Preparation method of porous Sc-doped Co3O4 nanosheet material and application of porous Sc-doped Co3O4 nanosheet material in low-temperature high-selectivity detection of p-xylene

Abstract

The invention provides a preparation method of a porous Sc-doped Co3O4 nanosheet material, which comprises the following steps: (1) dissolving Sc (NO3) 3.H2O, Co (NO3) 2.6 H2O and hexamethylenetetramine into 50mL of distilled water for 10 minutes according to the mass ratio of (0.01-0.05): 1: 3 to form a uniform solution, and heating for 6 hours at the temperature of 90 DEG C; (2) carrying out centrifugal treatment for 1 min, washing and drying to obtain alpha-Co (OH) 2 precursors with different Sc doping amounts; and (3) carrying out calcination treatment on the prepared precursor at the temperature of 400-600 DEG C and the heating rate of 2-6 DEG C min <-1 > to obtain the porous Sc-doped Co3O4 nanosheet material. According to the prepared porous Sc-doped Co3O4 porous nanosheet, the gas sensitive performance of a gas sensor can be improved, selective detection of p-xylene at a low working temperature (110 DEG C) is achieved, and the Sc-doped Co3O4 porous nanosheet has good reproducibility, low detection limit and long-term stability of p-xylene detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor gas sensors, and particularly relates to a preparation method of a porous Sc-doped Co3O4 nanosheet material and its application in the low-temperature and highly selective detection of p-xylene. Background Art

[0002] Currently, common methods for detecting p-xylene include chemical analysis, spectroscopic analysis, chromatographic analysis, and electrochemical analysis. These methods have high accuracy and good stability, but there are obvious deficiencies, such as being easily affected by environmental factors, having a long detection time, expensive analysis equipment, and high technical requirements for operators. In order to cope with the complexity of the detection environment and better carry out real-time detection work, the emergence of gas sensors has well filled the gap in these application requirements. A gas sensor is a device that can convert information such as the type and concentration of a gas to be detected into a digital signal that can be recognized by operators and instruments. It has characteristics such as high reliability, fast response speed, low power consumption, and easy operation, and has broad application prospects in fields such as industrial production, military aerospace, medical diagnosis, and food safety.

[0003] Comparison of Methods for Detecting p-Xylene

[0004]

[0005]

[0006] Semiconductor gas sensors achieve detection based on the gas-sensing characteristics of metal oxide semiconductor (MOS) sensitive materials. Its core principle is that when gas molecules to be detected (such as p-xylene) are adsorbed on the material surface, a reversible redox reaction occurs with active sites, resulting in a significant change in the carrier concentration inside the material, and then causing a regular change in the resistance value. Based on this characteristic, by quantifying the corresponding relationship between the resistance signal and the gas concentration, qualitative and quantitative analysis of the target gas can be achieved.

[0007] Gas sensors using metal oxide semiconductors (such as SnO2, WO3, Co3O4, etc.) as sensitive materials have become the most widely used gas sensing technology in current industrial and civilian fields due to their high sensitivity (able to detect gas concentrations at the ppm level), fast response / recovery characteristics (usually completing signal switching within seconds), miniaturized structure (easy to integrate into portable devices), and low-cost mass production advantages (supported by mature processes), covering scenarios such as environmental monitoring, industrial safety, and smart home. The direction of technology iteration focuses on further improving selectivity and reducing the working temperature through strategies such as nanostructure design (such as porous / hierarchical morphology), noble metal doping (such as Pt, Au modification), and heterojunction composite (such as ZnO / rGO).

