CN114314576B - Graphene oxide carboxyl functional modification method - Google Patents
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Abstract
The invention provides a method for modifying carboxyl groups of graphene oxide, which comprises the steps of taking graphene oxide as a raw material, reducing the graphene oxide by alkali to generate defect sites in a basal plane of the graphene oxide, and oxidizing the graphene oxide generating the defect sites by an oxidant to obtain carboxyl groups at the defect sites of the graphene oxide; the oxidant is potassium permanganate and concentrated sulfuric acid, or potassium permanganate and perchloric acid. According to the reduction mechanism of graphene oxide, a simple alkali reduction reaction is adopted, and hole-shaped defect sites are formed on a graphene basal plane while edge carboxyl groups are not reduced, and the defect sites are increased by the defects. Through further oxidation, a new carboxyl directly connected with graphene carbon atoms is obtained at the defect, and the carboxylation degree of graphene oxide is integrally improved while the hydroxyl and epoxy groups are reduced.
Description
Technical Field
The invention belongs to the technical field of graphene oxide, relates to graphene oxide modification, and in particular relates to a method for modifying carboxyl groups of graphene oxide in a functionalized manner.
Background
Graphene Oxide (GO) is an oxygen-containing derivative of graphene, and a commonly accepted structural model is that hydroxyl groups and epoxy groups are distributed on the basal plane of graphene oxide, and carboxyl groups and carbonyl groups are distributed at the edges. The graphene oxidation mechanism is as follows: in the oxidation process, a large number of hydroxyl groups are firstly generated on the surface and the edge of the graphene, and meanwhile, C=C double bonds connected with the hydroxyl groups are converted into C-C single bonds; as oxidation proceeds, part of the hydroxyl groups on the graphene surface are dehydrated to epoxy groups, and hydroxyl groups at the edges or basal plane defects of the graphene are oxidized to adjacent ketone groups, which are then converted to carboxyl groups. Although the original highly conjugated structure of graphene is destroyed in the oxidation process, graphene oxide still maintains excellent optical, electrical, mechanical and other unique physicochemical properties. The oxygen-containing functional groups weaken strong intermolecular force among graphene sheets, improve the problem of easy aggregation of graphene, and ensure that the graphene can keep better dispersibility and stability in polar solvents such as water, alcohol and the like. In addition, the oxygen-containing functional groups provide rich modification sites for the basal plane and the edge of the graphene oxide, and various graphene-based composite materials can be further synthesized easily. The type and the number of the oxygen-containing functional groups can also be used for regulating and controlling the performances of the graphene oxide, such as conductivity, band gap and the like, so that the controllable modification of the functional groups is an important means for modifying the graphene oxide.
The carboxyl of the graphene oxide can be subjected to amidation, esterification, neutralization and other reactions, and becomes an important functional group in modification research. However, the limited number of carboxyl functional groups in graphene oxide, limited by the edge sites, affects subsequent carboxyl-based functionalization applications. In recent years, more research results relate to carboxylation modification. The literature reports that the oxidation degree is regulated by regulating the content of potassium permanganate serving as an oxidant in the oxidation step of raw graphite to obtain graphene oxide with different carboxyl contents (the determination of the carboxyl functional group content of graphene oxide by an infrared spectroscopy, chinese test, 2016, 42, 38); there are also literature treatments of graphene oxide with NaOH and chloroacetic acid to convert basal hydroxyls to alkoxycarboxyl groups to increase carboxyl content (Nano-graphene oxide for cellular imaging and drug delivery, nano Res,2008,1, 203); or the C=C bond of the graphene oxide basal plane is subjected to free radical addition through succinic acid acyl peroxide, and carboxyl is grafted to the graphene oxide basal plane through ethyl (surface carboxylation and characterization of graphene oxide, package journal, 2018,2, 30); the patent with the application publication number of CN104445163A discloses a preparation method of carboxylated graphene, which comprises the steps of sequentially treating oxidized graphene by using hydrazine hydrate, aminophenyl acid, isoamyl nitrite alcohol solution, strong alkali and strong acid to obtain carboxylated graphene; the patent of the issued publication No. CN102433032B discloses a method for controllably synthesizing carboxylated graphene oxide and a prepared nano material, wherein the cyano group of the graphene is modified by an azo initiator, and then the cyano group is converted into the carboxyl group by an alcohol solution of alkali; application publication number CN108862268A discloses a macro preparation device and method of carboxyl functional graphene, and