Gas sensor based on noble metal / NiO composite material, preparation method and application

Abstract

The present invention relates to a gas sensor based on a noble metal / NiO composite material, its preparation method, and its application. The preparation method primarily involves reducing the noble metal on the surface of NiO nanosheets with a reducing alcohol to produce the noble metal / NiO composite material, which is then coated onto a MEMS chip. The composite material utilizes the electron sensitization of the noble metal to achieve highly sensitive and specific detection of xylene. Compared to existing technologies, the present invention offers a simpler preparation method. The noble metal reducing agent used can gently reduce the noble metal to produce uniform nanoparticles. The resulting xylene MEMS gas sensor exhibits highly sensitive and specific detection of xylene and improves the long-term stability of the gas sensor, offering broader application prospects.

Description

Technical Field

[0001] The present invention relates to the field of gas detection, and in particular to a xylene MEMS gas sensor based on a noble metal / NiO composite material, and a preparation method and application thereof. Background Art

[0002] Xylene is a toxic carcinogen that may irritate the eyes and respiratory tract and damage the central nervous system. Wastewater and exhaust gases from plants producing organic synthesis, synthetic rubber, paints and dyes, synthetic fibers, petroleum processing, pharmaceuticals, and cellulose are major sources of xylene in the environment. Accidental contamination can also occur from rollovers, leaks, and fires during transportation and storage. Therefore, xylene detection is particularly important.

[0003] Several papers have reported on MEMS gas sensors for xylene, primarily examining the effects of different sensitive materials on gas-sensing performance, such as operating temperature, sensitivity, response / recovery time, and minimum detection limit. Numerous studies have shown that factors such as morphology, crystal surface, and noble metal modification have significant influences on gas-sensing performance. Among these, noble metal modification is an effective means of improving sensitivity. Sodium borohydride and ascorbic acid are commonly used noble metal reducing agents, but their reactions are intense, often producing large metal particles that are ineffective in improving the sensor's gas-sensing performance. Small molecule alcohols, on the other hand, exhibit weak reducing properties and can gently reduce noble metals.

[0004] Therefore, small molecule alcohols can be used for further research in order to prepare a xylene MEMS gas sensor with strong gas sensitivity. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a xylene MEMS gas sensor based on precious metal / NiO composite material and its preparation method and application.

[0006] The present invention adopts a chemical reduction method to uniformly reduce precious metals on the surface of nickel oxide sheets to prepare precious metal / NiO sensitive materials. That is, precious metals are reduced on the surface of NiO sheets by small molecule alcohols to prepare precious metal / NiO composite materials, which are then combined with MEMS devices to prepare MEMS gas sensors suitable for xylene detection.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] One of the technical solutions of the present invention is to provide a method for preparing a gas sensor based on a noble metal / NiO composite material, comprising the following steps:

[0009] S1. Dissolve nickel nitrate, ammonium fluoride, and urea in deionized water and mix them by ultrasonication to obtain a green transparent solution;

[0010] S2, subjecting the green transparent solution obtained in step S1 to a high-temperature and high-pressure reaction, cooling the solution to room temperature after the reaction, and subjecting the solution to centrifugation, grinding, and high-temperature calcination to obtain gray-black NiO nanosheets;

[0011] S3, mixing the NiO nanosheets obtained in step S2 with a noble metal aqueous solution and an alcohol / water solution, and adjusting the pH to obtain a gray-black solution;

[0012] S4, stirring, centrifuging, drying, grinding, and high-temperature calcining the gray-black solution obtained in step S3 again to obtain noble metal-modified NiO nanosheets;

[0013] S5. The noble metal-modified NiO nanosheets obtained in step S4 are mixed and dispersed evenly with ethanol to obtain a dispersion liquid, and the dispersion liquid droplets are applied on a MEMS chip and air-dried to obtain a MEMS gas sensor coated with the noble metal-modified NiO composite material, that is, a gas sensor based on the noble metal / NiO composite material.

[0014] Furthermore, in step S1, the ratio of nickel nitrate, ammonium fluoride, urea, and deionized water is (5-7) mmol: (1-4) mmol: 9 mmol: 40 ml, and the ultrasonication time is at least 1 h.

[0015] Furthermore, in step S2, the conditions for the high temperature and high pressure reaction are: temperature of 110-140° C., time of 6 h, and pressure of 1-200 MPa.

[0016] Furthermore, in step S2, the temperature of high-temperature calcination is 400° C., the heating rate of high-temperature calcination is 1° C. / min, and the time of high-temperature calcination is 2 h.

[0017] Furthermore, in step S3, the noble metal aqueous solution is an aqueous solution containing noble metal, wherein the noble metal is selected from any one of Pt, Au or Pd, and the ratio of noble metal to deionized water is 0.1 mmol:10 mL; the alcohol / water solution is prepared by mixing alcohol and deionized water in a volume ratio of 1:3, wherein the alcohol is a reducing agent alcohol.

