A humidity fluctuation resistant nanofiber moisture absorption hydrogel, a preparation method and application thereof

Abstract

This invention provides a humidity-fluctuation-resistant nanofiber hygroscopic hydrogel, its preparation method, and its applications. Through electrospinning and sequential ion exchange strategies, a nanofiber hygroscopic hydrogel with a hierarchical three-dimensional nanofiber network structure is prepared using sodium alginate nanofiber membranes. A dual spatial constraint mechanism is constructed, consisting of gel swelling confinement within the fibers and capillary channel confinement between fibers. This hydrogel maintains high moisture absorption capacity, fast adsorption / desorption kinetics, and good structural stability over a wide humidity range, especially in high-humidity environments and under humidity fluctuation conditions. It exhibits significant humidity fluctuation resistance and is suitable for efficient atmospheric water collection in all weather conditions and multiple climate zones. This invention fills the application gap of existing adsorption-based atmospheric water collection technologies in dynamic humidity environments and provides a material basis for the stable operation of adsorbents in practical environments, demonstrating significant application value.

Description

Technical Field

[0001] This invention belongs to the technical field of hydrogel preparation, specifically relating to a nanofiber hygroscopic hydrogel resistant to humidity fluctuations, its preparation method, and its application. Background Technology

[0002] Global freshwater scarcity is a primary challenge to sustainable development in contemporary society. Atmospheric water harvesting (AWH) is a technology that directly extracts moisture from the air, mainly divided into three categories: mist collection, condensation harvesting, and adsorption harvesting. It can provide sustainable water sources in arid or water-scarce regions. Among them, adsorption-based atmospheric water harvesting technology has attracted much attention due to its strong environmental adaptability and holds promise for actively addressing the freshwater shortage crisis. In this technology, hygroscopic salt composite materials, with their excellent hygroscopic properties, have become the core functional material.

[0003] Current research on hygroscopic salt composite materials in atmospheric water collection mainly focuses on low-humidity adsorption capacity, mechanical property enhancement, and photothermal desorption performance. Most of these materials utilize synthetic polymers or other natural polysaccharides as substrates, with structural designs primarily based on bulk hydrogels or single-fiber networks. Studies have found that traditional bulk hydrogels struggle to reach adsorption equilibrium quickly under fluctuating humidity conditions, resulting in a decrease in hygroscopic capacity. Furthermore, salt migration is more likely to occur in high-humidity and fluctuating humidity environments, leading to rapid deterioration of hygroscopic performance, difficulty in maintaining stable operation, and poor cyclic stability.

[0004] Because the design and performance evaluation of existing atmospheric water collection materials are mainly based on low-humidity static conditions (such as arid environments with relative humidity of 20%, 30%, and 60%), their adsorption kinetics, desorption efficiency, and structural stability are often optimized under these specific low-humidity conditions. However, in actual outdoor environments, air humidity is not constant and often fluctuates significantly or even drastically. For example, in arid regions, relative humidity may suddenly rise to over 90% due to factors such as rainfall, nighttime cooling, and morning dew. Under such high-humidity or drastically fluctuating humidity conditions, existing materials face severe challenges such as the inherent contradiction between high salt load and salt leakage, the difficulty in balancing high moisture absorption capacity and rapid adsorption-desorption, and limited cycle life.

[0005] Therefore, how to ensure the synergistic improvement of high moisture absorption capacity, rapid adsorption and desorption, leakage resistance and long-term cycle stability of materials under conditions of drastic humidity fluctuations (especially high humidity conditions) remains a problem that urgently needs to be solved in the field of adsorption atmospheric water collection technology, but has not yet been fully studied. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the primary objective of this invention is to provide a method for preparing a nanofiber hygroscopic hydrogel resistant to humidity fluctuations.

[0007] The second objective of this invention is to provide a nanofiber hygroscopic hydrogel that is resistant to humidity fluctuations.

[0008] The third objective of this invention is to provide applications of the above-mentioned moisture-absorbing hydrogel with resistance to humidity fluctuations in atmospheric water collection, industrial and building dehumidification, moisture protection of electronic devices, and food and pharmaceutical storage and transportation.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention claims protection for a method for preparing a moisture-absorbing hydrogel resistant to humidity fluctuations using nanofibers, the method comprising the following steps: (1) Mix sodium alginate solution, polymer spinning aid solution, surfactant and organic solvent to obtain electrospinning precursor solution; (2) Electrospinning was performed using the obtained electrospinning precursor solution to obtain sodium alginate nanofiber membranes. (3) The obtained sodium alginate nanofiber membrane was immersed in calcium chloride solution to obtain calcium alginate nanofiber hydrogel membrane; (4) The calcium alginate nanofiber hydrogel membrane was immersed in a lithium salt solution to prepare a nanofiber hygroscopic hydrogel. The sodium alginate solution has a mass fraction of 3%-4%; The receiver roller rotates at a speed of 150-1200 rpm during electrospinning. The relative saturation concentration of the lithium salt solution is 10%-35%.

[0010] This invention is the first to apply sodium alginate nanofiber membrane materials to atmospheric water collection using a sequential ion exchange strategy. A dual constraint mechanism of gel swelling and capillary confinement was constructed. Through a simple, mild, and scalable preparation method, a nanofiber hygroscopic hydrogel was prepared that achieves synergistic enhancements in high moisture absorption capacity, rapid kinetics, and leak resistance under conditions of drastic humidity fluctuations (especially high humidity). This nanofiber hygroscopic hydrogel exhibits excellent resistance to humidity fluctuations under various humidity conditions. For example, it maintains extremely low salt leakage after continuous exposure for over 160 hours in a 90% RH environment. After 50 cycles at constant humidity levels, or 20 cycles in a dynamically fluctuating environment with relative humidity ranging from 30% to 60% to 90%, its moisture absorption performance did not significantly decrease, demonstrating good cyclic stability and salt leakage resistance.

