Gas sensor based on confinement type CeO2 nanoparticle film as well as preparation method and application of gas sensor

Abstract

The invention discloses a gas sensor based on a confinement type CeO2 nanoparticle film as well as a preparation method and application of the gas sensor. The gas sensor of the confinement type CeO2 nanoparticle film comprises a substrate, a confinement type CeO2 / carbon film layer is arranged on the surface of the substrate, the particle size of the confinement type CeO2 is 5-20 nm, and the confinement type CeO2 grows in an amorphous carbon matrix in a confinement mode and has high dispersity. The preparation method of the nano-particle film is simple and rapid, the whole preparation process only needs tens of minutes, namely, the CeO2 / carbon film is obtained by adopting a pulse laser deposition technology, and then the confinement type CeO2 nano-particle film is obtained by combining rapid annealing treatment. The confinement type CeO2 nano-particle film grows on the surface of a commercial flat plate type Al2O3 gas sensitive substrate in situ and can be directly used as a sensitive layer of a resistance type semiconductor gas sensor. The sensor can effectively detect a volatile organic compound (VOC) triethylamine, and shows remarkable response, excellent stability and selectivity.

Description

Technical Field

[0001] The present invention relates to the field of preparation and application of nanoparticle film gas sensors, and in particular to a gas sensor based on confined CeO2 nanoparticle film and a preparation method and application thereof. Background Art

[0002] Resistive gas sensors based on semiconductor metal oxides can effectively detect and monitor environmental gases and have received widespread attention in recent years. According to the device structure, resistive semiconductor gas sensors are mainly divided into three types: sintered type, thick film type and thin film type. Among them, thin film devices have great application potential due to their unique advantages, such as less gas-sensitive material usage and better device reliability and consistency compared with thick film and sintered devices. In addition, thin film gas sensors are easier to combine with micro / nano processing technology, which contributes to the miniaturization and low energy consumption of the device. However, due to the higher manufacturing process requirements of thin film devices, they are currently relatively less studied compared with sintered and thick film devices.

[0003] Regardless of the type of device, gas-sensitive materials are a key factor affecting the performance of gas sensors. Among various semiconductor gas-sensitive materials, rare earth metal oxides (such as CeO2, La2O3) have become a very important class of semiconductor gas-sensitive materials due to their strong ability to absorb / release oxygen and variable valence states. In particular, the specific 4f electronic structure and multiple electronic transition modes of rare earth elements give their surfaces efficient catalytic effects, making their gas-sensitive properties different from those of traditional metal oxide gas-sensitive materials. In previous studies, due to its excellent catalytic properties, CeO2 is often used as a co-catalyst to improve the gas-sensitive properties of traditional metal oxide semiconductors (including SnO2, ZnO). However, due to its poor gas-sensitive properties, there are relatively few reports on pure phase CeO2 as a gas-sensitive material.

[0004] In order to improve the gas sensing performance, designing gas sensing materials into nanostructures (including nanoparticles, nanowires, nanosheets, etc.) is an important strategy. However, for sintered and thick film devices, nanostructured gas sensing materials in powder form need to be dispersed to obtain a slurry, and then the final device is obtained through droplet coating, molding and calcination. In these processes, the agglomeration, growth and structural damage of the nanostructure are almost inevitable, which makes it difficult to maintain the high specific surface area and high activity of the nanostructure. In the process of gas detection, common metal oxide gas sensing materials usually require higher operating temperatures (generally above 200°C), and the above phenomenon is particularly obvious. How to maintain the high specific surface area and high activity of nanostructured gas sensing materials during device manufacturing and gas detection is an urgent problem to be solved. Summary of the invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a gas sensor based on a confined CeO2 nanoparticle film and a preparation method and application thereof.

[0006] A first aspect of the present invention provides a gas sensor based on a confined CeO2 nanoparticle film, comprising a substrate, and a confined CeO2 / carbon film layer on the surface of the substrate.

