Preparation method of cobalt oxide-based composite material for 3-octanone detection

Abstract

The invention discloses a preparation method of a cobalt oxide-based composite material for 3-octanone detection, which comprises the following steps: respectively dissolving cobalt nitrate hexahydrate and 2-methylimidazole in methanol to obtain a cobalt nitrate methanol solution and a 2-methylimidazole methanol solution; injecting the titanium dioxide quantum dot colloid into a cobalt nitrate methanol solution, and stirring to form a uniform colloid; slowly adding the mixed colloid into a 2-methylimidazole methanol solution, continuously stirring to generate purple suspension, centrifuging, cleaning and drying to obtain purple powder; and calcining to obtain the cobalt oxide-based composite material. Due to the introduction of titanium dioxide, the hollow structure of cobalt oxide is distorted, the grain size is reduced, the specific surface area is increased, and an energy band is bent; the charge modulation effect of the titanium dioxide / cobalt oxide heterojunction interface significantly improves the sensitivity and selectivity of the cobalt oxide-based sensor to 3-octanone.

Description

Technical Field

[0001] This invention belongs to the field of engineering and materials technology, and specifically relates to a method for preparing a cobalt oxide-based composite material for the detection of 3-octanone. Background Technology

[0002] 3-Octanone is a typical metabolite of filamentous fungi. Its volatilization rate increases monotonically in wheat and rice in the early stages of mold infection as the infection progresses. Therefore, it can be used as a marker of mold growth in wheat and rice.

[0003] Sensors targeting 3-octanone hold promise for real-time detection of wheat and rice. Electronic noses demonstrate excellent market potential in this area, widely employing chemielectric resistive sensors with good integration properties. Currently reported sensors are limited to a colorimetric sensor based on boron dipyrrole methylene dye (DOI: 10.1007 / s12161-019-01617-1) and a cobalt oxide-based chemielectric resistive sensor published by the inventors (DOI: 10.1016 / j.talanta.2025.127892). Therefore, there is an urgent need to develop sensing materials with good 3-octanone sensing capabilities for use in resistive gas sensors.

[0004] The modification method of constructing heterojunctions is feasible for significantly improving the sensitivity and selectivity of cobalt oxide to 3-octanone. Patent CN202411632222 discloses a method for preparing tin dioxide / cobalt oxide heterostructured nanofibers. This composite material exhibits enhanced sensitivity due to the optimized charge transfer efficiency of the heterojunction interface. Limiting the size of the second phase to improve the internal carrier transport efficiency and introducing catalytically active sites has been proven to be an effective strategy for improving the reactivity of materials. Patent CN120815566A discloses a porous carbon nitride photocatalyst supported on composite nanodots, its preparation method, and its applications. This composite material exhibits significantly improved catalytic activity due to the surface loading of size-constrained cobalt oxide and nickel nanodots. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a cobalt oxide-based composite material for the detection of 3-octanone.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a cobalt oxide-based composite material for the detection of 3-octanone, comprising, Tetrabutyl titanate was dissolved in nitric acid-ethanol solution to prepare a colorless and transparent precursor. Titanium dioxide quantum dots were synthesized by microwave-assisted hydrothermal method. After centrifugation, the upper quantum dot colloid was retained and freeze-dried to obtain a powder sample, which was then dispersed in ethanol to obtain titanium dioxide quantum dot colloid. Cobalt nitrate hexahydrate and 2-methylimidazole were dissolved in methanol to obtain cobalt nitrate methanol solution and 2-methylimidazole methanol solution, respectively. Titanium dioxide quantum dot colloid was injected into a cobalt nitrate methanol solution and stirred to form a homogeneous colloid. The mixed colloid was slowly added to a 2-methylimidazolium methanol solution, and a purple suspension was produced by continuous stirring. After centrifugation, washing, and drying, a purple powder was obtained. The purple powder was calcined at 450°C for 3 hours to obtain a black powder, thus obtaining a cobalt oxide-based composite material. The heating rate was 2°C per minute.

[0009] In a preferred embodiment of the preparation method described in this invention, the colorless and transparent precursor comprises a tetrabutyl titanate, nitric acid and ethanol in a ratio of 2 mL: 4 mL: 40 mL, and the nitric acid concentration is 68 wt%.

