Noxious gas detection using carbon nanotubes with Pd nanoparticles
© Choi et al; licensee Springer. 2011
Received: 14 July 2011
Accepted: 24 November 2011
Published: 24 November 2011
Noxious gas sensors were fabricated using carbon nanotubes [CNTs] with palladium nanoparticles [Pd NPs]. An increase in the resistance was observed under ammonia for both CNTs and CNT-Pd sensors. Under carbon monoxide [CO], the two sensors exhibited different behaviors: for CNT sensors, their resistance decreased slightly with CO exposure, whereas CNT-Pd sensors showed an increase in resistance. The sensing properties and effect of Pd NPs were demonstrated, and CNT-Pd sensors with good repeatability and fast responses over a range of concentrations may be used as a simple and effective noxious gas sensor at room temperature.
Carbon nanotubes [CNTs] have a broad variety of structures that have shown applications as materials for a rapid and innovative change in the field of gas sensing . CNTs have recently been proposed as chemical sensors due to their fast response and high sensitivity toward gaseous molecules. However, the chemical and physical interactions between gas molecules and sensing nanotubes are not yet completely understood . Upon exposure to gas molecules, the electrical conductance of CNTs changes and the threshold voltage is shifted due to charge transfer between the semiconducting CNTs and electron-donating (H2S, NH3, CO)/electron-withdrawing (NO2) molecules. Theoretical calculations showed the binding energy of CO and NH3 to carbon nanotubes, which indicates a weak charge transfer. The conductivity change may also be caused by contact between the metal electrode and carbon nanotubes and/or the contact between carbon nanotubes [3, 4].
CNT-based gas sensors offer significant advantages: unlike oxide-based sensors such as SiO2  and ZnO  operated at high temperatures for the detection of noxious gases, CNT-based sensors have various merits ranging from a room-temperature operation to a low detection limit. On the other hand, there are several problems to overcome for their practical application. Recently, the combination of CNTs with metal nanoparticles [NPs] has attracted much attention [7–10], given the possibility of use in electronics, as catalysts and as biochemical sensors [11–16]. Some researchers have modified CNTs with Pd NPs using chemical vapor deposition , sputtering , electron-beam evaporation, thermal evaporation [19, 20], dielectrophoresis [21, 22], or electrodeposition [23, 24]. There have been many efforts to detect noxious gases based on CNTs. In the case of the detection of NH3, single-walled carbon nanotube [SWNT]-SnO2 sensors can detect a low concentration of 10 ppm NH3 gases at room temperature . In addition, in order to improve the sensor's response, some works have been explored with increased operation temperature [26, 27]. For the detection of CO, a PANI-functionalized CNT sensor showed a reversible response to CO in the range of 100 to 500 ppm , and 10 ppm CO detection at 150°C was reported using WO3 films with CNTs . Nevertheless, noxious gas sensing at room temperature using CNT-based sensors appeared to be difficult. In this study, we synthesized noxious gas sensors based on CNTs with reduced Pd NPs. An improvement of the CNTs' response was achieved by employing the reduced Pd NPs, which are likely to react with NH3 and CO and result in more stable and sensitive sensors to these gases. The CNT-Pd sensors were highly sensitive to noxious gases with better repeatability and less noise compared with pure CNT sensors, and the differences in sensing properties of the CNTs and CNT-Pd sensors were compared.
All chemicals were of an analytical reagent grade. Purified arc-discharge nanotubes with a purity of 70% to 90% were purchased from IlJin Nanotech Co., Ltd. (Seoul, South Korea) Sulfuric acid, hydrochloric acid, and nitric acid were purchased from Sigma-Aldrich (St. Louis, MO, USA). Sodium dodecyl sulfate [SDS] surfactant was purchased from Samchun Chemistry (Seoul, South Korea). The purified SWNTs were dissolved in 0.2 wt.% solution of SDS surfactant using deionized water. Dispersion of SWNTs was performed in a bath sonicator for 4 h, and vacuum filtration was performed using Teflon filters (pore size 20 μm, Millipore, Seoul, South Korea). After filtration, the film was rinsed with deionized water for several minutes to remove the SDS surfactant until no bubbles were observed .
