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Formaldehyde sensing characteristics of hydrothermally synthesized Zn2SnO4 nanocubes
Materials Letters 259 (2020) 126896
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Formaldehyde sensing characteristics of hydrothermally synthesized Zn2SnO4 nanocubes Y. Tie, S.Y. Ma ⇑, S.T. Pei, K.M. Zhu, Q.X. Zhang, R. Zhang, B.J. Wang, J.L. Zhang, X.H. Xu, T. Han, W.W. Liu, P.F. Cao, Y. Ma Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
a r t i c l e
i n f o
Article history: Received 2 August 2019 Received in revised form 6 October 2019 Accepted 27 October 2019 Available online 30 October 2019 Keywords: Zn2SnO4 nanocube Mechanism Sensor Microstructure Semiconductor
a b s t r a c t Metal oxide semiconductor-based gas sensor preferentially possessing great attention due to its outstanding gas sensing performances. Nevertheless, monobasic oxides could not tackle problems such as high operating temperature, poor selectivity and durability. Here, a facile and cost-efficient hydrothermal method has been exploited to produce Zn2SnO4 nanocube as a multi-oxide semiconductor formaldehyde gas sensor. The fabricated gas sensor exhibited remarkable response value (Rair/Rgas = 23.57) and response/recovery time (15/17 s) to 50 ppm formaldehyde at the optimal operating temperature of 230 °C, respectively. The excellent gas sensing mechanism of sensor is carefully discussed which can be attributed to large specific surface area (24.83 m2/g), distinct nanocube structure and high pore size (83.19 nm). Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Formaldehyde (HCHO) is widely used in the chemical, wood industry, textile industry, anti-corrosion and other fields. Due to its serious toxicity and low-concentration (15 ppm) can lead to acute damages to health [1]. Consequently, it is an emergency to carry out effective and accurate detection of formaldehyde gas. Zn2SnO4 with low visible absorption, high electrical conductivity and high electron mobility, has been widely used in many fields such as photoelectrochemical [2] and gas sensor [3]. In the past few years, there have been many reports on the hydrothermal synthesis of Zn2SnO4. For example, Zn2SnO4 nanoflowers have been successfully synthesized under a simple hydrothermal method in the presence of CTAB and EDA, resulting in an enhanced sensing performance to ethanol [3]. Zn2SnO4 microcubes were prepared by hydrothermal conditions using NaOH [4]. Therefore, the hydrothermal method with CTAB and NaOH can be a reliable approach to synthesize Zn2SnO4 nanocube. In addition, as formaldehyde easily combines with water, environmental humidity was considered for gas sensing mechanism of Zn2SnO4 sensors [5]. In this work, we take advantage of a facile hydrothermal method to synthesize Zn2SnO4 nanocube in the presence of CTAB ⇑ Corresponding author. E-mail address: [email protected] (S.Y. Ma). https://doi.org/10.1016/j.matlet.2019.126896 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
and NaOH. The Zn2SnO4 nanocube presents an excellent crystal structure and gas sensing performance to formaldehyde. Furthermore, the gas sensing mechanism of sensor is carefully and rigorously discussed. 2. Experimental Zn2SnO4 nanocube was synthesized by hydrothermal method, the hydrothermal procedure was given as follows: 0.22 g Zn(CH3COO)22H2O and 0.20 g SnCl45H2O were dissolved in a mixed solution which contains 10 ml of ethanol and 10 ml of deionized water. At the same time, 0.3 g of NaOH and 0.35 g of CTAB were dissolved in 15 ml of deionized water. Subsequently, the above two solutions were mixed and stirred at 35 °C for 1 h to obtain a uniform solution. Secondly, the solution was transferred to a 50 ml Teflon-lined stainless steel autoclave and heated at 120 °C for 24 h. After the autoclave cooled naturally to room temperature, the reaction product was collected and washed several times with ethanol and deionized water alternately and dried in air at 80 °C. The samples was placed into a tube furnace and annealed at 600 °C for 2 h. X-ray diffraction (XRD, D8 Advance, Bruker AXS) using Cu Ka1 radiation (k = 0.15403 nm) was carried out to exam the crystal structures and composition. The microstructures were visualized by scanning electron microscopy (SEM, JEOL, JSM-5510LV) and transmission electron microscopy (TEM, 1200 EX, JEOL, Japan).
