Hydroquinone colorimetric sensing based on core–shell structured CoFe2O4@N-GQDs@CeO2 nanocomposites as oxidase mimics

Abstract

The core–shell structured CoFe₂O₄@N-GQDs@CeO₂ nanocomposites were successfully synthesized via hydrothermal and co-precipitation methods, where CeO₂ was uniformly dispersed on the outer shell layer with the assistance of nitrogen doped graphene quantum dots (N-GQDs). Due to its high oxygen absorption capacity and oxidase-like activity, the CoFe₂O₄@N-GQDs@CeO₂ could catalyze the oxidation of the colorless substrate 3,3′,5,5′-tetramethylbenzidine (TMB) into the blue product oxTMB in the absence of H₂O₂. Electron spin resonance (ESR) revealed that the superoxide radical (˙O₂⁻) and hydroxyl radical (˙OH) were the primary catalysts responsible for oxidase-like activity. At the same time, hydroquinone (HQ) reduced oxTMB, resulting in a transition from blue to colorless. Building on this reaction, a colorimetric method was established to detect HQ in the range of 0.25–60 μM, with a detection limit as low as 0.168 μM. This method was successfully applied to real water samples, and the recovery rate was between 98.57% and 103.78%. These primary results demonstrate that the CoFe₂O₄@N-GQDs@CeO₂ has excellent potential in the field of environmental chemistry.