The reduced CNT-Pd preparation process is described as follows: Both sulfuric and nitric acids (H2SO4/HNO3 = 1:3) were functionalized with carbon nanotubes (1 mg), which were added to an acetone/H2O (2:1/v:v) solution (15 ml), and ultrasonicated for 30 min. For synthesizing the CNT-Pd with an ethylenediaminetetraacetic acid [EDTA]-2Na/Pd ratio of 1:1, the corresponding 0.0186 g of EDTA-2Na in 5 ml of water was added to 10 ml of 5 mM Na2PdCl4(II) in water. The pH value of the mixture was adjusted to 7 to 8 with an aqueous 0.1 M NaOH solution under vigorous stirring. In the case of the CNT-Pd, 4 ml ethanol was added immediately. The resulting mixture was stirred at 60°C for 3.5 h. Finally, the products were filtered, washed with excess deionized water, and then dispersed in an acetone/H2O (2:1 v:v) solution (15 ml) . A product of reduced Pd on CNTs was fabricated. Transmission electron microscopy [TEM] analysis was performed to investigate the morphology and composition of the reduced CNT-Pd.
Results and discussion
Carboxylic acid group and defect sites may be formed on SWNT sidewalls as a result of purification steps, and interaction with CO molecules likely occurred . Consequently, the COOH functionality and defect sites may play a key role in CO detection, resulting in a decrease in the electrical resistance of CNTs despite the interaction with the electron-donating gas.
For CNTs with Pd NPs, different response properties were observed in Figures 3c, d when exposed to the same gas concentrations. It is inferred that the sensing response was changed by the Pd NPs, such that CNT-Pd sensors increased resistance for the two gases due to the electron transfer to the CNT-Pd sensors. Based on the sensing results, CNT-Pd sensors provided a more reversible reaction, relatively less noise, fast response, good repeatability, a low detection limit, room temperature capability, and complete recovery compared to the abilities of the pure CNT sensors. These responses indicate that the CNT sensors were directly influenced by the properties of the two gases.
where R initial and R after are the resistances before and after the presence of noxious gases, respectively . Figures 4b, d show that the sensitivity to each gas was nearly linear, so the gas concentrations can be calculated from the sensitivity during noxious gas exposure.
In addition, the response time, defined as the time to reach 90% of the total change in electrical resistance change, was also evaluated . For all gases, CNT-Pd sensors showed response times ranging from 8 to 16 s. The response time was generally faster with increasing gas concentrations. Figures 4b, d can be separated into two parts: the rapid and slow responses. The rapid response arises from molecular adsorption onto the low-energy binding sites, such as sp 2-bonded carbon, and the slow response arises from molecular interactions with higher-energy binding sites, such as vacancies, structural defects, and oxygen functional groups. Adsorption onto an sp 2-bonded carbon occurs through weak dispersive forces; however, at a defect such as a carboxylic acid group, single- and double-hydrogen bonds allow binding energies of at least several hundred millielectron volts/molecule, the main difference between the rapid and slow responses.
We successfully fabricated a noxious gas sensor for the detection of NH3 and CO gases at room temperature using CNTs with reduced Pd NPs. The carboxylic acid group and defect sites appeared to play an important role in the electrical change of pure CNTs to CO. However, the electrical resistance of CNT-Pd sensors increased with exposure to gas via electron transfer. Unlike pure CNT sensors, CNT-Pd sensors exhibited a fast response, linear sensitivity, a low detection limit, and good repeatability over a variety of NH3 and CO concentrations and also showed better repeatability and less noise. Moreover, CNT-Pd sensors detected concentrations as low as 7 ppm of NH3 and 20 ppm of CO, with a response time of less than 16 s. The characteristics of the CNT-Pd sensors suggest a hopeful candidate for noxious gas sensors, especially those for NH3 and CO.
- NH3 :
This work was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0093823).