[0008] Semiconductor metal oxides, as gas-sensitive materials for detecting VOCs, have the characteristics of simplicity, portability, good compatibility, simple configuration, and simple working principle. So far, many semiconductor metal oxides, including n-type oxides, p-type oxides, and heterojunctions, such as ZnO, SnO2, TiO2, In2O3, WO3, NiO, CuO, Co3O4, NiO / NiMoO4, and NiCo2O4 / WO3, have been widely studied for xylene sensing. In particular, Co3O4 is considered a promising candidate for detecting xylene due to its special catalytic oxidation activity, low cost, and high sensitivity. Many studies have shown that by adjusting the size and morphology of Co3O4, such as hierarchical porous (HP) Co3O4 microspheres, mesoporous Co3O4, and mesoporous Co3O4 nanosheets, the gas-sensing performance of Co3O4 can be improved. At the same time, Co3O4-based heterojunctions, such as SnO2-Co3O4 microstructures, Co3O4-In2O, Ni(OH)2 / Co3O4, Ag-Co3O4, Pd / Co3O4, Co3O4@NiMoO4, and NiO / Co3O4 nanosheets, have been prepared to improve the gas-sensing performance of xylene. In addition, metal doping is also an important method to improve the gas sensitivity of Co3O4. Currently, materials such as Fe-Co3O4, Mn-doped Co3O4, Cr-doped Co3O4, Mo-Co3O4, and In-Co3O4 are all for improving the sensing performance of xylene. Metal doping can regulate the microstructure, adjust the energy level, or provide higher catalytic activity, thereby synergistically enhancing the sensing performance of xylene. However, the optimal working temperature of the above Co3O4 sensors for xylene is still very high, which seriously hinders practical applications. Summary of the Invention

[0009] Aiming at the above deficiencies in the prior art, the purpose of the present invention is to provide a preparation method of a porous Sc-doped Co3O4 nanosheet material and its application in the low-temperature and highly selective detection of xylene. This porous Sc-doped Co3O4 nanomaterial can improve the gas-sensing performance of its gas sensor, realizing the selective detection of xylene at a lower working temperature (110 °C), with good reproducibility, a lower detection limit, and long-term stability for detecting xylene.

[0010] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of a porous Sc-doped Co3O4 nanosheet material, comprising the following steps:

[0011] (1) According to the molar ratio of (0.01 - 0.05):1:3, dissolve Sc(NO3)3·H2O, Co(NO3)2·6H2O, and hexamethylenetetramine in 50 mL of distilled water for 10 min to form a homogeneous solution, and then heat it at 90 °C for 6 h;

[0012] (2) Centrifuge for 1 min, wash and dry to obtain α-Co(OH)₂ precursors with different Sc doping amounts;

[0013] (3) Calcinate the above-prepared precursors at a temperature of 400 - 600 °C and a heating rate of 2 - 6 °C min -1 to obtain porous Sc-doped Co₃O₄ nanosheet materials.

[0014] Furthermore, in step (2), the centrifuged sample is washed 5 times with water and ethanol.

[0015] Furthermore, in step (2), the washed sample is dried in a vacuum oven at 60 °C for 12 h.

[0016] Furthermore, in step (3), the calcination conditions are: at 450 °C with a heating rate of 3 °C min -1 .

[0017] Furthermore, in step (3), the calcination time is 2 h.

[0018] An application of a porous Sc-doped Co₃O₄ nanosheet material, characterized in that a gas sensor is made of the porous Sc-doped Co₃O₄ nanosheet material prepared by the above method, and the application of the gas sensor in the low-temperature and highly selective detection of p-xylene.

[0019] Furthermore, the preparation method of the gas sensor is as follows: Use a simple spot welder to weld the dried planar Au multi-layer electrode core to the black hexagonal base; then, take an appropriate amount of metal element-doped Co₃O₄ powder and 100 μL of ethanol and add them to an agate mortar, grind for 5 min to form a uniform dispersion; afterwards, use a small brush to thinly and evenly coat the dispersion on the test surface of the planar Au multi-layer electrode and air-dry at room temperature.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. Low-temperature and high-efficiency sensing: The gas sensor made of the porous Sc-doped Co₃O₄ nanosheet material provided by the present invention significantly reduces the working temperature of the sensor (110 °C), (the existing Co₃O₄-based sensors are usually > 150 °C), and the energy consumption is reduced by more than 60%.

