TWI704108B - Method for preparing water-soluble quantum dots - Google Patents

Abstract

The present invention provides a method for preparing a water-soluble quantum dot material in a normal pressure environment, which includes preparing an oil phase precursor solution containing a sub-dot material under normal pressure; preparing an aqueous precursor solution containing a sub-dot material; and the oil phase The precursor solution and the aqueous phase precursor solution are mixed to form a two-phase precursor solution; the two-phase precursor solution is heated and stirred for a period of time and then the two-phase precursor solution is cooled; the aqueous phase solution is extracted and an aqueous phase is added for upgrading extraction Solution; and remove the oil phase solution. The present invention can simplify the existing synthesis method of quantum dots, and can work in the atmosphere, normal pressure, and low temperature environment below 100°C. By adjusting the reaction and process conditions, it can produce different particle sizes and PL excitation wavelengths. High-purity quantum dot material.

Description

Method for preparing water-soluble quantum dots

The present invention relates to the field of synthesis of quantum dots, especially the field of synthesis of quantum dots under atmospheric pressure and low temperature.

Nowadays, different methods have been developed to synthesize quantum dots, such as one-pot synthesis, sol-gel, co-precipitation, and hot-injection. Injection, hydrothermal and micro-fluidic reaction, each synthesis method has its own advantages and disadvantages.

The one-pot synthesis method allows the reactants to react continuously in multiple steps in a reactor, and the synthesis is carried out under a relatively high temperature environment. The literature has used this method to synthesize quantum dots. The metal precursors are mostly metal oxides or metal salts, and the anion precursors are mostly trimethylsilyl ((TMS) ₂ E, E = S, Se, Te ), the solvent is usually one with high boiling point and chelating ability, such as trioctylphosphine (TOP). Although the principle of this method is simple, the main solvent with high boiling point (such as TOP or octadecene (ODE)) must be used, and the synthesis must be carried out in a dull gas environment. These problems will limit the amount of this method in the industry. Production use.

The sol-gel method is a method of producing solid materials from small molecules. This method was first used to produce metal oxides. In recent years, non-oxide systems have been developed. The preparation process of the sulfur or selenide in the synthesis of quantum dots can generally be divided into three parts: thiolysis, nanoparticle condensation, and metathesis reaction. The raw material of the sol is a metal compound (usually an inorganic metal salt or metal alkoxide) that is easy to hydrolyze (or alcoholysis), which can be suspended in a certain solvent. In a typical sol-gel method, the reactants will undergo a series of hydrolysis reactions and (condensation) polymerization reactions to form a colloidal suspension, and the substances in it will condense into a new phase, that is, containing high solids. The solvent of the molecule, this is the gel. Although this method can control the purity of the product and the experiment temperature is low, the method contains multiple steps, also requires the use of a reducing agent (sodium borohydride), and the process requires close monitoring.

The co-precipitation method usually works under an inert gas. A mixed solution of two different metal salts is added dropwise to a solution containing a capping agent, and stirring is continued for several hours. In order to induce co-precipitation, the required molar ratio of sodium hydroxide (or ammonia) should be added during the reaction, and the pH of the solution should be adjusted to 7-8 (depending on the precursor solution). After the precipitate is produced, it is usually stirred for 24 hours, and then the precipitate is filtered, thoroughly washed with distilled water, and finally dried under vacuum. The disadvantage of this method is that it is not suitable for preparing products with high purity and precise chemical dosage, and it is also difficult to control the crystal size and shape.

Thermal injection method is one of the methods that can simply synthesize quantum dots. Taking the synthesis of CdSe quantum dots as an example, the first solution is selenium (Se) powder dissolved in the TOP solvent to form TOPSe. The second solution is CdO dissolved in the TOP solvent, and then the surfactant is added to the second solution and heated to 250-270°C. When the temperature is reached, quickly inject the first solution into the second solution. When the color of the solution changes, the reaction can be confirmed. After the color changed, the product was taken out at different times. Although the principle of this method is simple, it must use the main solvents with high boiling points (such as TOP and ODE), and the synthesis must be carried out in a dull atmosphere. In addition, the temperature and speed of the raw material injection must be strictly controlled, and the time must be different. Taking out quantum dots of different sizes inside, these problems limit the use of this method in industrial mass production.

The hydrothermal method is a method of using high temperature and high pressure aqueous solution to dissolve insoluble or poorly soluble substances under atmospheric conditions, and by controlling the temperature difference of the solution in the autoclave to generate convection to form a supersaturated state to precipitate and grow crystals. However, the hot solution in the autoclave may be corrosive, the high-pressure container may cause an explosion, and the autoclave is expensive, and the inability to observe the growth of crystals is the main disadvantage.

