A ZnO nanocluster, formaldehyde gas sensor and its preparation and application

Abstract

The present invention belongs to the technical field of gas sensors, and particularly relates to ZnO nanoclusters, a formaldehyde gas sensor, and their preparation and application. ZnO nano-seeds are prepared from an alkali and a zinc salt, and then reacted with ε-Zn(OH)₂ to obtain ZnO nanoclusters. The ZnO nanoclusters prepared by the present invention have a diameter of 5-10 μm, have abundant oxygen vacancies and a good pore structure; the formaldehyde gas sensor based on it has higher sensitivity, faster response speed and recovery speed to formaldehyde gas, and has broad application prospects in detecting the formaldehyde content in the detection environment.

Description

Technical Field

[0001] The invention belongs to the technical field of gas sensors, and in particular relates to a ZnO nanocluster, a formaldehyde gas sensor, and preparation and application thereof. The ZnO nanocluster is a three-dimensional, porous, defect-rich ZnO nanocluster. Background Art

[0002] Formaldehyde (HCHO) is a colorless gas with a special pungent odor. It is an important chemical raw material and is widely used in interior decoration materials such as adhesives and coatings. Long-term exposure to formaldehyde atmosphere can cause serious harm to human health. Direct contact of the skin with formaldehyde can cause allergic dermatitis, spots and necrosis. Inhalation of formaldehyde can induce physiological symptoms such as bronchitis, respiratory irritation, edema, eye irritation and headache. Therefore, the development of formaldehyde sensors that can effectively detect the formaldehyde content in the environment and effectively protect human health is a work of great practical significance.

[0003] Resistive gas sensors with metal oxide semiconductors as sensitive materials have the advantages of high sensitivity and low cost, and are currently one of the most widely used sensor types. ZnO is a common wide-bandgap n-type metal oxide semiconductor material, which is widely used as a sensitive material for gas sensing. However, sensors based on ZnO nanomaterials often require high-temperature excitation to obtain a good response, which greatly limits the application scope of ZnO-based gas sensors. Therefore, it is necessary to further improve the ZnO material to improve its gas-sensing performance. Summary of the invention

[0004] The present invention aims to provide a ZnO nanocluster, a formaldehyde gas sensor, and preparation and application thereof. The prepared three-dimensional ZnO nanocluster has abundant oxygen vacancies and a good pore structure. The three-dimensional ZnO nanocluster is covered on the outer surface of a sensor carrier. The prepared sensor has higher sensitivity, shorter response and recovery time under visible light at room temperature, and has broad application prospects in practical applications.

[0005] According to the technical solution of the present invention, the method for preparing ZnO nanoclusters comprises the following steps: a1: adding zinc salt and alkali into an ethanol aqueous solution, stirring and reacting to obtain ZnO nano seeds;

[0006] a2: The ZnO nano seeds and ε-Zn(OH) 2 Dissolve in water to obtain a mixed solution;

[0007] a3: Under microwave hydrothermal conditions, the mixed solution is heated to 80-100° C. and reacted for 5-10 minutes, and the microwave hydrothermal method is used to promote the growth of ZnO crystals and form defects to obtain the ZnO nanoclusters.

[0008] Furthermore, the zinc salt is a soluble zinc salt selected from zinc chloride or zinc acetate; the alkali is selected from sodium hydroxide or potassium hydroxide; and the volume fraction of ethanol in the ethanol aqueous solution is 40-70%, preferably 50%.

[0009] Furthermore, in the step a1, the molar ratio of the base to the zinc salt is 1.25-1.5:1.

[0010] Furthermore, in step a2, ZnO nano seeds and ε-Zn(OH) 2 The mass ratio is 2-4:1-3.

[0011] Specifically, the preparation method of the ZnO nanoclusters can be as follows:

[0012] a1: Weigh sodium hydroxide and zinc acetate in a molar ratio of 1.25-1.5:1 and add them to an ethanol aqueous solution, then stir vigorously at room temperature for 1-2 hours;

[0013] a2: The product obtained by filtering the solution in step a1 is rinsed with deionized water for 3-5 times and then dried in a drying oven to obtain ZnO nanoseeds;

[0014] a3: Weigh ε-Zn(OH) in a mass ratio of 1-3:2-4 2 (1.0-3.0 g), the ZnO nanoseeds (0.2-0.4 g) obtained in step a2, added to deionized water (40-50 mL), and stirred evenly;

[0015] a4: The solution obtained in step a3 was transferred to a polytetrafluoroethylene-lined autoclave (100 mL), and the temperature was raised to 80-100° C. under microwave hydrothermal conditions for reaction for 5-10 min;

[0016] a5: After the reactor in step a4 is cooled to room temperature, the obtained product is rinsed with deionized water for 3-5 times and then placed in a constant temperature drying oven, and continuously dried at 60-80°C for 8-12 hours. After the temperature is naturally cooled, a ZnO powder sample, i.e., the ZnO nanoclusters, is obtained.

