Preparation method of directional salt crystallization evaporator

Abstract

The invention discloses a preparation method of an evaporator with directional salt crystallization, which comprises the following steps: dissolving polyvinyl alcohol in water, heating and stirring to obtain a polyvinyl alcohol solution; the preparation method comprises the following steps: sequentially dropwise adding a sodium hydroxide solution, a calcium chloride solution and an anhydrous sodium dihydrogen phosphate solution into a mixed solution of oleic acid and absolute ethyl alcohol, stirring, carrying out hydrothermal reaction, and freeze-drying to obtain a hydroxyapatite nanowire; putting the hydroxyapatite nanowire into a polyvinyl alcohol solution, adding a solvent for dissolving, uniformly stirring, sequentially adding a cross-linking agent and cuttlefish meal, and freezing in a refrigerator; and unfreezing the frozen product, adding a layer of polyvinyl alcohol shell, and freezing and freeze-drying to obtain the evaporator with directional salt crystallization. The preparation method has the advantages of simple preparation process, low cost, large-scale application and the like; clean and green solar energy is utilized, efficient solar interface evaporation and salt collection performance is achieved, and seawater desalination, wastewater treatment and saline-alkali soil treatment are accelerated.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerogel preparation, and particularly relates to a preparation method with a directional salt crystallization evaporator. Background Art

[0002] Water is the most important natural resource on the earth and has a crucial impact on the survival, development of human beings and the social environment. Although about two-thirds of the total area of the earth is covered by water, seawater accounts for 97.5% of it, while fresh water resources only account for 2.5%. With the acceleration of the industrialization process and the rapid growth of the global population, the shortage and pollution problems of water resources are becoming increasingly serious. Especially in many regions, water quality deterioration and lack of fresh water resources have become one of the main challenges restricting the sustainable development of society. The sources of water pollution are diverse, including domestic sewage, industrial wastewater discharge, as well as excessive use of chemical fertilizers and pesticides in the agricultural production process, discharge of heavy metal wastewater, and pollution of toxic substances such as pharmaceutical wastewater. These pollutants not only threaten the ecological safety of water bodies, but also have a profound impact on human health and production and life.

[0003] Seawater desalination and sewage treatment are currently the best methods to solve the problems of insufficient water resources and poor water quality. However, the existing aerogel materials have many problems such as low light absorption, poor photothermal conversion ability, and the photothermal surface being covered by salt crystallization, resulting in inability to perform evaporation. Zhang et al. achieved high water evaporation rate and salt generation rate by constructing a surrounding and intertwined Janus structure with different wettabilities and introducing ribbons on a special surface to enhance salt crystallization (Advanced Functional Materials, 2024: 2408554). Li et al. developed a new type of mushroom-shaped cotton-based evaporator, which achieved efficient solar evaporation by depositing polyaniline (PANI) and carbon nanotubes (CNTs) on cotton cloth to form a hydrophobic photothermal layer, and promoted salt harvesting by using capillary force, cotton fiber water channels, and the gravity-assisted water delivery effect of the "mushroom cap" hypotenuse (Chemical Engineering Journal, 2024, 491: 151670). Dong et al. used chloroacetate fiber mat (CA) nanofibers as the substrate, coated a hydrophobic layer of polydimethylsiloxane (PDMS) / carbon nanotubes (CNTs) on the surface, carried out hydrophilic treatment by modifying with polyacrylonitrile (PAN) on the back, and designed it into a low-bending structure. By combining the hydrophilic channels of the Janus structure and the salt gradient effect, salt crystals were collected at the bend under the action of gravity (Small, 2022, 18(13): 2107156). The above methods for preparing aerogel materials have problems such as expensive materials and cumbersome preparation processes, which are not conducive to large-scale preparation. Summary of the Invention

[0004] The object of the present invention is to overcome the above-mentioned disadvantages of aerogels, and to provide a preparation method of a directional salt crystallization evaporator, so as to solve the problems that the materials used in existing gel materials are expensive and the preparation process is cumbersome.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method of a directional salt crystallization evaporator includes the following steps:

[0007] Step 1: Dissolve polyvinyl alcohol in water, and heat and stir to obtain a polyvinyl alcohol solution with a concentration of 3-5 wt%.

