Graphite cycle sieving composite and method of making

Abstract

This invention discloses a graphite circulating sieving composite material and its preparation method. The invention involves mixing graphene oxide with a pore-forming agent to form a three-dimensional graphene framework with vertically oriented pores using ice-templating technology. Subsequently, the mixture is impregnated in a prepolymer solution composed of N-isopropylacrylamide, acrylic acid, and a crosslinking agent for in-situ thermal polymerization, allowing a temperature-sensitive polymer network to grow uniformly within the pores. Finally, the composite material is obtained through chemical reduction. The material prepared by this invention exhibits excellent temperature response characteristics, achieving a sieving selectivity of over 55% within the 25-50℃ temperature range. It also possesses good electrical conductivity and cycling stability (performance retention >94% after 20 cycles), solving the problems of weak interfacial bonding and limited functionality in traditional composite materials, and has broad application prospects in the field of intelligent separation.

Description

Technical Field

[0001] This invention relates to the field of materials science and technology, and in particular to a graphite recycling sieving composite material and its preparation method. Background Technology

[0002] Graphene and its derivatives have been widely used in chemical industries, energy storage, and biomedicine due to their excellent electrical conductivity, thermal stability, and specific surface area. However, traditional graphene materials are mostly two-dimensional sheet structures, which are prone to aggregation during preparation and use, leading to a reduction in effective specific surface area and uneven pore structure, thus limiting their application in molecular sieving, drug controlled release, and catalyst supports. To improve their dispersibility and structural stability, researchers have attempted to construct three-dimensional porous graphene frameworks through gas foaming, self-assembly, or template methods. While these methods have improved the structural integrity and pore connectivity of the materials to some extent, their pore size distribution is usually fixed, lacking responsiveness to external stimuli and failing to achieve dynamic control over mass transfer behavior or molecular sieving processes. On the other hand, thermosensitive polymers such as N-isopropylacrylamide have been used in drug release, separation membranes, and smart sensing systems due to their reversible swelling-shrinkage transformation at different temperatures. However, single polymer materials suffer from insufficient mechanical strength, poor electrical conductivity, and limited structural stability, making them difficult to use in complex chemical and biological environments for extended periods. Existing research has made a few attempts to combine graphene with thermosensitive polymers, but most of these are simple physical mixing or surface coating, resulting in weak interfacial bonding and uneven polymer distribution, leading to poor response rate and structural stability.

[0003] Therefore, there is an urgent need for a graphite-based composite material with controllable structure, strong interfacial bonding, and temperature-responsive sieving function to achieve intelligent regulation of molecular sieving, drug controlled release, and catalytic processes. Summary of the Invention

[0004] One objective of this invention is to propose a graphite recycling sieving composite material and its preparation method. This invention achieves synergistic innovation in graphene porous structure design and thermosensitive polymer composites, overcoming problems such as fixed pore size, weak interfacial bonding, and limited functional response in traditional composite materials, thus providing a new approach and technical path for the development of intelligent functional materials.

[0005] The present invention adopts the following technical solution: Step 1: Mix the graphene oxide dispersion with a pore-forming agent, and form a three-dimensional porous graphene framework with a vertically oriented pore structure by using an ice template-freeze-drying technique; Step 2: Immerse the porous graphene framework in a prepolymer solution containing monomers and crosslinking agents, and carry out an in-situ thermally initiated polymerization reaction under nitrogen protection and in the presence of an initiator, so that the temperature-sensitive polymer network grows and anchors uniformly on the inner wall and surface of the graphene channels. Step 3: After the polymerization reaction is complete, the composite material is taken out, washed, dried, and subjected to chemical reduction treatment to obtain graphite recycling sieve composite material.

[0006] Preferably, the mass ratio of graphene oxide to pore-forming agent in step 1 is 1:(0.5-2).

[0007] Preferably, the pore-forming agent is polyethylene glycol or polyethylene oxide.

