Porous geopolymer seawater evaporator as well as preparation method and application thereof

Abstract

The invention relates to the technical field of inorganic nonmetal gelling, in particular to a porous geopolymer seawater evaporator and a preparation method and application thereof. The preparation method of the porous geopolymer seawater evaporator comprises the following steps: preparing meliendellite MHNT with geopolymerization activity, preparing an MHNT-based porous foam geopolymer by a chemical foaming method, preparing carbon-coated MHNT by a polydopamine method, and preparing the porous geopolymer evaporator. The porous foam geopolymer is prepared by adopting an alkali excitation method, the reaction process is simple, easy to control, free of by-products, environmentally friendly and free of pollution, large-scale preparation can be achieved, production is convenient, a multi-stage porous structure is generated through hollow glass microspheres and H2O2 foaming, and the porous foam geopolymer can float on the water surface through rich spherical holes. Polydopamine is used for carbonization to enhance the photo-thermal conversion capacity, and after internal MHNT is decomposed in the geological polymerization process, carbonized polydopamine retains a part of nanotube structure, so that the evaporation enthalpy of water is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic non-metallic cementing, and particularly to a porous geopolymers seawater evaporator and its preparation method and application. Background Art

[0002] With the continuous development of the economic society, the problems of energy crisis and shortage of fresh water resources are becoming increasingly serious. How to achieve the overall development and utilization of renewable energy and fresh water resources is crucial for promoting the sustainable development of the economic society. Extracting fresh water from seawater by solar interfacial evaporation is one of the important ways to solve the energy crisis and the shortage of fresh water resources. The heat of solar energy can be concentrated on the surface of the seawater evaporator, thus greatly improving the utilization efficiency of solar energy and the evaporation efficiency of seawater.

[0003] Excellent light absorption and solar-thermal conversion ability, low thermal conductivity, good hydrophilicity and high porosity are the essential conditions for the evaporator. Three-dimensional porous geopolymers are inorganic polymers with a zeolite-like pore structure, having the advantages of rich pores, high temperature resistance, fire resistance, high compressive and tensile strength, and strong chemical stability. Geopolymers also have excellent water absorption, and through the rich porous structure inside, water molecules can be quickly transported from the bottom to the top. In addition, compared with the aerogel materials commonly used in seawater desalination, the preparation method of geopolymers is simple, energy-consuming is low, raw materials are cheap and easy to obtain, and it has high mechanical strength. Therefore, it can be used as an ideal seawater evaporator.

[0004] Natural aluminosilicate mineral materials are one of the common raw materials for preparing geopolymers. A large number of hydroxyl groups exist in natural aluminosilicate mineral materials, which can form chemical bonds with aluminum atoms, etc. The existence of these chemical bonds limits their ability to directly participate in the geopolymerization reaction. After dehydroxylation to break the chemical bonds, a large number of active sites for geopolymerization reactions can be generated. Halloysite nanotubes (HNTs) are a kind of multi-water aluminosilicate mineral material with a tubular structure, and its chemical composition is similar to that of kaolinite. Although the reserves of halloysite nanotube deposits around the world are very large, due to relatively little research on halloysite nanotubes in history, they have not been widely used. Compared with kaolinite, halloysite has the following advantages: halloysite has a higher surface area and structural disorder degree than kaolinite; halloysite nanotubes have a unique morphology, high surface reactivity and hydrophilicity; the temperature required for the dehydroxylation of halloysite is lower than that of kaolinite, so the energy consumption during the dehydroxylation process is lower (Applied clayscience, 2020, 185, 105375); halloysite has higher geopolymerization activity (Cement & Concrete Composites, 2012, 34, 709-715), wide sources and low prices. Therefore, it can be used as an ideal raw material for preparing geopolymers.

[0005] In the prior art, the preparation methods for porous geopolymers generally fall into pre-foaming methods and chemical foaming methods. For example, K. Dhasindrakrishna et al. produced prefabricated foams by vigorously stirring sodium dodecyl sulfate solution and then mixing them with geopolymer slurries (Cement and Concrete Research, 2020, 138, 106233). D. Kioupis et al. obtained a porous structure using a zinc-aluminum powder chemical foaming method (Ceramics International, 2021, 47, 26280-26292). Although the pre-foaming method can yield a uniform structure, there may be a risk of defoaming with changes in external temperature, air pressure, etc.; while the chemical foaming method results in a more unevenly distributed porous structure. In addition, there is little research on the use of geopolymers for seawater desalination in the prior art. Deng et al. prepared a photoevaporation membrane device for treating simulated high-salt liquid radioactive waste by in-situ self-reducing graphene oxide on geopolymers, and its evaporation rate can reach 1.5 kg m -2 h -1 (Journal of Hazardous Materials, 2022, 424, 127433). In addition, they also designed and prepared a three-dimensional photoevaporation membrane in the shape of a pyramid using a geopolymer thin film and graphene oxide composite material. The pyramid structure increased the effective evaporation area, making the evaporation rate reach 2.39 kg m -2 h -1 (Materials Today Energy, 2022, 26, 101016). These evaporators use geopolymer thin films as supports for water transmission, but their non-floatability on the water surface limits their application scenarios. Additionally, the light absorption and photothermal conversion capabilities of halloysite nanotubes themselves are poor. Therefore, improving the light absorption and photothermal conversion properties of halloysite-based geopolymers is crucial for solar interfacial evaporation seawater desalination.

[0006] Therefore, there is an urgent need for a porous geopolymer seawater evaporator, its preparation method, and application to solve the above technical problems. Summary of the Invention

[0007] The object of the present invention is to overcome the existing technical problems, synthesize a geopolymer seawater evaporator using halloysite, and improve the photothermal conversion ability and increase the seawater evaporation rate through the method of carbonizing polydopamine.

[0008] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0009] A preparation method for a porous geopolymer seawater evaporator, comprising the following steps:

[0010] S1. Preparation of halloysite with geopolymeric activity

[0011] The halloysite is calcined in an air atmosphere to obtain metahalloysite, denoted as MHNT;

[0012] S2. Preparation of MHNT-based porous foam geopolymers by chemical foaming method

[0013] S2.1. The halloysite, MHNT, and hollow glass microspheres are dispersed into an alkali activator, and a non-ionic surfactant and an aqueous hydrogen peroxide solution are added. After mixing evenly, an MHNT-based geopolymer slurry is obtained;

[0014] S2.2. The MHNT-based geopolymer slurry is poured into a mold and foamed and expanded in an environment with a pressure of 0.08 - 0.1 MPa, and then cured. After the curing is completed, a cured product is obtained;

[0015] S2.3. The cured product is neutralized with an acid solution, washed, and dried to obtain an MHNT-based porous foam geopolymer, denoted as MH;

[0016] S3. Preparation of carbon-coated MHNT by polydopamine method

[0017] The MHNT and dopamine monomers are dispersed into a Tris-HCl solution and stirred and mixed. After the reaction is completed, the precipitate is collected; the precipitate is washed and dried to obtain PDA@MHNT; the PDA@MHNT is carbonized to obtain carbon-coated MHNT, denoted as CT-PDA@MHNT;

[0018] S4. Preparation of a porous geopolymer evaporator

[0019] The CT-PDA@MHNT is mixed with an alkali activator and coated on the upper surface of MH as a photothermal layer through a geopolymerization reaction, and then cured; after curing, it is neutralized with an acid solution, washed, and dried to obtain a porous geopolymer evaporator, denoted as CT-PDA@MH.

[0020] In the above step S3, in the prepared "CT-PDA@MHNT", the "T" in "CT" represents the carbonization temperature.

[0021] In the above step S4, in the prepared "CT-PDA@MH", the "T" in "CT" represents the carbonization temperature.

[0022] Preferably, in the above step S1, the calcination temperature is 650 - 850 °C and the calcination time is 3 h.

[0023] Preferably, in the above step S2.1, the mass ratio of halloysite, MHNT, and hollow glass microspheres is 1∶2∶(1 - 2);

[0024] In the step S2.1, halloysite, MHNT, and hollow glass microspheres are all solid raw materials;

[0025] The usage amount of the non-ionic surfactant is 0.1-0.5% of the total mass of the solid raw materials; the concentration of the hydrogen peroxide aqueous solution is 30 wt%, and the usage amount is 5-10% of the total mass of the solid raw materials; in the alkali activator, the molar ratio of SiO 2 , Na 2 O, H 2 O is 1.38∶1∶15.74;

[0026] The mass-volume ratio of the solid raw materials to the alkali activator is 1∶1.5, and the unit of the mass-volume ratio is g∶mL.

[0027] Preferably, in the step S2.2, the curing process is to carry out primary curing in a vacuum box at room temperature for 10-24 h, and then transfer it to a high-temperature environment of 50-80 °C for rapid curing for 6 h.

