CN110526238B - Preparation method of reduced graphene oxide and precipitation method of graphene oxide sol - Google Patents
Preparation method of reduced graphene oxide and precipitation method of graphene oxide sol Download PDFInfo
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- CN110526238B CN110526238B CN201910876198.2A CN201910876198A CN110526238B CN 110526238 B CN110526238 B CN 110526238B CN 201910876198 A CN201910876198 A CN 201910876198A CN 110526238 B CN110526238 B CN 110526238B
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Abstract
The invention provides a preparation method of reduced graphene oxide and a precipitation method of graphene oxide sol. The preparation method comprises the following steps: adjusting the pH value of the graphite oxide suspension to 9-11, and performing dispersion stripping and centrifugation treatment to obtain graphene oxide sol; mixing the graphene oxide sol and a coagulating precipitant, stirring, coagulating, standing, settling to obtain a graphene oxide aggregate, and then dehydrating and washing to obtain graphene oxide gel; and reducing the graphene oxide gel to obtain the reduced graphene oxide. The precipitation method comprises the following steps: mixing the graphene oxide sol and a coagulation precipitator, stirring, coagulating, standing, settling to obtain a graphene oxide aggregate, and dehydrating and/or washing to obtain a graphene oxide gel. The beneficial effects of the invention include: simple process, low cost and high production efficiency.
Description
Technical Field
The invention relates to the technical field of preparation of low-carbon nano materials, in particular to a preparation method of reduced graphene oxide and a precipitation method of graphene oxide sol.
Background
Graphene oxide is a functionalized graphene material, but due to strong hydrophilicity, the graphene oxide is difficult to condense and dehydrate and separate from sol after being dispersed in water, or has the defects of long period required by agglomeration and precipitation, difficulty in filtration, cleaning and drying and the like, which brings difficulty to the preparation of reduced graphene oxide by a thermal reduction method.
Disclosure of Invention
In view of the deficiencies in the prior art, it is an object of the present invention to address one or more of the problems in the prior art as set forth above. For example, an object of the present invention is to provide a method for preparing reduced graphene oxide and a method for precipitating graphene oxide sol, so as to solve the problems of long period required by agglomeration and precipitation of graphene oxide sol and difficulty in filtration, cleaning and drying.
In order to achieve the above object, an aspect of the present invention provides a method for preparing reduced graphene oxide.
The preparation method can comprise the following steps: adjusting the pH value of the graphite oxide suspension to 9-11, and performing dispersion stripping and centrifugation treatment to obtain graphene oxide sol; mixing the graphene oxide sol and a coagulation precipitator, stirring, coagulating, standing, settling to obtain a graphene oxide aggregate, and then dehydrating and washing to obtain graphene oxide gel, wherein the coagulation precipitator can comprise inorganic ammonium salt; and (3) carrying out vacuum freeze drying on the graphene oxide gel, and reducing at high temperature in a protective atmosphere to obtain the reduced graphene oxide.
In an exemplary embodiment of the method for preparing reduced graphene oxide, the addition amount of the coagulating sedimentation agent relative to the graphene oxide sol may be 1-3 g/100 ml.
In an exemplary embodiment of the method for preparing reduced graphene oxide according to the present invention, the total time of the stirring, condensing, standing and settling treatment may be 1-2 hours.
In an exemplary embodiment of the method for preparing reduced graphene oxide, the water content of the graphene oxide sol may be 95-99.9%, and the water content of the graphene oxide gel may be 70-80%.
In one exemplary embodiment of the method for preparing reduced graphene oxide according to the present invention, the inorganic ammonium salt may include at least one of ammonium chloride, ammonium bromide, ammonium nitrate, ammonium carbonate, ammonium bicarbonate, ammonium sulfate, and ammonium bisulfate.
In an exemplary embodiment of the method for preparing reduced graphene oxide, the number of layers of the reduced graphene oxide may be 1-5, and the carbon content may be not less than 99.5%.
The invention also provides a precipitation method of the graphene oxide sol.
