- Email: [email protected]
graphene nanocomposite by a microwave-assisted hydrothermal method and the gas-sensing properties to triethylamine
Materials Letters 155 (2015) 4–7
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of hemispherical WO3/graphene nanocomposite by a microwave-assisted hydrothermal method and the gas-sensing properties to triethylamine Yanghai Gui a,n, Jianbo Zhao a, Weimin Wang a, Junfeng Tian a, Ming Zhao b,nn a b
Department of Material and Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, China College of Mechanical and material engineering, North China University of Technology, Beijing 100144, China
art ic l e i nf o
a b s t r a c t
Article history: Received 11 February 2015 Accepted 21 April 2015 Available online 30 April 2015
WO3 nanoparticle and hemispherical WO3/graphene nanocomposite were successfully synthesized via a microwave-assisted hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) techniques. The gas-sensing performance of the as-synthesized materials was also investigated. The experimental results revealed that the graphene plays a very important role in the crystal structure evolution process from WO3 nanoparticle to hemispherical WO3/graphene nanocomposite. The hemispherical WO3/graphene nanocomposite with hollow structure shows far better gassensing performance for amine gases at room temperature, especially for triethylamine. & 2015 Elsevier B.V. All rights reserved.
Keywords: Graphene/WO3 Nanocomposite Powder technology Sensors
1. Introduction WO3 is found to be one of the most interesting materials because of its potential applications in many fields [1,2]. It can be obtained in different morphological forms such as nanowires [3], nanospheres [4], nanoplates [5] and sub-micron porous spheres [6], which were stated that the porous nanostructures can result in high sensitivity to volatile organic compounds (VOCs). The highly porous nanostructures providing large enhancements in the number of surface reaction sites can support modulation of the electron density across the full volume of the oxide particles rather than just a narrow depletion layer, given their nanosized cross sections [7]. But pure WO3 can only exhibit a high gassensing response at a higher working temperature often ranging from 200 to 500 1C [8]. Recently, many researchers attempted to alter the selectivity and lower the operating temperature of the gas sensors by mixing graphene or graphene oxide into metal oxide and obtained many results [9]. The hydrothermal method has also been known as an effective one to synthesize the graphene/WO3 nanocomposites [2,10]. More recently, the ongoing microwave-assisted hydrothermal (MH) method was proven to be a greener approach to synthesize nanomaterials, which has some advantages over the conventional hydrothermal method such as
n
Corresponding author. Tel./fax: þ 86 0371 86609676. Corresponding author. Tel./fax: þ 86 010 88803160. E-mail addresses: [email protected] (Y. Gui), [email protected] (M. Zhao).
nn
http://dx.doi.org/10.1016/j.matlet.2015.04.100 0167-577X/& 2015 Elsevier B.V. All rights reserved.
requiring lower temperature and shorter time [11]. However, to the best of our knowledge, the study on hemispherical WO3/ graphene nanocomposite and the gas-sensing properties for VOC detection has yet to be investigated, particularly to trimethylamine, which is toxic and harmful by inhalation, ingestion or by skin contact, corrosive and can cause severe burns. In the present work, we report on a new sensing material consisting of hemispherical WO3/graphene composites synthesized by utilizing the MH method, which demonstrates superior selectivity and sensitivity to trimethylamine gas.
