Fe-doped Co3O4 microsphere gas sensitive material, preparation method and application

Abstract

The invention belongs to the technical field of semiconductor metal oxide functional materials and gas-sensitive sensing, and particularly relates to a Fe-doped Co3O4 microsphere gas-sensitive material as well as a preparation method and application thereof. Cobalt acetate and anhydrous ferric trichloride are used as raw materials, CTAB is used as a template agent, ethylene glycol is used as a solvent, a one-step solvothermal method is adopted to prepare a ferrocobalt precursor, and the ferrocobalt precursor is subjected to heat treatment in an air atmosphere to obtain the Fe-doped Co3O4 microsphere structure gas sensitive material. Compared with a pure Co3O4 microsphere gas-sensitive material and a Fe-doped Co3O4 microsphere gas-sensitive material, the Fe-doped Co3O4 microsphere gas-sensitive material has a very high response value (101) to 100 ppm acetone at 210 DEG C, also has very good gas selectivity and repeatability test performance, can be used for high-sensitivity detection of acetone, and has important practical significance in early disease warning and real-time monitoring of acetone in industrial production. The method is simple in preparation process, low in cost and good in controllable effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor metal oxide functional materials and gas sensing technology, and particularly relates to an Fe-doped Co3O4 microsphere gas sensing material, a preparation method and an application thereof. Background Art

[0002] Acetone is a colorless, transparent and toxic liquid with strong volatility and is widely used in the fields of chemical industry, electronics industry, pharmaceutical industry, etc. Although it has a wide range of applications, acetone gas is toxic. According to the Occupational Exposure Limits for Hazardous Chemical Factors in the Workplace of China (GBZ2.1-2019), the weighted average allowable concentration of the toxic substance acetone in the air of the workplace is at most 300 mg / m 3 . Exceeding this concentration will cause great harm to the human respiratory system, nervous system and internal organs. In addition, acetone in human breath is a biomarker for type I diabetes. It has been confirmed that the concentration of acetone in the exhaled breath of diabetic patients exceeds 1.8 ppm, which is significantly higher than the range of 0.3 to 0.9 ppm for healthy individuals. Therefore, developing an acetone sensor with high response and low detection limit is of great significance for protecting human life and health.

[0003] In recent years, metal oxide semiconductor (MOS) gas sensors have been widely studied and applied in acetone gas detection due to their advantages such as small size, real-time monitoring and low manufacturing cost. In particular, Co3O4 is a typical p-type semiconductor material with high catalytic activity and excellent electrical conductivity, and is one of the ideal materials for acetone detection. However, some Co3O4 acetone sensors have problems of high detection limit and low sensitivity, which shortens their application range. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] The present invention provides an Fe-doped Co3O4 microsphere gas sensing material, a preparation method and an application thereof to solve the technical problem of low response value of pure Co3O4 gas sensing material to acetone.

[0006] (2) Technical Solutions

[0007] To solve the above technical problems, the present invention provides an Fe-doped Co3O4 microsphere gas sensing material and a preparation method. The Fe-doped Co3O4 microsphere gas sensing material has a large specific surface area and a porous structure, which can provide more active sites for gas sensing reactions. The doping of Fe changes the chemical environment on the surface of the material, which is more conducive to the adsorption of acetone and the generation of reactive oxygen species on the surface of the material, and is more conducive to the occurrence of gas sensing reactions.

[0008] The technical solutions adopted by the present invention are as follows:

[0009] In a first aspect, the present invention provides a method for preparing an Fe-doped Co3O4 microsphere gas-sensitive material. Using a soluble cobalt salt and a trivalent iron salt as raw materials, CTAB as a template agent, and ethylene glycol as a solvent, a cobalt-iron precursor is prepared by a one-step solvothermal method, and an Fe-doped Co3O4 microsphere gas-sensitive material is obtained through heat treatment in an air atmosphere; the specific preparation method includes the following steps:

[0010] S1. Preparation of the cobalt-iron precursor: Dissolve the soluble cobalt salt and the trivalent iron salt in ethylene glycol, then add cetyltrimethylammonium bromide CTAB to obtain a mixed solution; use a one-step solvothermal method to obtain the cobalt-iron precursor;

[0011] The Co:Fe molar ratio of the solution obtained after dissolving the soluble cobalt salt and the trivalent iron salt is 100:1 to 100:5;

[0012] S2. Preparation of the Fe-doped Co3O4 microsphere gas-sensitive material: Heat-treat the prepared cobalt-iron precursor in an air atmosphere at a heating rate of 0.5 °C / min to 2 °C / min at 350 °C to 450 °C to obtain the Fe-doped Co3O4 microsphere gas-sensitive material.

