Foaming gel ink, preparation method, graded porous photo-thermal hydrogel and application

Abstract

The invention relates to foaming gel ink, a preparation method, graded porous photo-thermal hydrogel and application, and belongs to the technical field of photo-thermal material engineering. The preparation method of the foaming gel ink comprises the following steps: mixing an amphiphilic graphene oxide dispersion liquid, a polyvinyl alcohol solution, a cross-linking agent and a surfactant to obtain a hydrogel precursor, and mechanically stirring to generate air bubbles in the hydrogel precursor to obtain the foaming gel ink. According to the preparation method, a mechanical stirring method is utilized, a stable bubble group is introduced into a hydrogel precursor as an air template, and a unique spherical hierarchical porous structure which is communicated with one another is constructed in the gel, so that the transmission of moisture in the gel is accelerated. Meanwhile, the rheological property of a hydrogel precursor is improved by introducing a bubble group, the viscosity of the hydrogel precursor is increased, the foaming gel ink capable of being used for writing and printing is successfully obtained, and simple and convenient construction of graded porous pores in a hydrogel evaporator and direct writing and printing of a three-dimensional shape are achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of photothermal material engineering, and particularly relates to a foamed gel ink, a preparation method, a hierarchical porous photothermal hydrogel and application. BACKGROUND

[0002] Due to global population growth, climate change, environmental pollution and energy consumption, freshwater resource shortage and energy consumption have become one of the important problems restricting sustainable development. In recent years, solar water evaporation technology for extracting clean water vapor from seawater using renewable green solar energy has attracted widespread attention. Hydrogel is a hydrophilic three-dimensional material composed of one or several polymers through physical or chemical crosslinking. By changing the composition and structure of the hydrogel, excellent photothermal performance, mechanical properties and good water retention can be imparted to the hydrogel, so the hydrogel is widely used in solar-driven water evaporation systems. However, the molecular chains of the hydrogel prepared by the traditional method are randomly entangled, resulting in tortuous internal pore channels of the hydrogel, lack of micrometer-scale pore structure, long water molecule transmission path and large resistance in the internal gel, which causes the water loss in the internal gel due to water evaporation in the process of using the hydrogel evaporator, and the water loss in the internal gel cannot be replenished in time, so the hydrogel evaporator cannot realize long-term stable operation.

[0003] The patent for invention with application publication number CN110183714A discloses a preparation method of a porous composite photothermal hydrogel based on polyvinyl alcohol and graphite powder. The preparation method of the porous composite photothermal hydrogel based on polyvinyl alcohol and graphite powder uses polyethylene glycol and acetone as a pore-forming agent to construct a porous structure in the internal gel. However, the method uses flammable and volatile toxic solvent acetone, and the porous structure produced in the internal gel is irregular and dispersed, and cannot form efficient water transmission channels connected to each other. The patent for invention with application publication number CN116102777A discloses a porous double-network air hydrogel and a preparation method and application thereof. The porous double-network air hydrogel utilizes mechanical stirring to produce air bubbles in a mixed solution of biological macromolecules and conductive polymers. However, the air bubbles produced in the system are not stable, and the mixture containing the air bubbles needs to be quickly crosslinked and fixed to fix the air bubbles. It can be seen from the scanning electron microscope image that the shape of the formed porous structure is irregular, and the spherical structure formed by taking the air bubbles as a template cannot be observed, which confirms that the air bubbles in the system are not stable. In addition, the air bubbles of the porous double-network air hydrogel are separated from each other in the internal gel, and cannot form water transmission channels connected to each other in the prepared hydrogel. SUMMARY

[0004] The first object of the present application is to provide a foamed gel ink to solve the technical problems that the existing hydrogel foaming uses toxic organic solvents or the foaming is unstable and cannot form water transmission channels connected to each other in the internal hydrogel.

[0005] The second object of the present application is to provide a preparation method of a foamed gel ink.

[0006] The third object of the present application is to provide a hierarchical porous photothermal hydrogel.

