Processing–microstructure–property correlations of gas sensors based on ZnO nanotetrapods

Abstract

After gas sensors based on ZnO nanotetrapods (T-ZnO) were processed by sintering at different temperatures from 350 to 850°C, a strong correlation was interestingly found among the sintering processing, material microstructure and gas-sensing properties. With increasing sintering temperature from 350 to 750°C, the feet and cross of T-ZnO became gradually shorter and bigger, respectively. And subsequently tetrahedron-shaped ZnO nanoparticles were produced instead of T-ZnO at 850°C. The morphological evolution was explained by a new physical model involving Thomson effect, leading to a decrease in the specific surface area. In addition, the contact between feet got better and then became poorer. Meanwhile, surface defects of T-ZnO were also altered: zinc interstitial (Zni••) was decreased in its amount while oxygen vacancy (VO×) showed an inverse trend as sintering temperature increased. Moreover, the best gas-sensing performance toward formaldehyde and methanol was obtained after sintering at 450°C. This was mainly attributed to the synergetic effect between the best grain contact (meaning that more T-ZnO can make contributions to the sensor response) and more zinc interstitial as well as larger specific surface area (supplying more chemisorbed oxygen). Our work could offer important guidance for the process selection and material design to develop nanostructure-based sensors.