Preparation method of broad-spectrum ultraviolet absorption oil-soluble carbon dots

Abstract

The application discloses a preparation method of a broad-spectrum ultraviolet absorption oil-soluble carbon dot. The oil-soluble carbon dot is obtained through three hydrothermal reactions of water-soluble carbon dots. During the hydrothermal process, an oily ligand is grafted on the surface of the water-soluble carbon dots, so that the water-soluble carbon dots with good ultraviolet absorption performance are converted into oil-soluble carbon dots. The oil-soluble carbon dots have stable ultraviolet absorption performance and can be applied in hydrophobic materials. The preparation method is simple, raw materials are easy to obtain, and the method is environment-friendly. The oil-soluble carbon dots provide a new type of ultraviolet absorber for hydrophobic application products such as high polymer and oily paint, and have a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of ultraviolet absorber synthesis technology, specifically relating to a method for preparing broad-spectrum ultraviolet absorbing oil-soluble carbon dots. Background Technology

[0002] With the rapid development of modern industrialization and urbanization, one of the accompanying negative impacts is the destruction of the atmospheric ozone layer, resulting in increasingly stronger ultraviolet radiation reaching the Earth's surface. Ultraviolet radiation not only causes skin darkening and redness, but more seriously, it can trigger melanoma and DNA damage, potentially leading to skin cancer.

[0003] Ultraviolet (UV) absorbers are highly effective at suppressing UV radiation. In sunscreen cosmetics, there are single-function absorbers, such as UVB or UVA absorbers, as well as broad-spectrum chemical UV absorbers and shielding agents such as nano-TiO2 and ZnO. In polymers, UV absorbers are diverse, commonly including benzophenones, benzotriazoles, triazines, and salicylic acids. In coatings, adding UV absorbers can delay the decomposition and yellowing of organic matter in solvent-based coatings. However, as research into the biological effects of UV absorbers deepens, it has been found that even with strict control of the amount of low-toxicity absorbers added, benzophenones and benzotriazoles are difficult to degrade and accumulate over time, ultimately causing potentially significant harm.

[0004] Quantum dots originated in the mid-1970s. Their research and development have led to a proliferation of various quantum dot types, resulting in widespread applications and establishing a new scientific discipline. Currently reported quantum dots mainly include semiconductor quantum dots, silicon, carbon, or graphene quantum dots, and other oxide quantum dots. Among these, carbon dots, as a novel fluorescent nanomaterial, have attracted considerable attention from researchers in recent years due to their outstanding performance characteristics. They typically refer to fluorescent carbon nanoparticles with a size less than 10 nm. Compared to traditional organic dyes and semiconductor quantum dots, carbon dots exhibit outstanding characteristics: simple preparation methods, convertible fluorescence emission, non-toxicity, good photostability, and biocompatibility. Summary of the Invention

[0005] This invention addresses the aforementioned technical problems by providing a method for preparing broad-spectrum ultraviolet-absorbing oil-soluble carbon dots. The preparation of oil-soluble carbon dots involves a three-stage hydrothermal process. First, a reducing agent is used to reduce the carboxyl groups on the citrate-based carbon dots, yielding carbon dots with amino groups on their surface (water-soluble carbon dot 1). Utilizing the amino group abundance on the carbon dot surface as reaction sites, an oily ligand is added, and a second hydrothermal reaction is performed to obtain two layers of carbon dot solution (the upper layer being oil-soluble carbon dot 1, and the lower layer being water-soluble carbon dot 2).

[0006] At this stage, oil-soluble carbon dot 1 can be dispersed in a nonpolar solvent, but its UVA absorption is not significant, and the carboxyl absorption peak is weak as indicated by infrared spectroscopy. This suggests that oil-soluble carbon dot 1 only has long carbon chains, allowing it to disperse in the oil phase, while its carboxyl content is relatively low. Meanwhile, water-soluble carbon dot 2, which is generated simultaneously, exhibits strong UVA and UVB absorption. This indicates that during the secondary hydrothermal process, a large amount of oily ligands decomposed, long carbon chains were shed, and the remaining carboxyl groups reacted with the carboxyl groups on the surface of water-soluble carbon dot 1, restoring its strong UVA absorption.