- Zhao J, Buldum A, Han J, Lu HP: Gas molecule adsorption in carbon nanotubes and nanotube bundles. Nanotechnology 2002, 13: 195.View Article
- Zhao Q, Nardelli MB, Lu W, Bernhoc J: Carbon nanotube-metal cluster composites: a new road to chemical sensors? Nano Lett 2005, 5: 847.View Article
- Chang YW, Choi HH, Yoo KH: Electrically refreshable carbon-nanotube-based gas sensors. Nanotechnology 2007, 18: 435504.View Article
- Santucci S, Picozzi S, Gregorio FD, Lozzi L, Cantalini C, Valentini L, Kenny JM, Delley B: NO and CO gas adsorption on carbon nanotubes: experiment and theory. J of Chem Physics 2003, 119: 10904.View Article
- Yu Q, Wang K, Luan C, Geng Y, Lian G, Cui D: A dual-functional highly responsive gas sensor fabricated from SnO 2 porous nanosolid. Sens Actuators B 2011, 159: 271.View Article
- Moon W, Jun Y, Kim H, Kim W, Hong S: CO gas sensing properties in Pd-added ZnO sensors. J Electroceram 2009, 23: 196.View Article
- Thelander C, Magnusson MH, Depper K, Samuelson L, Poulsen PR, Nygard J, Borggreen J: Gold nanoparticle single-electron transistor with carbon nanotube leads. Appl Phys Lett 2001, 79: 2106.View Article
- Rong LQ, Yang C, Qian QY, Xia XH: Study of the nonenzymatic glucose sensor based on highly dispersed Pt nanoparticles supported on carbon nanotubes. Talanta 2007, 72: 819.View Article
- Sun Z, Yuan H, Liu Z, Han B, Zhang X: A highly efficient chemical sensor material for H 2 S: α-Fe 2 O 3 nanotubes fabricated using carbon nanotube templates. Adv Mater 2005, 17: 2993.View Article
- Ju S, Lee JM, Jung Y, Lee E, Lee W, Kim S: Highly sensitive hydrogen gas sensors using single-walled carbon nanotubes grafted with Pd nanoparticles. Sens Actuators B 2010, 146: 122.View Article
- Lee HS, Lee HJ, Choi HH, Yook JG, Yoo KH: Carbon-nanotube-resonator-based biosensors. Small 2008, 4: 1723.View Article
- Wongwiriyapan W, Inoue S, Ito T, Shimazaki R, Maekawa T, Suzuki K, Ishikawa H, Honda S, Oura K, Katayama M: Highly sensitive detection of carbon monoxide at room temperature using platinum-decorated single-walled carbon nanotubes. Appl Phys Expr 2008, 1: 014004.View Article
- Suehiro J, Imakiire H, Hidaka S, Ding W, Zhou G, Imasaka K, Hara M: Schottky-type response of carbon nanotube NO 2 gas sensor fabricated onto aluminum electrodes by dielectrophoresis. Sens Actuators B 2006, 114: 943.View Article
- Star A, Joshi V, Skarupo S, Thomas D, Gabrie JP: Gas sensor array based on metal-decorated carbon nanotubes. J Phys Chem B 2006, 110: 21014.View Article
- Li J, Lu Y, Ye Q, Delzeit L, Meyyappan M: A gas sensor array using carbon nanotubes and microfabrication technology. Electrochem Solid State Lett 2005, 8: 100.View Article
- Lee HS, Lee HJ, Choi HH, Yoo KH, Yook JG: An RF circuit model for interdigital capacitors-based carbon nanotube biosensors. IEEE Trans Nanotech 2010, 9: 682.View Article
- Sun YP, Huang W, Lin Y, Kefu Y: Soluble dendron-functionalized carbon nanotubes: preparation, characterization, and properties. Chem Mater 2001, 13: 2864.View Article
- Sayago I, Terrado E, Lafuente E: Hydrogen sensors based on carbon nanotubes thin films. Synth Met 2005, 148: 15.View Article
- Sippel-Oakley J, Wang HT, Kang BS, Wu Z, Ren F, Rinzler AG, Pearton SJ: Carbon nanotube films for room temperature hydrogen sensing. Nanotechnology 2005, 16: 2218.View Article
