Method for green synthesis of CdSe quantum dots by low-temperature one-pot method

Abstract

The invention provides a method for green synthesis of CdSe quantum dots by a low-temperature one-pot method, and relates to the technical field of nano semiconductor materials, and the method comprises the following steps: mixing cadmium oxide, selenium powder and long-chain fatty acid in an air atmosphere, adding a non-coordination solvent with a boiling point greater than or equal to 250 DEG C, carrying out a stirring reaction at 160-250 DEG C for 5-180 min, cooling, and purifying to obtain the CdSe quantum dots. The quantum dot synthesized by the method is narrow in half-peak width (24 nm), large in controllable range (485-650 nm) and excellent in performance, and powerful support is provided for wide application of the colloidal cadmium selenide quantum dot in the fields of photoelectric devices, biological imaging, display technologies and the like; and the method is easy for large-scale production, can meet the requirements of industrial large-scale preparation, and has good economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of nano-semiconductor materials, and in particular to a low-temperature one-pot green synthesis method for CdSe quantum dots. Background Art

[0002] Colloidal cadmium selenide (CdSe) quantum dots, due to their unique optoelectronic properties, show great potential for applications in optoelectronic devices, bioimaging, and display technology. Currently, the mainstream method for preparing high-quality CdSe quantum dots is hot injection. This method involves rapidly injecting an active precursor (typically a selenium precursor) into a high-temperature (typically 300-320°C) cadmium precursor solution. The resulting instantaneous supersaturation induces uniform nucleation, resulting in quantum dots with uniform particle size and high luminescence efficiency.

[0003] Although hot injection performs relatively well in controlling quantum dot quality and yield, its practical application, especially for large-scale production, has significant limitations. First, the process must be carried out at extremely high temperatures, which not only results in significant energy consumption but also places stringent demands on the heat resistance of the reaction equipment. High temperatures can also easily cause temperature fluctuations, affecting the precise control of quantum dot nucleation, and potentially leading to a wider particle size distribution in the final product, affecting its uniformity.

[0004] Secondly, the hot injection method itself requires considerable precision. The critical precursor injection step is often performed quickly and manually, a process that is prone to human error and leads to poor experimental reproducibility. If the injection speed is not fast enough to achieve the required supersaturation state instantly, the quantum dot nucleation process will become uncontrolled, resulting in uneven particle size distribution and reduced product quality.

[0005] More notably, this method relies heavily on a key precursor, trioctylphosphine selenide (TOP-Se). The preparation and storage conditions for TOP-Se are extremely demanding, requiring a strict anhydrous and oxygen-free environment. This significantly increases operational difficulty and complicates production cost control. Furthermore, TOP-Se itself is expensive and quite toxic, which not only increases the final quantum dot production cost but also poses environmental and safety risks, contradicting current green and environmentally friendly production concepts.

[0006] Furthermore, the core mechanism of hot injection—relying on the instantaneous supersaturation of injection to control nucleation—limits the scale of single-shot synthesis. To ensure injection efficiency and controllable supersaturation, the volume of the reaction vessel is strictly limited, resulting in single-batch yields typically in the tens of milligrams. This low yield makes it difficult to meet the urgent industrial demand for large-scale, mass-production.

[0007] In summary, although hot injection is a mature technology for preparing high-quality CdSe quantum dots, its inherent disadvantages, such as high temperature, high precision, reliance on highly toxic and expensive precursors, and low yields that are difficult to scale up, have severely restricted its promotion and application in industrial large-scale production. Therefore, the development of a new method for synthesizing high-quality CdSe quantum dots that is greener, milder, simpler to operate, and easily scalable has important practical significance and application value. Summary of the Invention

[0008] In view of this, the present invention proposes a low-temperature one-pot green synthesis method for CdSe quantum dots to solve the problems existing in the above-mentioned prior art.

[0009] To achieve the above object, the present invention proposes a low-temperature one-pot green synthesis method for CdSe quantum dots, characterized by comprising the following steps: Cadmium oxide, selenium powder and long-chain fatty acids are mixed in an air atmosphere, a non-coordinating solvent with a boiling point ≥250°C is added, and the mixture is stirred at 160-250°C for 5-180 minutes to obtain CdSe quantum dots.

[0010] Furthermore, the long-chain fatty acid includes octadecanoic acid, eicosanoic acid, docosanoic acid or hexacosanoic acid.

[0011] Furthermore, the long-chain fatty acid is behenic acid.

[0012] Furthermore, the non-coordinating solvent is selected from 1-octadecene, hexadecane or liquid paraffin.

[0013] Furthermore, the non-coordinating solvent is 1-octadecene.

[0014] Furthermore, the molar ratio of the cadmium oxide, selenium powder and long-chain fatty acid is 1:1:1.

[0015] Furthermore, the reaction temperature is 180° C., and the reaction time is 20 minutes.

