PVA / PVP (Polyvinyl Acetate / Polyvinyl Pyrrolidone) hydrogel with two-stage pore structure as well as preparation method and application of PVA / PVP hydrogel

Abstract

The invention provides PVA / PVP hydrogel with a two-stage pore structure as well as a preparation method and application of the PVA / PVP hydrogel. The PVA / PVP hydrogel is of the two-stage pore structure; the average pore size of large pores in the two-stage pores is 45-72 microns, and the average pore size of small pores in the two-stage pores is 1-2 microns. According to the material, polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) are adopted as base materials, a photo-thermal material is added to form a composite precursor solution, the composite precursor solution and a glutaraldehyde cross-linking agent form a copolymer through a sol-gel method under the catalytic action of hydrochloric acid, and a two-stage pore structure with micron-grade (2 microns) and submicron-grade (72 microns) synergistic distribution is constructed through a freeze-drying process. And efficient water transportation and rapid evaporation are realized. The method is simple in operation process and low in cost, and compared with the prior art, the problem that a three-dimensional evaporator in the photo-thermal interface water evaporation field is insufficient in water transmission capacity is effectively solved through the two-stage hole structure, and efficient evaporation performance is achieved.

Description

Technical Field

[0001] This invention relates to the field of separation membrane preparation technology, and in particular to a PVA / PVP hydrogel with a bilevel pore structure, its preparation method and application. Background Technology

[0002] Water and energy are vital resources for human survival in the 21st century. Emerging solar-driven seawater desalination technology, due to its low cost and zero carbon emissions, is considered one of the most promising sustainable technologies for addressing the water crisis. Designing solar evaporators from a 2D to a 3D structure is considered a key strategy to break through the theoretical limits of solar-steam efficiency (Yang, B., Zhang, Z., Liu, P. et al. Flatband λ-Ti3O5 towards extraordinary solar steam generation. Nature 621, 96–102 (2023).). However, in actual seawater desalination processes, 3D solar evaporators generally face the problem of insufficient water transport capacity mismatched with their exposure height, severely limiting their evaporation rate and long-term stable operation performance.

[0003] To address these bottlenecks, researchers have gradually focused on optimizing and structurally controlling the evaporator substrate material. Traditional 3D photothermal materials (wood, paper-based, or sponge) have been initially applied due to their naturally porous structure, but they generally suffer from low mechanical strength, disordered pore size distribution, and low evaporation rate (<2.5 kg / m³). 2 h) and other limitations. In contrast, hydrogel materials, with their excellent hydrophilicity and tunable network structure, are considered ideal substrates for next-generation high-efficiency solar evaporators. In recent years, researchers have constructed hydrogel systems with certain structural orientations to enhance water supply and evaporation performance by introducing hydrophilic substances and using methods such as directional cryogenic casting. For example, researchers reduced the pore size of hydrogels by adjusting the polyvinyl alcohol / chitosan composition ratio, increasing the swelling rate to 1.5 g / min and the water evaporation rate to 3.6 kg / m³. 2 h (Zhou, X., Zhao, F., Guo, Y. et al. Architecting highly hydratable polymer networks totune the water state for solar water purification. Science Advances 5, eaaw5484 (2019).); Alternatively, N-isopropylacrylamide hydrogels with vertical channels can be prepared using directional self-assembly templates, significantly enhancing the swelling capacity to 4 g / min and achieving a water evaporation rate of 3.45 kg / m³.2 (Lei, C. et al. Biomimetically assembled sponge-like hydrogels for efficient solar waterpurification. Advanced Functional Materials 33, 2303883 (2023)). Therefore, existing technologies cannot simultaneously construct micron-submicron bipolar pores and their interconnected networks, making it difficult to synergistically improve water transport rates and evaporation efficiency.