[0008] Step 2: Sequentially dropwise add sodium hydroxide solution, calcium chloride solution, and sodium dihydrogen phosphate anhydrous solution into the mixed solution of oleic acid and absolute ethanol and stir. By volume ratio, the sodium hydroxide solution: calcium chloride solution: sodium dihydrogen phosphate anhydrous solution: oleic acid: absolute ethanol = (9-11): (9-11): (9-11): (7-9): (9-11), perform a hydrothermal reaction for 12-24 h, and obtain hydroxyapatite nanowires after freeze-drying.

[0009] Step 3: Add the hydroxyapatite nanowires obtained in Step 2 into the polyvinyl alcohol solution obtained in Step 1. By volume-mass ratio, the polyvinyl alcohol solution: hydroxyapatite nanowires = (25-100) mL: 1 g. After adding a solvent to dissolve and stirring evenly, sequentially add a cross-linking agent and cuttlefish powder. The addition amount of the cross-linking agent to the volume of the polyvinyl alcohol solution = (1.2-1.4): 1, and the addition amount of the cuttlefish powder to the mass of the hydroxyapatite nanowires = 1: (1-2). Place it in the refrigerator and freeze for 6-12 h.

[0010] Step 4: After thawing the product obtained in Step 3, add a layer of polyvinyl alcohol shell, and obtain an evaporator with directional salt crystallization after freezing and freeze-drying.

[0011] Further, in Step 1, put the polyvinyl alcohol into a beaker, heat and stir, the temperature is 60-100 °C, and the stirring time is 2-10 h.

[0012] Further, in Step 2, the concentration of the sodium hydroxide solution is 0.05 g / mL, the concentration of the calcium chloride solution is 0.0176 g / mL, and the concentration of the sodium dihydrogen phosphate anhydrous is 0.023 g / mL.

[0013] Further, in Step 2, the reaction product obtained from the hydrothermal reaction is alternately washed with ethanol and water 2-3 times, centrifuged, and then freeze-dried for 24-48 h. The temperature of the vertical blast drying oven used for drying is 180 °C.

[0014] Further, in step 3, the solvent is dilute hydrochloric acid and / or dilute sulfuric acid, and the stirring time is 5 - 20 min.

[0015] Further, in step 3, the crosslinking agent is glutaraldehyde and / or epichlorohydrin. After adding the crosslinking agent for 1 min, cuttlefish powder is added.

[0016] Further, in step 4, after thawing the product obtained in step 3, place it in a silicone mold, pour a polyvinyl alcohol solution with a concentration of 3 - 5 wt% around the silicone mold, put it in the refrigerator and freeze for 12 h, and then freeze-dry for 24 - 48 h.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention constructs an evaporator with directional salt crystallization performance using polyvinyl alcohol as the matrix, and at the same time adds hydrophilic hydroxyapatite nanowires to provide a more convenient pathway for water transmission. Using cuttlefish powder as the photothermal material has good light absorption ability and photothermal conversion ability; the above materials all have relatively low costs, and the addition of cuttlefish powder enhances the light absorption ability and utilization rate, avoiding waste of energy. The preparation process of the present invention is simple and low-cost, can be applied on a large scale, and has the advantages of environmental friendliness and no secondary pollution.

[0019] Using the directional salt crystallization evaporator prepared by the present invention, through clean and green solar energy, efficient solar interfacial evaporation is realized, accelerating seawater desalination, wastewater treatment, organic dye solution treatment and directional salt accumulation performance; moreover, this evaporator has excellent salt collection ability, which can address the impact that saline-alkali land cannot grow crops. Description of the Drawings

[0020] Figure 1 is a schematic diagram of the surface temperature of the aerogel prepared by the present invention under 1 sun intensity.

[0021] Figure 2 is a mass loss diagram of the aerogel prepared by the present invention under 1 sun intensity.

[0022] Figure 3(a) is a diagram of the degradation process of methylene blue by the aerogel prepared by the present invention; Figure 3(b) is a diagram of the degradation process of methyl orange by the aerogel prepared by the present invention.

