Aluminum-doped TiO2 nano-powders for gas sensors

Nano-powders of pure and Al-doped TiO2 ceramics were synthesized using a citrate–nitrate auto combustion method. Powders were then used to make thick film gas sensors to measure selectivity and sensitivity in CO and O2 environment. Titanyl nitrate solution was prepared using commercial TiO2 powder, hydrofluoric acid (HF) and concentrated nitric acid (HNO3). An optimized ratio of citrate to nitrate was used to produce TiO2 nanoparticles. Powder X-ray diffraction data showed that synthesized TiO2 nano-powders, pure as well as Al-doped, had stable anatase phase up to 800 °C. X-ray fluorescence confirmed the Al concentrations in synthesized nano-powders. BET surface area analysis showed a decrease at 5 wt.% Al addition, followed by an increase at 7.5 wt.% in specific average surface area. Particle size analysis showed particles below 100 nm for both pure and doped TiO2 even after calcination at 800 °C. The resistance of Al-doped TiO2 samples was found to be lower than that of pure TiO2 in O2 and CO environment. Al-doped TiO2 gas sensors were more selective and sensitive to CO and O2 at an operating temperature of 600 °C than pure TiO2 powders.