Polyethylene glycol-based composite phase change material, preparation method thereof and solar evaporator

Abstract

The invention discloses a polyethylene glycol-based composite phase change material and a preparation method thereof, and the preparation method comprises the following steps: growing a ZIF-67 metal organic framework material on expanded graphite in situ by adopting a precipitation method to form an EG-ZIF-67 composite material; the EG-ZIF-67 composite material is converted into an EG-Co3O4 composite material by means of calcination; based on the EG-Co3O4 composite material and polyethylene glycol, the PEG / EG-Co3O4 composite phase change material is obtained by utilizing a direct impregnation method. The prepared polyethylene glycol-based composite phase change material is high in heat conductivity, excellent in photo-thermal conversion efficiency and low in supercooling degree, and the preparation process is simple, low in cost and capable of being recycled for multiple times.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change materials, and particularly relates to a polyethylene glycol-based composite phase change material, a preparation method thereof, and a solar evaporator. Background Art

[0002] The increase in the global population and the accelerating pace of industrialization have led to serious pollution, which in turn has led to a shortage of clean water. Although more than 70% of the earth's surface is covered by water, the fresh water resources directly available for human use account for less than 1% of the total global water volume. To address the widespread water shortage problem, various technologies have been developed to produce fresh water from seawater or contaminated water sources. The earth receives approximately 885 million terawatt-hours of solar energy per year, which is approximately 6,200 times the energy required for all human commercial activities globally. In the context of seawater desalination, solar water evaporation represents a completely new environmental protection technology that operates entirely on solar energy and has relatively low equipment costs.

[0003] Solar interfacial evaporation technology directly absorbs sunlight through a photothermal material located at the water-air interface, converts light energy into heat energy, and directly heats the water at this interface, thereby achieving water evaporation. The energy efficiency of interfacial evaporation is significantly higher than that of conventional evaporation methods, about 4 times that of conventional evaporation methods. However, most research efforts have focused on developing high-light-to-heat conversion materials to improve the daytime evaporation efficiency. Many effective materials have been successfully developed, including carbon nanotubes, graphene, and metal nanoparticles. Although the efficiency of converting solar energy into steam has increased with the progress of photothermal conversion materials, the intermittency of sunlight severely limits the evaporation efficiency of the evaporator in a lightless environment. Only a limited number of studies have reported the performance of nighttime steam generation.

[0004] Phase change materials (PCMs) that utilize latent heat storage provide a potential solution to the intermittency of water evaporation when sunlight weakens. These materials can store the waste heat of solar energy input when there is sunlight and release the latent heat at night to promote steam generation. However, the inherent disadvantages of PCMs, such as high supercooling, low thermal conductivity, and leakage during the application process, have hindered their widespread application. Therefore, how to design a shape-stable phase change material with low supercooling and high thermal conductivity remains a challenge for the efficient utilization of solar energy and industrialization. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides a polyethylene glycol-based composite phase change material, a preparation method thereof, and a solar evaporator. The technical problems to be solved by the present invention are achieved through the following technical solutions:

[0006] The present invention provides a preparation method of a polyethylene glycol-based composite phase change material, comprising:

[0007] The ZIF-67 metal-organic framework material is in-situ grown on expanded graphite by a precipitation method to form an EG-ZIF-67 composite material;

[0008] The EG-ZIF-67 composite material is converted into an EG-Co3O4 composite material by calcination;

[0009] Based on the EG-Co3O4 composite material and polyethylene glycol, a PEG / EG-Co3O4 composite phase change material is obtained by a direct impregnation method.

[0010] In one embodiment of the present invention, the ZIF-67 metal-organic framework material is in-situ grown on expanded graphite by a precipitation method to form an EG-ZIF-67 composite material, including:

[0011] A predetermined amount of expanded graphite and Co(NO3)2·6H2O are stirred evenly in methanol to form solution A;

[0012] A predetermined amount of 2-methylimidazole is dissolved in methanol to form solution B;

[0013] Solution B is poured into solution A under magnetic force and stirred at room temperature to cause a chemical reaction to obtain a reacted solution;

[0014] The reacted solution is aged for a predetermined time at room temperature, and then washed and dried to obtain the EG-ZIF-67 composite material.

[0015] In one embodiment of the present invention, the mass ratio of the expanded graphite, the Co(NO3)2·6H2O and the 2-methylimidazole is 1:(2-2.3):(1.4-1.7).