[0023] Figure 4 is a diagram of the self-desalination process of the aerogel prepared by the present invention.

[0024] Figure 5 is a schematic diagram of salt accumulation of the aerogel prepared by the present invention.

[0025] Figure 6(a) is the salt directional crystallization diagram of the evaporator prepared by the present invention in the soil, and Figure 6(b) is the comparison diagram of the treated soil with the normal soil and saline-alkali land planting experiments. Detailed implementation mode

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] The present invention discloses a preparation method of an evaporator with directional salt crystallization. The preparation method specifically includes the following steps:

[0028] Step 1, put polyvinyl alcohol into a beaker, heat and stir at a temperature of 60-100°C for 2-10 hours to obtain a polyvinyl alcohol solution with a concentration of 3-5 wt%. The polyvinyl alcohol is purchased from brands such as Aladdin, Damao, and Merck, but not limited to these brands;

[0029] Step 2, dropwise add sodium hydroxide solution, calcium chloride solution, and sodium dihydrogen phosphate anhydrous solution into the mixed solution of oleic acid and absolute ethanol in sequence and stir. By volume ratio, the sodium hydroxide solution: calcium chloride solution: sodium dihydrogen phosphate anhydrous solution: oleic acid: absolute ethanol = (9-11): (9-11): (9-11): (7-9): (9-11), carry out hydrothermal reaction for 12-24 hours, and obtain hydroxyapatite nanowires after freeze-drying; the concentration of the sodium hydroxide solution is 0.05 g / mL, the concentration of the calcium chloride solution is 0.0176 g / mL, and the concentration of the sodium dihydrogen phosphate anhydrous is 0.023 g / mL

[0030] Step 3, add the hydroxyapatite nanowires obtained in Step 2 into the polyvinyl alcohol solution obtained in Step 1. By volume-mass ratio, the polyvinyl alcohol solution: hydroxyapatite nanowires = (25-100): 1. After adding a solvent to dissolve and stirring evenly, add a cross-linking agent and cuttlefish powder in sequence. The addition amount of the cross-linking agent to the volume of the polyvinyl alcohol solution = (1.2-1.4): 1, and the addition amount of the cuttlefish powder to the mass of the hydroxyapatite nanowires = 1: (1-2). Place it in the refrigerator and freeze for 6-12 hours;

[0031] Step 4, after thawing the product obtained in Step 3, add a layer of polyvinyl alcohol shell, and obtain an evaporator with directional salt crystallization after freezing and freeze-drying.

[0032] Example 1

[0033]

[0034]

[0035] Weigh 3.5 g of polyvinyl alcohol and dissolve it in 96.5 g of deionized water. Keep the temperature at 80 °C in a heated oil bath magnetic stirrer and stir for 6 h to obtain the required polyvinyl alcohol solution.

[0036] 8 mL of oleic acid, 9 mL of absolute ethanol, the concentration of sodium hydroxide solution is 0.05 g / mL, the concentration of calcium chloride solution is 0.0176 g / mL, and the concentration of anhydrous sodium dihydrogen phosphate is 0.023 g / mL. Add 10 mL of each in sequence. The temperature of the vertical forced air drying oven is 180 °C, the reaction time is 24 h, and after freeze-drying for 48 h, the required hydroxyapatite nanowires are obtained. Take 10 mL of the polyvinyl alcohol solution and dissolve 0.2 g of hydroxyapatite nanowires in it. Add 375 μL of dilute hydrochloric acid and stir for 10 min, then add 125 μL of glutaraldehyde, stir for 1 min, then add 0.1 g of cuttlefish powder, pour it into a silica gel cylinder mold with a diameter of 2 cm, and freeze for 8 h. Thaw the above evaporator, place it in a silica gel cylinder mold with a diameter of 3 cm, pour in a 3.5 wt% polyvinyl alcohol solution as the shell, put it in the refrigerator and freeze for 12 h, and after freeze-drying for 48 h, an evaporator with directional salt crystallization is obtained. As Figure 1 shown, under 1 sun intensity, the surface temperature of the hydrogel rapidly rises to 30.3 °C, showing good photothermal conversion ability.

