Chiral quantum rods and methods of making the same

Abstract

The application discloses a chiral quantum rod and a preparation method thereof, wherein the preparation method of the chiral quantum rod comprises the following steps: preparing a CdSe-TOP core mother liquor, coating a CdS shell layer to obtain a CdSe / CdS quantum rod solution, and finally adding a cysteine solution to prepare the chiral quantum rod. In the application, TBP is used to replace conventional TOP, and the CdSe core is prepared at a temperature far higher than the boiling point of TBP, so that the activity of the Se-TBP precursor is improved, the Se-TBP precursor is more easily reacted with the first precursor, the proportion of the precursors which do not react in the system is reduced, the precursors adsorbed on the surface of the prepared CdSe core can be effectively reduced, the prepared CdSe core is easier to purify, and the success rate of preparing the chiral quantum rod can be improved.

Description

Technical Field

[0001] This invention relates to the field of materials chemistry, and in particular to a chiral quantum rod and its preparation method. Background Technology

[0002] Quantum dots, also known as nanocrystals, typically have a particle size between 2 and 20 nanometers (nm), about one hundred-thousandth the thickness of a human hair. Based on their significant quantum effects and narrow peak width, quantum dots have broad application prospects in fields such as solar cells, display devices, lighting, and biolabeling. Chiral quantum rods (NCs) are an emerging type of chiral material that exhibits unique optical activity. Constructing chiral NCs holds promise for applications in biological and optoelectronic fields, including 3D displays, information storage, biosensors, optical spintronics, and biological probes.

[0003] In existing quantum dot preparation processes, on the one hand, due to the low activity of selenium, the yield of CdSe cores is low under the same reaction conditions, and the particle size of CdSe cores is small (usually less than 2.4 nm). When relying on rapid cooling, the raw materials cannot react fully, resulting in low utilization. A large number of Cd and Se precursors exist in the reaction system in a free state. This means that during CdSe purification, a large number of Cd or Se precursors are still adsorbed on the surface of the quantum dots or around the quantum dots and participate in the growth process of CdSe / CdS quantum rods, causing a red shift in the wavelength of CdSe / CdS quantum rods, making it difficult to prepare green luminescent quantum rods. On the other hand, the excess precursors also participate in the shell growth process, which increases the difficulty of controlling the thickness of the quantum rod shell, and thus affects the control of the anisotropy of the quantum rod. Summary of the Invention

[0004] The main objective of this invention is to propose a method for preparing chiral quantum rods, aiming to solve the problem of low precursor utilization in the preparation of chiral quantum rods.

[0005] To achieve the above objectives, this invention proposes a method for preparing a chiral quantum rod, comprising: S1: Tri-n-octylphosphine was injected into the first precursor at 320-350℃, followed by Se-TBP precursor. The reaction was carried out under an argon atmosphere for 5-60s and then rapidly cooled to room temperature. After purification, CdSe-TOP core mother liquor was obtained. S2: After mixing the CdSe-TOP core mother liquor and the sulfur precursor, the mixture is rapidly injected into the first precursor at 290℃-350℃, and a CdSe / CdS quantum rod solution is obtained after the reaction. S3: Add the CdSe / CdS quantum rod solution to the cysteine ​​solution, stir for 24-48 hours, and then separate and purify to obtain the chiral quantum rod.

[0006] Furthermore, The first precursor was prepared by mixing tri-n-octylphosphine oxide, long-chain alkylphosphonic acid, and a cadmium source; The Se-TBP precursor was prepared by mixing a selenium source and tributylphosphine. The sulfur precursor was prepared by mixing a sulfur source with tri-n-octylphosphine under an argon atmosphere and heating to 80-110°C. The cysteine ​​solution is obtained by dissolving a mixture of D-cysteine ​​hydrochloride monohydrate or L-cysteine ​​hydrochloride monohydrate and an alkaline substance in deionized water, and the pH value of the cysteine ​​solution is 8-12.

