CN100413938C - Au/CdSe heterostructure quantum dots and preparation method thereof - Google Patents

Abstract

Au/CdSe heterostructure quantum dots and the preparation method thereof in the present invention are characterized in that the HAuCl ₄ ·4H ₂ O aqueous solution is extracted with tetraoctyl ammonium bromide toluene solution, the water layer is colorless and left standing for stratification, and the upper layer of toluene After the solution is washed, collect and add dodecyl mercaptan, stir until the solution becomes colorless, which is the gold source solution; mix the toluene solution of CdSe quantum dots with the gold source solution, and stir until it turns brown; purify the crude product, That is, the heterostructure quantum dots formed by combining Au particles with an average particle diameter of 2.0nm and CdSe particles with an average particle diameter of 3.4nm; the present invention realizes the scale of Au/CdSe heterostructure quantum dots at room temperature chemical preparation; the Au/CdSe heterostructure quantum dots of the present invention have both metal and semiconductor light absorption properties and a special asymmetric structure, and have broad application prospects in the fields of nanoelectronic devices, photosensitive sensors and solar cells.

Description

Au/CdSe heterostructure quantum dots and preparation method thereof

Technical field:

The invention belongs to the technical field of quantum dots, in particular to Au/CdSe heterostructure quantum dots and a preparation method thereof.

Background technique:

In recent years, the research on heterostructure quantum dots has attracted more and more researchers' interest, especially the research on heterostructure quantum dots based on metal or semiconductor materials is changing rapidly, because the combination of two functional materials The all-in-one nanostructure has very novel application prospects, and it usually has the composite characteristics and mutual coupling characteristics of the two materials. Metal quantum dots have excellent electrical properties, providing a broad application horizon in nanoelectronic devices, electron transfer catalysis, etc.; semiconductor quantum dots have excellent optical properties, and have far-reaching applications in bioluminescence labeling, national defense coding, and optoelectronic devices. Application prospect. For example, "Journal of the American Chemical Society" (Journal of the American Chemical Society 126.5664-5665, 2004; Journal of the American Chemical Society 127.10269-10275, 2005) reported FePt/CdS and The thermal synthesis preparation technology of Fe ₂ O ₃ /ZnS, CdS or HgS quantum dots, but the preparation process requires a strict inert atmosphere and a high temperature (280°C), which makes it difficult to conduct experiments and cannot prepare products on a large scale. The United States "Nano Letters" (NanoLetters 5.379-382, 2005) reported the thermal decomposition preparation technology of Fe ₃ O ₄ /Au quantum dots based on metal Au. The preparation process also requires strict inert atmosphere and high temperature (300 ° C). , the experiment is not easy to carry out and cannot be scaled up. "Journal of the American Chemical Society" (Journal of the American Chemical Society 127.34-35, 2005) reported the preparation technology of FePt/Ag, Fe ₃ O ₄ /Ag and Au/Ag heterostructure quantum dots based on metal Ag, which The preparation process does not require an inert atmosphere and can be carried out at room temperature, but it is only applicable to the category of metal Ag-based heterostructure quantum dots and cannot be extended to more systems; because the preparation process is completed on the phase interface of micelles, limited The large phase interface space makes the preparation process difficult to scale up.

"Journal of the American Chemical Society 124.2049-2055, 2002" and Chinese Patent No. ZL200310111494.2 respectively reported the preparation technology of oil-soluble CdSe quantum dots, but the reaction system did not involve heterostructure quantum dots The preparation of CdSe quantum dots with controllable size is only given. "Journal of the American Chemical Society" (Journal of the American Chemical Society 125.12567-12575, 2003) reported oil-soluble CdSe/CdS core/shell quantum dots, the report includes a two-step process, the first step is to prepare oil-soluble CdSe core quantum dots , the second step is based on the CdSe quantum dots on the basis of epitaxial growth of CdS shell layer; but because of its use of ion layer adsorption reaction (Successive ion layer adsorption and reaction) technology, so that in the CdSe quantum dot surface epitaxial growth CdS process can only Isotropically uniform core/shell quantum dots are obtained, but heterogeneous structure quantum dots cannot be obtained.

So far, there has been no literature report on the homogeneous preparation of heterostructure quantum dots under mild conditions, especially the preparation of metal Au/semiconductor CdSe heterostructure quantum dots, mainly because the two have severe lattice Mismatch (lattice mismatch up to 50%) hinders epitaxial growth.

Invention content:

The purpose of the present invention is to provide a metal Au/semiconductor CdSe heterostructure quantum dot and its preparation method, to overcome the shortcomings of harsh conditions, difficult reaction control, and difficulty in homogeneous large-scale preparation in the existing heterostructure preparation technology, and to develop A homogeneous, large-scale, mild and easy-to-manipulate preparation route.

