CeO2 composite Co3O4 nanoflower, preparation method and application of CeO2 composite Co3O4 nanoflower as gas sensitive material

Abstract

The invention belongs to the field of nano materials, and particularly relates to a CeO2 composite Co3O4 nano flower, a preparation method and application of the CeO2 composite Co3O4 nano flower as a gas sensitive material. The CeO2 composite Co3O4 nanoflower is composed of a Co3O4 nanoflower and CeO2 nanoparticles uniformly dispersed on the surface of the Co3O4 nanoflower, the metal Ce is in a tetravalent state, and the doping amount of the metal Ce is 3-7% of the amount of the metal Co; the invention also provides a preparation method of the CeO2 composite Co3O4 nanoflower, and an application of the CeO2 composite Co3O4 nanoflower as a gas sensitive material in carbon monoxide detection, and the CeO2 composite Co3O4 nanoflower can be used for detecting 0.3-500ppm of CO at 0-500 DEG C. The invention also provides a preparation method of the CeO2 composite Co3O4 nanoflower. The preparation method of the CeO2 composite Co3O4 nanoflower is simple to operate, a three-dimensional polyhedral MOF is converted into a two-dimensional MOF through simple ionic heat assistance, the two-dimensional MOF is reassembled into a 3D nanoflower, further annealing is performed to obtain the bimetallic MOS nanoflower, the synthesis method is simple, environment-friendly and low in cost, and large-scale industrial production is convenient to realize; and the prepared CeO2 composite Co3O4 nanoflower gas sensitive material has a good sensitive characteristic on CO (carbon monoxide) of 0.3 to 500 ppm.

Description

Technical Field

[0001] The invention belongs to the technical field of nano materials, and specifically relates to a CeO2 composite Co3O4 nano flower, a preparation method and an application thereof as a gas-sensitive material. Background Art

[0002] Over the past few decades, industrial production and motor vehicle exhaust emissions, as well as incomplete combustion of fossil fuels, have produced a large amount of pollutants that are continuously discharged into the atmosphere. Among them, carbon monoxide (CO) is considered one of the most dangerous gases in exhaust because it easily binds to hemoglobin and causes hypoxia in the human body. It is also colorless and odorless, and is usually monitored by gas sensors.

[0003] Among the many CO detection methods, metal oxide semiconductor (MOS) sensors have received more and more attention due to their low cost, portability, simple production and good response. However, the CO detection ability of a single metal oxide is limited due to its high operating temperature and low response value. The usual strategy to solve this problem is to load precious metals to increase the response value and reduce the operating temperature of the sensor. However, the disadvantage of this solution is that precious metals are relatively scarce and expensive. Co3O4 is a black or gray powder. The CO in automobile exhaust is catalyzed by Co3O4 and can react with oxygen to produce CO2. At the same time, due to its high sensitivity, it is widely used as a gas-sensitive material in gas-sensitive detection.

[0004] It is reported that Co in the spinel structure Co3O4 is located at the octahedral coordination center. 3+ is the active site for low-temperature oxidation of CO, and the Co 3+ The higher the ratio, the more beneficial it will be to improve the CO gas sensing performance. Metal organic framework (MOF) can be used as a high-quality self-sacrificial template to prepare MOS materials with different structures. However, in recent years, the use of MOF (Metal organic Framework, metal organic framework compound) as a template to prepare MOS mostly stays at three-dimensional MOS derived from three-dimensional MOF, and the three-dimensional MOS structure is folded, which greatly limits the specific surface area and active site utilization of MOS.

[0005] Therefore, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a CeO2 composite Co3O4 nanoflower, a preparation method and its application as a gas-sensitive material. The present invention adopts a simple solvent thermal method and uses Co-Ce-MOF nanoflowers as templates to prepare CeO2 / Co3O4 nanoflower gas-sensitive materials with high sensitivity to CO gas.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A CeO2 composite Co3O4 nanoflower consists of Co3O4 nanoflowers and CeO2 nanoparticles uniformly dispersed on the surface of the Co3O4 nanoflowers, wherein metal Ce is in a tetravalent state and the doping amount of metal Ce is 3-7% of the amount of metal Co substance.

[0009] Furthermore, the diameter of the Co3O4 nanoflower is 8-12 μm, and the diameter of the CeO2 nanoparticle is 100-500 nm.