[0007] Furthermore, In the first precursor, the molar ratio of long-chain alkylphosphonic acid to cadmium oxide is 0.7-10; In the Se-TBP precursor, the molar ratio of selenium source to TBP is 0.01-1; In the sulfur precursor, the molar concentration of sulfur is 0.2-2.5 mol / L; The cysteine ​​concentration in the cysteine ​​solution is 0.01-0.2 mol / L.

[0008] Preferably, the molar ratio of long-chain alkylphosphonic acid to cadmium oxide is 0.7-3.

[0009] Furthermore, In S1, the molar ratio of selenium to tri-n-octylphosphine in the Se-TBP precursor is 0.01-1; the molar ratio of cadmium oxide in the first precursor to selenium in the Se-TBP precursor is 0.01-1. In S2, the molar ratio of sulfur in the sulfur precursor to CdSe in the CdSe-TOP core mother liquor is 1000-100000; the molar ratio of cadmium oxide in the first precursor to CdSe in the CdSe-TOP core mother liquor is 500-20000. In S3, the molar ratio of CdSe / CdS quantum rod solution to cysteine ​​solution is 0.0001-0.01; Furthermore, In S3, the CdSe-TOP core mother liquor and sulfur precursor are mixed and then injected into the first precursor at 290℃-350℃.

[0010] Furthermore, The cadmium source is one or more of cadmium oxide, cadmium acetate, cadmium stearate, cadmium acetylacetonate, and dimethyl cadmium. The sulfur source is sulfur powder, thiourea, dodecyl mercaptan, or octyl mercaptan. The selenium source is selenium powder or selenurea.

[0011] Furthermore, In S1, the time for the cadmium source to completely dissolve is 30-120 minutes. In S2, the time to cool to room temperature is 1-5 minutes; In S3, the rapid injection is completed within 1-2 seconds; the reaction time after injecting the CdSe-TOP core mother liquor and sulfur precursor is 1-5 minutes.

[0012] This invention also proposes a chiral quantum rod, prepared by the above-described method, comprising, The CdSe quantum dot core and the CdS shell covering the CdSe quantum dot core are rod-shaped.

[0013] Furthermore, The luminescent chiral quantum rod emits wavelengths of 530-590 nm.

[0014] The technical solution of this invention has the following advantages: 1. This invention uses TBP instead of conventional TOP and prepares CdSe cores at temperatures far exceeding the boiling point of TBP, which improves the activity of the Se-TBP precursor, making it easier for the Se-TBP precursor to react with the first precursor. This reduces the proportion of unreacted precursors in the system, effectively reducing the amount of precursors adsorbed on the surface of the prepared CdSe cores. The resulting CdSe cores are also easier to purify, and the impact on the subsequent growth of CdSe / CdS rod-shaped structures is also reduced. 2. In the synthesis of CdSe / CdS quantum rods, this invention uses tri-n-octylphosphine from the sulfur precursor as a surfactant and solvent for synthesizing nanoparticles, which can dissolve and activate the precursor and control the size and morphology of the nanoparticles. The synthesized core / shell structure CdSe / CdS quantum rods have good stability and higher quantum yield. 3. The preparation method of this invention is simple, requires no additional equipment, and is easy to implement. Attached Figure Description

[0015] Figure 1 The diagram shows the structure of the chiral quantum rods obtained in various embodiments of the present invention. Figure 2 This is a transmission electron microscope image of the chiral quantum rod obtained in Example 6 of the present invention; Figure 3 This is a transmission electron microscope image of the chiral quantum rod obtained in Example 7 of the present invention; Figure 4 This is a transmission electron microscope image of the chiral quantum rod obtained in Example 1 of the present invention; Figure 5The image shows the ultraviolet absorption spectrum of the chiral quantum rod obtained in Example 1 of this invention. Figure 6 The circular dichroism spectrum of the chiral quantum rod obtained in Example 1 of this invention; Figure 7 The asymmetry factor g of the chiral quantum rod obtained in Example 1 of this invention CD A diagram illustrating the values; Figure 8 The circularly polarized fluorescence spectrum of the chiral quantum rod obtained in Example 1 of this invention; Figure 9 The asymmetry factor g of the chiral quantum rod obtained in Example 1 of this invention lum A diagram illustrating the values; Figure 10 This is a schematic diagram of the circularly polarized fluorescence DC value of the chiral quantum rod obtained in Example 1 of the present invention. Detailed Implementation

