Preparation method and application of modified graphene oxide

Abstract

The invention belongs to the technical field of graphene, and particularly relates to a preparation method and application of modified graphene oxide. The preparation method of the modified graphene oxide comprises the following steps: (1) pre-modifying graphene oxide by adopting a molecule with a double bond at one end and an amino group at the other end or hydrochloride of the molecule as a modifier to obtain a pre-modified graphene oxide solution; (2) mixing a chain transfer reagent, a propylene monomer, an initiator, a solvent and the pre-modified graphene oxide solution, and reacting to obtain polymer grafted graphene oxide; in the step (1), whether a coupling agent and an activating agent are added or not is selected according to the content of carboxylic acid groups and epoxy groups of graphene oxide in the graphene oxide aqueous solution. According to the preparation method, a surface grafting method is adopted, a specific modifier is adopted for pre-modification, and then polymerization is performed, so that the dispersion stability of graphene oxide in a solvent can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of graphene, and particularly relates to a preparation method and application of modified graphene oxide. Background Art

[0002] Graphene's unique single-atom-layer two-dimensional structure gives it excellent mechanical properties, high electron mobility, strong thermal conductivity and large specific surface area. These excellent properties indicate that it has a 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 has a large specific surface area and is very easy to agglomerate. In addition, the π-π conjugation between graphene sheets makes it difficult to disperse evenly in organic solvents or polymer matrices, which seriously affects the preparation of high-performance composite materials.

[0003] Graphene oxide is a derivative of graphene with a two-dimensional structure similar to graphene. There are abundant oxygen-containing groups on the surface of graphene oxide, such as epoxy, hydroxyl, carboxyl, etc. These polar groups enable graphene oxide to be well dispersed in water, and the functional groups also help to modify graphene oxide by polymer grafting through chemical methods. On the one hand, the grafted polymer can provide steric hindrance and solvent compatibility to promote the dispersion of graphene oxide in solvents of different polarities. On the other hand, they improve the interfacial strength between graphene oxide and the polymer matrix, giving the related composite materials excellent properties.

[0004] At present, the commonly used graphene oxide surface grafting techniques are "grafting to the surface" and "grafting from the surface". The "grafting to the surface" method refers to the reaction of polymer chains with terminal functional groups with graphene oxide surface groups and covalent bonds to graphene oxide; the "grafting from the surface" method refers to the modification of initiators or chain transfer agents to the graphene oxide surface, and then the polymerization of monomers is controlled by them. For "grafting to the surface" and "grafting from the surface", both require the synthesis of new small molecules or polymers that can react with graphene oxide surface groups, and most of the modification processes involve at least one or more harsh reaction conditions that cause graphene oxide to agglomerate or break, such as strong acid and alkali, high temperature, anhydrous and oxygen-free, and high-power ultrasonic dispersion, etc., and the "grafting to the surface" method is limited by steric hindrance, and the polymerization density is low and the molecular weight is not high. At the same time, the graphene oxide grafted by these two methods has poor dispersibility in non-polar solvents, and the repeatability of the experimental results is not high.

[0005] Therefore, it is of great significance to provide a method for preparing modified graphene oxide that can improve the dispersion stability of graphene oxide in a solvent. Summary of the invention

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

[0007] The inventive concept of the present invention: The present invention adopts the "grafting-through" method to achieve the surface grafting of graphene oxide. The "grafting-through" method is to use the double bonds on the initial surface or the double bonds pre-modified to the surface to copolymerize with another monomer, so that the polymer is grafted to the surface of graphene oxide. That is, the present 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, and the amine end is pre-modified on the graphene oxide, and the double bond end participates in the polymerization; and according to the content of the functional groups on the surface of graphene oxide, the coupling agent and the activator combination are selected or not to be added to obtain a pre-modified graphene oxide solution; then, in combination with chain transfer agents, propylene monomers and other components, a polymerization reaction is carried out under specific conditions to obtain a suitable grafting molecular weight and grafting density, which greatly improves 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 method for preparing the modified graphene oxide comprises the following steps:

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

[0011] (2) cooling the first mixture, adding the second mixture to the first mixture, heating, reacting, and obtaining a pre-modified graphene oxide solution;

[0012] (3) mixing a chain transfer agent, a propylene monomer, an initiator, a solvent and the modified graphene oxide solution obtained in step (2), and reacting the mixture to obtain polymer-grafted graphene oxide;

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

[0014] The modifying agent includes a molecule having a double bond at one end and an amine group at the other end, or a hydrochloride thereof.