[0010] The present invention also proposes a method for preparing the aforementioned CeO2 composite Co3O4 nanoflowers, comprising the following steps:

[0011] (1) Dissolving Co(NO3)2·6H2O and Ce(NO3)3·6H2O in anhydrous methanol under stirring to obtain solution A, wherein the molar ratio of Ce element to Co element in solution A is (3-7):100; dissolving a certain amount of dimethylimidazole in anhydrous methanol to obtain solution B; adding solution B dropwise to solution A and continuously ultrasonicating to obtain a ZIF-CoCe mixed solution;

[0012] (2) transferring the ZIF-CoCe mixed solution obtained in step (1) to a reactor for a solvothermal reaction, wherein the temperature of the solvothermal reaction is 100 to 140° C. and the reaction time is 8 to 12 h; then naturally cooling to room temperature, washing with anhydrous methanol for multiple times and centrifuging to obtain a precipitate, and vacuum drying the precipitate to obtain a Co-Ce-MOF nanoflower precursor;

[0013] (3) The precursor obtained in step (2) is gradually heated to 280-320° C. in an air atmosphere for calcination to obtain CeO2 / Co3O4 nanoflower gas-sensitive material.

[0014] Furthermore, in solution A, the ratio of the total amount of metal salts Co(NO3)2·6H2O and Ce(NO3)3·6H2O to the volume of anhydrous methanol is 0.001-0.00321 mol:5-30 ml.

[0015] Furthermore, in solution B, the amount ratio of dimethylimidazole to anhydrous methanol is (0.035-0.04 g):1 ml.

[0016] Furthermore, in the ZIF-CoCe mixed solution, the ratio of the total amount of dimethylimidazole to the metal salts Co(NO3)2·6H2O and Ce(NO3)3·6H2O in solution A is (15-30):1.

[0017] Furthermore, in step (1), the ultrasonic treatment time is 5 to 30 minutes, the ultrasonic frequency is 40 kHz, and the ultrasonic power is 360 W.

[0018] Furthermore, the number of times of centrifugal washing with anhydrous methanol in step (2) is 3 to 6 times; the temperature of vacuum drying is 60 to 80°C, and the drying time is 8 to 12 hours. Note that anhydrous ethanol cannot be used to replace anhydrous methanol, as the Co-Ce-MOF nanoflower precursor will dissolve after contacting anhydrous ethanol.

[0019] Furthermore, in step (3), the precursor is gradually heated to 280-320° C. at a heating rate of 0.5-2° C. / min in an air atmosphere and maintained at this temperature for 2-4 h.

[0020] The application of the CeO2 composite Co3O4 nanoflower is to use it as a gas-sensitive material in carbon monoxide detection, and can detect 0.3-500ppm CO at 0-500°C; it is recommended to use it to detect 0.3-500ppm CO at 200°C, and it can exert the best performance at this working temperature.

[0021] The working principle of the present invention is: Co in Co3O4 3+ The higher the ratio, the more beneficial it is to improve the CO gas sensing performance. 4+ and Ce 3+ The reversible conversion between Co and Ce ions allows the following The redox reaction increases Co 3+ The present invention converts the three-dimensional polyhedron MOF into a two-dimensional MOF and reassembles it into a 3D nanoflower, which can not only shorten the electron transmission distance, but also expose the active sites on the oxide surface to a large extent. At the same time, the open pore structure will give MOS a larger comparative area. These factors are conducive to the improvement of the gas sensing performance of Co3O4.

[0022] The beneficial effects of the present invention are:

[0023] The present invention converts the polymetallic MOF polyhedron into a polymetallic MOF nanoflower by a solvothermal method; uses the polymetallic MOF nanoflower as a template and adjusts the annealing temperature to prepare a CeO2 composite Co3O4 gas-sensitive material with a 3D nanoflower morphology. The CeO2 composite Co3O4 nanoflower has a CeO2 and Co3O4 heterojunction structure, so that the CeO2 in the Co3O4 3+ The ratio of CO increases, and a large number of oxygen vacancies are introduced, allowing the target gas CO to participate more fully in the redox reaction, resulting in a significant increase in its response value.

