Pure SnO₂ Gas Sensor with High Sensitivity and Selectivity towards C₂H₅OH

Abeer Alhadi¹, Shuyi Ma^1*, Tingting Yang¹, Shitu Pei¹, Pengdou Yun¹, Khalid Ahmed Abbakar^2,3, Qianqian Zhang¹, Nina Ma¹, Manahil H. Balal^3,4, Hamouda Adam Hamouda^5,6, Khalid Mohammed Adam^5,6

¹Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province, College of Physics and Electronic Engi-neering, Northwest Normal University, Lanzhou, China.
²College of Mathematics and Statistics, Northwest Normal University, Lanzhou, China.
³Department of Mathematics and Physics, Faculty of Education, University of Gadarif, Gadarif, Sudan.
⁴Physics Department, Faculty of Science and Art, Al Baha University, Gilwah, Saudi Arabia.
⁵College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, China.
⁶Department of Chemistry, Faculty of Science, University of Kordofan, El Obeid, Sudan.

DOI: 10.4236/anp.2021.102005                

Abstract

To observation, poisonous gases in the environment, Sensors with high selectivity, high response and low operating temperature are required. In this work, pure SnO₂ nanoparticles was prepared by using a simple and inexpensive technique (hydrothermal method) without a template. Various confirmatory tests were performed to characterize SnO₂ nanoparticles such as energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transition Electron Microscopy (TEM), during the detection of the gas, we found that pure SnO₂ nanoparticles has a high selectivity for ethanol to 100 ppm at a low temperature (180°C) and a high response (about 27 s) and a low detection limit of 5 ppm, also it have response/recovery times about (4 s, 2 s) respectively. The distinctive sensing properties of SnO₂ sensor make it a promising candidate for ethanol detection. Furthermore, the gas-sensing mechanism have been examined.

Keywords

Hydrothermal Method, Nanoparticles, Ethanol, SnO₂, Gas Sensor

1. Introduction

Volatile organic compounds are considered a major component that participates in the formation of ozone, which are air pollutants, and their percentage increases from weakness in the outside air, due to their presence in many products in the home, as volatile organic compounds are now included in about 90% of the products that enter the home, Its sources include drinking water, carpets, paints, deodorants, cleaning methods, materials used for shoe polishing, cosmetics, dry cleaning clothes, moth repellents, air fresheners, and car exhaust [1] [2] [3]. One of the volatile organic compounds that must be detected is ethanol. Ethanol is an organic chemical compound that belongs to the alcohol family. It has the chemical formula: C₂H₅OH and it is called generalized alcohol [4]. Ethanol is a colorless, flammable substance formed from the fermentation of sugar. It is used in alcoholic beverages and in the manufacture of perfumes and is used as a fuel in mechanical engines prepared for ethanol [5]. Whereas, eating small to moderate amounts may lead to symptoms of toxicities, such as inconsistency in muscle work, poor vision, slurred speech … etc. As for eating large amounts, dampening of the bulb reflexes, such as drowsiness, forgetfulness, and memory impairment, amnesia, hypothermia, hypoglycemia, stupor, coma, respiratory depression may occur [6]. Therefore, it is necessary to find a high-efficiency and low-cost sensor material for the detection of ethanol [7]. TiO₂, Cr₂O₃, CuO, ZnO, and SnO₂, etc. are semiconducting metal oxides. Defined as high-efficiency and low-cost sensor materials for the detection of toxic and harmful gases [8] [9] [10] [11] [12]. Recently, different structures of MOS materials with a large specific surface area have been reported to improve the sensing response of sensors, for an example nanowires, nanoparticles, nanorods, hierarchical flower-like structure and hollow microspheres [13] [14].

The SnO₂ known as n-type semiconductor with band gap 3.6 eV. Also, it is promising for gas sensing materials in order to chemical stability, perfect thermal, excellent mobility of an electron and low cost [15]. To synthesis SnO₂ nanocrystal line, Different methods have been used such as chemical vapor deposition, sputtering, hydrothermal and sol-gel, among them hydrothermal method is simple and inexpensive method. Syntheses of pure SnO₂ nanoparticles by a hydrothermal method are still limited. In this work, pure SnO₂ nanoparticles were successfully synthesized by hydrothermal method without any template. The obtained sample was analyzed by SEM, TEM, EDX, and XRD. Moreover, the sensing performances and gas sensing mechanism were discussed.

