CN112852386A - High-orientation layered graphene aerogel phase-change composite material and preparation method thereof - Google Patents
High-orientation layered graphene aerogel phase-change composite material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a high-orientation layered graphene aerogel phase change composite material and a preparation method thereof, and belongs to the field of phase change energy storage. The method specifically comprises the following steps: carrying out hydrothermal reaction on the oxidized graphene suspension in a sectional heating mode to obtain reduced graphene hydrogel; pre-freezing treatment; carrying out vacuum freeze drying to obtain a layered aerogel material; high-temperature carbonization or graphitization treatment; and compounding with the phase-change material by vacuum impregnation. The graphene aerogel prepared by the method can rebound for many times and is not easy to break; the high-orientation layered graphene aerogel phase-change composite material prepared by the invention has excellent directional heat conduction performance, high energy storage characteristic and good leakage-proof performance, and has wide application prospect in the field of phase-change energy storage.
Description
Technical Field
The invention relates to the field of phase change energy storage, in particular to a highly-oriented layered graphene aerogel phase change composite material and a preparation method thereof.
Background
With the rapid development of society, the energy demand is increasing, and the problem of storing and utilizing limited energy efficiently is a subject with great research significance. The phase change material can absorb and release latent heat according to environmental changes, can relieve the rapid change of temperature, stores energy for recycling, and reduces the excessive consumption of energy. According to different material properties, phase change materials can be divided into organic phase change materials and inorganic phase change materials, and the inorganic phase change materials have high latent heat value but are easy to generate phase separation and supercooling phenomena. The organic phase change material has wide sources and low price, but is easy to leak during phase change and has poor heat conduction performance, so the organic phase change material is concerned by a plurality of researchers. In view of the above problems of the phase change material, researchers use porous Materials (Haiyue yang. low-cost, three-dimensional, high thermal reduction, carbon hardened wood-based composite phase change Materials for thermal Energy storage [ J ] Energy 159(2018)929-936) or support Materials (Zilu liu. novel light-drive CF/PEG/SiO2 composite phase change Materials with high thermal reduction [ J ] solvent Energy and solvent cells 174(2018) -538-544) to encapsulate the phase change material and prevent leakage; the heat transfer process is enhanced by adopting carbon material (Zhang Qiang, Zhang Qiu soldier, Yankee jade, graphite adsorption phase change energy storage powder, a preparation method and application thereof (P). CN110484216A.2019.08.26) or metal and oxide thereof (Fei Cheng, Xiaoang Zhang. Thermal conductivity enhancement of form-stable evaporative/expanded performance composite phase materials by adding Cu powder and carbon fiber for Thermal energy storage [ J ] Applied Thermal Engineering 156(2019) 653-659), so that the heat conductivity of the material is improved.
The graphene aerogel is an amorphous solid material taking gas as a dispersion medium, wherein graphene nanosheets can be spontaneously cross-linked and built into a three-dimensional network structure through II-II effect and the hydrophobic characteristic of a lamella. Because the catalyst has the characteristics of high specific surface area, ultralow density and porosity, the catalyst has huge application potential in the fields of adsorption, catalysis, phase change energy storage and the like.
At present, the Preparation of graphene aerogels mainly adopts chemical reduction (Yue Xu, Amy S. Fleischer, Gang Feng. Relnformance and shape stabilization of phase-change material via graphene oxide gel [ J ]. Carbon 114(2017) 334) 346), hydrothermal reduction (hong yan Li, Cong Su aerogels with affinity graphene part I: Preparation and mechanical property glass [ journal of Alloys and Composites 783 (2019)) 486 phase 493), template method (hong Hui Liao, Wenhua Chen, Yuan Liu, Qi Wang. A phase modified in a molecular structure gel [ J ]. technique and J108010) method of chemical reduction and molecular synthesis [ 1089 ] technique ] and J.. The aerogel is prepared by a template method, the three-dimensional structure of the template can be copied, and the internal structure of the aerogel is controlled in detail, but the large-scale preparation of the aerogel is difficult to realize due to the limitation of the template. The chemical reduction method is an effective means for preparing the graphene aerogel, but the method is disordered and random, the graphene nanosheets are easy to stack face to face during self-assembly to form a thick-wall graphene-like structure, and the obtained graphene aerogel is easy to break and poor in resilience. At present, some cases of preparing the aerogel by a one-step hydrothermal method have been successful, but the phenomena of unobvious lamellar structure and nonuniform lamella size still exist.