[0011] The inventors discovered that by using a sodium alginate solution of a specific concentration, a three-dimensional nanofiber network with uniform diameter, regular morphology, and good spatial interconnectivity can be constructed. This nanofiber network possesses a hierarchical structure and a dual spatial constraint mechanism, achieving precise cross-linking of the polymer network and efficient loading of hygroscopic salts at the nanofiber scale. It can significantly suppress salt solution leakage under high humidity conditions while maintaining high salt loading and high hygroscopic capacity. Simultaneously, controlling the receiver roller speed of the electrospinning process within a specific range helps maintain the pore structure of the fiber network within a suitable structural window, thus matching it with the subsequent gel swelling capacity and salt loading, better balancing the requirements of high humidity liquid retention and rapid mass transfer. Using a lithium salt solution of a specific relative saturation concentration is beneficial for improving the matching degree between salt loading, gel swelling, and pore structure, resulting in a nanofiber hydrogel that retains more effective adsorption sites and has a more stable structure. Under the combined conditions described above, the nanofiber hydrogel prepared by this invention can overcome the inherent contradiction between high salt load and salt leakage under high humidity conditions, improve the material's moisture absorption stability and salt leakage resistance under humidity fluctuation conditions, and achieve a significant improvement in humidity fluctuation resistance.

[0012] Preferably, the mass ratio of sodium alginate to polymeric spinning aid is 8-10:1. More preferably, the mass ratio of sodium alginate to polymeric spinning aid is 9:1.

[0013] Preferably, the mass ratio of the sodium alginate solution to the surfactant is 180-1800:1. More preferably, the mass ratio of the sodium alginate solution to the surfactant is 600-1200:1. Most preferably, the mass ratio of the sodium alginate solution to the surfactant is 900:1.

[0014] Preferably, the receiver roller speed in step (2) is 600-1000 rpm. More preferably, the receiver roller speed in step (2) is 780-1000 rpm. Most preferably, the receiver roller speed in step (2) is 800 rpm. Under these preferred electrospinning parameters, the pore structure of the fiber network in the nanofiber hygroscopic hydrogel has a suitable structural window, which is better matched with the swelling capacity and salt loading of the gel after subsequent crosslinking, so as to better balance high humidity retention and rapid mass transfer.

[0015] Preferably, the electrospinning parameters in step (2) further include: spinning voltage 15-30 kV and receiving distance 10-25 cm. More preferably, the electrospinning parameters in step (2) further include: spinning voltage 20 kV and receiving distance 20 cm.

[0016] Preferably, the mass fraction of sodium alginate in step (1) is 3.5%-4%. Most preferably, the mass fraction of sodium alginate in step (1) is 4%. At this preferred concentration, a three-dimensional nanofiber network with uniform diameter, regular morphology, and good spatial interconnectivity can be obtained.

[0017] More preferably, the relative saturation concentration of the lithium salt solution is 20%-30%. Most preferably, the relative saturation concentration of the lithium salt solution is 25%. At this preferred mass fraction, the matching relationship between salt loading, gel swelling, and pore structure is better, which is beneficial to the structural stability of the nanofiber hydrogel and the maintenance of effective adsorption sites.

[0018] Specifically, the relative saturation concentration is the volume percentage of the saturated aqueous solution of lithium salt after dilution with water, relative to the total volume of the diluted solution.

[0019] Specifically, the lithium salt solution is prepared by diluting it with deionized water at a volume ratio using a saturated aqueous solution of the lithium salt as the mother liquor at 25°C.

[0020] Preferably, the polymeric spinning aid in step (1) is selected from at least one of polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone. Most preferably, the polymeric spinning aid is polyethylene oxide.

[0021] Preferably, the surfactant in step (1) is selected from at least one of Triton, sodium dodecyl sulfate, and poloxamer. Most preferably, the surfactant is Triton.

[0022] Preferably, the organic solvent in step (1) is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and ethanol. Most preferably, the organic solvent is dimethyl sulfoxide.

[0023] Preferably, the immersion time in the calcium chloride solution in step (3) is 25-180 seconds. More preferably, the immersion time in the calcium chloride solution in step (3) is 25-120 seconds. Most preferably, the immersion time in the calcium chloride solution in step (3) is 30 seconds. Under these preferred conditions, the cross-linked calcium alginate nanofiber hydrogel membrane has a suitable reversible swelling space inside the fiber, and its gel network has the strongest buffering capacity against the volume expansion of deliquescent liquid, effectively avoiding the structural tightening caused by over-cross-linking, and the resulting slowdown in the adsorption equilibrium rate of the composite material, increased salt leakage under high humidity conditions, and decreased long-term cycling stability.

[0024] Preferably, the mass fraction of the calcium chloride solution in step (3) is 1%-3%. Most preferably, the mass fraction of the calcium chloride solution in step (3) is 2%.

[0025] Preferably, the lithium salt is selected from at least one of lithium chloride and lithium bromide. More preferably, the lithium salt is selected from lithium chloride. Lithium chloride has higher solubility and a lower deliquescence point, resulting in better moisture absorption performance. In this invention, immersing the calcium alginate nanofiber hydrogel membrane in a lithium chloride solution of a specific concentration can significantly improve the moisture absorption efficiency and humidity fluctuation resistance of the prepared lithium chloride-calcium alginate nanofiber hydrogel composite material.

