A multi-stage carbon dot assembly photothermal conversion material, a preparation method therefor, and an application thereof

Abstract

The application discloses a kind of multistage carbon dot assembly photo-thermal conversion materials and preparation method and application, and belongs to functional composite material technical field, wherein, the preparation method includes the following steps: citric acid is mixed with organic amine, and added to solvent to carry out ultrasonic dispersion, then high-temperature reaction is carried out, and carbon dot is obtained;Carbon dot is assembled into primary assembly, and super carbon dot is obtained;Super carbon dot solution is mixed with inorganic metal salt solution uniformly, and precipitate is obtained by centrifugation;The precipitate is washed and centrifuged, and freeze-drying treatment is carried out, and multistage carbon dot assembly photo-thermal conversion material is obtained.The multistage carbon dot assembly photo-thermal conversion material covers ultraviolet-visible-near infrared band to the absorption of sunlight, can be quickly heated in very short light time, shows very high evaporation rate and efficiency in simulated water evaporation experiment, and has wide application prospect in seawater desalination, sewage treatment, thermoelectricity and other fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional composite materials, and in particular to a multi-level carbon dot assembly photothermal conversion material and a preparation method and application thereof. BACKGROUND

[0002] Carbon-based materials can absorb the entire solar spectrum and release heat. Carbon-based materials, including carbon black, carbon nanotubes (CNTs), graphene, graphene oxide (GO), reduced graphene oxide (rGO), porous carbon, and other photothermal materials, are well known for their wide light absorption, high stability, light weight, and low cost. Nano-carbon materials have many advantages, such as no toxic metals, stable performance, easy to make into various structures, and different scale porous structures suitable for solar thermal applications.

[0003] Carbon dots, as a new type of carbon-based nanomaterial, are carbon nanoparticles with a size of less than 10 nm, usually composed of amorphous and crystalline carbon cores, and containing different oxygen-containing functional groups on the surface of the carbon core, such as hydroxyl and carboxyl groups. Carbon dots are mainly composed of elements such as carbon, hydrogen, oxygen, and nitrogen, with a relatively high content of carbon. Carbon dots have many excellent characteristics, such as low cost, simple synthesis, good water solubility, excellent biocompatibility, non-toxic or low toxicity, and significant electron donor and acceptor ability. The combination of these properties makes it possible for carbon dots to be widely used. The rich groups on the surface of carbon dots provide the possibility for chemical modification and further assembly, which promotes the synthesis of multifunctional carbon-based composite materials and provides new ideas and methods for the property regulation of carbon dots.

[0004] At present, carbon dot-based photothermal conversion materials have shown good application prospects in the fields of energy and optoelectronics. The existing carbon dots mainly absorb in the ultraviolet-visible region, and it is difficult to achieve absorption in the near-infrared region, which limits the utilization of solar energy by carbon dot materials. Therefore, it is very important to develop carbon dots that can absorb the entire solar spectrum for the development of carbon dots in the fields of photothermal conversion and solar energy utilization. SUMMARY

[0005] The present application aims to provide a preparation method of a multi-level carbon dot assembly photothermal conversion material to solve the problems raised in the background.

[0006] To achieve the above-mentioned purpose, the embodiments of the present application provide the following technical solutions:

[0007] A preparation method of a multi-level carbon dot assembly photothermal conversion material, first, carbon dot monomers are assembled through hydrogen bonding and electrostatic interaction in the first step to form super carbon dots with long-wavelength absorption; then the super carbon dots are further assembled with metal cations through coordination to form a multi-level carbon dot assembly that absorbs the entire ultraviolet-visible-near-infrared region, which specifically includes the following steps:

[0008] The citric acid is mixed with the organic amine, and is added to a solvent for ultrasonic dispersion, and then is subjected to high-temperature reaction to obtain carbon dots;

[0009] The carbon dots are assembled into primary assemblies to obtain super carbon dots;

[0010] The super carbon dots are dispersed in a solvent to obtain a super carbon dot solution;

[0011] The super carbon dot solution is mixed with an inorganic metal salt solution uniformly, and is centrifuged to obtain a precipitate;

[0012] The precipitate is subjected to washing and centrifugation, and is subjected to freeze-drying treatment to obtain the multi-level carbon dot assembly photothermal conversion material.