[0024] The preparation method is simple to operate. Through simple ion thermal assistance, the three-dimensional polyhedron MOF is converted into a two-dimensional MOF and reassembled into a 3D nanoflower, which is further annealed to obtain a bimetallic MOS nanoflower. The synthesis method is simple, environmentally friendly and pollution-free, no impurity ions are introduced, and the cost is low, which facilitates large-scale industrial production.

[0025] The CeO2 composite Co3O4 nanoflower gas-sensitive material prepared by the present invention has good sensitivity to CO. At the optimal working temperature of 200°C, the detection limit is 0.3ppm, and the response value corresponding to the detection limit is 17%. It has broad application prospects in manufacturing new high-efficiency gas sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0027] Figure 1 2 are XRD spectra of Co3O4, 3CeO2 / Co3O4, 5CeO2 / Co3O4 and 7CeO2 / Co3O4 in the comparative example of the present invention and Examples 1-3.

[0028] Figure 2 The XPS spectra of 5CeO2 / Co3O4 in the comparative example and Examples 1-3 of the present invention are shown in FIG.

[0029] (a) XPS spectrum of Co 2p of 5CeO2 / Co3O4;

[0030] (b) XPS spectrum of Ce 3d of 5CeO2 / Co3O4.

[0031] Figure 3 The SEM images of Co3O4, 3CeO2 / Co3O4, 5CeO2 / Co3O4 and 7CeO2 / Co3O4 nanoflowers in the comparative example and Examples 1-3 of the present invention are shown in FIG.

[0032] (a) and (b) are SEM images of Co3O4 nanoflower gas-sensitive materials in the comparative example;

[0033] (c) and (d) are SEM images of the 3CeO2 / Co3O4 nanoflower gas-sensitive material in Example 1, respectively;

[0034] (e) and (f) are SEM images of the 5CeO2 / Co3O4 nanoflower gas-sensitive material in Example 2, respectively;

[0035] (g) and (h) are SEM images of the 7CeO2 / Co3O4 nanoflower gas-sensitive material in Example 3, respectively.

[0036] Figure 4 The sensitivity curves of Co3O4, 3CeO2 / Co3O4, 5CeO2 / Co3O4 and 7CeO2 / Co3O4 nanoflowers in the comparative example of the present invention and Examples 1-3 to different concentrations of CO gas;

[0037] Figure 5 This is the real-time response recovery curve of 5CeO2 / Co3O4 nanoflowers to different concentrations of CO in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0039] A CeO2 composite Co3O4 nanoflower consists of Co3O4 nanoflowers and CeO2 nanoparticles uniformly dispersed on the surface of the Co3O4 nanoflowers, wherein metal Ce is in a tetravalent state and the doping amount of metal Ce is 3-7% of the amount of metal Co substance.

[0040] Furthermore, the diameter of the Co3O4 nanoflower is 8-12 μm, and the diameter of the CeO2 nanoparticle is 100-500 nm.

[0041] The preparation method of the CeO2 composite Co3O4 nanoflower comprises the following steps:

[0042] (1) Co(NO3)2·6H2O and Ce(NO3)3·6H2O are dissolved in anhydrous methanol under stirring conditions, the ratio of the total amount of Co(NO3)2·6H2O and Ce(NO3)3·6H2O to the volume of anhydrous methanol is 0.001-0.00321 mol:5-30 ml, to obtain solution A, wherein the amount of Ce element to Co element in solution A is (3-7):100; a certain amount of dimethylimidazole is dissolved in anhydrous methanol to obtain solution B, solution B The amount ratio of dimethylimidazole to anhydrous methanol is (0.035-0.04 g):1 ml; solution B is added dropwise to solution A and continuously ultrasonicated to obtain a ZIF-CoCe mixed solution, in which the amount ratio of dimethylimidazole to the total amount of metal salts Co(NO3)2·6H2O and Ce(NO3)3·6H2O in solution A is (15-30):1; the ultrasonic treatment time is 5-30 min, the ultrasonic frequency is 40 kHz, and the ultrasonic power is 360 W;

[0043] (2) The ZIF-CoCe mixed solution obtained in step (1) is transferred to a reactor for a solvothermal reaction, wherein the temperature of the solvothermal reaction is 100 to 140° C. and the reaction time is 8 to 12 h; then the mixture is naturally cooled to room temperature, washed 3 to 6 times with anhydrous methanol and centrifuged to obtain a precipitate, and the precipitate is vacuum dried to obtain a Co-Ce-MOF nanoflower precursor; the vacuum drying temperature is 60 to 80° C. and the drying time is 8 to 12 h; note that anhydrous ethanol cannot be used to replace anhydrous methanol, as the Co-Ce-MOF nanoflower precursor will dissolve after contacting anhydrous ethanol;

[0044] (3) The precursor obtained in step (2) is gradually heated to 280-320° C. at a heating rate of 0.5-2° C. / min under air atmosphere and maintained at this temperature for 2-4 h to obtain CeO2 / Co3O4 nanoflower gas-sensitive material.