[0022] 2. High selectivity: Sc doping enhances the adsorption of p-xylene, making the selectivity of p-xylene (R g / R a = 30.6) 3 times higher than that of toluene (R g / R a = 10.1) at a concentration of 100 ppm.

[0023] 3. Different response characteristics: The Sc-doped Co3O4 gas sensor has different response characteristics to xylene isomers, including o-xylene, m-xylene, and p-xylene. It responds faster and recovers faster to p-xylene.

[0024] 4. Low detection limit: The porous structure provides abundant active sites, enabling the detection of 2 ppm p-xylene at 110 °C.

[0025] 5. Long-term stability: Sc doping inhibits the lattice sintering of Co3O4, and the response value decays by less than 5% after 25 days of continuous testing.

[0026] 6. Controllable preparation and reproducibility: The hydrothermal-calcination method realizes uniform Sc doping. Through the preparation and testing of 10 batches of devices, the error is small and the reproducibility is high.

[0027] 7. Structure-property correlation: The synergistic design of the porous nanosheet thickness and mesopores shortens the gas diffusion path and increases the exposure of sensitive sites.

[0028] 8. The existing technologies require higher temperatures, generally exceeding 150 °C, and cannot detect xylene isomers well. They mostly use noble metal (Pt, Au) modification to improve performance. In contrast, the present invention achieves low-temperature, high-performance, low-cost, and high-stability detection through rare earth doping and structure regulation. Description of the Drawings

[0029] Figure 1 Schematic diagram of the preparation process of the porous Sc-doped Co3O4 nanosheet material and the preparation of the gas sensor of the present invention;

[0030] Figure 2 XRD patterns (a) and Raman spectra (b) of the Co3O4 and Sc-doped Co3O4 materials prepared by the present invention;

[0031] Figure 3 SEM images of Co3O4 (a, c) and 1-Sc-Co3O4 (b, d);

[0032] Figure 4 SEM photograph (a) of the prepared 1-Sc-Co3O4; elemental EDS mapping (b); EDS of the obtained 1-Sc-Co3O4 (c); O mapping (d); S mapping (e); and Co mapping (f);

[0033] Figure 5 TEM images and high-resolution HRTEM images of Co3O4 (a, b); TEM images and high-resolution HRTEM images of 1-Sc-Co3O4 (c, d);

[0034] Figure 6 Nitrogen adsorption / desorption and pore size distribution isotherms of Co3O4 (a), 1-Sc-Co3O4 (b), 3-Sc-Co3O4 (c) and 5-Sc-Co3O4 (d);

[0035] Figure 7 Full-scan XPS spectra (a), high-resolution Sc 2p spectra (b), Co 2p spectra (c), and O 1s spectra of Co3O4 (d) and 1-Sc-Co3O4;

[0036] Figure 8 Responses of Co3O4 and Sc-doped Co3O4 sensors to 100 ppm p-xylene at different operating temperatures (a); Resistance changes of Co3O4 and Sc-doped Co3O4 sensors in air at different operating temperatures (b);

[0037] Figure 9 Mixed response curves of 1-Sc-Co3O4 sensor to p-xylene, m-xylene and o-xylene (a); Response curves of 1-Sc-Co3O4 sensor to 100 ppm p-xylene (b), m-xylene (c) and o-xylene (d) respectively;

[0038] Figure 10 Selectivities of Co3O4 and Sc-doped Co3O4 sensors to 100 ppm various VOCs;

[0039] Figure 11 Five dynamic cycle responses of 1-Sc-Co3O4 sensor (a); Responses of 1-Sc-Co3O4 sensor to p-xylene at different concentrations at the optimal operating temperature (b); Fitting curves and equations for different concentrations (c); Long-term stability of 1-Sc-Co3O4 sensor (d). Detailed implementation manners