[0028] Preferably, in the step S2.3, the acid solution is 1 M hydrochloric acid solution; deionized water is used for multiple washing during the washing process; the drying temperature is 60 °C and the drying time is 12 h.

[0029] Preferably, in the step S2.1, the hollow glass microspheres are soda-lime borosilicate glass microspheres with a diameter of 20-75 μm; the non-ionic surfactant is F 108.

[0030] Preferably, in the step S3, the mass ratio of MHNT to dopamine monomer is 5∶1; the mass sum of MHNT and dopamine monomer to the mass-volume ratio of the Tris-HCl solution is 6∶50, and the unit of the mass-volume ratio is g∶mL;

[0031] The carbonization process is carried out in an inert gas environment, the carbonization temperature is 500-900 °C, and the carbonization time is 30 min.

[0032] Preferably, the alkali activator is obtained by dissolving sodium hydroxide and water glass in deionized water or water and stirring until it is clear and transparent.

[0033] Preferably, in the step S4, the mass ratio of CT-PDA@MHNT to the alkali activator is 1∶1.5; the thickness of the photothermal layer is 0.05 mm.

[0034] Preferably, in the step S4, the curing process includes primary curing and rapid curing; the primary curing is to place it at room temperature for 10-24 h; the rapid curing is to place it in an environment of 50-80 °C for 6 h.

[0035] Preferably, in the step S4, the acid solution is 1M hydrochloric acid solution; during the washing process, deionized water is used for multiple washings.

[0036] Specifically, the preparation method of the porous geopolymer seawater evaporator includes the following steps:

[0037] S1: Prepare halloysite with geopolymerization activity

[0038] Calcine halloysite (HNT) at 650 - 850 °C in an air atmosphere for 3 h to dehydroxylate it and obtain metahalloysite, denoted as MHNT;

[0039] S2: Prepare MHNT-based porous foam geopolymer by chemical foaming method

[0040] Dissolve a certain amount of sodium hydroxide and sodium silicate in a certain amount of deionized water so that the molar ratio of SiO 2 ∶Na 2 O∶H 2 O is 1.38∶1∶15.74, mix well and let it stand at room temperature until the solution is clear to obtain an alkali activator; then, disperse HNT, MHNT and hollow glass microspheres in the above alkali activator at a mass ratio of 1∶2∶(1 - 2), and then add a non-ionic surfactant F 108 and an aqueous solution of 30 wt% H 2 O 2 with a concentration of 5 - 10% of the total mass of the solid raw materials. The mass-volume ratio of the solid raw materials to the alkali activator is 1∶1.5, and the unit of the mass-volume ratio is g∶mL; next, stir the above mixture with a glass rod until it is evenly mixed to obtain an MHNT-based geopolymer slurry; then pour the MHNT-based geopolymer slurry into a cylindrical silicone mold (diameter × height = 30 mm × 15 mm), cover it with plastic wrap to prevent water evaporation, transfer it to a vacuum box with a pressure of 0.08 - 0.1 MPa, the sample rapidly foams and expands under a negative pressure environment and generates a large number of holes from top to bottom, then preliminarily cure the sample in the vacuum box at room temperature for 10 - 24 h, and then transfer it to a high-temperature environment of 50 - 80 °C for rapid curing for 6 h; after curing, take out the sample from the mold, neutralize and remove the excess alkali with an excessive 1M hydrochloric acid solution; then wash it several times with deionized water and dry it overnight to obtain an MHNT-based porous foam geopolymer, denoted as MH;

[0041] S3: Prepare carbon-coated MHNT by polydopamine method

[0042] Disperse MHNT and dopamine monomer in Tris-HCl solution at a mass ratio of 5:1. The mass sum of MHNT and dopamine monomer to the mass-volume ratio of Tris-HCl solution is 6:50, and the unit of the mass-volume ratio is g:mL. Mix and stir for 12 - 24 h to fully oxidize and polymerize dopamine. After the reaction is completed, collect the grayish-black precipitate, then wash and dry it to prepare PDA@MHNT. Then carbonize PDA@MHNT in an inert gas (such as Ar gas) environment at 500 - 900 °C to obtain carbon-coated MHNT, denoted as CT-PDA@MHNT. In "CT-PDA@MHNT", "T" in "CT" represents the carbonization temperature.

[0043] S4: Preparation of the photothermal layer by geopolymerization

[0044] Coat CT-PDA@MHNT onto the upper surface of MH as the photothermal layer through geopolymerization reaction.

[0045] Specifically, fully mix CT-PDA@MHNT and the alkali activator until a uniform coating slurry is formed, so that the carbon-coated MHNT decomposes into SiO 4 and AlO 4 monomers. Then evenly apply the slurry on the upper surface of MH to form a photothermal layer with a thickness of 0.05 mm. The mass ratio of CT-PDA@MHNT to the alkali activator is 1:1.5. Subsequently, place the sample at room temperature for 10 - 24 h for preliminary curing, and then transfer it to a high-temperature oven at 50 - 80 °C for 6 h for rapid curing. After curing, neutralize the sample with an excessive 1M hydrochloric acid solution to remove the excess alkali. Finally, wash the sample several times with deionized water and dry it overnight to obtain a porous geopolymer evaporator, denoted as CT-PDA@MH.

[0046] The present invention also includes the porous geopolymer seawater evaporator prepared by the above preparation method.

[0047] The present invention also includes the application of the above porous geopolymer seawater evaporator in seawater evaporation and wastewater purification.

[0048] The method of the present invention uses HNT as a raw material, and prepares a floatable lightweight foamed geopolymer (MH) with a rich pore structure by an alkali activation method and adding hollow glass microspheres, and introduces carbonized polydopamine as a photothermal material, greatly improving the evaporation rate. The results show that the evaporator has excellent hydrophilicity, can quickly transport water from the bottom to the top by capillary action, and effectively alleviates the deposition of salts on the photothermal layer. In addition, after carbonizing MHNT coated with polydopamine and then using the geopolymerization reaction to prepare the photothermal layer, it not only provides excellent photothermal performance (light absorption rate is 88.86 - 97.25%), but also reduces the evaporation enthalpy of water from 2412 kJ kg-1 Reduced to 1431-1476 kJ kg -1 . The test shows that the evaporator can maintain good evaporation performance in high light intensity and high concentration salt solution. In addition, the evaporator shows excellent purification effect in dye wastewater, acidic wastewater (1M hydrochloric acid) and alkaline wastewater (1M sodium hydroxide solution), indicating that it has a wide range of application environments.

[0049] Working principle:

[0050] Halloysite is used as raw material, and multi-level porous geopolymer is obtained as the substrate of the evaporator by chemical foaming and adding hollow glass microspheres. Then, pores from top to bottom are generated inside by vacuuming. Then, carbon-coated halloysite is obtained by coating polydopamine (PDA) on the surface of halloysite and then carbonizing it. Then, it is coated on the substrate as a photothermal layer by geopolymerization. The raw materials used in the present invention are cheap, easy to obtain, and environmentally friendly; the process is simple and the energy consumption is low. The prepared geopolymer seawater evaporator has a power of 1000W m -2 The light intensity is 2.57 kg m -2 h -1 It has a high evaporation rate and can maintain rapid evaporation under conditions of high light intensity and high concentration of brine, and has excellent purification effects on various wastewaters.

[0051] The present invention uses a chemical foaming method to add hollow glass microspheres that can participate in geopolymerization to obtain a geopolymer with a high porosity and porous structure and can float, which broadens its application scenarios. A cheaper photothermal material is prepared by the polydopamine carbonization method, which greatly reduces the production cost.

[0052] The present invention uses halloysite as a raw material, hydrogen peroxide as a foaming agent, and hollow glass microspheres that can participate in geopolymerization are added, and a chemical foaming method is used to prepare a lightweight foam geopolymer having a high-porosity porous structure and floating on the water surface. Then, a layer of polydopamine is wrapped on the surface of the halloysite through the oxidative self-polymerization reaction of dopamine, and carbon-coated halloysite is obtained after high-temperature carbonization, and then it is applied to the surface of the MHNT-based porous foam geopolymer as a photothermal layer by a geopolymerization method. This method can significantly enhance the light absorption and photothermal conversion capabilities of the porous geopolymer seawater evaporator of the present invention, and the retained tubular structure is conducive to reducing the evaporation enthalpy of water. Compared with graphene, carbon nanotubes, etc. used in other geopolymer seawater evaporators, it is cheap, and its light absorption capacity and surface hydrophilicity can be controlled by controlling the carbonization temperature. Therefore, the evaporator has good seawater evaporation performance and salt resistance.

