Composite photo-thermal hydrogel for seawater desalination as well as preparation method and application of composite photo-thermal hydrogel

Abstract

The invention provides a composite photo-thermal hydrogel for seawater desalination and a preparation method and application thereof, the hydrogel has a structural unit of a structure as shown in a formula I. COF with photo-thermal performance is compounded with the hydrogel, and the hydrogel has a three-dimensional long-range ordered pore structure to promote transmission of water molecules; and the COF dispersed in the material contains porphyrin and a C = N double-bond connection structure, so that the material has excellent photothermal conversion efficiency. Therefore, under the irradiation of sunlight, the composite photo-thermal hydrogel disclosed by the invention can realize photo-thermal conversion to realize seawater evaporation, the seawater evaporation rate reaches 3.6 kgm <-1 > h <-1 >, and the performance is improved by about 3 times compared with that of a traditional carbon-based material. According to the preparation method of the composite photo-thermal hydrogel, large and complex equipment is not involved in the preparation method, the preparation technological process is simple, and industrial large-scale production is facilitated; and the reaction temperature in the preparation process is low, the energy consumption is also reduced, and the cost advantage is remarkable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of covalent organic framework functional materials, and particularly relates to a composite photothermal hydrogel for seawater desalination and a preparation method and application thereof. BACKGROUND

[0002] With the increasing seriousness of global water resource shortage, seawater desalination as an important way to obtain water resources has attracted widespread attention. Photothermal seawater desalination technology has become one of the research hotspots due to its low energy consumption and simple equipment. Photothermal materials are the key to photothermal seawater desalination technology, and the development of efficient photothermal materials is crucial to improve the efficiency of seawater desalination.

[0003] Covalent organic framework (COF) material is a kind of periodic crystalline porous polymer formed by covalent bond. Its unique long-range ordered nanochannel structure can significantly reduce the mass transfer resistance, while the rich chemical functional groups and firm framework structure endow it with excellent anti-pollution performance and long-term stability, and exhibit a wide range of salt concentration adaptability, which is an ideal material in the field of pervaporation desalination. Porphyrin-based COFs have excellent light absorption performance due to the presence of porphyrin units, and are expected to be applied to seawater desalination as photothermal conversion materials. However, single COF material has some limitations in practical application, such as poor mechanical properties and difficulty in effective combination with other systems.

[0004] Hydrogel is a three-dimensional network structure material formed by cross-linking of high molecular chains, which has high water absorption, flexibility and controllable physical and chemical properties. Due to its excellent hydrophilicity and porous structure, hydrogel shows significant advantages in seawater desalination. The combination of photothermal materials and hydrogel is expected to prepare composite photothermal hydrogel with both photothermal performance and good formability for seawater desalination. SUMMARY

[0005] The embodiments of the present application provide a composite photothermal hydrogel for seawater desalination and a preparation method and application thereof to solve the problems in the related art, and the technical solutions are as follows: In a first aspect, the embodiments of the present application provide a composite photothermal hydrogel for seawater desalination, which has a structural unit with a structure shown in Formula I:

[0006] Formula I wherein n is an integer of 1-10.

[0007] In an embodiment, the structural unit with the structure shown in Formula I comprises a cross-linking agent cross-linking structure, and the cross-linking agent is N,N'-methylenebisacrylamide.

[0008] Secondly, embodiments of this application provide a method for preparing a composite photothermal gel for seawater desalination, comprising the following steps: The COF of the structural unit shown in Formula II and N-isopropylacrylamide were reacted with tetramethylethylenediamine and an initiator in the presence of a crosslinking agent to prepare the composite photothermal gel for seawater desalination.

[0009] Formula II.

[0010] In one embodiment, the crosslinking agent is N,N'-methylenebisacrylamide and the initiator is ammonium persulfate.

[0011] In one embodiment, the mass ratio of the COF of the structural unit shown in Formula II to N-isopropylacrylamide, crosslinking agent, tetramethylethylenediamine and initiator is 1:(30-50):(0.8-1.2):(0.8-1.2):(1.2-1.8).

