A V2C / V2O5 / NiO composite gas-sensitive material, its preparation method and application

Abstract

The application discloses a V2C / V2O5 / NiO composite gas-sensitive material and a preparation method and application thereof, and belongs to the technical field of gas sensors.The V2C MXene is partially oxidized, V2O5 nanoblocks are derived on the V2C MXene layer structure, uniform distribution of "instant noodle" structure nanometer V2O5 is obtained, NiO nanoparticles are obtained by heat treatment of Ni-MOF, the V2C / V2O5 / NiO composite gas-sensitive structure is synthesized, the methane sensor prepared from the V2C / V2O5 / NiO composite film has the advantages of reversibility, fast response / recovery speed, good selectivity and the like, the concentration detection range of the methane gas is 500ppm-4000ppm, even low-concentration methane gas can be effectively detected, the detection temperature is low, the deficiencies of slow response speed, poor sensitivity under low concentration and poor durability under high-temperature working conditions of traditional methane gas sensors are effectively solved, and the application has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor technology, specifically relating to a V2C / V2O5 / NiO composite gas-sensitive material, its preparation method, and its application. Background Technology

[0002] Methane (CH4) is a colorless and odorless gas, the simplest hydrocarbon compound, and one of the most important greenhouse gases in nature. It is ubiquitous in industrial production, natural gas extraction, landfills, and agriculture. Methane leaks not only waste resources but also exacerbate the greenhouse effect, significantly impacting global climate change. Furthermore, methane is explosive; at concentrations exceeding certain limits, it poses a threat to production safety and human life. Therefore, to effectively monitor and control methane emissions and protect human health and the environment, there is an urgent need to develop cost-effective, highly sensitive, and highly selective methane gas sensors. These sensors will be able to detect the presence of methane promptly and accurately, providing crucial technical support for leak prevention, emission reduction, and environmental monitoring.

[0003] Nickel oxide (NiO) is a metal oxide with significant semiconductor properties, typically exhibiting various crystal structures and good chemical stability. In the field of gas sensors, nickel oxide is widely used to detect a variety of harmful gases. Due to its excellent conductivity and high surface activity, nickel oxide materials demonstrate good gas-sensing performance during gas detection. However, unmodified nickel oxide requires higher temperatures to exhibit good gas-sensing characteristics, and its gas sensitivity is somewhat limited. This is mainly because at high temperatures, the conductivity of nickel oxide increases, making the interaction between gas molecules and the material surface more significant, thus improving sensor sensitivity. The low surface activity of nickel oxide leads to a reduced reaction rate between the gas and the sensor surface, affecting the sensor's response time and sensitivity. Pure nickel oxide's surface reactivity is not strong enough, limiting its effective chemical reaction with gas molecules. During gas detection, nickel oxide with low surface activity cannot provide sufficient gas-solid interface reaction, thus affecting the sensitivity of gas detection. However, high-temperature operation poses a challenge to the long-term stability and reliability of the sensor and may lead to increased energy consumption and material aging. This phenomenon makes the detection of specific gases in complex environments more difficult. Therefore, in order to improve the performance and application effect of nickel oxide in gas sensors, it is necessary to modify it to enhance sensitivity and reduce operating temperature, thereby achieving more efficient gas detection.

[0004] V₂C is a novel transition metal carbide with excellent electronic conductivity and mechanical strength, and its derivative oxide, V₂O₅, shows broad application prospects. V₂O₅ has become an important material in catalysis and energy storage due to its excellent electrocatalytic activity, good chemical stability, and high specific surface area. V₂O₅ has also attracted widespread attention in the field of gas sensors, mainly due to its excellent redox properties and electron transfer capabilities. In particular, the multivalent oxide nature of V₂O₅ allows it to react with a variety of gases, exhibiting good gas sensitivity. However, pure V₂O₅ materials often face challenges in practical applications, such as high resistance and high operating temperatures. These limiting factors may affect its performance and applicability in practical gas sensors. Therefore, performance optimization and low-temperature operation improvements for V₂O₅ to enhance its application in gas sensors are important research directions. Summary of the Invention

[0005] To address the above problems, this invention provides a V2C / V2O5 / NiO composite gas-sensitive material, its preparation method, and its applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of this invention is to provide a method for preparing a V2C / V2O5 / NiO composite gas-sensitive material, comprising the following steps:

[0008] HF, HCl, water and V2AlC were mixed and reacted. The product was washed with water until the pH value was 6-7 to obtain V2C MXene material.