the oxidized graphite is treated with NaOH, chloroacetic acid, glycine and the like under the protection of nitrogen to obtain the carboxylated graphene. However, these prior methods have more synthetic steps and are still limited by the edge sites of the carboxyl groups. Although carboxyl groups are introduced on the basal plane of graphene in the report, according to the reaction principle, alkyl chains or alkoxy chains with different lengths are required to be added between the carboxyl groups and the basal plane, so that larger steric hindrance is caused on two sides of the basal plane, and uncertain influence factors are caused on the subsequent functionalization of the carboxyl groups. Therefore, finding a carboxylation modification method which overcomes the limit of edge sites and directly connects carboxyl to the carbon atom of graphene oxide has important significance. It has been reported that graphene oxide can be reduced by alkali treatment with little effect on the carboxyl groups during reduction (Deoxygenation of exfoliated graphite oxide under alkaline conditions: a green route to graphene reparation, adv. Mater.2008,20,4490); in addition, there are reports that many hole-like defects are formed in graphene surface after reduction of graphene oxide (defect characterization generated in the reduction process of graphene oxide, carbon technology, 2016,3, 12). However, the above document does not mention the re-oxidation of such defective graphene oxide. Analysis of these properties of known graphene oxides as described above provides the potential for adding carboxyl modification sites within its basal plane.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a method for modifying graphene oxide by carboxyl functionalization, which solves the technical problem that the carboxylation degree of graphene oxide in the prior art is to be further improved.
In order to solve the technical problems, the invention adopts the following technical scheme:
the method takes graphene oxide as a raw material, reduces the graphene oxide by alkali, generates defect sites in a basal plane of the graphene oxide, oxidizes the graphene oxide generating the defect sites by an oxidant, and obtains carboxyl at the defect sites of the graphene oxide;
the oxidant is potassium permanganate and concentrated sulfuric acid, or potassium permanganate and perchloric acid.
The invention also has the following technical characteristics:
in the oxidant, the dosage of potassium permanganate is 0.1 to 3 times of the mass of the graphene oxide.
In the oxidant, concentrated sulfuric acid or perchloric acid is added into a reaction system, and then potassium permanganate is added.
In the oxidant, the consumption of the concentrated sulfuric acid is that 6mL of the concentrated sulfuric acid is correspondingly added into every 40mg of graphene oxide; or 3mL of perchloric acid is correspondingly added into the oxidant for every 40mg of graphene oxide.
In the process of adding the oxidant, the temperature of a reaction system is 0-10 ℃,
the reaction time of the oxidation is 10 minutes to 2 hours, and the reaction temperature is 0 to 40 ℃.
And adding water into the reaction system after the oxidation, heating to react, and then adding a terminator to terminate the reaction.
Every 40mg of graphene oxide is added with 6mL of water correspondingly, and the temperature is raised to 95 ℃ for reaction for 15 minutes.
The alkali is LiOH, naOH, KOH, rbOH, csOH or hydrazine hydrate.
The amount of the alkali is added in excess relative to the amount of the graphene oxide.
The reaction time of the reduction is 0.5-6 hours, and the reaction temperature is 40-90 ℃.
Compared with the prior art, the invention has the following technical effects:
according to the reduction mechanism of graphene oxide, a simple alkali reduction reaction is adopted, and hole-shaped defect sites are formed on a graphene basal plane while edge carboxyl groups are not reduced, and the defect sites are increased by the defects. Through further oxidation, a new carboxyl directly connected with graphene carbon atoms is obtained at the defect, and the carboxylation degree of graphene oxide is integrally improved while the hydroxyl and epoxy groups are reduced.
(II) the method of the invention can increase defect sites in the basal plane of graphene oxide under the condition that carboxyl groups are reserved at the reserved edge, further oxidize carbon atoms at the defect and generate new carboxyl groups, and the carboxyl groups are directly connected with the carbon atoms of the graphene oxide.
(III) by adopting the modification method, the obtained carboxylated graphene oxide is characterized by infrared spectrum (figure 1) and X-ray photoelectron spectrum (figure 2), and the carboxyl content is obviously improved.
And (IV) in order to further verify the effect of improving the carboxyl content, cesium atoms are loaded on carboxyl groups of graphene oxide before and after modification, and then the carboxyl groups are used as electron transport layers to respectively prepare organic photovoltaic cell devices, and the result shows that the improvement of the carboxyl groups can improve the open circuit voltage (V) of the devices by 44%. The method disclosed by the invention is simple to operate, low in cost and beneficial to carboxyl functional application of graphene oxide.
