A high-strength high-elasticity graphene aerogel-based surface molecular imprinting adsorption material and a preparation method thereof

Abstract

The application relates to a high-strength high-elasticity graphene aerogel-based surface molecular imprinting adsorption material. Oxidized graphene is taken as a carbon precursor, ammonium citrate is added for hydrothermal self-assembly, and graphene aerogel is obtained through freeze drying. The graphene aerogel is taken as a substrate, and an imprinting polymer layer is formed through in-situ hydrothermal imprinting reaction of the substrate, phenol template molecules, a vinylpyridine functional monomer and a crosslinking agent. The template molecules are washed away to obtain a macro block-shaped high-mechanical imprinting adsorption material. The imprinting adsorption material has excellent mechanical properties and regeneration, shows good adsorption capacity and selectivity for phenol molecules in a water solution, and can be recycled for multiple times.

Description

Technical Field

[0001] This invention belongs to the field of water treatment adsorption material technology, and relates to adsorption materials for selective adsorption of phenol in wastewater, particularly a surface molecular imprinted adsorption material with high compressive strength and high elasticity. Background Technology

[0002] Industrial wastewater contains a large amount of organic pollutants, with phenol accounting for a significant proportion, posing a serious threat to the natural environment and human health. However, phenol is an important organic chemical raw material with significant applications in synthetic rubber, synthetic fiber, and pharmaceutical production. Therefore, the deep, efficient, non-destructive, and selective adsorption, removal, and enrichment of phenol from industrial wastewater can achieve greater economic benefits while solving environmental pollution problems.

[0003] Surface-imprinted adsorbent materials possess advantages such as high adsorption rate, strong selectivity, non-destructive nature, mild operating conditions, and low equipment investment, making them a highly promising adsorbent material for phenol removal from wastewater. Qu et al. [Carbohydrate Polymers, 2023, 300: 120-268.] used chitosan carbon aerogel as a carrier, 4-vinylpyridine as a functional monomer, and ethylene glycol dimethacrylate as a crosslinking agent to obtain a surface-imprinted bulk adsorbent material with a saturated adsorption capacity of 246.6 mg / g for phenol. Zhang et al. [Separation and Purification Technology, 2021, 274: 119029.] prepared an aerogel using porous carbon nanospheres as a carrier, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a crosslinking agent to prepare a surface-imprinted bulk adsorbent material with a saturated adsorption capacity of 64.02 mg / g for phenol.

[0004] However, these existing carbon aerogel-based surface molecularly imprinted materials, as bulk adsorbents, have poor mechanical properties and are easily damaged during adsorption, resulting in poor regeneration performance of the corresponding imprinted adsorbents and difficulty in increasing the number of cycles.

[0005] Therefore, using graphene aerogel as a carbon precursor to develop a three-dimensional macroscopic bulk structure with high compressive strength elastic carbon aerogel-based surface imprinted adsorbent material has good research and development value and application potential for improving the adsorption and regeneration of imprinted adsorbent materials used for phenol removal from wastewater. Summary of the Invention

[0006] The purpose of this invention is to improve the poor mechanical and regeneration properties of existing macroscopic bulk carbon aerogel-based surface molecularly imprinted adsorbent materials, and to provide a graphene aerogel-based surface molecularly imprinted adsorbent material prepared using graphene oxide as a carbon precursor, as well as a method for preparing the adsorbent material.

[0007] Due to the abundance of oxygen-containing functional groups and superhydrophilic surface of graphene oxide, it is easy to disperse in water. Under hydrothermal treatment, graphene oxide sheets are easily reduced, oxygen-containing functional groups are reduced, the repulsive force between sheets is reduced, and they are interconnected and stacked to form a self-supporting three-dimensional network carbon aerogel framework. This promotes the corresponding graphene aerogel-based surface molecular imprinted adsorbent material to obtain higher mechanical properties and improve the recycling performance of the imprinted adsorbent material.

[0008] Therefore, the high-strength and high-elasticity graphene aerogel-based surface molecular imprinted adsorbent material of the present invention uses graphene aerogel as a matrix, and forms an imprinted polymer layer on the graphene aerogel through in-situ hydrothermal imprinting reaction with phenol template molecules, vinylpyridine functional monomers and crosslinking agents. The assembly of phenol template molecules and functional monomers is fixed in the imprinted polymer layer, and the phenol template molecules are washed away to obtain a three-dimensional macroscopic block-shaped highly recyclable surface molecular imprinted adsorbent material.

[0009] The graphene aerogel is obtained by using graphene oxide as a carbon precursor, reacting it with ammonium citrate in an aqueous solution via hydrothermal reduction to produce self-assembly behavior, and then freeze-drying it.