2. Experimental Materials synthesis and characterization: Graphene oxide (GO) was synthesized by a modified Hummers method [12]. The obtained GO after washing and freezedrying was then sonicated to form a stable suspension in aqueous media. The resulting aqueous GO solution had a concentration of 0.585 mg/mL. For a typical MH synthesis of the hemispherical WO3/graphene composite, 0.794 g WCl6 and 0.1200 g CO(NH2)2 were firstly added to 80.0 mL ethanol. The mixture was sonicated for 30 min. Then 4.0 mL GO solution was added and sonicated for another 30 min. The solution was transferred into a Teflon-lined autoclave and heated from room temperature to 180 1C for 18 min and kept for 60 min under autogenous pressure. The experiments were performed on a MWave-5000 multifunctional microwave chemical
Y. Gui et al. / Materials Letters 155 (2015) 4–7
should be attributed to O–W–O beading modes and O–W–O stretching modes [14]. Besides, the peaks at 1352 cm 1 and 1589 cm 1 also demonstrate the Raman shifts of D and G bands shift to lower values and verified the GO is reduced to graphene [15]. As shown in Fig. 1(c), the FT-IR spectra of WO3 and WO3/ graphene nanocomposite exhibit a broad absorption band at 3400–3500 cm 1, which is associated with the stretching vibration of the –OH functional group. The absorption band at about 1620 cm 1 could be attributed to the bending vibration absorption peak of the adsorbed water molecules. Compared with the pure WO3, an additional peak at 1519 cm 1 in FT-IR spectroscopy of WO3/graphene sample combined with the above-mentioned Raman shift provides reliable evidence of charge transfer between the graphene sheets and the WO3, which suggests a new bonding between the graphene and WO3 [13]. The SEM images of the as-prepared WO3 and WO3/graphene are shown in Fig. 2. The SEM images in Fig. 2(a) and (b) exhibited that the pure WO3 was mainly composed of numerous uniform nanoparticles. However, the WO3/graphene nanocomposite was composed of hemispherical products and their fragments shown in Fig. 2(c)–(e), which indicated that the GO solution has played a very important role in the process of the WO3/graphene crystal growth. The hemispherical WO3/graphene with a number of hollow structures should contribute to a better gas-sensing performance. The cross-sensitivities of WO3 and WO3/graphene composite to interferential gases are shown in Fig. 3(a). A series of possible interferential gases have been investigated, including NH3 H2O, aniline, triethylamine, toluene, methanol, xylene, ether, formamide, ethanol, trimethylamine, benzene and acetone. Both sensors based on WO3 and WO3/graphene composite show n-type response to these gases, as their resistance decreases under gas exposure. What is attractive is that both sensors show high sensitivity and good selectivity to these amine gases such as NH3 H2O, aniline, triethylamine and trimethylamine, especially the WO3/graphene for triethylamine. The sensitivity of WO3/graphene to 100 ppm triethylamine can reach 205, which is far higher than other gases. For amine gases, an obvious trend was also presented that there is Sr(triethylamine) 4Sr(trimethylamine)4Sr(NH3 H2O)4Sr(aniline), which may be related to the different drawing or repelling electron abilities for the different substituent groups on NH3 functional group. Moreover, the improved gas-sensing properties should be derived from the highly porous hemispherical composites based on graphene and thin-walled WO3 nanoparticles. As described in the literature [7], the hemispherical structure can not only provide more surface reaction sites but also modulate the electron density across the full volume of the WO3/graphene composite rather than just a narrow depletion layer, which resulted in the good gas-sensing performance. The
reaction apparatus (Sineo Microwave Chemistry Technology Company, Shanghai, China). Microwave irradiation with a maximum delivered power of 1000 W at a frequency of 2450 MHz can be dynamically adjusted by temperature and power feedbacks. The whole process is under magnetic stirring in the speed of 400 rpm. The naturally cooled products were filtered and washed with deionized water and ethanol several times and finally dried at 105 1C in air for 12 h. For comparison, pure WO3 was prepared through the similar procedure without adding GO solution. The morphologies of the products were observed by using a JEOL JSM7100F high-resolution thermal field emission scanning electron microscope (JEOL JSM-7100F FE-SEM). Raman spectra were recorded on a Renishaw inVia-Reflex confocal Raman microscope with 532 nm laser excitation. FT-IR spectra were obtained with a Thermo Scientific Nicolet 6700 instrument. The samples were characterized by means of XRD (Bruker D8) using Ni-filtered CuKα radiation (λ ¼0.154056 nm). Gas-sensing performance: The sensor device was fabricated by coating the mixed slurry of deionized water with the as-synthesized powders onto the interdigited gold electrodes. The interdigited gold electrodes were made by screen printing and ceramic slides were used as the substrates [8]. The electrode gap was 0.2 mm. The electrodes coated with slurry were calcined at 500 1C under argon atmosphere and aged for 3 days at 300 1C in air. Plane sensor measurement was performed on a CGS-1TP intelligent gas sensing analysis system (Beijing Elite Tech Co., Ltd, China). The system offered the external temperature control (from room temperature to about 600 1C), which could adjust the sensor temperature directly. The sensitivity (Sr ¼ Ra/Rg) of the sensor was defined as the ratio of the electrical resistance of the sensor in air (Ra) to that in the mixture of the detected gas and air (Rg).
