Nano composite gas sensor material with ultrahigh sensitivity at room temperature and preparation method of nano composite gas sensor material

Abstract

The invention discloses a nano composite gas sensor material with ultrahigh sensitivity at room temperature and a preparation method thereof, and relates to the field of gas sensing materials. The nano composite material is composed of gold-doped copper-cobalt oxide spinel nano particles and single-layer reduced graphene oxide (rGO), a ternary heterojunction structure is formed, and the nano composite material has excellent gas detection performance. The sensitivity of the nano composite gas sensing material at room temperature is improved through a synergistic sensitization strategy of Cu-Co charge redistribution, Au sensitization and the rGO conductive bracket. Through the synergistic effect of the three components, the working dependence of a traditional metal oxide sensor at high temperature is overcome, and the sensitivity, selectivity and stability of the material are remarkably improved. The nanocomposite solves the problems of sensitivity, stability, temperature dependence and the like of a traditional metal oxide gas sensor material through a synergistic sensitization strategy, has a wide application prospect, and is suitable for environment monitoring, medical expiration analysis and manufacturing of gas sensors of wearable equipment.

Description

Technical Field

[0001] The present invention belongs to the field of gas sensing materials, and particularly relates to a nano-composite gas sensor material with ultra-high sensitivity at room temperature and a preparation method thereof. Background Art

[0002] In contemporary society, the demand for the detection of toxic and harmful gases such as NO 2 is increasing. The World Health Organization has set the annual average exposure concentration of NO 2 not to exceed 10 μg / m3 (~5 ppb). Gas sensing materials that can exhibit high sensitivity at room temperature have also attracted increasing attention. Metal oxide semiconductors are one of the most common gas sensing materials and have been widely explored due to their high sensitivity and tunable material properties. However, traditional metal oxide gas sensing materials still have bottlenecks in terms of sensitivity, stability, temperature dependence, etc. They usually operate at high temperatures (about 200 - 400 °C), resulting in high power consumption, short lifespan, and insufficient stability, which greatly limits their application scenarios. At the same time, their detection thresholds usually exceed 50 ppb, failing to meet the strict requirements for low-concentration gas monitoring.

[0003] To address the above challenges, researchers have explored various sensing enhancement strategies, including noble metal doping, heterojunction engineering, and reduced graphene oxide (rGO) integration. Although these methods provide certain performance improvements, a single enhancement strategy alone cannot simultaneously achieve an ultra-low detection limit, high selectivity, and room-temperature operation. Each individual enhancement method has its inherent limitations: noble metal doping improves electron sensitization and promotes charge transfer, but the limited density of active sites and the weak adsorption ability of gases such as NO 2 at room temperature limit its efficiency; heterojunction engineering promotes charge separation, but a single heterostructure usually lacks sufficient regulation of surface oxygen vacancies, limiting its sensing performance; graphene-based composites have high conductivity and a large surface area, but their inherently weak chemisorption of NO 2 makes it difficult to achieve ppb-level sensitivity. Therefore, a multi-stage sensitization strategy using a synergistic mechanism is crucial for achieving ultra-sensitive room-temperature gas detection. Summary of the Invention

[0004] The purpose of the present invention is to propose a nano-composite gas sensor material with ultra-high sensitivity at room temperature and a preparation method thereof. The prepared composite material can detect harmful gases such as NO 2 at room temperature.

[0005] The solution adopted by the present invention is as follows:

[0006] A nano-composite gas sensor material with ultra-high sensitivity at room temperature and a preparation method thereof, comprising the following steps:

[0007] Step A: Synthesize high-performance reduced graphene oxide rGO powder through a finely tuned green reduction method; Step B: Precisely synthesize Au-rGO / Cu through an improved one-step hydrothermal method 2 Co 1 O 4 and Au / Cu 2 Co 1 O 4 and Cu 2 Co 1 O 4 -based nanocomposites and achieve multi-level synergistic sensitization and strengthening.