[0010] The graphene aerogel-based surface molecularly imprinted adsorbent material of the present invention uses graphene oxide as a carbon precursor. This is based on the fact that graphene oxide has a large-size two-dimensional structure and contains abundant oxygen-containing functional groups, which can easily form conjugated π bonds and hydrogen bonds with phenol, thereby improving the overall adsorption capacity of the corresponding graphene aerogel-based surface molecularly imprinted adsorbent material to a certain extent.

[0011] Furthermore, the graphene aerogel-based surface molecular imprinted adsorbent material of the present invention fixes the assembly of phenol and functional monomers in the imprinted polymer layer through in-situ hydrothermal imprinting. After washing away the phenol template molecules, the surface of the adsorbent material is rich in imprinted holes for phenol molecules. Through the action of functional monomers, size and shape matching and other aspects, selective adsorption of phenol molecules can be achieved.

[0012] The graphene aerogel-based surface molecular imprinted adsorbent material of the present invention is a black three-dimensional bulk adsorbent material. Its interior is composed of large-sized graphene sheets that are interconnected and covered with imprinted layers. It has a rich and stable three-dimensional porous structure with mutual cross-linking, which can achieve selective adsorption of phenol molecules in the liquid phase and multiple recycling.

[0013] Furthermore, the present invention also provides a suitable method for preparing the aforementioned high-strength, high-elasticity graphene aerogel-based surface molecularly imprinted adsorbent material:

[0014] 1) Using graphene oxide as a carbon precursor, ammonium citrate is added as a reducing agent to carry out a hydrothermal reaction, which reduces the graphene oxide and causes it to self-assemble. Graphene aerogel is obtained by freeze drying.

[0015] 2) Using the graphene aerogel as a matrix, phenol template molecules, vinylpyridine functional monomers, crosslinking agents and initiators are added to a toluene solvent system. An in-situ hydrothermal imprinting reaction is carried out under an inert atmosphere to fix the assembly of template molecules and functional monomers in the imprinted polymer layer formed on the graphene aerogel matrix, thereby obtaining the imprinting reaction product.

[0016] 3) Elute and remove the phenol template molecules from the imprinted reaction product to obtain a graphene aerogel-based surface molecular imprinted adsorbent material with high recyclability.

[0017] In this invention, graphene oxide with a thickness of 0–1 µm and a single-layer diameter of 0.2–10 µm is preferably used as a carbon precursor.

[0018] Specifically, this invention involves adding an aqueous solution of ammonium citrate dropwise into an aqueous solution of graphene oxide, heating the solution to 100–150°C, and carrying out a hydrothermal reaction for 8–12 hours to reduce the graphene oxide and allow it to self-assemble into a graphene hydrogel.

[0019] Specifically, the mass ratio of graphene oxide to ammonium citrate used in the hydrothermal reaction is 1:3 to 7.

[0020] Preferably, the concentration of the graphene oxide aqueous solution used in the hydrothermal reaction process is 3-5 g / L, and the concentration of the ammonium citrate aqueous solution is 50-80 g / L.

[0021] More preferably, the aqueous solution of graphene oxide needs to be thoroughly stirred and dispersed and subjected to ultrasonic treatment before the reaction, and the ultrasonic treatment time is preferably 1 to 2 hours; the aqueous solution of ammonium citrate also needs to be ultrasonically treated for 5 to 10 minutes.

[0022] In this invention, the ammonium citrate aqueous solution is preferably added dropwise to the graphene oxide aqueous solution at a rate of 3-5 drops per second during ultrasonic treatment. After the addition is complete, the mixed reaction system is ultrasonicated for another 10-15 minutes to ensure that the graphene oxide and ammonium citrate are uniformly mixed in the aqueous solution.

[0023] This invention uses an ethanol-water solution to dialyze the self-assembled graphene hydrogel to remove unreacted raw materials, and then freeze-dries it to form a graphene aerogel.

[0024] Specifically, the volume concentration of the ethanol-water solution used for dialysis is preferably 80-90%, the number of dialysis cycles is 4-6, and the dialysis time is 2-3 days.

[0025] More specifically, the present invention involves freezing and solidifying the dialyzed graphene hydrogel at -80°C, and then freeze-drying it at -80°C for 3 to 5 days to sublimate the solid water in the graphene hydrogel, thereby obtaining a graphene aerogel.

