Carbon dot long-afterglow composite material based on MFI molecular sieve load and preparation method and application of carbon dot long-afterglow composite material

Abstract

The invention belongs to the technical field of molecular sieve composite materials, and particularly relates to preparation of a carbon dot long-afterglow composite material based on MFI molecular sieve loading, and a molecular sieve with an MFI topological framework is used as a matrix for loading carbon dots for the first time. The obtained material has blue fluorescence and ultra-long afterglow room temperature phosphorescence and has wide application prospects in the fields of information encryption, counterfeiting prevention, sensing, biological imaging, photoelectric devices and the like, the preparation method is low in cost and simple in process, and mass production can be achieved.

Description

Technical Field

[0001] The present invention belongs to the field of luminescence of molecular sieve composites, and particularly relates to a carbon dot long afterglow composite material based on MFI molecular sieve loading, a preparation method thereof, and an application thereof. Background Art

[0002] Carbon-dots (CDs) are a class of carbon-based materials with a diameter less than 10 nanometers, usually composed of a carbon core with sp 2 or sp 3 hybridization and abundant surface functional groups. With the advantages of wide raw materials, environmental friendliness, adjustable luminescence color, low cost, and simple preparation process, as well as its unique optoelectronic properties - an easily activated long afterglow characteristic (i.e., the phenomenon of continuous luminescence for several seconds, several hours, or even several days after the excitation stops), this kind of material has broad application prospects in the field of luminescence. However, carbon dots also have some limitations: short emission wavelength, low quantum yield, and easy aggregation quenching under solid-state conditions. In addition, in solution, due to the problem of triplet energy dissipation caused by the free rotation of valence bonds, it is difficult to achieve persistent long afterglow luminescence.

[0003] In order to overcome the problems faced by carbon dots, the non-radiative transition process can be inhibited by constructing a rigid solid matrix to load carbon dots, and more effective intersystem crossing can be promoted, thereby realizing the long afterglow characteristic. Currently, molecular sieves show their unique advantages as matrix carriers of carbon dots: (1) Due to their adjustable regular nanoporous structure, high crystallinity, and rigid confined microenvironment, molecular sieves can effectively inhibit the π-π stacking caused by carbon dot aggregation and reduce non-radiative energy dissipation; (2) The organic templating agent in the main framework of the molecular sieve and its pores can couple and stabilize triplet excitons through hydrogen bonds or covalent bonds, significantly prolonging the afterglow lifetime; (3) The organic templating agent used for synthesizing molecular sieves can simultaneously serve as a carbon source to form carbon dots, which is beneficial to the simple preparation of composite materials. Currently, in the known carbon dot@molecular sieve composite long afterglow system, only carbon dot@molecular sieve composite long afterglow materials based on eight types of molecular sieve topological structures, namely AFI, SOD, CHA, LEV, SBT, MTW, RHO, and SYT, as the matrix have been reported. Therefore, expanding the types of molecular sieve matrices that can be used to achieve the long afterglow performance of carbon dots is of great significance to the development of the field of carbon dot@molecular sieve composite long afterglow materials.

[0004] Chinese Patent CN116676081 discloses a carbon dots@zeolite composite material with time-dependent phosphorescence properties. The reported carbon dots@zeolite material shows that the time-dependent afterglow color changes from blue to green, and the afterglow lifetime is about 8 s. In this patent, the zeolite matrix for loading carbon dots is the RHO topological framework, while in this patent, zeolite with the MFI topological framework is used as the matrix to load carbon dots. In addition, ethylenediamine and N, N'-dimethylethylenediamine are used as carbon sources in Chinese Patent CN116676081, while in this patent, the organic phosphonium templating agent 1-methyl-3-[4-(tributylphosphine)butyl]-1H-imidazolium hydroxide (TBPNZ) is used as the carbon source to prepare carbon dots. The carbon cores of the obtained carbon dots indicate that the functional groups and electronic structures are all different. Therefore, due to the differences in the zeolite matrix for confining carbon dots and the structure of the prepared carbon dots, the carbon dots in this patent only exhibit green afterglow properties after ultraviolet light irradiation, and the visible afterglow duration is more than 12 s. Summary of the Invention

[0005] The present invention provides a carbon dots long afterglow composite material based on MFI zeolite loading, its preparation method and application. This material has excellent long afterglow performance and obvious color change before and after the excitation light source is turned on and off. It has broad application prospects in the fields of information encryption, anti-counterfeiting, sensing, bioimaging, optoelectronic devices, etc. Moreover, the synthesis cost of this material is low, the synthesis process is simple, and mass production can be achieved.

