Rapid synthesis of tin oxide nanostructures by microwave-assisted thermal oxidation for sensor applications*

S Phadungdhitidhada, P Ruankham, A Gardchareon, D Wongratanaphisan and S Choopun

Abstract

In the present work nanostructures of tin oxides were synthesized by a microwave-assisted thermal oxidation. Tin precursor powder was loaded into a cylindrical quartz tube and further radiated in a microwave oven. The as-synthesized products were characterized by scanning electron microscope, transmission electron microscope, and x-ray diffractometer. The results showed that two different morphologies of SnO₂microwires (MWs) and nanoparticles (NPs) were obtained in one minute of microwave radiation under atmospheric ambient. A few tens of the SnO₂ MWs with the length of 10–50 µm were found. Some parts of the MWs were decorated with the SnO₂ NPs. However, most of the products were SnO₂ NPs with the diameter ranging from 30–200 nm. Preparation under loosely closed system lead to mixed phase SnO–SnO₂NPs with diameter of 30–200 nm. The single-phase of SnO₂ could be obtained by mixing the Sn precursor powders with CuO₂. The products were mostly found to be SnO₂ nanowires (NWs) and MWs. The diameter of SnO₂ NWs was less than 50 nm. The SnO₂ NPs, MWs, and NWs were in the cassiterite rutile structure phase. The SnO NPs was in the tetragonal structure phase. The growth direction of the SnO₂ NWs was observed in (1 1 0) and (2 2 1) direction. The ethanol sensor performance of these tin oxide nanostructures showed that the SnO–SnO₂ NPs exhibited extremely high sensitivity