[0009] Dimethylimidazole, nickel nitrate and benzotricarboxylic acid were dissolved in a solvent, stirred evenly, and then subjected to a solvothermal reaction to obtain Ni-MOF material;

[0010] The V2C MXene material and the Ni-MOF material are co-dispersed in a solvent and then the solvent is removed to obtain a preliminary composite material. The preliminary composite material is then calcined to obtain a V2C / V2O5 / NiO composite gas-sensitive material.

[0011] Preferably, the ratio of HF, HCl, water and V2AlC is 10mL:10mL:5mL:1g; the mixing reaction is carried out at a temperature of 40℃ for 48 hours.

[0012] Preferably, the molar ratio of dimethylimidazole, nickel nitrate and benzotricarboxylic acid is 1:1:1; the solvothermal reaction is carried out at a temperature of 180°C for 48 hours.

[0013] Preferably, the preliminary composite material is obtained by combining V2C MXene material and Ni-MOF material in a mass ratio of 1:2.

[0014] Preferably, the calcination temperature is 600–700°C, the holding time is 2–3 h, and the heating rate is 1–3°C / min.

[0015] The second technical solution of the present invention provides a V2C / V2O5 / NiO composite gas-sensitive material prepared according to the above-mentioned preparation method of V2C / V2O5 / NiO composite gas-sensitive material.

[0016] The third technical solution of the present invention provides an application of the above-mentioned V2C / V2O5 / NiO composite gas-sensitive material in the preparation of a methane gas sensor, wherein the gas-sensitive coating of the gas-sensitive element of the methane gas sensor is a V2C / V2O5 / NiO composite gas-sensitive material.

[0017] The sensing mechanism of the methane gas sensor provided by this invention is as follows:

[0018] First, NiO exhibits p-type semiconductor properties, with holes as the primary charge carriers. When NiO is exposed to air, oxygen molecules adsorb onto the NiO surface and trap electrons, forming chemisorbed oxygen, which leads to a hole accumulation layer on the NiO surface. Second, when NiO is exposed to methane gas, methane molecules adsorb onto the sensitive material surface, react with the chemisorbed oxygen, and release electrons back into the semiconductor, reducing the hole accumulation layer thickness and ultimately increasing the sensor resistance. Furthermore, because V₂O₅ has a lower work function than NiO, electrons flow from V₂O₅ to NiO, forming a pn heterojunction between them. A space charge region forms at the interface, creating a hole depletion layer on the NiO surface, resulting in a higher baseline resistance of the V₂O₅ / NiO composite material. When the V2C / V2O5 / NiO sensor is exposed to methane, the methane gas reacts with adsorbed oxygen, and trapped electrons return to the semiconductor to neutralize some holes. This widens the hole depletion layer, increases its potential barrier height, and leads to a significant increase in resistance. Furthermore, the multilayer V2C MXene-derived "instant noodle"-like V2C / V2O5 nanoporous structure facilitates the adsorption and diffusion of CH4 gas molecules. The attachment of NiO nanoparticles to the V2C / V2O5 surface greatly increases the surface reaction sites, promoting surface reactions and thus improving the gas-sensing performance of the composite material.

