Co₃O₄-SnO₂ Hollow Heteronanostructures: Facile Control of Gas Selectivity by Compositional Tuning of Sensing Materials via Galvanic Replacement

Co₃O₄ hollow spheres prepared by ultrasonic spray pyrolysis were converted into Co₃O₄-SnO₂ core-shell hollow spheres by galvanic replacement with subsequent calcination at 450 °C for 2 h for gas sensor applications. Gas selectivity of the obtained spheres can be controlled by varying the amount of SnO₂ shells (14.6, 24.3, and 43.3 at. %) and sensor temperatures. Co₃O₄ sensors possess an ability to selectively detect ethanol at 275 °C. When the amount of SnO₂ shells was increased to 14.6 and 24.3 at. %, highly selective detection of xylene and methylbenzenes (xylene + toluene) was achieved at 275 and 300 °C, respectively. Good selectivity of Co₃O₄ hollow spheres to ethanol can be explained by a catalytic activity of Co₃O₄; whereas high selectivity of Co₃O₄-SnO₂ core-shell hollow spheres to methylbenzenes is attributed to a synergistic effect of catalytic SnO₂ and Co₃O₄ and promotion of gas sensing reactions by a pore-size control of microreactors. (Figure Presented).