[0026] This invention introduces a functional monomer into the preparation of graphene aerogel-based surface molecularly imprinted adsorbent materials. This functional monomer interacts with phenol template molecules to construct imprinted cavities capable of recognizing and adsorbing phenol. The selection principle for the functional monomer is to ensure a moderate interaction strength with phenol, thereby guaranteeing effective adsorption of phenol by the adsorbent material. Furthermore, it allows for the elution of phenol and the regeneration of the adsorbent material after adsorption.

[0027] Specifically, the present invention preferably uses compounds containing N and O heteroatomic aromatic rings that can interact with phenol molecules via hydrogen bonding or π-π stacking as functional monomers, including but not limited to common functional monomers such as 2-vinylpyridine or 4-vinylpyridine.

[0028] Furthermore, by crosslinking polymerization of a crosslinking agent under the initiation of an initiator, a crosslinked polymer can be formed on the surface of graphene aerogel as an imprinted polymer layer, so as to fix the assembly of phenol template molecules and functional monomers in the imprinted polymer layer.

[0029] Specifically, the crosslinking agent used in this invention is preferably a binary crosslinking agent, including but not limited to conventional binary crosslinking agents such as ethylene glycol dimethacrylate, ethyl methacrylate, and divinylbenzene.

[0030] Meanwhile, the initiator described in this invention is also a conventional initiator used to initiate the crosslinking reaction of the crosslinking agent. For example, azo initiators with low activity can be used, including but not limited to azobisisobutyronitrile, azobisisoheptanenitrile, etc., or inorganic persulfate initiators can be used, including but not limited to ammonium persulfate, potassium persulfate, etc.

[0031] Specifically, in the in-situ hydrothermal imprinting reaction described in this invention, the mass of the phenol template molecule is preferably 5 to 16 times the mass of the graphene aerogel, and the mass of the functional monomer is preferably 3 to 5 times the mass of the phenol template molecule.

[0032] More specifically, the mass of the crosslinking agent is preferably 10 to 20 times the mass of the graphene aerogel, and the mass of the initiator is preferably 0.2 to 0.5 times the mass of the graphene aerogel.

[0033] More specifically, the amount of toluene solvent used in the in-situ hydrothermal imprinting reaction of the present invention is preferably 800 to 1000 times the mass of the graphene aerogel.

[0034] The in-situ hydrothermal imprinting reaction described in this invention needs to be carried out under stirring conditions, with a preferred stirring speed of 400-600 rpm.

[0035] Furthermore, the reaction temperature of the in-situ hydrothermal imprinting reaction described in this invention is 50–70°C, and the reaction time is preferably 14–20 h.

[0036] Furthermore, the inert atmosphere of the in-situ hydrothermal imprinting reaction described in this invention is formed by introducing an inert gas into the reaction system for 10-15 minutes and then sealing it, wherein the inert gas is preferably nitrogen.

[0037] The present invention preferably uses a methanol-acetic acid mixed solution as the eluent to remove phenol template molecules from the imprinted reaction product.

[0038] Specifically, the preferred volume ratio of the methanol-acetic acid mixed solution is 8–12:1. Washing the product of the in-situ hydrothermal imprinting with the mixed solution ensures that the phenol template molecules are fully eluted and removed.

[0039] The washed product is freeze-dried to obtain a graphene aerogel-based surface molecularly imprinted adsorbent material. The freeze-drying process is the same as that for the graphene aerogel described above.

[0040] The resulting graphene aerogel-based surface molecularly imprinted adsorbent material exhibits a three-dimensional macroscopic bulk shape, possessing excellent compressive strength and elasticity. This effectively improves upon the poor mechanical properties and regeneration performance of carbon aerogel-based surface molecularly imprinted adsorbent materials. Testing revealed that the adsorption equilibrium time for phenol in aqueous solution using this graphene aerogel-based surface molecularly imprinted adsorbent material is within 48 hours, with a saturated adsorption capacity reaching 53.1 mg / g. Notably, even after five cycles of use, the adsorption capacity still reaches 96.02% of the initial adsorption value.

[0041] The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent materials of this invention is simple, low-cost, has excellent mechanical properties, good regeneration performance, is convenient to use and operate, and is highly practical. It can be widely used in adsorption, separation, detection and other fields. Attached Figure Description

[0042] Figure 1 The images shown are (a) and (b) of the graphene aerogel-based surface molecularly imprinted adsorbent material, which is the product of Example 1.

[0043] Figure 2 This is a photograph of the compressive strength test of the graphene aerogel-based surface molecularly imprinted adsorbent material, which is the product of Example 1.

[0044] Figure 3 The infrared spectrum of the graphene aerogel-based surface molecularly imprinted adsorbent material, which is the product of Example 1, is shown.

[0045] Figure 4 The thermogravimetric analysis curves (a) and phenol adsorption selectivity (b) of the products of Example 1 and Comparative Example 1 are compared.