[0007] Preferably, the particle size of the confined CeO2 in the confined CeO2 / carbon film layer is 5 to 20 nm, and the confined CeO2 is grown in an amorphous carbon matrix.

[0008] Preferably, the substrate is an Al2O3 substrate having precious metal Pt interdigital electrodes.

[0009] The second aspect of the present invention provides a method for preparing a gas sensor based on a confined CeO2 nanoparticle film, comprising the following steps:

[0010] CeO2 and carbon are deposited on a substrate using pulsed laser deposition technology to obtain a CeO2 / carbon film;

[0011] Then the prepared CeO2 / carbon film is subjected to rapid annealing treatment to obtain a gas sensor of confined CeO2 nanoparticle film.

[0012] Preferably, the pulse laser deposition technology is specifically as follows: CeO2 target and carbon target surface are bonded with silver glue to form a composite target material, and the composite target material is ablated with laser under vacuum conditions.

[0013] Preferably, the rapid annealing treatment is performed at 500-700° C. under the protection of an inert gas.

[0014] Preferably, the vacuum degree of the vacuum condition is 1 to 5×10 -8 Torr, the wavelength of the laser is 248 nm, and the ablation time is 3 to 8 minutes.

[0015] Preferably, the inert gas is Ar gas.

[0016] Preferably, the annealing time is 3 to 8 minutes.

[0017] The third aspect of the present invention provides a gas sensor based on a confined CeO2 nanoparticle film that can be used for the detection of volatile organic compound (VOC) triethylamine. The present invention has at least one of the following beneficial effects:

[0018] 1. In the confined CeO2 nanoparticle thin film gas sensor of the present invention, the dispersion and fixation of CeO2 nanoparticles are achieved by in-situ confinement in the carbon matrix, thereby making full use of its high surface activity. In addition, the carbon matrix can serve as a transmission path for target gas molecules and electrons, achieving efficient gas-solid reaction and effective gas-sensitive signal collection.

[0019] 2. The preparation process of the confined CeO2 nanoparticle film gas sensor of the present invention is simple and fast, and the entire preparation process only takes tens of minutes. The confined CeO2 nanoparticle film is in-situ grown on the surface of the commercial alumina flat gas-sensitive substrate and can be directly used as the sensing layer of the gas sensor, thereby effectively avoiding the processes of droplet coating, molding and calcination in the preparation of traditional sintering and thick film devices, ensuring the stability and consistency of the sensor.

[0020] 3. The confined CeO2 nanoparticle thin film gas sensor of the present invention is applied to detect triethylamine gas and exhibits excellent gas-sensitive response. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a low-resolution TEM image of the confined CeO2 nanoparticle film, a high-resolution TEM image of a single CeO2 nanoparticle, and the preparation process of the confined CeO2 nanoparticle film in the present invention.

[0022] Figure 2 These are the Raman spectrum, Ce 3d high-resolution XPS spectrum and O1s high-resolution XPS spectrum of the confined CeO2 nanoparticle film in the present invention.

[0023] Figure 3 The gas-sensitive response of the confined CeO2 nanoparticle film of the present invention to a fixed concentration of triethylamine (100 ppm) at different operating temperatures (100-450°C).

[0024] Figure 4 The present invention is a dynamic triethylamine sensing performance and real-time triethylamine sensing cycle test of the confined CeO2 nanoparticle film at 400°C and 450°C.

[0025] Figure 5 It is the typical dynamic response / recovery transient of the confined CeO2 nanoparticle film in the present invention to 100ppm triethylamine, the gas sensitive response to different gases with a concentration of 100ppm, and the relationship between the logarithmic response value and the triethylamine concentration at 400℃ and 450℃.

[0026] Figure 6 The dynamic sensing performance of the confined CeO2 nanoparticle film of the present invention to low concentration triethylamine at 400°C and 450°C.

