A method for preparing and applying modified graphene oxide

Abstract

This invention belongs to the field of graphene technology, and specifically relates to a method for preparing and applying modified graphene oxide. The method for preparing modified graphene oxide according to this invention includes the following steps: (1) using a molecule containing a double bond at one end and an amine group at the other end, or its hydrochloride salt, as a modifier to pre-modify graphene oxide, obtaining a pre-modified graphene oxide solution; (2) mixing a chain transfer reagent, an propylene monomer, an initiator, a solvent, and the pre-modified graphene oxide solution, and reacting to obtain polymer-grafted graphene oxide; in step (1), whether to add a coupling agent and an activator is selected based on the content of carboxylic acid groups and epoxy groups in the graphene oxide aqueous solution. This invention improves the dispersion stability of graphene oxide in solvents by using a surface grafting method and pre-modifying with a specific modifier before polymerization.

Description

Technical Field

[0001] This invention belongs to the field of graphene technology, and specifically relates to a method for preparing and applying modified graphene oxide. Background Technology

[0002] Graphene's unique single-atom-layer two-dimensional structure endows it with excellent mechanical properties, high electron mobility, strong thermal conductivity, and a large specific surface area. These superior properties indicate its wide range of applications in composite materials and other fields. For example, it can be used as a filler to enhance the mechanical, electrical, thermal, and gas barrier properties of polymers. However, graphene's large specific surface area makes it highly prone to aggregation, and the π-π conjugation between graphene sheets makes it difficult to disperse uniformly in both organic solvents and polymer matrices, severely affecting the preparation of high-performance composite materials.

[0003] Graphene oxide is a derivative of graphene, possessing a similar two-dimensional structure. The surface of graphene oxide is rich in oxygen-containing groups, such as epoxy, hydroxyl, and carboxyl groups. These polar groups enable graphene oxide to disperse well in water, while the functional groups also facilitate polymer grafting modification of graphene oxide through chemical methods. On the one hand, the grafted polymers can provide steric hindrance and solvent compatibility, promoting the dispersion of graphene oxide in different polar solvents; on the other hand, they improve the interfacial strength between graphene oxide and the polymer matrix, endowing the related composite materials with excellent properties.

[0004] Currently, commonly used graphene oxide surface grafting techniques are "grafting-to" and "grafting-from." "Grafting-to" involves reacting polymer chains with terminal functional groups with surface groups of graphene oxide, covalently linking them to the graphene oxide. "Grafting-from" involves modifying the graphene oxide surface with initiators or chain transfer agents, then using these to control monomer polymerization. Both methods require the synthesis of new small molecules or polymers that can react with the surface groups of graphene oxide. Furthermore, the modification process often involves at least one or more harsh reaction conditions that cause graphene oxide agglomeration or fragmentation, such as strong acids and bases, high temperatures, anhydrous and oxygen-free environments, and high-power ultrasonic dispersion. "Grafting-to" is also limited by steric hindrance, resulting in low polymerization density and low molecular weight. Additionally, graphene oxide grafted using these two methods exhibits poor dispersibility in nonpolar solvents, leading to low reproducibility of experimental results.

[0005] Therefore, providing a method for preparing modified graphene oxide that can improve the dispersion stability of graphene oxide in solvents is of great significance. Summary of the Invention

[0006] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative. Specifically, the present invention provides a method for preparing modified graphene oxide, which can avoid the aggregation of graphene oxide and enable graphene oxide to have good dispersion stability in solvents (especially non-polar solvents).

[0007] The inventive concept of this invention is as follows: This invention employs a "grafting-through" method to achieve surface grafting of graphene oxide. The "grafting-through" method utilizes the double bonds present on the initial surface or pre-modified double bonds to copolymerize with another monomer, allowing the polymer to be grafted onto the graphene oxide surface. Specifically, this invention pre-modifies graphene oxide using a specific small-molecule modifier with a double bond at one end and an amine group at the other. The amine group is attached to the graphene oxide for pre-modification, while the double bond participates in the polymerization. Depending on the content of functional groups on the graphene oxide surface, coupling agents and activators are selectively added or not added to obtain a pre-modified graphene oxide solution. Then, combined with chain transfer reagents, propylene monomers, and other components, a polymerization reaction is carried out under specific conditions to obtain suitable graft molecular weight and graft density, significantly improving the dispersion stability of graphene oxide in solvents (especially non-polar solvents).

