Gradient graphene aerogel and preparation method and application thereof

Abstract

The application relates to a gradient graphene aerogel and a preparation method and application thereof. The preparation method comprises the following steps: dispersing graphene oxide and a reducing agent in a solvent to obtain a mixed dispersion liquid; a part of the mixed dispersion liquid is taken for a first heating reaction to obtain a first layer of graphene hydrogel; a part of the mixed dispersion liquid is added to the first layer of graphene hydrogel for a second heating reaction, so that a second layer of graphene hydrogel is formed on the first layer of graphene hydrogel, and the step is repeated to obtain a gradient graphene hydrogel; and the gradient graphene hydrogel is freeze-dried to obtain a gradient graphene aerogel. The improved gradient graphene aerogel obtained by the preparation method has good integrity, high interlayer bonding force, and excellent mechanical properties, and the whole has the characteristics of continuous deformation and discontinuous displacement field.

Description

Technical Field

[0001] This application relates to the field of aerogel technology, specifically to a gradient graphene aerogel, its preparation method, and its application. Background Technology

[0002] Flexible wearable pressure sensors have found wide applications in real-time monitoring of human physiological parameters and various movement states. These sensors offer comfort, a good fit, and wearability, providing reliable data to promote healthy lifestyles. Graphene aerogel is widely used in flexible piezoresistive sensors due to its remarkable properties, including robustness, elasticity, conductivity, and lightweight.

[0003] Functionally graded materials are a new type of composite material that combines two or more materials into a continuous gradient of composition and structure. They have no obvious interfaces, which reduces interfacial damage. The characteristics of graded materials are non-homogeneity of the structure, multi-scale and continuity of mechanical properties, as well as multi-level structure.

[0004] Although related works have proposed methods to prepare gradient graphene aerogels by combining layer-by-layer assembly and unidirectional freezing, and to combine the advantages of graphene aerogels with the custom structure design in FATPS (freeze-assisted transfer printing strategy), the bonding forces between each gradient structure in the gradient graphene aerogels prepared by these methods are weak, failing to form a complete integrated structure. Furthermore, since the freezing process is controlled individually for each layer, the overall structure cannot be controlled using the ice template method, which is detrimental to performance improvement. Therefore, proposing a method for preparing gradient graphene aerogels with integrated structure and controllable overall structure is of great significance. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in the related art. To this end, one objective of this application is to provide a method for preparing gradient graphene aerogels, which can prepare gradient graphene aerogels with integral structure and tunable overall structure.

[0006] In a first aspect, embodiments of this application provide a method for preparing gradient graphene aerogel, comprising the following steps:

[0007] Graphene oxide and a reducing agent are dispersed in a solvent to obtain a mixed dispersion;

[0008] A portion of the mixed dispersion was subjected to a first heating reaction to obtain the first layer of graphene hydrogel;

[0009] A portion of the mixed dispersion is added to the first layer of graphene hydrogel, and a second heating reaction is carried out to form a second layer of graphene hydrogel on the first layer of graphene hydrogel. This step is repeated to obtain a gradient graphene hydrogel.

[0010] The gradient graphene hydrogel was freeze-dried to obtain a gradient graphene aerogel.

[0011] Secondly, embodiments of this application provide a gradient graphene aerogel, which is obtained by the preparation method of the first aspect of this application.

[0012] Thirdly, embodiments of this application provide the application of gradient graphene aerogels from the second aspect of this application in microwave absorbing structures, sensing and monitoring, and the fields of building or energy.

[0013] Compared with the prior art, the beneficial effects of this application are:

[0014] 1. This application provides an improved method for preparing gradient graphene aerogels. The process is simple, requires no additional equipment development or the addition of new substances, is convenient and quick, low in cost, and suitable for large-scale production. The preparation method of this application forms gradient graphene hydrogels through a stepwise hydrothermal reaction. The gradient graphene hydrogel comprises multiple layers of hydrogel, each undergoing a hydrothermal reaction for a different time. The entire gradient graphene hydrogel is then freeze-dried, achieving overall structural control through an ice-templating method, thereby forming an integrated graphene aerogel with a gradient structure. Due to the hydrothermal reaction, π-π bonds are formed between each aerogel layer, resulting in strong interlayer bonding and improved mechanical properties.

[0015] 2. The improved gradient graphene aerogel obtained by the preparation method of this application has good integrity. π-π bonds are formed between different layers of aerogel due to hydrothermal reaction, which improves the interlayer bonding force and makes the gradient graphene aerogel have better mechanical properties. The whole has the characteristics of continuous deformation and discontinuous displacement field.

