A RE-MOF-based photothermal material, a photothermal interfacial evaporator, and a preparation method and application thereof

Abstract

The application provides a RE-MOF-based photothermal material, a photothermal interfacial evaporator and a preparation method and application thereof. The RE-MOF-based photothermal material comprises a two-dimensional nanosheet-shaped rare earth MOF material and a polydopamine coating layer on the surface of the rare earth MOF material. The RE-MOF-based photothermal material has high light absorption capacity and hydrothermal stability by coating the rare earth MOF material with polydopamine, so that the evaporation efficiency and photothermal conversion capacity of the photothermal interfacial evaporator can be effectively improved. When the photothermal material is applied to the photothermal interfacial evaporator, the photothermal interfacial evaporator with high solar light absorption capacity, stable performance structure, high photothermal conversion efficiency and good salt resistance can be obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solar-driven seawater desalination, and relates to a photothermal material based on RE-MOF, a photothermal interfacial evaporator and a preparation method and application thereof. BACKGROUND

[0002] The shortage of fresh water resources is a problem that cannot be ignored at the present stage, and extracting fresh water resources from seawater is a feasible solution. At present, the traditional seawater desalination technologies mainly include multi-stage flash evaporation, reverse osmosis, electrodialysis and membrane distillation, etc. However, these schemes more or less have some problems, such as high energy consumption, high cost, environmental pollution and the like.

[0003] Solar energy is a kind of inexhaustible green clean energy. If abundant solar energy is used in the production of fresh water resources, it has great significance. However, the efficiency of directly using solar energy to evaporate seawater is very low. Therefore, photothermal interfacial evaporation technology emerges as the times require. The solar photothermal interfacial evaporation technology effectively reduces the energy transfer process by selectively heating the thin layer of water at the interface, thereby improving the energy utilization rate and evaporation efficiency.

[0004] At present, the materials used in the field of photothermal interfacial evaporation are materials with high solar absorption rate, such as semiconductor materials, carbon-based materials, metal nanoparticles and organic polymers. However, most of the semiconductor materials have insufficient solar absorption bandwidth, which limits the solar photothermal conversion efficiency thereof. The traditional carbon-based materials have wide-band solar absorption rate, but are easily affected by pollutants in seawater. The metal nanoparticles have good photothermal conversion performance, but the high preparation cost restricts their large-scale application. Therefore, the high cost, narrow light absorption range, poor stability and low production efficiency restrict the practical application of these materials.

[0005] MOF has a large specific surface area and high porosity, and is an ideal choice for water treatment applications, attracting the interest of researchers in the field of photothermal interfacial evaporation. By customizing the structure of MOF or using it in combination with other photothermal agents, the light absorption and photothermal conversion capacity thereof can be effectively improved. RE-MOF is a special subset of MOF, which has more applications in the field of photothermal tumor treatment, and is a very potential photothermal conversion material. However, there is little research on RE-MOF in the field of photothermal interfacial evaporation, and the technology development is blank.

[0006] Based on the above research, it is necessary to provide a photothermal material based on RE-MOF, which has stable performance, strong solar light absorption capacity, high photothermal conversion efficiency and good salt deposition resistance. SUMMARY

[0007] The application aims to provide a RE-MOF-based photothermal material, a photothermal interfacial evaporator, and a preparation method and application thereof.

[0008] To achieve the above-mentioned purpose, the application adopts the following technical solutions.

[0009] In a first aspect, the application provides a RE-MOF-based photothermal material, which comprises a two-dimensional nanosheet-shaped rare earth MOF material and a polydopamine coating layer on the surface of the rare earth MOF material.

[0010] The application uses a two-dimensional nanosheet-shaped rare earth MOF coated with polydopamine as a photothermal material. The rare earth MOF material itself has excellent light-heat conversion capability. After the surface is coated with a polydopamine coating layer, the stability of the rare earth MOF material in water is improved, and the light absorption capability of the photothermal material is also improved. Therefore, the photothermal material has a large specific surface area, small particles, strong solar light absorption capability, and high water stability, thereby effectively improving the evaporation efficiency and light-heat conversion capability of the evaporator.

[0011] Preferably, the mass ratio of the rare earth MOF material to the polydopamine coating layer is 1:(0.1-10), for example, 1:0.1, 1:1, 1:5, or 1:10, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0012] The mass ratio of the rare earth MOF material to the polydopamine coating layer will affect the performance of the photothermal material. If the polydopamine coating layer is too much relative to the rare earth MOF material, the light-heat conversion capability of the MOF will be reduced. If the polydopamine coating layer is too little relative to the rare earth MOF material, the stability of the rare earth MOF in water will be affected.

[0013] Preferably, the rare earth atoms in the rare earth MOF material include any one or a combination of at least two of cerium, neodymium, erbium, or ytterbium, and ytterbium is preferred.

[0014] Preferably, the organic ligand in the rare earth MOF material includes porphyrin and / or porphyrin derivatives, and 5,10,15,20-tetra(4-carboxyphenyl)porphyrin is preferred.

[0015] In a second aspect, the application provides a preparation method of the RE-MOF-based photothermal material according to the first aspect, which comprises the following steps.

[0016] The rare earth MOF material, dopamine and a first solvent are mixed, and then the pH of the system is adjusted to allow the dopamine to polymerize on the surface of the rare earth MOF material, followed by solid-liquid separation, washing and drying to obtain the RE-MOF-based photothermal material.

[0017] The polydopamine coating layer is directly obtained by in-situ polymerization.

[0018] Preferably, the mass ratio of the rare earth MOF material to dopamine is 1:(0.1-10), for example, it can be 1:0.1, 1:1, 1:5 or 1:10, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0019] Preferably, the pH of the system is adjusted to 8-13, for example, it can be 8, 10, 12 or 13, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0020] Preferably, the mixing time is 8-24h, for example, it can be 8h, 10h, 15h, 20h or 24h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0021] Preferably, the mixing includes dispersing the rare earth MOF material in deionized water to form a rare earth MOF dispersion, adding dopamine to a mixed solution including Tris-HCL buffer, deionized water and ethanol to form a dopamine solution, and then mixing the rare earth MOF dispersion and the dopamine solution.

