CN115651274A - Preparation method of clay-based composite hydrogel for solar seawater desalination - Google Patents

Abstract

The invention relates to the field of preparation of hydrogel materials, and discloses a preparation method of clay-based solar energy composite hydrogel for solar seawater desalination. The specific steps of the method are as follows: dissolving sodium alginate in an aqueous solution, adding an appropriate amount of clay and Carbon-based materials make it evenly dispersed, slowly add calcium salt, stir evenly, add gluconolactone aqueous solution or powder, continue stirring evenly, pour into the mold and let the gel stand; the aged gel is subjected to multiple directional freezing A clay-based hydrogel with a vertical pore structure. The clay-based composite hydrogel prepared by the invention has simple process, green and pollution-free raw materials and low price, and is beneficial to industrial production. The obtained clay-based composite hydrogel has good light absorption efficiency and water evaporation efficiency, rich pore structure and good hydrophilicity, and can be used in sewage treatment, seawater desalination, brine concentration and other fields.

Description

A preparation method of clay-based composite hydrogel for solar seawater desalination

technical field

The invention belongs to the field of material preparation, and in particular relates to a preparation method of clay-based composite hydrogel for solar seawater desalination.

Background technique

Freshwater is an essential resource for the survival of humans and all ecosystems and plays a vital role. How to achieve the security of fresh water supply is a new challenge under the conditions of population growth, environmental change and fresh water resource pollution. The earth's available water resources only account for 3% of its total water volume, and more than 70% of this extremely small fresh water resources are frozen in the ice sheets of the Antarctic and Arctic, and less than 1% of the fresh water resources can be used for Humans use it. In addition, global freshwater resources are not only in short supply but also extremely uneven in regional distribution. It is estimated that by 2025, 3 billion people in the world will face water shortages, and 40 countries and regions will be seriously short of fresh water.

In order to solve this problem, various seawater desalination technologies emerge in an endless stream. Such as reverse osmosis (RO), multi-effect desalination (MED), thermal vapor compression (TVC), humidification and dehumidification (HDH), hybrid systems and multi-level flash memory (MSF). However, these technologies are difficult to obtain widespread application due to high operating costs. Solar energy is an almost inexhaustible renewable resource in nature. Solar energy-driven freshwater technology is superior to other technologies with low cost and high light-to-heat conversion efficiency, and has become one of the effective ways to alleviate water resource tension, such as: (CN112108084A, CN113735208A ) However, due to the low utilization efficiency of sunlight under natural light (solar intensity ≤ 1KW·m ^{-2 )} , the existing solar water purification technology cannot meet commercial expectations. In order to improve evaporation efficiency, the current work mainly focuses on the following three Problems: ① Improve light-to-heat conversion efficiency; ② Continuous and stable water supply during evaporation; ③ Prevent salt precipitation from clogging channels. Based on the above requirements, new solar evaporation materials such as plasma nanoparticles, conjugated polymers, and carbon-based materials, as well as thermal Solar evaporation devices such as localized thin films, biomimetic nanostructures, and mushroom biomimetic devices have been highly valued and developed rapidly.

Hydrogel is a long chain of polymers or colloidal particles whose medium is water, accumulate and aggregate to form a three-dimensional network structure, which can hold a large amount of water without dissolving. Owing to their highly tunable physicochemical properties, they have received extensive attention and application development in the fields of inclusive artificial tissues, hygiene products, contact lenses, drug delivery, and agricultural fertilizers. Hydrogel, as one of the most important materials in the process of water evaporation and desalination, has high water evaporation rate and efficiency, which is attributed to the thermal localization on the air-water interface; the thermal localization between water molecules and polymer chains Weak interactions can form intermediate water, reducing the energy requirement for water vaporization. Hu et al. prepared a double-layer cellulose hydrogel with an evaporation rate of 1.582 kg m ^-2 h ^-1 (Carbohydrate Polymer, 2020, 243, 116480). Zhao et al. prepared a novel hydrogel-based solar evaporator by one-step cross-linking method. Using sodium alginate and PEDOT:PSS composite hydrogel as the photothermal layer, an evaporation rate of 1.23 kg m ^-2 h ^-1 was achieved (Desalinatio, 2020, 482, 114385). Song et al. prepared a high-content attapulgite airgel with an evaporation rate of 1.41 kg m ^-2 h ^-1 by physical/chemical crosslinking (Journal of Materials ChemistryA, 2021, 9, 23117-23126). However, in practical applications, it still faces the problems of salt deposition and unstable evaporation performance.

