Porous gel adsorption material and preparation method thereof

Abstract

The invention provides a porous gel adsorption material and a preparation method thereof. The preparation method comprises the following steps: mixing a hydrophilic monomer, an ice crystal or chemical porous structure guiding agent and a doping material in a solvent to form a precursor solution; polymerizing the precursor solution to form a hydrogel; and finally freeze-drying to obtain the porous gel adsorption material. The material is internally provided with a three-dimensional through multistage pore channel structure which comprises micropores, mesopores and macropores, the surfaces of pore channels are rich in hydrophilic groups, the specific surface area is larger than or equal to 500 m < 2 > / g, and the compressive strength is larger than or equal to 0.8 MPa. The prepared material has the advantages of high adsorption capacity, fast mass transfer and good mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of functional materials and adsorption separation technology, and in particular to a porous gel adsorption material and its preparation method. Background Technology

[0002] With the increasing demand for air humidity control, volatile organic compound (VOC) removal, and water resource recycling in industrial production, environmental protection, and specific environments, the development of high-performance adsorption materials has become a research hotspot. Ideal adsorption materials need to possess high adsorption capacity, rapid adsorption / desorption rates, good cycling stability, and sufficient mechanical strength to adapt to the packing and long-term operation of dynamic adsorption beds.

[0003] Currently, commonly used adsorbent materials such as silica gel, activated alumina, and zeolite molecular sieves, while possessing high specific surface areas, have simple pore structures (mainly micropores), resulting in high mass transfer resistance and slow adsorption kinetics. Furthermore, during repeated adsorption-desorption processes, pore collapse or pulverization can easily occur due to capillary forces or thermal stress. On the other hand, hydrogel materials with abundant hydrophilic groups and three-dimensional network structures, while exhibiting strong affinity for water molecules, often suffer from low porosity, small pore size, and poor mechanical strength. They are prone to shrinkage and collapse after drying, making it difficult to form stable, interconnected hierarchical channels, thus limiting their application as highly efficient adsorbents. In recent years, although some studies have attempted to improve gel performance by doping with nanomaterials or employing special drying methods, these approaches often suffer from complex processes, difficulty in precisely controlling pore structure, and the challenge of achieving a balance between material strength and adsorption performance. For example, the introduction of reinforcing materials may clog pores, while excessive pore formation can sacrifice the material's mechanical properties.

[0004] Therefore, how to overcome the adverse effects of slow mass transfer and easy pulverization of traditional adsorption materials and low strength and unstable pore structure of hydrogel materials through the synergy of material design and process control, and achieve the simultaneous improvement of material adsorption capacity, mass transfer rate and mechanical strength, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a porous gel adsorption material and its preparation method, which solves the technical problems of slow mass transfer rate, difficulty in balancing mechanical strength and high adsorption capacity, and unstable and easily collapsed pore structure of hydrogel materials in the prior art.

[0006] On one hand, the present invention provides a method for preparing a porous gel adsorbent material, comprising the following steps: S1. A hydrophilic monomer, a porous structure directing agent, and a dopant are mixed in a solvent to form a homogeneous precursor solution; the porous structure directing agent is an ice crystal template agent or a chemical pore-forming agent; S2. The precursor solution is subjected to a polymerization reaction to form a hydrogel; S3. Freeze-dry the hydrogel to obtain the porous gel adsorbent material.

[0007] According to the present invention, a method for preparing a porous gel adsorbent material is provided, wherein the ice crystal template agent is the solvent itself, and the solvent is water or a mixture of water and ethanol; during the freezing process in step S3, the ice crystal template agent crystallizes in situ to form an ice crystal template, and sublimates in subsequent drying, thereby forming a macroporous structure in the material.

[0008] According to the present invention, a method for preparing a porous gel adsorbent material is provided, wherein the chemical pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate, polyvinyl alcohol, or polyethylene glycol; the chemical pore-forming agent decomposes or dissolves during the polymerization reaction in step S2 or the drying process in step S3, thereby introducing mesopores or macropores into the material.

[0009] According to the present invention, a method for preparing a porous gel adsorbent material is provided, wherein the hydrophilic monomer is selected from at least one of acrylamide, acrylic acid, N-isopropylacrylamide, dimethylaminoethyl methacrylate, or chitosan.