[0007] The fourth object of the present application is to provide an application of the hierarchical porous photothermal hydrogel.

[0008] In order to achieve the above objects, the technical scheme adopted by the present application is as follows:

[0009] A preparation method of a foamed gel ink, comprising the following steps: mixing an amphiphilic graphene oxide dispersion, a polyvinyl alcohol solution, a crosslinking agent and a surfactant to obtain a hydrogel precursor, and mechanically stirring to generate air bubbles in the hydrogel precursor, thereby obtaining the foamed gel ink.

[0010] Further, the rotation speed of the mechanical stirring is 500-3000 rpm, and the mechanical stirring time is 1-10 min; the volume ratio of the amphiphilic graphene oxide dispersion to the polyvinyl alcohol solution is 3:1-1:3.

[0011] Further, the preparation method of the amphiphilic graphene oxide dispersion is as follows: introducing a hydrophilic oxygen-containing functional group on graphene oxide nanosheets, and dialyzing and purifying to obtain the amphiphilic graphene oxide dispersion; the concentration of the amphiphilic graphene oxide dispersion is 0.5-2.0 wt%; the hydrophilic oxygen-containing functional group is one or more of hydroxyl and carboxyl.

[0012] Further, the preparation method of the polyvinyl alcohol solution is as follows: adding polyvinyl alcohol solid to water, and stirring at 80-95℃ until the polyvinyl alcohol solid is dissolved, thereby obtaining the polyvinyl alcohol solution; the mass-to-volume ratio of the polyvinyl alcohol solid to the water is 5-30 g:100 mL.

[0013] Further, the crosslinking agent is glutaraldehyde, the concentration of the glutaraldehyde is 20-50 wt%, the volume ratio of the amphiphilic graphene oxide dispersion to the glutaraldehyde is 500:1-50:1; and the surfactant is one or more of sodium dodecyl sulfate and sodium dodecyl laurate.

[0014] A foamed gel ink is prepared by the above preparation method of the foamed gel ink.

[0015] A preparation method of a hierarchical porous photothermal hydrogel, comprising the following steps:

[0016] S1: placing the foamed gel ink of claim 6 into a 3D printer injector, and extruding the foamed gel ink from the injector needle by using air pressure to construct a three-dimensional structure;

[0017] S2: The three-dimensional structure is placed at low temperature for physical cross-linking;

[0018] S3: After thawing the three-dimensional structure that has completed physical cross-linking in S2, perform thermal cross-linking;

[0019] S4: The three-dimensional structure after thermal cross-linking in S3 is immersed in a reducing agent and then washed with water to obtain the product.

[0020] Furthermore, the air pressure mentioned in S1 is 0.01–0.1 MPa, and the moving speed of the syringe needle in the 3D printer syringe is 1–10 mm / s. -1 The low temperature in S2 is -198 to -4℃, and the holding time at the low temperature is 6 to 48 hours; the thawing temperature in S3 is 5 to 40℃, the thermal crosslinking temperature is 40 to 80℃, and the thermal crosslinking time is 3 to 24 hours; the reducing agent in S4 is a 0.2 to 2 wt% ascorbic acid solution, the soaking temperature is 50 to 90℃, and the soaking time is 6 to 24 hours.

[0021] A hierarchical porous photothermal hydrogel was prepared using the above-described method for preparing hierarchical porous photothermal hydrogels.

[0022] Application of a graded porous photothermal gel as a photothermal evaporator in seawater desalination.

[0023] The beneficial effects of this invention are:

[0024] This invention utilizes mechanical stirring to introduce stable air bubble clusters as air templates into a hydrogel precursor, constructing a unique, interconnected, spherical hierarchical porous structure within the hierarchical porous photothermal hydrogel, thus accelerating water transport within the gel. Simultaneously, the introduction of the air bubble clusters improves the rheological properties and increases the viscosity of the hydrogel precursor, successfully yielding a foamed gel ink suitable for writing and printing. This enables the simple construction of hierarchical porous pores within the hierarchical porous photothermal hydrogel and direct writing and printing of three-dimensional shapes.