The precipitation method may comprise the steps of: mixing the graphene oxide sol and a coagulating precipitant, stirring, coagulating, standing, settling to obtain a graphene oxide aggregate, and then dehydrating and washing to obtain a graphene oxide gel, wherein the coagulating precipitant comprises an inorganic ammonium salt.
In an exemplary embodiment of the method for precipitating a graphene oxide sol according to the present invention, the addition amount of the condensed precipitant may be 1 to 3g/100ml relative to the graphene oxide sol.
In an exemplary embodiment of the method for precipitating a graphene oxide sol according to the present invention, the total time of the stirring, condensing, standing, and settling treatment may be 1 to 2 hours.
In an exemplary embodiment of the method for precipitating a graphene oxide sol according to the present invention, the water content of the graphene oxide sol may be 95 to 99.9%, and the water content of the graphene oxide gel may be 70 to 80%.
Compared with the prior art, the beneficial effects of the invention can include:
(1) the obtained graphene oxide sol can be separated from un-peeled and dispersed graphite oxide and impurities in the process of graphite oxide dispersion stripping and centrifugation, and the yield of reduced graphene oxide is improved;
(2) the graphene oxide is quickly coagulated and precipitated from the sol by adopting a coagulating precipitant so as to realize quick dehydration and separation, so that the subsequent filtering and drying process steps are simplified, and the production efficiency is improved;
(3) the method has the advantages that the graphene oxide is rapidly coagulated and dehydrated by adopting a coagulating precipitant, so that the water content of the product is greatly reduced, and the filtering time and the energy consumption required by drying the product are saved;
(4) ammonium ions which play an important role in the condensation and precipitation of the graphene oxide in the flocculation process are decomposed in the subsequent heating reduction treatment to form ammonia gas and water molecules which are volatilized and removed, so that high-purity reduced graphene oxide powder is obtained;
(5) the flocculant and the like can be directly gasified and removed through a later high-temperature thermal reduction process without washing after dehydration by adopting a certain coagulating sedimentation agent.
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The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:
fig. 1 shows a schematic flow diagram of a method for preparing reduced graphene oxide in an exemplary embodiment of the invention;
fig. 2 shows a schematic flow diagram of a method for preparing reduced graphene oxide in another exemplary embodiment of the invention;
fig. 3 shows an SEM image of reduced graphene oxide prepared in an exemplary embodiment of the present invention.
Detailed Description
Hereinafter, a method for preparing reduced graphene oxide and a method for precipitating a graphene oxide sol according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.
The invention provides a preparation method of reduced graphene oxide.
In an exemplary embodiment of the method for preparing reduced graphene oxide according to the present invention, as shown in fig. 1, the method may include:
s01: and adjusting the pH value of the graphite oxide suspension to 9-11, and performing dispersion stripping treatment and centrifugal treatment to obtain the graphene oxide sol.
In the embodiment, when the PH of the graphene oxide suspension is 9 to 11, the negative charge on the surface of the graphene oxide is high, and may be ± 60mv, and at this time, the dispersibility of the graphite oxide in water is the best, so that the graphite oxide can be sufficiently peeled off to form the graphene oxide.
In this embodiment, the water content of the graphene oxide sol may be 95 to 99.9%. Wherein, the dispersion stripping treatment and the centrifugal treatment can remove the graphite oxide and impurities which are not fully stripped from the graphite oxide suspension, and the impurities can comprise solid impurities of quartz, mica, feldspar and other minerals.
In this embodiment, the PH of the graphite oxide suspension may be adjusted by mixing the graphite oxide suspension and a strong alkali solution, and the strong alkali solution may include at least one of LiOH solution and NaOH solution. The reasons for adjusting the pH with LiOH solution and NaOH solution may include: both are strong alkali solutions, so that the pH value can be effectively adjusted; na (Na)+And Li+The precipitate is difficult to form and is easily removed in a later step. Reasons for not selecting KOH here may include: while KOH solutions are effective in adjusting the pH of the solution, K+The hydration radius of the graphene is small, so that the graphene is not beneficial to stripping and dispersing of the graphite oxide into the graphene oxide. While other strong or weak bases may also have properties similar to KOH or adverse effects.
