Water-based modified carbon nanotube nanofluid and preparation method thereof

Abstract

The application discloses a water-based modified carbon nanotube nanofluid and a preparation method thereof, and comprises the following steps: S1, cucurbituril is added to a persulfate salt to react under nitrogen protection to prepare hydroxylated cucurbituril; S2, N,N-carbonyl diimidazole is used as an activator to react with the hydroxylated cucurbituril to prepare activated hydroxylated cucurbituril; S3, the activated hydroxylated cucurbituril is used to modify amino-functionalized multi-walled carbon nanotubes to prepare water-based modified carbon nanotube nanoparticles; and S4, the water-based modified carbon nanotube nanoparticles are dispersed in a base fluid to obtain the water-based modified carbon nanotube nanofluid. The hydrophilic group cucurbituril with good thermal stability is introduced on the surface of the multi-walled carbon nanotube nanoparticles, the problems of poor stability of a working fluid and weak light capturing capacity are better solved, and the water-based modified carbon nanotube nanofluid has a good application prospect in a solar energy collection system.

Description

Technical Field

[0001] This invention belongs to the field of solar energy utilization technology, specifically relating to a water-based modified carbon nanotube nanofluid and its preparation method. Background Technology

[0002] In direct absorption solar collectors (DASCs), the strong solar energy capture and high heat transfer performance of the heat transfer fluid are crucial for designing solar thermal absorbers to improve photothermal conversion efficiency. However, traditional heat transfer fluids have two major drawbacks when used as absorption media: poor stability of the working fluid and weak light capture capability, which cannot meet the ever-increasing energy demand.

[0003] Current research indicates that nanofluids possess high thermal conductivity, enabling them to effectively absorb solar radiation without the addition of any dyes. Furthermore, the complementary optical absorption properties of different nanoparticles allow for controllable broadband absorption spectra, facilitating efficient solar energy absorption. Therefore, the combination of nanofluids and solar collectors provides a theoretical basis for significantly improving the photothermal conversion efficiency of solar energy.

[0004] Currently, the stability of nanofluids is mainly improved by adding surfactants or adjusting the pH value to enhance their dispersibility. However, as the operating temperature increases, the interaction between nanoparticles and surfactants weakens, leading to a decrease in the dispersibility of the nanofluid. Furthermore, adjusting the pH value can cause corrosion to the equipment or pipelines used in the application of nanofluids. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a water-based modified carbon nanotube nanofluid and its preparation method. This invention introduces a thermally stable hydrophilic group, cucurbitaurea, onto the surface of multi-walled carbon nanotube nanoparticles, which can effectively solve the problems of poor working fluid stability and weak light-harvesting ability, making it a promising candidate for application in solar thermal systems.

[0006] The technical solution adopted to achieve the above-mentioned objectives of this invention is as follows:

[0007] A method for preparing water-based modified carbon nanotube nanofluids includes the following steps:

[0008] S1. Add cucurbituril to deionized water and stir until homogeneous. Then add persulfate and heat to 75-95°C under nitrogen protection while stirring. Continue stirring and reacting for 6-10 hours under nitrogen protection and at 75-95°C. After the reaction is complete, stop heating and cool to room temperature. Add acetone to the resulting mixture to form a white precipitate. Wash the white precipitate with dimethyl sulfoxide and acetone in sequence and dry to obtain hydroxylated cucurbituril.

[0009] S2. Add hydroxylated cucurbita to dimethylformamide, stir to dissolve, and obtain a colorless and transparent solution. Add N,N-carbonyldiimidazole dropwise to the colorless and transparent solution and stir at room temperature for 2-4 hours to obtain activated hydroxylated cucurbita.

[0010] S3. Aminated multi-walled carbon nanotubes were uniformly dispersed in dimethylformamide, and then activated hydroxylated cucurbitaurea was slowly added. The mixture was stirred at room temperature for 20-28 hours. After the reaction was completed, the resulting mixed product was filtered, and the filter cake was washed with dimethylformamide, acetone and deionized water in sequence and dried to obtain water-based modified carbon nanotube nanoparticles.

[0011] S4. Disperse the water-based modified carbon nanotube nanoparticles in the base liquid to obtain the water-based modified carbon nanotube nanofluid.

[0012] The cucurbituril mentioned is cucurbituril[5] or cucurbituril[7].

[0013] The cucurbituril mentioned is cucurbituril[7] urea.

[0014] The persulfates mentioned include potassium persulfate, sodium persulfate, and ammonium persulfate.

[0015] The molar ratio of cucurbituril to persulfate is 0.058-0.103:1.

[0016] The molar ratio of the hydroxylated cucurbituril to N,N-carbonyldiimidazole is 1:6.05-10.1.