2
Y. Tie et al. / Materials Letters 259 (2020) 126896
The specific surface area and pore size were investigated using N2 adsorption-desorption apparatus Micromeritics 3Flex Surface Characterization Analyzer. Gas sensing properties were investigated by the WS-30A gas sensing measurement system (Wei Sheng Electronics Science and Technology Co., Ltd., Henan Province, China). To investigate gas sensing properties directly, the response was defined as Ra/Rg for reducing gas. The response and recovery time were counted as the time taken to complete 90% of the total resistance change [6].
3. Results and discussion Fig. 1(a) illustrates the XRD patterns of the Zn2SnO4 products. All the sharp diffraction peaks are consistent with the inverse spinel Zn2SnO4 (JCPDS: 24-1470) indicating the high crystallinity of Zn2SnO4. As illustrated in Fig. 1(b), nitrogen adsorptiondesorption measurement was carried out for Zn2SnO4 in order to detect the specific surface area and porosity. The nitrogen adsorption-desorption isotherms contribute to type IV and H3
Fig. 1. (a) XRD pattern of Zn2SnO4, (b) Nitrogen adsorption–desorption isotherm and pore size distribution plot (inset) of Zn2SnO4.
Fig. 2. (a–c) The low and high magnification SEM images of Zn2SnO4 nanocube, (d) Low magnification TEM and (e–f) HRTEM micrograph and SAED pattern of Zn2SnO4 nanocube.
3
Y. Tie et al. / Materials Letters 259 (2020) 126896
Fig. 3. (a) The response of the synthesized samples to 50 ppm formaldehyde under different operating temperatures; (b) the response of the synthesized samples to various test gases (concentration of 50 ppm) at 230 °C; (c) Response versus time curves of Zn2SnO4 nanocube to 5–200 ppm formaldehyde consecutively; (d) dynamic sensing transient of Zn2SnO4 nanocube to 50 ppm formaldehyde; (e) The response of the synthesized samples to different formaldehyde concentrations ranging from 10 to 2000 ppm; (f) Plot of ln(S-1) and ln(C) for Zn2SnO4 toward 5–100 ppm formaldehyde at 230 °C.
Table 1 Comparison of formaldehyde sensing ability of different gas sensors. Materials
Morphology
Con/ppm
Tem/°C
Response
Ref.
Y-SnO2 Zn2SnO4/SnO2 ZnSnO3 Ag-SnO2 Zn2SnO4
Nanoflowers Porous hollow microspheres Multishelled cubes Nanoparticle Nanocubes
50 100 100 10 100
180 330 220 125 230
18 ~40 37.2 14.4 40.8
[9] [10] [11] [12] Present work
hysteresis loop, indicating that the Zn2SnO4 sample is macropore materials. The test result shows that the BET specific surface area of Zn2SnO4 is 24.83 m2/g and the BJH Adsorption average pore width is 83.19 nm. The macropore structure and larger specific area enable to promote the transportation and diffusion of target gas, which ameliorates gas sensing performance [7].
