A green nanofluid absorbent for photothermal carbon capture and its preparation method

Abstract

The present invention discloses a green nanofluid absorbent for photothermal carbon capture and a preparation method thereof, belonging to the field of functional materials technology. The preparation method comprises: dispersing carboxyl carbon nanotubes in a dispersant and adjusting the dispersant to alkalinity; then adding tetraethyl silicate under high-speed stirring at 1000-2000 r / min; adjusting the pH value of the system to 7-7.5 after the reaction; centrifuging; washing the precipitate to obtain a black gel-like substance; drying and grinding the black gel-like substance to obtain nanoparticles composited with carboxyl carbon nanotubes and silicon dioxide; and dispersing the nanoparticles composited with carboxyl carbon nanotubes and silicon dioxide and a surfactant in a deep eutectic solvent to obtain the green nanofluid absorbent for photothermal carbon capture. The prepared green nanofluid absorbent for photothermal carbon capture has high photothermal conversion efficiency, high carbon capture capacity, and high stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and in particular relates to a green nanofluid absorbent for photothermal carbon capture and a preparation method thereof. Background Art

[0002] Deep eutectic solvents are environmentally friendly, recyclable, and green solvents with great potential in the field of carbon capture. They have gradually become a research hotspot in the fields of chemistry, physics, materials, and heat transfer. Carbon nanotubes are nanomaterials with nanotube diameters that have characteristics such as high thermal conductivity and high photothermal conversion efficiency. Using deep eutectic solvents as the base liquid for nanofluids has always been a research hotspot for nanofluid researchers. However, in the current nanofluid photothermal carbon capture technology, there are many problems. For example, if the particle content is too low, the mass transfer effect is poor and the increase is not obvious; if there are too many particles, it will lead to obvious agglomeration and rapid sedimentation, thereby losing the properties of the nanofluid; ordinary nanofluids cannot utilize photothermal heat during the photothermal carbon dioxide absorption process; and the stability is too poor.

[0003] Carbon nanotubes have good photothermal conversion efficiency, but their stability in deep eutectic solvents is poor. There is no research in this field on how to obtain a stable green nanofluid that can effectively utilize photothermal energy to achieve carbon capture requirements. Summary of the Invention

[0004] The present invention aims to provide a green nanofluid absorbent for photothermal carbon capture and its preparation method. By combining carboxyl carbon nanotubes with silica and dispersing them in a deep eutectic solvent, a green nanofluid absorbent with high photothermal conversion efficiency, high carbon capture capacity, and high stability is obtained.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a method for preparing a green nanofluid absorbent for photothermal carbon capture, comprising the following steps:

[0007] Carboxyl carbon nanotubes are dispersed in a dispersant and adjusted to alkalinity. Then, tetraethyl silicate is added under high-speed stirring at 1000-2000 r / min. After the reaction, the pH value of the system is adjusted to 7-7.5, centrifuged, and the precipitate is washed to obtain a black gel-like substance. The black gel-like substance is dried and ground to obtain nanoparticles of a composite of carboxyl carbon nanotubes and silicon dioxide (CNTs@SiO2). The nanoparticles of the composite of carboxyl carbon nanotubes and silicon dioxide and a surfactant are co-dispersed in a deep eutectic solvent to obtain the green nanofluid absorbent for photothermal carbon capture.

[0008] The present invention uniformly disperses carboxyl carbon nanotubes in a mixed solution of isopropyl alcohol and deionized water, creating an alkaline environment to accelerate the hydrolysis and condensation of tetraethyl silicate. During this reaction, tetraethyl silicate first generates silicic acid and siloxane in an alkaline environment. The silicic acids condense with each other, and the oligomers further polymerize to form long chains that extend three-dimensionally into a skeleton structure. The dispersed carboxyl carbon nanotubes now provide attachment points for the condensed silicic acid. Under high-speed stirring, the spherical morphology and small particle size of the formed silica can be maintained. Further dispersion in a deep eutectic solvent can produce a green nanofluid absorbent with high light-to-heat conversion efficiency, high carbon capture capacity, and high stability.