The microfluidic reaction method uses the microfluidic reaction carried out by the micro(fluid) reactor as a continuous flow reaction. The advantage is that the efficiency of mass transfer and heat transfer is high, and the reaction temperature and reaction can be controlled more easily than batch reactors. Process conditions such as time. Although the microfluidic reaction method can continuously synthesize quantum dot materials, the main solvent with high boiling point must be used, and the synthesis must be carried out in a dull gas environment, and the synthesis must be carried out in a pipeline that can withstand high temperature and high pressure. At the same time, it has the disadvantages of hydrothermal synthesis (that is, high-pressure pipelines may cause explosions, and pipelines that can withstand high pressure are expensive, and the growth of crystals cannot be observed). If the solution is corrosive, it will be accelerated by high temperature and high pressure Corroded the pipeline, causing the dilemma that synthesis could not proceed at all.

Although the aforementioned quantum dot synthesis method can change the composition and particle size of the quantum dot through the selection of the method and the control of the reaction conditions, to achieve the purpose of adjusting the energy gap of the quantum dot material and the wavelength of PL fluorescence, the aforementioned quantum dot The synthesis method is a discontinuous process except for the microfluidic reaction method, and the reaction time is very long, and it is impossible to control and change the reaction and process conditions in real time. The process operation not only needs to be carried out in a passive atmosphere, but also requires a large amount of high boiling point. In addition, expensive solvents (such as TOP and OA) and reducing agents (such as sodium borohydride) have caused problems such as the inability to increase the production of quantum dots and their high prices. Although the microfluidic reaction method can be continuously synthesized, it must still use a high boiling point main solvent. It must also be synthesized in a dull gas environment and in a pipeline that can withstand high temperature and pressure, and has the disadvantages of hydrothermal synthesis. It is also impossible to synthesize corrosive precursor solutions. If quantum dot materials can be used in large quantities in various fields in the future, it is necessary to find a synthesis method that can change the conditions immediately as required, and can use general solvents to carry out mass production and continuous synthesis methods under ordinary environments.

Because in some biochemical applications, quantum dots must be stably dispersed in an aqueous solution, so unless synthesized in an aqueous solution, the quantum dots must be synthesized in an organic solvent using the above method After centrifugation, cleaning, redispersion, surface modification of quantum dots, and aqueous phase extraction and transfer, the hydrophilic (that is, water-soluble) quantum dot materials can be prepared for applications in the biochemical field. If you want to avoid the increase in production costs and the decrease in production efficiency caused by such complicated procedures, of course, you can directly prepare quantum dot materials in an aqueous solution. However, the aqueous quantum dot materials reported in the literature can be lower than 100 ℃. The synthesis is carried out under the conditions of high temperature, but it still needs to be controlled in a passive atmosphere, and the reducing agent of sodium borohydride must be used. During the reaction process, even highly toxic hydrogen sulfide or hydrogen selenide will be produced. It is difficult to scale up mass production. Both the degree and the cost are very high, and it still needs to go through the process of centrifugation, cleaning and surface modification after synthesis, before it is suitable for application in the field of biochemistry. Therefore, a new method must be found to simplify the manufacturing process of water-soluble quantum dot materials and reduce the risk and cost of the manufacturing process.

Therefore, the purpose of the present invention is to provide a method for mass-producing high-purity water-soluble quantum dot materials with different particle sizes and PL excitation wavelengths under atmospheric, normal pressure, and low temperature environments.

The method of the present invention can use a general glass reaction tank in the atmosphere, normal pressure and low temperature environment, and adjust the reaction and process conditions without the need for reducing agents and a large amount of high-boiling organic liquid reactants. The preparation of high-purity water-soluble quantum dot materials can not only greatly simplify the process and time of the manufacturing process, improve the production efficiency of quantum dot materials, but also achieve the effect of reducing production costs and process risks.

The method of the present invention solves the problem that in the existing quantum dot synthesis method, a high melting point and expensive organic liquid must be used as the main solvent, and the synthesis must be carried out under high temperature, dull gas or even high pressure environment, which may cause danger, high energy consumption, and High energy and production facility costs, and the inability to scale up mass production.

