Surface Characterization and the Gas Response of a Mixed, Fe 2 O 3 Fe 2 (MoO 4 ) 3 , Oxide to Low Concentrations of H 2 S 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, β‐FeMoO 4 , was synthesized by a solvothermal method, followed by supercritical drying. Heat treatment of this material (oxidation) above 500 °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 °C. An improvement of the H 2 S sensing potential is obtained, using an intermediate short heat treatment at higher temperature (500 °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− .