[0008] Therefore, a first aspect of the present invention provides a method for preparing modified graphene oxide.

[0009] Specifically, the preparation method of the modified graphene oxide includes the following steps:

[0010] (1) Mix the aqueous solution of graphene oxide and the organic solvent, and evaporate under reduced pressure to obtain a first mixture; when the content of carboxylic acid groups of graphene oxide in the aqueous solution of graphene oxide is less than or equal to 2 atom%, and the content of epoxy groups is greater than or equal to 20 atom%, mix the modifier, the organic solvent and the base to obtain a second mixture;

[0011] (2) Cool the first mixture, add the second mixture to the first mixture, heat up, react, and obtain a pre-modified graphene oxide solution;

[0012] (3) Mix the chain transfer reagent, propylene monomer, initiator, solvent and the modified graphene oxide solution obtained in step (2) and react to obtain polymer-grafted graphene oxide.

[0013] In step (1), when the content of carboxylic acid groups of graphene oxide in the aqueous solution of graphene oxide is greater than 2 atom%, and the content of epoxy groups is less than 20 atom%, a coupling agent and an activator are also added to the second mixture.

[0014] The modifier includes a molecule or its hydrochloride salt containing a double bond at one end and an amino group at the other end.

[0015] Preferably, in step (1), the organic solvent includes at least one of dimethylformamide (DMF) and N,N-methylpyrrolidone.

[0016] Preferably, in step (1), the reduced pressure evaporation includes rotary evaporation, the temperature of the rotary evaporation is 40-50℃, and the time of the rotary evaporation is 30-40 min; more preferably, in step (1), the temperature of the rotary evaporation is 50℃, and the time of the rotary evaporation is 30 min.

[0017] Preferably, the rotary evaporation is vacuum rotary evaporation.

[0018] Specifically, in step (1), the water in the aqueous solution of graphene oxide is replaced with the above-mentioned organic solvent by solvent displacement.

[0019] Preferably, in step (1), the components of the first mixture are mixed in container A.

[0020] Preferably, the molecule containing a double bond at one end and an amino group at the other end includes (2-aminoethyl) methacrylate, that is, the modifier includes (2-aminoethyl) methacrylate or its hydrochloride salt.

[0021] Preferably, in step (1), the coupling agent includes at least one of carbodiimide coupling agents and urea coupling agents.

[0022] Preferably, the carbodiimide coupling agent includes at least one of N,N'-dicyclohexylcarbodiimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC).

[0023] Preferably, the urea coupling agent comprises 2-(7-azabenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate.

[0024] Preferably, in step (1), the activator includes 4-N,N-dimethylpyridine and 1-hydroxybenzotriazole (HOBt).

[0025] Preferably, in step (1), the base includes a nitrogen-containing organic base; more preferably, the nitrogen-containing organic base includes at least one of triethylamine, pyridine, and N,N-diisopropylethylamine (DIEA).

[0026] Preferably, in step (1), the amounts of each raw material component are as follows, based on mass parts: 0.5-1.6 parts of graphene oxide, 0.9-1.65 parts of modifier, 0.45-0.80 parts of coupling agent, 0.45-0.80 parts of activator, and 1.8-4.5 parts of alkali.

[0027] More preferably, in step (1), the amounts of each raw material component are as follows, by mass: 0.5-1.5 parts of graphene oxide, 1-1.5 parts of modifier, 0.5-0.75 parts of coupling agent, 0.5-0.75 parts of activator, and 2-4 parts of alkali.

[0028] Specifically, the mass fraction of graphene oxide mentioned above refers to the amount of graphene oxide used in the aqueous solution of graphene oxide.

[0029] Preferably, in step (1), the components of the second mixture are mixed in container B.

[0030] Preferably, in step (2), the first mixture is placed in a cold water bath for cooling, and the cooling temperature is 0-11°C; more preferably, the cooling temperature is 0-10°C.

[0031] Preferably, the container A is placed in a cold water bath for cooling.

[0032] Preferably, in step (2), the second mixture is stirred when it is added to the first mixture, and the stirring speed is 450-1100 rpm; more preferably, the stirring speed is 500-1000 rpm.

[0033] Preferably, in step (2), the temperature of the heating is room temperature.

[0034] Preferably, in step (2), container A is first removed from the cold water bath and then naturally heated to room temperature.

