A nitrogen-doped carbon dot material with high emulsification level and preparation method thereof

Abstract

A nitrogen-doped carbon dot material with a high emulsification level and its preparation method belong to the technical field of two-dimensional interface materials. First, a NaOH aqueous solution is added to an acetaldehyde aqueous solution, followed by adding hydrochloric acid to adjust the solution pH to neutral. After stirring for reaction, the solution is centrifuged to retain the precipitate, extracted with liquid nitrogen, and freeze-dried to obtain a carbon dot material. The carbon dot material is then added to a system of potassium methoxide and a nitrogen source, heated for reaction, centrifuged to retain the precipitate, and dried. The nitrogen-doped carbon dot material with a high emulsification level is prepared by controlling the reaction time, adjusting the acid amount, and varying the nitrogen source. The present invention can rapidly synthesize a large amount of nanoscale nitrogen-doped carbon dot material emulsifier with an amphiphilic emulsifying effect under mild reaction conditions. The resulting nitrogen-doped carbon dot material is uniform in size and highly dispersed, capable of meeting emulsification requirements under different oil phase conditions. The production process is simple, and in industrial production, dialysis and centrifugation are not required; only centrifugation and drying are required to prepare the nitrogen-doped carbon dot material with a high emulsification level.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional interface materials, and in particular relates to a nitrogen-doped carbon dot material with a high emulsification level and a preparation method thereof. Background Art

[0002] Emulsification systems are widely used in food, cosmetics, pharmaceuticals, and materials science, but existing emulsifiers often suffer from toxicity, poor stability, and environmental impact. Carbon dot materials, due to their unique surface chemistry and favorable environmental friendliness, are becoming a research hotspot in the emulsification field. The surface of carbon dot materials is rich in various functional groups (such as hydroxyl, carboxyl, and epoxy groups), and their hydrophilicity or hydrophobicity can be regulated through chemical modification. This surface property enables carbon dot materials to form a stable emulsified film at the oil-water interface, thereby enhancing the emulsification effect. Furthermore, by adjusting the size, morphology, and concentration of the carbon dot materials, precise control of the emulsification properties can be achieved.

[0003] Compared to traditional emulsifiers, carbon dot materials are non-toxic and biodegradable, aligning with current trends in green chemistry and sustainable development. In the food and cosmetics sectors, carbon dot materials can replace chemically synthesized emulsifiers, enabling the production of safer and more environmentally friendly emulsions. Furthermore, carbon dot materials can significantly improve the long-term stability of emulsion systems. The physical or chemical network they form within emulsions prevents stratification, aggregation, or precipitation.

[0004] In addition, carbon dot materials are usually prepared from cheap and abundant carbon sources, such as glucose, citric acid, waste biomass, etc. In practical applications, the preparation cost of carbon dot materials is relatively low, mainly reflected in the following aspects:

[0005] Low-cost raw materials: Carbon dot materials are often made from green raw materials (such as fruit peels and vegetable waste) or industrial byproducts, making them much cheaper than synthetic surfactants. Simple preparation processes: Low-energy preparation methods such as hydrothermal and microwave methods facilitate scalable production, further reducing manufacturing costs. Environmentally friendly: The biodegradability and non-toxicity of carbon dot materials reduce waste disposal costs, meeting the needs of sustainable development. Therefore, obtaining carbon dot materials with excellent emulsification properties is extremely urgent.

[0006] The use of post-modification methods to manipulate the amphiphilic properties of carbon dot materials objectively prolongs the preparation process and increases production costs, which contradicts the current ecological concept of economic and environmental protection. Therefore, it is imperative to precisely control various oxidation reaction conditions during the preparation of carbon dot materials to shorten the preparation process and reduce production costs, thereby obtaining carbon dot materials with different amphiphilic properties.

[0007] Currently reported methods for preparing carbon dot materials mainly fall into two categories: "top-down" and "bottom-up." The "top-down" method involves decomposing large carbon materials into nanoscale carbon dots through methods such as laser etching and chemical oxidation. The "bottom-up" method involves generating carbon dot materials from small organic precursors through methods such as hydrothermal, solvothermal, and pyrolysis. The "bottom-up" method produces carbon dot materials with higher purity. The present invention utilizes a solvothermal method, which, compared to the hydrothermal method, eliminates the need for reactor heating, resulting in lower costs and reduced energy consumption. Summary of the Invention

[0008] The object of the present invention is to provide a nitrogen-doped carbon dot material with a high emulsification level and a preparation method thereof.

