CN110217774B - Starch-based hollow carbon microsphere material, preparation method thereof and heat storage application - Google Patents

Starch-based hollow carbon microsphere material, preparation method thereof and heat storage application Download PDF

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CN110217774B
CN110217774B CN201910553652.0A CN201910553652A CN110217774B CN 110217774 B CN110217774 B CN 110217774B CN 201910553652 A CN201910553652 A CN 201910553652A CN 110217774 B CN110217774 B CN 110217774B
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starch
phase change
hollow carbon
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carbon microsphere
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CN110217774A (en
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张焕芝
季蓉
黄悦
魏胜
夏永鹏
黄朝玮
莫小叶
孙立贤
徐芬
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Guilin University of Electronic Technology
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Abstract

The invention provides a starch-based hollow carbon microsphere material, which adopts soluble starch as a carbon source and carboxyl functionalized polystyrene as a template agent, and can obtain hollow carbon microspheres with the appearance and the specific surface area of 1300-1350 m without an activation process after hydrothermal reaction and high-temperature carbonization 2 Carbon material per g. The preparation method comprises the following steps: 1) Preparing polystyrene/soluble starch composite microspheres; 2) And (3) preparing the starch-based hollow carbon microspheres. The composite phase change material is used as an adsorption support material of the n-octadecane phase change material, the phase change temperature of the obtained composite phase change material is 23.9-29.8 ℃, and the latent heat of phase change is 129.3-170.5J/g. The invention has the following advantages: the phase change material has a highly continuous hollow structure, so that the leakage of the phase change material is effectively prevented; the consistency is good, and the repeatability is high; the preparation method is simple and does not need an activation process; high phase change latent heat, excellent thermal stability and the like, has the characteristics of no toxicity and no harm, and has wide market prospect in the fields of buildings, energy storage materials and the like.

Description

Starch-based hollow carbon microsphere material, preparation method thereof and heat storage application
Technical Field
The invention relates to the field of phase change energy storage materials, in particular to a starch-based hollow carbon microsphere material and a preparation method and heat storage application thereof.
Background
In recent years, with the increasing consumption of fossil fuels, thermal energy storage has received a great deal of attention and has also proven to be a promising technology for energy efficient utilization. The phase-change material can absorb heat of the environment and release heat to the environment when needed in a certain temperature range in a process of converting a physical state or a molecular structure, so that the purpose of controlling the temperature of the surrounding environment is achieved, and the phase-change material is considered to be a good choice for energy storage. Meanwhile, the phase-change material plays an important role in the aspects of solar energy utilization, building energy conservation, electronic heat management, waste heat recovery and the like.
Phase change materials can be classified into solid-solid phase change materials, solid-liquid phase change materials, solid-gas phase change materials, and liquid-gas phase change materials according to a phase change process. The solid-liquid phase change material is the most studied and widely applied material in phase change materials, mainly comprises crystalline hydrate salts, molten salts, paraffin, fatty acid and the like, and has various types and different properties. However, whether the solid-liquid phase change material is inorganic or organic, the liquid loss in flowing manner is always a practical problem.
Common carbon materials include porous carbon, carbon nanotubes and graphene, and different carbon materials have great differences in physical and chemical properties due to different forms and microstructures. The porous carbon has the advantages of high specific surface area, moderate adsorption heat, good thermal conductivity, high mechanical stability and the like, and the porous carbon material is low in preparation cost and simple in process, and is the most common material in the composite phase-change material carrier. The porous carbon physically adsorbs the liquid phase-change material in the pore canal of the porous carbon material by utilizing the capillary adsorption effect and the surface tension of the internal microporous structure to form the composite phase-change material.
The prior art of porous carbon materials, chinese patent application No. 201610557581.8, provides a preparation method of a 3D porous carbon skeleton-based composite phase change material, organic ketone or aldehyde is used as a carbon source as a raw material, and the micro-morphology of porous carbon is obtained. The technology adopts common basic chemical raw materials, namely organic ketone or aldehyde, as a carbon source, and has the advantage of raw material consistency, but the reaction raw materials of the method have the problem of environmental pollution, and the application scene of a final product is limited to a certain extent.