2. Experimental

In a typical procedure, 1.6 g NaOH, 1.4 g SnCl₂·2H₂O and 1 g PVP were dissolved in mixed solution contained of 5 ml H₂O₂ and 35 ml DI under a magnetic stirring at 30˚C for 2 h. Then the above mixed solution was transferred to 50 ml Teflon-lined stainless-steel autoclave and reacted for 10 h at 180˚C, therefore, after the autoclave cooling down to room temperature naturally the precipitate was washed with deionized water and ethanol for serval time, finally the SnO₂ powders were obtained after dried in a furnace for 24 h. The crystal structure X-ray diffraction (XRD) of SnO₂ nanoparticles was tested by using an X-ray diffractometer (XRD, D/Max-2400) with Cu Kα1 radiation (λ = 0.15406 nm), Elemental composition was tested by (EDX) an energy-dispersive X-ray detector, surface morphological and microstructural of the sample was carried out on a scanning electron microscopy (SEM, S-4800) and transmission electron microscopy (TEM, JEM-2010). The gas sensing properties were evaluated by the WS-30B gas sensing apparatus (Wei Sheng Electronics Science and Technology Co., Ltd., Henan Province, China). The sensor response (R) to gas was defined as Ra/Rg, where Ra and Rg were the initial sensor resistance in air and gas [16].

3. Results and Discussion

The X-ray diffraction (XRD) analysis was used to examine the crystal structure of the sample, in Figure 1(a). The peak positions of the sample displayed a rutile type tetragonal structure of SnO₂, which were matched well with a standard card (JCPDS, 41-1445) with a = b = 4.736 Å and c = 3.185 Å. No impurity phase detected which indicates the high purity of the prepared SnO₂ [17]. The crystallite size d is measured using Debye-Scherer’s formula:

$d=\frac{0.9\lambda }{\beta \cos \theta }$

β is the Full Width at Half Maximum (FWHM) of the peak, θ is the Braggs angle, and λ is the wavelength of X-ray. After calculating by means of the above equation, he found that it is equal to 2.215 nm [18] [19]. (the EDX spectroscopy of SnO₂ nanoparticles) in Figure 1(b), indicating that our sample composed of Sn and O elements. Figure 2(a), Figure 2(b) showed the SEM images of SnO₂ nanoparticles, the nanoparticles are well crystallized, Figure 2(c) displays the TEM image of the as-synthesized product. It can be clearly seen that nanoparticles with rough surfaces, it is matched well with results of SEM, rough surfaces. It is very good to the desorption and adsorption of gas molecules [20] [21], the inner figure in Figure 2(c) is SAED pattern illustrated the polycrystalline nature of SnO₂ sample, the HRTEM image displayed in Figure 2(d), the lattice distance was calculated to be 0.175 nm. It corresponds to (211) crystallographic orientation, the optimum operating temperature was determined, the response values of

Figure 1. (a) The XRD pattern of SnO₂ nanoparticles; (b) showed EDS pattern of the SnO₂ nanoparticles.

Figure 2. (a) (b) displayed the morphologies of SnO₂ nanoparticles; (c) showed the TEM picture of SnO₂ nanoparticles, the inner figure in (c) showed the SAED pattern; (d) displayed HRTEM picture of SnO₂ nanoparticles.

SnO₂ nanoparticles to 100 ppm ethanol under different operating temperatures in the range of 140˚C → 340˚C are evaluated and depicted in Figure 3(a), when the increase of ethanol concentrations from 5 → 1000 gas response increases progressively, Figure 3(b), when the concentration is above 150 ppm, the gas sensor nearly be stable. The responses of SnO₂ nanoparticles to 100 ppm different gasses at 180˚C determined in Figure 3(c). Our sensor exhibits high selectivity to ethanol. The response and recovery times are about 4 s and 2 s, respectively, Figure 3(d). In Figure 3(e) indicated the sensor nearly to be stable. The results indicate that the SnO₂ nanoparticles based sensor can successfully differentiate ethanol at 180˚C. Table 1 showed the Comparison between various SnO₂ based gas sensors to C₂H₅OH.

