Preparation method of carbon dot composite material with time-varying phosphorescent color-changing property, and obtained product and application

Abstract

This invention belongs to the field of functional materials preparation, specifically relating to a method for preparing a carbon dot composite material with time-varying phosphorescent properties, the resulting product, and its applications. This invention uses diethylenetriaminepentaacetic acid and biuret as precursors to prepare green phosphorescent carbon dots via a conventional microwave-assisted synthesis method. The obtained carbon dots have an amorphous carbon structure. Subsequently, these carbon dots are mixed and ground with sodium hydroxide, melamine, and aluminum sulfate, and then subjected to solid-state heating under microwave assistance to successfully synthesize a carbon dot composite material (CDs-y@MA) with time-varying phosphorescent properties. This composite material exhibits time-varying phosphorescence from red to green after irradiation with 365 nm ultraviolet light and demonstrates excellent water resistance. The composite material prepared by this invention not only demonstrates the excellent performance of carbon dot composite materials in time-varying phosphorescence and underwater luminescence but also provides potential application prospects for the development of advanced encryption technologies.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional material preparation, and particularly relates to a preparation method of a carbon dot composite material with time-dependent phosphorescent color change characteristics and the obtained product and application. BACKGROUND

[0002] In recent years, photoluminescent materials have attracted widespread attention in the fields of information encryption, data protection, anti-counterfeiting labels, etc. By precisely controlling the wavelength and intensity of the external excitation source, the luminescent properties of the luminescent material can be efficiently adjusted, especially in terms of emission wavelength, luminescent intensity and persistence, etc. Among them, the time-dependent phosphorescence (TDPC) phenomenon is particularly attractive, which is characterized by the change of the afterglow color of the material over time. Combining materials with different phosphorescent characteristics and time response characteristics provides a new idea for developing multifunctional information encryption materials with high security and anti-counterfeiting performance. In addition, due to the interaction between water molecules and phosphorescent materials, the phosphorescent energy may be dissipated through energy transfer or non-radiative processes, thereby significantly reducing the photoluminescent efficiency. Therefore, it is a great challenge to achieve stable afterglow luminescence in water. These characteristics attract a large number of researchers due to their scarcity and great application potential, and also make the related research become more and more urgent.

[0003] Carbon dots (CDs) are a new type of zero-dimensional luminescent nanomaterials with unique optical, physical and chemical properties. By adjusting their synthesis methods, conjugated structures, doped elements and surface functional groups, their luminescent properties can be flexibly controlled. Carbon dots not only have high quantum efficiency and phosphorescent stability, but also have excellent biocompatibility, low toxicity and green and environmentally friendly synthesis process, and have been widely studied and applied. So far, many time-dependent phosphorescent (TDPC) materials based on carbon dots have been reported. However, there are still some challenges in realizing the TDPC performance of carbon dots in water. Due to the strong quenching effect of water molecules on triplet excitons, most of the reported carbon dots can only emit afterglow in the solid state, and their application in aqueous solution is limited. Carbon dots that achieve TDPC performance in water need to overcome two major difficulties. First, luminescent centers with diverse structures need to be designed and synthesized to ensure that these centers have different lifetime characteristics. Second, the quenching effect caused by water molecules must be prevented by optimizing the material design to ensure the stability of the luminescent centers. These challenges make the design and application of carbon dots face higher requirements and prompt researchers to continuously explore new solutions. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a preparation method of a carbon dot composite material with time-dependent phosphorescent color change characteristics.

[0005] The present application also provides a carbon dot composite material prepared by the above method.

[0006] Another object of the present invention is to provide the application of the above-mentioned carbon dot composite material.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0008] This invention provides a method for preparing a carbon dot composite material with time-varying phosphorescence properties, comprising the following steps:

[0009] (1) Add deionized water to diethylenetriaminepentaacetic acid and biuret, and then sonicate the mixture; thaw the mixture, and after the reaction is complete, cool it to room temperature, wash it and dry it to obtain CDs;

[0010] (2) CDs, aluminum sulfate octadecyl hydrate, sodium hydroxide and melamine are ground into powder and thawed again. After the reaction is completed, the mixture is cooled to room temperature to obtain the composite material CDs-g@MA.

