Method for macroscopically preparing solid-state fluorescent carbon dots and solid-state fluorescent carbon dots

Abstract

The invention discloses a method for macroscopically preparing solid-state fluorescent carbon dots and the solid-state fluorescent carbon dots. The method comprises the following steps: S1, mixing an amide substance and acetaldehyde according to a preset proportion to obtain a precursor solution; s2, weighing a preset amount of strong alkali solid as a catalyst, rapidly adding the strong alkali solid into the precursor solution, and performing ultrasonic mixing to obtain a reaction solution; s3, heating the reaction solution and carrying out reflux reaction; s4, after the reaction is completed, naturally cooling a reaction solution to room temperature, separating and purifying, and taking a solid product; and S5, drying the solid-state product in a drying oven to obtain the target product solid-state fluorescent carbon dot. According to the synthesis method disclosed by the invention, on the basis of a mature aldol condensation reaction mechanism, by accurately regulating and controlling key parameters such as the molar ratio of reactants, the reaction temperature and time and the like, the generation of byproducts is effectively inhibited, the yield is remarkably improved (the yield can be up to 70-80%), and large-scale efficient preparation from gram level to kilogram level is realized. Meanwhile, the adopted raw materials are low in cost and wide in source, the reaction can be carried out under the conditions of normal pressure and lower temperature, the operation safety is high, and the energy consumption is low. And the post-treatment process only relates to conventional centrifugation, washing and drying steps, and no complex purification equipment is needed, so that the production cost and the process complexity are greatly reduced. Therefore, the method has great industrial large-scale production potential.

Description

Technical Field

[0001] This invention belongs to the field of carbon dot preparation, specifically, it relates to a method for large-scale preparation of solid fluorescent carbon dots and solid fluorescent carbon dots. Background Technology

[0002] Since its first report in 2004, carbon dots have attracted widespread attention in academia. Due to their low toxicity, good biocompatibility, tunable fluorescence, and chemical inertness, carbon dots have become ideal alternatives to traditional organic dyes and colloidal semiconductor quantum dots. These unique physicochemical properties have led to the widespread application of carbon dots in cutting-edge fields such as light-emitting diodes, bioimaging, solar concentrators, anti-counterfeiting, catalysis, novel batteries, and sensors. In the process of moving carbon dots from the laboratory to commercial applications, large-scale synthesis technology has become a pressing problem to be solved, but current methods are still immature. Regardless of the preparation method used, the resulting carbon dots inevitably contain impurities of varying solubility and size, such as unreacted precursors, oligomers, polymers, amorphous carbon, or carbon particles. Attempting to explain the reaction or formation mechanism using unpurified or insufficiently purified samples is highly likely to lead to erroneous conclusions. Interestingly, the presence of impurities can sometimes actually improve the performance of optoelectronic devices.

[0003] In reported gram- or kilogram-scale preparation studies, the products are mostly simply filtered and considered as pure carbon dots, while the true purity and reaction conversion rate are rarely explored in depth. Low production yield, high impurity content, and high cost are the main factors hindering the industrial production and application of carbon dots.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a method for large-scale preparation of solid fluorescent carbon dots and solid fluorescent carbon dots. Based on the mature aldol condensation reaction mechanism, the generation of by-products can be reduced, the reaction yield can be improved, and large-scale preparation can be achieved. At the same time, the raw materials required by this method are relatively inexpensive, the range of raw materials that can be selected is wide, the reaction conditions are mild, and the post-processing is simple. It is suitable for industrial mass production and has broad application prospects.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for the large-scale preparation of solid-state fluorescent carbon dots, comprising the following steps: S1. Mix amide substances and acetaldehyde according to a preset ratio to obtain a precursor solution; S2. Weigh out a predetermined amount of strong base solid as a catalyst, quickly add it to the precursor solution, and mix it with ultrasound to obtain a reaction solution; S3. The reaction solution is heated to allow for reflux reaction; S4. After the reaction is complete, allow the reaction solution to cool naturally to room temperature, separate and purify, and take the solid product. S5. The solid product is dried in an oven to obtain the target product, solid fluorescent carbon dots.

[0007] In a preferred embodiment, in step S1, the amide substance is one of formamide, acetamide, propionamide, and benzamide.

[0008] In a preferred embodiment, in step S1, the molar ratio of the amide substance to acetaldehyde is 1~3:10.

[0009] In a preferred embodiment, in step S2, the strong alkali is sodium hydroxide or potassium hydroxide.