[0016] In one embodiment of the present invention, the EG-ZIF-67 composite material is converted into an EG-Co3O4 composite material by calcination, including:

[0017] The EG-ZIF-67 composite material is calcined at 650-750 °C for 2-3 hours in a nitrogen atmosphere;

[0018] After natural cooling, the obtained sample is transferred to a muffle furnace and kept at 150-200 °C for 3-4 hours in an air atmosphere to obtain the EG-Co3O4 composite material.

[0019] In one embodiment of the present invention, based on the EG-Co3O4 composite material and polyethylene glycol, a PEG / EG-Co3O4 composite phase change material is obtained by a direct impregnation method, including:

[0020] A predetermined amount of PEG 2000 and the EG-Co3O4 composite material are heated to melt in a water bath and stirred for a predetermined time to obtain a PEG / EG-Co3O4 mixture;

[0021] The cooled PEG / EG-Co3O4 mixture is added to a mold and a pressure of 2-10 Mpa is applied to mold it into a shape of a predetermined size.

[0022] Another aspect of the present invention provides a polyethylene glycol-based composite phase change material prepared by using the preparation method described in any one of the above embodiments.

[0023] Another aspect of the present invention provides a solar evaporator, which includes the polyethylene glycol-based composite phase change material described in claim 7, and a carbon black photothermal conversion coating is covered above the polyethylene glycol-based composite phase change material for transferring waste heat to the polyethylene glycol-based composite phase change material while performing photothermal conversion;

[0024] Moreover, the polyethylene glycol-based composite phase change material covered with the carbon black photothermal conversion coating is wrapped with a heat insulating material.

[0025] In an embodiment of the present invention, the heat insulating material is a foam board.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The present invention provides a polyethylene glycol-based composite phase change material with low supercooling degree and high thermal conductivity and its preparation method. This phase change material can be used in solar evaporators to overcome the problems of high supercooling degree, low thermal conductivity, leakage during application, low photothermal conversion efficiency, and difficulty in industrial application of organic phase change materials. The polyethylene glycol-based composite phase change material prepared by the present invention not only has high thermal conductivity, excellent photothermal conversion efficiency, and low supercooling degree, but also has a simple preparation process, low cost, and can be recycled and reused multiple times. It is a new preparation method with low cost and high efficiency, and can realize industrial application in fields such as solar-driven water treatment.

[0028] 2. In the present invention, metal nanoparticles Co3O4 are grown on expanded graphite to obtain EG-Co3O4 material, and it is compounded with polyethylene glycol PEG 2000. Due to the large porosity and high specific surface area of expanded graphite, polyethylene glycol PEG 2000 is adsorbed and encapsulated by expanded graphite, solving the problem of its leakage. The Co3O4 metal nanoparticles grown on expanded graphite provide more nucleation sites for PEG2000, reducing its supercooling degree. In addition, due to the high thermal conductivity of expanded graphite itself and Co3O4, the thermal conductivity is enhanced while overcoming the easy leakage and high supercooling of the phase change material.

[0029] 3. The polyethylene glycol-based composite phase change material of the present invention has the characteristics of high thermal conductivity and low supercooling degree. When used as a heat storage material in a solar evaporator, it exhibits efficient solar light-steam conversion ability.

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0031] Figure 1 It is a flowchart of a preparation method of a polyethylene glycol-based composite phase change material provided by an embodiment of the present invention;

[0032] Figure 2 It is an X-ray diffraction energy spectrum analysis diagram (XRD) of the PEG / EG-Co3O4 composite phase change material prepared in Example 2 of the present invention;

[0033] Figure 3 It is a scanning electron microscope image (SEM) of the PEG / EG-Co3O4 composite phase change material prepared in Example 2 of the present invention;

[0034] Figure 4 It is a diagram of the change in supercooling degree of the PEG / EG-Co3O4 composite phase change materials prepared in Examples 2, 3, 4, and 5 of the present invention;

[0035] Figure 5 It is the thermal conductivity of the PEG / EG-Co3O4 composite phase change materials prepared in Examples 2, 3, and 4 of the present invention;

[0036] Figure 6 It is a diagram of the mass change of the PEG / EG-Co3O4 composite phase change materials prepared in Examples 2, 3, 4, and 5 of the present invention during their application in a solar evaporator;

[0037] Figure 7 It is the evaporation efficiency of the PEG / EG-Co3O4 composite phase change materials prepared in Examples 2, 3, 4, and 5 of the present invention during their application in a solar evaporator. Detailed Embodiments

[0038] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following provides a detailed description of a polyethylene glycol-based composite phase change material, its preparation method, and a solar evaporator according to the present invention with reference to the accompanying drawings and specific embodiments.

