A gas sensor based on a confined CeO2 nanoparticle thin film, its preparation method and application

Abstract

The present invention discloses a gas sensor based on a confined CeO2 nanoparticle thin film, its preparation method and application. The gas sensor based on the confined CeO2 nanoparticle thin film includes a substrate, and a confined CeO2 / carbon thin film layer is on the surface of the substrate. The particle size of the confined CeO2 is 5-20 nm, and it is confined and grown in an amorphous carbon matrix, having a high degree of dispersion. The preparation method of the nanoparticle thin film is simple and rapid, and the whole preparation process only takes dozens of minutes. That is, first, a CeO2 / carbon thin film is obtained by pulsed laser deposition technology, and then a confined CeO2 nanoparticle thin film is obtained by combining rapid annealing treatment. The confined CeO2 nanoparticle thin film is in-situ grown on the surface of a commercial flat Al2O3 gas-sensitive substrate and can directly be used as the sensitive layer of a resistive semiconductor gas sensor. The sensor can effectively detect the volatile organic compound (VOC) triethylamine and exhibits remarkable response, excellent stability and selectivity.

Description

Technical Field

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

[0002] Resistive gas sensors based on semiconductor metal oxides can effectively detect and monitor ambient gases and have received extensive 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. For example, compared with thick film and sintered devices, they use less gas-sensitive material, and the device reliability and consistency are better. In addition, thin film gas sensors are more easily combined with micro / nano processing technologies, which helps the miniaturization and low energy consumption of the devices. However, due to the higher manufacturing process requirements of thin film devices, they have relatively less research at present compared with sintered and thick film devices.

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

[0004] In order to improve the gas-sensitive performance, designing the gas-sensitive material into a nanostructure (including nanoparticles, nanowires, nanosheets, etc.) is an important strategy. However, for sintered and thick film devices, the nanostructured gas-sensitive material in powder form needs to be dispersed to obtain a slurry, and then the final device is obtained through droplet coating, shaping 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. During the gas detection process, common metal oxide gas-sensitive materials usually require a relatively high working temperature (generally above 200 °C), and the above phenomenon is particularly obvious. How to maintain the high specific surface area and high activity of the nanostructured gas-sensitive material during device manufacturing and gas detection is an urgent problem to be solved. Summary of the Invention

[0005] The object 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 thin film, a preparation method thereof, and an application thereof.

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

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

[0008] Preferably, the substrate is an Al2O3 substrate with noble metal Pt interdigital electrodes.

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

[0010] Using pulsed laser deposition technology to deposit CeO2 and carbon on the substrate to obtain a CeO2 / carbon thin film;

[0011] Then, the obtained CeO2 / carbon thin film is subjected to rapid annealing treatment to obtain a gas sensor with a confined CeO2 nanoparticle thin film.

[0012] Preferably, the pulsed laser deposition technology is specifically: using silver glue to bond the surfaces of the CeO2 target and the carbon target to form a composite target, and ablating the composite target with a laser under vacuum conditions.

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

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

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

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

[0017] The third aspect of the present invention provides that the gas sensor based on the confined CeO2 nanoparticle thin film 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 through in-situ confinement in the carbon matrix, thus fully utilizing their high surface activity. In addition, the carbon matrix can serve as a transmission path for target gas molecules and electrons, enabling efficient gas-solid reactions and effective collection of gas-sensing signals.

[0019] 2. The preparation process of the confined CeO₂ nanoparticle thin film gas sensor of the present invention is simple and rapid, and the entire preparation process only takes dozens of minutes. The confined CeO₂ nanoparticle thin film grows in-situ on the surface of a commercial alumina planar gas-sensing substrate and can be directly used as the sensing layer of the gas sensor, thus effectively avoiding processes such as droplet coating, shaping, and calcination in traditional sintering and thick film device preparation, ensuring the stability and consistency of the sensor.

[0020] 3. Applying the confined CeO₂ nanoparticle thin film gas sensor of the present invention to detect triethylamine gas shows excellent gas-sensing response. Description of the Drawings

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

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

[0023] Figure 3 Gas-sensing response of the confined CeO₂ nanoparticle thin film in the present invention to a fixed concentration of triethylamine (100 ppm) at different working temperatures (100 - 450 °C).