[0053] The MH porous foam geopolymer obtained by the present invention is prepared by using a mixed solution of NaOH and water glass as an alkali activator, H2 O 2 As a foaming agent, it is prepared by inorganic polymerization. First, when halloysite, MHNT and hollow glass microspheres are added to the alkali activator, the raw materials will decompose into SiO 4 tetrahedrons and AlO 4 tetrahedron structures under the action of strong alkali. These monomer structures share an oxygen atom to form polymer monomers, and then polymerize in the same way to form a three-dimensional network structure. Next, H 2 O 2 is added to the geopolymer slurry, and then the geopolymer slurry is transferred to a specific mold and placed in a vacuum chamber. Since the geopolymer slurry is in a strong alkali environment, H 2 O 2 will quickly decompose and generate O 2 to foam the slurry, leaving a large number of pores. In a vacuum environment, the oxygen in the pores will move to the upper part with lower pressure due to the pressure difference, leaving a large number of pores from top to bottom. The preparation of the photothermal layer is obtained by the carbonization of polydopamine. When dopamine monomer (DA) and MHNT are simultaneously added to the Tris-HCl solution, DA will spontaneously undergo self-oxidative polymerization on the surface of MHNT to form MHNT coated with PDA (polydopamine), denoted as PDA@MHNT. Subsequently, through carbonization in an inert gas (Ar) environment, carbon-coated MHNT (denoted as CT-PDA@MHNT) is obtained. Finally, under the action of the alkali activator, the MHNT inside CT-PDA@MHNT decomposes into geopolymer monomers, and then solidifies on the upper surface of the MH substrate to form a photothermal layer to obtain a CT-PDA@MH porous geopolymer seawater evaporator.

[0054] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0055] 1. The present invention uses the alkali activation method to prepare porous foamed geopolymer, and the reaction process is simple and easy to control. In addition, there are no by-products during the reaction process, which is environmentally friendly, pollution-free, and can be prepared in large quantities, facilitating production.

[0056] 2. In the prior art, the method of interface evaporation seawater desalination through geopolymer mostly uses a geopolymer film and a graphene photothermal material, and only contains relatively small pores generated during the geopolymerization process. However, this method uses hollow glass microspheres and H 2 O 2 to foam and generate a hierarchical pore structure. The abundant spherical pores enable it to float on the water surface. Using the carbonization of polydopamine to enhance the photothermal conversion ability greatly reduces the cost compared with graphene. After the decomposition reaction of the internal MHNT, the carbonized polydopamine retains a part of the nanotube structure, effectively reducing the evaporation enthalpy of water.

[0057] 3. The CT-PDA@MH geopolmer seawater evaporator prepared by the present invention has an evaporation rate of 2.57 kg m -2 ) under a solar light intensity of 1000 Wm -2 h -1 , and its evaporation rate is better than that of the prior art (the prior art here refers to the related technologies of seawater desalination at the geopolmer interface). Description of the Drawings

[0058] Figure 1 It is a hydrophilicity test diagram of MH1 in Example 1;

[0059] Figure 2 It is an SEM diagram of MH1 in Example 1;

[0060] Figure 3 It is an FTIR diagram of PDA@MHNT and C800-PDA@MHNT in Example 1;

[0061] Figure 4 It is a comparison diagram of the light absorption rates of MHNT, PDA@MHNT, and C800-PDA@MHNT in Example 1;

[0062] Figure 5 It is a comparison diagram of the evaporation rates of PDA@MH1 in Comparative Example 1 and MH1 and C800-PDA@MH1 in Example 1;

[0063] Figure 6 It is an evaporation rate diagram of C800-PDA@MH1 in Example 1 under different light intensities;

[0064] Figure 7 It is an evaporation rate diagram of C800-PDA@MH1 in Example 1 under different concentrations of salt solutions;

[0065] Figure 8 It is a self-cleaning test and schematic diagram of the salt on the surface of the C800-PDA@MH1 evaporator in Example 1;

[0066] Figure 9 It is an effect diagram of the purification of different wastewaters by C800-PDA@MH1 in Example 1;

[0067] Figure 10 It is a cycle test result diagram of C800-PDA@MH1 in Example 1;

[0068] Figure 11 It is an outdoor test result diagram of C800-PDA@MH1 in Example 1;

[0069] Figure 12Absorbance comparison diagrams of MHNT, PDA@MHNT, and C500-PDA@MHNT in Example 2;

[0070] Figure 13 Evaporation rate comparison diagrams of PDA@MH1 in Comparative Example 1, MH1 in Example 1, and C500-PDA@MH2 in Example 2;

[0071] Figure 14 Absorbance comparison diagrams of MHNT, PDA@MHNT, and C600-PDA@MHNT in Example 3;

[0072] Figure 15 Evaporation rate comparison diagrams of PDA@MH1 in Comparative Example 1, MH1 in Example 1, and C600-PDA@MH3 in Example 3;

[0073] Figure 16 Absorbance comparison diagrams of MHNT, PDA@MHNT, and C700-PDA@MHNT in Example 4;

[0074] Figure 17 Evaporation rate comparison diagrams of PDA@MH1 in Comparative Example 1, MH1 in Example 1, and C700-PDA@MH4 in Example 4;

[0075] Figure 18 Absorbance comparison diagrams of MHNT, PDA@MHNT, and C900-PDA@MHNT in Example 5;

[0076] Figure 19 Evaporation rate comparison diagrams of PDA@MH1 in Comparative Example 1, MH1 in Example 1, and C900-PDA@MH5 in Example 5. Detailed implementation manners

[0077] The present invention will be further described below with specific examples. The illustrative examples and descriptions of the present invention are used to explain the present invention, but do not limit the present invention.

[0078] For all raw materials of the present invention, there is no special limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0079] For the devices involved in the present invention, those without special limitations are commonly used devices in the art, and those skilled in the art are familiar with their operations and usage methods.

[0080] The present invention will be further described below with specific examples. The illustrative examples and descriptions of the present invention are used to explain the present invention, but do not limit the present invention.

[0081] The alkali activator used in the following examples is obtained by dissolving a certain amount of sodium hydroxide and sodium silicate in a certain amount of deionized water. The specific steps are as follows: Sodium hydroxide, water glass, and water are mixed in a molar ratio of SiO 2 ∶Na 2 O∶H 2 O = 1.38∶1∶15.74, and then stirred for 6 - 8 h until the solution becomes clear and transparent to obtain the alkali activator.

[0082] In the following examples, the hollow glass microspheres are soda-lime borosilicate glass microspheres with a diameter of 20 - 75 μm.

[0083] Example 1

[0084] A preparation method of a porous geopolymers seawater evaporator includes the following steps:

[0085] Halloysite (HNT) is calcined at 750 °C for 3 h in an air atmosphere to dehydroxylate it, obtaining metahalloysite, denoted as MHNT;

[0086] HNT, MHNT, and hollow glass microspheres are dispersed in the alkali activator in a mass ratio of 1∶2∶1, and then a nonionic surfactant F 108 and 5% of 30 wt% H 2 O 2 aqueous solution based on the total mass of the solid raw materials are added. The mass-volume ratio of the solid raw materials to the alkali activator is 1∶1.5, and the unit of the mass-volume ratio is g∶mL. Next, the above mixture is stirred with a glass rod until it is evenly mixed to obtain an MHNT-based geopolymer slurry, which is then poured into a cylindrical silicone mold (diameter × height = 30 mm × 15 mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum chamber with a pressure of 0.08 MPa, and the sample rapidly foams and expands under a negative pressure environment, generating a large number of holes from top to bottom. Subsequently, the sample is preliminarily cured in the vacuum chamber at room temperature for 12 h, and then transferred to a high-temperature environment of 60 °C for rapid curing for 6 h. After curing, the sample is taken out of the mold, and the excess alkali is neutralized and removed by an excessive amount of 1M hydrochloric acid solution. Subsequently, the sample is washed several times with deionized water and dried overnight to obtain a foamed geopolymer, denoted as MH1.

[0087] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 800°C to obtain carbon-coated MHNT, represented by C800-PDA@MHNT.

[0088] C800-PDA@MHNT was coated on the upper surface of MH1 by geopolymerization to prepare the photothermal layer. Specifically, C800-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4 The monomer was then evenly applied to the upper surface of MH1 to form a photothermal layer with a thickness of 0.05 mm. The sample was placed at room temperature for 12 h for preliminary curing and then transferred to a 60 °C high-temperature oven for 6 h for rapid curing. After curing, excess 1M hydrochloric acid solution was used to neutralize the sample to remove excess alkali. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C800-PDA@MH1 geopolymer evaporator.

[0089] Evaporation rate test: Place the C800-PDA@MH1 geopolymer evaporator in a 50mL beaker, use a xenon lamp to simulate sunlight, and calculate the evaporation rate by recording the mass change of water in the beaker.

[0090] Cyclic stability performance test: The C800-PDA@MH1 geopolymer evaporator was subjected to continuous evaporation for 8 hours under one sunlight intensity, and the cycle test was repeated 10 times to record the changes in evaporation rate.

[0091] Outdoor performance test: C800-PDA@MH1 geopolymer evaporator was used to conduct actual measurements from 10 am to 4 pm, and the light intensity was recorded every half hour. The influence of wind was eliminated by covering with a PMMA (polymethyl methacrylate) hemispherical cover.

