the mass of cement, and the water-binder ratio of the slurry is 0.4-2.8. The cellulose ether viscosity modifier is used to stabilize the slurry system and prevent the sedimentation of cement particles during directional freezing, which helps to build a uniform directional pore structure. The appropriate water-binder ratio ensures that the slurry has appropriate fluidity and solid content, which is a key process parameter to form a porous skeleton with complete structure and certain mechanical strength after freeze-drying.

[0010] Further, the cellulose ether viscosity modifier is one or more of hydroxypropyl methylcellulose (HPMC), methylcellulose (MC) and hydroxyethyl cellulose (HEC).

[0011] Further, the composite light-heat coating raw material comprises polymer (3,4-ethylenedioxythiophene): polystyrene sulfonic acid and titanium trioxide, the polymer (3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS) has excellent light-heat conversion performance and good film-forming property, and the titanium trioxide is a wide-spectrum absorption material, and the introduction of the titanium trioxide into the PEDOT:PSS can further broaden the light absorption spectrum and enhance the overall light absorption capacity. The mass fraction of the titanium trioxide in the polymer (3,4-ethylenedioxythiophene): polystyrene sulfonic acid is 5%-20%, and the light-heat slurry with uniform dispersion and excellent performance can be obtained under the ratio.

[0012] In another embodiment, the cement-based porous substrate further comprises phase change microcapsules, and the content of the phase change microcapsules is 2% to 10% of the mass of the cement.

[0013] Further, the core material of the phase change microcapsules is paraffin, the shell material is polymethyl methacrylate, and the average particle size is 5-7 μm.

[0014] The phase change microcapsules can store and release latent heat by using the diurnal temperature difference and other environmental temperature fluctuations, thereby playing a role of heat buffering and adjusting, and helping to maintain the continuous water production capacity of the evaporator under non-ideal illumination conditions; the phase change temperature is selected to be close to the common environmental working temperature, and the phase change temperature is 28℃.

[0015] The application further provides a preparation method of the aforementioned directional hole structure cement-based interface solar evaporator, which comprises the following steps: Step one, slurry preparation: mixing cement, water and cellulose ether viscosity modifier to prepare a uniform cement-based slurry; during the mixing, the cellulose ether viscosity modifier is first dissolved in water, and then the cement is added and mixed to form a stable suspended slurry by mechanical stirring; Step two, directional freeze forming: placing the cement-based slurry in a mold and performing unidirectional freezing to make the water in the slurry crystallize to form an ice crystal template with a directional structure, thereby obtaining a sample with a mold; during the unidirectional freezing process, the water in the slurry grows into ice crystals with consistent orientation from bottom to top under the driving of the temperature gradient, thereby forming a through ice crystal template, and the cement particles are squeezed into the ice crystal gaps; the low-temperature cold source can be liquid nitrogen or a semiconductor refrigeration sheet, which is usually applied to the bottom of the mold to establish a vertical temperature gradient in the slurry, thereby guiding the growth of the ice crystals in the direction; the shape of the mold is not limited, and can be a square block, a cylinder, a thick plate, a pyramid and the like, which can be selected as required, and the cylinder is preferred; Step three, freeze drying: performing freeze drying treatment on the sample with a mold to sublimate the ice crystal template, thereby in-situ retaining the vertical directional pore structure composed of cement particles which reproduces the morphology of the ice crystal template, and obtaining a cement-based porous substrate; Step four, a uniform, firm and efficient composite photothermal coating is applied on the surface of the cement-based porous substrate to obtain the directional pore structure cement-based interface solar evaporator. If the upper surface of the cement-based porous substrate is uneven, the upper surface of the cement-based porous substrate is first polished to be flat, then the debris is sucked dry under negative pressure, and then the composite photothermal coating is applied.

[0016] Further, between step three, a step of standard curing and drying treatment of the obtained cement-based porous substrate is further included. The standard curing refers to curing for at least 3 days under the condition that the temperature and relative humidity are not less than 95%, aiming to promote the hydration reaction of cement, thereby significantly improving the mechanical strength and structural stability of the porous substrate. The drying treatment is to place it in a blast drying oven at 60-70°C until the constant weight.

[0017] Further, in step two, when unidirectional freezing is performed, the sample with the mold is placed at a position 0.5-1.5 cm above the liquid nitrogen surface, and the mold bottom is cooled unidirectionally by using the volatile cold gas of liquid nitrogen, and the cooling is continued for 30-60 min, until the slurry in the mold is completely frozen into a hard solid from bottom to top.

