Highly sensitive and selective nitric oxide sensor based on biomorphic ZnO microtubes with dual-defects assistance at low temperature

• Biomorphic ZnO microtube with rich defects was prepared by simple and controllable cajuput bark as bio-template. • ZnO-6 sensor exhibits the highest response value of 118 to NO among reported metal oxides at low temperature. • The excellent sensing performance root from the synergism of dual defects (V O , Zn i ) and unique microstructure. • The simple bio-template method provides a new strategy for preparing other oxide materials with rich defects. Fabrication of diverse surface defects-assisted metal oxide materials is an effective avenue to achieve rapid and accurate detection of harmful gases. Herein, through the confinement effect of tracheids and vesicles in cajuput bark template, biomorphic ZnO hierarchical materials (ZnO-6) constructed from spherical nanoparticles were simply synthesized by zinc salt immersion and calcination at 600 °C in air. Porous ZnO-6 microtubes can greatly improve the rapid transmission and desorption behavior of target gas. Especially, the presence of electron donor dual-defects oxygen vacancy (V O ) and zinc interstitial (Zn i ) can provide more active sites for surface gas adsorption and chemical reactions, thus effectively enhancing the detection ability of ZnO sensing material to toxic NO gas. At a low operating temperature of 92 °C, the high response value of 118 to 10 ppm NO for ZnO-6 sensor is 5.4 times higher than that of as-synthesized template-free ZnO-0 nanoparticles, and also represents the highest response among reported metal oxide-based gas sensors at low energy consumption. Meanwhile, this sensor has rapid recovery characteristic, good selectivity, long-term stability and moisture resistance. Moreover, the surface defects and their induced sensing mechanism are also characterized and explored.