[0039] The foregoing and other technical contents, features and effects of the present invention will be clearly presented in the following detailed description of the specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the predetermined purpose can be obtained. However, the accompanying drawings are only for reference and illustration, and are not used to limit the technical solutions of the present invention.

[0040] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, so that an article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the article or device including the said element.

[0041] Embodiment 1

[0042] This embodiment provides a preparation method of a polyethylene glycol-based composite phase change material for a solar evaporator. The preparation method is simple and easy to operate, and a composite phase change material with stable shape, low supercooling degree and high thermal conductivity can be prepared by the impregnation method.

[0043] Please refer to Figure 1 , Figure 1 which is a flow chart of a preparation method of a polyethylene glycol-based composite phase change material provided by an embodiment of the present invention. The preparation method includes:

[0044] S1: In-situ grow ZIF-67 metal-organic framework material on expanded graphite by the precipitation method to form EG-ZIF-67 composite material

[0045] A predetermined amount of expanded graphite (EG) and Co(NO3)2·6H2O are stirred evenly in methanol to form solution A; a predetermined amount of 2-methylimidazole is dissolved in methanol to form solution B; solution B is poured into solution A under magnetic force and stirred at room temperature to cause a chemical reaction to obtain the reacted solution; the reacted solution is aged for a predetermined time at room temperature, and then washed and dried to obtain EG-ZIF-67 composite material. The mass ratio of expanded graphite, Co(NO3)2·6H2O and 2-methylimidazole is 1:(2-2.3):(1.4-1.7).

[0046] S2: Convert the EG-ZIF-67 composite material into an EG-Co3O4 composite material by calcination.

[0047] The EG-ZIF-67 composite material was calcined in a nitrogen atmosphere at 650 - 750 °C for 2 - 3 h; after natural cooling, the obtained sample was transferred to a muffle furnace and maintained at 150 - 200 °C in an air atmosphere for 3 - 4 h to obtain the EG-Co3O4 composite material. When calcined at 650 - 750 °C, ZIF-67 was transformed into Co3O4, and the subsequent maintenance at 150 - 200 °C for 3 - 4 h was to retain more pores. The porosity of the calcined EG-Co3O4 composite material was increased compared to the EG-ZIF-67 composite material, and the specific surface area was enlarged. In the EG-Co3O4 composite material, Co3O4 nanoparticles were adsorbed on the EG, and the EG-Co3O4 composite material was in the form of relatively large particles of powder.

[0048] S3: Based on the EG-Co3O4 composite material and polyethylene glycol, the PEG / EG-Co3O4 composite phase change material was obtained by the direct impregnation method.

[0049] A predetermined amount of PEG 2000 (representing PEG with a molecular weight of 2000) and the EG-Co3O4 composite material were heated to melt in a water bath and stirred for a predetermined time to obtain a PEG / EG-Co3O4 mixture; the cooled PEG / EG-Co3O4 mixture was added to a mold and a pressure of 2 - 10 Mpa was applied to mold it into a shape with a predetermined size.

[0050] Preferably, in the PEG / EG-Co3O4 mixture, PEG 2000 accounted for 85% - 95% by mass, and the EG-Co3O4 composite material accounted for 5% - 15% by mass.

[0051] Another embodiment of the present invention also provides a polyethylene glycol-based composite phase change material prepared by the above preparation method.

[0052] Another embodiment of the present invention also provides a solar evaporator, including the above polyethylene glycol-based composite phase change material, and a carbon black photothermal conversion coating is covered above the polyethylene glycol-based composite phase change material to transfer the waste heat to the polyethylene glycol-based composite phase change material while performing photothermal conversion; and, the polyethylene glycol-based composite phase change material covered with the carbon black photothermal conversion coating is wrapped with a thermal insulation material. Preferably, the thermal insulation material is a foam board.