[0009] Preferably, the carboxyl carbon nanotubes have a diameter of 8 to 15 nm and a length of no more than 30 μm.

[0010] Preferably, the dispersant is obtained by mixing isopropyl alcohol and water.

[0011] Preferably, the usage ratio of the carboxyl carbon nanotubes to the dispersant is 0.4-0.6 g:50 mL.

[0012] Preferably, the mass ratio of the tetraethyl silicate to the carboxyl carbon nanotubes is 3-5:0.4-0.6.

[0013] Preferably, the adjustment to alkalinity is to adjust the pH value to 11.5-12 using aqueous ammonia.

[0014] Preferably, the tetraethyl silicate is added in 4 to 5 times, and the time for each addition is 1 to 2 minutes.

[0015] Preferably, the reaction temperature is 45-55° C. and the reaction time is 12-16 hours.

[0016] Preferably, the mass ratio of the carboxyl carbon nanotube and silicon dioxide composite nanoparticles to the deep eutectic solvent is 0.25-1.25:10000.

[0017] Preferably, the mass ratio of the surfactant to the deep eutectic solvent is 1 to 2:1000.

[0018] Optionally, the surfactant is sodium lauryl sulfate.

[0019] Preferably, the hydrogen bond acceptor of the deep eutectic solvent is choline chloride, and the hydrogen bond donor is urea and / or ethanolamine.

[0020] The second technical solution of the present invention is to provide a green nanofluid absorbent for photothermal carbon capture prepared according to the above-mentioned preparation method of the green nanofluid absorbent for photothermal carbon capture.

[0021] The third technical solution of the present invention is to provide an application of the green nanofluid absorbent for photothermal carbon capture in photothermal carbon capture.

[0022] The beneficial technical effects of the present invention are as follows:

[0023] The present invention forms silica spheres with regular morphology on the surface of carboxyl carbon nanotubes and further disperses them in a deep eutectic solvent to obtain a green nanofluid absorbent for photothermal carbon capture. The preparation steps are simple and the reagents used are green and pollution-free.

[0024] The green nanofluid absorbent for photothermal carbon capture provided by the present invention has high photothermal conversion efficiency, high carbon capture capacity and high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart for the preparation of CNTs@SiO2 / DES nanofluid in Example 1 of the present invention.

[0026] Figure 2 This is the SEM image of CNTs@SiO2 nanoparticles prepared in Example 1.

[0027] Figure 3 These are SEM images of the CNTs@SiO2 nanoparticles prepared in Comparative Example 1 and Comparative Example 2, wherein (a) is the SEM image of the CNTs@SiO2 nanoparticles prepared in Comparative Example 1, and (b) is the SEM image of the CNTs@SiO2 nanoparticles prepared in Comparative Example 2.

[0028] Figure 4 These are macroscopic images of CNTs@SiO2 / DES nanofluids of different concentrations prepared according to the method of Example 1 after being placed for 15 days, where (a) is a macroscopic image of CNTs@SiO2 / DES nanofluid with a concentration of 0 to 100 ppm, and (b) is a macroscopic image of CNTs@SiO2 / DES nanofluid with a concentration of 100 to 500 ppm.

[0029] Figure 5 Graph showing the transmittance of CNTs@SiO2 / DES nanofluids with different concentrations prepared according to the method of Example 1.

[0030] Figure 6 2 is the carbon dioxide absorption graph of 0 ppm and 150 ppm CNTs@SiO2 / DES nanofluid prepared according to the method of Example 1.

[0031] Figure 7 This is a carbon dioxide analysis diagram of 0 ppm and 150 ppm CNTs@SiO2 / DES nanofluids prepared according to the method of Example 1 after absorbing carbon dioxide under light conditions. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present invention are now described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0033] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range, and any other stated value or intervening value in the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] Unless otherwise specified, the "room temperature" mentioned in the present invention refers to a temperature of 20±5°C.

