Fe3O4 nano-octahedral Fe-Fe3O4 (1 1 1) polar surface coordinated Fe atom enhanced sensing properties and its sensing atomic mechanism

The determination of active crystal facets and active atoms for gas sensing is the basis of designing gas sensing materials and devices. Fe3O4 nano-octahedrons exposed with polar {1 1 1} crystal planes have been prepared by adsorbing selectively Cl– ions. The Fe3O4 nano-octahedrons showed higher sensitivity than Fe3O4 commercial powders to triethylamine, acetone and ethanol. The sensitivity of Fe3O4 nano-octahedrons is further improved through clearing in turn Cl- ions and O–H groups away on the Fe-Fe3O4 (1 1 1) polar crystal plane. The improved sensitivity originates from a rise in the number of unsaturated 3-coordinated (Fe3c) atoms on the (1 1 1) polar crystal plane. The unsaturated Fe3c atom is proved to be a sensing active site, and a sensing atomic mechanism is presented. The Fe3c atom has the ability of adsorbing oxygen, producing free electrons and catalyzing sensing reaction. This finding suggests that all surface unsaturated metal atoms are gas sensing active sites, and the mechanism is a general sensing mechanism. The clean polar crystal plane engineering can be employed to develop highly sensitive gas sensing materials.