CN11662688A discloses a boron nitride/graphene double-heat-conducting-base aerogel composite phase-change material and a preparation method thereof, and the obtained aerogel graphene nanosheets are stacked without establishing an efficient heat-conducting channel, and the heat conductivity of the graphene aerogel needs to be improved by boron nitride.
CN108439380A discloses a preparation method of a super-elastic super-hydrophobic pure graphene aerogel, which uses graphene oxide as a precursor, adjusts and controls distribution of oxygen-containing functional groups and graphitized structure size of graphene sheet layers by changing pH and temperature of the solution, and further introduces a reducing agent to obtain the pure graphene aerogel. The reducing agent added in the process of preparing the aerogel still has residual oxygen-containing functional groups and lattice defects, which can reduce phonon scattering in the process of heat transfer and reduce the thermal conductivity.
Disclosure of Invention
The invention aims to provide a high-orientation layered graphene aerogel phase-change composite material and a preparation method thereof, and aims to solve the problems in the prior art.
In order to achieve the purpose, the invention provides the following scheme:
one of the purposes of the invention is to provide a preparation method of a high-orientation layered graphene aerogel phase-change composite material, which comprises the following steps:
the method comprises the following steps: carrying out hydrothermal reaction on the oxidized graphene suspension in a sectional heating mode to obtain reduced graphene hydrogel;
step two: pre-freezing the reduced graphene hydrogel;
step three: carrying out vacuum freeze drying on the reduced graphene hydrogel subjected to pre-freezing treatment in the step two to obtain a layered aerogel material;
step four: carrying out high-temperature carbonization or graphitization treatment on the layered aerogel material;
step five: and compounding the layered aerogel material subjected to high-temperature carbonization or graphitization treatment in the step four with the phase-change material through vacuum impregnation.
Further, the segmented heating in the first step is divided into three steps: firstly, heating to 150-180 ℃ at a speed of 5-10 ℃/min, preserving heat for 60-120 min, and then cooling to room temperature at a speed of 1-5 ℃/min; secondly, preserving the heat at 150-180 ℃ for 60-120 min, and cooling to room temperature at normal temperature; thirdly, preserving the heat at 150-180 ℃ for 60-120 min, and then cooling to room temperature at 1-5 ℃/min; the hydrothermal reaction is carried out in a hydrothermal reaction kettle.
Further, the concentration of the graphene oxide suspension is 4-10 mg/ml.
Further, the graphene oxide is prepared by adopting an improved Hummers method, a Brodie method and a Staudenmaier method; the pre-freezing treatment in the second step is carried out in a cold hydrazine of a freeze dryer; the temperature of the pre-freezing treatment is-10 to-20 ℃, and the time is 2 to 6 hours.
Further, in the third step, the vacuum drying temperature is-40 to-50 ℃, the time is 48 to 72 hours, and the vacuum degree is less than 20 Pa.
Further, in the fourth step, the high-temperature carbonization or graphitization treatment is to heat the mixture to 1000-3000 ℃ at a speed of 3-10 ℃/min and preserve the heat for 30-120 min.
Further, in the fifth step, the vacuum degree of vacuum impregnation is not more than 20Pa, and the time is 3-5 h.
Further, in the fifth step, the phase change material is one of paraffin PA, stearic acid SA, lauric acid LA and polyethylene glycol PEG.
