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

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 Ni²⁺ through the oxidation of Ni⁰ on the CoNi@CN-2 surface significantly enhances the electron-donating capacity of Co⁰. The catalytic reaction of TMB is mediated by redox active species (SO₄^•−, •O₂⁻, •OH and ¹O₂). 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, R² = 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, R² = 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.