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

[0025] Figure 5 Typical dynamic response / recovery transient of the confined CeO₂ nanoparticle thin film in the present invention to 100 ppm triethylamine, gas-sensing response to different gases with a concentration of 100 ppm, and relationship between the logarithmic response value and triethylamine concentration at 400 °C and 450 °C.

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

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

[0028] Figure 8 Schematic diagram of the gas-sensing mechanism of the confined CeO2 nanoparticle thin film in the present invention. Detailed implementation manners

[0029] The technical solutions of the present invention and their 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 it shall not constitute any limitation to the implementation and protection scope of the present invention.

[0030] The gas sensor based on the confined CeO2 nanoparticle thin film provided by the present invention may include a substrate and a confined CeO2 / carbon thin film layer attached to the substrate in the form of a thin film; the size of the nanoparticles of the confined CeO2 is about 5-20 nm, and it is confined to grow in an amorphous carbon matrix; the confined CeO2 nanoparticles have a high degree of dispersion.

[0031] Preferably, the substrate is an Al2O3 substrate with noble metal Pt interdigital electrodes.

[0032] The preparation method of the gas sensor based on the confined CeO2 nanoparticle thin film provided by the present invention includes the following steps:

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

[0034] Step (2), obtaining a CeO2 / carbon thin film by pulsed laser deposition technology: First, prepare a target, which consists of a carbon target with a radius of 5-20 mm and a CeO2 target with a length of 5-15 mm; use silver paste to bond the surface of the CeO2 target and the carbon target to form a composite target of the two materials; then use a commercial flat Al2O3 gas-sensing substrate as the deposition substrate, and ablate the target with a 10 Hz laser (248 nm) for 3-8 minutes in an ultra-high vacuum (1-5×10 - 8 Torr) and an argon environment to obtain a CeO2 / carbon thin film; during the deposition process, the target rotates around the central axis at a constant speed;

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

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

[0037] The following uses specific embodiments to further elaborate on the present invention in detail, but the present invention is not limited to the following specific embodiments.

[0038] The following introduces several typical embodiments.

[0039] Example 1:

[0040] Before growth, first, the commercial flat Al2O3 gas-sensitive substrate is repeatedly washed in deionized water and absolute ethanol and then dried to obtain a clean surface for deposition. And a target is fabricated. The target consists of a carbon target with a radius of 20 mm and a CeO2 target with a length of 15 mm. The CeO2 target is bonded to the surface of the carbon target with silver paste to form a composite target of the two materials. Then, using the commercial flat Al2O3 gas-sensitive substrate as the deposition substrate, the target is ablated with a 10 Hz laser (248 nm) for 5 minutes under ultra-high vacuum (5×10 -8 Torr). During the deposition process, the target rotates around the central axis at a constant speed. After deposition, under the protection of a 100 sccm Ar gas flow, the deposited sample is rapidly annealed at 600 °C for 5 minutes, and then the gas sensor based on the confined CeO2 nanoparticle thin film is obtained. The gas sensor obtained in this example is labeled as CeO2-1.

[0041] Example 2:

[0042] Before growth, first, the commercial flat Al2O3 gas-sensitive substrate is repeatedly washed in deionized water and absolute ethanol and then dried to obtain a clean surface for deposition. And a target is fabricated. The target consists of a carbon target with a radius of 20 mm and a CeO2 target with a length of 15 mm. The CeO2 target is bonded to the surface of the carbon target with silver paste to form a composite target of the two materials. Then, using the commercial flat Al2O3 gas-sensitive substrate as the deposition substrate, the target is ablated with a 10 Hz laser (248 nm) for 5 minutes under ultra-high vacuum (5×10 -8The target was ablated for 3 minutes with a 10 Hz laser (248 nm) under 10 Torr. During the deposition process, the target rotated around the central axis at a constant speed. After deposition, under the protection of a flowing Ar gas of 100 sccm, the deposited sample was rapidly annealed at 600 °C for 6 minutes, and thus a gas sensor based on the confined CeO2 nanoparticle thin film was obtained. The gas sensor obtained in this example was labeled as CeO2-2.