[0019] The beneficial technical effects of the present invention are as follows:

[0020] This invention synthesizes a V2C / V2O5 / NiO composite gas-sensitive structure by partially oxidizing V2C MXene to derive V2O5 nanobulbs on the V2C MXene layered structure, obtaining uniformly distributed "instant noodle" structured nano-V2O5. NiO nanoparticles are then obtained through heat treatment of Ni-MOF. The resulting methane sensor, fabricated from the V2C / V2O5 / NiO composite film, exhibits advantages such as reversibility, fast response / recovery speed, and good selectivity. It can detect methane gas concentrations in the range of 500ppm to 4000ppm, effectively detecting even low concentrations of methane gas. Furthermore, it operates at low detection temperatures, effectively addressing the shortcomings of traditional methane gas sensors, such as slow response speed, poor sensitivity at low concentrations, and poor durability under high-temperature operating conditions. This invention demonstrates promising application prospects. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation process of the V2C / V2O5 / NiO composite gas-sensitive material in Example 1 of the present invention.

[0022] Figure 2 This is a schematic diagram of the structure of the methane gas sensor in Embodiment 1 of the present invention, wherein 1-substrate, 2-interdigital electrode substrate, 3-Cr / Ni / Au alloy interdigital electrode, and 4-gas-sensitive coating.

[0023] Figure 3 The images shown are SEM images of the V2C / V2O5 / NiO composite gas-sensitive material prepared in Example 1, where (a) and (b) are SEM images at different magnifications.

[0024] Figure 4 The image shows the X-ray diffraction pattern of the V2C / V2O5 / NiO composite gas-sensitive material prepared in Example 1.

[0025] Figure 5 The response resistance diagram of the methane gas sensor prepared in Example 1 to methane gas at a working temperature of 200°C and a concentration of 500 ppm to 4000 ppm.

[0026] Figure 6 Fitting curves of the response of the methane gas sensor prepared in Example 1 and the comparative methane gas sensor to various concentrations of methane gas at an operating temperature of 200°C.

[0027] Figure 7 The graph shows the sensitivity curves of the methane gas sensor prepared in Example 1 and the comparative methane gas sensor to 4000ppm methane gas at different operating temperatures.

[0028] Figure 8The repeatability test graphs of the response resistance of the methane gas sensor prepared in Example 1 to 2000ppm and 4000ppm methane gas at an operating temperature of 200°C.

[0029] Figure 9 The graph shows the response / recovery characteristics of the methane gas sensor prepared in Example 1 to 2000 ppm methane gas at an operating temperature of 200°C.

[0030] Figure 10 The selectivity of the methane gas sensor prepared in Example 1 to different types of gases at an operating temperature of 200°C is shown in the figure. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0032] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0034] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0035] Example 1

[0036] Preparation of multilayer V2C MXene: 20 mL of HF, 20 mL of HCl and 10 mL of deionized water were added to a 250 mL polytetrafluoroethylene liner to obtain a mixed solution. 2 g of V2AlC was added to the mixed solution, and the mixture was magnetically stirred at 40 degrees for 48 h. The black precipitate was then repeatedly washed with deionized water until the pH value was between 6 and 7. Finally, it was dried in a vacuum oven at 80 degrees for 8 h.

[0037] Preparation of Ni-MOF powder: 2 mmol dimethylimidazole, 2 mmol Ni(NO3)2·6H2O, and 2 mmol tricresylcarboxylic acid were dissolved in 100 mL dimethylformamide solution and stirred continuously at room temperature for 1 h. The solution was then transferred to a 100 mL polytetrafluoroethylene liner and reacted at 180 °C for 48 h, followed by cooling to room temperature. The Ni-MOF powder was washed three times with anhydrous ethanol by centrifugation and then dried in a vacuum oven at 80 °C for 8 h.

[0038] A V2C MXene dispersion was mixed with a Ni-MOF dispersion at a mass ratio of 1:2. The mixture was stirred continuously at room temperature for 1 hour, and then dried in a vacuum oven at 80°C. The resulting powder was then placed in a tube furnace and heated to 600°C at a rate of 2°C / min, and held at that temperature for 2 hours. The resulting powder is the V2C / V2O5 / NiO composite gas-sensitive material. The preparation flow chart of the V2C / V2O5 / NiO composite gas-sensitive material is shown below. Figure 1 .