3. Results and discussion
1589
WO
715 -OH
272
1352
WO 252
O-W-O
805
-OH
( 224)
(400)
WO /graphene
(222)
(022) ( 202) (202)
(002) (020) (200) ( 112) (120)
802 696
WO /graphene O-W-O
Intensity(a.u.)
Fig. 1(a) shows the XRD patterns of WO3 and WO3/graphene nanocomposites, both of which exhibited characteristic peaks of the monoclinic WO3 (JCPDS 43-1035) [13], indicating that the adding of graphene cannot change the WO3 phase structure for the nanocomposite. Any peak of the graphene diffraction peaks was not observed due to extremely small amount of graphene used in the nanocomposite. The crystallite sizes of WO3 and WO3/ graphene were estimated to be 22 nm and 20 nm, respectively, from the half width of the (002) peaks according to Scherrer's equation. Fig. 1(b) shows the Raman spectra peaks of WO3/ graphene nanocomposite shift to lower frequency in comparison to that of pure WO3 from 805 cm 1,715 cm 1 and 272 cm 1 to 802 cm 1, 696 cm 1 and 252 cm 1, respectively. These peaks
WO
5
WO /graphene
10
20
30
40
50
2theta (deg.)
60
70
0
500 1000 1500 2000 2500 3000 3500 4000
Wavelength
(cm -1)
4000
3000
2000
1000
Wavelength (cm -1 )
Fig. 1. (a) XRD patterns of WO3 and WO3/graphene; (b) Raman spectra and (c) FT-IR spectra of WO3 and WO3/graphene.
0
6
Y. Gui et al. / Materials Letters 155 (2015) 4–7
Fig. 2. FE-SEM images of WO3 (a, b) and WO3/graphene (c–e).
4.5
acetone benzene trimethylamine
WO /graphene
4.0
WO
3.5
ethanol
wo /graphene
Voltage/v
100 ppm at room temperature
ether xylene methanal toluene triethylamine
20ppm
10ppm
10ppm
2.5 2.0
50ppm 20ppm
50ppm 40ppm
3.0
formamide
wo
100ppm
1ppm
1ppm
1.5 1.0 0.5
aniline
0.0
NH ·Η Ο 0
25
50
75
100
125
150
175
200
225
0
200
400
600
800
Sr
1000 1200 1400 1600 1800
Time/s
200
WO /graphene
150
Sr
WO 100
50
0 0
10
20
30
40
50
60
70
80
90
100 110
The concentration of triethylamine vapor /ppm Fig. 3. (a) Selectivity of the sensors based on WO3 and WO3/graphene to twelve kinds of vapors (100 ppm) at room temperature; (b) Sensitivities of the sensors based on WO3 and WO3/graphene to different concentrations of triethylamine vapor; (c) Relationship between the sensitivities of the sensors based on WO3 and WO3/graphene and the concentrations of triethylamine vapor.
mechanism of the better gas-sensing performance to the amine gases than the other test gases are still under investigation. The responses of WO3 and WO3/graphene to increasing concentration of triethylamine (1–100 ppm) are shown in Fig. 3(b). The sensitivities of WO3 and WO3/graphene sensors as a function of gas concentration at room temperature are shown in Fig. 3(c). These experimental results indicate that both sensors based on the pure WO3 and WO3/graphene composite possess good reversibility and repeatability, but the sensor based on WO3/graphene composite has much higher sensitivity at room temperature.
4. Conclusions In summary, WO3 nanoparticles and hemispherical WO3/graphene nanocomposite are synthesized through the microwaveassisted hydrothermal method. As gas-sensing material, the assynthesized hemispherical WO3/graphene composite exhibits good gas-sensing performance to triethylamine at room temperature. It is attributed to the graphene effect during the crystal structure growth of hemispherical WO3/graphene composite and the good gas-sensing performance.