[0037] Unless otherwise specified, the raw materials used in the present invention are all commercially available products well known to those skilled in the art.

[0038] The carboxyl carbon nanotubes used in the examples and comparative examples of the present invention have a diameter of 8 to 15 nm and a length of no more than 30 μm.

[0039] The concentration of ammonia water used in the examples and comparative examples of the present invention is 26-28 wt.%.

[0040] The deep eutectic solvent used in the examples and comparative examples of the present invention is obtained by mixing choline chloride and urea in a molar ratio of 1:2 and stirring the mixture in a water bath at 85° C. until the mixture becomes clear.

[0041] Example 1

[0042] (1) At room temperature, 50 mL of a mixture of isopropanol and deionized water (containing 0.462 mol of isopropanol and 0.82 mol of deionized water) was added to a 50 mL beaker. 0.5 g of carboxyl carbon nanotubes was then added. After magnetic stirring at room temperature for 10 min, 3.5 g of ammonia water was added dropwise to the solution to adjust the pH to 11.67. The solution was then ultrasonicated for 30 min to achieve uniform dispersion.

[0043] (2) In a 50°C water bath, with a magnetic stirring speed of 1400 r / min, 4 g of tetraethyl silicate was injected into the stirring dispersion using a 2.5 mL syringe needle. Each injection lasted 1 minute, and the reaction was continued for 14 hours. Deionized water was added to bring the pH value to 7.5, and the mixture was centrifuged for the first time. After centrifugation, deionized water was added and centrifuged again, and this process was repeated three times. The mixture was then centrifuged twice with anhydrous ethanol, dried at 75°C for 24 hours, and ground to obtain CNTs@SiO2 nanoparticles.

[0044] (3) 5 mg of CNTs@SiO2 nanoparticles and 50 mg of sodium dodecyl sulfate were added to 50 g of deep eutectic solvent and ultrasonicated in an ultrasonic cell disruptor with a power of 325 W for 90 min to obtain CNTs@SiO2 / DES nanofluid.

[0045] Example 1 Preparation of CNTs@SiO2 / DES nanofluid flow chart Figure 1 .

[0046] The SEM images of CNTs@SiO2 nanoparticles prepared in Example 1 are shown in Figure 2 ,Depend on Figure 2 It can be seen that the prepared silica nanoparticles are mostly regular spherical particles without any breakage or large-scale agglomeration.

[0047] Example 2

[0048] The amount of ammonia water added was changed based on Example 1.

[0049] (1) At room temperature, 50 mL of a mixture of isopropanol and deionized water (containing 0.462 mol of isopropanol and 0.82 mol of deionized water) was added to a 50 mL beaker. 0.5 g of carboxyl carbon nanotubes was then added. After magnetic stirring at room temperature for 10 min, 3.0 g of ammonia water was added dropwise to the solution to adjust the pH to 11.5. The solution was then ultrasonicated for 30 min to achieve uniform dispersion.

[0050] (2) In a 50°C water bath, with a magnetic stirring speed of 1400 r / min, 4 g of tetraethyl silicate was injected into the stirring dispersion using a 2.5 mL syringe needle. Each injection lasted 1 minute, and the reaction was continued for 14 hours. Deionized water was added to bring the pH value to 7.5, and the mixture was centrifuged for the first time. After centrifugation, deionized water was added and centrifuged again, and this process was repeated three times. The mixture was then centrifuged twice with anhydrous ethanol, dried at 75°C for 24 hours, and ground to obtain CNTs@SiO2 nanoparticles.

[0051] (3) 5 mg of CNTs@SiO2 nanoparticles and 50 mg of sodium dodecyl sulfate were added to 50 g of deep eutectic solvent and ultrasonicated in an ultrasonic cell disruptor with a power of 325 W for 90 min to obtain CNTs@SiO2 / DES nanofluid.

[0052] Example 3

[0053] In Example 1, the amount of silicon source added was changed.

