A method for synthesizing CdSe / CdS colloidal semiconductor nanocrystal dimers

Abstract

The application discloses a synthesis method of CdSe / CdS colloidal semiconductor nanocrystal dimers, which comprises the following steps: preparing monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal monomers by using a multistage solvent precipitation strategy on a toluene solution of synthesized wurtzite CdSe / CdS colloidal semiconductor nanocrystals; and then synthesizing CdSe / CdS colloidal semiconductor nanocrystal dimers with a splicing yield of 80% by using a branched long-chain alkyl amine 2-octyl-dodecyl amine as a ligand, heating and inducing splicing of the nanocrystal monomers and again using the multistage solvent precipitation strategy under an inert atmosphere. The synthesis method has the advantages of simple flow, rapid preparation and high efficiency, and the prepared colloidal semiconductor nanocrystal dimers can be widely applied to frontier fields such as quantum information, photoelectric devices and biosensing.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial synthesis technology, and relates to a controllable synthesis method for colloidal semiconductor nanocrystal dimers, specifically a method for directional splicing synthesis using CdSe / CdS core-shell structured nanocrystals as building blocks. Background Technology

[0002] Colloidal semiconductor nanocrystal dimers with strong coupling interactions have shown significant application potential in quantum information science. The controllable synthesis of single-crystal dimers using monodisperse colloidal semiconductor nanocrystals as building blocks through precise crystal facet matching has become a core challenge and research hotspot in this field. Among them, CdSe / CdS core-shell nanocrystals are considered ideal material systems for constructing dimers due to their tunable size, morphology, and chemical composition. However, existing synthesis strategies still face significant bottlenecks in terms of yield, directionality, and scalability, mainly in the following aspects:

[0003] (1) Complex synthesis process: Traditional methods rely on DNA-mediated site-specific modification of nanocrystal surfaces to achieve spatial localization of splicing. This strategy not only requires extremely high precision in surface chemical modification, but also the modified ligands are prone to oxidation and desorption during the reaction, resulting in poor stability. In addition, the multi-step modification process significantly increases the complexity and time cost of the process, making it difficult to achieve large-scale preparation.

[0004] (2) Low yield of directional splicing: Existing methods generally lack efficient control over crystal plane selectivity. For example, although the SiO2 template method developed by UriBanin’s group can achieve a certain degree of splicing, the yield of directional splicing is still low (usually less than 30%). Traditional methods such as solvent evaporation-induced self-assembly and electrostatic adsorption are more likely to lead to random aggregation and polymer generation, which cannot meet the requirements of high-precision splicing.

[0005] (3) Difficulty in product separation and purification: In addition to the target dimer, there are a large number of unreacted monomers, polymers and other byproducts in the synthesis system. Since the difference between dimers and trimers is small in hydrodynamic size, conventional separation techniques such as size exclusion chromatography have limited resolution, resulting in the purity of the final product usually being less than 50%, which seriously limits its application performance in fields such as quantum optical devices.

[0006] In-depth analysis reveals that the essence of the above problems lies in the failure to achieve coordinated control across multiple scales: precise regulation of the core-shell structure, surface ligand stabilization, and directional crystal assembly. Specifically, traditional ligands are prone to desorption or degradation under high temperatures or chemical environments, which not only increases surface defects and degrades optical properties but also disrupts the surface chemical environment required for directional assembly. At the same time, the lack of precise control over the thermodynamics and kinetics of the bonding interface makes it difficult to achieve high selectivity in the assembly process.

[0007] It is worth noting that wurtzite-structured CdSe / CdS core-shell nanocrystals possess well-defined crystal orientations, excellent optical properties, and a mature synthesis process, providing an ideal platform for overcoming the aforementioned bottlenecks. The key lies in the ability to utilize organic ligands to differentially regulate the surface energy of different crystal faces. Through the rational design of ligand chemistry, selective activation and directional splicing of crystal faces can be achieved, thereby constructing high-quality single-crystal dimers.

