NO2 Sensing Properties of Porous In2O3-Based Powders Prepared by Utilizing Ultrasonic-Spray Pyrolysis Employing PMMA Microsphere Templates: Effects of the Size of the PMMA Microspheres on Their Gas-Sensing Properties

PMMA microspheres were synthesized in distilled water by ultrasonic-assisted emulsion polymerization. The average particle size of PMMA microspheres was dependent markedly on the kind of surfactant used. Porous (pr-) In2O3 powders were prepared by ultrasonic-spray pyrolysis of In(NO3)3 aqueous solution containing the PMMA microspheres synthesized. The NO2 response of pr-In2O 3 was much larger than that of conventional In2O 3 powder prepared by the similar technique employing PMMA-free In(NO3)3 aqueous solution. The introduction of controlled macroporous structure into the powder of the sensor material was found to be effective for improving NO2 response properties.