Preparation method and application of ag8snse6 nanocrystals

Abstract

The application relates to the technical field of nanocrystal materials, and discloses a preparation method and application of Ag8SnSe6 nanocrystals. The preparation method of the Ag8SnSe6 nanocrystals comprises the following steps: Se, oleylamine and dodecanethiol are added into a container one for ultrasonic treatment to obtain a Se precursor; AgNO3, SnCl4.5H2O, Se, oleylamine and oleic acid are added into a container two, vacuum pumping is carried out for primary stirring, then the temperature is increased to 80 DEG C, vacuum pumping is carried out again for secondary stirring, the material structure is low-dimensioned, so that the freedom of decoupling electric heat transport is increased; the quantum confinement effect of the nanomaterials is utilized to increase the state density of the Fermi surface, so that the Seebeck coefficient of the material is significantly enhanced, and a higher power factor is obtained; meanwhile, the nanocrystallization of the material also produces the dimension and size limitation effect and the interface scattering effect on the phonon transmission, so that the thermal conductivity is reduced; therefore, the low-dimensioning of the material structure effectively improves the thermoelectric performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of nanocrystal materials, in particular to a preparation method and application of Ag8SnSe6 nanocrystals. BACKGROUND

[0002] As a frontier new energy material, a thermoelectric conversion material can convert heat energy and electric energy, thereby improving fuel utilization efficiency, improving environmental pollution, and realizing energy regeneration. In addition, the thermoelectric conversion technology has important application prospects in the fields of refrigeration of small electronic devices such as semiconductor chips, temperature control of aerospace vehicles and related components, and the like.

[0003] The most direct strategy to improve the thermoelectric performance of a material is to improve the power factor and reduce the lattice thermal conductivity. In practical application, the reduction of the lattice thermal conductivity is mainly realized by introducing a defect structure in the matrix. However, the introduction of the defect structure not only scatters phonons, but also scatters carriers in the material, thereby affecting the electrical performance, resulting in that the improvement of the ZT value of most materials is limited. The development of an intrinsic low thermal conductivity material can well solve this problem. The lower intrinsic thermal conductivity of the material can avoid the carrier scattering caused by the introduction of the defect structure, so as to focus on the improvement of the electrical transport performance, and at the same time, the abundance of the material and the production cost are taken into account.

[0004] Among them, Ag8SnSe6 is one of the materials with the lowest sound velocity and thermal conductivity among the known thermoelectric materials, and the material has the advantages of environmental friendliness and high element abundance, and has a broad space in future commercial application. However, the current carrier concentration of Ag8SnSe6 is low, and the electrical transport performance is still poor, especially the thermoelectric performance near room temperature is not ideal, and the ZTave value is low. The multi-scale (low-dimensional) structure regulation of Ag8SnSe6 material is still blank, and the currently prepared material has the problems of large particle size and difficult decoupling regulation of electrical and thermal transport. SUMMARY

[0005] The application aims at solving the problems in the prior art, and provides a preparation method and application of Ag8SnSe6 nanocrystals.

[0006] In order to achieve the above purpose, the application adopts the following technical scheme:

[0007] A preparation method of Ag8SnSe6 nanocrystals comprises the following steps:

[0008] Step 1: Se, oleylamine and dodecanethiol are added into a container one and are ultrasonically treated to obtain a Se precursor;

[0009] Step 2: AgNO3, SnCl4.5H2O, oleylamine and oleic acid are added into container two, vacuum primary stirring, then heating to 80℃, vacuum secondary stirring, then nitrogen is introduced into container two, heating to 220℃, and the Se precursor obtained in step 1 is added for reaction;

[0010] Step 3: the reactant in container two in step 2 is naturally cooled to room temperature, then washed with n-hexane and ethanol for 2 times to obtain nanocrystals;

[0011] Step 4: ammonium thiocyanate is added into acetone to obtain ammonium thiocyanate solution, the nanocrystals obtained in step 2 are washed with the prepared ammonium thiocyanate solution for 1 time, then washed with ethanol for 1 time, finally put into a vacuum drying oven and dried overnight to obtain the Ag8SnSe6 nanocrystals.

