A method for preparing highly luminescent cadmium selenide quantum dots without water or oxygen isolation

Abstract

The present invention discloses a method for preparing highly luminescent cadmium selenide quantum dots without water and oxygen isolation, comprising: step S1, precursor preparation; step S2: synthesizing quantum dots; step S3, sample purification; step S4, ligand exchange preparation of products. In the present invention, since there is no need to prepare a shell structure, the problems of complex operation, high cost, low efficiency, poor repeatability, etc. of traditional quantum dot synthesis are further avoided, and the surface properties of the material are more controllable, which is conducive to further surface chemical regulation and is used in the fields of optoelectronic display, photovoltaics, fluorescence sensing, etc.

Description

Technical Field

[0001] The invention relates to the technical field of quantum dot contracts, and in particular to a method for preparing highly luminescent cadmium selenide quantum dots without water or oxygen isolation. Background Art

[0002] II-VI quantum dots have a wide range of potential applications, including light-emitting diodes (LEDs), solar cells, chemical sensors, optoelectronics, and bio-imaging / labeling, and have won the Nobel Prize. One of the current developments is to achieve further green synthesis to meet the needs of large-scale production and application of quantum dots. However, the synthesis of high-quality quantum dots is still highly dependent on anhydrous and oxygen-free operating conditions, such as the use of glove boxes or Schlenk pipelines for related synthesis operations.

[0003] Existing solutions:

[0004] Option 1: Grow a semiconductor shell layer with a larger bandgap width than the core material on the surface of the quantum dots, such as synthesizing CdSe / CdS and CdSe / ZnS core-shell structures. However, the core-shell passivation method not only needs to consider the spontaneous nucleation of the shell material, but also needs to ensure that the shell can grow uniformly and controllably on the surface of the quantum dots. To achieve this goal, the temperature and injection conditions must be strictly controlled. This obviously increases the time cost and operation complexity of quantum dot preparation, and increases the uncertainty of large-scale production of quantum dots. The shell structure also has the function of inhibiting carrier migration between quantum dots, which has a serious impact on the application of thin film devices based on quantum dots.

[0005] Option 2: Organic ligand passivation. Related work has shown that alkylamine and carboxylic acid metal salt ligands can effectively passivate surface defects of quantum dots and enhance the luminescence of quantum dots.

[0006] In summary:

[0007] The traditional method of preparing highly luminescent cadmium chalcogenide quantum dots requires water and oxygen isolation, which is complicated to operate, has high equipment and labor costs, and is easily affected by environmental factors.

[0008] In addition, the luminescence efficiency of quantum dots is generally improved through a core-shell structure, which has problems such as complex operation, high cost, low efficiency, poor repeatability, and the surface properties of the core material are difficult to reflect.

[0009] To sum up the above problems, we propose a method to prepare highly luminescent cadmium selenide quantum dots without water or oxygen isolation. Summary of the invention

[0010] The purpose of the invention is to provide a method for preparing high-luminescence cadmium selenide quantum dots without water or oxygen isolation, thereby solving the existing problems.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] A method for preparing highly luminescent cadmium selenide quantum dots without water or oxygen isolation, comprising:

[0013] Step S1, precursor preparation;

[0014] Step S2: synthesizing quantum dots;

[0015] Step S3, purifying the sample;

[0016] Step S4, preparing the product by ligand exchange.

[0017] Preferably, the step 1 comprises the following steps:

[0018] Drying cadmium acetate dihydrate at 90-120° C. for 1.5-3 h and repeatedly grinding to remove moisture to obtain anhydrous cadmium acetate;

[0019] In a 25 ml round-bottom flask, disperse 600-850 mg of selenium powder in 5-8 ml of tri-n-octylphosphine TOP, stir at room temperature for 2.5-3.5 h to obtain a transparent solution, i.e., TOP-Se stock solution, which is sealed for storage.

[0020] Preferably, the step S2 includes the following steps:

[0021] 0.2 mmol of cadmium acetate powder and 1 mmol of oleic acid OAm were added to a glass reaction bottle, mixed, and vigorously shaken for 5-10 min, then slightly heated, and continued to shake until the solid dissolved to obtain a clear solution;

[0022] Add 3-7ml1-octadecene ODE and 0.3-0.9ml oleylamine OLAm, and stir the mixture at 180-300 ° C for 2-5min;

[0023] Rapidly inject 0.5-1.2 ml of TOP-Se solution, and after 0.5-10 min, take out the sample and cool it to room temperature to obtain the sample;

[0024] After synthesis, the samples were purified.