[0016] In addition, the improved gradient graphene aerogel has a gradient structure, which makes the graphene aerogel exhibit non-uniformity of the tissue, multi-scale and continuity of mechanical properties, as well as multi-level structure.

[0017] 3. The gradient graphene aerogel of this application can be widely used in microwave absorbing structures, sensing and monitoring, construction, energy and other fields. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the steps of the method for preparing gradient graphene aerogel according to this application.

[0019] Figure 2 This is a schematic diagram of the gradient graphene aerogel structure of Example 1 of this application.

[0020] Figure 3 This is a physical image of the gradient graphene aerogel of Example 1 of this application.

[0021] Figure 4 The images show the microstructure (optical microscope images) of different gradient layers of the gradient graphene aerogel in Example 1 of this application. Figure 4 (a) is a 1-hour hydrothermal layer. Figure 4 (b) is a 2-hour hydrothermal layer. Figure 4 (c) is a 3-hour hydrothermal layer. Detailed Implementation

[0022] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application. Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. In the embodiments, unless otherwise specified, the raw materials used are commercially available, and the methods used in the following embodiments are conventional methods in the art unless otherwise specified.

[0023] In one aspect, embodiments of this application provide a method for preparing gradient graphene aerogel, the steps of which are shown in the flowchart below. Figure 1 As shown, it includes the following steps:

[0024] Graphene oxide and a reducing agent are dispersed in a solvent to obtain a mixed dispersion;

[0025] A portion of the mixed dispersion was subjected to a first heating reaction to obtain the first layer of graphene hydrogel;

[0026] A portion of the mixed dispersion is added to the first layer of graphene hydrogel, and a second heating reaction is carried out to form a second layer of graphene hydrogel on the first layer of graphene hydrogel. This step is repeated to obtain a gradient graphene hydrogel.

[0027] The gradient graphene hydrogel was freeze-dried to obtain a gradient graphene aerogel.

[0028] The preparation method of this application forms a gradient graphene hydrogel through a stepwise hydrothermal reaction. The gradient graphene hydrogel includes multiple layers of hydrogel, each of which undergoes a hydrothermal reaction for a different time. Then, the gradient graphene hydrogel is freeze-dried as a whole, and the overall structure is controlled by the ice template method to form an integrated graphene aerogel with a gradient structure. In this aerogel, π-π bonds are formed between each layer of aerogel due to the hydrothermal reaction, and the interlayer bonding force is very strong, which is beneficial to improving mechanical properties.

[0029] In some embodiments, the preparation method includes multiple heating reactions. The first heating reaction is carried out at a temperature of 70-90°C (e.g., 70°C, 75°C, 80°C, 85°C, or 90°C) for a time of 0.5-2 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, or 2 hours); the second heating reaction is carried out at a temperature of 70-90°C (e.g., 70°C, 75°C, 80°C, 85°C, or 90°C) for a time of 0.5-2 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, or 2 hours), and so on. Preferably, the final heating reaction is carried out at a temperature of 110-130°C (e.g., 110°C, 115°C, 120°C, 125°C, or 130°C) for a time of 0.5-2 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, or 2 hours). In other words, except for the final heating reaction which takes place at 110-130°C for 0.5-2 hours, the heating reactions (i.e., hydrothermal reactions) in all other steps are conducted at 70-90°C for 0.5-2 hours. The reaction temperatures in this application are conducive to the full conduct of the hydrothermal reaction, thereby facilitating the transformation of the mixed dispersion from a solution state to a hydrogel state. The final heating reaction temperature in this application is higher than the previous heating reaction temperatures, which is beneficial for the full conduct of the hydrothermal reaction and for the effective formation of π-π bonds between the layers, thereby improving the bonding strength between the layers.

[0030] In some specific embodiments, after the second layer of graphene hydrogel is formed, this step can be repeated 0-3 times (e.g., once, twice, or three times).

[0031] In some specific embodiments, after forming the second layer of graphene hydrogel, this step is repeated once to form a third layer of graphene hydrogel on the second layer, resulting in a gradient graphene hydrogel. The preparation method includes three heating reactions. The first and second heating reactions are both conducted at temperatures of 70-90°C (e.g., 70°C, 75°C, 80°C, 85°C, or 90°C) for 0.5-2 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, or 2 hours). The third heating reaction is conducted at temperatures of 110-130°C (e.g., 110°C, 115°C, 120°C, 125°C, or 130°C) for 0.5-2 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, or 2 hours).