[0025] The presence of amphiphilic nanosheet graphene oxide and surfactants allows the bubble clusters obtained by mechanical stirring in this invention to exist stably in the hydrogel precursor. After physical and chemical cross-linking, a unique, interconnected, spherical, multi-scale hierarchical porous structure at the micron and nanoscale is obtained. This provides abundant channels for the rapid transport of water within the hierarchical porous photothermal hydrogel, overcoming the shortcomings of current porous structure manufacturing methods, such as the use of volatile and toxic reagents, irregular pore structures, separation of pores, and inability to form efficient water transport channels. Furthermore, the introduced bubble clusters reduce the free-flowing liquid in the hydrogel precursor, fixing it within the mutually compressed bubble clusters. This guides the self-assembly of graphene oxide and polyvinyl alcohol molecules in the liquid film on the bubble cluster surface, inhibiting their movement within the hydrogel precursor and thus increasing its viscosity. This results in a foamed gel ink suitable for direct writing and printing. This foamed gel ink can achieve macroscopic shape design and construction of interconnected spherical hierarchical porous structures for hierarchical porous photothermal gels without the need for molds. The method has mild synthesis conditions, is easy to operate, and can realize the large-scale and inexpensive preparation of hierarchical porous gels. Attached Figure Description

[0026] Figure 1 The images shown are physical photos and printed images of the foamed gel ink from Example 1.

[0027] Figure 2 The images shown are of the hierarchical porous photothermal hydrogel in Example 2, where a is a physical image and b is a scanning electron microscope image.

[0028] Figure 3 This is a photograph of the hierarchical porous photothermal hydrogel prepared on a large scale in Example 2;

[0029] Figure 4 This is a scanning electron microscope image of the interconnected spherical hierarchical porous channels inside the hierarchical porous photothermal hydrogel in Example 2.

[0030] Figure 5 This is a scanning electron microscope image of the interior of the non-porous gel in Comparative Example 1;

[0031] Figure 6 This is an internal scanning electron microscope image of the foamed gel ink in Comparative Example 2;

[0032] Figure 7 This is a comparison graph showing the water transport rate inside the gel in Example 2 and Comparative Example 1.

[0033] Figure 8 The mass loss of water in the gels of Example 2 and Comparative Example 1 under sunlight irradiation;

[0034] Figure 9This is a comparison graph showing the gel water evaporation rates of Example 2 and Comparative Example 1;

[0035] Figure 10 The graph shows the changes in the concentration of various ions in seawater after treatment with the graded porous photothermal gel of Example 2. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0037] Figures 7-9 The hierarchical porous gel in this example is the hierarchical porous photothermal gel in Example 2.

[0038] Graphene oxide was prepared by the Hummers method, the modified Hummers method, the Brodie method, and the Staudenmaier method.

[0039] The preparation method of 1.0 wt% amphiphilic graphene oxide dispersion is as follows: 276 mL of concentrated sulfuric acid, 12 g of NaNO3, 36 g of KMnO4 and 12 g of graphite powder are mixed. After the mixture is kept at 35 °C for 4 h, 552 mL of deionized water is added and the temperature is raised to 98 °C and kept for 15 min. Then, 552 mL of deionized water and 30 mL of hydrogen peroxide are added. Through the above chemical oxidation method, hydrophilic carboxyl and hydroxyl oxygen-containing functional groups are introduced on the graphite sheets, while retaining some of the original hydrophobic graphitized structure on the graphite sheets. Finally, the amphiphilic graphene oxide dispersion with a concentration of 1.0 wt% is obtained by dialysis purification and ultrasonic exfoliation.

[0040] Example 1

[0041] The preparation method of the foamed gel ink in Example 1 includes the following steps:

[0042] S1: Graphene oxide nanosheets were prepared by chemical oxidation. Hydroxyl and carboxyl groups were introduced onto the graphene oxide nanosheets while partially retaining the hydrophobic graphitized structure, resulting in an amphiphilic graphene oxide dispersion with a concentration of 1.0 wt%.