[0045] The application of the CeO2 composite Co3O4 nanoflower is to use it as a gas-sensitive material in carbon monoxide detection, and can detect 0.3-500ppm CO at 0-500°C; it is recommended to use it to detect 0.3-500ppm CO at 200°C, and it can exert the best performance at this working temperature.

[0046] The present invention will be described in detail below in conjunction with the embodiments. In the following embodiments, the response value S of the gas sensor is expressed as (Rg-Ra) / Ra*100%.

[0047] Example 1

[0048] The preparation method of the CeO2 composite Co3O4 nanoflower comprises the following steps:

[0049] (1) 0.873 g of Co(NO3)2·6H2O and 0.039 g of CeN3O9·6H2O were dissolved in 15 ml of anhydrous methanol under stirring to obtain solution A1, in which the molar ratio of Ce element to Co element was 3%; 0.574 g of dimethylimidazole was dissolved in 15 ml of anhydrous methanol to obtain solution B; a portion of solution B was added dropwise to solution A1 under stirring, and the obtained mixed solution was ultrasonically treated for 30 min to obtain a mixed solution containing ZIF-CoCe polyhedrons;

[0050] (2) The mixed solution containing ZIF-CoCe polyhedrons obtained in step (1) was transferred to a 50 ml polytetrafluoroethylene reactor, heated at 120° C. for 10 h, then naturally cooled to room temperature, washed three times with anhydrous methanol, and centrifuged to obtain a precipitate, and the precipitate was vacuum dried at 60° C. for 12 h to obtain a CoCe-MOF nanoflower precursor;

[0051] (3) The precursor obtained in step (2) was heated at 1°C min in air atmosphere. -1 The heating rate was gradually increased to 300°C and annealed for 3 hours to obtain the comparison material 3CeO2 / Co3O4 nanoflower gas-sensitive material.

[0052] like Figure 1 As shown, from the XRD spectrum of the 3CeO2 / Co3O4 nanoflower gas-sensitive material prepared in this embodiment, it can be seen that the obtained 3CeO2 / Co3O4 is consistent with the diffraction peaks of CeO2 and Co3O4, without any impurity peaks and any phase separation, which proves that Co3O4 has been successfully synthesized to obtain a CeO2 / Co3O4 composite material. Figure 3 (c) and (d) are 3CeO2 / Co3O4 nanoflowers obtained in this example. It can be clearly seen from the photos that CeO2 particles are attached to the Co3O4 nanoflowers. Figure 4 As shown in FIG. 1 , the comparative material 3CeO2 / Co3O4 nanoflower gas-sensitive material prepared in this embodiment has a sensitivity curve to different concentrations of CO gas at 200°C. The response value of the gas-sensitive device is expressed as S=(R g -R a ) / R a *100%, of which R a is the resistance of the device in air, R g is the resistance of the device in CO gas. The test results show that as the concentration of the detected CO gas increases, the response value of the 3CeO2 / Co3O4 nanoflower gas-sensitive material to CO also gradually increases. The response value of the 3CeO2 / Co3O4 nanoflower gas-sensitive material to 50ppm CO gas is 150%.

