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Fe2O3 multilayer nanosheets for high sensitive acetone detection
Materials Letters 221 (2018) 57–61
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Controllable assembly of sandwich-structured SnO2/Fe2O3 multilayer nanosheets for high sensitive acetone detection Junping Liu, Yanzhe Wang, Lianqiang Wang, Hongwei Tian, Yi Zeng ⇑ College of Materials Science and Engineering, Key Laboratory of Automobile Materials of Ministry of Educations, and State Key Laboratory of Superhard Materials, Jilin University, Changchun, China
a r t i c l e
i n f o
Article history: Received 3 February 2018 Received in revised form 14 March 2018 Accepted 17 March 2018 Available online 17 March 2018 Keywords: Tin oxide Ferric oxide Multilayered structure Heterostructure Gas sensor
a b s t r a c t A new type of hierarchically nonspherical architecture with sandwich-structured multilayer nanosheets has been successfully prepared via a controllable multistep approach in case of SnO2/Fe2O3 heterostructures. The morphological characterization reveals that unique sandwich-structured SnO2/Fe2O3 multilayer nanosheets (MNSs) are constructed via the self-assembly of densely well-aligned Fe2O3 nanorod layers to cover and fill the interlayers of hexagonal SnO2 hollow multilayer nanosheets (HMNs). When used as the sensing materials for acetone detection, the sandwich hetero-nanostructures demonstrate evidently improved sensing performance compared to pure SnO2. The significantly improved sensing performance can be attributed not only to the rational microstructures for fast transfer of gas molecules, but also to the additional effects of loaded Fe2O3 ultrathin nanorods. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Semiconducting metal oxides, as one type of promising candidates for gas-sensing materials, have attracted tremendous attention owing to their low cost, easily tunable structural and sensing characters in detecting various target gases [1]. From the materials perspective, rational design of hierarchically porous or hollow architectures of desired candidates has been widely recognized as an effective route for the boost of their gas-sensing performances [2–4]. Beyond the strategy of optimizing material structures, hybrid-composite design is also proved to be highly desirable with respect to a dramatic improvement in the sensing performances in virtue of tunable composition and synergistic effect. In the case of n-type semiconducting oxides, tin dioxide (SnO2) has long been applied as an appealing sensing material with various shapes in detecting diverse gas species [5–9]. In the past few years, broadening the sensing materials from singlecomponent SnO2 to SnO2 matrix heterostructures, such as SnO2/Au, SnO2/Pd, SnO2/ZnO, SnO2/Fe2O3, SnO2/TiO2, and so on [10–14], has received more attention and significantly improved the performances. Despite considerable efforts being dedicated to integrate the fascinating merits of proper configuration and synergistic contribution, facile assembly of heterogeneous lowdimensional subunits on another oxide matrix often encounters ⇑ Corresponding author. E-mail address: [email protected] (Y. Zeng). https://doi.org/10.1016/j.matlet.2018.03.084 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
the compatibility issue, and in fact the resulting heterostructures are usually degraded to dense-agglomerated form. Understanding key factors for constructing heterogeneous oxides with desired porous architecture by a simple and economical route still remains challenging yet highly desirable. In this work, we present a multistep route for unique sandwichstructured SnO2/Fe2O3 MNSs through covering ultrathin Fe2O3 nanorod-assembled layers on all surfaces of hexagonal SnO2 HMNs. The morphology and microstructure of as-obtained SnO2/ Fe2O3 MNSs are examined. Benefitting from the porous feature and highly interconnected heterogeneous interfaces of SnO2/ Fe2O3 MNSs, the improved gas-sensing performances of the obtained SnO2/Fe2O3 MNSs can be anticipated. 2. Experimental All the chemical reagents are of analytical grade as purchased from Sinopharm Chemical Reagent Co. Ltd (China) and used without further purification. The route for SnO2 HMNs is according to our previous report with some modifications [15]. As for the final SnO2/Fe2O3 MNSs, the as-obtained SnO2 (20 mg) was dispersed into 40 mL of aqueous solution, including Na2SO410H2O (85.8 mg) and FeCl36H2O (71.6 mg). After stirring for 10 min, this suspension was transferred into a Teflon-lined stainless steel autoclave, sealed tightly, and then maintained at 120 °C for 2 h. After cooled naturally down to room temperature, the dark-red precipitates were centrifugally separated, washed with absolute
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ethanol/DI water for several times, and dried at 60 °C overnight. Finally, the precipitates were annealed at 450 °C for 2 h with a ramping rate of 5 °C min 1 to obtain the final SnO2/Fe2O3 MNSs. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD, Bruke D8 Advance) with Cu Ka radiation, field emission scanning electron microscopy (FESEM, JEOL JSM-6700F), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM, JEOL JEM-2100F). The detailed process of sensor fabrication was described in our previous reports [11]. The response (R) is defined as the ratio of the resistance of the sensor in dry air (Ra) to that in target gases (Rg). The response and recovery time (sres and srecov) are defined as the time taken by the sensor to achieve 90% of the total resistance change in the case of adsorption and desorption, respectively.
