A co3o4 / ti3c2t x Composite material, method for its production and use
By preparing Co3O4/Ti3C2Tx composite materials, the problems of insufficient conductivity of Co3O4 and easy accumulation of Ti3C2Tx were solved, realizing high-sensitivity acetone gas detection and low-temperature sensing, and improving the selectivity and response intensity of gas sensors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-23
- Publication Date
- 2026-04-07
AI Technical Summary
Existing Co3O4 as a semiconductor metal oxide gas-sensitive material has the disadvantages of high operating temperature and poor conductivity. In acetone gas-sensitive detection, Ti3C2Tx thin layers tend to accumulate, leading to coverage of active sites and affecting the detection effect.
Co3O4/Ti3C2Tx composite material was prepared by mixing Co3O4 nanosheets with Ti3C2Tx dispersion, followed by stirring and freeze-drying. The Co3O4 nanosheets were uniformly distributed on the Ti3C2Tx surface to avoid stacking. The template-etching-ultrasonic method was used to prepare Co3O4 nanosheets to improve conductivity and electron transport.
It improves the performance of gas sensing, especially acetone sensing, reduces the operating temperature, and achieves high-sensitivity acetone gas detection. The response intensity is increased by nearly three times, the operating temperature is reduced by 50°C, and it has the ability to selectively identify gases.
Smart Images
Figure CN117658231B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of composite materials technology, specifically to a Co3O4 / Ti3C2T x Composite materials, their preparation methods, and applications. Background Technology
[0002] Acetone is a volatile organic compound commonly used as a solvent and raw material in industry and laboratories, and is closely related to safe production. Long-term exposure to high concentrations of acetone can cause headaches, fatigue, and damage to the nervous system. Furthermore, acetone is a marker in the exhaled breath of diabetic patients. Therefore, monitoring acetone concentration is crucial for industrial production and health monitoring. Currently, various methods are used to detect acetone concentration. Among them, resistive gas sensors have attracted much attention due to their simplicity, speed, and low cost. The key to resistive sensors is the metal oxide sensitive material. Therefore, the rational design and synthesis of highly efficient metal oxide composite materials is crucial for the development of gas sensors.
[0003] The main reasons why Co3O4, as a semiconductor metal oxide gas-sensitive material, cannot be used in practical applications are its high operating temperature and insufficient conductivity. To reduce its operating temperature and improve its gas-sensitive performance, highly conductive two-dimensional materials are increasingly being used to synthesize composite materials. Existing technology discloses a Co3O4 / graphene composite material, which significantly improves the response sensitivity of Co3O4 as a gas-sensitive material to amine gases, but it has not achieved high sensitivity detection of acetone gas. Therefore, it is necessary to explore other two-dimensional materials, among which Ti3C2T... x As a novel two-dimensional material, Ti3C2T possesses unique advantages in the field of gas sensing: excellent electrical conductivity; a surface rich in functional groups and active sites, resulting in a high signal-to-noise ratio. Furthermore, Ti3C2T with a surface rich in hydroxyl groups exhibits... x The adsorption strength for acetone is more than twice that of other two-dimensional materials. However, thin-layer Ti3C2T x The main problem in the application of acetone gas sensing is the use of a single thin-layer Ti3C2T. x The sheets are unstable and prone to accumulation, resulting in a large number of active sites being covered, which is not conducive to acetone gas sensing.
[0004] Theoretically, Co3O4 nanosheets with metallic properties and thin-layer Ti3C2T x The construction of the composite material can improve the conductivity of Co3O4 on the one hand, and avoid thin-layer Ti3C2T on the other hand. x The accumulation and coverage of active sites enhance gas-sensing performance. Therefore, a suitable method is urgently needed to construct Co3O4 / Ti3C2T x Composite materials enable highly sensitive detection of acetone gas. Summary of the Invention
[0005] To solve the above technical problems, the present invention provides a Co3O4 / Ti3C2T x Composite materials, their preparation methods, and applications.
