A method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots

Abstract

The application provides a method for preparing high-performance skutterudite compounds by carbon quantum dot composite modification. The method for preparing high-performance skutterudite compounds by carbon quantum dot composite modification can make carbon quantum dots quickly enter the mesoporous system of CoSb3-based skutterudite by adopting the method of rapidly ultrasonic oscillation of carbon dot solution to make carbon quantum dots enter CoSb3-based skutterudite, so that the carbon quantum dots are uniformly dispersed in the CoSb3-based skutterudite thermoelectric material, and the effect of uniform composite is achieved. Then, the CoSb3-based skutterudite thermoelectric material is prepared by combining SPS sintering. The method can meet the requirements of rapid and uniform composite, simplify the composite process, optimize the process, and obtain the CoSb3-based skutterudite thermoelectric composite material with good thermoelectric performance. The application breaks the traditional method for improving the thermoelectric performance of the existing CoSb3-based skutterudite thermoelectric material, such as doping, filling and composite metal nanophase.

Description

Technical Field

[0001] The present invention relates to the field of preparation of thermoelectric materials, and in particular to a method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots. Background Art

[0002] Thermoelectric materials are environmentally friendly, highly efficient, clean energy materials. Based on the Seebeck and Peltier effects, thermoelectric materials can realize the mutual conversion of thermal energy and electrical energy, and can use low-grade heat sources such as temperature differences in nature and waste heat from thermal power plants to generate electricity and cool down. Due to the potential thermoelectric applications of skutterudite compounds, such as harvesting heat generated in industrial processes and automobile operations, and alternative refrigeration that avoids the use of gases that are harmful to the environment, they have attracted widespread interest. Binary skutterudite is a body-centered cubic structure compound with the general chemical formula MX3 (M represents a transition metal element, such as Co, Fe, Rh or Ir; X represents a phosphorus element, such as P, As or Sb), and its space group is Im3. Currently, the thermoelectric properties of skutterudites are mainly improved by doping, filling, nano-sizing or nano-composite methods.

[0003] The size and mass of the doped metal atoms differ from those of the framework atoms, causing local lattice distortion in the skutterudite and increasing point defects, which in turn scatter phonons, ultimately reducing the material's lattice thermal conductivity and improving the thermoelectric figure of merit. However, due to the size, electronegativity, and atomic mass differences between the replaced atoms, such as Te and Se, and the framework atoms, they cannot be replaced indefinitely. Each skutterudite unit cell contains two large vacancies (i.e., the icosahedral vacancies of Sb). Due to its unique structural properties, it can be filled with metal atoms (such as Na, Ba, Yb, Ce, In, etc.) or non-metal atoms (such as S, Se, I, Cl, Br, etc.), which strongly scatter phonons in the lattice, thereby reducing the material's thermal conductivity and lattice thermal conductivity, and exhibiting the conductive properties of a phononic glass-electron crystal (PGEC). Nanoscaling or nanocompositing of thermoelectric materials is a major new direction for further improving their thermoelectric performance. Nanomaterials have significantly different physical properties from bulk materials. When the size of a material reaches the nanoscale, the density of electronic states changes significantly. With nanoscaling and the reduction of the material's dimensionality, it is possible for α, σ, and κ to vary independently, thereby optimizing a single parameter to improve the material's thermoelectric performance. Furthermore, compared to the scattering of carriers, the high-density grain boundaries caused by nanomaterials have more selective scattering of phonons, which can significantly reduce the material's thermal conductivity, κ. The addition of a small amount of a nanosecond phase can greatly enhance the scattering of phonons, significantly reducing the thermal conductivity of the thermoelectric material, while increasing the Seekbeck coefficient and only slightly decreasing the electrical conductivity, thereby significantly improving the compound's thermoelectric performance index.

[0004] Therefore, it is necessary to provide a new method for preparing high-performance skutterudite compounds by carbon quantum dot composite modification to solve the above technical problems. SUMMARY