[0016] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0017] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0018] The following specific embodiments further illustrate the present invention. The examples given do not represent all embodiments of the present invention; only some embodiments are described as examples. Specific embodiments are as follows: The first precursor, Se-TBP precursor, sulfur precursor and cysteine ​​solution used in each embodiment and comparative example are pre-configured.

[0019] Preparation of the Se-TBP precursor used in each embodiment and comparative example: Weigh 0.4 mmol of selenium powder and add 4 ml (16.2 mmol) of tributylphosphine (TBP) to obtain a Se-TBP precursor with a selenium concentration of 1 mol / L.

[0020] Preparation of the sulfur precursors used in the various embodiments and comparative examples: A sulfur precursor with a sulfur concentration of 2.5 mol / L was prepared by dissolving 7.5 mmol of sulfur in 3 ml (6.7 mmol) of tri-n-octylphosphine (TOP).

[0021] Preparation of the cysteine ​​solution used in each example and comparative example: Dissolve 8 mmol of D- / L-cysteine ​​monohydrate in deionized water, then add 8 ml of 25% tetramethylammonium hydroxide (TMAH) solution to adjust the pH to 12, and dilute to 40 ml to obtain a cysteine ​​solution with a cysteine ​​concentration of 0.2 mol / L.

[0022] Example 1

[0023] This embodiment provides a method for preparing a chiral quantum rod, the specific steps of which are as follows: 1) Synthesis of CdSe-TOP core mother liquor: Weigh 3.9 mmol of tri-n-octylphosphine oxide (TOPO), 0.18 mmol of octadecylphosphonic acid (ODPA), and 0.23 mmol of cadmium oxide (CdO) and mix them in a 50 mL flask. Heat the mixture to 150 °C and expose it alternately to vacuum and argon atmosphere more than 5 times until cadmium oxide appears as a brown solid and the rest appears as a colorless liquid. Then, under an argon atmosphere, heat the solution to 320 °C to dissolve the cadmium oxide and obtain the first precursor.

[0024] 3.4 mmol of tri-n-octylphosphine was injected into the first precursor at 320 °C, followed by the injection of Se-TBP precursor. The reaction was maintained at a boiling state for 10 s, the heat source was removed, and the mixture was allowed to cool naturally to room temperature. An equal volume of n-hexane and twice the volume of anhydrous ethanol were added, and the mixture was centrifuged to obtain a solid. The solid was dissolved in n-hexane, ethanol was added, and the mixture was centrifuged to obtain CdSe quantum dot precipitate. A sample was taken for fluorescence photoluminescence testing, and the absorption wavelength of CdSe quantum dots was observed to be 488 nm. The CdSe quantum dot precipitate was dispersed in a tri-n-octylphosphine solution to obtain CdSe-TOP core mother liquor, in which the core particle size of CdSe quantum dots was 2.2 nm and the core concentration was 7 mmol / L.

[0025] 2) Preparation of CdSe / CdS quantum rods: Weigh 3.9 mmol of tri-n-octylphosphine oxide, 0.18 mmol of octadecylphosphonic acid, and 0.23 mmol of cadmium oxide and mix them in a 50 mL flask. Heat the mixture to 150 °C and expose it to vacuum and argon atmospheres alternately more than 5 times until cadmium oxide appears as a brown solid and the rest as a colorless liquid. Then, under an argon atmosphere, heat the solution to 320 °C to dissolve the cadmium oxide and obtain the first precursor.