[0032] In some specific embodiments, the final heating reaction is carried out under closed conditions. Gas is generated during the reaction. Under closed conditions, as the amount of gas increases, the system pressure increases. At higher temperatures, this is more conducive to the full hydrothermal reaction and the effective formation of π-π bonds between the layers, thereby improving the bonding strength between the layers.

[0033] In some embodiments, the preparation method further includes cooling after each heating reaction. Cooling before proceeding to the next step after each thermal reaction helps to stabilize the hydrogel formed by the thermal reaction and prevents the subsequently added mixed dispersion from damaging the already formed gel structure.

[0034] In some embodiments, the volume of the mixed dispersion is the same in each step, preferably 5-10 ml (e.g., 5 ml, 6 ml, 7 ml, 8 ml, 9 ml, or 10 ml). Ensuring the same volume allows for greater controllability of the aerogel structure and better uniformity of structural changes during use under pressure, preventing abrupt changes in mechanical properties due to excessive volume differences between each layer of the aerogel.

[0035] In some embodiments, the mixed dispersion is added dropwise in each step.

[0036] In some embodiments, the reducing agent includes one or more of ethylenediamine, ascorbic acid, polydopamine, sodium dodecyl sulfate, and sodium sulfide. These reducing agents facilitate the reduction of graphene oxide to graphene and, during the reduction process, transform the reaction system from a solution state to a hydrogel state.

[0037] In some embodiments, the mass ratio of the reducing agent to graphene oxide is 0.3:1 to 5:1, for example, 0.3:1, 0.5:1, 0.7:1, 1:1, 2:1, 3:1, 4:1, or 5:1. Preferably, when the reducing agent is ethylenediamine, the mass ratio can be 0.3:1 to 0.8:1. Preferably, when the reducing agent is ascorbic acid, the mass ratio can be 3:1 to 5:1. The amount of reducing agent affects the heating reaction and thus the change in the state of the reaction system. Insufficient reducing agent will prevent the reaction system from completely transforming from a solution state to a hydrogel state, causing the subsequently added mixed dispersion to destroy the already formed gel structure.

[0038] In some embodiments, the solvent includes water.

[0039] In some embodiments, the preparation method further includes: subjecting the gradient graphene aerogel to high-temperature reduction to obtain a highly reduced gradient graphene aerogel. Preferably, the high-temperature reduction temperature is 900-1100℃ (e.g., 900℃, 950℃, 1000℃, 1050℃, or 1100℃), and the time is 10-20 minutes (e.g., 10 minutes, 15 minutes, or 20 minutes). Preferably, the high-temperature reduction is carried out in an inert protective atmosphere (e.g., an argon atmosphere). The highly reduced gradient graphene aerogel has a more stable structure and higher conductivity, which is beneficial for improving the overall performance of the aerogel. The temperature range of this application is conducive to the full progress of the reduction reaction. If the reduction temperature is too low, it is not conducive to the complete reduction reaction, while if the reduction temperature is too high, it may cause graphene carbonization.

[0040] In some embodiments, freeze-drying includes low-temperature freezing and vacuum drying. Preferably, the low-temperature freezing temperature is -80°C to -100°C (e.g., -80°C, -85°C, -90°C, -95°C, or -100°C), and the time is 1-4 hours (e.g., 1 hour, 2 hours, 3 hours, or 4 hours). Preferably, the vacuum drying vacuum degree is 1-6 Pa (e.g., 1-3 Pa, 3-6 Pa, or 2-4 Pa), and the time is 60-84 hours (e.g., 60 hours, 66 hours, 72 hours, 78 hours, or 84 hours). In some specific embodiments, low-temperature freezing is low-temperature centripetal freezing. The temperature, pressure, and time of freeze-drying in this application are beneficial for completely freezing and fully drying the gradient graphene hydrogel, thereby enabling the hydrogel to completely transform into an aerogel and improving the stability of the aerogel structure.

[0041] In some embodiments, the preparation of the mixed dispersion includes:

[0042] Graphene oxide is dispersed in a solvent to obtain a graphene oxide dispersion.

[0043] The graphene oxide dispersion is mixed and dispersed with the reducing agent to obtain the mixed dispersion.

[0044] In some specific embodiments, the concentration of the graphene oxide dispersion is 5-10 mg / ml, for example, 5 mg / ml, 6 mg / ml, 7 mg / ml, 8 mg / ml, 9 mg / ml, or 10 mg / ml. Too low a concentration of the graphene oxide dispersion will prevent the hydrogel from forming during the reaction.