[0005] The technical problem solved by the present application is to provide a method for preparing high-performance skutterudite compounds by carbon quantum dot composite modification, which breaks the traditional method of improving the thermoelectric performance of CoSb3-based skutterudite thermoelectric materials by doping, filling and compounding metal nano-phase. Recently, organic and organic-inorganic thermoelectric materials have gradually attracted people's interest and received extensive attention. Compared with traditional TE materials, carbon-based materials generally exhibit high flexibility, fracture toughness, high strength and high temperature stability. Carbon has multiple allotropes because it can hybridize in sp, sp2, sp3 bonds, which enables it to form zero-dimensional (e.g., fullerenes), one-dimensional (e.g., carbon nanotubes), two-dimensional (e.g., graphene) and three-dimensional (e.g., diamond) structures, and thus is one of the most widely used elements in the periodic table. In addition, carbon is one of the most abundant elements on Earth (ranked 15th among all elements), and most of its allotropes are non-toxic and lightweight. Carbon nanomaterials as a second phase composite metal-based thermoelectric material can act as an electron transport channel to improve electrical conductivity, and the addition of carbon nanotubes can also reduce the carrier concentration, thereby improving the Seebeck coefficient, which often leads to a significant increase in power factor. At the same time, it also enhances the scattering of phonons, significantly reduces the thermal conductivity, and greatly improves the thermoelectric performance of the thermoelectric material. At present, there are many second phase composites of carbon nanomaterials, such as carbon nanotubes, graphene, etc. Compared with the 3D form of the same material, the low-dimensional structure can carry a higher ZT. Quantum dots (QD) can be regarded as quasi-zero-dimensional structures, and their state density can have σ-like sharp peaks due to the stronger quantum confinement in these maximally confined structures. These sharp peaks are predicted to be the best electronic structure for TE performance, especially to enhance the Seekbeck coefficient. In addition, the strong boundary scattering in quantum dots can also greatly reduce the thermal conductivity, even lower than that of alloys. In fact, quantum dots of various materials, including carbon quantum dots, have been found or predicted to have excellent TE properties.

[0006] Carbon quantum dots (CDs) are quasi-zero-dimensional carbon-based materials with sizes less than 10 nm. Since their discovery, they have attracted extensive research interest due to their diverse physicochemical properties, excellent biocompatibility, unique optical properties, low cost, low toxicity, eco-friendliness, abundant functional groups (such as amino, hydroxyl, and carboxyl groups), high stability, and high electron mobility. Their key advantages are their ease of preparation from a variety of carbon-based materials, low cost, environmental friendliness, and consistent development trends for sustainable materials. They have a wide range of applications, demonstrating strong potential in a variety of fields, including medical imaging, environmental monitoring, chemical analysis, catalyst preparation, and energy development, and possess a vast future. CDs hold great promise as a second phase in thermoelectric composites.

[0007] Furthermore, carbon quantum dots (CDs) can incorporate a variety of heteroatoms (nitrogen, sulfur, phosphorus, boron, fluorine, etc.) as well as metals (Zn, Mg, Ag, Au, Cu, Ga, etc.) as dopants to enhance the physicochemical properties of CDs. Compared to commonly used heteroatoms, metals are better electron donors, possessing more unoccupied orbitals and larger atomic radii. Therefore, when metal ions are doped into CDs, compared to heteroatom doping, the charge density and charge transfer patterns between the graphene matrix and the metal ions are more likely to be altered, thereby significantly improving the physicochemical properties of the CDs. The introduction of metal ions can alter the electronic structure of CDs, affecting their spin density and charge distribution, thereby increasing the number of catalytically active centers within them. Compared to undoped CDs, metal ion-doped CDs exhibit superior catalytic performance. Furthermore, the introduction of metal ions enhances the electrical conductivity and electron-donating and accepting capacity of CDs, thereby promoting electron transfer. Metal doping with Zn, Mn, and Gd facilitates the radiative recombination of electrons and holes on the CD surface.

[0008] In order to solve the above technical problems, the present invention provides a method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots, which comprises the following steps: Step 1: Preparation of CoSb3-based skutterudite thermoelectric materials

[0009] Yb, Te, Co, and Sb single-substance powders are used as raw materials and weighed according to the following mass ratio: Yb:Co:Sb:Te=0.4:4:11.8:0.2; acetone or ethanol as a grinding aid is added to the materials weighed in proportion, and the materials are fully ground and mixed, and then placed in a vacuum drying oven for drying; after the grinding aid is completely volatilized, the powder is cold-pressed into a shape by a tablet press, the cold-pressed block sample is sealed in a quartz tube and then vacuumed, the vacuumed quartz tube is placed in a ceramic dry pot, green silicon carbide is placed in the dry pot as a microwave-assisted absorber, asbestos is placed around the crucible as a heat-insulating material with a thickness of 50 to 100 mm, the quartz tube and the crucible are placed in a microwave oven for microwave synthesis, the synthesized sample is crushed and ground to obtain CoSb3-based skutterudite;

[0010] Step 2: Preparation of carbon quantum dots

[0011] Soybean meal carbon quantum dots: Pour crushed soybean meal and deionized water into a beaker at a mass ratio of 1:20. Ultrasonic mixing is carried out in a microwave digester for microwave hydrothermal synthesis. The synthesized product is centrifuged at high speed to obtain a yellow-brown supernatant, which is then dialyzed, rotary evaporated, and freeze-dried to obtain solid soybean meal carbon quantum dots.