[0008] Specifically, in Step A: Use a finely tuned green reduction method to reduce graphene oxide (GO) in a constant temperature water bath at 80 °C. Disperse GO (25 mg) in deionized water (20 mL) and sonicate for 1 hour at 40 °C to obtain a homogeneous GO dispersion. Subsequently, add an appropriate amount of green reducing agent (such as 200 mg of citric acid) to the GO dispersion and stir in a water bath at 80 °C for 24 hours. After cooling to room temperature, wash the dispersion 3 times with ethanol to remove impurities. Finally, dry the rGO in an oven at 70 °C overnight and collect the dried rGO powder.

[0009] The ultra-high sensitivity nano-composite gas sensor material detectable at room temperature described in Step A of its preparation method, the I 2 / I 0 Raman peak intensity ratio of rGO is 0.93 - 1.2, and Au-Cu 2 Co 1 O 4 nanoparticle clusters are uniformly anchored on its surface.

[0010] Specifically, in Step B: Disperse Cu(NO 3 ) 2 ·3H 2 O (0.16 mmol), Co(NO 3 ) 2 ·6H 2 O (0.08 mmol) and NaNO 3 (0.5 mmol) in 20 mL of deionized water and stir magnetically for 30 minutes, then sonicate at 40 °C for 1 hour to obtain a homogeneous and transparent solution. Next, sequentially add rGO powder (20 mg) and a basic substance (such as 2 mL of ammonium hydroxide), and continuously stir the mixture in a water bath at 40 °C for 3 hours. Then add a certain amount of HAuCl 4 ·3H 2O (The total molar ratios of Au to Cu and Co are 1%, 3%, 5%, 8%, and 10% respectively), and stir the mixture for 30 minutes. Transfer the mixed reagent to a hydrothermal autoclave and heat it at 180 °C for 12 hours. After natural cooling, wash the sample with ethanol and deionized water multiple times and dry it in an oven at 70 °C for 12 hours. Collect the final powder. The composite material synthesized by this one-step hydrothermal method utilizes the synergistic effect of Cu-Co charge redistribution, Au sensitization, and rGO conductive scaffold for multi-stage sensitization to obtain Au-rGO / Cu 2 Co 1 O 4 、Au / Cu 2 Co 1 O 4 、Cu 2 Co 1 O 4 nanocomposite materials.

[0011] Furthermore, the ultra-high sensitivity nanocomposite gas sensor material at room temperature described in step B of its preparation method synthesizes AGC nanocomposite materials by an improved one-step hydrothermal method, and the total molar amount of Cu and Co is 0.24 mmol.

[0012] Furthermore, for the ultra-high sensitivity nanocomposite gas sensor material at room temperature described in step B of its preparation method, the doping amount of Au is 1% to 10% of the total molar amount of Cu and Co, preferably 5%.

[0013] Furthermore, for the ultra-high sensitivity nanocomposite gas sensor material at room temperature described in step B of its preparation method, the molar ratio of Cu to Co is 1:1 to 3:1, preferably 2:1.

[0014] Furthermore, for the ultra-high sensitivity nanocomposite gas sensor material at room temperature described in step B of its preparation method, the intercepts of the lattice vectors of Cu2Co1O4 on the three main axes of the crystal are of the (311) type, with the characteristic of preferential exposure of the (311) crystal plane, and the average grain size is 8 - 40 nm.

[0015] The beneficial effects of the present invention are:

[0016] Novel heterojunction design: Construct an Au-rGO / Cu 2 Co 1 O 4 ternary heterojunction, and utilize Cu-Co charge redistribution and Au sensitization to enhance gas adsorption and charge transfer.

[0017] The gas sensor based on this material realizes the detection of ppb-level NO2 at room temperature, and the theoretical detection limit reaches 0.055 ppb.

[0018] A multi-level sensitization strategy using a synergistic mechanism breaks through the bottlenecks of traditional metal oxide gas sensors in terms of sensitivity, stability, temperature dependence, etc. through the synergistic effects of Cu-Co charge redistribution, Au sensitization, and rGO conductive scaffolds. Brief Description of the Drawings

[0019] Figure 1 FE-SEM image of the 5% Au-rGO / Cu 2 Co 1 O 4 nanocomposite material obtained in the synthesis of a super-high-sensitivity nanocomposite gas sensor material at room temperature in Example 1.

[0020] Figure 2 CuO, Cu used in the synthesis of a super-high-sensitivity nanocomposite gas sensor material at room temperature in Example 1 2 Co 1 O 4 , 5% Au-Cu 2 Co 1 O 4 , 5% Au-rGO / Cu 2 Co 1 O 4 XRD patterns.

