
Fig. 1.
A schematic diagram of the whole experimental process

Fig. 2.
XRD patterns of In2O3, In2O3/Co3O4-4, In2O3/Co3O4-3, In2O3/Co3O4-2, In2O3/Co3O4-1 and Co3O4 NFs

Fig. 3.
SEM images of In2O3 NFs, Co3O4 NFs, In2O3/Co3O4-1, In2O3/Co3O4-2, In2O3/Co3O4-3 and In2O3/Co3O4-4 :(a-f) before calcination, and (g-l) after calcination

Fig. 4.
TEM images of (a-b) In2O3/Co3O4-3 nanofibers and (c) HRTEM of In2O3/Co3O4-3

Fig. 5.
The elemental composition chart of (a) In2O3/Co3O4 NFs, (b) Au element, (c) Co element, (d) In element, (e) O element, and (f) EDS of In2O3/Co3O4-3

Fig. 6.
The schematic diagram of the calcination process model

Fig. 7.
Response of Co3O4, In2O3, In2O3/Co3O4-1, In2O3/Co3O4-2, In2O3/Co3O4-3 and In2O3/Co3O4-4 sensors to 40 ppm acetone at different operating temperatures

Fig. 8.
Transient curves of the gas sensors based on the Co3O4, In2O3, In2O3/Co3O4-1, In2O3/Co3O4-2, In2O3/Co3O4-3, and In2G3/Co3G4-4 to different acetone concentrations at 200°C

Fig. 9.
Selectivity of Co3O4, In2O3, In2O3/Co3O4-1, In2O3/Co3O4-2, In2O3/Co3O4-3, and In2O3/Co3O4-4 sensors

Fig. 10.
(a) Response and recovery curve of In2O3/Co3O4-3 to 0.7 ppm acetone at 200°C; (b) Long term stability of In2O3/Co3O4-3 toward 10 ppm acetone over a period of 5 months at an operating temperature of 200°C
Table 1.
Comparative analysis of sensor performance and preparation processes based on In2O3 sensing materials
| Sensor materials | Fabrication method | Operating temperature (°C) | Response/ppm | References |
|---|---|---|---|---|
| SnO2/In2O3 | Thermal evaporation | 300 | 1.05/100 | [29] |
| In2O3 microsphere | Solvothermal method | 250 | 36/20 | [30] |
| In2O3 | facile solution route | 260 | 8.60/100 | [31] |
| Bi2O3/ In2O3 | one-step process | 200 | 17.7/200 | [32] |
| Co3O4 | electrospinning | 200 | 1.71/40 | This work |
| In2O3 | electrospinning | 200 | 7/40 | This work |
| In2O3/Co3O4-3 | Double-jet electrospinning | 200 | 9.5/40 | This work |

Fig. 11.
Sensing mechanism of In2O3/Co3O4 (a) in air and (b) in VOCs, and (c) energy band diagram of Co3O4/Co3O4, Co3O4/In2O3 and In2O3/In2O3 grains