[0026] Preferably, the calcium alginate nanofiber hydrogel membrane is immersed in the lithium salt solution for 12-72 hours. More preferably, the calcium alginate nanofiber hydrogel membrane is immersed in the lithium salt solution for 12-36 hours. Most preferably, the calcium alginate nanofiber hydrogel membrane is immersed in the lithium salt solution for 24 hours. At this preferred time, the calcium alginate nanofiber hydrogel membrane retains continuous open interconnected channels after short-term cross-linking, so that the gel swelling domains within the fibers and the capillary channels between the fibers together form a dual spatial constraint on the deliquescent liquid, ultimately yielding a lithium chloride-calcium alginate nanofiber hydrogel composite material with a hierarchical nanofiber network structure.

[0027] This invention also applies for protection of a nanofiber hygroscopic hydrogel resistant to humidity fluctuations, wherein the nanofiber hygroscopic hydrogel is prepared by the preparation method described above.

[0028] Compared to existing hygroscopic salt composite materials used for atmospheric water collection, this invention constructs a nanofiber hygroscopic hydrogel resistant to humidity fluctuations. Structurally, it possesses two types of spatially confined units: one is the gel swelling domain within the fibers, which can absorb and confine the initial deliquescent liquid; the other is the interconnected capillary channels formed by the interwoven fibers, which can capillarily lock the further increase in liquid volume and provide a faster water vapor transport channel. Therefore, the nanofiber hygroscopic hydrogel of this invention can significantly suppress the macroscopic migration and leakage of deliquescent salt solutions under high humidity conditions while maintaining a high salt loading capacity and fast adsorption / desorption kinetics, thereby significantly improving its cycling stability under humidity fluctuation conditions and exhibiting excellent overall performance.

[0029] This invention also seeks to protect the application of the above-mentioned moisture-absorbing hydrogel with resistance to humidity fluctuations in atmospheric water collection, industrial and building dehumidification, moisture protection of electronic devices, and food and pharmaceutical storage and transportation.

[0030] This invention is applicable to atmospheric water collection in scenarios with complex humidity variations, providing a material basis for the stable operation of adsorbents in real-world environments. Compared to existing sodium alginate-based nanofiber materials, this invention expands its application from biomedical scaffolds to atmospheric water collection adsorbents. By constructing a continuous nanofiber hydrogel network, the material maintains a high moisture absorption capacity while exhibiting no macroscopic salt leakage observed for 168 consecutive hours at 90% RH, demonstrating the structural design advantages for high humidity fluctuation conditions and showcasing its potential functions and roles in multiple fields.

[0031] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a nanofiber hygroscopic hydrogel resistant to humidity fluctuations. Through a sequential ion exchange strategy, a nanofiber hygroscopic hydrogel with a hierarchical nanofiber network structure is prepared using a sodium alginate nanofiber membrane. The preparation process employs a specific concentration of sodium alginate solution, a specific range of electrospinning receiver roller speeds, and a specific relative saturation concentration of lithium salt solution to construct a dual constraint mechanism of gel swelling and capillary confinement. This achieves excellent resistance to humidity fluctuations over a wide humidity range, especially in high-humidity environments and fluctuating conditions. Under complex humidity conditions, it exhibits a synergistic improvement in high moisture absorption capacity, rapid adsorption-desorption kinetics, leakage resistance, and long-term cycling stability. It is suitable for efficient atmospheric water collection in all weather conditions and multiple climate zones, providing a material basis for the stable operation of adsorbents in actual humidity fluctuations and different humidity environments, and has significant application value. Attached Figure Description

[0032] Figure 1 Comparative images of the fiber diameter and scanning electron microscope images of the sodium alginate nanofiber membranes prepared in Examples 1, 2, 2, and 3. Figure 1 (a) in the example is Comparative Example 2; Figure 1 (b) in the example is Example 2; Figure 1 (c) in the example is Example 1; Figure 1 (d) in the example is Comparative Example 3.

[0033] Figure 2 The image shows the X-ray diffraction analysis results of the nanofiber hygroscopic hydrogel prepared in Example 1.

[0034] Figure 3 The pore size distribution of the sodium alginate nanofiber membranes prepared in Examples 1, 3 and 4 is shown in the figure. Figure 3 (a) in the text is Example 1; Figure 3 (b) in the text is Example 3; Figure 3 (c) in the example is Example 4.

[0035] Figure 4The graph shows the relationship between the average pore size of the sodium alginate nanofiber membrane prepared in Example 1 and the rotation speed.

[0036] Figure 5 A comparison of the adsorption kinetics and moisture absorption capacity of the nanofiber hygroscopic hydrogel prepared in Example 1 and the blocky lithium chloride-calcium alginate hydrogel prepared in Comparative Example 1 under different relative humidities. Figure 5 (a) in the text is Example 1; Figure 5 (b) in the example is Comparative Example 1.

[0037] Figure 6 The image shows a comparison of the adsorption isotherms of the nanofiber hygroscopic hydrogels prepared in Example 1, Comparative Example 4, and Comparative Example 5.

[0038] Figure 7 The stability results of the nanofiber hygroscopic hydrogel prepared in Example 1 after 50 adsorption-desorption cycles at a relative humidity of 30% are shown in the figure.

[0039] Figure 8 The stability results of the nanofiber hygroscopic hydrogel prepared in Example 1 after 50 adsorption-desorption cycles at a relative humidity of 60% are shown in the figure.