[0013] Preferably, the organic amine is one or more of urea, ammonia and biuret.

[0014] Preferably, the mass ratio of the citric acid to the organic amine is 1:(1-4).

[0015] Preferably, the temperature of the high-temperature reaction is 160-180 DEG C; and the method for assembling the carbon dots into primary assemblies is that the carbon dots are freeze-dried and then are assembled in a humid oxygen-rich environment, or the carbon dots are heated at a temperature of 40-60 DEG C for assembly.

[0016] Preferably, the solvent is deionized water.

[0017] Preferably, the cation in the inorganic metal salt solution is selected from metal cations capable of coordinating with carboxyl groups, and specifically includes but is not limited to one or more of iron ions, silver ions and calcium ions.

[0018] Preferably, the concentration of the inorganic metal salt solution is 0.2-2 mol / L; and the concentration of the super carbon dot solution is 10-25 mg / mL.

[0019] Preferably, the volume ratio of the super carbon dot solution to the inorganic metal salt solution is (3-7):1.

[0020] Another purpose of the embodiment of the present application is to provide a multi-level carbon dot assembly photothermal conversion material prepared by the above preparation method.

[0021] Another purpose of the embodiment of the present application is to provide an application of the above multi-level carbon dot assembly photothermal conversion material as a visible-near infrared photothermal conversion reagent in energy conversion.

[0022] The preparation method of the multistage carbon dot assembly photothermal conversion material provided by the embodiment of the present application adopts the interaction of the primary assembly super carbon dots and metal ions, can be assembled at room temperature, does not need harsh reaction conditions or additional reactants, and therefore has the advantages of simple preparation process, low cost and easy operation; the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application has the characteristics of wide spectrum absorption, and its absorption covers the ultraviolet-visible-near infrared band, can be quickly heated in a very short light irradiation time, shows very high evaporation rate and efficiency in the simulation water evaporation experiment, and has a wide application prospect in the fields of seawater desalination, sewage treatment, thermoelectricity and the like; in addition, due to the coordination of the metal cations and the functional groups on the surface of the carbon dots, i.e. the multistage assembly, the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application has higher structural and chemical stability than the super carbon dots formed through hydrogen bonds and electrostatic interaction, and is not easy to fall off and leak when attached to a substrate, and is more suitable for use in the water evaporation process than the primary assembly. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A scanning electron microscope image of the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application;

[0024] Figure 2 An X-ray photoelectron spectroscopy image of the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application;

[0025] Figure 3 An absorption spectrum image of the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application;

[0026] Figure 4 A Fourier transform infrared spectroscopy image of the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application;

[0027] Figure 5 A photothermal conversion performance test result image of the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application under simulated sunlight irradiation;

[0028] Figure 6 A thermoelectric performance test result image of the multistage carbon dot assembly photothermal conversion material prepared by the embodiment of the present application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] In one embodiment of the present application, a multi-level carbon dot assembly photothermal conversion material is provided, which is assembled by carbon dot assembly units into super carbon dots with long wavelength absorption, and further induced by metal cation coordination with the functional groups such as carboxylate on the surface of the super carbon dots to form a multi-level assembly; wherein the preparation method of the super carbon dots is a prior art, which is described in detail in Chinese patent (application number: CN201410425613) and literature (Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts, Dan Qu, Min Zheng, Peng Du, Yue Zhou, Ligong Zhang, Di Li, Huaqiao Tan, Zhao Zhao, Zhigang Xie, Zaicheng Sun, Nanoscale, 2013, 5, 12272).

