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SENSOR PROPERTIES OF CARBON NANOTUBES

SENSOR PROPERTIES OF CARBON NANOTUBES. Irina Zaporotskova Volgograd State University Russia.

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SENSOR PROPERTIES OF CARBON NANOTUBES

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  1. SENSOR PROPERTIES OF CARBON NANOTUBES Irina Zaporotskova Volgograd State University Russia

  2. The discovery of carbon nanotubes is one of the most important achievements of the advanced science. Nanotubes are the new materials with unique physicochemical properties. Carbon nanotubes can find applications in a great number of areas: • as additives to polymers, • in autoelectron emission for cathode rays of lighting components, • flat displays, • lithium battery anodes, • hydrogen storage, • composite materials, • nanoprobes, • Sensors , ect. [1,2] [1] M.S. Dresselhaus, G. Dresselhaus, P. Avouris, Сarbon Nanotubes: Synthesis, Structure, Properties, and Application, Springer-Verlag, 2000, p. 464. [2] P.N. D ׳yachkov, Elektronnye svoistva i primenenie nanotrubok [Electronic properties and applications of nanotubes], BINOM, Laboratoriya znanii, Moscow, 2010, p. 488.

  3. Carbon nanotube: A nanotube is a surface structure, so its whole weight is concentrated in its surface layers. This feature is the origin of the uniquely large unit surface of tubulenes which in turn predetermines their electrochemical and adsorption properties [3]. The high sensitivity of the electronic properties of nanotubes to molecules adsorbed on their surface and the unparalleled unit surface providing for this high sensitivity make CNT a promising starting material for the development of superminiaturized chemical and biological sensors. The operation principle of these sensors is based on changes in the V–I curves of nanotubes as a result of adsorption of specific molecules on their surface. The use of CNT in sensor devices is one of their most promising applications in electronics. [3] A.V. Eletskii, Sorption properties of carbon nanostructures, Phys. Usp. 47 (11)(2004) 1119–1154. http://dx.doi.org/10.1070/PU2004v047n11ABEH002017.

  4. Gas sensors based on carbon nanotubes Several types of gas sensors on the basis of the CNT are discussed in literature: – sorption gas sensors; – ionization gas sensors; – capacitance gas sensors; – resonance frequency shift gas sensors.

  5. Sorption gas sensors The main operation principle of sorption gas sensors is adsorption during which an adsorbed gas molecule transfers an electron to or takes it from a nanotube. This changes the electrical properties of the CNT, and this change can be detected [3]. [3] Zhang Wei-De, Zhang Wen-Hui, Carbon nanotubes as active components for gas sensors, J. Sens. 2009 (2009) 16. http://dx.doi.org/10.1155/2009/160698.

  6. There are gas sensors based: 1 - On pure CNT including mono and multiwalled ones, 2 - On CNT modified by functional groups, 3 - On CNT modified by metals, 4 - On CNT modified by polymers, 5 - On CNT containing various surface defects. CNT modification changes the electronic properties of the nanotubes and increases their selectivity and response to specific gases.

  7. 1 – gas sensors based on pure CNT A sensor was designed [4] for detecting gases and organic vapors at room temperature the detection limit of which was as low as 44 ppb for NO2 and 262 ppb for nitrotoluene. The recovery time of that sensor was ~10 h due to the high bond energy between the CNT and some gases. Then this recovery time was reduced to 10 min by exposing to UV radiation which facilitated the desorption of gas molecules. To reduce the sensor recovery time after gas detection by a sorption mechanism, attempts were made to accelerate gas desorption by heating sensor detectors [5]. [4] J. Li, Y. Lu, Q. Ye, M. Cinke, J. Han, M. Meyyappan, Carbon nanotube sensors for gas and organic vapor detection, Nano Lett. 3 (7) (2003) 929–933. http:// dx.doi.org/10.1021/nl034220x. [5]. Nguyen, H.-Q. Behavior of single-walled carbon nanotube-based gas sensors at various temperatures of treatment and operation / H.-Q. Nguyen, J.-S. Huh // Sensors and Actuators B.- 2006. - Vol. 117, no. 2. - P. 426–430.