[0040] Figure 9 The stability results of the nanofiber hygroscopic hydrogel prepared in Example 1 after 50 adsorption-desorption cycles at a relative humidity of 90% are shown in the figure.

[0041] Figure 10 The images show the morphological changes of the nanofiber hygroscopic hydrogel prepared in Example 1, the blocky lithium chloride-calcium alginate hydrogel prepared in Comparative Example 1, and the blank group at a relative humidity of 90%.

[0042] Figure 11 The graph shows the relationship between salt leakage of the nanofiber hygroscopic hydrogel prepared in Example 1 and the blocky lithium chloride-calcium alginate hydrogel without nanofiber structure prepared in Comparative Example 1 as a function of time at a relative humidity of 90%.

[0043] Figure 12 The stability results of the nanofiber hygroscopic hydrogel prepared in Example 1 under 20 cycles of relative humidity fluctuations from 30% to 60% to 90%.

[0044] Figure 13 The stability results of the nanofiber hygroscopic hydrogel prepared in Example 2 under 20 cycles of relative humidity fluctuations from 30% to 60% to 90%.

[0045] Figure 14 The graph shows the changes in the moisture absorption properties of the blocky lithium chloride-calcium alginate hydrogel prepared for Comparative Example 1 under three cycles of relative humidity fluctuations from 30% to 60% to 90%.

[0046] Figure 15 The figure shows the stability of the nanofiber hygroscopic hydrogel prepared for Comparative Example 6 under 20 cycles of relative humidity fluctuations from 30% to 60% to 90%.

[0047] Figure 16 The stability results of the nanofiber hygroscopic hydrogel prepared for Comparative Example 7 under 20 cycles of relative humidity fluctuations from 30% to 60% to 90%.

[0048] Figure 17 The water production performance of the nanofiber hygroscopic hydrogel prepared in Example 1 under 1 sun sunlight conditions is shown in the figure. Detailed Implementation

[0049] The present invention will be further described below with reference to the specification and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field. Unless otherwise specified, the reagents and materials used in the following embodiments are commercially available.

[0050] Example 1 A nanofiber hygroscopic hydrogel resistant to humidity fluctuations, the preparation method of which includes the following steps: (1) Weigh 4.0 g of sodium alginate powder (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), add it to 96.0 g of deionized water, stir at 25°C for 12 h, and then let it stand for 12 h to remove bubbles, so as to obtain a sodium alginate solution with a mass fraction of 4%.

[0051] (2) Weigh 3.0 g of polyethylene oxide powder (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), add it to 97.0 g of deionized water, stir at 60°C for 2 h, and then let it stand at room temperature for 12 h to remove bubbles, so as to obtain a polyethylene oxide solution with a mass fraction of 3%.

[0052] (3) Mix the sodium alginate solution obtained in step (1) with the polyethylene oxide solution obtained in step (2) at a mass ratio of 9:1 to obtain a mixed solution.

[0053] (4) Add 0.1 wt% of Triton X-100 (purchased from Shanghai Hushi Laboratory Equipment Co., Ltd.) and 1.0 wt% of dimethyl sulfoxide (purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) to the mixed solution in step (3), stir at 25°C for 3 h, and then let stand for 12 h to remove bubbles to obtain the electrospinning precursor solution, wherein the mass ratio of sodium alginate solution to Triton is 900:1.

[0054] (5) Electrospinning was performed using the electrospinning precursor solution obtained in step (4). The process parameters were: spinning voltage 20kV, receiving distance 20 cm, receiver roller speed 800 rpm, temperature 35℃, spinning time 8 h, flow rate 1 mL / h, and sodium alginate nanofiber membrane was collected.

[0055] (6) Immerse the sodium alginate nanofiber membrane obtained in step (5) in a 2% calcium chloride solution for 30 seconds to perform ionic cross-linking and obtain a calcium alginate nanofiber hydrogel membrane.

[0056] (7) At the experimental temperature (25℃), a lithium chloride saturated aqueous solution was used as the mother liquor, and deionized water was used to dilute it by volume to prepare a lithium chloride solution with a relative saturation concentration of 25% (i.e., 25 volume parts of saturated mother liquor were taken and diluted with deionized water to 100 parts of the total volume). The calcium alginate nanofiber hydrogel membrane obtained in step (6) was immersed in the lithium chloride solution for 24 h and then taken out to obtain the nanofiber hygroscopic hydrogel.

[0057] Example 2 The only difference between this embodiment and embodiment 1 is that in step (1), 3.0 g of sodium alginate powder is weighed and mixed with 97.0 g of deionized water to prepare a sodium alginate solution with a mass fraction of 3%. The remaining steps and parameters are the same as in embodiment 1.

[0058] Example 3 The only difference between this embodiment and embodiment 1 is that the receiver roller speed in step (5) is 200 rpm, and the other steps and parameters are the same as in embodiment 1.

[0059] Example 4 The only difference between this embodiment and embodiment 1 is that the receiver roller speed in step (5) is 1000 rpm, and the other steps and parameters are the same as in embodiment 1.

[0060] Example 5 The only difference between this embodiment and embodiment 1 is that in step (7), a lithium chloride solution with a relative saturation concentration of 15% is prepared, while the other steps and parameters are the same as in embodiment 1.

[0061] Example 6 The only difference between this embodiment and Example 1 is that in step (7), a lithium chloride solution with a relative saturation concentration of 35% is prepared, while the other steps and parameters are the same as in Example 1.