3. Results and discussion The phase purity and structure of the as-obtained samples after different steps were firstly characterized via XRD measurement. As can be seen in Fig. 1a, all the diffraction peaks from SnO2 sample are consistent with patterns from a standard SnO2 rutile phase (JCPDS card no. 41-1445) and no peaks from any other impurities are identified. As for the final hydrothermal sample, besides a part of diffraction peaks are assigned to tetragonal SnO2 phase, the residual peaks can be discerned to well match with the standard pattern from the rhombohedral a-Fe2O3 (JCPDS card no. 330664). It demonstrates that the final samples are constructed by
two mixed crystalline phases of SnO2 and Fe2O3. The morphological and structural characters of the as-prepared SnO2 and SnO2/ Fe2O3 samples are also examined, respectively. Fig. 1b confirms that the obtained SnO2 sample is composed of flowerlike aggregated nanosheets with coarse surfaces and partly cracked laterals (indicated by white arrow). More importantly, the unique hollow interior and multilayered structure of SnO2 nanosheets are identified through the relatively light contrast between the dark outlines and multiple pale/dark strips from their side projections (Fig. 1c). The inset SAED pattern and HRTEM image (Fig. 1d) presents that polycrystalline SnO2 nanosheets are assembled by primary nanoparticles with diameter of around 5 nm and the obvious spaces among nanoparticles confirm the highly porous merit (indicated by white arrow), which can guarantee the effective diffusion of gas molecules during the sensing process. A low-magnification image (Fig. 2a) indicates that SnO2/Fe2O3 samples generally maintain the basic shape and size of SnO2 HMNs. Evidently, numerous Fe2O3 outshoots are homogenously distributed on surfaces of SnO2 nanosheet to form more rougher and hairy appearance. As shown in Fig. 2b, these Fe2O3 rod-like primary building blocks with almost uniform diameter stand nearly perpendicularly on all the surfaces of different SnO2 layers to form the so-called sandwich-like structure of SnO2/Fe2O3 MNSs. The local enlarged TEM image (Fig. 2c) clearly displays that the average length of Fe2O3 primary nanorods is about 160 nm and the outmost layer assembled from well-aligned Fe2O3 primary nanorods is merged well with SnO2 layer (with outer Fe2O3 and inner SnO2 layers indicated by arrows). A slight deviation from 90° should be ascribed mainly to the jostle among the densely arranged primary
Fig. 1. XRD pattern of SnO2 HMNs and SnO2/Fe2O3 MNSs (a); typical FESEM (b), TEM (c) and HRTEM (d) images of SnO2 HMNs. The inset of Fig. 1c is a SAED pattern.
J. Liu et al. / Materials Letters 221 (2018) 57–61
59
Fig. 2. Typical FESEM (a), TEM (b and c) and HRTEM (d) images of SnO2/Fe2O3 MNSs. The inset (a) is the enlarged FESEM image.