[0016] Furthermore, the purification adopts a mixed system of n-hexane and alcohol solvents for centrifugal separation, wherein the alcohol solvent includes ethanol, isopropanol or methanol.

[0017] Furthermore, the method further comprises dispersing the CdSe quantum dots in dichloromethane, adding CdOAm passivation solution, and allowing the mixture to react.

[0018] The present invention also provides a CdSe quantum dot prepared by the above method, whose fluorescence emission peak is 485-650 nm and the half-peak width is ≤25 nm.

[0019] Compared with the prior art, the present invention has the following advantages: The present invention can synthesize high-quality quantum dots at a relatively low temperature of 180° C., thereby reducing energy consumption and requirements for reaction containers.

[0020] The present invention does not require a strict anhydrous and oxygen-free environment and manual rapid injection operation, simplifies the process, and reduces operational difficulty and experimental errors.

[0021] The present invention avoids the use of phosphine-containing reactants and adopts low-toxic reactants, thereby reducing environmental pollution and harm to human body.

[0022] The quantum dots synthesized by the present invention have a narrow half-width (24 nm), a large controllable range (485-650 nm), and excellent performance, providing strong support for the widespread application of colloidal cadmium selenide quantum dots in optoelectronic devices, bioimaging, and display technology. In addition, the method is easy to scale up for production, can meet the needs of industrial large-scale preparation, and has good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The experimental results of quantum dots with different reaction times; A. Actual image, B. Fluorescence and UV-visible absorption spectra, C. The image shows the size change of quantum dots within 1 hour of reaction time; D, E. Transmission electron micrographs of quantum dots obtained with a reaction time of 20 minutes at different magnifications, F. Selected area electron diffraction pattern of quantum dots obtained with a reaction time of 20 minutes DETAILED DESCRIPTION

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0026] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure raw materials or raw materials with a purity commonly used in the field of chemical synthesis.

[0027] Example 1 In an air atmosphere, 51.36 mg (0.4 mmol) of cadmium oxide (CdO), 31.6 mg (0.4 mmol) of selenium powder, and 136 mg (0.4 mmol) of docosanoic acid were weighed and placed in a 25 mL three-necked flask. 4 mL of 1-octadecene (ODE) solvent was added, and a magnetic stirrer was placed. The temperature was raised to 180°C at a rate of 10°C / min, while stirring was maintained at 800 rpm and a timer was started. After 20 minutes of reaction, heating was stopped and the mixture was allowed to cool naturally to room temperature. After dispersion with 2 mL of n-hexane, 4 mL of anhydrous ethanol was added dropwise, and the mixture was centrifuged at 5000 rpm for 10 minutes. The precipitate was dispersed with dichloromethane to obtain an orange-red colloidal solution.

[0028] Surface passivation treatment: First, prepare a surface passivation solution. Dissolve 333 mg (1.25 mmol) of Cd(Ac)2·5H2O in 2.5 mL of oleylamine (OAm) and stir at 120°C until the solution is completely clear. This CdOAm passivation solution is then added dropwise to 10 mL of the dichloromethane solution of the quantum dots. The solution is then allowed to react at room temperature for 24 hours. This passivation effectively repairs surface defects in the quantum dots, further enhancing their fluorescence intensity.

[0029] Data: Fluorescence peak at 550 nm, half-width at half-maximum 24 nm, quantum yield 20% (integrating sphere test), transmission electron microscopy shows a particle size of 2.8 nm (particle size distribution dispersion 4.3%). High-resolution electron microscopy reveals the lattice fringes of the quantum dots. Selected area electron diffraction clearly reveals the three main diffraction peaks (111), (220), and (311). After surface passivation treatment, the quantum yield reaches 67%.

[0030] Example 2 The reaction temperature was adjusted to 160° C., and other conditions were the same as those in Example 1. The reaction was stopped after 10 minutes, and blue fluorescent quantum dots were obtained by purification.

[0031] Data: Fluorescence peak at 485 nm, half-width at half maximum 25 nm, quantum yield 15%, particle size 2.2 nm (dispersion 4.8%). After surface passivation treatment, the quantum yield reaches 56%.

[0032] Example 3 Using a reaction temperature of 200°C and a reaction time of 120 minutes, the reaction solution turned from orange-red to deep red, and red light quantum dots were obtained after purification.

[0033] Data: Fluorescence peak at 620 nm, half-width at half maximum 25 nm, quantum yield 22%, particle size 5.1 nm (discrepancy 4.5%). XRD pattern shows characteristic peaks at (111) and (220) crystal planes, confirming the sphalerite structure. After surface passivation treatment, the quantum yield reaches 62%.

[0034] Example 4 Docosanoic acid was replaced with an equal molar amount of octadecanoic acid (115 mg), and the reaction was carried out at 180 °C for 20 min.