Furthermore, the mass percent of the high-orientation layered graphene aerogel phase-change composite material is 100%, and in the fifth step, the mass percent of the layered aerogel material is 2-4%, and the mass percent of the phase-change material is 96-98%.
The second purpose of the invention is to provide a highly oriented laminar graphene aerogel phase-change composite material prepared by the preparation method.
The invention discloses the following technical effects:
1. according to the invention, the graphene aerogel is prepared by adopting a sectional heating mode hydrothermal reaction, the face-to-face stacking of graphene nanosheets can be weakened, and the cross-linking lap joint between edges is enlarged, so that a regular layered structure is formed, and the graphene aerogel has the characteristics of high orientation and multiple rebounds. The highly oriented large-sheet layer structure increases the heat transfer area and provides more adsorption sites for the phase-change material, and compared with isotropic material, the heat transfer channel is more uniform, so that the heat conduction performance of the phase-change material can be greatly improved. Compared with the traditional graphene aerogel preparation process, the preparation of the aerogel has low requirements on the freeze drying technology, the microstructure regulation and control of the aerogel are realized only by a sectional heating mode, and the whole preparation process is green, safe and nontoxic;
2. according to the invention, redundant oxygen-containing functional groups on the surface of the graphene aerogel are removed through a carbonization or graphitization process, the self-structure defects are repaired, the thermal conductivity is further improved, and the application value of the carbon aerogel in the field of phase change energy storage is improved;
3. according to the invention, the graphene aerogel is selected as the packaging material and the heat transfer carrier at the same time, and the prepared high-orientation layered graphene aerogel phase-change composite material has excellent directional heat conduction performance, high energy storage characteristic and good leakage-proof performance, and has wide application prospect in the field of phase-change energy storage.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a DSC graph of a highly oriented layered graphene aerogel phase change composite prepared in example 3 of the present invention;
fig. 2 is a DSC graph of the graphene aerogel phase change composite prepared in comparative example 1;
fig. 3 is a scanning electron microscope image of the layered graphene aerogel prepared in example 3 of the present invention;
fig. 4 is a scanning electron microscope image of the graphene aerogel prepared in comparative example 1 of the present invention;
fig. 5 is a thermal conductivity graph of paraffin wax and the highly oriented layered graphene aerogel phase change composite material prepared in example 3 of the present invention and the graphene aerogel phase change composite materials prepared in comparative examples 1 and 2.
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.
The room temperature referred to in the present invention is the indoor temperature, which is well known to those skilled in the art and will not be described herein; in particular, the room temperature indicated in the examples of the present invention is 25 ℃.
Example 1
Step one, taking 10mg/ml graphene oxide suspension liquid in a polytetrafluoroethylene reaction kettle, and carrying out hydrothermal reaction in a sectional heating mode to obtain reduced graphene hydrogel, wherein the whole process is totally divided into three steps, namely, firstly, heating to 180 ℃ at a speed of 10 ℃/min, keeping the temperature for 120min, and then cooling a sample to room temperature at a cooling rate of 5 ℃/min; secondly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 120min, and the sample is taken out and cooled to room temperature; and thirdly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 120min, and the sample is cooled to the room temperature at the cooling rate of 5 ℃/min.
And step two, placing the hydrogel obtained in the step one in a cold hydrazine of a freeze dryer for pre-freezing, ensuring that the ice crystals in the hydrogel grow completely, wherein the pre-freezing temperature is-10 ℃, and the pre-freezing time is 2 hours.
And step three, taking out the sample in the step two, and performing vacuum freeze drying to obtain the highly oriented layered aerogel material, wherein the vacuum degree in the process is 19Pa, the vacuum freeze drying temperature is-40 ℃, and the time is 48 h.
And step four, carrying out graphitization treatment on the sample in the step three in a graphitization furnace, wherein the heating rate is 10 ℃/min, the graphitization temperature is 3000 ℃, the time is 120min, and cooling to room temperature along with the furnace.