[0018] Furthermore, in step S3, the ratio of NiO nanosheets to the noble metal aqueous solution and the alcohol / water solution is (0.7-0.75) g:10 mL:250 mL; and the pH is adjusted to 5-9.

[0019] Furthermore, in step S4, the stirring temperature is 30-50°C, the stirring rate is not higher than 400rpm / min, and the stirring time is 5-7h; the high-temperature calcination temperature is 400°C, the high-temperature calcination heating rate is 1°C / min, and the high-temperature calcination time is 2h.

[0020] Furthermore, in step S5, the ratio of noble metal modified NiO nanosheets to ethanol is 4 mg:1 mL.

[0021] The second technical solution of the present invention is to provide a gas sensor based on a noble metal / NiO composite material, based on the preparation method described in one of the above technical solutions.

[0022] The third technical solution of the present invention is to provide an application of a gas sensor based on a noble metal / NiO composite material as described in the second technical solution above, wherein the gas sensor based on a noble metal / NiO composite material is applied to high-sensitivity detection of xylene.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention can mildly reduce the noble metal on the surface of NiO nanosheets by reducing alcohol to obtain a noble metal / NiO composite material, which is then coated on a MEMS chip. The electron sensitization effect of the noble metal is utilized to achieve highly sensitive and specific detection of xylene.

[0025] (2) The preparation method of the present invention is simple. The sensitivity and selectivity of NiO material to gas response are improved by precious metal modification. It is made into a xylene MEMS gas sensor, which can increase the stability of the gas sensor under long-term working conditions and has a broader application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a high-resolution transmission image of the Pt / NiO material prepared in Example 1.

[0027] Figure 2 This is the XRD pattern of the Pt / NiO material prepared in Example 1.

[0028] Figure 3 This is the response-recovery curve of the xylene MEMS gas sensor based on the Pt / NiO composite material prepared in Example 1 to 10 ppm of xylene at an operating temperature of 250°C.

[0029] Figure 4 This is the response-recovery curve of the xylene MEMS gas sensor based on the Au / NiO composite material prepared in Example 2 to 10 ppm of xylene at an operating temperature of 250°C.

[0030] Figure 5 This is the response-recovery curve of the xylene MEMS gas sensor based on the Pd / NiO composite material prepared in Example 3 to 10 ppm of xylene at an operating temperature of 250°C. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] In the following examples and comparative examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0033] Example 1:

[0034] A MEMS gas sensor for xylene using platinum-modified nickel oxide nanosheets is prepared by reducing Pt on the surface of NiO material using a small molecule alcohol. The Pt / NiO composite material is then combined with a MEMS device to prepare a MEMS gas sensor for xylene detection, comprising the following steps:

[0035] Step 1: Dissolve 13 mmol nickel nitrate, 5 mmol ammonium fluoride, and 18 mmol urea in 80 mL deionized water to form a green, transparent solution. Sonicate the green, transparent solution for at least 1 hour.

[0036] Step 2: The ultrasonic solution was sealed in an autoclave and reacted at 110°C for 6 hours. After cooling to room temperature, the sample was centrifuged, dried at 80°C, and then ground. The sample was placed in a muffle furnace and heated at a rate of 1°C / min to 400°C in an air atmosphere and calcined for 2 hours. After cooling to room temperature, gray-black NiO nanosheets were obtained.

[0037] Step 3: Disperse 0.041 g of H2PtCl6 in 10 mL of deionized water to prepare an H2PtCl6 solution; disperse 100 mL of methanol in 300 mL of deionized water to prepare a methanol / water solution.

[0038] Step 4: Weigh 0.75 g of NiO nanosheets into a 500 mL beaker and add 10 mL of H2PtCl6 aqueous solution and 250 mL of methanol / water solution to obtain a gray-black solution. Adjust the pH of the solution to 6.0 with NaOH aqueous solution.

[0039] Step 5: The gray-black solution with adjusted pH value was magnetically stirred at 35°C and 400 rpm / min for 6 hours. After stirring, the sample was centrifuged, dried at 80°C and ground. The sample was placed in a muffle furnace and heated at a rate of 1°C / min to 400°C in an air atmosphere for 2 hours. After cooling to room temperature, a Pt-modified NiO nanosheet composite material was obtained.

[0040] Step 6: Take 20 mg of Pt-modified NiO composite material, mix it with 5 mL of ethanol, and disperse it for 5 minutes.

[0041] Step 7: Take 10 μL of the dispersed solution and drop it onto the MEMS chip. Allow it to air dry naturally. After air drying, a MEMS gas sensor based on the Pt / NiO composite material is obtained.