[0007] Based on this phenomenon, oil-soluble carbon dots 1 and water-soluble carbon dots 2 were reacted with oleic acid in a third hydrothermal reaction. After the reaction, the oil-soluble carbon dots obtained from the reaction of oil-soluble carbon dots 1 did not absorb UVA. However, after the reaction of water-soluble carbon dots 2 with oleic acid, the surface was rich in long carbon chains, thus reducing polarity and allowing it to be dispersed in non-polar solvents. During hydrothermal reaction, oily carboxyl-containing ligands decompose into two parts: carboxyl groups and long carbon chains, which react with the carbon dots. The carboxyl groups react with the amino groups on the surface of the carbon dots, restoring UVA absorption, but this part does not contain long carbon chains, so the resulting carbon dots are still water-soluble. The long carbon chains, due to their higher carbon content, may directly carbonize on the surface of the original carbon dots during hydrothermal reaction, similar to a core-shell coating process, increasing the size of the oil-soluble carbon dots and thus making them oil-soluble. Furthermore, since water-soluble carbon dots 2 have strong UVA and UVB absorption, the oil-soluble carbon dots obtained after three hydrothermal reactions retain the properties of water-soluble carbon dots 2.

[0008] The present invention adopts the following technical solution:

[0009] This invention provides a method for preparing broad-spectrum ultraviolet-absorbing oil-soluble carbon dots, comprising the following steps:

[0010] S1: Mix water-soluble carbon dots with sodium borohydride, adjust the pH value to greater than 7 with acidic or alkaline substances, place in a hydrothermal reactor and heat, filter, dialyze, freeze dry to obtain water-soluble carbon dots 2 after heating.

[0011] S2: Disperse the water-soluble carbon dot 1 in deionized water to obtain a carbon dot solution. Add an acidic substance to adjust the pH of the carbon dot solution to 7, and then use an alkaline substance to adjust the pH to greater than 7. Then add a nonpolar solvent containing an oily ligand, mix evenly, and then add it to a hydrothermal reactor for heating. After heating is completed, let it stand. After standing and separating into layers, take the lower layer solution and filter it to obtain water-soluble carbon dot 2.

[0012] S3: Add a nonpolar solvent containing an oily ligand to the water-soluble carbon dot 2, mix well, and then add it to a hydrothermal reactor for heating. After heating, let it stand, and after the layers separate, take the upper layer solution and filter it to obtain the oil-soluble carbon dot.

[0013] Preferably, the acidic substance is at least one of hydrochloric acid, sulfuric acid, and nitric acid, and the alkaline substance is at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0014] Preferably, the oily ligand includes one of a carboxyl-containing ligand and a mercapto-containing ligand. The carboxyl-containing ligand is a saturated or unsaturated organic acid with more than eight carbon chains, specifically at least one of oleic acid, stearic acid, hexadecanoic acid, and dodecanoic acid. The mercapto-containing ligand is a thiol with more than eight carbons, specifically at least one of octathiol, decanethiol, dodecylthiol, and octadecyl sulfuric acid.

[0015] Preferably, the nonpolar solvent is at least one selected from ethanol, n-hexane, n-pentane, n-pentanol, ethyl acetate, N,N-dimethylformamide, and xylene.

[0016] Preferably, in step S1, the temperature of the hydrothermal reactor is 180–220°C and the time is 3–7 h; in step S2, the temperature of the hydrothermal reactor is 160–200°C and the time is 3–10 h; in step S3, the temperature in the hydrothermal reactor is 140–180°C and the time is 3–8 h.