[0011] Preferably, in step (1), the mass ratio of diethylenetriaminepentaacetic acid to biuret is 1:1.30-1.35; and the material-to-liquid ratio of diethylenetriaminepentaacetic acid to deionized water is 0.3-0.4 g:5 mL.

[0012] Preferably, in step (1), the ultrasonic treatment time is 3-5 min; the thawing reaction is carried out at a power of 550-650W for 7-10 min; and the drying temperature is 60℃.

[0013] Preferably, in step (2), the mass ratio of CDs, aluminum sulfate octadecylhydrate, sodium hydroxide and melamine is 1.5:10-15:1:5-10.

[0014] Preferably, in step (2), the thawing reaction is carried out at a power of 550-650W for 10-15 minutes.

[0015] The present invention also provides a carbon dot composite material CDs-g@MA prepared by the preparation method according to any one of claims 1-5.

[0016] The present invention further provides the application of the above-mentioned carbon dot composite material CDs-g@MA in digital information encryption.

[0017] This invention utilizes diethylenetriaminepentaacetic acid and biuret as precursors to prepare green phosphorescent carbon dots via a conventional microwave-assisted synthesis method. The obtained carbon dots possess an amorphous carbon structure. Subsequently, these carbon dots were mixed and ground with sodium hydroxide, melamine, and aluminum sulfate, and then subjected to solid-state heating under microwave assistance to successfully synthesize a carbon dot composite material (CDs-y@MA) exhibiting time-varying phosphorescence properties. This composite material, after irradiation with 365 nm ultraviolet light, displays time-varying phosphorescence from red to green and exhibits excellent water resistance. The time-varying phosphorescence from red to green is mainly due to the synergistic effect of two luminescent centers. The green phosphorescence is primarily attributed to the luminescence of the carbon nucleus state, while the red phosphorescence is due to the presence of sodium hydroxide and aluminum sulfate, which promotes the formation of ionic bonds and enhances the spin-orbit coupling effect of the C=O / C=N groups. This effect promotes the inverse spin crossing (ISC) process, effectively filling the triplet exciton and forming new luminescent centers. Furthermore, melamine forms a protective film around the carbon dots, preventing the quenching effect of water and thus enabling the composite material to maintain stable phosphorescence emission in water. This design strategy provides a new solution for combining the time-varying phosphorescence of carbon dots with their luminescence properties in water.

[0018] The beneficial effects of this invention are as follows: The composite material prepared by this invention not only demonstrates the excellent performance of carbon dot composite materials in time-varying color phosphorescence and water luminescence, but also provides potential application prospects for the development of advanced encryption technology. Attached Figure Description

[0019] Figure 1 shows the TEM image of CDs;

[0020] Figure 2 shows the TEM image of CDs-y@MA;

[0021] Figure 3. (a) XPS spectra of CDs. (bd) High-resolution XPS fitting results of C1s, N1s, and O1s spectra of CDs;

[0022] Figure 4 shows the Fourier transform infrared spectrum of CDs;

[0023] Figure 5 shows the emission wavelengths of CDs and CDs-g under 365nm excitation;

[0024] Figure 6 shows the phosphorescence spectra of CDs-y@MA aqueous solution under different excitations;

[0025] Figure 7 shows the encryption application of CD and CDs composite materials. Detailed Implementation

[0026] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0027] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0028] Example 1

[0029] 1. Synthesis of CDs:

[0030] CDs were synthesized via a microwave-assisted method. First, 354 mg of diethylenetriaminepentaacetic acid and 464 mg of biuret were placed in a 50 mL beaker, and 5 mL of deionized water was added to dissolve the solid. The mixture was then sonicated for 3 minutes. The beaker was transferred to a microwave oven, and the reaction was allowed to thaw (at 600 W) for 7 minutes. After the reaction was complete, the mixture was cooled to room temperature and washed several times with deionized water. Finally, the solid was dried overnight in an oven at 60°C to obtain white solid CDs.