Experimental results of SnO₂ nanoparticles sensor have been compared with the results reported by the other workers on C₂H₅OH sensors and presented in Table 1. It can be seen that SnO₂ nanoparticles sensor can reach a relatively higher response toward C₂H₅OH at lower temperature. The obtained results indicate that the SnO₂ nanoparticles sensor is promising for C₂H₅OH gas sensing. In Figure 4 the gas-sensing mechanism of SnO₂ nanoparticles when the sample is exposed to air, oxygen molecules will be absorbed on the surface, trapping the conduction band’s electrons and creating chemisorbed oxygen species (e.g. ${\text{O}}^{\text{2}-}$, ${\text{O}}^{-}$ and ${\text{O}}_2^{-}$ ) through Eqs [30].

${\text{O}}_{\text{2}}+{\text{e}}^{-}\to {\text{O}}_2^{-}\left(\text{ads}\right)$ (1)

${\text{O}}_2^{-}\left(\text{ads}\right)+{\text{e}}^{-}\to {\text{O}}^{-}\left(\text{ads}\right)$ (2)

Figure 3. (a) displayed the gas sensor responses of sample to 100 ppm ethanol to different operating temperatures; (b) is gas sensor responses to different concentrations (5 - 1000 ppm) of ethanol; (c) displayed the response to 100 ppm ethanol at different gases; (d) is the response and recover time towards 100 ppm ethanol at 180˚C; (e) showed the stability of SnO₂ sample to 100 ppm ethanol at 180˚C.

Figure 4. Demonstrated gas sensing mechanism of SnO₂ nanoparticles.

Table 1. The Comparison between various SnO₂ based gas sensors to C₂H₅OH.

Where:EF ≡electrospinning followed; HM≡hydrothermal method; BM ≡ball-milling solid chemical reaction method; ES ≡electrospinning.

${\text{O}}^{-}\left(\text{ads}\right)+{\text{e}}^{-}\to {\text{O}}^{\text{2}-}\left(\text{ads}\right)$ (3)

which will generate an electron depletion layer on the surface, leading to high resistance of the material. When the sample is exposed to ethanol, the adsorbed ethanol molecules will react with the surface oxygen species. This process releases the trapped electrons back to the conduction band. Thus, the thickness of the electron depletion layer will decrease, resulting in low resistance of the sample. This progress can be described as follows [31]:

${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}+{\text{6O}}^{-}\left(\text{ads}\right)\to {\text{2CO}}_{\text{2}}+{\text{3H}}_{\text{2}}\text{O}+{\text{6e}}^{-}$ (4)

${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}+{\text{6O}}^{\text{2}-}\left(\text{ads}\right)\to {\text{2CO}}_{\text{2}}+{\text{3H}}_{\text{2}}\text{O}+{\text{12e}}^{-}$ (5)

4. Conclusion

In summary, SnO₂ nanoparticles have been successfully synthesized through a facile and low-cost hydrothermal method. The sensor exhibits excellent sensitivity about 27, fast response and recovery time (4 s and 2 s), long-term stability and the optimum operating temperate 180˚C. Thus SnO₂ nanoparticles can be used as a promising material for ethanol sensors.

Acknowledgements

The authors would like to thank the associate editor and the anonymous reviewer for their valuable comments and suggestions, which have led to a significant improvement of the whole manuscript. This work was supported by the National Natural Science Foundation of China (Grant No. 11864034 and 11964035), and the Scientific Research Project of Gansu Province (Grant No. 18JR3RA089 and 17JR5RA072).