[0008] Therefore, developing a simple, highly oriented, and scalable solution-phase synthesis method for dimers using wurtzite CdSe / CdS core-shell nanocrystals as monomers is of great significance for promoting the development of applications such as quantum luminescence, single-photon sources, and nano-optoelectronic integrators. Summary of the Invention

[0009] To address the core shortcomings of existing methods for preparing colloidal semiconductor nanocrystal dimers, such as poor controllability of directional splicing, low product yield, and low separation efficiency, especially the technical bottleneck of achieving synergistic control of "core-shell structure regulation, ligand stabilization, and crystal plane orientation" in the CdSe / CdS system, this invention provides a simple, high-yield, high-orientation, and well-separated method for synthesizing CdSe / CdS colloidal semiconductor nanocrystal dimers. This method aims to meet the demand for high-orientation-yield dimer materials in cutting-edge fields such as quantum information, optoelectronic devices, and biosensors.

[0010] The method for synthesizing CdSe / CdS colloidal semiconductor nanocrystal dimers provided by this invention includes the following steps:

[0011] Step 1: Purification of wurtzite CdSe / CdS colloidal semiconductor nanocrystals

[0012] A1: Add acetone dropwise to a toluene solution of wurtzite CdSe / CdS colloidal semiconductor nanocrystals until the solution becomes slightly turbid, then stop adding acetone and centrifuge to separate the nanocrystals.

[0013] A2: Add acetone to the supernatant obtained by centrifugation in A1, continue centrifugation, and repeat the above-mentioned steps of adding acetone and centrifugation until the bottom precipitate obtained by centrifugation dissolves in toluene to obtain a toluene solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals.

[0014] A3: Add methanol to a toluene solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals, heat at 80-100℃ for 1-3 min, centrifuge, redissolve the precipitate in toluene and add methanol, then repeat the aforementioned heating treatment and centrifugation; then dissolve the precipitate in octadecene to obtain a thermally purified monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal dispersion.

[0015] Step 2: Synthesis of CdSe / CdS colloidal semiconductor nanocrystal dimers

[0016] 2-Octyl-dodecaneamine and octadecene were mixed and heated to 140–180 °C under inert gas protection. After degassing for 10–15 min, the temperature was further increased to 240–290 °C. Then, the above-mentioned thermally purified monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal dispersion was added. The mixture was stirred at a constant temperature for 20–80 min. After the reaction was completed, the mixture was cooled to room temperature to obtain a mixed solution containing CdSe / CdS colloidal semiconductor nanocrystal dimers.

[0017] Step 3: Separation and purification of CdSe / CdS colloidal semiconductor nanocrystal dimers

[0018] B1: Add 2 to 4 times the volume of acetone to a mixed solution containing CdSe / CdS colloidal semiconductor nanocrystal dimers, centrifuge, and collect the bottom precipitate.

[0019] B2: Dissolve the precipitate in B1 in toluene, then add acetone dropwise until the solution becomes slightly turbid. Stop adding acetone and centrifuge.

[0020] B3: Add acetone to the supernatant obtained in B2, continue centrifugation, and repeat the above-mentioned steps of adding acetone and centrifugation until the bottom precipitate obtained by centrifugation dissolves in toluene to obtain high-yield CdSe / CdS colloidal semiconductor nanocrystalline dimers.

[0021] Furthermore, in step 1A2 above, it is preferable that the amount of acetone added to the supernatant is 0.15 to 0.25 times the volume of the supernatant.

[0022] Furthermore, in step 1A3 above, it is preferable to add 2 to 4 times the volume of methanol to a toluene solution of monodisperse wurtzite CdSe / CdS core-shell colloidal semiconductor nanocrystals, heat the solution at 90 to 100 °C for 1 to 3 min, centrifuge the solution, redissolve the precipitate in toluene, add 2 to 4 times the volume of methanol to the solution, and then perform the aforementioned heating treatment and centrifugation.

[0023] Furthermore, in step 2 above, it is preferable to mix 2-octyl-dodecaneamine and octadecene, heat to 160 °C under inert gas protection, degas for 10 min, and then continue to heat to 280 °C. Then, add the above-mentioned thermally purified monodisperse wurtzite CdSe / CdS core-shell colloidal semiconductor nanocrystal dispersion, and stir at a constant temperature for 30 min.