[0015] Preferably, in step (1), the organic solvent comprises 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°C, and the time of the rotary evaporation is 30-40 min; further preferably, in step (1), the temperature of the rotary evaporation is 50°C, 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 contained in the graphene oxide aqueous solution is replaced with the above-mentioned organic solvent by solvent replacement.

[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 amine group at the other end includes (2-aminoethyl) methacrylate, that is, the modifying agent includes (2-aminoethyl) methacrylate or its hydrochloride.

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

[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 includes 2-(7-azabenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate.

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

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

[0026] Preferably, in step (1), the amounts of the raw material components 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 base, respectively, by weight.

[0027] Further preferably, in step (1), the amounts of the raw material components are 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 base, respectively, by weight.

[0028] Specifically, the mass parts of the above graphene oxide are the amount of graphene oxide in the graphene oxide aqueous solution.

[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; further preferably, the cooling temperature is 0-10°C.

[0031] Preferably, the cooling is carried out by placing the container A in a cold water bath.

[0032] Preferably, in step (2), the second mixture is stirred when 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 heating temperature is room temperature.

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

[0035] Preferably, in step (2), the reaction time is 20-24 h; further preferably, the reaction time is 21-23 h; further preferably, the reaction time is 22 h.

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

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

[0038] Preferably, filtering is performed using a filter membrane, and the filtered solid product, i.e., the pre-modified graphene oxide, is washed, and 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 step (1) and step (2).

[0040] Preferably, in step (3), the chain transfer agent comprises at least one of a thiocarbonylthio compound and a methacrylate polymer containing a double bond at the end.

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

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

[0043] Specifically, the propylene monomer is not limited to the above types, and other free radical polymerizable monomers can be selected as needed.

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

[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 agent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2); further preferably, the amount of the propylene monomer accounts for 15-30% of the total mass of the chain transfer agent, initiator, solvent, propylene monomer, and the pre-modified graphene oxide solution obtained in step (2).

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

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

[0049] Preferably, the amount of the premodified 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 premodified graphene oxide solution obtained in step (2); further preferably, the amount of the premodified 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 premodified graphene oxide solution obtained in step (2); further preferably, the amount of the premodified graphene oxide solution accounts for 1-4% of the total mass of the chain transfer reagent, initiator, solvent, propylene monomer, and the premodified graphene oxide solution obtained in step (2).

[0050] Preferably, the reaction temperature is 60-80°C, and the reaction time is 18-24h; further preferably, the reaction temperature is 65-75°C, 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 more than 65%, and the reaction is terminated by introducing air and cooling to room temperature to obtain polymer-grafted graphene oxide.

[0053] Preferably, the reaction further includes a separation process.

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

[0055] The second aspect of the present invention provides an application of the preparation method described in the first aspect of the present invention in preparing a graphene oxide composite material.

[0056] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0057] (1) The present invention adopts a "grafting-through" method to achieve surface grafting of graphene oxide, that is, the present 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, and the amine end is connected to the graphene oxide for pre-modification, and the double bond end participates in polymerization. According to the content of functional groups on the surface of graphene oxide, a coupling agent and an activator combination are selected to be added or not to obtain a pre-modified graphene oxide solution; then, a chain transfer agent, an propylene monomer and other components are combined to perform a polymerization reaction under specific conditions to maximize the density of small molecules modified on the surface of graphene oxide, and obtain a suitable grafting molecular weight and grafting density, thereby greatly improving the dispersion stability of graphene oxide in solvents (especially non-polar solvents), and the product after drying maintains good redispersibility, and the experimental effect has high repeatability.