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References

[1]	Wang, X., et al. (2020) SnO2 Core-Shell Hollow Microspheres Co-Modification with Au and NiO Nanoparticles for Acetone Gas Sensing. Powder Technology, 364, 159-166. https://doi.org/10.1016/j.powtec.2020.02.006
[2]	Guo, W., Zhou, Q., Zhang, J., Fu, M., Radacsi, N. and Li, Y. (2019) Hydrothermal Synthesis of Bi-Doped SnO2/rGO Nanocomposites and the Enhanced Gas Sensing Performance to Benzene. Sensors and Actuators B: Chemical, 299, Article ID: 126959. https://doi.org/10.1016/j.snb.2019.126959
[3]	Cao, P.F., et al. (2020) Preparation and Characterization of a Novel Ethanol Gas Sensor Based on FeYO3 Microspheres by Using Orange Peels as Bio-Templates. Vacuum, 177, Article ID: 109359. https://doi.org/10.1016/j.vacuum.2020.109359
[4]	Ma, Z., Yu, R. and Song, J. (2019) Facile Synthesis of Pr-Doped In2O3 Nanoparticles and Their High Gas Sensing Performance for Ethanol. Sensors and Actuators B: Chemical, 305, Article ID: 127377. https://doi.org/10.1016/j.snb.2019.127377
[5]	Haron, W., Wisitsoraat, A. and Wongnawa, S. (2017) Nanostructured Perovskite Oxides—LaMO3 (M = Al, Co, Fe) Prepared by Co-Precipitation Method and Their Ethanol-Sensing Characteristics. Ceramics International, 43, 5032-5040. https://doi.org/10.1016/j.ceramint.2017.01.013
[6]	Ma, Y.T., et al. (2020) Hydrothermal-Synthesis Flower-Like SNS Microspheres Gas Sensors Bonded Physically by PVDF for Detecting Ethanol. Vacuum, 181, Article ID: 109657. https://doi.org/10.1016/j.vacuum.2020.109657
[7]	Xin, X., et al. (2019) UV-Activated Porous Zn2SnO4 Nanofibers for Selective Ethanol Sensing at Low Temperatures. Journal of Alloys and Compounds, 780, 228-236. https://doi.org/10.1016/j.jallcom.2018.11.320
[8]	Singh, G., Kohli, N. and Singh, R.C. (2017) Preparation and Characterization of Eu-Doped SnO2 Nanostructures for Hydrogen Gas Sensing. Journal of Materials Science: Materials in Electronics, 28, 2257-2266. https://doi.org/10.1007/s10854-016-5796-3
[9]	Enachi, M., et al. (2015) Integration of Individual TiO2 Nanotube on the Chip: Nanodevice for Hydrogen Sensing. Physica Status Solidi (RRL)—Rapid Research Letters, 9, 171-174. https://doi.org/10.1002/pssr.201409562
[10]	Singh, O. and Singh, R.C. (2012) Enhancement in Ethanol Sensing Response by Surface Activation of ZnO with SnO2. Materials Research Bulletin, 47, 557-561. https://doi.org/10.1016/j.materresbull.2011.12.049
[11]	Cretu, V., et al. (2016) Synthesis, Characterization and DFT Studies of Zinc-Doped Copper Oxide Nanocrystals for Gas Sensing Applications. Journal of Materials Chemistry A, 4, 6527-6539. https://doi.org/10.1039/C6TA01355D
[12]	Kohli, N., Singh, O. and Singh, R.C. (2011) Influence of pH on Particle Size and Sensing Response of Chemically Synthesized Chromium Oxide Nanoparticles to Alcohols. Sensors and Actuators B: Chemical, 158, 259-264. https://doi.org/10.1016/j.snb.2011.06.016
[13]	Lee, C.T., Lee, H.Y. and Chiu, Y.S. (2016) Performance Improvement of Nitrogen Oxide Gas Sensors Using Au Catalytic Metal on SnO2/WO3 Complex Nanoparticle Sensing Layer. IEEE Sensors Journal, 16, 7581-7585. https://doi.org/10.1109/JSEN.2016.2598349
[14]	Hu, J., et al. (2018) Enhanced Formaldehyde Detection Based on Ni Doping of SnO2 Nanoparticles by One-Step Synthesis. Sensors and Actuators B: Chemical, 263, 120-128. https://doi.org/10.1016/j.snb.2018.02.035
[15]	Xu, K., Zeng, D., Tian, S., Zhang, S. and Xie, C. (2014) Hierarchical Porous SnO2 Micro-Rods Topologically Transferred from Tin Oxalate for Fast Response Sensors to Trace Formaldehyde. Sensors and Actuators B: Chemical, 190, 585-592. https://doi.org/10.1016/j.snb.2013.09.021