[0004] Despite the progress made in controlling the pore size of hydrogels using the aforementioned methods, most hydrogels prepared to date still suffer from uneven pore size distribution, making it difficult to prepare hydrogels with excellent bipolar porous structures and water absorption properties. Furthermore, traditional freeze-drying methods suffer from inconsistent pore orientation and limited pore connectivity, resulting in limited photothermal evaporation capacity. Inspired by the rapid, long-distance water transport capabilities of vines, this invention provides a bipolar porous PVA / PVP hydrogel with efficient fluid transport and its preparation method. Using λ-Ti3O5 powder as a solar energy absorber, a bipolar channel structure combining micropores (2µm) and macropores (72µm) is constructed to achieve continuous and stable water supply. This results in a spectral absorption performance ≥98%, significantly improved swelling and water evaporation rates, and good adaptability and structural design flexibility, demonstrating broad application potential in high-performance solar evaporators. Summary of the Invention

[0005] Addressing the technical challenges of uneven pore distribution in existing hydrogel technologies, this invention provides a PVA / PVP hydrogel with a bilevel porous structure and its preparation method. PVA and PVP are used as hydrogel substrates, and a copolymer is formed with glutaraldehyde as a crosslinking agent via a sol-gel method under acid catalysis. The resulting PVA / PVP bilevel porous hydrogel is obtained through freeze-drying. The preparation process is simple, low-cost, and exhibits high light absorption and a high evaporation rate.

[0006] According to a first aspect of the present invention, the present invention provides a PVA / PVP hydrogel having a bipolar porous structure, wherein the PVA / PVP hydrogel has a bipolar porous structure; The bipolar porous structure is obtained by polymerizing polyvinyl alcohol and polyvinylpyrrolidone.

[0007] Furthermore, in the bi-level pore structure, the average pore diameter of the macropore is 45~72μm, and the average pore diameter of the micropore is 1~2μm.

[0008] Furthermore, in the bi-level pore structure, the average pore diameter of the large pore is 72 μm, and the average pore diameter of the small pore is 2 μm, that is, the average pore diameter is 2 μm / 72 μm; The hydrogel has a spectral absorbance of 95-99%.

[0009] According to a second aspect of the present invention, a method for preparing a PVA / PVP hydrogel with a bilevel porous structure is provided, the method comprising the following steps: Step 1: Dissolve polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution; Step 2: Dissolve and mix polyvinyl alcohol aqueous solution with polyvinylpyrrolidone to obtain hydrogel precursor solution; Step 3: Add photothermal material powder to deionized water and disperse it using ultrasound to obtain a dispersion; Step 4: Add the dispersion and crosslinking agent to the hydrogel precursor solution, stir, and pour into a cylindrical mold; Step 5: Add initiator to the mold, let stand to gel and form a gel product; Step 6: Freeze-dry the hydrogel material, and then fully swell it in deionized water to obtain a hydrogel material with a bipolar porous structure.

[0010] Furthermore, the temperature of the thermal dissolution in step 1 is 65~75℃, preferably 65℃; The mass concentration of the polyvinyl alcohol aqueous solution in step 1 is 5-10%, preferably 5%.

[0011] Furthermore, in step 2, the mass ratio of polyvinylpyrrolidone powder to polyvinyl alcohol powder is adjusted to 10-50%. Further, the photothermal material in step 3 is λ-Ti3O5, the concentration of the photothermal material in the dispersion is 320~400 mg / mL, preferably 320 mg / mL, and the ultrasonic dispersion time is 30~40 min; The photothermal material mentioned in step 3 also includes carbon nanotubes, Fe3O4, and Au nanoparticles.

[0012] Further, the crosslinking agent in step 4 is glutaraldehyde, preferably an aqueous solution of glutaraldehyde with a volume concentration of 50%; In step 4, the volume ratio of the hydrogel precursor liquid, dispersion liquid, and crosslinking agent is 20~21:0.5~1:0.25~0.3, the stirring time is 10~15 min, and the diameter of the cylindrical mold is 1.5 cm and the height is 4.0 cm.

[0013] Further, the initiator in step 5 is hydrochloric acid, preferably a hydrochloric acid solution with a molar concentration of 1.2 mol / L; The gel forming time in step 5 is 2~2.5h. Furthermore, the freeze-drying conditions described in step 6 are as follows: The vacuum degree of the freeze-drying is 2~4 Pa, preferably 2 Pa; The freeze-drying temperature is -70℃ to -60℃, preferably -60℃; The freeze-drying time is 20-24 hours, preferably 20 hours. According to a third aspect of the present invention, an application of a PVA / PVP hydrogel in water evaporation at a photothermal interface is provided.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The PVA / PVP hydrogel of the present invention has a dual-level porous interconnected structure and high porosity. While improving the water transport capacity, it can also improve the light absorption capacity.