[0010] As a preferred embodiment of the preparation method described in this invention, the microwave-assisted hydrothermal synthesis parameters are: power of 500W, temperature of 120℃, and time of 1h.

[0011] As a preferred embodiment of the preparation method described in this invention, the centrifugation parameters are 4000 revolutions per minute for 10 minutes.

[0012] As a preferred embodiment of the preparation method described in this invention, the titanium dioxide quantum dot colloid contains titanium dioxide quantum dot powder in a ratio of 100 mg to 100 mL of ethanol.

[0013] In a preferred embodiment of the preparation method described in this invention, the ratio of cobalt nitrate to methanol in the cobalt nitrate methanol solution is 3 mmol: 40 ml; and the ratio of 2-methylimidazole to methanol in the 2-methylimidazole methanol solution is 12 mmol: 40 ml.

[0014] In a preferred embodiment of the preparation method described in this invention, the titanium dioxide quantum dot colloid is injected into a cobalt nitrate methanol solution, wherein the ratio of the titanium dioxide quantum dot colloid to the cobalt nitrate methanol solution is 10-30 mL: 40 mL. In a preferred embodiment of the preparation method described in this invention, the mixed colloid is slowly and completely added to a 2-methylimidazolium methanol solution, wherein the ratio of the mixed colloid to the 2-methylimidazolium methanol solution is 40~70 mL: 40 mL.

[0015] Another objective of this invention is to overcome the shortcomings of the prior art and provide a cobalt oxide-based composite material.

[0016] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of a cobalt oxide-based composite material in the preparation of 3-octanone detection materials.

[0017] Beneficial effects of this invention: (1) The present invention utilizes centrifugation and freeze-drying strategies to obtain titanium dioxide quantum dots and uniformly disperses them in a ZIF-67 room temperature synthesis system to prepare a bulk dispersion titanium dioxide / cobalt oxide composite material with excellent component uniformity.

[0018] (2) The introduction of titanium dioxide causes distortion of the hollow structure of cobalt oxide, reduction of grain size, increase of specific surface area and band bending; the charge modulation effect of the titanium dioxide / cobalt oxide heterojunction interface significantly improves the sensitivity and selectivity of cobalt oxide-based sensors to 3-octanone.

[0019] (3) The titanium dioxide / cobalt oxide composite material prepared in this invention has a high response value (208) to 50 ppm 3-octanone at 210℃, which is much higher than the response value (87) of pure cobalt oxide to 50 ppm 3-octanone at the optimal operating temperature (220℃) in this study; the ratio of the sensor's response value to 3-octanone to the maximum value of the sensor's response value to other volatile organic compounds is used as the selectivity index; in this invention, the selectivity index of the titanium dioxide / cobalt oxide composite material at 210℃ is 4.2, which is higher than that of pure cobalt oxide (2.2); the paper DOI: 10.1016 / j.talanta.2025.127892 synthesized four different morphologies of cobalt oxide materials by hydrothermal method, and the best-performing cobalt oxide-based sensor showed a high response value (208) to 50 ppm 3-octanone at 210℃. The highest response value for 3-octanone was 174, and the selectivity index for 3-octanone was 2.5. This indicates that the titanium dioxide / cobalt oxide composite material of the present invention still has significant advantages in the application of chemielectric resistivity gas sensors for the efficient detection of 3-octanone. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 These are scanning electron microscope images of Examples 1, 2, 3, and 4.

[0021] Figure 2 X-ray diffraction patterns of titanium dioxide quantum dots and Examples 1, 2, 3, and 4.

[0022] Figure 3 This is a high-magnification transmission electron microscope image of Example 3.

[0023] Figure 4 The graph shows the response values ​​of 50 ppm volatile organic compounds from wheat / rice mold at different temperatures for Examples 1, 2, 3, and 4.

[0024] Figure 5 Images showing the dynamic response of Examples 1 and 3 to 1-4 ppm 3-octanone at the optimal operating temperature. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0026] All raw materials used in this invention are commercially available products.

