Surface Characterization and the Gas Response of a Mixed, Fe2O3-Fe2(MoO4)3, Oxide to Low Concentrations of H2S in Air

The preparation and H(2)S sensing potential of thick-films of a mixed oxide, Fe(2)O(3)-Fe(2)(MoO(4))(3), were investigated. A Fourier-transform infrared (FTIR) study confirmed the existence of sulfur species at the surface after the interaction of H(2)S gas with the mixed oxide. The starting material, beta-FeMoO(4), was synthesized by a solvothermal method, followed by supercritical drying. Heat treatment of this material (oxidation) above 500 degrees C resulted in the formation of Fe(2)O(3)-Fe(2)(MoO(4))(3) mixed oxide, where Fe(2)O(3) was a by-product. An increase in the conductivity of the films in the presence of H(2)S gas (concentration range 1-20 ppm in air) was observed with the simultaneous formation of water and sulfide ions at 225 degrees C. An improvement of the H(2)S sensing potential is obtained, using an intermediate short heat treatment at higher temperature (500 degrees C) in the beginning of recovery (desorption) phase. This intermediate high temperature, used before every expected exposure to H(2)S gas, may contribute the formation of an initial surface coverage of O(2-).