In this embodiment, an ultrasonic dispersion peeling process may be selected, and the advantages of ultrasonic dispersion peeling may include: high efficiency, can greatly shorten the time for stripping graphite oxide, is clean and does not pollute the graphite oxide or graphene oxide. In S01, NA+And Li+May enter the graphene oxide sol.
S02: mixing the graphene oxide sol and a coagulation precipitator, wherein the addition amount of the coagulation precipitator relative to the graphene oxide sol is 1-3 g/100ml, stirring, coagulating, settling and standing for 1-2 hours to enable the graphene oxide to form aggregates, and dehydrating and washing to obtain the graphene oxide gel.
In this embodiment, the water content of the graphene oxide gel may be 70-80%, and the recovery rate may be 85-99%. The coagulating sedimentation agent may include inorganic ammonium salts, and further, may include at least one of ammonium chloride, ammonium bromide, ammonium nitrate, ammonium carbonate, ammonium bicarbonate, ammonium sulfate, and ammonium bisulfate. The dehydration treatment method can comprise vacuum filtration and suction filtration, and the washing method can comprise the step of adding the product obtained by the vacuum filtration and suction filtration into industrial water to repeat uniform leaching and dehydration until the anion of the ammonium salt in the filtrate is not detected. Wherein, when the selected coagulating precipitant is ammonium chloride salt, the washing operation may be optionally not performed for the reasons that may include: the excess ammonium chloride can be volatilized at a temperature above 300 ℃, and part of the generated sodium chloride can be volatilized at a temperature above 1400 ℃ (flash point).
In the present embodiment, in S02, NH4 +And its corresponding anion will enter the graphene oxide gel. Ammonium salt (containing NH)4 +) When depositing graphene oxide, not only NH4 +In the substitution of Na+Or H+NH of two water molecule layers with fixed hydration radiuses formed between two graphene oxide layers in the process (the two hydration radiuses are not fixed)4 +The cation layer is hydrated to enable graphene oxide to form ordered laminated arrangement, condensation is further achieved, and due to the fact that ammonium salt is added to have a certain reduction effect on the graphene oxide, the double effects of increasing hydrophobicity after partial reduction of the graphene oxide and the graphene oxide sol accelerate condensation and settlement of the graphene oxide sol. The following table shows the graphene oxide GOs and the addition of NH4post-CL graphene oxide GOs-NH4Change in CL oxygen-containing functional group content.
| Sample (I) | C＝C/C-C(％) | C-O(％) | C-O-C(％) | O-C＝O(％) |
| GO | 45.19 | 32.71 | 16.1 | 6.00 |
| GO-NH4Cl | 61.23 | 20.53 | 13.17 | 5.07 |
S03: and (3) carrying out vacuum freeze drying on the obtained graphene oxide gel, and reducing at high temperature in a protective atmosphere to obtain the reduced graphene oxide.
In this embodiment, the number of layers of the high-purity reduced graphene oxide may be 1 to 5, and the purity (carbon content) may be 95.9 to 99.9%.
In this embodiment, the vacuum condition of the vacuum freeze drying may include a vacuum degree of 10-20 MPa, and the low temperature condition may include a temperature of-40 to-30 ℃, and the drying speed of the graphene oxide gel is moderate and the efficiency is high under the vacuum degree and temperature conditions given above, and the graphene oxide xerogel after drying shrinks less than the wet gel, and the drying efficiency is reduced and the effect is poor when the vacuum degree and temperature exceed the vacuum degree and temperature given above.
In this embodiment, the protective atmosphere may be a flowing protective gas, and in the process of the high-temperature thermal reduction treatment, the released volatile components may include ammonia gas, water molecules, sodium chloride, sodium bromide, and ammonium bromide, and the flowing gas can take away these volatile components, and meanwhile, these volatile components may also be collected by a spray (water) absorption method. The flowing gas may include at least one of air, nitrogen, helium and argon, and the advantages of using several of the above alternative gases in S03 may include: the inert gas is inactive in chemical property, cannot cause oxidation damage to the reduced graphene oxide under high temperature (such as higher than 450 ℃), has little pollution to the environment, and has low cost of air and inert gas. The gas flow of the flowing gas can be 30-60 ml/min, when the gas flow is less than 30ml/min, the volatile components cannot be brought out or cannot be brought out completely, when the gas flow is more than 60ml/min, the volatile components can be brought out completely, and the flowing gas is wasted or the reduced graphene oxide can be brought out by continuously increasing the gas flow.
