Full Length ArticleOptimal Pt mesoporous layer modified nanocomposite film with highly sensitive detection of ethanol at low temperature
Graphical abstract
Introduction
Volatile organic compounds (VOCs), such as ethanol, acetone, formaldehyde, and benzene, etc, are inimical to human health and the environment due to their mutagenicity, teratogenicity, and poisonousness [1]. Ethanol, as one kind of the common and extreme VOCs in life, is widely used in manufacturing [2], biomedical [3], and food industries [4]. However, some serious symptoms like narcosis and impaired perception will happen while a person gets in amounts of ethanol [5]. Thus, the detection of ethanol is of great significance for protecting human health. There was an abundant investigation about the ethanol gas sensors based on the metal oxide semiconductors (MOS) which are extensively used as the gas sensing materials for their stable, remarkable, and reversible surface resistance changes in the gas ambiance [6], [7], [8].
In recent three decades, research on gas sensing properties of various MOS (i.e., SnO2[9], [10], [11], TiO2[12], [13], [14], ZnO [15], Fe2O3[16], In2O3[17], [18], WO3[19], Co3O4[20], [21], V2O5[22] have been investigated and widely used to detect ethanol. Among them, SnO2 as the n-type MOS material with a wide bandgap of 3.6 eV, attracted much attention for its excellent chemical and electrical properties [23], [24], [25], [26]. To date, many studies have demonstrated good properties of SnO2 with various microstructures (i.e., flower-like, nanofibers, hollow nanoparticles) which can provide high surface areas. For example, Zeng et al. prepared the flower-like SnO2 nanostructures showing the response of about 17 to 400 ppm of ethanol at 350℃ [27]. Zhang et al. revealed that SnO2 nanofibers had a response of about 19 to 200 ppm of ethanol at 330℃ [28]. Zito et al. found that the hollow SnO2 particles can detect 100 ppm of ethanol with the response of 63.4 at 300℃ [29]. Although the response to ethanol can be improved by different microstructures of SnO2, there were still some problems, such as relatively low sensitivity and high working temperature.
Previous research has proven that some measures (i.e., using heterojunctions [30], metal surface modification [31], [32]) can effectively enhance the MOS gas sensing sensitivity and decrease the working temperature. The heterojunctions may improve gas sensing properties due to their synergistic effects in the composites [33], [34]. For example, Su et al. found the response of TiO2@SnO2 nanosphere to 10 ppm of formaldehyde reached 49.3, which is better than that of TiO2 nanosphere under the same testing condition [35]. Feng et al. revealed that the response of TiO2//SnO2 nanofibers to 10 ppm of ethanol exhibited about 7.5 at 368℃ [36]. Wang et al. prepared the TiO2-SnO2-TiO2 composite nanofibers showing the response of 13.3 to 1 ppm of acetone at 280℃ [37]. Therefore, the gas sensing properties of SnO2 can be enhanced by heterojunctions formed with TiO2 and greatly improved by multilayer heterojunctions of multi-layer TiO2/SnO2. However, the high working temperature is still a problem on many occasions. As another effective method, the metal surface modification can enormously enhance the sensing properties and decrease the working temperature because of their catalysis activity to gas and Schottky Barrier formed at the interface between metal and MOS. Huang et al. revealed that the optimal working temperature of the Pt modified SnO2 nanorod is lower than the pure SnO2 nanorods [38]. Mohammad et al. confirmed that Ag modified SnO2 based sensor attains the high response as well as the low working temperature of 180℃ compared to the pure SnO2 based sensor [32]. Therefore, the metal-modified heterojunctions are possible to enhance the gas sensing sensitivity at the low working temperature.
