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.