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carbon nanotubes based sensors: Influence of carbon nanotubes properties onto sensor s sensitivity
Procedia Engineering 5 (2010) 115–118 Procedia Engineering 00 (2009) 000±000
Procedia Engineering www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Proc. Eurosensors XXIV, September 5-8, 2010, Linz, Austria
Detection of O3 and NH3 using tin dioxide/carbon nanotubes based sensors: Influence of carbon nanotubes properties onto sensor¶s sensitivity. B. Ghaddab a, F. Berger a*, J. B. Sanchez a, C. Mavon a. a
Laboratoire de Chimie-Physique et Rayonnements Alain Chambaudet UMR CEA-E4, UFR ST, La Bouloie, 16 route de Gray, 25030 Besançon Cedex, France.
Abstract
This study deals with the development of a hybrid SnO2/SWNTs based gas sensor for the detection of O3 and NH3. Experiments concerned the study of the correlation between the physico-chemical properties of carbon nanotubes and the sensor¶s sensitivity. Four samples of SWNTs were investigated and the results showed a strong dependence between the characteristics of such nanomaterials and the efficiency of the hybrid layers for gas detection. c 2009
2010 Published by Elsevier Ltd. © Keywords: SnO2; carbon nanotubes; gas sensors; hybrid material; ozone; ammoniac.
1. Introduction Metal oxide chemical gas sensors are famous for detecting many gases at low concentrations. Nevertheless, these kind of sensors present two major problems: they need to be operated at high temperatures (up to 350°C) and have weak selectivity. Single-walled carbon nanotubes (SWNTs) have emerged as a new class of nanomaterials that receive considerable interest because of their unique structure, high stability and high surface/volume ratio. These properties make them extremely attractive for fabricating chemical sensors. Recent studies highlight the utilization of carbon nanotubes used solely [1, 2] or combined with metal oxide materials [3-6], in order to constitute efficient gas sensors, working at room temperature. This work presents a simple method to develop a hybrid film made with SWNTs and SnO2 using the sol gel method for application to NH3 and O3 gas detection. Results presented here mainly weared on the study of the influence of the properties of carbon nanotubes properties on the efficiency of SnO2/SWNTs hybrid layers.
* Corresponding author : Tel +33 381666517; Fax +33 381666522 E-mail address : [email protected]
c 2010 Published by Elsevier Ltd. 1877-7058 doi:10.1016/j.proeng.2010.09.061
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B. Ghaddab et al. / Procedia Engineering 5 (2010) 115–118 2
B.Ghaddab et al. / Procedia Engineering 00 (2010) 000±000
2. Sensor¶s elaboration and characterization: Four different samples of commercially SWNTs from Nanoledge® (electric arc (EA)) and Comocat® (CVD process), with controlled characteristics, were investigated in this study. SnO2 material was obtained using the solgel method. Carbon nanotubes powder and Triton X were added to a tin-based sol at a concentration of 0.3% and dispersed by ultrasonic vibration for about 1 hour to obtain a well-mixed suspension. The optimization of the sol-gel process (precursor concentration, pH, percent of suspended SWNTs in the sol) was made. Thin hybrid layers (200 nm) were coated onto interdigitated electrodes using the dip coating method. The thin sensitive layers were crystallized in an oxidising atmosphere (air) with a furnace temperatures fixed at either 100°C, 300°C or 500°C, for one hour. The sensor¶s responses to O3 (290 ppb to 21.5 ppb) and NH3 (100 ppm to 1 ppm) were obtained at operating temperature. 3. Results and discussion:
3.1. Interest of using hybrid sensors Experiments were conducted in order to highlight the interest of using hybrid layers compared to pure SWNTs or pure SnO2 layers. Results presented in Fig. 1 clearly show that a pure SnO2 layer did not give any significant results for O3 detection at room temperature. On the other hand, at room temperature, we noticed that hybrid layers enhanced the sensitivity to O3 compared to pure SWNTs layers. Same results were observed for NH3 detection.
Fig. 1. Electrical responses obtained at room temperature for the detection of 174 ppm O3 with pure SnO2 layer, pure SWNTs layer and hybrid SnO2/SWNTs layer.
