Metal–organic framework-derived Co3O4/CoFe2O4 double-shelled nanocubes for selective detection of sub-ppm-level formaldehyde

•Co3O4/CoFe2O4 double-shell nanocube was synthesized by a MOF-templated route.•The variety of techniques were used to explore the structure and morphology.•The response of Co3O4/CoFe2O4 can reach 12.9–10 ppm formaldehyde at 139 °C.•The formaldehyde detection limit of CCFO1 DSNCs sensor is as low as 300 ppb.