[0010] According to the present invention, a method for preparing a porous gel adsorbent material is provided, wherein the doping material is at least one of nano-silica, montmorillonite, metal-organic framework materials, graphene oxide, or carbon nanotubes.

[0011] According to the method for preparing a porous gel adsorbent material provided by the present invention, the precursor solution further comprises a crosslinking agent; the crosslinking agent is at least one selected from N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, or glutaraldehyde.

[0012] According to the method for preparing a porous gel adsorbent material provided by the present invention, the polymerization reaction in step S2 is solution polymerization, including: S2A1. Add an initiator to the precursor solution; S2A2. Add an accelerator and react at 25~80℃ for 2~12 hours to form the hydrogel.

[0013] According to the method for preparing a porous gel adsorbent material provided by the present invention, the polymerization reaction in step S2 is a sol-gel method, including: S2B1. Adjust the pH of the precursor solution to 4.0~7.0; S2B2. Perform a hydrolysis-condensation reaction at 40~80℃ for 4~24 hours to form the hydrogel.

[0014] On the other hand, the present invention provides a method for preparing a porous gel adsorbent material, wherein the porous gel adsorbent material has a three-dimensional interconnected hierarchical pore structure, the hierarchical pore structure including micropores, mesopores and macropores; and the pore surface of the material is distributed with hydrophilic groups.

[0015] The porous gel adsorbent material prepared by the method provided by the present invention has a multi-level pore structure in which the pore size of the mesopores ranges from 2 to 50 nm, and the pore size of the macropores is greater than 50 nm; the specific surface area of ​​the material is ≥500 m² / g. 2 / g, compressive strength ≥0.8MPa.

[0016] The porous gel adsorbent material and its preparation method provided by this invention have the following advantages compared with the prior art: (1) The porous gel adsorbent material and its preparation method provided by the present invention achieve multi-scale precise control of the internal pore structure of the material from micropores, mesopores to macropores through the use of ice crystal template method and chemical pore-forming agents alone or in combination. In particular, the use of unidirectional freezing technology can form highly oriented through-pore channels, which serve as macroscopic mass transfer "highways". Combined with the diffusion channels of mesopores and the high specific surface area adsorption sites of micropores, an ideal three-level pore system of "rapid mass transfer-efficient adsorption" is constructed, which significantly improves the adsorption kinetics performance of the material.

[0017] (2) The porous gel adsorbent material and its preparation method provided by this invention effectively enhance the mechanical strength and functional properties of the gel network without significantly sacrificing porosity by introducing nano-silica, montmorillonite, graphene oxide, carbon nanotubes, or metal-organic frameworks (MOFs) as dopants. The dopants can serve as physical crosslinking points to strengthen the network or impart additional functions to the material using their own properties. The prepared material maintains a high specific surface area and high porosity while achieving a compressive strength of over 0.8 MPa, thus resolving the contradiction that high adsorption capacity materials typically have low mechanical strength.

[0018] (3) The porous gel adsorbent material and its preparation method provided by this invention are flexible in process and widely applicable. The hydrophilic monomers can be selected from a variety of synthetic or natural polymers such as acrylamide, acrylic acid, and chitosan, and can be copolymerized and modified; the polymerization method can be thermally initiated solution polymerization or sol-gel method; the pore-forming strategy can be flexibly selected or combined as needed. This high degree of designability allows the material properties to be optimized for different application scenarios.

[0019] (4) The porous gel adsorbent material and its preparation method provided by the present invention exhibit excellent comprehensive adsorption performance and cycle stability. Under standard conditions (25℃, RH=60%), it shows a high equilibrium adsorption capacity for water vapor. The material has a stable structure, high adsorption capacity retention after multiple adsorption-desorption cycles, good temperature and acid / alkali resistance, long service life, and relatively low desorption energy consumption.

[0020] (5) The porous gel adsorption material and its preparation method provided by the present invention have adjustable material morphology, which can be made into both bulk materials and thin films, making it easy to process into adsorption modules of different forms to meet diverse application devices and process requirements. The combination of thin film morphology and oriented channels is particularly beneficial for constructing compact, low-resistance, and high-efficiency adsorption heat exchangers. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the process flow for preparing a porous gel adsorbent material provided by the present invention; Figure 2 This is the cyclic adsorption-desorption stability test curve of the porous gel adsorbent material provided in Example 1 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] The following is combined with Figures 1-2 This invention describes a porous gel adsorbent material and its preparation method.