Y. Gui et al. / Materials Letters 155 (2015) 4–7
Acknowledgments The authors are very grateful for the support of the National Natural Science Foundation of China (Grant nos. 21371158 and 51271003), the Foundation for University Key Teacher of Henan Province (Grant no. 122300410299), and the Program for Science and Technology of Zhengzhou (Grant no. 121PPTGG362-3). Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.04.100. References [1] Deb SK. Sol Energy Mater Sol Cells 2008;92:245–58.
[2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
7
Li T, Zeng W, Miao B, Zhao S, Li Y, Zhang H. Mater Lett 2015;144:106–9. Fu L, Cai W, Wang A, Zheng Y. Mater Lett 2015;142:201–3. Pudukudy M, Yaakob Z, Rajendran R. Pharma Chemica 2013;5(6):208–12. Yin L, Chen D, Feng M, Ge L, Yang D, Song Z, et al. RSC Adv 2015;5(1):328–37. Zeng W, Dong C, Miao B, Zhang H, Xu S, Ding X, et al. Mater Lett 2014;117:41–4. Choi S, Fuchs F, Demadrille R, Grévin B, Jang B, Lee S, et al. Appl Mater Interfaces 2014;6:9061–70. Su P, Peng S. Talanta 2015;132:398–405. Chu X, Hu T, Gao F, Dong Y, Sun W, Bai L. Mater Sci Eng B 2015;193:97–104. Song C, Li C, Yin Y, Xiao J, Zhang X, Song M, et al. Vacuum 2015;114:13–6. Wang Z, Zhou X, Li Z, Zhuo Y, Gao Y, Yang Q, et al. RSC Adv 2014;4 (44):23281–6. Ying H, Wang ZY, Guo ZD, Shi ZJ, Yang SF. Acta Phys Chim Sin 2011;27:1482–6. Guo J, Li Y, Zhu S, Chen Z, Liu Q, Zhang D, et al. RSC Adv 2012;2:1356–63. Rougier A, Portemer F, Quede A, Marssi ME. Appl Surf Sci 1999;153:1–9. Stankovich S, Dikin DA, Piner RD, Kohlhaas KA, Kleinhammes A, Jia Y, et al. Carbon 2007;45:1558–65.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of hemispherical WO3/graphene nanocomposite by a microwave-assisted hydrothermal method and the gas-sensing properties to triethylamine Yanghai Gui a,n, Jianbo Zhao a, Weimin Wang a, Junfeng Tian a, Ming Zhao b,nn a b
Department of Material and Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, China College of Mechanical and material engineering, North China University of Technology, Beijing 100144, China
art ic l e i nf o
a b s t r a c t
Article history: Received 11 February 2015 Accepted 21 April 2015 Available online 30 April 2015
WO3 nanoparticle and hemispherical WO3/graphene nanocomposite were successfully synthesized via a microwave-assisted hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) techniques. The gas-sensing performance of the as-synthesized materials was also investigated. The experimental results revealed that the graphene plays a very important role in the crystal structure evolution process from WO3 nanoparticle to hemispherical WO3/graphene nanocomposite. The hemispherical WO3/graphene nanocomposite with hollow structure shows far better gassensing performance for amine gases at room temperature, especially for triethylamine. & 2015 Elsevier B.V. All rights reserved.
Keywords: Graphene/WO3 Nanocomposite Powder technology Sensors
1. Introduction WO3 is found to be one of the most interesting materials because of its potential applications in many fields [1,2]. It can be obtained in different morphological forms such as nanowires [3], nanospheres [4], nanoplates [5] and sub-micron porous spheres [6], which were stated that the porous nanostructures can result in high sensitivity to volatile organic compounds (VOCs). The highly porous nanostructures providing large enhancements in the number of surface reaction sites can support modulation of the electron density across the full volume of the oxide particles rather than just a narrow depletion layer, given their nanosized cross sections [7]. But pure WO3 can only exhibit a high gassensing response at a higher working temperature often ranging from 200 to 500 1C [8]. Recently, many researchers attempted to alter the selectivity and lower the operating temperature of the gas sensors by mixing graphene or graphene oxide into metal oxide and obtained many results [9]. The hydrothermal method has also been known as an effective one to synthesize the graphene/WO3 nanocomposites [2,10]. More recently, the ongoing microwave-assisted hydrothermal (MH) method was proven to be a greener approach to synthesize nanomaterials, which has some advantages over the conventional hydrothermal method such as
n
Corresponding author. Tel./fax: þ 86 0371 86609676. Corresponding author. Tel./fax: þ 86 010 88803160. E-mail addresses: [email protected] (Y. Gui), [email protected] (M. Zhao).