[0045] In some specific embodiments, ultrasonic dispersion is employed. Ultrasonic dispersion is beneficial for improving dispersion uniformity. The ultrasonic dispersion time is 5-15 min (e.g., 5 min, 10 min, or 15 min). Ultrasonic dispersion is performed in a mode with a working time of 15-50 s and an interval time of 2-4 s.

[0046] Secondly, embodiments of this application provide a gradient graphene aerogel, which is obtained by the preparation method of the first aspect of this application.

[0047] Thirdly, embodiments of this application provide the application of gradient graphene aerogels from the second aspect of this application in microwave absorbing structures, sensing and monitoring, and the fields of building or energy.

[0048] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0049] Example 1

[0050] (1) A certain concentration of graphene oxide aqueous solution was dispersed by an ultrasonic cell disruptor to obtain a uniform dispersion. Specifically, 30 ml of 5 mg / ml graphene oxide aqueous solution was transferred into a beaker using a pipette. The beaker was placed in the ultrasonic cell disruptor, and the ultrasonic cell disruptor was set to 300 W power, 20 s working time, and 3 s interval time. The mixture was ultrasonically dispersed for 10 min to obtain 30 ml of uniform graphene oxide dispersion.

[0051] (2) Add a certain volume of reducing agent to the uniformly dispersed graphene oxide solution obtained in step one, and disperse it for ten minutes using an ultrasonic cell disruptor to obtain a mixed dispersion; specifically, add 90 μl of ethylenediamine (analytical grade) to the uniformly dispersed graphene oxide solution obtained in step one using a pipette, with a volume ratio of ethylenediamine to graphene oxide aqueous solution of 30 μl: 10 ml (ethylenediamine density 0.899 g / cm³). 3 The mass ratio of ethylenediamine to graphene oxide was 0.54:1. The mixed solution was placed in an ultrasonic cell disruptor, which was set to 400W power, 40s working time, and 3s interval time. The mixture was ultrasonically dispersed for 10min to obtain a mixed dispersion.

[0052] (3) Transfer the mixed dispersion obtained in step two to a medicine bottle, seal it, and place it in a drying oven for heating. React for 1 hour to obtain 1-hour graphene hydrogel. Specifically, transfer 10 ml of the mixed dispersion obtained in step two to a medicine bottle using a dropper, seal the medicine bottle with the cap, and transfer it to an oven for reaction. Set the oven temperature to 80°C and the reaction time to 1 hour to obtain a gel-like product. This product is called 1-hour graphene hydrogel (i.e., the first layer of graphene hydrogel).

[0053] (4) Add the same volume of the mixed dispersion obtained in step two to the 1-hour graphene hydrogel layer, seal it, and place it in a drying oven for heating; specifically, take out the medicine bottle and cool it to room temperature, then add 10 ml of the mixed dispersion obtained in step two to the 1-hour graphene hydrogel. Since the 1-hour graphene hydrogel is a gel-like substance, the added mixed dispersion will not destroy the gel structure that has already been formed. After sealing the medicine bottle with the cap, transfer it to an oven to continue the reaction. Set the oven temperature to 80°C and the reaction time to 1 hour to obtain a gradient gel-like product, including two layers of hydrogel, which are respectively called 1-hour graphene hydrogel (i.e., the second layer of graphene hydrogel) and 2-hour graphene hydrogel (i.e., the first layer of graphene hydrogel) transformed from the 1-hour graphene hydrogel in step three.

[0054] (5) Add the same volume of the mixed dispersion obtained in step two to the 1-hour graphene hydrogel layer, seal it, and place it in an oven for heating; specifically, take out the medicine bottle and cool it to room temperature, add 10 ml of the mixed dispersion obtained in step two to the two gradient hydrogel layers, seal the medicine bottle with the bottle cap, place the medicine bottle in the reaction vessel, keep the pressure valve closed, rotate the reaction vessel to seal it, place it in an oven with the temperature set at 120°C and the reaction time at 1 hour, cool the reaction vessel to room temperature, and obtain a gradient gel product, including 3 layers of hydrogel, which are respectively called 1-hour graphene hydrogel (i.e., the third layer of graphene hydrogel), 2-hour graphene hydrogel (i.e., the second layer of graphene hydrogel) transformed from the 1-hour graphene hydrogel obtained in step four, and 3-hour graphene hydrogel (i.e., the first layer of graphene hydrogel) transformed from the 2-hour graphene hydrogel obtained in step three.