[0006] This invention is achieved through the following technical solution:
[0007] The first aspect of this invention provides a Co3O4 / Ti3C2T x The preparation method of the composite material includes the following steps: mixing Co3O4 nanosheets with Ti3C2T x The dispersion was mixed and stirred, and then freeze-dried to obtain Co3O4 / Ti3C2T. x Composite materials.
[0008] The preparation method provided by this invention combines Co3O4 nanosheets with Ti3C2T x The dispersion was mixed and then stirred to allow Co3O4 nanosheets to be uniformly distributed on a thin layer of Ti3C2T. x On the surface, the combination of the two avoids the thin-layer Ti3C2T x By stacking and then freeze-drying, the composite structure of the two materials was preserved, thus preparing Co3O4 / Ti3C2T. x Composite materials. Effective composite of these two materials, Ti3C2T x The high conductivity of the composite material improves the conductivity of the composite material, promotes electron transfer, and is beneficial to improving the gas-sensitive performance of acetone.
[0009] Furthermore, the process after stirring also includes centrifugation and washing.
[0010] Furthermore, the Co3O4 nanosheets and Ti3C2T x The mass ratio of the dispersion is (0.5~10):1.
[0011] Furthermore, the Ti3C2T x The concentration of the dispersion is 1–5 mg / mL.
[0012] Furthermore, the Ti3C2T x It was prepared by the following method: using Ti3AlC2 as a precursor, Ti3C2T was obtained by etching with a mixed solution of LiF and HCl or hydrofluoric acid solution. x , wherein, the T x The surface terminator is indicated by a surface terminating group, wherein the surface terminator includes -O, -F, or -OH.
[0013] Furthermore, the Ti3C2T x The dispersion is Ti3C2T x An aqueous solution or organic solution, wherein the organic solution is an isopropanol or ethanol solution.
[0014] Furthermore, the stirring time is 6–24 h; the freeze-drying time is 12–72 h.
[0015] Further, the Co3O4 nanosheets are prepared by the following method: a cobalt source, a template and a surface modifier are mixed in a mass ratio of (5-15):(1-10):(1-10), heated and refluxed, and then calcined, etched and ultrasonically treated to obtain Co3O4 nanosheets.
[0016] This invention utilizes a template-etching-ultrasonic method to prepare Co3O4 nanosheets. The resulting Co3O4 nanosheets have hollow spheres rich in defects. The ultrasonically treated Co3O4 nanosheets not only retain the abundant internal defects but also facilitate their bonding with two-dimensional thin-layer Ti3C2T. x complex.
[0017] Further, the cobalt source is cobalt nitrate or cobalt chloride; the template is a hard template or a soft template, the hard template including but not limited to silica spheres and molecular sieves, the soft template including but not limited to polystyrene spheres, polypropylene glycol and ethylene oxide addition polymer (polyether) (F127), and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123); the surface modifier is urea or PVP.
[0018] Furthermore, the heating reflux temperature is 80–100°C; the calcination temperature is 350–500°C; and the ultrasonication time is 60–90 min.
[0019] Furthermore, the etching process employs a strong acid or hot alkaline solution, with hydrofluoric acid being the preferred strong acid and NaOH or KOH solution being the preferred alkaline solution.
[0020] A second aspect of the present invention provides a Co3O4 / Ti3C2T prepared by the method described in the first aspect. x Composite materials.
[0021] The Co3O4 / Ti3C2T provided by this invention x Composite materials can improve the conductivity of Co3O4 and avoid thin-layer Ti3C2T x The accumulation of Ti3C2T promotes electron transport and improves gas sensing performance, especially acetone sensing performance. x The low-temperature sensing characteristics of the gas sensor are beneficial for reducing the operating temperature of the composite material.
[0022] A third aspect of the present invention provides a Co3O4 / Ti3C2T as described in the second aspect. x Applications of composite materials in the fabrication of gas sensors or in the detection of gases.
[0023] Furthermore, the Co3O4 / Ti3C2T x The application of composite materials in the fabrication of gas sensors mainly involves the use of Co3O4 / Ti3C2T. x Composite material modified electrode.
[0024] Furthermore, the electrodes include, but are not limited to, Ag-Pd interdigitated electrodes, gold electrodes, and flexible electrodes.