[0022] Preferably, the concentration of the rare earth MOF dispersion is 0-10mg / mL, but 0mg / mL is not included, for example, it can be 2mg / mL, 5mg / mL, 8mg / mL or 10mg / mL, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0023] Preferably, the dopamine solution is prepared by adding 0-100mg (not including 0mg) of dopamine hydrochloride, for example, 10mg, 30mg, 50mg, 70mg, 90mg or 100mg, to 1mL of 1mol / L Tris-HCL buffer, 6mL of deionized water and 3mL of ethanol.

[0024] Preferably, the method for preparing the rare earth MOF material includes the following steps:

[0025] The organic ligand, the rare earth salt and a second solvent are mixed to obtain a reaction precursor solution, and then the reaction precursor solution is heated, followed by solid-liquid separation and washing to obtain the rare earth MOF material.

[0026] Preferably, the heating method comprises microwave heating.

[0027] Preferably, the specific step of microwave heating comprises transferring the reaction precursor solution into a glass vial, and heating the vial in a microwave oven at a certain power for a certain time.

[0028] Preferably, the volume of the reaction precursor solution is 1-10 mL, for example, it can be 1 mL, 5 mL or 10 mL, the volume of the glass vial is 10-50 mL, for example, it can be 10 mL, 30 mL or 50 mL, the power of the microwave heating is 100-700 W, for example, it can be 100 W, 300 W, 500 W or 700 W, and the time of the microwave heating is 5-30 min, for example, it can be 5 min, 10 min, 20 min or 30 min, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0029] Further preferably, the volume of the reaction precursor solution is 1-2 mL, for example, it can be 1 mL, 1.5 mL or 2 mL, the volume of the glass vial is 10-20 mL, for example, it can be 10 mL, 15 mL or 20 mL, the power of the microwave heating is 200-300 W, for example, it can be 200 W, 250 W or 300 W, and the time of the microwave heating is 10-20 min, for example, it can be 10 min, 15 min or 20 min, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0030] Preferably, the mass ratio of the organic ligand, the rare earth salt and the second solvent is (1-10):(1-10):(1000-2000), for example, it can be 1:1:1000, 5:5:1500 or 10:10:2000, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0031] Preferably, the rare earth salt comprises any one or a combination of at least two of cerium nitrate hexahydrate, neodymium nitrate hexahydrate, erbium nitrate pentahydrate or ytterbium nitrate pentahydrate, and is preferably ytterbium nitrate pentahydrate.

[0032] Preferably, the content of the rare earth salt in the reaction precursor solution is 0.005-0.1 wt%, for example, it can be 0.005 wt%, 0.01 wt%, 0.05 wt% or 0.1 wt%, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0033] Preferably, the content of the organic ligand in the reaction precursor solution is 0.005-0.1 wt%, for example, it can be 0.005 wt%, 0.01 wt%, 0.05 wt% or 0.1 wt%, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0034] Preferably, the organic ligand comprises porphyrin and / or porphyrin derivatives, preferably 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin.

[0035] Preferably, the second solvent comprises any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide or deionized water, preferably N,N-dimethylformamide.

[0036] In a third aspect, the present application provides a RE-MOF-based photothermal interfacial evaporator, comprising a hydrogel and a RE-MOF-based photothermal material as described in the first aspect, and the photothermal interfacial evaporator has a pore structure.

[0037] The present application uses a hydrogel as an evaporator substrate, and adds a RE-MOF-based photothermal material therein, and the photothermal interfacial evaporator has a pore structure, forming a high-strength double-network hydrogel photothermal interfacial evaporator. The channels formed by the pore structure not only effectively transport water, but also continuously dissolve and transport salt ions generated on the surface of the evaporator into the bulk water, hindering the deposition of salt on the surface of the evaporator, and improving the cycle stability of the interfacial evaporator.

[0038] Preferably, the photothermal interfacial evaporator has a vertically arranged pore structure.

[0039] The vertically arranged pore structure of the present application allows the evaporator to have vertically oriented channels, which can transport water in a directional manner and block the deposition of salt on the surface of the evaporator.

[0040] Preferably, the content of the photothermal material in the photothermal interfacial evaporator is 0.01-1 wt%, for example, it can be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0041] If the light-thermal material is too little, the evaporation rate and the light-thermal conversion efficiency of the photothermal interfacial evaporator will be reduced, and if the light-thermal material is too much, the internal pores of the hydrogel will be blocked, affecting the water transport performance, and thus the evaporation rate and the light-thermal conversion efficiency of the entire evaporator will be reduced.

[0042] In a fourth aspect, the application provides a preparation method of the RE-MOF-based photothermal interfacial evaporator according to the third aspect, and the preparation method comprises the following steps:

[0043] (1) mixing a water-soluble polymer material, the light-thermal material according to the first aspect, a crosslinking agent and a third solvent to obtain a mixed solution;

[0044] (2) transferring the mixed solution to a mold for directional freezing, wherein the mold has a temperature gradient in the vertical and horizontal directions during the directional freezing, and then thawing after the directional freezing;

[0045] (3) cyclically performing the directional freezing and thawing process of step (2), and then freeze-drying the product obtained by the last directional freezing to obtain the RE-MOF-based photothermal interfacial evaporator.

[0046] In the application, the water-soluble polymer material is used to form a hydrogel material under the action of a crosslinking agent, and the light-thermal material is added during the formation of the hydrogel material, and the directional freezing is assisted by the temperature gradient in the vertical and horizontal directions of the mold, so that the mixed solution can be frozen in a certain direction in the mold to form directional ice crystals, for example, the temperature at the bottom of the mold is low, and the temperature gradually increases upwards, so that the hydrogel ice crystals can be vertically directional growth, and finally the solvent is removed by freeze-drying, so that directional pores (for example, pores arranged vertically) are formed.

[0047] The application cyclically performs the directional freezing and thawing process of step (2) to play a physical crosslinking role to form a hydrogel, that is, the application uses the chemical crosslinking of the crosslinking agent and the physical crosslinking of the cyclic freezing and thawing to form a hydrogel.

[0048] Preferably, the mixing of step (1) comprises: adding the water-soluble polymer material into water to heat and dissolve to obtain a hydrogel precursor solution; mixing the light-thermal material with deionized water to obtain a light-thermal material dispersion liquid, and adding the light-thermal material dispersion liquid and the crosslinking agent into the hydrogel precursor solution for heating and stirring;

[0049] Preferably, the concentration of the photothermal material dispersion liquid is 0-10 mg / mL, but not including 0 mg / mL, for example, it can be 1 mg / mL, 3 mg / mL, 5 mg / mL, 7 mg / mL, 9 mg / mL or 10 mg / mL, but not limited to the listed values, other values not listed in the value range are also applicable, preferably 6-10 mg / mL.

