CN109437180B - Preparation method of low-layer graphene oxide and freeze-drying method of graphene oxide - Google Patents
Preparation method of low-layer graphene oxide and freeze-drying method of graphene oxide Download PDFInfo
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- CN109437180B CN109437180B CN201811492018.2A CN201811492018A CN109437180B CN 109437180 B CN109437180 B CN 109437180B CN 201811492018 A CN201811492018 A CN 201811492018A CN 109437180 B CN109437180 B CN 109437180B
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- C01B32/00—Carbon; Compounds thereof
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- C01B32/182—Graphene
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- C01B2204/00—Structure or properties of graphene
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B2204/00—Structure or properties of graphene
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B2204/00—Structure or properties of graphene
- C01B2204/20—Graphene characterized by its properties
- C01B2204/32—Size or surface area
Abstract
The invention provides a preparation method of low-layer graphene oxide and a freeze-drying method of graphene oxide. The preparation method comprises the following steps: dispersing graphene oxide having a first layer number in water, and forming a graphene oxide hydrogel; and placing the graphene oxide hydrogel at a first temperature and a first pressure to condense water molecules in the graphene oxide hydrogel into ice molecules and desublimate the ice molecules, so that graphene oxide with a second layer number is obtained, wherein the first layer number is tens of layers to tens of layers, and the second layer number is smaller than the first layer number. The beneficial effects of the invention include: the structure of the graphite oxide sheet layer cannot be damaged in the freeze drying process, functional groups are well preserved, and the graphite oxide subjected to freeze drying is not easy to agglomerate; the layer-to-layer spacing of the graphene oxide sheets after freeze drying is larger than that of a graphene oxide product dried by a conventional drying method, and the graphene oxide product has more excellent dispersing performance, fewer layers and larger specific surface area.
Description
Technical Field
The invention relates to the technical field of graphene oxide production, in particular to a preparation method of low-layer graphene oxide and a freeze drying method of graphene oxide.
Background
Generally, due to poor thermal stability of graphite oxide, a pyrolysis phenomenon often occurs in the drying process, and the heated and dried graphite oxide is easily agglomerated into hard blocks, which is not beneficial to subsequent dispersion.
Disclosure of Invention
The present invention aims to address at least one of the above-mentioned deficiencies of the prior art. For example, it is an object of the present invention to provide a new method for graphene oxide drying.
In order to achieve the above object, an aspect of the present invention provides a preparation method of graphene oxide with a low number of layers, including the steps of: dispersing graphene oxide having a first layer number in water, and forming a graphene oxide hydrogel; placing the graphene oxide hydrogel at a first temperature and a first pressure to condense water molecules in the graphene oxide hydrogel into ice molecules and desublimate the ice molecules, so that graphene oxide with a second layer number is obtained, wherein the first layer number is tens of layers to tens of layers, the second layer number is smaller than the first layer number, the first temperature is not higher than-50 ℃ and the temperature change is not more than +/-4 ℃, and the first pressure is lower than 1 atmosphere and the pressure change is not more than +/-100 Pa.
Another aspect of the present invention provides a method for freeze-drying graphene oxide, comprising the steps of: forming graphene oxide hydrogel; and placing the graphene oxide hydrogel at a first temperature and a first pressure to condense water molecules in the graphene oxide hydrogel into ice molecules and desublimate the ice molecules, so as to obtain a graphene oxide sheet layer, wherein the first temperature is not higher than-50 ℃ and the temperature variation is not more than +/-4 ℃, and the first pressure is lower than 1 atmosphere and the pressure variation is not more than +/-100 Pa.
Compared with the prior art, the invention has the beneficial effects that: (1) the structure of the graphite oxide sheet layer can not be damaged in the freeze drying process, functional groups can be well preserved, and the graphite oxide after freeze drying is not easy to agglomerate. (2) The graphene oxide product after freeze drying has more excellent dispersion performance, fewer layers and larger specific surface area, and the layer-to-layer distance of the graphene oxide sheets is larger than that of the graphene oxide product after being dried by other drying methods.
Detailed Description
Hereinafter, the method for preparing graphene oxide having a low number of layers and the method for freeze-drying graphene oxide according to the present invention will be described in detail with reference to exemplary embodiments.
