Preparation method of VOCs gas sensor based on in-situ growth of CuO nanorods of sensing electrode

Abstract

The present invention belongs to the technical field of gas sensors of metal oxide materials, and discloses a preparation method of a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode, comprising the following steps: S1, selecting an electrode, wetting and drying it, and preparing a substrate; S2, annealing the substrate at 100°C for 1 minute, and preparing a substrate; S3, preparing a CuO nano seed layer; S4, immersing the CuO nano seed layer 5 cm below the growth solution, with the electrode facing up; S5, preparing a CuO nanorod array; S6, preparing a VOCs gas sensor. The present invention adopts the above-mentioned preparation method of a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode, and by directly generating copper oxide nanorods on the surface of the electrode, it can overcome the shortcomings of the existing VOCs sensor, such as complex preparation process, slow response or recovery, etc.; the VOCs sensor prepared by the present invention has the advantages of simplified preparation process, reduced production cost, and suitability for mass production.

Description

Technical Field

[0001] The invention belongs to the technical field of gas sensors made of metal oxide materials, and in particular relates to a preparation method of a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode. Background Art

[0002] Volatile organic compounds (VOCs) are important precursors of secondary organic aerosols and surface ozone in the atmosphere. x Photochemical reactions occur, producing photochemical smog with serious hazards. In addition, many VOCs components are toxic and emit irritating odors. After entering the human body through the skin and respiratory tract, they will irritate the eyes, respiratory tract and skin, causing sore throat, skin allergies and other phenomena. When VOCs in the environment reach a certain concentration, people may suffer from headaches and vomiting in a short period of time. In severe cases, they may even have convulsions and coma. Some VOCs are also carcinogenic, neurotoxic, hepatotoxic and mutagenic, which may cause more serious health problems, such as lung cancer and colon cancer. Therefore, effective and real-time monitoring of VOCs gas can not only effectively avoid the occurrence of potential safety accidents, but also provide reliable early guarantees for subsequent VOCs gas treatment.

[0003] Current gas detection methods include gas chromatography, electrochemical sensors, photoacoustic spectroscopy, non-dispersive infrared spectroscopy, selected ion flow tube mass spectrometry, MOS gas sensors, etc. These methods are currently common means of detecting low-concentration VOCs, with the characteristics of high sensitivity and low detection limit, providing strong support for the realization of complex VOCs qualitative and quantitative detection. Among them, metal oxides play an important role in many fields of physics, chemistry and materials science due to their unique structure and advantages such as low cost, short response time and long life. Metal oxide semiconductor nanomaterials have become essential materials for manufacturing functional devices due to their nanomaterial properties and semiconductor material properties. They are widely used in many fields such as catalysis, gas sensors, photodetectors, and battery energy materials.

[0004] CuO materials are widely used in gas sensing due to their good thermal stability and adjustable surface structure. They have a narrow bandgap of only 1.4 eV and have excellent chemical properties and catalytic activity. The preparation methods of CuO metal-based gas semiconductor sensors include hydrothermal method, sol-gel method, microwave-assisted hydrothermal method, chemical etching method, etc. These methods usually synthesize CuO metal semiconductor materials first, then transfer the CuO materials to the electrode surface during the preparation of gas sensors, and finally perform corresponding gas-sensitive property detection. However, in the current preparation technology, there are still deficiencies in process complexity and VOCs gas testing. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method of a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode. By directly generating copper oxide nanorods on the surface of the electrode, the shortcomings of existing VOCs sensors, such as complex preparation process and slow response or recovery, can be overcome. The VOCs sensor prepared by the present invention has the advantages of simplified preparation process, reduced production cost, and suitability for mass production.

[0006] To achieve the above object, the present invention provides a method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode, comprising the following steps:

[0007] S1. Select electrodes, wet and dry them, and prepare substrates;

[0008] S2, annealing the substrate at 100° C. for 1 minute to prepare a substrate;

[0009] S3, preparing a CuO nano seed layer;

[0010] S4, immerse the CuO nanoseed layer 5 cm below the growth solution, with the electrode facing up;

[0011] The growth solution was a solution of an equimolar mixture of 25 mM copper nitrate trihydrate and hexamethylenetetramine in deionized water;

[0012] S5, preparing CuO nanorod arrays;

[0013] S51, heating water with electricity;

[0014] S52, when the water reaches the heating growth temperature, heating in a water bath for 2-5 hours to prepare a CuO nanorod array;

[0015] S6. Prepare VOCs gas sensor.

[0016] Preferably, step S1 specifically comprises:

[0017] S11. Select a clean electrode and wet it with a 10 mM ethanol solution of copper acetate monohydrate for 10 seconds;

[0018] S12. After being wetted for 10 seconds, take out the electrode and dry it in the air to obtain a substrate.