Contents of the invention

Purpose of the invention: Aiming at the problems existing in the prior art, the present invention provides a preparation method of clay-based composite hydrogel for solar seawater desalination, starting from the characteristics of the clay material itself, constructing a superhydrophilic water delivery channel, utilizing The pore size is adjusted by directional freezing, and the clay-based hydrogel with vertical micro-channel structure is obtained by multiple directional freezing and thawing. The clay-based composite hydrogel prepared by the invention has good light absorption efficiency and water evaporation efficiency, rich pore structure and good hydrophilicity, and the highest evaporation rate can reach 3.78kg·m ^-2 h ^-1 .

Technical solution: The present invention provides a preparation method for activating irradiation modified bentonite loaded nZVI with persulfate, comprising the following steps:

Step (1), adding sodium alginate to the aqueous solution to dissolve the sodium alginate aqueous solution, adding clay and carbon-based materials to the sodium alginate aqueous solution and mixing;

Wherein, the sodium alginate is added in an amount of 0.5% to 4wt% in the sodium alginate aqueous solution, and the clay is added in an amount of 0 to 15wt% in the sodium alginate aqueous solution;

Step (2), slowly add calcium salt to the mixed solution in step (1), and stir to obtain a mixed suspension;

Step (3), add gluconolactone to the mixed suspension in step (2), stir evenly, pour into the mold, and let the gel stand;

Step (4), after the obtained gel is aged, the clay-based composite hydrogel is obtained through several times of directional freezing and thawing.

Preferably, in step (1), the clay is one or a combination of two or more of nano-scale attapulgite, bentonite, kaolin, illite, diatomite or sepiolite.

Preferably, in step (1), the carbon-based material is added in an amount of 0.1 to 10 wt% in the sodium alginate aqueous solution.

Preferably, in step (1), the carbon-based material is one or a combination of two or more of graphite, graphene, carbon black, Mxene, fullerene, activated carbon, carbon nanotube or carbon fiber.

Preferably, in step (2), the calcium salt is added in an amount of 0.1 to 1 wt% in the mixed suspension;

And/or, the calcium salt is one or a combination of two or more of calcium carbonate, calcium sulfate, calcium sulfite, hydroxyapatite, and calcium phosphate.

Preferably, in step (3), the amount of gluconolactone added to the mixed suspension is 0.1-1 wt%.

Preferably, the mass ratio of the sodium alginate to the clay in the clay-based composite hydrogel is 1:1-1:4.

Preferably, the total solid content of the sodium alginate and the clay in the clay-based composite hydrogel is 4% to 8%.

Preferably, in step (4), the thickness of the clay-based composite hydrogel is 0.5-1.1 cm.

Preferably, in step (4), the number of times of directional freezing and thawing is 6 to 8 times;

And/or, the directional freezing temperature in the directional freezing and thawing is -20°C~-70°C.

Beneficial effects: the present invention constructs a superhydrophilic water transport channel based on the characteristics of the clay material itself, and uses directional freezing to adjust the pore size. The prepared clay-based composite hydrogel has good light absorption efficiency and water evaporation efficiency, and rich pore channels structure and good hydrophilicity, its specific beneficial effects are as follows:

1. The present invention utilizes the own characteristics of the clay material, which has good hydrophilicity and low thermal conductivity;

2. Use super-hydrophilic clay materials combined with sodium alginate to adjust the concentration ratio, and at the same time adjust the thickness of the hydrogel, and use directional freeze-thaw technology to expand the channels multiple times to construct vertical micron-scale macropores (pore size range 50~380μm), together with the mesoporous structure (2~45nm) built on the pore wall clay, it can effectively increase the flux of water vapor, and the evaporation rate can reach up to 3.78kg·m ^-2 h ^-1 ;

3. The preparation process of the present invention is simple, and the raw materials are green, pollution-free and cheap, which is beneficial to industrial production.

