A method for low-temperature one-pot green synthesis of CdSe quantum dots
The synthesis of CdSe quantum dots in air using a low-temperature one-pot method solves the problems of high temperature and high toxicity associated with the hot-injection method, achieving high-quality, low-cost quantum dot preparation suitable for optoelectronic devices, bioimaging, and display technologies.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING NORMAL UNIV AT ZHUHAI
- Filing Date
- 2025-08-11
- Publication Date
- 2026-06-23
AI Technical Summary
The existing hot-injection method for preparing CdSe quantum dots has problems such as high-temperature operation, high precision requirements, dependence on highly toxic and costly precursors, and low yield, which makes it difficult to meet the needs of large-scale industrial production.
CdSe quantum dots were synthesized in an air atmosphere using a low-temperature one-pot method. Long-chain fatty acids and non-coordinated solvents were used to avoid high temperature and anhydrous and oxygen-free environments. CdSe quantum dots were prepared by stirring the reaction and a simple purification step and surface passivation treatment were adopted to simplify the operation process.
This method enables the synthesis of high-quality CdSe quantum dots at low temperatures, reducing energy consumption and operational difficulty, minimizing environmental pollution, and improving the uniformity and yield of quantum dots, making it suitable for large-scale industrial production.
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Figure CN120681732B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of nano-semiconductor materials technology, and more specifically, to a method for the green synthesis of CdSe quantum dots in a low-temperature one-pot process. Background Technology
[0002] Colloidal cadmium selenide (CdSe) quantum dots exhibit great application potential in optoelectronic devices, bioimaging, and display technologies due to their unique photoelectric properties. Currently, the mainstream method for preparing high-quality CdSe quantum dots is the hot-injection method. This method involves rapidly injecting an active precursor (usually a selenium precursor) into a high-temperature (typically 300-320℃) cadmium precursor solution, utilizing the instantaneously generated supersaturation state to induce uniform nucleation, thereby obtaining quantum dots with uniform particle size and high luminescence efficiency.
[0003] While the hot-injection method performs relatively well in controlling quantum dot quality and yield, it has significant limitations in practical applications, especially for large-scale production. First, the process requires extremely high temperatures, leading to significant energy consumption and imposing stringent requirements on the heat resistance of the reaction equipment. The high-temperature environment also easily induces temperature fluctuations, affecting the precise control of quantum dot nucleation and potentially causing a widening of the final product's particle size distribution, thus compromising uniformity.
[0004] Secondly, the hot injection method itself requires considerable precision. The critical precursor injection step usually needs to be completed manually and rapidly, a process highly susceptible to human error, leading to poor experimental repeatability. If the injection speed is not fast enough to instantly form the required supersaturation state, the nucleation process of quantum dots will get out of control, resulting in uneven particle size distribution and reduced product quality.
[0005] More notably, this method heavily relies on a key precursor—trioctylphosphine selenide (TOP-Se). The preparation and storage of TOP-Se require extremely stringent conditions, necessitating a strictly anhydrous and oxygen-free environment. This significantly increases the operational difficulty and the complexity of production cost control. Furthermore, TOP-Se itself is expensive and quite toxic, not only raising the final production cost of quantum dots but also posing environmental and safety risks, contradicting current green and environmentally friendly production principles.
[0006] Furthermore, the core mechanism of the hot injection method—relying on the instantaneous formation of a supersaturated state to control nucleation—also limits the scale of a single synthesis. To ensure effective injection and controllable supersaturation, the volume of the reaction vessel is strictly limited, resulting in batch yields typically only in the tens of milligrams range. This low-yield characteristic makes it difficult to meet the industry's urgent need for large-scale, high-volume production.
[0007] In summary, although the hot-injection method is a mature technology for preparing high-quality CdSe quantum dots, its inherent drawbacks, such as high temperature, high operational precision requirements, dependence on highly toxic and costly precursors, and low yield that is difficult to scale up, severely restrict its promotion and application in large-scale industrial production. Therefore, developing a new, greener, milder, simpler, and easily scalable method for synthesizing high-quality CdSe quantum dots has significant practical importance 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 prior art.
[0009] To achieve the above objectives, this invention proposes a low-temperature one-pot green synthesis method for CdSe quantum dots, characterized by the following steps:
[0010] Cadmium oxide, selenium powder, and long-chain fatty acids were mixed in an air atmosphere, and a non-coordinated solvent with a boiling point ≥250℃ was added. The mixture was stirred at 160–250℃ for 5–180 minutes to obtain CdSe quantum dots.
[0011] Furthermore, the long-chain fatty acids include octadecanoic acid, eicosanoic acid, docosanoic acid, or hexadecanoic acid.
[0012] Furthermore, the long-chain fatty acid is docosanoic acid.
[0013] Furthermore, the noncoordinating solvent is selected from 1-octadecene, hexadecane, or liquid paraffin.
[0014] Furthermore, the noncoordinating solvent is 1-octadecene.
