NiO nanoparticles-decorated ZnO hierarchical structures for isopropanol gas sensing

In this paper, a three-dimensional (3D) hierarchical ZnO structure consisting of nanosheets modified with ultrafine NiO particles was synthesized via a facile two-step chemical precipitate method. Various techniques characterized the as-synthesized ZnO/NiO composites and pure ZnO. The p-NiO/n-ZnO junctions formed between adjacent ZnO and NiO nanoparticles, improving the gas sensing performance. The ZnO/NiO composite with the Ni:Zn atomic ratio of 7.42:100 exhibited the best isopropanol sensing properties. Compared to pure ZnO, it showed high selectivity and sensitivity (Ra/Rg = 221.3 toward 400 × $${10}^{-6}$$ isopropanol), fast response rate (less than 10 s), short recovery time, and simultaneously low operating temperature. Also, the ZnO/NiO composite exhibited a wide sensing range (1 × $${10}^{-6}$$ –1000 × $${10}^{-6}$$ ) to isopropanol and processed good long-term stability. The experimental results suggested the potential application in fabricating efficient isopropanol sensors using this ZnO/NiO composite. The enhanced isopropanol sensing mechanism is also discussed in charge transfer between heterojunctions, surface area, and surface defects.