[0092] Comparative Example 1

[0093] MH1 and PDA@MHNT were prepared according to the method in Example 1, and then PDA@MHNT was coated on MH1 as a photothermal layer according to the geopolymerization method in Example 1 to obtain a PDA@MH1 geopolymer evaporator.

[0094] like Figure 1 As shown, Figure 1It is a hydrophilicity test diagram of MH1 in Example 1. In the water contact angle test, the water droplet was completely absorbed instantly upon contacting the sample, presenting a water contact angle of 0°. When the sample was placed in water, water was rapidly transported to the upper surface by capillary action and was completely wetted at 4 s.

[0095] Perform SEM test on MH1 of Example 1, and the test results are as Figure 2 shown. A hierarchical three-dimensional porous structure with three types of pores evenly distributed can be observed in the figure. Specifically, oxygen bubbles in the geopolymer slurry generated by the decomposition of hydrogen peroxide formed large pores with diameters of 12 - 242 μm (average 118.47 μm), and due to the vacuum effect, there are a large number of through holes. The intermediate pores (spherical voids) inside the MH1 foam geopolymer skeleton are formed by hollow glass spheres. The main component on the shell of the hollow glass sphere is silica, which can participate in the geopolymerization reaction, thus leaving hollow spherical pores on the MH1 skeleton. These spherical pores are difficult for water to enter under normal atmospheric pressure, providing conditions for the evaporator to float on the water surface. In addition, there are also a large number of capillary pores inside the geopolymer, which is the result of MHNT geopolymerization and provides support for the capillary action to transport water. In addition, due to the addition of the original HNT, the inside of the evaporator is filled with nanotube structures, and the nanotubes overlap with each other to form more pores, further increasing the water channels and improving the hydrophilicity of the evaporator.

[0096] Perform FTIR test on PDA@MHNT and C800 - PDA@MHNT obtained in Example 1, and the results are as Figure 3 shown. In the spectrum of PDA@MHNT, the peaks in the range of 3400 - 3700 cm -1 are symmetric and asymmetric N - H stretching vibration peaks, which are caused by the amino molecules in the polydopamine molecules. The peak at about 1628 cm -1 is caused by the aromatic structure, for the aromatic ring structure in the polydopamine structure. The peaks at 830 - 1160 cm -1 correspond to the C - H bending vibration and C - N stretching vibration of the polydopamine molecule. The peaks at 530 - 830 cm -1 correspond to the C - H bending vibration and C - C vibration. In the spectrum of C800 - PDA@MHNT, the peaks of polydopamine are weakened or even disappeared to varying degrees, which is caused by high-temperature carbonization.

[0097] Figure 4Absorbance comparison of MHNT, PDA@MHNT, and C800-PDA@MHNT in Example 1. It can be seen from this that MHNT shows the lowest absorbance, only 28.30%, and the absorbance of the sample after wrapping with PDA rises to 58.91%. After carbonization at 800 °C, the absorbance of the sample increases rapidly to 97.25%, especially in the wavelength range of 700 - 2200 nm, where the increase is the most obvious.

[0098] Figure 5 Evaporation rate comparison chart of PDA@MH1 in Comparative Example 1 and MH1 and C800-PDA@MH1 in Example 1. The results show that MH1 with the lowest absorbance only shows an evaporation rate of 0.71 kg m -2 h -1 However, after introducing PDA, the evaporation rate increases to 1.32 kg m -2 h -1 After carbonization at 800 °C, the evaporation rate increases significantly to 2.57 kg m -2 h -1 .

[0099] Figure 6 Evaporation rate chart of C800-PDA@MH1 in Example 1 under different light intensities. The results show that when the light intensity increases from 1000 W m -2 to 1500 W m -2 the evaporation rate increases from 2.57 kg m -2 h -1 to 2.83 kg m -2 h -1 When the light intensity increases again to 2000 W m -2 the evaporation rate increases to 3.93 kg m -2 h -1 indicating that the evaporator can work under various light intensities.

[0100] Figure 7 Evaporation rate chart of C800-PDA@MH1 in Example 1 under different concentrations of salt solutions. As shown in the figure, with the increase in the concentration of the salt solution, although the evaporation rate decreases, the change is almost negligible. When the salt concentration increases to 10%, it can still maintain a high evaporation rate of 2.36 kg m -2 h -1 indicating that the evaporator can be applied to the desalination of high-concentration brine.

[0101] Table 1 shows the calculation of the thermal efficiency of C800-PDA@MH1 in Example 1.

[0102] Among them, the reflection loss is calculated by the formula λ absorption +λ reflection +λtransmission is calculated as = 1; the radiative loss is obtained from the equation ; the conductive loss is obtained from the formula is calculated; the convective loss is obtained from the formula .

[0103] The calculation results are shown in Table 1.

[0104] Table 1 Thermal Loss Calculation of C800 - PDA@MH1

[0105]

[0106] Table 2 shows the comparison of the enthalpy of evaporation of PDA@MH1 in Comparative Example 1, C800 - PDA@MH1 in Example 1, and pure water. It can be seen from the table that compared with pure water, the enthalpy of evaporation of both PDA@MH1 and C800 - PDA@MH1 is effectively reduced, and the enthalpy of evaporation of C800 - PDA@MH1 is lower. This is because there are carbon nanotubes on the surface of C800 - PDA@MH1, and the nanotube structure can effectively restrict water and reduce the enthalpy of evaporation of water.

[0107] Table 2 Enthalpy of Evaporation of PDA@MH1, C800 - PDA@MH1, and Pure Water

[0108] Pure water PDA@MH1 C800-PDA@MH1 <![CDATA[Evaporation rate(kg m -2 h -1 )]]> 0.06574 0.1051 0.1103 <![CDATA[Enthalpy(kJ kg -1 )]]> 2412 1509 1438

[0109] Figure 8 is the self - cleaning test and schematic diagram of the salt on the surface of the C800 - PDA@MH1 evaporator in Example 1. Currently, there are two feasible salt - resistant methods for solar seawater evaporators. One is surface hydrophobic modification to resist salt crystallization, and the other is to provide sufficient water flux to release high - concentration brine in a timely manner. To characterize the salt resistance of the evaporator, a long - term cyclic experiment of 8 h was carried out on the evaporator, and a small amount of salt accumulated on the surface of C800 - PDA@MH1 after drying. However, when C800 - PDA@MH1 comes into contact with water again, the salt on the water surface will dissolve, enabling it to self - clean. These results indicate that the excellent hydrophilicity of the evaporator surface can effectively prevent salt crystallization, and the vertically arranged microchannels in the evaporator are conducive to the diffusion of surface - crystallized high - concentration salt into water.

[0110] Figure 9 is the purification effect diagram of C800 - PDA@MH1 in Example 1 for different wastewaters. By measuring the resistance value, the change in ion concentration before and after purification was tested. From Figure 9It was observed in a that after purification by the evaporator, the resistance values of brines with concentrations of 0 - 10% all increased, and even the resistance value of the 10% brine after purification was greater than that of deionized water, indicating that the evaporator has good ion purification ability. In addition, K before and after seawater purification was measured by inductively coupled plasma - atomic emission spectrometry (ICP - AES). + 、Ca 2+ 、Na + 、Mg 2+ for concentration testing, as shown in Figure 9 b. The results show that their concentrations decreased significantly after purification and could meet the drinking water standards of the World Health Organization (WHO). The purification ability of the evaporator for dye wastewater was characterized by ultraviolet testing, as shown in Figure 9 c. The results show that almost no dye components were detected in the condensate after evaporation in the dye wastewater. The condensate collected in the acidic and alkaline waters in Figure 9 d was almost neutral. These results indicate that the C800 - PDA@MH1 evaporator has good pollution treatment ability and acid - base resistance.

[0111] Figure 10 It is the cyclic test result diagram of C800 - PDA@MH1 in Example 1. The results show that during 10 long cycles, the evaporation rate of the evaporator basically did not change, and the evaporation rate changes in each cycle were basically the same, and each change curve was basically parallel, indicating that the evaporator can maintain long - term stability during the evaporation process.

[0112] Figure 11 It is the outdoor test result diagram of C800 - PDA@MH1 in Example 1. The outdoor test was carried out in a self - made evaporation unit, which included a hemispherical light dome and two cylindrical containers with different diameters. PMMA with a light transmittance of 92% was used to hold seawater and the evaporator, and an external container was used to collect condensed water. The outdoor cycle lasted for three weeks. It can be seen from the figure that on sunny days, even though the average light intensity was lower than that simulated indoors, the evaporator could still maintain a rapid evaporation rate greater than 2 kg m -2 h -1 , indicating that the evaporator can be used in practical applications. Due to the influence of weather conditions, seasons, and geographical locations, the average evaporation rate fluctuates greatly, mainly due to differences in the amount of light.