[0042] The prepared MEMS gas sensor based on Pt / NiO composite material was tested, and the test results are as follows:

[0043] Figure 1 This is a high-resolution transmission image of the Pt-modified NiO composite material. It can be seen from the high-resolution transmission image that the Pt particles are evenly dispersed on the NiO nanoflowers.

[0044] Figure 2 This is the XRD pattern of the Pt-modified NiO composite material. All diffraction peaks in the XRD pattern are consistent with cubic NiO (JCPDS: 71-1179). The Pt content is low and no Pt peak appears.

[0045] Figure 3 The response-recovery curve of the prepared MEMS gas sensor based on Pt / NiO composite material to 10 ppm of xylene at an operating temperature of 250°C has a response sensitivity of 1.75, and the response / recovery is within 20s (13s / 17.3s), indicating that it has excellent response characteristics.

[0046] Example 2:

[0047] A gold-modified nickel oxide composite material for xylene MEMS gas sensor is prepared by reducing Au on the surface of NiO material with a small molecule alcohol to obtain an Au / NiO composite material, which is then combined with a MEMS device to prepare a MEMS gas sensor for xylene detection, comprising the following steps:

[0048] Step 1: Dissolve 10 mmol of nickel nitrate, 6 mmol of ammonium fluoride, and 18 mmol of urea in 80 mL of deionized water to form a green, transparent solution. Sonicate the green, transparent solution for at least 1 hour.

[0049] Step 2: The ultrasonic solution was sealed in an autoclave and reacted at 130°C for 6 hours. After cooling to room temperature, the sample was centrifuged, dried at 80°C and ground. The sample was placed in a muffle furnace and heated at a rate of 1°C / min to 400°C in an air atmosphere and calcined for 2 hours. After cooling to room temperature, gray-black NiO nanosheets were obtained.

[0050] Step 3: Disperse 0.04 g of AuCl3·HCl in 10 mL of deionized water to prepare an AuCl3·HCl solution; disperse 100 mL of methanol in 300 mL of deionized water to prepare a methanol / water solution.

[0051] Step 4: Weigh 0.72 g of NiO nanosheets into a 500 mL beaker and add 10 mL of AuCl₃·HCl aqueous solution and 250 mL of methanol / water solution, respectively, to obtain a gray-black solution. Adjust the pH of the solution to 7.4 with NaOH aqueous solution.

[0052] Step 5: The gray-black solution with adjusted pH value was magnetically stirred at 45°C and 350 rpm / min for 6 hours. After stirring, the sample was centrifuged, dried at 80°C and ground. The sample was placed in a muffle furnace and heated at a rate of 1°C / min to 400°C in an air atmosphere and calcined for 2 hours. After cooling to room temperature, Au-modified NiO nanocomposite materials were obtained.

[0053] Step 6: Take 20 mg of Au-modified NiO composite material, mix it with 5 mL of ethanol, and disperse it for 5 minutes.

[0054] Step 7: Take 10 μL of the dispersed solution and drop it onto the MEMS chip. Allow it to air dry naturally. After air drying, a MEMS gas sensor based on the Au / NiO composite material is obtained.

[0055] Figure 4 The response-recovery curve of the prepared MEMS gas sensor based on Au / NiO composite material to 10 ppm of xylene at an operating temperature of 250°C is shown. The response sensitivity is 1.54, and the response / recovery is within 20 s (10.8 s / 17 s).

[0056] Example 3:

[0057] A palladium-modified nickel oxide nanosheet xylene MEMS gas sensor is prepared by reducing Pd on the surface of NiO material using a small molecule alcohol to prepare a Pd / NiO composite material, which is then combined with a MEMS device to prepare a MEMS gas sensor for xylene detection, comprising the following steps:

[0058] Step 1: Dissolve 13 mmol of nickel nitrate, 3 mmol of ammonium fluoride, and 18 mmol of urea in 80 mL of deionized water to form a green, transparent solution. Sonicate the green, transparent solution for at least 1 hour.

[0059] Step 2: The ultrasonic solution was sealed in an autoclave and reacted at 120°C for 6 hours. After cooling to room temperature, the sample was centrifuged, dried at 80°C, and then ground. The sample was placed in a muffle furnace and heated at a rate of 1°C / min to 400°C in an air atmosphere and calcined for 2 hours. After cooling to room temperature, gray-black NiO nanosheets were obtained.

[0060] Step 3: Disperse 0.03 g of Na2PdCl4 in 10 mL of deionized water to prepare a Na2PdCl4 solution; disperse 100 mL of methanol in 300 mL of deionized water to prepare a methanol-water solution.

[0061] Step 4: Weigh 0.7 g of NiO nanosheets into a 500 mL beaker and add 10 mL of Na2PdCl4 aqueous solution and 250 mL of methanol aqueous solution to obtain a gray-black solution. Adjust the pH of the solution to 8.0 with NaOH aqueous solution.