[0058] (2) Compared with the "grafting to the surface" method and the "grafting from the surface" method, the "grafting through the surface" method of the present invention only involves two steps of graphene oxide pre-modification and polymer grafting, and the reactants are easily available, the reaction process is mild, and the aggregation of graphene oxide will not be caused. In addition, while reducing the cost, the present invention can increase the grafting amount and grafting density on the graphene oxide surface by changing basic parameters such as monomer concentration, chain transfer agent concentration, initiator concentration and polymerization time, and further improve the dispersion stability of grafted graphene oxide in solvents.

[0059] (3) The present invention can greatly broaden the application scope of graphene oxide by grafting different polymers, and has the potential for large-scale promotion and application and good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[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 Schematic diagram of preparing polymethyl methacrylate-grafted graphene oxide by the "surface grafting" method in Example 1 of the present invention;

[0062] Figure 3 The infrared spectra of the polymethyl methacrylate-grafted graphene oxide and the unmodified graphene oxide obtained in Example 1 of the present invention;

[0063] Figure 4 This is a graph showing the dispersion stability of graphene oxide grafted with polymethyl methacrylate prepared in Example 1 and Comparative Example 2 of the present invention in different solvents;

[0064] Figure 5This is a graph showing the dispersion stability of graphene oxide grafted with polymethyl methacrylate prepared in Example 1, Comparative Example 1, and Comparative Examples 3-5 of the present invention in tetrahydrofuran;

[0065] Figure 6 This is a diagram showing the repeatability and redispersibility of the experimental results of graphene oxide grafted with polymethyl methacrylate in Example 1 of the present invention. DETAILED DESCRIPTION

[0066] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0067] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or 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 comprises the following steps:

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

[0072] The purified GO aqueous solution (1wt.%, 5g) and 20g of organic solvent DMF were mixed and placed in container A, and the water contained in the GO aqueous solution was replaced with DMF by vacuum rotary evaporation; the modifier (2-aminoethyl) methacrylate hydrochloride (0.083g, 0.5mmol, 1eqv.), the coupling agent 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) (0.048g, 0.25mmol, 0.5eqv.), the activator 1-hydroxybenzotriazole (HOBt) (0.034g, 0.25mmol, 0.5eqv.), and the organic solvent DMF were added. 5g and base DIEA (0.194g, 1.5mmol, 3eqv.) were added to container B in sequence 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 under stirring at 800rpm. After the addition was completed, container A was taken out of the ice-water bath, allowed to naturally warm to room temperature and maintained for 22 hours to obtain a pre-modified GO solution ((AMA-GO) solution); the (AMA-GO) solution was precipitated and collected in an acetone solution (300mL) acidified with hydrochloric acid, and then quickly filtered through a polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.22 microns, and the filtered solid product was washed with acetone to obtain purified AMA-GO, which was redispersed in a DMF solution, and the residual acetone was removed by heating to obtain a purified AMA-GO suspension (solid content of 0.32wt.%);

[0073] (2) Preparation of polymer-grafted GO by “surface grafting” method:

[0074] The chain transfer reagent 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic 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 dimethyl sulfoxide 25.95 g were added into 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. Then nitrogen was passed into the mixed solution to expel oxygen, and the solution was placed in a nitrogen atmosphere. The nitrogen was always connected during the polymerization process. The polymerization reaction was carried out at 70°C for 24 h, and the reaction was terminated by passing air and cooling to room temperature. Then, polymethyl methacrylate grafted GO (PMMA-GO) was separated by centrifugation.

[0075] The schematic diagram of the pre-modification of graphene oxide in Example 1 of the present invention is as follows Figure 1 shown.

[0076] The schematic diagram of preparing polymethyl methacrylate grafted graphene oxide by the "surface grafting" method in Example 1 of the present invention is as follows Figure 2 shown.