[0008] Preferably, the freezing temperature of the ice template in step 1 is -20℃ to -50℃.

[0009] Preferably, the mass ratio of monomer to crosslinking agent in step 2 is 1:(1-5).

[0010] Preferably, the monomer is a mixture of N-isopropylacrylamide and acrylic acid, the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate.

[0011] Preferably, the molar ratio of N-isopropylacrylamide to acrylic acid is (5-8):1.

[0012] Preferably, the polymerization reaction in step 2 is carried out at a temperature of 50-70°C for 4-12 hours.

[0013] Preferably, the reducing agent used in step 3 for chemical reduction treatment is hydrazine hydrate vapor or vitamin C solution, and the reduction treatment time is 6-24 h.

[0014] The beneficial effects of this invention are: This invention provides a method for preparing graphite cyclic sieving composite materials. Vertically oriented channels constructed using ice template technology provide ideal deformation space for the temperature-sensitive polymer. Combined with in-situ polymerization and chemical crosslinking, a uniform distribution and strong interfacial bonding of the polymer network within the graphene framework are achieved. This results in a composite material exhibiting a high temperature-sensitive response sensitivity of 55-63% between 25°C and 50°C, with a low-temperature rejection rate exceeding 85% and a high-temperature rejection rate below 30%, endowing it with electrochemical regulation potential. After 20 temperature cycles, the composite material retains over 94% of its performance, exhibiting excellent mechanical and cyclic stability. It effectively overcomes the problems of fixed pore size, weak interfacial bonding, and slow response found in traditional composite materials, showing broad application prospects in drug controlled release and intelligent catalysis. Detailed Implementation

[0015] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0016] Example 1: This embodiment describes a method for preparing a graphite recycling sieving composite material, comprising the following steps: Step 1: Mix 5g of graphene oxide dispersion with 2.5g of pore-forming agent polyethylene glycol or polyethylene oxide, and form a three-dimensional porous graphene framework with vertically oriented pore structure by ice template-freeze-drying technology at -20℃. Step 2: Add 1.25 mol of N-isopropylacrylamide and 0.25 mol of acrylic acid to the flask, mix well to obtain the monomer; Step 3: The porous graphene framework is immersed in a prepolymer solution containing 4g of monomer and 4g of N,N'-methylenebisacrylamide. Under nitrogen protection and in the presence of 0.8mL of ammonium persulfate, the polymerization reaction is carried out at 50°C for 12 hours to allow the temperature-sensitive polymer network to grow and anchor uniformly on the inner wall and surface of the graphene pores. Step 4: After the polymerization reaction is complete, the composite material is taken out, washed, dried, and chemically reduced using hydrazine hydrate vapor for 6 hours to obtain the graphite circulating sieve composite material.

[0017] Example 2: This embodiment describes a method for preparing a graphite recycling sieving composite material, comprising the following steps: Step 1: Mix 5g of graphene oxide dispersion with 10g of pore-forming agent polyethylene glycol or polyethylene oxide, and form a three-dimensional porous graphene framework with vertically oriented pore structure by ice template-freeze-drying technology at -50℃. Step 2: Add 2 mol of N-isopropylacrylamide and 0.25 mol of acrylic acid to the flask and mix well to obtain the monomer; Step 3: The porous graphene framework is immersed in a prepolymer solution containing 4g of monomer and 20g of N,N'-methylenebisacrylamide. Under nitrogen protection and in the presence of 0.8mL of ammonium persulfate, the polymerization reaction is carried out at 70°C for 4 hours to allow the temperature-sensitive polymer network to grow and anchor uniformly on the inner wall and surface of the graphene pores. Step 4: After the polymerization reaction is complete, the composite material is taken out, washed, dried, and chemically reduced with vitamin C solution for 24 h to obtain graphite circulating sieve composite material.