The above problems can be solved by using a biomass raw material as a carbon source. The prior art Chinese patent (application number 201810722827.1) provides a preparation method of a high heat storage porous carbon-based hydrated inorganic salt composite phase change material. Coconut shells, fruit shells or other biomass materials are used as carbon sources, and the micro morphology of the porous carbon is obtained. However, the technology has the common problem of biomass materials, namely the consistency of raw materials cannot be ensured, so that the consistency of the appearance and the performance of products cannot be ensured; in addition, the carbon material prepared by the technology needs to be activated by a nitric acid solution, the nitric acid solution has strong stimulation and corrosion effects on the skin and mucosa of a human body, and the problems of environmental pollution and limited application scenes exist.
The starch is used as a carbon source, so that the technical problems that the starch has the characteristics of environmental friendliness and raw material consistency can be effectively solved, the cost of raw materials is obviously superior, and the price of analytical grade soluble starch is only 45.89 yuan/500 g (http:// www. Zhaoshiji.com/goods-18670. Html).
The prior art for preparing porous carbon materials by using starch as a carbon source currently has 2 relevant documents:
1. bo Tan et al (B, tan, Z, huang, Z, yin, X, min, Y.g. Liu, X, wu, M, fang, preparation and thermal properties of shape-stabilized composite phase change materials based on polyethylene glycol and pore carbon prepared from, RSC Advances 6 (19) (2016) 15821-15830.) use fresh potatoes as carbon source, although the microstructure of porous carbon is obtained, the specific surface area is only 42.6 m 2 (ii)/g, and the pore size distribution is not uniform, and the pore channels are partially collapsed;
2. fengyue Suo et al (F. Suo, X. Liu, C. Li, M. Yuan, B. Zhang, J. Wang, Y. Ma, Z. Lai, M. Ji, mesoporus activated carbon from stage for super ior rapid peptides removal, int J Biol Macromol 121 (2019) 806-813.) use starch as carbon source, although the micro-morphology of porous carbon is also obtained in order to improve the materialThe specific surface area of the material is only increased to 160.6 m, and the carbon material is treated by adopting an immersion activation method, so that the surface appearance of the carbon material is seriously damaged 2 /g；
Although consistency, safety and low cost can be taken into consideration to a certain extent, the obtained carbon materials are all in an open porous carbon structure, and the leakage problem cannot be solved fundamentally after the phase change materials are physically adsorbed.
In addition, prior art, ouyang Haibo et al (O. Haibo, L. Cuiyan, H. Jian Feng, F. Jie, synthesis of carbon/carbon composites by hydrothermal carbonization using starch as a carbon source, RSC adv. 4 (24) (2014) 12586-12589.) have obtained carbon fiber structures with diameters on the order of 10 microns using starch as a carbon source. The above problems cannot be solved because of the carbon fiber also having an open structure, but this technique shows that carbon materials having different morphologies can be obtained by an appropriate preparation method, thereby solving the problem of leakage.
Among a plurality of carbon materials, the carbon microsphere with a hollow structure has the characteristic of high continuity on the basis of having all the characteristics of the porous carbon material, so that the leakage problem of the phase change material can be effectively solved.
The prior art Wei Han et al (W. Han, S. Dong, B. Li, L. Ge, preparation of polyacrylonitrile-based porous carbon microspheres, colloids and Surfaces A: physical and Engineering applications 520 (2017) 467-476.) prepared polyaniline-based hollow carbon microspheres by a series of operations such as curing, water washing, supercritical drying, pre-oxidation, carbonization, etc. by using polyacrylonitrile emulsion as a precursor. Although the hollow carbon microsphere prepared by the method has certain application in the aspects of energy storage and adsorption, the preparation method of the technology is complicated and is not suitable for large-scale production; in addition, N-dimethylformamide is needed in the preparation process, and allergy, eczema and even burn are easy to occur after the N, N-dimethylformamide is contacted with a human body, so that the application range of the phase change material is limited.