[0012] In one embodiment, the reaction is carried out in a solvent, wherein the COF of the structural unit shown in Formula II is dispersed in water; the mass-to-volume ratio of the COF of the structural unit shown in Formula II to water is (4-10) mg: 1 mL.

[0013] In one embodiment, the reaction temperature is 0–5°C and the reaction time is 25–60 min.

[0014] In one embodiment, the reaction process is as follows: a crosslinking agent is added to an aqueous solution of COF of the structural unit shown in Formula II and N-isopropylacrylamide and stirred for 20 to 40 minutes; then an initiator is added and stirred for 5 to 15 minutes; finally, tetramethylethylenediamine is added and stirred for 2 to 5 minutes.

[0015] In one embodiment, after the reaction, the reaction solution is allowed to stand at room temperature for 1 to 5 hours to obtain the composite photothermal gel for seawater desalination.

[0016] In one embodiment, the method for preparing the COF of the structural unit shown in Formula II includes the following steps: 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, 2,5-bis(2-propynoxy)terephthalaldehyde and 2,5-dihydroxyterephthalaldehyde were subjected to a solvothermal reaction in a mixed solvent in the presence of acetic acid to prepare COF with the structural unit shown in Formula II.

[0017] In one embodiment, the mixed solvent is a mixed solution of n-butanol and o-dichlorobenzene in a volume ratio of (0.5-2):1.

[0018] In one embodiment, the molar ratio of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, 2,5-bis(2-propynoxy)-terephthalaldehyde and 2,5-dihydroxyterephthalaldehyde is (0.8-1):1:1.

[0019] In one embodiment, the amount of acetic acid added is 5 to 15% of the volume of the mixed solvent, consisting of (3 to 6) M acetic acid.

[0020] In one embodiment, the molar volume ratio of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin to the mixed solvent is (10-50) μmol:1 mL.

[0021] In one embodiment, the solvothermal reaction is carried out at a temperature of 80–100°C for 6–24 hours.

[0022] In one embodiment, after the solvothermal reaction is completed, the reaction liquid undergoes solid-liquid separation; the solid phase is washed with anhydrous acetone and dried to obtain the COF of the structural unit shown in Formula II.

[0023] Thirdly, embodiments of this application provide an application of a composite photothermal gel for seawater desalination as a photothermal conversion material in seawater desalination.

[0024] The advantages or beneficial effects of the above technical solutions include at least the following: The composite photothermal gel for seawater desalination presented in this application possesses a three-dimensional, long-range ordered pore structure that promotes water molecule transport. The dispersed COF within it, with its porphyrin and C=N double bond linkages, exhibits excellent photothermal conversion efficiency. Therefore, under sunlight irradiation, this composite photothermal gel can convert light into heat and evaporate the water within the pores, achieving high water evaporation efficiency. The seawater evaporation rate is 3.6 kg•m. -1 •h -1 It has about three times the performance of traditional carbon-based materials.

[0025] The method for preparing the composite photothermal gel for seawater desalination disclosed in this application does not involve large or complex equipment, and the preparation process is simple, which is conducive to industrial-scale production. Furthermore, the low reaction temperature during the preparation process reduces energy consumption, resulting in a significant cost advantage.

[0026] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of this application will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0027] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0028] Figure 1 A flowchart illustrating the steps involved in synthesizing the photothermal composite hydrogel provided by this invention; Figure 2 The images shown are SEM and TEM images of the COFs-PNIPAM composite photothermal hydrogel prepared in Example 4 of this invention. Figure 3 This is a SEM image of the COFs-PNIPAM cross section prepared in Example 4 of the present invention; Figure 4 The image shows the XRD pattern of the COFs-PNIPAM composite photothermal hydrogel prepared in Example 4 of this invention. Figure 5 The image shown is the FT-IR image of the COFs-PNIPAM composite photothermal gel prepared in Example 4 of this invention. Figure 6 XPS image of the COFs-PNIPAM composite photothermal gel prepared in Example 4 of this invention; Figure 7 The photothermal evaporation rate diagram is shown for the COFs-PNIPAM composite photothermal hydrogel prepared in Example 4 of this invention. Figure 8 The graph shows the photothermal evaporation rate of the COFs-PNIPAM composite photothermal gel prepared in Example 4 of this invention for repeated use. Detailed Implementation