And step five, compounding the sample in the step four with the phase-change material through vacuum impregnation. Firstly, placing the graphitized aerogel and stearic acid in a beaker, and vacuumizing for one hour until the vacuum degree is 19Pa, so as to ensure the discharge of air in the aerogel. Heating until the stearic acid is melted, soaking for 3h until the aerogel is adsorbed and saturated, and obtaining the high-orientation layered graphene aerogel phase-change composite material.
The calculation formula of the components of the graphene aerogel is as follows:
the mass percent of the graphene aerogel is 1-latent heat of phase change (heat release) of the composite material/latent heat of phase change (heat release) of the pure phase change material multiplied by 100 percent
And (3) detection results: the layered graphene aerogel can rebound for multiple times and is not easy to knead; the phase change latent heat of the highly-oriented laminar graphene aerogel phase change composite material is 188.30J/g (heat release) and 187.64J/g (heat absorption), and the thermal conductivity is 1.217 W.m-1·k-1(ii) a Stearic acid, a pure phase change material, has a latent heat of phase change of 193.62J/g (exothermic) and 192.57J/g (heat absorption), and the mass percentage of the graphene aerogel obtained by calculation is 2.75%.
Example 2
Step one, taking 10mg/ml graphene oxide suspension liquid in a polytetrafluoroethylene reaction kettle, and carrying out hydrothermal reaction in a sectional heating mode to obtain reduced graphene hydrogel, wherein the whole process is totally divided into three steps, namely, firstly, heating to 180 ℃ at a speed of 8 ℃/min, keeping the temperature for 100min, and then cooling a sample to room temperature at a cooling rate of 3 ℃/min; secondly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 100min, and the sample is taken out and cooled to room temperature; and thirdly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 100min, and the sample is cooled to the room temperature at the cooling rate of 3 ℃/min.
And step two, placing the hydrogel obtained in the step one in a cold hydrazine of a freeze dryer for pre-freezing, ensuring that the ice crystals in the hydrogel grow completely, wherein the pre-freezing temperature is-15 ℃, and the pre-freezing time is 4 hours.
And step three, taking out the sample in the step two, and performing vacuum freeze drying to obtain the highly oriented layered aerogel material, wherein the vacuum degree in the process is 15Pa, the vacuum freeze drying temperature is-45 ℃, and the time is 60 hours.
And step four, carrying out graphitization treatment on the sample in the step three in a graphitization furnace, wherein the heating rate is 8 ℃/min, the graphitization temperature is 2500 ℃, the time is 120min, and cooling to room temperature along with the furnace.
And step five, compounding the sample in the step four with the phase-change material through vacuum impregnation. Firstly, placing the graphitized aerogel and stearic acid in a beaker, and vacuumizing for one hour until the vacuum degree is 15Pa, so as to ensure the discharge of air in the aerogel. Heating until the stearic acid is melted, soaking for 4h until the aerogel is adsorbed and saturated, and obtaining the high-orientation layered graphene aerogel phase-change composite material.
And (3) detection results: the layered graphene aerogel can rebound for multiple times and is not easy to knead; the latent heat of phase change of the highly-oriented laminar graphene aerogel phase change composite material is 187.25J/g (heat release) and 186.93J/g (heat absorption), and the thermal conductivity is 1.136 W.m-1·k-1(ii) a The latent heat of phase change of stearic acid of the pure phase change material is 193.62J/g (exothermic) and 192.57J/g (endothermic), and graphene gas is calculatedThe mass percentage of the gel was 3.29%.
Example 3
Step one, taking 10mg/ml graphene oxide suspension liquid in a polytetrafluoroethylene reaction kettle, and carrying out hydrothermal reaction in a sectional heating mode to obtain reduced graphene hydrogel, wherein the whole process is totally divided into three steps, namely, firstly, heating to 180 ℃ at a speed of 10 ℃/min, keeping the temperature for 60min, and then cooling a sample to room temperature at a cooling rate of 1 ℃/min; secondly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 60min, and the sample is taken out and cooled to room temperature; and thirdly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 60min, and the sample is cooled to the room temperature at the cooling rate of 1 ℃/min.
