Nanocrystalline spinel Ni 0.6Zn 0.4Fe 2O 4: A novel material for H 2S sensing

Abstract

Nanocrystalline powders of Ni 1− x Zn x Fe 2O 4 (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 Ni 1− x Zn x Fe 2O 4 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 Ni 1− x Zn x Fe 2O 4. Especially, Ni 0.6Zn 0.4Fe 2O 4 composition exhibited high response with better selectivity to 50 ppm H 2S gas at 225 °C. Incorporation of palladium (Pd) further improved the response, selectivity and response time of Ni 0.6Zn 0.4Fe 2O 4 to H 2S with the shift in the operating temperature towards lower value by 50 °C. The enhanced H 2S sensing properties can mainly be attributed to the selectivity to oxidation of H 2S and noble metal additive sensitization. Furthermore, the sensor exhibited a fast response and a good recovery.