[0053] Example 2

[0054] The preparation method of the CeO2 composite Co3O4 nanoflower comprises the following steps:

[0055] (1) 0.873 g of Co(NO3)2·6H2O and 0.065 g of CeN3O9·6H2O were dissolved in 15 ml of anhydrous methanol under stirring to obtain solution A2, in which the molar ratio of Ce element to Co element was 3%; 0.574 g of dimethylimidazole was dissolved in 15 ml of anhydrous methanol to obtain solution B; a portion of solution B was added dropwise to solution A2 under stirring, and the obtained mixed solution was ultrasonically treated for 30 min to obtain a mixed solution containing ZIF-CoCe polyhedrons;

[0056] (2) The mixed solution containing ZIF-CoCe polyhedrons obtained in step (1) was transferred to a 50 ml polytetrafluoroethylene reactor, heated at 120° C. for 10 h, then naturally cooled to room temperature, washed three times with anhydrous methanol, and centrifuged to obtain a precipitate, and the precipitate was vacuum dried at 60° C. for 12 h to obtain a CoCe-MOF nanoflower precursor;

[0057] (3) The precursor obtained in step (2) was heated at 1°C min in air atmosphere. -1 The heating rate was gradually increased to 300°C and annealed for 3 hours to obtain the comparison material 5CeO2 / Co3O4 nanoflower gas-sensitive material.

[0058] like Figure 1 As shown, from the XRD spectrum of the 5CeO2 / Co3O4 nanoflower gas-sensitive material prepared in this embodiment, it can be seen that the obtained 5CeO2 / Co3O4 is consistent with the diffraction of CeO2 and Co3O4, without any impurity peaks, and no phase separation occurs. It proves that the CeO2 / Co3O4 composite material has been successfully synthesized by Co3O4. Figure 3 (e) and (f) are 5CeO2 / Co3O4 nanoflowers obtained in this example. It can be clearly seen from the photos that CeO2 particles are attached to the Co3O4 nanoflowers. Figure 3 The CeO2 particles in (f) appear larger than those in other embodiments. This is just because the selected area is different when taking the electron microscope image. The gas sensing performance is not directly related to the size of the CeO2 particles. For gas sensors, the performance is not only reflected in the response value, but also by many factors, such as selectivity, moisture resistance, and stability. Figure 4As shown in the figure, the sensitivity curve of the 5CeO2 / Co3O4 nanoflower gas-sensitive material prepared in this embodiment to different concentrations of CO gas at 210°C. The test results show that as the concentration of the detected CO gas increases, the influence value of the 5CeO2 / Co3O4 nanoflower gas-sensitive material on CO also gradually increases. The response value of the 5CeO2 / Co3O4 nanoflower gas-sensitive material to 50ppm CO gas is 184%, which has the highest sensitivity and is the best embodiment of the present invention.

[0059] Example 3

[0060] The preparation method of the CeO2 composite Co3O4 nanoflower comprises the following steps:

[0061] (1) 0.873 g of Co(NO3)2·6H2O and 0.091 g of CeN3O9·6H2O were dissolved in 15 ml of anhydrous methanol under stirring to obtain solution A3, in which the molar ratio of Ce element to Co element was 3%; 0.574 g of dimethylimidazole was dissolved in 15 ml of anhydrous methanol to obtain solution B; a portion of solution B was added dropwise to solution A3 under stirring, and the obtained mixed solution was ultrasonically treated for 30 min to obtain a mixed solution containing ZIF-CoCe polyhedrons;

[0062] (2) The mixed solution containing ZIF-CoCe polyhedrons obtained in step (1) was transferred to a 50 ml polytetrafluoroethylene reactor, heated at 120° C. for 10 h, then naturally cooled to room temperature, washed three times with anhydrous methanol, and centrifuged to obtain a precipitate, and the precipitate was vacuum dried at 60° C. for 12 h to obtain a CoCe-MOF nanoflower precursor;

[0063] (3) The precursor obtained in step (2) was heated at 1°C min in air atmosphere. -1 The heating rate was gradually increased to 300°C and annealed for 3 hours to obtain the comparison material 5CeO2 / Co3O4 nanoflower gas-sensitive material.

[0064] like Figure 1 As shown in the XRD spectrum of the 7CeO2 / Co3O4 nanoflower gas-sensitive material prepared in this embodiment, it can be seen that the diffraction peaks of the obtained 7CeO2 / Co3O4 correspond to those of CeO2 and Co3O4, without any impurity peaks and without any phase separation. This proves that the CeO2 / Co3O4 composite material was successfully synthesized. Figure 2 XPS spectrum analysis shows that the heterogeneous element Ce mainly exists in the +4 valence, which has stronger oxidizing properties than +3 valence Ce. Figure 3(g) and (h) are 7CeO2 / Co3O4 nanoflowers obtained in this example. It can be clearly seen from the photos that CeO2 particles are attached to the Co3O4 nanoflowers. Figure 4 and Figure 5 As shown in the figure, the sensitivity curve of the 7CeO2 / Co3O4 nanoflower gas-sensitive material prepared in this embodiment responds to different concentrations of CO gas in real time at 210°C. The test results show that as the concentration of the detected CO gas increases, the influence value of the 7CeO2 / Co3O4 nanoflower gas-sensitive material on CO also gradually increases. The response value of the 7CeO2 / Co3O4 nanoflower gas-sensitive material to 50ppm CO gas is 57%.