[0006] To achieve the above object, the present invention is realized through the following technical solutions: TBPNZ, water, and tetraethyl orthosilicate are stirred and mixed, heated to prepare a gel, and then hydrothermally reacted to obtain a carbon dots long afterglow (CDs@MFI) composite material based on MFI zeolite loading; The TBPNZ is the organic phosphonium templating agent 1-methyl-3-[4-(tributylphosphine)butyl]-1H-imidazolium hydroxide, and its molecular structure is shown in Formula I;

[0007] Formula I.

[0008] The CDs@MFI composite material of the present invention uses TBPNZ as a templating agent. The specific preparation method includes the following steps: A certain amount of TBPNZ, water, and tetraethyl orthosilicate are stirred for 6-10 hours, dried into a gel, and then the gel is transferred to a reactor and reacted at 140-200 °C for 10-30 days; after the reaction is completed, it is washed, dried, and separated to obtain microcrystalline powder, which is the CDs@MFI composite material.

[0009] Preferably, the amounts of the raw materials are such that the molar ratio of TBPNZ to Si element in the system reaches (0.2 - 0.5):1; the ratio of TBPNZ to water is such that its concentration reaches 0.1 - 0.4 mol / kg. The water content in the gel is such that the molar ratio of H2O to Si in the gel reaches (5 - 40):1 by drying with an infrared lamp.

[0010] Preferably, the preparation method of the TBPNZ includes the following steps: (1) Under nitrogen protection, N-methylimidazole is (slowly) added to a 1-bromo-4-chlorobutane solution, and the mixture is heated and stirred to react to obtain mixture I; Preferably, the molar ratio of N-methylimidazole to 1-bromo-4-chlorobutane is 1:(10 - 20).

[0011] Preferably, the reaction temperature is 20°C - 90°C, the stirring and mixing rate is 300 - 600 rpm, and the reaction time is 12 - 48 h.

[0012] Preferably, the solvent of the 1-bromo-4-chlorobutane solution is one of methanol, ethanol, acetonitrile, acetone, toluene, and tetrahydrofuran.

[0013] (2) Mixture I is first washed with water, then the aqueous phase is washed with an organic solvent, and after liquid separation, the solvent in the aqueous phase is evaporated to obtain the pure phase of product I (1-methyl-3-(4-chlorobutyl)-1H-imidazolium bromide); Preferably, the organic solvent is one of toluene, ethyl acetate, dichloromethane, diethyl ether, and petroleum ether.

[0014] (3) Under nitrogen protection, tributylphosphine is slowly added to the product I solution, and after heating and stirring to react, mixture II is obtained; Preferably, the molar ratio of product I to tributylphosphine is 1:(1 - 10).

[0015] Preferably, the reaction temperature is 60 - 110°C, the stirring and mixing rate is 300 - 600 rpm, and the reaction time is 12 - 48 h.

[0016] Preferably, the solvent of the product I solution is one of methanol, ethanol, acetonitrile, acetone, toluene, and tetrahydrofuran.

[0017] (4) After mixture II is concentrated (by rotary evaporation under reduced pressure), it is washed with water, then the aqueous phase is washed with an organic solvent, and after liquid separation, the aqueous phase is evaporated to obtain product II (1-methyl-3-[4-(tributylphosphine)butyl]-1H-imidazolium bromochloride; Preferably, the organic solvent is one of toluene, ethyl acetate, dichloromethane, diethyl ether, and petroleum ether.

[0018] (5) The obtained product is further subjected to resin exchange to obtain an aqueous solution of TBPNZ, and after concentration, 1-methyl-3-[4-(tributylphosphine)butyl]-1H-imidazolium hydroxide is obtained.

[0019] The present invention has the following positive and beneficial effects: With the aid of the hydrothermal synthesis of molecular sieves, TBPNZ is used as a carbon source in the reaction system, and carbon dots with luminescent properties are generated during the hydrothermal process and in-situ embedded into the molecular sieve matrix. Through the confinement effect, it has blue fluorescence and green long afterglow emission properties, and can display green afterglow with an ultra-long lifetime after being irradiated by ultraviolet light, and can be applied to related fields such as information encryption, anti-counterfeiting, sensing, and optoelectronic devices.