[0025] Furthermore, the Co3O4 / Ti3C2T x The amount of modification in the composite material is 0.5–2 mg.
[0026] Furthermore, applying algorithms to gas sensors can accurately identify various gases and improve the gas selectivity of gas sensors.
[0027] To capture important information from the sample data and remove redundant information, kernel principal component analysis (KPCA) is used to extract features from the original sample data. A Gaussian kernel function is used to map the original data to a high-dimensional feature space, and principal component analysis is used to reduce the feature space. The number of principal components to be retained is determined by judging that the cumulative contribution rate reaches 95%.
[0028] Integrating algorithms into the field of gas sensing can further promote its application in practical fields, especially in electronic devices and wearable devices.
[0029] Furthermore, the gas detected was acetone, and the present invention is Co3O4 / Ti3C2T x A gas sensor made of composite materials has achieved highly sensitive detection of acetone gas.
[0030] The beneficial effects of this invention are:
[0031] 1. The Co3O4 / Ti3C2T provided by this invention x The composite material was prepared using a template-etching-ultrasonic method to fabricate Co3O4 nanosheets. The resulting Co3O4 nanosheets contained hollow spheres rich in defects. Ultrasonic treatment of the Co3O4 nanosheets not only preserved these abundant internal defects but also facilitated their bonding with two-dimensional thin-layer Ti3C2T. x Composite. The preparation method provided by this invention combines Co3O4 nanosheets with Ti3C2T x The dispersion was mixed and then stirred to allow Co3O4 nanosheets to be uniformly distributed on a thin layer of Ti3C2T. x On the surface, the combination of the two avoids the thin-layer Ti3C2T x The stacking and freeze-drying process preserved the composite structure of the two materials. This effective composite of Ti3C2T... xThe high conductivity of the composite material improves the conductivity of the composite material, promotes electron transfer, and is beneficial to improving the gas-sensitive performance of acetone.
[0032] 2. The Co3O4 / Ti3C2T provided by this invention x Composite materials can improve the conductivity of Co3O4 and avoid thin-layer Ti3C2T x The accumulation of Ti3C2T promotes electron transport and improves gas sensing performance, especially acetone sensing performance. x The low-temperature sensing characteristics of the composite material are beneficial for reducing the operating temperature of the composite material in gas sensors. Compared with Co3O4 nanosheets or Co3O4 / graphene composites, the response intensity is nearly three times higher at the same operating temperature. Compared with Co3O4 nanowires, the optimal operating temperature of the composite material is reduced by 50°C.
[0033] 3. This invention utilizes algorithms to improve the performance of Co3O4 / Ti3C2T x Composite materials are used for the selectivity of gas sensors, enabling accurate identification of various gases and achieving high-sensitivity detection of acetone gas. They can be used in related electronic devices and wearable sensors. Attached Figure Description
[0034] Figure 1 It is Co3O4 / Ti3C2T x Synthesis roadmap for composite materials.
[0035] Figure 2 It is a thin-layer Ti3C2T x and Co3O4 / Ti3C2T x TEM image of the composite material.
[0036] Figure 3 These are SEM images of Co3O4 nanosheets prepared at different ultrasonic times.
[0037] Figure 4 It is Ti3C2T x Co3O4 nanowires and Co3O4 / Ti3C2T x XRD comparison diagrams of composite materials.
[0038] Figure 5 It is Co3O4 / Ti3C2T x XPS plot of composite material.
[0039] Figure 6 It is a thin-layer Ti3C2T x Co3O4 nanosheets and Co3O4 / Ti3C2T x Resistance comparison chart of composite materials.
[0040] Figure 7The Co3O4 / Ti3C2T samples from Examples 1-4 are examples. x Gas sensor made of composite material responds to 500 ppm acetone at different temperatures.
[0041] Figure 8 It is the Co3O4 / Ti3C2T of Example 3 x Comparison of the gas-sensing responses of gas sensors prepared from composite materials, Co3O4 / graphene composite material of Comparative Example 1, Co3O4 nanosheets of Comparative Example 2, and Co3O4 nanowires of Comparative Example 3 to 500 ppm acetone at different temperatures.