nn
http://dx.doi.org/10.1016/j.matlet.2015.04.100 0167-577X/& 2015 Elsevier B.V. All rights reserved.
requiring lower temperature and shorter time [11]. However, to the best of our knowledge, the study on hemispherical WO3/ graphene nanocomposite and the gas-sensing properties for VOC detection has yet to be investigated, particularly to trimethylamine, which is toxic and harmful by inhalation, ingestion or by skin contact, corrosive and can cause severe burns. In the present work, we report on a new sensing material consisting of hemispherical WO3/graphene composites synthesized by utilizing the MH method, which demonstrates superior selectivity and sensitivity to trimethylamine gas.
2. Experimental Materials synthesis and characterization: Graphene oxide (GO) was synthesized by a modified Hummers method [12]. The obtained GO after washing and freezedrying was then sonicated to form a stable suspension in aqueous media. The resulting aqueous GO solution had a concentration of 0.585 mg/mL. For a typical MH synthesis of the hemispherical WO3/graphene composite, 0.794 g WCl6 and 0.1200 g CO(NH2)2 were firstly added to 80.0 mL ethanol. The mixture was sonicated for 30 min. Then 4.0 mL GO solution was added and sonicated for another 30 min. The solution was transferred into a Teflon-lined autoclave and heated from room temperature to 180 1C for 18 min and kept for 60 min under autogenous pressure. The experiments were performed on a MWave-5000 multifunctional microwave chemical
Y. Gui et al. / Materials Letters 155 (2015) 4–7
should be attributed to O–W–O beading modes and O–W–O stretching modes [14]. Besides, the peaks at 1352 cm 1 and 1589 cm 1 also demonstrate the Raman shifts of D and G bands shift to lower values and verified the GO is reduced to graphene [15]. As shown in Fig. 1(c), the FT-IR spectra of WO3 and WO3/ graphene nanocomposite exhibit a broad absorption band at 3400–3500 cm 1, which is associated with the stretching vibration of the –OH functional group. The absorption band at about 1620 cm 1 could be attributed to the bending vibration absorption peak of the adsorbed water molecules. Compared with the pure WO3, an additional peak at 1519 cm 1 in FT-IR spectroscopy of WO3/graphene sample combined with the above-mentioned Raman shift provides reliable evidence of charge transfer between the graphene sheets and the WO3, which suggests a new bonding between the graphene and WO3 [13]. The SEM images of the as-prepared WO3 and WO3/graphene are shown in Fig. 2. The SEM images in Fig. 2(a) and (b) exhibited that the pure WO3 was mainly composed of numerous uniform nanoparticles. However, the WO3/graphene nanocomposite was composed of hemispherical products and their fragments shown in Fig. 2(c)–(e), which indicated that the GO solution has played a very important role in the process of the WO3/graphene crystal growth. The hemispherical WO3/graphene with a number of hollow structures should contribute to a better gas-sensing performance. The cross-sensitivities of WO3 and WO3/graphene composite to interferential gases are shown in Fig. 3(a). A series of possible interferential gases have been investigated, including NH3 H2O, aniline, triethylamine, toluene, methanol, xylene, ether, formamide, ethanol, trimethylamine, benzene and acetone. Both sensors based on WO3 and WO3/graphene composite show n-type response to these gases, as their resistance decreases under gas exposure. What is attractive is that both sensors show high sensitivity and good selectivity to these amine gases such as NH3 H2O, aniline, triethylamine and trimethylamine, especially the WO3/graphene for triethylamine. The sensitivity of WO3/graphene to 100 ppm triethylamine can reach 205, which is far higher than other gases. For amine gases, an obvious trend was also presented that there is Sr(triethylamine) 4Sr(trimethylamine)4Sr(NH3 H2O)4Sr(aniline), which