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

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.