[0009] The present invention uses acetaldehyde as a carbon source to synthesize nitrogen-doped carbon dot materials, and applies the prepared nitrogen-doped carbon dot materials to the emulsification of toluene organic solvent to obtain an emulsion system with a high emulsification level. The nitrogen-doped carbon dot materials with a high emulsification level are prepared by controlling the reaction time, regulating the acid amount, and changing the nitrogen source.

[0010] The method for preparing a nitrogen-doped carbon dot material with a high emulsification level according to the present invention comprises the following steps:

[0011] (1) Prepare 1-3 M NaOH aqueous solution, stir for 15-30 minutes and then let it stand;

[0012] (2) Slowly add the NaOH aqueous solution prepared in step (1) dropwise to the 30-50% by mass acetaldehyde aqueous solution, complete the addition within 15-30 minutes and stir evenly;

[0013] (3) Stir the system obtained in step (2) for 2 to 5 hours at room temperature to obtain a brown-red paste solution;

[0014] (4) Add the hydrochloric acid solution dropwise to the system obtained in step (3), adjust the pH of the solution to neutral, and continue stirring for 4 to 12 hours until the system becomes a golden yellow solution;

[0015] (5) Centrifuge the system obtained in step (4) at 10,000 to 12,000 rpm for 3 to 5 minutes, remove the supernatant after centrifugation, and retain the precipitate;

[0016] (6) Add deionized water to the precipitate obtained in step (5), disperse it evenly by ultrasonication, remove the supernatant after centrifugation, and retain the precipitate; repeat the operation of "adding deionized water to the precipitate - ultrasonication - centrifugation - retaining the precipitate" 2 to 5 times to obtain a brown-red precipitate;

[0017] (7) The brown-red precipitate obtained in step (6) is freeze-dried using liquid nitrogen extraction to obtain an orange-yellow carbon dot material;

[0018] (8) Disperse 1-2 g of potassium methoxide in 10-20 mL of methanol, add 0.5-2 g of nitrogen source, and stir until no solid precipitates.

[0019] (9) Add the carbon dot material obtained in step (7) to the system in step (8) and heat at 70-90°C for 30-60 minutes;

[0020] (10) The system obtained in step (9) was centrifuged at a speed of 10,000 to 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and dried to obtain a nitrogen-doped carbon dot material with a high emulsification level.

[0021] Furthermore, in step (2), the volume ratio of the NaOH aqueous solution to the acetaldehyde aqueous solution is 1:1-3, the concentration of the hydrochloric acid solution in step (4) is 1-3 M, the freeze-drying conditions in step (7) are a temperature of -70 to -60°C and a vacuum degree of <10 Pa, the nitrogen source in step (8) is urea, lysine, cysteine, glycine, aniline, citrulline, pyridine or arginine, and step (10) is vacuum drying at 70-90°C for 20-30 hours.

[0022] The nitrogen-doped carbon dot material obtained in step (11) is added to deionized water and ultrasonically dispersed to obtain a nitrogen-doped carbon dot material dispersion liquid, and the obtained nitrogen-doped carbon dot material dispersion liquid is then mixed and shaken with toluene in a certain volume ratio, and after shaking, it is quickly transferred to a colorimetric tube, and its emulsification rate is measured after standing for 24 hours to detect its amphiphilic emulsification performance;

[0023] Cottonseed oil and turpentine were used to prepare an oil phase with a gradient HLB value (HLB=7~13). The nitrogen-doped carbon dot material dispersion was then mixed with the gradient HLB value oil phase. Ultrasonic mixing and emulsification were performed at a certain power to prepare an emulsion. After standing for 24 hours, its emulsification rate was measured to detect the effect of the gradient HLB value oil phase on the emulsification properties of the nitrogen-doped carbon dot material.

[0024] Table: Data of "gradient HLB value oil phase" prepared with cottonseed oil and turpentine

[0025] HLB value 7 8 9 10 11 12 13 Cottonseed oil / g 0.845 0.751 0.657 0.563 0.469 0.375 0.282 Turpentine / g 0.15 0.244 0.338 0.432 0.526 0.62 0.713

[0026] The technical solution of the present invention can quickly synthesize a large number of nano-scale nitrogen-doped carbon dot material emulsifiers with amphiphilic emulsification effects under mild reaction conditions. The obtained nitrogen-doped carbon dot materials are uniform in size and highly dispersed, and can meet the emulsification requirements under different oil phase conditions. In addition, the cost is extremely low and the production process is simple. In industrial production, no dialysis and centrifugation are required, and only centrifugal drying is required for preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : Optical photograph of the nitrogen-doped carbon dot material obtained in Example 1;

