Hydrothermal synthesis of nanocrystalline SnO2 for gas sensors

Nanocrystalline SnO2 is prepared by hydrothermal synthesis (130-250degreesC, 2-5 h) using three different precursors and is characterized by x-ray diffraction, transmission electron microscopy, and nitrogen BET measurements. The crystallite size of SnO2 powders (d = 4-5 nm) prepared from amorphous stannic acid gels is found to vary very little with process temperature and duration. Air anneals at 500degreesC for 1-20 h demonstrate that the hi-hest stability toward crystallite growth is offered by the samples prepared by oxidizing SnSO4 with H2O2 (the crystallite size increases only slightly, from 4-5 to 5-7 nm), whereas the crystallite size of the samples prepared by high-temperature hydrolysis of SnCl4 increases markedly, from 4-5 to 16-17 nm. Nanocrystalline NiO-doped SnO2 is prepared by hydrothermal treatment, and its physicochemical properties are investigated. Both SnO2 and SnO2<NiO> exhibit gas sensitivity, as demonstrated by consecutively exposing the samples to different gaseous atmospheres: O-2 --> N-2 --> O-2 and O-2 --> N-2 + C2H5OH --> O-2.