[0042] Figure 9 It is Co3O4 / Ti3C2T x The response recovery curves of the gas sensor made of composite material to different concentrations of acetone at 200℃.
[0043] Figure 10 It is Co3O4 / Ti3C2T x Stability test results of a gas sensor made of composite materials for detecting acetone at 200°C.
[0044] Figure 11 It is Co3O4 / Ti3C2T x A comparison of the selectivity of a gas sensor made of composite materials for different gases at 500 ppm.
[0045] Figure 12 The algorithm is applied to Co3O4 / Ti3C2T x The results of a gas sensor made of composite materials identifying different gases are shown in the figure. Detailed Implementation
[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.
[0048] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.
[0049] This invention provides a Co3O4 / Ti3C2T x The preparation method of the composite material includes the following steps: mixing Co3O4 nanosheets with Ti3C2T x The dispersion was mixed and stirred, and then freeze-dried to obtain Co3O4 / Ti3C2T. x Composite materials.
[0050] like Figure 1 As shown, Figure 1 It is Co3O4 / Ti3C2T x Synthesis roadmap for composite materials.
[0051] Figure 2 It is a thin-layer Ti3C2T x and Co3O4 / Ti3C2T x TEM image of the composite material, showing the synthesized Ti3C2T x It is a thin sheet, and Co3O4 nanosheets were successfully loaded onto a thin Ti3C2T layer. x The surface.
[0052] The Co3O4 nanosheets were prepared by the following method: a cobalt source, a template and a surface modifier were mixed in a mass ratio of (5-15):(1-10):(1-10), heated and refluxed, and then calcined, etched and ultrasonically treated to obtain Co3O4 nanosheets.
[0053] In a specific embodiment, 0.5g of cobalt chloride, 0.1g of silica spheres and 1g of urea were mixed and heated under reflux at 95°C for 8 hours, calcined at 400°C for 4 hours, etched with hot NaOH solution, and ultrasonicated for a certain time to obtain Co3O4 nanosheets; the ultrasonication times were 10min, 20min, 30min, 40min, 50min and 60min respectively.
[0054] like Figure 3 As shown, Figure 3 These are SEM images of Co3O4 nanosheets prepared with different ultrasonic times. As can be seen from the images, as the ultrasonic time increases, Co3O4 gradually changes from hollow spheres to nanosheets.
[0055] The Co3O4 nanosheets used in the following examples were prepared by ultrasonication for 60 minutes.
[0056] The Ti3C2T x The preparation method is as follows: using Ti3AlC2 as a precursor, Ti3C2T is obtained by etching with a mixed solution of LiF and HCl or a hydrofluoric acid solution. x .
[0057] In the following examples, Ti3C2T xThe dispersion was prepared as follows: 1 g Ti3AlC2 was added to 20 mL of 9 mol / L HCl solution containing 1.32 g LiF, and the mixture was stirred in a sealed container for 48 h. The product was washed by centrifugation at 4000 rpm, and the supernatant was ultrasonically dispersed for 1 h. The upper dispersion was collected by centrifugation at 3500 rpm, and the Ti3C2T was collected by freeze-drying. x Dispersed in isopropanol solution, Ti3C2T was obtained. x Dispersion.
[0058] Example 1
[0059] A Co3O4 / Ti3C2T x The composite material is prepared by the following method:
[0060] Co3O4 nanosheets were mixed with 2 mg / mL Ti3C2T x The dispersions were mixed and stirred at a mass ratio of 0.5:1, and then centrifuged, washed, and freeze-dried to obtain Co3O4 / Ti3C2T. x Composite materials.
[0061] Example 2
[0062] A Co3O4 / Ti3C2T x The composite material was prepared using the same method as in Example 1, except that: Co3O4 nanosheets and Ti3C2T... x The mass ratio of the dispersion is 2:1.
[0063] Example 3
[0064] A Co3O4 / Ti3C2T x The composite material was prepared using the same method as in Example 1, except that: Co3O4 nanosheets and Ti3C2T... x The mass ratio of the dispersion is 5:1.