[0077] Example 2

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

[0079] Specifically, the preparation method of modified graphene oxide in Example 2 comprises 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 obtained is 0.36 wt.%, and the rest is the same as step (1) of Example 1;

[0081] (2) Preparation of polymer-grafted GO by “surface grafting” method:

[0082] The 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 into the reactor to obtain a mixed solution. Under stirring conditions, the monomer MMA (6.94 g, 0.070 mol, 700 eqv.) was added dropwise to the above mixed solution. Then, nitrogen was passed into the mixed solution to expel oxygen, and the solution was placed in a nitrogen atmosphere. The nitrogen was always kept connected during the polymerization process. The polymerization reaction was carried out at 70°C for 22 hours. The reaction was terminated by passing air and cooling to room temperature. Then, polymethyl methacrylate grafted GO (PMMA-GO) was separated by centrifugation.

[0083] Comparative Example 1

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

[0087] Comparative Example 3

[0088] The only difference between Comparative Example 3 and Example 1 is that no activator is added in Comparative Example 3, and the coupling agent is 2-(7-azabenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU) in an amount of 95 mg, 0.25 mmol. The rest is the same as Example 1.

[0089] Comparative Example 4

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

[0091] Comparative Example 5

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

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

[0094] Polymethyl methacrylate PMMA-SH (6 g, number average molecular weight Mn of 30 kDa, molecular weight distribution PDI of 1.6) containing a thiol group at the end, 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 into 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 was passed into the mixed solution to expel oxygen, and the solution was placed in a nitrogen atmosphere, and the nitrogen was always kept connected during the polymerization process. The polymerization reaction was carried out at 70°C for 24 hours, and the reaction was terminated by passing air and cooling to room temperature, and then polymethyl methacrylate-grafted GO was obtained by centrifugation.

[0095] Wherein, the preparation method of AMA-GO suspension is the same as that 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 spectrum test

[0100] The PMMA-GO obtained in Example 1 and the unmodified GO were subjected to infrared spectroscopy test. The infrared spectra are shown in FIG. Figure 3 shown.

[0101] Depend on Figure 3 It can be seen that since the polymer is grafted onto the GO surface, the characteristic peaks in its infrared spectrum are significantly different from the spectrum of GO, which indicates the success of the grafting modification of the GO surface.

[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 and methyl methacrylate (MMA), respectively, and allowed to stand at 25°C for 7 days. Then, the polymethyl methacrylate grafted GO prepared in each group was observed to see whether it agglomerated or precipitated in the above solvents. The results are shown in FIG. Figure 4 As shown. Among them, Figure 4 Figure (a) is a graph showing the dispersion stability of GO grafted with polymethyl methacrylate prepared in Comparative Example 2 in different solvents; Figure 4 Figure (b) shows the dispersion stability of GO grafted with polymethyl methacrylate 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 is dispersed in different solvents, no obvious aggregates and precipitates are observed, and this dispersion result is the dispersion condition after standing for 7 days, indicating that the polymethyl methacrylate grafted GO prepared in Example 1 of the present invention has good dispersion stability in both polar solvents and non-polar solvents, especially in non-polar solvents EtOAc, Toluene and MMA.

[0105] The polymerization time of Comparative Example 2 is 16 hours, so that the polymethyl methacrylate grafted GO prepared in Comparative Example 2 can be dispersed in different solvents, but it cannot remain stable in non-polar reagents EtOAc, Toluene and MMA, and precipitation can be generated within 1 hour, and the dispersion stability is poor. This is because the polymerization time of Comparative Example 2 is short, and the grafting amount and grafting efficiency of its polymer are significantly lower than the product with a polymerization time of 24 hours, which reduces the dispersion stability of the grafted GO in solvents (especially non-polar solvents).