The steps of the present invention are to dissolve the raw material containing the metal cation of the sub-point material in water to form an aqueous phase solution, and then dissolve the raw material containing the anion of the sub-point material in a water-immiscible solvent to form an oil Phase solution, and then take appropriate amount of water phase solution and oil phase solution and mix them in the reaction tank to form an oil-water two-phase immiscible two-phase precursor solution containing quantum dots in the required composition ratio; then, at atmospheric pressure The two-phase precursor solution is heated and stirred under the environment, and the reaction is carried out under controlled conditions. After the size of the quantum dots synthesized in the oil phase solution and the light-excited fluorescence (Photoluminescence, PL) laser wavelength reach the expected target, the reaction is terminated and the oil-water immiscible solution is cooled, and the raw water phase The solution is extracted and replaced with a modified extraction aqueous solution, and the new oil-water two-phase immiscible solution is stirred to perform the reaction of the hydrophilic modification of the quantum dot surface and the aqueous phase extraction. The quantum dots to be synthesized in the crude oil phase are transferred to the modified extraction aqueous solution of the water phase, and the preparation of water-soluble quantum dot materials is completed.

In order to make the above and/or other objectives, effects, and features of the present invention more obvious and understandable, preferred embodiments are described below in detail.

The "atmosphere" mentioned in the present invention is a layer of mixed gas surrounding the earth due to the gravitational force of the earth.

Under normal atmospheric atmosphere, the raw materials containing VIA (such as sulfur, selenium, tellurium) are added to a solvent that can completely dissolve them and are immiscible with water to form a VIA-containing oil phase precursor solution. The mixing weight ratio of the solvent and VIA element is 8 or more. Preferably, the ratio is 8-12. In one embodiment, the ratio is 8.31. The solvent includes, but is not limited to, Oleylamine (OLA), octadecene (ODE), or trioctylphosphine (TOP).

Then, dissolve the water-soluble raw materials (such as cadmium acetate or silver nitrate) containing the metal components of the sub-points in water to form an aqueous precursor solution containing the metal components of the sub-points. The weight mixing ratio of water and metal-containing water-soluble raw materials is 1 or more. Preferably, the ratio is 10 to 150.

According to the required component ratio, the two precursor solutions of the oil phase precursor solution and the water phase precursor solution are mixed in an atmospheric atmosphere to form a two-phase oil-water insoluble precursor solution required for the synthesis of quantum dots, including an oil phase solution And an aqueous solution. The reaction molar ratio of VIA elements and the water-soluble raw materials containing metal components is 0.5 or more. Preferably, the Mohr ratio is 1-3. The mixing volume ratio of the aqueous phase precursor solution and the oil phase precursor solution is 2-25.

The two-phase precursor solution is heated and stirred in a water bath to perform the synthesis reaction of quantum dots. After the reaction proceeds to the formation of quantum dots with the required particle size and PL laser wavelength in the oil phase solution, the oil-water The two-phase immiscible quantum dot solution is taken out of the water bath and cooled to stop the synthesis reaction. At this time, the required quantum dots have been formed in the oil phase solution. The temperature of the water bath reaction is preferably 40-120°C; more preferably 65-100°C. The reaction temperature can be 40, 50, 60, 70, 80, 90, 100, 110, 120°C, or ±10% of the above-mentioned temperature points.

Under normal atmosphere, extract the water-phase solution of the above-mentioned synthetic oil-water immiscible quantum dot solution and replace the hydrophilic water-phase modified extraction solution to form the modified and extracted oil-water immiscible quantum dot solution . The hydrophilic aqueous phase modified extraction solution includes, but is not limited to, 3-mercaptopropionic acid (mercaptopropionic acid, MPA), mercaptoundecanoic acid (mercaptoundecanoic acid, MUA), and dihydrolipoic acid (DHLA) , Or pyridine (Pyridine) solution.

After the above-mentioned modified and extracted oil-water two-phase immiscible quantum dot solution is modified and extracted at room temperature for a period of time, it can be found that the quantum dots in the oil phase solution will be modified and extracted into the aqueous phase solution. Forms water-soluble quantum dots. Then the oil phase solution is removed to complete the synthesis of the water-soluble quantum dot solution. The reaction time for upgrading and extraction is at least 10 minutes, preferably 30 to 40 minutes. The actual reaction time can be adjusted as required until the water-soluble quantum dots enter the aqueous solution and reach the required amount. The reaction time can be, for example, 10, 20, 30, 40, 50, 60, or more minutes.

The following takes the synthesis of CdSe water-soluble quantum dots as an example to illustrate the method of the present invention for the synthesis of two-phase water-soluble quantum dots at atmospheric pressure and low temperature.

Under normal pressure atmosphere, 0.680 g of cadmium acetate and 85 ml of deionized water are dissolved in a container such as a beaker to form an aqueous precursor solution containing cadmium.

In a normal pressure atmosphere, 0.8 g of selenium powder and 8 ml of TOP are placed in a sealed container and heated to dissolve to form a selenium-containing oil phase precursor solution.

Under a normal pressure atmosphere, the above-mentioned two precursor solutions are mixed to form an oil-water two-phase immiscible two-phase precursor solution required for the synthesis of CdSe quantum dots.

