Modifying the Surface Chemistry and Nanostructure of Carbon Nanotubes Facilitates the Detection of Aromatic Hydrocarbon Gases

Abstract

The benzene, toluene, and xylene (BTX) compounds currently utilized in many building materials and paints have been linked to deleterious health effects, and thus, monitoring the presence of these compounds is of increasing importance with respect to public health. As such, there is a critical need for next-generation low-cost, selective, and sensitive indoor BTX sensors. Current BTX detection systems require multicomponent, complex devices or require high power input to achieve BTX detection at meaningful concentrations, but this long-standing paradigm can be altered through the introduction of tailored nanomaterials. Specifically, we demonstrate a selective BTX resonant mass sensor platform that leverages the unique properties of single-walled carbon nanotubes (SWCNTs) treated with hydrochloric acid (HCl) and hydroxylamine hydrochloride (HHCl), as the resultant surface chemistry and nanostructure provides specific BTX response. That is, SWCNTs are used in this case because of their high surface area that provides a robust interaction with the target gas analyte. After the SWCNTs are treated with HCl, impurities residual from the commercial synthesis of the SWCNTs are removed, which includes reducing the amount of surface iron oxide (i.e., a residual component of the catalysis used to synthesize the SWCNTs) present into iron chlorides. There is then a following HHCl treatment that leads to the reduction of iron­(III)­chloride to iron­(II). This produces nitrous oxide gas, which provides a means to generate in-place surface functionalization of the SWCNTs; in turn, this allows for the selective adsorption of electron-dense aromatic analytes. Accordingly, these materials have selective interactions and unique responses toward each of the BTX analytes, and when these tailored nanomaterials are dropcast onto resonant devices, they provide for a chemically selective mass uptake response. In turn, this provides a clear pathway toward a practical, low-cost, efficient, and reusable sensor for BTX detection based on SWCNTs.

Carbon Nanotubes and its Potential Application in Sensing

“…In this study, benzene, toluene and xylene aromatic hydrocarbon gases had been detected using surface modifies SWCNTs. [182]…”

Sorption Kinetics of Poly(ethyleneimine)–Poly(ethylene Oxide) Blends and the Implication for Low-Cost, Small-Scale CO2 Sensors

“…At these concentrations, CO 2 can have substantial effects on human cognitive performance with statistically significant and meaningful reductions in decision-making performance. − However, even at significantly lower concentrations, CO 2 is a useful IAQ metric because it serves as a proxy measure for human occupancy and the proportional impacts on IAQ. , Thus, there is an increasing interest in developing low-cost IAQ sensors for smart and connected buildings to monitor the concentration of CO 2 while being seamlessly integrated with existing ventilation systems. Among the potential gas-sensing technologies available, microelectromechanical systems (MEMS) gas sensors (i.e., electrochemical, acoustic, and optical sensors) are a promising avenue for low-cost and small-scale gas-sensing applications. − In particular, adsorption-based electrochemical and electromechanical gas sensors have demonstrated potential for carbon dioxide (CO 2 ) monitoring in buildings, − which is a market that has historically been dominated by optical nondispersive infrared (NDIR) sensors. − In principle, in electrochemical and electromechanical gas sensor devices, the adsorption of a target gas analyte onto a chemically selective recognition layer induces a physical property change in the material, which is then transduced into a signal by the gas sensor. This physical property change can be a change in conductivity (i.e., electrochemical devices) or a change in mechanical behavior (i.e., resonance frequency).…”

Active and passive adsorption of 47 trace atmospheric volatile organic compounds onto carbon nanotubes

“…3 These applications all rely on the specic surface properties of the CNTs promoting physisorption processes. Several studies have also shown that CNTs are excellent sorbents for organic species, and have been used in solid phase extraction, chromatographic analysis, and sensor development, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] although to the best of our knowledge there are few reports that examine adsorption of volatile organic compounds (VOCs) at their trace atmospheric level (ppb (v/v)). [24][25][26] This leads to concerns whether gaseous VOCs that are naturally present in the atmosphere could spontaneously be introduced into the CNTs during their storage and transportation, thereby affecting their desirable surface features as well as inuencing their toxicological properties.…”