Environment-friendly Ag2Te quantum dot as well as one-step synthesis method and application thereof

Abstract

The invention discloses a one-step synthesis method of environment-friendly Ag2Te quantum dots. The one-step synthesis method comprises the following steps: providing a silver precursor and a tellurium precursor; the tellurium precursor is prepared by mixing tellurium dioxide and dodecanethiol; mixing oleylamine and octadecene, heating to a preset temperature, adding the silver precursor, rapidly injecting the tellurium precursor after a first reaction time, stopping heating after a second reaction time, and cooling to obtain a quantum dot crude solution; and purifying the quantum dot crude solution to obtain the required environment-friendly Ag2Te quantum dot. The size distribution and the exciton absorption peak of the environment-friendly Ag2Te quantum dots are related to the preset temperature. The invention further discloses the environment-friendly Ag2Te quantum dot obtained by the method and application thereof. The tellurium precursor and the silver precursor which do not contain phosphine are adopted, the synthesis process is simple and non-toxic, different size distribution and wide-range exciton absorption peaks of the Ag2Te quantum dots are achieved, and the monodispersity of the Ag2Te quantum dots can be guaranteed.

Description

Technical Field

[0001] The invention relates to the field of preparation of semiconductor quantum dots, and in particular to an environmentally friendly Ag2Te quantum dot and a one-step synthesis method and application thereof. Background Art

[0002] Quantum dots (CQDs) have broad application prospects in the field of photodetection due to their wide bandgap absorption tunability, low cost and solution processability. However, most short-wave infrared quantum dot photodetectors are based on chalcogenides (S, Se and Te) of Hg and Pb, and the presence of these toxic heavy metals limits their application. According to the National Environmental Quality Standard (GB15618-1995), the Hg element content shall not exceed 0.001 mg / L and the Pb element content shall not exceed 0.05 mg / L. Therefore, it is extremely important to develop a non-toxic photodetector that responds in the short-wave infrared band.

[0003] Ag2Te quantum dots have a small band gap and excellent fluorescence absorption ability in the short-wave infrared band. In addition, Ag2Te quantum dots have low toxicity, so they have attracted widespread attention. At present, the synthesis method of Ag2Te quantum dots is mainly hot injection. In the hot injection method, the most widely used tellurium precursor is trialkyl-phosphine-tellurium (R3P=Te). In trialkyl-phosphine-tellurium, the presence of phosphine will have an adverse effect on the surface passivation of quantum dots. According to calculations, the binding of phosphine-based ligands to Ag on the surface of quantum dots is stronger than that of thiols. However, to make the quantum dot film conductive, thiol ligand exchange is required. The strong binding of phosphine-based ligands will inevitably affect the thiol ligand exchange process, thereby affecting its photoelectric properties. In addition, various methods and precursors have been used to synthesize Ag2Te quantum dots. For example, a method for synthesizing Ag2Te quantum dots in an aqueous phase is proposed in the prior art, and Ag2Te quantum dots are prepared by mixing CdTe quantum dots of different sizes with AgNO3 solution. However, during the nucleation and growth stages, it is still difficult to accurately control the size of quantum dots due to the difficulty in accurately controlling multiple reaction conditions such as pH value and reactant concentration.

[0004] It can be seen that the current problems in the preparation of Ag2Te quantum dots are mainly: (1) the precursor contains phosphine, which will affect the surface passivation of quantum dots and thus have an adverse effect on the photoelectric properties of quantum dots. (2) The lack of understanding of its nucleation and growth mechanism makes it difficult to accurately control the size. Summary of the invention

[0005] In view of the above problems, the present invention proposes an environmentally friendly one-step synthesis method of Ag2Te quantum dots, which adopts tellurium precursor and silver precursor that do not contain phosphine. The synthesis process is simple and non-toxic, which not only realizes different size distributions and wide range of exciton absorption peaks of Ag2Te quantum dots, but also ensures the monodispersity of Ag2Te quantum dots.