[0015] Furthermore, the molar ratio of cadmium oxide, selenium powder, and long-chain fatty acids is 1:1:1.
[0016] Furthermore, the reaction temperature was 180℃ and the reaction time was 20 minutes.
[0017] Furthermore, the purification process involves centrifugation of a mixture of hexane and an alcohol solvent, wherein the alcohol solvent includes ethanol, isopropanol, or methanol.
[0018] Furthermore, it also includes dispersing the CdSe quantum dots in dichloromethane, adding CdOAm passivation solution, and allowing the reaction to proceed statically.
[0019] The present invention also provides a CdSe quantum dot prepared by the above method, which has a fluorescence emission peak position of 485–650 nm and a full width at half maximum (FWHM) of ≤25 nm.
[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0021] This invention enables the synthesis of high-quality quantum dots at a relatively low temperature of 180℃, reducing energy consumption and the requirements for reaction vessels.
[0022] This invention eliminates the need for a strictly anhydrous and oxygen-free environment and manual rapid injection, simplifying the process and reducing operational difficulty and experimental errors.
[0023] This invention avoids the use of phosphine-containing reactants and uses low-toxicity reactants, thus reducing environmental pollution and harm to the human body.
[0024] The quantum dots synthesized by this invention have a narrow half-width (24 nm) and a large controllable range (485-650 nm), exhibiting excellent performance. This provides strong support for the widespread application of colloidal cadmium selenide quantum dots in optoelectronic devices, bioimaging, and display technologies. Furthermore, this method is easy to scale up for production, meeting the needs of large-scale industrial preparation and offering significant economic and social benefits. Attached Figure Description
[0025] Figure 1 Figure 1 shows the experimental results of quantum dots at different reaction times; A. Physical image; B. Fluorescence and UV-Vis absorption spectra; C. Size change of quantum dots within a 1-hour reaction time; D, E. Transmission electron microscopy images of quantum dots obtained with a 20-minute reaction time at different magnifications; F. Selected area electron diffraction pattern of quantum dots obtained with a 20-minute reaction time. Detailed Implementation
[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.
[0027] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.
[0028] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.
[0029] Example 1
[0030] In an air environment, weigh 51.36 mg (0.4 mmol) cadmium oxide (CdO), 31.6 mg (0.4 mmol) selenium powder, and 136 mg (0.4 mmol) docosanoic acid into a 25 mL three-necked flask. Add 4 mL of 1-octadecene (ODE) solvent and place a magnetic stir bar in the flask. Increase the temperature to 180 °C at a rate of 10 °C / min, maintain stirring at 800 rpm, and start timing. After reacting for 20 minutes, stop heating and allow to cool naturally to room temperature. Add 2 mL of n-hexane to disperse the precipitate, then add 4 mL of anhydrous ethanol dropwise, and centrifuge at 5000 rpm for 10 minutes. Disperse the precipitate with dichloromethane to obtain an orange-red colloidal solution.
[0031] Surface passivation treatment: First, a surface passivation solution was prepared. 333 mg (1.25 mmol) of Cd(Ac)₂·5H₂O was dissolved in 2.5 mL of oleylamine (OAm), and the solution was stirred at 120 °C until completely clear, yielding a CdOAm passivation solution. Subsequently, 10 mL of a quantum dot solution in dichloromethane was taken, and 0.2 mL of the above CdOAm passivation solution was added dropwise. The solution was allowed to stand at room temperature for 24 h. This passivation effectively repaired surface defects in the quantum dots, further improving fluorescence intensity.
[0032] Data: Fluorescence peak position 550 nm, half-maximum width at half-maximum 24 nm, quantum yield 20% (integrating sphere test), transmission electron microscopy shows particle size 2.8 nm (particle size distribution dispersion 4.3%). High-resolution electron microscopy shows lattice fringes of quantum dots. Selected area electron diffraction clearly shows three main diffraction peaks (111), (220), and (311). After surface passivation treatment, the quantum yield reaches 67%.
[0033] Example 2
[0034] The reaction temperature was adjusted to 160℃, and other conditions were the same as in Example 1. The reaction was stopped after 10 minutes, and the blue fluorescent quantum dots were purified.
[0035] Data: Fluorescence peak position 485 nm, full width at half maximum (FWHM) 25 nm, quantum yield 15%, particle size 2.2 nm (dispersion 4.8%). After surface passivation treatment, the quantum yield reached 56%.
[0036] Example 3
[0037] The reaction temperature was 200 °C, and the reaction time was extended to 120 minutes. The reaction solution changed from orange-red to deep red, and red quantum dots were obtained after purification.
[0038] Data: Fluorescence peak position 620 nm, half-maximum width at half-maximum 25 nm, quantum yield 22%, particle size 5.1 nm (dispersion 4.5%). XRD pattern shows characteristic peaks of (111) and (220) crystal planes, confirming the zincblende structure. After surface passivation treatment, the quantum yield reached 62%.
