CN101049918A - Method for preparing CdTe Nano grains possible to be dissolved in water and organic solvent - Google Patents

Abstract

The invention relates to a preparation method of CdTe nanoparticles soluble in water and an organic solvent, which belongs to the technical field of semiconductor nanometer material preparation. The invention prepares water-soluble CdTe nanocrystals by means of an aqueous solution synthesis method, and uses straight-chain alkylamine to modify the surface of CdTe, so that the water-soluble CdTe nanocrystals can be transferred to an organic solvent. At the same time, by adjusting the pH value of the aqueous solution, the CdTe nanocrystals can be redissolved in the aqueous solution. The invention can arbitrarily regulate the solubility of CdTe nanocrystals in aqueous solution and organic solvent by controlling the pH value of the solution and the concentration of alkylamine. The fluorescence quantum efficiency and half-peak width of CdTe nanocrystals dissolved in different solvents did not change much. The method is simple and easy to operate, so that the CdTe semiconductor nanocrystal has a broader application prospect in the fields of biological probes, nano/polymer composite materials and the like.

Description

Preparation method of CdTe nanoparticles soluble in water and organic solvents

technical field

The invention belongs to the technical field of semiconductor nanometer material preparation, and relates to a method for preparing CdTe semiconductor nanoparticle soluble in water and organic solvents, which can be dissolved in aqueous solution and organic solvent through simple surface modification and pH value adjustment.

Background technique

Due to the unique quantum size effect and quantum confinement effect of semiconductor nanoparticles, CdTe nanoparticles have been widely used in optoelectronics, luminescence, etc. Diodes, solar cells, biological probes and other fields. At present, the synthesis of CdTe nanoparticles is mainly based on aqueous solution synthesis and metal organic synthesis. However, both methods have their own advantages and disadvantages, such as the literature "Thiol-Capping of CdTe Nanocrystals: An Alternative to Organometallic Synthetic Routes", Nikolai Gaponik, Dmitri V.Talapin, Andrey L.Rogach et al.J.Phys.Chem.B , 2002, 106, 7177-7185, systematically expounded the advantages and disadvantages of the two synthetic routes: the metal-organic preparation method is carried out at high temperature, and can obtain nanocrystals with better crystal form, narrow size distribution and high fluorescence quantum efficiency. However, the instability of the products in the air limits their potential applications; while the aqueous phase synthesis method is simple, cheap, green and environmentally friendly, can be mass-produced, and can synthesize nanocrystals with smaller particles than organic methods.

The most important thing is that the surface of CdTe nanocrystals obtained by different synthesis methods has different polar groups, so that they can only exist in corresponding solvents, which limits their wider application. By surface modification, adding or changing groups on the surface can change the polarity of the surface of nanoparticles, so that water-soluble nanocrystals can be dissolved in organic solvents; the same method can be used to dissolve oil-soluble nanocrystals in aqueous solutions.

Currently, the above-mentioned modification methods are realized by utilizing the ability of thiol compounds to coordinate covalently on the surface of nanocrystals. The mercapto compounds with long chains are modified on the surface of CdTe to dissolve the water-soluble nanocrystals in the organic phase (see "Efficient Phase Transfer of Luminescent Thiol-Capped Nanocrystals: From Water to Nonpolar Organic Solvents". Nikolai Gaponik, Dmitri V . Talapin, Andrey L. Rogach, et al. Nano Lett., 2(8), 803-806). Similarly, mercapto compounds containing hydrophilic groups (such as carboxyl groups, amino groups, etc.) can also be modified on the surface of nanocrystals, so that the lipophilic groups can be dissolved in aqueous solution. In addition, quaternary ammonium salts are often used to modify the surface of nanocrystals due to their strong electrostatic attraction, so that the nanocrystals in the aqueous solution can be dissolved in the organic phase.

Invention content:

The invention synthesizes water-soluble CdTe nano-particles through an aqueous solution synthesis method, and uses hexadecylamine as a surface modifier to dissolve the water-soluble CdTe nano-crystals in an organic phase. At the same time, by adjusting the pH value of the aqueous solution, the CdTe nanocrystals in the organic phase can be transferred back to the aqueous phase, thereby achieving the purpose of water solubility again. This method can adjust the polarity of the surface groups of CdTe nanocrystals arbitrarily with only a simple operation, so as to achieve the purpose of dissolving in aqueous solution and organic solvent, and broaden the application range of CdTe nanocrystals in various fields.

The invention comprises the following steps: 1. preparing water-soluble CdTe semiconductor nanocrystals; 2. modifying the surface of long-chain alkylamines so that they can be dissolved in organic solvents; 3. redissolving the CdTe nanocrystals dissolved in organic solvents in aqueous solutions middle.