nanorods. The HRTEM observation in Fig. 2d demonstrates that Fe2O3 rod-like primary building blocks hold uniform ultrathin diameter of about 10 nm and high aspect ratio. It also confirms that the primary ultrathin Fe2O3 nanorods are actually singlecrystalline structure in nature, where the lattice interplanar spacing determined to be 0.272 nm corresponds to the (1 0 4) plane of a-Fe2O3. Based on the experimental results, the preparation of SnO2 HMNs involves a three-step procedure, which has been described in our previous work [15]. The Fe2O3 nanorods are radially grown on the outmost surface and interlayer of SnO2 by a facile hydrothermal process, resulting in the final formation of alternately appeared sandwich-structured SnO2/Fe2O3 MNSs. Unlike most available hetero-architectures with random encapsulation of particle-like building blocks on another matrix, our Fe2O3 nanorod-assembled layers are well-aligned on the surfaces of SnO2 multilayers, which offer additional possibility for a fast mass transfer of gas molecules. The response character of SnO2/Fe2O3 MNSs to 50 ppm different gases, including acetone, ethanol, methanol, and toluene, is shown in Fig. 3a. The different selectivity of semiconducting oxide sensor seems to be attributed to the catalytic discrepancy between the sensing materials and various gases [16]. Single period transients of dynamic response-recovery process of different samples are shown in Fig. 3b. It can be observed that SnO2/Fe2O3 MNSs at 260 °C to 10 ppm acetone exhibits about 2.3 times enhancement in response value of 9.8 compared to that of SnO2 HMNs (4.3). More importantly, it is also found that sres and srecov of SnO2/ Fe2O3 MNSs to 10 ppm acetone are about 0.8 and 3.4 s, respectively. Compared with the characters of SnO2/Fe2O3 MNSs, SnO2
HMNs exhibit longer response-recovery behaviors of about 0.9 and 5.8 s, respectively. Concerning the sensing mechanism of SnO2 HMNs or SnO2/ Fe2O3 MNSs for acetone detection, the sensing behaviors can be derived from the reversible electrical transfer processes when sensing materials being exposed to different ambiences, which can be explained via the surface-controlled mechanism [5,17], as illustrated in Fig. 3c. Besides benefiting from the fascinating merits of porous multilayered structure to guarantee the effective mass transfer of gas molecules, the band modulation around SnO2-Fe2O3 interface is beneficial to the formation of the wider (DL) and higher (DH) depletion layer than pristine SnO2 [18], eventually resulting in the improved acetone sensing performances.
4. Conclusion In summary, the unique sandwich-like multilayered heterostructure of SnO2/Fe2O3 MNSs has been constructed by a facile hydrothermal route based on the templates of SnO2 HMNs. Detailed characteristics confirm that SnO2/Fe2O3 MNSs are composed of alternately appeared SnO2 and Fe2O3 layers, which can be hierarchically assembled by primary SnO2 nanoparticle and Fe2O3 nanorod subunits. Benefiting from their structural merits of highly porous and activated surfaces and heterogenous interfaces, the gas-sensing investigation demonstrates improved acetone sensing performance of SnO2/Fe2O3 MNSs in comparison with pristine SnO2 HMNs.
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Fig. 3. Response of SnO2/Fe2O3 MNSs to 50 ppm testing gases as a function of operating temperature (a); dynamic response transients of SnO2 HMNs and SnO2/Fe2O3 MNSs to a given 10 ppm acetone (b); schematic diagram of acetone sensing process and mechanism (c).
Acknowledgements This research work was financially supported by the Natural Science Foundation of China (Grant No. 51372095, 51402122, and 61376122), Science and Technology Development Project, Jilin Province (Grant No. 20170101168JC), and Independent Project of State Key Laboratory of Applied Optics, Changchun Institute of
Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CAS). References [1] T. Seiyama, A. Kato, K. Fujushi, M. Nagatani, Anal. Chem. 38 (1962) 1069–1073. [2] J.H. Lee, Sens. Actuat. B 140 (2009) 319–336.