[0043] S2: Add 15g of polyvinyl alcohol solid to 100mL of deionized water, heat and stir in a 90℃ water bath until the polyvinyl alcohol solid is completely dissolved to obtain a polyvinyl alcohol solution.

[0044] S3: Mix 10 mL of amphiphilic graphene oxide dispersion and 10 mL of polyvinyl alcohol solution, then add 0.1 mL of 50 wt% glutaraldehyde and 0.3 g of sodium dodecyl sulfate to obtain a hydrogel precursor. Stir continuously at 1000 rpm for 3 min to generate abundant bubbles in the hydrogel precursor, thus obtaining foamed gel ink.

[0045] Example 2

[0046] The preparation method of the hierarchical porous photothermal hydrogel in Example 2 includes the following steps:

[0047] S1: The foamed gel ink from Example 1 is extruded into the 3D printer syringe. Air pressure is used to force the foamed gel ink from the syringe needle onto a flat surface, constructing three-dimensional structures of different shapes. The air pressure is 0.05 MPa, and the syringe needle moves at a speed of 4 mm / s. -1 .

[0048] S2: The printed three-dimensional structure is placed at -20℃ for 24 hours to complete the physical cross-linking of graphene oxide and polyvinyl alcohol molecules;

[0049] S3: The three-dimensional structure that has been physically cross-linked in S2 is placed at 30°C to thaw and kept at 50°C for 8 hours to strengthen the gel skeleton and improve gel toughness.

[0050] S4: Immerse the gel from S3 in a 0.5wt% ascorbic acid solution and keep it at 80℃ for 12 hours. Then soak it in water to wash away impurities, thus obtaining a fractionated porous photothermal gel.

[0051] Example 3

[0052] The hierarchical porous photothermal gel of Example 2 was placed in seawater as a photothermal evaporator, and seawater desalination was achieved through interfacial photoevaporation under solar energy drive.

[0053] Example 4

[0054] The preparation method of the foamed gel ink and hierarchical porous photothermal gel in Example 4 includes the following steps:

[0055] The preparation method of foamed gel ink is as follows:

[0056] S1: Graphene oxide nanosheets were prepared by chemical oxidation. Carboxyl groups were introduced onto the graphene oxide nanosheets while retaining some hydrophobic graphitized structures. The amphiphilic graphene oxide dispersion with a concentration of 2.0 wt% was obtained by dialysis purification.

[0057] S2: Add 30g of polyvinyl alcohol solid to 100mL of deionized water, heat and stir in a 95℃ water bath until the polyvinyl alcohol solid is completely dissolved to obtain a polyvinyl alcohol solution.

[0058] S3: Mix 30 mL of amphiphilic graphene oxide dispersion and 10 mL of polyvinyl alcohol solution, then add 0.5 mL of glutaraldehyde (20 wt%) and 0.3 g of sodium dodecyl laurate to obtain a hydrogel precursor. Stir continuously at 3000 rpm for 3 min to generate abundant bubbles in the hydrogel precursor, thus obtaining foamed gel ink.

[0059] The preparation method of hierarchical porous photothermal hydrogel is as follows:

[0060] S1: Foaming gel ink is squeezed into a syringe and then extruded from the syringe needle onto a flat plate using air pressure to construct three-dimensional structures of different shapes; the air pressure is 0.1 MPa and the syringe needle moves at a speed of 10 mm / s. -1 .

[0061] S2: The printed three-dimensional structure is placed at -80℃ for 6 hours to complete the physical cross-linking of graphene oxide and polyvinyl alcohol molecules;

[0062] S3: The three-dimensional structure that has been physically cross-linked in S2 is placed at 40℃ to thaw and kept at 80℃ for 24 hours to strengthen the gel skeleton and improve gel toughness.

[0063] S4: Immerse the gel from S3 in a 2wt% ascorbic acid solution and keep it at 80℃ for 24 hours. Then, soak it in water to wash away impurities, thus obtaining a fractionated porous photothermal gel.