[0018] Further, in step four, the composite photothermal coating raw material is prepared, and then the composite photothermal coating raw material is uniformly sprayed onto the upper surface and peripheral surface of the cement-based porous substrate obtained in step three, and is uniformly sprayed in 3 times with cross paths, and each spraying is interval for more than 5 min to make the coating surface dry; after the spraying is completed, the sample is naturally air-dried at room temperature for more than 24 h, and then is placed in a drying oven at 60-80°C for more than 2 h, to obtain the directional pore structure cement-based interface solar evaporator.

[0019] For the preparation method of the directional pore structure cement-based interface solar evaporator containing phase change microcapsules, in step one, the cement and the phase change microcapsules are first placed in a ball mill jar, and are dry mixed at a speed of 150-200 rpm without grinding balls for 10-30 min to obtain a composite powder; then the composite powder is mixed with water and a cellulose ether viscosity modifier to prepare a uniform cement-based slurry; other preparation steps are the same as those of the directional pore structure cement-based interface solar evaporator without phase change microcapsules.

[0020] The technical scheme of the present application has the following beneficial effects: The cement-based porous substrate of the present application is made by directional freezing by ice template method, which constructs parallel directional pores in the cement-based body, can use capillary force to quickly and unobstructed pump the water below to the evaporation surface at the top, plus the cement-based material itself has certain hydrophilicity, which is conducive to the rapid spreading and wicking of water, ensuring the continuous supply of water; at the same time, the efficient water circulation can timely take the salt concentrated at the interface back to the bottom water body, effectively relieving the problem of pore blockage caused by salt crystallization, and ensuring the long-term stable operation of the evaporator when processing high-salt wastewater (such as seawater). The cement-based porous substrate has low cost, is easy to make, and can give the evaporator rigidity and high strength, which can resist the physical impact in the process of carrying and installation and the swelling or disintegration risk caused by long-term water soaking, which is significantly better than the traditional substrates such as fragile and aging polymer aerogels.

[0021] The preparation method of the directional pore structure cement-based interface solar evaporator of the present application controls the freezing direction and the growth direction of ice crystals to form highly ordered vertical pores in the cement-based body; the preparation method is simple and easy to implement, which can be implemented in laboratory conditions and industrial production, and is easy to realize automation and large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings accompanying the specification of the present application serve to provide further understanding of the present application, the schematic embodiments of the present application and the description thereof serve to explain the present application, and do not constitute an improper limitation on the present application. Among them: Figure 1 SEM image of the cement-based porous substrate prepared for Example 1 of the present application.

[0023] Figure 2 Water contact angle test image of the surface of the finished evaporator of Example 1 of the present application.

[0024] Figure 3 Structural schematic diagram of Example 1 of the present application.

[0025] Figure 4 Photo of the finished solar evaporator prepared for Example 1 of the present application.

[0026] Figure 5 Photo of the finished solar evaporator prepared for Example 1 of the present application. DETAILED DESCRIPTION

[0027] The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] The following raw materials are used in the examples and comparative examples: Cement: P.O 42.5 ordinary portland cement; PEDOT:PSS: the manufacturer is Shanghai Youyi Organic Photoelectric Material Co., Ltd., and the model is OE-001.

[0029] Hydroxypropyl methyl cellulose: the manufacturer is Shanghai Maikelin Biochemical Technology Co., Ltd., the model is ǁ, and the viscosity is 10000 mPa·s.

[0030] Titanium trioxide is analytical pure.

[0031] Example 1 A directional pore structure cement-based interface solar evaporator comprises a cement-based porous substrate and a composite photothermal coating layer laid on the surface of the cement-based porous substrate. The raw materials of the cement-based porous substrate are: 1 part by weight of hydroxypropyl methyl cellulose, 62.5 parts by weight of ordinary Portland cement, and 100 parts by weight of water, and the water-binder ratio is 1.6; The raw materials of the composite photothermal coating layer are: 1 part by weight of PEDOT:PSS aqueous dispersion and 0.09 parts by weight of titanium trioxide powder, and the solid content of the PEDOT:PSS aqueous dispersion is 1.3%.