[0027] Figure 7 The sensing performance of the confined CeO2 nanoparticle film of the present invention to 100 ppm triethylamine 90 days after preparation.

[0028] Figure 8 Schematic diagram of the gas-sensing mechanism of the confined CeO2 nanoparticle film in the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention and its beneficial effects will be described in detail below in conjunction with the accompanying drawings and specific embodiments, aiming to help readers better understand the essence of the present invention, but shall not constitute any limitation on the implementation and protection scope of the present invention.

[0030] The gas sensor based on confined CeO2 nanoparticle film provided by the present invention may include a substrate and a confined CeO2 / carbon film layer attached to the substrate in the form of a film; the size of the confined CeO2 nanoparticles is about 5 to 20 nm, and they are confined and grown in an amorphous carbon matrix; the confined CeO2 nanoparticles are highly dispersible.

[0031] Preferably, the substrate is an Al2O3 substrate having precious metal Pt interdigital electrodes.

[0032] The method for preparing a gas sensor based on a confined CeO2 nanoparticle film provided by the present invention comprises the following steps:

[0033] Step (1), providing a clean substrate: before growth, a commercial flat Al2O3 gas-sensitive substrate (produced by Huachuang Ruike Technology Co., Ltd.) was repeatedly washed in deionized water and anhydrous ethanol and then dried at 60°C for 12 hours to obtain a clean surface for deposition;

[0034] Step (2) is to obtain CeO2 / carbon film by pulse laser deposition technology: firstly, a target material is prepared, the target material is composed of a carbon target with a radius of 5 to 20 mm and a CeO2 target with a length of 5 to 15 mm; the CeO2 target and the carbon target surface are bonded with silver glue to form a composite target material of the two materials; then a commercial flat Al2O3 gas-sensitive substrate is used as a deposition substrate, and the target material is deposited in an ultra-high vacuum (1 to 5×10 - 8 The CeO2 / carbon film was obtained by ablating the target material with a 10 Hz laser (248 nm) for 3 to 8 minutes in a 300-1500 Hz (100-2000 MHz) 240-1200 MHz (40-500 MHz) argon atmosphere; during the deposition process, the target material rotated around the central axis at a constant speed;

[0035] Step (3), after deposition, a rapid annealing treatment is used to prepare a confined CeO2 nanoparticle film gas sensor: under the protection of 100sccm Ar gas flow, the deposited sample is rapidly annealed at 500-700°C for 3-8 minutes to obtain a gas sensor based on a confined CeO2 nanoparticle film; the Al2O3 substrate with the sensing layer is mounted on a commercial static gas sensing test device, and the gas sensing performance is tested after aging at a temperature of 20°C-100°C for 24 hours.

[0036] The gas sensor based on the confined CeO2 nanoparticle film provided by the present invention can realize efficient detection of triethylamine gas.

[0037] The present invention is further described in detail below with specific examples, but the present invention is not limited to the following specific examples.

[0038] Several typical embodiments are described below.

[0039] Embodiment 1:

[0040] Before growth, the commercial flat Al2O3 gas-sensitive substrate was first washed repeatedly in deionized water and anhydrous ethanol and then dried to obtain a clean surface for deposition. The target material was made, which consisted of a carbon target with a radius of 20 mm and a CeO2 target with a length of 15 mm. The CeO2 target was bonded to the carbon target surface with silver glue to form a composite target of the two materials. Then, the commercial flat Al2O3 gas-sensitive substrate was used as the deposition substrate and the deposition was carried out in an ultra-high vacuum (5×10 -8 The target was ablated with a 10 Hz laser (248 nm) for 5 minutes at 4000 rpm and 10000 rpm. During the deposition process, the target rotated at a constant speed around the central axis. After deposition, the deposited sample was rapidly annealed at 600° C. for 5 minutes under the protection of 100 sccm Ar gas flow, and a gas sensor based on a confined CeO2 nanoparticle film was obtained. The gas sensor obtained in this embodiment is marked as CeO2-1.