may be related to the different drawing or repelling electron abilities for the different substituent groups on NH3 functional group. Moreover, the improved gas-sensing properties should be derived from the highly porous hemispherical composites based on graphene and thin-walled WO3 nanoparticles. As described in the literature [7], the hemispherical structure can not only provide more surface reaction sites but also modulate the electron density across the full volume of the WO3/graphene composite rather than just a narrow depletion layer, which resulted in the good gas-sensing performance. The
reaction apparatus (Sineo Microwave Chemistry Technology Company, Shanghai, China). Microwave irradiation with a maximum delivered power of 1000 W at a frequency of 2450 MHz can be dynamically adjusted by temperature and power feedbacks. The whole process is under magnetic stirring in the speed of 400 rpm. The naturally cooled products were filtered and washed with deionized water and ethanol several times and finally dried at 105 1C in air for 12 h. For comparison, pure WO3 was prepared through the similar procedure without adding GO solution. The morphologies of the products were observed by using a JEOL JSM7100F high-resolution thermal field emission scanning electron microscope (JEOL JSM-7100F FE-SEM). Raman spectra were recorded on a Renishaw inVia-Reflex confocal Raman microscope with 532 nm laser excitation. FT-IR spectra were obtained with a Thermo Scientific Nicolet 6700 instrument. The samples were characterized by means of XRD (Bruker D8) using Ni-filtered CuKα radiation (λ ¼0.154056 nm). Gas-sensing performance: The sensor device was fabricated by coating the mixed slurry of deionized water with the as-synthesized powders onto the interdigited gold electrodes. The interdigited gold electrodes were made by screen printing and ceramic slides were used as the substrates [8]. The electrode gap was 0.2 mm. The electrodes coated with slurry were calcined at 500 1C under argon atmosphere and aged for 3 days at 300 1C in air. Plane sensor measurement was performed on a CGS-1TP intelligent gas sensing analysis system (Beijing Elite Tech Co., Ltd, China). The system offered the external temperature control (from room temperature to about 600 1C), which could adjust the sensor temperature directly. The sensitivity (Sr ¼ Ra/Rg) of the sensor was defined as the ratio of the electrical resistance of the sensor in air (Ra) to that in the mixture of the detected gas and air (Rg).
3. Results and discussion
1589
WO
715 -OH
272
1352
WO 252
O-W-O
805
-OH
( 224)
(400)
WO /graphene
(222)
(022) ( 202) (202)
(002) (020) (200) ( 112) (120)
802 696
WO /graphene O-W-O
Intensity(a.u.)
Fig. 1(a) shows the XRD patterns of WO3 and WO3/graphene nanocomposites, both of which exhibited characteristic peaks of the monoclinic WO3 (JCPDS 43-1035) [13], indicating that the adding of graphene cannot change the WO3 phase structure for the nanocomposite. Any peak of the graphene diffraction peaks was not observed due to extremely small amount of graphene used in the nanocomposite. The crystallite sizes of WO3 and WO3/ graphene were estimated to be 22 nm and 20 nm, respectively, from the half width of the (002) peaks according to Scherrer's equation. Fig. 1(b) shows the Raman spectra peaks of WO3/ graphene nanocomposite shift to lower frequency in comparison to that of pure WO3 from 805 cm 1,715 cm 1 and 272 cm 1 to 802 cm 1, 696 cm 1 and 252 cm 1, respectively. These peaks
WO
5
WO /graphene
10
20
30
40
50
2theta (deg.)
60
70
0
500 1000 1500 2000 2500 3000 3500 4000
Wavelength
(cm -1)
4000
3000
2000
1000
Wavelength (cm -1 )
Fig. 1. (a) XRD patterns of WO3 and WO3/graphene; (b) Raman spectra and (c) FT-IR spectra of WO3 and WO3/graphene.
0
6
Y. Gui et al. / Materials Letters 155 (2015) 4–7
Fig. 2. FE-SEM images of WO3 (a, b) and WO3/graphene (c–e).