[0015] (2) In the bi-porous PVA / PVP hydrogel of the present invention, the hydrogen bonds between water molecules can be weakened by the confined water in the pores, making the free water in the polymer network easier to be activated, which significantly improves the efficiency of water evaporation. Attached Figure Description

[0016] Figure 1 This is a schematic diagram illustrating the preparation process of the bilevel porous hydrogel described in Examples 1-3 of the present invention; Figure 2 This is a scanning electron microscope image of T-PVA / PVP5-h prepared in Example 5 of the present invention; Figure 3 The pore distribution curves are for the T-PVA-h prepared in Comparative Example 1 and the T-PVA / PVP5-h hydrogel prepared in Example 5 of this invention. Figure 4 The infrared spectra of T-PVA-h prepared in Comparative Example 1, T-PVA / PVP5-h prepared in Example 5, and PVA and PVP powders are shown. Figure 5 The diffuse reflectance spectra of T-PVA-h prepared in Comparative Example 1, T-PVA / PVP5-h hydrogel prepared in Example 5, and λ-Ti3O5 powder are shown in the figure. Figure 6 The swelling performance test results are for the T-PVA-h prepared in Comparative Example 1 and the T-PVA / PVP5-h prepared in Example 5 of this invention. Figure 7 The graph shows the water evaporation rate of the T-PVA-h prepared in Comparative Example 1 and the T-PVA / PVP5-h prepared in Example 5 of this invention. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0018] Example 1 This example provides a hydrogel, prepared by the following method: Step 1: Weigh 1g of PVA powder (polyvinyl alcohol) into a 50mL beaker, add 20mL of deionized water, heat to 65℃ and stir continuously for 30min to ensure that the PVA is completely dissolved, and obtain a PVA solution (mass concentration of 5%).

[0019] Step 2: Weigh 0.2g of PVP powder (polyvinylpyrrolidone) and pour it into the PVA solution obtained in Step 1. Stir in a magnetic stirrer for 20 minutes to obtain a PVA / PVP solution.

[0020] Step 3: Weigh 0.24g of λ-Ti3O5 powder and ultrasonically disperse it in 0.75ml of deionized water to achieve a concentration of 320mg / mL. -1 The ultrasonic dispersion time was 30 min, yielding 0.75 mL of λ-Ti3O5 solution.

[0021] Step 4: Thoroughly mix the PVA / PVP solution obtained in Step 2, the λ-Ti3O5 solution obtained in Step 3, and 0.28 mL of glutaraldehyde solution to obtain a PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution.

[0022] Step 5: Mix the PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution obtained in Step 4 with 1.5 mL of hydrochloric acid, place it in a cylindrical mold (diameter 1.5 cm, height 4.0 cm), and let it stand for 2 h to obtain the cross-linked hydrogel.

[0023] Step 6: The cross-linked hydrogel obtained in Step 5 is placed in a freeze dryer for freeze drying. The freeze drying vacuum degree is 2 Pa, the temperature is -60℃, and the drying time is 20 h. Then, it is placed in deionized water for full swelling to obtain a sponge-like hydrogel (T-PVA / PVP1-h). The preparation process of the hydrogel is as follows: Figure 1 As shown.

[0024] Example 2 This example provides a hydrogel, prepared by the following method: Step 1: Weigh 1g of PVA powder (polyvinyl alcohol) into a 50mL beaker, add 20mL of deionized water, heat to 65℃ and stir continuously for 30min to ensure that the PVA is completely dissolved, and obtain a PVA solution (mass concentration of 5%).

[0025] Step 2: Weigh 0.4g of PVP powder (polyvinylpyrrolidone) and pour it into the PVA solution obtained in Step 1. Stir in a magnetic stirrer for 20 minutes to obtain a PVA / PVP solution.

[0026] Step 3: Weigh 0.24 g of λ-Ti3O5 powder and ultrasonically disperse it in 0.75 ml of deionized water to obtain a concentration of 320 mg / mL. The ultrasonic dispersion time is 30 min, resulting in 0.75 mL of λ-Ti3O5 solution.

[0027] Step 4: Thoroughly mix the PVA / PVP solution obtained in Step 2, the λ-Ti3O5 solution obtained in Step 3, and 0.28 mL of glutaraldehyde solution to obtain a PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution.