J. Liu et al. / Materials Letters 221 (2018) 57–61 [3] L. Liu, P. Song, Q. Wei, X. Zhong, Z.X. Yang, Q. Wang, Mater. Lett. 201 (2017) 211–215. [4] Y. Zeng, L. Qiao, Y.F. Bing, M. Wen, B. Zou, W.T. Zheng, et al., Sens. Actuat. B 173 (2012) 897–902. [5] N. Yamazoe, J. Fuchigami, M. Kishikawa, T. Seiyama, Surf. Sci. 86 (1979) 335– 344. [6] L. Ma, S.Y. Ma, H. Kang, X.F. Shen, T.T. Wang, X.H. Jiang, et al., Mater. Lett. 209 (2017) 188–192. [7] Y.F. Bing, Y. Zeng, C. Liu, L. Qiao, W.T. Zheng, Nanoscale 7 (2015) 3276–3284. [8] Y.F. Bing, C. Liu, L. Qiao, Y. Zeng, S.S. Yu, Z.Z. Liang, et al., Sens. Actuat. B 231 (2016) 365–375. [9] P.T. Hernandez, A.J.T. Naik, E.J. Newton, S.M.V. Hailes, I.P. Parkin, J. Mater. Chem. A 2 (2014) 8952–8960. [10] I.J. Park, S. Park, D.H. Kim, H. Jeong, S. Lee, Mater. Lett. 202 (2017) 48–51.
61
[11] Y. Zeng, T. Zhang, L.J. Wang, M.H. Kang, H.T. Fan, R. Wang, Y. He, Sens. Actuat. B 140 (2009) 73–78. [12] J. Mizsei, J. Harsányi, Sens. Actuat. 4 (1983) 397–402. [13] D. Kotsikau, M. Ivanovskaya, D. Orlik, M. Falasconi, Sens. Actuat. B 101 (2004) 199–206. [14] S. Choi, J.Y. Park, S.S. Kim, Nanotechnology 20 (2009) 465603. [15] Y. Zeng, Y.Z. Wang, L. Qiao, Y.F. Bing, B. Zou, W.T. Zheng, Sens. Actuat. B 222 (2016) 354–361. [16] C. Della Pina, E. Falletta, L. Prati, M. Rossi, Chem. Soc. Rev. 37 (2008) 2077– 2095. [17] M. Egashira, Y. Shimizu, Y. Takao, S. Sako, Sens. Actuat. B 35 (1996) 62–67. [18] N.D. Khoang, D.D. Trung, N.V. Duy, N.D. Hoa, N.V. Hieu, Sens. Actuat. B 174 (2012) 594–601.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Controllable assembly of sandwich-structured SnO2/Fe2O3 multilayer nanosheets for high sensitive acetone detection Junping Liu, Yanzhe Wang, Lianqiang Wang, Hongwei Tian, Yi Zeng ⇑ College of Materials Science and Engineering, Key Laboratory of Automobile Materials of Ministry of Educations, and State Key Laboratory of Superhard Materials, Jilin University, Changchun, China
a r t i c l e
i n f o
Article history: Received 3 February 2018 Received in revised form 14 March 2018 Accepted 17 March 2018 Available online 17 March 2018 Keywords: Tin oxide Ferric oxide Multilayered structure Heterostructure Gas sensor
a b s t r a c t A new type of hierarchically nonspherical architecture with sandwich-structured multilayer nanosheets has been successfully prepared via a controllable multistep approach in case of SnO2/Fe2O3 heterostructures. The morphological characterization reveals that unique sandwich-structured SnO2/Fe2O3 multilayer nanosheets (MNSs) are constructed via the self-assembly of densely well-aligned Fe2O3 nanorod layers to cover and fill the interlayers of hexagonal SnO2 hollow multilayer nanosheets (HMNs). When used as the sensing materials for acetone detection, the sandwich hetero-nanostructures demonstrate evidently improved sensing performance compared to pure SnO2. The significantly improved sensing performance can be attributed not only to the rational microstructures for fast transfer of gas molecules, but also to the additional effects of loaded Fe2O3 ultrathin nanorods. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Semiconducting metal oxides, as one type of promising candidates for gas-sensing materials, have attracted tremendous attention owing to their low cost, easily tunable structural and sensing characters in detecting various target gases [1]. From the materials perspective, rational design of hierarchically porous or hollow architectures of desired candidates has been widely recognized as an effective route for the boost of their gas-sensing performances [2–4]. Beyond the strategy of optimizing material structures, hybrid-composite design is also proved to be highly desirable with respect to a dramatic improvement in the sensing performances in virtue of tunable composition and synergistic effect. In the case of n-type semiconducting oxides, tin dioxide (SnO2) has long been applied as an appealing sensing material with various shapes in detecting diverse gas species [5–9]. In the past few years, broadening the sensing materials from singlecomponent SnO2 to SnO2 matrix heterostructures, such as SnO2/Au, SnO2/Pd, SnO2/ZnO, SnO2/Fe2O3, SnO2/TiO2, and so on [10–14], has received more attention and significantly improved the performances. Despite considerable efforts being dedicated to integrate the fascinating merits of proper configuration and synergistic contribution, facile assembly of heterogeneous lowdimensional subunits on another oxide matrix often encounters ⇑ Corresponding author. E-mail address: [email protected] (Y. Zeng). https://doi.org/10.1016/j.matlet.2018.03.084 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
the compatibility issue, and in fact the resulting heterostructures are usually degraded to dense-agglomerated form. Understanding key factors for constructing heterogeneous oxides with desired porous architecture by a simple and economical route still remains challenging yet highly desirable. In this work, we present a multistep route for unique sandwichstructured SnO2/Fe2O3 MNSs through covering ultrathin Fe2O3 nanorod-assembled layers on all surfaces of hexagonal SnO2 HMNs. The morphology and microstructure of as-obtained SnO2/ Fe2O3 MNSs are examined. Benefitting from the porous feature and highly interconnected heterogeneous interfaces of SnO2/ Fe2O3 MNSs, the improved gas-sensing performances of the obtained SnO2/Fe2O3 MNSs can be anticipated. 2. Experimental All the chemical reagents are of analytical grade as purchased from Sinopharm Chemical Reagent Co. Ltd (China) and used without further purification. The route for SnO2 HMNs is according to our previous report with some modifications [15]. As for the final SnO2/Fe2O3 MNSs, the as-obtained SnO2 (20 mg) was dispersed into 40 mL of aqueous solution, including Na2SO410H2O (85.8 mg) and FeCl36H2O (71.6 mg). After stirring for 10 min, this suspension was transferred into a Teflon-lined stainless steel autoclave, sealed tightly, and then maintained at 120 °C for 2 h. After cooled naturally down to room temperature, the dark-red precipitates were centrifugally separated, washed with absolute
58
J. Liu et al. / Materials Letters 221 (2018) 57–61
ethanol/DI water for several times, and dried at 60 °C overnight. Finally, the precipitates were annealed at 450 °C for 2 h with a ramping rate of 5 °C min 1 to obtain the final SnO2/Fe2O3 MNSs. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD, Bruke D8 Advance) with Cu Ka radiation, field emission scanning electron microscopy (FESEM, JEOL JSM-6700F), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM, JEOL JEM-2100F). The detailed process of sensor fabrication was described in our previous reports [11]. The response (R) is defined as the ratio of the resistance of the sensor in dry air (Ra) to that in target gases (Rg). The response and recovery time (sres and srecov) are defined as the time taken by the sensor to achieve 90% of the total resistance change in the case of adsorption and desorption, respectively.