[0031] Specifically, the preparation method of the multi-level carbon dot assembly photothermal conversion material includes the following steps:

[0032] S1, mixing citric acid and organic amine, adding to a solvent for ultrasonic dispersion, and then high temperature reaction to obtain carbon dots;

[0033] S2, assembling the carbon dots into a primary assembly to obtain super carbon dots;

[0034] S3, dispersing the super carbon dots in a solvent to obtain a super carbon dot solution;

[0035] S4, uniformly mixing the super carbon dot solution and an inorganic metal salt solution, and centrifuging to obtain a precipitate;

[0036] S5, washing and centrifuging the precipitate, and freeze-drying to obtain the multi-level carbon dot assembly photothermal conversion material.

[0037] In one preferred embodiment of the present application, the organic amine is one or more of urea, ammonia and biuret, but is not limited thereto.

[0038] In one preferred embodiment of the present application, the mass ratio of citric acid to organic amine is 1:(1-4).

[0039] In one preferred embodiment of the present application, the temperature of the high temperature reaction is 160-180℃, and the time is 4-6h; the method of assembling the carbon dots into a primary assembly is to freeze-dry the carbon dots and then place them in a humid oxygen-rich environment for oxidation, or to heat the carbon dots at a temperature of 40-60℃.

[0040] In a preferred embodiment of the present application, the solvent is deionized water, but is not limited thereto.

[0041] In a preferred embodiment of the present application, the metal cation in the inorganic metal salt solution is one or more of iron ions, silver ions and calcium ions, but is not limited thereto; the metal cation can induce the super-carbon dots to further assemble through coordination with the functional groups such as carboxylate groups on the surface of the super-carbon dots; preferably, the inorganic metal salt is one or more of ferric chloride, silver nitrate and calcium chloride.

[0042] In a preferred embodiment of the present application, the concentration of the inorganic metal salt solution is 0.2-2 mol / L, which can be prepared by ultrasonic dispersion of the inorganic metal salt in deionized water; in addition, the concentration of the super-carbon dot solution is 10-25 mg / mL.

[0043] In a preferred embodiment of the present application, the volume ratio of the super-carbon dot solution to the inorganic metal salt solution is (3-7):1.

[0044] The multi-level carbon dot assembly photothermal conversion material prepared in the embodiment of the present application is a micron structure assembled by nanoparticles, which has effective wide absorption and good photothermal conversion performance in the visible-near infrared region.

[0045] In another embodiment of the present application, an application of the above multi-level carbon dot assembly photothermal conversion material as a visible-near infrared photothermal conversion reagent in energy conversion is also provided, including but not limited to applications in the fields of photothermal water evaporation and thermoelectric devices. In addition, the above multi-level carbon dot assembly photothermal conversion material can also be applied in other fields related to photothermal conversion, such as photothermal therapy, photoacoustic imaging, but is not limited thereto.

[0046] In another embodiment of the present application, a thermoelectric device is also provided, and the preparation method thereof comprises the following steps: uniformly attaching the above multi-level carbon dot assembly photothermal conversion material to a hydrophilic substrate to form an optical absorption layer; and then attaching the optical absorption layer to a thermoelectric sheet as a hot end by using a thermally conductive adhesive to form a thermoelectric device. The multi-level carbon dot assembly photothermal conversion material can be uniformly attached to the hydrophilic substrate by using a drop coating method or a blade coating method; the hydrophilic substrate can be a non-woven fabric substrate, but is not limited thereto.

[0047] The following embodiments are some specific implementation cases of the present application in practical application, but are not limited thereto.

