▎ 摘　　要

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, CoxMn3-xO4 nanoparticles were prepared in-situ on reduced graphene oxide sheets through a hydrothermal procedure. The morphologies, compositions, and oxidase-like activities of the CoxMn3-xO4 nanoparticles supported on reduced graphene oxide (CoxMn3-xO4 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 CoMn2O4 NPs/rGO4 with the rGO content of 80 % exhibits over all better oxidase-like catalytic performance. We constructed the oxidase-like catalysis mechanism of CoxMn3-xO4 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 Co2+/Co3+, Mn2+/Mn3+ and Mn3+/Mn4+ redox pairs. More importantly, Mn3+ was indispensable for the activation of Co2+/Co3+ couples. Based on the decent oxidase-like activity of the CoMn2O4 NPs/rGO composite, a proof-of concept colorimetric sensing system for L-cysteine detection was developed, which show low detection limit of 0.08 mu M (S/N=3), as well as excellent selectivity and anti-interference ability.