- Sun Y, Wang HH, Xia M: Single-walled carbon nanotubes modified with Pd nanoparticles: unique building blocks for high-performance, flexible hydrogen sensors. J Phys Chem C 2008, 112: 1250.View Article
- Suehiro J, Zhou G, Hara M: Fabrication of a carbon nanotube-based gas sensor using dielectrophoresis and its application for ammonia detection by impedance spectroscopy. J Phys D: Appl Phys 2003, 36: 109.View Article
- Suehiro J, Hidaka SI, Yamane S, Imasaka K: Fabrication of interfaces between carbon nanotubes and catalytic palladium using dielectrophoresis and its application to hydrogen gas sensor. Sens Actuators B 2007, 127: 505.View Article
- Sun Y, Wang HH: Electrodeposition of Pd nanoparticles on single-walled carbon nanotubes for flexible hydrogen sensors. Appl Phys Lett 2007, 90: 213107.View Article
- Schlecht U, Balasubramanian K, Burghard M: Electrochemically decorated carbon nanotubes for hydrogen sensing. Appl Surf Sci 2007, 253: 8394.View Article
- Hoa ND, Quy NV, Cho YS, Kim D: Nanocomposite of SWNTs and SnO 2 fabricated nanocomposite of SWNTs and SnO 2 fabricated. Phys Status Solidi A 2007, 204: 1820.View Article
- Cantalini C, Valentini L, Lozzi L, Armentano I, Kenny JM, Santucci S: NO 2 gas sensitivity of carbon nanotubes obtained by plasma enhanced chemical vapor deposition. Sens Actuators B 2003, 93: 333.View Article
- Nguyen HQ, Huh JS: Behavior of single-walled carbon nanotube-based gas sensors at various temperatures of treatment and operation. Sens Actuators B 2006, 117: 426.View Article
- Wanna Y, Srisukhumbowornchai N, Tauntranont A, Wisitsoraat A, Thavarungkul N, Singjai P: The effect of carbon nanotube dispersion on CO gas sensing characteristics of polyaniline gas sensor. J Nanosci Nanotechnol 2006, 6: 3893.View Article
- Bittencourt C, Felten A, Espinosa EH, Ionescu R, Llobet E, Correig X, Pireaux JJ: WO 3 films modified with functionalised multi-wall carbon nanotubes: morphological, compositional and gas response studies. Sens Actuators B 2006, 115: 33.View Article
- Hou PX, Liu C, Tong Y, Xu ST, Liu M, Cheng HM: Purification of single-walled carbon nanotubes synthesized by the hydrogen arc-discharge method. J Mater Res 2001, 16: 2526.View Article
- Liu JM, Meng H, Li JI, Liao S, Bu JH: Preparation of high performance Pt/CNT catalysts stabilized by ethylenediaminetetraacetic acid disodium salt. Fuel Cells 2007, 7: 402.View Article
- Peng N, Zhang Q, Chow CL, Tan OK, Marzari N: Sensing mechanisms for carbon nanotube based NH3 gas detection. Nano Lett 2009, 9: 1626.View Article
- Kauffman DR, Star A: Carbon nanotube gas and vapor sensors. Angew Chem Int Ed 2008, 47: 6550.View Article
- Fu D, Lim H, Shi Y, Dong X, Mhaisalkar SG, Chen Y, Moochhala S, Li L: Differentiation of gas molecules using flexible and all-carbon nanotube devices. J Phys Chem C 2008, 112: 650.View Article
- Ong KG, Zeng K, Grimes CA: A wireless, passive carbon nanotube-based gas sensor. IEEE Sens J 2002, 2: 88.
- Lee JM, Lee W: Effects of surface roughness on hydrogen gas sensing properties of single Pd nanowires. J Nanosci Nanotechnol 2011, 11: 2151.View Article
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.