[0027] The application of the composite material in the preparation of a 3-octanone gas-sensitive element in this invention includes the following steps: 10 mg of the composite material was added to 0.2 mL of deionized water and ground to form a paste. The paste was then uniformly coated on the outer surface of the gas sensor substrate and completely covered the platinum interdigitated electrodes (coating thickness 100 μm). The coating was dried at 60 °C for 2 h to form a gas-sensitive coating and calcined at 250 °C for 12 h to obtain the gas-sensitive element. The gas sensing performance of the prepared gas-sensitive element was tested using the SD101 four-channel material gas-sensitive performance tester produced by Wuhan Huachuang Ruike Technology Co., Ltd. (total gas flow rate of 1000 sccm, without additional humidity). The response values ​​of the element to different wheat / rice mold markers were tested at different temperatures to determine the specificity of the cobalt oxide-based sensor to 3-octanone and the optimal operating temperature.

[0028] In the industry, the response value S is usually used to measure the gas-sensing characteristics of a gas sensor. The response value of the gas sensor prepared in this invention is defined as the stable resistance value R in the target gas.g The stable resistance value R of the sensor in air a The ratio, i.e., S=R g / R a .

[0029] The technical solution of this invention is as follows: A method for preparing a cobalt oxide-based composite material for the detection of 3-octanone, the method comprising the following steps: Preparation of titanium dioxide quantum dots: (1) 4 mL of concentrated nitric acid (volume fraction 68%) was injected into 40 mL of methanol to obtain a nitric acid-methanol solution; (2) Inject 2 ml of tetrabutyl titanate into a nitric acid-methanol solution and stir for 30 minutes to form a mixed solution; (3) After the mixed solution was subjected to microwave-assisted hydrothermal reaction at 500 watts and 120°C for 1 hour, it was naturally cooled. (4) The product was washed by centrifugation with ethanol at 8000 rpm for 30 minutes, for a total of 3 times; the upper colloid was removed after each centrifugation. (5) Take the bottom sample and wash it with ethanol at 4000 rpm for 10 minutes; repeat 3 times; take the upper colloid after each centrifugation; (6) The upper colloid was solidified by liquid nitrogen and then freeze-dried to obtain a solid powder; (7) Disperse 100 mg of solid powder in 100 mL of ethanol to obtain titanium dioxide quantum dot colloid; Preparation of titanium dioxide quantum dot modified cobalt oxide composite materials: (1) Dissolve 3 mmol of cobalt nitrate hexahydrate and 12 mmol of 2-methylimidazole in 40 mL of methanol respectively; (2) Titanium dioxide quantum dot colloids are injected into cobalt nitrate-methanol solution to form a homogeneous colloid; (3) The mixed colloid was slowly added to the 2-methylimidazole-methanol solution and stirred continuously at 25°C for 6 hours to produce a purple suspension; (4) After washing with ethanol for 10 minutes at 4000 rpm and vacuum drying at 60°C for 12 hours, a purple powder was obtained. (5) The purple powder was calcined at 450°C for 3 hours to obtain black powder, and the heating rate was set to 2°C per minute.

[0030] Example 1 This embodiment provides a method for preparing a cobalt oxide-based composite material for the detection of 3-octanone, the main steps of which are: (1) Using a pipette with a volume of 10 ml, take 4 ml of concentrated nitric acid (volume fraction of 68%) and inject it into 40 ml of methanol. After sealing with plastic wrap, stir for 10 minutes to obtain nitric acid-methanol solution. (2) Using a pipette with a volume of 5 ml, take 2 ml of tetrabutyl titanate and inject it into the nitric acid-methanol solution. After sealing with plastic wrap, stir for 30 minutes to form a colorless and transparent mixed solution. (3) Transfer the mixed solution in (2) to a Teflon reactor and perform a microwave-assisted hydrothermal reaction at 500 watts and 120°C for 1 hour. After natural cooling, a white solid and an upper colloid are obtained. (4) After removing the upper colloid, the obtained product was transferred to a 100 ml centrifuge tube, dispersed with ethanol and balanced, centrifuged and washed at 8000 rpm for 30 minutes, for a total of 3 times. After each centrifugation, the upper colloid was removed and the dispersion was repeated with ethanol. The lower solid was fully dispersed using a shaker. (5) Take the lower solid layer and wash it with ethanol at 4000 rpm for 10 minutes, for a total of 3 times; after each centrifugation, take the upper colloid layer and reuse ethanol to disperse it; use a shaker to fully disperse the lower solid layer. (6) Place the upper colloid in liquid nitrogen for 3 days to ensure full solidification, and freeze-dry to obtain solid powder; (7) 100 mg of solid powder was dispersed in 100 mL of ethanol to obtain titanium dioxide quantum dot colloid with a size of 4.0 ± 1.1 nm; (8) Dissolve 3 mmol of cobalt nitrate hexahydrate and 12 mmol of 2-methylimidazole in 40 mL of methanol respectively; (9) In this embodiment, titanium dioxide quantum dot colloid is not added. Cobalt nitrate-methanol solution is slowly added to 2-methylimidazole-methanol solution and stirred continuously at 25°C for 6 hours to produce a purple suspension. (10) After washing with ethanol for 10 minutes at 4000 rpm and vacuum drying at 60°C for 12 hours, a purple powder was obtained. (11) The purple powder was calcined at 450°C for 3 hours to obtain black powder, and the heating rate was set to 2°C per minute.