[0053] In the present invention, metal nanoparticles Co3O4 are grown on expanded graphite to obtain EG-Co3O4 material, which is compounded with polyethylene glycol PEG 2000. Due to the large porosity and high specific surface area of expanded graphite, polyethylene glycol PEG 2000 is adsorbed and encapsulated by expanded graphite, solving the problem of its leakage. The Co3O4 metal nanoparticles grown on expanded graphite provide more nucleation sites for PEG 2000, reducing its supercooling degree. In addition, due to the high thermal conductivity of expanded graphite itself and Co3O4, the thermal conductivity is enhanced while overcoming the problems of easy leakage and high supercooling of phase change materials.

[0054] Example Two

[0055] On the basis of Example One, this example provides another specific preparation method of polyethylene glycol-based composite phase change material. The chemical expression of the prepared polyethylene glycol-based composite phase change material is PEG / EG-Co3O4. The specific preparation method includes:

[0056] (1) ZIF-67 is in-situ grown on EG by precipitation method to obtain EG-ZIF-67 composite material.

[0057] First, 0.5 g of EG and 1.047 g of Co(NO3)2·6H2O are magnetically stirred in 40 mL of methanol for 2 h, and the obtained mixture is marked as solution A. 0.791 g of 2-methylimidazole (C4H6N2) is dissolved in 40 mL of methanol to form a clear and uniform solution B. Subsequently, solution B is poured into solution A under magnetic stirring, and stirred at room temperature for 0.25 h for chemical reaction to obtain the reacted solution. The reacted solution is aged at room temperature for 20 h, and then washed 3 times with ethanol. The obtained precipitate after washing is dried in an oven at 80 °C for 12 h to obtain EG-ZIF-67 composite material.

[0058] (2) The EG-ZIF-67 composite material is converted into EG-Co3O4 composite material by calcination.

[0059] The EG-ZIF-67 composite material obtained in step (1) is calcined in a tube furnace at 700 °C for 2 h under nitrogen atmosphere. After natural cooling, the obtained sample is transferred to a muffle furnace and kept at 150 °C in air for 3 h to obtain EG-Co3O4 composite material.

[0060] (3) The PEG / EG-Co3O4 composite phase change material is prepared by direct impregnation method.

[0061] First, 8.5 g of PEG 2000 and 1.5 g of the EG-Co3O4 composite material were heated in a beaker in a water bath at 80 °C until melted. A uniform PEG / EG-Co3O4 mixture was obtained through 30 minutes of mechanical stirring. Subsequently, the cooled PEG / EG-Co3O4 mixture was added to a mold and a pressure of 2 Mpa was applied for 10 s to mold it into a cylindrical sample with a diameter of 3 cm.

[0062] (4) A carbon black photothermal conversion coating was covered above the cylindrical sample formed by the PEG / EG-Co3O4 composite phase change material for photothermal conversion. While evaporating the interfacial water, the waste heat was transferred to the composite phase change material, and the composite phase change material was wrapped with a heat-insulating material to prevent heat loss.

[0063] Subsequently, the xenon lamp light intensity was detected by a light intensity meter, and its mass change and evaporation efficiency were measured under one sun. When illuminated, water was directly evaporated at the interface while the waste heat was absorbed and stored by the phase change material. When in a lightless environment, the phase change material released heat to continuously evaporate water.

[0064] Please refer to Figure 2 , Figure 2 which is the X-ray diffraction energy spectrum analysis diagram (XRD) of the PEG / EG-Co3O4 composite phase change material prepared in Example 2 of the present invention. From Figure 2 it can be proved that the composite phase change material was successfully compounded and had good chemical compatibility. The compounding process was a physical process without chemical reactions. Please refer to Figure 3 , Figure 3 which is the scanning electron microscope image (SEM) of the PEG / EG-Co3O4 composite phase change material prepared in Example 2 of the present invention. Among them, (a) and (b) are SEM images of EG at different magnifications, (c) is the SEM image of PEG / EG-Co3O4 and the EDS images of C, O, and Co elements, (d) is the SEM image of EG-Co3O4, and (e) is the SEM image of PEG / EG-Co3O4. From Figure 3 (a) and (b) in Figure 3 it can be seen that the three-dimensional porous structure of EG can be used to adsorb PEG; from Figure 3 (c) in Figure 3 it can be seen that the uniform distribution of each element in the composite phase change material proves uniform mixing; from

[0065] Example 3

[0066] Based on Example 1, this example provides another specific preparation method of a polyethylene glycol-based composite phase change material. The chemical expression of the prepared polyethylene glycol-based composite phase change material is PEG / EG-Co3O4. The specific preparation method includes:

[0067] (1) In-situ growth of ZIF-67 on EG by precipitation method to obtain EG-ZIF-67 composite material.