Description of drawings

Fig. 1 is the diatomite-based hydrogel appearance diagram that makes in embodiment 3;

Fig. 2 is the SEM picture of the attapulgite-based aerogel after the freeze-drying that Fig. 2 makes in embodiment 2;

Fig. 3 is the SEM picture of the bentonite-based airgel after freeze-drying obtained in Example 5;

Figure 4 is a mesoporous structure built from attapulgite;

Fig. 5 is the adsorption-desorption curve of the clay-based airgel after freeze-drying;

Figure 6 is the pore size distribution of the clay-based airgel after freeze-drying;

Figure 7 is a diagram of the water evaporation experiment device.

Detailed ways

In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, the following will be further described in conjunction with the accompanying drawings and specific examples. The examples here are only used to explain the present invention and are not intended to limit the present invention.

Example 1

Dissolve 0.5g of sodium alginate in 49.5ml of deionized water, add 0.5g of activated carbon powder and disperse at high speed for 30 minutes until the activated carbon is completely dispersed; take 0.1g of hydroxyapatite and add it slowly during the stirring process, continue stirring for 10 minutes, and then add 0.5 g of gluconolactone, stirred for 2 minutes, poured into a mold and let the gel stand; after the gel was aged overnight, it was subjected to directional freeze-thaw treatment 6 times to obtain a hydrogel. The directional freezing temperature is -20°C. Through measurement, the specific surface area of the hydrogel reaches 20.72m ² /g, the directional freezing pore size ranges from 320 to 360μm, and the gel thickness is 1cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under one solar light intensity is 2.53kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 87.3%.

Example 2

Dissolve 1g of sodium alginate in 39.48ml of deionized water, add 1g of carbon black powder and 9.52g of dispersed attapulgite slurry with a mass fraction of 10.5wt%, and stir for 30min until dispersed; take 0.15g of calcium carbonate during stirring Add slowly, continue to stir for 10 minutes, then add 1 g of gluconolactone, stir for 2 minutes, pour into the mold and let the gel stand; after aging the gel overnight, perform directional freeze-thaw treatment 6 times to obtain a clay-based composite hydrogel. Figure 2 is the SEM picture under this condition. The directional freezing temperature is -30°C. Through measurement, the specific surface area of the hydrogel reaches 35.14m ² /g, the directional freezing pore size ranges from 260 to 300μm, and the gel thickness is 0.8cm. After testing with the device shown in Figure 7, The water evaporation efficiency of the hydrogel under one sunlight intensity is 2.76kg.m ^-2 ·h ^-1 , and the light-to-heat conversion efficiency is 86.2%.

Example 3

Dissolve 0.75g of sodium alginate in 30.5ml of deionized water, add 2g of graphene and 18.75g of dispersed diatomite slurry with a mass fraction of 8wt%, and stir for 30min until dispersed; take 0.3g of calcium phosphate during stirring Slowly add, continue to stir for 10 minutes, then add 1.5g gluconolactone, stir for 2 minutes, pour into the mold and let the gel stand; after the gel is aged overnight, perform directional freeze-thaw treatment 8 times to obtain a clay-based composite hydrogel, as shown in Figure 1 shown. The directional freezing temperature is -40°C. Through measurement, the specific surface area of the hydrogel reaches 38.62m ² /g, the directional freezing pore size ranges from 210 to 250μm, and the gel thickness is 1.1cm. Tested by the device shown in Fig. 7, the water evaporation efficiency of the hydrogel under one sunlight intensity is 3.11kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 89.6%.