[0010] In a preferred embodiment, in step S2, after adding a preset amount of strong alkali, the concentration of the strong alkali is 0.5~6 mol / L.

[0011] In a preferred embodiment, in step S3, the reflux reaction temperature is 50~100°C.

[0012] In a preferred embodiment, the reflux reaction time in step S3 is 1 to 3 hours.

[0013] In a preferred embodiment, the separation and purification method in step S4 includes performing the process at least once: Wash with deionized water, then centrifuge or filter under reduced pressure, discarding the supernatant or filtrate.

[0014] In a preferred embodiment, in step S5, the oven drying temperature is 60~80℃ and the time is 3~6h.

[0015] Secondly, the present invention provides a solid fluorescent carbon dot, which is prepared by the method described above. The solid fluorescent carbon dot contains amino, carbonyl, and aldehyde functional groups, has a particle size between 30 and 50 nm, and has a microstructure of spherical nanoparticles.

[0016] After adopting the above technical solution, the method for large-scale preparation of solid fluorescent carbon dots and the solid fluorescent carbon dots provided by the present invention have the following beneficial effects compared with the prior art: (1) The synthesis method of this invention is based on the mature aldol condensation reaction mechanism. By precisely controlling key parameters such as the molar ratio of reactants, reaction temperature, and time, the generation of by-products is effectively suppressed, and the yield is significantly improved (the yield can be as high as 70-80%). It also achieves large-scale and efficient preparation at the gram to kilogram level. At the same time, the raw materials used are inexpensive and widely available, and the reaction can be carried out under normal pressure and relatively low temperature conditions, which ensures high operational safety and low energy consumption. The post-processing only involves conventional centrifugation, washing, and drying steps, without the need for complex purification equipment, which greatly reduces production costs and process complexity. Therefore, this method has great potential for large-scale industrial production.

[0017] (2) The carbon dots prepared by the present invention contain functional groups such as amine, carbonyl, and aldehyde groups. The particle size of the carbon dots is between 30 and 50 nm, and the microstructure is spherical nanoparticles. Attached Figure Description

[0018] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 The UV-Vis absorption spectrum and steady-state fluorescence emission spectrum of the benzamide-based carbon dot ethanol solution (0.05 g / mL) prepared in Example 1 are shown. Figure (a) shows the UV-Vis absorption spectrum; Figure (b) shows the fluorescence emission spectrum with an excitation wavelength of 360 nm; and the inset is an optical photograph of the carbon dot ethanol solution under 365 nm UV light irradiation.

[0019] Figure 2 The excitation and fluorescence emission spectra of the benzamide-based carbon dot solid powder sample prepared in Example 1 are shown. In Figure (a), the excitation spectrum is shown, and the inset shows the appearance of the carbon dot powder sample and its optical photograph under ultraviolet light irradiation; Figure (b) shows the fluorescence emission spectra at different excitation wavelengths.

[0020] Figure 3 Transmission electron microscope (TEM) images of the benzamide-based carbon dots prepared in Example 1 and their Fourier transform diffraction patterns are shown.

[0021] Figure 4 The X-ray diffraction (XRD) pattern of the benzamide-based carbon dot powder sample prepared in Example 1 is shown.

[0022] Figure 5 The Fourier transform infrared (FTIR) spectrum of the benzamide-based carbon dot powder sample prepared in Example 1 is shown.

[0023] Figure 6 The X-ray photoelectron spectroscopy (XPS) spectra of the benzamide-based carbon dot powder sample prepared in Example 1 are shown. Among them, (a) is the full spectrum; (b) is the fine C1s spectrum; (c) is the fine N1s spectrum; and (d) is the fine O1s spectrum.

[0024] Figure 7 The 1H NMR spectrum of the benzamide-based carbon dots prepared in Example 1 using deuterated methanol as a solvent is shown. 1 HNMR).

[0025] Figure 8 High-resolution mass spectra (HRMS) of the benzamide-based carbon dots prepared in Example 1 using methanol as a solvent are shown.

[0026] Figure 9 A schematic diagram illustrating the formation mechanism of the benzamide-based carbon dots prepared in Example 1 is shown.

