Uncovering the effects of core and shell exchanges in CuO/Co3O4 composite on formaldehyde degradation via peroxymonosulfate activation

Herein, for the first time, MOF-on-MOF-derived CuO/Co 3 O 4 composites with core-shell structure is prepared. The internal electric field formed at the heterojunction interface can accelerate charge transfer and offer more active sites, so enhancing the performance of CuO/Co 3 O 4 composites in formaldehyde degradation via peroxymonosulfate (PMS) activation. It is surprised to find that the adjustment of core and shell position in CuO/Co 3 O 4 composites has an important impact on the mechanism of PMS activation. Under the mediation of internal electric field, free electron will gather around Co 3 O 4 component of CuO/Co 3 O 4 composites. When Co 3 O 4 is served as the shell of CuO/Co 3 O 4 composite (marked as CuO/Co 3 O 4 –1), CuO/Co 3 O 4 composite will become electron donor and provide electron to activate PMS for producing SO 4 •– and OH • , which can oxidize formaldehyde into CO 2 and H 2 O. Interestingly, CuO/Co 3 O 4 composite will become electron acceptor when CuO is employed as the shell (denoted as CuO/Co 3 O 4 –2), so PMS can be easily oxidized into SO 5 •– and then decomposed into 1 O 2 . Due to the feature of 1 O 2 being moderate oxidation ability, formaldehyde can be selectively converted by 1 O 2 into formic acid with high economic value. Additionally, theoretical calculation based on density functional theory further proves these results. This work clarifies the effects of core and shell exchanges in CuO/Co 3 O 4 composite on catalytic activity, sharing some new insights for selective degradation of formaldehyde.