Selective NO₂ sensor based on Bi₂O₃ branched SnO₂ nanowires

We present a highly sensitive and selective NO₂ sensor based on Bi₂O₃ branched SnO₂ nanowires (NWs). SnO₂ NWs were first synthesized by a vapor-liquid-solid method, were coated with an Au layer, and Bi₂O₃ branches were grown on their stems by the same procedure used for pure Bi powders. The fabricated sensor showed a high response (R_g/R_a) of 56.92 to 2 ppm of NO₂ gas at an optimal temperature. Furthermore, its response to other interfering gases such as ethanol, acetone, toluene, and benzene, was less than 1.55, which demonstrated excellent selectivity of the sensor towards NO₂ gas. For comparison and to better understand the sensing mechanism, a pristine SnO₂ NWs sensor was also tested. The superior sensing properties of the branched NW sensor relative to the pristine sensor were mainly attributed to the high surface area of the sensor resulting from Bi₂O₃ branching, as well as the formation of homo-and heterojunctions (Bi₂O₃-SnO₂). In addition, several factors including the presence of Au contributed to the excellent selectivity to NO₂ gas. Based on the results obtained in this work, we believe that the present sensor with an easy fabrication method, along with its high sensitivity and selectivity towards NO₂, can be used for the detection of NO₂ gas in real applications.