[0054] (1) At room temperature, 50 mL of a mixture of isopropanol and deionized water (containing 0.462 mol of isopropanol and 0.82 mol of deionized water) was added to a 50 mL beaker. 0.5 g of carboxyl carbon nanotubes was then added. After magnetic stirring at room temperature for 10 min, 3.5 g of ammonia water was added dropwise to the solution to adjust the pH to 11.67. The solution was then ultrasonicated for 30 min to achieve uniform dispersion.

[0055] (2) In a 50°C water bath, with a magnetic stirring speed of 1400 r / min, 3 g of tetraethyl silicate was injected into the stirring dispersion using a 2.5 mL syringe needle. Each injection lasted 1 min, and the reaction was continued for 14 h. Deionized water was added to bring the pH value to 7.5, and the mixture was centrifuged for the first time. After centrifugation, deionized water was added and centrifuged again, and this process was repeated three times. The mixture was then centrifuged twice with anhydrous ethanol, dried at 75°C for 24 h, and ground to obtain CNTs@SiO2 nanoparticles.

[0056] (3) 5 mg of CNTs@SiO2 nanoparticles and 50 mg of sodium dodecyl sulfate were added to 50 g of deep eutectic solvent and ultrasonicated in an ultrasonic cell disruptor with a power of 325 W for 90 min to obtain CNTs@SiO2 / DES nanofluid.

[0057] Comparative Example 1

[0058] Compared with Example 1, the only difference is that the amount of ammonia water in step (1) is adjusted to 2 g, and the final pH value is 11.2.

[0059] Comparative Example 2

[0060] Compared with Example 1, the only difference is that the stirring speed in step (2) is adjusted to 800 r / min.

[0061] The SEM images of CNTs@SiO2 nanoparticles prepared in Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 3 , wherein (a) is the SEM image of the CNTs@SiO2 nanoparticles prepared in Comparative Example 1, and (b) is the SEM image of the CNTs@SiO2 nanoparticles prepared in Comparative Example 2.

[0062] Depend on Figure 3 It can be seen that although the silica nanoparticles attached to the carbon nanotubes are still nearly spherical in shape, small-scale agglomeration has occurred.

[0063] According to the method of Example 1, CNTs@SiO2 / DES nanofluids with different concentrations were prepared. After 15 days, the macroscopic images of the CNTs@SiO2 / DES nanofluids were shown in Figure 1. Figure 4 , among which, (a) is a macroscopic image of CNTs@SiO2 / DES nanofluid with a concentration of 0-100 ppm (from left to right, 0 ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm and 100 ppm), and (b) is a macroscopic image of CNTs@SiO2 / DES nanofluid with a concentration of 100-500 ppm (from left to right, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 400 ppm and 500 ppm).

[0064] from Figure 4 It can be seen that the CNTs@SiO2 / DES nanofluids of various concentrations prepared in the present invention do not precipitate after long-term storage and have high stability.

[0065] The transmittance of the prepared CNTs@SiO2 / DES nanofluids with a concentration of 100 to 500 ppm was further measured. Figure 5 .

[0066] Depend on Figure 5 It can be seen that the transmittance of the prepared CNTs@SiO2 / DES nanofluid gradually decreases with the increase of the nanoparticle concentration therein, and when it reaches above 400 ppm, the transmittance is basically 0.

[0067] The carbon dioxide absorption performance and desorption performance of the prepared CNTs@SiO2 / DES nanofluid under light conditions were further preliminarily tested (the selected concentrations were 0 ppm and 150 ppm).

[0068] Methods: CNTs@SiO2 / DES nanofluid was added to the reactor, and a mixture of carbon dioxide and nitrogen was introduced. The inlet carbon dioxide concentration was 20%. The reaction time was about 3 h. The outlet carbon dioxide concentration was recorded using an infrared flue gas analyzer (MRU, Germany), and the total carbon dioxide absorption was calculated.