[0017] The second aspect of the present invention provides ZnO nanoclusters prepared by the above preparation method.

[0018] Specifically, the diameter of the ZnO nanoclusters contained in the ZnO powder sample is 5-10 μm, and the length of the ZnO nanorods constituting the ZnO nanoclusters is 1-2 μm.

[0019] A third aspect of the present invention provides a method for preparing a formaldehyde gas sensor, comprising the following steps:

[0020] b1: dispersing the above ZnO nanoclusters in anhydrous ethanol or water to obtain a mixed solution;

[0021] b2: coating the mixed solution on the electrode surface of the sensor carrier to form a sensitive material film, and drying to obtain the formaldehyde gas sensor.

[0022] Furthermore, in the step b1, the volume ratio of ZnO nanoclusters to anhydrous ethanol or water is 2-5:1, and the mixed solution is in a paste state.

[0023] Furthermore, the thickness of the sensitive material film is 10-30 μm.

[0024] Furthermore, the sensor carrier includes a single crystal silicon wafer substrate, a silicon dioxide insulating layer covering the surface of the single crystal silicon wafer substrate, and interdigitated electrodes integrated on the surface of the silicon dioxide insulating layer.

[0025] Specifically, the preparation method of the sensor carrier is as follows: a silicon dioxide insulating layer is grown on a single crystal silicon wafer substrate, and interdigitated electrodes are integrated on the single crystal silicon substrate covered with the silicon dioxide insulating layer by photolithography technology, radio frequency sputtering technology and stripping process.

[0026] Among them, the size of the single crystal silicon wafer substrate is 6*4*0.5mm, the thickness of the silicon dioxide insulating layer is 300nm, the interdigital electrode has 25 pairs of interdigits, a single interdigit is 20μm wide and 1.5mm long, the gap between adjacent interdigits is 20μm, and the electrode is composed of Cr / Au with a thickness of 10nm / 100nm.

[0027] Furthermore, in addition to the interdigital electrodes, the surface of the sensor carrier is also uniformly covered with a sensitive material film composed of the ZnO nanoclusters.

[0028] The fourth aspect of the present invention provides a formaldehyde gas sensor produced by the above-mentioned preparation method.

[0029] Furthermore, the formaldehyde gas sensor also includes an illumination module, and the illumination module is used to irradiate the sensitive material covered on the surface of the sensor carrier with visible light.

[0030] A fifth aspect of the present invention provides the use of the above-mentioned ZnO nanoclusters or formaldehyde gas sensors to detect formaldehyde at room temperature.

[0031] The technical solution of the present invention has the following advantages compared with the prior art:

[0032] The method of the present invention can prepare three-dimensional, porous, defect-rich ZnO nanoclusters with a diameter of 5-10 μm, and the three-dimensional, porous, defect-rich ZnO nanoclusters are covered on the outer surface of the sensor carrier to prepare a formaldehyde gas sensor. Because the prepared three-dimensional ZnO nanoclusters have a good pore structure, they are conducive to the penetration and diffusion of formaldehyde gas, promote the full contact reaction between formaldehyde and sensitive materials, and improve the sensitivity and reaction speed of the sensor;

[0033] The formaldehyde gas sensor of the present invention also includes an illumination module. Since the prepared three-dimensional ZnO nanoclusters have abundant defects, the band structure of ZnO can be adjusted and the band gap can be reduced, so that the absorption spectrum of the prepared ZnO nanomaterial is broadened to the visible light range, thereby improving the efficiency of light energy utilization; under visible light irradiation, the prepared ZnO nanomaterial can generate more electron-hole pairs and can effectively separate the electron-hole pairs, thereby increasing the amount of adsorbed oxygen, further improving the sensitivity of the sensor, shortening the response time and recovery time, and realizing a room temperature high-sensitivity formaldehyde gas sensor;

[0034] The formaldehyde gas sensor of the present invention can be manufactured based on a planar gas sensor as a carrier. The device has a simple process and a small size, is suitable for mass production, and is applied in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 These are SEM and TEM morphology images of the ZnO nanoclusters prepared in Example 1, where (a) is the SEM morphology image and (b) is the TEM morphology image.