[0026] 1.5 mL of CdSe-TOP core mother liquor was mixed with 3 mL of sulfur-modified substrate and sonicated for 5 min. The mixture was then rapidly injected into the first precursor prepared in this step at 350 °C. After reacting for 4 min, the precipitate, namely CdSe / CdS quantum rods, was obtained by centrifugation. A sample was taken and observed using a transmission electron microscope (TEM). The aspect ratio of the CdSe / CdS quantum rods was found to be 4.8. The TEM image is shown below. Figure 4 As shown, fluorescence photoluminescence testing revealed that the CdSe / CdS quantum rod emitted a wavelength of 530 nm, indicating it was a green-emitting quantum rod. It was dissolved in n-hexane solution and purified five times with methanol extraction. The top layer of n-hexane solution was preserved. The structure of the CdSe / CdS quantum rod is shown below. Figure 1 As shown.

[0027] 3) Preparation of chiral quantum rods: Add 2 mL of the above n-hexane solution to 2 mL of cysteine ​​solution. Stir the reaction mixture in the dark at room temperature for 48 hours, then let it stand for 1 hour to allow phase separation. Collect the bottom aqueous layer, dissolve it in a solution of chloroform and ethanol, and centrifuge to obtain the precipitate, which is the Cys-CdSe / CdS quantum rod, also known as the green luminescent chiral quantum rod. Dissolve the purified chiral quantum rod in deionized water and store it in the dark at room temperature. Its circular dichroism chromatogram is shown below. Figures 5 to 7 As shown, the gCD factor reaches 1.3 × 10⁻³, and its circularly polarized fluorescence spectrum is as follows. Figures 8 to 10 As shown, the glum factor reaches 5×10⁻⁴.

[0028] Example 2

[0029] This embodiment provides a method for preparing a chiral quantum rod. The difference from Embodiment 1 is that the 0.18 mmol octadecylphosphonic acid weighed in step 1 of Embodiment 1 is replaced with 0.27 mmol, and the 0.18 mmol octadecylphosphonic acid weighed in step 2 is replaced with 0.27 mmol, while the other conditions remain unchanged. The CdSe quantum dots have an absorption wavelength of 520 nm, a core particle size of 2.6 nm, and a core concentration of 8 mmol / L. The CdSe / CdS quantum rod has an emission wavelength of 570nm and is a yellow luminescent quantum rod. The chiral quantum rods achieved a gCD factor of 0.8 × 10⁻³ and a glum factor of 3.3 × 10⁻⁴.

[0030] Example 3

[0031] This embodiment provides a method for preparing a chiral quantum rod. The difference from Embodiment 1 is that the 0.18 mmol of octadecylphosphonic acid weighed in step 1 of Embodiment 1 is replaced with 0.36 mmol, and the 0.18 mmol of octadecylphosphonic acid weighed in step 2 is replaced with 0.36 mmol, while the other conditions remain unchanged. The CdSe quantum dots have an absorption wavelength of 550 nm, a core particle size of 3.0 nm, and a core concentration of 5 mmol / L. The CdSe / CdS quantum rod has an emission wavelength of 590nm and is an orange-emitting quantum rod. The chiral quantum rods achieved a gCD factor of 0.3 × 10⁻³ and a glum factor of 1.6 × 10⁻⁴.

[0032] Comparison with the chiral quantum rod data in Examples 1 and 2 shows that adding more octadecylphosphonic acid causes a red shift in the absorption wavelength of the prepared CdSe quantum dots, increases the core particle size, and ultimately results in a weaker chiral signal in the chiral quantum rod.

[0033] In the CdSe / CdS quantum rod prepared in Example 1, electrons in the lowest energy exciton state are localized in and around the CdSe core, resulting in strong electron-hole binding. In contrast, the lowest energy excitons in the CdSe / CdS quantum rods of Examples 2 and 3 are confined within the CdSe core. Therefore, the CdS shell of the CdSe / CdS quantum rod in Example 1 has a weaker ability to confine excitons, making it more likely to achieve high ligand-induced chiral activity. This provides favorable conditions for subsequent ligand exchange between the CdSe / CdS quantum rod and chiral molecules. The resulting chiral quantum rod exhibits unique anisotropy, achieving a better chiral signal response.