In this embodiment, the temperature of the high-temperature thermal reduction treatment may be 300 to 1600 ℃, when the temperature is lower than 300 ℃, the reduction degree of the graphene oxide is insufficient, and the volatile components are difficult to remove, and when the temperature is higher than 1800 ℃, the heat treatment equipment is difficult to reach too high a temperature, and the reduced graphene oxide structure is damaged. The treatment time can be 0.5-2 h, when the time is less than 0.5h, the treatment time is too short, the reduction degree of the graphene oxide is insufficient, volatile components are difficult to remove, when the time is more than 2h, the reduction degree of the graphene oxide is high, the graphene oxide cannot be remarkably improved along with the increase of the time, and only the energy consumption is increased and the efficiency is reduced when the time is continuously increased. Fig. 3 is an SEM image of the reduced graphene oxide prepared according to the present invention, in which the reduced graphene oxide has few layers, the number of layers is less than 4, the number of layers is 95% or more, and the purity is 99.8%.
In this embodiment, the graphene oxide hydrogel is vacuum freeze-dried, the graphene oxide hydrogel is first frozen to crystallize the water contained therein into ice, and the ice is made to grow under vacuum conditions to achieve the purpose of drying, and the graphene oxide xerogel is obtained after drying.
In the embodiment, the reduced graphene oxide is obtained by thermal reduction treatment of graphene oxide xerogel, and the graphene oxide structure contains various oxygen-containing functional groups, such as carboxyl, hydroxyl, epoxy and the like, and the oxygen-containing functional groups are heated at high temperature to form H2O、CO2And (4) removing the form. Therefore, the reduced graphene oxide is obtained after the graphene oxide is subjected to high-temperature heat treatment, and in order to prevent the graphene oxide from being oxidized by oxygen in the air at a higher temperature (such as more than 450 ℃), inert gas is selected as protective gas. Meanwhile, residual ammonium salt in the graphene oxide can be removed by sublimation at high temperature, such as sodium chloride, ammonium chloride, sodium bromide, ammonium bromide and the like, and high-purity reduced graphene oxide is obtained.
In this embodiment, before S01, the preparation method may further include the steps of: mixing graphite oxide and water according to a mass ratio of 1: 20-500, and washing with water to remove impurities to obtain the graphite oxide suspension. The graphite oxide turbid liquid can comprise a graphite oxide turbid liquid with the water content of 95.2-99.8%. Preferably, the water may be industrial/pure water, which may both reduce the cost of the water and avoid the introduction of impurities. Further, the mass ratio of graphite oxide to water may be 1: 50 to 100.
In another exemplary embodiment of the method for preparing reduced graphene oxide according to the present invention, as shown in fig. 2, the method may include the steps of:
(1) weighing crystalline flake graphite, placing the crystalline flake graphite in an acid-alkali resistant reactor with a stirring device, and preparing the graphite oxide by utilizing an improved Hummers method. Firstly, according to the use ratio of 1g of graphite to concentrated sulfuric acid: adding graphite and concentrated sulfuric acid into a stirring reaction device in an amount of 30 ml; after stirring for 30min, the mixture is stirred according to the dosage ratio of potassium permanganate to graphite of 3.5 g: adding 1g of the industrial water into a reactor, reacting for 3 hours at a low temperature of 0 ℃, reacting for 1 hour at a medium temperature of 37 ℃, transferring a reaction device containing a sample to an ice bath environment, adding a small amount of industrial water for multiple times, and controlling the temperature of the system to be 60-65 ℃ until the temperature of the system is reduced to be below 40 ℃. Adding 5% H into the prepared GO suspension2O2And (3) adding a proper amount of dilute hydrochloric acid when the solution is free from bubbles in the system, washing the graphite oxide with industrial water for several times until the pH value of the supernatant is close to neutral to obtain a graphite oxide turbid liquid, wherein the mass ratio of the graphite oxide in the turbid liquid to the industrial water is 1: 20-1: 500.