[0019] Preferably, step S3 specifically includes annealing the substrate at 250-350° C. for 2.5 h to obtain a CuO nano seed layer.

[0020] Preferably, in step S51, the heating rate is 1-5°C / min; in step S52, the heating growth temperature is 70-85°C.

[0021] Preferably, step S6 specifically comprises:

[0022] S61, taking out the prepared CuO nanorod array from the growth solution;

[0023] S62, observing the surface color of the entire CuO nanorod array and preparing the sample;

[0024] S63. Gently rinse the sample with deionized water several times and dry it in an air flow to obtain a VOCs gas sensor.

[0025] Preferably, in step S62, if a uniform dark red-brown layer is observed on the entire surface of the CuO nanorod array, a sample is obtained.

[0026] Therefore, the present invention adopts the above-mentioned preparation method of VOCs gas sensor based on in-situ growth of CuO nanorods on sensing electrodes, and can overcome the shortcomings of existing VOCs sensors such as complex preparation process and slow response or recovery by directly generating copper oxide nanorods on the electrode surface; the VOCs sensor prepared by the present invention has the advantages of simplified preparation process, reduced production cost, and suitability for mass production.

[0027] Beneficial effects of the present invention:

[0028] (1) The VOCs gas sensor prepared by the present invention is prepared by in-situ growth of copper oxide nanorods on the sensing electrode. Compared with the preparation method of the traditional VOCs gas sensor, the VOCs gas sensor prepared by the present invention has good sensitivity, response time, recovery time and reproducibility in the same gas test;

[0029] (2) The VOCs gas sensor prepared by the present invention has good reproducibility and power law relationship in the test of ethanol, formaldehyde and xylene gases, especially has good sensitivity, response and recovery time to 50ppm ethanol and formaldehyde gases.

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The XRD spectrum of copper oxide is prepared for the embodiment of the method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode of the present invention;

[0032] Figure 2The SEM images of copper oxide prepared in the embodiment of the preparation method of the VOCs gas sensor based on the in-situ growth of CuO nanorods on the sensing electrode of the present invention; wherein (a) is a sensing electrode without gas-sensitive material deposition and a sensing electrode after gas-sensitive material deposition; (b) is a scanning electron microscope image of the surface of the gas-sensitive material layer; (c) is a scanning electron microscope image of the cross section of the gas-sensitive material layer; (d) is an energy spectrum of the gas-sensitive material layer;

[0033] Figure 3 The present invention is a method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode, and is a graph showing the relationship between the operating temperature and the test performance of the VOCs gas sensor when exposed to 50ppm ethanol and formaldehyde; wherein, (a) is a graph showing the relationship between the sensitivity of the VOCs gas sensor at 50ppm ethanol and the operating temperature; (b) is a graph showing the relationship between the response time of the VOCs gas sensor at 50ppm ethanol and the operating temperature; (c) is a graph showing the relationship between the recovery time of the VOCs gas sensor at 50ppm ethanol and the operating temperature; (d) is a graph showing the relationship between the sensitivity of the VOCs gas sensor at 50ppm formaldehyde and the operating temperature; (e) is a graph showing the relationship between the response time of the VOCs gas sensor at 50ppm formaldehyde and the operating temperature; (f) is a graph showing the relationship between the recovery time of the VOCs gas sensor at 50ppm formaldehyde and the operating temperature;

[0034] Figure 4 The present invention is a method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode, and the reproducibility test graphs of the VOCs gas sensor when exposed to ethanol, formaldehyde, and xylene; wherein (a) is a reproducibility test graph of the VOCs gas sensor for ethanol at 200°C; (b) is a reproducibility test graph of the VOCs gas sensor for formaldehyde at 200°C; (c) is a reproducibility test graph of the VOCs gas sensor for xylene at 200°C;

[0035] Figure 5 This is a diagram showing the relationship between different gas concentrations and the corresponding sensitivity of the VOCs gas sensor according to an embodiment of the method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode of the present invention;

[0036] Figure 6 This is a relationship diagram of the selectivity of the VOCs gas sensor to other gases in an embodiment of the method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0038] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0039] VOCs sensor element based on in-situ growth of CuO nanorod array on the surface of ceramic tube electrode element, such as Figure 1-Figure 2 As shown, it consists of a ceramic tube, a gold electrode, a platinum lead and a gas-sensitive material layer. The gold electrode is covered on the surface of the ceramic tube, the platinum lead is welded to the surface of the gold electrode, and the gas-sensitive material grows on the entire ceramic tube and the surface of the gold electrode.

[0040] Embodiment 1

[0041] The preparation method of a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode comprises the following steps:

[0042] S1. Select electrodes, wet and dry them, and prepare substrates.

[0043] S11. Select a clean electrode and immerse it in copper acetate monohydrate (Cu(CH 3 COO 2 ·H 2 O) in 10 mM ethanol solution for 10 seconds.

