Electrospinning preparation of mesoporous spinel gallate (MGa2O4; MNi, Cu, Co) nanofibers and their M(II) ions-dependent gas sensing properties

Transition metal spinel semiconductors, with a general formula of AB 2 O 4 , have been shown as a promising group for gas sensor applications. This paper reports a simple and effective electrospinning method to systematically prepare mesoporous MGa 2 O 4 (M Ni, Cu, Co) nanofibers. It is found that gas sensing reaction process of the materials is decisively influenced by transition metal M(II)-ions. The gas response tends to decrease in the order of NiGa 2 O 4   >   CuGa 2 O 4   >   CoGa 2 O 4 . In addition, NiGa 2 O 4 and CoGa 2 O 4 show p-type behaviors, and CuGa 2 O 4 shows an n-type behavior. Further analysis reveals that charge carrier hopping (e − hopping or h + hopping) processes between different valent metal cations, which is mainly dominated by octahedral sites of spinel, are responsible for the conductivity type, the surface redox reaction and thereby the gas sensing properties.