[0012] Metal-based carbon quantum dots: Crushed industrial sludge is used as a metal-based carbon source, and a certain amount of aqueous solution of Ce(NO3)3, Yb(NO3)3, Eu(NO3)3, etc. is added as a metal dopant. The mass ratio of the carbon source to the aqueous solution is 1:5. Ultrasonic mixing is carried out in a microwave digester for microwave hydrothermal synthesis. The synthetic product is obtained by high-speed centrifugation to obtain a yellow-brown supernatant, which is then dialyzed using a dialysis bag and vacuum dried to finally obtain solid metal-based carbon quantum dots.

[0013] Step 3: Rapid ultrasonic compounding and SPS sintering

[0014] A certain amount of prepared carbon dots is dissolved in deionized water, ethanol or acetone, and crushed CoSb3-based skutterudite is added for ultrasonic vibration. After ultrasonic vibration, the composite material is centrifuged and vacuum dried, and then the carbon dot-composite skutterudite is subjected to spark plasma sintering (SPS sintering) to obtain a carbon quantum dot-composite skutterudite thermoelectric composite material.

[0015] The preparation process can prepare carbon quantum dots from agricultural waste soybean meal in large quantities, solves the problems of large amount of agricultural and forestry waste, difficult treatment, environmental pollution and the like, and develops a recycling technology of agricultural and forestry waste; the preparation process can prepare the composite pure carbon quantum dot CoSb3-based thermoelectric material with high thermoelectric performance, and effectively improves the purity and compactness of the obtained thermoelectric material; the preparation process uses industrial sludge as a carbon source to prepare metal-based carbon dots, and the metal-based carbon dots are compounded into the CoSb3-based skutterudite thermoelectric material to further improve the thermoelectric performance and mechanical performance of the CoSb3-based skutterudite thermoelectric material, provides a new direction for industrial sludge treatment, and achieves the purposes of waste resource utilization and environmental protection.

[0016] Preferably, the pressure of the cold pressing forming in the step one is 6-9 MPa.

[0017] Preferably, the vacuum degree in the quartz tube in the step one is greater than 10-3 MPa.

[0018] Preferably, the power of the microwave synthesis in the step one is 500-1000 W, and the heating time is 5-20 min.

[0019] Preferably, the CoSb3-based skutterudite bulk after the microwave synthesis in the step one is ground into a powder with a particle size of less than 200 mesh.

[0020] Preferably, the soybean meal and the industrial sludge raw materials in the step two are further crushed to a particle size of less than 60 mesh.

[0021] Preferably, the microwave hydrothermal temperature in the step two is 180-240 DEG C, and the reaction time is 6-12 h.

[0022] Preferably, the Ce(NO3)3.6H2O, Yb(NO3)3.5H2O and Eu(NO3)3.6H2O in the step two are prepared into aqueous solutions with a concentration of 5-30 mM.

[0023] Preferably, the speed of the high-speed centrifugation in the step two is 8000-16000 r / min, the centrifugation time is 10-20 min, and the centrifugation is repeated three times.

[0024] Preferably, the dialysis bag with a molecular weight of 500-2000 Da is used for dialysis for 10-48 h, and the freeze-drying time is 30-70 h.

[0025] Preferably, the purity of the Ce(NO3)3.6H2O, Yb(NO3)3.5H2O and Eu(NO3)3.6H2O in the step two is 99.99%.

[0026] Preferably, in step 3, the carbon quantum dots are ultrasonically compounded with skutterudite at a ratio of 0.05-0.3%, 0.5-1%, 1-3%, 3-5%, or 5-20% based on mass percentage.

[0027] Preferably, in step 3, the ultrasonic oscillation time is 10 to 30 minutes, the centrifugal speed is 4000 to 12000 r / min, the vacuum drying is 4 to 8 hours, and the drying temperature is 55 to 70°C.

[0028] Preferably, in step three, the SPS sintering temperature is 580-650° C., the pressure is 40-60 MPa, and the holding time is 10-15 min.