[0039] Example 4
[0040] Replace docosanoic acid with an equimolar amount of octadecanoic acid (115 mg), and react at 180 °C for 20 minutes.
[0041] Data: Fluorescence peak position 570 nm, full width at half maximum (FWHM) 27 nm, quantum yield 23%. After surface passivation treatment, the quantum yield reaches 58%.
[0042] Example 5
[0043] Add 513.6 mg CdO, 316 mg Se powder, and 1.36 g docosanoic acid to 40 mL of ODE at 10 times the feed ratio. Stir the mixture in a 500 mL reactor at 180°C for 30 minutes (ensuring uniform heating). After purification, 1.15 g of quantum dot solids are obtained.
[0044] Data: Fluorescence peak position 550 nm (shift <5 nm), full width at half maximum (FWHM) 25 nm, quantum yield 23%, verifying the scalability of the process. After surface passivation treatment, the quantum yield reaches 65%.
[0045] Comparative Example 1
[0046] Under argon protection, 0.4 mmol CdO was mixed with 0.8 mmol TDPA (tetradecylphosphonic acid) and 3.7768 g TOPO (trioctylphosphine oxide) and heated to 300 °C to dissolve. Separately, 0.4 mmol Se powder was dissolved in 0.32 mL TOP and rapidly injected into the reaction system. The reaction temperature was then lowered to 250 °C and the reaction was allowed to proceed for 3 minutes.
[0047] Data: The obtained quantum dots have a fibrous mineral structure, a fluorescence peak at 560 nm, a full width at half maximum (FWHM) of 30 nm, and a quantum yield of 25%. However, the operation requires strict anhydrous and oxygen-free conditions, with a single yield of only 42 mg, and the TOP-Se toxicity test results exceeded the limit (LC50 = 12 mg / kg).
[0048] Comparative Example 2
[0049] In Comparative Example 1, 0.8 mmol TDPA (tetradecylphosphonic acid) was replaced with an equimolar amount of stearic acid, and HDA (hexadecylamine) was added. The initial reaction temperature was adjusted to 320 °C. Separately, 2.0 mmol Se powder was dissolved in 1.6 mL TOP and rapidly injected into the reaction system. The reaction temperature was then lowered to 290 °C, and the reaction was allowed to proceed for 3 minutes.
[0050] Data: The obtained quantum dots have a fibrous mineral structure, a fluorescence peak at 630 nm, a full width at half maximum (FWHM) of 28 nm, and a quantum yield of 45%.
[0051] Comparative Example 3
[0052] In Comparative Example 1, 0.8 mmol TDPA (tetradecylphosphonic acid) was replaced with an equimolar amount of oleic acid, and 3.7768 g TOPO (trioctylphosphine oxide) was replaced with 4 mL ODE. Data: The obtained quantum dots mainly exhibited a fibrous mineral structure, with a fluorescence peak at 610 nm, a full width at half maximum (FWHM) of 30 nm, and a quantum yield of 15%. There was no significant difference compared to the results obtained in the air environment, confirming the feasibility of using an air atmosphere.
[0053] Experimental Example 1
[0054] The reaction time was adjusted to 60 minutes, with other conditions remaining the same as in Example 1. During the 60-minute synthesis period, samples were taken periodically for testing, and the results are as follows: Figure 1 As shown, within one hour of synthesis, the emission peak of the quantum dot ranged from 484 nm to 564 nm, with the full width at half maximum (FWHM) concentrated between 24 nm and 28 nm.
[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for the green one-pot synthesis of CdSe quantum dots at low temperature, characterized in that, Includes the following steps: Cadmium oxide, selenium powder and long-chain fatty acids were mixed in air, and a non-coordinated solvent with a boiling point ≥250℃ was added. The mixture was stirred at 160–250℃ for 5–180 minutes to obtain CdSe quantum dots. The molar ratio of cadmium oxide, selenium powder, and long-chain fatty acids is 1:1:
1. The reaction temperature was 180℃, and the reaction time was 20 minutes. Purification was performed by centrifugation using a mixture of hexane and an alcohol solvent, where the alcohol solvent included ethanol, isopropanol, or methanol.
2. The method according to claim 1, characterized in that, The long-chain fatty acids include octadecanoic acid, eicosanoic acid, docosanoic acid, or hexadecanoic acid.
3. The method according to claim 2, characterized in that, The long-chain fatty acid is docosanoic acid.
4. The method according to claim 1, characterized in that, The noncoordination solvent is selected from 1-octadecene, hexadecane, or liquid paraffin.
5. The method according to claim 1, characterized in that, The noncoordinating solvent is 1-octadecene.
6. The method according to claim 1, characterized in that, It also includes dispersing the CdSe quantum dots in dichloromethane, adding CdOAm passivation solution, and allowing the mixture to stand for reaction.
7. A CdSe quantum dot prepared by the method according to any one of claims 1-6, characterized in that, Its fluorescence emission peak position is 485–650 nm and its full width at half maximum (FWHM) is ≤25 nm.