[0064] Example 5

[0065] The preparation method of the foamed gel ink and hierarchical porous photothermal gel in Example 5 includes the following steps:

[0066] The preparation method of foamed gel ink is as follows:

[0067] S1: Graphene oxide nanosheets were prepared by chemical oxidation. Carboxyl groups were introduced onto the graphene oxide nanosheets while retaining some hydrophobic graphitized structures. The amphiphilic graphene oxide dispersion with a concentration of 0.5 wt% was obtained by dialysis purification.

[0068] S2: Add 5g of solid polyvinyl alcohol to 100mL of deionized water, heat and stir in an 80℃ water bath until the solid polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution.

[0069] S3: Mix 10 mL of amphiphilic graphene oxide dispersion and 30 mL of polyvinyl alcohol solution, then add 0.05 mL of glutaraldehyde (20 wt%) and 0.3 g of sodium dodecyl laurate to obtain a hydrogel precursor. Stir continuously at 3000 rpm for 3 min to generate abundant bubbles in the hydrogel precursor, thus obtaining foamed gel ink.

[0070] The preparation method of hierarchical porous photothermal hydrogel is as follows:

[0071] S1: Foaming gel ink is squeezed into a syringe and then extruded from the syringe needle onto a flat plate using air pressure to construct three-dimensional structures of different shapes; the air pressure is 0.01 MPa and the syringe needle moves at a speed of 1 mm / s. -1 .

[0072] S2: The printed three-dimensional structure is placed at -80℃ for 48 hours to complete the physical cross-linking of graphene oxide and polyvinyl alcohol molecules;

[0073] S3: The three-dimensional structure that has been physically cross-linked in S2 is placed at 5°C to thaw and kept at 80°C for 3 hours to strengthen the gel skeleton and improve gel toughness.

[0074] S4: Immerse the gel from S3 in a 0.2wt% ascorbic acid solution and keep it at 90℃ for 5 hours. Then soak it in water to wash away impurities, thus obtaining a fractionated porous photothermal gel.

[0075] Comparative Example 1

[0076] The preparation methods of the bubble-free cluster gel and the non-porous gel of Comparative Example 1 include the following steps:

[0077] S1: Graphene oxide nanosheets were prepared by chemical oxidation. Hydroxyl and carboxyl groups were introduced onto the graphene oxide nanosheets while partially retaining the hydrophobic graphitized structure. The amphiphilic graphene oxide dispersion with a concentration of 1.0 wt% was obtained by dialysis purification.

[0078] S2: Add 15g of polyvinyl alcohol solid to 100mL of deionized water, heat and stir in a 90℃ water bath until the polyvinyl alcohol solid is completely dissolved to obtain a polyvinyl alcohol solution.

[0079] S3: Mix 10 mL of amphiphilic graphene oxide dispersion and 10 mL of polyvinyl alcohol solution, then add 0.1 mL of 50 wt% glutaraldehyde to obtain a hydrogel precursor. Stir slowly at 10 rpm to mix evenly and avoid generating bubbles in the hydrogel precursor to obtain a bubble-free cluster gel.

[0080] S4: Pour the bubble-free gel into a mold and then place it at -20°C for 24 hours to complete the physical cross-linking of graphene oxide and polyvinyl alcohol molecules.

[0081] S5: Thaw the gel from S4 at 30°C and keep it at 50°C for 8 hours to strengthen the gel skeleton and improve gel toughness.

[0082] S6: Immerse the gel from S5 in a 0.5wt% ascorbic acid solution and keep it at 80℃ for 12 hours. Then soak it in water to wash away impurities to obtain a non-porous gel photothermal evaporator.

[0083] Comparative Example 2

[0084] The preparation methods of the foamed gel ink in Comparative Example 2 and the hierarchical porous photothermal gel include the following steps:

[0085] S1: Graphene oxide nanosheets were prepared by chemical oxidation. Hydroxyl and carboxyl groups were introduced onto the graphene oxide nanosheets while partially retaining the hydrophobic graphitized structure. The amphiphilic graphene oxide dispersion with a concentration of 1.0 wt% was obtained by dialysis purification.