[0029] Preferably, the purity of the raw material Co powder and Te powder is 99.99%, and the purity of the raw material Sb powder and Yb powder is 99.9%.

[0030] Compared with related technologies, the method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots provided by the present invention has the following beneficial effects:

[0031] (1) The present invention discloses a method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots. The method takes advantage of the fact that carbon quantum dots are easily soluble in water or organic solvents and can be evenly dispersed. The carbon quantum dots are composited into a CoSb3-based skutterudite thermoelectric material by rapid ultrasonic oscillation of a carbon dot solution. This allows the carbon quantum dots to quickly enter the mesoporous system of the CoSb3-based skutterudite, allowing the carbon quantum dots to be evenly dispersed in the CoSb3-based skutterudite thermoelectric material, achieving a uniform composite effect. Finally, the CoSb3-based skutterudite thermoelectric material is prepared by combining SPS sintering. While achieving the requirements of rapid and uniform composite, the composite process is simplified and the process is optimized, and a CoSb3-based skutterudite thermoelectric composite material with good thermoelectric performance can be obtained.

[0032] (2) The present invention provides a method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots. By using agricultural (industrial) waste such as soybean meal and industrial sludge as a carbon source to prepare carbon quantum dots, the carbon source of carbon nanomaterials can be easily obtained, thereby achieving a simple, economical, and green synthesis of carbon nanomaterials. Furthermore, the method solves the problems of large agricultural (industrial) waste production, difficulty in treatment, and environmental pollution, and develops a recycling technology for agricultural (industrial) waste. Agricultural (industrial) waste as a carbon source has become a new field for the green synthesis of carbon quantum dots due to its extensive economic advantages.

[0033] (3) A method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots of the present invention is to prepare quasi-zero-dimensional biomass carbon quantum dots with a size of less than 10 nm, which have a large number of electrons and holes on their surface and rich physical and chemical properties and good biocompatibility, unique optical properties, low cost, low toxicity, ecological affinity, rich functional groups (such as amino, hydroxyl, carboxyl), high stability and electron mobility. As a second-phase composite CoSb3-based skutterudite thermoelectric material, carbon quantum dots can serve as electron transmission channels, improve electrical conductivity, and appropriately reduce carrier concentration, thereby improving the Seebeck coefficient, which usually leads to a significant increase in power factor. At the same time, it also enhances the scattering of phonons, significantly reduces thermal conductivity, and greatly improves the thermoelectric performance of thermoelectric materials.

[0034] (4) The present invention provides a method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots, further preparing metal-based carbon quantum dots. Metals are better electron donors, have more unoccupied orbitals on their exterior, and have larger atomic radii. Therefore, after metal ions are doped into CDs, the chances of changing the charge density and charge transfer form between the graphene matrix and the metal ions will be greater than that of heteroatom doping, thereby improving the physicochemical properties of CDs to a greater extent. The introduction of metal ions can change the electronic structure of CDs, affect the spin density and charge distribution of CDs, improve the electrical conductivity of CDs and the ability to donate and accept electrons, thereby promoting the electron transfer process and facilitating the radiative recombination of electrons and holes on the surface of CDs. By incorporating metal-based carbon quantum dots into CoSb3-based skutterudite thermoelectric materials, their thermoelectric performance can be further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the XRD pattern of the skutterudite composite carbon dot thermoelectric material prepared by the present invention;

[0036] Figure 2 This is a transmission electron microscopy image of the carbon dots prepared by the present invention;

[0037] Figure 3 This is a power factor diagram of the skutterudite bulk thermoelectric material prepared in the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0039] Please refer to Figure 1 、 Figure 2 and Figure 3 ;

[0040] Example 1

[0041] A method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots comprises the following steps:

[0042] Step 1: Preparation of CoSb3-based skutterudite thermoelectric materials

[0043] Yb, Te, Co, and Sb single-substance powders are used as raw materials, and 10 g is weighed according to the following mass ratio: Yb: Co: Sb: Te = 0.4: 4: 11.8: 0.2; acetone or ethanol is added as a grinding aid and the mixture is fully ground and mixed for 30 minutes, and then placed in a vacuum drying oven at 60°C for drying; after the grinding aid is completely volatilized, the powder is cold-pressed into a shape by pressing at 9 MPa using a tablet press, and the cold-pressed block sample is sealed in a vacuum quartz tube and placed in a 900W microwave oven for microwave synthesis heating time of 10 minutes. The synthesized sample is crushed and ground to less than 200 mesh to obtain CoSb3-based skutterudite;

