Preparation of Fe1-xS@CNT Composite Nanozyme and Its Application in Colorimetric Detection of Hg2+
The escalating environmental contamination by mercury ions (Hg2+) poses severe risks to ecosystems and human health, necessitating the development of rapid, sensitive, and cost-effective detection methods. In this study, Fe1-xS@CNT composite nanozymes were synthesized via a straightforward solvothermal approach. The nanozymes exhibit uniform morphology, structural stability, and significant peroxidase (POD)-like activity. The incorporation of carbon nanotubes (CNT) facilitates electron transfer, enhancing the Fenton reaction between Fe2+/Fe3+ to generate abundant reactive oxygen species (ROS), primarily hydroxyl radicals (·OH) and superoxide anions (·O2−). The synergistic action of these ROS and photogenerated holes (h+) promotes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue-colored product (oxTMB), establishing a colorimetric system of Fe1-xS@CNT + H2O2 + TMB. The specific binding of S2− on the nanozyme surface to Hg2+ inhibits POD activity, reducing the absorbance of the system. This principle was harnessed to develop a colorimetric method for Hg2+ quantification in environmental water samples. The method demonstrates a linear range of 0.1–500 μg·L−1 and a limit of detection (LOD) of 0.04 μg·L−1. Validation in real water samples (campus and tap water) showed recoveries between 94.4% and 111.1% with relative standard deviations (RSD) below 3.0%, comparable to atomic fluorescence spectrometry. The method offers advantages of simplicity, rapid analysis, and naked-eye visibility, providing a novel approach for on-site monitoring of heavy metal pollutants.