Drawings
Fig. 1 is a fourier transform infrared spectrum comparison chart of modified graphene oxide and modified graphene oxide obtained in example 1 of the present invention.
Fig. 2 is a graph showing the comparison of the X-ray photoelectron spectra of the modified graphene oxide and the modified graphene oxide obtained in example 1 of the present invention.
Fig. 3 is a J-V curve of the electron transport layer for an organic photovoltaic device after cesium atoms are supported on the modified graphene oxide and the modified graphene oxide obtained in example 1 of the present invention.
The following examples illustrate the invention in further detail.
Detailed Description
All the raw materials in the present invention, unless otherwise specified, are known in the art.
According to the graphene oxide carboxyl functional modification method, graphene oxide is directly taken as a raw material, reduced by alkali, a certain defect site is generated in a basal plane, and oxidized by an oxidant, so that a new carboxyl is obtained at the defect site, and the carboxylation degree of the graphene oxide is integrally improved.
Specifically, in the method, oxygen-containing groups in the basal plane of graphene oxide are reduced under the treatment of alkali, and carboxyl groups at the edge are not reduced. By adjusting the kind of the base, the time and the temperature of the reduction reaction, certain structural defects are generated on the basal plane of the reduced graphene oxide, and the hole-shaped defects can be regarded as 'edges' in the basal plane, and new carboxyl groups are obtained at defect sites by oxidation of an oxidant to a proper degree.
Specifically, the process of the method is carried out according to the following reaction process:
the following specific embodiments of the present invention are given according to the above technical solutions, and it should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solutions of the present application fall within the protection scope of the present invention.
Example 1:
the embodiment provides a graphene oxide carboxyl functional modification method, which comprises the following steps:
100mg of graphene oxide and 100mL of deionized water are added into a round-bottom flask, and ultrasonic treatment is carried out for 30 minutes under the power of 600W by using an ultrasonic cell grinder, so that a uniform and stable graphene oxide aqueous dispersion liquid is obtained. Slowly adding 1g of KOH into the dispersion liquid under magnetic stirring, heating to 90 ℃, keeping the temperature, stirring for reaction for 1 hour, cooling to room temperature, centrifuging for 10 minutes at 9000 rpm, pouring out supernatant alkali liquor, washing the solid with deionized water, filtering with an aqueous membrane with the pore diameter of 0.45 mu m, and repeatedly washing and filtering for 5 times to remove residual KOH.
Adding 40mg of the obtained reduced graphene oxide and 6mL of concentrated sulfuric acid (with the mass concentration of 98%) into a round-bottom flask, carrying out ultrasonic treatment by adopting an ultrasonic bath to obtain stable dispersion liquid, slowly adding 80mg (2 times of potassium permanganate) into the stirred dispersion liquid at the temperature of 0 ℃, ensuring the temperature not to exceed 10 ℃, raising the temperature to 40 ℃ after the addition is finished to react for 2 hours, slowly adding 5mL of deionized water into the system, raising the temperature to 95 ℃ to continue the reaction for 15 minutes, adding deionized water for improving the carboxyl content, and adding 1mL of hydrogen peroxide terminator (with the mass concentration of 30%) to terminate the reaction. Cooling, filtering to remove reaction liquid, washing with dilute hydrochloric acid (with mass concentration of 5%) for 1 time, washing with deionized water repeatedly, filtering with water-based membrane with aperture of 0.45 μm after each washing, washing repeatedly for more than 10 times until acid and impurity ions are completely removed, and drying in a vacuum oven at 50deg.C to obtain carboxylated graphene oxide.
The modified graphene oxide prepared in this example was subjected to fourier transform infrared spectrum test and X-ray photoelectron spectrum test, and was used for an electron transport layer of an organic photovoltaic device and testing the device performance, and compared with that before modification, and the results are shown in fig. 1 to 3.
As can be seen from FIG. 1, in the IR spectrum of graphene oxide modified according to the method of the present invention, 1720cm -1 C=O stretching vibration peak of the carboxyl is enhanced, which indicates that the carboxylation degree is improved; 1617cm -1 The C=C stretching vibration peak of the unoxidized graphite area is relatively weakened, which indicates that some defect sites are formed in the reduction process, so that the conjugation of the graphene oxide is reduced; 1050cm -1 And 1224cm -1 The characteristic peak of C-O-C is changed from a sharp peak before modification into a blunt peak after modification, and the intensity is reduced, which shows that the graphene oxide is reduced and then oxidized according to the method of the invention, and the epoxy group content is reduced; in addition 3158cm -1 And 3373cm -1 The stretching vibration peak of-OH is 3158cm -1 The peak, which may be the hydroxyl group in the carboxylic acid shifted to this low wavenumber direction due to hydrogen bonding, is slightly enhanced after modification and further illustrates the increase in carboxylation.