[0044] Step 2: Preparation of carbon quantum dots

[0045] 20 ml of a mixture of soybean meal and deionized water was poured into a beaker, wherein the mass ratio of soybean meal to deionized water in the mixture was 1:20. The mixture was ultrasonically mixed and placed in a microwave digester for microwave hydrothermal synthesis at 180°C for 8 hours. The synthesized product was centrifuged at 10,000 r / min for 12 minutes to obtain a yellowish-brown supernatant, which was then dialyzed in a 500Da dialysis bag for 12 hours. The excess water was rotary evaporated and the product was freeze-dried at -80°C for 50 hours to obtain carbon quantum dots with high purity.

[0046] Step 3: Rapid ultrasonic compounding and SPS sintering

[0047] The carbon quantum dots in step 2 are weighed and dissolved in deionized water, and CoSb3-based skutterudite is added and mixed. According to the mass percentage, the ratio of CoSb3-based skutterudite to carbon quantum dots is 99.95%:0.05%; the mixed material is ultrasonically vibrated for 30 minutes, and the composite material is centrifuged after ultrasonication, the supernatant is removed, and vacuum dried at 55°C for 4 hours. Then, the carbon dot-composite skutterudite is subjected to spark plasma sintering (SPS sintering) at a sintering temperature of 650°C, a pressure of 50 MPa, and a holding time of 10 minutes to obtain a carbon quantum dot-composite skutterudite thermoelectric composite material.

[0048] Example 2

[0049] A method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots comprises the following steps:

[0050] Step 1: Preparation of CoSb3-based skutterudite thermoelectric materials

[0051] Yb, Te, Co, and Sb single-substance powders are used as raw materials, and 10 g is weighed according to the following mass ratio: Yb: Co: Sb: Te = 0.4: 4: 11.8: 0.2; acetone or ethanol is added as a grinding aid and the mixture is fully ground and mixed for 30 minutes, and then placed in a vacuum drying oven at 60°C for drying; after the grinding aid is completely volatilized, the powder is cold-pressed into a shape by pressing at 9 MPa using a tablet press, and the cold-pressed block sample is sealed in a vacuum quartz tube and placed in a 900W microwave oven for microwave synthesis heating time of 10 minutes. The synthesized sample is crushed and ground to less than 200 mesh to obtain CoSb3-based skutterudite;

[0052] Step 2: Preparation of carbon quantum dots

[0053] 20 ml of a mixture of soybean meal and deionized water was poured into a beaker, wherein the mass ratio of soybean meal to deionized water in the mixture was 1:20. The mixture was ultrasonically mixed and placed in a microwave digester for microwave hydrothermal synthesis at 220°C for 10 hours. The synthesized product was centrifuged at 10,000 r / min for 12 minutes to obtain a yellowish-brown supernatant, which was then dialyzed in a 500Da dialysis bag for 24 hours. The excess water was rotary evaporated and the product was freeze-dried at -80°C for 50 hours to obtain carbon quantum dots with high purity.

[0054] Step 3: Rapid ultrasonic compounding and SPS sintering

[0055] The carbon quantum dots in step 2 are weighed and dissolved in deionized water, and CoSb3-based skutterudite is added and mixed. According to the mass percentage, the ratio of CoSb3-based skutterudite to carbon quantum dots is 99.5%:0.5%; the material mixture is ultrasonically shaken for 30 minutes, and the composite material is centrifuged after ultrasonication, the supernatant is removed, and vacuum dried at 55°C for 4 hours. Then, the carbon dot-composite skutterudite is subjected to spark plasma sintering (SPS sintering) at a sintering temperature of 650°C, a pressure of 50 MPa, and a holding time of 10 minutes to obtain a carbon quantum dot-composite skutterudite thermoelectric composite material.

