Hydrothermal Synthesis of Nanocrystalline SnO₂ for Gas Sensors

Abstract

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.