Biotemplate synthesis of NiO/ZnO tubes rich in oxygen vacancies for enhanced sensing detection of hydrazine at low temperature

The development of conductometric sensors for high sensing and selective detection of very toxic and explosive hydrazine gas remains urgent challenge. Herein, waste and reproducible willow catkins were chosen as biotemplate and simply immersed into mixed Ni(NO3)2/Zn(NO3)2 solution with different Ni/Zn ratios. Afterwards, the isolated precursors were calcined at 500 ℃ in air to generate three biomorphic NiO/ZnO hetero-tubes, which were all replicated from small-size nanoparticles with good crystallinity. Amongst, 6.1 wt% NiO/ZnO composite achieves high sensing and rapid detection of trace N2H4. At 92 °C, its response value (S = 443) to 100 ppm N2H4 is significantly higher than those of 3.7 wt% NiO/ZnO (S = 113) and 7.2 wt% NiO/ZnO (S = 210). Especially, its response value is the highest among reported metal oxide-based sensors. Meanwhile, it also has short response time (6 s), low practical detection limit (10 ppb) along with satisfactory stability and moisture tolerance. Such well over-all sensing performance roots from the synergism of mesoporous hetero-tubes assembled by small-size nanoparticles, proper tube thickness, high concentration of Ni3+ Lewis acid, as well as rich oxygen vacancy defects. Moreover, the mechanism for enhanced N2H4 sensing performance was also discussed in detail.