[0050] The present application can change the content of the photothermal material in the evaporator by changing the concentration of the photothermal material dispersion liquid, thereby ensuring the evaporation efficiency and photothermal conversion capacity of the evaporator.

[0051] Preferably, the content of the water-soluble polymer material in the hydrogel precursor solution is 1-10 wt%, for example, it can be 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt% or 10 wt%, but not limited to the listed values, other values not listed in the value range are also applicable, preferably 3-7 wt%.

[0052] Preferably, the temperature for heating and dissolving the water-soluble polymer material is 90-120°C (preferably 100-105°C), for example, it can be 90°C, 100°C, 110°C or 120°C, and the time is 0.5-4h (preferably 1-2h), for example, it can be 0.5h, 1.5h, 2.5h, 3.5h or 4h, but not limited to the listed values, other values not listed in the value range are also applicable

[0053] Preferably, the temperature for heating and stirring is 90-120°C (preferably 100-105°C), for example, it can be 90°C, 100°C, 110°C or 120°C, and the time is 10-30min (preferably 15min), for example, it can be 10min, 20min or 30min, but not limited to the listed values, other values not listed in the value range are also applicable

[0054] Preferably, the water-soluble polymer material includes any one or a combination of at least two of polyvinyl alcohol, agar, sodium alginate or chitosan, preferably polyvinyl alcohol and agar.

[0055] Preferably, the mass ratio of the polyvinyl alcohol and agar is (1-9):(1-9), for example, it can be 9:1, 7:3, 5:5 or 3:7, but not limited to the listed values, other values not listed in the value range are also applicable.

[0056] Preferably, the crosslinking agent includes KH560 silane coupling agent or hydrochloric acid-glutaraldehyde mixed solution.

[0057] Preferably, the bottom of the mold in step (2) is made of metal, and the side wall is made of plastic.

[0058] Preferably, the bottom of the mold in step (2) is a brass plate, and the side is a polytetrafluoroethylene material.

[0059] Preferably, the mold in step (2) is a cylindrical mold with an inner diameter of 2-4 cm, such as 2 cm, 3 cm or 4 cm, and a height of 2-4 cm, such as 2 cm, 3 cm or 4 cm, but not limited to the listed values, and other values not listed within the value range are also applicable.

[0060] Preferably, the freezing source for directional freezing in step (2) is located at the bottom of the mold, and the mold has a temperature gradient gradually decreasing from top to bottom in the vertical and horizontal directions, so that the solution inside the mold is directionally frozen from bottom to top.

[0061] Preferably, the directional freezing method includes placing the bottom of the mold in liquid nitrogen, and allowing the hydrogel ice crystals in the mixed solution to grow vertically upward.

[0062] The specific steps of directional freezing of the present application include: placing the mold in a heat-insulating container (such as a foam box), adding a certain volume of liquid nitrogen at the bottom of the foam box, and the liquid nitrogen can completely cover the bottom of the mold, so that the mold has a temperature gradient in the vertical direction, and the mixed solution inside the mold is directionally frozen from bottom to top, and the directional freezing is completed after waiting for the mixed solution inside the mold to completely freeze; attention should be paid to keeping the freezing process of the mixed solution stable, so that the ice crystals grow uniformly vertically upward to form anisotropic ice crystal templates.

[0063] The multiple directional freezing and thawing cycles of the present application refer to the gel after freezing being thawed at room temperature again, and the freezing and thawing process being repeated multiple times, preferably 2-4 times, preferably 3 times.

[0064] Preferably, the vacuum degree for freeze-drying in step (3) is 5-30 pa, such as 5 pa, 10 pa, 15 pa, 20 pa, 25 pa or 30 pa, the temperature is -80 to -40℃, such as -40℃, -50℃, -60℃, -70℃ or -80℃, and the time is 12-48 h, such as 12 h, 20 h, 30 h, 40 h or 48 h, but not limited to the listed values, and other values not listed within the value range are also applicable.

[0065] In a fifth aspect, the present application provides an application of the RE-MOF-based photothermal interface evaporator according to the third aspect, and the application includes a seawater desalination device.

[0066] When the photothermal interface evaporator according to the present application is applied, it can be directly placed above the water body to be desalinated.

[0067] Compared with the prior art, the present application has the following beneficial effects:

[0068] (1) The photothermal material described in the present application is a RE-MOF material coated with polydopamine, which can not only improve the stability of RE-MOF in water, but also improve the light absorption capacity of the composite material, thereby effectively improving the evaporation efficiency and photothermal conversion capacity of the evaporator;

[0069] (2) The present application uses hydrogel as the base material of the evaporator, and adds a RE-MOF-based photothermal material to the hydrogel precursor, supplemented by directional freezing technology to form a high-strength double-network hydrogel interfacial evaporator with vertically oriented channels. The directional channels not only effectively transport water, but also continuously dissolve and transport salt ions generated on the surface of the evaporator to the bulk water, preventing salt deposition on the surface of the evaporator and improving the cycle stability of the interfacial evaporator. BRIEF DESCRIPTION OF DRAWINGS

[0070] Figure 1 XRD pattern of RE-MOF and RE-MOF@PDA prepared in Example 1 of the present application.

[0071] Figure 2 Scanning electron micrograph of the photothermal interfacial evaporator prepared in Example 1 of the present application under a 100 mu m scale.

[0072] Figure 3 Scanning electron micrograph of the photothermal interfacial evaporator prepared in Example 1 of the present application under a 1 mu m scale.

[0073] Figure 4 Temperature rise and fall curve of the RE-MOF dispersion liquid described in Example 1 of the present application under 532 nm laser irradiation.

[0074] Figure 5 Temperature rise and fall curve of the RE-MOF@PDA dispersion liquid described in Example 1 of the present application under 532 nm laser irradiation.

[0075] Figure 6 Physical schematic diagram of the photothermal interfacial evaporator described in the present application simulating a solar evaporation system.

