Synthesis of nanowire bundle-like WO₃-W₁₈O₄₉ heterostructures for highly sensitive NH₃ sensor application

Heterojunctions are very promising structures due to their hybrid properties, which are usually obtained via a multistep growth process. However, in this paper, WO₃-W₁₈O₄₉ heterostructures are synthesized via a novel one-step approach by using isopropanol as reaction media and are applied in NH₃ gas detection for the first time. The obtained WO₃-W₁₈O₄₉ heterostructures with loose nanowire bundle-like morphology show a response value of 23.3 toward 500 ppm NH₃ at 250 °C, which is 5.63 times higher than that of pristine W₁₈O₄₉. In addition, the WO₃-W₁₈O₄₉ sensor also exhibits great dynamic response/recovery characteristics (13 s/49 s @ 500 ppm NH₃), superb selectivity and low detection limit of 460 ppb. The substantial improvement in the response of WO₃-W₁₈O₄₉ heterostructures toward NH₃ can be explained by the formation of n-WO₃/n-W₁₈O₄₉ heterojunctions that facilitate the generation of a more extended depletion layer as well as the enhancement of specific surface area and pore volume. Our research results open an easy pathway for facile one-step preparation of heterojunctions with high response and low cost, which can be used for the development of other high-performance gas sensors.