[0031] 2. Synthesis of CDs composite materials:

[0032] First, 60 mg of CDs, 600 mg of aluminum sulfate octadecylhydrate, 40 mg of sodium hydroxide, and 400 mg of melamine were thoroughly ground into powder. The powder was then transferred to a 5 mL beaker and placed in a microwave oven to defrost (600 W) for 10 minutes. After the reaction was complete, the mixture was cooled to room temperature to obtain a white solid CDs composite material, CDs-g@MA.

[0033] Using the same method described above, CDs-g composite material was obtained without the addition of melamine; CDs-y@MA composite material was obtained without the addition of sodium hydroxide. All other experimental conditions remained the same.

[0034] Figure 1 Transmission electron microscopy (TEM) images of CDs are shown. The TEM images indicate that CDs are monodisperse spherical particles with an average diameter of 1.8 ± 0.7 nm. The lattice spacing is indistinct, indicating that CDs exhibit an amorphous CD structure. Figure 2 TEM images of CDs-g@MA are shown. At 50 nm resolution, CDs can be clearly observed to be encapsulated in the matrix, indicating that CDs are successfully bonded to the matrix material.

[0035] To investigate the structure, surface composition, and graphitization degree of CDs, elemental analysis and spectroscopic measurements were performed. XPS spectra ( Figure 3 a) shows characteristic peaks for carbon (C), nitrogen (N), and oxygen (O) at 284.8 eV, 400.0 eV, and 531.0 eV, respectively. Further analysis of the high-resolution XPS spectrum revealed the chemical composition of the CDs surface. C 1s spectrum ( Figure 3b) The deconvolution into three peaks, 284.8 eV, 286.2 eV, and 281.9 eV, are attributed to CC / C=C, CO / CN, and C=O bonds, respectively, indicating the presence of different types of chemical bonds on the CDs surface and confirming the covalent interaction between diethylenetriaminepentaacetic acid (DTPA) and biuret. Similarly, the O 1s spectrum ( Figure 3 c) The deconvolution peaks are located at 531.2 eV and 533.1 eV, attributed to C=O and CO functional groups, respectively, which further confirms the presence of oxygen groups on the CD surface. High-resolution N 1s spectrum ( Figure 3 d) The two peaks at 398.8 eV and 400.1 eV, respectively, are attributed to CN=C and CN bonds, indicating different binding states of nitrogen atoms on the CDs surface. Furthermore, Fourier transform infrared spectroscopy (FTIR) further analyzed the functional groups of the CDs ( Figure 4 ). At 3414 cm -1 The absorption peak at 1680 cm⁻¹ indicates the presence of -OH and -NH₂ groups in CDs, while the absorption peak at 1680 cm⁻¹ indicates the presence of -OH and -NH₂ groups in CDs. -1 The absorption peak is attributed to the C=O stretching vibration, 1623 cm⁻¹. -1 The peak represents the stretching vibration of the C=C bond in the benzene ring. 1406 cm⁻¹ -1 The nearby absorption peak corresponds to the in-plane bending vibration of CH, at 1337 cm⁻¹. -1 The peak is attributed to the stretching vibration of the CN bond. 1227 cm⁻¹ -1 and 1078 cm -1 The absorption peaks represent the vibrations of the CO bond. These spectroscopic features indicate that the surface of CDs is rich in various functional groups such as -OH, -NH2, C=O, CN, and CO, and also contains various chemical bonds, such as CO, CN, and C=O bonds. Notably, the XPS results are in high agreement with the FTIR results, providing a comprehensive understanding of the surface chemical properties and structural composition of carbon quantum dots.

