Porous In_2O_3 powders prepared by ultrasonic-spray pyrolysis as a NO_2-sensing material: Utilization of polymethylmethacrylate microspheres synthesized by ultrasonic-assisted emulsion polymerization as a template

摘要

NO_2-sensing properties of porous In_2O_3 (pr-In_2O_3) powders prepared by ultrasonic-spray pyrolysis employing polymethylmethacrylate (PMMA) microspheres as a template has been investigated in this study. The PMMA microspheres were synthesized in water by ultrasonic-assisted emulsion polymerization employing methyl methacrylate monomer, sodium lauryl sulfate as a surfactant and ammonium persulfate as an initiator. The PMMA microspheres synthesized was quite uniform and the particle size was ca. 60.2 nm (measured by dynamic light scattering). The microstructure of pr-In_2O_3 powders prepared was largely dependent on the kind of In_2O_3 sources. The pr-In_2O_3 which was prepared from In(NO_3)_3 as an In_2O_3 source (pr-In_2O_3(N)) consisted of submicron-sized spherical particles with well-developed spherical mesopores (several tens of nanometers in pore diameter) and each oxide wall among pores was constructed with meso-sized In_2O_3 particles connected continuously. On the other hand, the pr-In_2O_3 which was prepared from InCl_3 as an In_2O_3 source (pr-In_2O_3(Cl)) was composed of a large number of dispersed meso-sized particles and a few submicron-sized dense spherical particles. In contrast, the morphology of conventional In_2O_3 powder (c-In_2O_3) prepared by ultrasonic-spray pyrolysis of PMMA-free In(NO_3)_3 aqueous solution as a reference was relatively dense and roughly spherical with a diameter of ca. 100-700 nm. The responses to 1.0 and 10 ppm NO_2 of pr-In_2O_3 sensors in air were much larger than those of a c-In_2O_3(N) sensor in the temperature range of less than 250 ℃ and 300 ℃, respectively. In addition, the response and recovery speeds of both the pr-In_2O_3 sensors were much faster than those of the c-In_2O_3(N) sensor, because of the well-developed porous structure of the pr-In_2O_3 sensors.