Core–Shell Ag@UiO-66-NH2 with Enhanced Stability and Selective Enrichment for Sensitive SERS Detection of Cr(VI) in Environmental Water

A sensitive and stable substrate is crucial in Raman spectroscopic techniques for the effective detection of environmental contaminants. In this study, a novel core–shell composite, Ag@UiO-66, was developed by coating Ag nanospheres with a porous metal–organic framework (MOF), UiO-66-NH2. This composite combines high stability with selective enrichment capabilities for Cr(VI). Leveraging the unique properties of UiO-66-NH2, such as its porosity, abundant amine groups, and Zr nodes, Ag@UiO-66 effectively enriches Cr(VI) through pore-filling, electrostatic interactions, and Zr–O coordination. Direct analysis of water samples spiked with Cr(VI) showed detection limits of 6.53 × 10–8 M in pond water and 7.52 × 10–8 M in lake water. The composite also exhibited excellent signal uniformity and reproducibility, with a low relative standard deviation of 6.78% across 30 batches. Additionally, it demonstrated outstanding recyclability under simulated sunlight irradiation due to the solar photocatalytic properties of UiO-66-NH2. Ag@UiO-66 also showed superior stability compared to pristine Ag nanospheres when exposed to strong acids, bases, or oxidative environments (e.g., 1% H2O2 solution). Overall, Ag@UiO-66 shows great potential as a reliable substrate for the trace detection of chemical analytes via SERS.