[0017] Compared with the prior art, the beneficial effects of the present invention are: by carrying out three hydrothermal reactions between water-soluble carbon dots with broad-spectrum ultraviolet absorption and organic substances, oil-soluble carbon dots with broad-spectrum ultraviolet absorption are obtained. The oil-soluble carbon dots have stable ultraviolet absorption performance, the preparation method is simple, the raw materials are readily available, and it is environmentally friendly. It can be used in hydrophobic materials, which is beneficial to the subsequent application of carbon dots in polymers and coatings. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] In the attached image:

[0021] Figure 1 A reaction diagram of the preparation process of oil-soluble carbon dots;

[0022] Figure 2 The ultraviolet absorption and transmission spectra of the oil-soluble carbon dots prepared in Example 1;

[0023] Figure 3This is a transmission electron microscope (TEM) image of the oil-soluble carbon dots prepared in Example 1. Detailed Implementation

[0024] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and substance of the invention are all within the scope of protection of the present invention. Unless otherwise specified, the experimental materials, reagents, instruments, etc., used in the embodiments of the present invention are all commercially available; unless specifically specified, all technical means in the embodiments of the present invention are conventional means well known to those skilled in the art.

[0025] This invention provides a method for preparing broad-spectrum ultraviolet-absorbing oil-soluble carbon dots, comprising the following steps:

[0026] S1: Mix 0.1-2 parts of water-soluble carbon dots with 0.2-1.5 parts of sodium borohydride, adjust the pH value to greater than 7 with an acidic or alkaline substance, place it in a hydrothermal reactor, react at 180-220℃ for 3-7 hours, filter the resulting solution through a 0.22μm nylon filter membrane, dialyze, and freeze-dry to obtain water-soluble carbon dots 1;

[0027] S2: Disperse the above water-soluble carbon dot 1 in 10-20 parts of deionized water to obtain a carbon dot solution. Add an acidic substance to adjust the pH value to 7, and then use an alkaline substance to adjust the pH value to be greater than 7. Then add 5-10 parts of a non-polar solvent containing an oily carboxyl ligand, mix well, put it into a hydrothermal reactor, and react at 160-200℃ for 3-10 hours. After standing and separating into layers, take the lower layer solution and filter it with a 0.22μm aqueous nylon filter membrane to obtain water-soluble carbon dot 2.

[0028] S3: The water-soluble carbon dots 2 described above are further mixed with 5-10 parts of a nonpolar solvent containing oil and carboxyl ligands, and placed in a hydrothermal reactor. The mixture is reacted at 140-180℃ for 3-8 hours. After standing and separating into layers, the upper layer is taken and filtered through a 0.22μm organic nylon membrane to obtain oil-soluble carbon dots with broad-spectrum ultraviolet absorption. A schematic diagram of the reaction process is shown below. Figure 1 .

[0029] The acidic substance is at least one of hydrochloric acid, sulfuric acid, and nitric acid, and the alkaline substance is at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0030] The oily ligand includes one of a carboxyl-containing ligand and a mercapto-containing ligand. The carboxyl-containing ligand is a saturated or unsaturated organic acid with more than eight carbon chains, specifically at least one of oleic acid, stearic acid, hexadecanoic acid, and dodecanoic acid. The mercapto-containing ligand is a thiol with more than eight carbons, specifically at least one of octathiol, decanethiol, dodecylthiol, and octadecyl sulfuric acid.

[0031] The nonpolar solvent is at least one of ethanol, n-hexane, n-pentane, n-pentanol, ethyl acetate, N,N-dimethylformamide, and xylene.

[0032] In step S1, the temperature of the hydrothermal reactor is 180–220°C and the time is 3–7 h; in step S2, the temperature of the hydrothermal reactor is 160–200°C and the time is 3–10 h; in step S3, the temperature of the hydrothermal reactor is 140–180°C and the time is 3–8 h.

[0033] The present invention will be further explained and illustrated below through specific embodiments:

[0034] Example 1

[0035] S1: Mix 0.5g of water-soluble carbon dots with 0.5g of sodium borohydride, adjust the pH to 8 repeatedly with hydrochloric acid or sodium hydroxide, place the mixture in a hydrothermal reactor, react at 180℃ for 7h, filter the resulting solution through a 0.22μm nylon filter membrane, dialyze, and freeze dry to obtain water-soluble carbon dots 1;

[0036] S2: Disperse 0.5g of water-soluble carbon dot 1 in 10ml of deionized water to obtain a carbon dot solution. Add hydrochloric acid to adjust the pH to 7, then add sodium hydroxide to adjust it to 8. Add 5ml of isopropanol containing 5mmol of oleic acid, mix well, put it in a hydrothermal reactor, react at 180℃ for 3h, let it stand and separate into layers, take the lower layer solution, filter it with a 0.22μm aqueous nylon filter membrane, which is water-soluble carbon dot 2.