[0034] Example 4

[0035] This embodiment provides a method for preparing a chiral quantum rod. The difference from Embodiment 1 is that the 0.18 mmol octadecylphosphonic acid weighed in step 1 of Embodiment 1 is replaced with 0.11 mmol tetradecylphosphonic acid, and the 0.18 mmol octadecylphosphonic acid weighed in step 2 is replaced with 0.11 mmol tetradecylphosphonic acid, while the other conditions remain unchanged. The CdSe quantum dots have an absorption wavelength of 500 nm, a core particle size of 2.3 nm, and a core concentration of 6 mmol / L. The emission wavelength of the CdSe / CdS quantum rod is 545 nm; The chiral quantum rods achieved a gCD factor of 1.0 × 10⁻³ and a glum factor of 4.3 × 10⁻⁴.

[0036] Example 5

[0037] This embodiment provides a method for preparing a chiral quantum rod. The difference from Embodiment 1 is that the 3 ml sulfur precursor used in step 2 of Embodiment 1 is replaced with 7.5 ml sulfur precursor, while the other conditions remain unchanged. The CdSe / CdS quantum rod has an absorption wavelength of 550 nm, a core particle size of 3.0 nm, and a core concentration of 7 mmol / L. The emission wavelength of the CdSe / CdS quantum rod is 587 nm; The chiral quantum rods achieved a gCD factor of 0.6 × 10⁻³ and a glum factor of 2.2 × 10⁻⁴.

[0038] Comparison with the CdSe / CdS quantum rod data in Example 1 shows that as the proportion of S increases, the CdS shell grows faster, which in turn increases the thickness of the CdSe / CdS quantum rod during the CdS shell growth process, causing a redshift in the emission wavelength.

[0039] Example 6

[0040] This embodiment provides a method for preparing a chiral quantum rod. The difference from Embodiment 1 is that the reaction time of 4 minutes in step 2 of Embodiment 1 is replaced with a reaction time of 1 minute, while the other conditions remain unchanged. The CdSe / CdS quantum rod has an aspect ratio of 2.6, and its transmission electron microscopy image is shown below. Figure 2 As shown.

[0041] Example 7

[0042] This embodiment provides a method for preparing a chiral quantum rod. The difference from Embodiment 1 is that the reaction time of 4 minutes in step 2 of Embodiment 1 is replaced with a reaction time of 2 minutes, while the other conditions remain unchanged. The CdSe / CdS quantum rod has an aspect ratio of 3.4, and its transmission electron microscopy image is shown below. Figure 3 As shown.

[0043] Comparison with the CdSe / CdS quantum rod data in Examples 1 and 6 shows that as the reaction time of the mixture of CdSe-TOP core mother liquor and sulfur-driven substrate with the first precursor increases, the aspect ratio of the CdSe / CdS quantum rod also increases, as does the surface area to volume ratio and surface curvature. Since the physical and chemical properties of metal semiconductor nanocrystals are closely related to their exposed crystal faces, and the anisotropy of the CdSe / CdS quantum rod shell is mainly formed by different cores, surface energies of crystal faces, and growth rates in different directions, CdSe / CdS quantum rods with a larger aspect ratio have a higher proportion of uncoordinated surface atoms, resulting in superior anisotropy and catalytic performance.

[0044] Comparative Example 1 This comparative example provides a method for preparing quantum rods, which differs from Example 1 in that the tributylphosphine in the Se-TBP precursor in the first step of Example 1 is replaced with tri-n-octylphosphine, while the other conditions remain unchanged. like Figure 4 As shown, the CdSe core particle size is 3.7 nm and the core concentration is 3.9 mmol / L; The emission wavelength of the CdSe / CdS quantum rod is 620nm; The red luminescent chiral quantum rod has a gCD factor of 0.2×10⁻³ and a glum factor of 1×10⁻⁴.