[0068] First, 0.5 g of EG and 1.047 g of Co(NO3)2·6H2O are magnetically stirred in 40 mL of methanol for 2 h, and the resulting mixture is labeled as solution A. 0.791 g of 2-methylimidazole (C4H6N2) is dissolved in 40 mL of methanol to form a clear and uniform solution B. Subsequently, solution B is poured into solution A under magnetic stirring, and stirred at room temperature for 0.25 h for chemical reaction to obtain the reacted solution. The reacted solution is aged at room temperature for 20 h and then washed 3 times with ethanol. The obtained precipitate is dried in an oven at 80 °C for 12 h to obtain EG-ZIF-67 composite material.

[0069] (2) Convert the EG-ZIF-67 composite material into EG-Co3O4 composite material by calcination.

[0070] The EG-ZIF-67 composite material obtained in step (1) is calcined in a tubular furnace at 700 °C for 2 h under a nitrogen atmosphere. After natural cooling, the obtained sample is transferred to a muffle furnace and kept at 150 °C in air for 3 h to obtain EG-Co3O4 composite material.

[0071] (3) Prepare the PEG / EG-Co3O4 composite phase change material by direct impregnation method.

[0072] First, 9 g of PEG 2000 and 1 g of EG-Co3O4 composite material are heated in a water bath at 80 °C in a beaker to melt them. A uniform PEG / EG-Co3O4 mixture is obtained by mechanical stirring for 30 minutes. Subsequently, the cooled PEG / EG-Co3O4 mixture is added to a mold and a pressure of 2 Mpa is applied for 10 s to mold it into a cylindrical sample with a diameter of 3 cm.

[0073] (4) Cover the cylindrical sample formed by the PEG / EG-Co3O4 composite phase change material with a carbon black photothermal conversion coating for photothermal conversion, transfer the waste heat to the composite phase change material while evaporating the interfacial water, and wrap the composite phase change material with a thermal insulation material to prevent heat loss.

[0074] Subsequently, detect the xenon lamp light intensity with a light intensity meter and measure its mass change and evaporation efficiency under one sun.

[0075] Example 4

[0076] Based on Example 1, this example provides another specific preparation method of the polyethylene glycol-based composite phase change material. The chemical expression of the prepared polyethylene glycol-based composite phase change material is PEG / EG-Co3O4. The specific preparation method includes:

[0077] (1) In-situ growth of ZIF-67 on EG by precipitation method to obtain EG-ZIF-67 composite material.

[0078] First, 0.5 g of EG and 1.047 g of Co(NO3)2·6H2O are magnetically stirred in 40 mL of methanol for 2 h, and the obtained mixture is labeled as solution A. 0.791 g of 2-methylimidazole (C4H6N2) is dissolved in 40 mL of methanol to form a clear and uniform solution B. Subsequently, solution B is poured into solution A under magnetic stirring, and stirred at room temperature for 0.25 h for chemical reaction to obtain the reacted solution. The reacted solution is aged at room temperature for 20 h and then washed with ethanol 3 times. The obtained precipitate after washing is dried in an oven at 80 °C for 12 h to obtain EG-ZIF-67 composite material.

[0079] (2) Convert the EG-ZIF-67 composite material into EG-Co3O4 composite material by calcination.

[0080] The EG-ZIF-67 composite material obtained in step (1) is calcined in a tube furnace at 700 °C for 2 h under a nitrogen atmosphere. After natural cooling, the obtained sample is transferred to a muffle furnace and kept at 150 °C in air for 3 h to obtain EG-Co3O4 composite material.

[0081] (3) Prepare the PEG / EG-Co3O4 composite phase change material by direct impregnation method.

[0082] First, 9.2 g of PEG 2000 and 0.8 g of EG-Co3O4 composite material are heated in a water bath at 80 °C in a beaker until melted. A uniform PEG / EG-Co3O4 mixture is obtained through 30 minutes of mechanical stirring. Subsequently, the cooled PEG / EG-Co3O4 mixture is added to a mold and a pressure of 2 Mpa is applied for 10 s to mold it into a cylindrical sample with a diameter of 3 cm.