[0021] Figure 3 Dynamic response and recovery curves of the sensor based on 5% Au-rGO / Cu 2 Co 1 O 4 obtained in the synthesis of a super-high-sensitivity nanocomposite gas sensor material at room temperature in Example 1 for 2.5 - 100 ppb NO2 at room temperature.

[0022] Figure 4 Au-rGO / Cu 2 Co 1 O 4 multi-level sensitization enhanced, Au / Cu 2 Co 1 O 4 , rGO / Cu 2 Co 1 O 4 compared with the sensors made of Cu 2 Co 1 O 4 , Co 3 O 4 , rGO, CuO materials without multi-level sensitization enhancement for 5 ppm NO 2 Performance comparison chart of responses. Detailed Implementation Modes

[0023] Example 1: A preparation method of a nano-composite gas sensor material with ultra-high sensitivity at room temperature, comprising the following steps:

[0024] Step A: Synthesize high-performance reduced graphene oxide rGO powder by a finely tuned green reduction method; Step B: Precisely synthesize Au-rGO / Cu 2 Co 1 O 4 -, Au / Cu 2 Co 1 O 4 -, Cu 2 Co 1 O 4 -based nano-composites and achieve multi-level sensitization enhancement.

[0025] Specifically, Step A is as follows: Use citric acid (CA) as a green reducing agent to reduce graphene oxide (GO) in a constant temperature water bath at 80 °C. Disperse GO (25 mg) in deionized water (20 mL) and sonicate for 1 hour at 40 °C to obtain a uniform GO dispersion. Subsequently, add citric acid (200 mg) to the GO dispersion and stir in a water bath at 80 °C for 24 hours. After cooling to room temperature, wash the dispersion 3 times with ethanol to remove impurities. Finally, dry the rGO in an oven at 70 °C overnight and collect the dried rGO powder.

[0026] Specifically, Step B is as follows: Cu(NO 3 ) 2 ·3H 2 O (0.16 mmol), Co(NO 3 ) 2 ·6H 2 O (0.08 mmol) and NaNO 3 (0.5 mmol) are dispersed in 20 ml of deionized water and magnetically stirred for 30 minutes, then sonicated at 40 °C for 1 hour to obtain a uniform and transparent solution. Next, add rGO powder (20 mg) and ammonium hydroxide (2 ml) in sequence, and continuously stir the mixture in a water bath at 40 °C for 3 hours. Then, add a certain amount of HAuCl 4 ·3H 2 O (the total molar ratio of Au to Cu and Co is 5%), and stir the mixture for 30 minutes. Transfer the mixed reagent to a hydrothermal autoclave and heat at 180 °C for 12 hours. After natural cooling, wash the sample multiple times with ethanol and deionized water, and dry in an oven at 70 °C for 12 hours, then collect the final powder.

[0027] Figure 1 and Figure 2FE-SEM images and related XRD patterns of the as-prepared nanocomposites, respectively. It can be seen from the figure that 5% Au-rGO / Cu 2 Co 1 O 4 forms a uniformly dispersed network of nanoparticle clusters with an average size of about 40 nm, which is significantly smaller than the particle size of the nanoparticle clusters observed in the original Co 3 O 4 . This reduction increases the available surface area and provides a higher density of active sites for gas adsorption.

[0028] Taking the toxic and harmful NO 2 as an example, Figure 3 shows the dynamic response and recovery curves of the composite detection material for NO 2 . It can be seen that the gas-sensitive material can detect NO at the ppb level 2 , where the response value (resistance in air / resistance in target gas - 1) for 2.5 ppb is 7.76%, and the theoretically fitted detection limit can reach 0.055 ppb.

[0029] After a series of experimental analyses, Figure 4 shows the performance comparison diagrams of the sensors made of Au-rGO / Cu 2 Co 1 O 4 , Au / Cu 2 Co 1 O 4 , rGO / Cu 2 Co 1 O 4 with enhanced multi-level synergistic sensitization and the sensors made of Cu 2 Co 1 O 4 , Co 3 O 4 , rGO, CuO and other materials for the response to 5 ppm NO2. It can be seen from the comparison that the Au-rGO / Cu 2 Co 1 O 4 material with enhanced multi-level synergistic sensitization has the best effect. Its excellent performance can be attributed to the enhanced oxygen vacancies due to the Cu-Co charge redistribution, the promotion of NO 2 chemisorption and electron transfer by Au nanoparticles, and the provision of a highly conductive scaffold by rGO.