(2) and (2) adding NaOH or LiOH solution into the graphite oxide turbid liquid obtained in the step (1) while stirring to adjust the pH to 9-11, and obtaining graphene oxide sol after ultrasonic dispersion stripping and centrifugation to remove the graphite oxide and impurities which are not fully stripped.
(3) Adding inorganic ammonium salts such as ammonium chloride, ammonium bromide, ammonium nitrate, ammonium carbonate/ammonium bicarbonate and ammonium sulfate/ammonium bisulfate into the graphene oxide sol in the step (2) in an amount of 1-3 g/100ml, stirring, dissolving, coagulating, standing and settling to form graphene oxide aggregates, and performing dehydration and uniform leaching treatment by using a ceramic vacuum filter/a vacuum belt filter/a suction filter until ammonium salt anions in filtrate are not detected to obtain graphene oxide gel with low water content; for ammonium halide salts with flocculating settling agent such as ammonium chloride and ammonium bromide, only dehydration treatment is needed, and washing is not needed.
(4) Carrying out vacuum freeze drying on the graphene oxide gel obtained in the step (3) for 3d, and roasting at 300-1600 ℃ for 0.5-2 h under the condition that the flow of protective gas is 30-60 ml/min to remove volatile components, thereby obtaining high-purity reduced graphene oxide powder; and collecting the volatile components removed by the high-temperature thermal reduction treatment by a collecting device arranged at an exhaust port of the high-temperature thermal treatment device.
The invention also provides a precipitation method of the graphene oxide sol.
In one exemplary embodiment of the method for precipitating a graphene oxide sol of the present invention, the method for precipitating may include the steps of: mixing the graphene oxide sol and a coagulating precipitant, stirring, coagulating, standing, settling to obtain a graphene oxide aggregate, and then dehydrating and washing or dehydrating to obtain a graphene oxide gel, wherein the coagulating precipitant can comprise inorganic ammonium salt. This step may be the same as S02 in the first exemplary embodiment.
In order to better understand the above exemplary embodiments of the present invention, the following further description is given in conjunction with specific examples.
Example 1
1) Preparing a graphite oxide suspension: adding industrial water into the prepared graphite oxide to prepare a graphite oxide/industrial water mass ratio of 1: 20 of graphite oxide suspension.
2) Preparing graphene oxide sol: taking a certain amount of the graphite oxide suspension prepared in the step 1), adding a NaOH solution to adjust the pH to 9, placing the suspension after the pH adjustment in a stripping and dispersing device, carrying out ultrasonic treatment on the solution for 2 hours to obtain graphene oxide sol, and centrifuging the graphene oxide to remove graphite oxide and impurities which are not stripped sufficiently to obtain the graphene oxide sol with the water content of 95%;
3) adding 1gNH into 100ml of graphene oxide sol obtained in the step 2)4Stirring, dissolving, coagulating, standing and settling Cl medicine for 2 hours to obtain a graphene oxide aggregate, and then carrying out suction filtration for 30min to obtain graphene oxide gel with the water content of 70%; and finally, drying the obtained graphene oxide gel for 3d by using a vacuum freeze-drying method to obtain graphene oxide xerogel with the recovery rate of 99%.
4) Placing the graphene oxide xerogel obtained in the step 3) into a roasting reaction device, and roasting for 2 hours at 1600 ℃ under the nitrogen atmosphere with the gas flow of 30ml/min to obtain reduced graphene oxide, wherein the number of layers is 1-2, and the purity (carbon content) is 99.9%; volatile components such as ammonia gas, sodium chloride and the like released in the heating process are collected by adopting a spray (water) absorption method.
Example 2
1) Preparing a graphite oxide suspension: adding industrial water into the prepared graphite oxide to prepare a graphite oxide/industrial water mass ratio of 1: 50 of graphite oxide suspension.
