Anti-shrinkage rigid macroporous absorbent hydrogel, hydrogel sponge, and preparation method and application thereof

Abstract

The application discloses anti-shrinkage rigid macroporous hygroscopic hydrogel, hydrogel sponge and a preparation method and application thereof, and the method comprises the following steps: first, a hydrogel container is prepared, then the hydrogel container is soaked in a solution containing a cationic polymer to obtain a hydrogel container rich in the cationic polymer; the hydrogel container rich in the cationic polymer is soaked in a mixed foam solution containing an anionic polymer and a foaming agent to obtain a composite of a hydrogel matrix layer-hydrogel container; the composite is taken out and is placed under sealed conditions, then the hydrogel container is peeled off to obtain a hydrogel film. The hydrogel film is soaked in a hygroscopic inorganic salt solution, and a hydrogel sponge is obtained through drying. The obtained hydrogel sponge exhibits excellent hygroscopic / desorption rate and cycle stability in a wide humidity range, and provides a new way for the application of a high-performance atmospheric water collection system.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel technology, and particularly relates to anti-shrinkage rigid macroporous hygroscopic hydrogels and hydrogel sponges. Specifically, it relates to an anti-shrinkage rigid macroporous hygroscopic hydrogel and a hydrogel sponge with dual osmotic pressure-capillary mass transfer effect, and a preparation method thereof. Background Technology

[0002] Adsorption-based atmospheric water harvesting technology has attracted widespread attention due to its ability to sustainably produce freshwater from ubiquitous atmospheric water. Among numerous adsorbents, hygroscopic hydrogels show great potential due to their high moisture absorption capacity and wide adaptability to various humidity levels. However, existing hygroscopic hydrogels are still limited in practical applications by their slow adsorption / desorption rates. This is because, in the dehydrated state, traditional flexible polymer networks shrink into dense, coiled structures, resulting in the collapse and disappearance of micro- and nanopores. This collapse restricts water transport to a slow osmotic pressure gradient-driven process.

[0003] To address these challenges, researchers have attempted to shorten internal water transport distances and enhance adsorption / desorption kinetics by miniaturizing the hydrogel (e.g., thin-film hydrogels, microgels, fiber assemblies) or constructing interconnected macroporous networks (e.g., cryogels, foam drying, 3D printing). However, these strategies still face the challenge of pore blockage after water absorption and swelling on the hydrogel surface under high humidity conditions, leading to a decline in kinetic performance. Therefore, there is an urgent need to develop novel hygroscopic hydrogel materials that can maintain rapid adsorption / desorption kinetics over a wide humidity range. Summary of the Invention

[0004] To address the technical challenges of slow water transport rates and pore blockage leading to decreased kinetic performance in existing traditional flexible hygroscopic hydrogels due to dehydration shrinkage, this invention provides a shrinkage-resistant rigid interconnected macroporous network hygroscopic hydrogel with dual osmotic pressure-capillary mass transfer effect, a hydrogel sponge, and a preparation method.

[0005] One objective of this invention is to provide a method for preparing a shrinkage-resistant rigid macroporous hydrogel, comprising:

[0006] (1) A hydrogel container is prepared in a mold; preferably, a precursor solution containing vinyl monomers, crosslinking agents, initiators, and tertiary amine catalysts is injected into a hollow sealed mold for polymerization;

[0007] The process involves mixing raw materials, including vinyl monomers, crosslinking agents, initiators, and tertiary amine catalysts (such as tetramethyldiamine), to obtain a precursor solution. The precursor solution is then injected into a hollow sealed mold for polymerization to obtain a hydrogel container.

[0008] (2) The hydrogel container is immersed in a solution containing a cationic polymer and diffused to obtain a hydrogel container enriched with cationic polymer;

[0009] (3) The hydrogel container enriched with cationic polymer is immersed in a mixed foam solution containing anionic polymer and foaming agent, and a hydrogel matrix layer is formed on the surface of the hydrogel container (e.g., the upper and lower surfaces) by diffusion, thus obtaining a composite of hydrogel matrix layer-hydrogel container.

[0010] In one aspect, high-concentration cationic polymers diffuse from the hydrogel container to the low-concentration polyanionic solution through concentration gradient-induced diffusion. On the other hand, low-molecular-weight cationic polymers also readily diffuse to high-molecular-weight anionic polymers. Through electrostatic complexation, an anti-shrinkage rigid polymer network is formed, which can encapsulate air bubbles inside the network, thereby forming an anti-shrinkage rigid hydrogel matrix with a macroporous network on the surface of the hydrogel container.

[0011] (4) The composite is removed from the mixed foam solution, left to stand under sealed conditions, and the hydrogel film is obtained after peeling off the hydrogel container.

[0012] The static setting process promotes the directional transport of water molecules from the hydrogel matrix to the hydrogel container, while the cationic polymer continues to diffuse and further crosslinks with the polyanionic polymer to form a highly crosslinked network that stabilizes the porous structure.

[0013] In a preferred embodiment, the crosslinking agent in step (1) is selected from at least one of N,N'-methylenebisacrylamide, divinylbenzene, ethylene glycol dimethacrylate, and diisocyanate.

[0014] In a further preferred embodiment, the content of crosslinking agent in the precursor solution in step (1) is 0.01~0.6wt%, preferably 0.03~0.35wt%, for example 0.03wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt% or 0.35wt%.

[0015] Because N,N'-methylenebisacrylamide is low in cost and easily dispersed in aqueous solution, the crosslinking agent is preferably N,N'-methylenebisacrylamide. The content of N,N'-methylenebisacrylamide in the precursor solution is preferably 0.03~0.17 wt%.

[0016] In a preferred embodiment, the vinyl monomer in step (1) is selected from at least one of acrylamide, acrylic acid, methacrylic acid, N-isopropylacrylamide, and N-vinylpyrrolidone.

[0017] In a further preferred embodiment, the content of vinyl monomer in the precursor solution in step (1) is 2 to 70 wt%, preferably 5 to 50 wt%, for example 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0018] Due to its excellent comprehensive properties and process adaptability, acrylamide can form a stable three-dimensional network structure by simply adding a crosslinking agent, ensuring that the hydrogel container still has sufficient mechanical strength to maintain a specific shape in the swollen state. Furthermore, its excellent hydrophilicity endows the material with high water absorption and retention capacity. In addition, acrylamide polymerization has mild reaction conditions, low cost, and mature processes, facilitating the preparation of regularly shaped hydrogel containers through methods such as template polymerization and emulsion polymerization. Therefore, the hydrophilic polymer monomer is preferably acrylamide. The acrylamide content in the precursor solution is preferably 17-20 wt%.