Therefore, the starch which is wide in source, low in price, degradable and free of environmental pollution is used as a carbon source to prepare the hollow carbon microsphere structure with the high specific surface area, and the problems can be effectively solved.
Disclosure of Invention
The invention aims to provide a starch-based hollow carbon microsphere material and a preparation method thereof, aiming at the problems that in the prior art, an open porous carbon structure is prepared only by adopting environment-friendly and low-cost soluble starch and the leakage problem of a phase change material cannot be solved.
The simple preparation method for preparing the hollow carbon microspheres with high specific surface area can be realized through hydrothermal reaction and high-temperature carbonization without an activation process, so that the carbon material with excellent adsorption performance is obtained; and then the phase-change material is adsorbed, so that the leakage problem of the phase-change material is solved.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that:
a starch-based hollow carbon microsphere material is characterized in that: the method comprises the following steps of (1) taking soluble starch as a carbon source, taking carboxyl functionalized polystyrene as a template agent, and obtaining the carbon material with the hollow carbon microsphere shape without an activation process after hydrothermal reaction and high-temperature carbonization, wherein the mass ratio of the carboxyl functionalized polystyrene to the soluble starch is 1.
Wherein the specific surface area of the obtained starch-based hollow carbon microsphere material is 1300-1350 m 2 /g。
A preparation method of a starch-based hollow carbon microsphere material is characterized by comprising the following steps:
step 1) preparing polystyrene/soluble starch composite microspheres, namely, placing carboxyl functionalized polystyrene and soluble starch into a beaker for uniform mixing, carrying out hydrothermal reaction to obtain polystyrene/soluble starch composite microspheres, and further washing and drying;
step 2) preparation of the starch-based hollow carbon microspheres, namely, carrying out high-temperature carbonization on the polystyrene/soluble starch composite microspheres obtained in the step 1) to obtain the starch-based hollow carbon microspheres.
Wherein, the mixing condition of the carboxyl functionalized polystyrene and the soluble starch in the step 1) is that the mixture is stirred for 0.5 to 1 hour at the constant temperature of 30 ℃ and then is subjected to ultrasonic treatment for 0.5 to 2 hours.
Wherein, the hydrothermal reaction condition in the step 1) is that the hydrothermal temperature is controlled to be 170-190 ℃ and the hydrothermal reaction time is 10-15h.
Wherein the high-temperature carbonization in the step 2) is carried out under the conditions that the heating rate is 1-5 ℃/min, the carbonization temperature is 500-600 ℃, and the carbonization time is 12 h.
The heat storage application of the starch-based hollow carbon microsphere material as an adsorption phase-change material is characterized by comprising the following steps:
and mixing the starch-based hollow carbon microsphere and the phase change material by a vacuum impregnation method at a certain adsorption amount, and adsorbing under a certain condition to obtain the starch-based hollow carbon microsphere composite phase change material.
Wherein the adsorption capacity is 50-70%, the vacuum impregnation temperature is 50-70 ℃, and the time is 12-24 h.
Wherein the phase change material is n-octadecane.
The starch-based hollow carbon microsphere material is used as a heat storage application of a phase change material, and is characterized in that: the phase change temperature of the starch-based hollow carbon microsphere composite phase change material is 23.9-29.8 ℃, and the latent heat of phase change is 129.3-170.5J/g.
The experimental detection results of the starch-based hollow carbon microsphere material obtained by the invention are as follows:
SEM test shows that the starch-based hollow carbon microsphere material is spherical with uniformly distributed rough surfaces, has consistent size, does not collapse or crack, and has the particle size of 3.47-4.38 mu m.
According to TEM tests, the starch-based hollow carbon microsphere material is of a spherical hollow structure, and the thickness of an outer shell layer of the starch-based hollow carbon microsphere material is about 130 nm.