[0035] Preferably, in step (2), the reaction time is 20-24 hours; more preferably, the reaction time is 21-23 hours; and even more preferably, the reaction time is 22 hours.

[0036] Preferably, step (2) further includes a process of separating and purifying the pre-modified graphene oxide solution.

[0037] More preferably, the separation and purification process specifically involves mixing the pre-modified graphene oxide solution and the hydrochloric acid-acidified acetone solution, filtering, and then mixing the solid product with an organic solvent to obtain a purified pre-modified graphene oxide suspension.

[0038] Preferably, a filter membrane is used for filtration, and the filtered solid product, i.e., the pre-modified graphene oxide, is washed. Then, the washed solid product is redispersed in an organic solvent to obtain a purified pre-modified graphene oxide suspension.

[0039] Specifically, the pre-modification of graphene oxide is completed through steps (1) and (2).

[0040] Preferably, in step (3), the chain transfer agent includes at least one of a thiocarbonyl thio compound and a methacrylate polymer with a terminal double bond.

[0041] Preferably, the thiocarbonyl thio compound includes at least one of dithioesters or polymers thereof, dithiocarbamates or polymers thereof, trithiocarbonates or polymers thereof, and xanthate or polymers thereof.

[0042] Preferably, in step (3), the propylene monomer includes at least one of methacrylic acid, acrylic acid, acrylamide, methacrylate, acrylate, acrylamide ester, and acrylonitrile.

[0043] Specifically, the propylene monomers are not limited to the types mentioned above, and other monomers that can be polymerized by free radicals can be selected as needed.

[0044] Preferably, in step (3), the initiator includes at least one of azo initiators and peroxide initiators.

[0045] Preferably, in step (3), the solvent includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0046] Preferably, the amount of the propylene monomer accounts for 13.5-33% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2); more preferably, the amount of the propylene monomer accounts for 15-30% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2).

[0047] Preferably, the amount of chain transfer reagent is less than or equal to 1.1% of the amount of propylene monomer; more preferably, the amount of chain transfer reagent is less than or equal to 1% of the amount of propylene monomer; even more preferably, the amount of chain transfer reagent accounts for 0.1-0.8% of the amount of propylene monomer.

[0048] Preferably, the amount of the initiator is less than or equal to 1.1% of the amount of the propylene monomer; more preferably, the amount of the initiator is less than or equal to 1% of the amount of the propylene monomer; even more preferably, the amount of the initiator is 0.1-0.3% of the amount of the propylene monomer.

[0049] Preferably, the amount of the pre-modified graphene oxide solution is less than or equal to 5.5% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2); more preferably, the amount of the pre-modified graphene oxide solution is less than or equal to 5% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2); even more preferably, the amount of the pre-modified graphene oxide solution accounts for 1-4% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2).

[0050] Preferably, the reaction temperature is 60-80℃ and the reaction time is 18-24h; more preferably, the reaction temperature is 65-75℃ and the reaction time is 22-24h.

[0051] Preferably, the reaction is carried out in a nitrogen atmosphere.

[0052] Specifically, through the reaction, the conversion rate can reach over 65%, and the reaction is terminated by introducing air and cooling to room temperature to obtain polymer-grafted graphene oxide.

[0053] Preferably, the reaction is followed by a separation process.

[0054] Preferably, the separation method includes any one of centrifugation, dialysis, and filtration.

[0055] A second aspect of the present invention provides an application of the preparation method described in the first aspect of the present invention in the preparation of graphene oxide composite materials.

[0056] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0057] (1) This invention uses the "grafting-through" method to achieve surface grafting of graphene oxide. That is, this invention pre-modifies graphene oxide by using a specific small molecule modifier with a double bond at one end and an amine group at the other end. The amine end is attached to the graphene oxide for pre-modification, and the double bond end participates in polymerization. Depending on the content of functional groups on the surface of graphene oxide, coupling agents and activators are added or not added to obtain a pre-modified graphene oxide solution. Then, combined with chain transfer reagents, propylene monomers and other components, a polymerization reaction is carried out under specific conditions to maximize the density of small molecules modified on the surface of graphene oxide, obtain a suitable grafting molecular weight and grafting density, greatly improve the dispersion stability of graphene oxide in solvents (especially non-polar solvents), and the dried product maintains good redispersibility. The experimental results have high repeatability.

