Hydrothermal Synthesis of Nanocrystalline SnO2 for Gas Sensors

Nanocrystalline SnO2 is prepared by hydrothermal synthesis (130–250°C, 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 500°C for 1–20 h demonstrate that the highest 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: O2 → N2 → O2 and O2 → N2 + C2H5OH → O2.