Synthesis of hollow Co-N/C nanocage with superior oxidase-like activity for colorimetric sensing analysis and catalytic mechanism

It is of great significance to exploit simple and efficient methods for detecting hazardous substances in the fields related to food safety and environmental protection. Herein, for the first time, a newly-designed hollow Co-N/C nanocage with oxidase-like activity was synthesized via a feasible method. Benefiting from the construction of hollow structure and the introduction of carbon layer, the specific surface area of enzyme mimic was improved, so exposing more active sites. Importantly, hollow Co-N/C nanocage displayed an excellent performance in interfacial charge transfer, which provided convenience for the occurrence of chromatic reaction between enzyme mimic and TMB. As predicted, hollow Co-N/C nanocage can effectively oxidize colorless TMB to blue oxTMB in the absence of H2O2, and the analyses about catalytic mechanism suggested that both the redox couples of Co3+/Co2+ and O2•− were involved in the oxidation of TMB. Furthermore, a chromogenic sensing method for the detection of Na2SO3 and Cr6+ was exploited, and a broad linear range and a low LOD can be achieved. More interestingly, developed detection method still possessed good recovery even in real samples. In a word, current work will share novel insights into the design of enzyme mimics and the analyses on chromogenic mechanism.