- Email: [email protected]
Facile synthesis and gas sensing properties of hollow urchin-like SnO2 nanospheres synthesized by template-free hydrothermal route
Accepted Manuscript Facile synthesis and gas sensing properties of hollow urchin-like SnO2 nanospheres synthesized by template-free hydrothermal route Cheng Li, Jianhong Zhang, Xingping Ren, Yanping Zhao, Heyun Zhao PII: DOI: Reference:
S0167-577X(19)31022-5 https://doi.org/10.1016/j.matlet.2019.07.036 MLBLUE 26407
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
8 May 2019 2 July 2019 11 July 2019
Please cite this article as: C. Li, J. Zhang, X. Ren, Y. Zhao, H. Zhao, Facile synthesis and gas sensing properties of hollow urchin-like SnO2 nanospheres synthesized by template-free hydrothermal route, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.07.036
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Facile synthesis and gas sensing properties of hollow urchin-like SnO2 nanospheres synthesized by template-free hydrothermal route Cheng Lia,†, Jianhong Zhangb†, Xingping Renb,**, Yanping Zhaoa, Heyun Zhaoa,* a
College of Materials Science and Engineering, Yunnan University, Kunming, 650091, PR China;
b
Yunnan Security and Technology Co. Ltd., Kunming, 650033, PR China;
* Correspondence: [email protected] (H.Z.); Tel: +86-871-65031124; [email protected] (X.R.); Tel: +86871-65180618. †
Cheng Li and Jianhong Zhang contributed equally to this work.
Abstract: Hollow urchin-like SnO2 nanospheres with tetragonal rutile structure were synthesized by a templatefree hydrothermal route. The as-prepared products demonstrated a novel hollow urchin-like nanorods SnO2 nanosphere with the diameter of around 500 nm. It exhibited a high response and selectivity toward ethylene glycol at a lower heating voltage. The excellent ethylene glycol response was attributed to the hollow structures, the nanorods building blocks and the unique architecture structure. Keywords: Tin dioxide; semiconductors; nanorods nanosphere; hydrothermal route; sensor; ethylene glycol.
1. Introduction As a n-type semiconductor with a wide band gap of 3.62 eV, SnO2 is one of the most important functional materials, which has been extensively applied in a variety of fields, especially in gas sensors for detection of various volatile organic compounds (VOCs) [1-3]. Nano-scale 1D (one-dimensional) structures of SnO2, such as nanorods, nanowires and so on, were widely prepared and studied for detection of various VOCs, due to their large active surface area and highly effective electronic transmission [4,5]. However, those structures are easily aggregated and have orientation disorder, since the natural reduction of the overall surface energy by means of the van der Waals forces, etc. [6], which could hinder the electronic transport and the gas diffusion efficient in turn limit the gas-sensitive performances.
Instead, the three-dimensional (3D) hierarchical nanostructure assembled of one-dimensional (1D) units has excellent directionality and overcomes agglomeration, which is an effective and promising configuration for
detection of various VOCs. Therefore, 3D SnO2 hierarchical nanostructures assembled from 1D (e.g. nanorods) structure units with diverse properties are strongly expected to be prepared by a facile, eco-friendly and economical approaches for detection VOCs. Qin et al. prepared sphere-like hierarchical SnO2 structures assembled of nanowires via a template-free hydrothermal approach, which exhibited good sensitivity and selectivity toward acetone at as low as 20 ppm [7]. Hollow SnO2 nanoarray microcubes were fabricated by a simple template-free hydrothermal route and demonstrated superior sensitivity towards ether at the heating voltage of 4.5 V [8]. Zhao et al. synthesized the well-aligned SnO2 nanoarrays through a hydrothermal process which shows an excellent response for isopropanol of 100ppm at 250 oC [9]. Therefore, the development of various 3D SnO2 hierarchical architectures is of great significance for detection of various VOCs. In this work, hollow urchin-like nanorods SnO2 nanospheres, a 3D SnO2 hierarchical nanostructure assembled by nanorods, were successfully synthesized via a template-free hydrothermal route without any substrates. The as-prepared hierarchical structures were applied to fabricate gas sensors to detect ethylene glycol.