In an exemplary embodiment of the present invention, the preparation method of the graphene oxide with the low number of layers can be realized by the following steps:
(1) formation of graphene oxide hydrogels
The graphene oxide having the first number of layers is dispersed in water, and a graphene oxide hydrogel is formed. The number of the first layer can be tens of layers to tens of layers, for example, 20 to 30 layers. The graphene oxide contains an oxygen-containing functional group. For example, the graphene oxide having the first layer number may be prepared by intercalating graphite with protonic acid. In the dispersing process, the dispersing effect is preferably further enhanced by ultrasonic dispersion, so that water molecules fully enter a lamellar structure or folds of the graphene oxide, or are combined with functional groups on the surface of the graphene oxide to form hydrated ions, thereby forming the graphene oxide hydrogel. The graphene oxide hydrogel has a structure in which water molecules are bonded in its own sheet or wrinkle of graphene oxide. The solid content of the graphene oxide hydrogel can be 0.1-50 wt%. The water used for dispersing the graphene oxide is preferably secondary deionized water.
(2) Carrying out low-temperature vacuum freeze drying on graphene oxide hydrogel
And placing the graphene oxide hydrogel at a first temperature and a first pressure to condense water molecules in the graphene oxide hydrogel into ice molecules and desublimate the ice molecules, so that the graphene oxide with a second layer number is obtained. And the first temperature is controlled not to be higher than-50 ℃ and the variation of the first temperature is not more than + -4 ℃ at all times, the first pressure is controlled to be lower than 1 atmosphere and the variation of the first pressure is not more than + -100 Pa. Further, the first temperature may be selected within the range of-55 to-65 ℃ and the temperature variation does not exceed ± 2 ℃. The first pressure intensity can be selected within the range of 10-100 Pa, and the pressure intensity variation does not exceed +/-10 Pa.
Wherein the second number of layers is less than the first number of layers. The second number of layers may have a significant reduction compared to the first number of layers. Here, the second number of layers may be 1/3-1/6 of the first number of layers. For example, the second number of layers may be 5 to 7.
In an exemplary embodiment of the present invention, by controlling the first temperature to be not higher than-50 ℃ and the first pressure to be not higher than 1 standard atmospheric pressure, water molecules can be changed into ice molecules, and the lamellar structure of graphite can be further widened by volume expansion; and the ice can be desublimated and volatilized at low temperature and low pressure, the temperature is low, the entropy value is low, the strutted structure of the graphene oxide can be maintained, and the prepared graphene oxide material has good dispersibility and large specific surface area. Moreover, the relatively constant low temperature (for example, not higher than-50 ℃ and the temperature variation in the cavity of the whole cold dry cavity is controlled not to exceed +/-4 ℃) and the relatively constant vacuum degree (for example, lower than 1 atmosphere and the pressure variation in the whole cavity is controlled not to exceed +/-100 Pa) are beneficial to relatively stabilizing the condensation speed and degree of water molecules, so that the 'opening' effect on the graphene oxide layer is stable; but also the ice molecule desublimation speed and degree are relatively stable, thus being beneficial to avoiding local defects caused by the local stress of the graphene oxide layer to a certain degree. Furthermore, the temperature control unit and the pressure control unit are used for controlling the atmosphere of the cold drying cavity to be within the range of-55 to-65 ℃, the temperature change in the whole cavity is controlled not to exceed +/-2 ℃, the pressure is controlled to be 10 to 100Pa, the pressure change in the whole cavity is controlled not to exceed +/-10 Pa, the condensation speed and the degree of water molecules are further stabilized, and the opening effect of the graphene oxide layer is stabilized; but also the ice molecule desublimation speed and degree are further stabilized, thereby further avoiding local defects caused by the local stress of the graphene oxide layer.