[0025] Figure 1 This is a schematic diagram of the process flow for preparing a porous gel adsorbent material provided by the present invention.

[0026] like Figure 1As shown, this invention provides a method for preparing a porous gel adsorbent material. The core of this method lies in the synergistic effect of compositional design, pore structure guidance, and process control to prepare a gel adsorbent material with three-dimensional interconnected hierarchical pores, high specific surface area, strong hydrophilicity, and excellent mechanical strength. The method mainly includes: mixing a hydrophilic monomer, a porous structure guiding agent, and a dopant material in a solvent to form a homogeneous precursor solution; causing the precursor solution to undergo a polymerization reaction to form a hydrogel; and freeze-drying the hydrogel to obtain the porous gel adsorbent material.

[0027] In this invention, the hydrophilic monomers form the framework of the gel network, and their selection determines the basic hydrophilicity and chemical environment of the material. The doped materials are used to enhance mechanical properties or introduce additional functionalities. The porous structure directing agent is key to constructing hierarchical pores.

[0028] In a preferred embodiment of the invention, to achieve fine control over adsorption performance (such as capacity, rate, and selectivity), two or more hydrophilic monomers can be copolymerized. For example, the copolymerization of acrylic acid and acrylamide can simultaneously provide the ion exchange capacity of carboxyl groups and the strong hydrogen bonding of amide groups, enabling the material to exhibit high affinity for water molecules and various polar organic compounds. The molar ratio of the comonomers can be adjusted within the range of 90:10 to 10:90 to meet different application requirements. When chitosan is selected as the matrix, its good biocompatibility, biodegradability, and rich content of active groups can be utilized to further enhance its stability and functional diversity through crosslinking or grafting modification.

[0029] In a more preferred embodiment, the selection of the dopant material is closely related to its functional purpose: if the main purpose is to improve mechanical strength and thermal stability, nano-silica or montmorillonite is preferred, and the amount added can be 1-20% of the mass of the hydrophilic monomer; if the main purpose is to significantly increase the specific surface area and micropore adsorption capacity, metal-organic framework materials are preferred, and the amount added can be 5-40% of the total mass of the precursor solid; if it is necessary to improve the thermal conductivity of the material to accelerate the adsorption / desorption cycle and enhance the structural toughness, graphene oxide or carbon nanotubes are preferred, and the amount added can be 0.1-5% of the mass of the hydrophilic monomer.

[0030] In this invention, pore structure guiding agents are divided into two categories: ice crystal template agents and chemical pore-forming agents. They have different mechanisms of action and can be used alone or in combination to achieve multi-scale pore size distribution from micropores to macropores.

[0031] When using the ice crystal template method, the solvent (water or a water / ethanol mixture) itself serves as the template agent. By precisely controlling the freezing process, the morphology and size of the final pores can be controlled. For example, using unidirectional freezing technology (with the bottom of the sample in contact with the cold source), ice crystals grow vertically along the temperature gradient, forming highly oriented columnar macropore channels. This structure can significantly reduce airflow penetration resistance. The freezing rate is a key parameter; a slower freezing rate (e.g., 0.1-1 °C / min) is conducive to forming larger, more regularly structured pores, while a faster freezing rate (e.g., 5-20 °C / min) tends to form smaller, more uniformly distributed pores.

[0032] When using chemical pore-forming methods, the pore-forming agent decomposes or is removed during the reaction, leaving pores. Ammonium carbonate or ammonium bicarbonate decomposes at the polymerization temperature to produce gas, making it suitable for introducing mesopores or macropores of tens to hundreds of nanometers. Polyvinyl alcohol, as a pore-forming agent, has limited compatibility with many gel networks and can be dissolved by hot water washing after gel solidification, leaving pores occupied by its molecular chains. The amount of chemical pore-forming agent added is typically 5% to 50% of the mass of the hydrophilic monomer.