[0029] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0030] Hydrogels are three-dimensional network structures formed by cross-linking of polymer chains, possessing high water absorption, flexibility, and tunable physicochemical properties. Due to their excellent hydrophilicity and porous structure, hydrogels exhibit significant advantages in seawater desalination. N-isopropylacrylamide (NIPAM)-based hydrogels exhibit temperature responsiveness, undergoing a volume phase transition within a certain temperature range. Combining photothermal materials with hydrogels holds promise for preparing composite photothermal hydrogels that combine photothermal properties with good formability, suitable for use in seawater desalination.

[0031] Therefore, this application provides a composite photothermal gel for seawater desalination, having a structural unit with the structure shown in Formula I:

[0032] Formula I Where n is an integer from 1 to 10.

[0033] This application presents a composite photothermal hydrogel for seawater desalination, consisting of a tetraphenylporphyrin and a C=N bond-containing linking group forming a COF. Due to the presence of the porphyrin unit, it exhibits excellent light absorption properties, while the resulting COF possesses significant photothermal properties. Furthermore, this application modifies the linking group by attaching a thermosensitive N-isopropylacrylamide (NIPAM) polymer via a group reaction. This composite photothermal material is combined with the hydrogel to prepare a composite photothermal hydrogel that combines photothermal properties with good formability for use in seawater desalination.

[0034] In one embodiment, the structural unit of the structure shown in Formula I includes a crosslinking agent crosslinking structure, wherein the crosslinking agent is N,N'-methylenebisacrylamide. The crosslinking agent can enhance the three-dimensional network structure of the NIPAM polymer and improve the gel properties.

[0035] This application also provides a method for preparing a composite photothermal gel for seawater desalination, comprising the following steps: The COF of the structural unit shown in Formula II and N-isopropylacrylamide were reacted with tetramethylethylenediamine and an initiator in the presence of a crosslinking agent to prepare the composite photothermal gel for seawater desalination.

[0036] Formula II.

[0037] The COF of the structural unit shown in Formula II is uniformly dispersed in N-isopropylacrylamide. When N-isopropylacrylamide is in the presence of a crosslinking agent, it undergoes free radical polymerization initiated by a tetramethylethylenediamine catalytic initiator. N-isopropylacrylamide forms a linear polymerization, while the crosslinking agent transforms the linear polymerization into a three-dimensional network connection, forming a uniform hydrogel network structure. The COF of the structural unit shown in Formula II is uniformly linked in the gel by chemical bonds. The preparation process is as follows: Figure 1 As shown.

[0038] In one embodiment, the reaction is carried out in a solvent. First, the COF of the structural unit shown in Formula II is uniformly dispersed in water, preferably deionized water, to form an aqueous dispersion of COF. Water is also used as the solvent for subsequent reactions. In this embodiment, the mass-to-volume ratio of the COF of the structural unit shown in Formula II to water is (4–10) mg:1 mL. Preferably, the mass-to-volume ratio of the COF of the structural unit shown in Formula II to water is 5 mg:1 mL.

[0039] As one embodiment, NIPAM is added to the aqueous dispersion of the COF of the structural unit shown in Formula II, and the NIPAM is completely dissolved in the water; preferably, the dissolution and mixing can be performed by ultrasound.

[0040] In one embodiment, a mixed solution of COF and NIPAM of the structural unit shown in Formula II is placed in an ice-water bath at 0–5°C, followed by the addition of the crosslinking agent N,N'-methylenebisacrylamide, and the mixture is stirred to carry out the reaction. In this embodiment, the stirring reaction time is 20–40 min.

[0041] In one embodiment, an initiator is added to the solution, and the reaction is stirred in an ice-water bath at 0–5°C. In this embodiment, the stirring time is 5–15 minutes.

[0042] As one embodiment, tetramethylethylenediamine is added to the solution, and the reaction is stirred in an ice-water bath at 0–5°C; in this embodiment, the stirring time is 2–5 min.

[0043] In one embodiment, the crosslinking agent is N,N'-methylenebisacrylamide and the initiator is ammonium persulfate.