[0113] Example 2

[0114] The basic content (process and conditions) of this example is basically the same as that in Example 1, and the difference is that: a PDA carbonization temperature of 500 °C was used instead of 800 °C.

[0115] The specific sample treatment method is as follows:

[0116] Halloysite (HNT) was calcined at 750 °C for 3 h in an air atmosphere to dehydroxylate it, obtaining metahalloysite, denoted as MHNT;

[0117] HNT, MHNT and hollow glass microspheres were dispersed in an alkali activator in a mass ratio of 1:2:1, and then a non-ionic surfactant F 108 and 5% of the total mass of the solid raw materials of 30 wt% H 2 O 2 aqueous solution were added. The mass-volume ratio of the solid raw materials to the alkali activator was 1:1.5, and the unit of the mass-volume ratio was g:mL. Next, the above mixture was stirred with a glass rod until it was uniformly mixed to obtain an MHNT-based geopolmer slurry, which was then poured into a cylindrical silicone mold (diameter × height = 30 mm × 15 mm) and covered with plastic wrap to prevent water evaporation. The sample was transferred to a vacuum chamber with a pressure of 0.08 MPa, and the sample rapidly foamed and expanded under a negative pressure environment, generating a large number of holes from top to bottom. Subsequently, the sample was preliminarily cured in the vacuum chamber at room temperature for 12 h, and then transferred to a high-temperature environment of 60 °C for rapid curing for 6 h. After curing, the sample was taken out of the mold, and the excess alkali in the sample was neutralized and removed by an excessive amount of 1 M hydrochloric acid solution. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain a foamed geopolmer, denoted as MH2.

[0118] MHNT and dopamine monomer were dispersed in Tris-HCl solution in a mass ratio of 5:1. The mass sum of MHNT and dopamine monomer and the mass-volume ratio of Tris-HCl were 6:50, and the unit of the mass-volume ratio was g:mL. The mixture was stirred for 24 h to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. Then PDA@MHNT was carbonized in an inert gas (Ar) environment at 500 °C to obtain carbon-coated MHNT, denoted as C500-PDA@MHNT.

[0119] C500-PDA@MHNT was coated on the upper surface of MH2 by a geopolymerization reaction to prepare a photothermal layer. Specifically, C500-PDA@MHNT and the alkali activator were fully mixed in a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed into SiO 4 and AlO 4The monomer was then evenly coated on the upper surface of MH2 to form a photothermal layer with a thickness of 0.05 mm. The sample was placed at room temperature for preliminary curing and then transferred to a high-temperature oven at 60 °C for rapid curing. Subsequently, the sample was placed in a vacuum chamber at room temperature for 12 h of preliminary curing and then transferred to a high-temperature environment at 60 °C for rapid curing for 6 h. After curing, the excess alkali in the sample was neutralized and removed by an excessive amount of 1 M hydrochloric acid solution. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C500-PDA@MH2 geopolmer evaporator.

[0120] The seawater evaporator obtained in this example was tested using the same evaporation rate test and cyclic stability performance test as in Example 1.

[0121] Figure 12 It is a comparison chart of the light absorption rates of MHNT, PDA@MHNT, and C500-PDA@MHNT in Example 2.

[0122] The results are as Figure 12 shown. It can be seen from this that the absorption rate of PDA increased significantly after carbonization at 500 °C. The absorption rate of the sample increased rapidly to 88.86% after carbonization at 500 °C, especially in the wavelength range of 700 - 2200 nm, where the increase was most obvious.

[0123] Figure 13 It is a comparison chart of the evaporation rates of PDA@MH1 in Comparative Example 1, MH1 in Example 1, and C500-PDA@MH2 in Example 2. The results show that MH1 with the lowest light absorption rate only exhibited an evaporation rate of 0.71 kg m -2 h -1 , while after introducing PDA, the evaporation rate increased to 1.32 kg m -2 h -1 , and after carbonization at 500 °C, the evaporation rate increased significantly to 2.43 kg m - 2 h -1 .

[0124] Table 3 shows the calculation of the thermal efficiency of the sample C500-PDA@MH2 obtained in Example 2. The calculation formula is the same as that used in Table 1, and the calculation results are shown in Table 3.

[0125] Table 3 Thermal loss calculation of C500-PDA@MH2

[0126]

[0127] Table 4 shows the comparison of the enthalpy of evaporation of PDA@MH1 in Comparative Example 1, C500-PDA@MH2 in Example 2, and pure water. It can be seen from the table that compared with pure water, the enthalpy of evaporation of both PDA@MH1 and C500-PDA@MH2 is effectively reduced, and the enthalpy of evaporation of C500-PDA@MH2 is even lower. This is because there are carbon nanotubes on the surface of C500-PDA@MH2, and the nanotube structure can effectively restrict water and reduce the enthalpy of evaporation of water.

[0128] Table 4 Enthalpy of evaporation of PDA@MH1, C500-PDA@MH2, and pure water

[0129] Pure water PDA@MH1 C500-PDA@MH2 <![CDATA[Evaporation rate(kg m -2 h -1 )]]> 0.06574 0.1051 0.1074 <![CDATA[Enthalpy(kJ kg -1 )]]> 2412 1509 1476

[0130] Example 3

[0131] The basic content (process and conditions) of this example is basically the same as that in Example 1, except that: the PDA carbonization temperature of 600 °C is used instead of 800 °C.

[0132] The specific sample treatment method is as follows:

[0133] Halloysite (HNT) is calcined at 750 °C for 3 h in an air atmosphere to dehydroxylate it, obtaining metahalloysite, denoted as MHNT;

[0134] HNT, MHNT, and hollow glass microspheres are dispersed in an alkali activator in a mass ratio of 1:2:1, and then a non-ionic surfactant F 108 and 30 wt% H 2 O 2 aqueous solution with a mass of 5% of the total mass of the solid raw materials are added. The mass-volume ratio of the solid raw materials to the alkali activator is 1:1.5, and the unit of the mass-volume ratio is g:mL; Next, the above mixture is stirred with a glass rod until it is uniformly mixed to obtain an MHNT-based geopolmer slurry, which is then poured into a cylindrical silicone mold (diameter × height = 30 mm × 15 mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum chamber with a pressure of 0.08 MPa, and the sample rapidly foams and expands in a negative pressure environment, generating a large number of holes from top to bottom. Subsequently, the sample is preliminarily cured in the vacuum chamber at room temperature for 12 h, and then transferred to a high-temperature environment of 60 °C for rapid curing for 6 h; after curing, the sample is taken out of the mold, and the excess alkali in the sample is removed by neutralization with an excessive 1 M hydrochloric acid solution. Subsequently, the sample is washed several times with deionized water and dried overnight to obtain a foamed geopolmer, denoted as MH3.

[0135] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 600°C to obtain carbon-coated MHNT, represented by C600-PDA@MHNT.

[0136] C600-PDA@MHNT was coated on the upper surface of MH3 by geopolymerization to prepare the photothermal layer. Specifically, C600-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4 The monomer was then evenly applied to the upper surface of MH3 to form a photothermal layer with a thickness of 0.05 mm. The sample was then placed at room temperature for 12 h for preliminary curing and then transferred to a 60 °C high-temperature oven for 6 h for rapid curing. After curing, excess 1M hydrochloric acid solution was used to neutralize and remove excess alkali in the sample. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain a C600-PDA@MH3 geopolymer evaporator.

[0137] The seawater evaporator obtained in this embodiment was tested using the same evaporation rate test and cycle stability performance test as in Example 1.

[0138] Figure 14 The absorbance comparison chart of MHNT, PDA@MHNT and C600-PDA@MHNT in Example 3 is shown in FIG. Figure 14 As shown, it can be seen that the absorptivity of PDA increases significantly after carbonization at 600°C. The absorptivity of the sample increases rapidly to 93.5% after carbonization at 600°C, especially in the wavelength range of 700-2200nm.

[0139] Figure 15 The evaporation rates of PDA@MH1 in comparative example 1, MH1 in example 1, and C600-PDA@MH3 in example 2 are compared. The results show that MH1 with the lowest absorbance only exhibits an evaporation rate of 0.71 kg m -2 h -1 After the introduction of PDA, the evaporation rate increased to 1.32 kg m -2 h -1 After carbonization at 600 °C, the evaporation rate increased significantly to 2.51 kg m -2 h -1 。

[0140] Table 5 shows the calculation of the thermal efficiency of the sample C600-PDA@MH3 obtained in Example 3. The calculation formula is the same as that used in Table 1, and the calculation results are shown in Table 5.

[0141] Table 5 Calculation of heat loss of C600-PDA@MH3

[0142]

[0143] Table 6 shows the comparison of the enthalpy of evaporation of PDA@MH1 in Comparative Example 1, C600-PDA@MH3 in Example 3, and pure water. It can be seen from the table that compared with pure water, the enthalpy of evaporation of both PDA@MH1 and C600-PDA@MH3 is effectively reduced, and the enthalpy of evaporation of C600-PDA@MH3 is lower. This is because carbon nanotubes exist on the surface of C600-PDA@MH3, and the nanotube structure can effectively restrict water and reduce the enthalpy of evaporation of water.