[0033] In a preferred embodiment, a composite pore-forming strategy combining ice crystal templates and chemical pore-forming can be employed. For example, an appropriate amount of ammonium carbonate is first added to the system to form dispersed mesopores during the polymerization stage; then, the resulting hydrogel is unidirectionally freeze-dried, utilizing the ice crystal template to form a through-pore macroporous framework. In this way, an ideal three-tiered pore system can be constructed, characterized by "rapid mass transfer through macropores - uniform distribution of mesopores - microporous adsorption provided by gel network and metal-organic framework material doping."

[0034] In this invention, successful polymerization is a prerequisite for obtaining a uniform gel network. For solution polymerization systems, ammonium persulfate or potassium persulfate can be used as initiators, with an amount of 0.05-1.0% of the monomer mass; tetramethylethylenediamine or sodium bisulfite can be used as accelerators, and the reaction temperature is preferably between 40-60°C, with a reaction time of 4-8 hours, to obtain a suitable polymerization rate and a uniform crosslinked network.

[0035] For sol-gel systems (especially those using silicon sources or specific metal alkoxides as doped precursors), strict control of hydrolysis and condensation conditions is necessary. A weakly acidic environment with a pH of 4.0–6.0 is generally beneficial for obtaining dense, high-strength gels. Reaction temperatures of 50–70°C and reaction times of 6–12 hours ensure sufficient reaction to form a stable three-dimensional network.

[0036] Freeze-drying is the core step in this method for forming fixed pores. The pre-freezing temperature must be below the eutectic point of the solvent system; for water-based systems, this is typically below -20°C, preferably -40 to -80°C, to ensure complete freezing and formation of a solid ice crystal template. The vacuum level in the freeze-drying chamber should be stably maintained below 10 Pa, and the cold trap temperature should be below -50°C to ensure that the ice crystals can continue to sublimate without melting or collapsing. The drying time depends on the sample size and thickness, typically requiring 24 to 72 hours until the sample quality is constant.

[0037] This invention also provides a porous gel adsorbent material with interconnected hierarchical pores. The micropores (<2 nm) mainly originate from the doped metal-organic framework material or the dense regions of the gel network itself, providing a high specific surface area (≥600 m²). 2 The material exhibits strong adsorption capacity; mesopores (2~50 nm) serve as the main channels for adsorbate diffusion within the gel framework; macropores (>50 nm, even reaching hundreds of micrometers) act as macroscopic mass transfer channels, ensuring low airflow resistance. The inner surface of the pores is rich in functional groups such as carboxyl, amide, hydroxyl, and amino groups provided by hydrophilic monomers. These hydrophilic groups not only efficiently capture water molecules through physicochemical processes (equilibrium adsorption capacity can reach over 0.5 g / g at 25℃ and RH=60%), but their hydration layer also helps buffer stress during wet-dry cycles, maintaining the long-term stability of the pore structure. Through the synergistic enhancement of crosslinking agents (typically 0.5~2.0% of monomer mass) and rigid dopants, the material maintains high porosity while achieving a compressive strength of 0.8 MPa or even higher, meeting the mechanical requirements for adsorption bed packing, vibration, and repeated cycles.

[0038] In a further optimized embodiment of the present invention, the dried porous gel may be post-treated to expand the application of the material or improve specific properties.

[0039] Ion crosslinking reinforcement: impregnating the material with calcium ions (Ca). 2+ ), aluminum ions (Al) 3+ In solutions containing polyvalent anions (such as citrate), the network is further enhanced through ionic bonding, improving its stability in acidic or alkaline environments (such as pH 4-9).

[0040] Functional group grafting: Utilizing the active groups on the surface of materials (such as the amino groups of chitosan), specific selective functional groups (such as amine groups for CO2 capture and thiol groups for heavy metal capture) are grafted through chemical reactions to achieve customized adsorption functions.

[0041] Hydrophobic region construction: By partially hydrophobizing the material (such as by lightly coating it with a low surface energy material), its water absorption / retention properties can be controlled, or it can exhibit better selectivity when adsorbing organic vapors.

[0042] Example 1 This embodiment provides an acrylamide / acrylic acid copolymer-ice crystal template-nano silica reinforced porous gel.

[0043] Weigh out 5.0g of acrylamide, 2.0g of acrylic acid, 100mL of deionized water, 0.5g of nano silica, 0.035g of N,N'-methylenebisacrylamide, 0.035g of ammonium persulfate, and 50μL of tetramethylethylenediamine.