[0045] Comparing the quantum rod data obtained in Comparative Example 1 with that in Example 1, it can be seen that tributylphosphine is crucial for the preparation of CdSe cores. Tri-n-octylphosphine has weaker activation ability than tributylphosphine, and a large amount of unreacted precursor remains in the system after the reaction. This means that the residual precursor will participate in the growth of the shell layer, resulting in a larger shell thickness, a certain wavelength redshift, and a reduction in the preparation efficiency of green-emitting CdSe / CdS quantum rods.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a chiral quantum rod, characterized in that, include: S1: Tri-n-octylphosphine was injected into the first precursor at 320-350℃, followed by Se-TBP precursor. The reaction was carried out under an argon atmosphere for 5-60s and then rapidly cooled to room temperature. After purification, CdSe-TOP core mother liquor was obtained. S2: After mixing the CdSe-TOP core mother liquor and the sulfur precursor, the mixture is rapidly injected into the first precursor at 290℃-350℃, and a CdSe / CdS quantum rod solution is obtained after the reaction. S3: Add the CdSe / CdS quantum rod solution to the cysteine ​​solution, stir for 24-48 hours, and then separate and purify to obtain the chiral quantum rod; The first precursor was prepared by mixing tri-n-octylphosphine oxide, long-chain alkylphosphonic acid and cadmium oxide; The Se-TBP precursor was prepared by mixing a selenium source and tributylphosphine. The sulfur precursor was prepared by mixing a sulfur source with tri-n-octylphosphine under an argon atmosphere and heating to 80-110°C. The cysteine ​​solution is obtained by dissolving a mixture of D-cysteine ​​hydrochloride monohydrate or L-cysteine ​​hydrochloride monohydrate and an alkaline substance in deionized water, and the pH value of the cysteine ​​solution is 8-12. In the first precursor, the molar ratio of long-chain alkylphosphonic acid to cadmium oxide is 0.7-10; In the Se-TBP precursor, the molar ratio of selenium source to TBP is 0.01-1; In the sulfur precursor, the molar concentration of sulfur is 0.2-2.5 mol / L; The cysteine ​​concentration in the cysteine ​​solution is 0.01-0.2 mol / L; In S1, the molar ratio of selenium to tri-n-octylphosphine in the Se-TBP precursor is 0.01-1; the molar ratio of cadmium oxide in the first precursor to selenium in the Se-TBP precursor is 0.01-1. In S2, the molar ratio of sulfur in the sulfur precursor to CdSe in the CdSe-TOP core mother liquor is 1000-100000; the molar ratio of cadmium oxide in the first precursor to CdSe in the CdSe-TOP core mother liquor is 500-20000. In S3, the molar ratio of CdSe / CdS quantum rods in the CdSe / CdS quantum rod solution to cysteine ​​in the cysteine ​​solution is 0.0001-0.

01.

2. The preparation method according to claim 1, characterized in that, In S2, the CdSe-TOP core mother liquor and sulfur precursor are mixed and then injected into the first precursor at 290℃-350℃.

3. The preparation method according to claim 1, characterized in that, The sulfur source is sulfur powder, thiourea, dodecyl mercaptan, or octyl mercaptan. The selenium source is selenium powder or selenurea.

4. The preparation method according to any one of claims 1-3, characterized in that, In S1, the time for cadmium oxide to completely dissolve is 30-120 min; In S1, the time to cool to room temperature is 1-5 minutes; In S2, the rapid injection is completed within 1-2 seconds; The reaction time after injecting CdSe-TOP core mother liquor and sulfur precursor is 1-5 min.

5. A chiral quantum rod, prepared by the method according to any one of claims 1-4, characterized in that, It includes a CdSe quantum dot core and a CdS shell covering the CdSe quantum dot core, wherein the CdSe quantum dot core and the CdS shell are rod-shaped.

6. The chiral quantum rod according to claim 5, characterized in that, The chiral quantum rod emits wavelengths of 530-590 nm.

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