In this work, three-dimensional (3D) hierarchical In2O3@SnO2 core–shell nanofiber
(In2O3@SnO2) was designed and successfully
prepared via a facile electrospinning and further hydrothermal methods.
Vertically aligned SnO2 nanosheets uniformly grown on the
outside surface of In2O3 nanofibers were clearly
observed by field emission scanning electron microscopy. Besides,
hierarchical core–shell nanostructure of In2O3@SnO2 was characterized by elemental maps using
scanning transmission electron microscopy. The formaldehyde (HCHO)
sensing performances of pure In2O3 nanofibers,
SnO2 nanosheets, and In2O3@SnO2 core–shell nanocomposite were compared, and the In2O3@SnO2 nanocomposite possessed highest
response value, fast response/recovery speed, best selectivity, and
lowest HCHO detection limit. Specifically, the response value (R
a/R
g) of the In2O3@SnO2 nanocomposite reached 180.1
toward 100 ppm of HCHO gas, which was near 9 and 6 times higher than
that of the pure In2O3 nanofibers (R
a/R
g = 19.7) and pure SnO2 nanosheets (R
a/R
g = 33.2), respectively. In addition, the gas sensor showed
instantaneous response/recovery time (3/3.6 s) toward 100 ppm of HCHO
at the optimal operation temperature of 120 °C. More importantly,
the detection limit toward HCHO gas was as low as 10 ppb (R
a/R
g = 1.9), which
could be used for trace HCHO gas detection. The excellent sensing
properties of the In2O3@SnO2 were
attributed to the synergistic effect of large specific surface areas
of SnO2 nanosheet arrays, abundant adsorbed oxygen species
on the surface, unique electron transformation between core–shell
heterogeneous materials, and long electronic transmission channel
of SnO2 transition layer. This work provides an efficient
route for the preparation of novel hierarchical sensitive materials.