[0017] The mass ratio of the aminated multi-walled carbon nanotubes to the activated hydroxylated cucurbita is 1:1-3.

[0018] The base liquid is at least one of water, ethylene glycol, molten salt (53% KNO3 + 40% NaNO2 + 7% NaNO3 molar ratio), and ionic liquid [HMIM]BF4.

[0019] The molten salt is composed of potassium nitrate, sodium nitrite, and sodium nitrate, with a molar ratio of 53:40:7. The ionic liquid is [Hmim]BF4.

[0020] A water-based modified carbon nanotube nanofluid prepared by the above method.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0022] 1. In this invention, a hydrophilic functional group cucurbita (such as CB[7]) with good thermal stability is introduced on the surface of carbon nanotube nanoparticles that are difficult to dissolve in water, so that the modified carbon nanotube nanoparticles can be uniformly and stably dispersed in the base liquid.

[0023] 2. When the modified carbon nanotube nanoparticles of this invention are added to a traditional base liquid, on the one hand, the ultra-high thermal conductivity (3000~6000W / m·K) of the modified carbon nanotubes can improve the thermal conductivity of the fluid, and on the other hand, the modified carbon nanotubes can improve the photothermal conversion efficiency of the base liquid.

[0024] 3. The nanofluid prepared by this invention has excellent optical properties and photothermal conversion efficiency. Experiments show that the solar extinction coefficient of the nanofluid of this invention can reach up to 10 cm⁻¹. -1 The photothermal conversion efficiency can reach up to 95.68%.

[0025] 4. The preparation method of the present invention is simple, easy to operate, and the operating conditions are easy to control, thus the production cost is relatively low. Attached Figure Description

[0026] Figure 1 Stability diagram of the water-based modified carbon nanotube nanofluid prepared in Example 1.

[0027] Figure 2 The thermal conductivity of the water-based modified carbon nanotube nanofluid prepared in Example 1 is shown in the figure.

[0028] Figure 3 The light absorption capacity diagram of the water-based modified carbon nanotube nanofluid prepared in Example 1 is shown.

[0029] Figure 4 The photothermal conversion efficiency diagram of the water-based modified carbon nanotube nanofluid prepared in Example 1. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific embodiments.

[0031] Example 1

[0032] 1. Take 7g of cucurbita[7]urea (CB[7]) and add it to 100mL of water. After stirring evenly, add 21g of K2S2O8 and heat to 85℃ under nitrogen protection. At this time, the solution becomes clear. Then, continue stirring the reaction for 6h under nitrogen protection and 85℃. After the reaction is completed, stop heating. Add acetone to the obtained mixed product to form a white precipitate. Wash the white precipitate with 30mL of dimethyl sulfoxide, then wash it 5 times with acetone, and finally dry it to obtain 1.624g of hydroxylated cucurbita[7]urea.

[0033]

[0034] IR(KBr)ν:3459,3208,3015,2954,1745,1471,1425,1376,1322,1260,1203,1052,967,799,765,674,587cm -1 .

[0035] 2. Take 11g of hydroxylated cucurbita and add it to 120mL of dimethylformamide (DMF). After stirring and dissolving, a colorless and transparent solution is obtained. Slowly add 8mL of N,N-carbonyldiimidazole to the colorless and transparent solution and stir at room temperature for 3h to activate the hydroxyl groups on the surface of cucurbita, to obtain 8.635g of activated hydroxylated cucurbita.

[0036]

[0037] IR(KBr)ν:3449,3219,2958,1760,1680,1468,1435,1380,1332,1258,1227,1026,995,860,761,745,649,641cm -1

[0038] 3. Add 6g of aminated multi-walled carbon nanotubes to 110ml of dimethylformamide (DMF) and stir continuously for 1 hour to uniformly disperse the aminated multi-walled carbon nanotubes in the DMF. Then, slowly add 12g of activated hydroxylated cucurbitaurea and stir the mixture with a magnetic stirrer at room temperature for 24 hours. After the reaction is complete, wash the resulting mixture with DMF, acetone and deionized water in sequence, and dry it in a vacuum oven to obtain 3.912g of modified carbon nanotube nanoparticles.

[0039]

[0040] IR(KBr)ν:3500-3400,3212,2958,2880,1725,1670,1480,1435,1376,1328,1262,1034,965,765,669,590cm -1

[0041] As can be seen from the infrared spectrum, 3500-3400 cm⁻¹ -1 There is a relatively broad absorption peak at 1670 cm⁻¹, which is the stretching vibration peak of the hydroxyl group. This is because hydroxylated cucurbitacin contains a large number of hydroxyl groups. -1 The peak represents the stretching vibration of the C=O bond in amides, at 1262 cm⁻¹. -1 The peak for stretching vibration of the CN bond in amides is 1034 cm⁻¹. -1 The stretching vibration of the CO bond, at 2880 cm⁻¹ -1The peak at this point represents the symmetric stretching vibration of the methylene group in the -CH2- group. This demonstrates the formation of a significant number of carbonyl and hydroxyl groups in the modified amino-carbon nanotubes, indicating the success of cucurbituril-modified amino-carbon nanotubes.