[0036] Figure 2 This is the XRD pattern of the ZnO nanoclusters prepared in Example 1.

[0037] Figure 3 This is the XPS graph of the ZnO nanoclusters prepared in Example 1.

[0038] Figure 4 This is the UV-vis-NIR image of the ZnO nanoclusters prepared in Example 1.

[0039] Figure 5 This is the response-recovery characteristic curve of the formaldehyde gas sensor prepared in Example 2 to 1 ppm formaldehyde under room temperature and dark conditions.

[0040] Figure 6 This is the response-recovery characteristic curve of the formaldehyde gas sensor prepared in Example 2 to 1 ppm formaldehyde under visible light conditions at room temperature.

[0041] Figure 7 Response-recovery characteristic curve of the formaldehyde gas sensor prepared in Example 2 to different concentrations of formaldehyde under visible light conditions at room temperature. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0043] Example 1 Preparation of three-dimensional, porous, defect-rich ZnO nanoclusters

[0044] a1: Sodium hydroxide and zinc acetate were weighed in a molar ratio of 1.25:1 and added to an ethanol solution (50% v / v), and then vigorously stirred at room temperature for 1 h;

[0045] a2: The product obtained by filtering the solution in step a1 is rinsed with deionized water three times and then dried in a drying oven to obtain ZnO nanoseeds;

[0046] a3: Weigh 2.0g of ε-Zn(OH) 2 , 0.3 g of the ZnO nanoseeds obtained in step a2 were added to 40 mL of deionized water and stirred evenly;

[0047] a4: The solution obtained in step a3 was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, and heated to 80°C for 5 min under microwave hydrothermal conditions;

[0048] a5: After the reactor in step a4 is cooled to room temperature, the obtained product is rinsed with deionized water for 3-5 times and then placed in a constant temperature drying oven, and dried at 60°C for 12 hours. After the temperature is cooled naturally, a ZnO powder sample is obtained.

[0049] Example 2 Preparation of formaldehyde gas sensor based on three-dimensional, porous, defect-rich ZnO nanoclusters

[0050] b1: A silicon dioxide insulating layer is grown on a single crystal silicon wafer substrate, and Cr / Au interdigital electrodes are integrated on the single crystal silicon substrate covered with the silicon dioxide insulating layer by photolithography, radio frequency sputtering and lift-off process to obtain a sensor carrier with gas sensor function; wherein, the single crystal silicon wafer substrate has a size of 6*4*0.5mm, the silicon dioxide insulating layer is 300nm thick, the interdigital electrode has 25 pairs of interdigits, a single interdigit is 20μm wide and 1.5mm long, the gap between adjacent interdigits is 20μm, and the electrode is composed of Cr / Au with a thickness of 10nm / 100nm;

[0051] b2: mixing the ZnO powder sample and anhydrous ethanol in a ratio of 3:1, and ultrasonically treating for 5 minutes to uniformly disperse the ZnO powder sample to obtain a paste-like mixed solution containing the ZnO nanoclusters;

[0052] b3: Spin coating the mixed solution obtained in b2 to evenly and completely cover the outer surface of the sensor carrier, ensuring that the mixed solution completely covers the electrode to form a sensitive material film of about 20 μm;

[0053] b4: After the sensor carrier covered with the sensitive material film is dried in a drying oven at 80°C for 12 hours, a formaldehyde gas sensor based on ZnO nanoclusters is obtained.

[0054] Comparative Example Formaldehyde gas sensor based on commercially available ZnO nanomaterials and its preparation

[0055] a1: preparing a sensor carrier having a gas sensor function in the manner of step b1 in Example 2;

[0056] a2: Mix a commercially available ZnO powder sample and anhydrous ethanol in a ratio of 3:1, and perform ultrasonic treatment for 5 minutes to uniformly disperse the sample to obtain a paste-like mixed solution containing the commercially available ZnO nanomaterial;

[0057] a3: Spin-coat the mixed solution obtained in a2 to evenly and completely cover the outer surface of the sensor carrier, ensuring that the mixed solution completely covers the electrode to form a sensitive material film of about 20 μm;

[0058] a4: Dry the sensor carrier covered with the sensitive material film in a drying oven at 80° C. for 12 hours to obtain a formaldehyde gas sensor based on commercially available ZnO nanomaterials.

