Enhanced ammonia detection using wrinkled porous CoFe2O4 double-shelled spheres prepared by a thermally driven contraction process

Hierarchical CoFe2O4 double-shelled hollow spheres (DHSs) with wrinkled porous surfaces are successfully synthesized via a self-templating strategy followed by a simple post-annealing process. The crystallinity, morphology, and microstructure of CoFe2O4 DHSs are detailedly characterized. The as-prepared CoFe2O4 DHSs are composed of homogeneous primary nanoparticles with uniform size and morphology that are hierarchically assembled into well-defined double-shelled spheres with high porosity. The formation mechanism of double-shelled hollow structure is also discussed. Because of their large specific surface area and easily penetrable hierarchical shells, the as-synthesized CoFe2O4 DHSs exhibit high sensitivity to ammonia and fast response-recovery capability at the optimal working temperature.