In a water bath close to the boiling point of alcohol (78°C), the two-phase precursor solution is heated and stirred under a normal pressure atmosphere to perform the synthesis reaction of CdSe quantum dots.

After the reaction proceeds to form the required particle size in the oil phase solution (Figure 1, Figure 1 is the TEM micrograph of the synthesized CdSe quantum dots, the average particle size is 6.3 nm by image analysis software), color (It appears orange under a fluorescent lamp, as shown in Figure 2; it appears green under a UV lamp, as shown in Figure 3), and quantum dots with PL laser wavelength (PL peak is about 540-550 nm, as shown in Figure 4), That is, the immiscible quantum dot solution of oil and water phases is taken out of the water bath and cooled to stop the synthesis reaction. At this time, the required CdSe quantum dots have been formed in the oil phase solution. Figure 5 shows the XRD pattern of the powder obtained after drying the oil phase solution.

Mix 0.4 ml of MPA with 1.2 ml of pure water and 4 ml of methanol, and add 40 wt% (v/v) sodium hydroxide to adjust the pH to 10 to prepare approximately 8 ml of the required water MPA buffer solution for phase modification extraction

Under normal pressure atmosphere, extract the water phase solution of the CdSe quantum dot solution which is immiscible between the oil and water phases after synthesis, and use the above-mentioned hydrophilic water phase modification extraction MPA buffer to replace the original water phase solution to form modified extraction oil and water Two-phase immiscible CdSe quantum dot solution.

Under normal pressure atmosphere and room temperature, the oil-water two-phase immiscible CdSe quantum dot solution of the above-mentioned modified extraction is modified and extracted, and the reaction is about 40 minutes. It can be found that the CdSe quantum dots in the oil phase solution will be modified. The mass is extracted into the aqueous solution to complete the hydrophilic modification, and form a water-soluble CdSe quantum dot solution in the aqueous solution. Figure 6 shows the FTIR spectra of CdSe quantum dots before and after modification.

Under normal pressure atmosphere, the oil phase solution is removed to complete the synthesis of the water-soluble CdSe quantum dot solution.

The above embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent replacements and improvements made within the spirit and principles of the above implementation manners should be included in the protection scope of the technical solution.

The method requested by the present invention is not limited to cadmium sulfide, but can also be used to synthesize quantum dot materials of other components such as silver sulfide, zinc sulfide, and cadmium selenide.

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Fig. 1 is a TEM micrograph (X 250K) of CdSe quantum dots synthesized by the method of the present invention. Fig. 2 shows the condition of the CdSe quantum dot solution with immiscible oil and water phases synthesized in the embodiment of the present invention under a fluorescent lamp. FIG. 3 shows the condition of the CdSe quantum dot solution with immiscible oil and water phases synthesized in the embodiment of the present invention under ultraviolet light excitation. Figure 4 shows the UV and PL spectra of the synthesized CdSe quantum dots according to the embodiment of the present invention. FIG. 5 is an XRD pattern of the CdSe quantum dot powder obtained by drying the oil phase CdSe quantum dot solution synthesized in the embodiment of the present invention. Fig. 6 shows the FTIR spectra of the synthesized CdSe quantum dots before and after hydrophilic modification.

Claims (3)

A method for preparing water-soluble quantum dots includes: a. uniformly mixing a VIA group anionic material and a lipophilic ligand solvent in a weight ratio of 1:8-1:12 to form an oil phase precursor solution, wherein the The lipophilic ligand solvent is selected from trioctylphosphine (TOP), oleylamine (OLA) or octadecene (ODE); b. A metal cation water-soluble material containing cadmium or silver Mix evenly with water in a weight ratio of 1:10-1:150 to form an aqueous phase precursor solution; c. mix the oil phase precursor solution and the aqueous phase precursor solution to form a two-phase precursor solution, the The two-phase precursor solution includes an aqueous phase solution and an oil phase solution; d. The two-phase precursor solution is heated and stirred in a non-enclosed appliance under atmospheric pressure and 65-100°C until required The quantum dots are formed in the oil phase solution; e. cooling the two-phase precursor solution; f. extracting the aqueous phase solution and adding an aqueous phase modified extraction solution to react at room temperature, wherein the aqueous phase is modified The mass extraction solution is a solution containing 3-mercaptopropionic acid (mercaptopropionic acid, MPA), thioundecanoic acid (mercaptoundecanoic acid, MUA), or dihydrolipoic acid (DHLA) Pyridine); g. Remove the oil phase solution. Such as the method of item 1 in the scope of patent application, wherein the VIA group element is sulfur, selenium or tellurium. Such as the method of the first item in the scope of patent application, wherein the metal cation water-soluble material is cadmium acetate or silver nitrate.

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