[0044] S12. After being wetted for 10 seconds, take out the electrode and dry it in the air to obtain a substrate.

[0045] S2. Annealing the substrate at 100° C. for 1 minute to enhance adhesion, thereby preparing a substrate.

[0046] S3. Prepare a CuO nano seed layer.

[0047] The substrate was annealed at 250 °C for 2.5 h to obtain a CuO nanoseed layer.

[0048] S4. Immerse the CuO nanoseed layer in an equimolar solution of 25 mM copper nitrate trihydrate (Cu(NO 3 ) 2 ·3H 2 O) and hexamethylenetetramine (HMTA, C 6 H 12 N 4 ) 5 cm below the solution of the mixture in deionized water, with the electrodes facing up.

[0049] S5. Prepare CuO nanorod arrays.

[0050] S51. Use electricity to heat water at a heating rate of 3°C / min.

[0051] S52. When the water reaches the heating growth temperature of 78°C, the CuO nanorod array is prepared by heating in a water bath for 3.5 hours.

[0052] S6. Prepare VOCs gas sensor.

[0053] S61. Take out the prepared CuO nanorod array from the growth solution.

[0054] S62. A uniform dark red-brown layer was observed on the entire surface of the CuO nanorod array, and the sample was obtained.

[0055] S63. Gently rinse the sample with deionized water several times and dry it in an air flow to obtain a VOCs gas sensor.

[0056] Embodiment 2

[0057] The preparation method of a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode comprises the following steps:

[0058] S1. Select electrodes, wet and dry them, and prepare substrates.

[0059] S11. Select a clean electrode and immerse it in copper acetate monohydrate (Cu(CH 3 COO 2 ·H 2 O) in 10 mM ethanol solution for 10 seconds.

[0060] S12. After being wetted for 10 seconds, take out the electrode and dry it in the air to obtain a substrate.

[0061] S2. Annealing the substrate at 100° C. for 1 minute to enhance adhesion, thereby obtaining a substrate.

[0062] S3. Prepare a CuO nano seed layer.

[0063] The substrate was annealed at 250 °C for 2.5 h to obtain a CuO nanoseed layer.

[0064] S4. Immerse the CuO nanoseed layer in an equimolar solution of 25 mM copper nitrate trihydrate (Cu(NO 3 ) 2 ·3H 2 O) and hexamethylenetetramine (HMTA, C 6 H 12 N 4 ) 5 cm below the solution of the mixture in deionized water, with the electrodes facing up.

[0065] S5. Prepare CuO nanorod arrays.

[0066] S51. Use electricity to heat water at a heating rate of 2°C / min.

[0067] S52. When the water reaches the heating growth temperature of 70°C, the CuO nanorod array is prepared by heating in a water bath for 5 hours.

[0068] S6. Prepare VOCs gas sensor.

[0069] S61. Take out the prepared CuO nanorod array from the growth solution.

[0070] S62. A uniform dark red-brown layer was observed on the entire surface of the CuO nanorod array, and the sample was obtained.

[0071] S63. Gently rinse the sample with deionized water several times and dry it in an air flow to obtain a VOCs gas sensor.

[0072] Embodiment 3

[0073] The preparation method of a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode comprises the following steps:

[0074] S1. Select electrodes, wet and dry them, and prepare substrates.

[0075] S11. Select a clean electrode and immerse it in copper acetate monohydrate (Cu(CH 3 COO 2 ·H 2 O) in 10 mM ethanol solution for 10 seconds.

[0076] S12. After being wetted for 10 seconds, take out the electrode and dry it in the air to obtain a substrate.

[0077] S2. Annealing the substrate at 100° C. for 1 minute to enhance adhesion, thereby obtaining a substrate.

[0078] S3. Prepare a CuO nano seed layer.

[0079] The substrate was annealed at 250 °C for 2.5 h to obtain a CuO nanoseed layer.

[0080] S4. Immerse the CuO nanoseed layer in an equimolar solution of 25 mM copper nitrate trihydrate (Cu(NO 3 ) 2 ·3H 2 O) and hexamethylenetetramine (HMTA, C 6 H 12 N 4 ) 5 cm below the solution of the mixture in deionized water, with the electrodes facing up.

[0081] S5. Prepare CuO nanorod arrays.

[0082] S51. Use electricity to heat water at a heating rate of 5°C / min.

[0083] S52. When the water reaches the heating growth temperature of 85°C, the CuO nanorod array is prepared by heating in a water bath for 2 hours.

[0084] S6. Prepare VOCs gas sensor.

[0085] S61. Take out the prepared CuO nanorod array from the growth solution.

[0086] S62. A uniform dark red-brown layer was observed on the entire surface of the CuO nanorod array, and the sample was obtained.