[0028] Figure 2 : Transmission electron micrograph of the nitrogen-doped carbon dot material obtained in Example 1;

[0029] Figure 3 : XRD pattern of the nitrogen-doped carbon dot material obtained in Example 1;

[0030] Figure 4 : XPS graph of the nitrogen-doped carbon dot material obtained in Example 1;

[0031] Figure 5 : Infrared image of the nitrogen-doped carbon dot material obtained in Example 1;

[0032] Figure 6 ; Optical photograph of the emulsification effect of the nitrogen-doped carbon dot material obtained in Example 1;

[0033] Figure 7 : Leica electron microscope emulsification bubble image of the nitrogen-doped carbon dot material obtained in Example 1;

[0034] Figure 8 : Surface tension change curve of the water / toluene system after adding the nitrogen-doped carbon dot material dispersion in Example 1;

[0035] Figure 9 : Optical photograph of the oil phase with gradient HLB value after adding the nitrogen-doped carbon dot material dispersion in Example 1. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme, effect advantage of the embodiments of the present invention clearer, the embodiments will be described in more detail below, and it should be noted that the embodiments described below are not all embodiments, but only embodiments of the preferred invention conditions of the present invention. The reagents and instruments used in the embodiments can be purchased through normal commercial channels. Based on the embodiments of the present invention, those of ordinary skill in the art directly obtain the present embodiments without creative activities, and belong to the scope of protection of the present invention.

[0037] Example 1

[0038] (1) Prepare 10 mL of 1 M NaOH aqueous solution, stir for 20 minutes, and then let it stand;

[0039] (2) Slowly add the NaOH aqueous solution prepared in step (1) dropwise into 20 mL of 40% acetaldehyde aqueous solution, complete the addition within 20 minutes, and stir evenly;

[0040] (3) Stir the system obtained in step (2) for 3 h at room temperature to obtain a brown-red paste solution;

[0041] (4) Prepare 30 mL of 1 M hydrochloric acid solution; add the obtained hydrochloric acid solution dropwise to the system obtained in step (3), adjust the solution to pH = 7.0, and obtain a golden yellow solution;

[0042] (5) Centrifuge the system obtained in step (4) at 12,000 rpm for 3 minutes, remove the supernatant after centrifugation, and retain the precipitate;

[0043] (6) Add deionized water to the precipitate obtained in step (5), disperse it evenly by ultrasonication, remove the supernatant after centrifugation, and retain the precipitate; repeat the operation of "adding deionized water to the precipitate - ultrasonication - centrifugation - retaining the precipitate" three times to obtain a brown-red precipitate;

[0044] (7) The brown-red precipitate obtained in step (6) was freeze-dried using liquid nitrogen extraction (-65°C, vacuum degree <10 Pa) to obtain 2.2 g of orange-yellow carbon dot material;

[0045] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 1 g of urea, and stir for 10 minutes until no solid precipitates;

[0046] (9) Add 0.25 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0047] (10) The system obtained in step (9) was centrifuged at 12000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.27 g of nitrogen-doped carbon dot material.

[0048] 20 mg of nitrogen-doped carbon dot material was added to 5 mL of deionized water and ultrasonicated for 10 minutes (frequency 40 kHz) to obtain a nitrogen-doped carbon dot material dispersion. The obtained nitrogen-doped carbon dot material dispersion was added to 5 mL of toluene to form a water-oil system. The system was then placed in a constant temperature shaker at 300 rpm for 1 hour, transferred to a glass bottle, sealed and allowed to stand for more than 24 hours, and the height of the emulsion layer H was measured. 乳 And the total height H of the oil-water system 总 , according to the emulsification rate = (H 乳 / H 总 ) * 100%, the calculated emulsification rate was 80%. Leica electron microscope observation revealed an average diameter of 38 μm for the formed emulsified bubbles. The resulting nitrogen-doped carbon dot dispersion was added to 5 mL of an oil phase with a gradient of HLB values ​​(HLB = 7-13). After mixing, the mixture was sonicated for 30 minutes (40 kHz) and allowed to stand for 24 hours. The system with the highest stability and emulsion layer height corresponded to an HLB value of 10-11.