FT-IR test shows that the starch-based hollow carbon microsphere material of the invention has been successfully synthesized, and partial characteristic peaks of carboxyl functionalized polystyrene and soluble starch can be seen to overlap, but actually the carboxyl functionalized polystyrene is completely carbonized; the characteristic peaks of the soluble starch were substantially retained on the obtained hollow carbon microspheres, but the characteristic peaks of the partially soluble starch also disappeared.
Warp of N 2 The adsorption-desorption test and the BET calculation prove that the specific surface area of the starch-based hollow carbon microsphere material is 1300-1350 m 2 (iv) g. The analysis of BJH pore size distribution shows that the pore size distribution of the starch-based hollow carbon microsphere material is 1.8-6.2 nm.
When the starch-based hollow carbon microsphere material is applied to heat storage of adsorption phase change materials, the experimental detection result of the performance of the obtained starch-based hollow carbon microsphere composite phase change material is as follows:
FT-IR tests show that the starch-based hollow carbon microsphere material successfully adsorbs n-octadecane to form the starch-based hollow carbon microsphere composite phase change material.
SEM tests show that the starch-based hollow carbon microsphere composite phase change material maintains the spherical structure of the starch-based hollow carbon microsphere material, has rough material surface and basically accords with the particle size distribution of the starch-based hollow carbon microsphere.
DSC tests show that the phase transition temperature of the starch-based hollow carbon microsphere composite phase change material is 23.9-29.8 ℃, the latent heat of phase transition is 129.3-170.5J/g, and is higher than the theoretical value of 118.2-165.5J/g of 50-70% of adsorption capacity.
The thermal stability of the starch-based hollow carbon microsphere composite phase change material is good through 100 DSC cycle tests.
Therefore, compared with the prior art, the invention has the following advantages:
1. the phase-change material is adsorbed by the high-continuity hollow structure, so that the leakage of the phase-change material can be effectively prevented;
2. the soluble starch is used as the carbon source, so that the source consistency of the carbon source can be ensured, and the component identity of the material is effectively ensured, thereby controlling the consistency of the morphology and the performance of the prepared starch-based hollow carbon microsphere and ensuring high repeatability;
3. the preparation method is simple, and the starch-based hollow carbon microspheres with high specific surface area and high adsorption performance can be obtained only by hydrothermal reaction and high-temperature carbonization without activation process;
4. the starch-based hollow carbon microsphere prepared by the invention is used for heat storage application of an adsorption phase change material, and the obtained starch-based hollow carbon microsphere composite phase change material has high phase change latent heat and excellent thermal stability.
In conclusion, compared with the prior art, the invention has the advantages of low raw material cost, simple preparation method, only hydrothermal reaction and high-temperature carbonization, and no activation process; the prepared starch-based hollow carbon microsphere has the advantages of large specific surface area and excellent adsorption capacity, and the starch-based hollow carbon microsphere composite phase change material has high phase change latent heat and excellent thermal stability, and can prevent leakage in the solid-liquid phase change process; the final product is non-toxic and harmless, and has wide market prospect in the fields of buildings, energy storage materials and the like.