2. Experimental All the chemical reagents utilized in the experiment are
of analytical grade. Typically, 0.285 g
Na2SnO3•4H2O was added into 20 mL distilled water under vigorous magnetic stirring for 30 min. Afterwards, 60 mL absolute ethanol was slowly added into the above solution with stirring to get a white suspension solution. The precursor solution was transferred into a 100 mL Teflon-lined autoclave and heated in an oven at 200 oC for 48 h. The precipitates were collected by centrifugation, washed three times with distilled water and absolute ethanol, respectively, and dried at the 80 oC for 24 h to obtain the final product and further characterization. The X-ray diffraction (XRD) measurement was taken on a Rigaku D/MAX-3B diffractometer. The morphology investigation employed an FEI Quanta 200 scanning electron microscope (SEM). The highresolution transmission electron microscopy (TEM, HRTEM) investigations were carried out by a JEOL JEM2100UHR microscope. Raman-scattering spectra was obtained using a Renishaw INVIA Laser Micro-Raman spectrometer. The indirect heating structural gas sensor was elected to investigate the response to ethylene glycol, and the sensing properties were tested by an automatic test system (JF02F, Jin Feng Electronics) using ambient air as the dilute. The sensor response is defined as the ratio of Ra/Rg, where Ra and Rg are the resistance of the sensor in the air and in testing gas, respectively. And the response (τon) and recovery time (τoff) are assessed as the time required to achieve 80-90% of the total response variation when the gas goes in and out. The sensor fabrication and measurement details were seen in the recent reports [10,11].
3. Results and discussion The typical XRD pattern of the prepared SnO2 architecture (shown in Fig. 1a) exhibits sharper and clearer diffraction peaks, indicating a good crystallinity.
All the observed diffraction peaks could be indexed to the
tetragonal rutile structure of SnO2 (JCPDS file no.70-4177). Remarkably enhanced (101) peak are observed, showing the (101) is the favored growth face and the dominant exposed surface is (101), but not (110). It deviates the specific surface energies sequence of (110) < (100) < (101) < (001) of crystalline SnO2 in different crystallographic orientations, which was studied by J Oviedo via computer simulation and reported in reference [12]. Therefore, the SnO2 architectures have high surface energy, leading increase the absorption of oxygen and in turn benefit the gas-sensing performance of the prepared SnO2. Fig. 1b exhibits the Raman spectra of the prepared structure measured at room temperature. Besides the typical peaks at 631.6, 778 and 466.7 cm-1, which are attributed to the A1g, B2g, Eg of the Sn-O vibration modes [13,14], respectively, the other Raman modes at 350 and 577.5 cm-1 are observed. The Raman mode at 578 cm-1 originates strongly from the surface imperfections such as the oxygen vacancy and the surface related defect peak, and the band at 350 cm-1 might be related to the small grain size effect [15]. small grain size effects
The oxygen vacancy and the
are the important reasons for increasing the active points centers for chemical reaction,
improving the adsorption capacity of gas molecules, resulting in the high gas response [9,16]. As shown in Fig. 2a, the nanostructures of SnO2 are composed of typical sphere structures and uniform nanoscale size with a diameter of around 500 nm. The broken surface observed from the inset as shown in Fig. 2b clearly reflects the sphere structure is hollow. TEM images testify the detailed structures of the as-prepared SnO2 as shown in Fig. 2c-d. It is observed that there are dense and long spikes on the outer shell walls and the hollow spherical structure, which likes a sea urchin. The higher magnification TEM image of the single sphere (shown in