[0065] Comparative Example

[0066] In this comparative example, CeN3O9·6H2O is not added, and the other steps are the same as those in Examples 1-3, and finally a Co3O4 nanoflower gas-sensitive material is prepared. Specifically, the preparation method thereof comprises the following steps:

[0067] (1) 0.873 g of Co(NO3)2·6H2O was dissolved in 15 ml of anhydrous methanol under stirring to obtain solution Aa; 0.574 g of dimethylimidazole was dissolved in 15 ml of anhydrous methanol to obtain solution B; a portion of solution B was added dropwise to solution A under stirring, and the obtained mixed solution was ultrasonically treated for 30 min to obtain a mixed solution containing ZIF-67 polyhedrons;

[0068] (2) The mixed solution containing ZIF-67 obtained in step (1) was transferred to a 50 ml polytetrafluoroethylene reactor, heated at 120° C. for 10 h, then naturally cooled to room temperature, washed three times with anhydrous methanol, and centrifuged to obtain a precipitate; the precipitate was vacuum dried at 60° C. for 12 h to obtain a Co-MOF nanoflower precursor;

[0069] (3) The Co-MOF nanoflower precursor obtained in step (2) is gradually heated to 300°C at a heating rate of 1°C / min in an air atmosphere and then annealed for 3 hours to obtain a Co3O4 nanoflower gas-sensitive material.

[0070] The characterization results of the Co3O4 nanoflower gas-sensitive material obtained in this example are as follows:

[0071] like Figure 1 As shown in FIG. 1 , from the XRD spectrum of the Co3O4 nanoflower gas-sensitive material prepared in this embodiment, it can be seen that there are no impurity peaks and no phase separation. This proves that Co3O4 was successfully prepared. Figure 3 As shown, (a) and (e) are the final obtained Co3O4 nanoflowers. Figure 4As shown, the comparative material Co3O4 exhibits a lower response to CO. The test results show that as the concentration of the detected CO gas increases, the influence value of the Co3O4 nanoflower gas-sensitive material on CO also gradually increases. The response value of the Co3O4 nanoflower gas-sensitive material to 50ppm CO gas is 34%.

[0072] Comparing Examples 1-3 of the present invention with the comparative example, it can be seen that attaching CeO2 to Co3O4 nanoflowers can improve the response value of CO gas. This is because CeO2 in the introduced CeO2 4+ and Ce 3+ The reversible transformation between Co 3+ At the same time, the introduced oxygen vacancies enable the target gas CO to participate more fully in the redox reaction, resulting in a significant increase in its response value.

[0073] Comparative Examples 1-3, such as Figure 4 As shown in the figure, with the increase of Ce element content in CeO2 composite Co3O4 nanoflowers, its response value to CO gas at various concentrations increases first and then decreases. The best effect is achieved when the doping amount of metal Ce is 5% of the amount of metal Co substance. It is speculated that this is because compared with the other three materials, 5CeO2 / Co3O4 has a higher oxygen vacancy content. High oxygen vacancies can provide more unpaired electrons for gas sensing materials, further allowing more oxygen ions to be adsorbed on the surface, resulting in enhanced response. In addition, the appropriate proportion of CeO2 makes Co 3+ The content of Co 3+ The oxidizing property is better than Co 2 + Strong, CO molecules preferentially bind to Co 3+ Combined with Co 3+ Nearby oxygen species combine to form CO2, while Co 3+ is reduced to Co 2+ Therefore, 5CeO2 / Co3O4 exhibits better sensing performance compared to the other three materials. However, when the CeO2 content is too high, CeO2 may agglomerate on the Co3O4 surface. This reduces the activity of the heterojunction and leads to a decrease in sensing performance.