[0044] Acrylamide, acrylic acid, nano-silica, and N,N'-methylenebisacrylamide were added to a three-necked flask containing 80 mL of deionized water. The mixture was mechanically stirred in an ice-water bath for 2 hours to form a homogeneous dispersion. The acrylic acid was slowly neutralized with 1 M NaOH solution to approximately pH 7.0. Then, deionized water was added to bring the total volume to 100 mL, and stirring was continued for 30 minutes to obtain a homogeneous precursor solution.

[0045] Nitrogen gas was bubbled into the precursor solution for 30 minutes to remove dissolved oxygen. Ammonium persulfate was added and stirred until dissolved, followed by tetramethylethylenediamine, which was then rapidly mixed until homogeneous. The reaction system was transferred to a 50°C water bath and allowed to stand for 6 hours to obtain a transparent, somewhat elastic cylindrical hydrogel.

[0046] The hydrogel was placed in the sample tray of a freeze dryer and pre-frozen in an ultra-low temperature freezer at -80°C for 12 hours to ensure complete freezing. The sample was then transferred to the freeze dryer, the cold trap temperature was set to -60°C, the vacuum degree was maintained below 5 Pa, and the sample was dried for 48 hours to obtain a white, porous cylindrical gel block.

[0047] Scanning electron microscopy revealed a highly oriented layered macroporous structure within the material, with pore sizes ranging from 50 to 200 μm. Uniformly attached nano-SiO2 particles were observed on the pore wall surfaces. Nitrogen adsorption-desorption tests showed that the material exhibited a typical type IV isotherm and a BET specific surface area of ​​580 m². 2 / g, the pore size distribution shows two mesoporous peaks in 2~10nm and 20~50nm.

[0048] The compressive strength of a cylindrical sample (10 mm in diameter and 10 mm in height) was tested using a universal testing machine, and the result was 1.2 MPa.

[0049] The equilibrium adsorption capacity of the material for water vapor was tested in a constant temperature and humidity chamber (25℃, RH=60%). The dried sample was placed in this environment until its mass became constant, and the equilibrium adsorption capacity was calculated to be 0.68 g / g. Adsorption kinetics tests showed that the adsorption capacity reached more than 80% of the equilibrium value within the initial 30 minutes.

[0050] After the sample is saturated with adsorption at 25℃ and RH=60%, it is placed in an 80℃ oven for desorption for 2 hours; this constitutes one cycle. Figure 2 As shown, after 50 cycles, the adsorption capacity of the material is retained at 92% of the initial value.

[0051] The material was filled into an adsorption column with an inner diameter of 20 mm. Under the condition that the gas velocity in the empty tower was 0.5 m / s, the pressure drop of the bed was measured to be 45 Pa.

[0052] Example 2 This embodiment provides a chitosan-based chemically pore-forming metal-organic framework material-doped porous gel.

[0053] Weigh out 3.0g of chitosan (degree of deacetylation ≥90%, viscosity 100~200mPa·s), 3.0g of ammonium bicarbonate, 1.5g of ZIF-8, 0.3mL of glutaraldehyde (25% aqueous solution), and 100mL of 2% (v / v) acetic acid aqueous solution.

[0054] Chitosan powder was slowly added to a 2% aqueous acetic acid solution and stirred in a 40°C water bath until completely dissolved, yielding a clear, viscous chitosan solution. ZIF-8 powder and ammonium bicarbonate were then added to this solution, and the mixture was sonicated for 30 minutes to ensure uniform dispersion, thus obtaining the precursor sol.

[0055] Glutaraldehyde solution was added dropwise to the above sol, and the mixture was stirred at room temperature for 2 hours, during which the system gradually thickened. The mixture was then transferred to a mold and placed in a 60°C oven for 12 hours. During this process, glutaraldehyde crosslinked the chitosan to form a network, while ammonium bicarbonate decomposed upon heating to produce NH3 and CO2 gases, creating pores in the gel.

[0056] The formed hydrogel was removed from the mold and soaked in deionized water for 3 days, changing the water 3 times a day, to remove residual acetic acid, glutaraldehyde, and soluble salts. The washed gel was then freeze-dried (pre-frozen at -40°C, dried for 60 hours) to obtain a light yellow, lightweight porous bulk material.