[0042] 4. Different masses of water-based modified carbon nanotube nanoparticles were dispersed in deionized water to obtain water-based modified carbon nanotube nanofluids with volume fractions of 0.02 vol.%, 0.04 vol.%, 0.06 vol.%, 0.08 vol.%, and 0.1 vol.%.

[0043] Comparative Example 1

[0044] Carbon nanotube nanoparticles of different masses were dispersed in deionized water to obtain carbon nanotube nanofluids with volume fractions of 0.02 vol.%, 0.04 vol.%, 0.06 vol.%, 0.08 vol.%, and 0.1 vol.%.

[0045] The water-based modified carbon nanotube nanofluid prepared in Example 1 and the carbon nanotube nanofluid prepared in Comparative Example 1 were placed in the atmosphere, and their Zeta potentials were measured on days 0, 7, and 30. The results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the zeta potential of the water-based modified carbon nanotube nanofluid prepared in Example 1 remained basically unchanged after 30 days, still exceeding 50mV, indicating good stability. In contrast, the zeta potential of the unmodified carbon nanotube nanofluid gradually decreased, indicating that the unmodified carbon nanotubes were prone to aggregation and had poor stability.

[0046] Thermal conductivity of water-based modified carbon nanotube nanofluids with different volume fractions, such as Figure 2 As shown, by Figure 2 It can be seen that, due to the aggregation of unmodified carbon nanotubes, the thermal conductivity of water-based modified carbon nanotube nanofluids with the same volume concentration is better than that of unmodified carbon nanotube nanofluids, and the thermal conductivity increases with the increase of volume fraction. The thermal conductivity of 0.1 vol.% modified nanofluid increased by 46.12% compared with that of the base liquid, while the thermal conductivity of unmodified nanofluid only increased by 18.86%.

[0047] The extinction coefficients (light absorption capacity) of water-based modified carbon nanotube nanofluids and unmodified nanofluids with different volume fractions are as follows: Figure 3 As shown, when the volume fraction of water-based modified carbon nanotube nanofluid increases to 0.1 vol.%, the average extinction coefficient of the water-based modified carbon nanotube nanofluid exceeds 10 cm⁻¹ in the wavelength range of 190-1100 nm. -1 The extinction coefficient of unmodified carbon nanotube nanofluids is relatively low.

[0048] Photothermal conversion efficiency of water-based modified carbon nanotube nanofluids with different volume fractions, such as Figure 4 As shown, by Figure 4 It can be seen that the photothermal conversion efficiency of the base liquid deionized water is only 42%. The photothermal conversion efficiency of both water-based modified carbon nanotube nanofluid and unmodified carbon nanotube nanofluid increases with increasing concentration. The photothermal conversion efficiency of 0.1 vol.% water-based modified carbon nanotube nanofluid can reach 95.68%, while the photothermal conversion efficiency of 0.1 vol.% unmodified carbon nanotube nanofluid is only 75.02%.

[0049] Example 2

[0050] 1. Take 6g of cucurbita[7]urea (CB[7]) and add it to 100mL of water. After stirring evenly, add 18g of K2S2O8 and heat to 75℃ under nitrogen protection. At this time, the solution becomes clear. Then, continue stirring the reaction for 6h under nitrogen protection and 75℃. After the reaction is completed, stop heating. Add acetone to the obtained mixed product to form a white precipitate. Wash the white precipitate with 30mL of dimethyl sulfoxide, then wash it 5 times with acetone, and finally dry it to obtain hydroxylated cucurbita.

[0051] 2. Take 11g of hydroxylated cucurbita and add it to 100mL of dimethylformamide (DMF). After stirring and dissolving, a colorless and transparent solution is obtained. Slowly add 6mL of N,N-carbonyldiimidazole to the colorless and transparent solution and stir at room temperature for 2h to activate the hydroxyl groups on the surface of cucurbita to obtain activated hydroxylated cucurbita.

[0052] 3. Add 6g of aminated multi-walled carbon nanotubes to 100ml of dimethylformamide (DMF) and stir continuously for 1 hour to uniformly disperse the aminated multi-walled carbon nanotubes in the DMF. Then, slowly add 6g of activated hydroxylated cucurbitaurea and stir the mixture with a magnetic stirrer at room temperature for 20 hours. After the reaction is complete, wash the resulting mixture with DMF, acetone and deionized water in sequence, and dry it in a vacuum oven to obtain modified carbon nanotube nanoparticles.

