Bimetal carbonaceous templates for multi-shelled NiCo2O4 hollow sphere with enhanced xylene detection

Xylene (C8H10) is one of the most hazardous volatile organic compounds, thus highly sensitive gas sensor with real-time monitoring capabilities at lower concentration level is crucial. Hollow and multi-shelled oxide nanostructures are very promising design options for gas sensors due to their low density, high surface area and well-aligned nano-porous structures with less agglomerated configurations. Here, NiCo2O4 double-shelled hollow spheres (DHSs) with porous surfaces are successfully synthesized via a self-templating strategy followed by a simple post-annealing process, in which bimetal self-assembly carbonaceous microspheres (CMS) are employed as a sacrificial template. The crystallinity, morphology, and microstructure of NiCo2O4 DHSs are detailedly characterized. The formation mechanism of double-shelled hollow structure is also discussed. The as-prepared NiCo2O4 DHSs possess large specific surface area as high as ∼93.5 m2 g−1, which not only supply outstanding gas permeability and more reactive sites but also accelerate the diffusion of gas molecules. The sensitivity and response time based on NiCo2O4 DHSs are 23.3 and 15.4 s to 100 ppm xylene at the optimal working temperature (240 °C), respectively.