Hierarchical porous NiO doped ZnO nanocomposite for formaldehyde gas sensor with high sensitivity, fast response/recovery and good selectivity

Formaldehyde (HCHO) is a kind of indoor pollution gas which seriously harms human health. High properties gas sensor for formaldehyde are essential for indoor air quality monitoring. The development of new nanostructured composites as gas sensing materials is seen as a viable way to improve sensing performance. In this study, a new type of layered porous nickel oxide doped zinc oxide nanocomposite with sunflower straw as a template (SFS NiO/ZnO) was synthesised. The structure and morphology of the material was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These results exhibit that the synthetic SFS NiO/ZnO successfully maintains the original pore morphology of the sunflower straw material and the framework consists of a large number of nanoparticles of uniform size and shape. The gas sensing performance of the prepared samples was tested and the results showed that the SFS NiO/ZnO biocomposite had promising sensing performance for formaldehyde. The response of the SFS NiO/ZnO gas sensor working at 240 °C was 42 for 100 ppm formaldehyde with response and recovery times of 9 s and 8 s, respectively. The lower limit of detection is 148 ppb. Compared with SFS ZnO, the significant improvement of formaldehyde sensing properties could be attributed to its increased oxygen vacancy concentration and the presence of p-n type heterojunctions.