[0037] Example 2

[0038]

[0039]

[0040] Weigh 3.5 g of polyvinyl alcohol and dissolve it in 96.5 g of deionized water. Keep the temperature at 100 °C in a heated oil bath magnetic stirrer and stir for 4 h to obtain the required polyvinyl alcohol solution.

[0041] 8 mL of oleic acid, 9 mL of absolute ethanol, the concentration of sodium hydroxide solution is 0.05 g / mL, the concentration of calcium chloride solution is 0.0176 g / mL, and the concentration of anhydrous sodium dihydrogen phosphate is 0.023 g / mL. Add 10 mL of each in sequence. The temperature of the vertical forced air drying oven is 180 °C, the reaction time is 24 h, and after freeze-drying for 48 h, the required hydroxyapatite nanowires are obtained. Take 10 mL of the polyvinyl alcohol solution and dissolve 0.15 g of hydroxyapatite nanowires in it. Add 375 μL of dilute hydrochloric acid and stir for 10 min, then add 125 μL of glutaraldehyde, stir for 1 min, then add 0.2 g of cuttlefish powder, pour it into a silica gel cylinder mold with a diameter of 2 cm, and freeze for 8 h. Thaw the above evaporator, place it in a silica gel cylinder mold with a diameter of 3 cm, pour in a 3.5 wt% polyvinyl alcohol solution as the shell, put it in the refrigerator and freeze for 12 h, and after freeze-drying for 48 h, an evaporator with directional salt crystallization is obtained. As Figure 2As shown, at 1 sun intensity, the evaporation rate of the evaporator in pure water is 2.66 kg m -2 h -1 , with a good evaporation rate.

[0042] Example 3

[0043]

[0044]

[0045] Weigh 4 g of polyvinyl alcohol and dissolve it in 96 g of deionized water. Keep the temperature at 100 °C in a heated oil bath magnetic stirrer and stir for 6 h to obtain the required polyvinyl alcohol solution.

[0046] 8 mL of oleic acid, 9 mL of absolute ethanol, the concentration of sodium hydroxide solution is 0.05 g / mL, the concentration of calcium chloride solution is 0.0176 g / mL, and the concentration of anhydrous sodium dihydrogen phosphate is 0.023 g / mL. Add 10 mL in sequence. The temperature of the vertical blast drying oven is 180 °C, the reaction time is 24 h, and freeze-dry for 48 h to obtain the required hydroxyapatite nanowires. Take 10 mL of the polyvinyl alcohol solution and dissolve 0.1 g of hydroxyapatite nanowires in it. Add 375 μL of dilute hydrochloric acid and stir for 10 min, then add 125 μL of glutaraldehyde, stir for 1 min, add 0.05 g of cuttlefish powder, pour it into a silicone cylinder mold with a diameter of 2 cm, and freeze for 10 h. Thaw the above evaporator, place it in a silicone cylinder mold with a diameter of 3 cm, pour in a 4 wt% polyvinyl alcohol solution as the shell, put it in the refrigerator and freeze for 12 h, and then freeze-dry for 48 h to obtain an evaporator with directional salt crystallization. As shown in Figure 3, the treatment of water in organic dyes by the hydrogel proves that the hydrogel has excellent organic dye wastewater treatment function, and the absorption peaks of methylene blue and methyl orange disappear. Among them, (a) shows the light absorption before and after the evaporation of the methylene blue solution; (b) shows the light absorption before and after the evaporation of the methyl orange solution.

[0047] Example 4

[0048]

[0049]

[0050] Weigh 4 g of polyvinyl alcohol and dissolve it in 96 g of deionized water. Keep the temperature at 80 °C in a heated oil bath magnetic stirrer and stir for 10 h to obtain the required polyvinyl alcohol solution.

