Preparation method of carbon dot@silica long-life phosphorescent nanocomposite with adjustable particle size

Abstract

The application discloses a preparation method of carbon dot@silica long-life phosphorescent nanocomposites with adjustable particle size, and relates to the technical field of new materials, aiming at solving the problem that there is no method which is simple in steps, green and cheap in raw materials and easy to control in small size range, and simultaneously providing new multi-heteroatom doping expansion; the application comprises the following steps: adopting epichlorohydrin as a chlorine source and an oxygen source, adopting ethylenediamine as a nitrogen source, and preparing N / O / Cl heteroatom carbon dot materials through one-step hydrothermal method; then, tetraethyl orthosilicate is used to provide a silica matrix, and the prepared carbon dot materials are coated; in the coating process, the pH condition is adjusted to realize the control of the particle size of the product within 0-20nm, and the particle size is negatively correlated with the pH value; the preparation method is simple, the raw materials are novel, cheap and green, the product has good water dispersibility, the product has excellent and stable photochemical characteristics, and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a method for preparing a carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size. Background Technology

[0002] Room-temperature phosphorescent materials possess advantages such as long lifetime, large Stokes shift, and high signal-to-noise ratio, making them valuable for applications in bioimaging, chemical sensing, and optoelectronic devices. However, current phosphorescent materials are mainly limited to metal coordination compounds, which are typically expensive, highly toxic, and unstable, limiting their practical applications. Carbon dots (CDs) are an emerging class of photoluminescent nanomaterials that have attracted widespread attention due to their excellent optical, electrical, and chemical properties. Most CDs exhibit relatively short lifetimes and phosphorescent emission quenched in aqueous solutions due to defects and nonradiative inactivation of triplet excitons, which is generally insufficient for long-lifetime room-temperature phosphorescent nanomaterials used in bioimaging, nanoprobes, and other applications. Current research focuses on improving their luminescence properties through heteroatom doping and matrix protection methods to prepare nanocomposite materials with long-lifetime phosphorescence, thereby addressing these issues.

[0003] The excited triplet state of heteroatom-doped carbon dots can be activated through an efficient intersystem transition process (i.e., the transition from the excited singlet state to the triplet state). Heteroatom doping in carbon dots (CDs) represents a versatile technique that can further improve their chemical composition and structural properties, making them promising nanomaterials for many applications (such as fluorescent nanoprobes). Patent CN115287065B, entitled "A Method for Preparing Nitrogen-Phosphorus Co-doped Carbon Dots and Its Applications," discloses a one-step hydrothermal synthesis of N,P-CDs using 3,4-diaminopyridine, nitric acid, and phosphoric acid as precursors, achieving a quantum yield of 38.45%. However, this method uses inexpensive and environmentally friendly raw materials, limiting its application prospects. Furthermore, the method only achieves doping with conventional nitrogen and phosphorus heteroatoms. Therefore, it is necessary to broaden the range of raw materials and heteroatom types that can be used for carbon doping to lay the foundation for more future applications of co-doped carbon dots.

[0004] Matrix protection methods, such as using silica matrices, enhance structural rigidity through hydrogen and covalent bonds between carbon dots and the matrix. Simultaneously, the nanoscale spatial confinement effect further stabilizes the excited triplet state. Therefore, within the matrix, the combined effects of rigid network protection, strong covalent bonds, and effective spatial confinement generate a stable excited triplet state T1*, making carbon dot@silica nanocomposites excellent phosphorescent nanoprobes among water-dispersible composite materials. Consequently, matrix encapsulation and size control have naturally become important research directions. The invention patent application with publication number CN110371992A, entitled "A Method for Synthesizing Monodisperse Silica Spheres by Controlling Microemulsion, and Its Products and Uses," discloses a method for obtaining monodisperse silica spheres by cutting the microemulsion used to prepare the spheres and then subjecting it to a solvothermal reaction. This method involves cutting the microemulsion and controlling the size of the resulting microemulsion droplets, thereby controlling the particle size of the prepared monodisperse silica spheres. The particle size of the monodisperse silica spheres prepared by this method is in the nanometer or submicrometer range. However, this method is more suitable for controlling silica spheres within a large size range (100nm-1400nm) and cannot well meet the control requirements for smaller sizes, especially those ranging from a few nanometers to tens of nanometers.