4.5
acetone benzene trimethylamine
WO /graphene
4.0
WO
3.5
ethanol
wo /graphene
Voltage/v
100 ppm at room temperature
ether xylene methanal toluene triethylamine
20ppm
10ppm
10ppm
2.5 2.0
50ppm 20ppm
50ppm 40ppm
3.0
formamide
wo
100ppm
1ppm
1ppm
1.5 1.0 0.5
aniline
0.0
NH ·Η Ο 0
25
50
75
100
125
150
175
200
225
0
200
400
600
800
Sr
1000 1200 1400 1600 1800
Time/s
200
WO /graphene
150
Sr
WO 100
50
0 0
10
20
30
40
50
60
70
80
90
100 110
The concentration of triethylamine vapor /ppm Fig. 3. (a) Selectivity of the sensors based on WO3 and WO3/graphene to twelve kinds of vapors (100 ppm) at room temperature; (b) Sensitivities of the sensors based on WO3 and WO3/graphene to different concentrations of triethylamine vapor; (c) Relationship between the sensitivities of the sensors based on WO3 and WO3/graphene and the concentrations of triethylamine vapor.
mechanism of the better gas-sensing performance to the amine gases than the other test gases are still under investigation. The responses of WO3 and WO3/graphene to increasing concentration of triethylamine (1–100 ppm) are shown in Fig. 3(b). The sensitivities of WO3 and WO3/graphene sensors as a function of gas concentration at room temperature are shown in Fig. 3(c). These experimental results indicate that both sensors based on the pure WO3 and WO3/graphene composite possess good reversibility and repeatability, but the sensor based on WO3/graphene composite has much higher sensitivity at room temperature.
4. Conclusions In summary, WO3 nanoparticles and hemispherical WO3/graphene nanocomposite are synthesized through the microwaveassisted hydrothermal method. As gas-sensing material, the assynthesized hemispherical WO3/graphene composite exhibits good gas-sensing performance to triethylamine at room temperature. It is attributed to the graphene effect during the crystal structure growth of hemispherical WO3/graphene composite and the good gas-sensing performance.
Y. Gui et al. / Materials Letters 155 (2015) 4–7
Acknowledgments The authors are very grateful for the support of the National Natural Science Foundation of China (Grant nos. 21371158 and 51271003), the Foundation for University Key Teacher of Henan Province (Grant no. 122300410299), and the Program for Science and Technology of Zhengzhou (Grant no. 121PPTGG362-3). Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.04.100. References [1] Deb SK. Sol Energy Mater Sol Cells 2008;92:245–58.
[2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
7
Li T, Zeng W, Miao B, Zhao S, Li Y, Zhang H. Mater Lett 2015;144:106–9. Fu L, Cai W, Wang A, Zheng Y. Mater Lett 2015;142:201–3. Pudukudy M, Yaakob Z, Rajendran R. Pharma Chemica 2013;5(6):208–12. Yin L, Chen D, Feng M, Ge L, Yang D, Song Z, et al. RSC Adv 2015;5(1):328–37. Zeng W, Dong C, Miao B, Zhang H, Xu S, Ding X, et al. Mater Lett 2014;117:41–4. Choi S, Fuchs F, Demadrille R, Grévin B, Jang B, Lee S, et al. Appl Mater Interfaces 2014;6:9061–70. Su P, Peng S. Talanta 2015;132:398–405. Chu X, Hu T, Gao F, Dong Y, Sun W, Bai L. Mater Sci Eng B 2015;193:97–104. Song C, Li C, Yin Y, Xiao J, Zhang X, Song M, et al. Vacuum 2015;114:13–6. Wang Z, Zhou X, Li Z, Zhuo Y, Gao Y, Yang Q, et al. RSC Adv 2014;4 (44):23281–6. Ying H, Wang ZY, Guo ZD, Shi ZJ, Yang SF. Acta Phys Chim Sin 2011;27:1482–6. Guo J, Li Y, Zhu S, Chen Z, Liu Q, Zhang D, et al. RSC Adv 2012;2:1356–63. Rougier A, Portemer F, Quede A, Marssi ME. Appl Surf Sci 1999;153:1–9. Stankovich S, Dikin DA, Piner RD, Kohlhaas KA, Kleinhammes A, Jia Y, et al. Carbon 2007;45:1558–65.