[0051] 8 mL of oleic acid, 9 mL of absolute ethanol, the concentration of sodium hydroxide solution is 0.05 g / mL, the concentration of calcium chloride solution is 0.0176 g / mL, the concentration of anhydrous sodium dihydrogen phosphate is 0.023 g / mL. 10 mL is added dropwise in sequence. The temperature of the vertical forced air drying oven is 180 °C, the reaction time is 24 h, and after freeze-drying for 48 h, the required hydroxyapatite nanowires are obtained. Take 10 mL of polyvinyl alcohol solution, dissolve 0.2 g of hydroxyapatite nanowires in it, add 375 μL of dilute hydrochloric acid and stir for 10 min, then add 125 μL of glutaraldehyde, stir for 1 min, add 0.1 g of cuttlefish powder, pour it into a silica gel cylinder mold with a diameter of 2 cm, and freeze for 8 h. Thaw the above evaporator, place it in a silica gel cylinder mold with a diameter of 3 cm, pour a 4 wt% polyvinyl alcohol solution as the shell, put it in the refrigerator and freeze for 12 h, and after freeze-drying for 24 h, an evaporator with directional salt crystallization is obtained. As Figure 4 shown, this aerogel has self-cleaning function. Place 2 g of NaCl solid on its surface, and it completely disappears within 140 minutes, indicating that it can achieve self-cleaning function when there is salt pollution on its surface.

[0052] Example 5

[0053]

[0054]

[0055] Weigh 5 g of polyvinyl alcohol and dissolve it in 95 g of deionized water. Keep the temperature at 100 °C in a heating oil bath magnetic stirrer, and stir and keep warm for 10 h to obtain the required polyvinyl alcohol solution.

[0056] 8 mL of oleic acid, 9 mL of absolute ethanol, the concentration of sodium hydroxide solution is 0.05 g / mL, the concentration of calcium chloride solution is 0.0176 g / mL, the concentration of anhydrous sodium dihydrogen phosphate is 0.023 g / mL. 10 mL is added dropwise in sequence. The temperature of the vertical forced air drying oven is 180 °C, the reaction time is 24 h, and after freeze-drying for 48 h, the required hydroxyapatite nanowires are obtained. Take 10 mL of polyvinyl alcohol solution, dissolve 0.15 g of hydroxyapatite nanowires in it, add 375 μL of dilute hydrochloric acid and stir for 10 min, then add 125 μL of glutaraldehyde, stir for 1 min, add 0.15 g of cuttlefish powder, pour it into a silica gel cylinder mold with a diameter of 2 cm, and freeze for 10 h. Thaw the above evaporator, place it in a silica gel cylinder mold with a diameter of 3 cm, pour a 5 wt% polyvinyl alcohol solution as the shell, put it in the refrigerator and freeze for 12 h, and after freeze-drying for 48 h, an evaporator with directional salt crystallization is obtained. As Figure 5 shown, this evaporator has excellent salt collection ability in salt water, and salt particles crystallize directionally on the polyvinyl alcohol shell.

[0057] Example 6

[0058]

[0059]

[0060] Weigh 5 g of polyvinyl alcohol and dissolve it in 95 g of deionized water. Keep the temperature at 100 °C in a heated oil bath magnetic stirrer and stir for 6 h to obtain the required polyvinyl alcohol solution.

[0061] 8 mL of oleic acid, 9 mL of absolute ethanol, the concentration of sodium hydroxide solution is 0.05 g / mL, the concentration of calcium chloride solution is 0.0176 g / mL, and the concentration of anhydrous sodium dihydrogen phosphate is 0.023 g / mL. Add 10 mL in sequence. The temperature of the vertical forced air drying oven is 180 °C, the reaction time is 24 h, and after freeze-drying for 48 h, the required hydroxyapatite nanowires are obtained. Take 10 mL of polyvinyl alcohol solution and dissolve 0.1 g of hydroxyapatite nanowires in it. Add 375 μL of dilute hydrochloric acid and stir for 10 min, then add 125 μL of glutaraldehyde, stir for 1 min, then add 0.1 g of cuttlefish powder, pour it into a silica gel cylinder mold with a diameter of 2 cm, and freeze for 12 h. Thaw the above evaporator, place it in a silica gel cylinder mold with a diameter of 3 cm, pour in a 5 wt% polyvinyl alcohol solution as the shell, put it in the refrigerator and freeze for 12 h, and after freeze-drying for 48 h, an evaporator with directional salt crystallization is obtained. As shown in Fig. 6(a), the evaporator shows excellent directional salt crystallization ability in the soil. The treated soil in Fig. 6(b) is compared with the normal soil and saline-alkali soil planting experiments. The wheat germination in the treated soil is basically the same as that in the normal soil.