The invention provides a method for preparing CdTe nanoparticles soluble in water and organic solvents, characterized in that it comprises the following steps:

(1) Adjust the pH of the mixed aqueous solution of cadmium salt and mercaptocarboxylic acid to 11.2-11.8 with NaOH, and pass tellurium source H ₂ Te into the solution under the protection of N ₂ to obtain a precursor solution, in which the concentration of cadmium salt is 2× 10 ^-2 mol/L, the molar ratio of cadmium salt, tellurium source, and mercaptocarboxylic acid is 1:0.5:2.4, and the precursor solution is refluxed at 100°C for 15min-24h to obtain a CdTe nanocrystal solution;

(2) Adjust the pH of the above-mentioned CdTe nanocrystal aqueous solution to 5-10 with NaOH, mix it with an organic solvent in which a surface modifier is dissolved, the concentration of the surface modifier is 0.008-0.032mol/L, and after stirring the mixed solution, dissolve it in an organic solvent CdTe nanocrystals dissolved in organic solvents are obtained;

(3) Adjust the pH value of the aqueous solution in the mixed solution in step (2) to 11-14 with NaOH, and re-dissolve the CdTe nanoparticles in the aqueous solution after stirring.

The cadmium salt is CdCl ₂ , and the mercaptocarboxylic acid is thioglycolic acid.

The surface modifier used is hexadecylamine, and the organic solvents are chloroform and toluene. The concentration of the surface modifier is 0.016mol/L-0.032mol/L, and the pH of the above CdTe nanocrystal aqueous solution is adjusted to 5-8 with NaOH.

Step (3) adjusting the pH value of the aqueous solution in the mixed solution to 12-14 with NaOH.

The invention prepares thioglycolic acid-stabilized CdTe nanocrystals that can be dissolved in an aqueous solution through an aqueous solution synthesis method. Utilizing the weak basicity of linear alkylamines, the surface of CdTe nanocrystals is electrostatically modified in the form of Lewis acid-base pairs, so that they can be dissolved in organic solvents. By adjusting the pH of the aqueous solution and the concentration of alkylamine, different amounts of CdTe nanocrystals can be dissolved in the organic solvent (as shown in Figure 1). By adjusting the pH value in the aqueous solution, the CdTe nanocrystals dissolved in the organic solvent can be redissolved in the aqueous solution. Absorption and fluorescence spectra showed that the absorption and fluorescence properties of CdTe nanocrystals in the original aqueous solution, CdTe nanocrystals in organic solution and re-dissolved in aqueous solution did not change significantly. The method is simple to operate, and can realize arbitrary control of the dissolution of CdTe nanocrystals in aqueous solutions and organic solvents, so that it has greater application value in biological probes and semiconductor/organic polymer materials.

Description of drawings:

Fig. 1 is the absorption spectrum of the CdTe nanocrystal of the solution prepared in the present invention in chloroform solution.

Fig. 2 is the fluorescence spectrum of CdTe nanocrystals in aqueous solution prepared by the present invention, CdTe nanocrystals dissolved in chloroform solution and CdTe nanocrystals redissolved in aqueous solution.

Detailed ways:

The content of the present invention can be better understood through the following representative examples and figures.

Example 1

1: Preparation of water-soluble CdTe nanocrystals from CdCl ₂ , H ₂ Te and mercaptoacetic acid

Dissolve 228.4mg of CdCl ₂ ·2.5H ₂ O in 50ml of water, add 0.16ml of mercaptoacetic acid drop by drop with stirring, adjust the pH to 11.2 with 1mol/L NaOH, pass N ₂ , and pass H ₂ Te into the solution with nitrogen gas while stirring , the resulting solution was refluxed at 100°C to obtain CdTe nanocrystals of different particle sizes. The absorption of the solution after heating for 5 hours is shown in curve 1 in Figure 1, and the fluorescence spectrum is shown in curve 1 in Figure 2.

2: Surface modification of alkylamines to prepare CdTe nanocrystals dissolved in chloroform solution

Take 4ml of the solution and heat 4ml of the solution for 5 hours according to step 1, adjust the pH=6, mix with 4ml of chloroform solution dissolved with 30.8mg of hexadecylamine, stir, and the CdTe nanocrystals gradually dissolve in the chloroform solution. After standing still for 2 hours, the solution was separated into layers, and the measured chloroform phase absorption was shown in curve 2 in Figure 1, and the fluorescence spectrum was shown in curve 2 in Figure 2.

3: CdTe nanocrystals are redissolved in aqueous solution.

Adjust the pH of the aqueous layer solution in step 2 to 11, continue stirring, and the CdTe nanocrystals will gradually redissolve in the aqueous solution. After standing still, the solution separated into layers. The fluorescence spectrum of the aqueous solution is shown in Figure 2, curve 3.

The quantum efficiency and half-peak width of the CdTe nanocrystals obtained in the above steps are listed in Table 1.

Example 2

1: The synthesis method of CdTe nanocrystals is as described in Example 1.

2: Surface modification of alkylamines to prepare CdTe nanocrystals dissolved in chloroform solution

Take 4ml of the solution and heat 4ml of the solution for 5 hours according to step 1, adjust the pH=5, mix with 4ml of chloroform solution dissolved with 15.4mg of hexadecylamine, stir, and the CdTe nanocrystals gradually dissolve in the chloroform solution. After standing still for 2 hours, the solution was separated into layers, and the absorption of the chloroform phase was measured as shown in curve 3 of FIG. 1 .

3: CdTe nanocrystals are redissolved in aqueous solution as shown in Example 1.