[0044] As one embodiment, the mass ratio of COF of the structural unit shown in Formula II to N-isopropylacrylamide, crosslinking agent, tetramethylethylenediamine and initiator is 1:(30-50):(0.8-1.2):(0.8-1.2):(1.2-1.8).

[0045] In one embodiment, after the reaction, the reaction solution is allowed to stand at room temperature for 1–5 hours to obtain the composite photothermal gel for seawater desalination. In this embodiment, the reaction solution can be placed in a mold and allowed to stand, allowing the gel to form different shapes for easy application.

[0046] As one embodiment, the method for preparing the COF of the structural unit shown in Formula II includes the following steps: 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, 2,5-bis(2-propynoxy)terephthalaldehyde and 2,5-dihydroxyterephthalaldehyde were subjected to a solvothermal reaction in a mixed solvent in the presence of acetic acid to prepare COF with the structural unit shown in Formula II.

[0047] COFs are prepared via a solvothermal reaction. The solvothermal reaction conditions are mild, simple, and not demanding, and the post-processing is straightforward, enabling the large-scale preparation of COF materials. This application prepares COFs containing alkynyl groups as linking groups, providing modification sites for subsequent COF modifications. In this application, the alkynyl groups are linked to NIPAM, thus incorporating the COF material into the hydrogel structure.

[0048] As one implementation method, after the reactants are dissolved in a solvent, they are sequentially frozen with liquid nitrogen, vacuumed, and thawed, repeated three times to remove dissolved oxygen from the mixed solution.

[0049] As one implementation method, after the solvothermal reaction is completed, the reaction solution is subjected to solid-liquid separation; the solid phase is washed with anhydrous acetone and dried to obtain the COF of the structural unit shown in Formula II.

[0050] In one embodiment, the mixed solvent is a mixed solution of n-butanol and o-dichlorobenzene in a volume ratio of (0.5 to 2):1.

[0051] In one embodiment, the molar ratio of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, 2,5-bis(2-propynoxy)-terephthalaldehyde and 2,5-dihydroxy-terephthalaldehyde is (0.8-1):1:1.

[0052] In one embodiment, the amount of acetic acid added is 5 to 15% of the volume of the mixed solvent, consisting of (3 to 6) M acetic acid.

[0053] In one embodiment, the molar volume ratio of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin to the mixed solvent is (10-50) μmol:1 mL.

[0054] As one implementation method, the solvothermal reaction is carried out at a temperature of 80–100°C for 6–24 hours.

[0055] As one implementation method, freeze drying is used.

[0056] The following is a further explanation using specific embodiments.

[0057] Example 1: Preparation of Porphyrin-based COFs Materials 0.8 mmol of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, 0.8 mmol of 2,5-bis(2-propynoxy)-terephthalaldehyde, and 0.8 mmol of 2,5-dihydroxy-terephthalaldehyde were mixed thoroughly and then added to a Schlenk tube containing 40 mL of a 1:1 mixture of n-butanol and o-dichlorobenzene. 4 mL of 3M acetic acid was then added. The mixture was subjected to a three-cycle process of liquid nitrogen freezing for 20 min, vacuuming for 15 min, and thawing for 30 min. The mixture was then reacted at 80 °C for 12 h. The resulting liquid mixture was filtered, and the solid was washed three times with anhydrous acetone. The washed solid was freeze-dried for 6 h to obtain porphyrin-based COFs materials with the structural unit shown in Formula II.

[0058] Example 2 0.8 mmol of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, 1.0 mmol of 2,5-bis(2-propynoxy)-terephthalaldehyde, and 1.0 mmol of 2,5-dihydroxyterephthalaldehyde were mixed thoroughly and then added to a Schlenk tube containing 16 mL of a mixture of n-butanol and o-dichlorobenzene at a volume ratio of 0.5:1. 2.4 mL of 5M acetic acid was then added. The mixture was subjected to a three-cycle process of liquid nitrogen freezing for 20 min, vacuuming for 15 min, and thawing for 30 min. The mixture was then reacted at 90 °C for 24 h. The resulting liquid mixture was filtered, and the solid was washed three times with anhydrous acetone. The washed solid was freeze-dried for 6 h to obtain porphyrin-based COFs materials with the structural unit shown in Formula II.