[0041] Embodiment 2:

[0042] Before growth, the commercial flat Al2O3 gas-sensitive substrate was first washed repeatedly in deionized water and anhydrous ethanol and then dried to obtain a clean surface for deposition. The target material was made, which consisted of a carbon target with a radius of 20 mm and a CeO2 target with a length of 15 mm. The CeO2 target was bonded to the carbon target surface with silver glue to form a composite target of the two materials. Then, the commercial flat Al2O3 gas-sensitive substrate was used as the deposition substrate and the deposition was carried out in an ultra-high vacuum (5×10 -8The target was ablated with a 10 Hz laser (248 nm) for 3 minutes at 4000 rpm and 10000 rpm. During the deposition process, the target rotated at a constant speed around the central axis. After deposition, the deposited sample was rapidly annealed at 600° C. for 6 minutes under the protection of 100 sccm Ar gas flow, and a gas sensor based on a confined CeO2 nanoparticle film was obtained. The gas sensor obtained in this embodiment is marked as CeO2-2.

[0043] Embodiment 3:

[0044] Before growth, the commercial flat Al2O3 gas-sensitive substrate was first washed repeatedly in deionized water and anhydrous ethanol and then dried to obtain a clean surface for deposition. The target material was made, which consisted of a carbon target with a radius of 20 mm and a CeO2 target with a length of 15 mm. The CeO2 target was bonded to the carbon target surface with silver glue to form a composite target of the two materials. Then, the commercial flat Al2O3 gas-sensitive substrate was used as the deposition substrate and the deposition was carried out in an ultra-high vacuum (5×10 -8 Torr) with a 10 Hz laser (248 nm) to ablate the target for 7 minutes. During the deposition process, the target rotates around the central axis at a constant speed. After deposition, the deposited sample is rapidly annealed at 600°C for 8 minutes under the protection of 100 sc cm Ar gas flow, and a gas sensor based on a confined CeO2 nanoparticle film is obtained. The gas sensor obtained in this embodiment is marked as CeO2-3.

[0045] The size of the confined CeO2 nanoparticles prepared in Examples 1 to 3 is about 5 to 20 nm, and they are confined and grown in an amorphous carbon matrix; the nanoparticles are highly dispersible; and the amorphous carbon matrix is ​​attached to a commercial flat Al2O3 gas-sensitive substrate.

[0046] The steps of performing gas sensitivity testing on the gas sensors prepared in Examples 1-3 are as follows:

[0047] The sensor was mounted on a commercial static gas sensing test device and aged at 20°C-100°C for 24 hours before gas sensing performance testing. The gas sensing performance was tested using a commercial static test device (produced by Huachuang Ruike Technology Co., Ltd.). During the test, the target gas was injected into the test chamber, which was then raised to introduce ambient air. The sensor temperature can be adjusted by an external temperature control system connected to a computer. The gas sensing response is defined as the ratio of the resistance in air and the target gas (R a / R g or R g / R a ), the response time and recovery time of the sensor are defined as the time required for its resistance to reach 90% of the equilibrium resistance when exposed to the target gas and removed from the target gas, respectively.

[0048] The specific results of characterization and performance testing of the sensors prepared in Examples 1-3 are as follows:

[0049] Figure 1 a shows that a large number of uniformly sized CeO2 nanoparticles are confined and grown in the carbon matrix. The average size of the nanoparticles is about 10nm. High-resolution TEM images show that the nanoparticles show clear lattice fringes ( Figure 1 b), which is consistent with the (220) crystal plane of fluorite structure CeO2, indicating that the nanoparticles have good crystallinity. The preparation process of confined CeO2 nanoparticle film is as follows Figure 1 c. First, a CeO2 / carbon film was in situ deposited on a commercial Al2O3 flat plate using pulsed laser deposition technology. Then, the in situ confined growth of CeO2 nanoparticles in the carbon matrix was achieved by rapid annealing. During the rapid annealing process, the phase separation process between CeO2 nanoparticles and the carbon matrix led to the formation of a confined CeO2 nanoparticle film.