[0032] The preparation method of the above-mentioned directional pore structure cement-based interface solar evaporator comprises the following steps: (1) Preparation of slurry: 1 part by weight of hydroxypropyl methyl cellulose is dissolved in 99 parts by weight of deionized water, and a magnetic stirrer is used to stir at a speed of 600 rpm for 2 h until complete dissolution, to obtain a HPMC solution A with a mass fraction of 1 wt%. Another part of ordinary Portland cement is added to the solution A, and the mixture is stirred in a planetary mixer at a speed of 500 rpm for 10 min to obtain a macroscopically uniform, non-aggregated gray cement-based slurry; (2) Directional freezing: the above-mentioned slurry is slowly injected into a polytetrafluoroethylene cylindrical mold with an inner diameter of 50 mm and a height of 30 mm, and the mold is filled. Then, the bottom of the mold is carefully placed about 1 cm above the liquid surface of the dewar flask containing liquid nitrogen, and the bottom of the mold is cooled in one direction by using the volatilization of liquid nitrogen. Continue to cool for about 30 min, until the slurry in the mold is completely frozen into a hard solid from bottom to top; (3) Freeze-drying: the frozen sample together with the mold is quickly taken out from the liquid nitrogen environment, demolded, and immediately transferred to the sample holder of a pre-cooled freeze-drier, and the cold trap temperature is set to -80℃. Start the vacuum pump, and when the system vacuum pressure is lower than 20 Pa, perform freeze-drying treatment for 3.5 days to completely sublimate the ice crystal template in the sample; (4) Curing and drying: the loose and porous cement-based embryo taken out from the freeze dryer is placed in a standard curing box for curing for 7 days, the curing temperature is 20±1℃, and the relative humidity is ≥95%. After the curing, the embryo is moved into a 60℃ air-drying oven for drying for 24h to constant weight, to obtain a cement-based porous substrate with excellent mechanical strength; (5) Preparation and spraying of photo-thermal layer: the PEDOT:PSS aqueous dispersion and titanium trioxide powder are weighed and mixed, and ultrasonic treatment is performed for 30min under a power of 300W to form a uniformly dispersed black composite photo-thermal slurry. Using a spray pen with a caliber of 0.3mm, the photo-thermal slurry is sprayed onto the upper surface of the cement-based porous substrate prepared in step (4) from a distance of 3.5cm from the upper surface of the substrate in 3 times, uniformly and in a cross path under a gas pressure of 0.2MPa. Each spraying is separated by 5min to allow the coating to dry. After the spraying is completed, the sample is naturally air-dried at room temperature for 24h, and then placed in a 60℃ oven for final drying for 2h, to obtain a finished solar evaporator.

[0033] The cement-based solar evaporator with standard directional hole structure in this embodiment has a diameter of 50mm and a height of 30mm. Figure 1 The scanning electron microscope (SEM) image of the cement-based porous substrate shows that the cement-based porous substrate has a large number of parallel directional channels inside, and the diameter of the directional channels is about 100μm-200μm, which is a typical micron-level channel structure. The channel structure can quickly transport the water at the bottom to the surface of the evaporator through capillary action, to ensure that the evaporation interface is continuously supplied with water. At the same time, the channel structure makes the surface of the evaporator rough, and the effective evaporation area of the smooth surface is larger, which can directly improve the water evaporation amount per unit time. Figure 2 The water contact angle test image of the surface of the finished product of the evaporator shows that the contact angle is 42.8°, which has excellent hydrophilic properties, and facilitates the spreading of water on the surface of the evaporator to continuously promote water evaporation. Figure 3 The cement-based porous substrate obtained in Example 1 is shown in the following figure. Figure 4 、 Figure 5 The perspective view and top view of the finished product of the solar evaporator coated with the composite photo-thermal coating are shown in the following figures.

[0034] Example 2 The difference between this embodiment 2 and Example 1 is that the amount of cement in the cement-based porous substrate slurry is 125 parts by weight, and the water-binder ratio is 0.8.

[0035] The raw materials of the cement-based porous substrate slurry are: hydroxypropyl methylcellulose 1 part by weight, ordinary Portland cement 125 parts by weight, and water 100 parts by weight, and the water-binder ratio is 0.8.

[0036] The preparation method of the composite photo-thermal coating and the directional hole structure cement-based interface solar evaporator is exactly the same as that of Example 1.

[0037] This example aims to verify the applicability of the technical solutions of the present application under different water-binder ratios.

[0038] Example 3 The difference between this example 3 and example 1 is that 5% PMMA@paraffin phase change microcapsules by mass of cement are added into the cement-based porous substrate slurry. The PMMA@paraffin phase change microcapsules have paraffin as the core material and PMMA (polymethyl methacrylate) as the shell material, with a phase change temperature of 28℃ and an average particle size of 5μm.

[0039] The raw materials of the cement-based porous substrate slurry are: 1 part by weight of hydroxypropyl methyl cellulose, 125 parts by weight of ordinary Portland cement, 6.25 parts by weight of PMMA@paraffin phase change microcapsules, and 100 parts by weight of water, with a water-binder ratio of 0.8.

