Preparation of Electrospun In<sub>2</sub>O<sub>3</sub>/CdO Composite and Its Formaldehyde-Sensing Properties

In(NO3)3/polyvinyl pyrrolidone (PVP) nanofiber precursors were synthesized using a traditional electrospinning method, and were then annealed at 500, 600, and 700 °C to form In2O3 nanofibers. The as-prepared In2O3 nanofibers were characterized using X-ray diffraction (XRD), thermal gravimetry and differential thermal analysis (TG/DTA), and field-emission scanning electron microscopy (FE-SEM). The results show that the In2O3 nanofibers crystallize well, with a small average grain size (about 24 nm) and a good mesoporous structure, when annealed at 500 °C. The In2O3 nanofibers annealed at the three temperatures were further used to fabricate gas sensors. The test results show that the sensor based on In2O3 annealed at 500 °C has the highest response (about 7) to 10×10 - 6 (volume fraction, φ) formaldehyde (HCHO) at an operating temperature of 240 °C. CdO nanoparticles were also prepared using the same method; XRD and FE-SEM show that the average grain size of CdO is about 68 nm. Finally, the as-prepared In2O3 nanofibers were mixed with the as-prepared CdO in molar ratios of 1:1, 10:1, and 20:1, and the mixtures were used to fabricate gas sensors. The HCHO-sensing properties of the sensors based on pure In2O3 and In2O3/CdO composites with different molar ratios were investigated at each optimum temperature. The results show that the In2O3/CdO composite with a molar ratio of 10:1 has excellent