[0050] Figure 2 The Raman spectrum, high-resolution Ce 3d XPS spectrum and O1s XPS spectrum of confined CeO2 nanoparticle film are shown in Figure 2. Figure 2 a) shows that at 459cm -1 There is a typical Raman peak at , which corresponds to the symmetric stretching vibration of Ce-O-Ce and belongs to the triple degenerate F of cubic fluorite structure CeO2. 2g The results further confirmed the crystalline phase and good crystallinity of the samples. Figure 2 b shows the high-resolution XPS spectrum of Ce 3d, which mainly contains four pairs of spin-orbit doublets. The peaks at 902.82 eV and 884.57 eV represent Ce 3+ , while the other three double peaks, 900.99eV and 882.48eV, 907.49eV and 889.1eV, 916.8eV and 898.47eV, are Ce 4+ The above results show that the CeO2 nanoparticles 3+ and Ce 4+ coexistence, which is reported to be important for improving gas sensing activity. The high-resolution XPS spectrum of O 1s is shown in Figure 2 c. The peaks of 529.57 eV and 531.47 eV correspond to lattice oxygen and chemically adsorbed oxygen, respectively. According to the classical oxygen adsorption mechanism of resistive gas sensors, chemically adsorbed oxygen is considered to be the key active species in the gas-sensing reaction. The confined CeO2 nanoparticle film contains a rich chemically adsorbed oxygen component (about 31.2%), which means that it is expected to exhibit good gas-sensing performance.

[0051] Figure 3 The results show that the gas-sensitive response of confined CeO2 nanoparticle film to a fixed concentration of triethylamine (100 ppm) at different operating temperatures (100-450°C) is almost non-existent at low operating temperatures (below 200°C). As the operating temperature increases, its gas-sensitive response to triethylamine gradually increases.

[0052] Figure 4 a and Figure 4 b shows the dynamic gas-sensitive response of confined CeO2 nanoparticle film to different concentrations of triethylamine gas at working temperatures of 400℃ and 450℃, respectively. The results show that as the concentration of triethylamine gas increases, its gas-sensitive response also increases. Figure 4 c and Figure 4 d shows the cyclic response / recovery curves of the confined CeO2 nanoparticle film to 100 ppm triethylamine gas at working temperatures of 400°C and 450°C, respectively. The results show that it has good repeatability over multiple cycles.

[0053] Figure 5 a is a typical dynamic response / recovery curve of the confined CeO2 nanoparticle film to 100ppm triethylamine. The results show that the response time is ~2s and the recovery time is ~186s, indicating that the sensor has fast response and recovery characteristics. In addition, the sensing performance of the confined CeO2 nanoparticle film to ten other typical VOC gases was tested under the same conditions ( Figure 5 b). The results showed that it had almost no gas-sensitive response to other VOC gases such as methanol, ethanol and ethyl acetate, indicating that it has good selectivity for triethylamine. This is very important in practical applications because it can avoid interference from other gases. Considering that the concentration of triethylamine in the environment may be very low, the detection performance of the sensor for low-concentration triethylamine is crucial. According to the National Institute for Occupational Safety and Health, the acceptable exposure limit of triethylamine in factories is 10ppm. In this study, a similar linear relationship was observed between the triethylamine concentration and the logarithm of the response value ( Figure 5 c and Figure 5 d). According to the formula LOD = Kσ / S (where LOD stands for limit of detection, K is a constant usually set to 3, σ is the standard deviation of the measured value, and S is the slope), it can be determined that the LOD of the confined CeO2 nanoparticle film for detecting triethylamine at working temperatures of 400°C and 450°C is 0.5819 and 0.4036 ppm, respectively. This value is significantly lower than the allowable exposure concentration of triethylamine, indicating that it is suitable for detecting low concentrations of triethylamine.

