The effect of purification of single-walled carbon nanotube bundles on the alcohol sensitivity of nanocomposite Langmuir-Blodgett films for SAW sensing applications

HiPco ( high-pressure CO dissociation process) single-walled carbon nanotube ( SWCNT) bundles containing Fe particles were purified in a two-step purification process by thermal annealing in oxygen and post-treatment in HCl. Nanocomposite films of pristine and purified SWCNTs embedded in an organic matrix of cadmium arachidate ( CdA) were prepared by a Langmuir-Blodgett ( LB) molecular engineering technique with a fixed weight filler content of 75 wt% onto a surface acoustic wave ( SAW) transducer operating as an oscillator at a frequency of 433 MHz. The raw and purified samples were characterized at various stages of the purification process using thermogravimetric analysis ( TGA), high-resolution transmission electron microscopy ( HR-TEM), along with energy-dispersive x-ray spectroscopy ( EDS), field emission scanning electron microscopy ( FE-SEM) and x-ray diffraction ( XRD). Functional characterizations of the SWCNT-nanocomposite-based SAW sensors were investigated towards methanol, isopropanol and ethanol, and demonstrated high sensitivity, reversibility, fast response and ppm level detection at room temperature. Results indicate that the sensitivity of the SAW sensors based on a nanocomposite film of oxygen-annealed SWCNTs is enhanced to the alcohols tested at room temperature. Purification of the SWCNTs in the nanocomposite film affects the SAW sensitivity to alcohol by modulating the sensing properties. The sensing mechanisms are analysed and discussed.