[0013] Preferably, in step S1, the operation of the one-step solvothermal method is: the reaction temperature is 160 °C to 180 °C, and the reaction time is 8 h to 12 h.

[0014] Preferably, in step S1, the mixed solution is ultrasonically dispersed and dissolved to achieve uniformity.

[0015] Preferably, in step S1, the mass of CTAB is 5 to 20 times the mass of the iron salt.

[0016] Preferably, in step S1, the cobalt salt and the trivalent iron salt are cobalt acetate and anhydrous ferric chloride, respectively.

[0017] Preferably, in step S2, the heat treatment duration is 1 to 2 h; after the reaction, it is centrifuged, washed with deionized water and anhydrous ethanol respectively, and then dried.

[0018] In a second aspect, the present invention provides an Fe-doped Co3O4 microsphere gas-sensitive material prepared by the method described in the first aspect.

[0019] In a third aspect, the present invention provides a method for preparing a gas-sensitive element, which specifically includes the following steps:

[0020] Mix the Fe-doped Co3O4 gas-sensitive material with water to form an Fe-doped Co3O4 gas-sensitive material slurry; brush the Fe-doped Co3O4 gas-sensitive material slurry on an Ag-Pd electrode and dry it to obtain the gas-sensitive element.

[0021] Fourthly, the present invention provides an application of the Fe-doped Co3O4 gas-sensitive material in the third aspect. The Fe-doped Co3O4 microsphere gas-sensitive material is used to detect acetone at 180°C to 240°C;

[0022] Through the fitting curve of the gas-sensitive response value S = Rg / Ra of the resistance value (Rg) of the material in the target gas and the resistance value (Ra) of the material in the air environment, acetone is quantitatively detected.

[0023] (III) Beneficial effects

[0024] The present invention provides an Fe-doped Co3O4 microsphere gas-sensitive material, a preparation method and an application. Since the radius of Fe 3+ is similar to that of Co 2+ and the number of three-dimensional orbital electrons is different, Fe has a unique regulatory effect on the electronic structure of the Co-based catalyst. The incorporation of iron not only causes lattice distortion of Co3O4 but also leads to the formation of a large number of oxygen vacancies, which has potential application prospects in gas-sensitive sensing, and the sensing performance of the porous and regular structure is significantly better than that of the solid structure. The preparation process of the present invention is simple, the cost is low, and the controllable effect is good. The cobalt-iron precursor is prepared by a self-assembly method, and then the Fe-doped Co3O4 microsphere gas-sensitive material is derived. The doping of Fe changes the chemical environment on the surface of the material, which is more conducive to the adsorption of acetone and the generation of active oxygen species on the surface of the material, and is more conducive to the occurrence of gas-sensitive reactions. And the unique porous structure can provide more adsorbed oxygen for the diffusion and adsorption of gases, thereby further improving the gas-sensitive performance to acetone. Compared with the pure Co3O4 microsphere gas-sensitive material, the Fe-doped Co3O4 microsphere gas-sensitive material has a high response value and a low detection limit for acetone, and at the same time has good gas selectivity and repeatability test performance. It can be used for highly sensitive detection of acetone, which has important practical significance for early disease warning and real-time monitoring of acetone in industrial production. Description of the drawings

[0025] Figure 1 XRD diffraction patterns of the Fe-doped Co3O4 gas-sensitive materials prepared at a series of different cobalt-iron molar ratios;

[0026] Figure 2 Scanning electron microscope (SEM) image of the Fe-doped Co3O4 gas-sensitive material prepared in Example 2;

[0027] Figure 3 Transmission electron microscope (TEM) image of the Fe-doped Co3O4 gas-sensitive material prepared in Example 2;

[0028] Figure 4 Raman images of the Fe-doped Co3O4 gas-sensitive materials prepared in Examples 1 to 3;

[0029] Figure 5 The electrochemical impedance spectroscopy diagram of the Fe-doped Co3O4 gas-sensing material prepared in Example 2;

[0030] Figure 6 The broken line diagram of the gas-sensing response of the Fe-doped Co3O4 gas-sensing materials prepared in Examples 1-3 to 100 ppm of acetone in the temperature range of 180-240 °C;

[0031] Figure 7 The gas-sensing response curve of the Fe-doped Co3O4 gas-sensing material prepared in Example 2 to 100-1 ppm of acetone at 210 °C;

[0032] Figure 8 The gas-sensing response curve of the Fe-doped Co3O4 gas-sensing material prepared in Example 2 to 100 ppm of acetone at 210 °C;

[0033] Figure 9 The response diagram of the Fe-doped Co3O4 gas-sensing material prepared in Example 2 to 100 ppm of acetone and the other four interfering gases at 210 °C. Detailed implementation manners

[0034] To make the objectives, contents and advantages of the present invention clearer, the following further describes in detail the specific implementation manners of the present invention in conjunction with the accompanying drawings and examples.