[0046] Figure 5 This is a photograph of the compressive strength test of the brittle graphene aerogel-based surface molecularly imprinted adsorbent material, which is the product of Comparative Example 2.

[0047] Figure 6 This is a comparison of the regeneration performance of the products of Example 1(a) and Comparative Example 2(b).

[0048] Figure 7 This is a photograph of the fragile graphene aerogel-based surface molecularly imprinted adsorbent material, which is the product of Comparative Example 3. Implementation

[0049] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.

[0050] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, which are very clear and distinct in the relevant application areas. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0051] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art. Example

[0052] Example 1

[0053] Weigh 0.21 g of graphene oxide into 70 mL of deionized water and sonicate at 25 °C for 1.5 h to disperse it evenly to obtain an aqueous solution of graphene oxide.

[0054] Weigh 1g of ammonium citrate into 20mL of deionized water, and sonicate at 25℃ for 10min to disperse it evenly, thus obtaining an aqueous solution of ammonium citrate.

[0055] Take 3.6 mL of ammonium citrate aqueous solution and add it dropwise to 12 mL of graphene oxide aqueous solution at a rate of 3 drops per second. After the addition is complete, continue to sonicate the mixed reaction system at 25 °C for 15 min. After mixing evenly, place it in a reaction vessel with a polytetrafluoroethylene liner, seal it, and heat it in an oven to 120 °C for hydrothermal reaction for 12 h, so that the graphene oxide is reduced and self-assembled to form a graphene hydrogel.

[0056] The graphene hydrogel was immersed in an 85% ethanol solution for dialysis, with the dialysis solution replaced every 12 hours for four times. After dialysis, the hydrogel was rinsed repeatedly with water. The washed graphene hydrogel was then placed in a -80°C freezer to freeze-solidify the water in the gel, and then freeze-dried in a -80°C freeze-drying oven for 3 days to sublimate the solid water in the gel, thus obtaining graphene aerogel.

[0057] 0.17 g of phenol was weighed as a template molecule and dissolved in 20 mL of toluene solvent. 0.619 g of 4-vinylpyridine functional monomer, 0.316 g of ethylene glycol dimethacrylate crosslinking agent, and 0.008 g of azobisisobutyronitrile initiator were added to obtain a mixed solution. A 0.02 g piece of graphene aerogel was placed in the mixed solution as a matrix. After purging with nitrogen for 15 min, the solution was sealed and subjected to in-situ hydrothermal imprinting at 65 °C for 18 h under continuous magnetic stirring at 500 rpm. An imprinted polymer layer was formed on the graphene aerogel, and the assembly of phenol and functional monomer was fixed in the imprinted polymer layer to obtain the imprinted reaction product.

[0058] A methanol-acetic acid mixture with a volume ratio of 9:1 was used as the eluent to remove phenol template molecules from the imprinted reaction product. The phenol content in the eluent was monitored to ensure complete removal of phenol. The washed product was placed in a -80°C freezer and then freeze-dried in a -80°C freeze-drying oven for 3 days to obtain a three-dimensional macroscopic bulk graphene aerogel-based surface molecular imprinted adsorbent material with high mechanical properties.

[0059] Figure 1 Photograph (a) and field emission scanning electron microscope (FESEM) image (b) of the prepared graphene aerogel-based surface molecularly imprinted adsorbent material are presented. The photograph shows that the imprinted adsorbent material is a black, cylindrical block adsorbent with a cross-sectional diameter of 1.2 cm and a height of 2 cm. The FESEM image reveals that the graphene aerogel-based surface molecularly imprinted adsorbent material has a three-dimensional spatial grid structure formed by large-sized graphene sheets, giving the adsorbent material abundant surface area for phenol adsorption, which contributes to the material's structural stability and adsorption capacity.

[0060] Figure 2These are photos of a pressure test of a graphene aerogel-based surface molecularly imprinted adsorbent material. As can be seen, after applying a 100g weight, the graphene aerogel-based surface molecularly imprinted adsorbent material undergoes 80% longitudinal compression; however, after the weight is removed, the material quickly returns to its initial height.

[0061] from Figure 3 Infrared spectroscopy of graphene aerogel-based surface molecularly imprinted adsorbent materials shows that at 621 and 1621 cm⁻¹... -1 The presence of characteristic peaks for NH2 and C=N functional groups indicates that the introduction of ammonium citrate promotes the reduction of graphene oxide and induces self-assembly, thereby constructing a structurally stable three-dimensional spatial grid structure of graphene sheets.

