Oxygen vacancy-enriched WO3 hierarchical tubes inherited from pine needle for the enhanced detection to ppb-level hydrazine at near room temperature

Abstract

It is of great importance to develop low-temperature gas sensors for monitoring hydrazine (N₂H₄) with high toxicity and easy explosion. However, how to highly sense its ppb-level concentration remains challenging. For this purpose, biomorphic WO₃ structure replicated by small-size nanoparticles was simply prepared though air calcinations of tungsten salt-immersed pine needle (PN) template. The mesoporous WO₃-PN tubes with pore volume of 0.096 cc·g⁻¹ had relatively large specific surface area (38 m²·g⁻¹) for exposing more active sites, as well as rich oxygen vacancies (g = 2.005) and small band gap for promoting electron migration. With the assistance of W⁶⁺ Lewis acid catalytic sites, such unique multilevel structure facilitated the rapid transport and adsorption of basic N₂H₄ molecules, as well as their chemical reactions with high content of oxygen species (37.4 %) in sensing layer, thus first achieving the highly sensitive detection of ppb-level N₂H₄ gas at near room temperature. At 50 °C, WO₃-PN sensor exhibited ultra-high response (S = 307), fast response time (T_res = 16 s) for 1 ppm N₂H₄, and low actual detection concentration (5 ppb). These key indicators were remarkably superior to reported semiconductor gas sensors. In addition, the enhanced low-temperature sensing mechanism of WO₃-PN sensor was explored by means of analytical tests and DFT calculations.