[0076] Figure 7 Schematic diagram of the application mode of the photothermal interfacial evaporator described in the present application.

[0077] Figure 8 Infrared temperature graph of the photothermal interfacial evaporator described in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present application during the evaporation process.

[0078] Figure 9 Surface salt accumulation change of the photothermal interfacial evaporator described in Example 2 of the present application under high-concentration salt water (15%) irradiation.

[0079] Figure 10A schematic diagram of the surface salt dissolution process of the photothermal interfacial evaporator according to Embodiment 2 of the present application.

[0080] Wherein, 1-solar simulator, 2-photothermal interfacial evaporator, 3-electronic balance, 4-polyethylene foam, 5-beaker. DETAILED DESCRIPTION

[0081] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0082] Embodiment 1

[0083] The present embodiment provides a RE-MOF-based photothermal material, which comprises a two-dimensional nanosheet-shaped rare earth MOF material and a polydopamine coating layer on the surface of the rare earth MOF material, and the mass ratio of the rare earth MOF material and the polydopamine coating layer is 1:2.

[0084] The preparation method of the RE-MOF-based photothermal material comprises the following steps:

[0085] (1) 23.7 mg of ligand TCPP (5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin), 40.5 mg of ytterbium nitrate hexahydrate are dissolved in 90 mL of DMF, and the mass ratio of TCPP, ytterbium nitrate hexahydrate and DMF is about 3:5:1125, and the reaction precursor solution is obtained by ultrasonic-assisted dissolution;

[0086] (2) Take 2 mL of the above reaction precursor solution and transfer it to a glass vial, heat it in a microwave oven at a power of 270 W for 10 min, and after centrifugal washing and drying, obtain nanosheet RE-MOF material, and then dissolve it in deionized water to form a RE-MOF dispersion solution with a concentration of 10 mg / mL;

[0087] (3) Take 3 mL of the above RE-MOF dispersion solution, and add 10 mL of a dopamine hydrochloride solution with a solubility of 6 mg / mL to it, wherein the dopamine hydrochloride solution is prepared by adding 60 mg of dopamine hydrochloride to 1 mL of 1 mol / L Tris-HCL buffer solution, 6 mL of deionized water and 3 mL of ethanol mixed solution;

[0088] Stir the above solution at room temperature for 8 h to allow dopamine to oxidize and polymerize on the surface of RE-MOF, and finally obtain RE-MOF@PDA photothermal material, i.e. RE-MOF coated with polydopamine, through filtration, washing and drying.

[0089] The embodiment also provides a RE-MOF-based photothermal interfacial evaporator, which comprises a hydrogel and the RE-MOF-based photothermal material as described in the embodiment, and the content of the photothermal material is 0.15wt%;

[0090] The preparation method of the photothermal interfacial evaporator comprises the following steps:

[0091] (I) dispersing the photothermal material obtained in the above embodiment 1 in deionized water to form a RE-MOF@PDA photothermal material dispersion;

[0092] 0.5g of polyvinyl alcohol and 0.5g of agar are added to 15mL of deionized water, and the solution is dissolved in an oil bath at 105℃ and a rotation speed of 300rpm to obtain a hydrogel precursor solution;

[0093] (II) 3mL of the RE-MOF@PDA photothermal material dispersion with a concentration of 10mg / mL is added to the hydrogel precursor solution and stirred uniformly, and then 0.2g of a KH560 crosslinking agent is added and stirred for 5min, after which the mixture is transferred into a mold with a brass side wall and a polytetrafluoroethylene material on the bottom, the inner diameter of the mold is 2cm, and the height is 4cm;

[0094] (III) liquid nitrogen assisted hydrogel directional freezing: the mold is placed in a foam box, liquid nitrogen is added to the bottom of the foam box, the liquid nitrogen covers the bottom of the mold, a vertical temperature gradient is formed in the mold, and after the solution in the mold is completely frozen, the mold is transferred into deionized water for dissolution, and the freezing and thawing is repeated three times, and finally the frozen hydrogel is placed in a freeze dryer and freeze-dried at-55℃ for 24h to obtain the photothermal interfacial evaporator.

[0095] The XRD patterns of the RE-MOF and the RE-MOF@PDA prepared in the embodiment are as shown in Figure 1 Figure 1 It can be seen that the MOF synthesized by the microwave method has obvious crystal peaks, indicating that the sample has good crystallinity, and the structure of the MOF coated with polydopamine has not changed, and the spectrum matches well.

[0096] The scanning electron microscope image of the photothermal interfacial evaporator prepared in the embodiment 1 under a 100μm scale is as shown in Figure 2 Figure 3 It can be seen that the photothermal interfacial evaporator prepared in the embodiment 1 under a 1μm scale is as shown in Figure 2 and Figure 3 It can be seen that the photothermal interfacial evaporator prepared in the embodiment 1 presents a vertically arranged pore structure, and the photothermal material is uniformly dispersed on the hydrogel substrate.

[0097] Embodiment 2

[0098] ​​The embodiment provides a RE-MOF-based photothermal material, which comprises a two-dimensional nanosheet-shaped rare earth MOF material and a polydopamine coating layer on the surface of the rare earth MOF material, and the mass ratio of the rare earth MOF material and the polydopamine coating layer is 1:0.1.

[0099] The preparation method of the RE-MOF-based photothermal material comprises the following steps:

[0100] (1) 23.7 mg of ligand TCPP (5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin) and 40.5 mg of ytterbium nitrate hexahydrate are dissolved in 90 mL of DMF, and the mass ratio of TCPP, ytterbium nitrate hexahydrate and DMF is about 3:5:1125. Ultrasonic-assisted dissolution obtains a reaction precursor solution;

[0101] (2) 2 mL of the reaction precursor solution is taken and transferred to a glass vial, which is placed in a microwave oven and heated at a power of 700 W for 5 min. After centrifugal washing and drying, a nanosheet RE-MOF material is obtained, and then the RE-MOF material is dissolved in deionized water to form a RE-MOF dispersion solution with a concentration of 10 mg / mL;

[0102] (3) 3 mL of the RE-MOF dispersion solution is taken, and 10 mL of a dopamine hydrochloride solution with a solubility of 0.3 mg / mL is added, wherein the dopamine hydrochloride solution is prepared by adding a certain amount of dopamine hydrochloride into 1 mL of 1 mol / L Tris-HCL buffer solution, 6 mL of deionized water and 3 mL of ethanol mixed solution;

[0103] The above solution is stirred at room temperature for 24 h to allow dopamine to be oxidized and polymerized on the surface of the RE-MOF, and finally, the RE-MOF@PDA photothermal material, i.e., the RE-MOF coated with polydopamine, is obtained through filtration, washing and drying.