[0059] Results Analysis

[0060] like Figure 1 As shown, (a) is the SEM image of the ZnO nanoclusters, and (b) is the TEM image of the ZnO nanoclusters; it can be seen that the ZnO nanorods are relatively uniform in length, loosely arranged side by side or entangled together to form ZnO nanoclusters, and have a good pore structure inside the clusters.

[0061] like Figure 2 As shown, a is the standard peak of ZnO in the spectral library, and b is the XRD peak of the ZnO nanoclusters prepared in Example 1. By comparison, all the peak positions in curve b are consistent with the standard peaks, and all the peak positions are very sharp, proving the successful synthesis of ZnO.

[0062] like Figure 3 As shown in the figure, it can be seen that the oxygen vacancy V of the ZnO nanoclusters prepared in Example 1 O and adsorbed oxygen O C The ratio is much larger than that of oxygen vacancies V in the comparative example. O and adsorbed oxygen O C ratio, proving that the prepared ZnO nanoclusters have abundant defects.

[0063] like Figure 4 As shown, the light absorption range of the comparative example is mainly concentrated in the ultraviolet light region, and the absorption in the visible light range is negligible, while the ZnO nanoclusters prepared in Example 1 have a wider light absorption range of 352nm-609nm, indicating that the absorption spectrum of the prepared porous defect-rich three-dimensional ZnO nanoclusters is successfully broadened to the visible light region.

[0064] like Figure 5 As shown, when the sensor is in a dark environment at room temperature and the formaldehyde gas concentration is 1 ppm, the control example has no obvious response characteristics to formaldehyde, while the formaldehyde gas sensor prepared in Example 2 has a response of 5.75% to formaldehyde, a response time of 85 s, and a recovery time of more than 150 s. The example device exhibits a responsive behavior to formaldehyde, indicating that the prepared three-dimensional porous defect-rich three-dimensional ZnO nanoclusters are beneficial to the penetration and diffusion of formaldehyde gas and promote the reaction of formaldehyde with sensitive materials.

[0065] like Figure 6 As shown, when the sensor is in a visible light environment at room temperature and the formaldehyde gas concentration is 1 ppm, the responses of the comparative example and the embodiment are 2.3% and 63% respectively, the response time is 66s and 32s respectively, and the recovery time is 61s and 20s respectively. The embodiment device shows a higher response, faster response and recovery speed, indicating that the prepared porous defect-rich three-dimensional ZnO nanoclusters can obtain better sensor performance under visible light excitation.

[0066] like Figure 7 As shown, under room temperature visible light irradiation environment, the response of the embodiment sensor increases with the increase of formaldehyde concentration, indicating that the embodiment sensor has good recognition ability for formaldehyde gas concentration.

[0067] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing a formaldehyde gas sensor, It is characterized in that The following steps are involved: a1: adding zinc salt and alkali into ethanol aqueous solution and stirring to react to obtain ZnO nanoseeds; a2: The ZnO nano seeds and ε-Zn(OH) 2 Dissolve in water to obtain a mixed solution; a3: Under microwave hydrothermal conditions, heating the mixed solution to 80-100° C. and reacting for 5-10 minutes to obtain ZnO nanoclusters; a4: dispersing the ZnO nanoclusters in ethanol or water to obtain a mixed solution; a5: coating the mixed solution on the electrode surface of the sensor carrier to form a sensitive material film, and drying to obtain the formaldehyde gas sensor.

2. The method for preparing the formaldehyde gas sensor according to claim 1, It is characterized in that In the step a1, the molar ratio of the base to the zinc salt is 1.25-1.5:

1.

3. The method for preparing the formaldehyde gas sensor according to claim 1, It is characterized in that In the step a2, ZnO nano seeds and ε-Zn(OH) 2 The mass ratio is 2-4:1-3.

4. The method for preparing the formaldehyde gas sensor according to claim 1, It is characterized in that The thickness of the sensitive material film is 10-30 μm.

5. The method for preparing the formaldehyde gas sensor according to claim 1, It is characterized in that The sensor carrier comprises a single crystal silicon wafer substrate, a silicon dioxide insulating layer covering the surface of the single crystal silicon wafer substrate, and interdigitated electrodes integrated on the surface of the silicon dioxide insulating layer.

6. A formaldehyde gas sensor prepared by the preparation method according to any one of claims 1 to 5.

7. The formaldehyde gas sensor according to claim 6, It is characterized in that The formaldehyde gas sensor further comprises an illumination module, and the illumination module is used for irradiating the sensitive material with visible light.

8. Use of the formaldehyde gas sensor according to claim 6 or 7 in detecting formaldehyde at room temperature.

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