[0062] Example 2

[0063] Weigh 0.23 g of graphene oxide into 70 mL of deionized water and sonicate at 25 °C for 1.6 h to disperse it evenly to obtain an aqueous solution of graphene oxide.

[0064] Weigh 1.1g of ammonium citrate into 20mL of deionized water, and sonicate at 25℃ for 11min to disperse it evenly, thus obtaining an aqueous solution of ammonium citrate.

[0065] Take 3.7 mL of ammonium citrate aqueous solution and add it dropwise to 12 mL of graphene oxide aqueous solution at a rate of 4 drops per second. After the addition is complete, continue to sonicate the mixed reaction system at 25 °C for 16 min. After mixing evenly, place it in a reaction vessel with a polytetrafluoroethylene liner, seal it, and heat it in an oven to 125 °C for hydrothermal reaction for 11 h, so that the graphene oxide is reduced and self-assembled to form a graphene hydrogel.

[0066] The graphene hydrogel was immersed in an 86% ethanol solution for dialysis, with the dialysis solution changed every 10 hours, for a total of 5 times. After dialysis, the hydrogel was rinsed repeatedly with water. The washed graphene hydrogel was then placed in a -80°C freezer to freeze-solidify the water in the gel, and then freeze-dried in a -80°C freeze-drying oven for 3.5 days to sublimate the solid water in the gel, thus obtaining graphene aerogel.

[0067] 0.17 g of phenol was weighed as a template molecule and dissolved in 19 mL of toluene solvent. 0.619 g of 4-vinylpyridine functional monomer, 0.316 g of ethyl dimethacrylate crosslinking agent, and 0.008 g of ammonium persulfate initiator were added to obtain a mixed solution. A 0.02 g piece of graphene aerogel was placed in the mixed solution as a matrix. After purging with nitrogen for 15 min, the solution was sealed and subjected to in-situ hydrothermal imprinting at 65 °C for 18 h under continuous magnetic stirring at 400 rpm. An imprinted polymer layer was formed on the graphene aerogel, and the assembly of phenol and functional monomer was fixed in the imprinted polymer layer to obtain the imprinted reaction product.

[0068] The phenol template molecules on the imprinted reaction product were removed by eluting with a methanol-acetic acid mixed solution with a volume ratio of 9:1. After washing, the product was placed in a freezer at -80℃ and then freeze-dried in a freeze dryer at -80℃ for 3 days to obtain a graphene aerogel-based surface molecular imprinted adsorbent material.

[0069] Upon testing, its properties and phenol adsorption performance were found to be consistent with the product of Example 1.

[0070] Example 3

[0071] Weigh 0.21 g of graphene oxide into 70 mL of deionized water and sonicate at 25 °C for 1.5 h to disperse it evenly to obtain an aqueous solution of graphene oxide.

[0072] Weigh 1g of ammonium citrate into 20mL of deionized water, and sonicate at 25℃ for 10min to disperse it evenly, thus obtaining an aqueous solution of ammonium citrate.

[0073] Take 3.6 mL of ammonium citrate aqueous solution and add it dropwise to 12 mL of graphene oxide aqueous solution at a rate of 3 drops per second. After the addition is complete, continue to sonicate the mixed reaction system at 25 °C for 15 min. After mixing evenly, place it in a reaction vessel with a polytetrafluoroethylene liner, seal it, and heat it in an oven to 120 °C for hydrothermal reaction for 12 h, so that the graphene oxide is reduced and self-assembled to form a graphene hydrogel.

[0074] The graphene hydrogel was immersed in an 85% ethanol solution for dialysis, with the dialysis solution replaced every 12 hours for four times. After dialysis, the hydrogel was rinsed repeatedly with water. The washed graphene hydrogel was then placed in a -80°C freezer to freeze-solidify the water in the gel, and then freeze-dried in a -80°C freeze-drying oven for 3 days to sublimate the solid water in the gel, thus obtaining graphene aerogel.

[0075] 0.22 g of phenol was weighed as a template molecule and dissolved in 22 mL of toluene solvent. 0.75 g of 2-vinylpyridine functional monomer, 0.4 g of ethylene glycol dimethacrylate crosslinking agent, and 0.009 g of azobisisobutyronitrile initiator were added to obtain a mixed solution. A 0.02 g piece of graphene aerogel was placed in the mixed solution as a matrix. After purging with nitrogen for 15 min, the solution was sealed and subjected to in-situ hydrothermal imprinting at 60 °C for 16 h under continuous magnetic stirring at 600 rpm. An imprinted polymer layer was formed on the graphene aerogel, and the assembly of phenol and functional monomer was fixed in the imprinted polymer layer to obtain the imprinted reaction product.