[0028] Step 5: Mix the PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution obtained in Step 4 with 1.5 mL of hydrochloric acid, place it in a cylindrical mold (diameter 1.5 cm, height 4.0 cm), and let it stand for 2 h to obtain the cross-linked hydrogel.

[0029] Step 6: The cross-linked hydrogel obtained in Step 5 is placed in a freeze dryer for freeze drying at a vacuum degree of 2 Pa and a temperature of -60℃ for 20 hours. Then, it is placed in deionized water for complete swelling to obtain a sponge-like hydrogel (T-PVA / PVP2-h). The preparation process of the hydrogel is as follows: Figure 1 As shown.

[0030] Example 3 This example provides a hydrogel, prepared by the following method: Step 1: Weigh 1g of PVA powder (polyvinyl alcohol) into a 50mL beaker, add 20mL of deionized water, heat to 65℃ and stir continuously for 30min to ensure that the PVA is completely dissolved, and obtain a PVA solution (mass concentration of 5%).

[0031] Step 2: Weigh 0.6g of PVP powder (polyvinylpyrrolidone) and pour it into the PVA solution obtained in Step 1. Stir in a magnetic stirrer for 20 minutes to obtain a PVA / PVP solution.

[0032] Step 3: Weigh 0.24g of λ-Ti3O5 powder and ultrasonically disperse it in 0.75ml of deionized water. The concentration is 320mg / mL. The ultrasonic dispersion time is 30min, resulting in 0.75mL of λ-Ti3O5 solution.

[0033] Step 4: Thoroughly mix the PVA / PVP solution obtained in Step 2, the λ-Ti3O5 solution obtained in Step 3, and 0.28 mL of glutaraldehyde solution to obtain a PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution.

[0034] Step 5: Mix the PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution obtained in Step 4 with 1.5 mL of hydrochloric acid, place the mixture into a cylindrical mold (1.5 cm in diameter and 4.0 cm in height), and let it stand for 2 h to obtain the cross-linked hydrogel.

[0035] Step 6: The cross-linked hydrogel obtained in Step 5 is placed in a freeze dryer for freeze drying. The freeze drying vacuum degree is 2 Pa, the temperature is -60℃, and the drying time is 20 h. Then, it is placed in deionized water for full swelling to obtain a sponge-like hydrogel (T-PVA / PVP3-h). The preparation process of the hydrogel is as follows: Figure 1 As shown.

[0036] Example 4 This example provides a hydrogel, prepared by the following method: Step 1: Weigh 1g of PVA powder (polyvinyl alcohol) into a 50mL beaker, add 20mL of deionized water, heat to 65℃ and stir continuously for 30min to ensure that the PVA is completely dissolved, and obtain a PVA solution (mass concentration of 5%).

[0037] Step 2: Weigh 0.8g of PVP powder (polyvinylpyrrolidone) and pour it into the PVA solution obtained in Step 1. Stir in a magnetic stirrer for 20 minutes to obtain a PVA / PVP solution.

[0038] Step 3: Weigh 0.24 g of λ-Ti3O5 powder and ultrasonically disperse it in 0.75 ml of deionized water to obtain a concentration of 320 mg / mL. The ultrasonic dispersion time is 30 min, resulting in 0.75 mL of λ-Ti3O5 solution.

[0039] Step 4: Thoroughly mix the PVA / PVP solution obtained in Step 2, the λ-Ti3O5 solution obtained in Step 3, and 0.28 mL of glutaraldehyde solution to obtain a PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution.

[0040] Step 5: Mix the PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution obtained in Step 4 with 1.5 mL of hydrochloric acid, place it in a cylindrical mold (diameter 1.5 cm, height 4.0 cm), and let it stand for 2 h to obtain the cross-linked hydrogel.

[0041] Step 6: The cross-linked hydrogel obtained in Step 5 is placed in a freeze dryer for freeze drying. The freeze drying vacuum degree is 2 Pa, the temperature is -60℃, and the drying time is 20 h. Then, it is placed in deionized water for full swelling to obtain a sponge-like hydrogel (T-PVA / PVP4-h). The preparation process of the hydrogel is as follows: Figure 1 As shown.