[0104] The embodiment also provides a RE-MOF-based photothermal interfacial evaporator, which comprises a hydrogel and the RE-MOF-based photothermal material as described in the embodiment, and the content of the photothermal material is 0.15 wt%.

[0105] The preparation method of the photothermal interfacial evaporator comprises the following steps:

[0106] (I) The photothermal material obtained in the embodiment 2 is dispersed in deionized water to form a RE-MOF@PDA photothermal material dispersion solution;

[0107] 0.5 g of polyvinyl alcohol and 0.5 g of agar are added to 15 mL of deionized water, and the mixture is dissolved in an oil bath at 120 DEG C and a rotation speed of 300 rpm to obtain a hydrogel precursor solution.

[0108] (II) Take 3 mL of RE-MOF@PDA photothermal material dispersion solution with a concentration of 10 mg / mL, add it to the hydrogel precursor solution and stir until uniform, then add 0.2 g of KH560 crosslinking agent and continue stirring for 5 min. Then, while hot, transfer it to a mold with a brass bottom and a polytetrafluoroethylene side wall. The mold has an inner diameter of 2 cm and a height of 4 cm;

[0109] (III) Use liquid nitrogen to assist in the directional freezing of the hydrogel. Place the mold in a foam box and add liquid nitrogen to the bottom of the foam box. The liquid nitrogen covers the bottom of the mold, forming a vertical temperature gradient in the mold. Wait for the solution in the mold to completely freeze, then transfer the mold to deionized water for dissolution. Repeat the freezing and thawing process three times. Finally, place the frozen hydrogel in a freeze dryer and freeze dry at -40°C for 48 h to obtain the photothermal interface evaporator.

[0110] Example 3

[0111] This example provides a RE-MOF-based photothermal material, which includes a two-dimensional nanosheet-shaped rare earth MOF material and a polydopamine coating layer on the surface of the rare earth MOF material. The mass ratio of the rare earth MOF material and the polydopamine coating layer is 1:10.

[0112] The preparation method of the RE-MOF-based photothermal material includes the following steps:

[0113] (1) Dissolve 23.7 mg of ligand TCPP and 40.5 mg of ytterbium nitrate hexahydrate in 90 mL of DMF. The mass ratio of TCPP, ytterbium nitrate hexahydrate, and DMF is about 3:5:1125. Ultrasonic-assisted dissolution is used to obtain a reaction precursor solution;

[0114] (2) Take 2 mL of the above reaction precursor solution and transfer it to a glass vial. Place it in a microwave oven and heat it at a power of 100 W for 30 min. After centrifugal washing and drying, obtain a nanosheet RE-MOF material. Then, re-dissolve it in deionized water to form a RE-MOF dispersion solution with a concentration of 10 mg / mL;

[0115] (3) Take 3 mL of the above RE-MOF dispersion solution and add 10 mL of a dopamine hydrochloride solution with a concentration of 30 mg / mL to it. The dopamine hydrochloride solution is prepared by adding a certain amount of dopamine hydrochloride to 1 mL of 1 mol / L Tris-HCL buffer solution, 6 mL of deionized water, and 3 mL of ethanol mixed solution;

[0116] The above solution is stirred at room temperature for 8 h to allow dopamine to be oxidized and polymerized on the surface of the RE-MOF, and finally the RE-MOF@PDA photothermal material, i.e., the RE-MOF coated with polydopamine, is obtained through filtration, washing and drying.

[0117] The embodiment also provides an RE-MOF-based photothermal interfacial evaporator, which comprises a hydrogel and the RE-MOF-based photothermal material as described in the embodiment, and the content of the photothermal material is 0.15wt%.

[0118] The preparation method of the photothermal interfacial evaporator comprises the following steps:

[0119] (I) dispersing the photothermal material obtained in the above embodiment 3 in deionized water to form a RE-MOF@PDA photothermal material dispersion;

[0120] 0.5 g of polyvinyl alcohol and 0.5 g of agar are taken into 15 mL of deionized water, and the solution is dissolved in an oil bath at 90℃ and a rotation speed of 300 rpm to obtain a hydrogel precursor solution;

[0121] (II) 3 mL of the RE-MOF@PDA photothermal material dispersion with a concentration of 10 mg / mL is taken and added into the hydrogel precursor solution and stirred uniformly, and then 0.2 g of KH560 crosslinking agent is added and stirred for 5 min, and then the mixture is transferred into a mold with a brass side wall and a polytetrafluoroethylene material at the bottom while hot, the inner diameter of the mold is 2 cm, and the height is 4 cm;

[0122] (III) liquid nitrogen assisted hydrogel directional freezing: the mold is placed in a foam box, liquid nitrogen is added at the bottom of the foam box, the liquid nitrogen covers the bottom of the mold, a vertical temperature gradient is formed in the mold, and after the solution in the mold is completely frozen, the mold is transferred into deionized water for dissolution, and the freezing and thawing is repeated for three times, and finally the frozen hydrogel is placed in a freeze dryer and freeze-dried at-80℃ for 12 h to obtain the photothermal interfacial evaporator.

[0123] Example 4

[0124] The embodiment provides an RE-MOF-based photothermal material, and the RE-MOF-based photothermal material and the preparation method of the RE-MOF-based photothermal material are the same as those in embodiment 1.

[0125] The embodiment also provides an RE-MOF-based photothermal interfacial evaporator, and the preparation method of the photothermal interfacial evaporator is the same as that in embodiment 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion in step (II) is 8 mg / mL, so that the content of the photothermal material in the photothermal interfacial evaporator is changed to 0.12wt%.

[0126] Example 5

[0127] This embodiment also provides a RE-MOF-based photothermal interface evaporator, a preparation method of the photothermal interface evaporator is the same as that of Example 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion liquid in step (II) is 6 mg / mL, so that the content of the photothermal material in the photothermal interface evaporator becomes 0.09 wt%.