[0040] The method of the present invention will be described in detail below in conjunction with specific embodiments. Hexamethylenetetramine in the present invention can be abbreviated as HMT. In the present invention, X-ray diffraction (XRD) patterns were collected on a Shimadzu X-ray diffractometer (XRD-6100, Shimadzu, Japan). Raman spectra were measured on a HORIBA HR Evolution spectrometer (Japan) with an excitation wavelength of 532 nm. Scanning electron microscope (SEM) images were collected on a Thermo Fisher Scientific Quattro S. Elemental mapping analysis was recorded by energy-dispersive X-ray spectroscopy (EDAX ELECT PIUS). Transmission electron microscope (TEM) characterization was performed on a JEM-F200 instrument (200 kV, Japan). The specific surface area and pore size distribution were obtained by nitrogen (N2) adsorption / desorption isotherm tests using the Brunauer-Emmett-Teller (BET) method on an analyzer (Micromeritics Tristar II 3020). X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Fisher Science K-Alpha spectrometer equipped with a monochromatic Al K α source (11.7 kV, 6 mA). The samples were analyzed under vacuum conditions (5×10 Pa) and measured and scanned at an energy of 50 eV. Figure 1 Schematic diagram of the preparation process of the porous Sc-doped Co3O4 nanosheet material of the present invention and the preparation of the gas sensor.

[0041] I. Preparation of a porous Sc-doped Co3O4 nanosheet material

[0042] Example 1

[0043] (1) According to the molar ratio of 0.01:1:3, Sc(NO3)3·H2O, Co(NO3)2·6H2O and hexamethylenetetramine (HMT) were dissolved in 50 mL of distilled water for 10 min to form a homogeneous solution, and then heated at 90 °C for 6 h;

[0044] (2) After centrifugation for 1 min, it was washed 5 times with water and ethanol, and the washed sample was placed in a vacuum oven at 60 °C and dried for 12 h to obtain a 1% Sc-doped α-Co(OH)2 precursor;

[0045] (3) The above-prepared precursor was calcined at 450 °C with a heating rate of 3 °C min -1 for 2 h to obtain a porous Sc-doped Co3O4 nanosheet material, named 1-Sc-Co3O4.

[0046] Example 2

[0047] (1) Dissolve Sc(NO3)3·H2O, Co(NO3)2·6H2O and hexamethylenetetramine (HMT) in 50 mL of distilled water in a molar ratio of 0.03:1:3 for 10 min to form a homogeneous solution, and then heat it at 90 °C for 6 h;

[0048] (2) After centrifugation for 1 min, wash it 5 times with water and ethanol, and dry the washed sample in a vacuum oven at 60 °C for 12 h to obtain an α-Co(OH)2 precursor with a Sc doping amount of 1%;

[0049] (3) Calcinate the above-prepared precursor at 400 °C with a heating rate of 6 °C min -1 for 2 h to obtain a porous Sc-doped Co3O4 nanosheet material, named 3-Sc-Co3O4.

[0050] Example 3

[0051] (1) Dissolve Sc(NO3)3·H2O, Co(NO3)2·6H2O and hexamethylenetetramine (HMT) in 50 mL of distilled water in a molar ratio of 0.05:1:3 for 10 min to form a homogeneous solution, and then heat it at 90 °C for 6 h;

[0052] (2) After centrifugation for 1 min, wash it 5 times with water and ethanol, and dry the washed sample in a vacuum oven at 60 °C for 12 h to obtain an α-Co(OH)2 precursor with a Sc doping amount of 1%;

[0053] (3) Calcinate the above-prepared precursor at 600 °C with a heating rate of 2 °C min -1 for 2 h to obtain a porous Sc-doped Co3O4 nanosheet material, named 5-Sc-Co3O4.

[0054] Comparative Example 4

[0055] (1) Dissolve Co(NO3)2·6H2O and hexamethylenetetramine (HMT) in 50 mL of distilled water in a molar ratio of 1:3 for 10 min to form a homogeneous solution, and then heat it at 90 °C for 6 h;

[0056] (2) After centrifugation for 1 min, wash it 5 times with water and ethanol, and dry the washed sample in a vacuum oven at 60 °C for 12 h to obtain an α-Co(OH)2 precursor;

[0057] (3) Calcinate the above-prepared precursor at 450 °C with a heating rate of 3 °C min -1 for 2 h to obtain a Co3O4 nanosheet material, named Co3O4.