[0019] In a preferred embodiment, the initiator in step (1) is at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0020] In a further preferred embodiment, the content of the initiator in the precursor solution in step (1) is 0.03~0.5wt%, preferably 0.03~0.16wt%, for example 0.03wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.4wt% or 0.5wt%.

[0021] In a preferred embodiment, the tertiary amine catalyst in step (1) is selected from at least one of tetramethylethylenediamine, triethanolamine, and triethylamine.

[0022] In a further preferred embodiment, the content of tertiary amine catalyst in the precursor solution in step (1) is 0.05~0.15 wt%, preferably 0.06~0.10 wt%, for example 0.05wt%, 0.06wt%, 0.08wt%, 0.10wt%, 0.12wt%, 0.14wt% or 0.15wt%.

[0023] Since the redox initiation system composed of tetramethylethylenediamine and ammonium persulfate can efficiently initiate the free radical polymerization of vinyl monomers at relatively low temperatures (such as 40~70℃), the reaction rate is controllable, and it has good compatibility with monomers such as acrylamide, the tertiary amine catalyst is preferably tetramethylethylenediamine.

[0024] In a preferred embodiment, the polymerization in step (1) is a thermal polymerization, preferably at 40~80℃ for 0.5~5h, more preferably at 40~70℃ for 1~4h.

[0025] In a preferred embodiment, the cationic polymer in step (2) is selected from at least one of chitosan, gelatin, polymethacryloyloxyethyltrimethylammonium chloride, and polyallylamine hydrochloride.

[0026] In a further preferred embodiment, the weight-average molecular weight of the cationic polymer in step (2) is 1000~8000 g / mol, preferably 2000~5000 g / mol, for example 2000 g / mol, 2500 g / mol, 3000 g / mol, 3500 g / mol, 4000 g / mol, 4500 g / mol or 5000 g / mol.

[0027] In a further preferred embodiment, the cationic polymer content in the solution containing the cationic polymer in step (2) is 10-50 wt%, preferably 20-50 wt%, for example 10 wt%, 20 wt%, 30 wt%, 40 wt% or 50 wt%.

[0028] Since cationic polymers can form stable polyelectrolyte composite films with anionic polymers through electrostatic interactions, they not only have good film-forming properties but also excellent mechanical strength, making them ideal materials for achieving layer-by-layer self-assembly and constructing functional film layers. Therefore, the preferred polyanionic polymer is chitosan.

[0029] In a preferred embodiment, the soaking time in step (2) is 5 to 25 hours, preferably 8 to 20 hours, for example 5 hours, 10 hours, 15 hours, 20 hours or 25 hours.

[0030] In a preferred embodiment, the anionic polymer in step (3) is selected from at least one of the following polymers: sodium alginate, xanthan gum, carrageenan, carboxymethyl cellulose, etc., preferably sodium alginate; and / or, the foaming agent in step (3) is selected from cellulose ethers, preferably at least one of hydroxypropyl methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose.

[0031] Because sodium alginate molecules are rich in carboxyl groups, they can undergo strong electrostatic complexation with cation-rich hydrogel containers, rapidly forming a polyelectrolyte membrane with excellent mechanical properties. Simultaneously, it does not disrupt the interconnected macroporous structure formed by the foam solution, synergistically with chitosan to construct a rigid porous network possessing both anti-shrinkage and high hygroscopic properties. Due to the excellent surface activity and thickening / foam-stabilizing ability of the foaming agent, a stable foam solution can be formed through the entanglement and arrangement of molecular chains under intense mechanical stirring, thereby constructing a uniform and controllable interconnected macroporous template. Furthermore, its non-ionic properties prevent electrostatic interference with the system, ensuring the deposition of the polyelectrolyte composite membrane.

[0032] In a further preferred embodiment, in the mixed foam solution of step (3), the content of the anionic polymer is 0.25~2.0wt%, preferably 0.5~1.0wt%; and / or, the content of the foaming agent is 0.05~0.50wt%, preferably 0.15~0.3wt%.

[0033] For example, in the mixed foam solution described in step (3), the content of the anionic polymer is 0.25wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2.0wt%; and the content of the foaming agent is 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, or 0.50wt%.

[0034] Prior to step (3), a mixed foam solution containing polyanionic polymers and a foaming agent is prepared under mechanical stirring. Preferably, the stirring speed is 500-800 rpm (e.g., 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, or 800 rpm), and the stirring time is 0.5-5 h (e.g., 0.5 h, 1 h, 2 h, 3 h, 4 h, or 5 h). More preferably, when the mixed foam solution in step (3) contains functional fillers, it is subjected to mechanical stirring-ultrasonic treatment-mechanical stirring to fully foam the solution, thereby obtaining a foam solution. Ultrasonic treatment can be performed for 5-100 min (preferably 10-80 min, e.g., 20-60 min). The purpose of ultrasonic treatment is to effectively disperse the functional fillers. After ultrasonic treatment, mechanical stirring is required again to fully foam the solution.

[0035] In a preferred embodiment, the viscosity-average molecular weight of the anionic polymer in step (3) is 100,000 to 195,000 higher than the weight-average molecular weight of the cationic polymer, for example, 100,000, 120,000, 140,000, 180,000 or 195,000 higher.

[0036] In a further preferred embodiment, the viscosity-average molecular weight of the anionic polymer in step (3) is 120,000 to 200,000 g / mol, for example, 120,000 g / mol, 140,000 g / mol, 160,000 g / mol, 180,000 g / mol or 200,000 g / mol.

[0037] In a further preferred embodiment, the viscosity-average molecular weight of the anionic polymer in step (3) is 140,000 to 170,000 g / mol.

[0038] In a preferred embodiment, the mixed foam solution in step (3) optionally contains a functional filler, which is preferably a carbon material, more preferably at least one of carbon nanotubes, graphene, and graphite.