[0048] Embodiment 1: The embodiment provides a preparation method of a multi-level carbon dot assembly photothermal conversion material, which comprises the following steps:

[0049] (1) 1 g citric acid was mixed with 2 g urea and added to 10 mL deionized water for ultrasonic dispersion, and then transferred to a 25 mL polytetrafluoroethylene reactor for high-temperature reaction at 160°C for 4 h to obtain yellow carbon dots;

[0050] (2) The yellow carbon dot stock solution was heated in a 50°C oven until the solution color changed from yellow to black, and then the remaining water was dried to assemble a primary assembly black carbon dot to obtain super carbon dots;

[0051] (3) 25 mg of the above super carbon dot powder was ultrasonically dispersed in an appropriate amount of deionized water to prepare a super carbon dot solution with a concentration of 25 mg / mL;

[0052] (4) 32.4 mg of iron chloride powder was ultrasonically dispersed in an appropriate amount of deionized water to prepare a 0.2 mol / L iron chloride solution;

[0053] (5) The above super carbon dot solution and inorganic metal salt solution were mixed uniformly at a volume ratio of 5:1, and the precipitate was obtained by centrifugation;

[0054] (6) The above precipitate was washed and centrifuged several times, and then freeze-dried to obtain a black multi-level carbon dot assembly photothermal conversion material.

[0055] The multi-level carbon dot assembly photothermal conversion material prepared in Example 1 was tested for various properties; wherein the scanning electron micrograph of the multi-level carbon dot assembly photothermal conversion material prepared in Example 1 is shown in FIG. Figure 1 The material as a whole showed a loose and porous structure under the scanning electron microscope, and the spherical particles showed obvious aggregation, with a size of several tens of nanometers.

[0056] The X-ray photoelectron spectrum of the multi-level carbon dot assembly photothermal conversion material prepared in Example 1 is shown in FIG. Figure 2 , wherein 715 eV corresponds to the binding energy of iron, indicating that iron ions participate in the reaction with carbon dots.

[0057] The absorption spectrum of the multi-level carbon dot assembly photothermal conversion material prepared in Example 1 (denoted as CDs@Fe 3+ ) is shown in FIG. Figure 3 It can be seen that the material maintains strong absorption within 300-1500 nm, covering the ultraviolet-visible-near infrared band.

[0058] The Fourier transform infrared spectrum of the multi-level carbon dot assembly photothermal conversion material prepared in Example 1 (denoted as CDs@Fe 3+ ) is shown in FIG. Figure 4 ; and Figure 4 CDs@Fe 3+Refers to the multi-level carbon dot assembly light-thermal conversion material, CDs refers to the super carbon dots which have not reacted with metal cations; It can be seen that the absorption peak in the range of 3500-3000 cm -1 obviously changes, combined with the information in Figure 2 , it shows that the interaction between iron ions and carbon dots has occurred, and the chemical environment of the related groups on the surface of carbon dots has changed.

[0059] The light-thermal conversion performance test results of the multi-level carbon dot assembly light-thermal conversion material prepared in the above embodiment 1 are shown in Figure 5 ; wherein, Figure 5 a gives the temperature rise diagram of the material under the irradiation of simulated sunlight 1kWm -2 ; and

[0060] Figure 5 In a of the above, P-CDs@Fe 3+ refers to the multi-level carbon dot assembly light-thermal conversion material, and P-CDs refers to the super carbon dots which have not reacted with metal cations; It can be seen from the figure that the material can quickly rise in temperature in a very short time, and finally stably maintain at a high temperature of about 60℃, showing strong light-thermal performance.

[0061] Embodiment 2: The embodiment provides a preparation method of a multi-level carbon dot assembly light-thermal conversion material, which comprises the following steps:

[0062] (1) Mix 1g of citric acid with 2.2mL of ammonia water, and add to 10mL of deionized water for ultrasonic dispersion, then transfer to a 25mL polytetrafluoroethylene reaction kettle, and react at 160℃ for 4h to obtain yellow carbon dots;

[0063] (2) Heat the above yellow carbon dot stock solution in a 50℃ oven until the solution color changes from yellow to black, then dry the remaining water to assemble the first assembly black carbon dots to obtain super carbon dots;

[0064] (3) Take 25mg of the above super carbon dot powder and ultrasonically disperse it in an appropriate amount of deionized water to prepare a super carbon dot solution with a concentration of 25mg / mL;

[0065] (4) Take 32.4mg of iron chloride powder and ultrasonically disperse it in an appropriate amount of deionized water to prepare a 0.2mol / L iron chloride solution;

[0066] (5) Mix the above super carbon dot solution and inorganic metal salt solution uniformly according to a volume ratio of 5:1, and centrifuge to obtain a precipitate;

[0067] (6) Wash and centrifuge the above precipitate for multiple times, then freeze-dry to obtain a multi-level carbon dot assembly light-thermal conversion material.