[0005] In summary, there is an urgent need for a method to prepare carbon dot@silica long-life phosphorescent nanocomposites with tunable particle size to solve these problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size, so as to solve the problem that there is no method that is simple in steps, uses green and inexpensive raw materials, and is easy to control in a small size range, while providing a new multi-heteroatom doping extension.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size, comprising using epichlorohydrin as a chlorine source and oxygen source as a precursor, and ethylenediamine as a nitrogen source, preparing N / O / Cl heteroatom carbon dot material by a one-step hydrothermal method, and then using tetraethyl orthosilicate to provide a silica matrix to coat the prepared carbon dot material. During the coating process, the product particle size can be controlled within 0-20 nm by adjusting the pH conditions, and the particle size is negatively correlated with the pH value.

[0008] Preferably, the preparation process of the above-mentioned carbon dot material includes the following specific steps:

[0009] S1: Add epichlorohydrin and ethylenediamine to water and mix them evenly under ultrasonic treatment;

[0010] S2: The homogeneous mixed solution obtained by ultrasound is transferred to a stainless steel autoclave lined with polytetrafluoroethylene for hydrothermal treatment.

[0011] S3: After the mixed solution after hydrothermal treatment is naturally cooled to room temperature, it is filtered to obtain carbon dot material.

[0012] Preferably, in step S1 above, the molar ratio of epichlorohydrin to ethylenediamine is between 4:1 and 1:2.

[0013] Preferably, in step S2 above, the hydrothermal treatment temperature is 160–220°C, and the reaction time is 8–12 h.

[0014] Preferably, the preparation process of the above-mentioned carbon dot@silica material includes the following specific steps:

[0015] S1: The epichlorohydrin-ethylenediamine carbon dot material prepared by hydrothermal method is added to a sufficient amount of alkaline buffer solution and stirred evenly to obtain a homogeneous mixed solution.

[0016] S2: Add sufficient tetraethyl orthosilicate to the mixed solution, and react fully under stirring and heating conditions to obtain the crude product.

[0017] Preferably, in the preparation process of the above-mentioned carbon dot@silica material, the alkaline buffer solution is NH4Cl-NH3 buffer solution with a pH of 9.5 to 10.5.

[0018] Preferably, in the preparation process of the above-mentioned carbon dot@silica material, the heating temperature is 90℃, the stirring speed is 900rpm, and the reaction time is 24h.

[0019] Preferably, in the preparation process of the above-mentioned carbon dot@silica material, the volume ratio of epichlorohydrin-ethylenediamine carbon dot material, alkaline buffer solution, and tetraethyl orthosilicate is 1:60:4.8.

[0020] Preferably, the preparation process of the above-mentioned carbon dot@silica material further includes step S3, in which the crude product is naturally cooled to room temperature, and then purified carbon dot@silica composite material is obtained by filtration, centrifugal washing or dialysis, and freeze drying.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. The preparation method of this carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size uses epichlorohydrin as the chlorine and oxygen source and ethylenediamine as the nitrogen source. A novel carbon dot with excellent water dispersibility, multi-element doping and excellent photochemical performance is prepared by a one-step hydrothermal method. A new raw material and carbon dot synthesis route has been developed. The raw materials are cheaper and greener, which opens up a wider road for the preparation of phosphorescent carbon dots and is conducive to further expansion of future application prospects.

[0023] 2. The preparation method of the carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size improves the chemical composition and structural characteristics of CDs by doping with multiple heteroatoms such as N, O and Cl and the interaction between carbon quantum dots and silica matrix, giving them better and more stable photochemical properties. The prepared composite material has the advantages of high luminescence intensity and long phosphorescence lifetime at room temperature, thus realizing long-life and room temperature phosphorescence emission in aqueous solution.