[0144] Table 4 Enthalpy of evaporation of PDA@MH1, C600-PDA@MH3, and pure water

[0145] Pure water PDA@MH1 C600-PDA@MH3 <![CDATA[Evaporation rate(kg m -2 h -1 )]]> 0.06574 0.1051 0.1103 <![CDATA[Enthalpy(kJ kg -1 )]]> 2412 1509 1438

[0146] Example 4

[0147] The basic content (process and conditions) of this example is basically the same as that in Example 1, and the difference is that: the PDA carbonization temperature of 700 °C is used instead of 800 °C.

[0148] The specific sample treatment method is as follows:

[0149] The halloysite (HNT) is calcined at 750 °C for 3 h in an air atmosphere to dehydroxylate it to obtain metahalloysite, denoted as MHNT;

[0150] HNT, MHNT, and hollow glass microspheres are dispersed in an alkali activator in a mass ratio of 1:2:1, and then a non-ionic surfactant F 108 and 5% of the total mass of the solid raw materials of 30 wt% H 2 O 2The mass volume ratio of the aqueous solution, the solid raw material and the alkali activator is 1:1.5, and the unit of the mass volume ratio is g:mL; Next, the above mixture is stirred with a glass rod until it is evenly mixed to obtain the MHNT-based geopolymer slurry, which is then poured into a cylindrical silica gel mold (diameter × height = 30mm × 15mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum box with a pressure of 0.08MPa. The sample rapidly foams and expands under negative pressure and produces a large number of top-down holes. The sample is then initially cured in a vacuum box at room temperature for 12h, and then transferred to a high temperature environment of 60℃ for rapid curing for 6h; After curing, the sample is removed from the mold and the excess alkali in the sample is neutralized and removed by an excess of 1M hydrochloric acid solution. Subsequently, the sample is washed with deionized water several times and dried overnight to obtain a foamed geopolymer, recorded as MH4.

[0151] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 700°C to obtain carbon-coated MHNT, represented by C700-PDA@MHNT.

[0152] C700-PDA@MHNT was coated on the upper surface of MH4 by geopolymerization to prepare the photothermal layer. Specifically, C700-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4 The monomer was then evenly applied to the upper surface of MH4 to form a photothermal layer with a thickness of 0.05 mm. The sample was then placed at room temperature for 12 h for preliminary curing and then transferred to a 60 °C high-temperature oven for 6 h for rapid curing. After curing, excess 1M hydrochloric acid solution was used to neutralize and remove excess alkali from the sample. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C700-PDA@MH4 geopolymer evaporator.

[0153] The seawater evaporator obtained in this embodiment was tested using the same evaporation rate test and cycle stability performance test as in Example 1.

[0154] Figure 16 The absorbance comparison diagram of MHNT, PDA@MHNT, and C700-PDA@MHNT in Example 4. The absorbance test results are as follows Figure 16As shown, it can be seen that the absorption rate of PDA increases significantly after carbonization at 700 °C. The absorption rate of the sample after carbonization at 700 °C increases rapidly to 95.68%, especially in the wavelength range of 700 - 2200 nm, where the increase is most obvious.

[0155] Figure 17 For the comparison of the evaporation rates of PDA@MH1 in Comparative Example 1, MH1 in Example 1, and C700-PDA@MH4 obtained in Example 4. The results show that MH1 with the lowest light absorption rate only exhibits an evaporation rate of 0.71 kg m -2 h -1 , while after introducing PDA, the evaporation rate increases to 1.32 kg m -2 h -1 , and after carbonization at 500 °C, the evaporation rate increases significantly to 2.54 kg m -2 h -1 .

[0156] Table 7 shows the calculation of the thermal efficiency of the sample C700-PDA@MH4 obtained in Example 4. The calculation formula is the same as that used in Table 1, and the calculation results are shown in Table 7.

[0157] Table 7 Thermal loss calculation of C700-PDA@MH4

[0158]

[0159] Table 8 shows the comparison of the evaporation enthalpies of PDA@MH1 in Comparative Example 1, C700-PDA@MH4 in Example 4, and pure water. It can be seen from the table that compared with pure water, the evaporation enthalpies of PDA@MH1 and C700-PDA@MH4 are both effectively reduced, and the evaporation enthalpy of C700-PDA@MH4 is lower, which is due to the presence of carbon nanotubes on the surface of C700-PDA@MH4, and the nanotube structure can effectively restrict water and reduce the evaporation enthalpy of water.

[0160] Table 8 Evaporation enthalpies of PDA@MH1, C700-PDA@MH4, and pure water

[0161] Pure water PDA@MH1 C700-PDA@MH4 <![CDATA[Evaporation rate(kg m -2 h -1 )]]> 0.06574 0.1051 0.1108 <![CDATA[Enthalpy(kJ kg -1 )]]> 2412 1509 1431

[0162] Example 5

[0163] The basic content (process and conditions) of this example is basically the same as that in Example 1, and the difference is that: the PDA carbonization temperature of 900 °C is used instead of 800 °C.

[0164] The specific sample treatment method is as follows:

[0165] Halloysite (HNT) was calcined at 750°C in air atmosphere to dehydroxylate it. The calcination time was 3 h to obtain meta-haloysite, which was recorded as MHNT.

[0166] HNT, MHNT and hollow glass microspheres were dispersed in an alkali activator at a mass ratio of 1:2:1, and then a nonionic surfactant was added at 0.25% of the total mass of the solid raw materials. F 108 and 5% of the total mass of solid raw materials 30wt% H 2 O 2 The mass volume ratio of the aqueous solution, the solid raw material and the alkali activator is 1:1.5, and the unit of the mass volume ratio is g:mL; Next, the above mixture is stirred with a glass rod until it is evenly mixed to obtain the MHNT-based geopolymer slurry, which is then poured into a cylindrical silica gel mold (diameter × height = 30mm × 15mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum box with a pressure of 0.08MPa. The sample rapidly foams and expands under negative pressure and produces a large number of top-down holes. The sample is then initially cured in a vacuum box at room temperature for 12h, and then transferred to a high temperature environment of 60℃ for rapid curing for 6h; After curing, the sample is removed from the mold and the excess alkali in the sample is neutralized and removed by an excess of 1M hydrochloric acid solution. Subsequently, the sample is washed with deionized water several times and dried overnight to obtain a foamed geopolymer, recorded as MH5.

[0167] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 900°C to obtain carbon-coated MHNT, represented by C900-PDA@MHNT.

[0168] C900-PDA@MHNT was coated on the upper surface of MH5 by geopolymerization to prepare the photothermal layer. Specifically, C900-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4The monomer was then evenly coated on the upper surface of MH5 to form a photothermal layer with a thickness of 0.05 mm. The sample was placed at room temperature for 12 h for preliminary curing and then transferred to a high-temperature oven at 60 °C for 6 h for rapid curing. After curing, the excess alkali in the sample was neutralized and removed by an excessive amount of 1 M hydrochloric acid solution. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C900-PDA@MH5 geopolmer evaporator.

[0169] The seawater evaporator obtained in this example was tested using the same evaporation rate test and cyclic stability performance test as in Example 1.

[0170] Figure 18 Figure for the comparison of the light absorption rates of MHNT, PDA@MHNT, and C900-PDA@MHNT in Example 5, and the results are as Figure 18 shown. It can be seen therefrom that the absorption rate increased significantly after carbonization of PDA at 900 °C, and the absorption rate of the sample increased rapidly to 97.25% after carbonization at 900 °C, especially the most obvious increase in the wavelength range of 700 - 2200 nm.

[0171] Figure 19 Figure for the comparison of the evaporation rates of PDA@MH1 in Comparative Example 1, MH1 in Example 1, and C900-PDA@MH5 in Example 5. The results show that MH1 with the lowest light absorption rate only exhibited an evaporation rate of 0.71 kg m -2 h -1 , while after introducing PDA, the evaporation rate increased to 1.32 kg m -2 h -1 , and after carbonization at 900 °C, the evaporation rate increased significantly to 2.60 kg m - 2 h -1 .

[0172] Table 9 shows the calculation of the thermal efficiency of the sample C900-PDA@MH5 obtained in Example 5. The calculation formula is the same as that used in Table 1, and the calculation results are shown in Table 9.

[0173] Table 9 Thermal loss calculation of C900-PDA@MH5

[0174]

[0175] Table 10 shows the comparison of the enthalpy of vaporization of PDA@MH1 in Comparative Example 1, C900-PDA@MH5 in Example 5, and pure water. It can be seen from the table that compared with pure water, the enthalpy of vaporization of both PDA@MH1 and C900-PDA@MH5 is effectively reduced, and the enthalpy of vaporization of C900-PDA@MH5 is even lower. This is because there are carbon nanotubes on the surface of C900-PDA@MH5, and the nanotube structure can effectively restrict water and reduce the enthalpy of vaporization of water.