[0020] The present invention prepares a long afterglow composite material based on MFI molecular sieve loading by an in-situ one-pot method, which has simple operation, low cost, good repeatability, and is suitable for industrial batch production. Description of the Drawings

[0021] Figure 1 is a schematic diagram of the synthesis of the template TBPNZ.

[0022] Figure 2 is a comparison diagram of the experimental PXRD of the CDs@MFI material obtained in Example 1 and the simulated PXRD of the MFI molecular sieve framework, indicating that the synthesized sample in Example 1 is a pure phase, and the molecular sieve matrix loaded with carbon dots has an MFI topological structure.

[0023] Figure 3 is a high-resolution transmission electron microscope image of the CDs@MFI material obtained in Example 1.

[0024] Figure 4 is the fluorescence spectrum of the CDs@MFI material obtained in Example 1 at different excitation wavelengths at room temperature.

[0025] Figure 5 is the room temperature steady-state spectrum and delayed spectrum of the CDs@MFI material obtained in Example 1 excited at 395 nm.

[0026] Figure 6 is the luminescence photograph of the CDs@MFI material obtained in Example 1 under excitation by an ultraviolet lamp (wavelength: 395 nm) and after stopping excitation.

[0027] Figure 7 : is the fluorescence quantum yield test spectrum of the CDs@MFI material obtained in Example 1.

[0028] Figure 8 : is the time-resolved decay spectrum of the CDs@MFI material obtained in Example 1 excited at 395 nm. Detailed implementation mode

[0029] In the following examples, the TBPNZ aqueous solution used is an aqueous solution of 1-methyl-3-[4-(tributylphosphine)butyl]-1H-imidazolium hydroxide, preferably prepared by the following steps: Under nitrogen protection, N-methylimidazole (20 mmol, 1.64 g) was added to acetonitrile (10 mL) dissolved with 1-bromo-4-chlorobutane (300 mmol, 51.4 g), and the reaction was carried out at 40 °C for 24 h to obtain mixture I; Mixture I was washed 3 times with 20 mL of water, and the aqueous phase was washed 3 times with 20 mL of ether each time. After liquid separation, the aqueous phase was taken, and all solvents were removed using a rotary evaporator to obtain product I: 1-methyl-3-(4-chlorobutyl)-1H-imidazolium bromide (4.8 g, yield ~95%); Under nitrogen protection, tributylphosphine (60 mmol, 12.12 g) was added to ethanol (25 mL) dissolved with product I (10 mmol, 2.53 g), and the reaction was carried out at 100 °C for 18 h to obtain mixture II; After removing ethanol from mixture II by rotary evaporation under reduced pressure, it was washed 3 times with 30 mL of deionized water, and the aqueous phase was washed 3 times with 30 mL of petroleum ether each time. After liquid separation, the aqueous phase was taken, and all solvents were removed using a rotary evaporator to obtain product II: 1-methyl-3-[4-(tributylphosphine)butyl]-1H-imidazolium bromochloride (4.45 g, yield ~98%); 40 g of anion resin was weighed (2.0 g of resin corresponding to each 1 mmol of product II), washed 3 times with deionized water, and then product II (20 mmol, 9.1 g) and 100 g of deionized water were added, and the exchange was carried out by stirring overnight in the dark to obtain the TBPNZ aqueous solution. The aqueous solution was rotary evaporated, and its concentration was determined to be 0.2807 mol / kg by acid-base titration.

[0030] Unless otherwise specified, the raw materials used in the present invention are all commercially available The present invention provides a carbon dot long afterglow composite material based on MFI zeolite loading prepared by the above preparation method, including MFI zeolite and carbon dots with long afterglow luminescence properties embedded in the MFI zeolite structure.

[0031] With the aid of the hydrothermal synthesis of zeolite, the present invention synthesized a carbon dot long afterglow composite material with the MFI zeolite topological framework as the matrix by an in-situ one-pot method. The best fluorescence emission of the loaded carbon dots is at 459 nm, the best long afterglow emission is at 515 nm, and the visible duration of green light by the naked eye is about 12 s, which can be applied to related fields such as information encryption, anti-counterfeiting, sensing, and optoelectronic devices.