[0058] II. Performance Testing of Porous Sc-Doped Co3O4 Nanosheet Materials

[0059] (1) XRD Testing

[0060] Figure 2 XRD patterns (a) and Raman spectra (b) of the Co3O4 and Sc-doped Co3O4 materials prepared in this invention. In Figure 2 (a) the XRD pattern, the diffraction peaks of Co3O4 centered at 18.7, 31.1, 36.6, 38.4, 44.7, 55.6, 59.3, 65.1, and 77.3° are the (111), (220), (311), (222), (440), (422), (511), (440), and (533) crystal planes respectively. The XRD pattern of Sc-doped Co3O4 has similar characteristic peaks to Co3O4, and no obvious Sc2O3 peak is observed, indicating that Sc elements are doped into the lattice of Co3O4.

[0061] Figure 2 (b) is the Raman spectrum. The vibration peaks at 193, 480, 520, 617, and 688 cm -1 are respectively attributed to F 1 2g , E 2g , F 2 2g , F 2g and A 1g . However, no other vibration modes of Sc2O3 are observed, indicating that the structure of single-phase Co3O4 is retained after Sc doping, while the peak values of the F 2g and A 1g modes respectively correspond to the vibrations of tetrahedral sites (Co 2+ ) and octahedral sites (Co 3+ ) in Co3O4. In particular, the A 1g peak in Sc-doped Co3O4 has an obvious downward shift compared with Co3O4, which may be due to the Sc-O bond weakening the strength of the Co-O bond.

[0062] (2) SEM Testing

[0063] Figure 3 SEM images of Co3O4 (a, c) and 1-Sc-Co3O4 (b, d). In Figure 3 (a), Co3O4 presents characteristics similar to hydrangea, and the hydrangea is composed of ultra-thin Co3O4 nanosheets. There are abundant pores in the Co3O4 nanosheets, as Figure 3 (b) shows. 1-Sc-Co3O4 maintains a morphological characteristic similar to Co3O4 ( Figure 3(c)) Figure 3 The magnified image in (d) also shows the gaps between adjacent nanosheets and the abundant pores in the nanosheets.

[0064] Figure 4 SEM images of the prepared 1-Sc-Co3O4: (a); elemental EDS mapping (b); EDS of the obtained 1-Sc-Co3O4 (c); O mapping (d); Sc mapping (e); and Co mapping (f). It can be seen from the figure that the elements Co, O, and Sc are uniformly distributed on the surface of the sample. According to the EDS analysis, the atomic percentage of Sc element is 0.41, which is lower than the theoretical doping amount of scandium.

[0065] (3) BET test

[0066] Figure 5 TEM images and high-resolution HRTEM images of Co3O4 (Figures (a, b)); TEM images and high-resolution HRTEM images of 1-Sc-Co3O4 (Figures (c, d)). It can be seen from the figure that the Co3O4 and 1-Sc-Co3O4 samples exhibit a similar porous nanosheet structure (Figures (a, c)), which is consistent with the magnified SEM images ( Figure 3 (b, d)). In the HRTEM image of Co3O4 ( Figure 5 (b)), the lattice fringes with spacings of 0.244 and 0.289 nm correspond to the (311) and (220) planes of Co3O4. In the Figure 5 HRTEM image of 1-Sc-Co3O4 in (d), the same crystal planes are also observed, demonstrating that the 1% content of Sc doping does not destroy the structure of Co3O4.