[0039] The role of adding carbon materials is to give hydrogel materials photothermal conversion properties, enabling them to absorb heat and desorb water under sunlight.

[0040] In a further preferred embodiment, the concentration of the functional filler in the mixed foam solution is 0.2 to 1.5 wt%, preferably 0.5 to 0.75 wt%, for example 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, or 1.5 wt%.

[0041] In a preferred embodiment, the soaking time in step (3) is 0.2 to 8 hours, preferably 0.5 to 5 hours, for example 0.2 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0042] In a preferred embodiment, in step (4), the sample is left to stand for 2 to 30 minutes, preferably 4 to 20 minutes, for example 2 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes.

[0043] A second objective of this invention is to provide a hygroscopic hydrogel film obtained by the preparation method described in one objective of this invention.

[0044] In this invention: (1) the hydrogel has a high swelling ratio in water, reaching 435%; (2) it has an extremely high swelling ratio in salt solutions, such as lithium chloride, reaching 998%; (3) during repeated swelling and drying, the hydrogel film can stably maintain the physical cross-linked network structure, so that it always has good structural rigidity and anti-shrinkage ability.

[0045] The third objective of this invention is to provide a method for preparing a hygroscopic hydrogel sponge with a shrinkage-resistant rigid interconnected macroporous network, comprising: preparing a hydrogel film using the preparation method described in steps (1) to (4) of the first objective of this invention; step (5) immersing the hydrogel film in a hygroscopic inorganic salt solution and then drying it to obtain a hygroscopic hydrogel sponge with a shrinkage-resistant rigid interconnected macroporous network.

[0046] In step (5), inorganic salts with high hygroscopic capacity (such as lithium chloride, calcium chloride, etc.) are loaded into the hydrogel network.

[0047] In a preferred embodiment, the hygroscopic inorganic salt solution in step (5) is selected from chloride salts, preferably from at least one of lithium chloride, calcium chloride, and magnesium chloride.

[0048] Among them, lithium chloride is chosen because it has extremely strong hygroscopic capacity and does not interfere with film formation, thus exhibiting better compatibility with the system.

[0049] In a further preferred embodiment, the hygroscopic inorganic salt solution in step (5) is an aqueous solution with a concentration of 1 to 20 wt%, preferably 5 to 15 wt%, for example 1 wt%, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%.

[0050] In a further preferred embodiment, step (5) involves soaking for 0.5 to 10 hours, preferably 1 to 5 hours, for example 0.5 hours, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, or 10 hours.

[0051] In a preferred embodiment, the drying in step (5) is freeze-drying, oven drying, or air drying, with freeze-drying being preferred.

[0052] The principle of the preparation method described in this invention is as follows:

[0053] (1) This invention utilizes a foaming-assisted diffusion-complexation method to prepare a shrinkage-resistant, rigid, interconnected macroporous network hygroscopic hydrogel sponge. The strong electrostatic complexation of polycations and anions forms a polymer network with high rigidity and shrinkage resistance. This network maintains a low volume shrinkage rate after drying and shrinks along its thickness, thus maintaining high porosity in a dehydrated state.

[0054] (2) By introducing a foaming agent, bubbles are encapsulated in the polymer network during polymerization, thereby constructing an interconnected macroporous structure, which together with the inherent micro- and nano-pores of the polymer network forms a hierarchical porous structure. This structure can resist collapse in the dehydrated state, thus retaining interconnected mass transfer channels;

[0055] (3) When the rigid network hydrogel is dehydrated, the rigid interconnected macroporous structure will generate osmotic pressure gradient and capillary force effect. The two work together to make the water transport rate significantly exceed the osmotic pressure driven theoretical limit of traditional hygroscopic hydrogels, thus realizing ultra-fast water molecule transport.

[0056] The fourth objective of this invention is to provide a hygroscopic hydrogel sponge obtained by the preparation method described in one objective of this invention.

[0057] The network of the hygroscopic hydrogel sponge exhibits a gradient structure along the thickness direction.

[0058] The fifth objective of this invention is to provide the application of the hygroscopic hydrogel sponge obtained by the preparation method described in the third objective of this invention in atmospheric water collection, air-to-water conversion, space dehumidification, or battery moisture power generation.

[0059] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) The present invention uses a foaming-assisted diffusion-complexation strategy to prepare a shrinkage-resistant rigid interconnected macroporous network hygroscopic hydrogel sponge. The preparation process is simple, the raw materials are widely available, the cost is low, and no expensive preparation instruments are required during the preparation process. It has good application prospects.

[0062] (2) The anti-shrinkage rigid interconnected macroporous hygroscopic hydrogel sponge prepared by the present invention can maintain a hierarchical porous structure in the dehydrated state, effectively avoiding the problem of network collapse and pore disappearance after drying of traditional flexible hydrogels;

[0063] (3) The anti-shrinkage rigid interconnected macroporous hygroscopic hydrogel sponge prepared by the present invention is different from the traditional flexible hydrogel which only relies on osmotic pressure for mass transfer. The rigid network hydrogel significantly improves the internal transport rate of water molecules through the dual synergistic effect of osmotic pressure gradient and capillary force, and achieves ultra-fast hygroscopic and desorption kinetics in a wide humidity range (30%-90% relative humidity).

[0064] (4) The anti-shrinkage rigid interconnected macroporous network hygroscopic hydrogel sponge prepared by the present invention has a fast hygroscopic kinetic rate and desorption kinetic rate, and has strong climate adaptability and wide application range. It has good application prospects in the fields of air-to-water, space dehumidification, and battery moisture power generation.

[0065] (5) The anti-shrinkage rigid interconnected macroporous network hygroscopic hydrogel sponge prepared by the present invention has excellent moisture absorption capacity and moisture absorption rate, and the adsorption rate is significantly better than that of existing hygroscopic hydrogel materials.

[0066] (6) The anti-shrinkage rigid interconnected macroporous network hygroscopic hydrogel sponge prepared by the present invention has excellent solar desorption performance and its desorption rate is at a leading level;

[0067] (7) The hygroscopic hydrogel sponge of the present invention can still maintain stable performance in 20 consecutive adsorption-desorption cycles. Based on its rapid kinetics, a continuous circulating atmospheric water collection device was designed, which can still achieve a high freshwater production under cold and dry winter conditions (-1.3-2.7°C, 40-46% relative humidity).

