Novel Mixed Phase SnO₂ Nanorods Assembled with SnO₂ Nanocrystals for Enhancing Gas-Sensing Performance toward Isopropanol Gas

Abstract

The synthesis and the gas sensing properties of novel mixed phase (i.e., tetragonal and orthorhombic phase) coexistence SnO2 nanorods are presented. The mixed phases SnO2 nanorods were obtained by calcinations of SnC2O4 synthesized with a chemical precipitation method using SnCl2·2H2O and PEG 400 as precursors. The resulting nanorods appear as polycrystalline composed of spherical mixed phases SnO2 nanocrystals and have a high surface area. It was observed that the calcination temperature was the key parameter determining the content of the orthorhombic phase. The as-synthesized compounds were used as sensing materials of the sensors of indirect heating structure and tested for their ability to detect volatile organic compounds (VOCs), such as isopropanol, acetone, alcohol, and formaldehyde. Gas sensing tests showed that these mixed phases SnO2 nanorods are highly promising for gas sensor applications, as the gas response for isopropanol was significantly enhanced by the presence of orthorhombic phase (S = 61.5 at 1000 ppm isopropanol and response time and recovery time of 4 and 10 s). The as-prepared two phases SnO2 nanorods with the highest content of the orthorhombic phase exhibit excellent gas response, selectivity, and stability toward isopropanol gas at the optimized operating temperature of 255 °C. The enhancement in sensitivity is attributed to the presence of small orthorhombic SnO2 crystals with average radius shorther than the Debye screening length of 7 nm for SnO2.