[0058] (2) Compared to the "grafting to surface" and "grafting from surface" methods, the "grafting via surface" method of this invention only involves two steps: pre-modification of graphene oxide and polymer grafting. Furthermore, the reactants are readily available, the reaction process is mild, and it does not cause graphene oxide aggregation. In addition, while reducing costs, this invention can improve the grafting amount and density on the graphene oxide surface by changing fundamental parameters such as monomer concentration, chain transfer agent concentration, initiator concentration, and polymerization time, thereby further improving the dispersion stability of grafted graphene oxide in solvents.

[0059] (3) By grafting different polymers, the present invention can greatly broaden the application range of graphene oxide, and has the potential for large-scale application and good economic benefits. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the pre-modification of graphene oxide in Example 1 of the present invention;

[0061] Figure 2 This is a schematic diagram of the preparation of polymethyl methacrylate-grafted graphene oxide by the "surface grafting" method in Example 1 of the present invention;

[0062] Figure 3 The infrared spectra of polymethyl methacrylate-grafted graphene oxide and unmodified graphene oxide obtained in Example 1 of this invention are shown.

[0063] Figure 4 The graph shows the dispersion stability of polymethyl methacrylate-grafted graphene oxide prepared in Examples 1 and 2 of this invention in different solvents.

[0064] Figure 5The dispersion stability diagram of polymethyl methacrylate-grafted graphene oxide prepared in Example 1, Comparative Example 1, and Comparative Examples 3-5 of this invention in tetrahydrofuran.

[0065] Figure 6 The diagram shows the repeatability and redispersion of the polymethyl methacrylate-grafted graphene oxide in Example 1 of this invention. Detailed Implementation

[0066] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0067] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0068] Example 1

[0069] In Example 1, the content of carboxylic acid groups O=CO on the surface of the graphene oxide raw material was 6.37 atom%, and the content of epoxy groups COC was 14.13 atom%.

[0070] A method for preparing modified graphene oxide includes the following steps:

[0071] (1) Pre-modification of graphene oxide (GO):

[0072] The purified GO aqueous solution (1 wt.%, 5 g) and the organic solvent DMF (20 g) were mixed and placed in container A. Solvent displacement was performed by vacuum rotary evaporation to replace the water in the GO aqueous solution with DMF. The following components were added: (2-aminoethyl) methacrylate hydrochloride (0.083 g, 0.5 mmol, 1 eqv.), coupling agent 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) (0.048 g, 0.25 mmol, 0.5 eqv.), activator 1-hydroxybenzotriazole (HOBt) (0.034 g, 0.25 mmol, 0.5 eqv.), and organic solvent DMF. 5 g of DIEA and 0.194 g of alkali DIEA (3 eqv.) were added sequentially to container B and stirred to dissolve. Container A was placed in an ice-water bath (4 °C) to cool, and the solution in container B was added dropwise to container A while stirring at 800 rpm. After the addition was completed, container A was removed from the ice-water bath and allowed to naturally warm to room temperature and be kept there for 22 hours to obtain a pre-modified GO solution ((AMA-GO) solution). The (AMA-GO) solution was precipitated and collected in acetone solution (300 mL) acidified with hydrochloric acid, and then rapidly filtered through a polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.22 μm. The filtered solid product was washed with acetone to obtain purified AMA-GO, which was then redispersed in DMF solution and heated to remove residual acetone to obtain a purified AMA-GO suspension (solid content of 0.32 wt.%).

[0073] (2) Preparation of polymer-grafted GO using the "surface grafting" method:

[0074] Chain transfer reagent 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid (CDPT) (0.04 g, 0.099 mmol, 1 eqv.), AMA-GO suspension (13.39 g, 0.32 wt.%), initiator 4,4'-azobis(4-cyanovaleric acid) (ACVA) (6.6 mg, 0.0198 mmol, 0.2 eqv.), and solvent 25.95 g of dimethyl sulfoxide were added to the reactor to obtain a mixed solution. Under stirring conditions, monomer methyl methacrylate (MMA) (6.94 g, 0.070 mol, 700 eqv.) was added dropwise to the above mixed solution. Nitrogen gas was then introduced into the mixed solution to purge oxygen, and the reactor was placed in a nitrogen atmosphere. Nitrogen gas was maintained throughout the polymerization process. The polymerization reaction was carried out at 70 °C for 24 h. The reaction was terminated by introducing air and cooling to room temperature. The polymethyl methacrylate-grafted GO (PMMA-GO) was then separated by centrifugation.