And step two, placing the hydrogel obtained in the step one in a cold hydrazine of a freeze dryer for pre-freezing, ensuring that the ice crystals in the hydrogel grow completely, wherein the pre-freezing temperature is-20 ℃, and the pre-freezing time is 6 hours.
And step three, taking out the sample in the step two, and performing vacuum freeze drying to obtain the highly oriented layered aerogel material, wherein the vacuum degree in the process is 6Pa, the vacuum freeze drying temperature is-50 ℃, and the time is 72 hours.
And step four, carrying out high-temperature carbonization treatment on the sample in the step three in a tubular furnace, wherein the heating rate is 3 ℃/min, the carbonization temperature is 1500 ℃, the carbonization time is 30min, and cooling to room temperature along with the furnace.
And step five, compounding the sample in the step four with the phase-change material through vacuum impregnation. Firstly, placing the carbonized aerogel and paraffin in a beaker, and vacuumizing for one hour until the vacuum degree is 6Pa, so as to ensure the discharge of air in the aerogel. Heating until paraffin is melted, soaking for 5h until the aerogel is adsorbed and saturated, and obtaining the high-orientation layered graphene aerogel phase-change composite material.
And (3) detection results: the layered graphene aerogel can rebound for multiple times and is not easy to knead, and a scanning electron microscope image of the layered graphene aerogel is shown in fig. 3; the latent heat of phase change of the highly oriented layered graphene aerogel phase change composite material is 242.67J/g (heat release) and 243.69J/g (heat absorption) as shown in figure 1, and the thermal conductivity of the highly oriented layered graphene aerogel phase change composite material is 0.727 W.m as shown in figure 5-1·k-1(ii) a Phase change potential of pure phase change material paraffinThe heat was 247.65J/g (exothermic) and 246.79J/g (endothermic), calculated as 2% by mass of graphene aerogel.
Example 4
Step one, taking 8mg/ml graphene oxide suspension liquid in a polytetrafluoroethylene reaction kettle, and carrying out hydrothermal reaction in a sectional heating mode to obtain reduced graphene hydrogel, wherein the whole process is totally divided into three steps, namely, firstly, heating to 180 ℃ at a speed of 8 ℃/min, keeping the temperature for 80min, and then cooling a sample to room temperature at a cooling rate of 2 ℃/min; secondly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 80min, and the sample is taken out and cooled to room temperature; and thirdly, after the sample is completely cooled, the sample is placed into a muffle furnace at 180 ℃ for heat preservation for 80min, and the sample is cooled to the room temperature at the cooling rate of 2 ℃/min.
And step two, placing the hydrogel obtained in the step one in a cold hydrazine of a freeze dryer for pre-freezing, ensuring that the ice crystals in the hydrogel grow completely, wherein the pre-freezing temperature is-12 ℃, and the pre-freezing time is 3 hours.
And step three, taking out the sample in the step two, and performing vacuum freeze drying to obtain the highly oriented layered aerogel material, wherein the vacuum degree in the process is 10Pa, the vacuum freeze drying temperature is-42 ℃, and the time is 52 h.
And step four, carrying out graphitization treatment on the sample in the step three in a graphitization furnace, wherein the heating rate is 10 ℃/min, the graphitization temperature is 2000 ℃, the time is 120min, and cooling to room temperature along with the furnace.
And step five, compounding the sample in the step four with the phase-change material through vacuum impregnation. Firstly, placing the carbonized aerogel and polyethylene glycol in a beaker, and vacuumizing for one hour until the vacuum degree is 10Pa, so as to ensure the discharge of air in the aerogel. Heating until the polyethylene glycol is melted, soaking for 3.5 hours until the aerogel is adsorbed and saturated, and obtaining the high-orientation layered graphene aerogel phase-change composite material.