Example 4

Dissolve 1g of sodium alginate in 19.37ml of deionized water, add 3g of carbon black powder and 29.63g of dispersed kaolin slurry with a mass fraction of 13.5wt%, and stir for 30 minutes until dispersed; take 0.45g of hydroxyapatite during the stirring process Slowly add in the medium, continue to stir for 10 min, then add 2 g of gluconolactone, stir for 2 min, pour into the mold and let the gel stand; after aging the gel overnight, perform directional freeze-thaw treatment 7 times to obtain a clay-based composite hydrogel. The directional freezing temperature is -55°C. Through measurement, the specific surface area of the hydrogel reaches 50.54m ² /g, the directional freezing pore size ranges from 60 to 80μm, and the gel thickness is 0.9cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel is 3.66kg.m ^-2 ·h ^-1 under one sunlight intensity, and the photothermal conversion efficiency is 90.4%.

Example 5

Dissolve 1g of sodium alginate in 49ml of deionized water, add 3g of carbon nanotubes and 29.63g of dispersed bentonite slurry with a mass fraction of 13.5wt%, and stir for 30 minutes until dispersed; take 0.12g of hydroxyapatite during the stirring process Add slowly, continue to stir for 10 minutes, then add 1.6 g of gluconolactone, stir for 2 minutes, pour into the mold and let the gel stand; after aging the gel overnight, perform directional freeze-thaw treatment 7 times to obtain a clay-based composite hydrogel. Figure 3 is the SEM picture under this condition. The directional freezing temperature is -70°C. Through measurement, the specific surface area of the hydrogel reaches 52.28m ² /g, the directional freezing pore size ranges from 30 to 50 μm, and the gel thickness is 0.6cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under a sunlight intensity is 3.78 kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 92.7%.

Example 6

Dissolve 2g of sodium alginate in 34.67ml of deionized water, add 2.25g of carbon black powder and 13.33g of dispersed attapulgite slurry with a mass fraction of 7.5wt%, and stir for 30 minutes until dispersed; take 0.3g of hydroxyapatite in Add slowly during the stirring process, continue stirring for 10 minutes, then add 1.5 g of gluconolactone, stir for 2 minutes, pour into the mold and let the gel stand; after aging the gel overnight, perform directional freeze-thaw treatment 8 times to obtain a clay-based composite hydrogel. The directional freezing temperature is -70°C. Through measurement, the specific surface area of the hydrogel reaches 36.49m ² /g, the directional freezing pore size ranges from 50 to 80μm, and the gel thickness is 0.5cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under one solar light intensity is 3.06kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 89.1%.

Example 7

Dissolve 0.75g of sodium alginate in 49.25ml of deionized water, add 2.4g of graphite, and stir for 30 minutes to disperse; take 0.15g of calcium carbonate and add it slowly during stirring, continue stirring for 10 minutes, then add 1g of gluconolactone, and stir for 2 minutes Then pour it into a mold and let the gel stand; after aging the gel overnight, perform directional freeze-thaw treatment 8 times to obtain a hydrogel. The directional freezing temperature is -40°C. Through measurement, the specific surface area of the hydrogel reaches 21.56m ² /g, the directional freezing pore size ranges from 220 to 250μm, and the gel thickness is 1cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under one solar light intensity is 2.59kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 88.6%.

Example 8

Dissolve 2g of sodium alginate in 96.4ml of deionized water, add 1g of carbon black and 1.6g of attapulgite powder, and continue stirring for 30 minutes to disperse; take 0.3 g of hydroxyapatite and slowly add it during stirring, continue stirring for 10 minutes, and then add 1g of gluconolactone was stirred for 2 minutes and then poured into the mold to let the gel stand; after the gel was aged overnight, it was subjected to directional freeze-thaw treatment 6 times to obtain a clay-based composite hydrogel. Through measurement, when the ratio of clay to sodium alginate is 5:4, and the directional freezing temperature is -30°C, the specific surface area of the hydrogel reaches 29.37m ² /g, and the directional freezing pore size ranges from 240 to 280μm. The thickness of the gel was 1.5 cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under a sunlight intensity is 1.74 kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 83.2%.

