CN101767816A - Method for preparing monodisperse CdS nanocrystal - Google Patents

Abstract

The invention discloses a method for preparing monodisperse cadmium sulfide nanocrystals, comprising the following steps: (1) preparing a cadmium oleate solution by using cadmium acetate, oleic acid and a solvent or cadmium oxide, oleic acid and a solvent; the solvent is Octadecene or liquid paraffin; (2) the temperature of the cadmium oleate solution is lowered to room temperature, and sulfur powder is added; (3) the temperature of the reaction solution in step (2) is raised to 220°C to 300°C for reaction until the reaction End; (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol for centrifugal purification, remove the supernatant, disperse the precipitate in a non-polar solvent, then add ethanol for centrifugation, repeat this process several times, and obtain the final product . The cadmium sulfide nanocrystal obtained by the method of the invention has good monodispersity and uniformity, adjustable size and excellent fluorescence performance, and can be used in the fields of photoelectric detection, quantum dot light-emitting diodes and the like.

Description

A method for preparing monodisperse cadmium sulfide nanocrystals

technical field

The invention relates to a method for preparing monodisperse cadmium sulfide nanocrystals, belonging to the field of semiconductor materials.

Background technique

Cadmium sulfide is an important semiconductor material, which can be used in optoelectronic devices such as photodetectors and compound thin film solar cells. With the development of preparation technology of nanomaterials and devices, cadmium sulfide nanocrystals have attracted more and more attention. When the size of cadmium sulfide nanocrystals is reduced to its excitonic Bohr radius (about 3nm), due to the quantum confinement effect, the energy band width of the material becomes larger, making cadmium sulfide quantum dots the preferred material for blue quantum dot light-emitting diodes . When cadmium sulfide is used in the window layer of compound thin-film solar cells, the increase of energy band width can increase its transparency in the visible light region, so that more sunlight can be transmitted through and absorbed by the absorbing layer, and converted into electric current, thereby improving solar energy. The efficiency of the battery.

At present, the most commonly used method for preparing monodisperse cadmium sulfide nanocrystals is the hot injection method, that is, the cold precursor solution is injected into a high-temperature reaction solvent. This process ensures the effective separation of the nucleation stage and the growth stage of the nanocrystals, thereby obtaining Nanocrystals of uniform size. However, the hot injection method requires a fast injection process, which obviously cannot be used for industrial-scale preparation of nanocrystals. The non-implantation method is a method suitable for the large-scale preparation of cadmium sulfide nanocrystals, but in the previous method, saturated long carbon chain carboxylic acid was used to stabilize the growth of nanocrystals, and it was necessary to add a nucleation trigger to increase the reactivity of elemental sulfur and increase cost of synthesis. However, organic sulfur sources with high reactivity are expensive, toxic and easy to oxidize, so it is necessary to develop a simpler, greener and mass-producible method to prepare high-quality monodisperse cadmium sulfide nanocrystals.

Contents of the invention

The invention provides a method for preparing monodisperse cadmium sulfide nanocrystals without heat injection and nucleation triggering agent.

A method for preparing monodisperse cadmium sulfide nanocrystals, comprising the steps of:

(1) Heating the mixture of cadmium acetate, oleic acid and solvent to 100°C to 120°C to obtain a colorless and transparent cadmium oleate solution, vacuumize to remove water and acetic acid in the system; or heat cadmium oxide, oleic acid and solvent The mixture is heated to 200°C to 300°C and kept warm for a period of time until the cadmium oxide is completely dissolved to obtain a cadmium oleic acid solution; the molar ratio of cadmium acetate or cadmium oxide to oleic acid is 1:2 to 1:10; the solvent is eighteen olefin or liquid paraffin;

(2) the temperature of described cadmium oleate solution is down to room temperature, add sulfur powder, the mol ratio of cadmium oleate and sulfur is 4: 1～1: 4;

(3) The temperature of the reaction solution in step (2) is raised to 220° C. to 300° C. for reaction until the reaction ends;

(4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol for centrifugal purification, remove the supernatant, disperse the precipitate in a non-polar solvent, then add ethanol for centrifugation, repeat this process several times (generally more than 3 times) ) to get the final product.

The operations from step (1) to step (3) are carried out under the protective atmosphere of argon flow, so as to prevent the oxidation of oleic acid and the cadmium sulfide nanocrystals obtained by the reaction at high temperature.

Described non-polar solvent is hexane, cyclohexane, toluene or chloroform etc.

The process of preparing monodisperse cadmium sulfide nanocrystals in the present invention is mainly divided into two stages, first preparing cadmium oleic acid solution, then mixing it with sulfur, and raising the temperature to the reaction temperature. In this process, sulfur is reduced by solvent (octadecene or liquid paraffin) to hydrogen sulfide, hydrogen sulfide reacts with cadmium oleate to obtain cadmium sulfide, and the reaction initiation temperature is about 220°C. The above reaction conditions ensure the successful preparation of highly uniform cadmium sulfide nanocrystals with quantum confinement effects.

The chemicals used in the present invention are all commercially available, relatively cheap, and stable in air. By adding oleic acid into the reaction system, the reactivity of the cadmium salt is improved, and the growth of the cadmium sulfide nanocrystals is stabilized, thereby avoiding the use of nucleation promoters.

The beneficial effect of the present invention is: 1) avoid the use of nucleation accelerator, reduce synthesis cost; Time to control, in addition, it also has the advantage of large output.

Description of drawings

The transmission electron microscope photo of Fig. 1 embodiment 1 cadmium sulfide nanocrystal;

The absorption spectrum and fluorescence emission spectrum of Fig. 2 embodiment 1 cadmium sulfide nanocrystals;

The X-ray diffraction spectrum of Fig. 3 embodiment 1 cadmium sulfide nanocrystal.