[0075] A schematic diagram of the pre-modification of graphene oxide in Example 1 of this invention is shown below. Figure 1 As shown.

[0076] A schematic diagram of the preparation of polymethyl methacrylate-grafted graphene oxide by surface grafting in Example 1 of this invention is shown below. Figure 2 As shown.

[0077] Example 2

[0078] In Example 2, the content of carboxylic acid groups O=CO on the surface of the GO raw material was 1.13 atom%, and the content of epoxy groups COC was 31.11 atom%. Therefore, the main difference between Example 2 and Example 1 is that no coupling agent or activator was added during the pre-modification process of GO in Example 2.

[0079] Specifically, the preparation method of modified graphene oxide in Example 2 includes the following steps:

[0080] (1) Pre-modification of GO: The only difference between step (1) and step (1) of Example 1 is that no coupling agent and activator are added, and the solid content of the purified AMA-GO suspension is 0.36 wt.%, and the rest is the same as step (1) of Example 1.

[0081] (2) Preparation of polymer-grafted GO using the "surface grafting" method:

[0082] Chain transfer reagent CDPT (0.04 g, 0.099 mmol, 1 eqv.), AMA-GO suspension (13.15 g, 0.36 wt.%), initiator ACVA (6.6 mg, 0.0198 mmol, 0.2 eqv.), and solvent dimethyl sulfoxide (25.5 g) were added to the reactor to obtain a mixed solution. Under stirring, monomer MMA (6.94 g, 0.070 mol, 700 eqv.) was added dropwise to the above mixed solution. Nitrogen gas was then introduced into the mixed solution to purge oxygen, and the reactor was placed in a nitrogen atmosphere. Nitrogen gas was maintained throughout the polymerization process. The polymerization reaction was carried out at 70 °C for 22 h. The reaction was terminated by introducing air and cooling to room temperature. The polymethyl methacrylate-grafted GO (PMMA-GO) was then separated by centrifugation.

[0083] Comparative Example 1

[0084] The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses an equal amount of hydroxypropyl methacrylate to replace the (2-aminoethyl) methacrylate hydrochloride modifier, while the rest is the same as in Example 1.

[0085] Comparative Example 2

[0086] The only difference between Comparative Example 2 and Example 1 is that in step (2) of Comparative Example 2, the polymerization reaction time is 16 hours, while the rest is the same as in Example 1.

[0087] Comparative Example 3

[0088] The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not add an activator, and the coupling agent used is 2-(7-azabenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate (HATU), with an amount of 95 mg and 0.25 mmol. The rest is the same as in Example 1.

[0089] Comparative Example 4

[0090] The only difference between Comparative Example 4 and Example 1 is that Comparative Example 4 uses 29 mg, 0.25 mmol of N-hydroxysuccinimide (NHS) as the activator instead of HOBt in Example 1. Otherwise, they are the same as in Example 1.

[0091] Comparative Example 5

[0092] Comparative Example 5 uses the "grafting to surface" method to prepare polymethyl methacrylate-grafted GO.

[0093] The specific preparation method of Comparative Example 5 includes the following steps:

[0094] A mixture of 6 g of thiol-terminated polymethyl methacrylate (PMMA-SH, number-average molecular weight Mn of 30 kDa, molecular weight distribution PDI of 1.6), 13.15 g of AMA-GO suspension (0.36 wt.%), initiator ACVA (6.6 mg, 0.0198 mmol, 0.2 eqv.), and 25.5 g of dimethyl sulfoxide solvent was added to a reactor to obtain a mixed solution. Under stirring, monomer MMA (7 g, 0.07 mol) was added dropwise to the above mixed solution. Nitrogen gas was introduced into the mixed solution to purge oxygen, and the reactor was placed in a nitrogen atmosphere. Nitrogen gas was kept on throughout the polymerization process. The polymerization reaction was carried out at 70 °C for 24 h. The reaction was terminated by introducing air and cooling to room temperature. The polymethyl methacrylate-grafted GO was then obtained by centrifugation.

[0095] The preparation method of the AMA-GO suspension is the same as in Example 1.

