Enhancing the Oxidase‐like Performances of CoxMn3‐xO4 Nanoparticles by Tuning the Mn Content and Decorating Reduced Graphene Oxide

Abstract Binary transition‐metal oxides nanomaterials as oxidase‐mimic have attracted great attention, but their catalytic activity and stability remain to be improved, and the underneath mechanism needs to be debated. In this work, Co x Mn 3‐x O 4 nanoparticles were prepared in‐situ on reduced graphene oxide sheets through a hydrothermal procedure. The morphologies, compositions, and oxidase‐like activities of the Co x Mn 3‐x O 4 nanoparticles supported on reduced graphene oxide (Co x Mn 3‐x O 4 NPs/rGO) were studied systematically. It is demonstrated that the oxidase‐like catalytic activities can be regulated by tuning not only the ratio of Co to Mn but also the content of rGO. It is illustrated that the CoMn 2 O 4 NPs/rGO4 with the rGO content of 80 % exhibits over all better oxidase‐like catalytic performance. We constructed the oxidase‐like catalysis mechanism of Co x Mn 3‐x O 4 NPs/rGO composites. It is found that the oxidase‐like activity of the composites mainly depends on Co−Mn synergy effect, including the cooperation of Co 2+ /Co 3+ , Mn 2+ /Mn 3+ and Mn 3+ /Mn 4+ redox pairs. More importantly, Mn 3+ was indispensable for the activation of Co 2+ /Co 3+ couples. Based on the decent oxidase‐like activity of the CoMn 2 O 4 NPs/rGO composite, a proof‐of concept colorimetric sensing system for L‐cysteine detection was developed, which show low detection limit of 0.08 μM (S/N=3), as well as excellent selectivity and anti‐interference ability.