[0067] (4) N2 adsorption-desorption test

[0068] Figure 6 Nitrogen adsorption / desorption and pore size distribution isotherms of Co3O4 (a), 1-Sc-Co3O4 (b), 3-Sc-Co3O4 (c), and 5-Sc-Co3O4 (d). It can be seen from the figure that all these isotherms are classic Type-IV curves, and the main pores of the prepared Co3O4 and Sc-doped Co3O4 samples are mesopores. The specific surface areas of the prepared Co3O4, 1-Sc-Co3O4, 3-Sc-Co3O4, and 5-Sc-Co3O4 are 22.67, 39.52, 54.79, and 74.04 m 2 / g. Apparently, after doping with Sc, the specific surface areas of 1-Sc-Co3O4, 3-Sc-Co3O4, and 5-Sc-Co3O4 increase significantly. In the inset, the main pore diameters of Co3O4, 1-Sc-Co3O4, 3-Sc-Co3O4, and 5-Sc-Co3O4 are 18.3, 19.6, 43.4, and 108.5 nm, respectively. The results show that the increase in specific surface area and appropriate mesopore size are beneficial to providing more active sites for gas-solid interaction and gas diffusion, which may contribute to the improvement of sensor response.

[0069] (5) XPS test

[0070] Figure 7 For the full-scan XPS spectra (a), high-resolution Sc 2p spectra (b), Co 2p spectra (c), and O 1s spectra of Co3O4 (d) and 1-Sc-Co3O4. The full scan is as Figure 7 (a) shown, where the presence of O and Co elements in Co3O4 and 1-Sc-Co3O4, and the presence of Sc element in 1-Sc-Co3O4 are clearly confirmed. In Figure 7 (b), the high-resolution Sc 2p spectra also confirm the presence of Sc element in 1-Sc-Co3O4, and the center of the Sc 2p peak is located at 402.11 eV. In addition, the content of Sc element in 1-Sc-Co3O4 is 1.42%, and the difference from EDS may be due to the very low doping concentration of scandium. Figure 7 (c), the high-resolution spectra of Co 2p are fitted to a pair of Co 2p 1 / 2 and Co 2p 2 / 3 and two satellites (804.81 and 789.76 eV). In Co3O4, the peaks located at 780.15 and 794.87 eV are Co(III), and the peaks centered at 781.89 and 796.70 eV are Co(II). Similarly, Co(III) and Co(II) are also detected in 1-Sc-Co3O4, but there is a slight shift in the binding energy.

[0071] In addition, the high-resolution spectra of O 1s in Co3O4 and 1-Sc-Co3O4 are fitted to three peaks: lattice oxygen (O L ), oxygen vacancy (O V ), and surface chemisorbed oxygen (O C ). The content of Ov in 1-Sc-Co3O4 is higher than that in Co3O4, which is beneficial to attracting O2 molecules and promoting sensor response.

[0072] III. Application of Porous Sc-Doped Co3O4 Nanosheet Gas Sensors

[0073] (1) Preparation of Porous Sc-doped Co3O4 Nanosheet Gas Sensor:

[0074] Use a simple spot welder to weld the dried planar Au multi-layer electrode core to the black hexagonal base; then, take an appropriate amount of metal element-doped Co3O4 powder and 100 μL of ethanol and add them to an agate mortar, grind for 5 minutes to form a uniform dispersion; after that, use a small brush to thinly and evenly coat the dispersion on the test surface of the planar Au multi-layer electrode and dry it at room temperature.

[0075] (2) Gas Sensitivity Test:

[0076] The gas sensitivity test in this work relies on the CGS-8R intelligent gas sensitivity analysis system (Beijing Elite Technology Co., Ltd.), and the volume of the test chamber is about 20 L. This system uses a static gas distribution mode to test the gas sensor device. The specific gas environment is to inject the corresponding volatile organic compounds (VOCs) (toluene, xylene, triethylamine, n-butanol, ethanol, methanol, acetone, ammonia water) into the internal evaporation box of the test chamber. The ambient air background is at room temperature (28 ± 2 °C) and the relative humidity is 32 ± 2%. The evaporation box is set at a temperature 5 - 10 °C higher than the boiling point of the organic solvent for easy volatilization. Insert the prepared gas sensor element into the slot of the test chamber, turn on the power of the device, and select an appropriate working temperature. Inject the target gas into the test chamber through the gas injection hole, and calculate the sensitivity of the device through the resistance change.

