Synthesis method of fluorescent emission adjustable aluminum quantum dot material

Abstract

The application discloses a synthesis method of aluminum quantum dot material with adjustable fluorescence emission, and belongs to the field of novel quantum dot material. The application adopts a reverse micelle synthesis method, uses a surfactant to prepare a microemulsion, uses aluminum halide as a precursor, and is reduced by a strong reducing agent to prepare colloidal aluminum quantum dots with uniform particle size and monodispersion. Meanwhile, the surface of the synthesized aluminum quantum dots is modified through surface engineering, so that the fluorescence emission of the aluminum quantum dots can be adjusted. The synthesis route disclosed by the application has the advantages of simple and easily obtained raw materials, simple and easy-to-operate reaction conditions, simple operation and high product quality, and is the first time to use surface engineering to regulate the emission behavior of aluminum quantum dots.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, and specifically relates to an aluminum quantum dot material and its synthesis method that modulates the fluorescence emission wavelength of aluminum quantum dots through surface engineering. Background Technology

[0002] The synthesis and subsequent functionalization of semiconductor nanocrystals for various applications has become a broad scientific research question. Colloidal quantum dots, due to the quantum confinement effect caused by their small size, exhibit unique physical and chemical properties and have therefore been widely used in photovoltaic devices such as light collectors, biolabeling, and light-emitting diodes. Preliminary research on colloidal quantum dots has mainly focused on their crystal structure and size, which are also the primary sources of their unique photoelectric properties. Recent studies have determined that the surface ligands of quantum dots not only stabilize them but are also a crucial factor determining their photoluminescence. Two main explanations for the photoluminescence mechanism have gradually been accepted by researchers. One is the quantum confinement effect, meaning that when the size of the quantum dot material approaches the Fermi wavelength of a metal (typically <1 nm), the continuous band of energy levels becomes discrete, leading to the emergence of molecular properties. The other explanation is the charge transfer caused by the interaction between the functional ligands and the metal core.

[0003] Currently, most metallic quantum dots are composed of noble metals such as gold and silver, with very few reports on lightweight metals such as aluminum and magnesium. In particular, research on materials like aluminum, which exhibit unique optical responses in the ultraviolet band, offers significant advantages for ultraviolet light sources, LEDs, and ultraviolet sensors. Regarding the preparation of aluminum nanoclusters provided in patent CN 111203547 A, there is a lack of practical methods to control their fluorescence emission, thus limiting its practical applications in optical imaging, biosensing, and LED displays. Researching and achieving control over the fluorescence emission of aluminum quantum dots also has profound implications.

[0004] This invention is a further improvement on the basis of patent CN 111203547 A. By modifying the surface of aluminum quantum dots with different surface ligands, the technical effect of tunable fluorescence emission is achieved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for synthesizing aluminum quantum dot materials with tunable fluorescence emission.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A fluorescently tunable aluminum quantum dot material is synthesized as follows:

[0008] A reverse micelle synthesis method was employed, using surfactants to prepare microemulsions. Aluminum halide was used as a precursor and reduced with a strong reducing agent to prepare colloidal aluminum quantum dots. Simultaneously, surface engineering was used to modify the surface of the synthesized aluminum quantum dots, thereby achieving tunable fluorescence emission. The specific steps include:

[0009] (1) Dissolve the surfactant in anhydrous xylene, sonicate to homogenize, and purge the air in the reaction apparatus with argon to obtain a reverse micelle solution with a concentration of 1-3 mmol / L; add anhydrous aluminum halide to the prepared reverse micelle solution and sonicate to homogenize to obtain a reverse micelle solution containing a metal precursor.

[0010] (2) Add a strong reducing agent to the mixed solution obtained in step (1), and stir magnetically at room temperature under the protection of an inert gas atmosphere; add ethanol to quench the strong reducing agent that has not participated in the reaction;

[0011] (3) Add different surface ligands to the solution obtained in step (2) to modify the surface of the synthesized quantum dots; heat the solution to the reaction temperature and keep it at that temperature for a certain time;

[0012] (4) Cool the solution from step (3) to room temperature, extract by separation, and remove organic solvents, including xylene, ethanol, etc., by rotary evaporation.

[0013] (5) Add polar or non-polar solvents for ultrasonic dispersion, vacuum filtration, rotary evaporation concentration, and finally dialysis purification to obtain colloidal aluminum quantum dots with adjustable fluorescence emission.

[0014] In step (1) of this invention, the molar ratio of anhydrous aluminum halide to surfactant is 1:1 to 3.

[0015] The surfactants described in this invention include sodium (2-ethyl-1-hexyl)sulfosuccinate (AOT), sodium alkyl sulfonate (SAS), tetraoctyl ammonium bromide (TOAB), etc.