[0039] Preparation of gas-sensitive element: The V2C / V2O5 / NiO composite gas-sensitive material was ultrasonically treated for 0.5 h to fully dissolve it in deionized water to form a uniform paste. The paste was then coated onto the Cr / Ni / Au interdigitated electrode to form a gas-sensitive coating with a thickness of approximately 200 μm. The gas-sensitive element coated with the gas-sensitive coating was dried at 50 °C for 5 h and aged at 300 °C for 24 h on an aging bench.

[0040] Methane gas sensor: see structural schematic diagram. Figure 2 It consists of an alumina ceramic heating substrate 1 at the bottom, an interdigital electrode substrate 2 made of ceramic material, an interdigital electrode 3 made of Cr / Ni / Au alloy material, and a gas-sensitive coating 4 coated on the interdigital electrode 3.

[0041] The SEM image of the V2C / V2O5 / NiO composite gas-sensitive material prepared in Example 1 is shown below. Figure 3 Among them, (a) and (b) are SEM images at different magnifications.

[0042] Depend on Figure 3 It can be seen that the NiO nanoparticles are uniformly distributed, and the "instant noodle" structure of the nanoporous V2O5 is composed of blocky V2O5 with a very rough surface and obvious cracks, which greatly increases the specific surface area of ​​the nano V2O5. Furthermore, the NiO nanoparticles and porous V2O5 have good connection in the V2C / V2O5 / NiO composite gas-sensitive material.

[0043] In the V2C / V2O5 / NiO composite gas-sensitive material prepared in Example 1, the NiO nanoparticles have a diameter of 10–30 nm, and the V2O5 nanobulbs have a length of 100–300 nm, a width of 100–200 nm, and a thickness of 50–100 nm.

[0044] The X-ray diffraction pattern of the V2C / V2O5 / NiO composite gas-sensitive material prepared in Example 1 is shown in Figure 1. Figure 4 .

[0045] Figure 4 The sample exhibits all diffraction peaks belonging to V2C MXene, V2O5, and NiO, with no obvious diffraction from other crystalline phases, indicating that the prepared sample has very high purity.

[0046] Sensor performance testing method: Using air as the carrier gas, different methane gas concentrations were prepared in the test chamber using a standard methane sample gas. The sensor's repeatability, response / recovery, and selectivity were tested by switching between air and methane gas environments. The switching time interval for the sensor was 180 seconds (the same applies to other gases).

[0047] The response resistance diagram of the methane gas sensor prepared in Example 1 for 500ppm to 4000ppm methane gas at an operating temperature of 200℃ is shown below. Figure 5 .

[0048] Depend on Figure 5 It can be seen that the methane gas sensor prepared in Example 1 has a fast response and recovery time. In eight consecutive reaction cycles, it has good reversibility of response to methane gas at concentrations of 500 ppm to 4000 ppm. The resistance change shows an increasing trend with the increase of methane gas concentration.

[0049] The fitting curves of the response of the methane gas sensor prepared in Example 1 and the comparative methane gas sensor to various concentrations of methane gas at an operating temperature of 200℃ are shown in the figure. Figure 6 .

[0050] Figure 6 The results show that the V2C / V2O5 / NiO composite gas sensor exhibits sensitivities of 9.5%, 16.4%, 25.9%, 30.5%, 37.1%, 41.9%, 47.3%, and 56.8% for methane gas at concentrations of 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, and 4000 ppm, respectively, demonstrating good linearity. The influence of the V2C / V2O5 composite gas sensor and the NiO gas sensor is significantly lower than that of the V2C / V2O5 / NiO composite gas sensor.

[0051] The sensitivity curves of the methane gas sensor prepared in Example 1 and the comparative methane gas sensor for 4000 ppm methane gas at different operating temperatures are shown in the figure. Figure 7 .

[0052] Depend on Figure 7 It is known that the optimal operating temperature of the V2C / V2O5 / NiO composite gas-sensitive material is 200℃.

