Alkaline- and template-free hydrothermal synthesis of stable SnO2 nanoparticles and nanorods for CO and ethanol gas sensing

SnO2 nanoparticles and nanorods are synthesized via a facile template-free hydrothermal method, using SnCl2·2H2O and deionized water without any alkaline solution. The influences of the hydrothermal reaction time in the range of 5–48 h and temperatures of 130 and 160 °C and also calcination temperature on the size and morphological and gas-sensing properties of SnO2 particles were investigated. The SnO2 samples were characterized by X-ray diffraction analysis (XRD), surface area analyzer (using BET method) and scanning electron microscopy. The response of the SnO2 nanostructures sensors to ethanol and various concentrations of CO were measured in an automated flow setup at different temperatures. As the hydrothermal synthesis temperature and time increases, the crystallite sizes enlarge nonlinearly and morphology of SnO2 nanostructures changes from nanoparticles to nanorods. The most SnO2 samples are thermally stable at calcination temperature of 350 °C. SnO2 nanoparticles as small as 3.1 nm with the highest specific surface area of 254 m2/g are hydrothermally synthesized at 130 °C in 5 h. This sample shows the highest response of 30 and 2565 to 1000 ppm CO and ethanol at 200 and 250 °C, respectively.