ZnO/MOx Nanofiber Heterostructures: MOx Receptor's Role in Gas Detection.

ZnO/MOx (M = FeIII, CoII,III, NiII, SnIV, InIII, GaIII; [M]/([Zn] + [M]) = 15 mol%) nanofiber heterostructures were obtained by co-electrospinning and characterized by X-ray diffraction, scanning electron microscopy and X-ray fluorescence spectroscopy. The sensor properties of ZnO and ZnO/MOx nanofibers were studied toward reducing gases CO (20 ppm), methanol (20 ppm), acetone (20 ppm), and oxidizing gas NO2 (1 ppm) in dry air. It was demonstrated that the temperature of the maximum sensor response of ZnO/MOx nanofibers toward reducing gases is primarily influenced by the binding energy of chemisorbed oxygen with the surface of the modifier's oxides. When detecting oxidizing gas NO2, high sensitivity at a low measurement temperature can be achieved with a high concentration of free electrons in the near-surface layer of zinc oxide grains, which is determined by the band bending at the ZnO/MOx interface characterized by the difference in the electron work function of ZnO and MOx.