[0006] The first aspect of the present invention discloses a one-step synthesis method of environmentally friendly Ag2Te quantum dots, comprising:

[0007] Providing a silver precursor and a tellurium precursor; the tellurium precursor is prepared by mixing tellurium dioxide and dodecanethiol in a molar ratio of 1:4 to 1:5;

[0008] Mixing oleylamine and octadecene in a molar ratio of 8:5 to 10:5, heating to a preset temperature, adding the silver precursor, and after a first reaction time, quickly injecting the tellurium precursor to obtain a reaction system in which the molar ratio of silver to tellurium is 12:5 to 14:5. After a second reaction time, stopping heating, and cooling to obtain a crude quantum dot solution;

[0009] Purifying the crude quantum dot solution to obtain the desired environmentally friendly Ag2Te quantum dots;

[0010] The size distribution and exciton absorption peak of the environmentally friendly Ag2Te quantum dots are related to the preset temperature.

[0011] As an optional solution, the preset temperature is 120-140°C.

[0012] As an optional solution, the first reaction time is 5±1 min, and the second reaction time is 15±5 min.

[0013] As an optional solution, the preparation method of the tellurium precursor is as follows: at 100±5° C. and in an inert gas atmosphere, tellurium dioxide and dodecanethiol in a molar ratio of 1:4 to 1:5 are mixed and dissolved to obtain the tellurium precursor.

[0014] As an optional solution, the silver precursor is prepared by mixing silver iodide and oleylamine in a molar ratio of 1:3 to 1:4.

[0015] As an optional solution, the preparation method of the silver precursor is as follows: at room temperature and in an inert gas atmosphere, silver iodide and oleylamine are mixed in a molar ratio of 1:3 to 1:4, and the mixture is heated to 50±5° C. to dissolve to obtain the silver precursor.

[0016] As an optional scheme, the purification specifically includes:

[0017] adding a polar solvent to the crude quantum dot solution and precipitating the quantum dots by centrifugation;

[0018] The obtained quantum dot-immobilized particles are completely dispersed in toluene;

[0019] Adding a silver precursor to the dispersed quantum dot crude solution, and removing unreacted tellurium precursor impurities through centrifugation to obtain a supernatant;

[0020] adding the polar solvent to the supernatant, discarding the precipitate after centrifugation, and retaining the supernatant containing the quantum dot solution;

[0021] The polar solvent is added to the supernatant, and the supernatant is discarded after centrifugation to obtain the desired environmentally friendly Ag2Te quantum dots.

[0022] The second aspect of the present invention discloses an environmentally friendly Ag2Te quantum dot, characterized in that it is obtained by the one-step synthesis method of the environmentally friendly Ag2Te quantum dot described in the first aspect of the present invention and any optional scheme.

[0023] The Ag2Te quantum dots are monodisperse, with a size distribution of 3.5 to 6.3 nm and an exciton absorption peak of 1350 to 1700 nm.

[0024] The third aspect of the present invention discloses the application of environmentally friendly Ag2Te quantum dots in the field of short-wave infrared photoelectric detection.

[0025] The present invention adopts a one-step synthesis method to prepare a non-toxic and environmentally friendly Ag2Te quantum dot. Since a tellurium precursor without phosphine is used, the adverse effect of phosphine on the surface passivation of the quantum dot is eliminated. In addition, the synthesis method is simple, the precursor solution used is non-toxic and environmentally friendly, and the cost is also lower.

[0026] The present invention can realize the preparation of quantum dots with a size distribution of 3.5 to 6.3 nm and monodispersity by controlling the reaction temperature from 120° C. to 140° C., and the exciton absorption peak of the quantum dots is at 1350 to 1700 nm, which can be applied to the field of short-wave infrared photoelectric detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the XRD pattern of Ag2Te quantum dots synthesized in Example 1;

[0028] Figure 2 is a TEM image of Ag2Te quantum dots synthesized in Example 1;

[0029] Figure 3 is the mapping diagram of the Ag2Te quantum dots synthesized in Example 1;

[0030] Figure 4is the normalized absorption spectrum of the Ag2Te quantum dots synthesized in Examples 1-3, wherein the gray curve represents the Ag2Te quantum dots synthesized in Example 1, the red curve represents the Ag2Te quantum dots synthesized in Example 2, and the blue curve represents the Ag2Te quantum dots synthesized in Example 3;

[0031] Figure 5 It is a physical picture of the Ag2Te quantum dot sol synthesized in Example 1 and the Tyndall effect;

[0032] Figure 6 is a particle size diagram of the Ag2Te quantum dots synthesized in Examples 1-3, wherein the gray curve represents the Ag2Te quantum dots synthesized in Example 1, the red curve represents the Ag2Te quantum dots synthesized in Example 2, and the blue curve represents the Ag2Te quantum dots synthesized in Example 3;

[0033] Figure 7 is a TEM image of Ag2Te quantum dots synthesized in Example 2;

[0034] Figure 8 This is the TEM image of the Ag2Te quantum dots synthesized in Example 3. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below in conjunction with embodiments and drawings.