[0027] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0029] [Example 1] Weigh out 4.50 g of benzamide and 10.0 g of acetaldehyde (molar ratio 1.68:10) sequentially into a 100 mL round-bottom flask, and mix thoroughly by sonication to obtain a precursor solution. Weigh out 1.6 g of sodium hydroxide solid as a catalyst (4 mol / L), and quickly add it to the precursor solution. Sonicate to fully dissolve the catalyst and mix thoroughly to obtain a reaction solution. Heat the reaction solution to 80 °C and reflux the reaction. Start timing after the system temperature reaches the set value and continue the reaction for 2 hours. After the reaction is complete, allow the solution to cool naturally to room temperature, transfer it to a 250 mL beaker, add 80 mL of deionized water, stir thoroughly, and transfer to a 50 mL centrifuge tube. Centrifuge at 8000 r / min for 10 minutes. Discard the supernatant, add 80 mL of deionized water to the resulting precipitate, and centrifuge again at 8000 r / min for 10 minutes. Repeat the water washing-centrifugation operation 3 times, and finally collect the precipitate. The collected solid products were dried in a 60°C oven for 5 hours to obtain purified, dried solid fluorescent carbon dot samples.

[0030] The mass of the prepared benzamide-based carbon dots (BA-CDs) was 10.19 g, and the calculated reaction yield was 70.3%.

[0031] Figure 1 The UV-Vis absorption and fluorescence emission spectra of a BA-CDs ethanol solution (0.05 g / mL) are shown. Figure 1 (a) It can be seen that the sample exhibits two characteristic absorption peaks at 200–230 nm and 270–320 nm, which are attributed to the π–π* transition of π electrons in the aromatic structure and the n–π* transition of n electrons in the surface functional groups, respectively. Figure 1 (b) shows that the sample exhibits yellow fluorescence under ultraviolet light irradiation, with its fluorescence emission peak located at 484 nm. This is attributed to the wide half-width of the emission peak, which covers the wavelength region to which the human eye is sensitive to yellow-green light. Figure 2 The excitation and fluorescence emission spectra of the BA-CDs solid powder sample are shown. Figure 2 (a) It can be seen that the peak of the excitation spectrum of the powder sample is located at 450 nm, which belongs to the n–π* transition of a specific chromophore; the BA-CDs powder sample has a brown appearance and emits orange-yellow fluorescence under 365 nm ultraviolet light. Figure 2 (b) shows that the fluorescence emission spectrum of the powder sample has a slight excitation light dependence, with its fluorescence emission peak located at 616 nm, which is 120 nm redshifted compared to the ethanol solution sample. This phenomenon indicates that BA-CDs are aggregated to a certain extent in the solid state.

[0032] Figure 3 The image shows a TEM image of BA-CDs. The TEM sample preparation process is as follows: a small amount of carbon dot sample was dispersed in ethanol, sonicated for 30 minutes to ensure uniform dispersion, filtered through a 0.22 μm filter membrane, and the resulting dispersion was dropped onto an ultrathin carbon film. After natural drying, the TEM test sample was obtained. The results show that the microstructure of BA-CDs consists of spherical nanoparticles with a uniform particle size distribution in the range of 30–50 nm. Combined with Fourier transform diffraction pattern analysis, BA-CDs did not exhibit significant lattice fringes, indicating that their internal structure is disordered. Figure 4 The XRD pattern of the BA-CDs powder sample shows that it has limited crystallinity and amorphous structure characteristics, which is consistent with the TEM analysis results.

[0033] Figure 5 This is the FTIR spectrum of BA-CDs. In the spectrum, 2700–2900 cm⁻¹ -1 The absorption peak at 1750 cm⁻¹ is attributed to the stretching vibration of –CH in the aliphatic chain. -1 The peak at 1380–1450 cm⁻¹ represents the stretching vibration of the carbonyl group (C=O). -1The absorption peak at 1100–1250 cm⁻¹ corresponds to the stretching vibration of aromatic structures or unsaturated C=C structures; -1 The peaks at these locations are characteristic vibrational peaks belonging to C–O–C and C–OH. Figure 6 The XPS analysis results are for BA-CDs. Figure 6 The full spectrum of (a) shows that the sample mainly contains three elements: C, O, and N, with N doping ratio of 0.5%; Figure 6 (b)–(d) are high-resolution XPS spectra of C1s, N1s and O1s, respectively. The functional groups corresponding to each peak are marked in the figure. The results are consistent with the FTIR analysis. Figure 7 For BA-CDs 1 HNMR spectrum. During the test, the sample was dissolved in deuterated methanol (CD3OD), and the solvent residue peak was located at 3.31 ppm. The assignments of each NMR peak in the spectrum have been marked. There is no clear integral ratio relationship between the peaks, indicating that the molecular composition of the sample is not a single structure, but is rich in multiple functional groups and polymer segments. Figure 8 The HRMS plots of BA-CDs show that the mass-to-charge ratio (m / z) of the samples ranges from 50 to 400, further confirming that they are not composed of a single molecule. Combined with FTIR, XPS, and other data... 1 The characterization results of HNMR and HRMS can corroborate each other and jointly confirm the structural characteristics of BA-CDs, namely, that they have a typical polymer-carbon hybrid structure.