[0024] Furthermore, in step 2 above, the preferred volume ratio of the 2-octyl-dodecaneamine, octadecene, and the thermally purified monodisperse wurtzite CdSe / CdS core-shell colloidal semiconductor nanocrystal dispersion is 8–12:15–20:1.

[0025] Furthermore, in step 3B3 above, it is preferable that the amount of acetone added to the supernatant is 0.05 to 0.4 times the volume of the supernatant.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Good monodispersity of monomers: By using a multi-stage solvent precipitation strategy on a toluene solution of wurtzite CdSe / CdS colloidal semiconductor nanocrystals, a monodisperse nanocrystal solution was obtained, which provides uniform building blocks for directional splicing and solves the problem of non-directional splicing caused by uneven monomer morphology in the prior art.

[0028] 2. Significantly improved yield of directional splicing: By leveraging the steric hindrance and crystal face selectivity of 2-octyl-dodecaneamine, the splicing yield of nanocrystalline dimers can exceed 60%, which is far superior to the traditional template method or solvent-induced method, effectively solving the technical bottleneck of difficult directional splicing.

[0029] 3. High product yield and separation efficiency: The multi-stage solvent precipitation strategy achieves efficient separation based on density differences, with a final product yield of up to 80%, overcoming the shortcomings of low separation efficiency and low yield of existing separation technologies.

[0030] 4. Simple process and wide applicability: The entire process does not require complex surface modification or template assistance, and adopts one-step splicing of solution phase, simplifying the operation process; this method can be extended to the preparation of other II-VI group semiconductor nanocrystalline dimers, and has good universality. Attached Figure Description

[0031] Figure 1 This is a transmission electron microscope (TEM) image of the monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal monomer obtained in step A2 of Example 1.

[0032] Figure 2 This is a size distribution diagram of the monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal monomers obtained in step A2 of Example 1.

[0033] Figure 3 This is a transmission electron microscope (TEM) image of the CdSe / CdS colloidal semiconductor nanocrystal dimer obtained in step 3 of Example 1.

[0034] Figure 4 This is a size distribution diagram of the CdSe / CdS colloidal semiconductor nanocrystal dimer obtained in step 3 of Example 1. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0036] The wurtzite CdSe / CdS core-shell colloidal nanocrystals used in Example 1 below have a particle size of 12 nm ± 1 nm and were synthesized according to the method described in the reference "Wang, Y.; Pu, C.; Lei, H.; Qin, H.; Peng, X. CdSe@CdS Dot@PlateletNanocrystals: Controlled Epitaxy, Monoexponential Decay of Two-Dimensional Exciton, and Nonblinking Photoluminescence of Single Nanocrystal. J. Am.Chem. Soc. 2019, 141 (41), 17617−17628." Example 1

[0037] Step 1: Purification of wurtzite CdSe / CdS colloidal semiconductor nanocrystals

[0038] A1: Add acetone dropwise to a 4 mL toluene solution of wurtzite CdSe / CdS colloidal nanocrystals until the solution becomes slightly turbid. Stop adding acetone and immediately transfer the mixture to a high-speed centrifuge. Centrifuge at 12,000 rpm for 1 min. Collect the bottom precipitate and dissolve it in 1 mL toluene as sample 1 for separating gradient monomers.

[0039] A2: Add 0.2 times the volume of acetone to the supernatant obtained from centrifugation in A1, and continue centrifugation. Repeat the above-mentioned steps of adding acetone and centrifugation on the supernatant. Collect the bottom precipitate from each centrifugation and dissolve it in 1 mL of toluene. The obtained separation gradient monomer samples are numbered sequentially. The fluorescence emission spectra of each separation gradient monomer sample are measured by a fluorescence emission spectrometer. The screening criterion is that the emission peak position is stable at 624 nm ± 1 nm. In this way, a toluene solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals is obtained.

