Enhanced isopropanol sensing of coral-like ZnO-ZrO₂ composites

Both p-type ZrO₂ and n-type ZnO are widely adopted oxides towards trace gas detections; however, their combinations to achieve an enhanced gas sensing performance are rarely reported. Herein, we adopted a simple solution combustion technique to synthesize ZnO-ZrO₂ composites for isopropanol sensing. The one-step combustion achieved coral-like macro/mesoporous hierarchical architectures. It is found that, when the Zr/Zn molar ratio is less than 0.02, all Zr atoms were doped into ZnO crystallites; whilst ZrO₂ appeared when the ratio is beyond 0.03. When utilized to detect trace isopropanol in air, the response increases linearly with the increasing concentration of the target gas in the range of 10-1000 ppm. At the optimal operation temperature of 350 °C, the largest slope (0.18 ppm^-1) is recorded for the ZnO-ZrO₂ composite with a Zr/Zn molar ratio of 0.04 and the slope is 23 times that of pure ZnO (0.0078 ppm^-1). It exhibits also a fast response time and recovery time of 19 s and 8 s, respectively, under 100 ppm isopropanol. The impressive gas sensing property can be contributed to both the macro-/mesoporous structure, which facilitates an intimate contact between the target gas and the sensing site, and the p-n junction induced built-in electric field, which favors the charge separation.