[0034] Based on the above characterization results and the principle of aldol condensation, the formation mechanism of BA-CDs is as follows: Figure 9 As shown: Under the catalysis of sodium hydroxide, the α-carbon atom of acetaldehyde loses a hydrogen atom to form an enol anion. This anion then undergoes a nucleophilic addition reaction with the carbonyl group of another aldehyde or amide molecule to generate a β-hydroxy aldehyde. β-hydroxy aldehydes are unstable and readily dehydrate to form α,β-unsaturated aldehydes. Due to the high reactivity of the α-hydrogen atom, the unsaturated aldehyde can further undergo a series of substitution and condensation reactions. After the aldol condensation reaction, a large number of chain structures and tiny carbon clusters are formed in the system. Subsequently, polymer chains containing different functional groups or branches and small carbon clusters crosslink through coiling, entanglement, or carbonization, ultimately forming carbon dots.

[0035] [Example 2] Weigh out 1.67 g of formamide and 10.0 g of acetaldehyde (molar ratio 1.63:10) sequentially and add them to a 100 mL round-bottom flask. Mix thoroughly by sonication to obtain a precursor solution. Weigh out 1.6 g of sodium hydroxide solid as a catalyst (4 mol / L) and quickly add it to the precursor solution. Sonicate to fully dissolve the catalyst and mix thoroughly to obtain a reaction solution. Heat the reaction solution to 80 °C and reflux. Start timing after the system temperature reaches the set value and continue the reaction for 2 hours. After the reaction is complete, purify the reaction product according to the purification steps in Example 1.

[0036] The prepared formamide-based carbon dots (FA-CDs) are brown in appearance and emit red fluorescence under 365 nm ultraviolet light. Their mass is 8.89 g, and the calculated yield is 76.2%.

[0037] [Example 3] 2.18 g of acetamide and 10.0 g of acetaldehyde (molar ratio 1.63:10) were weighed sequentially and added to a 100 mL round-bottom flask. The mixture was ultrasonically stirred until homogeneous to obtain a precursor solution. 1.6 g of sodium hydroxide solid (4 mol / L) was weighed as a catalyst and rapidly added to the precursor solution. The catalyst was ultrasonically dissolved and thoroughly mixed to obtain a reaction solution. The reaction solution was heated to 80 °C and refluxed. Timing was started after the system temperature reached the set value, and the reaction was continued for 2 hours. After the reaction was completed, the reaction product was purified according to the purification steps in Example 1.

[0038] The prepared acetamide-based carbon dots (AA-CDs) are light brown in appearance and emit orange fluorescence under 365 nm ultraviolet light. Their mass is 8.95 g, and the calculated yield is 73.5%.

[0039] [Example 4] 2.70 g of propionamide and 10.0 g of acetaldehyde (molar ratio 1.63:10) were weighed sequentially and added to a 100 mL round-bottom flask. The mixture was ultrasonically stirred until homogeneous to obtain a precursor solution. 1.6 g of sodium hydroxide solid (4 mol / L) was weighed as a catalyst and rapidly added to the precursor solution. The catalyst was ultrasonically dissolved and thoroughly mixed to obtain a reaction solution. The reaction solution was heated to 80 °C and refluxed. Timing was started after the system temperature reached the set value, and the reaction was continued for 2 hours. After the reaction was completed, the reaction product was purified according to the purification steps in Example 1.

[0040] The prepared propionamide-based carbon dots (PA-CDs) are brown in appearance and emit red-orange fluorescence under 365nm ultraviolet light. Their mass is 9.13g, and the calculated yield is 71.9%.

[0041] [Example 5] 2.75 g of benzamide and 10.0 g of acetaldehyde (molar ratio 1:10) were weighed sequentially and added to a 100 mL round-bottom flask. The mixture was ultrasonically stirred until homogeneous to obtain a precursor solution. 0.2 g of sodium hydroxide solid (0.5 mol / L) was weighed as a catalyst and rapidly added to the precursor solution. The catalyst was ultrasonically dissolved and thoroughly mixed to obtain a reaction solution. The reaction solution was heated to 50 °C and refluxed. Timing was started after the system temperature reached the set value, and the reaction was continued for 1 hour. After the reaction was completed, the reaction product was purified according to the purification steps in Example 1.