Example 3

1: The synthesis method of CdTe nanocrystals is as described in Example 1.

2: Surface modification of alkylamines to prepare CdTe nanocrystals dissolved in chloroform solution

Take 4ml and heat 4ml of the solution for 5h according to step 1, adjust the pH=6, mix with 4ml of chloroform solution dissolved with 7.7mg of hexadecylamine, stir, and the CdTe nanocrystals gradually dissolve in the chloroform solution. After standing still for 2 hours, the solution was separated into layers, and the absorption of the chloroform phase was measured as shown in curve 4 of FIG. 1 .

3: CdTe nanocrystals are redissolved in aqueous solution as shown in Example 1.

Example 4

1: The synthesis method of CdTe nanocrystals is as described in Example 1.

2: Surface modification of alkylamines to prepare CdTe nanocrystals dissolved in chloroform solution

Take 4ml and heat 4ml of the solution for 1h according to step 1, adjust the pH=8, mix with 4ml of chloroform solution dissolved with 30.8mg of hexadecylamine, stir, and the CdTe nanocrystals gradually dissolve in the chloroform solution. After standing still for 2h, the solution was separated into layers.

3: Adjust the pH of the aqueous layer solution in step 2 to 14, continue stirring, and the CdTe nanocrystals will gradually redissolve in the aqueous solution. After standing still, the solution separated into layers.

The quantum efficiency and half-peak width of the CdTe nanocrystals obtained in the above steps are listed in Table 1.

Example 5

1: The synthesis method of CdTe nanocrystals is as described in Example 1.

2: Surface modification of alkylamines to prepare CdTe nanocrystals dissolved in chloroform solution

Take 4ml of the solution and heat it for 15min according to step 1, adjust the pH to 6, mix with 4ml of chloroform solution dissolved with 30.8mg of hexadecylamine, stir, and the CdTe nanocrystals gradually dissolve in the chloroform solution. After standing still for 2h, the solution was separated into layers.

3: CdTe nanocrystals are redissolved in aqueous solution as shown in Example 1.

Example 6

1: The synthesis method of CdTe nanocrystals is as described in Example 1.

2: Alkylamine surface modification Preparation of CdTe nanocrystals dissolved in chloroform solution is as described in Example 1.

3: CdTe nanocrystals are redissolved in aqueous solution.

The pH of the aqueous layer solution in step 2 is adjusted to 14, and the stirring is continued, and the CdTe nanocrystals are gradually re-dissolved in the aqueous solution.

The quantum efficiency and half-peak width of the CdTe nanocrystals obtained in the above steps are listed in Table 1.

Table I Example Raw solution Chloroform solution Redissolve in aqueous solution Quantum efficiency (%) Width at half maximum (nm) Quantum efficiency (%) Width at half maximum (nm) Quantum efficiency (%) Width at half maximum (nm) 1 15.8 43.7 19.4 45.5 15.0 44.5 4 10.8 41.8 14.4 42.2 11.9 41.5 5 5.2 37.9 9.8 37.6 5.5 38.1

Claims (5)

1. A method for preparing CdTe nanoparticles soluble in water and organic solvents, comprising the following steps: (1) Adjust the pH of the mixed aqueous solution of cadmium salt and mercaptocarboxylic acid to 11.2-11.8 with NaOH, and pass tellurium source H ₂ Te into the solution under the protection of N ₂ to obtain a precursor solution, in which the concentration of cadmium salt is 2× 10 ^-2 mol/L, the molar ratio of cadmium salt, tellurium source, and mercaptocarboxylic acid is 1:0.5:2.4, and the precursor solution is refluxed at 100°C for 15min-24h to obtain a CdTe nanocrystal solution; (2) Adjust the pH of the above-mentioned CdTe nanocrystal aqueous solution to 5-10 with NaOH, mix it with an organic solvent in which a surface modifier is dissolved, the concentration of the surface modifier is 0.008-0.032mol/L, and after stirring the mixed solution, dissolve it in an organic solvent CdTe nanocrystals dissolved in organic solvents are obtained; (3) Adjust the pH value of the aqueous solution in the mixed solution in step (2) to 11-14 with NaOH, and re-dissolve the CdTe nanoparticles in the aqueous solution after stirring. 2. The method for preparing CdTe nanoparticles soluble in water and organic solvents according to claim 1, characterized in that: the cadmium salt is CdCl ₂ , and the mercaptocarboxylic acid is thioglycolic acid. 3. The method for preparing CdTe nanoparticles soluble in water and organic solvents according to claim 1, characterized in that: the surface modifier used is hexadecylamine, and the organic solvents are chloroform and toluene. 4. The method for preparing CdTe nanoparticles soluble in water and organic solvents as claimed in claim 1, characterized in that: the surface modifier concentration is 0.016mol/L-0.032mol/L, and the above-mentioned CdTe nanocrystal aqueous solution is made of NaOH Adjust the pH to 5-8. 5. The method for preparing CdTe nanoparticles soluble in aqueous solution and organic solvent as claimed in claim 1, characterized in that step (3) uses NaOH to adjust the pH value of the aqueous solution in the mixed solution to 12-14.

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