Example 9

Dissolve 2g of sodium alginate in 88ml of deionized water, add 1g of carbon black and 10g of attapulgite powder, and continue stirring for 30 minutes until dispersed; slowly add 0.3 g of hydroxyapatite during stirring, continue stirring for 10 minutes, and then add 1g of glucose Acid lactone, stirred for 2 minutes, poured into the mold and let the gel stand; after the gel was aged overnight, it was subjected to directional freeze-thaw treatment 6 times to obtain a clay-based composite hydrogel. Through measurement, when the ratio of clay to sodium alginate is 5:1, and the directional freezing temperature is -30°C, the specific surface area of the hydrogel reaches 33.19m ² /g, and the directional freezing pore size ranges from 100 to 120μm. The thickness of the gel was 1.5 cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under a sunlight intensity is 1.86 kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 84.9%.

Example 10

Dissolve 2g of sodium alginate in 94ml of deionized water, add 1g of carbon black and 4g of attapulgite powder, and continue stirring for 30 minutes until dispersed; take 0.3 g of hydroxyapatite and slowly add it during stirring, continue stirring for 10 minutes, and then add 1g of glucose Acid lactone, stirred for 2 minutes, poured into the mold and let the gel stand; after the gel was aged overnight, it was subjected to directional freeze-thaw treatment 6 times to obtain a clay-based composite hydrogel. According to measurements, when the ratio of clay to sodium alginate is 2:1, and the directional freezing temperature is -30°C, the specific surface area of the hydrogel reaches 35.76m ² /g, and the directional freezing pore size ranges from 120 to 180μm. The gel thickness was 0.3 cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under a sunlight intensity is 1.51 kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 82.7%.

Example 11

Dissolve 2g of sodium alginate in 94ml of deionized water, add 1g of carbon black and 4g of attapulgite powder, and continue stirring for 30 minutes until dispersed; take 0.3 g of hydroxyapatite and slowly add it during stirring, continue stirring for 10 minutes, and then add 1g of glucose Acid lactone, stirred for 2 minutes, poured into the mold and let the gel stand; after the gel was aged overnight, it was subjected to directional freeze-thaw treatment 10 times to obtain a clay-based composite hydrogel. According to measurements, when the ratio of clay to sodium alginate is 2:1, and the directional freezing temperature is -30°C, the specific surface area of the hydrogel reaches 36.73m ² /g, and the directional freezing pore size ranges from 80 to 120μm. The gel thickness was 0.3 cm. Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under one sunlight intensity is 1.65kg.m ^-2 ·h ^-1 , and the light-to-heat conversion efficiency is 84.5%.

Example 12

Dissolve 2g of sodium alginate in 96.4ml of deionized water, add 1g of carbon black and 1.6g of attapulgite powder, and continue stirring for 30 minutes to disperse; take 0.3 g of hydroxyapatite and slowly add it during stirring, continue stirring for 10 minutes, and then add 1g of gluconolactone was stirred for 2 minutes and then poured into the mold to let the gel stand; after the gel was aged overnight, it was subjected to directional freeze-thaw treatment 6 times to obtain a clay-based composite hydrogel. By determination, in clay and sea

The ratio of sodium alginate is 1:1, and when the directional freezing temperature is -90°C, the specific surface area of the hydrogel reaches 29.73m ² /g, the directional freezing pore size ranges from 130 to 160μm, and the gel thickness is 1.5cm . Tested by the device shown in Figure 7, the water evaporation efficiency of the hydrogel under one solar light intensity is 1.44kg.m ^-2 ·h ^-1 , and the photothermal conversion efficiency is 83.8%.

The following compares Examples 8-12 to discuss the effects of freezing temperature, freeze-thaw times, and the ratio of clay to sodium alginate on the water evaporation efficiency of the clay-based composite hydrogel prepared by the present invention. The results are shown in Table 1:

Table 1

sample Lighting time/h Ratio of Attapulgite to Sodium Alginate Freezing temperature/℃ Freezing and thawing times Water evaporation rate/kg/(m²·h) Photothermal conversion efficiency/% Example 8 1 1:0.8 -30 6 1.74 83.2 Example 9 1 5:1 -30 6 1.86 84.9 Example 10 1 2:1 -30 6 1.51 82.7 Example 11 1 2:1 -30 10 1.65 84.5 Example 12 1 1:0.8 -90 6 1.44 83.8