[0062] Example 7

[0063] Step 1: Dissolve polyvinyl alcohol in water, heat and stir at a temperature of 60 °C for 2 h to obtain a 3 wt% polyvinyl alcohol solution.

[0064] Step 2: Add sodium hydroxide solution, calcium chloride solution and anhydrous sodium dihydrogen phosphate solution dropwise into the mixed solution of oleic acid and absolute ethanol in sequence and stir. By volume ratio, the sodium hydroxide solution: calcium chloride solution: anhydrous sodium dihydrogen phosphate solution: oleic acid: absolute ethanol = 9:9:9:7:9.5. Carry out hydrothermal reaction for 12 h. Wash the reaction product obtained from the hydrothermal reaction with ethanol and water alternately twice, centrifuge and then freeze-dry for 24 h. The temperature of the vertical forced air drying oven used for drying is 180 °C. After freeze-drying, hydroxyapatite nanowires are obtained. The concentration of the sodium hydroxide solution is 0.05 g / mL, the concentration of the calcium chloride solution is 0.0176 g / mL, and the concentration of the anhydrous sodium dihydrogen phosphate is 0.023 g / mL.

[0065] Step 3: Add the hydroxyapatite nanowires obtained in Step 2 into the polyvinyl alcohol solution obtained in Step 1. By volume-mass ratio, polyvinyl alcohol solution:hydroxyapatite nanowires = 25:1. After adding dilute sulfuric acid to dissolve and stirring for 5 min until evenly mixed, add epichlorohydrin. Add cuttlefish powder 1 min after adding epichlorohydrin. The addition amount of epichlorohydrin to the volume of the polyvinyl alcohol solution = 1.2:1. The addition amount of cuttlefish powder to the mass of the hydroxyapatite nanowires = 1:1.6. Place it in the refrigerator and freeze for 6 h.

[0066] Step 4: After thawing the product obtained in Step 3, place it in a silicone mold. Pour the polyvinyl alcohol solution with a concentration of 3 wt% around the silicone mold. Place it in the refrigerator and freeze for 12 h, and then freeze-dry for 30 h to obtain an evaporator with directional salt crystallization.

[0067] Example 8

[0068] Step 1: Dissolve polyvinyl alcohol in water, heat and stir at a temperature of 70 °C for 8 h to obtain a polyvinyl alcohol solution with a concentration of 4.5 wt%.

[0069] Step 2: Dropwise add sodium hydroxide solution, calcium chloride solution and sodium dihydrogen phosphate anhydrous solution into the mixed solution of oleic acid and absolute ethanol and stir. By volume ratio, the sodium hydroxide solution:calcium chloride solution:sodium dihydrogen phosphate anhydrous solution:oleic acid:absolute ethanol = 9.5:9.5:9.5:7.5:10. Carry out hydrothermal reaction for 15 h. Wash the reaction product obtained from the hydrothermal reaction alternately with ethanol and water 3 times, centrifuge and then freeze-dry for 30 h. The temperature of the vertical blast drying oven used for drying is 180 °C. After freeze-drying, hydroxyapatite nanowires are obtained. The concentration of the sodium hydroxide solution is 0.05 g / mL, the concentration of the calcium chloride solution is 0.0176 g / mL, and the concentration of the sodium dihydrogen phosphate anhydrous is 0.023 g / mL.

[0070] Step 3: Add the hydroxyapatite nanowires obtained in Step 2 into the polyvinyl alcohol solution obtained in Step 1. By volume-mass ratio, polyvinyl alcohol solution:hydroxyapatite nanowires = 90:1. After adding dilute sulfuric acid to dissolve and stirring for 13 min until evenly mixed, add epichlorohydrin. Add cuttlefish powder 1 min after adding epichlorohydrin. The addition amount of epichlorohydrin to the volume of the polyvinyl alcohol solution = 1.3:1. The addition amount of cuttlefish powder to the mass of the hydroxyapatite nanowires = 1:1.8. Place it in the refrigerator and freeze for 11 h.

