Substituent Effect-Driven Porphyrin Catalytic Reaction Enabling Dehalogenation and a Visual Assay of Organochlorines

Abstract

The pronounced lipophilicity and inherent stability of the C–Cl bond in organochlorine pesticides (OCPs) pose significant challenges to their simultaneous degradation and visual detection. Herein, we have developed a visual colorimetric platform for OCP degradation and detection using nano ZnTPyP. Theoretical calculations and experimental results reveal that the nature of the substituent plays a critical role in modulating the catalytic activity of Zn-based porphyrins, with the strongly electron-withdrawing pyridyl group notably enhancing their oxidase-like activity. Subsequently, pyridine-substituted zinc porphyrins effectively catalyze the generation of reactive oxygen species (ROS) from O2, thereby attacking the C–Cl bonds in OCPs and leading to their degradation. To prevent self-aggregation and improve analytical performance, we developed a solvent-effect-enabled exfoliation-convolution strategy to fabricate ZnTPyP hollow nanotubes: the stacked porphyrins exfoliate in aqueous solution and self-convolute under surface tension into hollow nanotubes. Upon nano ZnTPyP-mediated degradation of OCPs, the released H+ ions are captured by bromothymol green (BG), triggering a distinct green-to-yellow color change. Based on this principle, a rotatable colorimetric device enables rapid on-site semiquantitative analysis with a detection limit of 0.01 μg/mL. Linear discriminant analysis achieves 100% accurate differentiation among five structurally similar OCPs. Finally, the applicability of this device was validated in four different real samples, such as cabbage, lily, chrysanthemum, and lake water, with recoveries ranging from 90.20% to 109.40%. This work not only provides mechanistic insights into porphyrin-based nanozymes for pollutant degradation but also establishes an integrated platform for simultaneous OCP degradation and on-site visual detection.