[0065] Example 4
[0066] A Co3O4 / Ti3C2T x The composite material was prepared using the same method as in Example 1, except that: Co3O4 nanosheets and Ti3C2T... x The mass ratio of the dispersion is 8:1.
[0067] Comparative Example 1
[0068] A Co3O4 / graphene composite material was prepared by the following method:
[0069] Co3O4 nanosheets and 2 mg / mL graphene dispersion were mixed and stirred at a mass ratio of 5:1, and then centrifuged, washed, and freeze-dried to obtain Co3O4 / graphene composite material.
[0070] Comparative Example 2
[0071] A Co3O4 nanosheet was prepared by the following method:
[0072] Co3O4 nanosheets were prepared by mixing 0.5g cobalt chloride, 0.1g silica spheres and 1g urea, heating at 95℃ under reflux for 8h, calcining at 400℃ for 4h, etching with hot NaOH solution and sonicating for 60min.
[0073] Comparative Example 3
[0074] A Co3O4 nanowire was prepared by the following method:
[0075] Co3O4 nanowires were prepared by mixing 0.5g of cobalt chloride and 1g of urea, heating under reflux at 95°C for 8 hours, calcining at 400°C for 4 hours, and sonicating for 60 minutes.
[0076] Figure 4 It is Ti3C2T x Co3O4 nanowires and Co3O4 / Ti3C2T x The XRD comparison images of the composite materials show that the two materials have been successfully bonded together.
[0077] Figure 5 It is Co3O4 / Ti3C2T x The XPS image of the composite material shows that the presence of Ti, C, Co, O, and F proves the successful composite material formation.
[0078] Figure 6 It is a thin-layer Ti3C2T x Co3O4 nanosheets and Co3O4 / Ti3C2T x The resistivity comparison graph of the composite materials shows the difference between Co3O4 nanosheets and thin-layer Ti3C2T. x The composite effectively improves the electrical conductivity of the material.
[0079] Example 5 Gas Sensitivity Test
[0080] Take Co3O4 / Ti3C2T from Examples 1 to 4 respectively x Gas sensors were prepared using composite materials, the Co3O4 / graphene composite material of Comparative Example 1, the Co3O4 nanosheets of Comparative Example 2, and the Co3O4 nanowires of Comparative Example 3. The preparation methods are as follows:
[0081] 2 mg of the prepared material was dispersed in 1 mL of DMF solution. The dispersion was then applied to the surface of the Ag-Pd substrate electrode by drop coating. The modified substrate electrode was then mounted on the Sino Aggtech / CGS-MT gas-sensitive testing instrument.
[0082] Test Examples 1-4 of Co3O4 / Ti3C2T x The gas sensor made of composite materials exhibits strong gas-sensing response to 500 ppm acetone at different temperatures. The test results are as follows: Figure 7 As shown in the figure, Co3O4 nanosheets and Ti3C2T x The mass ratio of the dispersion is 5:1 for Co3O4 / Ti3C2T x The composite material exhibits the strongest acetone gas-sensitive response signal, meaning the optimal ratio of the composite material is 5:1.
[0083] Test Example 3 Co3O4 / Ti3C2T x The gas sensors prepared from the composite materials, the Co3O4 / graphene composite material of Comparative Example 1, the Co3O4 nanosheets of Comparative Example 2, and the Co3O4 nanowires of Comparative Example 3 were tested for their gas-sensitive response intensity to 500 ppm acetone at different temperatures. The test results are as follows: Figure 8 As shown in the comparison chart, Co3O4 / Ti3C2T x The composite material has a 50°C lower sensing temperature than Co3O4 nanowires alone, and its response strength at 200°C is about three times that of Co3O4 nanosheets alone and Co3O4 / graphene composites, effectively improving its sensing performance.
[0084] Example 6 Detection Limit Test
[0085] For the Co3O4 / Ti3C2T of Example 3 x The detection limit test of the gas sensor made of composite materials for detecting acetone was performed, and the test results are as follows: Figure 9 As shown, Figure 9 It is Co3O4 / Ti3C2T x The response recovery curves of the gas sensor made of composite material to different concentrations of acetone at 200℃ are shown. The low-concentration detection curves show that the composite material has a significant response to 1 ppm acetone. (R) g / R a The value was 1.03, and the lowest detection limit was 1 ppm.