And (3) detection results: the layered graphene aerogel can rebound for multiple times and is not easy to knead; the phase change latent heat 168.28J/g (heat release) and 167.89J/g (heat absorption) of the highly-oriented laminar graphene aerogel phase change composite material and the thermal conductivity of the highly-oriented laminar graphene aerogel phase change composite material are 0.826W m-1·k-1(ii) a The phase change latent heat of the pure phase change material polyethylene glycol is 175.29J/g (exothermic) and 174.91J/g (endothermic)) And calculating that the mass percentage of the graphene aerogel is 4%.
Example 5
Step one, 6mg/ml of graphene oxide suspension is taken to be placed in a polytetrafluoroethylene reaction kettle, a sectional heating mode is adopted for hydrothermal reaction to obtain reduced graphene hydrogel, the whole process is totally divided into three steps, firstly, the temperature is increased to 160 ℃ at the rate of 8 ℃/min, the temperature is kept for 60min, and then a sample is cooled to room temperature at the rate of 1.5 ℃/min; secondly, after the sample is completely cooled, the sample is placed into a muffle furnace at 160 ℃ for heat preservation for 60min, and the sample is taken out and cooled to room temperature; and thirdly, after the sample is completely cooled, the sample is placed into a muffle furnace at 160 ℃ for heat preservation for 60min, and the sample is cooled to the room temperature at the cooling rate of 1.5 ℃/min.
And step two, placing the hydrogel obtained in the step one in a cold hydrazine of a freeze dryer for pre-freezing, ensuring that the ice crystals in the hydrogel grow completely, wherein the pre-freezing temperature is-17 ℃, and the pre-freezing time is 5 hours.
And step three, taking out the sample in the step two, and performing vacuum freeze drying to obtain the highly oriented layered aerogel material, wherein the vacuum degree in the process is 2Pa, the vacuum freeze drying temperature is-47 ℃, and the time is 65 hours.
And step four, carrying out high-temperature carbonization treatment on the sample in the step three in a tubular furnace, wherein the heating rate is 5 ℃/min, the carbonization temperature is 1500 ℃, the time is 60min, and cooling to room temperature along with the furnace.
And step five, compounding the sample in the step four with the phase-change material through vacuum impregnation. Firstly, placing the carbonized aerogel and lauric acid in a beaker, vacuumizing for one hour until the vacuum degree is 2Pa, and ensuring the discharge of air in the aerogel. Heating until the lauric acid is melted, soaking for 4.5 hours until the aerogel is adsorbed and saturated, and obtaining the high-orientation layered graphene aerogel phase-change composite material.
And (3) detection results: the layered graphene aerogel can rebound for multiple times and is not easy to knead; the phase change latent heat 171.35J/g (heat release) and 170.637J/g (heat absorption) of the highly-oriented laminar graphene aerogel phase change composite material have the thermal conductivity of 0.833 W.m-1·k-1(ii) a The pure phase-change material lauric acid has the latent heat of phase change of 176.65J/g (exothermic) and 176.58J/g (endothermic), and the mass percent of the calculated graphene aerogel is3％。
Example 6
Step one, taking 4mg/ml of graphene oxide suspension liquid in a polytetrafluoroethylene reaction kettle, and carrying out hydrothermal reaction in a sectional heating mode to obtain reduced graphene hydrogel, wherein the whole process is totally divided into three steps, namely, firstly, heating to 150 ℃ at a speed of 5 ℃/min, keeping the temperature for 60min, and then cooling a sample to room temperature at a cooling rate of 1 ℃/min; secondly, after the sample is completely cooled, the sample is placed into a muffle furnace at the temperature of 150 ℃ for heat preservation for 60min, and the sample is taken out and cooled to the room temperature; and thirdly, after the sample is completely cooled, the sample is placed into a muffle furnace at the temperature of 150 ℃ for heat preservation for 60min, and the sample is cooled to the room temperature at the cooling rate of 1 ℃/min.