[0035] Example 1

[0036] Preparation of the Fe-doped Co3O4 gas-sensing material with a cobalt-to-iron molar ratio of 100:1

[0037] S1. Weigh 0.050 g of cetyltrimethylammonium bromide (CTAB) and ultrasonically disperse it in 60 ml of ethylene glycol until it is completely dissolved.

[0038] S2. Add 0.75 g of cobalt acetate tetrahydrate (Co(CH3COO)2·4H2O) and 0.005 g of anhydrous ferric chloride (FeCl3) to the solution in step S1, and continuously stir for 30 min until it is completely dissolved.

[0039] S3. Transfer the solution obtained in step S2 to a reaction kettle and react it at 180 °C for 12 hours.

[0040] S4. After the reaction kettle is naturally cooled, centrifuge to collect the product, wash it 3 times with deionized water and absolute ethanol, and dry it overnight at 60 °C to obtain the cobalt-iron precursor material.

[0041] S5. Spread the cobalt-iron precursor obtained in step S4 evenly in a ceramic crucible and calcine it in a muffle furnace at 400 °C (1 °C / min) for 4 hours to obtain an Fe-doped Co3O4 gas-sensitive material.

[0042] Example 2

[0043] Preparation of an Fe-doped Co3O4 gas-sensitive material with a cobalt-iron molar ratio of 100:3

[0044] Same as Example 1, only change the raw material input ratio, that is, take 0.75 g of cobalt acetate tetrahydrate (Co(CH3COO)2·4H2O) and 0.015 g of anhydrous ferric chloride (FeCl3).

[0045] Example 3

[0046] Preparation of an Fe-doped Co3O4 gas-sensitive material with a cobalt-iron molar ratio of 100:5

[0047] Same as Example 1, only change the raw material input ratio, that is, take 0.75 g of cobalt acetate tetrahydrate (Co(CH3COO)2·4H2O) and 0.025 g of anhydrous ferric chloride (FeCl3).

[0048] Example 4

[0049] Fabrication of a sensor based on an Fe-doped Co3O4 gas-sensitive material with a cobalt-iron molar ratio of 100:3.

[0050] The manufacturing process of the gas-sensitive element is as follows:

[0051] S1. Weigh 5 mg of the Fe-doped Co3O4 gas-sensitive material in an agate mortar, add 1 ml of deionized water, and grind it into a slurry.

[0052] S2. Brush the slurry onto a cleaned Ag-Pd electrode (14 mm × 7 mm) with a paintbrush and let it dry naturally at room temperature to obtain a gas sensor.

[0053] Before testing, the gas sensor should be continuously aged at 210 °C for 12 h to make the molecular structure of the material denser and obtain better test results.

[0054] The specific calculation method of sensitivity is to use the resistance value (Rg) of the material in the target gas and the resistance value (Ra) of the material in the air environment, and define the gas-sensitive response value as S = (Rg / Ra).

[0055] Figure 1XRD diffraction patterns of the Fe-doped Co3O4 gas-sensitive materials obtained in Examples 1-3. As shown in the figure, the diffraction peaks of all samples are consistent with the standard Co3O4 phase (JCPDS No. 74-2120), corresponding to planes such as (220), (311), (222), (400), etc., and no other impurity peaks are seen, indicating its high purity. It can be seen from the figure that as the Fe doping amount increases, the position of the characteristic peaks shifts slightly towards a smaller diffraction angle. This phenomenon can be attributed to the substitution of smaller Co 2+ ions and Co 3+ ions by larger Fe 3+ ions. It is proved that the Fe-doped Co3O4 material of the present invention is successfully synthesized.

[0056] From SEM( Figure 2 ) and TEM( Figure 3 ), it can be seen that the structure of the Fe-doped Co3O4 gas-sensitive material is a porous microsphere structure with a diameter of about 0.8 um and a large number of pores.

[0057] Figure 4 The Raman results show that all Fe-doped Co3O4 samples have characteristic peaks near 680 cm -1 , 600 cm -1 , 510 cm -1 , 480 cm -1 and 190 cm -1 respectively belonging to the lattice vibration modes of A 1g , F 2g(3) , F 2g(2) , E 2g and F 2g(1) of spinel Co3O4. No new Raman peaks appear after introducing the Fe source, and the A 1g vibration mode shows different degrees of blue shift and broadening compared with pure Co3O4. The results show that Fe elements are doped into the lattice of Co3O4, changing the crystal grain size and crystal defects.

[0058] Figure 5 The electrochemical impedance spectra of three groups of Fe-doped Co3O4 materials are shown. Compared with the Fe-Co3O4-1 (Example 1) and Fe-Co3O4-5 (Example 3) gas-sensitive materials, the Rct of Fe-Co3O4-3 (Example 2) is the lowest, indicating that it has higher electron transport ability and good gas sensitivity.