[0036] Example 1 of the present invention provides a one-step synthesis method of environmentally friendly Ag2Te quantum dots, and the specific steps are as follows:

[0037] Step S1, preparation of silver precursor: at room temperature and nitrogen atmosphere, silver iodide and oleylamine in a molar ratio of 1:3 are mixed, and preheated at 50±5° C. to promote their dissolution. After dissolution, the silver precursor required for the reaction can be obtained.

[0038] It is worth noting that oleylamine, as a common quantum dot synthesis ligand, can make the quantum dots more dispersed; silver iodide, as a silver source, can be well dissolved in oleylamine. In other embodiments, silver acetate can also be selected as the silver source, but the solubility will be worse.

[0039] Step S2, preparation of a tellurium precursor: under heating at 100±5° C. and in an inert gas atmosphere, tellurium dioxide and dodecanethiol in a molar ratio of 1:4 are mixed and dissolved to obtain a tellurium precursor.

[0040] It is worth noting that the present invention uses tellurium dioxide as the tellurium source because tellurium dioxide is not only cheap but can be dissolved in a variety of solvents. The traditional method usually uses tri-n-butylphosphine as a solvent for dissolving tellurium dioxide, but the presence of phosphine will seriously affect the stability of quantum dots. Therefore, the patent uses dodecanethiol instead of tri-n-butylphosphine to effectively remove the influence of phosphine.

[0041] Step S3, synthesis of Ag2Te quantum dots: oleylamine and octadecene are added to a three-necked flask at a molar ratio of 8:5; the three-necked flask is then heated, and oxygen and moisture in the flask are removed at about 100±5°C; when heated to 120°C, a silver precursor solution is added to the flask; after 5±1 minutes, a tellurium precursor solution is quickly injected into the three-necked flask, and the molar ratio of Ag to Te contained in the silver precursor and the tellurium precursor in the reaction system is 12:5; during the injection process, the solution immediately turns dark black, indicating that Ag2Te quantum dots are nucleated; after 15 minutes, the heating is stopped, and a crude solution is obtained after natural cooling.

[0042] Among them, the long-chain alkyl structure of oleylamine can form a coordination bond with the surface of quantum dots, thereby forming a layer of organic ligand shell on the surface of quantum dots, which helps to stabilize the quantum dots and prevent them from agglomerating, thereby obtaining quantum dots of uniform size. As a high-temperature solvent, octadecene can effectively dissolve the reaction precursors and provide an inert and stable environment for the growth of quantum dots.

[0043] Understandably, at high temperatures, the silver precursor is first added to the reaction system, which helps to form silver active centers in the solution. These active centers can serve as nucleation sites, providing a basis for the subsequent addition and reaction of tellurium precursors. By forming silver active centers first, the nucleation process of quantum dots can be better controlled, thereby obtaining quantum dots of uniform size. Conversely, if the tellurium precursor is added first, it may lead to premature nucleation, forming uneven particles or agglomeration.

[0044] It is worth noting that in the quantum dot synthesis step, as the reaction temperature increases, the quantum dot size will continue to increase, resulting in a red shift in the absorption peak. This is because high temperature increases the reaction rate of the precursor, which helps the quantum dot nucleation, and can also provide a lot of energy to help the quantum dot grow during the growth stage.

[0045] S4, purification of Ag2Te quantum dots: After the reaction is completed, the crude solution obtained in step S3 is transferred to a glove box filled with inert gas for purification.

[0046] In this embodiment, the purification process mainly includes the following steps:

[0047] First, 20 ml of methanol was added to the crude solution and the quantum dots were precipitated at 6000 rpm for 5 min to obtain quantum dot solid particles; then the solid particles were completely dispersed in 30±5 ml of toluene. Further, in order to remove the unreacted tellurium precursor in the crude solution, 3±0.5 ml of silver precursor was added to the quantum dot crude solution, centrifuged at 6000 rpm for 5 min, and then the unreacted tellurium precursor and other impurities were removed to obtain a supernatant.