[0053] The methane gas sensor for comparison is a V2C / V2O5 composite gas-sensitive material and a NiO gas-sensitive material obtained by calcining multilayer V2C MXene and Ni-MOF powders in Example 1 (calcination conditions are the same as in Example 1). The methane gas sensor is prepared by referring to the preparation method of gas-sensitive element and methane gas sensor in Example 1 (the amount of gas-sensitive material coated on the gas-sensitive element is the same as in Example 1).

[0054] The repeatability test graphs of the response resistance of the methane gas sensor prepared in Example 1 to 2000 ppm and 4000 ppm methane gas at an operating temperature of 200°C are shown below. Figure 8 .

[0055] Depend on Figure 8 It can be seen that the methane gas sensor prepared in Example 1 showed no significant change in repeatability measurement for three reversible response cycles of methane gas at 2000 and 4000 ppm, indicating that the sensor has good stability and repeatability.

[0056] The response / recovery characteristics of the methane gas sensor prepared in Example 1 to 2000 ppm methane gas at an operating temperature of 200°C are shown in the graph. Figure 9 .

[0057] Depend on Figure 9 It can be seen that the response and recovery times of the methane gas sensor prepared in Example 1 to 2000 ppm methane gas are 72 s and 113 s, respectively. The response time and recovery time are defined as the time it takes for the sensor to reach 90% of its final response value during the adsorption and desorption of the detected gas.

[0058] The selectivity of the methane gas sensor prepared in Example 1 for different types of gases at an operating temperature of 200°C is shown in the figure. Figure 10 .

[0059] Depend on Figure 10 It can be seen that the methane gas sensor prepared in Example 1 has the following sensitivity order for the five detected gases: methane > ethane > hydrogen > sulfur dioxide > carbon monoxide. This indicates that under the same detection conditions, the selectivity for methane gas is the best, while the selectivity for carbon monoxide gas is the worst.

[0060] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a V2C / V2O5 / NiO composite gas-sensitive material for methane detection, characterized in that, The preparation steps of the V2C / V2O5 / NiO composite gas-sensitive material include: (1) HF, HCl, water and V2AlC are mixed and reacted. The product is washed with water until the pH value is 6~7 to obtain V2C MXene material; (2) Dimethylimidazole, nickel nitrate and tricresylbenzene were dissolved in a solvent, stirred evenly and then subjected to a solvothermal reaction to obtain Ni-MOF material; (3) Mix the V2C MXene dispersion with the Ni-MOF dispersion. Stir the mixture continuously at room temperature for 1 hour, then dry it in a vacuum oven. Place the resulting powder in a tube furnace and heat it to 600°C at a heating rate of 2°C / min and keep it at that temperature for 2 hours. The resulting powder is the V2C / V2O5 / NiO composite gas-sensitive material.

2. The preparation method of the V2C / V2O5 / NiO composite gas-sensitive material for methane detection according to claim 1, characterized in that, In step (1), the ratio of HF, HCl, water and V2AlC is 10mL:10mL:5mL:1g; the temperature of the mixing reaction is 40℃ and the time is 48h.

3. The preparation method of the V2C / V2O5 / NiO composite gas-sensitive material for methane detection according to claim 1, characterized in that, In step (2), the molar ratio of dimethylimidazole, nickel nitrate and benzoic acid is 1:1:1; the temperature of the solvothermal reaction is 180°C and the time is 48h.

4. The preparation method of the V2C / V2O5 / NiO composite gas-sensitive material for methane detection according to claim 1, characterized in that, In step (3), the mass ratio of V2C MXene in the V2C MXene dispersion to Ni-MOF in the Ni-MOF dispersion is 1:

2.

5. A V2C / V2O5 / NiO composite gas-sensitive material for methane detection prepared by the method described in any one of claims 1 to 4.

6. A methane gas sensor, characterized in that, The gas-sensitive coating of the gas-sensitive element of the methane gas sensor is the V2C / V2O5 / NiO composite gas-sensitive material for methane detection as described in claim 5.

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