[0068] In summary, this invention presents a method for preparing shrinkage-resistant, rigidly interconnected macroporous hydrogels and hygroscopic hydrogel sponges using a foaming-assisted diffusion-composite strategy. By constructing a rigid, shrinkage-resistant network macroporous structure, it achieves a dual synergistic effect of osmotic pressure and capillary force, fundamentally overcoming the problem of slow water transport kinetics in traditional hygroscopic hydrogels. This preparation method is simple and controllable, and the resulting materials exhibit excellent moisture absorption / desorption rates and cycling stability over a wide humidity range, providing a new material design and technical pathway for the practical application of high-performance atmospheric water harvesting systems. Attached Figure Description

[0069] Figure 1 The diagram illustrates the mass transfer mechanism of a traditional flexible network hydrogel sponge and the anti-shrinkage rigid interconnected macroporous network hygroscopic hydrogel sponge of the present invention: (i) is a schematic diagram of the mass transfer mechanism of a traditional flexible network macroporous hydrogel sponge, where the right side of (i) represents the state after water absorption as shown in the left side diagram; (ii) is a schematic diagram of the mass transfer mechanism of the macroporous hydrogel sponge of the present invention, where the right side of (ii) represents the state after water absorption as shown in the left side diagram. The comparison shows that the water transport in traditional flexible hydrogels relies solely on a slow osmotic pressure gradient (…). Driven by ) and slow transmission rate; the anti-shrinkage rigid interconnected macroporous hydrogel of the present invention can generate both osmotic pressure gradient and capillary pumping effect when transporting water. The two work together to achieve ultra-fast water transport without significant shrinkage deformation.

[0070] Figure 2The preparation process of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge involved in this invention is described in Example 1.

[0071] Figure 3-1 The SEM images of the anti-shrinkage rigid interconnected macroporous network hygroscopic hydrogel sponge prepared in Example 1 of the present invention under different states show that the pore size varies in a gradient along the thickness direction, gradually increasing from top to bottom.

[0072] Figure 3-2 SEM images of the cross-sections of the anti-shrinkage rigid interconnected macroporous network hygroscopic hydrogel sponge prepared in Comparative Example 2 of this invention under different states.

[0073] Figure 4 The swelling kinetics curves of the hydrogel film prepared in step (4) of Example 1 of the present invention in different solutions.

[0074] Figure 5 The swelling kinetics curve of the hydrogel film prepared in step (4) of Example 1 of the present invention during the cyclic swelling / drying process in 5wt% LiCl solution.

[0075] Figure 6 The moisture absorption kinetics curves of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 1 of the present invention under different relative humidity conditions.

[0076] Figure 7 The moisture absorption kinetics curves of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 2 of the present invention under different relative humidity conditions.

[0077] Figure 8-a The moisture desorption kinetics of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared in Example 2 of this invention after absorbing water for 90 min at 30% relative humidity under different solar irradiation intensities.

[0078] Figure 8-b The water desorption kinetics of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge hydrogel prepared in Example 2 of this invention after absorbing water for 90 min at different relative humidities of 60% were investigated under different solar irradiation intensities.

[0079] Figure 8-c The water desorption kinetics of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge hydrogel prepared in Example 2 of this invention after absorbing water for 90 min at different relative humidities and under different solar irradiation intensities.

[0080] Figure 9The anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 2 of this invention was subjected to moisture adsorption at 30% relative humidity and 25°C, and moisture desorption was carried out under 1x solar irradiation intensity in the laboratory. Each cycle took 1 hour, for a total of 20 cycles.

[0081] Figure 10 The adsorption-desorption curves of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 2 of the present invention are shown in the first and 20th cycles.

[0082] Figure 11 The changes in mass, temperature, humidity, and water yield of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 2 of the present invention were measured in a laboratory test under 1 times the solar irradiation intensity for 8 hours.

[0083] Figure 12 The changes in mass, temperature, humidity, and water yield of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 2 of the present invention were measured in a laboratory test under 5 times the solar irradiation intensity for 8 hours.

[0084] Figure 13 The water yield and water production rate of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 2 of the present invention were measured over a 7-day period under a continuous solar-assisted atmospheric water collection device with 5 times the solar irradiation intensity.

[0085] Figure 14 The changes in mass, temperature, humidity, and water yield of the anti-shrinkage rigid interconnected macroporous network hygroscopic gel sponge prepared according to Example 2 of the present invention were measured in a cold outdoor environment. Detailed Implementation

[0086] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0087] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0088] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0089] Unless otherwise specified, the raw materials used in the examples and comparative examples are all publicly available in the prior art, and can be directly purchased or prepared according to publicly available methods. Acrylamide (AM, 99%) and N,N'-methylenebisacrylamide (MBAA, 98%) were purchased from Shanghai Maclean's Biochemical Co., Ltd., and tetramethylethylenediamine (TEMED, 96%) was purchased from Shanghai Aladdin Reagent Co., Ltd. Ammonium persulfate (APS, 98%) was purchased from Sinopharm Chemical Reagent Co., Ltd. SA was purchased from Qingdao Haizhilin Biotechnology Development Co., Ltd., HPMC was purchased from Shanghai Aladdin Reagent Co., Ltd., CS was purchased from Weifang Dongxing Chitin Products Factory, and LiCl was purchased from Shanghai Maclean's Biochemical Co., Ltd. Carbon nanotubes were purchased from Zhongke Times Nanomaterials Co., Ltd.

[0090] Example 1:

[0091] (1) Preparation of PAM hydrogel containers

[0092] Acrylamide and N,N'-methylenebisacrylamide were added to deionized water and stirred for 0.5 h. Then, ammonium persulfate and tetramethylethylenediamine were injected into the solution under ice-water bath conditions and mechanically stirred at 300 rpm until homogeneous. The stirred mixture was then sonicated in an ice-water bath for 2 min to obtain the AM precursor solution.

[0093] The AM precursor solution was injected into a pre-prepared glass mold (the glass mold consists of two glass plates and a 4 mm spacer placed between the two glass plates), and then the glass mold was fixed in an oven at 50°C for thermal polymerization for 2 h to obtain a PAM hydrogel container.

