Electrospinning driven metal oxide nanofibers based exhaled breath sensors

Abstract

In semiconducting metal oxides (SMOs) based gas sensor field, one-dimensional nanostructures such as nanofiber (NF), nanobelt (NB) and nanotube (NT) have received great attention because of their high surface-to-volume ratio which offers high gas accessibility for enhanced surface reactions. To further improve sensitivi-ty and selectivity of gas sensing layers, SMO nanofabrication techniques have been widely explored, especially for synthesis of highly porous SMOs nanostructures with further increased reaction surface area through burn-ing out of incorporation of diverse sacrificial templates or control of calcination heating rate to induce Ostwald-ripening. In addition, introducing heterojunctions, i.e., n-n, p-p, and p-n can induce energy band bending and expansion of depletion region on SMOs nanostructures. Here in, Bi-modally meso- (2-50 nm) and macro-porous (>50 nm) $WO_3$ NBs functionalized with sub-3 nm Pt catalysts were fabricated via electrospinning technique followed by subsequent calcination. Furthermore, Porous $Co_3O_4$/$SnO_2$ NTs$ were prepared via electrospinning technique combined with galvanic replacement reac-tion (GRR). Bi-modally porous $WO_3$ NBs functionalized by Pt catalysts showed remarkably high hydrogen sul-fide ($H_2S$) response ($R_{air}$/$R_{gas}$ = 61 @ 1 ppm) and superior selectivity to $H_2S$ against other interfering gases, i.e., acetone ($CH_3COCH_3$), ethanol ($C_2H_5OH$), ammonia ($NH_3$), and carbon monoxide (CO). Also, the designed sensing layers of $Co_3O_4$/$SnO_2$ NTs, which are obtained by 4h of GRR, exhibited remarkably enhanced gas response ($R_{air}/R_{gas} = 68.2$), compared with that of $Co_3O_4$ NFs ($R_{gas}$/$R_{air}$ = 1.2) at 5 ppm of acetone molecule as well as superior cross-selectivity against 7 other molecules, i.e., $C_2H_5OH$, $CH_3SH$, $H_2S$, $C_7H__8$, $C_5H_{12}$, $NH_3$ and CO.