[0031] XRD and SEM analyses of the powder from Example 1 confirmed that it was cobalt oxide with a hollow ZIF-67 truncated dodecahedron morphology. Figure 1 a and Figure 2 XRD fine-fit fitting analysis yielded a grain size of 23.8 nanometers. The specific surface area of ​​the powder from Example 1, calculated using the BET method, was 41.0 m², based on nitrogen adsorption-desorption testing. 2 / g.

[0032] Example 1 showed a response value of 87 to 50 ppm 3-octanone at 220°C. Figure 4 a); Perform dynamic testing of low-concentration 3-octanone, testing the dynamic response of Example 1 to 1-4 ppm 3-octanone at 220°C ( Figure 5 This demonstrates the effective detection capability of Example 1 for low concentrations of 3-octanone.

[0033] Example 2 The difference between this embodiment and embodiment 1 is that in step (9), 10 ml of titanium dioxide quantum dot colloid needs to be added to the cobalt nitrate-methanol solution, stirred for 10 minutes to form a uniform mixed sol, and then slowly added to the 2-methylimidazole-methanol solution. Other conditions are the same as in embodiment 1.

[0034] At this point, the ZIF-67 truncated dodecahedron is slightly deformed. Figure 1 (b) The atomic ratio of titanium to cobalt is 4.9%, and the XRD pattern mainly shows the main peak of cobalt oxide. o A slight protrusion appears at the location ( Figure 2 The cobalt oxide has a grain size of 22.8 nanometers and a specific surface area of ​​51.3 m². 2 / g; Example 2 showed the highest response value of 153 to 50 ppm 3-octanone at 210°C. Figure 4 b).

[0035] Example 3 The difference between this embodiment and embodiment 2 is that the amount of titanium dioxide quantum dot colloid injected in step (9) is 20 ml, and the other processes are the same as in embodiment 2.

[0036] At this point, the ZIF-67 truncated dodecahedron is clearly deformed. Figure 1 c) The atomic ratio of titanium to cobalt is 9.2%, and the XRD pattern mainly shows the main peak of cobalt oxide. o The protrusion phenomenon is obvious ( Figure 2 The cobalt oxide has a grain size of 21.4 nanometers and a specific surface area of ​​55.8 m². 2 / g; In the high-magnification transmission electron microscope of Example 3, 1, 2, and 3 are cobalt oxide phases, and 4 is titanium dioxide. Combined with the high uniformity of titanium element distribution, it is confirmed that titanium dioxide quantum dots are dispersed in the cobalt oxide main phase. Figure 3 ); Example 3 showed the highest response value to 50 ppm 3-octanone at 210°C, which was 208 ( Figure 4 c) Example 3 exhibited a more significant response to 1-4 ppm 3-octanone gas at 210°C compared to Example 1. Figure 5 ).

[0037] Example 4 The difference between this embodiment and embodiment 2 is that the amount of titanium dioxide quantum dot colloid injected in step (9) is 30 ml, and the other processes are the same as in embodiment 2.

[0038] At this point, the ZIF-67 truncated dodecahedron was severely deformed and partially collapsed. Figure 1 d) The atomic ratio of titanium to cobalt is 15.0%, and the XRD pattern mainly shows the main peak of cobalt oxide. o A prominent protrusion ( Figure 2 The cobalt oxide has a grain size of 20.6 nanometers and a specific surface area of ​​45.1 m². 2 / g; Example 4 showed the highest response value to 50 ppm 3-octanone at 210°C, at 124 ( Figure 4 d); The introduction of titanium dioxide quantum dots induced truncated dodecahedral morphology distortion in ZIF-67, reduced the grain size of the host material cobalt oxide, and increased the specific surface area. The uniform distribution of titanium dioxide promotes the presence of abundant and uniformly distributed bulk phase titanium dioxide / cobalt oxide heterojunction interfaces inside the hollow ZIF-67 truncated dodecahedral cobalt oxide structure. The band bending at the interface induces a unique charge modulation effect, which enhances the electron-hole separation efficiency and carrier migration efficiency, and significantly improves the 3-octanone detection capability of the cobalt oxide-based sensor.