Analysis of Examples 8-12 shows that the present invention can obtain a pore diameter in the range of 80 to 380 μm and a mesoporous structure formed by attapulgite on the pore wall by adjusting the directional freezing temperature, the number of freeze-thaw cycles, and the ratio of attapulgite to sodium alginate. Mainly distributed in 2~50nm. The attapulgite on the pore wall and the formed mesoporous structure can greatly improve the hydrophilicity of the hydrogel and achieve rapid water absorption, as shown in Figure 4. When the content of attapulgite is too high, the growth rate of ice crystals is hindered, the pore size gradually decreases, the structure becomes compact, and water vapor cannot pass smoothly in the steam channel of the directional freezing structure. When the attapulgite content is too low, the mesopore structure built by the attapulgite on the pore wall decreases, and the water absorption capacity decreases, thereby affecting the water evaporation rate; with the decrease of the directional freezing temperature, although the ice crystal growth rate is fast, the pore size range gradually decreases , but its overall water transfer effect is still not good, showing a low water evaporation rate. The increase in the number of freezing and thawing can construct a larger pore structure and enhance water transport, but due to capillary action, the water evaporation rate is still not high. Therefore, choosing the appropriate freezing temperature, freezing-thawing times, and the ratio of clay to sodium alginate is of great significance to the water evaporation efficiency.

The above is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All method or process steps may be combined in any way, except for mutually exclusive features and/or steps.

Claims (10)

1. A preparation method of clay-based composite hydrogel for solar seawater desalination is characterized by comprising the following steps:

step (1), adding sodium alginate into an aqueous solution to dissolve to obtain a sodium alginate aqueous solution, adding clay and a carbon-based material into the sodium alginate aqueous solution, and mixing;

wherein the addition amount of the sodium alginate in the sodium alginate aqueous solution is 0.5-4 wt%, and the addition amount of the clay in the sodium alginate aqueous solution is 0-15wt%;

step (2), slowly adding calcium salt into the mixed solution obtained in the step (1), and stirring to obtain a mixed suspension;

adding glucolactone into the mixed suspension obtained in the step (2), uniformly stirring, pouring into a mold, and standing for gelation;

and (4) aging the obtained gel, and performing multiple directional freeze thawing to obtain the clay-based composite hydrogel with the preset thickness.

2. The method for preparing a clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: in the step (1), the clay is one or a combination of more than two of nanoscale attapulgite, bentonite, kaolin, illite, diatomite or sepiolite.

3. The method for preparing a clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: in the step (1), the addition amount of the carbon-based material in the sodium alginate aqueous solution is 0.1-10wt%.

4. The method for preparing a clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: in the step (1), the carbon-based material is one or a combination of more than two of graphite, graphene, carbon black, mxene, fullerene, activated carbon, carbon nano-tubes or carbon fibers.

5. The method for preparing a clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: in the step (2), the addition amount of the calcium salt in the mixed suspension is 0.1 to 1wt%;

and/or the calcium salt is one or the combination of more than two of calcium carbonate, calcium sulfate, calcium sulfite, hydroxyapatite and calcium phosphate.

6. The method for preparing the clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: in the step (3), the addition amount of the gluconolactone in the mixed suspension is 0.1 to 1wt%.

7. The method for preparing a clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: the mass ratio of the sodium alginate to the clay in the clay-based composite hydrogel is 1 to 1.

8. The method for preparing a clay-based composite hydrogel according to claims 1 to 7, wherein: the total solid content of the sodium alginate and the clay in the clay-based composite hydrogel is 4-8%.

9. The method for preparing the clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: in the step (4), the preset thickness is 0.5 to 1.1cm.

10. The method for preparing a clay-based composite hydrogel according to claim 1, wherein the method comprises the following steps: in the step (4), the directional freezing and thawing times are 6 to 8;

and/or the directional freezing temperature in the directional freezing and thawing is-20 ℃ to-70 ℃.

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