[0042] Example 5 This example provides a hydrogel, prepared by the following method: Step 1: Weigh 1g of PVA powder (polyvinyl alcohol) into a 50mL beaker, add 20mL of deionized water, heat to 65℃ and stir continuously for 30min to ensure that the PVA is completely dissolved, and obtain a PVA solution (mass concentration of 5%).

[0043] Step 2: Weigh 1g of PVP powder (polyvinylpyrrolidone) and pour it into the PVA solution obtained in Step 1. Stir in a magnetic stirrer for 20 minutes to obtain a PVA / PVP solution.

[0044] Step 3: Weigh 0.24g of λ-Ti3O5 powder and ultrasonically disperse it in 0.75ml of deionized water. The concentration is 320mg / mL. The ultrasonic dispersion time is 30min, resulting in 0.75mL of λ-Ti3O5 solution.

[0045] Step 4: Thoroughly mix the PVA / PVP solution obtained in Step 2, the λ-Ti3O5 solution obtained in Step 3, and 0.28 mL of glutaraldehyde solution to obtain a PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution.

[0046] Step 5: Mix the PVA / PVP / λ-Ti3O5 / glutaraldehyde mixed solution obtained in Step 4 with 1.5 mL of hydrochloric acid, place it in a cylindrical mold (diameter 1.5 cm, height 4.0 cm), and let it stand for 2 h to obtain the cross-linked hydrogel.

[0047] Step 6: The cross-linked hydrogel obtained in Step 5 is placed in a freeze dryer for freeze drying. The freeze drying vacuum degree is 2 Pa, the temperature is -60℃, and the drying time is 20 h. Then, it is placed in deionized water for full swelling to obtain a sponge-like hydrogel (T-PVA / PVP5-h). The preparation process of the hydrogel is as follows: Figure 1 As shown; the scanning electron microscopy test results of the T-PVA / PVP5-h hydrogel are as follows. Figure 2 As shown, by Figure 2It can be seen that the hydrogel obtained in this embodiment forms a bilevel pore size distribution, with macropores having a diameter of approximately 72 μm and micropores having a diameter of approximately 2 μm, i.e., a bilevel hydrogel with an average pore size of 2 μm / 72 μm. The formation of the bilevel porous structure should be related to the compatibility of the PVA / PVP blend, which will change the local crosslinking density during the gelation process; the porosity distribution of the T-PVA / PVP5-h hydrogel is as follows. Figure 3 As shown; the infrared spectral test results of the PVA powder, PVP powder, and T-PVA / PVP5-h are shown in the figure. Figure 4 Infrared results showed that the T-PVA / PVP5-h sample should have been at 1652, 1695, and 1084 cm⁻¹. -1 Three characteristic peaks appeared, corresponding to the symmetric stretching vibrations of the C=O, free (non-interacting) C=O, and CN groups, respectively. Due to the hydrogen bonding between the C=O group of PVP and the -OH group of PVA, the peak position of the C=O stretching vibration increased from 1645 cm⁻¹. -1 Offset to 1652cm -1 1695cm -1 The intensity of free C=O stretching vibration at the point decreases, 3468cm -1 The hydroxyl peak shifted to lower wavenumbers, confirming the successful preparation of the T-PVA / PVP5-h hydrogel; the spectral absorption results of the T-PVA / PVP5-h hydrogel are shown below. Figure 5 The spectral absorbance was 98.5%, indicating that the synergistic effect of λ-Ti3O5 and PVA / PVP (T-PVA / PVP5-h) hydrogel led to an average light absorbance of >98%, achieving broad-spectrum solar energy capture in the range of 250 to 2500 nm.

[0048] Comparative Example 1 This comparative example provides a hydrogel, which is prepared by the following method: Step 1: Weigh 1g of PVA powder (polyvinyl alcohol) into a 50mL beaker, add 20mL of deionized water, heat to 65℃ and stir continuously for 30min to ensure that the PVA is completely dissolved, and obtain a PVA solution (mass concentration of 5%).

[0049] Step 2: Weigh 0.24g of λ-Ti3O5 powder and ultrasonically disperse it in 0.75ml of deionized water. The concentration is 320mg / mL. The ultrasonic dispersion time is 30min, resulting in 0.75mL of λ-Ti3O5 solution.