2) Preparing graphene oxide sol: taking a certain amount of the graphite oxide suspension prepared in the step 1), adding a NaOH solution to adjust the pH to 9.5, placing the suspension after the pH adjustment in a stripping and dispersing device, carrying out ultrasonic treatment on the solution for 2 hours to obtain graphene oxide sol, and centrifuging the graphene oxide to remove graphite oxide and impurities which are not stripped sufficiently to obtain the graphene oxide sol with the water content of 98.1%;
3) adding 1.5g of NH into 100ml of graphene oxide sol obtained in the step 2)4Br medicine, stirring, dissolving, coagulating, standing and settling for 1.7h to obtain graphene oxide aggregate, and then performing suction filtration for 30min to obtain graphene oxide gel with the water content of 73%; and finally, drying the obtained graphene oxide gel for 3d by using a vacuum freeze-drying method to obtain graphene oxide xerogel with the recovery rate of 97%.
4) Placing the graphene oxide xerogel obtained in the step 3) in a roasting reaction device, and placing the graphene oxide xerogel in the roasting reaction device at 1500 ℃ and N2Gas flow rate of 35ml/minRoasting for 1.5h to obtain the few-layer reduced graphene oxide, wherein the number of layers is 2-4, and the purity (carbon content) is 99.7%; the volatile components such as ammonia gas, sodium bromide and the like released in the heating process are collected by adopting a spray (water) absorption method.
Example 3
1) Preparing a graphite oxide suspension: adding industrial water into the prepared graphite oxide to prepare a graphite oxide/industrial water mass ratio of 1: 100 of graphite oxide suspension.
2) Preparing graphene oxide sol: taking a certain amount of the graphite oxide suspension prepared in the step 1), adding LiOH solution to adjust the pH to 10, placing the suspension after adjusting the pH in a stripping and dispersing device, carrying out ultrasonic treatment on the solution for 2 hours to obtain graphene oxide sol, and centrifuging the graphene oxide to remove graphite oxide and impurities which are not stripped sufficiently to obtain the graphene oxide sol with the water content of 99.1%;
3) adding 2g of NH into 100mL of graphene oxide sol obtained in the step 2)4HCO3Stirring, dissolving, coagulating, standing, and settling for 1.5 hr to obtain graphene oxide aggregate, filtering with vacuum ceramic filter for 15min, and uniformly leaching for several times until no HCO is detected in the washing solution—Obtaining oxidized graphene gel with the water content of 74%; finally, drying the obtained graphene oxide gel for 3d by using a vacuum freeze-drying method to obtain graphene oxide xerogel, wherein the recovery rate is 85%; volatile components such as ammonia released in the heating process are collected by adopting a spray (water) absorption method.
4) And (3) placing the graphene oxide xerogel obtained in the step 3) into a roasting reaction device, and roasting for 1.5h at the temperature of 300 ℃ and under the condition that the air flow is 40ml/min to obtain the few-layer reduced graphene oxide, wherein the number of layers is less than 4, the number of layers accounts for more than 95%, and the purity (carbon content) is 99.8%.
Example 4
1) Preparing a graphite oxide suspension: adding industrial water into the prepared graphite oxide to prepare a graphite oxide/industrial water mass ratio of 1: 200 of a graphite oxide suspension.
2) Preparing graphene oxide sol: taking a certain amount of the graphite oxide turbid liquid prepared in the step 1), adding a LiOH solution to adjust the pH to 10.5, placing the turbid liquid with the adjusted pH in a stripping and dispersing device, carrying out ultrasonic treatment on the solution for 2 hours to obtain graphene oxide sol, and centrifuging the graphene oxide to remove graphite oxide and impurities which are not stripped sufficiently to obtain the graphene oxide sol with the water content of 99.6%;
3) adding 2.5g (NH) into 100mL of graphene oxide sol in the step 2)4)2CO3Stirring, dissolving, coagulating, standing, and settling for 1.5 hr to obtain graphene oxide aggregate, filtering with vacuum ceramic filter for 30min, and uniformly leaching for several times until no CO is detected in the washing solution3 2—Obtaining graphene oxide gel with the water content of 72%; finally, drying the obtained graphene oxide gel for 3d by using a vacuum freeze-drying method to obtain graphene oxide xerogel, wherein the recovery rate is 89%; volatile components such as ammonia released in the heating process are collected by adopting a spray (water) absorption method.