[0176] Table 10 Enthalpy of Vaporization of PDA@MH1, C900-PDA@MH5, and Pure Water

[0177] Pure water PDA@MH1 C900-PDA@MH5 <![CDATA[Evaporation rate(kg m -2 h -1 )]]> 0.06574 0.1051 0.1107 <![CDATA[Enthalpy(kJ kg -1 )]]> 2412 1509 1432

[0178] Example 6

[0179] The basic content (process and conditions) of this example is basically the same as that in Example 1, and the difference is that: HNT, MHNT, and hollow glass microspheres are in a mass ratio of 1:2:2 instead of 1:2:1.

[0180] The specific sample treatment method is as follows:

[0181] Halloysite (HNT) is calcined at 750 °C in an air atmosphere for 3 h to dehydroxylate it, and the obtained metahalloysite is denoted as MHNT;

[0182] HNT, MHNT, and hollow glass microspheres are dispersed in an alkali activator in a mass ratio of 1:2:2, and then a non-ionic surfactant F 108 and 30 wt% H 2 O 2 aqueous solution with a mass ratio of solid raw materials to alkali activator of 1:1.5 (the unit of the mass ratio is g:mL) are added. Next, the above mixture is stirred with a glass rod until it is evenly mixed to obtain an MHNT-based geopolmer slurry, which is then poured into a cylindrical silicone mold (diameter × height = 30 mm × 15 mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum chamber with a pressure of 0.08 MPa, and the sample rapidly foams and expands in a negative pressure environment, generating a large number of holes from top to bottom. Subsequently, the sample is preliminarily cured in the vacuum chamber at room temperature for 12 h, and then transferred to a high-temperature environment of 60 °C for rapid curing for 6 h; after curing, the sample is taken out of the mold, and the excess alkali in the sample is neutralized and removed by an excessive 1 M hydrochloric acid solution. Subsequently, the sample is washed several times with deionized water and dried overnight to obtain a foamed geopolmer, denoted as MH6.

[0183] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 800°C to obtain carbon-coated MHNT, represented by C800-PDA@MHNT.

[0184] C800-PDA@MHNT was coated on the upper surface of MH6 by geopolymerization to prepare the photothermal layer. Specifically, C800-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4 The monomer was then evenly applied to the upper surface of MH6 to form a photothermal layer with a thickness of 0.05 mm. The sample was placed at room temperature for 12 h for preliminary curing and then transferred to a 60 ° C high temperature oven for 6 h for rapid curing. After curing, excess 1 M hydrochloric acid solution was used to neutralize and remove excess alkali in the sample. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C800-PDA@MH6 geopolymer evaporator.

[0185] The seawater evaporator obtained in this embodiment was tested using the same evaporation rate test and cycle stability performance test as in Example 1.

[0186] Example 7

[0187] The basic contents (process and conditions) of this embodiment are substantially the same as those of embodiment 1, except that a calcination temperature of 650° C. is used instead of 750° C. in the preparation process of MHNT.

[0188] The specific sample processing method is as follows:

[0189] Halloysite (HNT) was calcined at 650°C in air atmosphere for 3 h to dehydroxylate it and obtain meta-haloysite, which was recorded as MHNT.

[0190] HNT, MHNT and hollow glass microspheres were dispersed in an alkali activator at a mass ratio of 1:2:1, and then a nonionic surfactant was added at 0.25% of the total mass of the solid raw materials. F 108 and 5% of the total mass of solid raw materials 30wt% H 2 O 2The mass volume ratio of the aqueous solution, the solid raw material and the alkali activator is 1:1.5, and the unit of the mass volume ratio is g:mL; Next, the above mixture is stirred with a glass rod until it is evenly mixed to obtain the MHNT-based geopolymer slurry, which is then poured into a cylindrical silica gel mold (diameter × height = 30mm × 15mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum box with a pressure of 0.08MPa. The sample rapidly foams and expands under negative pressure and produces a large number of top-down holes. The sample is then initially cured in a vacuum box at room temperature for 12h, and then transferred to a high temperature environment of 60℃ for rapid curing for 6h; After curing, the sample is removed from the mold and the excess alkali in the sample is neutralized and removed by an excess of 1M hydrochloric acid solution. Subsequently, the sample is washed with deionized water several times and dried overnight to obtain a foamed geopolymer, recorded as MH7.

[0191] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 800°C to obtain carbon-coated MHNT, represented by C800-PDA@MHNT.

[0192] C800-PDA@MHNT was coated on the upper surface of MH7 by geopolymerization to prepare the photothermal layer. Specifically, C800-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4 The monomer was then evenly applied to the upper surface of MH7 to form a photothermal layer with a thickness of 0.05 mm. The sample was then initially cured in a vacuum oven at room temperature for 12 hours, and then transferred to a high temperature environment of 60°C for rapid curing for 6 hours; after curing, excess 1M hydrochloric acid solution was used to neutralize and remove excess alkali in the sample. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C800-PDA@MH7 geopolymer evaporator.

[0193] The seawater evaporator obtained in this embodiment was tested using the same evaporation rate test and cycle stability performance test as in Example 1.

[0194] Example 8

[0195] The basic content (process and conditions) of this example is basically the same as that of Example 1, and the difference is that: during the preparation of MHNT, a calcination temperature of 700 °C is used instead of 750 °C.

[0196] The specific sample treatment method is as follows:

[0197] Halloysite (HNT) is calcined at 700 °C in an air atmosphere for 3 h to dehydroxylate it, obtaining metahalloysite, denoted as MHNT;

[0198] HNT, MHNT and hollow glass microspheres are dispersed in an alkali activator in a mass ratio of 1:2:1, and then a non-ionic surfactant F 108 and 5% of the total mass of the solid raw materials of 30 wt% H 2 O 2 aqueous solution are added. The mass-volume ratio of the solid raw materials to the alkali activator is 1:1.5, and the unit of the mass-volume ratio is g:mL. Next, the above mixture is stirred with a glass rod until it is uniformly mixed to obtain an MHNT-based geopolmer slurry, which is then poured into a cylindrical silica gel mold (diameter × height = 30 mm × 15 mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum box with a pressure of 0.08 MPa, and the sample rapidly foams and expands under a negative pressure environment, generating a large number of holes from top to bottom. Subsequently, the sample is preliminarily cured in the vacuum box at room temperature for 12 h, and then transferred to a high-temperature environment of 60 °C for rapid curing for 6 h. After curing, the sample is taken out of the mold, and the excess alkali in the sample is neutralized and removed by an excessive amount of 1 M hydrochloric acid solution. Subsequently, the sample is washed several times with deionized water and dried overnight to obtain a foamed geopolmer, denoted as MH8.

[0199] MHNT and dopamine monomer are dispersed in Tris-HCl solution in a mass ratio of 5:1. The mass sum of MHNT and dopamine monomer and the mass-volume ratio of Tris-HCl is 6:50, and the unit of the mass-volume ratio is g:mL. The mixture is stirred for 24 h to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate is collected, washed and dried, and recorded as PDA@MHNT. Then PDA@MHNT is carbonized in an inert gas (Ar) environment at 800 °C to obtain carbon-coated MHNT, denoted as C800-PDA@MHNT.

[0200] C800-PDA@MHNT is coated on the upper surface of MH8 by a geopolymerization reaction to prepare a photothermal layer. Specifically, C800-PDA@MHNT and the alkali activator are fully mixed in a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposes into SiO 4 and AlO 4The monomer was then evenly applied to the upper surface of MH8 to form a photothermal layer with a thickness of 0.05 mm. The sample was placed at room temperature for 12 h for preliminary curing and then transferred to a high-temperature oven at 60 °C for 6 h for rapid curing. After curing, the excess alkali in the sample was neutralized and removed by an excessive amount of 1 M hydrochloric acid solution. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C800-PDA@MH8 geopolmer evaporator.

[0201] The seawater evaporator obtained in this example was tested using the same evaporation rate test and cyclic stability performance test as in Example 1.

[0202] Example 9

[0203] The basic content (process and conditions) of this example was basically the same as that in Example 1, except that: during the preparation of MHNT, a calcination temperature of 800 °C was used instead of 750 °C.