Drawings
FIG. 1 is an SEM image of a starch-based hollow carbon microsphere carrier obtained by using carboxyl functionalized polystyrene and soluble starch in a ratio of 1;
FIG. 2 is a TEM spectrum of a starch-based hollow carbon microsphere carrier obtained by using carboxyl functionalized polystyrene and soluble starch in a ratio of 1;
FIG. 3 is FT-IR spectrum of starch-based hollow carbon microsphere carrier obtained by the ratio of carboxyl functionalized polystyrene to soluble starch of 1;
FIG. 4 is a graph showing the N ratio of carboxyl-functionalized polystyrene to soluble starch of a starch-based hollow carbon microsphere carrier obtained in example 1 of the present invention at 1 2 Adsorption-removal of attached figures;
FIG. 5 is a diagram showing the pore size distribution of a starch-based hollow carbon microsphere carrier obtained in example 1, wherein the ratio of carboxyl functionalized polystyrene to soluble starch is 1;
FIG. 6 is FT-IR spectra of 70% n-octadecane adsorbed by starch-based hollow carbon microsphere carrier obtained by the method of example 1 according to the invention, wherein the ratio of carboxyl-functionalized polystyrene to soluble starch is 1;
FIG. 7 is an SEM image of 70% n-octadecane adsorbed onto a starch-based hollow carbon microsphere carrier, which is obtained by using carboxyl-functionalized polystyrene and soluble starch at a ratio of 1 in example 1 of the present invention;
FIG. 8 is a DSC chart of 70% n-octadecane adsorbed on a starch-based hollow carbon microsphere carrier, which is obtained by using carboxyl functionalized polystyrene and soluble starch in a ratio of 1;
FIG. 9 is a DSC cycle chart of 100 times of adsorption of 70% n-octadecane on the starch-based hollow carbon microsphere carrier, which is obtained from example 1 according to the invention and has a ratio of 1;
FIG. 10 is an SEM image of a starch-based hollow carbon microsphere carrier obtained by comparing example 1 according to the present invention, wherein the ratio of carboxyl-functionalized polystyrene to soluble starch is 1;
FIG. 11 is an SEM image of a starch-based hollow carbon microsphere carrier obtained by comparing example 2 of the present invention, wherein the ratio of carboxyl-functionalized polystyrene to soluble starch is 1;
FIG. 12 shows the N ratio of carboxyl-functionalized polystyrene to soluble starch of comparative example 1 of the present invention to that of hollow carbon microsphere support obtained in the ratio of 1 2 Adsorption-removal of attached figure;
FIG. 13 is a graph showing the distribution of pore diameters of a hollow carbon microsphere carrier obtained by using comparative example 1 in which the ratio of carboxyl-functionalized polystyrene to soluble starch is 1;
FIG. 14 shows the N ratio of carboxyl functionalized polystyrene to soluble starch of comparative example 2 of the present invention to the hollow carbon microsphere carrier of 1 2 Adsorption-removal of attached figures;
FIG. 15 is a graph showing the pore size distribution of a hollow carbon microsphere carrier obtained in comparative example 2 in which the ratio of carboxyl-functionalized polystyrene to soluble starch is 1;
FIG. 16 is an SEM image of 80% n-octadecane adsorbed on a starch-based hollow carbon microsphere carrier obtained in comparative example 3, wherein the ratio of carboxyl-functionalized polystyrene to soluble starch is 1;
FIG. 17 is a DSC chart of 50% of n-octadecane adsorbed on the starch-based hollow carbon microsphere carrier, which is obtained by using 1 ratio of carboxyl-functionalized polystyrene to soluble starch in example 2 of the present invention;
FIG. 18 is a DSC chart of 60% n-octadecane adsorbed on the starch-based hollow carbon microsphere carrier, which is obtained by using 1 ratio of carboxyl functionalized polystyrene and soluble starch in example 3 of the present invention.
Detailed Description
The invention is further described in detail by the embodiments and the accompanying drawings, but the invention is not limited thereto.
Example 1
A preparation method of a starch-based hollow carbon microsphere material with a ratio of carboxyl functionalized polystyrene to soluble starch of 1:
step 1) preparation of polystyrene/soluble starch composite microspheres,
mixing 1 g of carboxyl functionalized polystyrene and 3 g of soluble starch, putting the mixture into a beaker, stirring the mixture for 0.5 h at constant temperature in a 35 ℃ water bath kettle, performing ultrasonic treatment for 1 h, putting the mixture into a high-temperature high-pressure reaction kettle at 180 ℃ for hydrothermal reaction for 12 h, performing suction filtration and cleaning on a product obtained after hydrothermal reaction, putting the product into a 60 ℃ drying oven, and drying the product for 24 h;
step 2) preparation of the starch-based hollow carbon microsphere material,
putting the polystyrene/soluble starch composite microspheres obtained in the step 1) into a tubular furnace, heating to 550 ℃ at a heating rate of 5 ℃/min, and carbonizing for 12 hours in a nitrogen atmosphere.