[0106] (2) The polymethyl methacrylate grafted GO prepared in Example 1, Comparative Example 1, and Comparative Examples 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 prepared in each group in THF was then observed. The results are as follows: Figure 5 As shown. Among them, Figure 5 Figure (a) is the dispersion stability result of GO grafted with polymethyl methacrylate in THF in Example 1; Figure 5 Figure (b) is the dispersion stability result of GO grafted with polymethyl methacrylate in THF in Comparative Example 1; Figure 5 Figure (c) is a dispersion stability result diagram of GO grafted with polymethyl methacrylate in THF of Comparative Examples 3 and 4, and the left side diagram of Figure (c) is a dispersion stability result diagram of Comparative Example 3, and the right side diagram of Figure (c) is a dispersion stability result diagram of Comparative Example 4; Figure 5 Figure (d) in the middle is the dispersion stability result of GO grafted with polymethyl methacrylate in THF of Comparative Example 5.

[0107] It can be seen from the results that the polymethyl methacrylate grafted GO prepared in Example 1 did not show agglomeration in THF, and this dispersion result is the dispersion condition after standing for 3 days, indicating that the polymethyl methacrylate grafted GO has good dispersion stability in THF.

[0108] In Comparative Example 1, the modifier (2-aminoethyl) methacrylate hydrochloride was replaced by the modifier hydroxypropyl methacrylate in an equal amount, so that the polymethyl methacrylate-grafted GO prepared in Comparative Example 1 showed obvious agglomeration in THF and had poor dispersion stability. This indicates 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] In Comparative Example 3, no activator was added, so that the polymethyl methacrylate grafted GO prepared in Comparative Example 3 showed obvious agglomeration in THF, and the dispersion stability was poor. 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%, it is necessary to add a coupling agent and an activator at the same time to prepare pre-modified GO.

[0110] Comparative Example 4 uses an activator N-hydroxysuccinimide (NHS) to replace HOBt, so that the polymethyl methacrylate-grafted GO prepared in Comparative Example 4 shows obvious agglomeration in THF, and the dispersion stability is poor. This shows that the specific activator and coupling agent are compounded to improve the dispersion stability of graphene oxide in the solvent.

[0111] Comparative Example 5 adopts the "grafting to the surface" method to prepare GO grafted with polymethyl methacrylate, so that the GO grafted with polymethyl methacrylate prepared in Comparative Example 5 shows obvious agglomeration in THF and has poor dispersion stability. This shows that the present invention adopts a specific "surface grafting" method, that is, the double bonds pre-modified on the surface of GO are copolymerized with the monomer methyl methacrylate, so that the polymer is grafted to the surface of GO, which can improve the dispersion stability of GO in the solvent.

[0112] In addition, Reference 1 of Comparative Example 6 adopts the "grafting from the surface" method to achieve graphene oxide surface grafting. 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] X-ray light scattering (XPS) full spectrum scanning was used to perform elemental analysis on the pre-modified purified AMA-GO and the unpre-modified GO prepared in step (1) of Example 1 and Comparative Example 3-4, respectively. The results are shown in Table 1.

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

[0116] Group Coupling agent and activator combination 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 can be seen from Table 1, different coupling agent and activator combinations will result in different N contents. The N content in the AMA-GO obtained by using the combination of EDC / HOBt 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 will introduce nitrogen elements on the GO surface, so that the nitrogen content in the modified AMA-GO increases, and different coupling agent and activator combinations result in different increases in the corresponding nitrogen content, which means that the small molecular weight introduced into the GO surface is different, that is, the density of the grafting sites is different. The nitrogen content in the AMA-GO of Example 1 is high, which makes the density of the grafting sites large and the grafting amount large, thereby making the dispersion stability of the grafted GO in the solvent better, which is consistent with the above-mentioned dispersibility results.

[0118] 4. Experimental effect repeatability test and redispersibility test

[0119] Two batches of polymethyl methacrylate-grafted GO were independently prepared 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 effect and then observe the repeatability of the experimental effect.