The preparation method of the Au/CdSe heterostructure quantum dots of the present invention is characterized in that: at room temperature and in an air atmosphere, 20 to 30 mmol/L of tetraoctyl ammonium bromide is extracted with a toluene solution of 0.8 to 1.2 mmol/L. HAuCl ₄ 4H ₂ O aqueous solution, the volume ratio of the toluene solution of tetraoctylammonium bromide/the aqueous solution dissolved in HAuCl ₄ 4H ₂ O is 5/1~5/3; after the water layer is colorless, let it stand When the solution is separated, wash and collect the bright red toluene solution in the upper layer; add dodecyl mercaptan to make its volume fraction 0.7% to 1%, and stir until the solution becomes colorless, which is the gold source solution; then Mix and stir the toluene solution of CdSe quantum dots with a particle concentration of 1.0×10 ^-3 to 1.5×10 ^-3 mmol/L and the gold source solution at a volume ratio of 8/1 to 12/1, and the system changes rapidly from bright red to It is dark red, and finally gradually changes to brown to obtain a crude product; the crude product is purified to obtain Au/CdSe heterostructure quantum dots.

The product can be stored dissolved in a non-polar solvent including toluene, chloroform or n-hexane.

The Au/CdSe heterostructure quantum dot of the present invention is characterized in that: 80% to 90% of it is a dumbbell-shaped dimer type heterostructure quantum dot formed by combining a single Au particle and a single CdSe particle; 10% to 15% % is a trimer-type heterostructure quantum dot formed by combining two Au particles and a single CdSe particle at the same time; the rest is an isolated precursor CdSe quantum dot without forming a heterostructure; the average particle size of the Au particles is 2nm , the average particle diameter of CdSe particles is 3.4nm, and the standard deviation of particle size is less than 20.0%.

The method of the present invention forms a homogeneous system with oil-soluble CdSe quantum dots by extracting the gold source solution from the water phase to the oil phase. The bright red trivalent gold ions are reduced to more active colorless monovalent gold ions, so that the gold source solution can self-catalyze the formation of Au particles on the surface of CdSe quantum dots at room temperature, and then prepare Au/CdSe heterostructure quantum dots. point. The method of the present invention is different from the thermal synthesis and thermal decomposition methods under high temperature and inert atmosphere in the prior art, and the gold source solution in the present invention does not require an inert atmosphere in the process of self-catalyzing the formation of heterostructure quantum dots on the surface of CdSe quantum dots The protection can be carried out at room temperature, easy to operate and control; also different from the preparation technology of micellar phase interface reaction in the prior art, the preparation process of the method of the present invention is completed in the same oil phase toluene environment, can realize Large-scale preparation. At the same time, because the method of the present invention adopts the self-catalyzed preparation route of monovalent gold on the surface of CdSe quantum dots, it breaks through the defect that the prior art cannot be applied to Au and CdSe systems whose lattice mismatch reaches 50%, and realizes Au, CdSe The heterogeneous linkage of materials in the quantum dot system has not been reported in the literature so far. The Au/CdSe heterostructure quantum dot of the present invention has both metal and semiconductor light absorption characteristics, and this characteristic and its special asymmetric structure make it have broad application prospects in the fields of nanoelectronic devices, photosensitive sensors and solar cells.

Description of drawings:

Fig. 1 is the transmission electron micrograph of the product Au/CdSe heterostructure quantum dot of embodiment 1 of the present invention;

Figure 2 is a statistical diagram of particle morphology of Au/CdSe heterostructure quantum dots;

Figure 3 is a size distribution diagram of Au particles in Au/CdSe heterostructure quantum dots;

Figure 4 is a size distribution diagram of CdSe particles in Au/CdSe heterostructure quantum dots;

Figure 5 is a high-resolution transmission electron microscope photo of Au/CdSe heterostructure quantum dots;

Figure 6 is an electron diffraction photo of Au/CdSe heterostructure quantum dots;

Fig. 7 is the X-ray energy scattering spectrogram of Au/CdSe heterostructure quantum dot;

Fig. 8 is an ultraviolet-visible absorption spectrum diagram of Au/CdSe heterostructure quantum dots.