[0055] (6) The gradient gel product obtained in step five is subjected to low-temperature freezing in a freeze dryer; specifically, the gradient gel product obtained in step five is placed in the cold trap of the freeze dryer, the cold trap is set at -90°C, pre-cooled for 3 hours in advance to ensure uniform internal temperature, and frozen for 2 hours at this temperature to ensure that the gradient graphene hydrogel is completely frozen.

[0056] (7) Further vacuum drying is performed to obtain gradient graphene aerogel; specifically, the frozen gradient graphene hydrogel is placed in a freeze dryer for vacuum drying, the vacuum pump is turned on, the vacuum degree inside the freeze dryer is maintained at 1-6 Pa, and the drying time is 72 h to obtain gradient graphene aerogel.

[0057] (8) The gradient graphene aerogel obtained in step seven is further reduced at high temperature in a high-temperature tube furnace to obtain highly reduced gradient graphene aerogel. Specifically, the gradient graphene aerogel obtained in step seven is placed in a high-temperature tube muffle furnace for high-temperature reduction treatment to improve its conductivity. An argon atmosphere of one atmosphere is maintained in the muffle furnace, the temperature is set to 1000℃, and the reaction time is 15min to obtain highly reduced gradient graphene aerogel.

[0058] A schematic diagram of the highly reduced gradient graphene aerogel prepared in Example 1 is shown below. Figure 2 As shown in the picture, the actual product is as follows. Figure 3 As shown in the figure. Microscopic morphology images of different gradient layers in a highly reduced gradient graphene aerogel are shown in the figure. Figure 4 As shown.

[0059] Example 2

[0060] (1) A certain concentration of graphene oxide aqueous solution was dispersed by an ultrasonic cell disruptor to obtain a uniform dispersion. Specifically, 30 ml of 5 mg / ml graphene oxide aqueous solution was transferred into a beaker using a pipette. The beaker was placed in the ultrasonic cell disruptor, and the ultrasonic cell disruptor was set to 300 W power, 20 s working time, and 3 s interval time. The mixture was ultrasonically dispersed for 10 min to obtain 30 ml of uniform graphene oxide dispersion.

[0061] (2) Add a certain volume of reducing agent to the uniformly dispersed graphene oxide solution obtained in step one, and disperse it for ten minutes using an ultrasonic cell disruptor to obtain a mixed dispersion; specifically, add 105 μl of ethylenediamine (analytical grade) to the uniformly dispersed graphene oxide solution obtained in step one using a pipette, with a volume ratio of ethylenediamine to the graphene oxide aqueous solution of 35 μl: 10 ml (ethylenediamine density 0.899 g / cm³). 3 The mass ratio of ethylenediamine to graphene oxide was 0.63:1. The mixed solution was placed in an ultrasonic cell disruptor, which was set to 400W power, 40s working time, and 3s interval time. The mixture was ultrasonically dispersed for 10min to obtain a mixed dispersion.

[0062] (3) Transfer the mixed dispersion obtained in step two to a medicine bottle, seal it, and place it in a drying oven for heating. React for 2 hours to obtain 2-hour graphene hydrogel. Specifically, transfer 10 ml of the mixed dispersion obtained in step two to a medicine bottle using a dropper, seal the medicine bottle with the cap, and transfer it to an oven for reaction. Set the oven temperature to 70°C and the reaction time to 2 hours to obtain a gel-like product. This product is called 2-hour graphene hydrogel (i.e., the first layer of graphene hydrogel).

[0063] (4) Add the same volume of the mixed dispersion obtained in step two to the 2-hour graphene hydrogel layer, seal it, and place it in a drying oven for heating; specifically, take out the medicine bottle and cool it to room temperature, then add 10 ml of the mixed dispersion obtained in step two to the 2-hour graphene hydrogel. Since the 2-hour graphene hydrogel is a gel-like substance, the added mixed dispersion will not destroy the gel structure that has already been formed. After sealing the medicine bottle with the cap, transfer it to an oven to continue the reaction. Set the oven temperature to 70°C and the reaction time to 2 hours to obtain a gradient gel-like product, including two layers of hydrogel, which are respectively called 2-hour graphene hydrogel (i.e., the second layer of graphene hydrogel) and 4-hour graphene hydrogel (i.e., the first layer of graphene hydrogel) transformed from the 2-hour graphene hydrogel in step three.

