Mechanism of TMB Discoloration Catalyzed by Layered CoNi@CN Nanozymes: Application Based on Smart Phone for Resorcinol Detection

Abstract

Real-time on-site monitoring of resorcinol (RS) concentrations is crucial for detecting hazardous levels, enabling prompt response measures to mitigate potential environmental and health risks. In this study, we developed an innovative method using CoNi@CN-2 nanozymes to activate peroxymonosulfate (PMS) for oxidizing 3, 3′, 5, 5′-tetramethylbenzidine (TMB). Our results show that the formation of Ni ²⁺ through the oxidation of Ni ⁰ on the CoNi@CN-2 surface significantly enhances the electron-donating capacity of Co ⁰. The catalytic reaction of TMB is mediated by redox active species (SO ₄ ^•-, •O ₂ ^-, •OH and  ¹O ₂). RS drives colorimetry by transferring electrons to the benzene ring and specific nitrogen atoms in ox-TMB, reducing ox-TMB to TMB. Furthermore, the colorimetric assay shows a robust linear correlation between RS concentration and absorbance (Abs), described by Abs = -0.44[RS] + 0.886 (0—200 µmol/L, R ² = 0.983). Also, we introduce a novel smartphone-integrated autonomous detection software that can analyze RS concentration and grayscale values (GSV), yielding GSV = 0.327[RS] + 63.601 (0—200 µmol/L,   R ² = 0.990) with a detection limit of 5.29 µmol/L. Additionally, excess PMS leads to ROS attacking specific sites in ox-TMB, forming secondary oxidation products. This study has enabled rapid and accurate detection of RS, making a significant contribution to environmental safety and protection.

Keywords

Resorcinol / Colorimetric reaction / Nanozymes / TMB / Smartphone

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