[0128] This embodiment also provides a RE-MOF-based photothermal interface evaporator, a preparation method of the photothermal interface evaporator is the same as that of Example 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion liquid in step (II) is 6 mg / mL, so that the content of the photothermal material in the photothermal interface evaporator becomes 0.09 wt%.

[0129] Example 6

[0130] This embodiment also provides a RE-MOF-based photothermal interface evaporator, a preparation method of the photothermal interface evaporator is the same as that of Example 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion liquid in step (II) is 6 mg / mL, so that the content of the photothermal material in the photothermal interface evaporator becomes 0.09 wt%.

[0131] This embodiment also provides a RE-MOF-based photothermal interface evaporator, a preparation method of the photothermal interface evaporator is the same as that of Example 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion liquid in step (II) is 6 mg / mL, so that the content of the photothermal material in the photothermal interface evaporator becomes 0.09 wt%.

[0132] Example 7

[0133] This embodiment also provides a RE-MOF-based photothermal interface evaporator, a preparation method of the photothermal interface evaporator is the same as that of Example 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion liquid in step (II) is 6 mg / mL, so that the content of the photothermal material in the photothermal interface evaporator becomes 0.09 wt%.

[0134] This embodiment also provides a RE-MOF-based photothermal interface evaporator, a preparation method of the photothermal interface evaporator is the same as that of Example 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion liquid in step (II) is 6 mg / mL, so that the content of the photothermal material in the photothermal interface evaporator becomes 0.09 wt%.

[0135] Example 8

[0136] This embodiment also provides a RE-MOF-based photothermal interface evaporator, a preparation method of the photothermal interface evaporator is the same as that of Example 1, except that the concentration of the RE-MOF@PDA photothermal material dispersion liquid in step (II) is 6 mg / mL, so that the content of the photothermal material in the photothermal interface evaporator becomes 0.09 wt%.

[0137] The embodiment also provides a RE-MOF-based photothermal interfacial evaporator, which is the same as that in the embodiment 1 except that the photothermal material in the embodiment is used.

[0138] Embodiment 9

[0139] The embodiment provides a RE-MOF-based photothermal material, which is the same as that in the embodiment 1 except that the mass ratio of the rare earth MOF material and the polydopamine coating layer is 1:10; and the preparation method of the photothermal material is also the same as that in the embodiment 1 except that the formula amount is adaptively changed.

[0140] The embodiment also provides a RE-MOF-based photothermal interfacial evaporator, which is the same as that in the embodiment 1 except that the photothermal material in the embodiment is used.

[0141] Embodiment 10

[0142] The embodiment provides a RE-MOF-based photothermal material, which is the same as that in the embodiment 1.

[0143] The embodiment also provides a RE-MOF-based photothermal interfacial evaporator, which is the same as that in the embodiment 1 except that the step (III) is not directional freezing but freezing in a refrigerator, so that the obtained photothermal interfacial evaporator is adaptively changed.

[0144] Comparative Example 1

[0145] The comparative example provides a photothermal material, which is the same as that in the embodiment 1 except that the photothermal material does not contain a polydopamine coating layer; and the preparation method of the photothermal material is also the same as that in the embodiment 1 except that the step of coating polydopamine is not performed.

[0146] The comparative example also provides a photothermal interfacial evaporator, which is the same as that in the embodiment 1 except that the photothermal material in the comparative example is not coated with polydopamine.

[0147] Comparative Example 2

[0148] The comparative example provides a photothermal material, which is the same as that in the embodiment 1 except that the photothermal material is a pure polydopamine material; and the preparation method of the photothermal material is also the same as that in the embodiment 1 except that the step of preparing a rare earth MOF is not performed.

[0149] The comparative example also provides a photothermal interfacial evaporator which is the same as that of Example 1 except that the polydopamine material of the comparative example is used as the photothermal material.

[0150] Comparative Example 3

[0151] The comparative example provides a photothermal interfacial evaporator which is the same as that of Example 1 except that the photothermal material is not contained.

[0152] The preparation method of the photothermal interfacial evaporator of the comparative example is the same as that of Example 1 except that the photothermal material is not added during preparation.

[0153] Performance test:

[0154] A 532 nm laser is used to irradiate the photothermal material dispersion liquid, and an external thermal imaging camera is used to record the temperature change of the dispersion liquid, and the photothermal conversion efficiency of the photothermal material obtained in the above examples is tested through the temperature rise and fall curves of the solution; the temperature rise and fall curve of the RE-MOF dispersion liquid under the irradiation of the 532 nm laser is as shown in Figure 4 , and the temperature rise and fall curve of the RE-MOF@PDA dispersion liquid under the irradiation of the 532 nm laser is as shown in Figure 5 The laser heat conversion efficiency of the two under the irradiation of the 532 nm laser is calculated through the temperature drop curve, which is 33.1% and 42.5% respectively, and it can be seen that the polydopamine coating effectively improves the photothermal conversion efficiency.

[0155] The photothermal interfacial evaporators prepared in the above examples and comparative examples are subjected to solar simulation evaporation test, and the evaporation rate and photothermal conversion efficiency of the photothermal interfacial evaporators under pure water conditions are tested.

[0156] The specific test steps are as follows:

[0157] (1) Evaporation rate

[0158] The evaporation performance of the RE-MOF-based interfacial device is tested by using a simulated sunlight interfacial evaporation system, and the actual diagram of the entire evaporation system is as shown in Figure 6 , wherein the schematic diagram of the photothermal interfacial evaporator placed in the beaker is as shown in Figure 7 , the simulated sunlight interfacial evaporation system comprises a xenon lamp sunlight simulator 1, a beaker 5, an electronic balance 3, a polyethylene foam 4 and a photothermal interfacial evaporator 2. By adjusting the current size of the xenon lamp and the distance between the light source surface and the hydrogel surface, the light intensity received by the surface of the photothermal interfacial evaporator is 1 standard sunlight intensity 1 kW / m 2During the test, the mass change of water in the beaker was recorded using an electronic balance, and the surface temperature change of the evaporator was recorded using a thermal imager. The entire test was conducted at approximately 25°C and 50% humidity. After the evaporation process stabilized, the mass of simulated seawater evaporated over a certain period of time was recorded. The test was repeated three times, and the average value was taken.

[0159] The evaporation rate is calculated using Equation 1, which is:

[0160]

[0161] Where Δm is the mass change of the entire system, A is the area of ​​the evaporator surface receiving light, and T is the evaporation time.