[0083] (4) Cover a carbon black photothermal conversion coating above the cylindrical sample formed by the PEG / EG-Co3O4 composite phase change material for photothermal conversion, transfer the waste heat to the composite phase change material while evaporating the interfacial water, and wrap the composite phase change material with a heat-insulating material to prevent heat loss.

[0084] Subsequently, the intensity of the xenon lamp was detected by a light intensity meter, and its mass change and evaporation efficiency were measured under one sun.

[0085] Example 5

[0086] On the basis of Example 1, this example provides another specific preparation method of the polyethylene glycol-based composite phase change material. The chemical expression of the prepared polyethylene glycol-based composite phase change material is PEG / EG-Co3O4. The specific preparation method includes:

[0087] (1) ZIF-67 was in-situ grown on EG by the precipitation method to obtain the EG-ZIF-67 composite material.

[0088] First, 0.5 g of EG and 1.047 g of Co(NO3)2·6H2O were magnetically stirred in 40 mL of methanol for 2 h, and the resulting mixture was labeled as solution A. 0.791 g of 2-methylimidazole (C4H6N2) was dissolved in 40 mL of methanol to form a clear and uniform solution B. Subsequently, solution B was poured into solution A under magnetic stirring, and stirred at room temperature for 0.25 h for a chemical reaction to obtain the reacted solution. The reacted solution was aged at room temperature for 20 h and then washed 3 times with ethanol. The obtained precipitate after washing was dried in an oven at 80 °C for 12 h to obtain the EG-ZIF-67 composite material.

[0089] (2) The EG-ZIF-67 composite material was converted into the EG-Co3O4 composite material by calcination.

[0090] The EG-ZIF-67 composite material obtained in step (1) was calcined in a tubular furnace at 700 °C for 2 h under a nitrogen atmosphere. After natural cooling, the obtained sample was transferred to a muffle furnace and kept at 150 °C in air for 3 h to obtain the EG-Co3O4 composite material.

[0091] (3) The PEG / EG-Co3O4 composite phase change material was prepared by the direct impregnation method.

[0092] First, 9.5 g of PEG 2000 and 0.5 g of the EG-Co3O4 composite material were heated in a water bath at 80 °C in a beaker to melt them. A uniform PEG / EG-Co3O4 mixture was obtained by mechanical stirring for 30 minutes. Subsequently, the cooled PEG / EG-Co3O4 mixture was added to a mold and a pressure of 2 Mpa was applied for 10 s to mold it into a cylindrical sample with a diameter of 3 cm.

[0093] (4) A carbon black photothermal conversion coating is covered on the cylindrical sample formed by the PEG / EG-Co3O4 composite phase change material for photothermal conversion. While evaporating the interfacial water, the waste heat is transferred to the composite phase change material, and the composite phase change material is wrapped with a thermal insulation material to prevent heat loss.

[0094] Subsequently, the intensity of the xenon lamp light was detected by a light intensity meter, and its mass change and evaporation efficiency were measured under one sun.

[0095] The performance of the polyethylene glycol-based composite phase change material obtained in the embodiment of the present invention is further described below through experiments.

[0096] The composite phase change material obtained in Example 2 has a PEG content of 85 wt%. Figures 4 to 7 PEG 0.85 / EG-Co 0.15 It is indicated that the Co3O4 nanoparticles grown on EG provide a nucleation basis for PEG molecules. Since the size of Co3O4 nanoparticles is much larger than that of PEG molecules, it can be considered that the nucleation basis provided by Co3O4 for PEG is similar to a plane. At this time, the nucleation process of the crystal nucleus is heterogeneous nucleation, which makes the nucleation process easier. Its supercooling is compared with PEG (15.7℃) and PEG with the same PEG ratio. 0.85 / EG 0.15 The composite phase change material (10.8℃) is reduced to 7℃, such as Figure 4 Its thermal conductivity increases from 0.3515 W / m·K of pure PEG to 10.66 W / m·K, as shown in Figure 5 When the PEG / EG-Co3O4 composite phase change material in this embodiment is used as a heat storage material in a solar evaporator, it shows excellent evaporation performance. The evaporation mass change under lightless conditions is significantly lower than that without phase change material (0.31 Kg·m within 75 min). -2 ) and PEG / EG (0.44Kg·m within 75min -2 ) showed a more efficient evaporation mass change (0.69Kg·m within 75min) -2 ),like Figure 6 As shown. The PEG in this example 0.85 / EG-Co 0.15 When composite phase change materials are used as heat storage materials in solar evaporators, the evaporation efficiency in a lightless environment is much higher than that using PEG 0.85 / EG 0.15 The evaporation efficiency with and without phase change material, such as Figure 7 shown.

