Abstract
Different grades of chemically functionalized carbon nanotubes (CNT) have been processed by spraying layer-by-layer (sLbL) to obtain an array of chemoresistive transducers for volatile organic compound (VOC) detection. The sLbL process led to random networks of CNT less conductive, but more sensitive to vapors than filtration under vacuum (bucky papers). Shorter CNT were also found to be more sensitive due to the less entangled and more easily disconnectable conducting networks they are making. Chemical functionalization of the CNT’ surface is changing their selectivity towards VOC, which makes it possible to easily discriminate methanol, chloroform and tetrahydrofuran (THF) from toluene vapors after the assembly of CNT transducers into an array to make an e-nose. Interestingly, the amplitude of the CNT transducers’ responses can be enhanced by a factor of five (methanol) to 100 (chloroform) by dispersing them into a polymer matrix, such as poly(styrene) (PS), poly(carbonate) (PC) or poly(methyl methacrylate) (PMMA). COOH functionalization of CNT was found to penalize their dispersion in polymers and to decrease the sensors’ sensitivity. The resulting conductive polymer nanocomposites (CPCs) not only allow for a more easy tuning of the sensors’ selectivity by changing the chemical nature of the matrix, but they also allow them to adjust their sensitivity by changing the average gap between CNT (acting on quantum tunneling in the CNT network). Quantum resistive sensors (QRSs) appear promising for environmental monitoring and anticipated disease diagnostics that are both based on VOC analysis.
Highlights
Carbon nanotubes (CNT), which were discovered by Lukyanovich et al [1] and further popularized by Iijima [2], have initially attracted a considerable amount of attention, due to their capability to adsorb/desorb small gas molecules, such as hydrogen [3,4,5,6] or oxygen [7]
(90%), are not subject to chirality restrictions on electrical properties, are less sensitive to damages resulting from chemical grafting, are generally amenable to more aggressive processing and can be produced with a lower price at a larger scale. This is why we have reported in this paper different ways to optimize the sensitivity and the selectivity of CNT-based quantum resistive sensors (QRS) for volatile organic compound (VOC)
The results further indicate that both the selectivity and sensitivity of the transducers can be improved through several mechanisms that optimize the CNT network structure or enhance the interactions between VOC and carbon nanotubes
Summary
Carbon nanotubes (CNT), which were discovered by Lukyanovich et al [1] and further popularized by Iijima [2], have initially attracted a considerable amount of attention, due to their capability to adsorb/desorb small gas molecules, such as hydrogen [3,4,5,6] or oxygen [7]. Conductance, providing a chemical gating effect that could be utilized for molecular sensing [15] Most of these studies have focused on single-walled carbon nanotubes (SWNT), whereas on the other hand, multi-walled carbon nanotubes (MWNT) can be produced with relatively high purity (90%), are not subject to chirality restrictions on electrical properties, are less sensitive to damages resulting from chemical grafting, are generally amenable to more aggressive processing and can be produced with a lower price at a larger scale. This is why we have reported in this paper different ways to optimize the sensitivity and the selectivity of CNT-based quantum resistive sensors (QRS) for VOC analysis at room temperature, by controlling their conducting architecture’s structure and chemical nature
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