3.2. Evaluation of the efficiency sensitivity Hybrid SnO2/SWNTs layers were tested for ozone and ammonia detection at various concentration in air. Experiments conducted at room temperature, using different diluted O3 (Fig. 2a) and NH3 (Fig. 2b) atmospheres, allowed the determination of efficiency of detection for both pollutants. Sensors obtained with hybrid sensitive layers enabled the detection of 1 ppm of NH3 and about 21 ppb of O3.
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B. Ghaddab et al. / Procedia Engineering 5 (2010) 115–118 B.Ghaddab et al. / Procedia Engineering 00 (2010) 000±000
(a)
3
(b)
Fig. 2. (a) Electrical responses for various O3 concentrations (21.5 to 290 ppb); (b) Electrical responses for various NH3 concentrations (1 to 100 ppm).
3.3. Influence of SWNTs characteristics onto sensor¶s sensitivity The study of the influence of the properties of carbon nanotubes onto the performance of hybrid layers was investigated. Results presented in Fig. 3 clearly pointed out that the sensor¶s electrical response under O3 strongly depends on the characteristics of the carbon nanotubes. The same behaviour was also observed for NH3 detection. Layers made with large diameters (1 nm) and small diameters (0.8 nm) led to a low electrical response compared to those obtained using medium carbon nanotubes diameter (0.9 nm). Results also showed that process fabrication of carbon nanotubes influence the efficiency of sensor detection. These results confirmed that the steric effect is not the only parameter to be taken into account during the adsorption mechanism.
Fig. 3. Influence of SWNTs characteristics onto sensor¶s sensitivity (O3 174 ppm).
3.4. Influence of annealing temperature Other results connected to the influence of annealing temperature are presented in Fig. 4. It has been shown that unannealing layers present a very weak electrical response to NH3 flow compared to layers annealed at a higher temperature (300°C). In a similar way, a layer annealed at 500°C induced a lowering in NH3 sensitivity. This may
118
B. Ghaddab et al. / Procedia Engineering 5 (2010) 115–118 B.Ghaddab et al. / Procedia Engineering 00 (2010) 000±000
4
be explained by the fact that at 500°C, the annealing process in oxidizing atmospheres, may lead to strong physicochemical modifications of SWNTs properties. Same results were observed for O3 detection.
Fig. 4. Influence of annealing temperature onto sensor¶s sensitivity for various NH3 concentrations.
Conclusion: To conclude, in addition to the fact that these hybrid layers present, a strong sensitivity to O3 and NH3 at room temperature, it appears that carbon nanotubes also play an important role in the adsorption mechanism of target gases and thus on the sensitivity of the chemical gas sensors.
Acknowledgements The authors acknowledge the FEMTO-ST Institute in Besançon, for permitting them entry and free use of the clean room.
References [1] M.Arab, F.Berger, F.Picaud, C.Ramseyer, J. Glory, M. Mayne-L¶Hermite, Direct growth of the multi-walled carbon nanotubes as a tool to detect ammonia at room temperature, Chemical Physics Letters 2006; 433: 175-181. [2] Y.Park, K.Y.Dong, J.Lee, J.Choi, G.N.Bae, B.K.Ju, Development of an ozone gas sensor using singlewalled carbon nanotubes, Sensors and Actuators B 2009; 140: 407-411. [3] B.Y.Wei, M.C.Hsu, P.G.Su, H.M.Lin, R.J.Wu, H.J.Lai, A novel SnO2 gas sensor doped with carbon nanotubes operating at room temperature, Sensors and Actuators B 2004; 101: 81-89. [4] N.D.Hoa, N. V. Quy, Y. S. Cho, D. Kim, Nanocomposite of SWNTs and SnO2 fabricated by soldering process for ammonia gas sensor application, Phys. Stat. Sol. 2007; 204(6): 1820-1824. [5] Y.L.Liu, H.F.Yang, Y.Yang, Gas sensing properties of tin dioxide coated onto multi-walled carbon nanotubes, Thin solid films 2006; 497: 355-360. [6] J.Gong, J.Sun, Q.Chen, Micromachined sol±gel carbon nanotube/SnO2 nanocomposite hydrogen sensor, Sensors and Actuators B 2008; 130: 829-835.