The morphology and microstructures of Zn2SnO4 sample were shown in Fig. 2. As depicted in Fig. 2(a, b), the sample is a cubeshaped and uniformly nano-sized with an average diameter of about 517 nm. The higher magnification SEM image is illustrated in Fig. 2(b, c), where vividly depicts that the surface of nanocube is concave-convex and distributed with some small pores. TEM
4
Y. Tie et al. / Materials Letters 259 (2020) 126896
and HRTEM were further utilized to detect the morphology and crystal structure of Zn2SnO4 nanocube. Fig. 2(e) and (f) clearly show the interplanar spacing of 0.304 and 0.497 nm which match with (2 2 0) and (1 1 1) crystal planes of Zn2SnO4. The polymorphic property of Zn2SnO4 is further confirmed by inset of Fig. 2(f). The optimum operating temperature is an important parameter for gas sensors, so we first measure the optimal operating temperature of Zn2SnO4 nanocube sensor. Fig. 3(a) shows the Zn2SnO4 nanocube sensor to 50 ppm formaldehyde at different temperatures (130–330 °C). It is obviously found that the temperature response curve displays a tendency that as the temperature augments, the response value is first increased to the maximum value and then decreased. The maximum response value is 23.57 at 230 °C which is applied in following experiment tests. To investigate the selectivity of the Zn2SnO4 nanocube sensor, the responses toward 6 kinds of gases (50 ppm of formaldehyde, ethanol, acetic acid, acetone, methanol and Benzene) are depicted in Fig. 3(b). It can be seen Zn2SnO4 nanocube shows the maximum response to formaldehyde, and response value is 1.26–8.89 times higher than other gases indicating that Zn2SnO4 have a good selectivity to formaldehyde. The excellent selectivity can be ascribed to the different reducibility between the testing gases and their adsorption capacity on the sensing material [8,9]. As illustrated in Fig. 3(c), the response of Zn2SnO4 nanocube sensors toward formaldehyde with 5, 10, 25, 50, 100, 200 ppm are 4.6, 6.8, 11.7, 23.6, 40.8 and 79.8. It can be seen that the response curve rises rapidly when injecting formaldehyde and decreases rapidly after exposure to air. Meanwhile, after six consecutive gas sensitive test, our sensor can maintain stable and restore as ever, which also verifies the stability and durability of the sensor. As indicated in Fig. 3(d), the response and recovery times of Zn2SnO4 nanocube to 50 ppm formaldehyde are 15 and 17 s. Fig. 3(e) depicts the response of Zn2SnO4 nanocube to different formaldehyde concentrations at 230 °C. It can be found when the concentration is in the range of 5–200 ppm, the response value increases linearly with the increase of concentration. If the concentration exceeds 200 ppm, the growth trend shows a significant saturation phenomenon. Usually, the linear relationship between response and concentration is fitted and evaluated using a logarithmic coordinate system over a relatively low concentration range [10]. As shown in Fig. 3(f), the fitted formula is ln(S-1) = 0.73489ln (C) + 0.25373 (R2 = 0.9831, where R2 is the linear correlation coefficient), which can conclude that our sensor is suitable for low concentration formaldehyde detection. The differences between other formaldehyde gas sensors [11–14] and present work are listed in Table 1. In general, the mechanism of n-type semiconductor gas sensor is explained in terms of Wolkenstein’s model [15]. For Zn2SnO4 nanocube sensors, when it is in air ambience, oxygen molecules adsorb on the surface of the material and combine with electrons
is a strong hydrogen bond between hydroxyl groups and formaldehyde [17], which can accelerate the reaction with formaldehyde [18] thereby enhancing its response time. On the other hand, according to the theory of Knudsen diffusion [19], the rate of gas diffusion depends on pore width, temperature and molecular weight. The BET test reveals that pore width of Zn2SnO4 nanocube is 83.19 nm, which demonstrates a high diffusing rate. Furthermore, the distinct nanocube structure and large specific surface area are also important factors to enhance the gas sensing properties.