[0062] Comparative Example 1 This comparative example uses a one-pot synthesis method without electrospinning. Specifically, a 4 wt% sodium alginate aqueous solution is directly mixed with a sufficient amount of 2 wt% calcium chloride solution, with a mass ratio of 4 wt% sodium alginate solution to 2 wt% calcium chloride solution of 1:6, forming a blocky calcium alginate hydrogel. Subsequently, this hydrogel is immersed in a lithium chloride solution of the same relative saturation concentration as in Example 1 for 24 h to obtain a blocky lithium chloride-calcium alginate hydrogel without nanofiber structure.

[0063] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step (1), 2.0 g of sodium alginate powder is weighed and mixed with 98.0 g of deionized water to prepare a sodium alginate solution with a mass fraction of 2%. The remaining steps and parameters are the same as in Example 1.

[0064] Comparative Example 3 The only difference between this comparative example and Example 1 is that in step (1), 5.0 g of sodium alginate powder is weighed and mixed with 95.0 g of deionized water to prepare a sodium alginate solution with a mass fraction of 5%. The remaining steps and parameters are the same as in Example 1.

[0065] Comparative Example 4 The only difference between this comparative example and Example 1 is that step (7) is omitted, and only step (6) is performed to obtain the calcium alginate nanofiber hydrogel membrane, without lithium chloride loading. The remaining steps and parameters are the same as in Example 1.

[0066] Comparative Example 5 The only difference between this comparative example and Example 1 is that in step (7), a lithium chloride solution with a relative saturation concentration of 45% is prepared, while the other steps and parameters are the same as in Example 1.

[0067] Comparative Example 6 The only difference between this comparative example and Example 1 is that the receiver roller speed is adjusted to 50 rpm in step (5), while the other steps and parameters are the same as in Example 1.

[0068] Comparative Example 7 The only difference between this comparative example and Example 1 is that the receiver roller speed is adjusted to 3000 rpm in step (5), while the other steps and parameters are the same as in Example 1.

[0069] Test Example 1 Structural Characterization 1. Morphological test Scanning electron microscopy was performed on the sodium alginate nanofiber membranes electrospun from Examples 1, 2, 2, and 3, respectively. X-ray diffraction (XRD) analysis was then performed on the nanofiber hygroscopic hydrogel prepared in Example 1.

[0070] Scanning electron microscopy results showed that sodium alginate concentration had a significant impact on fiber morphology. For example... Figure 1 As shown, when the mass fraction of sodium alginate is low (2 wt%), the molecular chains are insufficiently entangled, resulting in finer fibers that are prone to beading or spindle-shaped defects. When the mass fraction is too high (5 wt%), the solution viscosity is too high, the fibers tend to be flat and ribbon-like, and there is a risk of nozzle clogging. In contrast, a sodium alginate concentration of 3 wt% yields nanofibers with relatively regular morphology; and a concentration of 4 wt% yields a three-dimensional nanofiber network with uniform diameter, regular morphology, and good spatial interconnectivity. Therefore, 4 wt% is determined to be the optimal concentration for the electrospinning precursor solution.

[0071] like Figure 2 As shown, XRD results indicate that no characteristic diffraction peaks of LiCl were observed in the sodium alginate nanofiber membrane before or after calcium ion crosslinking, serving as a blank control. However, characteristic peaks of LiCl appeared in the LiCl-impregnated hygroscopic hydrogel (dry state), confirming that LiCl was successfully loaded into the calcium alginate nanofiber matrix. Furthermore, the characteristic peaks of LiCl disappeared in the hygroscopic sample, indicating that LiCl underwent a transformation from a solid state to a hydrated / deliquescent state during the hygroscopic process.

[0072] 2. Aperture distribution test The pore size distribution of sodium alginate nanofiber membranes electrospun in Examples 1, 3, and 4 was tested using a capillary flow pore size analyzer (CFP-1500-LP, Porous Materials Inc., USA). Galwick (surface tension 15.9 mN / m) was used as the wetting fluid. The pore size distribution of the nanofiber membranes was calculated using the Young-Laplace equation by detecting the gas flow rate-pressure relationship curves of the wetted and dry membranes under different pressures. A rotational speed-average pore size relationship diagram was plotted based on the test results of Example 1. The results are as follows: Figure 3 , 4 As shown.

[0073] The pore size distribution results at different roller speeds show that as the roller speed increases, the fiber packing becomes denser, and the overall pore size decreases. When the speed exceeds 800 rpm, the pore size reduction trend becomes more gradual, indicating a relatively stable structural window for the pore size in this system. Specifically, when the speed exceeds 800 rpm, the average pore size stabilizes at 470-600 nm. The average pore size is smallest at 800 rpm, at 470 nm. Therefore, 800 rpm is determined to be the optimal roller speed for the receiver.

[0074] Test Example 2 Performance Test 1. Adsorption kinetics test Adsorption kinetics were tested on the nanofiber hygroscopic hydrogel prepared in Example 1 and the bulk lithium chloride-calcium alginate hydrogel without nanofiber structure prepared in Comparative Example 1, using a gravimetric vapor adsorption analyzer (IGAsorp, Hiden Isochema Ltd, UK). Specifically, the samples were dried to constant weight at 80°C and then placed in the instrument chamber. A constant temperature (25°C) and a fixed relative humidity were set. The instrument automatically controlled the temperature and humidity within the sealed chamber and recorded the sample mass change in real time. The moisture absorption rate at different times was calculated, and a hygroscopic adsorption kinetic curve was plotted with time on the x-axis and moisture absorption rate on the y-axis. The adsorption kinetics and equilibrium moisture absorption capacity were investigated under relative humidity conditions of 20%, 30%, 60%, and 90%. The test results are as follows: Figure 5 As shown.