Fig. 2e) further testified that the surfaces of the hollow urchin-like SnO2 architecture are organized by continuous and dense arrays nanorods. The high-resolution HRTEM images exhibits that the spacing between the adjacent lattice fringes perpendicular to the nanorod growth direction is 0.35 nm, belonging to the (110) planes of rutile SnO2, indicating that the [001] direction is the favored growth direction [17]. Fig. 3 shows the gas response characteristics for ethylene glycol. Fig. 3a shows the responses toward 200 ppm ethylene glycol as a function of the heating voltage. The response continuously increases and reaches its maximum of 108 at 3.1 V. Afterward, it gradually decreases as the heating voltage further increases, which might be related to these factors that the points of absorbed oxygen decrease and the desorption of the gas molecules is overwhelming than the absorption as the increasing heating voltage [4]. As a result, the optimum
operating heating voltage is confirmed as 3.1 V, which is lower than that of the other reported [8]. The dynamic response versus gas concentration curve for ethylene glycol at 3.1 V were
investigated. As
shown in Fig. 3b, the sensor exhibits good sensitivity and reproducibility when it was exposed to various concentrations ethylene glycol. The response and recovery properties are important parameters for gas sensors. The response time (τon) and recovery time (τoff) are measured to be about 21 and 38 s from Fig. 3c, respectively, indicating the response is fast enough to meet the practical application. Fig. 3d reveals the selectivity of the sensor when exposed to various gases at a fixed concentration of 200 ppm at 3.1 V. It can be seen that the response of the sensor to ethylene glycol is around 108, which is much higher than other tested gases, indicating
good selectivity toward ethylene glycol. The selectivity is affected by
several factors, such as the surface structures, the LUMO (lowest unoccupied molecule orbit) energy and the activation energy. For a different value of the LUMO energy, the energy needed for the gas-sensing reaction will be different. This indicates that the conditions of the reaction between the gas molecules and the adsorbed oxygen is not the same for different gases. The ethylene glycol molecule has two hydroxyls at both ends, beneficial for the interaction between the gas and the chemisorbed oxygen. Additionally, the architecture of the as-prepared SnO2 is urchin-like and hollow, which has different activation energy of adsorption compared with other SnO2 structures, leading to adsorb different gases. Hence, ethylene glycol reacts more easily than other gases using the sensor. The gas-sensing mechanism of SnO2 can be summarized as the change of electrical conductivity, caused by chemical reaction between surface oxygen species and reductive gas [18]. The schematic of the excellent sensitive mechanism of nanorods SnO2 nanospheres is demonstrated in Fig. 3e. By comparison with our previous studies on the gas-sensing properties of SnO2 [8], the enhancement in the properties may be ascribed to the hollow structures, the nanorods building blocks and the unique architectures, causing a large surface for more active sites of gas absorption and macroporosity for effective gas diffusion.
4. Conclusion In summary, hollow urchin-like nanorods SnO2 nanospheres were synthesized by a template-free hydrothermal route. Gas sensor fabricated from the as-synthesized hierarchical SnO2 structures shows excellent response, selectivity towards ethylene glycol at a relatively lower heating voltage of 3.1 V. The SnO2 hierarchical structure materials are expected to a promising candidate to detect ethylene glycol applications.
Acknowledgement This work was financially supported by the National Natural Science Foundation of China (Grant no.
61564009, 61161008).