[0074] Among them, Figure 4As shown in the figure, under the conditions of working temperature of 200℃ and gas concentration of 5~500ppm, the response value of Co3O4 gas sensor to CO gas is 2.6%~94%. Under the conditions of working temperature of 200℃ and gas concentration of 1~500ppm, the response value of 3CeO2 / Co3O4 gas sensor to CO gas is 13%~372%. Under the conditions of working temperature of 200℃ and gas concentration of 0.3~500ppm, the response value of 5CeO2 / Co3O4 gas sensor to CO gas is 17%~500%, among which the response value corresponding to 0.3ppm CO gas is 17%. Under the conditions of working temperature of 200℃ and gas concentration of 2~500ppm, the response value of 7CeO2 / Co3O4 gas sensor to CO gas is 8%~165%.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A CeO2 composite Co3O4 nanoflower, characterized in that: The CeO2 composite Co3O4 nanoflowers are composed of Co3O4 nanoflowers and CeO2 nanoparticles uniformly dispersed on the surface of the Co3O4 nanoflowers, wherein the metal Ce is in a tetravalent state and the doping amount of the metal Ce is 3-7% of the amount of the metal Co substance.

2. The CeO2 composite Co3O4 nanoflower according to claim 1, characterized in that: The diameter of the Co3O4 nanoflower is 8-12 μm, and the diameter of the CeO2 nanoparticle is 100-500 nm.

3. A method for preparing CeO2 composite Co3O4 nanoflowers as claimed in claim 1 or 2, characterized in that: The following steps are involved: (1) Dissolving Co(NO3)2·6H2O and Ce(NO3)3·6H2O in anhydrous methanol under stirring to obtain solution A, wherein the molar ratio of Ce element to Co element in solution A is (3-7):100; dissolving a certain amount of dimethylimidazole in anhydrous methanol to obtain solution B; adding solution B dropwise to solution A and continuously ultrasonicating to obtain a ZIF-CoCe mixed solution; (2) transferring the ZIF-CoCe mixed solution obtained in step (1) to a reactor for a solvothermal reaction, wherein the temperature of the solvothermal reaction is 100 to 140° C. and the reaction time is 8 to 12 h; then naturally cooling to room temperature, washing with anhydrous methanol for multiple times and centrifuging to obtain a precipitate, and vacuum drying the precipitate to obtain a Co-Ce-MOF nanoflower precursor; (3) The precursor obtained in step (2) is gradually heated to 280-320° C. in an air atmosphere for calcination to obtain CeO2 / Co3O4 nanoflower gas-sensitive material.

4. The method for preparing CeO2 composite Co3O4 nanoflowers according to claim 3, characterized in that: In solution A, the ratio of the total amount of metal salts Co(NO3)2·6H2O and Ce(NO3)3·6H2O to the volume of anhydrous methanol is (0.001~0.00321mol):(5~30ml).

5. The method for preparing CeO2 composite Co3O4 nanoflowers according to claim 3, characterized in that: In solution B, the ratio of dimethylimidazole to anhydrous methanol is (0.035-0.04 g):1 ml.

6. The method for preparing CeO2 composite Co3O4 nanoflowers according to claim 3, characterized in that: In the ZIF-CoCe mixed solution, the ratio of the total amount of dimethylimidazole to the total amount of metal salts Co(NO3)2·6H2O and Ce(NO3)3·6H2O in solution A is (15-30):

1.

7. The method for preparing CeO2 composite Co3O4 nanoflowers according to claim 3, characterized in that: The ultrasonic treatment time in step (1) is 5 to 30 minutes.

8. The method for preparing CeO2 composite Co3O4 nanoflowers according to claim 3, characterized in that: In step (2), the number of times of centrifugal washing with anhydrous methanol is 3 to 6 times; the temperature of vacuum drying is 60 to 80° C., and the drying time is 8 to 12 hours.

9. The method for preparing CeO2 composite Co3O4 nanoflowers according to claim 3, characterized in that: In step (3), the precursor is gradually heated to 280-320° C. at a heating rate of 0.5-2° C. / min in an air atmosphere and maintained at this temperature for 2-4 hours.

10. An application of CeO2 composite Co3O4 nanoflowers as claimed in claim 1, characterized in that: It is used as a gas-sensitive material in carbon monoxide detection and is used to detect 0.3 to 500 ppm CO at a temperature of 200°C.

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