[0040] The composite photothermal coating ratio is the same as in the example, and the first step of the preparation method of the directional pore structure cement-based interface solar evaporator is adjusted. The other steps are the same as in example 1. Step one is adjusted as follows: The cement and microcapsule powder are placed in a ball mill jar and dry mixed at a speed of 200rpm for 10min without grinding balls to ensure uniform mixing of the two, and then the composite powder is added to 100g of solution A.

[0041] This example aims to introduce phase change microcapsules to give the evaporator the ability of thermal management. In sufficient light, the microcapsules absorb and store part of the heat; in weakened or interrupted light, the stored latent heat is released, thereby smoothing the fluctuation of the evaporation rate and achieving more stable all-weather water production performance.

[0042] Comparative Example 1 This comparative example is made of ordinary cement mortar evaporator, which is compared with example 1, aiming to prove the necessity of directional pore structure for efficient evaporation.

[0043] The preparation method of the ordinary cement mortar evaporator includes the following steps: (1) Slurry preparation: mix 62.5g of ordinary Portland cement with 100g of water and stir uniformly to prepare a standard cement neat paste; (2) Molding and curing: pour the above cement neat paste into the same mold as in example 1, then directly place it in a standard curing box for 7 days to allow it to harden naturally; the curing temperature is 20±1℃, and the relative humidity is ≥95%; (3) Drying and coating: dry the cured cement block in a 60℃ air-drying oven for 24h to constant weight. Then, perform the same photothermal layer spraying process as in example 1 on the upper surface. The final sample is a basically dense cement block with random internal pores and poor connectivity.

[0044] The samples prepared in the above Examples 1-3 and Comparative Example 1 were subjected to performance characterization, including evaporation performance test, night evaporation performance test, and evaporation efficiency.

[0045] Evaporation performance test: the sample was floated in deionized water and irradiated under 1sun (AM 1.5G, light intensity 1000W / m 2 Standard conditions) of a solar simulator, and the mass change of water was recorded in real time by a high-precision electronic balance to calculate the evaporation rate.

[0046] Night evaporation performance test: after the light irradiation experiment was completed, the device was moved into a dark environment without light, and the mass change was continuously recorded for 1h to calculate the night evaporation rate.

[0047] Evaporation efficiency Calculation: ; ; Wherein, Q is the heat for evaporating water, unit: J or W; Qtotal is the total heat absorbed by the system, unit: J or W; m is the mass of water evaporated per unit time caused by light irradiation, unit: kg / s or kg / h; L is the latent heat of water evaporation, unit: J / kg. I is the solar radiation intensity, unit: W / m 2 ; A is the light-receiving area of the evaporator, unit: m 2 ; C is the optical concentration factor, usually 1.

[0048] The control group was pure water. The test data of the examples and the comparative example are as follows, and the change rate in the table is calculated based on Comparative Example 1: Table 1 Test data of examples and comparative examples

[0049] From the test results in Table 1, it can be seen that Example 1 has the best three indicators and is the best example. The evaporation efficiency of the three examples of the present application is better than that of Comparative Example 1, because the directional channels constructed by the ice template method provide a high-efficiency and low-resistance path for water from the bottom to the evaporation surface, ensuring sufficient water supply, which can show an advantage in evaporation rate during the day and night. The internal capillary pores of the ordinary cement mortar of Comparative Example 1 are random and not connected, the water transmission resistance is extremely large, and the water supply speed is far behind the surface evaporation speed, resulting in that its performance is only slightly higher than that of natural water evaporation.

[0050] The water binder ratio will affect the evaporation performance of the evaporator. The water binder ratio of Example 1, Comparative Example 1 is 1.6, and the water binder ratio of Example 2, Example 3 is 0.8; Example 2, Example 3 shows lower evaporation rate and night evaporation rate than Comparative Example 1. This is because, in Comparative Example 1, although there is no directional pore, the water content is high, the cement evaporator has a large number of random pores, and has a certain capillary effect, which can provide sufficient water supply for the evaporation of surface water. The slurry of Example 2, Example 3 is more viscous, resulting in lower pore density and connectivity of the directional pores than Example 1, and the water supply speed of the two cannot keep up with the evaporation speed, resulting in lower evaporation water quantity (rate) per unit time.

[0051] Comparing Comparative Example 2 and Example 3, after adding phase change microcapsules, the evaporation performance can be increased to a certain extent, and the evaporation rate, night evaporation rate and evaporation efficiency of Example 3 are all greater than those of Example 2. This is due to the fact that the phase change microcapsules incorporated absorb part of the solar energy during the day and store it in the form of latent heat, and when the ambient temperature decreases at night, the phase change material solidifies and releases the stored heat, which is of great significance for practical application.