Claims

1. Ultra-high sensitivity nanocomposite gas sensor material at room temperature, characterized by: Au nanoparticles are doped in a Cu2Co1O4 spinel structure; reduced graphene oxide rGO forms a ternary heterojunction structure with the Au-doped Cu2Co1O4. The specific preparation steps of the nanocomposite gas sensing material include: Step A: Synthesize high-performance reduced graphene oxide rGO powder through a finely controlled green reduction method; Step B: Precisely synthesize Au-rGO / Cu2Co1O4, Au / Cu2Co1O4, and Cu2Co1O4-based nanocomposites through an improved single-step hydrothermal method and achieve multi-level synergistic sensitization enhancement.

2. The ultra-high sensitivity nanocomposite gas sensor material at room temperature according to claim 1, characterized in that: Step A in the preparation method is specifically as follows: using a finely controlled green reduction method to reduce graphene oxide (GO) in a constant temperature water bath to obtain high-performance reduced graphene oxide (rGO) powder; first, dispersing GO in deionized water and ultrasonically treating it at a constant temperature for several hours to obtain a uniform GO dispersion; then, adding a green reducing agent to the GO dispersion and stirring it in a constant temperature water bath for several hours; after cooling to room temperature, washing the dispersion with ethanol to remove impurities; finally, drying the rGO in an oven overnight and collecting the dried rGO powder.

3. The ultra-high sensitivity nanocomposite gas sensor material at room temperature according to claim 1, characterized in that: Step B in the preparation method is specifically as follows: by an improved single-step hydrothermal method, Au-doped reduced graphene oxide (rGO) / copper cobalt oxide (Cu2Co1O4), Au-doped copper cobalt oxide (Cu2Co1O4), and copper cobalt oxide (Cu2Co1O4) nanocomposites are precisely synthesized, and multi-stage synergistic sensitization enhancement is achieved during the synthesis process; appropriate amounts of Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and NaNO3 are dispersed in deionized water and magnetically stirred for a suitable number of minutes, and then ultrasonically treated at a constant temperature for several hours to obtain a uniform, transparent solution; next, rGO powder and alkaline substances are added in sequence, and continuously stirring the mixture in a constant temperature water bath for several hours; then, adding a certain amount of HAuCl4·3H2O according to the total molar ratio of Au to Cu and Co, and stirring the mixture; transferring the mixed reagent to a hydrothermal autoclave and heating it at a constant temperature for several hours; after natural cooling, washing the sample with ethanol and deionized water for multiple times, drying it in an oven for several hours, and collecting the final powder; and obtaining the composite material synthesized by the single-step hydrothermal method through multi-stage sensitization by utilizing the synergistic effect of Cu-Co charge redistribution, Au sensitization and rGO conductive support to obtain Au-rGO / Cu2Co1O4, Au / Cu2Co1O4, and Cu2Co1O4 nanocomposites.

4. The ultra-high sensitivity nanocomposite gas sensor material at room temperature according to claim 2, characterized in that: The I2 / I0 Raman peak intensity ratio of the rGO is 0.93-1.2, and Au-Cu2Co1O4 nanoparticle clusters are uniformly anchored on its surface.

5. The ultra-high sensitivity nanocomposite gas sensor material at room temperature according to claim 3, characterized in that: The doping amount of Au is 1% to 10% of the total molar amount of Cu and Co.

6. The ultra-high sensitivity nanocomposite gas sensor material at room temperature according to claim 3, characterized in that: The molar ratio of Cu to Co is 1:1 to 3:

1.

7. The ultra-high sensitivity nanocomposite gas sensor material at room temperature according to claim 3, characterized in that: The lattice vectors of the Cu2Co1O4 spinel structure are of intercept (311) type on the three main axes of the crystal, and have the characteristic of preferential exposure of the (311) crystal plane, and the average grain size is 8-40nm.

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