4) And (3) placing the graphene oxide xerogel obtained in the step 3) into a roasting reaction device, and roasting for 1.2h at 400 ℃ and under the condition that the air flow is 43ml/min to obtain the few-layer reduced graphene oxide, wherein the number of layers is 3-4, the number of layers is more than 95%, and the purity (carbon content) is 99.8%.
Example 5
1) Preparing a graphite oxide suspension: adding industrial water into the prepared graphite oxide to prepare a graphite oxide/industrial water mass ratio of 1: 300 of graphite oxide suspension.
2) Preparing graphene oxide sol: taking a certain amount of the graphite oxide suspension prepared in the step 1), adding a NaOH solution to adjust the pH to 11, placing the suspension after the pH adjustment in a stripping and dispersing device, carrying out ultrasonic treatment on the solution for 2 hours to obtain graphene oxide sol, and centrifuging the graphene oxide to remove graphite oxide and impurities which are not stripped sufficiently to obtain the graphene oxide sol with the water content of 99.7%;
3) adding 3g of NH into 100ml of graphene oxide sol obtained in the step 2)4NO3Stirring, dissolving, coagulating, standing, and settling for 1 hr to obtain oxidized stoneCarrying out suction filtration on the graphene aggregate for 1h, and uniformly leaching for several times until NO NO is detected in the washing liquid3 —Obtaining graphene oxide gel with the water content of 79%; and finally, drying the obtained graphene oxide gel for 3d by using a vacuum freeze-drying method to obtain graphene oxide xerogel, wherein the recovery rate is 95%.
4) Placing the graphene oxide xerogel obtained in the step 3) into a roasting reaction device, and roasting for 1h at 600 ℃ and under the condition that the He gas flow is 50ml/min to obtain the few-layer reduced graphene oxide, wherein the average layer number is 5, and the purity (carbon content) is 99.5%; volatile components such as ammonia released in the heating process are collected by adopting a spray (water) absorption method.
Example 6
1) Preparing a graphite oxide suspension: adding industrial water into the prepared graphite oxide to prepare a graphite oxide/industrial water mass ratio of 1: 500 parts of a graphite oxide suspension.
2) Preparing graphene oxide sol: taking a certain amount of graphite oxide turbid liquid, adding LiOH solution to adjust the pH value to 10, placing the turbid liquid with the adjusted pH value in a stripping and dispersing device, carrying out ultrasonic treatment on the solution for 2 hours to obtain graphene oxide sol, and centrifuging the graphene oxide to remove graphite oxide and impurities which are not stripped sufficiently to obtain the graphene oxide sol with the water content of 99.9%;
3) adding 2.5g of NH into 100mL of graphene oxide sol obtained in the step 2)4HSO4Stirring, dissolving, coagulating, standing, and settling for 1.8 hr to obtain graphene oxide aggregate, filtering with vacuum belt filter for 19min, and uniformly leaching for several times until no SO is detected in the washing solution4 2—Obtaining graphene oxide gel with the water content of 80%; and finally, drying the obtained graphene oxide gel for 3d by using a vacuum freeze-drying method to obtain graphene oxide xerogel, wherein the recovery rate is 97.4%.
4) Placing the graphene oxide xerogel obtained in the step 3) into a roasting reaction device, and roasting for 0.5h at 1200 ℃ under the condition that the Ar gas flow is 50ml/min to obtain single-layer reduced graphene oxide with the purity (carbon content) of 99.6%; volatile components such as ammonia released in the heating process are collected by adopting a spray (water) absorption method.
Example 7
1) Preparing a graphite oxide suspension: adding industrial water into the prepared graphite oxide to prepare a graphite oxide/industrial water mass ratio of 1: 400 of a graphite oxide suspension.