[0077] The concentration C (ppm) of the target gas is controlled by the volume S (mL) of the injected corresponding solvent, as shown in the following formula:

[0078]

[0079] In the formula, V (L), C (ppm), and M (g) represent the space volume of the test chamber, the concentration of the VOC gas, and the molecular weight of the target gas respectively, and d and ρ (g / cm 3 ) represent the purity and density of the injected organic solvent respectively. The response of the gas sensor is obtained by calculating the ratio of the resistance (R g ) of the target gas to the resistance (R a ) in ambient air, usually expressed as R g / R a . The response time and recovery time are defined as the time required for the resistance change to reach 90% after the introduction and depletion of the target gas respectively.

[0080] Figure 8 Response of Co3O4 and Sc-doped Co3O4 sensors to 100 ppm p-xylene at different working temperatures (a); Resistance change of Co3O4 and Sc-doped Co3O4 sensors in air at different working temperatures (b).Figure 8 (a) shows the responses (R g / R a ) of Co3O4 and Sc-doped Co3O4 sensors to 100 ppm p-xylene. The responses of all sensors increase with increasing temperature and then decrease. The optimal operating temperature of the Co3O4 sensor is 140 °C, and the response (R g / R a ) is 16.4. However, the optimal operating temperatures of the 1-Sc-Co3O4, 3-Sc-Co3O4, and 5-Sc-Co3O4 sensors are all 110 °C, indicating that Sc doping significantly reduces the operating temperature of Co3O4.

[0081] The highest response of the 1-Sc-Co3O4 sensor is 30.6, which is 13.3 times that of the Co3O4 sensor at the optimal operating temperature of 110 °C and 1.8 times that of the Co3O4 sensor at 140 °C. Therefore, 110 °C is the optimal operating temperature for these sensors to sense p-xylene, which is significantly lower than that of the p-xylene sensor based on Co3O4.

[0082] In Figure 8 (b), the resistance of all sensors in air decreases with increasing temperature, which can be attributed to thermal excitation. The resistance of the Sc-doped Co3O4 sensors is lower than that of the Co3O4 sensors, and with the increase in the amount of Sc doping, the resistance of the Sc-doped Co3O4 sensors decreases. The resistance change indicates that Sc element doping can affect the transfer of carrier charges in Co3O4.

[0083] Figure 9 Figure (a) is the mixed response curve of the 1-Sc-Co3O4 sensor to p-xylene, m-xylene, and o-xylene; Figures (b), (c), and (d) are the response curves of the 1-Sc-Co3O4 sensor to 100 ppm p-xylene, m-xylene, and o-xylene, respectively. Figure 9 (a) is the corresponding comparison diagram of the three isomers of xylene. Figure (b) is the response to 100 ppm p-xylene at 110 °C, with a response time of 16 s and a recovery time of 66 s.

[0084] , such as Figure 9 Figures (c-d) are the response diagrams of m-xylene and p-xylene. The responses (R g / R aThey are 18.1 and 24.0 respectively, lower than that of p-xylene. The response times and recovery times of m-xylene and o-xylene are 32 and 357 s, 46 and 236 s respectively. In addition, for m-xylene and o-xylene, it is difficult for the 1-Sc-Co3O4 sensor to recover to the initial state. The response behaviors of the 1-Sc-Co3O4 sensor to the three xylene isomers are quite different, indicating that the 1-Sc-Co3O4 sensor can be used to distinguish xylene isomers.

[0085] Figure 10 are the selectivities of Co3O4 and Sc-doped Co3O4 sensors to various VOCs at 100 ppm. Figure 10 Among them, the responses of the 1-Sc-Co3O4 sensor to p-xylene, methanol, n-butanol, ethanol, triethylamine, ammonia, m-xylene, o-xylene, toluene and acetone are 30.6, 8.8, 13.6, 10.5, 11.8, 4.6, 10.2, 18.1, 24.0 and 9.34 respectively. It can be seen that the 1-Sc-Co3O4 sensor has the largest response to p-xylene, and the responses to other gases except m-xylene and o-xylene are basically more than twice, meeting the requirements of practical applications. However, for the detection of xylene isomers, in addition to the response (R g / R a ), the response time and recovery time can also be used as important indicators. Therefore, even in the presence of other xylene isomers, the 1-Sc-Co3O4 sensor still has the ability to detect p-xylene.