[0040] Figure 1 and Figure 2 The images show scanning electron microscope (SEM) images and particle size distribution maps of the monomer samples collected after four repeated precipitation operations, where the bottom precipitate was dissolved in toluene. Figure 1 and Figure 2As can be seen, the obtained nanocrystalline monomers have a regular hexagonal morphology and a size of 12.06 nm ± 0.91 nm, proving that monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals were successfully prepared.

[0041] A3: Mix 1 mL of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals in toluene with 2 mL of methanol, heat at 100 °C for 1 min, centrifuge at 12000 rpm for 1 min, and collect the precipitate; redissolve the precipitate in 1 mL of toluene and add 2 mL of methanol to repeat the above heating treatment and centrifugation separation, and then dissolve the precipitate in 0.5 mL of octadecene to obtain the thermally purified monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal dispersion.

[0042] Step 2: Synthesis of CdSe / CdS colloidal semiconductor nanocrystal dimers

[0043] Add 5.7 mL of 2-octyl-dodecaneamine and 8 mL of octadecene to a 50 mL three-necked flask, heat to 160 °C under argon protection, degas for 10 min, and then continue heating to 280 °C. Inject 0.5 mL of thermally purified monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal dispersion, stir at a constant temperature for 30 min, and cool to room temperature after the reaction to obtain a mixed solution containing CdSe / CdS colloidal semiconductor nanocrystal dimer.

[0044] Step 3: Separation and purification of CdSe / CdS colloidal semiconductor nanocrystal dimers

[0045] B1: Transfer the mixed solution containing CdSe / CdS colloidal semiconductor nanocrystal dimers to a 10 mL centrifuge tube, add 3 times its volume of acetone, centrifuge at 12000 rpm for 3 min, and collect the bottom precipitate.

[0046] B2: Dissolve the precipitate from B1 in 1 mL of toluene, then add acetone dropwise until the solution becomes slightly turbid. Stop adding acetone and immediately transfer the mixture to a high-speed centrifuge. Centrifuge at 12,000 rpm for 1 min, collect the bottom precipitate and dissolve it in 1 mL of toluene as the separation gradient product sample 1.

[0047] B3: Add 0.1 times the volume of acetone to the supernatant obtained by centrifugation of B2, continue centrifugation, and repeat the above-mentioned operation of adding acetone and centrifugation on the supernatant. Collect the bottom precipitate of each centrifugation and dissolve it in 1 mL of toluene. Observe the particle morphology by transmission electron microscopy until the bottom precipitate dissolves in toluene to obtain high-yield CdSe / CdS colloidal semiconductor nanocrystal dimers.

[0048] Figure 3 and Figure 4 The images show scanning electron microscope (SEM) images and particle size distribution maps of the product sample obtained after the bottom precipitate was dissolved in toluene following five repeated precipitation cycles. Figure 3 As shown, the resulting dimer is formed by the connection of nearly spherical particles, exhibiting a directional splicing structure, and the dimer yield is as high as 80%. Figure 4 The statistical distribution of the monomer size in the dimer shows that its size is 11.64 nm ± 1.08 nm. This size is slightly smaller than the size of the aforementioned nanocrystalline monomer, indicating that slight morphological rounding and size shrinkage occurred during the process of nanocrystals splicing together to form a dimer. Example 2

[0049] In step 2 of this embodiment, 5.7 mL of 2-octyl-dodecaneamine and 8 mL of octadecene were added to a 50 mL three-necked flask. The mixture was heated to 160 °C under argon protection, degassed for 10 min, and then heated to 260 °C. 0.5 mL of the thermally purified monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystal dispersion was injected, and the mixture was stirred at a constant temperature for 60 min. After the reaction was completed, the mixture was cooled to room temperature to obtain a mixed solution containing CdSe / CdS colloidal semiconductor nanocrystal dimers. The other steps were the same as in Example 1.

[0050] The results showed that, under the conditions of a reaction temperature of 260℃ and a reaction time of 1 h, the supernatant in step 3 was repeated 7 times, and the morphology characterization results of the obtained CdSe / CdS core-shell colloidal semiconductor nanocrystal dimers were consistent with those of the previous step. Figure 3 The results are largely consistent, with the yield of dimers reaching 78%.