[0025] Preferably, the step S3 includes the following steps:

[0026] Add an appropriate amount of dichloromethane to the solution, and then add an appropriate amount of ethanol until the solution becomes turbid;

[0027] After centrifugation at 6000 rpm for 5 min, the supernatant was discarded and the precipitate was collected;

[0028] A mixture of dichloromethane and ethanol in a 1:1 ratio (vol / vol) was added sequentially, and centrifugation at 6000 rpm for 2 min was repeated;

[0029] This process of centrifugation and re-dispersion was repeated three times to remove unreacted precursor and dissociated ligand;

[0030] The CdSe quantum dots were dispersed in dichloromethane and sealed for storage and labeled as “raw quantum dots QDs”.

[0031] Preferably, the step S4 includes the following steps:

[0032] For Z*-type cadmium carboxylate-amine ligands, 2.5 mmol of anhydrous cadmium acetate was mixed in 1-3 ml of the corresponding octylamine OAm by shaking at room temperature to obtain CdOAm in the form of a clear solution;

[0033] Take an appropriate amount of CdSe quantum dots and 1-2 ml of dichloromethane and add them to a 2 ml vial, and adjust the concentration of quantum dots to 0.55 µM-0.75 µM;

[0034] 30 µL of different ligands were added and the reactions were allowed to proceed at room temperature and characterized at different time points and stored sealed.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The preparation process of the invention is simple, the operation flow is simple, and no water or oxygen isolation is required, which not only reduces the equipment cost, but also reduces the labor cost and the operation difficulty.

[0037] The preparation conditions of the invention are mild, conventional harmful chemicals and high temperature conditions are not used, and it is beneficial to protect the environment and human health.

[0038] The quantum dots prepared by the present invention have the characteristics of long-term stability and high luminescence.

[0039] In the present invention, since there is no need to prepare a shell structure, the problems of complex operation, high cost, low efficiency, poor repeatability, etc. of traditional quantum dot synthesis are further avoided, and the surface properties of the material are more controllable, which is conducive to further surface chemical regulation and is used in optoelectronic display, photovoltaic, fluorescence sensing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0042] Embodiment 1:

[0043] A method for preparing highly luminescent cadmium selenide quantum dots without water or oxygen isolation, comprising:

[0044] Step S1, precursor preparation;

[0045] Drying cadmium acetate dihydrate at 90-120° C. for 1.5-3 h and repeatedly grinding to remove moisture to obtain anhydrous cadmium acetate;

[0046] In a 25 ml round-bottom flask, disperse 600-850 mg of selenium powder in 5-8 ml of tri-n-octylphosphine TOP, stir at room temperature for 2.5-3.5 h to obtain a transparent solution, i.e., TOP-Se stock solution, which is sealed for storage.

[0047] Step S2: synthesizing quantum dots;

[0048] Add 0.2 mmol of cadmium acetate powder and 1 mmol of oleic acid into a 15 ml glass bottle and shake until a clear solution is obtained;

[0049] Add 3-7ml1-octadecene ODE and 0.3-0.9ml oleylamine OLAm, and stir the mixture at 180-300 ° C for 2-5min;

[0050] Rapidly inject 0.5-1.2 ml of TOP-Se solution, and after 0.3-0.6 min, take out the sample and cool it to room temperature to obtain the sample;

[0051] After synthesis, the samples were purified.

[0052] Step S3, purifying the sample:

[0053] Add an appropriate amount of dichloromethane to the solution, and then add an appropriate amount of ethanol until the solution becomes turbid;

[0054] After centrifugation at 6000 rpm for 5 min, the supernatant was discarded and the precipitate was collected;

[0055] A mixture of dichloromethane and ethanol in a 1:1 ratio (vol / vol) was added sequentially, and centrifugation at 6000 rpm for 2 min was repeated;

[0056] This process of centrifugation and re-dispersion was repeated three times to remove unreacted precursor and dissociated ligand;

[0057] The CdSe quantum dots were dispersed in dichloromethane and sealed for storage and labeled as “raw quantum dots QDs”.