[0076] The phenol template molecules on the imprinted reaction product were removed by eluting with a methanol-acetic acid mixed solution with a volume ratio of 10:1. After washing, the product was placed in a freezer at -80℃ and then freeze-dried in a freeze dryer at -80℃ for 4 days to obtain a graphene aerogel-based surface molecular imprinted adsorbent material.

[0077] Upon testing, its properties and phenol adsorption performance were found to be consistent with the product of Example 1.

[0078] Comparative Example 1

[0079] Weigh 0.21 g of graphene oxide into 70 mL of deionized water and sonicate at 25 °C for 1.5 h to disperse it evenly to obtain an aqueous solution of graphene oxide.

[0080] Weigh 1g of ammonium citrate into 20mL of deionized water, and sonicate at 25℃ for 10min to disperse it evenly, thus obtaining an aqueous solution of ammonium citrate.

[0081] Take 3.6 mL of ammonium citrate aqueous solution and add it dropwise to 12 mL of graphene oxide aqueous solution at a rate of 3 drops per second. After the addition is complete, continue to sonicate the mixed reaction system at 25 °C for 15 min. After mixing evenly, place it in a reaction vessel with a polytetrafluoroethylene liner, seal it, and heat it in an oven to 120 °C for hydrothermal reaction for 12 h, so that the graphene oxide is reduced and self-assembled to form a graphene hydrogel.

[0082] The graphene hydrogel was immersed in an 85% ethanol solution for dialysis, with the dialysis solution replaced every 12 hours for four times. After dialysis, the hydrogel was rinsed repeatedly with water. The washed graphene hydrogel was then placed in a -80°C freezer to freeze-solidify the water in the gel, and then freeze-dried in a -80°C freeze-drying oven for 3 days to sublimate the solid water in the gel, thus obtaining graphene aerogel.

[0083] To verify the effect of the imprinted polymer layer on the adsorption selectivity of the graphene aerogel-based surface molecularly imprinted adsorbent material, thermogravimetric analysis and adsorption selectivity tests were performed on the graphene aerogel-based surface molecularly imprinted adsorbent material of Example 1 and the unimprinted graphene aerogel of Comparative Example 1.

[0084] Under a nitrogen atmosphere, the thermogravimetric curves of the products of Example 1 and Comparative Example 1 in the temperature range of 100–900°C are as follows: Figure 4 As shown in Figure (a), the total weight loss rates of the two materials are 28.61% and 26.88%, respectively. After imprinting modification, the total weight loss rate of the graphene aerogel-based surface molecular imprinted adsorbent material increases significantly due to the pyrolysis of the surface imprinted polymer layer at high temperature.

[0085] p-Nitrophenol, with a molecular structure similar to phenol, was selected as the interfering molecule. A mixed solution containing both phenol and p-nitrophenol molecules was prepared. The products of Example 1 and Comparative Example 1 were added separately, and adsorption treatment was carried out under the same adsorption conditions. The contents of phenol and p-nitrophenol in the solution after adsorption equilibrium were measured using a UV-Vis spectrophotometer. The adsorption selectivity of the two adsorbents for phenol in the mixed solution was calculated. The results are as follows: Figure 4 As shown in (b).

[0086] It is evident that the graphene aerogel-based surface molecularly imprinted adsorbent material exhibits selectivity, and its adsorption performance is increased compared to Comparative Example 1. This indicates that the imprinted polymer layer enables the graphene aerogel-based surface molecularly imprinted adsorbent material to achieve excellent selective adsorption performance, which is beneficial for the recognition, adsorption, separation, and recovery of phenol from wastewater.

[0087] Comparative Example 2

[0088] Weigh 0.036 g of graphene oxide into 12 mL of deionized water and sonicate at 25 °C for 1.5 h to disperse it evenly to obtain an aqueous solution of graphene oxide.

[0089] Weigh out 0.4g of melamine and 0.4g of terephthalaldehyde, add each to 20mL of dimethyl sulfoxide solution, and sonicate for 15min until uniformly dispersed.

[0090] Take 2 mL each of the above melamine solution and terephthalaldehyde solution, add them to the above graphene oxide aqueous solution, sonicate for 5 min, place the mixed solution in a reaction vessel with a polytetrafluoroethylene liner, seal it, and heat it in an oven to 100℃ for hydrothermal reaction for 10 h, so that the graphene oxide is reduced and self-assembled to form a graphene hydrogel.

[0091] The graphene hydrogel was frozen solidified in a -80℃ freezer and then freeze-dried in a -80℃ freeze-drying oven for 3 days to obtain graphene aerogel.