[0075] The results showed that Example 1, with its nanofiber structure, exhibited superior moisture absorption capacity and adsorption rate. Under RH conditions of 20%, 30%, 60%, and 90%, its equilibrium moisture absorption capacity reached 1.06, 1.30, 2.33, and 6.46 g·g⁻¹, respectively. -1 The hydrogels prepared in Comparative Example 1 reached adsorption equilibrium within 90, 50, 60, and 360 minutes, respectively. In contrast, the adsorption kinetics and moisture absorption capacity of the hydrogel prepared in Comparative Example 1 were inferior to those in Example 1 at various relative humidities. Specifically, at 20%, 30%, and 60% RH, the equilibrium moisture absorption capacities of Comparative Example 1 were approximately 0.87, 1.28, and 2.25 g·g⁻¹, respectively. -1 The times required to reach adsorption equilibrium were approximately 200, 150, and 200 min, respectively, all significantly longer than those in Example 1 (90, 50, and 60 min, respectively). Under 90% RH conditions, Comparative Example 1 failed to reach adsorption equilibrium within 500 min of testing time. Furthermore, due to the lack of spatial constraint from the nanofiber network, significant macroscopic migration and exudation of the deliquescent salt solution occurred, leading to a continuous decrease in the actual amount of hygroscopic salt solution remaining in the sample. This resulted in distorted weighing data, rendering it meaningless. Therefore, its equilibrium hygroscopic capacity under 90% RH is not listed. The above results demonstrate that the nanofiber network structure of this invention not only significantly accelerates adsorption kinetics under high humidity conditions but also effectively inhibits salt solution leakage, thereby ensuring the stable operation of the material in high humidity environments.

[0076] Depend on Figure 5 Data shows that the nanofiber hygroscopic hydrogel provided by this invention is particularly suitable for applications in high humidity environments. At 90% RH, its performance is significantly better than the hydrogel prepared in Comparative Example 1, reaching 90% of its equilibrium moisture absorption capacity (approximately 6.0 g·g) within 200 min. -1Compared with the hydrogel prepared in Comparative Example 1, the hydrogel prepared in Example 1 not only reached the equilibrium moisture absorption capacity faster, but also had a relatively higher moisture absorption capacity at the same adsorption time.

[0077] The above results show that the nanofiber network structure of the present invention significantly improves the water vapor transport path and structural utilization efficiency, and has both higher moisture absorption capacity and faster adsorption kinetics over a wide humidity range.

[0078] 2. Adsorption isotherm test Adsorption isotherms were tested on the nanofiber hygroscopic hydrogels prepared in Example 1, Comparative Example 4, and Comparative Example 5, respectively. The testing method was as follows: a dynamic water vapor adsorption analyzer (Vsorp-Plus, ProUmid, Germany) was used. Specifically, the samples were dried to constant weight at 80℃ and then placed inside the instrument chamber. Under constant temperature conditions of 25℃, humidity nodes were set according to a gradient within a relative humidity range of 10%-90%. After the sample mass reached adsorption equilibrium at each humidity node, the equilibrium moisture absorption rate was recorded, and a relative humidity-moisture absorption rate correlation curve was established to obtain the sample moisture absorption isotherm. The results are as follows: Figure 6 As shown.

[0079] The results showed that the hygroscopic capacity of Comparative Example 4, which was not loaded with lithium chloride, was significantly reduced, while the hygroscopic capacity of the hydrogel prepared by Comparative Example 5, which had a high salt load (45%), was also lower than that of Example 1 in the high humidity region. This is because Comparative Example 4 lacked a major hygroscopic component; while the higher salt load in Comparative Example 5 caused a stronger tendency for salting out and network shrinkage, disrupting the matching relationship between salt load, gel swelling, and pore structure, which is detrimental to structural stability and the maintenance of effective adsorption sites. These results indicate that there is a suitable window for the hygroscopic salt load to match the network structure, rather than a higher load being always better. Therefore, 25% was determined to be the optimal lithium chloride loading concentration.

[0080] Test Example 3: Constant Humidity Cyclic Stability Test The nanofiber hygroscopic hydrogel prepared in Example 1 was placed in constant environments with relative humidity of 30%, 60%, and 90%, and subjected to 50 cycles of cyclic testing under adsorption-desorption conditions. The specific testing methods are as follows: The static temperature and humidity weighing method was used at 25℃. The samples were placed in constant temperature and humidity chambers under different relative humidity conditions for adsorption, and desorption was performed using thermal desorption at 80℃. Specific parameters for each humidity condition are as follows: 30% RH: adsorption for 2 h, thermal desorption at 80℃ for 2 h, for a total of 50 cycles; 60% RH: adsorption for 4 h, thermal desorption at 80℃ for 4 h, for a total of 50 cycles; 90% RH: adsorption for 8 h, thermal desorption at 80℃ for 8 h, for a total of 50 cycles.

[0081] At the end of each adsorption cycle, the sample mass was weighed, the moisture absorption rate was calculated, and a cycle stability curve was plotted with the number of cycles as the x-axis.

[0082] The test results are as follows: Figure 7-9 As shown in the figure. The results show that after 50 cycles under the three constant humidity conditions, the hygroscopic performance of Example 1 did not show a significant decrease, indicating that the nanofiber hygroscopic hydrogel prepared by the present invention is not only suitable for a constant single humidity point, but also has good cycling stability under low humidity, medium humidity and high humidity conditions.