[0087] S63. Gently rinse the sample with deionized water several times and dry it in an air flow to obtain a VOCs gas sensor.

[0088] The corresponding gas-sensing properties of the VOCs gas sensor based on in-situ growth of copper oxide nanorods on the sensing electrode prepared in Example 1 were tested.

[0089] (a) If Figure 3 As shown, the operating temperature and performance test of the VOCs gas sensor when exposed to 50ppm ethanol and formaldehyde.

[0090] Test conclusion: Figure 3 As shown in (a), the sensitivity of the VOCs gas sensor exposed to 50 ppm ethanol increases with increasing temperature, reaches a maximum value at 175°C, and then begins to decrease. Figure 3 As shown in (b), the response time shows an overall downward trend as the temperature increases. Figure 3 As shown in (c), the recovery time first increases and then decreases with increasing temperature, reaching the maximum value at 175°C.

[0091] like Figure 3 Middle (d), Figure 3 Middle (e), Figure 3 As shown in (f), when testing 50 ppm formaldehyde, the sensor sensitivity, response time, and recovery time generally show a downward trend as the temperature increases.

[0092] (ii) Figure 4 As shown, the reproducibility test of VOCs gas sensor after exposure to ethanol, formaldehyde and xylene.

[0093] Test conclusion: The VOCs gas sensor achieved very good reproducibility in repeated test cycles of 10, 20, 50, 80, 100, 200, and 500 ppm.

[0094] (III) Figure 5 As shown, the sensitivity test of VOCs gas sensor in different gas concentrations.

[0095] Test conclusion: There is a good power law relationship between the sensor response signal and the gas concentration. The formaldehyde power law function is: y = 0.94531x 0.07932 , the power law function of ethanol is: y = 0.99397x 0.08002 , the power law function of xylene is: y = 1.01042x 0.08814 .

[0096] (IV) Figure 6 As shown, VOCs gas sensor is tested for selectivity of various gases.

[0097] Test conclusion: The response of VOCs gas sensor is 1.008-20ppm nitrogen dioxide (NO 2 ), followed by 1.03-100 ppm hydrogen (H 2 ), 1.009-1000ppm methane (CH 4 ), 1.65-100ppm ethanol (C 2 H 5 OH), 1.3-100ppm formaldehyde (CH 2 O), 1.39-100ppm xylene (C 8 H 10 ).

[0098] VOCs gas sensor for ethanol (C 2 H 5 OH), formaldehyde (CH 2 O), xylene (C 8 H 10 )The reaction is more obvious.

[0099] In summary, the VOCs sensor based on the in-situ growth of CuO nanorod array on the surface of ceramic tube electrode element was prepared, which had good gas sensing performance for ethanol, formaldehyde and xylene gases at 50-300°C.

[0100] Therefore, the present invention adopts the above-mentioned preparation method of the VOCs gas sensor based on the in-situ growth of CuO nanorods on the sensing electrode, and directly generates copper oxide nanorods on the electrode surface, which can overcome the shortcomings of the existing VOCs sensors such as complex preparation process and slow response or recovery. The VOCs sensor prepared by the present invention has the advantages of simplified preparation process, reduced production cost, and suitability for mass production.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode, characterized in that: The following steps are involved: S1. Select electrodes, wet and dry them, and prepare substrates; S11. Select a clean electrode and wet it with a 10 mM ethanol solution of copper acetate monohydrate for 10 seconds; S12, taking out the electrode after being wetted for 10 seconds, and drying it in the air to obtain a substrate; S2, annealing the substrate at 100° C. for 1 minute to prepare a substrate; S3, preparing a CuO nano seed layer; The substrate was annealed at 250-350°C for 2.5 h to obtain a CuO nanoseed layer; S4, immerse the CuO nanoseed layer 5 cm below the growth solution, with the electrode facing up; The growth solution was a solution of an equimolar mixture of 25 mM copper nitrate trihydrate and hexamethylenetetramine in deionized water; S5, preparing CuO nanorod arrays; S51, heating the water with electricity; the heating rate is 1-5°C / min; S52, when the water reaches the heating growth temperature, heating in a water bath for 2-5 hours to prepare a CuO nanorod array; the heating growth temperature is 70-85°C; S6. Prepare VOCs gas sensor.

2. The method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode according to claim 1, characterized in that: Step S6 specifically comprises: S61, taking out the prepared CuO nanorod array from the growth solution; S62, observing the surface color of the entire CuO nanorod array and preparing the sample; S63. Gently rinse the sample with deionized water several times and dry it in an air flow to obtain a VOCs gas sensor.

3. The method for preparing a VOCs gas sensor based on in-situ growth of CuO nanorods on a sensing electrode according to claim 2, characterized in that: In step S62, if a uniform dark red-brown layer is observed on the entire surface of the CuO nanorod array, a sample is obtained.

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