[0092] 0.17 g of phenol was weighed as a template molecule and dissolved in 20 mL of toluene solvent. 0.619 g of 4-vinylpyridine functional monomer, 0.316 g of ethylene glycol dimethacrylate crosslinking agent, and 0.008 g of azobisisobutyronitrile initiator were added to obtain a mixed solution. A 0.02 g piece of graphene aerogel of this comparative example was placed in the mixed solution as a matrix. After purging with nitrogen for 15 min, the solution was sealed and subjected to in-situ hydrothermal imprinting at 65 °C for 18 h under continuous magnetic stirring at 400 rpm. An imprinted polymer layer was formed on the graphene aerogel, and the assembly of phenol and functional monomer was fixed in the imprinted polymer layer to obtain the imprinting reaction product.

[0093] The phenol template molecules on the imprinted reaction product were removed by eluting with a methanol-acetic acid mixed solution with a volume ratio of 9:1. After washing, the product was placed in a freezer at -80℃ and then freeze-dried in a freeze dryer at -80℃ for 3 days to obtain a three-dimensional brittle graphene aerogel-based surface molecular imprinted adsorbent material.

[0094] Figure 5 These are images of the compressive strength test of the brittle graphene aerogel-based surface molecularly imprinted adsorbent material prepared above. It can be seen that the adsorbent material is compressed by 50% and its structure is damaged after being subjected to a 100g weight; after the weight is removed, the damage to the adsorbent material is obvious and irreversible.

[0095] The regeneration performance of the graphene aerogel-based surface molecularly imprinted adsorbent material prepared in Example 1 and the brittle graphene aerogel-based surface molecularly imprinted adsorbent material prepared in this comparative example were tested.

[0096] The surface-imprinted adsorbent material was placed in a phenol solution. After initial adsorption to equilibrium, the maximum adsorption capacity during the first use was calculated. The saturated adsorbent material was then removed from the phenol solution and thoroughly washed with a methanol-acetic acid mixture to remove phenol molecules. It was then freeze-dried at -80°C for 3 days to obtain regenerated surface-imprinted adsorbent material. This regenerated material was then placed back into a phenol solution, and adsorption tests were performed in the same manner to obtain the maximum adsorption capacity for the second use. Multiple adsorption-elution processes were repeated to determine the regenerated adsorption performance of the adsorbent material.

[0097] Figure 6 In the middle (a) and (b), the regeneration performance of the graphene aerogel-based surface molecular imprinted adsorbent material of Example 1 and the brittle graphene aerogel-based surface molecular imprinted adsorbent material of Comparative Example 2 are compared.

[0098] Figure 6 In (a), the saturated adsorption capacity of the adsorbent material in Example 1 was 53.10 mg / g when used for the first time. After four regenerations, the adsorption capacity dropped to 50.96 mg / g in the fifth use. That is, after four cycles, the adsorption capacity was still 96.02% of the initial value. This is due to its superior mechanical properties, which can maintain the stability of its internal structure during the adsorption process and ensure the good regeneration performance of the imprinted adsorbent material.

[0099] And from Figure 6 As can be seen in (b), after two cycles of use, the adsorption capacity of the adsorbent material in Comparative Example 2 was rapidly lost due to the damage to its structure during use.

[0100] Comparative Example 3

[0101] Weigh 0.21 g of graphene oxide into 70 mL of deionized water and sonicate at 25 °C for 1.5 h to disperse it evenly to obtain an aqueous solution of graphene oxide.

[0102] Weigh 1g of ammonium citrate into 20mL of deionized water, and sonicate at 25℃ for 10min to disperse it evenly, thus obtaining an aqueous solution of ammonium citrate.

[0103] Take 3.6 mL of ammonium citrate aqueous solution and add it dropwise to 12 mL of graphene oxide aqueous solution at a rate of 3 drops per second. After the addition is complete, continue to sonicate the mixed reaction system at 25 °C for 15 min. After mixing evenly, place it in a reaction vessel with a polytetrafluoroethylene liner, seal it, and heat it in an oven to 120 °C for hydrothermal reaction for 12 h, so that the graphene oxide is reduced and self-assembled to form a graphene hydrogel.

[0104] The graphene hydrogel was immersed in an 85% ethanol solution for dialysis, with the dialysis solution replaced every 12 hours for four times. After dialysis, the hydrogel was rinsed repeatedly with water. The washed graphene hydrogel was then placed in a -80°C freezer to freeze-solidify the water in the gel, and then freeze-dried in a -80°C freeze-drying oven for 3 days to sublimate the solid water in the gel, thus obtaining graphene aerogel.