[0032] The following is a detailed description of a carbon dot long afterglow composite material based on MFI zeolite loading, its preparation method and application provided by the present invention in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0033] Example 1: Tetraethyl orthosilicate and TBPNZ aqueous solution were used to synthesize CDs@MFI composite material. The synthesis molar ratio was: Si = 0.006 mol, TBPNZ / Si = 0.25, H2O / Si = 10.

[0034] 5.34 g of 0.28 mol / kg TBPNZ aqueous solution was added to a beaker, and then 1.26 g of tetraethyl orthosilicate was added. After stirring evenly for 6 hours, water was evaporated by heating under an infrared lamp (~50 °C). The gel mass was controlled by weighing to reach the above synthesis molar ratio. Finally, the obtained gel was transferred to a 10 mL polytetrafluoroethylene liner and placed in a stainless steel autoclave, which was sealed and placed in an oven at 190 °C and reacted for 10 days under the autogenous pressure of the reaction kettle.

[0035] After the reaction was completed, the autoclave was taken out and naturally cooled at room temperature. The microcrystalline samples generated in the kettle were washed 3 times with deionized water and acetone in turn, and the samples were naturally dried to obtain the composite long afterglow material of the present invention.

[0036] The comparison chart of the structural simulation XRD pattern and the experimental XRD pattern of the CDs@MFI composite material is as Figure 2 shown. It can be Figure 2 seen that the diffraction peak positions of the powder X-ray diffraction spectrum of the solid sample MFI measured experimentally and the simulated XRD spectrum are basically the same, indicating that the synthesized compound is a pure phase and the zeolite matrix has an MFI topological structure.

[0037] The high-resolution transmission electron microscope picture of the CDs@MFI composite material is as Figure 3 shown. It can be Figure 3 clearly seen that the carbon dots are dispersed in the zeolite matrix, indicating that the carbon dots are successfully embedded in the zeolite matrix.

[0038] Example 2: Tetraethyl orthosilicate and TBPNZ aqueous solution were used to synthesize CDs@MFI composite material. The synthesis molar ratio was: Si = 0.06 mol, TBPNZ / Si = 0.25, H2O / Si = 30.

[0039] Add 53.44 g of 0.28 mol / kg BPNZ aqueous solution into a beaker, then add 12.62 g of tetraethyl orthosilicate, stir evenly for 10 hours, heat to evaporate water under an infrared lamp (~60 °C), control the gel mass by weighing to reach the above synthesis molar ratio, and finally transfer the obtained gel to a 25 mL polytetrafluoroethylene liner and place it in a stainless steel autoclave, seal it and place it in an oven at 150 °C, and react for 25 days under the autoclave's own pressure.

[0040] After the reaction is completed, take out the autoclave and let it cool naturally at room temperature. Wash the microcrystalline samples generated in the autoclave 3 times successively with deionized water and acetone, and dry the samples naturally to obtain the composite long afterglow material of the present invention.

[0041] Example 3: Synthesize CDs@MFI composite materials from tetraethyl orthosilicate and TBPNZ aqueous solution, with a synthesis molar ratio of: Si = 0.006 mol, TBPNZ / Si = 0.4, H2O / Si = 20.

[0042] Add 8.55 g of 0.2807 mol / kg BPNZ aqueous solution into a beaker, then add 1.26 g of tetraethyl orthosilicate, stir evenly for 6 hours, heat to evaporate water under an infrared lamp (~50 °C), control the gel mass by weighing to reach the above synthesis molar ratio, and finally transfer the obtained gel to a 25 mL polytetrafluoroethylene liner and place it in a stainless steel autoclave, seal it and place it in an oven at 200 °C, and react for 7 days under the autoclave's own pressure.

[0043] After the reaction is completed, take out the autoclave and let it cool naturally at room temperature. Wash the microcrystalline samples generated in the autoclave 3 times successively with deionized water and acetone, and dry the samples naturally to obtain the composite long afterglow material of the present invention.