[0048] Next, 15±3 ml of methanol was added to the supernatant, and the mixture was centrifuged again. After centrifugation, the quantum dot precipitate was discarded, and the supernatant containing the quantum dot solution was retained.

[0049] Then, 30±5 ml of methanol was added to the supernatant containing the quantum dot solution and centrifuged at 6000 rpm for 5±1 min to fully precipitate the Ag2Te quantum dots.

[0050] Finally, the solid particles are collected and the supernatant is discarded to obtain the desired environmentally friendly Ag2Te quantum dots (abbreviated as "Ag2Te quantum dots").

[0051] It is understandable that methanol, as a polar solvent, can effectively destroy the non-polar ligands on the surface of quantum dots and cause the precipitation of quantum dots. In other embodiments, other polar solvents, such as ethanol, isopropanol, etc., can also be used.

[0052] It should be noted that the present invention does not impose any specific restrictions on the purification method of Ag2Te quantum dots. Conventional quantum dot purification operations can be used. This embodiment is only an optional method.

[0053] Based on the Ag2Te quantum dots synthesized at 120°C in Example 1, they were placed in a vacuum oven at 100±5°C and dried for 20±10 min to ensure that the quantum dots were dry and to prevent the quantum dots from containing a small amount of solvent such as methanol or toluene that would affect the results of the X-ray diffraction analysis. The Ag2Te quantum dot powder was then subjected to X-ray diffraction analysis. Figure 1 Obvious diffraction peaks can be observed in the sample. By comparing with the standard diffraction peak card of Ag2Te (PDF#81-1824), it can be seen that the diffraction peak of the synthesized Ag2Te quantum dots at 41° corresponds to the (211) crystal plane, indicating that the structure of the synthesized substance is consistent with that of Ag2Te quantum dots, further proving that the synthesized substance is Ag2Te quantum dots.

[0054] Figure 2 and Figure 3 They are the transmission electron microscope (TEM) image of the Ag2Te quantum dots synthesized in Example 1 and the mapping image of the region. Figure 2 It can be seen that the size of quantum dots is 4±0.3nm, the size is relatively uniform, and has good monodispersity. Figure 3 It can be seen that the element content distribution of Ag2Te quantum dots at this size includes Ag and Te elements, which fully proves that the synthesized substance is Ag2Te quantum dots.

[0055] like Figure 4 As shown, the exciton absorption peak of the Ag2Te quantum dots synthesized in Example 1 is at 1350nm, indicating that it has good application value in the fields of short-wave infrared photoelectric detectors and the like.

[0056] like Figure 5 As shown, it can be seen that the Ag2Te quantum dot sol synthesized in Example 1 has an obvious Tyndall effect, and no sedimentation occurs after being stored in the air for one week.

[0057] Figure 6 The particle size diagram of the Ag2Te quantum dots synthesized in Example 1 is shown in Figure 1. The size distribution of the quantum dots is within the range of 5-13nm as measured by a ZSU3200 particle size analyzer, proving that the size of the Ag2Te quantum dots is uniform. It should be noted that the specific value of the quantum dot size cannot be simply obtained from the particle size analyzer measurement data. The measurement data can only indicate the size uniformity. The specific value of the quantum dot size must be obtained after TEM testing.

[0058] The present invention also provides another one-step synthesis embodiment of environmentally friendly Ag2Te quantum dots, namely, embodiment 2. The difference between embodiment 2 and embodiment 1 mainly lies in the temperature during the synthesis of quantum dots in step S3 and the molar ratio of oleylamine to octadecene. In step S3 of embodiment 2, the synthesis temperature is 130° C., and the molar ratio of oleylamine to octadecene is 9:5.

[0059] The present invention provides another one-step synthesis embodiment of environmentally friendly Ag2Te quantum dots, namely, embodiment 3. The difference between embodiment 3 and embodiment 1 mainly lies in the temperature during the synthesis of quantum dots in step S3 and the molar ratio of oleylamine to octadecene. In step S3 of embodiment 3, the synthesis temperature is 140°C, and the molar ratio of oleylamine to octadecene is 10:5.