[0012] Preferably, in step 1, the concentration of oleylamine is 80%-90%; in step 1, the ultrasonic treatment time is 30 min.

[0013] Preferably, in step 2, the vacuum primary stirring time is 30 min; the vacuum secondary stirring time when heating to 80℃ is 1 h; the reaction time after adding the Se precursor obtained in step 1 is 30 min.

[0014] Preferably, in step 4, the temperature in the drying oven is 80℃.

[0015] The Ag8SnSe6 nanocrystals prepared by the above preparation method of Ag8SnSe6 nanocrystals are applied in the field of thermoelectricity.

[0016] The beneficial effects of the present application are:

[0017] 1. The Ag8SnSe6 nanocrystals are successfully synthesized by the colloidal method, the material structure is low-dimensioned, thereby increasing the freedom of decoupling electric heat transport; the quantum confinement effect of the nanomaterials is utilized to increase the state density of the Fermi surface, thereby significantly enhancing the Seebeck coefficient of the material, and further obtaining a higher power factor; meanwhile, the nanometerization of the material also produces dimension and size limitation effect and interface scattering effect on the phonon transport, thereby reducing the thermal conductivity; therefore, the low-dimensioning of the material structure effectively improves the thermoelectric performance thereof.

[0018] 2. The structure low-dimensioning method is utilized to effectively increase the state density near the Fermi level, increase the carrier concentration, and effectively improve the electrical conductivity of the material.

[0019] 3. The ammonium thiocyanate solution is used for phase exchange and removal of molecular chains; the Ag8SnSe6 nanocrystals prepared by the present application have a grain size of 11-15 nm; the ZT value of the Ag8SnSe6 nanocrystals prepared by the present application reaches 0.5. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Flow chart for preparation of Ag8SnSe6nanocrystals;

[0021] Figure 2 TEM images and particle size images of Ag8SnSe6nanocrystals synthesized at different temperatures;

[0022] Figure 3 XRD images of Ag8SnSe6nanocrystals synthesized at different temperatures;

[0023] Figure 4 HRTEM images and EELS images of Ag8SnSe6nanocrystals;

[0024] Figure 5 XPS images of Ag8SnSe6nanocrystals;

[0025] Figure 6 Temperature-dependent XRD images of Ag8SnSe6bulk after hot pressing;

[0026] Figure 7 Cross-sectional SEM images and EDX energy spectrum images of Ag8SnSe6bulk;

[0027] Figure 8 Thermoelectric performance images of Ag8SnSe6;

[0028] Figure 9 Thermogravimetric analysis images of Ag8SnSe6;

[0029] Figure 10 Mechanical hardness images of Ag8SnSe6. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application.

[0031] Embodiment: Take preparation of 1 mmol of Ag8SnSe6as an example;

[0032] 1 mmol of Se and 6 ml of oleylamine with a concentration of 80%-90% and 6 ml of dodecanethiol were added into a 30 ml centrifuge tube and ultrasonicated for 30 min to obtain a Se precursor;

[0033] 8 mmol of AgNO3, 1 mmol of SnCl4.5H2O, 100 ml of oleylamine and 16 mL of oleic acid were added into a 250 ml three-necked flask, vacuumized and stirred for 30 min initially, then heated to 80℃ and vacuumized and stirred for 1 h again, then nitrogen was introduced into the three-necked flask, heated to 220℃, and the above Se precursor was injected and reacted for 30 min; after natural cooling to room temperature, the nanocrystals were washed twice with n-hexane and ethanol, and dried in a vacuum drying oven at 80℃ overnight to obtain 1 mmol of the Ag8SnSe6nanocrystals.

[0034] 0.07612 g of ammonium thiocyanate was added into 20 ml of acetone to obtain an ammonium thiocyanate solution, the above nanocrystals were washed once with the prepared ammonium thiocyanate solution, then washed once with ethanol, and finally placed in a vacuum drying oven and dried at 80℃ overnight to obtain 1 mmol of the Ag8SnSe6nanocrystals.

