Chlorine Gas Sensing Performance of On-Chip Grown ZnO, WO₃, and SnO₂ Nanowire Sensors

Monitoring toxic chlorine (Cl₂) at the parts-per-billion (ppb) level is crucial for safe usage of this gas. Herein, ZnO, WO₃, and SnO₂ nanowire sensors were fabricated using an on-chip growth technique with chemical vapor deposition. The Cl₂ gas-sensing characteristics of the fabricated sensors were systematically investigated. Results demonstrated that SnO₂ nanowires exhibited higher sensitivity to Cl₂ gas than ZnO and WO₃ nanowires. The response (<i>R</i>_Cl₂/<i>R</i>_air) of the SnO₂ nanowire sensor to 50 ppb Cl₂ at 50 °C was about 57. Hence, SnO₂ nanowires can be an excellent sensing material for detecting Cl₂ gas at the ppb level under low temperatures. Abnormal sensing characteristics were observed in the WO₃ and SnO₂ nanowire sensors at certain temperatures; in particular, the response level of these sensors to 5 ppm of Cl₂ was lower than that to 2.5 ppm of Cl₂. The sensing mechanism of the SnO₂ nanowire sensor was also elucidated by determining Cl₂ responses under N₂ and dry air as carrier gases. We proved that the Cl₂ molecule was first directly adsorbed on the metal oxide surface and was then substituted for pre-adsorbed oxygen, followed by lattice oxygen