[0105] 0.17 g of phenol template molecules were dissolved in 20 mL of toluene solvent. 34 μL of methacrylic acid functional monomer, 0.419 g of ethylene glycol dimethacrylate crosslinking agent, and 0.065 g of azobisisobutyronitrile initiator were added to obtain a mixed solution. A 0.02 g piece of graphene aerogel was placed in the mixed solution as a matrix. After purging with nitrogen for 10 min, the solution was sealed and subjected to in-situ hydrothermal imprinting at 65 °C for 18 h under continuous magnetic stirring at 700 rpm. An imprinted polymer layer was formed on the graphene aerogel, and the assembly of phenol and functional monomer was fixed in the imprinted polymer layer to obtain the imprinted reaction product.

[0106] Phenol template molecules on the imprinted reaction product were removed by eluting with a methanol-acetic acid mixed solution with a volume ratio of 9:1. After washing, the product was placed in a freezer at -80℃ and then freeze-dried in a freeze dryer at -80℃ for 3 days to obtain a three-dimensional fragile graphene aerogel-based surface molecular imprinted adsorbent material.

[0107] Figure 7 Photographs of the prepared fragile graphene aerogel-based surface molecularly imprinted adsorbent material are provided. Compared to Figure 1 In Example 1, the product is intact and well-formed after imprinting. In contrast, the three-dimensional block structure of this comparative example has been greatly damaged after imprinting, and its loose graphite sheets will fall off in the aqueous phase, making it unusable for subsequent adsorption tests of phenol in the liquid phase.

[0108] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-strength, high-elasticity graphene aerogel-based surface molecularly imprinted adsorbent material, which uses graphene aerogel as a matrix, and forms an imprinted polymer layer on the graphene aerogel through an in-situ hydrothermal imprinting reaction with phenol template molecules, vinylpyridine functional monomers and crosslinking agents. The assembly of phenol template molecules and functional monomers is fixed in the imprinted polymer layer. The phenol template molecules are washed away to obtain a three-dimensional macroscopic block-shaped surface molecularly imprinted adsorbent material that can be recycled and reused multiple times. The graphene aerogel is obtained by using graphene oxide as a carbon precursor, which undergoes a hydrothermal reduction reaction with ammonium citrate in an aqueous solution to produce self-assembly behavior, and then freeze-drying.

2. The preparation method of the graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 1, comprising: 1) Using graphene oxide as a carbon precursor, ammonium citrate is added as a reducing agent to carry out a hydrothermal reaction, so that graphene oxide is reduced and produces self-assembly behavior to form graphene hydrogel, and graphene aerogel is obtained by freeze drying. 2) Using the graphene aerogel as a matrix, phenol template molecules, vinylpyridine functional monomers, crosslinking agents and initiators are added to a toluene solvent system. An in-situ hydrothermal imprinting reaction is carried out under an inert atmosphere to fix the assembly of template molecules and functional monomers in the imprinted polymer layer formed on the graphene aerogel matrix, thereby obtaining the imprinting reaction product. 3) Elute and remove the phenol template molecules from the imprinted reaction product to obtain a graphene aerogel-based surface molecular imprinted adsorbent material with high recyclability.

3. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: With a mass ratio of graphene oxide to ammonium citrate of 1:3 to 7, an aqueous solution of ammonium citrate was added dropwise to an aqueous solution of graphene oxide, and the mixture was heated to 100 to 150°C for a hydrothermal reaction for 8 to 12 hours.

4. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: Graphene hydrogels were dialyzed with an ethanol aqueous solution with a volume concentration of 80-90%, and then freeze-dried to obtain graphene aerogels.

5. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: The vinylpyridine functional monomer is 2-vinylpyridine or 4-vinylpyridine.

6. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: The crosslinking agent is ethylene glycol dimethacrylate, ethyl methacrylate, or divinylbenzene.

7. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: The mass of the phenol template molecule is 5 to 16 times the mass of the graphene aerogel, the mass of the functional monomer is 3 to 5 times the mass of the phenol template molecule, and the mass of the crosslinking agent is 10 to 20 times the mass of the graphene aerogel.

8. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: The in-situ hydrothermal imprinting reaction was carried out in toluene solvent at a stirring speed of 400–600 rpm at a concentration of 800–1000 times the mass of the graphene aerogel.

9. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: The in-situ hydrothermal imprinting reaction was carried out under an inert atmosphere at 50–70°C for 14–20 hours.

10. The method for preparing graphene aerogel-based surface molecularly imprinted adsorbent material according to claim 2, characterized in that: The phenol template molecules were removed by elution with a methanol-acetic acid mixture with a volume ratio of 8 to 12:1.

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