Hierarchical flower-like NiCo2O4 applied in n-butanol detection at low temperature

•Hierarchical flower-like structure NiCo2O4 assembled by hexagonal sheets was controllable synthesized.•Hierarchical flower-like structure NiCo2O4 evolutionary conditions and formation mechanism were studied systematically.•The best gas sensor towards n-butanol exhibited an ultra-low temperature (165 oC) and high sensitivity (240 %).•This sensitivity (240 %) is the highest response value of NiCo2O4 based sensor in detecting n-butanol so far. In this work, hierarchical flower-like NiCo2O4 assembled by hexagonal sheets was prepared in one-step hydrothermal method, in which 2-mIM (2-Methylimidazole) acted as the structure-directing agent. The amount of 2-mIM had a great influence on the morphology and the composition of products, which further influenced the n-butanol gas-sensing performance. In addition, the systematic gas tests were carried out. It was concluded that compared with other corresponding samples, the hierarchical NiCo2O4 prepared with 18 mmol 2-mIM (NC-2) presented the highest gas sensitivity (240 %) and selectivity to 100 ppm of n-butanol at a low operation temperature 165 °C, with a response/recovery time of 68 s/107 s and an excellent long-term stability. Furthermore, the detailed analyses of the gas sensing mechanism were discussed in this paper. The best gas sensing performance of NC-2 based sensor was attributed to its unique hierarchical structure, which can provide more active sites for the process of oxygen adsorption. In addition, the content of chemical adsorbed oxygen species and the specific surface area of samples had an intimate relationship with the response for sensing materials. In summary, this research provided a simple way in designing n-butanol sensor based on hierarchical flower-like NiCo2O4 at a low operation temperature.