[0071] Step 4: After thawing the product obtained in Step 3, place it in a silicone mold. Pour the polyvinyl alcohol solution with a concentration of 4.5 wt% around the silicone mold. Place it in the refrigerator and freeze for 12 h, and then freeze-dry for 36 h to obtain an evaporator with directional salt crystallization.

[0072] Example 9

[0073] Step 1: Dissolve polyvinyl alcohol in water, heat and stir at a temperature of 90 °C for 2 h to obtain a polyvinyl alcohol solution with a concentration of 3 wt%.

[0074] Step 2: Sequentially and dropwise add sodium hydroxide solution, calcium chloride solution, and sodium dihydrogen phosphate anhydrous solution into the mixed solution of oleic acid and absolute ethanol and stir. By volume ratio, the sodium hydroxide solution: calcium chloride solution: sodium dihydrogen phosphate anhydrous solution: oleic acid: absolute ethanol = 10.5:10.5:10.5:8.5:10.5. Carry out a hydrothermal reaction for 21 h. Wash the reaction product obtained from the hydrothermal reaction alternately with ethanol and water 4 times, centrifuge, and then freeze-dry for 36 h. The temperature of the vertical blast drying oven used for drying is 180 °C. Hydroxyapatite nanowires are obtained after freeze-drying; the concentration of the sodium hydroxide solution is 0.05 g / mL, the concentration of the calcium chloride solution is 0.0176 g / mL, and the concentration of the sodium dihydrogen phosphate anhydrous is 0.023 g / mL;

[0075] Step 3: Add the hydroxyapatite nanowires obtained in Step 2 into the polyvinyl alcohol solution obtained in Step 1. By volume-mass ratio, the polyvinyl alcohol solution: hydroxyapatite nanowires = 25:1. After adding and dissolving with dilute sulfuric acid and stirring evenly for 17 min, add epichlorohydrin. Add cuttlefish powder 1 min after adding epichlorohydrin. The addition amount of epichlorohydrin is in a volume ratio to the polyvinyl alcohol solution = 1.35:1, and the addition amount of cuttlefish powder is in a mass ratio to the hydroxyapatite nanowires = 1:1.6. Place it in the refrigerator and freeze for 6 h;

[0076] Step 4: After thawing the product obtained in Step 3, place it in a silicone mold, pour the polyvinyl alcohol solution with a concentration of 3 wt% around the silicone mold, place it in the refrigerator and freeze for 12 h, and obtain an evaporator with directional salt crystallization after freeze-drying for 42 h.

[0077] Example 10

[0078] Step 1: Dissolve polyvinyl alcohol in water, heat and stir at a temperature of 70 °C for 8 h to obtain a polyvinyl alcohol solution with a concentration of 4.5 wt%.

[0079] Step 2: Sodium hydroxide solution, calcium chloride solution, and anhydrous sodium dihydrogen phosphate solution were successively added dropwise to the mixed solution of oleic acid and anhydrous ethanol with stirring. By volume ratio, the sodium hydroxide solution: calcium chloride solution: anhydrous sodium dihydrogen phosphate solution: oleic acid: anhydrous ethanol = 11:11:11:9:11. Hydrothermal reaction was carried out for 12 h. The reaction product obtained from the hydrothermal reaction was washed alternately with ethanol and water twice, centrifuged, and then freeze-dried for 42 h. The temperature of the vertical blast drying oven used for drying was 180 °C. Hydroxyapatite nanowires were obtained after freeze-drying. The concentration of the sodium hydroxide solution was 0.05 g / mL, the concentration of the calcium chloride solution was 0.0176 g / mL, and the concentration of the anhydrous sodium dihydrogen phosphate was 0.023 g / mL.