[0068] Embodiment 3: The embodiment provides a preparation method of a multi-level carbon dot assembly photothermal conversion material, which comprises the following steps:

[0069] (1) 1 g of citric acid is mixed with 2 g of urea and added to 10 mL of deionized water for ultrasonic dispersion, and then transferred to a 25 mL polytetrafluoroethylene reaction kettle for high-temperature reaction at 160 DEG C for 4 h to obtain yellow carbon dots;

[0070] (2) The above yellow carbon dot stock solution is heated in a 50 DEG C oven until the solution color changes from yellow to black, and then the remaining water is dried to assemble a one-level assembly black carbon dot to obtain super carbon dots;

[0071] (3) 25 mg of the above super carbon dot powder is ultrasonically dispersed in an appropriate amount of deionized water to prepare a super carbon dot solution with a concentration of 10-25 mg / mL;

[0072] (4) 34 mg of silver nitrate powder is ultrasonically dispersed in an appropriate amount of deionized water to prepare a 0.2 mol / L silver nitrate solution;

[0073] (5) The above super carbon dot solution and inorganic metal salt solution are mixed uniformly according to a volume ratio of 5:1, and the precipitate is obtained by centrifugation;

[0074] (6) The above precipitate is washed and centrifuged for multiple times, and then freeze-dried to obtain a multi-level carbon dot assembly photothermal conversion material.

[0075] Embodiment 4: The embodiment provides a preparation method of a multi-level carbon dot assembly photothermal conversion material, which comprises the following steps:

[0076] (1) 1 g of citric acid is mixed with 2 g of urea and added to 10 mL of deionized water for ultrasonic dispersion, and then transferred to a 25 mL polytetrafluoroethylene reaction kettle for high-temperature reaction at 160 DEG C for 4 h to obtain yellow carbon dots;

[0077] (2) The above yellow carbon dot stock solution is heated in a 50 DEG C oven until the solution color changes from yellow to black, and then the remaining water is dried to assemble a one-level assembly black carbon dot to obtain super carbon dots;

[0078] (3) 25 mg of the above super carbon dot powder is ultrasonically dispersed in an appropriate amount of deionized water to prepare a super carbon dot solution with a concentration of 10-25 mg / mL;

[0079] (4) 22.2 mg of calcium chloride powder is ultrasonically dispersed in an appropriate amount of deionized water to prepare a 0.2 mol / L calcium chloride solution;

[0080] (5) Take the above super carbon point solution and inorganic metal salt solution and mix them uniformly according to a volume ratio of 5:1, and centrifuge to obtain a precipitate;

[0081] (6) The precipitate is washed and centrifuged for multiple times, and then freeze-dried to obtain a multi-level carbon point assembly photothermal conversion material.

[0082] Example 5: The embodiment provides a preparation method of a multi-level carbon point assembly photothermal conversion material, which comprises the following steps:

[0083] (1) 1g of citric acid and 1g of biuret are mixed and added to 10mL of deionized water for ultrasonic dispersion, and then transferred to a 25mL polytetrafluoroethylene reaction kettle for high-temperature reaction at 180°C for 6h to obtain carbon dots;

[0084] (2) The carbon dot stock solution is heated in a 40°C oven until the solution changes color, and then the remaining water is dried to assemble a primary assembly to obtain super carbon points;

[0085] (3) 10mg of the above super carbon point powder is ultrasonically dispersed in an appropriate amount of deionized water to prepare a super carbon point solution with a concentration of 10mg / mL;

[0086] (4) Iron chloride powder is ultrasonically dispersed in an appropriate amount of deionized water to prepare a 2mol / L iron chloride solution;

[0087] (5) The above super carbon point solution and inorganic metal salt solution are mixed uniformly according to a volume ratio of 3:1, and centrifuged to obtain a precipitate;

[0088] (6) The precipitate is washed and centrifuged for multiple times, and then freeze-dried to obtain a multi-level carbon point assembly photothermal conversion material.