[0096] Comparative Example 6

[0097] Comparative Example 6 is reference 1 (Lee, SH; Dreyer, DR; An, J.; Velamakanni, A.; Piner, RD; Park, S.; Zhu, Y.; Kim, SO; Bielawski, CW; Ruoff, RS Polymer Brushes via Controlled, Surface-Initiated Atom Radical Polymerization Transfer (ATRP) from Graphene Oxide. Macromol. Rapid Commun. 2010, 31, 281–288), Document 2 (Ohno, K.; Zhao, C.; Nishina, Y. Polymer-Brush-Decorated Graphene Oxide: Precision Synthesis and Liquid-Crystal Formation. Langmuir 2019, 35(33), 10900–10909).

[0098] Performance testing

[0099] 1. Infrared spectroscopy test

[0100] Infrared spectroscopy tests were performed on the PMMA-GO obtained in Example 1 and the unmodified GO. The infrared spectra are shown below. Figure 3 As shown.

[0101] Depend on Figure 3 As can be seen, the characteristic peaks in the infrared spectrum of the polymer grafted onto the GO surface are significantly different from those of GO, indicating the success of the GO surface grafting modification.

[0102] 2. Observation of dispersion stability

[0103] (1) The polymethyl methacrylate-grafted GO prepared in Example 1 and Comparative Example 2 were dispersed in 2-butanone (MEK), tetrahydrofuran (THF), ethyl acetate (EtOAc), toluene (Toluene), and methyl methacrylate (MMA), respectively, and allowed to stand at 25°C for 7 days. Then, it was observed whether the polymethyl methacrylate-grafted GO prepared in each group agglomerated or precipitated in the above solvents. The results are as follows: Figure 4 As shown. Among them, Figure 4 Figure (a) shows the dispersion stability of polymethyl methacrylate-grafted GO prepared in Comparative Example 2 in different solvents. Figure 4 Figure (b) shows the dispersion stability of the polymethyl methacrylate-grafted GO prepared in Example 1 in different solvents.

[0104] Depend on Figure 4 It can be seen that after the polymethyl methacrylate-grafted GO prepared in Example 1 was dispersed in different solvents, no obvious aggregates or precipitates were observed. Moreover, this dispersion result is the dispersion situation after standing for 7 days. This indicates that the polymethyl methacrylate-grafted GO prepared in Example 1 of the present invention has good dispersion stability in both polar and non-polar solvents, especially in non-polar solvents such as EtOAc, Toluene and MMA.

[0105] Comparative Example 2, with a polymerization time of 16 hours, resulted in the polymethyl methacrylate-grafted GO prepared in Comparative Example 2 being able to disperse in polar solvents, but failing to maintain stability in non-polar reagents such as EtOAc, Toluene, and MMA, precipitating within 1 hour, indicating poor dispersion stability. This is because the shorter polymerization time of Comparative Example 2 resulted in significantly lower grafting amount and efficiency compared to the product with a polymerization time of 24 hours, reducing the dispersion stability of the grafted GO in solvents (especially non-polar solvents).

[0106] (2) The polymethyl methacrylate-grafted GO prepared in Examples 1, 1, and 3-5 were dispersed in tetrahydrofuran (THF) and allowed to stand at 25°C for 3 days. The dispersion stability of the polymethyl methacrylate-grafted GO in THF was then observed. The results are as follows: Figure 5 As shown. Among them, Figure 5 Figure (a) shows the dispersion stability of GO grafted with polymethyl methacrylate in THF in Example 1. Figure 5 Figure (b) shows the dispersion stability of GO grafted with polymethyl methacrylate in THF in Comparative Example 1. Figure 5 Figure (c) shows the dispersion stability results of GO grafted with polymethyl methacrylate in THF for Comparative Examples 3 and 4. The left side of Figure (c) shows the dispersion stability results of Comparative Example 3, and the right side of Figure (c) shows the dispersion stability results of Comparative Example 4. Figure 5 Figure (d) shows the dispersion stability of GO grafted with polymethyl methacrylate in THF, as described in Comparative Example 5.

[0107] The results show that the polymethyl methacrylate-grafted GO prepared in Example 1 did not exhibit agglomeration in THF, and this dispersibility result is the dispersion after standing for 3 days, indicating that the polymethyl methacrylate-grafted GO has good dispersion stability in THF.

[0108] In Comparative Example 1, hydroxypropyl methacrylate was used to replace an equal amount of (2-aminoethyl) methacrylate hydrochloride as the modifier. This resulted in significant agglomeration of the polymethyl methacrylate-grafted GO prepared in Comparative Example 1 in THF, exhibiting poor dispersion stability. This demonstrates that the present invention uses a specific modifier to pre-modify GO, which can improve the dispersion stability of GO in the solvent THF.