[0016] The anhydrous aluminum halide selected in this invention is a high-purity anhydrous aluminum halide to prevent oxygen and water impurities from affecting the synthesized quantum dots during the reaction process, such as weakening fluorescence emission and causing unpredictable redshift of fluorescence emission. The anhydrous aluminum halide includes aluminum chloride, lithium bromide, aluminum fluoride, and aluminum iodide.

[0017] In this invention, ultra-small aluminum quantum dots are obtained by one-step reduction using a strong reducing agent, which is selected from lithium aluminum hydride and sodium borohydride.

[0018] In step (3) of this invention, the molar ratio of the surface ligand to anhydrous aluminum halide is 1:1 to 3.

[0019] In this invention, the selection of different surface ligands significantly affects the fluorescence emission, thereby achieving tunable fluorescence emission. Surface ligand modification also ensures the stable preservation of quantum dots. The surface ligands are selected from one or more of oleic acid, octadecylamine, oleylamine, dodecylphosphonic acid, tetradecylphosphonic acid, p-xylbenzene diphosphonic acid, hexylphosphonic acid, and propylene diphosphonic acid.

[0020] In this invention, the modification reaction temperature depends on the specific reaction temperature required for different ligand modifications. For example, the modification of phosphonic acid derivatives generally maintains a temperature of 120℃-150℃.

[0021] Furthermore, in step (1) of this invention, both the container and the raw materials used must be anhydrous. The container is dried at 140°C for 12 hours to ensure that it is sufficiently dry. Anhydrous xylene is generally dehydrated by rotary evaporation before use. Aluminum halide must be anhydrous and of high purity.

[0022] The aluminum quantum dot material prepared by the synthesis method of the present invention is a small-sized, fluorescently tunable aluminum nanocluster material.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. The aluminum quantum dots prepared by this invention are extremely small, have good dispersibility, and exhibit significant photoluminescence. Furthermore, their fluorescence properties can be significantly affected by modifying the type of surface ligands.

[0025] 2. The aluminum quantum dots prepared by this invention can be used in the preparation and application of biosensors to improve biosensor performance, etc.

[0026] 3. The aluminum quantum dots prepared by this invention are expected to have significant advantages in photocatalysis.

[0027] 4. The synthetic route involved in this invention has the advantages of simple and readily available raw materials, simple and easy-to-implement reaction conditions, simple operation, and high product quality. Attached Figure Description

[0028] Figure 1 Transmission electron microscope (TEM) image of the small-sized 3.74±0.29 nm aluminum quantum dots prepared for Example 1;

[0029] Figure 2 The particle size distribution of small-sized aluminum quantum dots (3.74 ± 0.29 nm) prepared in Example 1;

[0030] Figure 3 The photoluminescence spectra of small-sized 3.74±0.29 nm aluminum quantum dots prepared in Example 1 after surface modification of dodecylphosphonic acid and tetradecylphosphonic acid are shown.

[0031] Figure 4Transmission electron microscope (TEM) image of aluminum quantum dots with small size (3.46 ± 0.03 nm) prepared in Example 2, modified with 6-phosphonohexanoic acid and hexylphosphonic acid as surface mixing ligands;

[0032] Figure 5 The particle size distribution of aluminum quantum dots with a small size of 3.46±0.03 nm, prepared in Example 2, after surface modification with 6-phosphonohexanoic acid and hexylphosphonic acid as surface mixing ligands;

[0033] Figure 6 The photoluminescence spectrum of aluminum quantum dots surface-modified with small-sized 3.46±0.03 nm 6-phosphonohexanoic acid and hexylphosphonic acid as surface mixing ligands prepared in Example 2 is shown. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Example 1: Synthesis of aluminum quantum dots with fluorescence emission wavelengths of 293 nm and 313 nm by surface ligand modification of dodecylphosphonic acid and tetradecylphosphonic acid, respectively.

[0036] 1) In the experimental preparation stage, place the flasks and other glass containers in an oven at 140℃ for 12 hours to ensure they are sufficiently dry. Pour 100 ml of anhydrous xylene into the flask and then rinse the flask containing xylene with argon gas for 5 min to remove any remaining air. The argon gas flow rate is 5 L / min. Weigh 1 mmol of AlCl3 and add it to the xylene, then sonicate to disperse it; the solution will be pale yellow at this point. Then weigh 3 mmol of TOAB (tetraoctylammonium bromide) and add it to the xylene, then sonicate to disperse it; the solution will become clear, transparent, and colorless. Rinse with argon gas for 5 min at a flow rate of 5 L / min.

[0037] 2) Add 2 ml of LiAlH4 (2 mol / L concentration) to the solution, using THF (tetrahydrofuran) as the solvent. Stir magnetically for 1 hour at room temperature, with the entire experiment conducted under an argon atmosphere. The stirring speed should be such that the solution just begins to vortex. Weigh 8 ml of DMF (dimethylformamide) and rotary evaporate at 60°C for 5 minutes to remove moisture. Weigh 450 mg of dodecylphosphonic acid (DDPA) and 560 mg of tetradecylphosphonic acid (TDPA) separately, dissolve them in the rotary-evaporated DMF, and then disperse by ultrasonication.