References [1] Y.F. Wang, K.N. Li, C.L. Liang, et al., J. Mater. Chem. 22 (2012) 21495. [2] Y.J. Hong, M.Y. Son, Y.C. Kang, Adv. Mater. 25 (2013) 2279–2283. [3] M.M. Guan, X.R. Zhao, L.B. Duan, et al., J. Appl. Phys. 114 (2013) 114302. [4] J.Y. Liu, M.J. Dai, T.S. Wang, et al., ACS Appl. Mater. Interfaces 8 (2016) 6669−6677. [5] L.Luo, Q.P. Jiang, G.H. Qin er al., Sensors and Actuators B 218 (2015) 205–214. [6] S. Das, V. Jayaraman, Prog. Mater. Sci. 66 (2014) 112–255. [7] L. P. Qin, J. Q. Xu, X. W. Dong, et al., Nanotechnology 19 (2008) 185705. [8] W. J. Wan, Y. H. Li, J. H. Zhang, et al., Mater. Lett. 236 (2019) 46–50. [9] Y. P. Zhao, Y. H. Li, W. J. Wan, et al., Mater. Lett. 218 (2018) 22–26 [10] W.J. Wan, Y.H. Li, X.P. Ren, et al., Nanomaterials 8 (2018) 1–20. [11] Y. Zeng, L. Qiao, Y. Bing, et al., Sens. Actuators, B, 173 (2012) 897–902. [12] Oviedo J, Gillan M. J Surf Sci 463 (2000) 93–101. [13] M. Tarini, N. Prakash, I.K.M.M. Sahib, et al., IEEE J. Photovolt. 7 (2017) 1050–1057. [14] O. Lupana, L. Chow, G. Chai, et al., Mater. Sci. Eng. B 157 (2009) 101–104. [15] L.Z. Lju, X.L. Wu, F. Gao, et al., Solid State Commun. 151 (2011) 811–814. [16] G.H. Qin, F. Gao, Q.P. Jiang, et al., Phys. Chem. Chem. Phys., 18 (2016) 5537–5549. [17] B. Cheng, J.M. Russell, W.S. Shi, et al., J. Am. Chem. Soc. 126 (2004) 5972–5973. [18] C. X. Wang, L. W. Yin, L. Y. Zhang et al., Sensors 10 (2010) 2088–2106.
Figure captions
Fig. 1. (a) XRD patterns; (b) Raman spectra. Fig. 2 (a)-(b) SEM images. Inset indicating the hollow urchin-like SnO2 nanorods. Inset: an urchin picture; (c)-(e) TEM images of hollow urchin-like SnO2 nanorods ball; (f) HRTEM image of the SnO2 nanorods. Inset: an enlarge lattice fringes. Fig. 3 The response of the hollow urchin-like SnO2 nanorods. (a) Dependence of the response on heating voltage; (b) Dynamic response–recovery curve of concentration; (c) Response and recovery times; (d) Selectivity of sensors to various gases. (e) Schematic of the gas-sensing mechanism.
(101)
Fig. 1
Intensity (Counts)
(211)
(110)
577.5 778
10.0k
(321)
(222)
(202)
(112) (301)
40
(310)
(220) (002)
(200)
Intensity/cps
12.0k
80
0
8.0k 6.0k
JCPDS 70-4177 20
b
631.6
Experimental data
160 120
14.0k
a
30
40
50
60
70
2 Theta/Degree
80
90
4.0k 300
466.7
350
400
500
600
700
-1
Raman shift (cm )
800
Fig. 2
a
b
5 μm
c
d
e
f
Fig. 3 120 110 100 90 80 70 60 50 40 30 20 10 0
200
a
800ppm b
180 Heating voltage: 600ppm 400ppm 3.1 V 160
Response (Ra/Rg)
Response (Ra/Rg)
3.1 V
140
200 ppm
120
200ppm
100 80
100ppm
60
50ppm
40
20 20ppm 0 -20 0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Heating Voltage (V)
250 500
c
70 Heating voltage: 3.1 V
Methanal Acetone
50 34 s
40 24s
20
Gas species
Response (Ra/Rg)
d
Methane
60 100 ppm
30
750 1000 1250 1500
Time (s)
Ethyl ether Isopropanol Ammonium
Ethylene glycol
Toluene
10 In
Ethanol
Out Xylene
0 500 520 540 560 580 600 620 640 660
Time (s)
0 10 20 30 40 50 60 70 80 90 100110
Response (Ra/Rg)
e
Conflict of interest statement
The authors declared that they do not have any commercial or associative interest that represents a conflict of interest in connection with the submitted
work.
2019-06-30
Highlights
The hollow urchin-like SnO2 nanospheres were synthesized by a template-free hydrothermal route.