Detailed ways:

Example 1:

1. Prepare oil-soluble CdSe quantum dots with an average particle size of 3.4 nm.

The method reported in "Journal of the American Chemical Society 125.12567-12575, 2003" (the method disclosed in Chinese Patent No. ZL200310111494.2 can also be used) was used to prepare oil-soluble CdSe quantum dots, only for this report The first step of preparing the oil-soluble CdSe core quantum dot step, without doing the second step of the epitaxial growth CdS shell step, the specific steps are: 2mmol of selenium powder, 0.472g of tri-n-butylphosphine (TBP) Add it to 1.37g of octadecene, heat to 100°C, cool down to room temperature after the solution turns colorless, and prepare a stock solution of selenium; 0.2mmol of CdO, 0.8mmol of stearic acid and 2g of octadecene Carbene mixed and placed in a 25ml three-necked flask, heated to 200°C, cooled to room temperature after the solution became transparent, added 1.5g of octadecylamine and 0.5g of tri-n-octylphosphine oxide (TOPO), in an inert atmosphere Heating to 280°C under low temperature, inject all the stock solution of selenium within 2 seconds, then keep the reaction system at 250°C for 30 seconds, stop heating and cool to room temperature; add 6ml of n-hexane to the above system, and centrifuge at 120 rpm , after discarding the lower precipitate, add 8ml of acetone to the solution, let it stand for 10 minutes to precipitate the product, centrifuge at 120 rpm, discard the upper clear night, dissolve the precipitate with 5ml of toluene, then add 5ml of methanol to mix evenly, 120 rpm After centrifuging and discarding the supernatant, the precipitate was dissolved with 85ml of toluene to obtain a toluene solution of CdSe quantum dots with a particle concentration of 1.18×10 ^-3 mmol/L, which was sealed and kept away from light for future use.

2. Preparation of Au/CdSe heterostructure quantum dots.

1. Configure the gold source solution for preparing Au/CdSe heterostructure quantum dots. The steps are: take 8ml of 24.5mmol/L HAuCl ₄ 4H ₂ O aqueous solution and place it in a separatory funnel, add 20ml containing 200mg tetraoctyl The toluene solution of ammonium bromide, the volume ratio of the toluene solution of tetraoctyl ammonium bromide/the aqueous solution dissolved in HAuCl ₄ 4H ₂ O is 5/1~5/3; shake vigorously to extract, and the lower aqueous solution is colorless After that, let it stand for 10 minutes until the solution is separated, discard the aqueous solution of the lower layer; wash the toluene solution of the upper layer, that is, add 10ml deionized water and vibrate vigorously for 3 minutes, and let it stand for 10 minutes until the solution is separated, discard the aqueous solution of the lower layer, so Repeat 3 times; remove the bright red toluene solution in the separatory funnel, take 10ml of it, add 80 microliters of dodecyl mercaptan, and magnetically stir for 10 minutes, the solution gradually becomes colorless, and the gold source solution is obtained. The concentration of the toluene solution of tetraoctylammonium bromide in this step can be distributed in 0.8～1.2mmol/L, the concentration of HAuCl ₄ ·4H ₂ O aqueous solution can be distributed in 20～30mmol/L, and dodecyl mercaptan can be distributed in 70-100 microliters can prepare a colorless gold source solution.

2. To prepare Au/CdSe heterostructure quantum dots, the steps are: take 5ml of the toluene solution of CdSe quantum dots with a particle concentration of 1.18×10 ^-3 mmol/L, put them in a 25ml round bottom flask, and add 0.5ml gold source solution, the reaction system turns from bright red to dark red rapidly, and gradually turns to brown after stirring for 10-20 minutes, and is purified. In this step, the particle concentration of CdSe quantum dots can be distributed in the range of 1.0×10 ^-3 to 1.5×10 ^-3 mmol/L, and the volume ratio of CdSe quantum dots and gold source solution can be distributed in the range of 8/1 to 12/1, which means Au/CdSe heterostructure quantum dots can be prepared.

3. The purification steps are: add 6ml of methanol to the crude product, the solution is turbid, centrifuge at 120 rpm for 10 minutes, discard the upper clear night; dissolve the precipitate with 5ml of toluene, add 5ml of methanol and centrifuge at 120 rpm, discard the upper layer After clearing the night, the precipitate is the product, which can be dissolved in non-polar solvents such as toluene, chloroform or n-hexane for preservation.

