Synthesis and gas-sensing properties of nano- and meso-porous MoO3-doped SnO2

Nano- and meso-porous SnO2 powders doped with and without 1–10 wt% MoO3 have been synthesized by an ultrasonic spray-pyrolysis method employing a precursor aqueous solution containing tin (IV) chloride pentahydrate (SnCl4·5H2O), ammonium heptamolybdate and polymethylmethacrylate (PMMA) microspheres as a template, and the effects of MoO3-doping and the addition of PMMA microspheres on the structural, morphological and gas-sensing properties of SnO2 were investigated in this study. It is confirmed that control of the amounts of PMMA microspheres in the precursor solution was effective in realizing well-developed nano- and meso-porous structures of SnO2 by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and the measurement of specific surface area and pore size distribution using a N2 adsorption isotherm. Gas-sensing properties of their thick films (about 50 μm thick), which were fabricated by screen-printing to various gases (NO2, C2H5OH and H2) were tested in ambient air. The doped thick films showed a high response and selectivity to 5 ppm NO2 gas in the case of 10 wt% MoO3-doping in both nano- and meso-porous structures of SnO2. We observed that the presence of Mo species in SnO2 lattice can improve the sensor response and selectivity towards NO2 gas. The effect of the MoO3-doping on the sensing characteristics of these films towards NO2 was discussed.