[0109] Comparative Example 3, without the addition of an activator, showed significant agglomeration and poor dispersion stability in THF of the polymethyl methacrylate-grafted GO prepared in Comparative Example 3. This indicates that when the content of carboxylic acid groups in graphene oxide is greater than 2 atom%, and the content of epoxy groups is less than 20 atom%, both coupling agents and activators need to be added simultaneously to prepare pre-modified GO.

[0110] Comparative Example 4 used N-hydroxysuccinimide (NHS) as the activator to replace HOBt, resulting in significant agglomeration of the polymethyl methacrylate-grafted GO prepared in Comparative Example 4 in THF, exhibiting poor dispersibility and stability. This demonstrates that specific combinations of activators and coupling agents can improve the dispersion stability of graphene oxide in solvents.

[0111] Comparative Example 5 used a "grafting to surface" method to prepare polymethyl methacrylate-grafted GO. The polymethyl methacrylate-grafted GO prepared in Comparative Example 5 exhibited significant agglomeration in THF, resulting in poor dispersion stability. This indicates that the present invention employs a specific "surface grafting" method, utilizing pre-modified double bonds on the GO surface to copolymerize with the monomer methyl methacrylate, thereby grafting the polymer onto the GO surface and improving the dispersion stability of GO in solvents.

[0112] Furthermore, Reference 1 of Comparative Example 6 uses the "surface grafting" method to achieve surface grafting of graphene oxide, while Reference 2 points out that directly using this method cannot achieve the dispersibility and stability of GO in non-polar organic solvents.

[0113] 3. Elemental Analysis

[0114] Elemental analysis was performed on the pre-modified purified AMA-GO and unmodified GO prepared in step (1) of Example 1 and Comparative Examples 3-4 using X-ray light scattering (XPS) full-spectrum scanning. The results are shown in Table 1.

[0115] Table 1: Elemental analysis results of pre-modified purified AMA-GO and unmodified GO prepared in step (1) of Examples 1 and Comparative Examples 3-4

[0116] Group Combination of coupling agents and activators C O N S Example 1 EDC / HOBt 69.6 28.1 2.2 0.1 Comparative Example 3 HATU 70.3 27.5 2 0.2 Comparative Example 4 EDC / NHS 70.4 27.9 1.6 0.1 GO none 68.9 30.2 0.6 0.3

[0117] As shown in Table 1, different combinations of coupling agents and activators result in different nitrogen contents. The nitrogen content in AMA-GO obtained using the EDC / HOBt combination in Example 1 is higher than that in Comparative Examples 3 and 4. This is because the present invention uses nitrogen-containing small molecules for pre-modification, which introduces nitrogen elements into the GO surface, increasing the nitrogen content in the modified AMA-GO. Different combinations of coupling agents and activators result in different increases in nitrogen content, which means that the small molecular weights introduced into the GO surface are different, i.e., the density of grafting sites is different. The high nitrogen content in AMA-GO of Example 1 results in a high density of grafting sites and a large grafting amount, which in turn leads to better dispersion stability of the grafted GO in the solvent, consistent with the above dispersion results.

[0118] 4. Repeatability test and redispersion test of experimental results

[0119] Two batches of polymethyl methacrylate-grafted GO were prepared independently according to the scheme of Example 1, and dispersed in THF respectively. They were left to stand at 25°C for 3 days to observe the dispersion stability and then to observe the repeatability of the experimental effect.

[0120] After the dispersion stability test of polymethyl methacrylate-grafted GO in THF solvent in Example 1 was completed, it was dried and then dispersed in THF. It was then allowed to stand at 25°C for 3 days to observe the dispersion stability effect, and thus determine whether the polymethyl methacrylate-grafted GO in Example 1 has good redispersibility.

[0121] The results are as follows Figure 6 As shown, where, Figure 6 The left and middle images in the figure are both diagrams showing the repeatability results of the GO experiment for polymethyl methacrylate grafted in Example 1. Figure 6 The right-hand figure in the image shows the effect of redispersing GO grafted with polymethyl methacrylate in Example 1.

[0122] Depend on Figure 6 It can be seen that the preparation method of Example 1 has good repeatability, and the products obtained from the two independent experiments both have good dispersibility. In addition, the polymethyl methacrylate-grafted GO prepared in Example 1 still has good dispersion stability after being dried and redispersed in the solvent, indicating that the polymethyl methacrylate-grafted GO prepared in this invention has good redispersibility.