[16]	Yang, A.H.M., et al. (2017) Synthesis of La2O3 Doped Zn2SnO4 Hollow Fibers by electrospinning Method and Application in Detecting of Acetone. Applied Surface Science, 425, 585-593. https://doi.org/10.1016/j.apsusc.2017.07.073
[17]	Wang, Q., et al. (2011) Porous SnO2 Nanoflakes with Loose-Packed Structure: Morphology Conserved Transformation from SnS2 Precursor and Application in Lithium Ion Batteries and Gas Sensors. Journal of Physics and Chemistry of Solids, 72, 630-636. https://doi.org/10.1016/j.jpcs.2011.02.004
[18]	Almamoun, O. and Ma, S.Y. (2017) Effect of Mn Doping on the Structural, Morphological and Optical Properties of SnO2 Nanoparticles Prepared by Sol-Gel Method. Materials Letters, 199, 172-175. https://doi.org/10.1016/j.matlet.2017.04.075
[19]	Cheng, L., et al. (2014) Highly Sensitive Acetone Sensors Based on Y-Doped SnO2 Prismatic Hollow Nanofibers Synthesized by Electrospinning. Sensors and Actuators B: Chemical, 200, 181-190. https://doi.org/10.1016/j.snb.2014.04.063
[20]	Zhang, G.H., Chen, Q., Deng, X.Y., Jiao, H.Y., Wang, P.Y. and Gengzang, D.J. (2019) Synthesis and Characterization of In-Doped LaFeO3 Hollow Nanofibers with Enhanced Formaldehyde Sensing Properties. Materials Letters, 236, 229-232. https://doi.org/10.1016/j.matlet.2018.10.062
[21]	Liao, L., et al. (2007) Size Dependence of Gas Sensitivity of ZnO Nanorods. The Journal of Physical Chemistry C, 111, 1900-1903. https://doi.org/10.1021/jp065963k
[22]	Jiang, X.H., et al. (2015) 3D Porous Flower-Like SnO2 Microstructure and Its Gas Sensing Properties for Ethanol. Materials Letters, 159, 5-8. https://doi.org/10.1016/j.matlet.2015.06.050
[23]	Yan, S., Xue, J. and Wu, Q. (2018) Synchronous Synthesis and Sensing Performance of Α-Fe2O3/SnO2 Nanofiber Heterostructures for Conductometric C2H5OH Detection. Sensors and Actuators B: Chemical, 275, 322-331. https://doi.org/10.1016/j.snb.2018.07.079
[24]	Li, R., et al. (2017) Fabrication of Porous SnO2 Nanowires Gas Sensors with Enhanced Sensitivity. Sensors and Actuators B: Chemical, 252, 79-85. https://doi.org/10.1016/j.snb.2017.05.161
[25]	Zhao, C., et al. (2018) Facile Synthesis of SnO2 Hierarchical Porous Nanosheets from Graphene Oxide Sacrificial Scaffolds for High-Performance Gas Sensors. Sensors and Actuators B: Chemical, 258, 492-500. https://doi.org/10.1016/j.snb.2017.11.167
[26]	Zhu, Y., et al. (2019) High-Performance Gas Sensors Based on the WO3-SnO2 Nanosphere Composites. Journal of Alloys and Compounds, 782, 789-795. https://doi.org/10.1016/j.jallcom.2018.12.178
[27]	Xiang, X., Zhu, D. and Wang, D. (2016) Enhanced Formaldehyde Gas Sensing Properties of La-Doped SnO2 Nanoparticles Prepared by Ball-Milling Solid Chemical Reaction Method. Journal of Materials Science: Materials in Electronics, 27, 7425-7432. https://doi.org/10.1007/s10854-016-4718-8
[28]	Ren, H., Zhao, W., Wang, L., Ryu, S.O. and Gu, C. (2015) Preparation of Porous Flower-Like SnO2 Micro/Nano Structures and Their Enhanced Gas Sensing Property. Journal of Alloys and Compounds, 653, 611-618. https://doi.org/10.1016/j.jallcom.2015.09.065
[29]	Li, W., et al. (2015) Enhanced Ethanol Sensing Performance of Hollow ZnO-SnO2 Core-Shell Nanofibers. Sensors and Actuators B: Chemical, 211, 392-402. https://doi.org/10.1016/j.snb.2015.01.090
[30]	Li, Z. and Yi, J. (2017) Enhanced Ethanol Sensing of Ni-Doped SnO2 Hollow Spheres Synthesized by a One-Pot Hydrothermal Method. Sensors and Actuators B: Chemical, 243, 96-103. https://doi.org/10.1016/j.snb.2016.11.136
[31]	Fan, C., et al. (2020) Enhanced H2S Gas Sensing Properties by the Optimization of p-CuO/n-ZnO Composite Nanofibers. Journal of Materials Science, 55, 7702-7714. https://doi.org/10.1007/s10853-020-04569-8