2) Preparing graphene oxide sol: taking a certain amount of the graphite oxide suspension prepared in the step 1), adding LiOH solution to adjust the pH to 11, placing the suspension after the pH adjustment in a stripping and dispersing device, carrying out ultrasonic treatment on the solution for 2 hours to obtain graphene oxide sol, and centrifuging the graphene oxide to remove graphite oxide and impurities which are not stripped sufficiently to obtain the graphene oxide sol with the water content of 99.8%;
3) adding 3g of (NH) into 100mL of graphene oxide sol obtained in step 2)4)2SO4Stirring, dissolving, coagulating, standing, and settling for 2 hr to obtain graphene oxide aggregate, filtering with vacuum belt filter for 25min, and uniformly leaching for several times until no SO is detected in the washing solution4 2—Obtaining graphene oxide gel with the water content of 75%; and finally, drying the obtained graphene oxide gel for 3d by using a vacuum freeze-drying method to obtain graphene oxide xerogel, wherein the recovery rate is 98.5%.
4) Placing the graphene oxide xerogel obtained in the step 3) into a roasting reaction device, and roasting for 0.5h at 1100 ℃ under the condition that the Ar gas flow is 55ml/min to obtain single-layer reduced graphene oxide with the purity (carbon content) of 99.9%; volatile components such as ammonia released in the heating process are collected by adopting a spray (water) absorption method.
In summary, the advantages of the method for preparing reduced graphene oxide and the method for precipitating graphene oxide sol according to the present invention include:
(1) the obtained graphene oxide sol can be separated from the graphite oxide which is not peeled and dispersed and impurities in the process of graphite oxide dispersion peeling and centrifugation, and the yield of reduced graphene oxide is improved.
(2) The graphene oxide is quickly condensed and precipitated from the sol by adopting the coagulating precipitant so as to realize quick dehydration and separation, so that the method is beneficial to simplifying the subsequent filtering and drying process steps, and the production efficiency is improved.
(3) The method has the advantages that the graphene oxide is rapidly coagulated and dehydrated by adopting a coagulating precipitant, so that the water content of the product is greatly reduced, and the filtering time and the energy consumption required by drying the product are saved.
(4) Ammonium ions which play an important role in the condensation and precipitation of the graphene oxide in the flocculation process are decomposed in the subsequent heating and reduction treatment to form ammonia gas and water molecules which are volatilized and removed, so that the high-purity reduced graphene oxide powder is obtained.
(5) The flocculant and the like can be directly gasified and removed through a later high-temperature thermal reduction process without washing after dehydration by adopting a certain coagulating sedimentation agent.
Although the present invention has been described above in connection with exemplary embodiments, it will be apparent to those skilled in the art that various modifications and changes may be made to the exemplary embodiments of the present invention without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (5)
1. A preparation method of reduced graphene oxide is characterized by comprising the following steps:
adjusting the pH value of the graphite oxide suspension to 9-10.5 by using a strong alkali solution, and performing dispersion stripping and centrifugal treatment to obtain graphene oxide sol, wherein the strong alkali solution comprises at least one of a LiOH solution and a NaOH solution and is not selected from KOH, other strong alkali or weak alkali;
mixing the graphene oxide sol and a coagulation precipitator, stirring, coagulating, standing, settling to obtain a graphene oxide aggregate, and then dehydrating and washing to obtain a graphene oxide gel, wherein the coagulation precipitator comprises inorganic ammonium salt, and the inorganic ammonium salt comprises at least one of ammonium chloride, ammonium bromide, ammonium nitrate, ammonium carbonate, ammonium bicarbonate, ammonium sulfate and ammonium bisulfate;
and (3) carrying out vacuum freeze drying on the graphene oxide gel, and reducing at high temperature in a protective atmosphere to obtain the reduced graphene oxide.
2. The method for producing reduced graphene oxide according to claim 1, wherein the amount of the coagulating precipitant added to the graphene oxide sol is 1 to 3g/100 ml.
3. The method for preparing reduced graphene oxide according to claim 1, wherein the total time of the stirring, coagulation, standing and settling treatment is 1-2 hours.
4. The method for preparing reduced graphene oxide according to claim 1, wherein the water content of the graphene oxide sol is 95-99.9%, and the water content of the graphene oxide gel is 70-80%.
5. The method for preparing reduced graphene oxide according to any one of claims 1 to 4, wherein the number of layers of the reduced graphene oxide is 1 to 5, and the carbon content is not less than 99.5%.
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