In order to prove that the starch-based hollow carbon microsphere material prepared by the method has a spherical micro-morphology, SEM test is carried out. The test result is shown in figure 1, the material of the invention is in the form of spheres with uniformly distributed rough surfaces, has uniform shape distribution and consistent size, does not collapse or crack, and has the grain diameter of between 3.47 and 4.38 μm.
In order to prove that the starch-based hollow carbon microsphere material prepared by the method has a hollow structure, a TEM test is carried out. The test result is shown in fig. 2, the material of the invention is spherical, the outer part is darker, and the inner part is brighter, which indicates that the material of the invention is a spherical hollow structure; the thickness of the outer shell layer is about 130 nm.
To determine the functional group structure of the starch-based hollow carbon microsphere material, an FT-IR test was performed. As a result, as shown in fig. 3, the starch-based hollow carbon microsphere material of the present invention has been successfully synthesized, and it can be seen that some characteristic peaks of the carboxyl-functionalized polystyrene and the soluble starch overlap, but actually the carboxyl-functionalized polystyrene has been completely carbonized; the characteristic peaks of the soluble starch were substantially retained on the obtained hollow carbon microspheres, but the characteristic peaks of the partially soluble starch also disappeared.
To demonstrate the specific surface area of the starch-based hollow carbon microsphere material, N was performed on the hollow carbon microsphere 2 Adsorption-desorption test and pore size distribution analysis. As a result, N in the starch-based hollow carbon microspheres was shown in FIGS. 4 and 5 2 The adsorption-desorption curve belongs to a type IV isotherm, and the BET calculation shows that the specific surface area of the starch-based hollow carbon microsphere material of the embodiment is 1312 m 2 The pore size distribution is 1.8-6.2 nm.
A preparation method of a starch-based hollow carbon microsphere composite phase change material with 70% of adsorption capacity comprises the following steps:
placing 1 g of starch-based hollow carbon microsphere into a glass bottle, adding 2.33 g of n-octadecane, then placing the mixed sample into a vacuum drying oven, and keeping the temperature at 60 ℃ for 12 hours by using a vacuum impregnation method to prepare the starch-based hollow carbon microsphere composite phase change material.
In order to prove that the starch-based hollow carbon microsphere material successfully adsorbs the phase change material, an FT-IR test is carried out. The test result is shown in fig. 6, the infrared spectrum of the starch-based hollow carbon microsphere composite phase change material is the same as the spectrum of n-octadecane, which indicates that the starch-based hollow carbon microsphere material successfully adsorbs the n-octadecane, and the starch-based hollow carbon microsphere composite phase change material is synthesized.
In order to prove that the starch-based hollow carbon microsphere material prepared by the method has spherical microscopic morphology, SEM test is carried out. The test result is shown in fig. 7, the starch-based hollow carbon microsphere composite phase change material maintains the spherical structure of the starch-based hollow carbon microsphere material, the surface of the material is rough, and the particle size distribution of the material is basically consistent with that of the starch-based hollow carbon microsphere.
In order to prove the performance of the starch-based hollow carbon microsphere composite phase change material, a DSC test is carried out. The test result is shown in fig. 8, the melting temperature of the starch-based hollow carbon microsphere composite phase change material is 29.8 ℃, and the crystallization temperature is 24.2 ℃; the observed latent heat of phase change was 170.5J/g and 169.0J/g, over 70% of the theoretical value of adsorption 165.5J/g. The reason for the fact that the phase change material n-octadecane is uniformly dispersed in the structure of the hollow carbon microspheres to form a continuous heat conduction network, so that the phase of n-octadecane is completely changed in the phase change process, and therefore, the enthalpy value of 70% adsorption can be larger than the theoretical value of 70% adsorption. The phenomenon also proves that the hollow carbon microsphere as a phase-change composite material carrier has the characteristics which are not possessed by the common porous carbon material.
In order to prove the thermal stability of the starch-based hollow carbon microsphere composite phase change material in practical application, 100 DSC (differential scanning calorimetry) cycle tests are carried out. The test result is shown in fig. 9, after 100 times of thermal cycle, the phase change temperature and the latent heat of phase change of the starch-based hollow carbon microsphere composite phase change material are basically unchanged, and the starch-based hollow carbon microsphere composite phase change material shows good thermal cycle performance in the phase change process, and can be widely applied to the field of heat storage.