[0043] Example 3:

[0044] Before growth, first, a commercial flat Al2O3 gas-sensitive substrate was repeatedly washed in deionized water and absolute ethanol and then dried to obtain a clean surface for deposition. And a target was fabricated. The target 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 surface of the carbon target with silver paste to form a composite target of the two materials. Then, using the commercial flat Al2O3 gas-sensitive substrate as the deposition substrate, under an ultra-high vacuum (5×10 -8 Torr), the target was ablated for 7 minutes with a 10 Hz laser (248 nm). During the deposition process, the target rotated around the central axis at a constant speed. After deposition, under the protection of a flowing Ar gas of 100 sccm, the deposited sample was rapidly annealed at 600 °C for 8 minutes, and thus a gas sensor based on the confined CeO2 nanoparticle thin film was obtained. The gas sensor obtained in this example was labeled as CeO2-3.

[0045] The size of the confined CeO2 nanoparticles prepared in Examples 1 to 3 was about 5 - 20 nm, and they were confined to grow in the amorphous carbon matrix; the nanoparticles had a high degree of dispersion; the amorphous carbon matrix was attached to the commercial flat Al2O3 gas-sensitive substrate.

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

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

[0048] The specific results of the 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 CeO2 nanoparticles with uniform size are confined and grown in the carbon matrix. The average size of the nanoparticles is about 10 nm. The high-resolution TEM image shows that the nanoparticles exhibit clear lattice fringes ( Figure 1 b), which is consistent with the (220) crystal plane of the fluorite structure CeO2, indicating that the nanoparticles have good crystallinity. The preparation process of the confined CeO2 nanoparticle thin film is as Figure 1 shown in c. First, a CeO2 / carbon film was in-situ deposited on a commercial Al2O3 plate using pulsed laser deposition technology. Then, in-situ confined growth of CeO2 nanoparticles in the carbon matrix was achieved through rapid annealing treatment. 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 thin film.

[0050] Figure 2 are the Raman spectrum, high-resolution Ce 3d high-resolution XPS spectrum, and O 1s high-resolution XPS spectrum of the confined CeO2 nanoparticle thin film. The Raman spectrum (as Figure 2 shown in a) shows that there is a typical Raman peak at 459 cm -1 , corresponding to the symmetric stretching vibration of Ce-O-Ce, belonging to the triple degenerate F 2g vibration mode of cubic fluorite structure CeO2. The results further confirm the crystal phase and good crystallinity of the sample. Figure 2 b shows the high-resolution XPS spectrum of Ce 3d, mainly presenting four pairs of spin-orbit doublets. The peaks at 902.82 eV and 884.57 eV represent Ce 3+ , while the other three doublets, 900.99 eV and 882.48 eV, 907.49 eV and 889.1 eV, 916.8 eV and 898.47 eV, are characteristic of Ce 4+ . The above results indicate that Ce 3+ and Ce 4+ coexist in the obtained CeO2 nanoparticles, which is reported to be important for improving gas-sensing activity. The high-resolution XPS spectrum of O 1s is as Figure 2 shown in c. The peaks at 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 thin film contains a rich component of chemically adsorbed oxygen (about 31.2%), which means it is expected to exhibit good gas-sensing performance.

[0051] Figure 3 The gas-sensing response of the confined CeO2 nanoparticle thin film to a fixed concentration of triethylamine (100 ppm) at different working temperatures (100 - 450 °C) was investigated. The results showed that there was almost no gas-sensing response at low working temperatures (below 200 °C). As the working temperature increased, the gas-sensing response to triethylamine gradually enhanced.

[0052] Figure 4 a and Figure 4 b respectively show the dynamic gas-sensing responses of the confined CeO2 nanoparticle thin film to triethylamine gas at different concentrations at working temperatures of 400 °C and 450 °C. The results showed that as the concentration of triethylamine gas increased, the gas-sensing response also increased. Figure 4 c and Figure 4 d respectively show the cyclic response / recovery curves of the confined CeO2 nanoparticle thin film to 100 ppm triethylamine gas at working temperatures of 400 °C and 450 °C. The results showed that it had good repeatability in multiple cycles.