3. Analysis of Au/CdSe heterostructure quantum dots:

Figure 1 is a transmission electron microscope photo of Au/CdSe heterostructure quantum dots. The darker particles in the figure are Au particles, and the lighter particles are CdSe particles. It can be seen that the Au particles and CdSe particles have been combined to form structural asymmetry. Au/CdSe heterostructure quantum dots, and presents a uniform monodisperse state; Figure 2 is the particle type statistical diagram of Au/CdSe heterostructure quantum dots, the figure shows that 84.6% of the particles in the product form a CdSe particle Dumbbell-shaped dimer-type heterostructure quantum dots coupled with an Au particle, another 12.1% of the particles formed a trimer-type heterostructure quantum dots coupled with a CdSe particle and two Au particles at the same time, only 3.3 % of the particles still maintain the original isolated CdSe quantum dot shape; after many experiments, it is found that the proportion of dumbbell-shaped dimer heterostructure quantum dots is distributed between 80% and 90%, and the proportion of trimer The proportion of heterostructure quantum dots is distributed between 10% and 15%, and the rest are isolated precursor CdSe quantum dots that do not form heterostructure; the high yield of heterostructure quantum dots shows that the preparation method of the present invention is very effective ; Fig. 3 is the statistical diagram of size distribution of Au particles in Au/CdSe heterostructure quantum dots, the average size of visible Au particles in the figure is 2.0nm; Fig. 4 is the size distribution statistics of CdSe particles in Au/CdSe heterostructure quantum dots The figure shows that the average size of CdSe particles is 3.4nm; in the statistical distribution of Figures 3 and 4, the standard deviation of particle size is <20.0%; Figure 5 is a high-resolution electron microscope photo of Au/CdSe heterostructure quantum dots, in the The lattice fringe images of the Au particle part and the CdSe particle part in the heterostructure quantum dots are clearly visible; Figure 6 is the electron diffraction pattern of the Au/CdSe heterostructure quantum dots, except for the hexagonal close-packed structure of cadmium selenide. In addition to the diffraction rings of the four crystal planes (002), (110), (112) and (213), the (111) and (220) planes of gold with a face-centered cubic structure (fcc) can also be clearly seen; Figure 7 shows the X-ray energy scattering spectrum of /CdSe heterostructure quantum dots, the signal of Cd element, Se element and Au element appears in the figure at the same time, the result of quantitative analysis is that Cd:Se:Au is 34:34:32; Figure 8 It is the ultraviolet-visible absorption spectrum diagram of Au/CdSe heterostructure quantum dots. The long-wavelength region larger than 650nm in the figure shows the continuous absorption characteristics of Au. The absorption peak near 585nm is not as sharp as that of CdSe quantum dots. It is due to the heterogeneity As a result of the coupling of Au particles and CdSe particles in the structural quantum dots, the strong absorption in the short wavelength region of less than 500nm comes from the joint contribution of Au particles and CdSe particles. In summary, the Au/CdSe heterostructure quantum dots have a special asymmetric shape in the structure, and the coupling characteristics of Au and CdSe in the ultraviolet-visible absorption spectrum.

The present invention efficiently prepares Au/CdSe heterostructure quantum dots under the mild conditions of homogeneous phase, normal temperature and air atmosphere, overcomes the lattice mismatch between Au and CdSe, and achieves The completed epitaxial growth of Au and CdSe heterostructure quantum dots provides a way to prepare heterostructure quantum dots on a large scale. The Au/CdSe heterostructure quantum dots produced by the invention have a special asymmetric structure and light absorption and coupling properties of metals and semiconductors, and have broad application prospects in the fields of nanoelectronic devices, photosensitive sensors and solar cells.

Claims (2)

1. the preparation method of an Au/CdSe heterojunction structure quantum dot is characterized in that: under room temperature, air atmosphere, with the HAuCl of the toluene solution extraction 20～30mmol/L of the four octyl group ammonia bromides of 0.8～1.2mmol/L ₄4H ₂The O aqueous solution, the toluene solution of this four octyl groups ammonia bromide/be dissolved with HAuCl ₄4H ₂The volume ratio of the aqueous solution of O is 5/1～5/3; After treating that water layer is colourless, leave standstill, cherry toluene solution washing back, upper strata is collected to the solution layering; Add lauryl mercaptan, making its volume fraction is 0.7%～1%, is stirred to solution and becomes colorless, and is golden source solution; Be 1.0 * 10 with granule density then ^-3～1.5 * 10 ^-3The toluene solution of the CdSe quantum dot of mmol/L and Jin Yuan solution mix, stir according to 8/1～12/1 volume ratio, and system is become garnet rapidly, faded to brownly gradually at last by shiny red, promptly obtains crude product; Crude product is purified, promptly obtain Au/CdSe heterojunction structure quantum dot.

2. the Au/CdSe heterojunction structure quantum dot of claim 1 method preparation is characterised in that: 80%～90% dumbbell shaped dimerization build heterojunction structure quantum dot that is combined together to form for single Au particle and single CdSe particle wherein; 10%～15% is the trimerization build heterojunction structure quantum dot that two Au particles and single CdSe particle are combined together to form simultaneously; All the other are not for forming the stand alone precursor C dSe quantum dot of heterojunction structure; Wherein Au particulate median size is 2nm, and CdSe particulate median size is 3.4nm, particle size standard variance＜20.0%.

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