The hollow urchin-like SnO2 architecture were organized by oriented nanorods.
Hollow urchin-like nanorods SnO2 nanosphere exhibited a excellent ethylene glycol response.
The high response was attributed to the hollow structure and the unique architecture structure.
S0167-577X(19)31022-5 https://doi.org/10.1016/j.matlet.2019.07.036 MLBLUE 26407
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
8 May 2019 2 July 2019 11 July 2019
Please cite this article as: C. Li, J. Zhang, X. Ren, Y. Zhao, H. Zhao, Facile synthesis and gas sensing properties of hollow urchin-like SnO2 nanospheres synthesized by template-free hydrothermal route, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.07.036
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Facile synthesis and gas sensing properties of hollow urchin-like SnO2 nanospheres synthesized by template-free hydrothermal route Cheng Lia,†, Jianhong Zhangb†, Xingping Renb,**, Yanping Zhaoa, Heyun Zhaoa,* a
College of Materials Science and Engineering, Yunnan University, Kunming, 650091, PR China;
b
Yunnan Security and Technology Co. Ltd., Kunming, 650033, PR China;
* Correspondence: [email protected] (H.Z.); Tel: +86-871-65031124; [email protected] (X.R.); Tel: +86871-65180618. †
Cheng Li and Jianhong Zhang contributed equally to this work.
Abstract: Hollow urchin-like SnO2 nanospheres with tetragonal rutile structure were synthesized by a templatefree hydrothermal route. The as-prepared products demonstrated a novel hollow urchin-like nanorods SnO2 nanosphere with the diameter of around 500 nm. It exhibited a high response and selectivity toward ethylene glycol at a lower heating voltage. The excellent ethylene glycol response was attributed to the hollow structures, the nanorods building blocks and the unique architecture structure. Keywords: Tin dioxide; semiconductors; nanorods nanosphere; hydrothermal route; sensor; ethylene glycol.
1. Introduction As a n-type semiconductor with a wide band gap of 3.62 eV, SnO2 is one of the most important functional materials, which has been extensively applied in a variety of fields, especially in gas sensors for detection of various volatile organic compounds (VOCs) [1-3]. Nano-scale 1D (one-dimensional) structures of SnO2, such as nanorods, nanowires and so on, were widely prepared and studied for detection of various VOCs, due to their large active surface area and highly effective electronic transmission [4,5]. However, those structures are easily aggregated and have orientation disorder, since the natural reduction of the overall surface energy by means of the van der Waals forces, etc. [6], which could hinder the electronic transport and the gas diffusion efficient in turn limit the gas-sensitive performances.
Instead, the three-dimensional (3D) hierarchical nanostructure assembled of one-dimensional (1D) units has excellent directionality and overcomes agglomeration, which is an effective and promising configuration for
detection of various VOCs. Therefore, 3D SnO2 hierarchical nanostructures assembled from 1D (e.g. nanorods) structure units with diverse properties are strongly expected to be prepared by a facile, eco-friendly and economical approaches for detection VOCs. Qin et al. prepared sphere-like hierarchical SnO2 structures assembled of nanowires via a template-free hydrothermal approach, which exhibited good sensitivity and selectivity toward acetone at as low as 20 ppm [7]. Hollow SnO2 nanoarray microcubes were fabricated by a simple template-free hydrothermal route and demonstrated superior sensitivity towards ether at the heating voltage of 4.5 V [8]. Zhao et al. synthesized the well-aligned SnO2 nanoarrays through a hydrothermal process which shows an excellent response for isopropanol of 100ppm at 250 oC [9]. Therefore, the development of various 3D SnO2 hierarchical architectures is of great significance for detection of various VOCs. In this work, hollow urchin-like nanorods SnO2 nanospheres, a 3D SnO2 hierarchical nanostructure assembled by nanorods, were successfully synthesized via a template-free hydrothermal route without any substrates. The as-prepared hierarchical structures were applied to fabricate gas sensors to detect ethylene glycol.