[0059] Figure 6The response of the gas sensors obtained in Examples 1 to 3 to 100 ppm acetone at 180 - 210 °C. From the results, it can be clearly observed that the curve trends between the operating temperature and the gas response values are all inverted V-shaped. By analyzing the response values of the three groups of samples to acetone gas, the optimal operating temperature of the Fe-doped Co3O4 gas-sensitive material was determined to be 210 °C. Among them, the response value of Fe-Co3O4-3 to 100 ppm acetone gas is as high as 101.

[0060] Figure 7 The response curve of the Fe-doped Co3O4 gas-sensitive material prepared in Example 2 to acetone with concentrations ranging from 100 to 1 ppm at 210 °C. It can be seen that its response value increases significantly with the increase in acetone concentration. More notably, the detection limit of the Fe-Co3O4-3 sensor is below 1 ppm, indicating that this sensor has broad application prospects in practical detection.

[0061] Figure 8 The response curve of the Fe-doped Co3O4 gas-sensitive material prepared in Example 2 to 100 ppm acetone at 210 °C. It can be clearly seen that the response time for the response to reach 101 is 110 s, and the recovery time is 128 s. The fast response and recovery speed are due to the porous structure and large specific surface area of the material.

[0062] Figure 9 The response diagram of the Fe-doped Co3O4 gas-sensitive material prepared in Example 2 to 100 ppm acetone and the other four interfering gases at 210 °C. The results clearly show that Fe-Co3O4-3 has significant selectivity to acetone.

[0063] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing Fe-doped Co3O4 micron-sphere gas-sensitive material, characterized in that: The preparation method specifically comprises the following steps: S1. Preparation of cobalt iron precursor: dissolving soluble cobalt salt and trivalent iron salt in ethylene glycol, and then adding hexadecyltrimethylammonium bromide (CTAB) to obtain a mixed solution; reacting at 160°C to 180°C by a one-step solvothermal method to obtain a cobalt iron precursor; The molar ratio of Co:Fe in the solution obtained after dissolving cobalt acetate tetrahydrate and anhydrous ferric chloride is 100:1 to 100:5; S2. Preparation of Fe-doped Co3O4 micron-sphere gas-sensitive material: The prepared cobalt-iron precursor is heat-treated at 350°C to 450°C in an air atmosphere at a heating rate of 0.5°C / min to 2°C / min to obtain Fe-doped Co3O4 micron-sphere gas-sensitive material.

2. The method for preparing the Fe-doped Co3O4 micron-sphere gas-sensitive material according to claim 1, characterized in that: In step S1, the one-step solvothermal reaction time is 8 h to 12 h.

3. The method for preparing the Fe-doped Co3O4 micron-sphere gas-sensitive material according to claim 1, characterized in that: In the step S1, the mixed solution is dispersed and dissolved by ultrasound to achieve uniformity.

4. The method for preparing the Fe-doped Co3O4 micron-sphere gas-sensitive material according to claim 1, characterized in that: In the step S1, the mass of CTAB is 5 to 20 times the mass of the iron salt.

5. The method for preparing the Fe-doped Co3O4 micron-sphere gas-sensitive material according to claim 1, characterized in that: In the step S1, the cobalt salt and the ferric salt are cobalt acetate and anhydrous ferric chloride respectively.

6. The method for preparing the Fe-doped Co3O4 micron-sphere gas-sensitive material according to claim 1, characterized in that: In the step S2, the heat treatment time is 1 to 2 hours; after the reaction, the mixture is centrifuged, washed and dried with deionized water and anhydrous ethanol respectively.

7. An Fe-doped Co3O4 micron-sphere gas-sensitive material prepared by the method described in any one of claims 1 to 6.

8. A method for preparing a gas sensor, characterized in that: The specific steps include: The Fe-doped Co3O4 gas-sensitive material according to claim 7 is mixed with water to form a Fe-doped Co3O4 gas-sensitive material slurry; the Fe-doped Co3O4 gas-sensitive material slurry is applied on the Ag-Pd electrode and dried to obtain a gas-sensitive element.

9. An application of the Fe-doped Co3O4 gas-sensitive material according to claim 8, characterized in that: The Fe-doped Co3O4 micron-sphere gas-sensitive material is used to detect acetone at 180℃~240℃.

10. The use of the Fe-doped Co3O4 gas-sensitive material according to claim 9, characterized in that: A fitting curve is prepared by the gas-sensitive response value S=Rg / Ra of the resistance value (Rg) of the material in the target gas and the resistance value (Ra) of the material in the air environment to quantitatively detect acetone.

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