3. Results and discussion The phase purity and structure of the as-obtained samples after different steps were firstly characterized via XRD measurement. As can be seen in Fig. 1a, all the diffraction peaks from SnO2 sample are consistent with patterns from a standard SnO2 rutile phase (JCPDS card no. 41-1445) and no peaks from any other impurities are identified. As for the final hydrothermal sample, besides a part of diffraction peaks are assigned to tetragonal SnO2 phase, the residual peaks can be discerned to well match with the standard pattern from the rhombohedral a-Fe2O3 (JCPDS card no. 330664). It demonstrates that the final samples are constructed by
two mixed crystalline phases of SnO2 and Fe2O3. The morphological and structural characters of the as-prepared SnO2 and SnO2/ Fe2O3 samples are also examined, respectively. Fig. 1b confirms that the obtained SnO2 sample is composed of flowerlike aggregated nanosheets with coarse surfaces and partly cracked laterals (indicated by white arrow). More importantly, the unique hollow interior and multilayered structure of SnO2 nanosheets are identified through the relatively light contrast between the dark outlines and multiple pale/dark strips from their side projections (Fig. 1c). The inset SAED pattern and HRTEM image (Fig. 1d) presents that polycrystalline SnO2 nanosheets are assembled by primary nanoparticles with diameter of around 5 nm and the obvious spaces among nanoparticles confirm the highly porous merit (indicated by white arrow), which can guarantee the effective diffusion of gas molecules during the sensing process. A low-magnification image (Fig. 2a) indicates that SnO2/Fe2O3 samples generally maintain the basic shape and size of SnO2 HMNs. Evidently, numerous Fe2O3 outshoots are homogenously distributed on surfaces of SnO2 nanosheet to form more rougher and hairy appearance. As shown in Fig. 2b, these Fe2O3 rod-like primary building blocks with almost uniform diameter stand nearly perpendicularly on all the surfaces of different SnO2 layers to form the so-called sandwich-like structure of SnO2/Fe2O3 MNSs. The local enlarged TEM image (Fig. 2c) clearly displays that the average length of Fe2O3 primary nanorods is about 160 nm and the outmost layer assembled from well-aligned Fe2O3 primary nanorods is merged well with SnO2 layer (with outer Fe2O3 and inner SnO2 layers indicated by arrows). A slight deviation from 90° should be ascribed mainly to the jostle among the densely arranged primary
Fig. 1. XRD pattern of SnO2 HMNs and SnO2/Fe2O3 MNSs (a); typical FESEM (b), TEM (c) and HRTEM (d) images of SnO2 HMNs. The inset of Fig. 1c is a SAED pattern.
J. Liu et al. / Materials Letters 221 (2018) 57–61
59
Fig. 2. Typical FESEM (a), TEM (b and c) and HRTEM (d) images of SnO2/Fe2O3 MNSs. The inset (a) is the enlarged FESEM image.
nanorods. The HRTEM observation in Fig. 2d demonstrates that Fe2O3 rod-like primary building blocks hold uniform ultrathin diameter of about 10 nm and high aspect ratio. It also confirms that the primary ultrathin Fe2O3 nanorods are actually singlecrystalline structure in nature, where the lattice interplanar spacing determined to be 0.272 nm corresponds to the (1 0 4) plane of a-Fe2O3. Based on the experimental results, the preparation of SnO2 HMNs involves a three-step procedure, which has been described in our previous work [15]. The Fe2O3 nanorods are radially grown on the outmost surface and interlayer of SnO2 by a facile hydrothermal process, resulting in the final formation of alternately appeared sandwich-structured SnO2/Fe2O3 MNSs. Unlike most available hetero-architectures with random encapsulation of particle-like building blocks on another matrix, our Fe2O3 nanorod-assembled layers are well-aligned on the surfaces of SnO2 multilayers, which offer additional possibility for a fast mass transfer of gas molecules. The response character of SnO2/Fe2O3 MNSs to 50 ppm different gases, including acetone, ethanol, methanol, and toluene, is shown in Fig. 3a. The different selectivity of semiconducting oxide sensor seems to be attributed to the catalytic discrepancy between the sensing materials and various gases [16]. Single period transients of dynamic response-recovery process of different samples are shown in Fig. 3b. It can be observed that SnO2/Fe2O3 MNSs at 260 °C to 10 ppm acetone exhibits about 2.3 times enhancement in response value of 9.8 compared to that of SnO2 HMNs (4.3). More importantly, it is also found that sres and srecov of SnO2/ Fe2O3 MNSs to 10 ppm acetone are about 0.8 and 3.4 s, respectively. Compared with the characters of SnO2/Fe2O3 MNSs, SnO2
HMNs exhibit longer response-recovery behaviors of about 0.9 and 5.8 s, respectively. Concerning the sensing mechanism of SnO2 HMNs or SnO2/ Fe2O3 MNSs for acetone detection, the sensing behaviors can be derived from the reversible electrical transfer processes when sensing materials being exposed to different ambiences, which can be explained via the surface-controlled mechanism [5,17], as illustrated in Fig. 3c. Besides benefiting from the fascinating merits of porous multilayered structure to guarantee the effective mass transfer of gas molecules, the band modulation around SnO2-Fe2O3 interface is beneficial to the formation of the wider (DL) and higher (DH) depletion layer than pristine SnO2 [18], eventually resulting in the improved acetone sensing performances.
