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

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.