[0086] S2: Add 15g of polyvinyl alcohol solid to 100mL of deionized water, heat and stir in a 90℃ water bath until the polyvinyl alcohol solid is completely dissolved to obtain a polyvinyl alcohol solution.

[0087] S3: Mix 10 mL of amphiphilic graphene oxide dispersion and 10 mL of polyvinyl alcohol solution, then add 0.1 mL of 50 wt% glutaraldehyde and 0.3 g of sodium dodecyl sulfate to obtain a hydrogel precursor. Stir continuously at 4000 rpm for 3 min to generate abundant bubbles in the hydrogel precursor, thus obtaining foamed gel ink.

[0088] S4: Foaming gel ink is squeezed into a syringe and then extruded from the syringe needle onto a flat plate using air pressure to construct three-dimensional structures of different shapes; the air pressure is 0.05 MPa and the syringe needle moves at a speed of 4 mm / s. -1 .

[0089] S5: Place the printed three-dimensional structure at -20℃ for 24 hours to complete the physical cross-linking of graphene oxide and polyvinyl alcohol molecules.

[0090] S6: Place the three-dimensional structure that has completed physical cross-linking in S5 at 30°C to thaw, and keep it at 50°C for 8 hours to strengthen the gel skeleton and improve gel toughness.

[0091] S7: Immerse the gel of S6 in a 0.5wt% ascorbic acid solution and keep it at 80℃ for 12 hours. Then soak it in water to wash away impurities, and you will get a fractionated porous photothermal gel.

[0092] from Figure 1 It can be seen that the foamed gel ink prepared by the present invention has greatly reduced fluidity and significantly increased viscosity. When the beaker containing the foamed gel ink of Example 1 is inverted, the foamed gel ink inside will not flow out of the beaker, exhibiting a unique ability to resist gravity deformation.

[0093] from Figure 2 It can be seen that direct extrusion printing using the foaming gel ink of Example 1 can construct a well-structured inverted pyramid structure of hierarchical porous photothermal gel, which has an interconnected open spherical hierarchical porous structure inside.

[0094] from Figure 3 It can be seen that the present invention can realize the large-scale preparation of hierarchical porous photothermal hydrogels.

[0095] from Figure 4 As can be seen from the figure, the hierarchical porous photothermal hydrogel of Example 2 has spherical pores formed with air bubbles as templates. There are some open pore structures inside the pores. At the same time, there are abundant micron and nano pores inside the hierarchical porous photothermal hydrogel framework. These unique hierarchical porous structures provide a large number of diffusion channels for the rapid transport of water inside the gel.

[0096] from Figure 5 It can be seen that the gel without introduced air bubbles exhibits a dense, non-porous internal structure. Figure 6 It can be seen that when too many air bubbles are introduced, the gel skeleton becomes too weak and the internal hierarchical porous structure collapses.

[0097] from Figure 7 It can be seen that the water transport resistance inside the non-porous gel of Comparative Example 1 is large. During the 120s test time, the water at the bottom cannot diffuse through the non-porous gel of Comparative Example 1 to the top. However, in the hierarchical porous photothermal gel test experiment, the water at the bottom can quickly diffuse through the pore structure inside the hierarchical porous photothermal gel to the top. It can be seen that the filter paper at the top is gradually wetted by water.

[0098] from Figure 8 It can be seen that under sunlight, the water loss rate in the non-porous gel test system in Comparative Example 1 gradually slows down, while in the hierarchical porous photothermal hydrogel system, the water loss rate does not decrease during the test time. The rapid water transport inside ensures the stable water evaporation performance of the hierarchical porous photothermal hydrogel.

[0099] from Figure 9 It can be seen that during the 360-minute test, the water evaporation rate of the hierarchical porous photothermal hydrogel remained stable, while the water evaporation rate of the non-porous gel in Comparative Example 1 gradually decreased.