[0058] Step S4, ligand exchange to prepare product:

[0059] For Z*-type cadmium carboxylate-amine ligands, 2.5mmol of anhydrous cadmium acetate was mixed with n-butylamine BAm and n-octylamine OAm at room temperature to obtain CdBAm and CdOAm, or mixed with dodecylamine LAm, oleylamine OLAm and dioctylamine DOAm at 100°C to obtain CdLAm, CdOLAm and CdDOAm. All the above solutions need to be shaken to obtain clear solutions;

[0060] Take an appropriate amount of CdSe quantum dots and 1-2 ml of dichloromethane and add them to a 2 ml vial, and adjust the concentration of quantum dots to 0.55 µM-0.75 µM;

[0061] 30 µL of different ligands were added and the reactions were allowed to proceed at room temperature and characterized at different time points and stored sealed. Specific embodiment 1:

[0063] (1) Synthesis of quantum dots

[0064] like Figure 1 As shown, first, cadmium acetate dihydrate was dried at 110 ° C for 3 hours and repeatedly ground to remove moisture to obtain anhydrous cadmium acetate. Then, in a 25 ml round-bottom flask, 790 mg of selenium powder was dispersed in 6.67 ml of tri-n-octylphosphine (TOP), stirred at room temperature for 3 hours to obtain a transparent solution, namely TOP-Se stock solution (1.5M), and then sealed for storage. Next, 46 mg (0.2 mmol) of cadmium acetate powder and 1 mmol of oleic acid were added to a 15 ml glass bottle and shaken until a clear solution was obtained. Subsequently, 4 ml of 1-octadecene (ODE) and 0.5 ml of oleylamine (OLAm) were added, and the mixture was stirred at 240 ° C for 3 minutes. Subsequently, 0.8 ml of TOP-Se solution (1.5M) was quickly injected, and after 30 seconds, the sample was taken out and cooled to room temperature to obtain the sample. After synthesis, the sample was purified. First, an appropriate amount of dichloromethane was added to the solution, and then an appropriate amount of ethanol was added until the solution became turbid. After centrifugation at 6000rpm for 5 minutes, the supernatant was discarded and the precipitate was collected. Subsequently, a mixture of dichloromethane and ethanol in a 1:1 ratio (volume / volume) was added in sequence, and centrifugation at 6000rpm was repeated for 2 minutes. This centrifugation and re-dispersion process was repeated three times to remove unreacted precursors and dissociated ligands. Finally, the CdSe quantum dots were dispersed in dichloromethane and sealed for storage and labeled as "raw QDs". The entire reaction process does not require an inert gas atmosphere, but should be carried out in a fume hood to reduce gas evaporation at high temperatures.

[0065] (2) Ligand exchange reaction

[0066] For Z*-type cadmium carboxylate-amine ligands, 2.5 mmol of anhydrous cadmium acetate was mixed in 3 ml of the corresponding amine at room temperature (for CdBAm and CdOAm) or 100 °C (for CdLAm, CdOLAm, and CdDOAm) by shaking to obtain a clear solution.

[0067] Afterwards, take an appropriate amount of CdSe quantum dots and 1.5 ml of dichloromethane into a 2 ml vial to adjust the concentration of quantum dots to about 0.75 µM. Subsequently, add 30 µL of different ligands, and allow the reaction to proceed at room temperature and characterize at different time points. To prevent solvent evaporation, seal and store.

[0068] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing highly luminescent cadmium selenide quantum dots without water or oxygen isolation, characterized in that: include: Step S1, precursor preparation: drying and grinding cadmium acetate dihydrate to obtain anhydrous cadmium acetate, dispersing selenium powder in tri-n-butylphosphine oxide (TOP) to prepare TOP-Se stock solution; Step S2, synthesizing quantum dots: mixing anhydrous cadmium acetate, oleic acid, dodecyl alcohol ether (ODE), and oleyl amide (OLAm), injecting into TOP-Se solution, and cooling after reaction; Step S3, sample purification: centrifugation and purification with dichloromethane and ethanol to remove unreacted precursors; Step S4, ligand exchange: reacting the purified CdSe quantum dots with a Z*-type cadmium carboxylate-amine ligand at room temperature, wherein the ligand is selected from CdLAm, CdOLAm or CdDOAm.

2. The method for preparing high-luminescence cadmium selenide quantum dots without water and oxygen isolation according to claim 1, characterized in that: In step S1, the mass volume ratio of selenium powder to TOP is 600-850 mg:5-8 mL.

3. The method for preparing high-luminescence cadmium selenide quantum dots without water and oxygen isolation according to claim 1, characterized in that: In step S2, the reaction temperature is 240-260° C. and the reaction time is 2-3 minutes.

4. The method for preparing high-luminescence cadmium selenide quantum dots without water and oxygen isolation according to claim 1, characterized in that: In step S3, the centrifugal speed is 6000 rpm, and the centrifugation is repeated three times.

5. The method for preparing high-luminescence cadmium selenide quantum dots without water and oxygen isolation according to claim 1, characterized in that: In step S4, the Z*-type cadmium carboxylate-amine ligand is CdOLAm, and the reaction time is 10-30 minutes.

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