[0089] Example 6: The embodiment provides a preparation method of a multi-level carbon point assembly photothermal conversion material, which comprises the following steps:

[0090] (1) 1g of citric acid, 2g of urea and 2mL of ammonia water are mixed and added to 10mL of deionized water for ultrasonic dispersion, and then transferred to a 25mL polytetrafluoroethylene reaction kettle for high-temperature reaction at 170°C for 5h to obtain yellow carbon dots;

[0091] (2) The yellow carbon dot stock solution is heated in a 60°C oven until the solution color changes from yellow to black, and then the remaining water is dried to assemble a primary assembly black carbon dot to obtain super carbon points;

[0092] (3) Take 20 mg of the above super-carbon dot powder and ultrasonically disperse it in a proper amount of deionized water to prepare a super-carbon dot solution with a concentration of 20 mg / mL;

[0093] (4) Take the iron chloride powder and ultrasonically disperse it in a proper amount of deionized water to prepare an iron chloride solution with a concentration of 1 mol / L;

[0094] (5) Mix the above super-carbon dot solution and the inorganic metal salt solution uniformly according to a volume ratio of 4:1, and centrifuge to obtain a precipitate;

[0095] (6) Wash and centrifuge the above precipitate for multiple times, and then perform freeze-drying treatment to obtain the multi-level carbon dot assembly photothermal conversion material.

[0096] Embodiment 7: The embodiment provides a preparation method of a multi-level carbon dot assembly photothermal conversion material, which comprises the following steps:

[0097] (1) Mix 1 g of citric acid and 2.5 g of urea, and add them to 10 mL of deionized water for ultrasonic dispersion, and then transfer them to a 25 mL polytetrafluoroethylene reaction kettle for high-temperature reaction at 170℃ for 5 h to obtain yellow carbon dots;

[0098] (2) Freeze-dry the above yellow carbon dot stock solution, place it in a humid oxygen-rich environment for oxidation until the color changes from yellow to black, and then dry the remaining moisture to assemble into a one-level assembly black carbon dot to obtain super-carbon dots;

[0099] (3) Take 20 mg of the above super-carbon dot powder and ultrasonically disperse it in a proper amount of deionized water to prepare a super-carbon dot solution with a concentration of 20 mg / mL;

[0100] (4) Take the iron chloride powder and ultrasonically disperse it in a proper amount of deionized water to prepare an iron chloride solution with a concentration of 1 mol / L;

[0101] (5) Mix the above super-carbon dot solution and the inorganic metal salt solution uniformly according to a volume ratio of 4:1, and centrifuge to obtain a precipitate;

[0102] (6) Wash and centrifuge the above precipitate for multiple times, and then perform freeze-drying treatment to obtain the multi-level carbon dot assembly photothermal conversion material.

[0103] Application Example 1: The multi-level carbon dot assembly photothermal conversion material prepared in the above embodiment 1 is attached to a non-woven fabric by a drop coating method and dried, and the light-heat performance of the material is further verified by a water evaporation experiment; wherein, the scanning electron microscope image of the blank non-woven fabric is shown in FIG. b, and the scanning electron microscope image of the non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material is shown in FIG. Figure 1 Figure 1 ​It can be seen from the figure that the surface of the non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material becomes rougher compared with the blank non-woven fabric.