to produce oxygen anions (O-2 , O- , O2- ), increasing the resistance of the sensor. Conversely, when it is in formaldehyde atmosphere, formaldehyde reacts with the oxygen anion to release the electrons back to the material, which decreases the resistance of the sensor. According to the above test, superior gas sensitivity can be attributed to two factors. On one hand, Zn2SnO4 particles react with water molecules and oxygen anions to produce a composition of terminal hydroxyl groups [16] such as Sn-OH and Zn-OH. There
[14] [15]
4. Conclusion The hydrothermal method with CTAB and NaOH was applied to prepare Zn2SnO4 nanocube and the gas sensing properties was discussed at length. Various techniques such as SEM, TEM, and BET were used to detect the microstructure and morphology of materials. The sensor based on Zn2SnO4 nanocube had remarkable sensing properties to 50 ppm formaldehyde at 230 °C. Forasmuch, Zn2SnO4 nanocube sensor was a potential candidate material for rapid and effective detection of formaldehyde. 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. Acknowledgements This work was supported by the National Natural Science Foundations of China (Grant No. 11864034 and 51562035), and the Scientific Research Project of Gansu Province (Grant No. 18JR3RA089 and 17JR5RA072). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
[16] [17] [18] [19]
B. Geng, C. Fang, F. Zhan, et al., Small 4 (9) (2008) 1337–1343. M.A. Alpuche-Aviles, Y. Wu, J. Am. Chem. Soc. 131 (9) (2009) 3216–3224. Z. Chen, M. Cao, C. Hu, J. Phys. Chem. C 115 (13) (2011) 5522–5529. H.M. Yang, S.Y. Ma, H.Y. Jiao, et al., Mater. Lett. 182 (2016) 264–268. Z. Wang, A. Sackmann, S. Gao, et al., Sens. Actuators B 285 (2019) 590–600. L. Dai, L. Wang, G.J. Shao, et al., J. Alloys Compd. 526 (2012) 145–150. R. Zhang, Y. He, L. Xu, J. Mater. Chem. A 2 (42) (2014) 17979–17985. J. Sun, S. Bai, Y. Tian, et al., Sens. Actuators B 257 (2018) 29–36. L. Shi, J. Cui, F. Zhao, et al., Phys. Chem. Chem. Phys. 17 (46) (2015) 31316– 31323. N. Hongsith, E. Wongrat, T. Kerdcharoen, et al., Sens. Actuators B 144 (1) (2010) 67–72. K. Zhu, S. Ma, Y. Tie, et al., J. Alloys Compd. 792 (2019) 938–944. G. Sun, G. Ma, Y. Li, et al., Mater. Lett. 191 (2017) 145–149. T. Zhou, T. Zhang, R. Zhang, et al., ACS Appl. Mater. Interfaces 9 (16) (2017) 14525–14533. D. Liu, J. Pan, J. Tang, et al., J. Phys. Chem. Solids 124 (2019) 36–43. H. Haick, M. Ambrico, T. Ligonzo, et al., J. Am. Chem. Soc. 128 (21) (2006) 6854–6869. D. Koziej, N. Bârsan, U. Weimar, et al., Chem. Phys. Lett. 410 (4–6) (2005) 321– 323. R. Rivelino, J. Phys. Chem. A 112 (2) (2008) 161–165. C. Zhang, H. He, Catal. Today 126 (3–4) (2007) 345–350. G. Sakai, N. Matsunaga, K. Shimanoe, et al., Sens. Actuators B 80 (2) (2001) 125–131.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Formaldehyde sensing characteristics of hydrothermally synthesized Zn2SnO4 nanocubes Y. Tie, S.Y. Ma ⇑, S.T. Pei, K.M. Zhu, Q.X. Zhang, R. Zhang, B.J. Wang, J.L. Zhang, X.H. Xu, T. Han, W.W. Liu, P.F. Cao, Y. Ma Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
a r t i c l e
i n f o
Article history: Received 2 August 2019 Received in revised form 6 October 2019 Accepted 27 October 2019 Available online 30 October 2019 Keywords: Zn2SnO4 nanocube Mechanism Sensor Microstructure Semiconductor
a b s t r a c t Metal oxide semiconductor-based gas sensor preferentially possessing great attention due to its outstanding gas sensing performances. Nevertheless, monobasic oxides could not tackle problems such as high operating temperature, poor selectivity and durability. Here, a facile and cost-efficient hydrothermal method has been exploited to produce Zn2SnO4 nanocube as a multi-oxide semiconductor formaldehyde gas sensor. The fabricated gas sensor exhibited remarkable response value (Rair/Rgas = 23.57) and response/recovery time (15/17 s) to 50 ppm formaldehyde at the optimal operating temperature of 230 °C, respectively. The excellent gas sensing mechanism of sensor is carefully discussed which can be attributed to large specific surface area (24.83 m2/g), distinct nanocube structure and high pore size (83.19 nm). Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Formaldehyde (HCHO) is widely used in the chemical, wood industry, textile industry, anti-corrosion and other fields. Due to its serious toxicity and low-concentration (15 ppm) can lead to acute damages to health [1]. Consequently, it is an emergency to carry out effective and accurate detection of formaldehyde gas. Zn2SnO4 with low visible absorption, high electrical conductivity and high electron mobility, has been widely used in many fields such as photoelectrochemical [2] and gas sensor [3]. In the past few years, there have been many reports on the hydrothermal synthesis of Zn2SnO4. For example, Zn2SnO4 nanoflowers have been successfully synthesized under a simple hydrothermal method in the presence of CTAB and EDA, resulting in an enhanced sensing performance to ethanol [3]. Zn2SnO4 microcubes were prepared by hydrothermal conditions using NaOH [4]. Therefore, the hydrothermal method with CTAB and NaOH can be a reliable approach to synthesize Zn2SnO4 nanocube. In addition, as formaldehyde easily combines with water, environmental humidity was considered for gas sensing mechanism of Zn2SnO4 sensors [5]. In this work, we take advantage of a facile hydrothermal method to synthesize Zn2SnO4 nanocube in the presence of CTAB ⇑ Corresponding author. E-mail address: [email protected] (S.Y. Ma). https://doi.org/10.1016/j.matlet.2019.126896 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
and NaOH. The Zn2SnO4 nanocube presents an excellent crystal structure and gas sensing performance to formaldehyde. Furthermore, the gas sensing mechanism of sensor is carefully and rigorously discussed. 2. Experimental Zn2SnO4 nanocube was synthesized by hydrothermal method, the hydrothermal procedure was given as follows: 0.22 g Zn(CH3COO)22H2O and 0.20 g SnCl45H2O were dissolved in a mixed solution which contains 10 ml of ethanol and 10 ml of deionized water. At the same time, 0.3 g of NaOH and 0.35 g of CTAB were dissolved in 15 ml of deionized water. Subsequently, the above two solutions were mixed and stirred at 35 °C for 1 h to obtain a uniform solution. Secondly, the solution was transferred to a 50 ml Teflon-lined stainless steel autoclave and heated at 120 °C for 24 h. After the autoclave cooled naturally to room temperature, the reaction product was collected and washed several times with ethanol and deionized water alternately and dried in air at 80 °C. The samples was placed into a tube furnace and annealed at 600 °C for 2 h. X-ray diffraction (XRD, D8 Advance, Bruker AXS) using Cu Ka1 radiation (k = 0.15403 nm) was carried out to exam the crystal structures and composition. The microstructures were visualized by scanning electron microscopy (SEM, JEOL, JSM-5510LV) and transmission electron microscopy (TEM, 1200 EX, JEOL, Japan).
2
Y. Tie et al. / Materials Letters 259 (2020) 126896
The specific surface area and pore size were investigated using N2 adsorption-desorption apparatus Micromeritics 3Flex Surface Characterization Analyzer. Gas sensing properties were investigated by the WS-30A gas sensing measurement system (Wei Sheng Electronics Science and Technology Co., Ltd., Henan Province, China). To investigate gas sensing properties directly, the response was defined as Ra/Rg for reducing gas. The response and recovery time were counted as the time taken to complete 90% of the total resistance change [6].
3. Results and discussion Fig. 1(a) illustrates the XRD patterns of the Zn2SnO4 products. All the sharp diffraction peaks are consistent with the inverse spinel Zn2SnO4 (JCPDS: 24-1470) indicating the high crystallinity of Zn2SnO4. As illustrated in Fig. 1(b), nitrogen adsorptiondesorption measurement was carried out for Zn2SnO4 in order to detect the specific surface area and porosity. The nitrogen adsorption-desorption isotherms contribute to type IV and H3
Fig. 1. (a) XRD pattern of Zn2SnO4, (b) Nitrogen adsorption–desorption isotherm and pore size distribution plot (inset) of Zn2SnO4.
Fig. 2. (a–c) The low and high magnification SEM images of Zn2SnO4 nanocube, (d) Low magnification TEM and (e–f) HRTEM micrograph and SAED pattern of Zn2SnO4 nanocube.
3
Y. Tie et al. / Materials Letters 259 (2020) 126896
Fig. 3. (a) The response of the synthesized samples to 50 ppm formaldehyde under different operating temperatures; (b) the response of the synthesized samples to various test gases (concentration of 50 ppm) at 230 °C; (c) Response versus time curves of Zn2SnO4 nanocube to 5–200 ppm formaldehyde consecutively; (d) dynamic sensing transient of Zn2SnO4 nanocube to 50 ppm formaldehyde; (e) The response of the synthesized samples to different formaldehyde concentrations ranging from 10 to 2000 ppm; (f) Plot of ln(S-1) and ln(C) for Zn2SnO4 toward 5–100 ppm formaldehyde at 230 °C.