[0060] like Figure 4 As shown, it shows the normalized absorption spectra of Ag2Te quantum dots of Examples 1-3. It can be seen that with the increase of temperature, the position of the exciton absorption peak red-shifts from 1353nm in Example 1 to 1660nm in Example 3, indicating that at 120-140°C, the size of quantum dots increases with increasing temperature, and the purpose of controlling the size of quantum dots can be achieved by changing the temperature.

[0061] Figure 7 and Figure 8 As shown, the transmission electron microscope (TEM) images of Ag2Te quantum dots of Example 2 and Example 3 are shown respectively, and combined with Figure 6It can be seen that the size of the Ag2Te quantum dots synthesized in Example 2 is 5±0.2 nm, and the size of the Ag2Te quantum dots synthesized in Example 3 is 6±0.3 nm, and the Ag2Te quantum dots of both sizes still have good monodispersity.

[0062] In summary, the present invention proposes a novel method for synthesizing Ag2Te quantum dots without phosphine precursor liquid, and obtains an environmentally friendly Ag2Te quantum dot. By using n-dodecanethiol to dissolve TeO2, a phosphine-free tellurium precursor is prepared, and Ag2Te quantum dots with different exciton absorption peaks and good monodispersity are synthesized at different reaction temperatures, and their exciton absorption peak is controlled in the short-wave infrared band.

[0063] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A one-step synthesis method of environmentally friendly Ag2Te quantum dots, characterized in that: include: Providing a silver precursor and a tellurium precursor; the tellurium precursor is prepared by mixing tellurium dioxide and dodecanethiol in a molar ratio of 1:4 to 1:5; Mixing oleylamine and octadecene in a molar ratio of 8:5 to 10:5, heating to a preset temperature, adding the silver precursor, and after a first reaction time, quickly injecting the tellurium precursor to obtain a reaction system in which the molar ratio of silver to tellurium is 12:5 to 14:

5. After a second reaction time, stopping heating, and cooling to obtain a crude quantum dot solution; Purifying the crude quantum dot solution to obtain the desired environmentally friendly Ag2Te quantum dots; The size distribution and exciton absorption peak of the environmentally friendly Ag2Te quantum dots are related to the preset temperature.

2. The one-step synthesis method according to claim 1, characterized in that The preset temperature is 120-140°C.

3. The one-step synthesis method according to claim 2, characterized in that: The first reaction time is 5±1 min, and the second reaction time is 15±5 min.

4. The one-step synthesis method according to any one of claims 1 to 3, characterized in that: The preparation method of the tellurium precursor is as follows: under an inert gas atmosphere at 100±5° C., tellurium dioxide and dodecanethiol in a molar ratio of 1:4 to 1:5 are mixed and dissolved to obtain the tellurium precursor.

5. The one-step synthesis method according to any one of claims 1 to 3, characterized in that: The silver precursor is prepared by mixing silver iodide and oleylamine in a molar ratio of 1:3 to 1:

4.

6. The one-step synthesis method according to claim 5, characterized in that: The preparation method of the silver precursor is as follows: at room temperature and in an inert gas atmosphere, silver iodide and oleylamine in a molar ratio of 1:3 to 1:4 are mixed, and the mixture is heated to 50±5° C. to dissolve to obtain the silver precursor.

7. The one-step synthesis method according to any one of claims 1 to 3, characterized in that: The purification specifically comprises: adding a polar solvent to the crude quantum dot solution, and precipitating the quantum dots by centrifugation; The obtained quantum dot-immobilized particles are completely dispersed in toluene; Adding a silver precursor to the dispersed quantum dot crude solution, and removing unreacted tellurium precursor impurities through centrifugation to obtain a supernatant; adding the polar solvent to the supernatant, discarding the precipitate after centrifugation, and retaining the supernatant containing the quantum dot solution; The polar solvent is added to the supernatant, and the supernatant is discarded after centrifugation to obtain the desired environmentally friendly Ag2Te quantum dots.

8. An environmentally friendly Ag2Te quantum dot, characterized in that: The environmentally friendly Ag2Te quantum dots are obtained by the one-step synthesis method according to any one of claims 1 to 7.

9. The environmentally friendly Ag2Te quantum dots according to claim 8, characterized in that: The Ag2Te quantum dots are monodisperse, with a size distribution of 3.5-6.3 nm and an exciton absorption peak of 1350-1700 nm.

10. Apply the environmentally friendly Ag2Te quantum dots described in claim 8 or 9 in the field of short-wave infrared photoelectric detection.

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