In order to research the influence of the ratio of carboxyl functionalized polystyrene to starch on the morphology, the specific surface area and the pore size distribution of the starch-based hollow carbon microsphere material, namely the influence of the ratio of experimental components on the material performance, the raw material components are controlled to be completely the same, and the ratio of the experimental components is only changed to prepare the starch-based hollow carbon microsphere materials with different ratios of carboxyl functionalized polystyrene to starch, namely comparative examples 1 and 2.
Comparative example 1
A preparation method of a starch-based hollow carbon microsphere material with a ratio of carboxyl functionalized polystyrene to soluble starch of 1: the steps not specifically described in the specific steps are the same as the preparation method of the above example 1, except that: the ratio of the carboxyl functionalized polystyrene to the soluble starch in the step 1) is 1.
Comparative example 2
A preparation method of a starch-based hollow carbon microsphere material with a ratio of carboxyl functionalized polystyrene to soluble starch of 1: the steps not specifically described in the specific steps are the same as the preparation method of the above example 1, except that: the ratio of the carboxyl functionalized polystyrene to the soluble starch in the step 1) is 1.
In order to investigate the effect of the ratio of carboxyl functionalized polystyrene and starch on the morphology of the starch-based hollow carbon microsphere material, SEM tests were performed on the materials obtained in comparative examples 1 and 2 above.
The test results at an addition ratio of 1. As a result, many starch-based hollow carbon microspheres have a cracking phenomenon.
The test results at the addition ratio of 1.
The experiments are combined to know that the proportion of the carboxyl functionalized polystyrene to the soluble starch has a decisive influence on the microscopic morphology of the obtained hollow carbon microsphere.
To investigate the effect of the ratio of carboxyl functionalized polystyrene to starch on the specific surface area and pore size distribution of the starch-based hollow carbon microsphere materials, N was applied to the materials obtained in comparative examples 1 and 2 2 Adsorption-desorption test and pore size distribution analysis.
The test results with the addition ratio of 1 2 The pore diameter distribution is 3.2-5.3 nm.
The test results at an addition ratio of 1 2 (iv) g; the pore size distribution is 3.6-4.6 nm.
By comparing the specific surface area of the material prepared in example 1 with the ratio of carboxyl-functionalized polystyrene to soluble starch of 1 2 3 times and 3.8 times the ratio of 1.
Through comparative analysis of the experiments of example 1 and comparative examples 1 and 2, the ratio of the carboxyl functionalized polystyrene and the soluble starch has a decisive influence on the morphology, the specific surface area and the pore size distribution of the starch-based hollow carbon microsphere material. Therefore, only the starch-based hollow carbon microsphere material prepared by the process technology provided by the invention can realize excellent specific surface area and stronger adsorption performance.
In order to study the influence of the adsorption capacity on the performance of the starch-based hollow carbon microsphere composite phase change material, the n-octadecane and the starch-based hollow carbon microsphere material are controlled to be completely the same, and the starch-based hollow carbon microsphere composite phase change material with different adsorption capacities is prepared by only changing the proportion of experimental components, namely the starch-based hollow carbon microsphere composite phase change material in example 2, example 3 and comparative example 2.
Example 2
A preparation method of a starch-based hollow carbon microsphere composite phase change material with an adsorption capacity of 50 percent comprises the following steps: the steps not specifically described in the specific steps are the same as the preparation method of the above example 1, except that: the mass of the n-octadecane is 1 g.
Example 3
A preparation method of a starch-based hollow carbon microsphere composite phase change material with an adsorption capacity of 60% comprises the following steps: the steps not specifically described in the specific steps are the same as the preparation method of the above example 1, except that: the mass of the n-octadecane is 1.5 g.