[0094] In step (1), the AM precursor solution contains 20% acrylamide, 0.0345% N,N'-methylenebisacrylamide, 0.032% ammonium persulfate, and 0.0619% tetramethylethylenediamine. The upper and lower surfaces of the glass mold are transparent glass, while the four sides are opaque gaskets, forming a hollow structure.

[0095] (2) The hydrogel container obtained in step (1) is immersed in a chitosan (CS) solution with a weight average molecular weight of 2500 g / mol and a mass fraction of CS of 20% for 12 h to obtain a hydrogel container enriched with polycations.

[0096] (3) Sodium alginate solution with a viscosity-average molecular weight of 148000 g / mol and hydroxypropyl methylcellulose (HPMC) were added to deionized water and mixed evenly under strong mechanical stirring (650 rpm, stirring for 2 h) to make it fully foamed to obtain a mixed foam solution with a mass fraction of SA of 0.5% and a mass fraction of HPMC of 0.3%; the hydrogel container enriched with polycations obtained in step (2) was immersed in the mixed foam solution and reacted for 2 h to obtain a composite of hydrogel matrix layer-hydrogel container;

[0097] (4) The generated membrane, together with the hydrogel container (i.e. the composite), is taken out from the mixed foam solution, left to stand in a sealed environment for 10 min, and then the hydrogel container is peeled off to obtain the hydrogel film.

[0098] (5) The obtained hydrogel film was immersed in a lithium chloride (LiCl) solution with a mass fraction of 5% for 3 h, and then freeze-dried to obtain an anti-shrinkage rigid macroporous hygroscopic gel sponge.

[0099] The cross-section of the hygroscopic gel sponge prepared in this embodiment was characterized by SEM, and the results are as follows: Figure 3-1 As shown, the hydrogel network exhibits a gradient structure along the thickness direction.

[0100] The hygroscopic, shrinkage-resistant rigid macroporous hydrogel sponge maintains ultra-fast water absorption dynamics, reaching absorption equilibrium in about 45 minutes at 30% relative humidity and in about 90 minutes at 90% relative humidity.

[0101] Example 2:

[0102] This embodiment repeats the process of embodiment 1, except that step (3) of embodiment 1 is changed. Sodium alginate, hydroxypropyl methylcellulose and carbon nanotubes are added to deionized water and mixed evenly under strong mechanical stirring. The mixed solution is then ultrasonically treated for 40 min and then stirred thoroughly to make it foamy to obtain a foam solution. The mass fraction of carbon nanotubes is 0.5%, the mass fraction of SA is 0.5%, and the mass fraction of HPMC is 0.3%.

[0103] Example 3: The process of Example 1 was repeated, except that in step (5), natural air drying was used instead of freeze drying. The resulting hygroscopic sponge was characterized by SEM of its cross-section, and the results are as follows. Figure 3-2 As shown, even when the hydrogel film is allowed to air dry naturally, it still retains abundant micro- and nano-pores in its naturally dried state.

[0104] Example 4:

[0105] The difference between this embodiment and embodiment 1 is that step (2) of embodiment 1 is changed, in which the hydrogel container is immersed in a chitosan (CS) solution with a number average molecular weight of 2500 and a mass fraction of CS of 30%.

[0106] The described hygroscopic, shrinkage-resistant, rigid macroporous hydrogel sponge maintains ultrafast water absorption kinetics, reaching absorption equilibrium in approximately 60 minutes at 30% relative humidity and approximately 120 minutes at 90% relative humidity; the corresponding equilibrium adsorption capacities can reach 0.96 g g. -1 With 2.82gg -1 .

[0107] Example 5:

[0108] The difference between this embodiment and embodiment 1 is that step (2) of embodiment 1 is changed, in which the hydrogel container is immersed in a chitosan (CS) solution with a number average molecular weight of 2500 and a mass fraction of CS of 50%.

[0109] The described hygroscopic, shrinkage-resistant, rigid macroporous hydrogel sponge maintains ultrafast water absorption kinetics, reaching absorption equilibrium in approximately 75 minutes at 30% relative humidity and approximately 150 minutes at 90% relative humidity; the corresponding equilibrium adsorption capacity can reach 0.73 g g. -1 With 2.47gg -1 .

[0110] Example 6:

[0111] The difference between this embodiment and embodiment 1 is that the mass fraction of SA in step (3) of embodiment 1 is changed to 0.75%.

[0112] The described hygroscopic, shrinkage-resistant, rigid macroporous hydrogel sponge maintains ultrafast water absorption kinetics, reaching absorption equilibrium in approximately 75 minutes at 30% relative humidity and approximately 120 minutes at 90% relative humidity; the corresponding equilibrium adsorption capacity can reach 0.88 g. -1 With 2.03gg -1 .

[0113] Example 7:

[0114] The difference between this embodiment and embodiment 1 is that the mass fraction of SA in step (3) of embodiment 1 is changed to 1.0%.

[0115] The described hygroscopic, shrinkage-resistant, rigid macroporous hydrogel sponge maintains ultrafast water absorption kinetics, reaching absorption equilibrium in approximately 90 minutes at 30% relative humidity and approximately 135 minutes at 90% relative humidity; the corresponding equilibrium adsorption capacity can reach 0.64 g. -1 With 1.80gg -1 .

[0116] Example 8:

[0117] The difference between this embodiment and embodiment 1 is that step (2) of embodiment 1 is changed to immerse the hydrogel container in a chitosan (CS) solution with a number average molecular weight of 3500, and step (5) of embodiment 1 is changed to soaking in LiCl with a mass fraction of 10%.

[0118] The described hygroscopic, shrinkage-resistant, rigid macroporous hydrogel sponge maintains ultrafast water absorption kinetics, reaching 3.14 g / cm³ in approximately 180 minutes at 90% relative humidity. -1 Balanced moisture absorption.

[0119] Implementation 9:

[0120] The difference between this embodiment and embodiment 1 is that step (2) of embodiment 1 is changed to immerse the hydrogel container in a chitosan (CS) solution with a number average molecular weight of 3500, and step (5) of embodiment 1 is changed to soaking in LiCl with a mass fraction of 15%.

[0121] The hygroscopic, shrinkage-resistant, rigid macroporous hydrogel sponge maintains ultrafast water absorption kinetics, reaching 2.66 gg in approximately 210 minutes at 90% relative humidity. -1 Balanced moisture absorption.