[0083] Test Example 4: High Humidity Leakage Resistance Test The nanofiber hygroscopic hydrogel prepared in Example 1 and the blocky lithium chloride-calcium alginate hydrogel without nanofiber structure prepared in Comparative Example 1 were simultaneously placed in a constant temperature and humidity chamber at 90% RH. An iron sheet was placed under each material, with the material containing only the iron sheet serving as a control group. The materials were continuously exposed for 168 hours, and the morphology of the three groups under high humidity and the changes in the iron sheet were observed. Separately, the materials from Example 1 and Comparative Example 1 were simultaneously placed in a constant temperature and humidity chamber at 90% RH. The mass of collected salt solution that underwent macroscopic migration was recorded at 1, 3, 6, 12, 24, and 48 h, and normalized to the mass of adsorbent unit. The test results are as follows: Figure 10 , Figure 11 As shown.

[0084] Figure 10 The results showed that, like the blank group, no significant changes were observed in the iron sheet in Example 1, but significant corrosion of the iron sheet in Comparative Example 1 was caused by salt leakage.

[0085] Figure 11 The results showed that, under 90% high humidity conditions, the salt leakage of Comparative Example 1 (without nanofiber structure) continuously increased over time, reaching a relatively high plateau after 24-48 h. In contrast, the nanofiber hygroscopic hydrogel prepared in Example 1 maintained extremely low salt leakage throughout the entire test, indicating that the nanofiber hydrogel network can significantly suppress the macroscopic migration of deliquescent liquids under high humidity. This performance can be attributed to the dual spatial constraints formed by the hierarchical nanofiber network: the gel swelling domains within the fibers accommodate the initial deliquescent liquid, while the interconnected capillary channels between the fibers capillarily lock in the further increased liquid volume.

[0086] The above results indicate that no macroscopic salt leakage or significant migration was observed under the aforementioned high humidity conditions, demonstrating that the material of this invention exhibits excellent resistance to salt leakage in high humidity environments. This result is consistent with the dual spatial constraint mechanism proposed in this invention, namely, the gel swelling domains within the fibers preferentially accommodate the initial deliquescent liquid, while the interconnecting channels between fibers further restrict liquid leakage through capillary action. Figure 11The leakage-time monitoring results further demonstrate that the material of this invention has a sustained inhibitory effect on salt migration under high humidity conditions, rather than just showing stability for a short period of time.

[0087] Test Example 5: Humidity Fluctuation Cyclic Stability Test The hygroscopic hydrogels prepared in Examples 1, 2, 1, 6, and 7 were placed in a dynamic fluctuation environment with relative humidity ranging from 30% to 60% to 90%, and subjected to 20 cycles of testing, each cycle lasting 24 hours. The specific test steps were as follows: During the adsorption stage, humidification was increased stepwise, sequentially adsorbing at 30% RH for 4 hours, then at 60% RH for 4 hours, and finally at 90% RH for 8 hours, simulating the dynamic fluctuation process from low to high humidity in actual outdoor conditions; during the desorption stage, thermal desorption was performed at 80℃ for 8 hours, completing one full cycle. The water absorption rate was recorded and plotted at the end of each cycle during the test. Figure 12-16 The water absorption rates at the completion of the 15th and 20th cycles were calculated, as shown in Table 1. The retention rate was calculated using the formula: Retention rate (%) = Water absorption rate at the completion of the nth cycle (g·g -1 ) ÷ Water absorption rate at the end of the first cycle (g·g) -1 ) × 100%, n = 1 - 20.

[0088] Table 1

[0089] As shown in Table 1, Examples 1 and 2 both exhibited retention rates exceeding 96% after the 15th and 20th cycles, demonstrating the excellent resistance to humidity fluctuations and cyclic stability of the nanofiber hygroscopic hydrogel prepared in this invention. Example 1 showed the highest retention rate, reaching 99.80% and 99.58% after the 15th and 20th cycles, respectively. Comparative Examples 1, 6, and 7 showed significantly lower retention rates after the 15th and 20th cycles. The retention rate of the blocky lithium chloride-calcium alginate hydrogel without nanofibers prepared in Comparative Example 1 decreased to 35.46% after the 15th cycle and further decreased to 27.11% after the 20th cycle, indicating poorer cyclic stability compared to Examples 1 and 2. This suggests that the stability of blocky materials without a continuous nanofiber network structure under humidity fluctuation conditions is significantly worse than that of the nanofiber hygroscopic hydrogel of this invention. Constructing a suitable nanofiber network structure helps improve the cyclic stability of the material. The decrease in retention rate in Comparative Examples 6 and 7 further illustrates that the roller speed of the electrospinning receiver has a significant impact on the material's resistance to humidity fluctuations. The pore size changes caused by excessively fast or slow speeds can affect the formation of the hierarchical nanofiber network in the nanofiber hygroscopic hydrogel, thereby affecting the long-term cycling stability of the material under humidity fluctuation conditions.

[0090] Figure 12 The test results show that the nanofiber hygroscopic hydrogel prepared in Example 1 can still maintain stable hygroscopic performance under continuous humidity fluctuation conditions, without significant attenuation, demonstrating good adaptability to real outdoor humidity change scenarios.

