Self-template derived ZnFe2O4 double-shell microspheres for chemresistive gas sensing

Porous ZnFe2O4 double-shell, york-shell, and solid microspheres are synthesized using a combination of hydrothermal method and thermal treatment (carried out at appropriate temperature determined via gravimetry). The specific surface area is varied by adopting different heating rates during the thermal treatment; double-walled structure is formed at higher heating rates. Gas sensors based on ZnFe2O4 double-shell microspheres showed a promising response (when compared to york-shell and solid microspheres), when tested with ∼20 ppm acetone (Rair/Rgas = 13.6). There is little or no response to interferential gases, including ethanol, methanol, xylene, toluene, benzene, carbon monoxide, hydrogen sulfide and nitrogen dioxide. The gas sensor showed an almost linear response to acetone concentration and a low detection limit for acetone of 0.13 ppm (making it compliant with analytic requirements for acetone-threat or diabetes-breathalyzer tests). The observed gas sensing performance (includes response time ∼6-10 s at 206 °C operating temperature and good cyclability) suggests that the ZnFe2O4 double-shell microspheres presented here are prospective sensing materials for acetone detection.