[0050] Step 3: Thoroughly mix the PVA solution obtained in Step 1, the λ-Ti3O5 solution obtained in Step 2, and 0.28 mL of glutaraldehyde solution to obtain a PVA / λ-Ti3O5 / glutaraldehyde mixed solution.

[0051] Step 4: Mix the PVA / λ-Ti3O5 / glutaraldehyde mixed solution obtained in Step 3 with 1.5 mL of hydrochloric acid, place it in a cylindrical mold (diameter 1.5 cm, height 4.0 cm), and let it stand for 2 h to obtain the cross-linked hydrogel.

[0052] Step 5: The cross-linked hydrogel obtained in Step 4 is placed in a freeze dryer for freezing. The freeze-drying vacuum degree is 2 Pa, the temperature is -60℃, and the drying time is 20 h. Then, it is placed in deionized water for full swelling to obtain hydrogel (T-PVA-h). The pore distribution of the T-PVA-h hydrogel is as follows: Figure 3 As shown, the porosity is 59%; the infrared spectral results of the T-PVA-h hydrogel are shown in [reference needed]. Figure 4 This indicates that T-PVA-h at 3470cm -1 and 1643cm -1 The two peaks at 1149 cm⁻¹ were designated as the -OH stretching vibration and the -OH bending vibration, respectively. -1 The peak is attributed to the COC stretching vibration, indicating that an acetalization reaction occurred between the hydroxyl group (-OH) of PVA and the aldehyde group (-CHO) of glutaraldehyde, thus confirming the successful preparation of T-PVA-h hydrogel; the absorption spectra of λ-Ti3O5 and T-PVA-h are as follows. Figure 5 As shown in the diffuse reflectance spectrum test results, the spectral absorption rate is 95%. The test results indicate that the high efficiency of full-spectrum light absorption of λ-Ti3O5 is mainly attributed to the internal flat band and Ti-Ti dimer structure. The bipolar pore structure on the surface of T-PVA / PVP5-h hydrogel effectively scatters and captures incident light, thereby extending the propagation path of light within the material. This allows light to be locally confined within the structure, enhancing light absorption. The synergistic effect of λ-Ti3O5 and PVA / PVP (T-PVA / PVP5-h) hydrogels resulted in an average light absorption rate (>98%), achieving broad-spectrum solar energy capture in the 250 to 2500 nm range. Furthermore, mercury porosimetry tests showed that the porosity of T-PVA / PVP5-h evaporators increased to 81% compared to the 59% porosity of pure PVA hydrogels. In addition, the T-PVA-h hydrogels prepared in this comparative example formed 10 μm pore sizes, while the T-PVA / PVP5-h hydrogels formed hierarchical pore distributions (2 μm / 72 μm) at the micron and submicron scales. The increased porosity and hierarchical pore structure improved the water storage, water extraction, and evaporation rates of the hydrogels.

[0053] Test Example 1 The swelling properties of the T-PVA / PVP5-h and T-PVA-h hydrogels prepared in Example 5 and Comparative Example 1 were tested by immersing completely dried T-PVA-h and T-PVA / PVP5-h samples (diameter 1.5 cm, height 4.0 cm) in deionized water at 25°C until swelling equilibrium was reached at time t.

[0054] Calculate the equilibrium swelling rate using the formula shown in Equation 1:

[0055] Formula 1; In Equation 1, mm d The change in mass before and after swelling is expressed in grams. t is the equilibrium swelling time, in minutes.

[0056] It can be seen that, under the same test conditions, the swelling rate of T-PVA-h with an average pore size of 10 μm is 6.2 g / min, while the swelling rate of the dual-stage structure (2 μm / 72 μm) T-PVA / PVP5-h with excellent water transport capacity is 7.7 g / min. Specific test results are as follows... Figure 6 As shown, the high water conveyance capacity of the T-PVA / PVP5-h prepared in Example 5 is confirmed.

[0057] Test Example 2 The evaporation performance of the T-PVA / PVP5-h and T-PVA-h hydrogels prepared in Example 5 and Comparative Example 1 was tested, using a xenon lamp to simulate sunlight with a light intensity of 1 kW·m. -2 .

[0058] The evaporation rate is calculated using the formula shown in Equation 2:

[0059] Formula 2; In Equation 2, Δm represents the mass change of the evaporation system, in kg; t is the evaporation time, in hours; S is the effective projected area of ​​the solar evaporator, in meters. 2 .