[0039] In summary, the method of this invention can prepare cobalt oxide-based composite materials with excellent sensing properties for 3-octanone and uniform bulk distribution characteristics.

[0040] Current methods for modifying titanium dioxide typically involve direct composite formation with nanoparticles or subsequent modification on the cobalt oxide surface. These processes often encounter issues such as second-phase separation and uneven distribution in actual production. In this invention, the size of the titanium dioxide is controlled through two high-speed centrifugations, confining it to a quantum dot range of 4.0 ± 1.1 nm. Simultaneously, the titanium dioxide quantum dots are freeze-dried to form a quantum dot colloid of known concentration. This colloid is then injected into a metal salt solution, ensuring uniform contact between the cobalt ions and the titanium dioxide quantum dots. During subsequent coordination at room temperature, the titanium dioxide quantum dots are uniformly encapsulated within ZIF-67, resulting in a titanium dioxide-modified cobalt dioxide composite material with high bulk dispersion after calcination.

[0041] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing a cobalt oxide-based composite material for the detection of 3-octanone, characterized in that: include, Tetrabutyl titanate was dissolved in nitric acid-ethanol solution to prepare a colorless and transparent precursor. Titanium dioxide quantum dots were synthesized by microwave-assisted hydrothermal method. After centrifugation, the upper quantum dot colloid was retained and freeze-dried to obtain a powder sample, which was then dispersed in ethanol to obtain titanium dioxide quantum dot colloid. Cobalt nitrate hexahydrate and 2-methylimidazole were dissolved in methanol to obtain cobalt nitrate methanol solution and 2-methylimidazole methanol solution, respectively. Titanium dioxide quantum dot colloid was injected into a cobalt nitrate methanol solution and stirred to form a homogeneous colloid. The mixed colloid was slowly added to a 2-methylimidazolium methanol solution, and a purple suspension was produced by continuous stirring. After centrifugation, washing, and drying, a purple powder was obtained. The purple powder was calcined at 450°C for 3 hours to obtain a black powder, thus obtaining a cobalt oxide-based composite material. The heating rate was 2°C per minute.

2. The preparation method according to claim 1, characterized in that: The colorless and transparent precursor contains tetrabutyl titanate, nitric acid and ethanol in a ratio of 2 mL: 4 mL: 40 mL, with a nitric acid concentration of 68 wt%.

3. The preparation method according to claim 1 or 2, characterized in that: The microwave-assisted hydrothermal synthesis parameters are: power 500W, temperature 120℃, and time 1h.

4. The preparation method according to claim 1, characterized in that: The centrifugation parameters are 4000 revolutions per minute for 10 minutes.

5. The preparation method according to claim 1, characterized in that: The titanium dioxide quantum dot colloid is wherein the ratio of titanium dioxide quantum dot powder to ethanol is 100 mg: 100 mL.

6. The preparation method according to claim 1, characterized in that: The ratio of cobalt nitrate to methanol in the cobalt nitrate methanol solution is 3 mmol: 40 ml; the ratio of 2-methylimidazole to methanol in the 2-methylimidazole methanol solution is 12 mmol: 40 ml.

7. The preparation method according to claim 1, characterized in that: The process involves injecting titanium dioxide quantum dot colloid into a cobalt nitrate methanol solution, wherein the ratio of titanium dioxide quantum dot colloid to cobalt nitrate methanol solution is 10~30 mL : 40 mL.

8. The preparation method according to claim 1, characterized in that: The mixed colloid is slowly and completely added to the 2-methylimidazolium methanol solution, wherein the ratio of the mixed colloid to the 2-methylimidazolium methanol solution is 40~70 mL: 40 mL.

9. The cobalt oxide-based composite material prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the cobalt oxide-based composite material according to claim 9 in the preparation of 3-octanone detection materials.

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