[0056] Example 3

[0057] A method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots comprises the following steps:

[0058] Step 1: Preparation of CoSb3-based skutterudite thermoelectric materials

[0059] Take Yb, Te, Co, Sb single element powder as raw material, weigh 10g according to the following mass ratio: Yb: Co: Sb: Te = 0.4: 4: 11.8: 0.2; and add grinding aid acetone or ethanol for sufficient grinding mixing for 30min, and put into 60℃ vacuum drying oven for drying; after the grinding aid is completely volatilized, the powder is cold pressed into a block by a tablet press at 9MPa, and the cold pressed block sample is sealed in a vacuum quartz tube and placed in a 900W microwave oven for microwave synthesis heating for 10min, the synthesized sample is ground to 200 mesh or less after crushing, and a CoSb3-based skutterudite is obtained;

[0060] Step two, preparation of metal-based carbon quantum dots

[0061] Pour 20ml of sludge and deionized water mixture into a beaker, the mass ratio of sludge to deionized water in the mixture is 1:20, the mixture is mixed by ultrasonic mixing and put into a microwave digestion instrument for microwave hydrothermal synthesis at 220℃ for 12h, the synthesis product is obtained by 10000r / min high speed centrifugation for 12min to obtain yellow brown supernatant, and put into a 500Da dialysis bag for dialysis for 12h, vacuum drying at 55℃ for 5h, finally get high purity of miscellaneous metal-based carbon quantum dots;

[0062] Step three, rapid ultrasonic compounding and SPS sintering

[0063] The carbon quantum dots in step two are weighed and dissolved in deionized water, and CoSb3-based skutterudite is mixed, according to the mass percentage, the ratio of CoSb3-based skutterudite to carbon quantum dots is 99%:1%; the material is mixed and ultrasonically oscillated for 30min, and the composite material is centrifuged after ultrasonic, the supernatant is removed, vacuum dried at 55℃ for 4h, then the carbon dot composite skutterudite is subjected to spark plasma sintering (SPS sintering), the sintering temperature is 650℃, the pressure is 50MPa, and the holding time is 10min, so as to obtain carbon quantum dot composite skutterudite thermoelectric composite material.

[0064] Example 4

[0065] A method for preparing high-performance skutterudite compound by carbon quantum dot composite modification includes the following steps:

[0066] Step one, preparation of CoSb3-based skutterudite thermoelectric material

[0067] Take Yb, Te, Co, Sb single element powder as raw material, weigh 10g according to the following mass ratio: Yb: Co: Sb: Te = 0.4: 4: 11.8: 0.2; and add grinding aid acetone or ethanol for sufficient grinding mixing for 30min, and put into 60℃ vacuum drying oven for drying; after the grinding aid is completely volatilized, the powder is cold pressed into a block by a tablet press at 9MPa, and the cold pressed block sample is sealed in a vacuum quartz tube and placed in a 900W microwave oven for microwave synthesis heating for 10min, the synthesized sample is ground to 200 mesh or less after crushing, and a CoSb3-based skutterudite is obtained;

[0068] Step two, preparation of ytterbium-based carbon quantum dots

[0069] Pour 20ml of sludge and deionized water mixture into a beaker, the mass ratio of sludge to deionized water in the mixture is 1:20, then add 1ml of 10mM Yb(NO3)3 solution, ultrasonic mixing and put into microwave digestion instrument for microwave hydrothermal synthesis at 220℃ for 12h, the synthesis product is obtained by 10000r / min high speed centrifugation for 12min to get yellow brown supernatant, and put into 500Da dialysis bag for dialysis for 24h, vacuum drying at 55℃ for 5h, finally get high purity ytterbium-based carbon quantum dots;

[0070] Step three, rapid ultrasonic compounding and SPS sintering

[0071] The carbon quantum dots in step two are weighed and dissolved in deionized water, and CoSb3-based skutterudite is mixed, according to the mass percentage, the ratio of CoSb3-based skutterudite to carbon quantum dots is 97%:3%; after the material is mixed, ultrasonic oscillation is carried out for 30min, and the composite material is centrifuged after ultrasonic, the supernatant is removed, vacuum drying at 55℃ for 4h, then the carbon dot composite skutterudite is subjected to spark plasma sintering (SPS sintering), the sintering temperature is 650℃, the pressure is 50MPa, and the holding time is 10min, so as to obtain carbon quantum dot composite skutterudite thermoelectric composite material.

[0072] Example 5

[0073] A method for preparing high-performance skutterudite compounds by carbon quantum dot composite modification comprises the following steps:

[0074] Step one, preparation of CoSb3-based skutterudite thermoelectric material

[0075] Yb, Te, Co, and Sb single-substance powders are used as raw materials, and 10 g is weighed according to the following mass ratio: Yb: Co: Sb: Te = 0.4: 4: 11.8: 0.2; acetone or ethanol is added as a grinding aid and the mixture is fully ground and mixed for 30 minutes, and then placed in a vacuum drying oven at 60°C for drying; after the grinding aid is completely volatilized, the powder is cold-pressed into a shape by pressing at 9 MPa using a tablet press, and the cold-pressed block sample is sealed in a vacuum quartz tube and placed in a 900W microwave oven for microwave synthesis heating time of 10 minutes. The synthesized sample is crushed and ground to less than 200 mesh to obtain CoSb3-based skutterudite;