[0064] (5) Add the same volume of the mixed dispersion obtained in step two to the 2-hour graphene hydrogel layer, seal it, and place it in an oven for heating; specifically, take out the medicine bottle and cool it to room temperature, add 10 ml of the mixed dispersion obtained in step two to the two gradient hydrogel layers, seal the medicine bottle with the bottle cap, place the medicine bottle in the reaction vessel, keep the pressure valve closed, rotate the reaction vessel to seal it, place it in an oven with the temperature set at 110°C and the reaction time at 2 hours, cool the reaction vessel to room temperature, and obtain a gradient gel product, including 3 layers of hydrogel, which are respectively called 2-hour graphene hydrogel (i.e., the third layer of graphene hydrogel), 4-hour graphene hydrogel (i.e., the second layer of graphene hydrogel) transformed from the 2-hour graphene hydrogel obtained in step four, and 6-hour graphene hydrogel (i.e., the first layer of graphene hydrogel) transformed from the 4-hour graphene hydrogel obtained in step three.

[0065] (6) The gradient gel product obtained in step five is subjected to low-temperature freezing in a freeze dryer; specifically, the gradient gel product obtained in step five is placed in the cold trap of the freeze dryer, the cold trap is set at -80°C, pre-cooled for 3 hours in advance to ensure uniform internal temperature, and frozen for 4 hours at this temperature to ensure that the gradient graphene hydrogel is completely frozen.

[0066] (7) Further vacuum drying is performed to obtain gradient graphene aerogel; specifically, the frozen gradient graphene hydrogel is placed in a freeze dryer for vacuum drying, the vacuum pump is turned on, the vacuum degree inside the freeze dryer is maintained at 1-6 Pa, and the drying time is 72 h to obtain gradient graphene aerogel.

[0067] (8) The gradient graphene aerogel obtained in step seven is further reduced at high temperature in a high-temperature tube furnace to obtain highly reduced gradient graphene aerogel. Specifically, the gradient graphene aerogel obtained in step seven is placed in a high-temperature tube muffle furnace for high-temperature reduction treatment to improve its conductivity. An argon atmosphere of one atmosphere is maintained in the muffle furnace, the temperature is set to 900℃, and the reaction time is 20min to obtain highly reduced gradient graphene aerogel.

[0068] The structural schematic diagram of the highly reduced gradient graphene aerogel prepared in Example 2 is similar to that of... Figure 2 The actual product image is similar to Figure 3 The microstructure diagrams of different gradient layers are similar. Figure 4 .

[0069] Example 3

[0070] (1) A certain concentration of graphene oxide aqueous solution was dispersed by an ultrasonic cell disruptor to obtain a uniform dispersion. Specifically, 30 ml of 5 mg / ml graphene oxide aqueous solution was transferred into a beaker using a pipette. The beaker was placed in the ultrasonic cell disruptor, and the ultrasonic cell disruptor was set to 300 W power, 20 s working time, and 3 s interval time. The mixture was ultrasonically dispersed for 10 min to obtain 30 ml of uniform graphene oxide dispersion.

[0071] (2) Add a certain volume of reducing agent to the uniformly dispersed graphene oxide solution obtained in step one, and disperse it for ten minutes using an ultrasonic cell disruptor to obtain a mixed dispersion; specifically, add 90 μl of ethylenediamine (analytical grade) to the uniformly dispersed graphene oxide solution obtained in step one using a pipette, with a volume ratio of ethylenediamine to graphene oxide aqueous solution of 30 μl: 10 ml (ethylenediamine density 0.899 g / cm³). 3 The mass ratio of ethylenediamine to graphene oxide was 0.54:1. The mixed solution was placed in an ultrasonic cell disruptor, which was set to 400W power, 40s working time, and 3s interval time. The mixture was ultrasonically dispersed for 10min to obtain a mixed dispersion.

[0072] (3) Transfer the mixed dispersion obtained in step two to a medicine bottle, seal it, and place it in a drying oven for heating. The reaction time is 0.5 hours to obtain 0.5-hour graphene hydrogel. Specifically, transfer 10 ml of the mixed dispersion obtained in step two to a medicine bottle using a dropper, seal the medicine bottle with the cap, and transfer it to an oven for reaction. The oven temperature is set to 90°C and the reaction time is 0.5 hours to obtain a gel-like product. This product is called 0.5-hour graphene hydrogel (i.e., the first layer of graphene hydrogel).