[0122] Implementation 10:

[0123] The difference between this embodiment and embodiment 1 is that the viscosity-average molecular weight of SA in step (3) of embodiment 1 is changed to 170,000 g / mol, and the mass fraction of LiCl in step (5) of embodiment 1 is changed to 10%.

[0124] Implementation 11:

[0125] The difference between this embodiment and embodiment 1 is that the anionic polymer in step (3) of embodiment 1 is changed, and sodium alginate is replaced with carrageenan, with a mass fraction of 0.3% for carrageenan.

[0126] Implementation 12:

[0127] The difference between this embodiment and embodiment 1 is that the anionic polymer in step (3) of embodiment 1 is changed, and sodium alginate is replaced with xanthan gum, with a mass fraction of 0.5% for xanthan gum.

[0128] Implementation 13:

[0129] The difference between this embodiment and embodiment 1 is that the cationic polymer in step (3) of embodiment 1 is changed, and chitosan is replaced with gelatin, with a mass fraction of 10% for the gelatin.

[0130] Comparative Example 1

[0131] Prepare a chitosan (CS) solution identical to step 2 of Example 1, and a mixed foam solution identical to step 3 of Example 1. Mix the two solutions to prepare a hydrogel.

[0132] Without PAM matrix-assisted diffusion, the electrostatic complexation of CS / SA-HPMC is too rapid and uncontrollable, easily leading to structural inhomogeneity and collapse. Furthermore, the moisture absorption rate of the hydrogel sponge prepared by soaking in lithium chloride and freeze-drying is significantly lower than that in Example 1.

[0133] Test Example 1:

[0134] The hydrogel film obtained in step (4) of Example 1 was immersed in deionized water, 5wt% LiCl solution, and 15wt% LiCl solution respectively to test its swelling performance. The change in its mass over time was recorded using an electronic balance, and the swelling ratio was calculated. The changes in swelling performance are shown in the figure. Figure 4 As shown.

[0135] from Figure 4 It can be seen that the ultra-high swelling kinetics of hydrogel films means that, in addition to the traditional hydrogels... In addition, there is an additional driving force for water transport (i.e., capillary force). The swelling ratio of the hydrogel film increases with increasing LiCl concentration. This trend is attributed to the ability of salt ions to screen charged groups on sodium alginate and chitosan, thereby disrupting their electrostatic complexation. Furthermore, increasing the LiCl concentration from 5 wt% to 15 wt% also slightly prolongs the swelling equilibrium time of the hydrogel film due to the salt-responsive anti-polyelectrolyte effect.

[0136] Test Example 2:

[0137] This test example involves the swelling kinetics test of the hydrogel film obtained in step (4) of Example 1 in a 5 wt% LiCl solution during 10 swelling-drying cycle experiments. After each swelling reached equilibrium, the sample was dried to constant weight at 60°C before the next swelling test was performed. The obtained curves are shown below. Figure 5 As shown.

[0138] This embodiment differs from Test Example 1 in that it only studies the swelling kinetics of the hydrogel film in a 5 wt% LiCl solution, and increases the number of swelling-drying cycles to ten. The changes are as follows: Figure 5 As shown.

[0139] from Figure 5It was found that in a 5wt% LiCl solution, the hydrogel film maintained rapid and repeatable swelling behavior during at least 10 swelling-drying cycles, indicating its good stability. Although the introduction of LiCl enhanced the electrostatic shielding effect and weakened the electrostatic complexation between sodium alginate and chitosan, during the drying process, as the moisture content decreased and the volume fraction increased, the interchain distance shortened, which actually facilitated the reformation of the electrostatic complex between sodium alginate and chitosan. Therefore, during the repeated alternation of swelling and drying, the hydrogel film can maintain a high density of physical cross-linked network, thereby stably maintaining structural rigidity and shrinkage resistance.

[0140] Test Example 3:

[0141] This test example demonstrates the water absorption performance of the anti-shrinkage rigid macroporous hygroscopic gel sponge obtained in Example 1 under different relative humidities. The freeze-dried sample was placed in a constant temperature and humidity chamber at 25°C and different relative humidities (30%, 45%, 60%, 75%, 90%), and the change in sample mass over time was recorded. The resulting moisture absorption curves are shown below. Figure 6 As shown.

[0142] from Figure 6 It can be seen that the shrinkage-resistant rigid macroporous hygroscopic gel sponge exhibits excellent and rapid moisture absorption performance over a wide humidity range of 30%-90%. Under typical relative humidity conditions of 30%, 60%, and 90%, the samples reached 1.15, 2.24, and 3.39 g / cm³ at 45 min, 60 min, and 90 min, respectively. -1 The equilibrium moisture absorption capacity is significantly higher than that of existing advanced adsorbents. These results indicate that the rapid moisture absorption characteristics of the anti-shrinkage rigid macroporous gel sponge are mainly due to the dual mass transfer effect of its anti-shrinkage rigid polymer, which enables high-speed water vapor transport through osmotic pressure and capillary action, thereby significantly accelerating the moisture enrichment and adsorption process.

[0143] Test Example 4:

[0144] This test example involves the water absorption performance of the carbon nanotube-containing, anti-shrinkage, rigid, macroporous, hygroscopic gel sponge prepared in Example 2 under different relative humidities. The test method is the same as in Test Example 3, and the resulting moisture absorption curves are shown below. Figure 7 As shown.

[0145] from Figure 7 It is known that after incorporating carbon nanotubes, the resulting hygroscopic, shrinkage-resistant, rigid macroporous hydrogel sponge still maintains ultrafast water absorption kinetics, reaching absorption equilibrium in about 60 minutes at 30% relative humidity and in about 90 minutes at 90% relative humidity.

[0146] Test Example 5:

[0147] This test case involves the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2. When the sponge reached hygroscopic equilibrium at 25°C and relative humidity of 30%, 60%, and 90%, it was irradiated under different solar irradiation intensities (1 sun, 2 sun, 3 sun, 4 sun, and 5 sun). The mass change of the sample was recorded at all times, and the solar-driven desorption curve results are shown in Figure 8.

[0148] Figure 8a shows the solar-driven desorption curves of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2 when it reaches moisture absorption equilibrium at 25°C and 30% RH relative humidity, under different solar irradiance intensities.