[0059] Example 3 0.8 mmol of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, 0.89 mmol of 2,5-bis(2-propynoxy)-terephthalaldehyde, and 1.0 mmol of 2,5-dihydroxyterephthalaldehyde were mixed thoroughly and then added to a Schlenk tube containing 80 mL of a 2:1 mixture of n-butanol and o-dichlorobenzene. 4 mL of 6M acetic acid was then added. The mixture was subjected to a three-cycle process of liquid nitrogen freezing for 20 min, vacuuming for 15 min, and thawing for 30 min. The mixture was then reacted at 100 °C for 6 h. The resulting liquid mixture was filtered, and the solid was washed three times with anhydrous acetone. The washed solid was then freeze-dried for 6 h to obtain porphyrin-based COFs materials with the structural unit shown in Formula II.

[0060] Example 4: Preparation of COFs-PNIPAM composite photothermal hydrogel The porphyrin-based COFs material with the structural unit shown in Formula II prepared in Example 1 was ground into powder. 200 mg of COFs powder was placed in a 40 mL deionized water beaker and sonicated for 15 min to disperse the COFs in the deionized water. Add 9.0 g of NIPAM to the COFs mixed solution and sonicate for 15 min to completely dissolve the NIPAM in the solution. Then, place it in an ice-water bath environment at 2-3℃, and then add 0.2 g of crosslinking agent N,N'-methylenebisacrylamide and stir magnetically for 30 min. Next, add 0.2 g of ammonium persulfate to the solution and stir magnetically for 10 min. Then, add 390 μL of tetramethylethylenediamine (about 0.3 g) to the solution and stir magnetically for 2 min. Pour the solution after the reaction is completed into a mold and let it stand at room temperature for 2 h to obtain the composite photothermal gel for seawater desalination, named COFs-PNIPAM.

[0061] Example 5 The porphyrin-based COFs material with the structural unit shown in Formula II prepared in Example 1 was ground into powder. 200 mg of COFs powder was placed in a 50 mL deionized water beaker and sonicated for 15 min to disperse the COFs in the deionized water. Add 6.0 g of NIPAM to the COFs mixed solution and sonicate for 15 min to completely dissolve the NIPAM in the solution. Then, place it in an ice-water bath environment at 2-3℃, and then add 0.16 g of crosslinking agent N,N'-methylenebisacrylamide and stir magnetically for 20 min. Next, add 0.16 g of ammonium persulfate to the solution and stir magnetically for 15 min. Then, add 310 μL of tetramethylethylenediamine (about 0.24 g) to the solution and stir magnetically for 3 min. Pour the solution after the reaction is completed into a mold and let it stand at room temperature for 1 h to obtain the composite photothermal gel for seawater desalination, named COFs-PNIPAM.

[0062] Example 6 The porphyrin-based COFs material with the structural unit shown in Formula II prepared in Example 1 was ground into powder. 200 mg of COFs powder was placed in a 10 mL deionized water beaker and sonicated for 15 min to disperse the COFs in the deionized water. 10.0 g of NIPAM was added to the COFs mixed solution and sonicated for 15 min to completely dissolve the NIPAM in the solution. Then, the solution was placed in an ice-water bath at 0-5℃, followed by the addition of 0.24 g of crosslinking agent N,N'-methylenebisacrylamide and magnetic stirring for 40 min. Then, 0.24 g of ammonium persulfate was added to the solution and magnetic stirring was carried out for 5 min. Finally, 460 μL of tetramethylethylenediamine (approximately 0.36 g) was added to the solution and magnetic stirring was carried out for 5 min. The solution after the reaction was completed was poured into a mold and allowed to stand at room temperature for 5 h to obtain the composite photothermal gel for seawater desalination, named COFs-PNIPAM.

[0063] Material characterization: (1) The COFs-PNIPAM prepared in Example 4 was observed by scanning electron microscopy and transmission electron microscopy. The SEM images are shown below. Figure 2 As shown in Figure a; TEM image as shown Figure 2 As shown in b; the cross-sectional image of the COFs-PNIPAM gel is shown in Figure 1. Figure 3 As shown.