[0062] Step 5: The gray-black solution with adjusted pH value was magnetically stirred at 40°C and 300 rpm / min for 6 hours. After stirring, the sample was centrifuged, dried at 80°C and ground. The sample was placed in a muffle furnace and heated at a rate of 1°C / min to 400°C in an air atmosphere for 2 hours. After cooling to room temperature, Pd-modified NiO nanocomposite materials were obtained.

[0063] Step 6: Take 20 mg of Pd-modified NiO composite material, mix it with 5 mL of ethanol, and disperse it for 5 minutes.

[0064] Step 7: Take 10 μL of the dispersed solution and drop it onto the MEMS chip. Allow it to air dry naturally. After air drying, a MEMS gas sensor based on the Pd / NiO composite material is obtained.

[0065] Figure 5 The response-recovery curve of the prepared MEMS gas sensor based on Pd / NiO composite material to 10 ppm of xylene at an operating temperature of 250°C is shown. The response sensitivity is 1.40, and the response recovery is within 20s (11.4s / 19.1s).

[0066] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a gas sensor based on a noble metal / NiO composite material, characterized in that: The steps include: S1. Dissolve nickel nitrate, ammonium fluoride, and urea in deionized water and mix them by ultrasonication to obtain a green transparent solution; S2, subjecting the green transparent solution obtained in step S1 to a high-temperature and high-pressure reaction, cooling the solution to room temperature after the reaction, and subjecting the solution to centrifugation, grinding, and high-temperature calcination to obtain gray-black NiO nanosheets; S3, mixing the NiO nanosheets obtained in step S2 with a noble metal aqueous solution and an alcohol / water solution, and adjusting the pH to obtain a gray-black solution; S4, stirring, centrifuging, drying, grinding, and high-temperature calcining the gray-black solution obtained in step S3 again to obtain noble metal-modified NiO nanosheets; S5. The noble metal-modified NiO nanosheets obtained in step S4 are mixed and dispersed evenly with ethanol to obtain a dispersion liquid, and the dispersion liquid droplets are applied on a MEMS chip and air-dried to obtain a MEMS gas sensor coated with the noble metal-modified NiO composite material, that is, a gas sensor based on the noble metal / NiO composite material.

2. The method for preparing a gas sensor based on a noble metal / NiO composite material according to claim 1, characterized in that: In step S1, the ratio of nickel nitrate, ammonium fluoride, urea, and deionized water is (5-7) mmol: (1-4) mmol: 9 mmol: 40 ml, and the ultrasonication time is at least 1 h.

3. The method for preparing a gas sensor based on a noble metal / NiO composite material according to claim 1, characterized in that: In step S2, the high temperature and high pressure reaction conditions are: temperature of 110-140° C., time of 6 h, and pressure of 1-200 MPa.

4. The method for preparing a gas sensor based on a noble metal / NiO composite material according to claim 1, characterized in that: In step S2, the high-temperature calcination temperature is 400° C., the heating rate of the high-temperature calcination is 1° C. / min, and the high-temperature calcination time is 2 h.

5. The method for preparing a gas sensor based on a noble metal / NiO composite material according to claim 1, characterized in that: In step S3, the noble metal aqueous solution is an aqueous solution containing noble metal, wherein the noble metal is selected from any one of Pt, Au or Pd, and the ratio of noble metal to deionized water is 0.1 mmol:10 mL; the alcohol / water solution is prepared by mixing alcohol and deionized water in a volume ratio of 1:3, wherein the alcohol is a reducing agent alcohol.

6. The method for preparing a gas sensor based on a noble metal / NiO composite material according to claim 5, characterized in that: In step S3, the ratio of NiO nanosheets to noble metal aqueous solution and alcohol / water solution is (0.7-0.75) g:10 mL:250 mL; and the pH is adjusted to 5-9.

7. The method for preparing a gas sensor based on a noble metal / NiO composite material according to claim 1, characterized in that: In step S4, the stirring temperature is 30-50°C, the stirring rate is not higher than 400rpm / min, and the stirring time is 5-7h; the high-temperature calcination temperature is 400°C, the high-temperature calcination heating rate is 1°C / min, and the high-temperature calcination time is 2h.

8. The method for preparing a gas sensor based on a noble metal / NiO composite material according to claim 1, characterized in that: In step S5, the ratio of noble metal-modified NiO nanosheets to ethanol was 4 mg:1 mL.

9. A gas sensor based on a noble metal / NiO composite material, characterized in that: A method for preparing a gas sensor based on a noble metal / NiO composite material according to any one of claims 1-8.

10. An application of a gas sensor based on a noble metal / NiO composite material as claimed in claim 9, characterized in that: The gas sensor based on the noble metal / NiO composite material is applied to the high-sensitivity detection of xylene.

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