As can be seen from FIG. 2, the carboxyl characteristic peak at 288.8eV had a corresponding content of 3.1% before modification, and the peak intensity after modification became large, and the content was increased to 9.0%. In addition, the characteristic peak at 286.7eV is related to hydroxyl and epoxy, the peak intensity is obviously reduced after modification, and the corresponding content is reduced from 17.8% before modification to 16.8% after modification. The result of the X-ray photoelectron spectrum shows that the carboxyl content of the modified graphene oxide is obviously improved, and the hydroxyl and epoxy group contents are reduced.
As can be seen from FIG. 3, the modified graphene oxide is loaded with cesium atoms and then used as an electron transport layer of an organic photovoltaic device, when the short-circuit current density is 0mA/cm 2 When the open circuit voltage reaches 0.81V, which is obviously higher than the open circuit voltage of 0.56V before modification, the carboxyl content which is improved after modification increases the load of cesium atoms, thereby improving the energy level of the electron transport layer and obviously improving the open circuit voltage. The practical application value of the graphene oxide carboxylation modification method is embodied.
Example 2:
the embodiment provides a graphene oxide carboxyl functional modification method, which comprises the following steps:
100mg of graphene oxide and 100mL of deionized water are added into a round-bottom flask, and ultrasonic treatment is carried out for 30 minutes under the power of 600W by using an ultrasonic cell grinder, so that a uniform and stable graphene oxide aqueous dispersion liquid is obtained. Slowly adding 1g of NaOH into the dispersion liquid under magnetic stirring, heating to 40 ℃, keeping the temperature, stirring for reaction for 1 hour, cooling to room temperature, centrifuging for 10 minutes at 9000 rpm, pouring out supernatant alkali liquor, washing the solid with deionized water, filtering with an aqueous membrane with the pore diameter of 0.45 mu m, and repeatedly washing and filtering for 5 times to remove residual NaOH.
40mg of the obtained reduced graphene oxide and 10mL of deionized water are added into a round-bottomed flask, the mixture is dispersed into a stable dispersion by ultrasonic, 3mL of perchloric acid (the mass concentration is 50%) and 4mg (0.1 times of the amount) of potassium permanganate are slowly added into the dispersion at about 0 ℃, and after the mixture is fully stirred for 10 minutes, 5mL of a citric acid aqueous solution terminator (0.2 g/mL) is added to terminate the reaction. Filtering to remove reaction liquid, washing with deionized water, filtering with water system film with aperture of 0.45 μm, repeatedly washing for more than 10 times until acid and impurity ions are completely removed, and drying in vacuum oven at 50deg.C to obtain carboxylated graphene oxide.
The fourier transform infrared spectrum contrast chart, the X-ray photoelectron spectrum contrast chart, and the J-V curve for the electron transport layer of the organic photovoltaic device of the present example are substantially the same as those of example 1.
Example 3:
the embodiment provides a graphene oxide carboxyl functional modification method, which comprises the following steps:
100mg of graphene oxide and 100mL of deionized water are added into a round-bottom flask, and ultrasonic treatment is carried out for 30 minutes under the power of 600W by using an ultrasonic cell grinder, so that a uniform and stable graphene oxide aqueous dispersion liquid is obtained. Under magnetic stirring, 1g of CsOH was slowly added to the dispersion, the temperature was raised to 40℃and the reaction was maintained under stirring for 0.5 hours, after cooling to room temperature, the mixture was centrifuged at 9000 rpm for 10 minutes, the supernatant was removed, the solid was washed with deionized water, and filtered with an aqueous membrane having a pore size of 0.45 μm, and the washing and filtration were repeated for 5 times to remove the residual CsOH.
Adding 40mg of the obtained reduced graphene oxide and 6mL of concentrated sulfuric acid (with the mass concentration of 98%) into a round-bottomed flask, performing ultrasonic treatment by adopting an ultrasonic bath to obtain a stable dispersion liquid, slowly adding 20mg (0.5 times of amount) of potassium permanganate into the stirred dispersion liquid at the temperature of 0 ℃, ensuring the temperature not to exceed 10 ℃, raising the temperature to 40 ℃ after the addition is finished for 2 hours, and adding 1mL of hydrogen peroxide terminator (with the mass concentration of 30%) to terminate the reaction. Cooling, filtering to remove reaction liquid, washing with dilute hydrochloric acid (with mass concentration of 5%) for 1 time, washing with deionized water repeatedly, filtering with water-based membrane with aperture of 0.45 μm after each washing, washing repeatedly for more than 10 times until acid and impurity ions are completely removed, and drying in a vacuum oven at 50deg.C to obtain carboxylated graphene oxide.