[0035] Data: Fluorescence peak at 570 nm, half-width at half maximum 27 nm, quantum yield 23%. After surface passivation treatment, the quantum yield reaches 58%.

[0036] Example 5 Add 40 mL of ODE to a 10-fold feedstock of 513.6 mg of CdO, 316 mg of Se powder, and 1.36 g of docosanoic acid. Stir the reaction in a 500 mL reactor at 180°C for 30 minutes (ensuring uniform heating). After purification, 1.15 g of quantum dot solid was obtained.

[0037] Data: Fluorescence peak at 550 nm (offset <5 nm), half-width at half-peak of 25 nm, and quantum yield of 23%, verifying the scalability of the process. After surface passivation treatment, the quantum yield reached 65%.

[0038] Comparative Example 1 Under argon, 0.4 mmol of CdO was mixed with 0.8 mmol of TDPA (tetradecylphosphonic acid) and 3.7768 g of TOPO (trioctylphosphine oxide) and heated at 300°C to dissolve. Separately, 0.4 mmol of Se powder was dissolved in 0.32 mL of TOP and rapidly injected into the reaction system. The reaction temperature was then lowered to 250°C and allowed to react for 3 minutes.

[0039] Data: The resulting quantum dots have a fibrous mineral structure, with a fluorescence peak at 560 nm, a half-width at half-maximum of 30 nm, and a quantum yield of 25%. However, the process requires strict anhydrous and oxygen-free conditions, resulting in a single yield of only 42 mg. Furthermore, the toxicity of TOP-Se exceeded the recommended limit (LC50 = 12 mg / kg).

[0040] Comparative Example 2 The 0.8 mmol of TDPA (tetradecylphosphonic acid) in Comparative Example 1 was replaced with an equimolar amount of stearic acid. HDA (hexadecylamine) was also added, and the reaction temperature was adjusted to 320°C. Separately, 2.0 mmol of Se powder was dissolved in 1.6 mL of TOP and rapidly injected into the reaction system. The reaction temperature was then lowered to 290°C and allowed to react for 3 minutes.

[0041] Data: The obtained quantum dots have a fiber mineral structure, with a fluorescence peak at 630 nm, a half-maximum width of 28 nm, and a quantum yield of 45%.

[0042] Comparative Example 3 The 0.8 mmol of TDPA (tetradecylphosphonic acid) in Comparative Example 1 was replaced with an equal molar amount of oleic acid, and 3.7768 g of TOPO (trioctylphosphine oxide) was replaced with 4 mL of ODE. Data: The resulting quantum dots primarily exhibited a fibrous mineral structure, with a fluorescence peak at 610 nm, a half-width (FWHM) of 30 nm, and a quantum yield of 15%. The results were not significantly different from those obtained in an air environment, confirming the feasibility of the experiment in an air environment.

[0043] Test Example 1 The reaction time was adjusted to 60 minutes, and the other conditions were the same as in Example 1. During the 60-minute synthesis time, samples were taken at regular intervals for testing. The results were as follows: Figure 1 As shown in the figure, within 1 hour of synthesis, the emission peak of the quantum dots increased from 484 nm to 564 nm, and the half-peak width was concentrated between 24 nm and 28 nm.

[0044] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A low-temperature one-pot green synthesis method for CdSe quantum dots, characterized in that: The following steps are involved: Cadmium oxide, selenium powder and long-chain fatty acids are mixed in an air atmosphere, a non-coordinating solvent with a boiling point ≥250°C is added, and the mixture is stirred at 160-250°C for 5-180 minutes to obtain CdSe quantum dots.

2. The method according to claim 1, characterized in that The long-chain fatty acid includes octadecanoic acid, eicosanoic acid, docosanoic acid or hexacosanoic acid.

3. The method according to claim 2, characterized in that The long-chain fatty acid is behenic acid.

4. The method according to claim 1, wherein The non-coordinating solvent is selected from 1-octadecene, hexadecane or liquid paraffin.

5. The method according to claim 1, wherein The non-coordinating solvent is 1-octadecene.

6. The method according to claim 1, characterized in that The molar ratio of the cadmium oxide, selenium powder and long-chain fatty acid is 1:1:

1.

7. The method according to claim 1, characterized in that The reaction temperature was 180° C., and the reaction time was 20 minutes.

8. The method according to claim 1, characterized in that The purification adopts a mixed system of n-hexane and alcohol solvents for centrifugal separation, wherein the alcohol solvent includes ethanol, isopropanol or methanol.

9. The method according to claim 1, characterized in that The method further comprises dispersing the CdSe quantum dots in dichloromethane, adding CdOAm passivation solution, and allowing the mixture to stand for reaction.

10. A CdSe quantum dot prepared by the method according to any one of claims 1 to 9, characterized in that: Its fluorescence emission peak is located at 485–650 nm and the half-peak width is ≤25 nm.

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