[0204] The specific sample treatment method was as follows:

[0205] Halloysite (HNT) was calcined at 800 °C for 3 h in an air atmosphere to dehydroxylate it, obtaining metahalloysite, denoted as MHNT;

[0206] HNT, MHNT, and hollow glass microspheres were dispersed in the alkali activator at a mass ratio of 1:2:1, and then a nonionic surfactant F 108 and 30 wt% H 2 O 2 aqueous solution with a total mass of the solid raw materials of 5% were added. The mass-to-volume ratio of the solid raw materials to the alkali activator was 1:1.5, and the unit of the mass-to-volume ratio was g:mL. Next, the above mixture was stirred with a glass rod until it was evenly mixed to obtain the MHNT-based geopolmer slurry, which was then poured into a cylindrical silicone mold (diameter × height = 30 mm × 15 mm) and covered with plastic wrap to prevent water evaporation. The sample was transferred to a vacuum chamber with a pressure of 0.08 MPa, and the sample rapidly foamed and expanded in a negative-pressure environment, generating a large number of holes from top to bottom. Subsequently, the sample was preliminarily cured in the vacuum chamber at room temperature for 12 h and then transferred to a high-temperature environment at 60 °C for rapid curing for 6 h. After curing, the sample was taken out of the mold, and the excess alkali in the sample was neutralized and removed by an excessive amount of 1 M hydrochloric acid solution. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the foamed geopolmer, denoted as MH9.

[0207] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 800°C to obtain carbon-coated MHNT, represented by C800-PDA@MHNT.

[0208] C800-PDA@MHNT was coated on the upper surface of MH9 by geopolymerization to prepare the photothermal layer. Specifically, C800-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4 The monomer was then evenly applied to the upper surface of MH9. The sample was placed at room temperature for 12 h for preliminary curing and then transferred to a 60 °C high temperature oven for 6 h for rapid curing. After curing, excess 1 M hydrochloric acid solution was used to neutralize and remove excess alkali in the sample. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C800-PDA@MH9 geopolymer evaporator.

[0209] The seawater evaporator obtained in this embodiment was tested using the same evaporation rate test and cycle stability performance test as in Example 1.

[0210] Example 10

[0211] The basic contents (process and conditions) of this embodiment are substantially the same as those of embodiment 1, except that a calcination temperature of 850° C. is used instead of 750° C. in the preparation process of MHNT.

[0212] The specific sample processing method is as follows:

[0213] Halloysite (HNT) was calcined at 850°C in air atmosphere for 3 h to dehydroxylate it and obtain meta-haloysite, which was recorded as MHNT.

[0214] HNT, MHNT and hollow glass microspheres were dispersed in an alkali activator at a mass ratio of 1:2:1, and then a nonionic surfactant was added at 0.25% of the total mass of the solid raw materials. F 108 and 5% of the total mass of solid raw materials 30wt% H 2 O 2The mass volume ratio of the aqueous solution, the solid raw material and the alkali activator is 1:1.5, and the unit of the mass volume ratio is g:mL; Next, the above mixture is stirred with a glass rod until it is mixed evenly to obtain the MHNT-based geopolymer slurry, which is then poured into a cylindrical silica gel mold (diameter × height = 30mm × 15mm) and covered with plastic wrap to prevent water evaporation. The sample is transferred to a vacuum box with a pressure of 0.08MPa. The sample rapidly foams and expands under negative pressure and produces a large number of top-down holes. The sample is then initially cured in a vacuum box at room temperature for 12h, and then transferred to a high temperature environment of 60℃ for rapid curing for 6h; After curing, the sample is removed from the mold and the excess alkali in the sample is neutralized and removed by an excess of 1M hydrochloric acid solution. Subsequently, the sample is washed with deionized water several times and dried overnight to obtain a foamed geopolymer, recorded as MH10.

[0215] MHNT and dopamine monomer were dispersed in Tris-HCl solution at a mass ratio of 5:1, the mass and volume ratio of MHNT and dopamine monomer to Tris-HCl was 6:50, and the unit of mass volume ratio was g:mL. The mixture was stirred for 24 hours to completely oxidize and polymerize dopamine. Subsequently, the gray-black precipitate was collected, washed and dried, and recorded as PDA@MHNT. PDA@MHNT was then carbonized in an inert gas (Ar) environment at 800°C to obtain carbon-coated MHNT, represented by C800-PDA@MHNT.

[0216] C800-PDA@MHNT was coated on the upper surface of MH10 by geopolymerization to prepare the photothermal layer. Specifically, C800-PDA@MHNT and alkali activator were fully mixed at a mass ratio of 1:1.5 to form a uniform slurry, so that the carbon-coated MHNT decomposed SiO 4 and AlO 4 The monomer was then evenly applied to the upper surface of MH10. The sample was placed at room temperature for 12 h for preliminary curing and then transferred to a 60 °C high-temperature oven for 6 h for rapid curing. After curing, excess 1M hydrochloric acid solution was used to neutralize and remove excess alkali in the sample. Subsequently, the sample was washed several times with deionized water and dried overnight to obtain the C800-PDA@MH10 geopolymer evaporator.

[0217] The seawater evaporator obtained in this embodiment was tested using the same evaporation rate test and cycle stability performance test as in Example 1.

[0218] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a porous geopolymer seawater evaporator, characterized in that: The following steps are involved: S1, Preparation of geopolymerizable heliumite The halloysite is calcined in an air atmosphere to obtain meta-haloysite, which is denoted as MHNT; S2, Preparation of MHNT-based porous foam geopolymer by chemical foaming S2.1, dispersing halloysite, MHNT, and hollow glass microspheres in an alkali activator, adding a nonionic surfactant and an aqueous hydrogen peroxide solution, and mixing them evenly to obtain a MHNT-based geopolymer slurry; S2.2, pouring the MHNT-based geopolymer slurry into a mold, foaming and expanding it under a pressure of 0.08-0.1 MPa, and then curing it to obtain a cured product; S2.3, neutralizing the solidified product with an acid solution, washing and drying the product after neutralization to obtain a MHNT-based porous foam geopolymer, denoted as MH; S3, Preparation of carbon-coated MHNTs by polydopamine method MHNT and dopamine monomer are dispersed in Tris-HCl solution and stirred and mixed. After the reaction is completed, the precipitate is collected; the precipitate is washed and dried to obtain PDA@MHNT; PDA@MHNT is carbonized to obtain carbon-coated MHNT, which is recorded as CT-PDA@MHNT; S4, Preparation of porous geopolymer evaporator CT-PDA@MHNT is mixed with an alkaline activator, coated on the upper surface of MH as a photothermal layer through a geopolymerization reaction, and then cured; after curing, it is neutralized with an acid solution, washed and dried after neutralization to obtain a porous geopolymer evaporator, recorded as CT-PDA@MH.

2. The method for preparing the porous geopolymer seawater evaporator according to claim 1, characterized in that: In the step S1, the calcination temperature is 650-850° C. and the calcination time is 3 hours.

3. The method for preparing the porous geopolymer seawater evaporator according to claim 1, characterized in that: In the step S2.1, the mass ratio of halloysite, MHNT and hollow glass microspheres is 1:2:(1-2); In the step S2.1, halloysite, MHNT, and hollow glass microspheres are all solid raw materials; The amount of the nonionic surfactant used is 0.1-0.5% of the total mass of the solid raw material; the concentration of the hydrogen peroxide aqueous solution is 30wt%, and the amount used is 5-10% of the total mass of the solid raw material; in the alkaline activator, the molar ratio of SiO2, Na2O, and H2O is 1.38:1:15.74; The mass volume ratio of the solid raw material to the alkali activator is 1:1.5, and the unit of the mass volume ratio is g:mL.

4. The method for preparing a porous geopolymer seawater evaporator according to claim 1, characterized in that: In step S2.3, the acid solution is a 1M hydrochloric acid solution; deionized water is used for multiple washings during the washing process; the drying temperature is 60° C., and the drying time is 12 hours.

5. The method for preparing the porous geopolymer seawater evaporator according to claim 1, characterized in that: In step S2.1, the hollow glass microspheres are soda lime borosilicate glass microspheres with a diameter of 20-75 μm; the nonionic surfactant is F 108.

6. The method for preparing a porous geopolymer seawater evaporator according to claim 1, characterized in that: In the step S3, the mass ratio of MHNT to dopamine monomer is 5:1; the mass volume ratio of the sum of the mass of MHNT and dopamine monomer to the mass of Tris-HCl solution is 6:50, and the unit of mass volume ratio is g:mL; The carbonization process is carried out in an inert gas environment, the carbonization temperature is 500-900°C, and the carbonization time is 30 minutes.

7. The method for preparing a porous geopolymer seawater evaporator according to claim 1, characterized in that: In the step S4, the mass ratio of CT-PDA@MHNT to the alkaline activator is 1:1.5; and the thickness of the photothermal layer is 0.05 mm.

8. The method for preparing a porous geopolymer seawater evaporator according to claim 1, characterized in that: In step S4, the curing process includes preliminary curing and rapid curing; the preliminary curing is placed at room temperature for 10-24 hours; Rapid curing is to place it in an environment of 50-80℃ for 6 hours.

9. A porous geopolymer seawater evaporator prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the porous geopolymer seawater evaporator according to claim 9 in seawater purification and wastewater purification.

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