Shape-controlled and stable hollow frame structures of SnO and their highly sensitive NO₂ gas sensing

In this work, tin monoxide (SnO) is synthesized successfully using a simple solvothermal method. SnCl₂ as a stannous source in the presence of oleylamine (OLA), by changing the amount of NH₃∙H₂O, we prepare a series of SnO microstructures with novel and unique hollow frame morphologies, such as convex corner quadrilateral-, square- and octagonal-like structures. Meanwhile, these hollow structures are attributed to Ostwald Ripening process and the joint action of OH⁻ and NH₄⁺. In addition, these obtained hollow frame-like SnO nanostructures show excellent gas-sensing performances, including low detection limits, short response/recovery time, selectivity to NO₂ and good reproducibility. The minimum detection limit (MDL) of the sensor devices is 5 ppb at 200 °C. In addition, at a wide NO₂ concentrations detection range (e.g. 5 ppb–10 ppm), both the response and recovery time are within 60 s. The NO₂ gas sensor device still remains excellent performance after being stored over 3 months. All these advantages demonstrate a promising means of using frame-like and hollow SnO microstructures for NO₂ gas sensors application.