And step two, placing the hydrogel obtained in the step one in a cold hydrazine of a freeze dryer for pre-freezing, ensuring that the ice crystals in the hydrogel grow completely, wherein the pre-freezing temperature is-18 ℃, and the pre-freezing time is 5 hours.
And step three, taking out the sample in the step two, and performing vacuum freeze drying to obtain the highly oriented layered aerogel material, wherein the vacuum degree in the process is 8Pa, the vacuum freeze drying temperature is-48 ℃, and the time is 62 h.
And step four, carrying out high-temperature carbonization treatment on the sample in the step three in a tubular furnace, wherein the heating rate is 3 ℃/min, the carbonization temperature is 1000 ℃, the time is 60min, and cooling to room temperature along with the furnace.
And step five, compounding the sample in the step four with the phase-change material through vacuum impregnation. Firstly, placing the carbonized aerogel and stearic acid in a beaker, and vacuumizing for one hour until the vacuum degree is 8Pa, so as to ensure the discharge of air in the aerogel. Heating until the stearic acid is melted, soaking for 4.5h until the aerogel is adsorbed and saturated, and obtaining the high-orientation layered graphene aerogel phase-change composite material.
And (3) detection results: the layered graphene aerogel can rebound for multiple times and is not easy to knead; the latent heat of phase change of the highly-oriented laminar graphene aerogel phase change composite material is 189.75J/g (heat release) and 190.38J/g (heat absorption); the thermal conductivity of the highly-oriented laminar graphene aerogel phase-change composite material is 0.529 W.m-1·k-1(ii) a The phase change latent heat of stearic acid of the pure phase change material is 193.62J/g (exothermic) and 192.57J/g (endothermic), and the mass percent of the graphene aerogel is calculatedThe content was 2%.
Comparative example 1
The difference from embodiment 3 is that, in the first step, a one-step hydrothermal method is adopted to prepare the reduced graphene hydrogel, and the method specifically comprises the following steps: and (4) heating the graphene oxide suspension to 180 ℃ at the speed of 10 ℃/min, preserving the temperature for 180min, and cooling to room temperature along with the furnace. And finally preparing the graphene aerogel phase-change composite material.
As a result: the graphene aerogel is easy to knead and cannot rebound, and a scanning electron microscope image of the graphene aerogel is shown in fig. 4; the latent heat of phase change of the graphene aerogel phase change composite material is shown in FIG. 2 and is 218.48J/g (exothermic) and 217.41J/g (endothermic); the thermal conductivity graph of the graphene aerogel phase change composite material is shown in fig. 5 and is 0.662 W.m-1·k-1(ii) a The phase change latent heat of the pure phase change material paraffin wax is 247.65J/g (exothermic) and 246.79J/g (endothermic), and the mass percent of the calculated graphene aerogel is 11.8%.
Comparative example 2
The difference from embodiment 3 is that, in the first step, a one-step hydrothermal method is adopted to prepare the reduced graphene hydrogel, and the method specifically comprises the following steps: heating the graphene oxide suspension to 180 ℃ at a speed of 10 ℃/min, preserving the heat for 180min, and cooling to room temperature along with the furnace; and the step of the carbonization treatment in the fourth step is omitted. And finally preparing the graphene aerogel phase-change composite material.
As a result: the graphene aerogel is easy to knead and cannot rebound; the phase change latent heat of the graphene aerogel phase change composite material is 215.37J/g (heat release) and 214.85J/g (heat absorption); the thermal conductivity of the graphene aerogel phase-change composite material is 0.364 W.m, as shown in FIG. 5-1·k-1(ii) a The phase change latent heat of the pure phase change material paraffin wax is 247.65J/g (exothermic) and 246.79J/g (endothermic), and the mass percent of the calculated graphene aerogel is 13%.