[0024] 3. The preparation method of this carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size is simple and convenient. It not only achieves multi-heteroatom doping in one step, but also the coating process is significantly better than commonly used microemulsion coating of silica, reverse microemulsion coating of silica, and seeding method. In terms of particle size control, only the pH of the buffer solution needs to be adjusted to achieve adjustable particle size of the product at a small nanometer scale.

[0025] 4. The preparation method of this carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size has the advantages of simple preparation method, novel, inexpensive and green raw materials, good water dispersibility of product, and excellent and stable photochemical properties of product. It is expected to have a wider application prospect in the fields of material modification, analysis and detection, and bioimaging. Attached Figure Description

[0026] Figure 1 The image shows a transmission electron microscope (TEM) image of the CDs prepared in Example 1 of this invention.

[0027] Figure 2 This is a particle size distribution diagram of the CDs prepared in Example 1 of the present invention;

[0028] Figure 3 This is a high-resolution transmission electron microscope image of the CDs prepared in Example 1 of the present invention;

[0029] Figure 4 The Fourier transform infrared spectroscopy (FT-IR) image of the CDs prepared in Example 1 of this invention;

[0030] Figure 5 The image shows the ultraviolet-visible spectrum (UV-vis) of the CDs prepared in Example 1 of this invention.

[0031] Figure 6The UV-Vis spectra of the ethylenediamine carbon dots and epichlorohydrin carbon dots prepared in Comparative Example 1 are shown.

[0032] Figure 7 The phosphorescence excitation and emission spectra of CDs@SiO2 prepared in Example 2 of this invention are shown.

[0033] Figure 8 This is a room temperature phosphorescence lifetime curve of CDs@SiO2 prepared in Example 2 of the present invention;

[0034] Figure 9 The Fourier transform infrared (FT-IR) spectrum of CDs@SiO2 prepared in Example 2 of this invention is shown below.

[0035] Figure 10 The images show transmission electron microscopy (TEM) images of CDs@SiO2 coated in NH4Cl-NH3 buffer solutions at different pH values ​​in Example 3 of this invention. In the images, af corresponds to pH = 9.5, 9.6, 9.7, 9.8, 9.9, and 10.0, respectively. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0037] Example 1

[0038] Preparation of epichlorohydrin-ethylenediamine carbon dots: Add 0.157 mL of epichlorohydrin to 15 mL of ultrapure water and disperse thoroughly by sonication. Then add 0.0334 mL of ethylenediamine and stir until homogeneous. Transfer the solution to a 25 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 200 °C for 10 h. After naturally cooling to room temperature, remove the resulting liquid and filter it using a 0.22 μm syringe filter.

[0039] Figure 1 This is a transmission electron microscope image of CDs. Figure 2 The particle size distribution diagram of CDs shows that the prepared CDs are spherical with a small particle size, with a diameter of 3.8 nm. Figure 3 The lattice fringes of CDs are 0.21 nm, which corresponds to the graphite (100) crystal plane, indicating that the nanoparticles are carbon dots.

[0040] The FT-IR test results for CDs can be found in [link to CDs]. Figure 4The infrared spectrum of CDs shows that they have multiple characteristic peaks and functional groups such as carbon-oxygen double bonds, carbon-oxygen single bonds or carbon-oxygen-carbon bonds, oxygen-hydrogen bonds, nitrogen-hydrogen bonds, carbon-chlorine bonds, carbon-carbon single bonds and carbon-nitrogen single bonds. This indicates that the successful introduction of N / O / Cl heteroatoms further proves that the chemical composition and structural properties of CDs have been improved.

[0041] See the UV-Vis spectrum of CDs. Figure 5 As can be seen from the illustration, the prepared CDs are a homogeneous yellowish-brown solution under fluorescent light, but exhibit bright blue fluorescence when irradiated with a 365 nm ultraviolet lamp. The UV-Vis spectrum of the CDs shows two absorption peaks at approximately 275 and 346 nm in the aqueous solution, which may originate from π-π* and n-π* transitions.