[0018] Example 3: This embodiment describes a method for preparing a graphite recycling sieving composite material, comprising the following steps: Step 1: Mix 5g of graphene oxide dispersion with 6.25g of pore-forming agent polyethylene glycol or polyethylene oxide, and form a three-dimensional porous graphene framework with vertically oriented pore structure by ice template-freeze-drying technology at -35℃. Step 2: Add 1.125 mol of N-isopropylacrylamide and 0.25 mol of acrylic acid to the flask, mix well to obtain the monomer; Step 3: The porous graphene framework is immersed in a prepolymer solution containing 4g of monomer and 12g of N,N'-methylenebisacrylamide. Under nitrogen protection and in the presence of 0.8mL of ammonium persulfate, the polymerization reaction is carried out at 60°C for 8 hours to allow the temperature-sensitive polymer network to grow and anchor uniformly on the inner wall and surface of the graphene pores. Step 4: After the polymerization reaction is complete, the composite material is taken out, washed, dried, and chemically reduced using hydrazine hydrate vapor for 15 h to obtain the graphite circulating sieve composite material.

[0019] Comparative Example 1: The difference between this comparative example and Example 1 is that room temperature drying molding is used instead of ice template-freeze drying.

[0020] Step 1: Mix 5g of graphene oxide dispersion with 2.5g of pore-forming agent polyethylene glycol or polyethylene oxide, and dry at room temperature to form a film, thereby forming a three-dimensional porous graphene framework. Step 2: Add 1.25 mol of N-isopropylacrylamide and 0.25 mol of acrylic acid to the flask, mix well to obtain the monomer; Step 3: The porous graphene framework is immersed in a prepolymer solution containing 4g of monomer and 4g of N,N'-methylenebisacrylamide. Under nitrogen protection and in the presence of 0.8mL of ammonium persulfate, the polymerization reaction is carried out at 50°C for 12 hours to allow the temperature-sensitive polymer network to grow and anchor uniformly on the inner wall and surface of the graphene pores. Step 4: After the polymerization reaction is complete, the composite material is taken out, washed, dried, and chemically reduced using hydrazine hydrate vapor for 6 hours to obtain the composite material.

[0021] Comparative Example 2: The difference between this comparative example and Example 1 is that acrylic acid is not added.

[0022] Step 1: Mix 5g of graphene oxide dispersion with 2.5g of pore-forming agent polyethylene glycol or polyethylene oxide, and form a three-dimensional porous graphene framework with vertically oriented pore structure by ice template-freeze-drying technology at -20℃. Step 2: The porous graphene framework is immersed in a prepolymer solution containing 1.25 mol of N-isopropylacrylamide and 4 g of N,N'-methylenebisacrylamide. Under nitrogen protection and in the presence of 0.8 mL of ammonium persulfate, the polymerization reaction is carried out at 50 °C for 12 h to allow the temperature-sensitive polymer network to grow and anchor uniformly on the inner wall and surface of the graphene pores. Step 3: After the polymerization reaction is complete, the composite material is taken out, washed, dried, and chemically reduced using hydrazine hydrate vapor for 6 hours to obtain the composite material.

[0023] Comparative Example 3: The difference between this comparative example and Example 1 is that no crosslinking agent is added.

[0024] Step 1: Mix 5g of graphene oxide dispersion with 2.5g of pore-forming agent polyethylene glycol or polyethylene oxide, and form a three-dimensional porous graphene framework with vertically oriented pore structure by ice template-freeze-drying technology at -20℃. Step 2: Add 1.25 mol of N-isopropylacrylamide and 0.25 mol of acrylic acid to the flask, mix well to obtain the monomer; Step 3: Immerse the porous graphene framework in a prepolymer solution containing 4g of monomer, and carry out the polymerization reaction at 50°C for 12 h under nitrogen protection and in the presence of 0.8mL of ammonium persulfate, so that the temperature-sensitive polymer network grows and anchors uniformly on the inner wall and surface of the graphene pores. Step 4: After the polymerization reaction is complete, the composite material is taken out, washed, dried, and chemically reduced using hydrazine hydrate vapor for 6 hours to obtain the composite material.