  8. The possibility of fabricating multiwalled CNT based sensors was discussed in [6,7]. Sensor on the basis of ultrathin CNT films [8] was used for NO2 and NH3 detection at room temperature. The authors proposed a method of synthesizing ~5 nm thick films with a high density of nanotubes ensuring high sensitivity and reproducibility of the sensor, i.e. 1 ppm for NO2 and 7 ppm for NH3. Gas desorption was accelerated by UV exposure. [6] O.K. Varghese, P.D. Kichambre, D. Gong, K.G. Ong, E.C. Dickey, C.A. Grimes, Gas sensing characteristics of multi-wall carbon nanotubes, Sens. Actuators B: Chem. 81 (1) (2001) 32–41. http://dx.doi.org/10.1016/S0925-4005(01)00923-6. [7] L.H. Nguyen, T.V. Phi, P.Q. Phan, H.N. Vu, C. Nguyen-Duc, F. Fossard, Synthesis of multi-walled carbon nanotubes for NH3 gas detection, Physica E. 37 (1–2) (2007) 54–57. http://dx.doi.org/10.1016/j.physe.2006.12.006. [8] C. Piloto, F. Mirri, E.A. Bengio, M. Notarianni, B. Gupta, M. Shafiei, M. Pasquali, N. Motta, Room temperature gas sensing properties of ultrathin carbon nanotube films by surfactant-free dip coating, Sens. Actuators B: Chem. 227 (2016) 128–134. http://dx.doi.org/10.1016/j.snb.2015.12.051.

  9. 2 - gas sensors based on CNT modified by functional groups CNT are often modified by adding the carboxyl group –СООН. This group creates reactive sections at the terminations and the side walls of the CNT where active interaction with various compounds occurs. For example, it was shown [9] that sensors synthesized from carboxylated single-walled CNT were sensitive to CO with a 1 ppm detection limit whereas pure single-walled CNT did not respond to this gas. [9] D. Fu, H. Lim, Y. Shi, X. Dong, S.G. Mhaisalkar, Y. Chen, S. Moochhala, L.-J. Li, Differentiation of gas molecules using flexible and all-carbon nanotube devices, J. Phys. Chem. C 112 (3) (2008) 650–653. http://dx.doi.org/10.1021/jp710362r.

  10. The NO2 gas sensitivity of single-walled CNT functionalized by the amino group –NH2 was studied [10]. The amino group acts as a charge transfer agent of the semiconducting CNT that increases the number of electrons transferred from the nanotube to the NO2 molecule. [10] T.H. Tran, J.-W. Lee, K. Lee, Y.D. Lee, B.-K. Ju, The gas sensing properties of single-walled carbon nanotubes deposited on an aminosilane monolayer, Sens. Actuators B: Chem. 129 (1) (2008) 67–71. http://dx.doi.org/10.1016/j.snb.2007.07.104.

  11. 3 - Gas sensors based on CNT modified by metallic nanoparticles There are gas sensors based on CNT modified by metallic nanoparticles. The working principle of a sensor on the basis of single-walled CNT with palladium (Pd) nanoparticles for hydrogen detection at room temperature was described [11]. The response time of the sensor was 5–10 s, the recovery time being ~400 s. Adsorbed H2 molecules are known to dissociate at room temperature into hydrogen atoms that are dissolved in Pd and reduce the metal work function. As a result the carrier concentration in the nanotubes decreases and their conductivity drops. Other metals can also be used for the design of CNT based gas sensors. Sensors on the basis of multilayered nanotubes functionalizedby Pt or Pd were fabricated [12,13]. They showed good H2 sensitivity and recovery at room temperature. ________________________________________________________________________________________________ [11] J. Kong, M.G. Chapline, H.J. Dai, Functionalized carbon nanotubes for molecular hydrogen sensors, Adv. Mater. 13 (18) (2001) 1384–1386. http://dx.doi.org/10.1002/1521-4095(200109)13:18 < 1384::AID-ADMA1384 > 3.0.CO;2-8. [12] M.K. Kumar, S. Ramaprabhu, Palladium dispersed multiwalled carbon nanotube based hydrogen sensor for fuel cell applications, Int. J. Hydrog. Energy. 32 (13) (2007) 2518–2526. http://dx.doi.org/10.1016/j.ijhydene.2006.11.015. [13] Q.Nie,W.Zhang,L.Wang, Z.Guo et al. Sensitivity enhanced, stability improved ethanol gas sensor based on multi-wall carbon nanotubes functionalized with Pt-Pd nanoparticles//Sensors and Actuators B: Chemical, Volume 270, 1 October 2018, Pages 140-148, https://doi.org/10.1016/j.snb.2018.04.170