[0162] (2) Photothermal conversion efficiency:

[0163] Hydrogel evaporators and blank evaporators with the same evaporation surface area were placed in a dark chamber under identical conditions, and their mass changes over a period of time were recorded. First, the latent heat H of the bulk water was calculated using Equation 2. LV Then, the equivalent enthalpy of vaporization ΔH of water in the hydrogel photothermal interface evaporator is calculated using Equation 3. equ Then, the latent heat H of the hydrogel photothermal interface evaporator is estimated using Equation 4. LV，Absorber Sensible heat of hydrogel photothermal interface evaporator The total energy H required for water evaporation in a hydrogel photothermal interface evaporator can be calculated using Equation 5. total It equals the sum of latent heat and sensible heat. Finally, the photothermal conversion efficiency of the entire system is calculated according to Equation 7.

[0164]

[0165] ΔH vap m0=ΔH equ m g #(3)

[0166] Among them, H LV BW represents the latent heat of bulk water, and T represents the latent heat of bulk water. s Represents the surface temperature of the evaporator, C p，l It is the heat capacity of liquid water, C p，v It is the heat capacity of steam water. C p，l =4.18JK -1 g -1 H LV，373.15K =2257.2J g -1 C p，v = (3.47 + 1.45 × 10) -3 ×T+1.21×10 4 ×T -2) x R / M(JK -1 g -1 ), R = 8.314 JK -1 mol -1 , M = 18.02 J mol -1 , ΔH vap m0is the evaporation enthalpy and mass change of the blank evaporator water, ΔH equ m g is the equivalent evaporation enthalpy and mass change of the water-gel photothermal interfacial evaporator. H LV，Absorber is the latent heat required for water evaporation in the water-gel photothermal interfacial evaporator, is the sensible heat required for water evaporation in the water-gel photothermal interfacial evaporator. H total is the total energy required for water evaporation in the water-gel photothermal interfacial evaporator, V is the evaporation rate of the evaporator, E in is the total solar radiation intensity received by the evaporator.

[0167] Table 1 is the evaporation rate and photothermal conversion efficiency of the photothermal interfacial evaporator described in the above examples and comparative examples in pure water.

[0168] Table 1

[0169]

[0170]

[0171] From Table 1, it can be seen that:

[0172] (1) From Example 1 and Examples 4-7, it can be seen that there is an optimal value for the loading amount of the photothermal material in the water-gel evaporator. As the loading amount increases from 0 to 30 mg, the evaporation rate of the evaporator shows a trend of first increasing and then decreasing, and the optimal loading amount is about 24 mg, and the evaporation rate can reach 2.27 kg / m 2 / h. This is because RE-MOF@PDA has good absorbance and photothermal conversion capacity. The increase of the loading amount will improve the light absorption capacity and photothermal conversion efficiency of the entire evaporator. However, as the content of the photothermal material further increases, the performance of the evaporator decreases, which is due to the excessive addition of the photothermal material, causing the blockage of the internal pores of the water-gel, affecting its water transport performance, and thus the evaporation rate and photothermal conversion efficiency of the entire evaporator decrease.

[0173] (2) As can be seen from Examples 1 and 8-9, in the photothermal material of the present invention, the mass ratio of rare earth MOF material to polydopamine is preferably within a specific range, which is beneficial to further improve the performance of the evaporator; As can be seen from Examples 1 and 10, the introduction of directional freezing technology in the hydrogel synthesis process can effectively improve the evaporation efficiency. This is because the vertically arranged channels generated by directional freezing can effectively improve the water transport capacity of the hydrogel, further improving the evaporation efficiency. At the same time, the porous channels can also increase the refraction and reflection of sunlight inside, and improve the light absorption, etc.

[0174] (3) As can be seen from Example 1 and Comparative Examples 1-3, the photothermal conversion capability of RE-MOF@PDA is stronger than that of RE-MOF alone or polydopamine alone. This is because polydopamine can not only protect the RE-MOF material, but also synergize with RE-MOF to improve the photothermal conversion capability. The comparison diagram of the evaporator surface temperature during the evaporation process in Example 1 and Comparative Examples 1-3 is shown below. Figure 8 As shown, by Figure 8 It can be seen that the surface temperature of Example 2 is higher than that of Comparative Examples 1 and 2, which effectively proves that the photothermal conversion capability of RE-MOF / PDA is stronger than that of simple RE-MOF material or simple polydopamine material.

[0175] In addition, the pure water in the beaker of the above system was replaced with a simulated salt water of a certain concentration, and the above solar simulated evaporation test was repeated to obtain the photothermal evaporation performance of the evaporator in salt water. Table 2 shows the test results of Example 2 in salt water of different concentrations.

[0176] Table 2

[0177]

[0178] As can be seen from Table 2, in low-concentration brine, the evaporation performance of the hydrogel evaporator only decreases slightly and is not significantly affected, with a similar evaporation rate to that in pure water. However, as the brine concentration increases, the evaporation performance of the evaporator decreases to some extent.

[0179] To further explore the salt deposition resistance of the evaporator, the photothermal interface evaporator described in Example 2 was irradiated in a 15% brine evaporation system for 8 hours, and the surface salt accumulation during the evaporation process was observed. Figure 9 The changes in salt accumulation are shown. Before 2 hours, there was basically no salt deposition on the surface of the evaporator. After 4 hours, salt deposition gradually appeared on the evaporator.

[0180] Salt was added to the surface of the evaporator under no-light conditions to investigate the salt solubility of the evaporator. A schematic diagram of the salt dissolution process on the surface of the photothermal interface evaporator described in Example 2 is shown below.Figure 10 As shown, the evaporator has good salt dissolution capacity, and can completely dissolve the surface salt particles within 1h. The excellent salt dissolution capacity of the evaporator is due to the vertically arranged channels in the hydrogel. When the surface moisture evaporates and causes the salt concentration on the top layer to rise, the vertically arranged channels can transport the high-concentration salt ions on the top to the bottom, thereby largely avoiding the deposition of salt on the surface.

[0181] To sum up, the application provides a RE-MOF-based photothermal material, a photothermal interface evaporator and a preparation method and application thereof. The RE-MOF-based photothermal material is coated with polydopamine and rare earth MOF material, so that the photothermal material has high light absorption capacity and hydrothermal stability, and can effectively improve the evaporation efficiency and photothermal conversion capacity of the photothermal interface evaporator.