[0037] S3: The above water-soluble carbon dot 2 was further mixed with 5 ml of isopropanol containing 5 mmol of oleic acid, placed in a hydrothermal reactor, and reacted at 160°C for 3 h. After standing and separating into layers, the upper layer solution was taken and filtered through a 0.22 μm organic nylon filter membrane to obtain an oil-soluble carbon dot modified with carboxylic acid that has broad-spectrum ultraviolet absorption.

[0038] Example 2

[0039] S1: Mix 1g of water-soluble carbon dots with 0.5g of sodium borohydride, adjust the pH to 10 repeatedly with acid or alkaline substances, put it into a hydrothermal reactor, react at 220℃ for 3h, filter the resulting solution with a 0.22μm nylon filter membrane, dialyze, freeze dry to obtain water-soluble carbon dots 1;

[0040] S2: Disperse 2g of the above-mentioned water-soluble carbon dot 1 in 15ml of deionized water to obtain a carbon dot solution. Add sulfuric acid to adjust the pH to 7, and then adjust it to alkaline 10 with potassium hydroxide. Then add 10ml of n-hexane containing 8mmol of octathiol, mix well, put it into a hydrothermal reactor, react at 200℃ for 10h, let it stand and separate into layers, take the lower layer solution, filter it with a 0.22μm aqueous nylon filter membrane, and obtain water-soluble carbon dot 2.

[0041] S3: The above water-soluble carbon point 2 was further mixed with 5 ml of n-hexane containing 7 mmol of octathiol, placed in a hydrothermal reactor, and reacted at 140°C for 5 h. After standing and separating into layers, the upper layer solution was taken and filtered through a 0.22 μm organic nylon filter membrane to obtain thiol-modified oily carbon points with broad-spectrum ultraviolet absorption.

[0042] Example 3

[0043] S1: Mix 1.5g of water-soluble carbon dots with 2g of sodium borohydride, adjust the pH to 12 with an acid or alkaline substance, put it into a hydrothermal reactor, react at 200℃ for 5h, filter the resulting solution through a 0.22μm nylon filter membrane, dialyze, freeze dry to obtain water-soluble carbon dots 1;

[0044] S2: Disperse 1g of the above-mentioned water-soluble carbon dot 1 in 20ml of deionized water to obtain a carbon dot solution. Add hydrochloric acid to adjust the pH to 7, and then adjust it to 12 with potassium hydroxide. Then add 7ml of ethyl acetate containing 1mmol of stearic acid, mix well, put it into a hydrothermal reactor, react at 160℃ for 5h, let it stand and separate into layers, take the lower layer solution, filter it with a 0.22μm aqueous nylon filter membrane, and obtain water-soluble carbon dot 2.

[0045] S3: The above water-soluble carbon dot 2 was further mixed with 10 ml of ethyl acetate containing 10 mmol stearic acid, placed in a hydrothermal reactor, and reacted at 180 °C for 8 h. After standing and separating into layers, the upper layer solution was taken and filtered through a 0.22 μm organic nylon filter membrane to obtain carboxylic acid modified oil-soluble carbon dots with broad-spectrum ultraviolet absorption.

[0046] Experimental Example

[0047] UV absorption performance test:

[0048] The oil-soluble carbon dots prepared in Example 1 were subjected to ultraviolet absorption performance testing using a UV-Vis spectrometer. The oil-soluble carbon dots prepared in Example 1 were placed in the instrument for testing. According to the spectrum, the oil-soluble carbon dots prepared in Example 1 exhibited a good absorption peak in the 200–400 nm ultraviolet region, with a corresponding transmittance of only 1%. This indicates that the oil-soluble carbon dots prepared in Example 1 can absorb ultraviolet light in the 200–400 nm region, possessing broad-spectrum ultraviolet absorption capability. (The spectrum is shown below.) Figure 2 .