[0073] (4) Add the same volume of the mixed dispersion obtained in step two to the 0.5-hour graphene hydrogel layer, seal it, and place it in a drying oven for heating; specifically, take out the medicine bottle and cool it to room temperature, then add 10 ml of the mixed dispersion obtained in step two to the 0.5-hour graphene hydrogel. Since the 0.5-hour graphene hydrogel is a gel-like substance, the added mixed dispersion will not destroy the gel structure that has already been formed. After sealing the medicine bottle with the cap, transfer it to an oven to continue the reaction. Set the oven temperature to 90°C and the reaction time to 0.5 h to obtain a gradient gel-like product, including two layers of hydrogel, which are respectively called the 0.5-hour graphene hydrogel (i.e., the second layer of graphene hydrogel) and the 1-hour graphene hydrogel (i.e., the first layer of graphene hydrogel) transformed from the 0.5-hour graphene hydrogel in step three.

[0074] (5) Add the same volume of the mixed dispersion obtained in step two to the 0.5-hour graphene hydrogel layer, seal it, and place it in an oven for heating; specifically, take out the medicine bottle and cool it to room temperature, add 10 ml of the mixed dispersion obtained in step two to the two gradient hydrogel layers, seal the medicine bottle with the bottle cap, place the medicine bottle in the reaction vessel, keep the pressure valve closed, rotate and seal the reaction vessel, place it in an oven with the temperature set at 130°C and the reaction time at 0.5 h, cool the reaction vessel to room temperature, and obtain a gradient gel product, including 3 layers of hydrogel, which are respectively called 0.5-hour graphene hydrogel (i.e., the third layer of graphene hydrogel), 1-hour graphene hydrogel (i.e., the second layer of graphene hydrogel) transformed from the 0.5-hour graphene hydrogel obtained in step four, and 1.5-hour graphene hydrogel (i.e., the first layer of graphene hydrogel) transformed from the 1-hour graphene hydrogel obtained in step three.

[0075] (6) The gradient gel product obtained in step five is subjected to low-temperature freezing in a freeze dryer; specifically, the gradient gel product obtained in step five is placed in the cold trap of the freeze dryer, the cold trap is set at -100℃, pre-cooled for 3 hours in advance to ensure uniform internal temperature, and frozen for 1 hour at this temperature to ensure that the gradient graphene hydrogel is completely frozen.

[0076] (7) Further vacuum drying is performed to obtain gradient graphene aerogel; specifically, the frozen gradient graphene hydrogel is placed in a freeze dryer for vacuum drying, the vacuum pump is turned on, the vacuum degree inside the freeze dryer is maintained at 1-6 Pa, and the drying time is 72 h to obtain gradient graphene aerogel.

[0077] (8) The gradient graphene aerogel obtained in step seven is further reduced at high temperature in a high-temperature tube furnace to obtain highly reduced gradient graphene aerogel. Specifically, the gradient graphene aerogel obtained in step seven is placed in a high-temperature tube muffle furnace for high-temperature reduction treatment to improve its conductivity. An argon atmosphere of one atmosphere is maintained in the muffle furnace, the temperature is set to 1100℃, and the reaction time is 10min to obtain highly reduced gradient graphene aerogel.

[0078] The structural schematic diagram of the highly reduced gradient graphene aerogel prepared in Example 3 is similar to that of... Figure 2 The actual product image is similar to Figure 3 The microstructure diagrams of different gradient layers are similar. Figure 4 .

[0079] Example 4

[0080] Gradient graphene aerogels were prepared according to the method of Example 1, except that step 2 was different. Specifically, (2) a certain volume of reducing agent was added to the uniformly dispersed graphene oxide solution obtained in step 1, and the solution was dispersed for ten minutes by an ultrasonic cell disruptor to obtain a mixed dispersion. Specifically, ascorbic acid powder (mass ratio of ascorbic acid to graphene oxide was 4:1) was added to the uniformly dispersed graphene oxide solution obtained in step 1 using a pipette. The mixed solution was placed in an ultrasonic cell disruptor, and the ultrasonic cell disruptor power was set to 400W, working time to 40s, and interval time to 3s. The solution was ultrasonically dispersed for 10min to obtain a mixed dispersion.

[0081] The structural schematic diagram of the highly reduced gradient graphene aerogel prepared in Example 4 is similar to that of... Figure 2 The actual product image is similar to Figure 3 The microstructure diagrams of different gradient layers are similar. Figure 4 .

[0082] Comparative Example 5

[0083] Gradient graphene aerogels were prepared according to the method in Example 1, except that in step two, the amount of ethylenediamine used was 60 μl, and the volume ratio of ethylenediamine to the aqueous graphene oxide solution was 20 μl: 10 ml (ethylenediamine density 0.899 g / cm³). 3 The mass ratio of ethylenediamine to graphene oxide is 0.36:1.

[0084] Because the amount of ethylenediamine was too small, the mixed dispersion in step three could not be transformed from a solution state to a hydrogel state, and the gradient graphene aerogel was not ultimately obtained.