[0042] In this Example 1, not only was multiple heteroatoms doped in one step using a one-step hydrothermal method, which is simple and easy to operate, but the prepared CDs also had small particle size, good water dispersibility, and emitted bright blue fluorescence under ultraviolet irradiation, exhibiting excellent photochemical performance. This demonstrates that the chemical composition and structural characteristics of CDs were improved by using different precursor raw materials, resulting in excellent and stable photochemical properties. These advantages make it promising for large-scale production and further application in various fields.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that a single precursor was selected to prepare the carbon dot material, while other conditions are exactly the same as in Example 1.

[0045] Preparation of ethylenediamine carbon dots: Add 0.0334 mL of ethylenediamine to 15 mL of ultrapure water and mix thoroughly by sonication. Transfer the solution to a 25 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 200 °C for 10 h. After naturally cooling to room temperature, remove the resulting liquid and filter it using a 0.22 μm syringe filter.

[0046] Preparation of epichlorohydrin carbon dots: Add 0.157 mL of epichlorohydrin to 15 mL of ultrapure water and mix thoroughly by sonication. Transfer the solution to a 25 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 200 °C for 10 h. After naturally cooling to room temperature, remove the resulting liquid and filter it using a 0.22 μm syringe filter.

[0047] The UV-Vis spectra of ethylenediamine carbon dots and epichlorohydrin carbon dots are shown below. Figure 6 First, as can be seen from the illustrations, the prepared epichlorohydrin CDs are a pale yellow homogeneous solution under fluorescent light, while the ethylenediamine CDs are a colorless, transparent, homogeneous solution under fluorescent light. UV-vis spectrum. Figure 6a shows that this material's aqueous solution has no obvious ultraviolet absorption peak. Figure 6 b shows that this material has only a significant absorption peak at 277 nm in aqueous solution, which may originate from π-π* transitions. Therefore, our study (e.g., ratio 1) demonstrates that the presence of both precursors is essential and plays a crucial role in the preparation of carbon dot materials.

[0048] Example 2

[0049] Preparation of long-lifetime phosphorescent nanocomposite material of carbon dots@silica: 0.5 mL of the epichlorohydrin-ethylenediamine carbon dot material prepared above was dispersed in 30 mL of NH4Cl-NH3 buffer (pH = 10.5) and stirred evenly. Then, 2.4 mL of tetraethyl orthosilicate was added and reacted in a metal bath at 900 rpm at 90 °C for 24 h. After naturally cooling to room temperature, the resulting liquid was removed. This material has excellent water solubility, exhibits bright blue fluorescence under 365 nm ultraviolet light irradiation, and displays a high-intensity green afterglow after the ultraviolet light is turned off, with a visible lifetime of approximately 15 s.

[0050] The test results are as follows Figure 7 As shown, first from Figure 7 As shown in the illustration, the prepared CDs@SiO2 is a colorless and transparent solution under fluorescent light, exhibits blue fluorescence under 365nm ultraviolet light, and displays high-intensity green phosphorescence after the excitation source is removed. Figure 7 The dashed and solid lines represent the phosphorescence emission spectrum of the material. When the excitation wavelength is 350 nm, the emission peak of CDs@SiO2 is strongest near 507 nm, indicating that the prepared CDs@SiO2 exhibits green phosphorescence with high intensity. The black curve represents the excitation spectrum of the material.

[0051] The room temperature phosphorescence lifetime curve of CDs@SiO2 is as follows: Figure 8 As shown, at an excitation wavelength of 350 nm and an emission wavelength of 507 nm, the phosphorescence lifetime of the CDs@SiO2 nanocomposite material is 1.58 s.