[0054] Figure 6The dynamic gas-sensing response of the confined CeO2 nanoparticle film to low concentration (1-5ppm) triethylamine gas is shown. It can be seen that with the increase of triethylamine concentration, its response value gradually increases.

[0055] Figure 7 The sensing performance of the confined CeO2 nanoparticle film of the present invention to 100ppm triethylamine 90 days after preparation. It was found that after being placed naturally for 90 days, the gas sensing performance of triethylamine showed no signs of attenuation, indicating that it has excellent long-term stability.

[0056] Figure 8 A schematic diagram of the gas-sensing mechanism of the confined CeO2 nanoparticle film is shown. In the triethylamine sensing process of the confined CeO2 nanoparticle film sensor, electrons are the main charge carriers due to the n-type semiconductor characteristics of CeO2. When exposed to air, oxygen molecules adsorbed on the surface of CeO2 will absorb electrons from the semiconductor conduction band to form surface-adsorbed oxygen, while the material loses electrons and forms an electron depletion layer on the surface, resulting in a decrease in charge carrier concentration and an increase in sensor resistance. When triethylamine gas is introduced, the surface-adsorbed oxygen absorbs electrons from the reduced triethylamine gas molecules, increasing the number of electrons in the conduction band of the CeO2 nanoparticle film, thereby reducing the resistance. The change in resistance leads to the generation of the sensor signal. In addition, Ce in the rare earth metal oxide semiconductor CeO2 3+ and Ce 4+ The mutual electronic transitions between them can store oxygen and significantly enhance its ability to adsorb / release oxygen, thus enabling the effective detection of triethylamine.

[0057] The embodiments described above are merely descriptions of preferred implementation modes of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A gas sensor based on confined CeO2 nanoparticle film, characterized in that: The invention comprises a substrate, and a limited domain CeO2 / carbon film layer is formed on the surface of the substrate.

2. A gas sensor based on confined CeO2 nanoparticle film according to claim 1, characterized in that: The particle size of the confined CeO2 in the confined CeO2 / carbon film layer is 5-20 nm, and the confined CeO2 is grown in an amorphous carbon matrix.

3. A gas sensor based on confined CeO2 nanoparticle film according to claim 1, characterized in that: The substrate is an Al2O3 substrate with precious metal Pt interdigital electrodes.

4. A method for preparing a gas sensor based on a confined CeO2 nanoparticle film according to claims 1 to 3, characterized in that: The following steps are involved: CeO2 and carbon are deposited on a substrate using pulsed laser deposition technology to obtain a CeO2 / carbon film; Then the prepared CeO2 / carbon film is subjected to rapid annealing treatment to obtain a gas sensor of confined CeO2 nanoparticle film.

5. The method according to claim 4, characterized in that The pulsed laser deposition technology is specifically: The CeO2 target and the carbon target surface are bonded by silver glue to form a composite target material, and the composite target material is ablated by laser under vacuum conditions.

6. The method according to claim 5, characterized in that The rapid annealing treatment is performed at 500-700° C. under the protection of an inert gas.

7. The method according to claim 5, characterized in that The vacuum degree of the vacuum condition is 1 to 5×10 -8 Torr, the wavelength of the laser is 248 nm, and the ablation time is 3 to 8 minutes.

8. The method according to claim 6, characterized in that The inert gas is Ar gas.

9. The method according to claim 8, characterized in that The annealing time is 3 to 8 minutes.

10. The use of a gas sensor based on a confined CeO2 nanoparticle film according to any one of claims 1 to 3, characterized in that: The gas sensor based on the confined CeO2 nanoparticle film can be used for the detection of volatile organic compound (VOC) triethylamine.

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