Raspberry-like hollow SnO2-based nanostructures for sensing VOCs and ammonia

The raspberry-like hollow SnO₂-based (bare SnO₂ and Pd-doped SnO₂) nanostructures with different dominant crystal facets were prepared facilely using carbon nanospheres as templates via solvothermal method. Volatile organic compounds (VOCs) and ammonia (NH₃) gas sensing performances of the hollow SnO₂-based structures were studied systematically. The gas sensing performances were investigated in a temperature range of 150–315 °C. It was found that 285 °C was the optimum operating temperature for both the sensors. The SnO₂ sensor showed excellent VOCs (1–100 ppm) sensing performances, with a fast response/recovery behavior (around 4 s/30 s) at 285 °C. While the Pd-SnO₂ sensor displayed selective NH₃ sensing characteristics at low concentrations of 1.5–12 ppm, interestingly, with a response/recovery time of about 4 s/80 s at 285 °C. Both the SnO₂ and Pd-SnO₂ sensors showed great repeatability for 8 response/recovery cycles, and very slight response recession for a long period. It was found that not only the morphology, the synergistic effect from the heterojunctions of doped Pd and SnO₂, and the Pd catalysis, but also the crystal facets could modulate the sensing performance of metal oxides.