  12. 4 - Sensors on the basis of CNT functionalized by polymers There are also gas sensors on the basis of CNT functionalized by polymers that show good performance at room temperature [14-16]. It was shown that field effect transistors based on monolayer CNT modified by polyethyleneimine can be used as gas sensors with improved response and selectivity for NO2, CO, CO2, CH4, H2 and O2.These sensors were able to detect less than 1 ppm NO2 within a response time of 1–2 min. [14] Y. Zhou, Y. Jiang, G. Xie, X. Du, H. Tai, Gas sensors based on multiple-walled carbon nanotubes-polyethylene oxide films for toluene vapor detection, Sens.Actuators B: Chem. 191 (2014) 24–30. http://dx.doi.org/10.1016/j.snb.2013.09.079. [15] S.F. Liu, S. Lin, T.M. Swager, An organocobalt-carbon nanotube chemiresistive carbon monoxide detector, ACS Sens. 1 (4) (2016) 354–357. http://dx.doi.org/10.1021/acssensors.6b00005. [16] P. Slobodian, P. Riha, R. Olejnik, J. Matyas, M. Kovar. Poisson effect enhances compression force sensing with oxidized carbon nanotube network/polyurethane sensor//Sensors and Actuators A: Physical, Volume 271, 1 March 2018, Pages 76-82. https://doi.org/10.1016/j.sna.2017.12.035

  13. 5 - Sensors on the basis of CNT containing various surface defects Many researchers dealt with CNT based gas sensors containing various surface defects. For example, CNT based sensors doped with boron and nitrogen were described [17]. These sensors were used for detecting low NO2, CO, C2H4 and H2O concentrations at room temperature and at 150 °C. ____________________________________________________________________________________________________________________________ [17] J.-J. Adjizian, R. Leghrib, A.A. Koos, I. Suarez-Martinez, A. Crossley, Wagner Ph, N. Grobert, E. Llobet, Ch. P. Ewels, Boron- and nitrogen-doped multi-wall carbon nanotubes for gas detection, Carbon 66 (2014) 662–673. http://dx.doi.org/10.1016/j.carbon.2013.09.064.

  14. Another study [18] dealt with sensors on the basis of single-walled CNT containing vacancy surface defects formed as a result of high temperature exposure (300–800 °C). Measurements of the sensitivity of those sensors to NO2, NH3 and H2 showed higher sensitivity of defect containing sensors compared to defect free ones at room temperature. The authors hypothesized that part of gas molecules are adsorbed on nanotube surfaces while others penetrate into openings produced on nanotube walls as a result of high temperature exposure. (a) Model of sensor on the basis of monolayer CNT modified by defects and (b)SEM image of CNT on sensor. [18] J. Kim, S.-W. Choi, J.-H. Lee, Y. Chung, Y.T. Byun, Gas sensing properties of defect-induced single-walled carbon nanotubes, Sens. Actuators B: Chem. 228 (2016) 688–692. http://dx.doi.org/10.1016/j.snb.2016.01.094.

