Design of Gas Sensor Based on Fe-Doped ZnO Nanosheet-Spheres for Low Concentration of Formaldehyde Detection

In this work, ZnO nanosheet-spheres with various Fe-doping concentrations were successfully fabricated by a one-step hydrothermal method. The ZnO nanosheet-spheres were assembled by many thin ZnO nanosheets and exhibited a unique hierarchical structure. Technologies of XRD, SEM, TEM, BET, UV-vis, PL and XPS were used to characterize the morphological and structural properties of the products, while the corresponding gas sensing properties were determined by using formaldehyde (HCHO) as the target gas. The results revealed that Fe doping into ZnO nanosheet-spheres improved its gas sensing performance efficiently and narrowed the bandgap of ZnO, but the optimal Fe doping concentration in ZnO was 2.5 wt%, further increased doping concentration can form the ZnFe2O4 phase and was adverse to the gas sensing performance of ZnO. Moreover, 2.5 wt% Fe-doped ZnO has more electron donors and oxygen vacancies (Vo) than that of pure ZnO sample, leading to the enhancement of gas sensing performance. Finally, the gas sensing mechanism of Fe doping ZnO was proposed from the aspects of structural and electronic sensitization. Our results demonstrated that Fe doping was a promising approach to achieving a good gas sensing performance for the development of ZnO gas sensors to detect formaldehyde.