[0097] The composite phase change material obtained in Example 3 has a PEG content of 90 wt%. Figures 4 to 7 PEG0.90 / EG-Co 0.10 indicates that the Co3O4 nanoparticles grown on EG provide a nucleation basis for PEG molecules. Since the size of Co3O4 nanoparticles is much larger than that of PEG molecules, it can be considered that the nucleation basis provided by Co3O4 for PEG is similar to a plane. PEG 0.90 / EG-Co 0.10 has a supercooling degree lower than that of PEG (15.7 °C) and PEG 0.9 / EG 0.1 composite phase change materials (11.2 °C) to 8.1 °C, as Figure 4 shown. Its thermal conductivity is increased from 0.3515 W / m·K of pure PEG to 8.627 W / m·K, as Figure 5 shown. When the PEG / EG-Co3O4 composite phase change material in this example is used as a heat storage material for a solar evaporator, it shows excellent evaporation performance. The evaporation mass change under lightless conditions is more efficient compared to the non-phase change material (0.31 Kg·m within 75 min -2 ) and PEG 0.9 / EG 0.1 (0.43 Kg·m within 75 min -2 ), showing a more efficient evaporation mass change (0.73 Kg·m within 75 min -2 ), as Figure 6 shown. When the PEG 0.9 / EG-Co 0.1 composite phase change material in this example is used as a heat storage material for a solar evaporator, its evaporation efficiency in a lightless environment is much higher than that when using PEG 0.9 / EG 0.1 and the evaporation efficiency under the condition of no phase change material, as Figure 7 shown.

[0098] For the composite phase change material obtained in Example 4, the PEG content is 92 wt%, and in Figures 4 to 7 it is represented by PEG 0.92 / EG-Co 0.08 . Its supercooling degree is reduced to 9.6 °C compared to PEG (15.7 °C) and PEG 0.92 / EG 0.08 composite phase change materials (12 °C), as Figure 4 shown. Its thermal conductivity is increased from 0.3515 W / m·K of pure PEG to 6.432 W / m·K, as Figure 5 shown. When the PEG / EG-Co3O4 composite phase change material in this example is used as a heat storage material for a solar evaporator, it shows excellent evaporation performance. The evaporation mass change under lightless conditions is compared to the non-phase change material (0.31 Kg·m within 75 min-2 ) and PEG 0.92 / EG 0.08 (0.43 Kg·m within 75 min -2 ) shows a more efficient evaporation mass change (0.8 Kg·m within 75 min -2 ), as Figure 6 shown. The PEG 0.92 / EG-Co 0.08 composite phase change material in this example, when used as a heat storage material for a solar evaporator, has a much higher evaporation efficiency in a dark environment than when using PEG 0.92 / EG 0.08 and without a phase change material, as Figure 7 shown.

[0099] For the composite phase change material obtained in Example 5, with a PEG content of 95 wt%, in Figures 4 to 7 it is denoted as PEG 0.95 / EG-Co 0.05 . Its supercooling degree is reduced to 8°C compared to PEG (15.7°C) and the PEG 0.95 / EG 0.05 composite phase change material with the same PEG ratio (10.7°C), as Figure 4 shown. The PEG / EG-Co3O4 composite phase change material in this example, when used as a heat storage material for a solar evaporator, shows excellent evaporation performance. The evaporation mass change under dark conditions is higher than that without a phase change material (0.31 Kg·m within 75 min -2 ) and PEG 0.92 / EG 0.08 (0.42 Kg·m within 75 min -2 ), showing a more efficient evaporation mass change (0.55 Kg·m within 75 min -2 ), as Figure 6 shown. The PEG 0.95 / EG-Co 0.05 composite phase change material in this example, when used as a heat storage material for a solar evaporator, has a much higher evaporation efficiency in a dark environment than when using PEG 0.95 / EG 0.05 and without a phase change material, as Figure 7 shown.

