APTES-functionalized thin-walled porous WO3 nanotubes for highly selective sensing of NO2 in a polluted environment

Abstract

High sensitivity and reliable selectivity are the main requirements for gas sensors to be applied in portable devices, especially for semiconducting metal oxide (SMO)-based gas sensors. However, SMO-based sensors suffer from insufficient selectivity, which limits their practical applications. In this work, a high-performance NO₂ sensor based on a self-assembled monolayer-modified semiconducting metal oxide is presented. Controllable porous WO₃ nanotubes with an ultrathin wall thickness are prepared through a new and simple method by using electrospun fibres as a sacrificial template followed by a facile soaking process, providing a large surface area and fast transport pathway for gas molecules. Through the introduction of 3-aminopropyltriethoxysilane (APTES), which acts as an electron acceptor on the surface, the as-designed sensor exhibited a highly improved response compared to that based on bare WO₃ nanotubes due to the specific interaction between APTES and NO₂. Importantly, the detection limit of the as-prepared sensor approaches 10 ppb, which is the lowest detection limit of all WO₃-based NO₂ sensors to date. In addition, it shows a very fast response and recovery time with a high response value, maintaining 80% of the initial response, even in a saturated humid environment, due to the hydrophobic group of APTES. The optimized sensor was successfully used for the real-time detection of NO₂ in the daytime under different air quality conditions, even in a heavily polluted environment. These results provide a model platform to achieve a simple, inexpensive sensor design with a high recognition capability.