Fabrication of ZnO-SnO2 heterojunction inverse opal photonic balls for chemiresistive acetone sensing

The development of metal oxide semiconductor-based chemiresistive gas sensors with ultra-fast response/recovery for toxic and flammable gases is of great importance, but still challenging. Here, ZnO-SnO2 heterojunction three-dimensional (3D) inverse opal photonic crystal balls (IOPBs) were fabricated based on rapid and liquid waste-free spray drying. The spherical three-dimensional (3D) ordered macroporous skeleton can provide more active sites and faster gas diffusion channels. Furthermore, the n-n heterojunction established by ZnO and SnO2 is favorable for electron transport. The response (Ra/Rg) of IOPBs to 50 ppm acetone reaches 40.3 at an optimal operating temperature of 260 °C when the Zn/Sn atomic ratio is 1:4, which is 5 times higher than that of the pure SnO2 sensor. Response/recovery time also reduces from 23/47 s for pure SnO2 to 6/10 s. In addition, the IOPBs gas sensors also exhibit good selectivity and excellent long-term stability. This work provides a straightforward and versatile synthetic route for the preparation of 3D IOPBs to explore novel gas sensors with ultra-fast response speed.