In this paper, we proposed a method to fabricate the high-performance MEMS gas sensor for detecting ethanol. To enhance the gas sensing sensitivity of MOS material and decreasing the working temperature by the above-mentioned measures (microstructures, heterojunctions, and metal modification), a Pt mesoporous layer modified multi-layer TiO2/SnO2 (Pt/TiO2/SnO2) nanocomposite thin film was prepared by magnetron sputtering technique. This Pt mesoporous layer activated multi-layer MOS materials are compatible with the MEMS process, and as far as this method has not been reported yet. The contribution of different Pt sputtering time and annealing temperature to the formation of Pt mesoporous layer was investigated, showing the Pt sputtering time of 30 s and the annealing temperature of 500℃ are the opening condition and forming condition of Pt mesoporous layer, respectively, which has the most mesoporous of 5–50 nm. The MEMS ethanol gas sensors with the Pt/TiO2/SnO2 nanocomposite thin film has the high sensitivity to ethanol at 130℃ and shows the response of 3.32 to 0.1 ppm of ethanol, which can be attributed to the plenty of Pt mesoporous and Schottky Barrier formed at the interface between Pt and TiO2. The Pt mesoporous layer and multilayer heterojunctions created entirely by sputtering techniques verify the effectiveness of this method for preparing enhanced MOS gas sensing materials for the gas sensors.
Section snippets
Preparation of Pt/TiO2/SnO2 nanocomposite thin film
Pt mesoporous layer modified TiO2/SnO2 nanocomposite thin film was completely prepared by a sputtering technique. The pure Pt (three-inch, 99.99%, Zhongnuo New Material Technology Co., Ltd.), SnO2(three-inch, 99.99%, Zhongnuo New Material Technology Co., Ltd.), and TiO2(three-inch, 99.99%, Zhongnuo New Material Technology Co., Ltd.) target were used to deposit Pt/TiO2/SnO2 nanocomposite thin film by magnetron sputtering in the order from Table 1. Five sets of parameters for the sputtering time
Structural and morphological characteristics
The microstructure and morphologies of the as-prepared samples S1, S2, S3, S4, S5 were investigated by FESEM observation. Fig. 3 shows the Pt layer with the different sputtering times of Pt at the same annealed temperature of 400℃ in N2. The FESEM images in (Fig. 3a-b) clearly show the smooth plane of sample S1 completely prepared by sputtering. The Pt particles turned into larger from sample S2 to sample S3. The Pt mesoporous layer is formed at sample S4 and disappears in sample S5, as shown
Conclusion
In summary, a complete MEMS process was developed to prepare the Pt mesoporous layer modified the multi-layer TiO2/SnO2 nanocomposite thin film as the gas sensing material for ethanol sensing, which can be integrated with the microheater and IDE. The morphology and microstructure of the Pt/TiO2/SnO2 nanocomposite thin film were characterized by various instruments, which demonstrates that the optimal preparing process of Pt mesoporous is 30 s sputtering time of Pt and annealing temperature of
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work is supported by Science and Technology Planning Project of Shenzhen (Grant No. JSGG20191129102808151), NSAF (Grant No. U1930205), Key Research and Development Projects of Shaanxi Province (Grant No. 2019GY-121, 2020GY-137), Fundamental Research Funds for the Central Universities (Grant No. xzd012019020). We appreciate the support from International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies
References (68)
- et al.
Core-shell structure of ZnO/Co3O4 composites derived from bimetallic-organic frameworks with superior sensing performance for ethanol gas
Appl Surf Sci
(2019) - et al.
Low temperature ethanol response enhancement of ZnO nanostructures sensor decorated with gold nanoparticles exposed to UV illumination
Sensor Actuat a-Phys
(2016) - et al.
Highly sensitive and selective Gd2O3-doped SnO2 ethanol sensors synthesized by a high temperature and pressure solvothermal method in a microreactor
Sensor Actuat B-Chem
(2016) - et al.
Ultra-sensitive ethanol gas sensors based on nanosheet-assembled hierarchical ZnO-In2O3 heterostructures
J Hazard Mater
(2020) - et al.
Humidity compensation based on power-law response for MOS sensors to VOCs
Sensor Actuat B-Chem
(2021) - et al.