[0076] Step 2: Preparation of Europium-based Carbon Quantum Dots

[0077] 20 ml of a mixture of sludge and deionized water was poured into a beaker, with a mass ratio of sludge to deionized water of 1:20. 5 ml of a 10 mM Eu(NO3)3 solution was added, and the mixture was ultrasonically mixed and placed in a microwave digester for microwave hydrothermal synthesis at 220°C for 12 hours. The synthesized product was centrifuged at 10,000 r / min for 12 minutes to obtain a yellowish-brown supernatant, which was then placed in a 500 Da dialysis bag for dialyzation for 24 hours, and then vacuum-dried at 55°C for 5 hours to obtain europium-based carbon quantum dots with high purity.

[0078] Step 3: Rapid ultrasonic compounding and SPS sintering

[0079] The carbon quantum dots in step 2 are weighed and dissolved in deionized water, and CoSb3-based skutterudite is added and mixed. According to the mass percentage, the ratio of CoSb3-based skutterudite to carbon quantum dots is 95%:5%; after the materials are mixed, ultrasonic vibration is performed for 30 minutes, and the composite material is centrifuged after ultrasonication, the supernatant is removed, and vacuum dried at 55°C for 4 hours. Then, the carbon dot-composite skutterudite is subjected to spark plasma sintering (SPS sintering) at a sintering temperature of 650°C, a pressure of 50 MPa, and a holding time of 10 minutes to obtain a carbon quantum dot-composite skutterudite thermoelectric composite material.

[0080] Example 6

[0081] A method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots comprises the following steps:

[0082] Step 1: Preparation of CoSb3-based skutterudite thermoelectric materials

[0083] Yb, Te, Co, and Sb single-substance powders are used as raw materials, and 10 g is weighed according to the following mass ratio: Yb: Co: Sb: Te = 0.4: 4: 11.8: 0.2; acetone or ethanol is added as a grinding aid and the mixture is fully ground and mixed for 30 minutes, and then placed in a vacuum drying oven at 60°C for drying; after the grinding aid is completely volatilized, the powder is cold-pressed into a shape by pressing at 9 MPa using a tablet press, and the cold-pressed block sample is sealed in a vacuum quartz tube and placed in a 900W microwave oven for microwave synthesis heating time of 10 minutes. The synthesized sample is crushed and ground to less than 200 mesh to obtain CoSb3-based skutterudite;

[0084] Step 2: Preparation of Cerium-based Carbon Quantum Dots

[0085] 20 ml of a mixture of sludge and deionized water was poured into a beaker, with a mass ratio of sludge to deionized water of 1:20. 10 ml of a 10 mM Ce(NO3)3 solution was added, and the mixture was ultrasonically mixed and placed in a microwave digester for microwave hydrothermal synthesis at 220°C for 12 hours. The synthesized product was centrifuged at 10,000 r / min for 12 minutes to obtain a yellowish-brown supernatant, which was then placed in a 500 Da dialysis bag for dialyzation for 24 hours and vacuum dried at 55°C for 5 hours to obtain cerium-based carbon quantum dots with high purity.

[0086] Step 3: Rapid ultrasonic compounding and SPS sintering

[0087] The carbon quantum dots in step 2 are weighed and dissolved in deionized water, and CoSb3-based skutterudite is added and mixed. According to the mass percentage, the ratio of CoSb3-based skutterudite to carbon quantum dots is 90%:10%; after the materials are mixed, ultrasonic vibration is performed for 30 minutes, and the composite material is centrifuged after ultrasonication, the supernatant is removed, and vacuum dried at 55°C for 4 hours. Then, the carbon dot-composite skutterudite is subjected to spark plasma sintering (SPS sintering) at a sintering temperature of 650°C, a pressure of 50 MPa, and a holding time of 10 minutes to obtain a carbon quantum dot-composite skutterudite thermoelectric composite material.