[0035] The morphology and grain size of the Ag8SnSe6nanocrystals prepared by controlling the synthesis temperature are illustrated by the particle size distribution of the nanocrystals prepared at a reaction temperature of 220℃, which is uniform Figure 2 The X-ray diffraction (XRD) peak of the nanocrystals prepared at a reaction temperature of 220℃ is completely consistent with the standard card of cubic phase Ag8SnSe6nanocrystals Figure 3 , indicating that the sample is a pure phase and does not contain other impurities. In addition, the high-resolution transmission electron microscope (HRTEM) image and EELS image of the nanocrystals can observe the corresponding lattice spacing, which is consistent with Ag8SnSe6, and the Ag, Sn and Se elements are uniformly distributed Figure 4 . The X-ray photoelectron spectroscopy (XPS) image shows the characteristic peaks of Ag 3d, Sn 3d and Se 2p, which further proves the successful synthesis of Ag8SnSe6nanocrystals Figure 5 .

[0036] The X-ray diffraction (XRD) peak of the bulk sample after hot pressing is completely consistent with the standard card of orthorhombic phase Ag8SnSe6nanocrystals, indicating that the sample is a pure phase and does not contain other impurities, and the phase transition occurs between 348K and 373K, which is consistent with the phase transition rule of the material Figure 6 . The corresponding element mapping image and energy spectrum analysis by scanning electron microscope (SEM) show that the Ag, Sn and Se elements in the bulk are uniformly distributed Figure 7 . The conductivity, Seebeck coefficient and thermal conductivity of the Ag8SnSe6bulk sample were tested and the ZT value was calculated, which can reach 0.5 at 723 K Figure 8 . In addition, the thermogravimetric analysis result shows that the sample has good thermal stability Figure 9). Finally, the mechanical hardness of the sample was tested, and the result shows that the sample has good mechanical hardness, indicating that the material has great potential application prospect in future commercial application Figure 10 ).

[0037] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, should be covered within the protection scope of the present application.

Claims

1. A method for preparing Ag8SnSe6 nanocrystals, characterized in that, Includes the following steps: Step 1: Add Se, oleylamine, and dodecyl mercaptan to container 1 and sonicate to obtain the Se precursor; Step 2: Add AgNO3, SnCl4·5H2O, oleylamine and oleic acid to container two, vacuum and stir for the first time, then heat to 80°C and vacuum and stir again, then introduce nitrogen into container two and heat to 220°C, and add the Se precursor obtained in step 1 to react fully. Step 3: After the reactants obtained in container 2 in step 2 are naturally cooled to room temperature, they are washed twice with n-hexane and ethanol to obtain nanocrystals; Step 4: Add ammonium thiocyanate to acetone to obtain an ammonium thiocyanate solution. Wash the nanocrystals prepared in Step 2 once with the prepared ammonium thiocyanate solution, then wash them once with ethanol, and finally place them in a vacuum drying oven and dry them overnight to obtain the Ag8SnSe6 nanocrystals.

2. The method for preparing Ag8SnSe6 nanocrystals according to claim 1, characterized in that, In step 1, the concentration of oleylamine is 80%-90%; in step 1, the duration of ultrasonic treatment is 30 minutes.

3. The method for preparing Ag8SnSe6 nanocrystals according to claim 1, characterized in that, In step 2, the initial stirring under vacuum lasts for 30 minutes; the stirring under vacuum again after heating to 80°C lasts for 1 hour; and the reaction time after adding the Se precursor obtained in step 1 lasts for 30 minutes.

4. The method for preparing Ag8SnSe6 nanocrystals according to claim 1, characterized in that, In step 4, the temperature inside the drying oven is 80℃.

5. The application of Ag8SnSe6 nanocrystals prepared by the method described in any one of claims 1-4 in the field of thermoelectricity.

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