[0085] Comparative Example 6

[0086] Gradient graphene aerogels were prepared according to the method in Example 1, except that the concentration of the graphene oxide aqueous solution in step two was 2 mg / ml (ethylenediamine density 0.899 g / cm³). 3 The mass ratio of ethylenediamine to graphene oxide is 1.3:1.

[0087] Because the concentration of the graphene oxide aqueous solution was too low, the mixed dispersion in step three could not be transformed from a solution state to a hydrogel state, and gradient graphene aerogel was ultimately not obtained.

[0088] As can be seen from the above embodiments and comparative examples, the preparation method of this application forms a gradient graphene hydrogel through a stepwise hydrothermal reaction. The gradient graphene hydrogel includes multiple layers of hydrogel, each of which undergoes a hydrothermal reaction for a different time. The entire gradient graphene hydrogel is then freeze-dried, achieving overall structural control through an ice-templating method, thereby forming an integrated graphene aerogel with a gradient structure. The preparation method of this application is simple, requires no additional equipment development or the addition of new substances, is convenient and fast, low in cost, and suitable for large-scale production.

[0089] The terms "first" and "second" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature marked "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0091] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a gradient graphene aerogel, characterized by, Includes the following steps: Graphene oxide and a reducing agent are dispersed in a solvent to obtain a mixed dispersion; A portion of the mixed dispersion was subjected to a first heating reaction to obtain the first layer of graphene hydrogel; A portion of the mixed dispersion is added to the first layer of graphene hydrogel, and a second heating reaction is carried out to form a second layer of graphene hydrogel on the first layer of graphene hydrogel. This step is repeated to obtain a gradient graphene hydrogel. The gradient graphene hydrogel was freeze-dried to obtain a gradient graphene aerogel. The preparation method includes multiple heating reactions. The temperature of the first heating reaction is 70-90℃ and the time is 0.5-2h; the temperature of the second heating reaction is 70-90℃ and the time is 0.5-2h, and so on; the temperature of the last heating reaction is 110-130℃ and the time is 0.5-2h. The preparation method further includes: subjecting the gradient graphene aerogel to high-temperature reduction to obtain a highly reduced gradient graphene aerogel.

2. The production method according to claim 1, characterized by, After each heating reaction is completed, the preparation method also includes cooling.

3. The preparation method according to claim 2, characterized in that, After the second layer of graphene hydrogel is formed, repeat this step 1-3 times.

4. The preparation method according to claim 1 or 2, characterized in that, In each step, the volume of the mixed dispersion is the same, ranging from 5 to 10 ml.

5. The preparation method according to claim 4, characterized in that, In each step, the mixed dispersion is added dropwise.

6. The preparation method according to claim 1 or 2, characterized in that, The reducing agent includes one or more of ethylenediamine, ascorbic acid, polydopamine, sodium dodecyl sulfate, and sodium sulfide.

7. The preparation method according to claim 6, characterized in that, The solvent includes water.

8. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of reducing agent to graphene oxide is 0.3:1 to 5:

1.

9. The preparation method according to claim 1 or 2, characterized in that, The high-temperature reduction is carried out at a temperature of 900-1100℃ for 10-20 minutes.

10. The preparation method according to claim 9, characterized in that, High-temperature reduction is carried out in an inert protective atmosphere.

11. The preparation method according to claim 1 or 2, characterized in that, Freeze-drying includes low-temperature freezing and vacuum drying.

12. The preparation method according to claim 11, characterized in that, The low-temperature freezing temperature is -80℃ to -100℃, and the time is 1-4 hours.

13. The preparation method according to claim 11, characterized in that, The vacuum degree of vacuum drying is 1-6 Pa, and the time is 60-84 h.

14. The preparation method according to claim 1 or 2, characterized in that, The preparation of the mixed dispersion includes: Graphene oxide is dispersed in a solvent to obtain a graphene oxide dispersion. The graphene oxide dispersion is mixed and dispersed with the reducing agent to obtain the mixed dispersion.

15. The preparation method according to claim 14, characterized in that, The concentration of the graphene oxide dispersion is 5-10 mg / ml.

16. The preparation method according to claim 14, characterized in that, Dispersion was performed using ultrasound.

17. A gradient graphene aerogel, characterized in that, Obtained by the preparation method according to any one of claims 1-16.

18. The application of the gradient graphene aerogel of claim 17 in the fields of microwave absorbing structures, sensing and monitoring, construction or energy.

Images