[0088] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots, characterized in that: The following steps are involved: Step 1: Preparation of CoSb3-based skutterudite thermoelectric materials Yb, Te, Co, and Sb single-substance powders are used as raw materials and weighed according to the following mass ratio: Yb:Co:Sb:Te=0.4:4:11.8:0.2; acetone or ethanol as a grinding aid is added to the materials weighed in proportion, and the materials are fully ground and mixed, and then placed in a vacuum drying oven for drying; after the grinding aid is completely volatilized, the powder is cold-pressed into a shape by a tablet press, the cold-pressed block sample is sealed in a quartz tube and then vacuumed, the vacuumed quartz tube is placed in a ceramic dry pot, green silicon carbide is placed in the dry pot as a microwave-assisted absorber, asbestos is placed around the crucible as a heat-insulating material with a thickness of 50 to 100 mm, the quartz tube and the crucible are placed in a microwave oven for microwave synthesis, the synthesized sample is crushed and ground to obtain CoSb3-based skutterudite; Step 2: Preparation of carbon quantum dots Soybean meal carbon quantum dots: Pour crushed soybean meal and deionized water into a beaker at a mass ratio of 1:

20. Ultrasonic mixing is carried out in a microwave digester for microwave hydrothermal synthesis. The synthesized product is centrifuged at high speed to obtain a yellow-brown supernatant, which is then dialyzed, rotary evaporated, and freeze-dried to obtain solid soybean meal carbon quantum dots. Metal-based carbon quantum dots: Crushed industrial sludge is used as a metal-based carbon source, and a certain amount of aqueous solution of Ce(NO3)3, Yb(NO3)3, Eu(NO3)3, etc. is added as a metal dopant. The mass ratio of the carbon source to the aqueous solution is 1:

5. Ultrasonic mixing is carried out in a microwave digester for microwave hydrothermal synthesis. The synthetic product is obtained by high-speed centrifugation to obtain a yellow-brown supernatant, which is then dialyzed using a dialysis bag and vacuum dried to finally obtain solid metal-based carbon quantum dots. Step 3: Rapid ultrasonic compounding and SPS sintering A certain amount of prepared carbon dots is dissolved in deionized water, ethanol or acetone, and crushed CoSb3-based skutterudite is added for ultrasonic vibration. After ultrasonic vibration, the composite material is centrifuged and vacuum dried, and then the carbon dot-composite skutterudite is subjected to spark plasma sintering (SPS sintering) to obtain a carbon quantum dot-composite skutterudite thermoelectric composite material.

2. The method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots according to claim 1, characterized in that: The pressure of the cold pressing in step 1 is 6-9 MPa.

3. The method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 1, the vacuum degree in the quartz tube is ensured to be above 10-3 MPa.

4. The method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots according to claim 1, characterized in that: The power of the microwave synthesis in the step 1 is 500-1000W, and the heating time is 5-20 minutes.

5. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: The CoSb3-based skutterudite block synthesized by microwave in the step 1 is ground into powder with a mesh size of less than 200.

6. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 2, the soybean meal and industrial sludge raw materials must be further crushed to below 60 mesh.

7. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 2, the microwave hydrothermal temperature is 180-240° C., and the reaction time is 6-12 hours.

8. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 2, Ce(NO3)3·6H2O, Yb(NO3)3·5H2O, and Eu(NO3)3·6H2O are respectively prepared into aqueous solutions with a concentration of 5 to 30 mM.

9. The method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots according to claim 1, characterized in that: The rotation speed of the high-speed centrifugation in the step 2 is 8000-16000 r / min, the centrifugation time is 10-20 min, and it is repeated three times.

10. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 2, a 500-2000 Da dialysis bag is used for dialysis for 10-48 hours, and freeze-dried for 30-70 hours.

11. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 2, the purity of Ce(NO3)3·6H2O, Yb(NO3)3·5H2O and Eu(NO3)3·6H2O are all 99.99%.

12. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: According to the mass percentage, the carbon quantum dots in step three are ultrasonically compounded with skutterudite at a ratio of 0.05-0.3%, 0.5-1%, 1-3%, 3-5%, and 5-20%.

13. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 3, the ultrasonic oscillation time is 10 to 30 minutes, the centrifugal speed is 4000 to 12000 r / min, the vacuum drying is 4 to 8 hours, and the drying temperature is 55 to 70°C.

14. The method for preparing a high-performance skutterudite compound by composite modification of carbon quantum dots according to claim 1, characterized in that: In the step 3, the SPS sintering temperature is 580-650° C., the pressure is 40-60 MPa, and the holding time is 10-15 minutes.

15. The method for preparing high-performance skutterudite compounds by composite modification of carbon quantum dots according to claim 1, characterized in that: The purity of the raw material Co powder and Te powder is 99.99%, and the purity of the raw material Sb powder and Yb powder is 99.9%.

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