Facilely prepared Fe3O4/nitrogen-doped graphene quantum dot hybrids as a robust nonenzymatic catalyst for visual discrimination of phenylenediamine isomers

Abstract

In this work, we report a reducing agent-free strategy for the synthesis of Fe₃O₄ nanoparticle/nitrogen-doped graphene quantum dot (Fe₃O₄/N-GQD) hybrids, and constructed a sensing platform based on Fe₃O₄/N-GQDs for the visual discrimination of phenylenediamine isomers. Fe₃O₄/N-GQDs were facilely prepared by hydrothermal treatment of Fe³⁺/N-GQD solutions under alkaline conditions without other reagents. The prepared Fe₃O₄/N-GQDs exhibited outstanding peroxidase-like activity and were stable under a wide range of pH values and temperatures. The phenylenediamine isomers (o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine) were discriminated through the H₂O₂-mediated oxidation reaction using Fe₃O₄/N-GQDs as novel peroxidase mimics, which resulted in appreciable color changes. The proposed method is simple, economical, and effective for discrimination of isomers, and can be used for sensitive and selective quantitative analysis of o-phenylenediamine and p-phenylenediamine. A good linear relationship from 1 to 90 μM and a detection limit of 230 nM for o-phenylenediamine were achieved, and the linear relationship for p-phenylenediamine was from 2 to 70 μM with a detection limit of 530 nM. The proposed method may open new applications of Fe₃O₄/N-GQDs in biomedicine and environmental chemistry.