[0053] Figure 5 a is the typical dynamic response / recovery curve of the confined CeO2 nanoparticle thin film to 100 ppm triethylamine. The results showed that the response time was ~2 s and the recovery time was ~186 s, indicating that the sensor had fast response and recovery characteristics. In addition, the sensing performance of the confined CeO2 nanoparticle thin 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-sensing reaction to other VOC gases such as methanol, ethanol, and ethyl acetate, indicating its good selectivity to 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 report of the National Institute for Occupational Safety and Health of the United States, the acceptable exposure limit of triethylamine in factories is 10 ppm. In this study, a similar linear relationship was observed between the concentration of triethylamine and the logarithm of the response value ( Figure 5 c and Figure 5 d). According to the formula LOD = Kσ / S (where LOD represents the detection limit, K is a constant usually set to 3, σ is the standard deviation of the measured values, and S is the slope), the LODs of the confined CeO2 nanoparticle thin film for detecting triethylamine at working temperatures of 400 °C and 450 °C were determined to be 0.5819 and 0.4036 ppm, respectively. This value was significantly lower than the allowable exposure concentration of triethylamine, indicating its suitability for detecting low-concentration triethylamine.

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

[0055] Figure 7 This is the sensing performance of the confined CeO2 nanoparticle thin film in the present invention for 100 ppm triethylamine after 90 days of preparation. It is found that when the gas-sensing test is carried out again after 90 days of natural placement, there is no sign of attenuation in the gas-sensing performance of triethylamine, indicating its excellent long-term stability.

[0056] Figure 8 The schematic diagram of the gas-sensing mechanism of the confined CeO2 nanoparticle thin film is shown. During the triethylamine sensing process of the confined CeO2 nanoparticle thin film sensor, due to the n-type semiconductor characteristics of CeO2, electrons are the main charge carriers. When exposed to air, the 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 the charge carrier concentration and an increase in the sensor resistance. When triethylamine gas is introduced, the surface-adsorbed oxygen will absorb electrons from the reduced triethylamine gas molecules, increasing the number of electrons in the conduction band of the CeO2 nanoparticle thin film, thereby reducing the resistance. The change in resistance leads to the generation of a sensor signal. In addition, the mutual electron transition between Ce 3+ and Ce 4+ can store oxygen and significantly enhance its ability to adsorb / desorb oxygen, thus enabling the effective detection of triethylamine.

[0057] The embodiments described above are only used to describe the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A gas sensor based on a confined CeO2 nanoparticle thin film, characterized in that, It includes a substrate, on the surface of which there is a confined CeO2 / carbon thin film layer. The particle size of the confined CeO2 in the confined CeO2 / carbon thin film layer is 5 - 20 nm, and it is confined and grown in an amorphous carbon matrix. The substrate is an Al2O3 substrate with noble metal Pt interdigital electrodes. The preparation method of the gas sensor based on the confined CeO2 nanoparticle thin film includes the following steps: First, CeO2 and carbon were deposited on the substrate by pulsed laser deposition technology to obtain CeO2 / carbon thin film; Then, the prepared CeO2 / carbon thin film was subjected to rapid annealing treatment to obtain a gas sensor based on a confined CeO2 nanoparticle thin film.

2. The gas sensor based on the confined CeO2 nanoparticle thin film according to claim 1, characterized in that, The specific steps of the pulsed laser deposition technique are as follows: Use silver glue to bond the surfaces of the CeO2 target and the carbon target to form a composite target, and ablate the composite target with pulsed laser under vacuum conditions. The vacuum degree of the vacuum conditions is 1-5×10 -8 Torr, the wavelength of the laser is 248 nm, and the ablation time is 3-8 minutes.

3. The gas sensor based on the confined CeO2 nanoparticle thin film according to claim 1, characterized in that, The rapid annealing treatment is carried out under the protection of an inert gas at 500 - 700 °C.

4. The gas sensor based on the confined CeO2 nanoparticle thin film according to claim 3, characterized in that, The inert gas is Ar gas.

5. The gas sensor based on the confined CeO2 nanoparticle thin film according to claim 1, wherein, The annealing time is 3 - 8 minutes.

6. The application of the gas sensor based on the confined CeO2 nanoparticle thin film according to claim 1, characterized in that, The gas sensor based on the confined CeO2 nanoparticle thin film can be used for the detection of volatile organic compound (VOC) triethylamine.

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