[0052] Figure 9 3450 cm⁻¹ in the FT-IR spectrum -1 The absorption peak centered at 1630 cm⁻¹ is due to the stretching vibration of the OH bonds on the SiO₂ surface. -1 This can be attributed to the OH bending vibration peak, 1106 cm⁻¹ -1 The corresponding stretching vibrations of Si-O-Si are 797 and 465 cm⁻¹. -1 The absorption peak at that point is a characteristic vibration of Si-O, proving that the silicon dioxide coating has been achieved.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 2 is that different carbon dot materials are used, while other conditions are exactly the same as in Example 2.

[0055] Preparation of citric acid carbon dots: The carbon dots were prepared according to the method disclosed in Chemistry-A European Journal, 2019, 25(51), 11963. Citric acid monohydrate (4200 mg, 20 mmol) was placed in a 50 mL round-bottom flask and stirred in an oil bath at 180 °C and 100 rpm for 120 min to obtain a thick, viscous liquid, which was the citric acid carbon dot material.

[0056] Preparation of citric acid carbon dots@silica nanocomposites: 0.5 mL of citric acid carbon dots were dispersed in 30 mL of NH₄Cl-NH₃ buffer (pH = 10.5) and stirred until homogeneous. Then, 2.4 mL of tetraethyl orthosilicate was added, and the mixture was reacted in a metal bath at 900 rpm at 90 °C for 24 h. After natural cooling to room temperature, the resulting liquid was removed. This material exhibits bright blue fluorescence under 365 nm UV light irradiation, but no phosphorescence is observed when the UV light is turned off. Replacing epichlorohydrin-ethylenediamine carbon dots with citric acid carbon dots does not allow for the preparation of long-lifetime phosphorescent nanocomposites using this method.

[0057] Example 3

[0058] Particle size control of carbon dot@silica long-life phosphorescent nanocomposites: Preparation of carbon dot@silica long-life phosphorescent nanocomposites: 0.5 mL of the prepared epichlorohydrin-ethylenediamine carbon dots were dispersed in 30 mL of NH4Cl-NH3 buffer solution (pH = 9.5, 9.6, 9.7, 9.8, 9.9, 10.0) and stirred until homogeneous. Then, 2.4 mL of tetraethyl orthosilicate was added and reacted in a metal bath at 900 rpm at 90 °C for 24 h. After naturally cooling to room temperature, the resulting liquid was removed and filtered using a 0.22 μm syringe filter.

[0059] Figure 10 (af) shows the transmission electron microscope image of CDs@SiO2. In different NH4Cl-NH3 buffer solutions (pH = 9.5, 9.6, 9.7, 9.8, 9.9, 10.0), long-lifetime phosphorescent nanocomposites of carbon dots@silica with particle sizes of 18.80 nm, 16.97 nm, 14.65 nm, 10.25 nm, 9.15 nm, and 7.64 nm were obtained. Further experiments showed that at pH 9.5–10.5, the particle size of the product CDs@SiO2 was negatively correlated with pH, ​​and the product size was uniform within the same batch, while the product size consistency was good between different batches under the same conditions.

[0060] The six materials prepared in this embodiment exhibit excellent water solubility, still displaying bright blue fluorescence under 365nm ultraviolet light irradiation, and all possessing a visible lifetime of approximately 15 seconds after the ultraviolet light is turned off, along with a long-lasting and high-intensity green afterglow. Therefore, the photochemical properties of CDs@SiO2 did not change significantly due to size control.

[0061] Examples 2 and 3 above both use silica as a matrix and TEOS as a matrix material to encapsulate epichlorohydrin carbon dots inside the composite material. The particle size of the product is controlled at the small nanoscale simply by changing the pH of the ammonia buffer solution. The prepared nanocomposite material has small particle size and uniform and adjustable size.