Comparative example 3
A preparation method of a starch-based hollow carbon microsphere composite phase change material with an adsorption capacity of 80 percent comprises the following steps: the steps not specifically described in the specific steps are the same as the preparation method of the above example 1, except that: the mass of the n-octadecane is 4 g.
In order to research the maximum adsorption capacity of the starch-based hollow carbon microsphere composite phase change material, the composite phase change material obtained in the comparative example 3 is subjected to SEM test. The test result is shown in fig. 16, most of the composite phase change materials are seriously stacked, the surface becomes agglomerated and rough, and the size is greatly different. These experimental phenomena indicate that the amount of n-octadecane adsorbed at this time is excessive, that is, only n-octadecane originally adsorbed on the inside of the hollow carbon microspheres starts to be adsorbed on the outside of the hollow carbon microspheres. The n-octadecane inevitably leaks in the circulation process, and the aim of the invention cannot be achieved.
In order to investigate the influence of the adsorption amount on the performance of the starch-based hollow carbon microsphere composite phase change material, DSC tests were performed on the materials obtained in examples 2 and 3.
The results of the test at 50% adsorption are shown in FIG. 17, where the melting temperature was 29.3 ℃, the crystallization temperature was 24.0 ℃, and the enthalpy of phase transition was 130.1J/g and 129.3J/g.
The results of the test at an adsorption amount of 60% are shown in FIG. 18, where the melting temperature was 29.5 ℃, the crystallization temperature was 23.9 ℃, and the enthalpy of phase transition was 140.6J/g and 139.9J/g.
The experiments of examples 1, 2 and 3 are compared and analyzed, and it can be known that when the adsorption capacity is between 50% and 70%, the latent heat of phase change tends to increase, and the maximum adsorption capacity of the starch-based hollow carbon microsphere material is not exceeded, so that the problem of n-octadecane leakage can be effectively solved.

Claims (4)

1. A starch-based hollow carbon microsphere material is characterized in that: the method comprises the following steps of (1) taking soluble starch as a carbon source, carboxyl functionalized polystyrene as a template agent, and the mass ratio of the carboxyl functionalized polystyrene to the soluble starch being 1;
the specific surface area of the obtained starch-based hollow carbon microsphere material is 1300-1350 m 2 /g。
2. The preparation method of the starch-based hollow carbon microsphere material according to claim 1, which is characterized by comprising the following steps:
step 1) preparation of polystyrene/soluble starch composite microspheres: placing carboxyl functionalized polystyrene and soluble starch into a beaker, uniformly mixing, carrying out hydrothermal reaction to obtain polystyrene/soluble starch composite microspheres, and further washing and drying;
the mixing conditions of the carboxyl functionalized polystyrene and the soluble starch in the step 1) are as follows: stirring at 30 deg.C for 0.5-1 h, and performing ultrasonic treatment for 0.5-2 h;
the conditions of the hydrothermal reaction in the step 1) are as follows: controlling the hydrothermal temperature to be 170-190 ℃ and the hydrothermal reaction time to be 10-15 h;
step 2) preparation of starch-based hollow carbon microspheres: carbonizing the polystyrene/soluble starch composite microspheres obtained in the step 1) at high temperature to obtain starch-based hollow carbon microspheres;
the high-temperature carbonization condition in the step 2) is as follows: the heating rate is 1-5 ℃/min, the carbonization temperature is 500-600 ℃, and the carbonization time is 12 h.
3. The heat storage application of the starch-based hollow carbon microsphere material as an adsorption phase change material according to claim 1, wherein: mixing the starch-based hollow carbon microspheres and the phase change material by a vacuum impregnation method with a certain adsorption amount, and adsorbing under certain conditions to obtain the starch-based hollow carbon microsphere composite phase change material;
the adsorption amount is 50-70%, the vacuum impregnation temperature is 50-70 ℃, and the time is 12-24 h;
the phase change temperature of the starch-based hollow carbon microsphere composite phase change material is 23.9-29.8 ℃, and the latent heat of phase change is 129.3-170.5J/g.
4. The heat storage application of claim 3, wherein: the phase change material is n-octadecane.
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