[0038] 3) Add ethanol to the solution after one hour of reaction in step 2) to quench unreacted LiAlH4 until no more bubbles are generated. Divide the resulting reaction solution into two portions. Then add the dodecylphosphonic acid dispersion and tetradecylphosphonic acid dispersion prepared in step 2) to the reaction solution respectively, and stir magnetically for 15 minutes at room temperature. The entire experiment was carried out under a nitrogen atmosphere.

[0039] 4) After the solution in step 3) reacts for 15 minutes, the solution is heated to 130°C and kept at that temperature for 6 hours. The entire experiment is conducted under a nitrogen atmosphere, with magnetic stirring at a speed of 1200 r / min.

[0040] 5) After the reaction in step 4) is complete, allow the solution to cool naturally to room temperature and begin liquid-liquid extraction. Take the upper layer of the extract and heat it for rotary evaporation to remove the organic solvents xylene, ethanol, and DMF. Add n-hexane to the flask after rotary evaporation and sonicate to dissolve the product. Then, take the solution and vacuum filter it. Take the filtered solution and concentrate it by rotary evaporation, and finally purify it by dialysis to obtain the final product.

[0041] In this example, dodecylphosphonic acid and tetradecylphosphonic acid were used to modify the surface of aluminum quantum dots. The prepared aluminum quantum dots had a particle size of 3.74±0.29 nm and showed fluorescence emission of 290 nm and 312 nm, respectively.

[0042] Example 2: Synthesis of small-sized aluminum quantum dots with hybrid surface ligands

[0043] We modified the surface of ultrasmall aluminum quantum dots by mixing two structurally similar but differently polarized surface ligand mixtures to achieve different fluorescence emission wavelengths. In our specific experimental protocol, we modified the aluminum quantum dot surface differently by varying the concentration of a mixture of 6-phosphonohexanoic acid (PHA) and hexylphosphonic acid (HPA). Specifically, we prepared 0.25M PHA and HPA ethanol solutions. We then prepared 1 ml of a 0.25M mixed phosphonic acid ligand solution from each of the two ethanol solutions, adding it to the reaction solution to maintain a final concentration of 2.5 mM. Other experimental procedures were consistent with those in Example 1. By changing the mixed concentration of the surface ligands, we prepared aluminum quantum dots with tunable fluorescence emission from 295 nm to 400 nm.

Claims

1. A method for synthesizing aluminum quantum dot materials with tunable fluorescence emission, characterized in that, Specifically, the following steps are included: (1) Dissolve the surfactant in anhydrous xylene, sonicate to homogenize, and purge the air in the reaction apparatus with argon to obtain a reverse micelle solution with a concentration of 1~3 mmol / L; add anhydrous aluminum halide to the prepared reverse micelle solution, sonicate to homogenize to obtain a reverse micelle solution containing a metal precursor; the surfactant is tetraoctylammonium bromide. (2) Under the protection of an inert gas atmosphere, add a strong reducing agent to the mixed solution obtained in step (1) and stir magnetically until the reaction is complete; add ethanol to quench the strong reducing agent that has not participated in the reaction; (3) Under an inert gas atmosphere, add the surface ligand to the solution obtained in step (2) and stir until homogeneous. Heat to the reaction temperature and keep warm to carry out the modification reaction. The surface ligand is composed of 6-phosphonohexanoic acid and hexylphosphonic acid. (4) Cool the solution obtained from step (3) to room temperature, extract by separation, and remove the organic solvent from the solution by rotary evaporation. (5) Add polar or non-polar solvent to the product of step (4) and disperse by ultrasonication, vacuum filter, rotary evaporation and concentration, and finally dialysis and purification to obtain colloidal aluminum quantum dots with adjustable fluorescence emission.

2. The method for synthesizing aluminum quantum dot materials with tunable fluorescence emission according to claim 1, characterized in that, The molar ratio of the anhydrous aluminum halide to the surfactant is 1:1 to 3.

3. The method for synthesizing aluminum quantum dot materials with tunable fluorescence emission according to claim 1, characterized in that, The strong reducing agent is selected from lithium aluminum hydride and sodium borohydride.

4. The method for synthesizing aluminum quantum dot materials with tunable fluorescence emission according to claim 1, characterized in that, The molar ratio of the surface ligand to anhydrous aluminum halide is 1:1 to 3.

5. The method for synthesizing aluminum quantum dot materials with tunable fluorescence emission according to claim 1, characterized in that, The specific reaction temperature is determined by the reaction conditions of the surface ligands used.

6. The method for synthesizing aluminum quantum dot materials with tunable fluorescence emission according to claim 1, characterized in that, The containers, raw materials, and solvents used in the reaction are all anhydrous.

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