[0064] pass Figure 2 The microstructure of COFs-PNIPAM composite photothermal gel was determined by SEM, and long-range ordered channels were observed. Figure 3 In the study, the hydrogel cross-section exhibits a loose, porous structure, with the size and arrangement of the pores tending to be regular. TEM images show that COFs are distributed within the gel structure.

[0065] (2) X-ray diffraction analysis was performed on the COFs-PNIPAM prepared in Example 4. The XRD pattern is shown below. Figure 4 As shown.

[0066] Figure 4 In the figure, the peak value of 3.55° corresponds to the (001) and (100) crystal planes of the material, proving the presence of COFs in the composite photothermal hydrogel.

[0067] (3) Infrared spectroscopy was performed on the COFs-PNIPAM prepared in Example 4, the raw material PNIPAM, and the porphyrin-based COFs material with the structural unit shown in Formula II prepared in Example 1. The results are as follows: Figure 5 As shown.

[0068] Figure 5 In the middle, the infrared spectrum at 1600 cm⁻¹ -1 A C=N characteristic peak belonging to COFs was observed at 3300 cm⁻¹, and a similar peak was observed at 3300 cm⁻¹. -1 The disappearance of another characteristic peak of C≡CH belonging to COFs indicates that COFs and PNIPAM have bonded, and COFs-PNIPAM composite photothermal gel has been successfully synthesized.

[0069] (4) XPS analysis was performed on the COFs-PNIPAM prepared in Example 4, and the results are as follows: Figure 6 As shown.

[0070] from Figure 6 C1s energy spectrum of COFs ( Figure 6 a) Obvious C≡C characteristic peaks can be observed. After covalent bonding, the C≡C characteristic peaks in COFs-PNIPAM ( Figure 6 b) The significant decrease in strength indicates that the alkynyl groups in COFs participate in the free radical polymerization reaction of NIPAM to generate CC bonds.

[0071] Material performance testing: The COFs-PNIPAM composite photothermal gel prepared in Example 4 was used as a photothermal conversion material for seawater desalination, and seawater desalination research was conducted; details are as follows: (1) The COFs-PNIPAM composite hydrogel sample was cut into a cylindrical shape with a diameter of 2 cm, and the test area was approximately 3.14 × 2 cm. 2 cm 2 ; (2) Prepare a 3.5 wt% NaCl solution to simulate seawater as test solution 1; use pure water as the blank group and actual seawater as test solution 2; (3) Place the hydrogel sample into simulated seawater, pure water and actual seawater, and let it float naturally on the water surface.

[0072] (4) The photothermal evaporation efficiency was tested by simulating sunlight under one solar intensity using a xenon lamp light source system; (5) Place the evaporation device on an electronic balance, connect the electronic balance to a computer, and monitor the mass change of the evaporation device in real time through the computer software program; conduct a continuous evaporation test for 60 minutes; (6) Plot a graph of mass change versus time. Based on the mathematical relationship between mass change, illumination time, and test area, convert the mass change value into the photothermal evaporation rate value of the composite hydrogel; the results are as follows. Figure 7 As shown.

[0073] (7) The material was circulated in simulated seawater in 60-minute test cycles. After each test, it was washed with water and acetone, dried, and then tested again. The effect of circulation was as follows: Figure 8 As shown.

[0074] like Figure 7 As shown, under one solar irradiance, the COFs-PNIPAM composite photothermal gel exhibits a seawater evaporation rate of 3.58 kg·m⁻². -1 •h -1This value is comparable to that of traditional carbon-based materials (approximately 1.2 kg·m³). -1 •h -1 The evaporation rate is increased by approximately three times. Furthermore, its evaporation rate shows a linear relationship with time, indicating a stable evaporation rate. The evaporation rate in seawater, pure water, or simulated seawater shows little difference, suggesting that the material is less affected by salt in the water and has good salt resistance. This can also be seen from... Figure 8 The cyclic test graph shows that after 15 cycles, the seawater evaporation rate of the COFs-PNIPAM composite photothermal gel remains basically unchanged, and it also shows good salt resistance and stability.