4. Conclusion In summary, the unique sandwich-like multilayered heterostructure of SnO2/Fe2O3 MNSs has been constructed by a facile hydrothermal route based on the templates of SnO2 HMNs. Detailed characteristics confirm that SnO2/Fe2O3 MNSs are composed of alternately appeared SnO2 and Fe2O3 layers, which can be hierarchically assembled by primary SnO2 nanoparticle and Fe2O3 nanorod subunits. Benefiting from their structural merits of highly porous and activated surfaces and heterogenous interfaces, the gas-sensing investigation demonstrates improved acetone sensing performance of SnO2/Fe2O3 MNSs in comparison with pristine SnO2 HMNs.
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Fig. 3. Response of SnO2/Fe2O3 MNSs to 50 ppm testing gases as a function of operating temperature (a); dynamic response transients of SnO2 HMNs and SnO2/Fe2O3 MNSs to a given 10 ppm acetone (b); schematic diagram of acetone sensing process and mechanism (c).
Acknowledgements This research work was financially supported by the Natural Science Foundation of China (Grant No. 51372095, 51402122, and 61376122), Science and Technology Development Project, Jilin Province (Grant No. 20170101168JC), and Independent Project of State Key Laboratory of Applied Optics, Changchun Institute of
Optics, Fine Mechanics and Physics, Chinese Academy of Sciences (CAS). References [1] T. Seiyama, A. Kato, K. Fujushi, M. Nagatani, Anal. Chem. 38 (1962) 1069–1073. [2] J.H. Lee, Sens. Actuat. B 140 (2009) 319–336.
J. Liu et al. / Materials Letters 221 (2018) 57–61 [3] L. Liu, P. Song, Q. Wei, X. Zhong, Z.X. Yang, Q. Wang, Mater. Lett. 201 (2017) 211–215. [4] Y. Zeng, L. Qiao, Y.F. Bing, M. Wen, B. Zou, W.T. Zheng, et al., Sens. Actuat. B 173 (2012) 897–902. [5] N. Yamazoe, J. Fuchigami, M. Kishikawa, T. Seiyama, Surf. Sci. 86 (1979) 335– 344. [6] L. Ma, S.Y. Ma, H. Kang, X.F. Shen, T.T. Wang, X.H. Jiang, et al., Mater. Lett. 209 (2017) 188–192. [7] Y.F. Bing, Y. Zeng, C. Liu, L. Qiao, W.T. Zheng, Nanoscale 7 (2015) 3276–3284. [8] Y.F. Bing, C. Liu, L. Qiao, Y. Zeng, S.S. Yu, Z.Z. Liang, et al., Sens. Actuat. B 231 (2016) 365–375. [9] P.T. Hernandez, A.J.T. Naik, E.J. Newton, S.M.V. Hailes, I.P. Parkin, J. Mater. Chem. A 2 (2014) 8952–8960. [10] I.J. Park, S. Park, D.H. Kim, H. Jeong, S. Lee, Mater. Lett. 202 (2017) 48–51.
61
[11] Y. Zeng, T. Zhang, L.J. Wang, M.H. Kang, H.T. Fan, R. Wang, Y. He, Sens. Actuat. B 140 (2009) 73–78. [12] J. Mizsei, J. Harsányi, Sens. Actuat. 4 (1983) 397–402. [13] D. Kotsikau, M. Ivanovskaya, D. Orlik, M. Falasconi, Sens. Actuat. B 101 (2004) 199–206. [14] S. Choi, J.Y. Park, S.S. Kim, Nanotechnology 20 (2009) 465603. [15] Y. Zeng, Y.Z. Wang, L. Qiao, Y.F. Bing, B. Zou, W.T. Zheng, Sens. Actuat. B 222 (2016) 354–361. [16] C. Della Pina, E. Falletta, L. Prati, M. Rossi, Chem. Soc. Rev. 37 (2008) 2077– 2095. [17] M. Egashira, Y. Shimizu, Y. Takao, S. Sako, Sens. Actuat. B 35 (1996) 62–67. [18] N.D. Khoang, D.D. Trung, N.V. Duy, N.D. Hoa, N.V. Hieu, Sens. Actuat. B 174 (2012) 594–601.