[0049] Transmission electron microscopy observation:

[0050] To observe the morphological characteristics of the prepared oil-soluble carbon dots, high-resolution transmission electron microscopy was used to observe the morphology of the oil-soluble carbon dots prepared in Example 1. Figure 3 The transmission electron microscope image shows that the oil-soluble carbon dots have a circular structure.

[0051] By subjecting water-soluble carbon dots with broad-spectrum ultraviolet absorption to three hydrothermal reactions with organic substances, oil-soluble carbon dots with broad-spectrum ultraviolet absorption are obtained. These oil-soluble carbon dots have stable ultraviolet absorption performance, are simple to prepare, use readily available raw materials, are environmentally friendly, and can be used in hydrophobic materials, which is beneficial for the subsequent application of carbon dots in polymers and coatings.

[0052] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for preparing broad-spectrum ultraviolet-absorbing oil-soluble carbon dots, characterized in that, It is prepared by three hydrothermal reactions of water-soluble carbon dots and oily ligands, specifically including the following steps: S1: Mix water-soluble carbon dots with sodium borohydride, adjust the pH value to greater than 7 with acidic or alkaline substances, place in a hydrothermal reactor and heat, filter, dialyze, freeze dry to obtain water-soluble carbon dots 1 after heating. S2: Disperse the water-soluble carbon dot 1 in deionized water to obtain a carbon dot solution. Add an acidic substance to adjust the pH of the carbon dot solution to 7, and then use an alkaline substance to adjust the pH to greater than 7. Then add a nonpolar solvent containing an oily ligand, mix evenly, and then add it to a hydrothermal reactor for heating. After heating is completed, let it stand. After standing and separating into layers, take the lower layer solution and filter it to obtain water-soluble carbon dot 2. S3: Add a nonpolar solvent containing an oily ligand to the water-soluble carbon dot 2, mix well, and then add it to a hydrothermal reactor for heating. After heating, let it stand, and after the layers separate, take the upper layer solution and filter it to obtain the oil-soluble carbon dot.

2. The method for preparing a broad-spectrum ultraviolet-absorbing oil-soluble carbon dot according to claim 1, characterized in that, The acidic substance is at least one of hydrochloric acid, sulfuric acid, and nitric acid, and the alkaline substance is at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

3. The method for preparing a broad-spectrum ultraviolet-absorbing oil-soluble carbon dot according to claim 1, characterized in that, The oily ligands include at least one of carboxyl-containing ligands and thiol-containing ligands.

4. The method for preparing a broad-spectrum ultraviolet-absorbing oil-soluble carbon dot according to claim 3, characterized in that, The carboxyl-containing ligand is a saturated or unsaturated organic acid with more than eight carbon chains, specifically at least one of oleic acid, stearic acid, hexadecanoic acid, and dodecanoic acid; the mercapto-containing ligand is a thiol with more than eight carbon chains, specifically at least one of octathiol, decanethiol, dodecylthiol, and octadecyl sulfuric acid.

5. The method for preparing a broad-spectrum ultraviolet-absorbing oil-soluble carbon dot according to claim 1, characterized in that, The nonpolar solvent is at least one of ethanol, n-hexane, n-pentane, n-pentanol, ethyl acetate, N,N-dimethylformamide, and xylene.

6. The method for preparing a broad-spectrum ultraviolet-absorbing oil-soluble carbon dot according to claim 1, characterized in that, In step S1, the temperature of the hydrothermal reactor is 180–220°C and the time is 3–7 hours. In step S2, the temperature of the hydrothermal reactor is 160–200°C and the time is 3–10 hours. In step S3, the temperature in the hydrothermal reactor is 140–180°C and the time is 3–8 hours.

7. A broad-spectrum ultraviolet-absorbing oil-soluble carbon dot, characterized in that, It is prepared by the method for preparing a broad-spectrum ultraviolet-absorbing oil-soluble carbon dot according to any one of claims 1-6.

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