[0062] The epichlorohydrin used in this invention has no precedent in the field of carbon dot preparation. It is worth noting that the selection of carbon dot raw materials is not something that can be easily determined by assumption. In the field of carbon dot preparation, most of the existing raw materials have undergone long-term and repeated verification. It is difficult to obtain a new carbon dot synthesis route by directly changing one or a few of them. The adoption and final determination of new materials often require a great deal of screening and experimentation, and even luck cannot be ruled out. In addition, as in Comparative Example 1 above, even if the raw materials that may be correct are selected, if not all of them are selected or a suitable combination is not found, it is also possible to miss the opportunity. Even if a green new raw material that can synthesize carbon dots is found, it is not certain that nanomaterials with long phosphorescence lifetime can be prepared. At the same time, it is even more difficult to have small and controllable particle size. Therefore, in the field of carbon dot preparation, finding suitable new raw materials has always been an important research direction.

[0063] In summary, this invention achieves N / O / Cl heteroatom doping in one step using special raw materials. Simultaneously, through the interaction between the prepared carbon quantum dots and the matrix, it realizes long-lifetime phosphorescence emission in aqueous solution at room temperature. The long lifetime of phosphorescence allows for an appropriate delay time, thereby easily avoiding background interference such as fluorescence emission and scattered light, making it widely applicable.

[0064] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0065] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing a carbon dot@silica long-life phosphorescent nanocomposite material with tunable particle size, characterized in that: The N / O / Cl heteroatom carbon dot material is prepared by one-step hydrothermal method, using epichlorohydrin as chlorine source and oxygen source, and using ethylenediamine as nitrogen source, with hydrothermal treatment temperature of 160-220 DEG C and reaction time of 8-12h; then the prepared carbon dot material is coated with silicon dioxide matrix provided by tetraethyl orthosilicate, and the particle size of the product is controlled within 0-20nm by adjusting pH condition during the coating process, and the particle size is negatively correlated with pH value.

2. The method for preparing a carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size according to claim 1, characterized in that, The preparation process of the carbon dot material comprises the following specific steps: S1: adding epichlorohydrin and ethylenediamine into water and mixing uniformly under ultrasonic action; S2: transferring the obtained uniform mixed solution into a stainless steel autoclave lined with polytetrafluoroethylene for hydrothermal treatment; S3: after the mixed solution after hydrothermal treatment is naturally cooled to room temperature, the carbon dot material is obtained by filtration.

3. The preparation method of the carbon dot@silica long-life phosphorescent nanocomposite with adjustable particle size according to claim 2, characterized in that: In the step S1, the molar ratio of epichlorohydrin to ethylenediamine is between 4:1 and 1:

2.

4. The method for preparing a carbon dot@silica long-life phosphorescent nanocomposite material with adjustable particle size according to claim 1, characterized in that, The preparation process of the carbon dot@silica material comprises the following specific steps: S1: taking the epichlorohydrin-ethylenediamine carbon dot material prepared by hydrothermal method and adding into sufficient alkaline buffer solution to stir uniformly, to obtain a uniform mixed solution; S2: adding sufficient tetraethyl orthosilicate into the mixed solution, and fully reacting under stirring and heating condition to prepare a crude product.

5. The preparation method of the carbon dot@silica long-life phosphorescent nanocomposite with adjustable particle size according to claim 4, characterized in that: In the step S1, the alkaline buffer solution is NH4Cl-NH3 buffer solution with pH of 9.5-10.

5.

6. The preparation method of the carbon dots@silica long-life phosphorescent nanocomposite with adjustable particle size according to claim 4, characterized in that: In the step S2, the heating temperature is 90 DEG C, the stirring speed is 900 rpm, and the reaction time is 24h.

7. The method according to claim 4, wherein the method is characterized by: The volume ratio of the epichlorohydrin-ethylenediamine carbon dot material, the alkaline buffer solution and the tetraethyl orthosilicate is 1:60:4.

8. 8.The method of claim 4, wherein the carbon dot@silica long-lifetime phosphorescent nanocomposite has a tunable particle size. Further comprising step S3: after the crude product is naturally cooled to room temperature, the purified carbon dot@silica composite material is obtained by filtration, centrifugal washing or dialysis, and freeze-drying.

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