[0069] After absorption, the CNTs@SiO2 / DES nanofluid saturated absorber was analyzed under simulated light conditions. Using a xenon lamp (Zhongjiao Jinyuan, China) as the light source, the light power density was measured at 1000Mw / cm 2 The carbon dioxide desorption rate and desorption amount under the conditions of 100 nm CMOS were obtained.

[0070] Figure 6 Carbon dioxide absorption diagram of 0 ppm and 150 ppm CNTs@SiO2 / DES nanofluid.

[0071] Figure 7 Carbon dioxide decomposition diagram of 0ppm and 150ppm CNTs@SiO2 / DES nanofluid after absorbing carbon dioxide under light conditions.

[0072] Figure 6 and Figure 7 The results show that CNTs@SiO2 nanoparticles have a positive impact on both the absorption and photolysis processes. For the absorption process, adding 150ppm of CNTs@SiO2 nanoparticles to the CNTs@SiO2 / DES nanofluid not only increased the absorption rate but also significantly enhanced the total amount absorbed over the same time period. For the photolysis process, the 150ppm CNTs@SiO2 / DES nanofluid released carbon dioxide more quickly under photolysis due to its faster heating rate.

[0073] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a green nanofluid absorbent for photothermal carbon capture, characterized in that: The following steps are involved: The carboxyl carbon nanotubes are dispersed in a dispersant and adjusted to alkalinity. Then, tetraethyl silicate is added under high-speed stirring at 1000-2000 r / min. After the reaction, the pH value of the system is adjusted to 7-7.5, centrifuged, and the precipitate is washed to obtain a black gel-like substance. The black gel-like substance is dried and ground to obtain nanoparticles composited with carboxyl carbon nanotubes and silicon dioxide. The nanoparticles composited with carboxyl carbon nanotubes and silicon dioxide and a surfactant are co-dispersed in a deep eutectic solvent to obtain the green nanofluid absorbent for photothermal carbon capture.

2. The method for preparing a green nanofluid absorbent for photothermal carbon capture according to claim 1, characterized in that: The carboxyl carbon nanotubes have a diameter of 8 to 15 nm and a length of no more than 30 μm; and / or the dispersant is obtained by mixing isopropyl alcohol and water.

3. The method for preparing a green nanofluid absorbent for photothermal carbon capture according to claim 1, characterized in that: The amount ratio of the carboxyl carbon nanotubes to the dispersant is 0.4-0.6 g:50 mL; and / or the mass ratio of the tetraethyl silicate to the carboxyl carbon nanotubes is 3-5:0.4-0.

6.

4. The method for preparing a green nanofluid absorbent for photothermal carbon capture according to claim 1, characterized in that: The adjustment to alkalinity is to use ammonia water to adjust the pH value to 11.5-12.

5. The method for preparing a green nanofluid absorbent for photothermal carbon capture according to claim 1, characterized in that: The tetraethyl silicate is added in 4 to 5 times, and the time for each addition is 1 to 2 minutes.

6. The method for preparing a green nanofluid absorbent for photothermal carbon capture according to claim 1, characterized in that: The reaction temperature is 45-55° C. and the reaction time is 12-16 hours.

7. The method for preparing a green nanofluid absorbent for photothermal carbon capture according to claim 1, characterized in that: The mass ratio of the carboxyl carbon nanotube and silicon dioxide composite nanoparticles to the deep eutectic solvent is 0.25-1.25:10000; and / or the mass ratio of the surfactant to the deep eutectic solvent is 1-2:1000.

8. The method for preparing a green nanofluid absorbent for photothermal carbon capture according to claim 1, characterized in that: The hydrogen bond acceptor of the deep eutectic solvent is choline chloride, and the hydrogen bond donor is urea and / or ethanolamine.

9. A green nanofluid absorbent for photothermal carbon capture prepared according to the preparation method of a green nanofluid absorbent for photothermal carbon capture according to any one of claims 1 to 8.

10. Use of the green nanofluid absorbent for photothermal carbon capture according to claim 9 in photothermal carbon capture.

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