Silver Nanoparticle‐Grafted Amidoxime Covalent Organic Framework: A Highly Sensitive and Selective SERS Substrate for Uranium Detection in Natural Water Systems

Abstract Uranium is a critical nuclear material and a significant environmental contaminant due to its high toxicity, making its detection important. Surface‐enhanced Raman Scattering (SERS) has been used for the rapid and sensitive analysis of uranyl, but achieving both high sensitivity and selectivity in natural water systems remains a challenge. Herein, a novel Ag@COF‐TpDb‐AO substrate by depositing silver nanoparticles (AgNPs) onto amidoxime groups functionalized ketoenamine‐based covalent organic framework (COF‐TpDb‐AO) for uranyl detection is fabricated. This method achieves a low detection limit of 3.72 µg L⁻¹, significantly below the World Health Organization (WHO) maximum contamination standard of 30 µg L⁻¹ in drinking water. It also demonstrates a high enhancement factor of 1.26 × 10⁶, excellent interference resistance, reproducibility, and stability. Importantly, this method can detect uranyl in practical samples, including tap, river, and lake water, with recoveries ranging from 93.1% to 104.8%. The detection capability arises from the adsorption of trace uranyl onto COF‐TpDb‐AO, followed by enhancement of Raman intensity through electromagnetic and chemical synergistic effects. The enhancement mechanism is demonstrated by Finite‐Difference Time‐Domain (FDTD) and Density Functional Theory (DFT) calculations. This study presents a novel SERS substrate for trace uranyl detection in natural water systems, paving the way for improved environmental monitoring.