Claims

1. A method for the synthesis of CdSe / CdS colloidal semiconductor nanocrystal dimers, characterized in that, The synthesis method comprises the following steps: Step 1: purification of wurtzite CdSe / CdS colloidal semiconductor nanocrystals A1: dropwise add acetone to the toluene solution of wurtzite CdSe / CdS colloidal semiconductor nanocrystals until the solution appears slightly turbid, stop adding acetone, and centrifugal separation; A2: add acetone to the supernatant obtained by centrifugal separation in A1, continue centrifugal separation, and the supernatant is subjected to the aforementioned operation of adding acetone and centrifugal separation until the bottom precipitate obtained by centrifugal separation is dissolved in toluene to obtain a toluene solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals; A3: add methanol to the toluene solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals, heat at 80-100 ℃ for 1-3 min, centrifugal separation, redissolve the precipitate in toluene, add methanol, and perform the aforementioned heating treatment and centrifugal separation again; then dissolve the precipitate in octadecene to obtain a dispersion solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals after thermal purification; Step 2: synthesis of CdSe / CdS colloidal semiconductor nanocrystal dimers Mix 2-octyl-dodecylamine and octadecene, heat to 140-180 ℃ under inert gas protection, continue to heat to 240-290 ℃ after degassing for 10-15 min, then add the dispersion solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals after thermal purification, constant temperature stirring reaction for 20-80 min, and cool to room temperature after the reaction is completed to obtain a mixed solution containing CdSe / CdS colloidal semiconductor nanocrystal dimers; Step 3: separation and purification of CdSe / CdS colloidal semiconductor nanocrystal dimers B1: add acetone with a volume of 2-4 times that of the mixed solution containing CdSe / CdS colloidal semiconductor nanocrystal dimers, centrifugal separation, and collect the bottom precipitate; B2: dissolve the precipitate in B1 in toluene, then dropwise add acetone until the solution appears slightly turbid, stop adding acetone, and centrifugal separation; B3: add acetone to the supernatant obtained by centrifugal separation in B2, continue centrifugal separation, and the supernatant is subjected to the aforementioned operation of adding acetone and centrifugal separation until the bottom precipitate obtained by centrifugal separation is dissolved in toluene to obtain high-yield CdSe / CdS colloidal semiconductor nanocrystal dimers.

2. The method for synthesizing CdSe / CdS colloidal semiconductor nanocrystal dimers according to claim 1, characterized in that, In A2 of step 1, the amount of acetone added to the supernatant is 0.15-0.25 times the volume of the supernatant.

3. The method of synthesis of CdSe / CdS colloidal semiconductor nanocrystal dimers according to claim 1, characterized in that, In A3 of step 1, add methanol with a volume of 2-4 times that of the toluene solution of monodisperse wurtzite CdSe / CdS colloidal semiconductor nanocrystals, heat at 90-100 ℃ for 1-3 min, centrifugal separation, redissolve the precipitate in toluene, add methanol with a volume of 2-4 times that of toluene, and perform the aforementioned heating treatment and centrifugal separation again.

4. The method of synthesis of CdSe / CdS colloidal semiconductor nanocrystal dimers according to claim 1, characterized in that, In step 2, mix 2-octyl-dodecylamine and octadecene, heat to 160 ℃ under inert gas protection, continue to heat to 280 ℃ after degassing for 10 min, then add the dispersion solution of monodisperse wurtzite CdSe / CdS core-shell colloidal semiconductor nanocrystals after thermal purification, and constant temperature stirring reaction for 30 min.

5. The method for synthesizing CdSe / CdS colloidal semiconductor nanocrystalline dimers according to claim 1 or 4, characterized in that, In step 2, the volume ratio of the 2-octyl-dodecylamine, octadecene, and the monodisperse wurtzite CdSe / CdS core-shell colloidal semiconductor nanocrystal dispersion liquid after thermal purification is 8-12:15-20:

1.

6. The method for synthesizing CdSe / CdS colloidal semiconductor nanocrystalline dimers according to claim 1, characterized in that, In B3 of step 3, the amount of the added acetone in the supernatant is 0.05-0.4 times the volume of the supernatant.

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