[0036] To study the optical properties of CDs composite materials, this invention recorded the emission spectra of CDs and CDs-g solids under 365 nm ultraviolet excitation. Figure 5 The results showed that the emission wavelengths of both CDs and CDs-g solids were concentrated at 423 nm, and the emission wavelengths did not change significantly with the addition of the solid matrix, indicating that the matrix did not affect the fluorescence emission wavelength of CDs. In contrast, CDs-g solids with added aluminum sulfate and sodium hydroxide showed a significantly enhanced emission intensity, indicating that the matrix had a certain enhancing effect on the luminescence performance of CDs. In addition, the CDs composite material CDs-g@MA prepared by adding extra melamine exhibited excellent water resistance. This water resistance is due to the fact that melamine can form a protective matrix through hydrogen bonding, protecting CDs from quenching by water and oxygen.Figure 6 The figure shows the phosphorescence spectra of CDs-g@MA in aqueous solution under different excitation wavelengths. At 523 nm, the emission intensity gradually decreases with increasing excitation wavelength, while at around 620 nm, the red wavelength intensity first decreases and then increases with increasing excitation wavelength. This indicates that the introduction of the matrix alters the optical properties of CDs, possibly due to the formation of ionic bonds by metal ions (aluminum and sodium ions) on the CDs surface, stabilizing the surface-active groups. This ionic bond formation suppresses the radiative transition from singlet to triplet state, reduces the energy of non-radiative vibrational processes, thus enhancing the luminescence intensity and introducing new red luminescent centers. The coexistence of red and green luminescent centers leads to the TDPC phenomenon in the CDs composite material. Furthermore, we can see that when the excitation wavelength is 365 nm, the two luminescent centers in the CDs-g@MA aqueous solution exhibit the optimal ratio, with the red luminescent center dominating.

[0037] Based on the variable afterglow TDPC performance and excellent waterproof properties of CDs and their composite materials, this invention demonstrates the potential applications of digital secondary information encryption. For example... Figure 7 As shown, CDs-g@MA, CDs-y@MA (CDs composite material without sodium hydroxide), and melamine-free CDs-g powder were placed on filter paper. Under normal light, the number "8" formed by the CDs composite material was clearly visible on the filter paper. After irradiation with 120W ultraviolet light, the number "8" did not change significantly, indicating that the composite material remained stable under ultraviolet excitation. After the ultraviolet light source was turned off, the "1" formed by CDs-y@MA instantly lost its afterglow, while the other two materials showed a red afterglow of the number "3," indicating that sodium hydroxide played an important role. Over time, the number "1" gradually showed an afterglow change from orange to green, while the number "3" changed from red to green, eventually forming a dynamic pattern from "8" to "3," then to "13," and back to "8." In addition, when water droplets were applied to the CDs composite material, because CDs-g was not protected by melamine, the water quickly quenched the afterglow, causing the numbers to change. Thus, the number changes from "8" to "7" and then to "17". This phenomenon not only reveals the excellent optical and waterproof properties of the composite material, but also verifies the feasibility and potential of digital information encryption based on afterglow variations.

Claims

1. A method for preparing a carbon dot composite material with time-varying phosphorescent properties, characterized in that, Includes the following steps: (1) Add deionized water to diethylenetriaminepentaacetic acid and biuret, and then sonicate the mixture; microwave heat the mixture, and after the reaction is complete, cool to room temperature, wash and dry to obtain CDs; The microwave heating is performed at a power of 550-650W for 7-10 minutes. (2) CDs, aluminum sulfate octadecylhydrate, sodium hydroxide and melamine were thoroughly ground into powder, and microwave-heated again. After the reaction was completed, the mixture was cooled to room temperature to obtain the composite material CDs-g@MA; The microwave heating is performed at a power of 550-650W for 10-15 minutes.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of diethylenetriaminepentaacetic acid and biuret is 1:1.30-1.35; the material-to-liquid ratio of diethylenetriaminepentaacetic acid and deionized water is 0.3-0.4g:5mL.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the ultrasonic treatment time is 3-5 minutes; the drying temperature is 60°C.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of CDs, aluminum sulfate octadecylhydrate, sodium hydroxide and melamine is 1.5:10-15:1:5-10.

5. A carbon dot composite material CDs-g@MA prepared by the preparation method according to any one of claims 1-4.

6. The application of the carbon dot composite material CDs-g@MA as described in claim 5 in digital information encryption.

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