[0149] Figure 8b shows the solar-driven desorption curves of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2 when it reaches hygroscopic equilibrium at 25°C and 60% RH relative humidity, under different solar irradiance intensities.

[0150] Figure 8c shows the solar-driven desorption curves of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge of Example 2 at different solar irradiance intensities when it reaches hygroscopic equilibrium at 25°C and 90% RH relative humidity.

[0151] As shown in Figure 8, with the increase in solar irradiance from 1 times the intensity of sunlight to 5 times the intensity of sunlight, the desorption rate of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge significantly accelerates, and the final desorbed amount increases with increasing light intensity. Simultaneously, the higher the relative humidity, the greater the initial moisture absorption of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge, and the higher the desorbable water content. Under 30% RH and 1 times the intensity of sunlight, the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge can complete water desorption within approximately 29.5 minutes. Under 5 times the intensity of sunlight, the equilibrium water desorption time after reaching absorption equilibrium at 30-90% relative humidity can be shortened to 11.5-19 minutes, demonstrating excellent solar-driven desorption performance.

[0152] Test Example 6:

[0153] This embodiment's test case involves the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2, which adsorbs moisture at 30% relative humidity and 25°C, and then conducts a cyclic experiment of moisture desorption under 1x sunlight irradiation in the laboratory. Each cycle requires adsorption for 35 minutes in a constant temperature and humidity chamber at 30% relative humidity, followed by moisture desorption for 25 minutes under 1x sunlight irradiation. This cycle is repeated, with each cycle taking 1 hour, for a total of 20 cycles.

[0154] Figure 9 Cyclic adsorption-desorption performance over 20 cycles;

[0155] Figure 10 This is a comparison of the adsorption-desorption performance between the first and twentieth cycles.

[0156] from Figure 9 and Figure 10 It can be seen that the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge maintains stable adsorption-desorption properties over 20 cycles, with no significant decrease in equilibrium adsorption capacity and dynamic response characteristics. After a 35-minute water adsorption and 25-minute water desorption cycle, the freshwater yield of the shrinkage-resistant, rigid macroporous hygroscopic gel sponge can reach 0.57 gg. -1 This fully demonstrates its applicability in arid climate conditions and its application potential in practical solar-assisted atmospheric water collection scenarios.

[0157] Test Example 7:

[0158] This test case involves placing the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2 into a continuous atmospheric water collection device. The sponge was continuously irradiated for 8 hours under 1x and 5x solar irradiation intensities in the laboratory. Environmental parameters were monitored in real time using a temperature and humidity recorder to obtain the changes in test temperature and humidity. The mass change of the collected water was also monitored at all times to calculate the cumulative water yield.

[0159] Figure 11 The changes in mass, temperature, humidity, and water yield of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2 were measured during an 8-hour indoor test under 1x sunlight irradiation.

[0160] Figure 12 The changes in mass, temperature, humidity, and water production of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2 were measured during an 8-hour indoor test under 5 times sunlight irradiation.

[0161] A continuous solar-driven atmospheric water harvesting device constructed based on this shrinkage-resistant, rigid, macroporous, hygroscopic gel sponge material exhibits significant light intensity-dependent water harvesting performance. Figure 11 and Figure 12 It can be seen that the continuous solar-assisted atmospheric water collection device collected 10.23 g of water in 8 hours under 1 times the sunlight irradiation, corresponding to a water collection rate of 0.61 g. -1 Under five times the sunlight intensity, 54.93 g of water was collected within 8 hours, corresponding to a water collection rate of 2.54 g / kg. -1 .

[0162] Test Example 8:

[0163] This test case involves evaluating the water collection stability of the hygroscopic, shrinkage-resistant, rigid macroporous hydrogel prepared in Example 2 under long-term cyclic operation conditions. The sample was placed in a continuous atmospheric water collection device and continuously irradiated for 8 hours under 5 times the intensity of sunlight in a laboratory setting. Environmental parameters were monitored in real time using a temperature and humidity recorder to obtain changes in test temperature and humidity, and the mass change of collected water was constantly monitored to calculate the cumulative water yield. This yielded the daily average temperature, humidity, and changes in mass and water yield.

[0164] Figure 13 The study demonstrated the dynamic changes in water yield and water collection volume of a continuous solar-assisted atmospheric water collection device under 5 times the sunlight exposure, over a 7-day period with 8 hours of effective time each day.

[0165] from Figure 13 The continuous solar-assisted atmospheric water collection device exhibited highly stable water collection performance during the 7-day cyclic test. Within each test day (8-hour operating cycle), the water collection volume remained consistently between 49.16 and 51.77 g, without significant performance degradation. Correspondingly, the water yield per unit mass of material also remained highly consistent, demonstrating the excellent cyclic stability of the device under continuous operating conditions. This result fully verifies that the prepared hygroscopic, shrinkage-resistant rigid macroporous hydrogel did not undergo significant deterioration in its microstructure, hygroscopic capacity, and thermal response characteristics during repeated adsorption-desorption cycles, possessing long-term reliable atmospheric water collection potential.

[0166] Test Example 9:

[0167] This test case involves verifying the water collection performance of the hygroscopic, shrinkage-resistant, rigid macroporous hygroscopic gel sponge prepared in Example 2 under actual low-temperature outdoor conditions. The sample was placed in a continuous atmospheric water collection device and water was continuously collected outdoors at low temperatures for 7 hours. Environmental parameters were monitored in real time for each time period using a temperature and humidity recorder to obtain changes in test temperature and humidity. The light intensity was monitored for each time period using a solar power meter, and the mass change of the collected water was constantly monitored to calculate the cumulative water yield. This yielded the changes in temperature, humidity, and water yield for each time period.

[0168] Figure 14 The study demonstrates the freshwater production and related parameter changes of a continuous solar-assisted atmospheric water collection device based on this hygroscopic, shrinkage-resistant, rigid, macroporous, hygroscopic gel sponge during a 7-hour test in a low-temperature outdoor environment, from 10:00 to 16:00.