[0100] The present invention provides a polyethylene glycol-based composite phase change material with low supercooling degree and high thermal conductivity, and a preparation method thereof. This phase change material can be used in a solar evaporator to overcome the problems of high supercooling degree, low thermal conductivity, leakage during application, low photothermal conversion efficiency, and difficulty in industrial application of organic phase change materials. The polyethylene glycol-based composite phase change material prepared by the present invention not only has high thermal conductivity, excellent photothermal conversion efficiency, and low supercooling degree, but also has a simple preparation process, low cost, and can be recycled and reused multiple times. It is a new preparation method with low cost and high efficiency, and can realize industrial applications in fields such as solar-driven water treatment. The polyethylene glycol-based composite phase change material of the present invention has the characteristics of high thermal conductivity and low supercooling degree. When used as a heat storage material in a solar evaporator, it exhibits high-efficient solar light-steam conversion ability.

[0101] In several embodiments provided by the present invention, it should be understood that the devices and methods disclosed by the present invention can be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of the modules is only a logical function division. In actual implementation, there may be other division methods. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0102] In addition, each functional module in various embodiments of the present invention can be integrated in a processing module, or each module can exist physically alone, or two or more modules can be integrated in one module. The above-mentioned integrated modules can be implemented in the form of hardware, or in the form of a combination of hardware and software functional modules.

[0103] The above content is a further detailed description of the present invention in combination with specific preferred implementation manners. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing a polyethylene glycol-based composite phase change material, characterized in that: include: The ZIF-67 metal organic framework material was in situ grown on expanded graphite by precipitation method to form EG-ZIF-67 composite material; converting the EG-ZIF-67 composite material into an EG-Co3O4 composite material by calcining; Based on the EG-Co3O4 composite material and polyethylene glycol, a PEG / EG-Co3O4 composite phase change material is obtained by a direct impregnation method.

2. The method for preparing a polyethylene glycol-based composite phase change material according to claim 1, characterized in that: The ZIF-67 metal organic framework material is in situ grown on expanded graphite by a precipitation method to form an EG-ZIF-67 composite material, comprising: A predetermined amount of expanded graphite and Co(NO3)2·6H2O were stirred uniformly in methanol to form solution A; Dissolving a predetermined amount of 2-methylimidazole in methanol to form solution B; Pour the solution B into the solution A under the action of magnetic force and stir at room temperature to cause a chemical reaction to obtain a reacted solution; The reacted solution was aged at room temperature for a predetermined time, and then washed and dried to obtain the EG-ZIF-67 composite material.

3. The method for preparing a polyethylene glycol-based composite phase change material according to claim 2, characterized in that: The mass ratio of the expanded graphite, the Co(NO3)2·6H2O and the 2-methylimidazole is 1:(2-2.3):(1.4-1.7).

4. The method for preparing a polyethylene glycol-based composite phase change material according to claim 2, characterized in that: The EG-ZIF-67 composite material is converted into an EG-Co3O4 composite material by calcination, comprising: calcining the EG-ZIF-67 composite material at 650-750° C. for 2-3 hours under a nitrogen atmosphere; After natural cooling, the obtained sample was transferred to a muffle furnace and maintained at 150-200 °C for 3-4 hours in an air atmosphere to obtain the EG-Co3O4 composite material.

5. The method for preparing a polyethylene glycol-based composite phase change material according to claim 2, characterized in that: Based on the EG-Co3O4 composite material and polyethylene glycol, a PEG / EG-Co3O4 composite phase change material is obtained by a direct impregnation method, comprising: heating a predetermined amount of PEG 2000 and the EG-Co3O4 composite material in a water bath until they are melted, and stirring for a predetermined time to obtain a PEG / EG-Co3O4 mixture; The cooled PEG / EG-Co3O4 mixture is added into a mold and a pressure of 2-10 MPa is applied to mold it into a shape of a predetermined size.

6. The method for preparing a polyethylene glycol-based composite phase change material according to claim 5, characterized in that: In the PEG / EG-Co3O4 mixture, the PEG 2000 accounts for 85% to 95% by weight, and the EG-Co3O4 composite material accounts for 5% to 15% by weight.

7. A polyethylene glycol-based composite phase change material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

8. A solar evaporator, characterized in that: The polyethylene glycol-based composite phase change material according to claim 7 is provided, wherein a carbon black photothermal conversion coating is provided on the polyethylene glycol-based composite phase change material to transfer waste heat to the polyethylene glycol-based composite phase change material during photothermal conversion; In addition, the polyethylene glycol-based composite phase change material covered with the carbon black light-to-heat conversion coating is wrapped with a thermal insulation material.

9. The solar evaporator according to claim 8, characterized in that: The heat-insulating material is a foam board.

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