Design and construction of core-shelled Co3O4-CoFe2O4 heterojunction for highly sensitive and selective detection of ammonia

In this study, the fabrication process and the gas sensing performance toward ammonia of core-shelled Co3O4-CoFe2O4 heterojunction composites with the abundant mesoporous structures were presented detailedly. The hierarchical Co3O4-CoFe2O4 was prepared by using Fe-Co glycerate as a precursor combined with a subsequent thermolysis method. The well-designed core-shelled heterojunction architecture was investigated through SEM and TEM. Apparently, the internal and external structure of the glycerate-derived sensing materials can be efficiently regulated by adjusting the molar ratio of the Fe and Co in the precursor. It was worth pointing out that the core-shelled heterojunction structure possessed a large specific surface area (198.6 m2/g), which not only can provide more active sites in both interior and exterior of the composites sphere, but also accelerate absorption-penetration efficiency of gas molecules. Compared with other prepared nanoparticles and hollow spheres, the sensor fabricated by Co3O4-CoFe2O4 with a core–shell structure revealed the best sensing characteristics, and the response toward 100 ppm ammonia at 220 °C was as high as 35. Moreover, it also showed excellent selectivity and long-term stability. These admirable advancements can be ascribed to the synergistic effect of unique core–shell architecture and p-p heterojunction. This work may offer a promising strategy to realize the practical application of Co3O4-CoFe2O4 p-p heterojunction in ammonia detection.