[0182] The above is only a specific embodiment of the application, but the protection scope of the application is not limited to this. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the application.

Claims

1. A RE-MOF based photothermal material, characterized in that, The RE-MOF-based photothermal material comprises a two-dimensional nanosheet-shaped rare earth MOF material, and a polydopamine coating layer on the surface of the rare earth MOF material. The mass ratio of the rare earth MOF material and the polydopamine coating layer is 1:(0.1-10). The rare earth atom in the rare earth MOF material comprises any one or a combination of at least two of cerium, neodymium, erbium or ytterbium. The organic ligand in the rare earth MOF material comprises porphyrin and / or porphyrin derivatives.

2. The RE-MOF based photothermal material of claim 1, wherein, The rare earth atom in the rare earth MOF material is ytterbium.

3. A method of preparing a RE-MOF based photothermal material according to claim 1 or 2, characterized in that, The preparation method comprises the following steps: mixing the rare earth MOF material, dopamine and a first solvent, then adjusting the pH of the system to make the dopamine polymerize on the surface of the rare earth MOF material, then performing solid-liquid separation, washing and drying to obtain the RE-MOF-based photothermal material; The mass ratio of the rare earth MOF material and dopamine is 1:(1-2), the pH of the system is adjusted to 8-13, and the mixing time is 8-24 hours. The mixing comprises dispersing the rare earth MOF material in deionized water to form a rare earth MOF dispersion, adding dopamine to a mixed solution comprising Tris-HCL buffer, deionized water and ethanol to form a dopamine solution, and then mixing the rare earth MOF dispersion and the dopamine solution.

4. The production method according to claim 3, characterized by, The method for preparing the rare earth MOF material comprises the following steps: mixing an organic ligand, a rare earth salt and a second solvent to obtain a reaction precursor solution, then heating the reaction precursor solution, and then performing solid-liquid separation and washing to obtain the rare earth MOF material.

5. The preparation method according to claim 4, characterized in that, The heating mode comprises microwave heating.

6. The preparation method according to claim 5, characterized in that, The microwave heating power is 100-700 W, and the time is 5-30 min.

7. The preparation method according to claim 4, characterized in that, The mass ratio of the organic ligand, the rare earth salt and the second solvent is (1-10):(1-10):(1000-2000).

8. The preparation method according to claim 4, characterized in that, The rare earth salt comprises any one or a combination of at least two of cerium nitrate hexahydrate, neodymium nitrate hexahydrate, erbium nitrate pentahydrate or ytterbium nitrate pentahydrate.

9. The preparation method according to claim 4, characterized in that, The organic ligand comprises porphyrin and / or porphyrin derivatives.

10. The method of claim 4, wherein, The second solvent comprises any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide or deionized water.

11. A RE-MOF based photothermal interface evaporator, characterized in that, The RE-MOF-based photothermal interfacial evaporator comprises a hydrogel and the RE-MOF-based photothermal material according to claim 1 or 2, and has a pore structure.

12. The RE-MOF based photothermal interface evaporator of claim 11, wherein, The RE-MOF-based photothermal interfacial evaporator has a vertically arranged pore structure.

13. The RE-MOF based photothermal interface evaporator of claim 11, wherein, The content of the RE-MOF-based photothermal material in the RE-MOF-based photothermal interfacial evaporator is 0.01-1 wt%.

14. A method of preparing a RE-MOF based photothermal interface evaporator according to any one of claims 11 to 13, characterized in that, The preparation method comprises the following steps: (1) mixing a water-soluble polymer material, the photothermal material according to claim 1 or 2, a crosslinking agent and a third solvent to obtain a mixed solution; (2) transferring the mixed solution to a mold for directional freezing, the mold has a temperature gradient in the vertical and horizontal directions during the directional freezing, and then thawing after the directional freezing. (3) repeating the directional freezing and thawing process of step (2), freeze-drying the last obtained directional frozen product to obtain the RE-MOF-based photothermal interface evaporator.

15. The method of claim 14, wherein, The mixing of step (1) comprises: adding the water-soluble polymer material into water to heat and dissolve, to obtain a hydrogel precursor solution; mixing the photothermal material with deionized water to obtain a photothermal material dispersion liquid, and adding the photothermal material dispersion liquid and a crosslinking agent into the hydrogel precursor solution to heat and stir.

16. The method of claim 15, wherein, The concentration of the photothermal material dispersion liquid is 0-10 mg / mL, but not including 0 mg / mL.

17. The method of claim 16, wherein the method further comprises, The concentration of the photothermal material dispersion liquid is 6-10 mg / mL.

18. The method of claim 15, wherein, The content of the water-soluble polymer material in the hydrogel precursor solution is 1-10 wt%.

19. The method of claim 15, wherein, The temperature for heating and dissolving the water-soluble polymer material is 90-120℃, and the time is 0.5-4 h.

20. The method of claim 15, wherein, The temperature for heating and stirring is 90-120℃, and the time is 10-30 min.

21. The method of claim 15, wherein, The water-soluble polymer material comprises any one or a combination of at least two of polyvinyl alcohol, agar, sodium alginate or chitosan.

22. The method of claim 15, wherein, The crosslinking agent comprises a KH560 silane coupling agent or a hydrochloric acid-glutaraldehyde mixed solution.

23. The method of claim 14, wherein, The bottom of the mold of step (2) is made of metal, and the sidewall is made of plastic.

24. The method of claim 14, wherein, The mold of step (2) is a cylindrical mold with an inner diameter of 2-4 cm and a height of 2-4 cm.

25. The method of claim 14, wherein, The freezing source of the directional freezing of step (2) is located at the bottom of the mold.

26. The method of claim 14, wherein, The directional freezing of step (2) comprises placing the bottom of the mold in liquid nitrogen, so that the hydrogel ice crystals in the mixed solution grow vertically upward.

27. The method of claim 14, wherein, The vacuum degree of the freeze-drying of step (3) is 5-30 pa, the temperature is -80~-40℃, and the time is 12-48 h.

28. Use of a RE-MOF based photothermal interface evaporator according to any one of claims 11 to 13, characterized in that, The application comprises seawater desalination.

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