[0086] Example 7 Stability Test
[0087] For the Co3O4 / Ti3C2T of Example 3 x The stability of the gas sensor made of composite materials for detecting acetone was tested, and the test results are as follows: Figure 10 As shown, Figure 10 It is Co3O4 / Ti3C2T xThe stability test graph of the gas sensor made of composite material for detecting acetone at 200℃ shows that the composite material has good stability.
[0088] Example 8 Selective Testing
[0089] Selectivity refers to the ability of a gas sensor to differentiate between target and non-target gases when they come into contact with each other. Gas sensitivity performance was tested at 200℃ for 500ppm DMF, ammonia, acetone, methanol, formaldehyde, chloroform, and hydrogen peroxide. The test results are as follows: Figure 11 As shown, Figure 11 It is Co3O4 / Ti3C2T x A comparison of the selectivity of the gas sensor made of composite material to different gases at 500 ppm is shown in the figure. It can be seen from the figure that the composite material has specific detection of acetone and strong selectivity.
[0090] Example 9 Algorithm Application
[0091] The testing method was as follows: Experimental data were collected from the sensor's response to seven different gases. Measurements were taken in triplicate; for each concentration, 50 sampling points were selected as samples once the sensor reached a steady state. The dataset was then divided into training and test sets in a 6:4 ratio. The training set consisted of 30x3x7 data points, while the test set consisted of 20x3x7 data points. To capture important information from the sample data and remove redundant information, we used Kernel Principal Component Analysis (KPCA) to extract features from the raw sample data. A Gaussian kernel function was used to map the raw data to a high-dimensional feature space, and principal component analysis was used to reduce the feature space. The number of principal components to be retained was determined by whether the cumulative contribution rate reached 95%. In KPCA, we used a Gaussian kernel function with a kernel parameter of 8; the weak classifier threshold was set to 1; and the optimal results were achieved when the range of the number of GS-optimized classifiers was set to [1:1:30].
[0092] Test results are as follows Figure 12 As shown, Figure 12 The algorithm is applied to Co3O4 / Ti3C2T x The gas sensor made of composite materials identifies different gases. A comparison of theoretical and experimental results shows that the accuracy of identification reaches 99.7619%. Gas 1 is acetone, gas 2 is DMF, gas 3 is ammonia, gas 4 is methanol, gas 5 is formaldehyde, gas 6 is chloroform, and gas 7 is hydrogen peroxide. The application of this accurate identification method will be beneficial for related electronic devices and wearable sensors.
[0093] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.
Claims
1. A Co3O4 / Ti3C2T x The application of composite materials in the fabrication of gas sensors or in the detection of gases is characterized by, The gas detected was acetone, using the Co3O4 / Ti3C2T... x Composite material modified electrode; the Co3O4 / Ti3C2T x The preparation method of the composite material includes the following steps: mixing Co3O4 nanosheets with Ti3C2T x The dispersion was mixed and stirred, and then freeze-dried to obtain Co3O4 / Ti3C2T. x Composite material; the Co3O4 nanosheets are prepared by the following method: a cobalt source, a template and a surface modifier are mixed in a mass ratio of (5~15):(1~10):(1~10) and heated under reflux, followed by calcination, etching and ultrasonic treatment to obtain Co3O4 nanosheets.
2. The application according to claim 1, characterized in that, The Co3O4 nanosheets and Ti3C2T x The mass ratio of the dispersion is (0.5~10):
1.
3. The application according to claim 1, characterized in that, The Ti3C2T x The concentration of the dispersion is 1~5 mg / mL.
4. The application according to claim 1, characterized in that, The cobalt source is cobalt nitrate or cobalt chloride; the template is silica spheres, molecular sieves or polystyrene spheres; the surface modifier is urea or PVP.
5. The application according to claim 1, characterized in that, The heating reflux temperature is 80~100 ℃; the calcination temperature is 350~500 ℃; and the ultrasonication time is 60~90 min.