[0057] SEM images revealed that the material possesses abundant, interconnected spherical pores with a wide pore size distribution, ranging from hundreds of nanometers to tens of micrometers. High-magnification SEM showed that ZIF-8 particles were encapsulated within a chitosan network framework. The BET specific surface area reached a high of 720 m². 2 / g, with significant microporous characteristics, mainly derived from ZIF-8.

[0058] At 25℃ and RH=60%, the equilibrium adsorption capacity for water vapor is 0.55 g / g. Furthermore, due to the introduction of ZIF-8, the material also exhibits good adsorption performance for toluene vapor (concentration 1000 ppm, 25℃), with a saturated adsorption capacity reaching 0.45 g / g.

[0059] The compressive strength is 0.9 MPa. After immersing the material in buffer solutions with pH=4 and pH=9 for 72 hours, its mass loss rate is less than 5%, and the structure remains intact, indicating that it has good acid and alkali resistance.

[0060] Example 3 This embodiment provides a composite pore-forming (chemical + ice crystal) - graphene oxide-enhanced rapid desorption gel.

[0061] Weigh out 7.0g of acrylic acid, 1.5g of polyvinyl alcohol, 100mL of deionized water, 20mL of graphene oxide dispersion (5mg / mL), 0.16g of polyethylene glycol diacrylate (Mn=400), and 0.02g of 2-hydroxy-2-methylphenylacetone.

[0062] Acrylic acid, polyethylene glycol diacrylate, and polyvinyl alcohol were dissolved in 80 mL of deionized water and stirred at 60 °C until completely dissolved. After cooling to room temperature, graphene oxide dispersion was added, and the mixture was sonicated for 1 hour to obtain a uniform black dispersion. Finally, 2-hydroxy-2-methylphenylacetone was added and stirred in the dark to dissolve.

[0063] The precursor solution was injected into a 1mm thick mold sandwiched between two glass plates and placed under a UV lamp (wavelength 365nm, light intensity 15mW / cm²). 2 Irradiation for 5 minutes under a light source initiates polymerization, resulting in a composite hydrogel membrane containing PVA.

[0064] The gel membrane was immersed in 60°C hot water and stirred for 4 hours to dissolve PVA and form primary pores. The membrane was then removed, laid flat on a copper plate, and the copper plate was vertically immersed in liquid nitrogen for unidirectional freezing. After complete freezing, it was transferred to a freeze dryer and dried for 36 hours to obtain a black porous gel film with vertically oriented pores.

[0065] SEM cross-sectional images clearly show that the material has a highly vertically oriented channel structure with channel diameters of approximately 20-50 μm, and the pore walls have abundant wrinkles and smaller pores. This structure greatly promotes mass transfer.

[0066] Due to the incorporation of graphene oxide, the thermal conductivity of the material is increased by approximately three times compared to pure gel. Desorption tests conducted under 80°C hot air showed that the adsorption-saturated material achieved a desorption rate of over 90% within 30 minutes, demonstrating a significantly accelerated desorption rate.

[0067] At 25℃ and RH=60%, the equilibrium adsorption capacity is 0.52 g / g. Its vertical pore structure results in a bed pressure drop of only 30 Pa even at high gas velocities during dynamic adsorption tests, exhibiting extremely low airflow resistance.

[0068] The thin film material exhibits good flexibility and can be bent to a certain extent. Its tensile strength is 2.5 MPa.

[0069] Example 4 This embodiment provides a temperature-responsive N-isopropylacrylamide-based porous gel and its adsorption test for dyes. Weigh out 5.0 g of N-isopropylacrylamide, 100 mL of water / ethanol mixed solvent (volume ratio 7:3), 0.5 g of montmorillonite, 0.05 g of carbon nanotubes, 0.03 g of N,N'-methylenebisacrylamide, 0.025 g of potassium persulfate, and 0.015 g of sodium bisulfite.

[0070] N-Isopropylacrylamide, N,N'-methylenebisacrylamide, montmorillonite, and carbon nanotubes were added to a water / ethanol mixed solvent and then sonicated and stirred to ensure thorough dispersion.

[0071] After purging with nitrogen to remove oxygen, potassium persulfate and sodium bisulfite are added, and the mixture is polymerized at 25°C for 24 hours to form a hydrogel.