[0123] In summary, this invention employs a "surface grafting" method to graft polymers onto the surface of graphene oxide. Graphene oxide is pre-modified using a specific small-molecule modifier with a double bond at one end and an amine group at the other. The amine group is attached to the graphene oxide for pre-modification, while the double bond participates in polymerization. Depending on the content of functional groups on the graphene oxide surface, coupling agents and activators are selectively added or omitted to obtain a pre-modified graphene oxide solution. Then, combined with chain transfer reagents, propylene monomers, and other components, a polymerization reaction is carried out under specific conditions to maximize the density of small-molecule modifications on the graphene oxide surface, obtaining suitable graft molecular weight and graft density, which greatly improves the dispersion stability of graphene oxide in solvents.

[0124] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing modified graphene oxide, characterized in that, Includes the following steps: (1) Mix the aqueous solution of graphene oxide and the organic solvent, and evaporate under reduced pressure to obtain a first mixture; when the content of carboxylic acid groups of graphene oxide in the aqueous solution of graphene oxide is less than or equal to 2 atom%, and the content of epoxy groups is greater than or equal to 20 atom%, mix the modifier, the organic solvent and the base to obtain a second mixture; (2) Cool the first mixture, add the second mixture to the first mixture, heat up, react, and obtain a pre-modified graphene oxide solution; (3) Mix the chain transfer reagent, propylene monomer, initiator, solvent and the pre-modified graphene oxide solution obtained in step (2), and react to obtain polymer-grafted graphene oxide. In step (1), when the content of carboxylic acid groups of graphene oxide in the aqueous solution of graphene oxide is greater than 2 atom%, and the content of epoxy groups is less than 20 atom%, a coupling agent and an activator are also added to the second mixture. The coupling agent includes at least one of carbodiimide coupling agents and urea coupling agents; the activator includes at least one of 4-N,N-dimethylpyridine and 1-hydroxybenzotriazole. The modifier is (2-aminoethyl) methacrylate or its hydrochloride salt.

2. The preparation method according to claim 1, characterized in that, In step (1), the organic solvent includes at least one of dimethylformamide and N,N-methylpyrrolidone; and / or, the reduced pressure evaporation includes rotary evaporation, the temperature of the rotary evaporation is 40-50°C, and the time of the rotary evaporation is 30-40 min.

3. The preparation method according to claim 1, characterized in that, In step (1), the base includes nitrogen-containing organic bases.

4. The preparation method according to claim 1, characterized in that, By mass fraction, in step (1), the amounts of each raw material component are 0.5-1.6 parts of graphene oxide, 0.9-1.65 parts of modifier, 0.45-0.80 parts of coupling agent, 0.45-0.80 parts of activator, and 1.8-4.5 parts of alkali.

5. The preparation method according to claim 1, characterized in that, In step (2), the first mixture is placed in a cold water bath for cooling at a temperature of 0-11°C; and / or, the second mixture is added to the first mixture and stirred at a speed of 450-1100 rpm; and / or, the temperature for heating is room temperature; and / or, the reaction time is 20-24 h.

6. The preparation method according to any one of claims 1-5, characterized in that, Step (2) also includes the process of separating and purifying the pre-modified graphene oxide solution.

7. The preparation method according to claim 1, characterized in that, In step (3), the chain transfer agent includes at least one of thiocarbonyl thio compounds and methacrylate polymers with terminal double bonds; and / or, the propylene monomer includes at least one of methacrylates, acrylic acids, acrylamides, methacrylates, acrylates, acrylamide esters, and acrylonitrile; and / or, the initiator includes at least one of azo initiators and peroxide initiators; and / or, the solvent includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

8. The preparation method according to claim 1, characterized in that, The amount of the propylene monomer is 13.5-33% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2); and / or, the amount of the chain transfer reagent is less than or equal to 1.1% of the amount of the propylene monomer; and / or, the amount of the initiator is less than or equal to 1.1% of the amount of the propylene monomer; and / or, the amount of the pre-modified graphene oxide solution is less than or equal to 5.5% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2); and / or, the reaction temperature is 60-80℃, and the reaction time is 18-24h.

9. The application of the preparation method according to any one of claims 1-8 in the preparation of graphene oxide composite materials.

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