Enhanced sensing properties of CoFe2O4 nanosheet and sensing reaction molecule mechanism of polar CoFe2O4 {111} surfaces

The sensitivity of nanostructures to gases can be improved by exposing their polar surfaces. In this project, a CoFe2O4 nanosheet with {111} polar surface was obtained by selective adsorption of -OH, -OHC2H5OH, and SO42-. By hydrogenating the polar surface of Fe-CoFe2O4 (111), the -OH, -OC2H5OH and SO42- groups were effectively removed, which greatly improved the gas sensing sensitivity of CoFe2O4 nanosheets. This innovative technique provides a feasible way to improve the gas sensing performance of nanosheets. The results show a significant increase in the number of coordination-unsaturated metal-iron atoms (Fe3c) on polar surfaces, which improves sensitivity. As a gas sensing centre, Fe3c can adsorb oxygen, generate free electrons and catalyse sensing re-actions. A microscopic mechanism for gas sensing is thus proposed. These results suggest that coordinated un-saturated metal atoms on the surface of metal oxides are active sites for gas sensing and that this gas sensing mechanism is universal.