The graphene aerogel prepared in the comparative example 1 is of a non-laminated structure and is easy to knead and cannot rebound, while the laminated graphene aerogels prepared in the examples 1 to 6 can rebound and are not easy to knead for many times; although the thermal conductivity of the graphene aerogel phase change composite material prepared in comparative example 1 is not much different from that of example 3, the mass percentage of the graphene aerogel in example 3 is only 2%, and the mass percentage of the graphene aerogel in comparative example 1 is as high as 11.8%; the graphene aerogel prepared in the comparative example 2 is of a non-laminated structure, is easy to knead and cannot rebound, and the thermal conductivity of the graphene aerogel phase change composite material is far lower than that of the graphene aerogel phase change composite material in the example 3.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (10)
1. The preparation method of the high-orientation layered graphene aerogel phase-change composite material is characterized by comprising the following steps of:
the method comprises the following steps: carrying out hydrothermal reaction on the oxidized graphene suspension in a sectional heating mode to obtain reduced graphene hydrogel;
step two: pre-freezing the reduced graphene hydrogel;
step three: carrying out vacuum freeze drying on the reduced graphene hydrogel subjected to pre-freezing treatment in the step two to obtain a layered aerogel material;
step four: carrying out high-temperature carbonization or graphitization treatment on the layered aerogel material;
step five: and compounding the layered aerogel material subjected to high-temperature carbonization or graphitization treatment in the step four with the phase-change material through vacuum impregnation.
2. The preparation method of the highly oriented laminar graphene aerogel phase change composite material as claimed in claim 1, wherein the step one of heating in stages is divided into three steps: firstly, heating to 150-180 ℃ at a speed of 5-10 ℃/min, preserving heat for 60-120 min, and then cooling to room temperature at a speed of 1-5 ℃/min; secondly, preserving the heat at 150-180 ℃ for 60-120 min, and cooling to room temperature at normal temperature; and thirdly, preserving the heat at 150-180 ℃ for 60-120 min, and then cooling to room temperature at 1-5 ℃/min.
3. The preparation method of the highly oriented laminar graphene aerogel phase change composite material according to claim 1, wherein the concentration of the graphene oxide suspension is 4-10 mg/ml.
4. The preparation method of the highly oriented laminar graphene aerogel phase-change composite material according to claim 1, wherein the temperature of the pre-freezing treatment in the second step is-10 to-20 ℃, and the time is 2 to 6 hours.
5. The preparation method of the highly-oriented laminar graphene aerogel phase-change composite material according to claim 1, wherein the temperature of the vacuum freeze drying in the step three is-40 to-50 ℃, the time is 48 to 72 hours, and the vacuum degree is less than 20 Pa.
6. The preparation method of the highly oriented laminar graphene aerogel phase change composite material according to claim 1, wherein the high temperature carbonization or graphitization treatment in the fourth step is raising the temperature to 1000-3000 ℃ at 3-10 ℃/min, and keeping the temperature for 30-120 min.
7. The preparation method of the highly-oriented layered graphene aerogel phase-change composite material according to claim 1, wherein in the fifth step, the vacuum degree of vacuum impregnation is not more than 20Pa, and the time is 3-5 h.
8. The preparation method of the highly oriented laminar graphene aerogel phase change composite material according to claim 1, wherein in the fifth step, the phase change material is one of paraffin, stearic acid, lauric acid and polyethylene glycol.
9. The preparation method of the highly-oriented layered graphene aerogel phase-change composite material as claimed in claim 1, wherein the mass percent of the highly-oriented layered graphene aerogel phase-change composite material is 100%, and in the fifth step, the mass percent of the layered aerogel material is 2-4%, and the mass percent of the phase-change material is 96-98%.
10. The highly oriented laminar graphene aerogel phase change composite material prepared by the preparation method according to any one of claims 1 to 9.
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