[0052] Cement has an unparalleled cost advantage as a base material, and has excellent mechanical strength, weather resistance and long-term stability in water immersion, and the present application successfully combines high performance with low cost and high stability; at the same time, through innovative design of the microstructure of low-cost cement material, not only the evaporation performance of the present application exceeds that of high-performance polymer evaporators, but also the working ability of the evaporator under lightless conditions is further expanded by introducing functional phase change materials, effectively solving the key pain points of the prior art.

[0053] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A directional hole structure cement-based interface solar energy evaporator, characterized in that, The cement-based porous substrate and the composite photothermal coating laid on the surface of the cement-based porous substrate; The cement-based porous substrate is prepared by an ice template method; the cement-based porous substrate has a plurality of micron-level directional pores penetrating through the thickness direction.

2. The oriented-pore structured cement-based interface solar evaporator according to claim 1, characterized in that: The cement-based porous substrate is prepared from a slurry containing cement, water and a cellulose ether viscosity modifier; the cellulose ether viscosity modifier accounts for 0.1%-2% of the mass of the cement, and the water-binder ratio of the slurry is 0.4-2.

8.

3. The oriented-pore structured cement-based interface solar evaporator according to claim 2, characterized in that: The cellulose ether viscosity modifier is one or more of hydroxypropyl methylcellulose, methylcellulose and hydroxyethyl cellulose.

4. The oriented-pore structured cement-based interface solar evaporator according to claim 1, characterized in that: The raw material of the composite photothermal coating includes a polymer (3,4-ethylenedioxythiophene):polystyrene sulfonic acid and titanium trioxide, and the mass fraction of the titanium trioxide is 5%-20% of the polymer (3,4-ethylenedioxythiophene):polystyrene sulfonic acid.

5. The oriented-pore structured cement-based interface solar evaporator according to claim 1, characterized in that: The cement-based porous substrate further contains phase change microcapsules, and the content of the phase change microcapsules is 2%-10% of the mass of the cement.

6. The oriented-porous structure cement-based interface solar evaporator according to claim 5, characterized in that: The core material of the phase change microcapsules is paraffin, the shell material is polymethyl methacrylate, the phase change temperature is 28℃, and the average particle size is 5-7μm.

7. A method of making a directional hole structured cement-based interface solar evaporator as claimed in any one of claims 1 to 4, characterized in that, The method comprises the following steps: Step one, slurry preparation: mixing cement, water and a cellulose ether viscosity modifier to prepare a uniform cement-based slurry; Step two, directional freeze forming: placing the cement-based slurry in a mold and unidirectionally freezing the cement-based slurry to make the water in the slurry crystallize into an ice crystal template with a directional structure, thereby obtaining a sample with a mold; Step three, freeze drying: freeze-drying the sample with a mold to sublimate the ice crystal template, thereby obtaining the cement-based porous substrate with directional pores inside; Step four, laying a composite photothermal coating on the surface of the cement-based porous substrate to obtain the directional pore structure cement-based interface solar evaporator.

8. The method of producing a directional hole structured cement-based interface solar evaporator according to claim 7, characterized in that: In step two, the sample with a mold is placed at a position 0.5-1.5cm above the liquid nitrogen surface, the mold bottom is unidirectionally cooled by using the volatilized cold gas of the liquid nitrogen, and the cooling is continued for 30-60min until the slurry in the mold is completely frozen into a hard solid from bottom to top.

9. The method of producing a directional hole structured cement-based interface solar evaporator according to claim 7, characterized in that: In step four, the raw material of the composite photothermal coating is prepared, and then the raw material is uniformly sprayed onto the surface of the cement-based porous substrate obtained in step three, and the spraying is uniformly performed in three times with intersecting paths, and the interval between each spraying is more than 5min to make the coating surface dry; After the spraying is completed, the sample is naturally air-dried at room temperature for more than 24h, and then the sample is placed in an oven at 60-80℃ for drying for more than 2h, thereby obtaining the directional pore structure cement-based interface solar evaporator.

10. The method of producing a directional hole structured cement-based interface solar evaporator according to claim 7, characterized in that: The cement-based porous substrate further contains phase change microcapsules; In step one, the cement and the phase change microcapsules are first placed in a ball mill jar, and dry mixing is performed at a speed of 150-200rpm without grinding balls for 10-30min to obtain a composite powder; then the composite powder is mixed with water and a cellulose ether viscosity modifier to prepare a uniform cement-based slurry.

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