[0091] Figure 13 The test results show that the nanofiber hygroscopic hydrogel prepared using 3 wt% sodium alginate in Example 2 performed better in the 30%→60%→90% humidity fluctuation cycle test. In the early stage (1-5 cycles), the difference between Example 1 and Example 2 using 4 wt% sodium alginate was not significant. However, in the middle and later stages (after 5 cycles), the performance degradation trend appeared slightly earlier than in Example 1 with increasing cycle count. Therefore, considering the overall humidity fluctuation resistance, Example 1 is superior to Example 2, highlighting the optimal dual constraint effect of the gel swelling domain and the capillary channels between fibers in Example 1, resulting in the best cycle stability.

[0092] Figure 14 The test results show that the hygroscopic properties of the bulk lithium chloride-calcium alginate hydrogel prepared in Comparative Example 1 decreased significantly with cycling at all humidity levels, indicating that bulk materials without a continuous nanofiber network structure are difficult to maintain stable operation under fluctuating humidity conditions and have poor cycling stability. Combined with the result of continuously increasing salt leakage under 90% RH conditions, it can be further explained that this type of bulk structure is more prone to salt migration in high humidity and fluctuating humidity environments, leading to rapid deterioration of hygroscopic properties. In contrast, Example 1 maintained greater stability under the same conditions, further demonstrating that the continuous nanofiber network structure of the present invention plays an important role in maintaining the cycling stability of the material in environments with fluctuating humidity.

[0093] Figure 15 , Figure 16 The test results showed that Comparative Example 6, with excessively large pores, suffered from insufficient capillary liquid retention capacity, resulting in continuous leakage of deliquescent liquid during the high humidity stage, and its performance deteriorated significantly after the 20th cycle. Comparative Example 7, with excessively small pores, experienced increased mass transfer resistance, slower adsorption kinetics, and gradual accumulation of residual moisture. Both were inferior to the stable performance of Example 1 after the 20th cycle.

[0094] Therefore, the excellent high-humidity salt leakage resistance and long-term cycling stability of this invention depend on a suitable pore size window, rather than the higher the roller speed or the smaller the pore size. The roller speed corresponding to Example 1 is more conducive to forming a network structure that balances capillary liquid retention capacity and mass transfer efficiency, thereby achieving a synergistic improvement in salt leakage resistance and cycling stability under high humidity conditions.

[0095] Application Example 1 The water production performance of the nanofiber hygroscopic hydrogel prepared in Example 1 was tested.

[0096] Specifically, a modular, layered solar water collection device was employed. Under standard 1.0 sun sunlight intensity, a composite material that had been adsorbed to equilibrium in a 60% RH environment was placed in the device, and the change in condensate mass over time was continuously collected and recorded. The device features a vertical heat conduction structure: the upper layer is a nano-carbon copper foil tape (as a photothermal conversion component), tightly bonded to nanofiber hygroscopic hydrogel via a highly thermally conductive adhesive layer to reduce interfacial thermal resistance; the lower layer consists of stainless steel reinforced heat dissipation fins (as a condensation component) for efficiently releasing the latent heat of condensation of water vapor. Results are as follows... Figure 17 As shown.

[0097] The results show that the device rapidly heats up, with the material surface temperature reaching 69.7℃ within 5 minutes and stabilizing at 76.1℃ after 10 minutes. After 1 hour of photothermal-driven desorption and condensation, the system's water production was measured to be 1.80 g·g⁻¹. -1 (Based on the mass of the adsorbent), this demonstrates that the material of the present invention can be effectively regenerated and has the potential for practical atmospheric water collection applications.

[0098] The foregoing examples are merely illustrative, used to explain some features of the method described in this invention. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are demonstrated by the applicant's actual experimental results. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of the invention. Some numerical ranges used in the claims also include sub-ranges within them, and variations within these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for preparing a moisture-absorbing hydrogel with resistance to humidity fluctuations using nanofibers, characterized in that, The preparation method includes the following steps: (1) Mix sodium alginate solution, polymer spinning aid solution, surfactant and organic solvent to obtain electrospinning precursor solution; (2) Electrospinning was performed using the obtained electrospinning precursor solution to obtain sodium alginate nanofiber membranes. (3) The obtained sodium alginate nanofiber membrane was immersed in calcium chloride solution to obtain calcium alginate nanofiber hydrogel membrane; (4) The calcium alginate nanofiber hydrogel membrane was immersed in a lithium salt solution to prepare a nanofiber hygroscopic hydrogel. The sodium alginate solution has a mass fraction of 3%-4%; The receiver roller rotates at a speed of 150-1200 rpm during electrospinning. The relative saturation concentration of the lithium salt solution is 10%-35%.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the sodium alginate solution to the polymeric spinning aid solution is 8-10:

1.

3. The preparation method according to claim 1, characterized in that, The mass ratio of sodium alginate solution to surfactant is 900:

1.

4. The preparation method according to claim 1, characterized in that, In step (2), the receiver roller speed of electrospinning is 780-1000 rpm.

5. The preparation method according to claim 1, characterized in that, The parameters for electrospinning in step (2) also include: spinning voltage 15-30 kV and receiving distance 10-25 cm.

6. The preparation method according to claim 1, characterized in that, In step (1), the polymeric spinning aid is selected from at least one of polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone.

7. The preparation method according to claim 1, characterized in that, In step (1), the surfactant is selected from at least one of Triton, sodium dodecyl sulfate, and poloxamer.

8. The preparation method according to claim 1, characterized in that, In step (1), the organic solvent is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and ethanol.

9. A nanofiber hygroscopic hydrogel resistant to humidity fluctuations, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the moisture-absorbing hydrogel with humidity fluctuation resistance as described in claim 9 in atmospheric water collection, industrial and building dehumidification, moisture protection of electronic devices, and food and pharmaceutical storage and transportation.

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