Hydrophilicity and carbon chain length effects on the gas sensing properties of chemoresistive, self-assembled monolayer carbon nanotube sensors

Abstract

Here we describe the development of chemoresistive sensors employing oxygen-plasma-treated, Au-decorated multiwall carbon nanotubes (MWCNTs) functionalized with self-assembled monolayers (SAMs) of thiols. For the first time, the effects of the length of the carbon chain and its hydrophilicity on the gas sensing properties of SAMs formed on carbon nanotubes are studied, and additionally, the gas sensing mechanisms are discussed. Four thiols differing in the length of the carbon chain and in the hydrophobic or hydrophilic nature of the head functional group are studied. Transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy are used to analyze the resulting gas-sensitive hybrid films. Among the different nanomaterials tested, short-chain thiols having a hydrophilic head group, self-assembled onto Au-decorated carbon nanotubes were most responsive to nitrogen dioxide and ethanol vapors, even in the presence of ambient humidity. In particular, this nanomaterial was about eight times more sensitive to nitrogen dioxide than bare Au-decorated carbon nanotubes when operated at room temperature. This response enhancement is attributed to the interaction, via strong hydrogen bonding, of the polar molecules tested to the polar surface of hydrophilic thiols. The approach discussed here could be extended further by combining hydrophilic and hydrophobic thiol SAMs in Au-MWCNT sensor arrays as a helpful strategy for tuning sensor response and selectivity. This would make the detection of polar and nonpolar gas species employing low-power gas sensors easier, even under fluctuating ambient moisture conditions.

Multiwalled carbon nanotube based aromatic volatile organic compound sensor: sensitivity enhancement through 1-hexadecanethiol functionalisation

“…It was also shown to improve the sensor response dynamics. These results combined with previous results [22,32] could be interesting for the development of functionalised multisensor arrays combined with an artificial intelligence algorithm for selectivity enhancement.…”

“…Moreover, other techniques were used for thiol monolayer characterisation. In previous work [31–32], different thiol chains were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. In summary, the obtained FTIR results confirm the covalent functionalisation of Au-decorated MWCNTs with HDT.…”

“…The effect of ambient moisture on the sensor response was studied in a previous work [32]. The response to vapours remains basically unchanged for sensors employing hydrophobic thiols due to their hydrophobicity [31].…”

Thiol-Amine Functionalized Decorated Carbon Nanotubes for Biomarker Gases Detection

“…The functionalization of MWCNTs with SAMs of highly hydrophobic thiols, such as the one employed here, has been found to result in a gas-sensitive material highly resilient to ambient moisture. Casanova and co-workers reported in [79] that the gas sensing properties of MWCNT mats functionalized with hydrophobic thiols via the SAM technique were barely affected by strong humidity changes. Therefore, we can expect the results discussed here to remain valid under conditions similar to the ones of a real breath sample analysis.…”

Spacer Engineering of Thiophene-Based Two-Dimensional/Three-Dimensional Hybrid Perovskites for Stable and Efficient Solar Cells

“…Although the steric hindrance of BA is small, the hydrophobicity of the short alkyl chain is relatively weak, so the stability of 2D/3D PSC-based BA in the air is not good enough. 21 The aromatic ring structure of PEA has strong hydrophobicity, but the steric hindrance of the benzene ring is relatively large, which will reduce the charge transfer efficiency. 22 Relatively speaking, thiophene-based organic amines have the π−π conjugate structure of aromatic amines, and their interlayer spacing is smaller than that of benzenebased organic amines, which may further improve the photoelectric properties.…”