  15. Ionization gas sensors The problem of detecting gas molecules with low adsorption energies was resolved by using ionization gas sensors. The working principle of these sensors is based on the determination of gas ionization parameters during accelerated ion collision with gas molecules. If voltage is applied between the anode and the cathode the nanotubes induce high electric field at their terminations due to their high aspect ratio [19]. These conditions are favorable for the formation of discharge at lower voltages required. Results for NH3, CO2, N2, O2, He and Ar gas detection with these sensors were reported. __________________________________________________________ [19] Z. Hou, D. Xu, B. Cai, Ionization gas sensing in a microelectrode system with carbon nanotubes, Appl. Phys. Lett. 89 (21) (2006) 213502. http://dx.doi.org/10.1063/1.2392994.

  16. Capacitance gas sensors A capacitance sensor was described [20] the sensitive element of which was an array of misoriented nanotubes grown on a SiO2 layer. The first plate of the sensor was a CNT array, the other plate being silicon. If external voltage is supplied between the two plates, high magnitude electric fieldis generated at the CNT terminations causing polarization of adsorbed molecules and an increase in the capacity. High sensitivity of that sensor to vapors of benzene, hexane, heptanes, toluene, isopropylalcohol, ethanol, chlorobenzene, methyl alcohol, acetone and dinitrotoluenewas demonstrated. The main drawback of capacitance gas sensors are irreversible CNT changes caused by gas chemisorptions. So this sensors must be replacement. ____________________________________________________________________________  [20] J.T.W. Yeow, J.P.M. She, Carbon nanotube-enhanced capillary condensation for a capacitive humidity sensor, Nanotechnology 17 (21) (2006) 5441–5448. http://dx.doi.org/10.1088/0957-4484/17/21/026.

  17. Electrochemical and biological sensors on the basis of CNT A special group of sensors are electrochemical and biosensors that contain CNT. Their typical working principleis based on oxidation and reduction reactions occurring during the interaction with biomolecules. Electrochemical sensors with CNT have found general application in biomedical research [21]. Electrochemical sensors and biosensors were studied [22] the electrodes of which were CNT modified by redox polymers acting as catalysts of the electron transfer reaction between biomolecules and nanotubes [23,24]. These biosensors allow detecting glucose, ethanol, hydrogen peroxide, nitride, sorbitol, uric and ascorbicacids, dopamine etc. [21] V.A. Buzanovskii, Electrochemical sensors based on carbon nanotubes and their use in biomedical research, Biomeditsinskayakhimiya 57 (6) (2011) 12–31. http://dx.doi.org/10.18097/pbmc20125801012. [22] M.M. Barsan, M.E. Ghica, C.M.A. Brett, Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes, Anal. Chim. Acta 881 (2015) 1–23. http://dx.doi.org/10.1016/j.aca.2015.02.059. [23] A. Chen, S. Chatterjee, Nanomaterials based electrochemical sensors for biomedical applications, Chem. Soc. Rev. 42 (12) (2013) 5425–5438. http://dx.doi.org/10.1039/C3CS35518G. [24] J. Jiao, J. Zuo, H. Pang, L.Tan, T.Chen, H.Ma. A dopamine electrochemical sensor based on Pd-Pt alloy nanoparticles decorated polyoxometalate and multiwalled carbon nanotubes//Journal of Electroanalytical Chemistry, Volume 827, 15 October 2018, Pages 103-111. https://doi.org/10.1016/j.jelechem.2018.09.014

  18. Boundary modified CNT as active components of sensor devices Sensors can also be based on boundary modified CNT. This nanotube with a functional group can be located on the tip of the atomic force microscope. Experiments were reported [25] in which CNT were obtained with one of the boundaries being modified by carboxyl group. In the experiments the authors used a multi-walled nanotube attached to the golden pyramid of the microscope׳s silicon cantilever. A carboxyl group (–СООН) formed at the open nanotube boundary. It was reported that carboxylated CNT are sensitive to ethanol vapors and NO, СО and NO2 gases. If necessary the carboxyl group can be substituted for other functional groups using methods applied in organic chemistry. [25] Maklin, J. Nitric oxide gas sensors with functionalized carbon nanotubes / J. Maklin, T. Mustonen, K. Kordas, S. Saukko, G. Toth, J. Vahakangas // Physica Status Solidi B. - 2007. - Vol. 244, no. 11. - P. 4298.