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

[0121] The results are as follows Figure 6 As shown, Figure 6 The left and middle figures in the figure are both the repeatability results of the experimental effect of GO grafted with polymethyl methacrylate in Example 1. Figure 6 The right picture in the figure is a diagram showing the redispersion effect of 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 in two independent experiments have good dispersibility. In addition, the polymethyl methacrylate-grafted GO prepared in Example 1 is redispersed in the solvent after drying and still has good dispersion stability, indicating that the polymethyl methacrylate-grafted GO prepared in the present invention has good redispersibility.

[0123] In summary, the present invention adopts "surface grafting" to graft the polymer onto the surface of graphene oxide, and pre-modifies the graphene oxide through a specific small molecule modifier with a double bond at one end and an amine group at the other end, and the amine end is connected to the graphene oxide for pre-modification, and the double bond end participates in the polymerization, and according to the content of the functional groups on the surface of the graphene oxide, a coupling agent and an activator combination are selected to be added or not to obtain a pre-modified graphene oxide solution; then, a chain transfer agent, an propylene monomer and other components are combined to carry out a polymerization reaction under specific conditions to maximize the density of the small molecules modified on the surface of the graphene oxide, obtain a suitable grafted molecular weight and grafting density, and greatly improve the dispersion stability of the graphene oxide in the solvent.

[0124] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing modified graphene oxide, characterized in that: The following steps are involved: (1) mixing a graphene oxide aqueous solution and an organic solvent, and evaporating them under reduced pressure to obtain a first mixture; when the content of carboxylic acid groups of graphene oxide in the graphene oxide aqueous solution is less than or equal to 2 atom%, and the content of epoxy groups is greater than or equal to 20 atom%, mixing a modifier, an organic solvent, and a base to obtain a second mixture; (2) cooling the first mixture, adding the second mixture to the first mixture, heating, reacting, and obtaining a pre-modified graphene oxide solution; (3) mixing a chain transfer agent, an propylene monomer, an initiator, a solvent and the pre-modified graphene oxide solution obtained in step (2), and reacting the mixture to obtain polymer-grafted graphene oxide; In step (1), when the content of carboxylic acid groups of graphene oxide in the graphene oxide aqueous solution is greater than 2 atom%, and the content of epoxy groups is less than 20 atom%, a coupling agent and an activator are further added to the second mixture; The modifying agent includes a molecule having a double bond at one end and an amine group at the other end, or a hydrochloride thereof.

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 rotary evaporation temperature is 40-50° C., and the rotary evaporation time is 30-40 min.

3. The preparation method according to claim 1, characterized in that: In step (1), the coupling agent includes at least one of a carbodiimide coupling agent and a urea coupling agent; and / or the activator includes at least one of 4-N,N-dimethylpyridine and 1-hydroxybenzotriazole; and / or the base includes a nitrogen-containing organic base.

4. The preparation method according to claim 1, characterized in that: The molecule having a double bond at one end and an amine group at the other end includes (2-aminoethyl) methacrylate.

5. The preparation method according to claim 1, characterized in that: In step (1), the amounts of the raw material components used are respectively 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 base.

6. 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, and the cooling temperature is 0-11°C; and / or, the second mixture is stirred when added to the first mixture, and the stirring speed is 450-1100rpm; and / or, the heating temperature is room temperature; and / or, the reaction time is 20-24h.

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

8. The preparation method according to claim 1, characterized in that: In step (3), the chain transfer agent includes at least one of a thiocarbonylthio compound and a methacrylate polymer containing a double bond at the end; and / or the acrylic monomer includes at least one of methacrylic acid, acrylic acid, acrylamide, methacrylate, acrylic acid ester, acrylamide ester, and acrylonitrile; and / or the initiator includes at least one of an azo initiator and a peroxide initiator; and / or the solvent includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

9. 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 agent, initiator, solvent, propylene monomer and the pre-modified graphene oxide solution obtained in step (2); and / or, the amount of the chain transfer agent 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 agent, initiator, solvent, propylene monomer and the pre-modified graphene oxide solution obtained in step (2); and / or, the reaction temperature is 60-80° C., and the reaction time is 18-24 h.

10. Use of the preparation method according to any one of claims 1 to 9 in preparing graphene oxide composite materials.

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