Microstructural control of porous In2O3 powders prepared by ultrasonic-spray pyrolysis employing self-synthesized polymethylmethacrylate microspheres as a template and their NO2-sensing properties

Abstract

NO2-sensing properties of porous In2O3 powders prepared by ultrasonic-spray pyrolysis employing self-synthesized polymethylmethacrylate (PMMA) microspheres as a template have been investigated in this study. The PMMA microspheres were synthesized by ultrasonic-assisted emulsion polymerization. The pore-size distribution, crystallite size (CS), and specific surface area (SSA) of the porous In2O3 powders prepared with the PMMA microspheres with a diameter of ca. 77nm (pr-In2O3(Tp), Tp: pyrolysis temperature, 600–1100 (°C)) are largely dependent on the pyrolysis temperature of the ultrasonic-spray pyrolysis. On the other hand, the porous In2O3 powder prepared by ultrasonic-spray pyrolysis at 1100°C employing PMMA microspheres with a diameter of ca. 26nm (pr-In2O3(Tp)S) had larger pore volume and smaller SSA than the pr-In2O3(1100) powder, whereas the CS of the pr-In2O3(Tp)S powder was comparable to that of the pr-In2O3(1100) powder. The pr-In2O3(Tp) and pr-In2O3(1100)S sensors (Tp: 600 or 1100) showed larger response and faster response speed to 10ppm NO2 than the conventional In2O3 sensor (the sensor fabricated with In2O3 powder prepared by ultrasonic-spray pyrolysis without PMMA microspheres at 1100°C) at lower temperatures, because of their well-developed porous structure, small CS, and large SSA. In addition, the magnitude of response of the pr-In2O3(1100) sensor to 10ppm NO2 was larger than that of the pr-In2O3(600) sensor at less than 250°C, whereas smaller CS and larger SSA of the pr-In2O3(600) powder were effective in improving the magnitude of response to NO2 at a low concentration. The pr-In2O3(1100)S sensor showed relatively larger response and faster response speed to NO2 at a low concentration than the pr-In2O3(1100) sensor at lower temperatures, which probably indicated that the well-developed medium pores was important for enhancing these NO2-sensing properties.