[0053] 4. Dissolve the water-based modified carbon nanotube nanoparticles in deionized water to obtain the water-based modified carbon nanotube nanofluid.

[0054] Example 3

[0055] 1. Take 8g of cucurbit[7]urea (CB[7]) and add it to 100mL of water. After stirring evenly, add 24g of K2S2O8 and heat to 85℃ under nitrogen protection. At this time, the solution becomes clear. Then, continue stirring the reaction for 6h under nitrogen protection and 85℃. After the reaction is completed, stop heating. Add acetone to the obtained mixed product to form a white precipitate. Wash the white precipitate with 30mL of dimethyl sulfoxide, then wash it 5 times with acetone, and finally dry it to obtain hydroxylated cucurbituril.

[0056] 2. Take 11g of hydroxylated cucurbita and add it to 140mL of dimethylformamide (DMF). After stirring and dissolving, a colorless and transparent solution is obtained. Slowly add 10mL of N,N-carbonyldiimidazole to the colorless and transparent solution and stir at room temperature for 4h to activate the hydroxyl groups on the surface of cucurbita to obtain activated hydroxylated cucurbita.

[0057] 3. Add 6g of aminated multi-walled carbon nanotubes to 120ml of dimethylformamide (DMF) and stir continuously for 1 hour to uniformly disperse the aminated multi-walled carbon nanotubes in the DMF. Then, slowly add 18g of activated hydroxylated cucurbitaurea and stir the mixture with a magnetic stirrer at room temperature for 28 hours. After the reaction is complete, wash the resulting mixture with DMF, acetone and deionized water in sequence, and dry it in a vacuum oven to obtain modified carbon nanotube nanoparticles.

[0058] 4. Dissolve the water-based modified carbon nanotube nanoparticles in deionized water to obtain the water-based modified carbon nanotube nanofluid.

Claims

1. A method for preparing a water-based modified carbon nanotube nanofluid, characterized by It comprises the following steps: S1, cucurbituril is added to deionized water, stirred uniformly, then persulfate is added, heated to 75-95℃ under stirring under nitrogen protection, then continue to stir at 75-95℃ under nitrogen protection for 6-10 h, after the reaction is completed, stop heating, cool to room temperature, then add acetone to the obtained mixture to form white precipitate, wash the white precipitate with dimethyl sulfoxide and acetone in turn, dry to obtain hydroxylated cucurbituril; S2, the hydroxylated cucurbituril is added to dimethylformamide, stirred and dissolved to obtain a colorless transparent solution, then N, N-carbonyl diimidazole is added dropwise, stirred at room temperature for 2-4 h to obtain activated hydroxylated cucurbituril; S3, the aminated multi-walled carbon nanotube is uniformly dispersed in dimethylformamide, then the activated hydroxylated cucurbituril is slowly added, stirred at room temperature for 20-28 h, after the reaction is completed, the obtained mixture is filtered, the filter cake is washed with dimethylformamide, acetone and deionized water in turn, and dried to obtain water-based modified carbon nanotube nanoparticles; S4, the water-based modified carbon nanotube nanoparticles are dispersed in a base fluid to obtain the water-based modified carbon nanotube nanofluid.

2. The method for preparing water-based modified carbon nanotube nanofluid according to claim 1, characterized in that: The cucurbituril is cucurbit[5]uril or cucurbit[7]uril.

3. The method for preparing water-based modified carbon nanotube nanofluid according to claim 2, characterized in that: The cucurbituril is cucurbit[7]uril.

4. The method for preparing water-based modified carbon nanotube nanofluid according to claim 1, characterized in that: The persulfate includes potassium persulfate, sodium persulfate and ammonium persulfate.

5. The method for preparing water-based modified carbon nanotube nanofluid according to claim 1, characterized in that: The molar ratio of the cucurbituril to the persulfate is 0.058-0.103:

1.

6. The method for preparing water-based modified carbon nanotube nanofluid according to claim 1, characterized in that: The molar ratio of the hydroxylated cucurbituril to N, N-carbonyl diimidazole is 1:6.05-10.

1.

7. The method for preparing water-based modified carbon nanotube nanofluid according to claim 1, characterized in that: The mass ratio of the aminated multi-walled carbon nanotube to the activated hydroxylated cucurbituril is 1:1-3.

8. The method for preparing water-based modified carbon nanotube nanofluid according to claim 1, characterized in that: The base fluid is at least one of water, ethylene glycol, a molten salt with a molar ratio of 53% KNO3+40% NaNO2+7% NaNO3, and an ionic liquid [HMIM]BF4.

9. A water-based modified carbon nanotube nanofluid prepared by the method of any one of claims 1-8.

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