Procedia Engineering www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Proc. Eurosensors XXIV, September 5-8, 2010, Linz, Austria
Detection of O3 and NH3 using tin dioxide/carbon nanotubes based sensors: Influence of carbon nanotubes properties onto sensor¶s sensitivity. B. Ghaddab a, F. Berger a*, J. B. Sanchez a, C. Mavon a. a
Laboratoire de Chimie-Physique et Rayonnements Alain Chambaudet UMR CEA-E4, UFR ST, La Bouloie, 16 route de Gray, 25030 Besançon Cedex, France.
Abstract
This study deals with the development of a hybrid SnO2/SWNTs based gas sensor for the detection of O3 and NH3. Experiments concerned the study of the correlation between the physico-chemical properties of carbon nanotubes and the sensor¶s sensitivity. Four samples of SWNTs were investigated and the results showed a strong dependence between the characteristics of such nanomaterials and the efficiency of the hybrid layers for gas detection. c 2009
2010 Published by Elsevier Ltd. © Keywords: SnO2; carbon nanotubes; gas sensors; hybrid material; ozone; ammoniac.
1. Introduction Metal oxide chemical gas sensors are famous for detecting many gases at low concentrations. Nevertheless, these kind of sensors present two major problems: they need to be operated at high temperatures (up to 350°C) and have weak selectivity. Single-walled carbon nanotubes (SWNTs) have emerged as a new class of nanomaterials that receive considerable interest because of their unique structure, high stability and high surface/volume ratio. These properties make them extremely attractive for fabricating chemical sensors. Recent studies highlight the utilization of carbon nanotubes used solely [1, 2] or combined with metal oxide materials [3-6], in order to constitute efficient gas sensors, working at room temperature. This work presents a simple method to develop a hybrid film made with SWNTs and SnO2 using the sol gel method for application to NH3 and O3 gas detection. Results presented here mainly weared on the study of the influence of the properties of carbon nanotubes properties on the efficiency of SnO2/SWNTs hybrid layers.
* Corresponding author : Tel +33 381666517; Fax +33 381666522 E-mail address : [email protected]
c 2010 Published by Elsevier Ltd. 1877-7058 doi:10.1016/j.proeng.2010.09.061
116
B. Ghaddab et al. / Procedia Engineering 5 (2010) 115–118 2
B.Ghaddab et al. / Procedia Engineering 00 (2010) 000±000
2. Sensor¶s elaboration and characterization: Four different samples of commercially SWNTs from Nanoledge® (electric arc (EA)) and Comocat® (CVD process), with controlled characteristics, were investigated in this study. SnO2 material was obtained using the solgel method. Carbon nanotubes powder and Triton X were added to a tin-based sol at a concentration of 0.3% and dispersed by ultrasonic vibration for about 1 hour to obtain a well-mixed suspension. The optimization of the sol-gel process (precursor concentration, pH, percent of suspended SWNTs in the sol) was made. Thin hybrid layers (200 nm) were coated onto interdigitated electrodes using the dip coating method. The thin sensitive layers were crystallized in an oxidising atmosphere (air) with a furnace temperatures fixed at either 100°C, 300°C or 500°C, for one hour. The sensor¶s responses to O3 (290 ppb to 21.5 ppb) and NH3 (100 ppm to 1 ppm) were obtained at operating temperature. 3. Results and discussion:
3.1. Interest of using hybrid sensors Experiments were conducted in order to highlight the interest of using hybrid layers compared to pure SWNTs or pure SnO2 layers. Results presented in Fig. 1 clearly show that a pure SnO2 layer did not give any significant results for O3 detection at room temperature. On the other hand, at room temperature, we noticed that hybrid layers enhanced the sensitivity to O3 compared to pure SWNTs layers. Same results were observed for NH3 detection.
Fig. 1. Electrical responses obtained at room temperature for the detection of 174 ppm O3 with pure SnO2 layer, pure SWNTs layer and hybrid SnO2/SWNTs layer.