[0025] Comparative Example 4: The difference between this comparative example and Example 1 is that no chemical reduction treatment is performed after polymerization.

[0026] Step 1: Mix 5g of graphene oxide dispersion with 2.5g of pore-forming agent polyethylene glycol or polyethylene oxide, and form a three-dimensional porous graphene framework with vertically oriented pore structure by ice template-freeze-drying technology at -20℃. Step 2: Add 1.25 mol of N-isopropylacrylamide and 0.25 mol of acrylic acid to the flask, mix well to obtain the monomer; Step 3: The porous graphene framework is immersed in a prepolymer solution containing 4g of monomer and 4g of N,N'-methylenebisacrylamide. Under nitrogen protection and in the presence of 0.8mL of ammonium persulfate, the polymerization reaction is carried out at 50°C for 12 hours to allow the temperature-sensitive polymer network to grow and anchor uniformly on the inner wall and surface of the graphene pores. Step 4: After the polymerization reaction is complete, remove the composite material, wash it, and dry it to obtain the composite material.

[0027] Performance testing 1. Temperature response performance S1. Cut the composite material into original pieces of the same diameter to serve as a filter membrane. Then fix the membrane in the ultrafiltration cup and connect it to a pressurized nitrogen source and a filtrate collection device. S2. Prepare a 100 mg / L dextran standard solution as the test solution; S3. Place the entire ultrafiltration system sequentially in a constant temperature water bath at 25℃ and 50℃ for 15 min to allow the material to fully swell. Filter under a nitrogen pressure of 0.1 MPa, collect the first 10 mL of filtrate, and measure the absorbance of the original solution and filtrate at 490 nm using a UV-Vis spectrophotometer. Calculate the dextran rejection rate. Thermosensitive response sensitivity .

[0028] Table 1 Test Data of Temperature-Sensitive Response Performance

[0029] As shown in Table 1, during the preparation of composite materials in Examples 1-3, the vertically oriented channels formed after ice template-freeze-drying provided ideal growth and deformation space for the polymer. The introduction of appropriate crosslinking agents and acrylic acid enabled the polymer network to undergo significant swelling and shrinkage while maintaining structural stability and response sensitivity. The temperature-sensitive response of the prepared composite material is relatively high. In contrast, Comparative Example 1, due to the lack of directional channels formed by the ice template, has a disordered pore structure and poor connectivity, which severely limits the responsiveness of the polymer network and the transport of molecules, resulting in an extremely weak temperature-sensitive response. Comparative Example 3, without the addition of a crosslinking agent, cannot form a stable network. Although it can shrink at high temperatures, it cannot effectively swell to block the channels at low temperatures, essentially losing its temperature-sensitive sieving function.

[0030] 2 Screening performance The testing method is the same as the testing method for temperature-sensitive response performance.

[0031] Table 2 Screening Performance Test Data

[0032] As shown in Table 2, the retention rate of dextran in Examples 1-3 was as high as 89%-92% at low temperatures, but decreased to 28%-32% at high temperatures, indicating good sieve selectivity. All exceeded 57%, indicating that the synergistic effect of the ice template's qualitative pores and the in-situ polymerized temperature-sensitive polymer network achieved efficient pore size control. In contrast, Comparative Example 1 showed a significant decrease in sieving performance, with the disordered pore structure severely limiting its temperature-sensitive response and molecular sieving ability; Comparative Example 3, lacking a crosslinking agent, resulted in an unstable polymer network, failing to form an effective sieving structure, and almost completely losing its sieving performance.

[0033] 3. Recycling performance The test method is the same as the test method for temperature-sensitive response performance. The composite material sample undergoes step S3 20 times, with the result from the first cycle being used as the starting point. Based on this, calculate the subsequent performance retention rate.