[0060] It can be seen that, under the same test conditions, the evaporation rate of the bilevel distributed hydrogel T-PVA / PVP5-h with high water transport capacity is 5.1 kg·m³. -2 ·h -1 The evaporation rate of T-PVA-h is only 4.2 kg·m³. -2 ·h -1 The specific test results are as follows: Figure 7 As shown, the high evaporation performance of the solar evaporator in Example 5 is demonstrated.

[0061] In summary, the present invention synthesizes a bipolar hydrogel by mixing polyvinyl alcohol and polyvinylpyrrolidone and chemically crosslinking them with glutaraldehyde, adding λ-Ti3O5 powder inside the gel, and then using a freeze-drying process. The bipolar porous structure and high porosity of the hydrogel facilitate more efficient water transport, and the three-dimensional porous structure of the hydrogel weakens the hydrogen bonds between water molecules, thereby improving the evaporation performance of the evaporator. This method solves the problem of insufficient water transport capacity commonly faced by existing PVA hydrogel evaporators and holds promise for further application in industrial production.

[0062] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A PVA / PVP hydrogel with a bilevel porous structure, characterized in that, The PVA / PVP hydrogel has a bilevel porous structure; The bipolar porous structure is obtained by polymerizing polyvinyl alcohol and polyvinylpyrrolidone.

2. The PVA / PVP hydrogel according to claim 1, characterized in that, The average pore diameter of the macropores in the bi-level pores is 45~72μm, and the average pore diameter of the micropores is 1~2μm; The hydrogel has a spectral absorbance of 95-99%.

3. The method for preparing the hydrogel according to any one of claims 1 and / or 2, characterized in that, The preparation method includes the following steps: Step 1: Dissolve polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution; Step 2: Dissolve and mix polyvinyl alcohol aqueous solution with polyvinylpyrrolidone to obtain hydrogel precursor solution; Step 3: Add photothermal material powder to deionized water and disperse it using ultrasound to obtain a dispersion; Step 4: Add the dispersion and crosslinking agent to the hydrogel precursor solution, stir, and pour into a cylindrical mold; Step 5: Add initiator to the mold, let stand to gel and form a gel product; Step 6: Freeze-dry the hydrogel material, and then fully swell it in deionized water to obtain a hydrogel material with a bipolar porous structure.

4. The method for preparing PVA / PVP hydrogel according to claim 3, characterized in that, The temperature for thermal dissolution in step 1 is 65~75℃; The mass concentration of the polyvinyl alcohol aqueous solution in step 1 is 5-10%.

5. The preparation method according to claim 3, characterized in that, In step 2, the mass ratio of polyvinylpyrrolidone powder to polyvinyl alcohol powder is adjusted to 10-50%.

6. The preparation method according to claim 3, wherein the photothermal material in step 3 is λ-Ti3O5, the concentration of the photothermal material in the dispersion is 320~400 mg / mL, and the ultrasonic dispersion time is 30~40 min; The photothermal material mentioned in step 3 also includes carbon nanotubes, Fe3O4, and Au nanoparticles.

7. The preparation method according to claim 3, characterized in that, The crosslinking agent mentioned in step 4 is glutaraldehyde, preferably an aqueous solution of glutaraldehyde with a volume concentration of 50%; In step 4, the volume ratio of the hydrogel precursor liquid, dispersion liquid, and crosslinking agent is 20~21:0.5~1:0.25~0.30, the stirring time is 10~15 min, and the diameter of the cylindrical mold is 1.5 cm and the height is 4.0 cm.

8. The method according to claim 3, characterized in that, In step 5, the initiator is hydrochloric acid, preferably a hydrochloric acid solution with a molar concentration of 1.2 mol / L; The gel forming time in step 5 is 2~2.5h.

9. The preparation method according to claim 3, characterized in that, The freeze-drying conditions described in step 6 are as follows: The vacuum degree of the freeze-drying process is 2~4 Pa; The freeze-drying temperature is -70~-60℃; The freeze-drying time is 20-24 hours.

10. The application of the PVA / PVP hydrogel according to any one of claims 1-2 and / or the PVA / PVP hydrogel prepared by any one of the preparation methods of claims 3-9 in the evaporation of water at the photothermal interface.

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