[0075] In summary, the COFs-PNIPAM composite hydrogel of this application exhibits excellent photothermal evaporation performance, confirming the significant role of the COFs-PNIPAM composite photothermal hydrogel in improving the solar energy absorption and conversion process.

[0076] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0077] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0078] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A composite photothermally hydrogel for seawater desalination, characterized in that, A structural unit having a structure shown in formula I: ； Formula I Wherein n is an integer from 1 to 10.

2. The composite photothermal hydrogel for seawater desalination according to claim 1, wherein, The structural unit shown in formula I comprises a crosslinking structure of a crosslinking agent, and the crosslinking agent is N,N'-methylene bisacrylamide.

3. A method for the preparation of the composite photothermally hydrogel for seawater desalination according to claim 1 or 2, characterized by, Comprising the following steps: The COF of the structural unit shown in formula II is reacted with N-isopropyl acrylamide in the presence of a crosslinking agent, tetramethyl ethylenediamine and an initiator to prepare the composite photothermal hydrogel for seawater desalination. ； Formula II.

4. The preparation method of the composite photothermal hydrogel for seawater desalination according to claim 3, wherein, The crosslinking agent is N,N'-methylene bisacrylamide, and the initiator is ammonium persulfate; The mass ratio of the COF of the structural unit shown in formula II, N-isopropyl acrylamide, the crosslinking agent, tetramethyl ethylenediamine and the initiator is 1: (30-50): (0.8-1.2): (0.8-1.2): (1.2-1.8); The reaction is carried out in a solvent, and the COF of the structural unit shown in formula II is dispersed in water; the mass-volume ratio of the COF of the structural unit shown in formula II to water is (4-10) mg: 1 mL; The reaction temperature is 0-5°C, and the reaction time is 25-60 min.

5. The preparation method of the composite photothermal hydrogel for seawater desalination according to claim 3, wherein, In the reaction process, the COF of the structural unit shown in formula II is added into an aqueous solution of N-isopropyl acrylamide, and the crosslinking agent is stirred for 20-40 min; then the initiator is added and stirred for 5-15 min; finally, the tetramethyl ethylenediamine is added and stirred for 2-5 min.

6. The preparation method of the composite photothermal hydrogel for seawater desalination according to claim 3, wherein, After the reaction, the reaction solution is left to stand at room temperature for 1-5 h to obtain the composite photothermal hydrogel for seawater desalination.

7. The preparation method of the composite photothermal hydrogel for seawater desalination according to claim 3, wherein, The preparation method of the COF of the structural unit shown in formula II comprises the following steps: The COF of the structural unit shown in formula II is prepared by solvothermal reaction of 5,10,15,20-tetrakis (4-aminophenyl) -21H,23H-porphyrin, 2,5-bis (2-propynoxy) terephthaldehyde and 2,5-dihydroxy terephthaldehyde in a mixed solvent in the presence of acetic acid.

8. The preparation method of the composite photothermal hydrogel for seawater desalination according to claim 7, wherein, The mixed solvent is a mixed solution of n-butanol and o-dichlorobenzene in a volume ratio of (0.5-2): 1; The molar ratio of 5,10,15,20-tetrakis (4-aminophenyl) -21H,23H-porphyrin, 2,5-bis (2-propynoxy) terephthaldehyde and 2,5-dihydroxy terephthaldehyde is (0.8-1): 1: 1; The amount of acetic acid added is 5-15% of the volume of the mixed solvent; 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin and mixed solvent molar volume ratio is (10-50) μmol:1 mL; The temperature of the solvothermal reaction is 80-100 DEG C, and the reaction time is 6-24 h. 9.The method of claim 7, wherein the temperature of the solvothermal reaction is 80-100 DEG C, and the reaction time is 6-24 h. After the solvothermal reaction is completed, the reaction solution is subjected to solid-liquid separation; and the solid phase is washed with anhydrous acetone and dried to obtain the COF of the structural unit shown in formula II. 10.The application of the composite photothermal hydrogel for seawater desalination in claim 1 or 2 as a photothermal conversion material in seawater desalination.

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