In another exemplary embodiment of the present invention, the method for freeze-drying graphene oxide may be implemented by:
A. formation of graphene oxide hydrogels
The graphene oxide having the first number of layers is sufficiently dispersed in water to form a graphene oxide hydrogel. The number of the first layer can be tens of layers to tens of layers, for example, 20 to 30 layers. The graphene oxide contains an oxygen-containing functional group. For example, the graphene oxide having the first layer number may be prepared by intercalating graphite with protonic acid. In the dispersing process, the dispersing effect is preferably further enhanced through ultrasonic dispersion, so that water molecules fully enter a lamellar structure of the graphene oxide to form the graphene oxide hydrogel. The solid content of the graphene oxide hydrogel can be 0.1-50 wt%. The water used for dispersing the graphene oxide is preferably secondary deionized water.
(2) Carrying out low-temperature vacuum freeze drying on graphene oxide hydrogel
And placing the graphene oxide hydrogel at a first temperature and a first pressure to condense water molecules in the graphene oxide hydrogel into ice molecules and desublimate the ice molecules, so that the graphene oxide with a second layer number is obtained. For example, a container (e.g., a crucible) containing the graphene oxide hydrogel can be conveyed to a low-temperature low-pressure cooling device through a conveying mechanism (e.g., a crawler belt) to realize condensation and desublimation of water molecules in the graphene oxide hydrogel, so that low-temperature low-pressure cooling and drying of the graphene oxide hydrogel are completed, and graphene oxide with a desired low number of layers is obtained.
Wherein the second number of layers is less than the first number of layers. The second number of layers may have a significant reduction compared to the first number of layers. Here, the second number of layers may be 1/3-1/6 of the first number of layers. For example, the second number of layers may be 5 to 7. The first temperature is controlled to be not higher than-50 ℃ and the first temperature always has a temperature variation of not more than + -4 ℃, the first pressure is controlled to be lower than 1 atmosphere and the variation of the first pressure is not more than + -100 Pa. Further, the first temperature may be selected within the range of-55 to-65 ℃ and the temperature variation does not exceed ± 2 ℃. The first pressure intensity can be selected within the range of 10-100 Pa, and the pressure intensity variation does not exceed +/-10 Pa.
Exemplary embodiments of the present invention will be described in further detail below with reference to specific examples.
Example 1
And dispersing the graphene oxide with the layer number of 25 +/-2 in secondary deionized water, and further enhancing the dispersion effect through ultrasonic dispersion in the dispersion process to obtain the graphene oxide hydrogel. Through detection, the specific surface area of the graphene oxide before dispersion is 170m2(ii)/g; the solid content of the graphene oxide hydrogel was 10 wt%.
1000g of graphene oxide hydrogel was loaded into a ceramic crucible. Conveying the ceramic crucible to a pre-freezing system by using a crawler belt, then conveying the ceramic crucible to a freeze-drying constant-temperature area, treating the ceramic crucible at the temperature of minus 58 +/-3 ℃ and 1000 +/-50 Pa for 10 hours, and then conveying the ceramic crucible to a discharge hole by using the crawler belt.
Through detection, the water content in the graphene oxide product is lower than 0.01 wt%, the dispersibility is good, the number of layers is 5-7, and the specific surface area is 350m2/g。
Example 2
And (3) ultrasonically dispersing the graphene oxide with the layer number of 30 +/-2 in distilled water to obtain the graphene oxide hydrogel. Through detection, the specific surface area of the graphene oxide is 150m before dispersion2(ii)/g; the solid content of the graphene oxide hydrogel was 10 wt%.
2000g of graphene oxide hydrogel was loaded into a ceramic crucible. Conveying the ceramic crucible to a freeze-drying constant-temperature area by using a crawler belt, treating the ceramic crucible at the temperature of minus 54 +/-2 ℃ and 300 +/-10 Pa for 20 hours, and conveying the ceramic crucible to a discharge hole by using the crawler belt.
Through detection, the water content in the graphene oxide product is lower than 0.01 wt%, the dispersibility is good, the number of layers is 5-7, and the specific surface area is 375m2/g。
Example 3
And (3) dispersing the graphene oxide with the number of layers of 20 in purified water by stirring and ultrasonic dispersion to obtain the graphene oxide hydrogel. Through detection, before dispersion, the specific surface area of the graphene oxide is 200m2(ii)/g; the solid content of the graphene oxide hydrogel was 5 wt%.