The fourier transform infrared spectrum contrast chart, the X-ray photoelectron spectrum contrast chart, and the J-V curve for the electron transport layer of the organic photovoltaic device of the present example are substantially the same as those of example 1.
Example 4:
the embodiment provides a graphene oxide carboxyl functional modification method, which comprises the following steps:
100mg of graphene oxide and 100mL of deionized water are added into a round-bottom flask, and ultrasonic treatment is carried out for 30 minutes under the power of 600W by using an ultrasonic cell grinder, so that a uniform and stable graphene oxide aqueous dispersion liquid is obtained. Under magnetic stirring, 6mL of hydrazine hydrate (with the mass concentration of 85%) is slowly added into the dispersion, the temperature is raised to 90 ℃ and the reaction is kept at the temperature for 6 hours under stirring, the mixture is cooled to room temperature and centrifuged for 10 minutes at 9000 rpm, the supernatant alkali liquor is poured out, the solid is washed by deionized water, and the solid is filtered by an aqueous membrane with the pore diameter of 0.45 mu m, and the washing and the filtering are repeated for 5 times to remove the residual hydrazine hydrate.
40mg of the obtained reduced graphene oxide and 10mL of deionized water are added into a round-bottomed flask, the mixture is dispersed into a stable dispersion by ultrasonic, 3mL of perchloric acid (the mass concentration is 50%) and 8mg (0.2 times of the amount) of potassium permanganate are slowly added into the dispersion at about 0 ℃, and after the mixture is fully stirred for 10 minutes, 5mL of a citric acid aqueous solution terminator (0.2 g/mL) is added to terminate the reaction. Filtering to remove reaction liquid, washing with deionized water, filtering with water system film with aperture of 0.45 μm, repeatedly washing for more than 10 times until acid and impurity ions are completely removed, and drying in vacuum oven at 50deg.C to obtain carboxylated graphene oxide.
The fourier transform infrared spectrum contrast chart, the X-ray photoelectron spectrum contrast chart, and the J-V curve for the electron transport layer of the organic photovoltaic device of the present example are substantially the same as those of example 1.
Claims (7)
1. The method is characterized in that graphene oxide is used as a raw material, the graphene oxide is reduced by alkali, defect sites are generated in a basal plane of the graphene oxide, and the graphene oxide generating the defect sites is oxidized by an oxidant, so that carboxyl is obtained at the defect sites of the graphene oxide;
the oxidant is potassium permanganate and concentrated sulfuric acid, or potassium permanganate and perchloric acid;
in the oxidant, concentrated sulfuric acid or perchloric acid is firstly added into a reaction system, and then potassium permanganate is added;
in the process of adding the oxidant, the temperature of a reaction system is 0-10 ℃;
the alkali is LiOH, naOH, KOH, rbOH, csOH or hydrazine hydrate.
2. The method for modifying carboxyl groups of graphene oxide according to claim 1, wherein the amount of potassium permanganate in the oxidizing agent is 0.1-3 times the mass of the graphene oxide.
3. The method for modifying carboxyl groups of graphene oxide according to claim 1, wherein the amount of concentrated sulfuric acid in the oxidizing agent is 6mL of concentrated sulfuric acid for every 40mg of graphene oxide; or 3mL of perchloric acid is correspondingly added into the oxidant for every 40mg of graphene oxide.
4. The method for modifying carboxyl groups of graphene oxide according to claim 1, wherein the reaction time of the oxidation is 10 minutes to 2 hours and the reaction temperature is 0 ℃ to 40 ℃.
5. The method for modifying carboxyl groups of graphene oxide according to claim 1, wherein water is added into the reaction system after oxidation, the temperature is raised for reaction, and then a terminator is added for terminating the reaction.
6. The method for carboxyl functional modification of graphene oxide according to claim 5, wherein 6mL of water is added for every 40mg of graphene oxide, and the temperature is raised to 95 ℃ for reaction for 15 minutes.
7. The method for modifying carboxyl groups of graphene oxide according to claim 1, wherein the reaction time of the reduction is 0.5-6 hours and the reaction temperature is 40-90 ℃.
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