[0042] The prepared BA-CDs weighed 7.10 g, and the calculated reaction yield was 55.7%. The sample was brown in appearance and emitted orange-yellow fluorescence under 365 nm ultraviolet light.

[0043] [Example 6] 8.25 g of benzamide and 10.0 g of acetaldehyde (molar ratio 3:10) were weighed sequentially and added to a 100 mL round-bottom flask. The mixture was ultrasonically stirred until homogeneous to obtain a precursor solution. 2.4 g of sodium hydroxide solid (6 mol / L) was weighed as a catalyst and rapidly added to the precursor solution. The catalyst was ultrasonically dissolved and thoroughly mixed to obtain a reaction solution. The reaction solution was heated to 100 °C and refluxed. Timing was started after the system temperature reached the set value, and the reaction was continued for 3 hours. After the reaction was completed, the reaction product was purified according to the purification steps in Example 1.

[0044] The prepared BA-CDs weighed 12.04 g, and the calculated reaction yield was 66.0%. The sample was brown in appearance and emitted orange-yellow fluorescence under 365 nm ultraviolet light.

[0045] [Example 7] 4.50 g of benzamide and 10.0 g of acetaldehyde (molar ratio 1.68:10) were weighed sequentially and added to a 100 mL round-bottom flask. The mixture was ultrasonically stirred until homogeneous to obtain a precursor solution. 2.24 g of potassium hydroxide solid (4 mol / L) was weighed as a catalyst and rapidly added to the precursor solution. The catalyst was ultrasonically dissolved and thoroughly mixed to obtain a reaction solution. The reaction solution was heated to 80 °C and refluxed. Timing was started after the system temperature reached the set value, and the reaction was continued for 2 hours. After the reaction was completed, the reaction product was purified according to the purification steps in Example 1.

[0046] The prepared BA-CDs weighed 9.24 g, and the calculated reaction yield was 63.7%. The sample was brown in appearance and emitted orange-yellow fluorescence under 365 nm ultraviolet light.

[0047] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for large-scale preparation of solid-state fluorescent carbon dots, characterized in that, Includes the following steps: S1. Mix amide substances and acetaldehyde according to a preset ratio to obtain a precursor solution; S2. Weigh out a predetermined amount of strong base solid as a catalyst, quickly add it to the precursor solution, and mix it with ultrasound to obtain a reaction solution; S3. The reaction solution is heated to allow for reflux reaction; S4. After the reaction is complete, allow the reaction solution to cool naturally to room temperature, separate and purify, and take the solid product. S5. The solid product is dried in an oven to obtain the target product, solid fluorescent carbon dots.

2. The method for preparing solid-state fluorescent carbon dots as described in claim 1, characterized in that: In step S1, the amide substance is one of formamide, acetamide, propionamide, and benzamide.

3. The method for preparing solid-state fluorescent carbon dots as described in claim 1 or 2, characterized in that: In step S1, the molar ratio of the amide substance to acetaldehyde is 1~3:

10.

4. The method for preparing solid-state fluorescent carbon dots as described in claim 1, characterized in that: In step S2, the strong base is sodium hydroxide or potassium hydroxide.

5. The method for preparing solid-state fluorescent carbon dots as described in claim 1, characterized in that: In step S2, after adding a preset amount of strong alkali, the concentration of the strong alkali is 0.5~6 mol / L.

6. The method for preparing solid-state fluorescent carbon dots as described in claim 1, characterized in that: In step S3, the reflux reaction temperature is 50~100℃.

7. The method for preparing solid-state fluorescent carbon dots as described in claim 1, characterized in that: In step S3, the reflux reaction time is 1 to 3 hours.

8. The method for preparing solid-state fluorescent carbon dots as described in claim 1, characterized in that, In step S4, the separation and purification method includes performing the following at least once: Wash with deionized water, then centrifuge or filter under reduced pressure, discarding the supernatant or filtrate.

9. The method for preparing solid-state fluorescent carbon dots as described in claim 1, characterized in that: In step S5, the oven drying temperature is 60~80℃ and the time is 3~6h.

10. A solid-state fluorescent carbon dot, characterized in that: The solid fluorescent carbon dots are prepared by the method described in any one of claims 1-9. The solid fluorescent carbon dots contain amino, carbonyl, and aldehyde functional groups, have a particle size between 30 and 50 nm, and have a microstructure of spherical nanoparticles.

Images