2. Experimental All the chemical reagents utilized in the experiment are
of analytical grade. Typically, 0.285 g
Na2SnO3•4H2O was added into 20 mL distilled water under vigorous magnetic stirring for 30 min. Afterwards, 60 mL absolute ethanol was slowly added into the above solution with stirring to get a white suspension solution. The precursor solution was transferred into a 100 mL Teflon-lined autoclave and heated in an oven at 200 oC for 48 h. The precipitates were collected by centrifugation, washed three times with distilled water and absolute ethanol, respectively, and dried at the 80 oC for 24 h to obtain the final product and further characterization. The X-ray diffraction (XRD) measurement was taken on a Rigaku D/MAX-3B diffractometer. The morphology investigation employed an FEI Quanta 200 scanning electron microscope (SEM). The highresolution transmission electron microscopy (TEM, HRTEM) investigations were carried out by a JEOL JEM2100UHR microscope. Raman-scattering spectra was obtained using a Renishaw INVIA Laser Micro-Raman spectrometer. The indirect heating structural gas sensor was elected to investigate the response to ethylene glycol, and the sensing properties were tested by an automatic test system (JF02F, Jin Feng Electronics) using ambient air as the dilute. The sensor response is defined as the ratio of Ra/Rg, where Ra and Rg are the resistance of the sensor in the air and in testing gas, respectively. And the response (τon) and recovery time (τoff) are assessed as the time required to achieve 80-90% of the total response variation when the gas goes in and out. The sensor fabrication and measurement details were seen in the recent reports [10,11].
3. Results and discussion The typical XRD pattern of the prepared SnO2 architecture (shown in Fig. 1a) exhibits sharper and clearer diffraction peaks, indicating a good crystallinity.
All the observed diffraction peaks could be indexed to the
tetragonal rutile structure of SnO2 (JCPDS file no.70-4177). Remarkably enhanced (101) peak are observed, showing the (101) is the favored growth face and the dominant exposed surface is (101), but not (110). It deviates the specific surface energies sequence of (110) < (100) < (101) < (001) of crystalline SnO2 in different crystallographic orientations, which was studied by J Oviedo via computer simulation and reported in reference [12]. Therefore, the SnO2 architectures have high surface energy, leading increase the absorption of oxygen and in turn benefit the gas-sensing performance of the prepared SnO2. Fig. 1b exhibits the Raman spectra of the prepared structure measured at room temperature. Besides the typical peaks at 631.6, 778 and 466.7 cm-1, which are attributed to the A1g, B2g, Eg of the Sn-O vibration modes [13,14], respectively, the other Raman modes at 350 and 577.5 cm-1 are observed. The Raman mode at 578 cm-1 originates strongly from the surface imperfections such as the oxygen vacancy and the surface related defect peak, and the band at 350 cm-1 might be related to the small grain size effect [15]. small grain size effects
The oxygen vacancy and the
are the important reasons for increasing the active points centers for chemical reaction,
improving the adsorption capacity of gas molecules, resulting in the high gas response [9,16]. As shown in Fig. 2a, the nanostructures of SnO2 are composed of typical sphere structures and uniform nanoscale size with a diameter of around 500 nm. The broken surface observed from the inset as shown in Fig. 2b clearly reflects the sphere structure is hollow. TEM images testify the detailed structures of the as-prepared SnO2 as shown in Fig. 2c-d. It is observed that there are dense and long spikes on the outer shell walls and the hollow spherical structure, which likes a sea urchin. The higher magnification TEM image of the single sphere (shown in