3.2. Evaluation of the efficiency sensitivity Hybrid SnO2/SWNTs layers were tested for ozone and ammonia detection at various concentration in air. Experiments conducted at room temperature, using different diluted O3 (Fig. 2a) and NH3 (Fig. 2b) atmospheres, allowed the determination of efficiency of detection for both pollutants. Sensors obtained with hybrid sensitive layers enabled the detection of 1 ppm of NH3 and about 21 ppb of O3.
117
B. Ghaddab et al. / Procedia Engineering 5 (2010) 115–118 B.Ghaddab et al. / Procedia Engineering 00 (2010) 000±000
(a)
3
(b)
Fig. 2. (a) Electrical responses for various O3 concentrations (21.5 to 290 ppb); (b) Electrical responses for various NH3 concentrations (1 to 100 ppm).
3.3. Influence of SWNTs characteristics onto sensor¶s sensitivity The study of the influence of the properties of carbon nanotubes onto the performance of hybrid layers was investigated. Results presented in Fig. 3 clearly pointed out that the sensor¶s electrical response under O3 strongly depends on the characteristics of the carbon nanotubes. The same behaviour was also observed for NH3 detection. Layers made with large diameters (1 nm) and small diameters (0.8 nm) led to a low electrical response compared to those obtained using medium carbon nanotubes diameter (0.9 nm). Results also showed that process fabrication of carbon nanotubes influence the efficiency of sensor detection. These results confirmed that the steric effect is not the only parameter to be taken into account during the adsorption mechanism.
Fig. 3. Influence of SWNTs characteristics onto sensor¶s sensitivity (O3 174 ppm).
3.4. Influence of annealing temperature Other results connected to the influence of annealing temperature are presented in Fig. 4. It has been shown that unannealing layers present a very weak electrical response to NH3 flow compared to layers annealed at a higher temperature (300°C). In a similar way, a layer annealed at 500°C induced a lowering in NH3 sensitivity. This may
118
B. Ghaddab et al. / Procedia Engineering 5 (2010) 115–118 B.Ghaddab et al. / Procedia Engineering 00 (2010) 000±000
4
be explained by the fact that at 500°C, the annealing process in oxidizing atmospheres, may lead to strong physicochemical modifications of SWNTs properties. Same results were observed for O3 detection.
Fig. 4. Influence of annealing temperature onto sensor¶s sensitivity for various NH3 concentrations.
Conclusion: To conclude, in addition to the fact that these hybrid layers present, a strong sensitivity to O3 and NH3 at room temperature, it appears that carbon nanotubes also play an important role in the adsorption mechanism of target gases and thus on the sensitivity of the chemical gas sensors.
Acknowledgements The authors acknowledge the FEMTO-ST Institute in Besançon, for permitting them entry and free use of the clean room.
References [1] M.Arab, F.Berger, F.Picaud, C.Ramseyer, J. Glory, M. Mayne-L¶Hermite, Direct growth of the multi-walled carbon nanotubes as a tool to detect ammonia at room temperature, Chemical Physics Letters 2006; 433: 175-181. [2] Y.Park, K.Y.Dong, J.Lee, J.Choi, G.N.Bae, B.K.Ju, Development of an ozone gas sensor using singlewalled carbon nanotubes, Sensors and Actuators B 2009; 140: 407-411. [3] B.Y.Wei, M.C.Hsu, P.G.Su, H.M.Lin, R.J.Wu, H.J.Lai, A novel SnO2 gas sensor doped with carbon nanotubes operating at room temperature, Sensors and Actuators B 2004; 101: 81-89. [4] N.D.Hoa, N. V. Quy, Y. S. Cho, D. Kim, Nanocomposite of SWNTs and SnO2 fabricated by soldering process for ammonia gas sensor application, Phys. Stat. Sol. 2007; 204(6): 1820-1824. [5] Y.L.Liu, H.F.Yang, Y.Yang, Gas sensing properties of tin dioxide coated onto multi-walled carbon nanotubes, Thin solid films 2006; 497: 355-360. [6] J.Gong, J.Sun, Q.Chen, Micromachined sol±gel carbon nanotube/SnO2 nanocomposite hydrogen sensor, Sensors and Actuators B 2008; 130: 829-835.