Detailed ways

Example 1:

(1) Heat 1 mmol of cadmium acetate, 6 mmol of oleic acid, and 15 milliliters of octadecene to 120° C., vacuumize for 30 minutes to remove acetic acid and water in the system, and then fill with argon. (2) Stop heating, and when the temperature drops to room temperature, add 0.5 mmol of sulfur powder. (3) The temperature of the reaction solution was raised to 240° C. and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product.

Figure 1 is a transmission electron microscope photo of the synthesized cadmium sulfide nanocrystals, the size distribution of the nanocrystals is uniform, and the average size is 3.6nm.

Figure 2 is the absorption spectrum and fluorescence emission spectrum of cadmium sulfide nanocrystals. The clear absorption peaks indicate the high quality of the nanocrystals, and the fluorescence emission spectrum includes intrinsic luminescence and defect luminescence.

Fig. 3 is an X-ray diffraction pattern of cadmium sulfide nanocrystals, which shows that the cadmium sulfide nanocrystals obtained by this method have a cubic sphalerite structure.

Example 2:

(1) Heat 1 mmol of cadmium acetate, 6 mmol of oleic acid, and 15 milliliters of liquid paraffin to 120° C., vacuumize for 30 minutes to remove acetic acid and water in the system, and then fill with argon. (2) Stop heating, and when the temperature drops to room temperature, add 0.5 mmol of sulfur powder. (3) The temperature of the reaction solution was raised to 240° C. and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product. The result was similar to Example 1.

Example 3:

(1) Heat 1 mmol of cadmium acetate, 10 mmol of oleic acid, and 15 ml of octadecene to 120° C., vacuumize the system for 30 minutes to remove acetic acid and water, and then fill with argon. (2) Stop heating, and when the temperature drops to about room temperature, add 0.5 mmol of sulfur powder. (3) The temperature of the reaction solution was raised to 240° C. and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product. The result was similar to Example 1.

Example 4:

(1) Heat 1 mmol of cadmium acetate, 2 mmol of oleic acid, and 15 ml of octadecene to 120° C., vacuumize for 30 minutes to remove acetic acid and water in the system, and then fill with argon. (2) Heating was stopped, and when the temperature dropped to room temperature, 0.5 mmol of sulfur powder was added. (3) The temperature of the reaction solution was raised to 240° C., and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product. The result was similar to Example 1.

Example 5:

(1) Heat 1 mmol of cadmium acetate, 6 mmol of oleic acid, and 15 milliliters of octadecene to 120° C., vacuumize for 30 minutes to remove acetic acid and water in the system, and then fill with argon. (2) Stop heating, and when the temperature drops to about room temperature, add 0.5 mmol of sulfur powder. (3) The temperature of the reaction solution was raised to 300° C. and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product. The result was similar to Example 1.

Embodiment 6:

(1) Heat 1 mmol of cadmium acetate, 6 mmol of oleic acid, and 15 milliliters of octadecene to 120° C., vacuumize for 30 minutes to remove acetic acid and water in the system, and then fill with argon. (2) stop heating, treat that temperature drops to room temperature, add the sulfur powder (3) of 0.25 millimole. The temperature of the reaction solution was raised to 240° C. and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product. The result was similar to Example 1.

Embodiment 7:

(1) Heat 1 mmol of cadmium acetate, 6 mmol of oleic acid, and 15 milliliters of octadecene to 120° C., vacuumize for 30 minutes to remove acetic acid and water in the system, and then fill with argon. (2) stop heating, wait for temperature to drop to room temperature, add the sulfur powder of 2 millimoles. (3) The temperature of the reaction solution was raised to 240° C. and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product. The result was similar to Example 1.

Embodiment 8:

(1) Heat 1 mmol of cadmium oxide, 6 mmol of oleic acid, and 15 milliliters of octadecene to 280° C. under argon, and heat for 15 minutes to dissolve the cadmium oxide. (2) Stop heating, and when the temperature drops to room temperature, add 0.5 mmol of sulfur powder. (3) The temperature of the reaction solution was raised to 240° C. and reacted for 1 hour. (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in cyclohexane, add ethanol and centrifuge, repeat this process 3 times to obtain the final product. The result was similar to Example 1.

Claims (3)

1. A method for preparing monodisperse cadmium sulfide nanocrystals, comprising the steps of: (1) Heating the mixture of cadmium acetate, oleic acid and solvent to 100°C to 120°C to obtain cadmium oleate solution, vacuuming to remove water and acetic acid in the system; or heating the mixture of cadmium oxide, oleic acid and solvent to 200°C ~300°C, keep warm until the cadmium oxide is completely dissolved to obtain a cadmium oleate solution; the molar ratio of cadmium acetate or cadmium oxide to oleic acid is 1:2~1:10; Described solvent is octadecene or liquid paraffin; (2) the temperature of described cadmium oleate solution is down to room temperature, add sulfur powder, the mol ratio of cadmium oleate and sulfur is 4: 1～1: 4; (3) The temperature of the reaction solution in step (2) is raised to 220° C. to 300° C. for reaction until the reaction ends; (4) Stop heating, wait for the temperature of the reaction solution to drop to room temperature, add ethanol and centrifuge to purify, remove the supernatant, disperse the precipitate in a non-polar solvent, add ethanol and centrifuge, and repeat several times to obtain the final product. 2. The method according to claim 1, characterized in that: the operations from step (1) to step (3) are carried out under the protective atmosphere of argon flow. 3. The method according to claim 1, characterized in that: said non-polar solvent is hexane, hexanaphthene, toluene or chloroform.

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