[0072] The hydrogel was frozen in a -20°C freezer for 12 hours, and then freeze-dried (-50°C, 40Pa, 48 hours) to obtain a porous material.

[0073] This material exhibits a distinct low critical solution temperature (LCT) characteristic, approximately 32°C. Below the LCT, it swells and becomes hydrophilic, while above the LCT, it shrinks and becomes hydrophobic.

[0074] Utilizing its temperature-responsive properties, it was used to adsorb methylene blue dye from water. At 25℃ (below the lower critical solution temperature), the swollen gel efficiently adsorbed the dye, with a saturated adsorption capacity of up to 180 mg / g. After adsorption saturation, the system was heated to 40℃ (above the lower critical solution temperature), causing the gel to shrink and rapidly desorb the dye, with a desorption rate exceeding 85%, achieving low-temperature adsorption and high-temperature desorption regeneration of the adsorbent.

[0075] BET has a specific surface area of ​​520m². 2 / g, compressive strength 1.0MPa.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. For example, changing the type and proportion of hydrophilic monomers, replacing different types of metal-organic framework materials or nano-doped materials, adjusting the freeze-drying rate and temperature, or combining the post-processing methods in the embodiments, etc. These modifications or substitutions do not depart from the basic principle and spirit of the present invention, which takes "hydrophilic monomers, porous structure guiding agents, and doped materials" as the core and prepares gel adsorbent materials with multi-level pores and hydrophilic surfaces through a "polymerization-freeze-drying" process, and should fall within the protection scope of the present invention.

Claims

1. A method for preparing a porous gel adsorbent material, characterized in that, Includes the following steps: S1. A hydrophilic monomer, a porous structure directing agent, and a dopant are mixed in a solvent to form a homogeneous precursor solution; the porous structure directing agent is an ice crystal template agent or a chemical pore-forming agent; S2. The precursor solution is subjected to a polymerization reaction to form a hydrogel; S3. Freeze-dry the hydrogel to obtain the porous gel adsorbent material.

2. The preparation method according to claim 1, characterized in that, The ice crystal template agent is the solvent itself, which is water or a mixture of water and ethanol. During the freezing process in step S3, the ice crystal template agent crystallizes in situ to form an ice crystal template, and then sublimates during subsequent drying, thereby forming a macroporous structure in the material.

3. The preparation method according to claim 1, characterized in that, The chemical pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate, polyvinyl alcohol, or polyethylene glycol; the chemical pore-forming agent decomposes or dissolves during the polymerization reaction in step S2 or the drying process in step S3, thereby introducing mesopores or macropores into the material.

4. The preparation method according to claim 1, characterized in that, The hydrophilic monomer is selected from at least one of acrylamide, acrylic acid, N-isopropylacrylamide, dimethylaminoethyl methacrylate, or chitosan.

5. The preparation method according to claim 1, characterized in that, The doping material is at least one of nano-silica, montmorillonite, metal-organic framework materials, graphene oxide, or carbon nanotubes.

6. The preparation method according to claim 1, characterized in that, The precursor solution also contains a crosslinking agent; the crosslinking agent is at least one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, or glutaraldehyde.

7. The preparation method according to claim 1, characterized in that, The polymerization reaction in step S2 is solution polymerization, including: S2A1. Add an initiator to the precursor solution; S2A2. Add an accelerator and react at 25~80℃ for 2~12 hours to form the hydrogel.

8. The preparation method according to claim 1, characterized in that, The polymerization reaction in step S2 is a sol-gel process, including: S2B1. Adjust the pH of the precursor solution to 4.0~7.0; S2B2. Perform a hydrolysis-condensation reaction at 40~80℃ for 4~24 hours to form the hydrogel.

9. A porous gel adsorbent material prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The material has a three-dimensional, multi-level pore structure, which includes micropores, mesopores, and macropores; the pore surfaces of the material are distributed with hydrophilic groups.

10. The porous gel adsorbent material according to claim 9, characterized in that, In the multi-level pore structure, the mesopores have a diameter range of 2~50nm, and the macropores have a diameter >50nm; the specific surface area of ​​the material is ≥500m². 2 / g, compressive strength ≥0.8MPa.

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