[0104] In addition, the non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material can be heated to 70°C under the irradiation of the simulated sunlight 1 kW / m2. -2 The temperature rising of the material under the irradiation is shown in FIG. 2b. Figure 5 Figure 5 In FIG. 2b, F-CDs@Fe 3+ It is indicated that the non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material, and the pristine fabric indicates the blank non-woven fabric. It can be seen from the figure that the non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material can be quickly heated in a very short time, and finally stably maintained at a high temperature of 70°C, showing strong photothermal performance.

[0105] The actual water evaporation experiment results of the above-mentioned non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material are shown in FIG. 3c. Figure 5 Figure 5 In FIG. 3c, F-CDs@Fe 3+ It is indicated that the non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material is the actual water evaporation experiment, and the seawater indicates the direct water evaporation experiment. It can be seen from the figure that compared with the direct water evaporation, the evaporation rate of the non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material is increased by nearly 3 times, and the water evaporation efficiency is as high as 90%.

[0106] Application Example 1: The non-woven fabric attached with the multi-level carbon dot assembly photothermal conversion material obtained in Application Example 1 is used as an optical absorption layer, and the optical absorption layer is attached to a thermoelectric piece as a hot end by using a heat-conducting adhesive, to form a thermoelectric device, as shown in FIG. 4a. Figure 6 In the thermoelectric piece, one end loaded with the above-mentioned material is a hot end, and the other end in contact with circulating water is a cold end, and there is a temperature difference between the upper and lower ends under one sunlight, so as to generate a voltage. The thermoelectric performance test results of the thermoelectric device are shown in FIG. 4b. Figure 6 It can be seen from the figure that the thermoelectric device can generate a voltage of about 60 mV under one sunlight.

[0107] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents in the specification.​​

Claims

1. A method for preparing a multi-stage carbon dot assembly photothermal conversion material, characterized by comprising the following steps: 1) preparing a carbon dot assembly; 2) preparing a multi-stage carbon dot assembly photothermal conversion material by mixing the carbon dot assembly with a carbon dot assembly carrier. Firstly, carbon dot monomers are assembled by hydrogen bonds and electrostatic interactions in a first step to form super carbon dots with long wavelength absorption; Then, the super carbon dots are further assembled with metal cations by coordination to form multi-level carbon dot assemblies that absorb throughout the ultraviolet-visible-near infrared region, including the following steps: dispersing the super carbon dots in a solvent to obtain a super carbon dot solution; mixing the super carbon dot solution with an inorganic metal salt solution uniformly and centrifuging to obtain a precipitate; washing and centrifuging the precipitate and performing freeze-drying treatment to obtain the multi-level carbon dot assembly photothermal conversion material; the cations in the inorganic metal salt solution are metal cations capable of coordinating with carboxyl groups; the concentration of the inorganic metal salt solution is 0.2-2 mol / L; the concentration of the super carbon dot solution is 10-25 mg / mL; and the volume ratio of the super carbon dot solution to the inorganic metal salt solution is (3-7):

1. 2.The method of claim 1, wherein, The preparation method of the super carbon dots includes the following steps: mixing citric acid with organic amine and adding to a solvent for ultrasonic dispersion, then performing high-temperature reaction to obtain carbon dots; assembling the carbon dots into a primary assembly to obtain super carbon dots. 3.The method of claim 2, wherein, The organic amine is one or more of urea, ammonia and biuret; and the mass ratio of the citric acid to the organic amine is 1:(1-4). 4.The method of claim 2, wherein, The temperature of the high-temperature reaction is 160-180 ℃; and the method of assembling the carbon dots into a primary assembly is to freeze-dry the carbon dots and then assemble them in a humid oxygen-rich environment, or to assemble the carbon dots at a temperature of 40-60 ℃. 5.The method of claim 1 or 2, wherein, The solvent is deionized water.

6. A multi-level carbon dot assembly photothermal conversion material prepared by the preparation method of any one of claims 1-5.

7. Use of the multi-level carbon dot assembly photothermal conversion material of claim 6 as a visible-near infrared photothermal conversion reagent in energy conversion.

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