[0086] Figure 11 are the five dynamic cycle responses of the 1-Sc-Co3O4 sensor (a); the responses of the 1-Sc-Co3O4 sensor to p-xylene at different concentrations at the optimal working temperature (b); the fitting curves and equations at different concentrations (c); the long-term stability of the 1-Sc-Co3O4 sensor (d). In Figure 11 (a), when exposed to 100 ppm p-xylene, the five dynamic cycle responses of the 1-Sc-Co3O4 sensor are almost the same, and the relative standard deviation (RSD) is 0.72% (n = 5), confirming the excellent reproducibility of the 1-Sc-Co3O4 sensor.

[0087] In addition, the responses of the 1-Sc-Co3O4 sensor at the optimal working temperature to p-xylene at different concentrations are shown in Figure 11 (b). At low concentrations of p-xylene, the response increases rapidly and then slowly increases. The fitting curves and equations are shown in Figure 11 (c). The detection limit of the 1-Sc-Co3O4 sensor for p-xylene obtained by experiment is 2.87 ppm.

[0088] Finally, the long-term stability of the 1-Sc-Co3O4 sensor was investigated. As Figure 11 shown in (d), although the response of the 1-Sc-Co3O4 sensor decreased slightly, it still maintained a response value of 92% after 25 days, indicating that the 1-Sc-Co3O4 sensor has high stability. Therefore, based on the above gas sensing performance, the prepared porous 1-Sc-Co3O4 nanosheets can be used as potential candidates for sensing p-xylene.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A preparation method of a porous Sc-doped Co3O4 nanosheet material, characterized in that, It includes the following steps: (1) Dissolve Sc(NO3)3·H2O, Co(NO3)2·6H2O and hexamethylenetetramine in 50 mL of distilled water for 10 min in a molar ratio of (0.01 - 0.05):1:3 to form a homogeneous solution, and then heat it at 90 °C for 6 h; (2) Centrifuge for 1 min, wash and dry to obtain α-Co(OH)2 precursors with different Sc doping amounts; (3) Calcinate the above-prepared precursor at a temperature of 400 - 600 °C and a heating rate of 2 - 6 °C min -1 to obtain a porous Sc-doped Co3O4 nanosheet material.

2. The preparation method of the porous Sc-doped Co3O4 nanosheet material according to claim 1, characterized in that, In step (2), the centrifuged sample is washed 5 times with water and ethanol.

3. The preparation method of the porous Sc-doped Co3O4 nanosheet material according to claim 2, wherein, In step (2), the washed sample is dried in a vacuum oven at 60 °C for 12 h.

4. The preparation method of the porous Sc-doped Co3O4 nanosheet material according to claim 3, characterized in that, In step (3), the calcination conditions are as follows: at 450 °C, the heating rate is 3 °C / min -1 .

5. The preparation method of the porous Sc-doped Co3O4 nanosheet material according to claim 4, wherein, In step (3), the calcination time is 2 h.

6. Application of a porous Sc-doped Co3O4 nanosheet material, characterized in that, A gas sensor is made of the porous Sc-doped Co3O4 nanosheet material prepared by the method according to any one of claims 1 to 5, and the application of the gas sensor in the low-temperature and highly selective detection of p-xylene.

7. Use of the porous Sc-doped Co3O4 nanosheet material according to claim 6, characterized in that, The preparation method of the gas sensor is as follows: Use a simple spot welder to weld the dried planar Au multi-layer electrode core to the black hexagonal base; then, take an appropriate amount of Co3O4 powder doped with metal elements and 100 μL of ethanol and add them to an agate mortar, grind for 5 min to form a homogeneous dispersion; then, use a small brush to thinly and evenly coat the dispersion on the test surface of the planar Au multi-layer electrode, and air-dry at room temperature.

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