A rapid discreteness correction scheme for reproducibility enhancement among a batch of MOS gas sensors
Sensor Actuat a-Phys
(2014) - et al.
Atmospheric plasma sprayed SnO2 coating for ethanol detection
J Alloy Compd
(2018) - et al.
Facile one-step hydrothermal synthesis of SnO2 microspheres with oxygen vacancies for superior ethanol sensor
J Alloy Compd
(2020) - et al.
Hydrothermal self-assembly of novel porous flower-like SnO2 architecture and its application in ethanol sensor
Appl Surf Sci
(2015) - et al.
Enhanced ethanol sensing properties of TiO2 nanotube sensors
Sensor Actuat B-Chem
(2012)
Ethanol sensing behaviour of sol-gel dip-coated TiO2 thin films
Sensor Actuat B-Chem
Size-controlled growth of TiO2 nanowires by oxidation of titanium substrates in the presence of ethanol vapor
Scripta Mater
Ethanol sensing behavior of Pd-nanoparticles decorated ZnO-nanorod based chemiresistive gas sensors
Sensor Actuat B-Chem
Nano-crystalline Fe2O3 thin films for ppm level detection of H2S
Sensor Actuat B-Chem
Detection of ethanol gas using In2O3 nanoparticle-decorated ZnS nanowires
Sensor Actuat B-Chem
Thiourea-assistant growth of In2O3 porous pompon assembled from 2D nanosheets for enhanced ethanol sensing performance
Talanta
Cr2O3 nanoparticle-functionalized WO3 nanorods for ethanol gas sensors
Appl Surf Sci
Rational design of Bi-doped rGO/Co3O4 nanohybrids for ethanol sensing
Sensor Actuat B-Chem
Synthesis of hollow and hollowed-out Co3O4 microspheres assembled by porous ultrathin nanosheets for ethanol gas sensors: Responding and recovering in one second
Sensor Actuat B-Chem
Highly sensitive and selective ultrasonically nebulized V2O5 thin films towards ethanol and NO2 gas detection
Sens. Actuators, B
A novel room temperature ethanol gas sensor based on 3D hierarchical flower-like TiO2 microstructures
Mater Lett
Structural and optical properties of SnO2 nanotowers and interconnected nanowires prepared by carbothermal reduction method
J Alloy Compd
Synthesis and characterization of hierarchical porous SnO2 for enhancing ethanol sensing properties
Appl Surf Sci
Hydrothermal synthesis of hierarchical flower-like SnO2 nanostructures with enhanced ethanol gas sensing properties
Mater Res Bull
Fabrication and ethanol-sensing properties of micro gas sensor based on electrospun SnO2 nanofibers
Sensor Actuat B-Chem
Impact of reduced graphene oxide on the ethanol sensing performance of hollow SnO2 nanoparticles under humid atmosphere
Sensor Actuat B-Chem
Hydrogen gas sensing properties of MoS2/Si heterojunction
Sensor Actuat B-Chem
Controlled modification of Pt/Al2O3 for the preferential oxidation of CO in hydrogen: A comparative study of modifying element
Appl Catal B-Environ
Describing the effect of Ag/Au modification on operating temperature and gas sensing properties of thick film SnO2 gas sensors by gas diffusion theory
Mater Chem Phys
Nanoscale metal oxide-based heterojunctions for gas sensing: A review
Sensor Actuat B-Chem
UV-activated formaldehyde sensing properties of hollow TiO2@SnO2 heterojunctions at room temperature
Sens. Actuators, B
Electrospun TiO2//SnO2 Janus nanofibers and its application in ethanol sensing
Mater Lett
Hollow hierarchical TiO2-SnO2-TiO2 composite nanofibers with increased active-sites and charge transfer for enhanced acetone sensing performance
Sensor Actuat B-Chem
Highly efficient and stable electrooxidation of methanol and ethanol on 3D Pt catalyst by thermal decomposition of ln2O3 nanoshells
J Energy Chem
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