[0044] Study the luminescence properties of the CDs@MFI composite material obtained in Example 1. First, test the fluorescence emission spectra of the material at different excitation wavelengths, as Figure 4 , it is found that the fluorescence emission wavelength of the material gradually redshifts with the increase of the excitation wavelength and the intensity of the emission spectrum gradually weakens after reaching the maximum under the excitation of 390 nm. Use 395 nm as the excitation wavelength to study the fluorescence and room temperature phosphorescence properties of the material, as Figure 5 , under the excitation of 395 nm, the emission peak of the steady-state emission spectrum of the material is at 459 nm while the delayed emission spectrum is at 515 nm, indicating that the material has dual luminescence properties of fluorescence and room temperature phosphorescence. In addition, as Figure 6As shown, the material emits bright blue fluorescence under the irradiation of a 395 nm ultraviolet lamp. After turning off the ultraviolet lamp, it shows green long-afterglow luminescence properties, and the afterglow time is visible to the naked eye for up to more than 10 seconds. The time-resolved decay spectrum of the excitation test shows that the phosphorescence lifetime of the material is as long as 1.26 s ( Figure 7 ), indicating that the material has room-temperature phosphorescence properties with ultra-long afterglow. This property is also consistent with the Figure 5 steady-state spectrum and delayed spectrum data of the material under 395 nm excitation obtained from the test. In addition, the fluorescence quantum yield of the material is as high as 40% ( Figure 8 ), further confirming that the material has excellent photoluminescence properties and showing its application potential in multiple dynamic information encryption, visual identification of latent fingerprints, and graphic anti-counterfeiting.

[0045] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing a carbon dot long afterglow composite material based on MFI molecular sieve loading, characterized in that: The method comprises the following steps: mixing TBPNZ, water and tetraethyl orthosilicate, drying to prepare a gel and then performing a hydrothermal reaction to obtain the gel.

2. The preparation method according to claim 1, characterized in that: The TBPNZ is an organic phosphonium template 1-methyl-3-[4-(tributylphosphino)butyl]-1H-imidazolium hydroxide, and its molecular structure is shown in the following formula: 。 3. The preparation method according to claim 1, characterized in that: The hydrothermal reaction conditions are 140-200° C. for 10-30 days. After the hydrothermal reaction is completed, washing, drying and separation are performed in sequence to obtain microcrystalline powder.

4. The preparation method according to claim 1, characterized in that: The dosage of TBPNZ and tetraethyl orthosilicate is such that the molar ratio of TBPNZ to Si element in the system reaches (0.2-0.5):1; in the process of preparing the hydrogel, the molar ratio of H2O to Si in the gel is made to reach (5-40):1 by infrared lamp drying.

5. The preparation method according to claim 2, characterized in that: The TBPNZ is prepared by a preparation method comprising the following steps: (1) Under nitrogen protection, N-methylimidazole was added to the 1-bromo-4-chlorobutane solution, and the mixture was heated and stirred to obtain a mixture I; (2) washing the mixture I with water, then washing the aqueous phase with an organic solvent, and evaporating the solvent in the aqueous phase after separation to obtain a pure phase of the product I; (3) Under nitrogen protection, tributylphosphine is slowly added to the product I solution, and the mixture is heated and stirred to react to obtain a mixture II; (4) After the mixture II is concentrated, it is washed with water, and then the aqueous phase is washed with an organic solvent. After liquid separation, the aqueous phase is evaporated to obtain the product II; (5) The obtained product is then exchanged with a resin to obtain a TBPNZ aqueous solution, which is then concentrated to obtain 1-methyl-3-[4-(tributylphosphino)butyl]-1H-imidazolium hydroxide.

6. The preparation method according to claim 5, characterized in that: In step (1), the molar ratio of N-methylimidazole to 1-bromo-4-chlorobutane is 1:(10-20); the reaction temperature is 20°C-90°C, the stirring mixing rate is 300-600rpm, and the reaction time is 12-48 h; the solvent of the 1-bromo-4-chlorobutane solution is one of methanol, ethanol, acetonitrile, acetone, toluene and tetrahydrofuran.

7. The preparation method according to claim 5, characterized in that: The organic solvent in step (2) is one of toluene, ethyl acetate, dichloromethane, ether and petroleum ether.

8. The preparation method according to claim 5, characterized in that: In step (3), the molar ratio of the product I to tributylphosphine is 1:(1-10); the reaction temperature is 60-110°C, the stirring mixing rate is 300-600 rpm, and the reaction time is 12-48 h; the solvent of the product I solution is one of methanol, ethanol, acetonitrile, acetone, toluene, and tetrahydrofuran.

9. The preparation method according to claim 5, characterized in that: The organic solvent in step (4) is one of toluene, ethyl acetate, dichloromethane, ether and petroleum ether.

10. Use of the carbon dot long afterglow composite material prepared according to any one of claims 1 to 9 in information encryption, anti-counterfeiting, sensing, bio-imaging or optoelectronic devices.

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