[0049] Figure 1 It is a nitrogen-doped carbon dot material with a solid appearance and is a yellow powder. Figure 2From the transmission electron microscope photo, it can be seen that the obtained nitrogen-doped carbon dot material has an average particle size of 2~4nm. Figure 3 This is the X-ray diffraction (XRD) spectrum of the nitrogen-doped carbon dot material. It can be seen that the nitrogen-doped carbon dot material has a broad peak at 20 degrees, corresponding to the highly graphitized structure of the nitrogen-doped carbon dot material. Figure 4 This is the X-ray photoelectron spectroscopy (XPS) spectrum of the nitrogen-doped carbon dot material. The peak at 284.8 eV corresponds to graphitized sp2 carbon, and the peaks at 286.1 e V and 287.0 e V correspond to CO and C=O. It can be seen that the surface of the nitrogen-doped carbon dot material has epoxy functional groups such as hydroxyl and carboxyl groups. Figure 5 This is the infrared (IR) spectrum of nitrogen-doped carbon dots. It can be seen that at 3345 cm -1 and 3453cm -1 There is a stretching vibration peak of NH at 1620 cm -1 There is a NH bending vibration peak at , which proves that the amino functional group has been successfully introduced. Figure 6 This is the emulsification effect diagram of nitrogen-doped carbon dot materials. In the water / toluene system, the formed emulsion layer occupies the entire oil phase and part of the water phase (oil phase on top, water phase on the bottom), forming a stable Pickering emulsion. Figure 7 The Leica electron microscope image of emulsified bubbles after adding nitrogen-doped carbon dot material to the water / toluene system shows that the emulsified bubbles formed are uniform in size, with a diameter of 30~50μm. Figure 8 This is a graph showing the changes in surface tension. It can be clearly seen that after adding nitrogen-doped carbon dot materials, the surface tension of the water / toluene system drops from 43.6 mN / m to 7.3 mN / m, and the interfacial tension of the system decreases by 83.3%. Figure 9 This is an optical photograph of the dispersion in Example 1 in the oil phase with a gradient HLB value. It can be clearly seen that the emulsion layers of numbers 10 and 11 have the highest heights and the best stabilization effects, indicating that the HLB value range of the nitrogen-doped carbon dot material is 10-11.

[0050] Example 2

[0051] Steps (1) to (7) were the same as in Example 1, and 2.2 g of orange-yellow carbon dot material was obtained;

[0052] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 0.5 g of lysine, and stir for 10 minutes until no solid precipitates;

[0053] (9) Add 0.5 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0054] (10) The system obtained in step (9) was centrifuged at 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.55 g of nitrogen-doped carbon dot material with a diameter of 4 to 10 nm, an emulsification rate of 55%, and an average diameter of the emulsified bubbles of 45 μm.

[0055] Example 3

[0056] Steps (1) to (7) were the same as in Example 1, and 2.2 g of orange-yellow carbon dot material was obtained;

[0057] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 0.5 g of cysteine, and stir for 10 minutes until no solid precipitates;

[0058] (9) Add 0.5 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0059] (10) The system obtained in step (9) was centrifuged at 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.54 g of nitrogen-doped carbon dot material with a diameter of 4 to 8 nm, an emulsification rate of 56%, and an average diameter of the emulsified bubbles of 48 μm.

[0060] Example 4

[0061] Steps (1) to (7) were the same as in Example 1, and 2.2 g of orange-yellow carbon dot material was obtained;

[0062] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 0.5 g of glycine, and stir for 10 minutes until no solid precipitates;

[0063] (9) Add 0.5 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0064] (10) The system obtained in step (9) was centrifuged at 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.55 g of nitrogen-doped carbon dot material with a diameter of 4 to 10 nm, an emulsification rate of 53%, and an average diameter of the emulsified bubbles of 50 μm.

[0065] Example 5

[0066] Steps (1) to (7) were the same as in Example 1, and 2.2 g of orange-yellow carbon dot material was obtained;

[0067] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 0.5 g of citrulline, and stir for 10 minutes until no solid precipitates;

[0068] (9) Add 0.5 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0069] (10) The system obtained in step (9) was centrifuged at 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.58 g of nitrogen-doped carbon dot material with a diameter of 6 to 9 nm, an emulsification rate of 52%, and an average diameter of the emulsified bubbles of 60 μm.

[0070] Example 6

[0071] Take 20 mL of 40% acetaldehyde aqueous solution and 20 mL of ammonia water (concentration is 27%) and mix them. React at 20°C for 3 hours. Add 30 mL of 1 M hydrochloric acid solution and adjust the pH to neutral. The rest of the operation is the same as in Example 1. No carbon dot material is produced after step (7).

[0072] Example 7

[0073] Steps (1) to (7) were the same as in Example 1, and 2.2 g of orange-yellow carbon dot material was obtained;

[0074] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 0.5 g of aniline, and stir for 10 minutes until no solid precipitates;

[0075] (9) Add 0.5 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0076] (10) The system obtained in step (9) was centrifuged at 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.57 g of nitrogen-doped carbon dot material with a diameter of 8 to 10 nm. The emulsification effect was very poor, the emulsion layer was unstable, and the emulsion broke quickly.