[0169] like Figure 14As shown, even under low outdoor temperatures, the device maintains stable and reliable water collection performance. During the midday period (11:00-13:00) with relatively good sunlight, the device achieved a water collection efficiency of 0.75 gg. -1 The device achieved a freshwater production of 1.07 gg during the complete 7-hour test period. -1 This data strongly confirms that the prepared hygroscopic, shrinkage-resistant, rigid, macroporous hygroscopic gel sponge still possesses good hygroscopic kinetics and desorption efficiency under low-temperature conditions, effectively overcoming the adverse effects of ambient temperature and achieving stable freshwater production, demonstrating its reliable and stable atmospheric water collection performance under low-temperature and arid climate conditions.

[0170] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing a shrinkage-resistant, rigid, macroporous, hygroscopic hydrogel, comprising: (1) Preparation of hydrogel containers; (2) The hydrogel container is immersed in a solution containing a cationic polymer and diffused to obtain a hydrogel container enriched with cationic polymer; (3) The hydrogel container enriched with cationic polymer is immersed in a mixed foam solution containing anionic polymer and foaming agent, and a hydrogel matrix layer is formed on the surface of the hydrogel container by diffusion, thus obtaining a composite of hydrogel matrix layer-hydrogel container. (4) The composite is removed from the mixed foam solution, left to stand under sealed conditions, and the hydrogel film is obtained after peeling off the hydrogel container.

2. The method according to claim 1, characterized in that, Step (1) includes: injecting a precursor solution containing vinyl monomers, crosslinking agents, initiators, and tertiary amine catalysts into a hollow sealed mold for polymerization to obtain the hydrogel container; preferably: The crosslinking agent in step (1) is selected from at least one of N,N'-methylenebisacrylamide, divinylbenzene, ethylene glycol dimethacrylate, and diisocyanate; and / or, The crosslinking agent content in the precursor solution described in step (1) is 0.01~0.6wt%, preferably 0.03~0.35wt%; and / or, In step (1), the vinyl monomer is selected from at least one of acrylamide, acrylic acid, methacrylic acid, N-isopropylacrylamide, and N-vinylpyrrolidone; and / or, The content of vinyl monomer in the precursor solution in step (1) is 2-70 wt%, preferably 5-50 wt%; and / or, In step (1), the initiator is at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; and / or, In step (1), the initiator content in the precursor solution is 0.03~0.5 wt%, preferably 0.03~0.16 wt%; and / or, The tertiary amine catalyst in step (1) is selected from at least one of tetramethylethylenediamine, triethanolamine, and triethylamine; and / or, The content of tertiary amine catalyst in the precursor solution is 0.05~0.15 wt%, preferably 0.06~0.10 wt%; and / or, The polymerization in step (1) is a thermal polymerization, preferably at 40~80℃ for 0.5~5h, more preferably at 40~70℃ for 1~4h.

3. The method according to claim 1, characterized in that, The cationic polymer in step (2) is selected from at least one of chitosan, gelatin, polymethacryloyloxyethyltrimethylammonium chloride, and polyallylamine hydrochloride; The cationic polymer in step (2) has a weight-average molecular weight of 1000~8000 g / mol, preferably 2000~5000 g / mol; and / or, The cationic polymer content in the solution containing the cationic polymer in step (2) is 10~50wt%, preferably 20~50wt%.

4. The method according to claim 1, characterized in that, The anionic polymer in step (3) is selected from at least one of the following polymeric materials: sodium alginate, xanthan gum, carrageenan, carboxymethyl cellulose, etc.; and / or, The viscosity-average molecular weight of the anionic polymer in step (3) is 100,000 to 195,000 higher than that of the cationic polymer, and the viscosity-average molecular weight of the anionic polymer in step (3) is 100,000 to 200,000 g / mol, more preferably 140,000 to 170,000 g / mol; and / or, The foaming agent in step (3) is selected from hydroxylated cellulose, preferably at least one of hydroxypropyl methylcellulose and hydroxypropyl cellulose; and / or, In the mixed foam solution described in step (3), the content of the anionic polymer is 0.25~2.0 wt%, preferably 0.5~1.0 wt%; and / or, In the mixed foam solution described in step (3), the content of the foaming agent is 0.05~0.50wt%, preferably 0.15~0.3wt%.

5. The method according to any one of claims 1 to 4, characterized in that, The mixed foam solution in step (3) optionally contains a functional filler, which is preferably a carbon material, more preferably at least one of carbon nanotubes, graphene, and graphite; More preferably, the concentration of the functional filler in the mixed foam solution is 0.2~1.5wt%, more preferably 0.5~0.75wt%.

6. The method according to claim 5, characterized in that, The soaking time in step (2) is 5-25 hours, preferably 8-20 hours; and / or, Before step (3), a mixed foam solution containing polyanionic and foaming agents is prepared under mechanical stirring; preferably, the stirring speed is 500~800 rpm, and the stirring time is 0.5~5 h; more preferably, when the mixed foam solution in step (3) contains functional fillers, it is stirred in the order of mechanical stirring-ultrasonic treatment-mechanical stirring to fully foam the solution, and / or, The soaking time in step (3) is 0.2~8h, preferably 0.5~5h; and / or, In step (4), let stand for 2 to 30 minutes, preferably for 4 to 20 minutes.

7. A hydrogel obtained by the preparation method according to any one of claims 1 to 6.

8. A method for preparing a hygroscopic hydrogel sponge with a shrinkage-resistant rigid interconnected macroporous network, comprising: Hydrogel films are prepared using the preparation method described in steps (1) to (4) of any one of claims 1 to 6; Step (5): The hydrogel film is immersed in a hygroscopic inorganic salt solution and then dried to obtain a hygroscopic hydrogel sponge with a shrinkage-resistant, rigid, interconnected macroporous network; preferably: The hygroscopic inorganic salt solution in step (5) is selected from chloride salts, preferably from at least one of lithium chloride, calcium chloride, and magnesium chloride; preferably, the hygroscopic inorganic salt solution is an aqueous solution with a concentration of 1-20 wt%, more preferably 5-15 wt%; and / or, The drying process in step (5) can be freeze-drying, oven drying, or air drying, with freeze-drying being preferred.

9. The hydrogel sponge obtained by the preparation method of claim 8, preferably, the network of the hydrogel sponge exhibits a gradient structure along the thickness direction.

10. The application of the hydrogel sponge obtained by the preparation method of claim 8 in atmospheric water collection, air-to-water generation, space dehumidification, or battery moisture power generation.

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