Fig. 2e) further testified that the surfaces of the hollow urchin-like SnO2 architecture are organized by continuous and dense arrays nanorods. The high-resolution HRTEM images exhibits that the spacing between the adjacent lattice fringes perpendicular to the nanorod growth direction is 0.35 nm, belonging to the (110) planes of rutile SnO2, indicating that the [001] direction is the favored growth direction [17]. Fig. 3 shows the gas response characteristics for ethylene glycol. Fig. 3a shows the responses toward 200 ppm ethylene glycol as a function of the heating voltage. The response continuously increases and reaches its maximum of 108 at 3.1 V. Afterward, it gradually decreases as the heating voltage further increases, which might be related to these factors that the points of absorbed oxygen decrease and the desorption of the gas molecules is overwhelming than the absorption as the increasing heating voltage [4]. As a result, the optimum
operating heating voltage is confirmed as 3.1 V, which is lower than that of the other reported [8]. The dynamic response versus gas concentration curve for ethylene glycol at 3.1 V were
investigated. As
shown in Fig. 3b, the sensor exhibits good sensitivity and reproducibility when it was exposed to various concentrations ethylene glycol. The response and recovery properties are important parameters for gas sensors. The response time (τon) and recovery time (τoff) are measured to be about 21 and 38 s from Fig. 3c, respectively, indicating the response is fast enough to meet the practical application. Fig. 3d reveals the selectivity of the sensor when exposed to various gases at a fixed concentration of 200 ppm at 3.1 V. It can be seen that the response of the sensor to ethylene glycol is around 108, which is much higher than other tested gases, indicating
good selectivity toward ethylene glycol. The selectivity is affected by
several factors, such as the surface structures, the LUMO (lowest unoccupied molecule orbit) energy and the activation energy. For a different value of the LUMO energy, the energy needed for the gas-sensing reaction will be different. This indicates that the conditions of the reaction between the gas molecules and the adsorbed oxygen is not the same for different gases. The ethylene glycol molecule has two hydroxyls at both ends, beneficial for the interaction between the gas and the chemisorbed oxygen. Additionally, the architecture of the as-prepared SnO2 is urchin-like and hollow, which has different activation energy of adsorption compared with other SnO2 structures, leading to adsorb different gases. Hence, ethylene glycol reacts more easily than other gases using the sensor. The gas-sensing mechanism of SnO2 can be summarized as the change of electrical conductivity, caused by chemical reaction between surface oxygen species and reductive gas [18]. The schematic of the excellent sensitive mechanism of nanorods SnO2 nanospheres is demonstrated in Fig. 3e. By comparison with our previous studies on the gas-sensing properties of SnO2 [8], the enhancement in the properties may be ascribed to the hollow structures, the nanorods building blocks and the unique architectures, causing a large surface for more active sites of gas absorption and macroporosity for effective gas diffusion.
4. Conclusion In summary, hollow urchin-like nanorods SnO2 nanospheres were synthesized by a template-free hydrothermal route. Gas sensor fabricated from the as-synthesized hierarchical SnO2 structures shows excellent response, selectivity towards ethylene glycol at a relatively lower heating voltage of 3.1 V. The SnO2 hierarchical structure materials are expected to a promising candidate to detect ethylene glycol applications.
Acknowledgement This work was financially supported by the National Natural Science Foundation of China (Grant no.
61564009, 61161008).
