Spatial Confinement of Mn3o4 in Hollow Carbon Sphere to Boost the Oxidase-Like Activity for Colorimetric Sensing Analysis of Hydroquinone and Hexavalent Chromium

Abstract

It is very meaningful to develop simple and effective methods for detecting hazardous substances. Herein, a newly-designed HCS/Mn3O4 composite with oxygen vacancy is synthesized and employed as oxidase-like mimic for conducting chromogenic analysis. After loading Mn3O4 in HCS, the hydrophobicity of Mn3O4 is remarkably enhanced, thereby creating a microscopic three-phase interface to boost the capturing ability towards O2. Interestingly, hollow structure of HCS can provide the spatial confinement effect for Mn3O4, shortening mass transfer process and improving catalytic activity. Thus, HCS/Mn3O4 composite possesses low interfacial resistance and rapid charge transfer rate. More importantly, HCS/Mn3O4 composite can simulate the activity of oxidase-like mimics, which can oxidize colorless TMB to blue oxTMB in a short time. Further analysis indicates that O2•‒ plays an important role, and the direct oxidation of TMB over HCS/Mn3O4 composite also plays a part in the color reaction of TMB. Based on the cascade reactions among TMB, HCS/Mn3O4 and target compound (namely hydroquinone and Cr6+), a simple chromogenic sensing method with broad linear range and low LOD for detecting hydroquinone and Cr6+ is proposed. In short, current study can give a valuable reference for the design of enzyme mimics and the research on chromogenic mechanism.

Keywords: Enzyme mimic, Spatial confinement, Oxidase-like activity, Colorimetric assay, Chromogenic mechanism