[0080] Step 3: The hydroxyapatite nanowires obtained in Step 2 were added to the polyvinyl alcohol solution obtained in Step 1. By volume-mass ratio, the polyvinyl alcohol solution: hydroxyapatite nanowires = 90:1. After adding dilute hydrochloric acid and dilute sulfuric acid to dissolve and stirring for 20 min until evenly mixed, glutaraldehyde and epichlorohydrin were added. One minute after the addition of glutaraldehyde and epichlorohydrin, cuttlefish powder was added. The addition amount of glutaraldehyde and epichlorohydrin was in a volume ratio to the polyvinyl alcohol solution of 1.4:1. The addition amount of cuttlefish powder was in a mass ratio to the hydroxyapatite nanowires of 1:1.8. It was placed in the refrigerator and frozen for 11 h.

[0081] Step 4: After thawing the product obtained in Step 3, it was placed in a silicone mold, and polyvinyl alcohol solution with a concentration of 4.5 wt% was poured around the silicone mold. It was placed in the refrigerator and frozen for 12 h. After freeze-drying for 30 h, an evaporator with directional salt crystallization was obtained.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method having a directional salt crystallization evaporator, characterized in that: The following steps are involved: Step 1, dissolving polyvinyl alcohol in water, heating and stirring to obtain a polyvinyl alcohol solution with a concentration of 3-5wt%; Step 2, adding sodium hydroxide solution, calcium chloride solution and anhydrous sodium dihydrogen phosphate solution dropwise to a mixed solution of oleic acid and anhydrous ethanol and stirring, according to the volume ratio of sodium hydroxide solution: calcium chloride solution: anhydrous sodium dihydrogen phosphate solution: oleic acid: anhydrous ethanol = (9-11): (9-11): (9-11): (7-9): (9-11), hydrothermally reacting for 12-24 hours, and freeze-drying to obtain hydroxyapatite nanowires; Step 3, adding the hydroxyapatite nanowires obtained in step 2 to the polyvinyl alcohol solution obtained in step 1, in a volume-to-mass ratio of polyvinyl alcohol solution: hydroxyapatite nanowires = (25-100) mL: 1 g, adding a solvent to dissolve, stirring evenly, adding a crosslinking agent and cuttlefish powder in sequence, the ratio of the amount of the crosslinking agent added to the volume of the polyvinyl alcohol solution = (1.2-1.4): 1, the ratio of the amount of the cuttlefish powder added to the mass of the hydroxyapatite nanowires = 1: (1-2), and freezing in a refrigerator for 6-12 hours; Step 4, after thawing the product obtained in step 3, a layer of polyvinyl alcohol shell is added, and after freezing and freeze drying, an evaporator with oriented salt crystals is obtained.

2. The preparation method of a directional salt crystallization evaporator according to claim 1, characterized in that: In the step 1, polyvinyl alcohol is placed in a beaker and heated and stirred at a temperature of 60-100° C. for 2-10 hours.

3. The preparation method of a directional salt crystallization evaporator according to claim 1, characterized in that: In step 2, the concentration of the sodium hydroxide solution is 0.05 g / mL, the concentration of the calcium chloride solution is 0.0176 g / mL, and the concentration of anhydrous sodium dihydrogen phosphate is 0.023 g / mL.

4. The preparation method with a directional salt crystallization evaporator according to claim 1, characterized in that: The reaction product obtained by the hydrothermal reaction in step 2 is washed alternately with ethanol and water for 2-3 times, centrifuged and freeze-dried for 24-48 hours, and the temperature of the vertical forced air drying oven used for drying is 180°C.

5. The preparation method with a directional salt crystallization evaporator according to claim 1, characterized in that: In step 3, the solvent is dilute hydrochloric acid and / or dilute sulfuric acid, and the stirring time is 5-20 min.

6. The preparation method with a directional salt crystallization evaporator according to claim 1, characterized in that: In step 3, the cross-linking agent is glutaraldehyde and / or epichlorohydrin, and cuttlefish powder is added 1 minute after the cross-linking agent is added.

7. The preparation method with a directional salt crystallization evaporator according to claim 1, characterized in that: In the step 4, after the product obtained in step 3 is thawed, it is placed in a silica gel mold, polyvinyl alcohol solution with a concentration of 3-5wt% is poured around the silica gel mold, and the solution is placed in a refrigerator for 12 hours and freeze-dried for 24-48 hours.

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