[0077] Example 8

[0078] Steps (1) to (7) were the same as in Example 1, and 2.2 g of orange-yellow carbon dot material was obtained;

[0079] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 0.5 g of pyridine, and stir for 10 minutes until no solid precipitates;

[0080] (9) Add 0.5 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0081] (10) The system obtained in step (9) was centrifuged at 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.51 g of nitrogen-doped carbon dot material with a diameter of 10-15 nm, an emulsification rate of 51%, and an average diameter of the emulsified bubbles of 70 μm.

[0082] Example 9

[0083] Steps (1) to (7) were the same as in Example 1, and 2.2 g of orange-yellow carbon dot material was obtained;

[0084] (8) Disperse 1 g of potassium methoxide in 10 mL of methanol, add 0.5 g of arginine, and stir for 10 minutes until no solid precipitates;

[0085] (9) Add 0.5 g of the carbon dot material obtained in step (7) to the system obtained in step (8) and stir at 80°C for 30 minutes;

[0086] (10) The system obtained in step (9) was centrifuged at 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and vacuum dried at 80°C for 24 hours to obtain 0.53 g of nitrogen-doped carbon dot material with a diameter of 8-10 nm, an emulsification rate of 51%, and an average diameter of the emulsified bubbles of 72 μm.

Claims

1. A method for preparing a nitrogen-doped carbon dot material with a high emulsification level, comprising the following steps: (1) Prepare 1-3 M NaOH aqueous solution, stir for 15-30 minutes and then let it stand; (2) Slowly add the NaOH aqueous solution prepared in step (1) dropwise to the 30-50% by mass acetaldehyde aqueous solution, complete the addition within 15-30 minutes and stir evenly; (3) Stir the system obtained in step (2) for 2 to 5 hours at room temperature to obtain a brown-red paste solution; (4) Add the hydrochloric acid solution dropwise to the system obtained in step (3), adjust the pH of the solution to neutral, and continue stirring for 4 to 12 hours until the system becomes a golden yellow solution; (5) Centrifuge the system obtained in step (4) at 10,000 to 12,000 rpm for 3 to 5 minutes, remove the supernatant after centrifugation, and retain the precipitate; (6) Add deionized water to the precipitate obtained in step (5), disperse it evenly by ultrasonication, remove the supernatant after centrifugation, and retain the precipitate; repeat the operation of "adding deionized water to the precipitate - ultrasonication - centrifugation - retaining the precipitate" 2 to 5 times to obtain a brown-red precipitate; (7) The brown-red precipitate obtained in step (6) is freeze-dried using liquid nitrogen extraction to obtain an orange-yellow carbon dot material; (8) Disperse 1-2 g of potassium methoxide in 10-20 mL of methanol, add 0.5-2 g of nitrogen source, and stir until no solid precipitates. (9) Add the carbon dot material obtained in step (7) to the system in step (8) and heat at 70-90°C for 30-60 minutes; (10) The system obtained in step (9) was centrifuged at a speed of 10,000 to 12,000 rpm for 3 minutes, the supernatant was removed, and the precipitate was retained and dried to obtain a nitrogen-doped carbon dot material with a high emulsification level.

2. The method for preparing a nitrogen-doped carbon dot material with a high emulsification level according to claim 1, wherein: In step (2), the volume ratio of the NaOH aqueous solution to the acetaldehyde aqueous solution is 1:1-3.

3. The method for preparing a nitrogen-doped carbon dot material with a high emulsification level according to claim 1, wherein: The concentration of the hydrochloric acid solution in step (4) is 1~3 M.

4. The method for preparing a nitrogen-doped carbon dot material with a high emulsification level according to claim 1, wherein: The freeze-drying conditions in step (7) are a temperature of -70 to -60°C and a vacuum degree of <10Pa.

5. The method for preparing a nitrogen-doped carbon dot material with a high emulsification level according to claim 1, wherein: In step (8), the nitrogen source is urea, lysine, cysteine, glycine, citrulline, aniline, pyridine or arginine.

6. The method for preparing a nitrogen-doped carbon dot material with a high emulsification level according to claim 1, wherein: In step (10), vacuum drying is performed at 70-90° C. for 20-30 hours.

7. A nitrogen-doped carbon dot material with a high emulsification level, characterized by: The method is prepared by any one of claims 1 to 6.

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