References [1] Y.F. Wang, K.N. Li, C.L. Liang, et al., J. Mater. Chem. 22 (2012) 21495. [2] Y.J. Hong, M.Y. Son, Y.C. Kang, Adv. Mater. 25 (2013) 2279–2283. [3] M.M. Guan, X.R. Zhao, L.B. Duan, et al., J. Appl. Phys. 114 (2013) 114302. [4] J.Y. Liu, M.J. Dai, T.S. Wang, et al., ACS Appl. Mater. Interfaces 8 (2016) 6669−6677. [5] L.Luo, Q.P. Jiang, G.H. Qin er al., Sensors and Actuators B 218 (2015) 205–214. [6] S. Das, V. Jayaraman, Prog. Mater. Sci. 66 (2014) 112–255. [7] L. P. Qin, J. Q. Xu, X. W. Dong, et al., Nanotechnology 19 (2008) 185705. [8] W. J. Wan, Y. H. Li, J. H. Zhang, et al., Mater. Lett. 236 (2019) 46–50. [9] Y. P. Zhao, Y. H. Li, W. J. Wan, et al., Mater. Lett. 218 (2018) 22–26 [10] W.J. Wan, Y.H. Li, X.P. Ren, et al., Nanomaterials 8 (2018) 1–20. [11] Y. Zeng, L. Qiao, Y. Bing, et al., Sens. Actuators, B, 173 (2012) 897–902. [12] Oviedo J, Gillan M. J Surf Sci 463 (2000) 93–101. [13] M. Tarini, N. Prakash, I.K.M.M. Sahib, et al., IEEE J. Photovolt. 7 (2017) 1050–1057. [14] O. Lupana, L. Chow, G. Chai, et al., Mater. Sci. Eng. B 157 (2009) 101–104. [15] L.Z. Lju, X.L. Wu, F. Gao, et al., Solid State Commun. 151 (2011) 811–814. [16] G.H. Qin, F. Gao, Q.P. Jiang, et al., Phys. Chem. Chem. Phys., 18 (2016) 5537–5549. [17] B. Cheng, J.M. Russell, W.S. Shi, et al., J. Am. Chem. Soc. 126 (2004) 5972–5973. [18] C. X. Wang, L. W. Yin, L. Y. Zhang et al., Sensors 10 (2010) 2088–2106.
Figure captions
Fig. 1. (a) XRD patterns; (b) Raman spectra. Fig. 2 (a)-(b) SEM images. Inset indicating the hollow urchin-like SnO2 nanorods. Inset: an urchin picture; (c)-(e) TEM images of hollow urchin-like SnO2 nanorods ball; (f) HRTEM image of the SnO2 nanorods. Inset: an enlarge lattice fringes. Fig. 3 The response of the hollow urchin-like SnO2 nanorods. (a) Dependence of the response on heating voltage; (b) Dynamic response–recovery curve of concentration; (c) Response and recovery times; (d) Selectivity of sensors to various gases. (e) Schematic of the gas-sensing mechanism.
(101)
Fig. 1
Intensity (Counts)
(211)
(110)
577.5 778
10.0k
(321)
(222)
(202)
(112) (301)
40
(310)
(220) (002)
(200)
Intensity/cps
12.0k
80
0
8.0k 6.0k
JCPDS 70-4177 20
b
631.6
Experimental data
160 120
14.0k
a
30
40
50
60
70
2 Theta/Degree
80
90
4.0k 300
466.7
350
400
500
600
700
-1
Raman shift (cm )
800
Fig. 2
a
b
5 μm
c
d
e
f
Fig. 3 120 110 100 90 80 70 60 50 40 30 20 10 0
200
a
800ppm b
180 Heating voltage: 600ppm 400ppm 3.1 V 160
Response (Ra/Rg)
Response (Ra/Rg)
3.1 V
140
200 ppm
120
200ppm
100 80
100ppm
60
50ppm
40
20 20ppm 0 -20 0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Heating Voltage (V)
250 500
c
70 Heating voltage: 3.1 V
Methanal Acetone
50 34 s
40 24s
20
Gas species
Response (Ra/Rg)
d
Methane
60 100 ppm
30
750 1000 1250 1500
Time (s)
Ethyl ether Isopropanol Ammonium
Ethylene glycol
Toluene
10 In
Ethanol
Out Xylene
0 500 520 540 560 580 600 620 640 660
Time (s)
0 10 20 30 40 50 60 70 80 90 100110
Response (Ra/Rg)
e
Conflict of interest statement
The authors declared that they do not have any commercial or associative interest that represents a conflict of interest in connection with the submitted
work.
2019-06-30
Highlights
The hollow urchin-like SnO2 nanospheres were synthesized by a template-free hydrothermal route.
The hollow urchin-like SnO2 architecture were organized by oriented nanorods.
Hollow urchin-like nanorods SnO2 nanosphere exhibited a excellent ethylene glycol response.
The high response was attributed to the hollow structure and the unique architecture structure.