Table 1 Comparison of formaldehyde sensing ability of different gas sensors. Materials
Morphology
Con/ppm
Tem/°C
Response
Ref.
Y-SnO2 Zn2SnO4/SnO2 ZnSnO3 Ag-SnO2 Zn2SnO4
Nanoflowers Porous hollow microspheres Multishelled cubes Nanoparticle Nanocubes
50 100 100 10 100
180 330 220 125 230
18 ~40 37.2 14.4 40.8
[9] [10] [11] [12] Present work
hysteresis loop, indicating that the Zn2SnO4 sample is macropore materials. The test result shows that the BET specific surface area of Zn2SnO4 is 24.83 m2/g and the BJH Adsorption average pore width is 83.19 nm. The macropore structure and larger specific area enable to promote the transportation and diffusion of target gas, which ameliorates gas sensing performance [7].
The morphology and microstructures of Zn2SnO4 sample were shown in Fig. 2. As depicted in Fig. 2(a, b), the sample is a cubeshaped and uniformly nano-sized with an average diameter of about 517 nm. The higher magnification SEM image is illustrated in Fig. 2(b, c), where vividly depicts that the surface of nanocube is concave-convex and distributed with some small pores. TEM
4
Y. Tie et al. / Materials Letters 259 (2020) 126896
and HRTEM were further utilized to detect the morphology and crystal structure of Zn2SnO4 nanocube. Fig. 2(e) and (f) clearly show the interplanar spacing of 0.304 and 0.497 nm which match with (2 2 0) and (1 1 1) crystal planes of Zn2SnO4. The polymorphic property of Zn2SnO4 is further confirmed by inset of Fig. 2(f). The optimum operating temperature is an important parameter for gas sensors, so we first measure the optimal operating temperature of Zn2SnO4 nanocube sensor. Fig. 3(a) shows the Zn2SnO4 nanocube sensor to 50 ppm formaldehyde at different temperatures (130–330 °C). It is obviously found that the temperature response curve displays a tendency that as the temperature augments, the response value is first increased to the maximum value and then decreased. The maximum response value is 23.57 at 230 °C which is applied in following experiment tests. To investigate the selectivity of the Zn2SnO4 nanocube sensor, the responses toward 6 kinds of gases (50 ppm of formaldehyde, ethanol, acetic acid, acetone, methanol and Benzene) are depicted in Fig. 3(b). It can be seen Zn2SnO4 nanocube shows the maximum response to formaldehyde, and response value is 1.26–8.89 times higher than other gases indicating that Zn2SnO4 have a good selectivity to formaldehyde. The excellent selectivity can be ascribed to the different reducibility between the testing gases and their adsorption capacity on the sensing material [8,9]. As illustrated in Fig. 3(c), the response of Zn2SnO4 nanocube sensors toward formaldehyde with 5, 10, 25, 50, 100, 200 ppm are 4.6, 6.8, 11.7, 23.6, 40.8 and 79.8. It can be seen that the response curve rises rapidly when injecting formaldehyde and decreases rapidly after exposure to air. Meanwhile, after six consecutive gas sensitive test, our sensor can maintain stable and restore as ever, which also verifies the stability and durability of the sensor. As indicated in Fig. 3(d), the response and recovery times of Zn2SnO4 nanocube to 50 ppm formaldehyde are 15 and 17 s. Fig. 3(e) depicts the response of Zn2SnO4 nanocube to different formaldehyde concentrations at 230 °C. It can be found when the concentration is in the range of 5–200 ppm, the response value increases linearly with the increase of concentration. If the concentration exceeds 200 ppm, the growth trend shows a significant saturation phenomenon. Usually, the linear relationship between response and concentration is fitted and evaluated using a logarithmic coordinate system over a relatively low concentration range [10]. As shown in Fig. 3(f), the fitted formula is ln(S-1) = 0.73489ln (C) + 0.25373 (R2 = 0.9831, where R2 is the linear correlation coefficient), which can conclude that our sensor is suitable for low concentration formaldehyde detection. The differences between other formaldehyde gas sensors [11–14] and present work are listed in Table 1. In general, the mechanism of n-type semiconductor gas sensor is explained in terms of Wolkenstein’s model [15]. For Zn2SnO4 nanocube sensors, when it is in air ambience, oxygen molecules adsorb on the surface of the material and combine with electrons
is a strong hydrogen bond between hydroxyl groups and formaldehyde [17], which can accelerate the reaction with formaldehyde [18] thereby enhancing its response time. On the other hand, according to the theory of Knudsen diffusion [19], the rate of gas diffusion depends on pore width, temperature and molecular weight. The BET test reveals that pore width of Zn2SnO4 nanocube is 83.19 nm, which demonstrates a high diffusing rate. Furthermore, the distinct nanocube structure and large specific surface area are also important factors to enhance the gas sensing properties.