  19. ? It is logical to assume that the use of modified CNT as sensors may not be restricted to gas detection. Other chemical elements, e.g. metals, can also be sensed. It is also possible to differentiate between metal atoms and their ions contained in salts and alkali. !

  20. Carboxylated CNT We studied the mechanism of –СООН functional group attachment to a single-walled semi-infinite carbon nanotube zig-zag (6,0). Nanotubes were simulated within the molecular cluster model using the DFT calculation method. One of the cluster boundaries was terminated by pseudoatoms hydrogen, and a carboxyl group was attached to the carbon atom at the other CNT boundary. Model of semi-infinite CNT (6, 0) with functional carboxyl group

  21. We studied the interaction mechanism between potassium, sodium and lithium atoms with terminal oxygen and hydrogen atoms of the carboxyl group. The process was simulated by step-by-step approximation of the selected metal atoms to the O or H atom of the functional group. Energy curve of this process - Fig. 1. а) b) Fig. 1. Energy profiles of interaction between CNT modified by carboxyl group –СООН and Na, K and Li depending on distance between (a) metal atoms and hydrogen atom of the group and (b) metal atoms and oxygen atom of the group.

  22. The main parameters of К, Li and Na atom attachment to the atoms of the carboxyl group are in the Table 1. The interaction distances corresponding to the minima in the energy profiles are quite large. So we can assume that the interaction between the functional group atoms and the selected metal atoms is the weak Vander-Waals one. This is an important result confirming the possibility of multiple reusing of these probes without destruction which could be caused by chemical interaction with the selected alkaline metal atoms. Table 1. Main parameters of К, Li and Na attachment to the O and H atoms of the carboxyl group.

  23. We studied the scanning of a surface containing sodium, potassium or lithium atoms to be initialized and determined the sensitivity of CNT with functional groups to selected chemical elements. Fig. 2. Simulation of scanning of an arbitrary surface area containing Na atom (shown as purple ball). Dashed line shows sodium atom migration relative to nanotube with functional carboxyl group. Green balls in the figure show carbon atoms, red balls are oxygen atoms and white ones are hydrogen atoms.

  24. Fig. 3. Profiles of energy interaction between (a) atoms or (b) ions of metal (K, Li, Na)and CNT + СООН system obtained by simulation of scanning. r = 0 is the point under the hydrogen atom of the carboxyl group. Table 2 Main parameters of interaction of carboxylated CNT (6, 0) with metal atoms and ions asdetermined by surface scanning.

  25. Carbon nanotubes boundary modified by amino group and nitro group

  26. The study of the attachment of metal atoms and ions to the system "CNT-functional group" (a) (b) Fig. 4. The energy curves of the interaction between atoms (or ions) of metals (Na, K, Li) and CNT (6, 6), modified amino (a) and nitro (b) group

  27. Table 3. Main parameters of К, Li and Na attachment to CNT (6, 6) modified by amino group. Table 4. Main parameters of interaction of CNT (6, 0) modified by amino group with sodium, potassium and lithium atoms and ions as determined by arbitrary surface scanning simulation.

  28. Table 5. Some of the main parameters characterizing the scanning process.

  29. These theoretical studies provided an explanation of the mechanism of the formation of a sensor on the base of carbon nanotube boundary modified by some functional group. The use of chemically modified nanotubes in atomic force microscopy is a way to the fabrication of probes with specified chemical characteristics.

  30. Summary Experimental and theoretical studies showed that CNT are an extremely promising material for further use in the field. Further development of nanotube technologies will provide new physical objects the properties of which will be of great scientific and practical interest. Thanks to their unique structure and properties the CNT can be used as active elements of sensors for the detection of numerous materials including gases, organic compounds, metals etc. Sensors fabricated on their basis will have high selectivity and response to the presence of ultralow quantities of materials, e.g. metals included in salts and alkali, and this shows good promise for their use in chemistry, biology, medicine etc.

  31. THANK YOU FOR ATTENTION!

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