Gas Sensing Characteristics of Nano-Structured Metal Oxides

Four nano-structured metal oxides: H₂Ti₃O₇ nanotubes, TiO₂ nanotubes, Li₄Ti₅O₁₂ nanotubes and LiAlO₂ nanobelts have been synthesized successfully by using sonochemical-hydrothermal processes. Sensors based on the materials have been prepared on alumina substrates for detecting NO₂, H₂ and CO. The SEM micrographs showed that the sensing films kept nanostructures with many holes owing to the ruleless conformation of nanotubes. Li₄Ti₅O₁₂ nanotubes sensor showed an obvious sensing characteristic to NO₂ at 150 °C, and the sensitivity increased with increasing NO₂ concentration operated from 150 °C to 300 °C. The best sensitivity (1000) for 1880 ppm NO₂ was obtained at 300 °C. Sensors based on pure and doped TiO₂ nanotubes with Nb⁵⁺, Sn⁴⁺, Mn⁴⁺ and Cr³⁺, respectively, were prepared and the gas response characteristics were investigated in detail. Sensors based on TiO₂ nanotubes doped with Nb⁵⁺ showed the best H₂ sensing properties at 300 °C. Sensor based on pure TiO₂ nanotubes showed better selectivity for H₂ than CO measured at 350 °C and 400 °C.