The graphene oxide hydrogel was loaded into a ceramic crucible. Conveying the ceramic crucible to a freeze-drying constant-temperature area by using a crawler belt, treating the ceramic crucible at the temperature of minus 60 +/-4 ℃ and 80 +/-10 Pa for 20 hours, and conveying the ceramic crucible to a discharge hole by using the crawler belt.
Through detection, the water content in the graphene oxide product is lower than 0.01 wt%, the dispersibility is good, the number of layers is 5-7, and the specific surface area is 395m2/g。
In conclusion, the graphene oxide lamella can be further expanded in the drying process, and meanwhile, the graphene oxide material keeps a low entropy value at a low temperature, so that the microstructure of the expanded graphene oxide lamella can be kept, and the graphene oxide lamella is beneficial to keeping, so that the graphene oxide lamella is further expanded in the drying process, and the graphene oxide lamella is further kept in the microstructure of the expanded graphene oxide lamellaCan obtain a graphene oxide product with higher quality. For example, the graphene prepared by the method has a complete microstructure, and the number of layers of the graphene oxide can be reduced to 1/3-1/6 in the prior art, for example, the number of layers can be reduced from 20-30 to 5-7; the specific surface area of the graphene oxide is increased to 1.5-2.5 times of the original specific surface area, for example, the specific surface area can be from 100-200 m2The/g is increased to 200-400 m2/g。
While the present invention has been described in connection with the exemplary embodiments, it will be apparent to those of ordinary skill in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.
Claims (7)
1. The preparation method of the graphene oxide with the low layer number is characterized by comprising the following steps:
dispersing graphene oxide with a first layer number in water to form graphene oxide hydrogel, wherein the solid content of the graphene oxide hydrogel is 0.1-50 wt%, and the graphene oxide hydrogel has a structure that water molecules are combined in a sheet layer or a fold of graphene oxide;
and placing the graphene oxide hydrogel at a temperature which is not higher than-55 ℃ and has a temperature variation of not more than +/-4 ℃ and a pressure which is lower than 1 atmosphere and has a pressure variation of not more than +/-100 Pa, so that water molecules in the graphene oxide hydrogel are condensed into ice molecules at a relatively stable condensation speed and degree, and are sublimated at a relatively stable sublimation speed and degree, thereby obtaining graphene oxide with a second layer number, wherein the first layer number is ten to tens of layers, the second layer number is smaller than the first layer number, and the second layer number is 1/3-1/6 of the first layer number.
2. The method for preparing graphene oxide with a low number of layers according to claim 1, wherein the first number of layers is 20 to 30 layers, and the second number of layers is 5 to 7 layers.
3. The method for preparing graphene oxide with a low number of layers according to claim 1, wherein the temperature is selected from the range of-55 ℃ to-65 ℃ and the temperature variation is not more than ± 2 ℃.
4. The method for preparing graphene oxide with a low number of layers according to claim 1, wherein the pressure is selected within a range of 10-100 Pa and the variation of the pressure is not more than +/-10 Pa.
5. A method for freeze-drying graphene oxide, comprising the steps of:
forming a graphene oxide hydrogel, wherein the solid content of the graphene oxide hydrogel is 0.1-50 wt%, and the graphene oxide hydrogel has a structure in which water molecules are bonded in a sheet or a wrinkle of graphene oxide of the graphene oxide hydrogel;
and (2) placing the graphene oxide hydrogel at a temperature which is not higher than-55 ℃ and has a temperature variation of not more than +/-4 ℃ and a pressure which is lower than 1 atmosphere and has a pressure variation of not more than +/-100 Pa, so that water molecules in the graphene oxide hydrogel are condensed into ice molecules at a relatively stable condensation speed and degree and are sublimated at a relatively stable sublimation speed and degree, and thus the graphene oxide sheet layer is obtained.
6. The method for freeze-drying graphene oxide according to claim 5, wherein the temperature is selected in the range of-55 to-65 ℃ and the temperature variation does not exceed ± 2 ℃.
7. The method for freeze-drying graphene oxide according to claim 5, wherein the pressure is selected within a range of 10 to 100Pa and the variation of the pressure is not more than + -10 Pa.
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