Nanocrystalline spinel Ni0.6Zn0.4Fe2O4: A novel material for H2S sensing

Nanocrystalline powders of Ni1−xZnxFe2O4 (0 ≤ x ≤ 0.5) mixed ferrites, with cubic spinel structure and average crystallite size ranging from 28 to 42 nm, were synthesized by the ethylene glycol mediated citrate sol–gel method. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). The response of prepared Ni1−xZnxFe2O4 mixed ferrites to different reducing gases (liquefied petroleum gas, hydrogen sulfide, ethanol gas and ammonia) was investigated. The sensor response largely depends on the composition, temperature and the test gas species. The Zn content has a significant influence on the gas-sensing properties of Ni1−xZnxFe2O4. Especially, Ni0.6Zn0.4Fe2O4 composition exhibited high response with better selectivity to 50 ppm H2S gas at 225 °C. Incorporation of palladium (Pd) further improved the response, selectivity and response time of Ni0.6Zn0.4Fe2O4 to H2S with the shift in the operating temperature towards lower value by 50 °C. The enhanced H2S sensing properties can mainly be attributed to the selectivity to oxidation of H2S and noble metal additive sensitization. Furthermore, the sensor exhibited a fast response and a good recovery.