[0034] Table 3 Performance test data for cyclic use

[0035] *** indicates that the function has been largely lost.

[0036] As shown in Table 3, after 20 cycles, the performance retention rate of Examples 1-3 was over 94%, indicating that the polymer network fixed by ice template-freeze-drying technology, in-situ polymerization, and crosslinking agent has a stable and fatigue-resistant composite structure. The polymer network is unlikely to detach from the inner wall of the pores during repeated swelling and shrinkage, and the pore structure remains intact, ensuring long-term performance stability. In contrast, the performance retention rate of Comparative Examples 1, 2, and 4 was as low as 59.8%, indicating poor stability. The composite material prepared in Comparative Example 3 essentially lost its stability because the polymer could not form a network and dissolved or detached from the pores during the first or initial few swelling-shrinkage cycles. However, the sieving function quickly and completely failed.

[0037] 4 Electrical conductivity S1. Cut the composite material into 10 mm × 5 mm rectangles and accurately measure the thickness d of the sample using vernier calipers; S2. Place the four equally spaced metal probes of the resistivity meter parallel to each other and lightly touch the sample surface. Pass a constant small current (I) between the two outer probes and measure the voltage drop (V) between the two inner probes. S3. For thin-film samples, resistivity electrical conductivity .

[0038] Table 4 Conductivity Test Data

[0039] As shown in Table 4, the conductivity of the sample samples in the examples ranged from 0.67 to 0.83 S / cm, indicating that the chemical reduction treatment largely reduced the insulating graphene oxide framework to conductive reduced graphene oxide, forming a continuous electronic conduction pathway. In contrast, the conductivity of Comparative Examples 1-3 decreased significantly, indicating poor conductivity, while the graphene oxide framework of Comparative Example 4 remained unreduced, resulting in extremely low conductivity. This demonstrates that the chemical reduction step is a crucial step in imparting conductivity to the composite material.

[0040] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a graphite cycle sieved composite material, characterized by, Includes the following steps: Step 1: Mix the graphene oxide dispersion with a pore-forming agent, and form a three-dimensional porous graphene framework with a vertically oriented pore structure using an ice template-freeze-drying technique; the pore-forming agent is polyethylene glycol or polyethylene oxide. Step 2: The three-dimensional porous graphene framework is immersed in a prepolymer solution containing monomers and crosslinking agents. Under nitrogen protection and in the presence of an initiator, an in-situ thermally initiated polymerization reaction is carried out to allow the temperature-sensitive polymer network to grow and anchor uniformly on the inner wall and surface of the graphene pores. The monomer is a mixture of N-isopropylacrylamide and acrylic acid, with a molar ratio of N-isopropylacrylamide to acrylic acid of (5-8):

1. The crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate. The temperature of the in-situ thermally initiated polymerization reaction is 50-70℃, and the time is 4-12 h. Step 3: After the polymerization reaction is completed, the composite material is taken out, washed, dried, and then subjected to chemical reduction treatment to obtain the graphite circulating sieve composite material; the reducing agent used in the chemical reduction treatment is hydrazine hydrate vapor or vitamin C solution, and the reduction treatment time is 6-24 h.

2. The method for preparing a graphite recycling sieving composite material according to claim 1, characterized in that, In step 1, the mass ratio of graphene oxide dispersion to pore-forming agent is 1:(0.5-2).

3. The method for preparing a graphite recycling sieving composite material according to claim 1, characterized in that, In step 1, the freezing temperature of the ice template is -20℃ to -50℃.

4. The method for preparing a graphite recycling sieving composite material according to claim 1, characterized in that, In step 2, the mass ratio of monomer to crosslinking agent is 1:(1-5).

5. A graphite cycle sieving composite characterized in that, The graphite circulating sieving composite material is prepared by the preparation method according to any one of claims 1-4.

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