[0100] from Figure 10 As can be seen, after treatment with the hierarchical porous photothermal hydrogel of Example 2, the ion concentration in the simulated seawater was significantly reduced, reaching the standards for healthy drinking water stipulated by the World Health Organization (WHO). The hierarchical porous photothermal hydrogel effectively reduced the concentration of Na+ ions. + K + Ca 2+ Mg 2+ B 3+ The desalination rate of all of them reached over 99%.

Claims

1. A method for preparing a foamed gel ink, characterized in that, Includes the following steps: A hydrogel precursor is obtained by mixing an amphiphilic graphene oxide dispersion, a polyvinyl alcohol solution, a crosslinking agent, and a surfactant. The precursor is then mechanically stirred to generate air bubbles, thus obtaining the final product.

2. The method for preparing foamed gel ink according to claim 1, characterized in that, The mechanical stirring speed is 500-3000 rpm, and the mechanical stirring time is 1-10 min; the volume ratio of the amphiphilic graphene oxide dispersion to the polyvinyl alcohol solution is 3:1-1:

3.

3. The method for preparing foamed gel ink according to claim 1, characterized in that, The preparation method of the amphiphilic graphene oxide dispersion is as follows: hydrophilic oxygen-containing functional groups are introduced onto graphene oxide nanosheets, and purified by dialysis; the concentration of the amphiphilic graphene oxide dispersion is 0.5-2.0 wt%; the hydrophilic oxygen-containing functional groups are one or more of hydroxyl and carboxyl groups.

4. The method for preparing foamed gel ink according to claim 1, characterized in that, The polyvinyl alcohol solution is prepared by adding solid polyvinyl alcohol to water and stirring at 80-95°C until the solid polyvinyl alcohol dissolves. The mass-volume ratio of the solid polyvinyl alcohol to the water is 5-30 g: 100 mL.

5. The method for preparing foamed gel ink according to claim 1, characterized in that, The crosslinking agent is glutaraldehyde, the concentration of which is 20-50 wt%, and the volume ratio of the amphiphilic graphene oxide dispersion to the glutaraldehyde is 500:1-50:1; the surfactant is one or more of sodium dodecyl sulfate and sodium dodecyl laurate.

6. A foaming gel ink, characterized in that, It is prepared by the method for preparing foamed gel ink according to any one of claims 1 to 5.

7. A method for preparing a hierarchical porous photothermal hydrogel, characterized in that, Includes the following steps, S1: The foamed gel ink of claim 6 is placed into the 3D printer syringe, and the foamed gel ink is squeezed out from the syringe needle by air pressure to construct a three-dimensional structure; S2: The three-dimensional structure is placed at low temperature for physical cross-linking; S3: After thawing the three-dimensional structure that has completed physical cross-linking in S2, perform thermal cross-linking; S4: The three-dimensional structure after thermal cross-linking in S3 is immersed in a reducing agent and then washed with water to obtain the product.

8. The method for preparing hierarchical porous photothermal hydrogel according to claim 7, characterized in that, The air pressure mentioned in S1 is 0.01–0.1 MPa, and the moving speed of the syringe needle in the 3D printer syringe is 1–10 mm / s. -1 The low temperature in S2 is -198 to -4℃, and the holding time at the low temperature is 6 to 48 hours; the thawing temperature in S3 is 5 to 40℃, the thermal crosslinking temperature is 40 to 80℃, and the thermal crosslinking time is 3 to 24 hours; the reducing agent in S4 is a 0.2 to 2 wt% ascorbic acid solution, the soaking temperature is 50 to 90℃, and the soaking time is 6 to 24 hours.

9. A hierarchical porous photothermal hydrogel, characterized in that, The hierarchical porous photothermal hydrogel was prepared using the method described in claim 7.

10. The application of the hierarchical porous photothermal gel as described in claim 9 as a photothermal evaporator in seawater desalination.

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