Chemically Engineered Single‐Walled Carbon Nanotube Materials for the Electronic Detection of Hydrogen Chloride

Abstract

The detection of gas analytes relies on a variety of operating mechanisms which include ionization of gases, modulation of optical properties, gas chromatography, mass spectrometry, electrochemistry, conductance modulation in field effect transistors, and chemical resistors. The modulation of the electronic characteristics of a sensor device based on a chemical resistor is a very attractive approach because of its simplicity. In the search for novel sensor materials, which can broaden the range of detected molecules and the limits of detection, single-walled carbon nanotubes (SWNTs) have emerged as a promising candidate. Most of the research in the field has been focused on understanding and exploring the sensitivity of the electronic structure of SWNTs to charge transfer from adsorbed molecules. [1][2][3][4][5][6][7][8] It has been shown that defects, [9,10] non-covalently attached polymers, [11][12][13][14] and metal [15,16] or metal oxide nanoparticles [17] can affect the sensitivity of SWNTs to gas molecules. The research on the ability of SWNTs to act as a sensor material has primarily used gas molecules with electron donating or withdrawing properties such as ammonia and nitrogen dioxide. [1,8,18,19] The mechanism of modulation of the transport properties of SWNTs is usually attributed to charge transfer between the dopant and carbon nanotubes, which is assumed to lead to refilling or depletion of the valence band of the semiconducting SWNTs.Previously we reported that covalent functionalization can dramatically increase the resistance change of SWNT films during exposure to gas molecules. [5,7] The advantages of covalently functionalized SWNT materials for sensor applications are obvious: i) facile dispersibility in solvents and enhanced processability, ii) reproducible and well-defined chemical composition, and iii) possibility of attaching organic moieties specifically engineered to interact with analyte molecules. In our previous work on the sensing mechanism of poly-(m-aminobenzene sulfonic acid)-functionalized SWNTs (SWNT-PABS) toward ammonia, [5,7] we argued that the electron affinity of the attached PABS functionality was modulated by an acid-base equilibrium and that this directly influenced the conductivity by controlling the concentration of holes in the valence band of the semiconducting SWNTs.In the present study we explore the generality of this approach by employing chemically functionalized SWNT materials with a range of basicities and electronic structures and studying the change of their electronic properties on exposure to hydrogen chloride.For this study we synthesized three types of functionalized SWNT materials with covalently attached functional groups of varying basicity (Table 1) and compared the change of their electronic properties to that of purified non-functionalized SWNTs on exposure to HCl. Thin films of the SWNT materials were deposited on a glass substrate with pre-patterned interdigitated gold contacts (Fig. 1a). The SWNT materials were dispersed in a solvent (Table 1) by ...

Sensory Arrays of Covalently Functionalized Single‐Walled Carbon Nanotubes for Explosive Detection

“…An increased base resistance has the effect of lowering the sensitivity for the detection of analyte‐induced resistance increases. Nevertheless, with modest degrees of functionalization, quality sensors have been obtained from covalently functionalized SWCNTs 10b, 14. An important advantage of covalent functionalization is that it produces a more durable sensor relative to non‐covalent compositions that are prone to changes in structure, which can lead to CNT/selector phase separation and decreased sensor performance.…”

New Multifunctional Porous Materials Based on Inorganic–Organic Hybrid Single‐Walled Carbon Nanotubes: Gas Storage and High‐Sensitive Detection of Pesticides

“…Reagents and chemicals: Solvents were distilled under a nitrogen atmosphere from CaH 2 (CH 2 Cl 2 ) or Mg turnings (MeOH) and sparged with ni- www.chemeurj.org trogen gas prior to use. DMF was distilled and dried with molecular sieves (Linde,4 ). Doubly distilled water and 0.1 m phosphate buffer solution (PBS, pH 5.7) were prepared as required.…”

“…[3] Recently, modified SWNTs have shown improved properties for gas storage and as chemical sensors. [4] Kim et al [5] found that the treatment of SWNTs with a mixed HNO 3 /H 2 SO 4 solution re-markably increases the number of narrow micropores on the material, which then exhibits much-improved capacity for H 2 and CH 4 than the original SWNTs. Tour and co-workers [6] introduced covalently linked organic spacer groups into SWNT fibers to provide 3D frameworks that can physisorb twice as much hydrogen per unit surface area as typical macroporous carbon materials.…”

Qualitative Detection Toward Military and Improvised Explosive Vapors by a Facile TiO2 Nanosheet-Based Chemiresistive Sensor Array

“…However, it is confirmed that the covalent functionalization of the SWCNTs can disrupt the extended electronic states and thus increase the base resistance, which may lower the sensitivity (Schnorr et al, 2013). Although quality sensors can be obtained by modest degree of functionalization, the experiment procedure is rather complicated (Bekyarova et al, 2010;Schnorr et al, 2013). In addition, the chemically modified selectors may increase the contact distance due to the existence of the functionalized molecular chains between analytes and the sensing materials, which may lower the sensor sensitivity.…”