to produce oxygen anions (O-2 , O- , O2- ), increasing the resistance of the sensor. Conversely, when it is in formaldehyde atmosphere, formaldehyde reacts with the oxygen anion to release the electrons back to the material, which decreases the resistance of the sensor. According to the above test, superior gas sensitivity can be attributed to two factors. On one hand, Zn2SnO4 particles react with water molecules and oxygen anions to produce a composition of terminal hydroxyl groups [16] such as Sn-OH and Zn-OH. There
[14] [15]
4. Conclusion The hydrothermal method with CTAB and NaOH was applied to prepare Zn2SnO4 nanocube and the gas sensing properties was discussed at length. Various techniques such as SEM, TEM, and BET were used to detect the microstructure and morphology of materials. The sensor based on Zn2SnO4 nanocube had remarkable sensing properties to 50 ppm formaldehyde at 230 °C. Forasmuch, Zn2SnO4 nanocube sensor was a potential candidate material for rapid and effective detection of formaldehyde. 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. Acknowledgements This work was supported by the National Natural Science Foundations of China (Grant No. 11864034 and 51562035), and the Scientific Research Project of Gansu Province (Grant No. 18JR3RA089 and 17JR5RA072). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
[16] [17] [18] [19]
B. Geng, C. Fang, F. Zhan, et al., Small 4 (9) (2008) 1337–1343. M.A. Alpuche-Aviles, Y. Wu, J. Am. Chem. Soc. 131 (9) (2009) 3216–3224. Z. Chen, M. Cao, C. Hu, J. Phys. Chem. C 115 (13) (2011) 5522–5529. H.M. Yang, S.Y. Ma, H.Y. Jiao, et al., Mater. Lett. 182 (2016) 264–268. Z. Wang, A. Sackmann, S. Gao, et al., Sens. Actuators B 285 (2019) 590–600. L. Dai, L. Wang, G.J. Shao, et al., J. Alloys Compd. 526 (2012) 145–150. R. Zhang, Y. He, L. Xu, J. Mater. Chem. A 2 (42) (2014) 17979–17985. J. Sun, S. Bai, Y. Tian, et al., Sens. Actuators B 257 (2018) 29–36. L. Shi, J. Cui, F. Zhao, et al., Phys. Chem. Chem. Phys. 17 (46) (2015) 31316– 31323. N. Hongsith, E. Wongrat, T. Kerdcharoen, et al., Sens. Actuators B 144 (1) (2010) 67–72. K. Zhu, S. Ma, Y. Tie, et al., J. Alloys Compd. 792 (2019) 938–944. G. Sun, G. Ma, Y. Li, et al., Mater. Lett. 191 (2017) 145–149. T. Zhou, T. Zhang, R. Zhang, et al., ACS Appl. Mater. Interfaces 9 (16) (2017) 14525–14533. D. Liu, J. Pan, J. Tang, et al., J. Phys. Chem. Solids 124 (2019) 36–43. H. Haick, M. Ambrico, T. Ligonzo, et al., J. Am. Chem. Soc. 128 (21) (2006) 6854–6869. D. Koziej, N. Bârsan, U. Weimar, et al., Chem. Phys. Lett. 410 (4–6) (2005) 321– 323. R. Rivelino, J. Phys. Chem. A 112 (2) (2008) 161–165. C. Zhang, H. He, Catal. Today 126 (3–4) (2007) 345–350. G. Sakai, N. Matsunaga, K. Shimanoe, et al., Sens. Actuators B 80 (2) (2001) 125–131.