A highly sensitive SERS sensor based on magnetic-enrichment Ag@Fe3O4/UiO-66-NH2 for detection and solar photo-reduction of hexavalent chromium in water environment

In this study, a novel magnetic composite, Ag@Fe 3 O 4 /UiO-66-NH 2 (Ag@FUN), was developed by incorporating a porous metal-organic framework (MOF), UiO-66-NH 2 , which offers selective enrichment capabilities and facilitates solar-driven photoreduction of Cr(VI). The surface coverage of silver nanoparticles on Ag@FUN was precisely controlled by adjusting the AgNO 3 feed concentration, enabling tunable SERS sensitivity. SERS measurements revealed that the Ag@FUN composites exhibited strong signal intensity for Cr(VI), along with excellent signal reproducibility and storage stability. These composites were capable of detecting Cr(VI) at concentrations of as low as 7.81 × 10 -8 M in tap water and 8.89 × 10 -8 M in pond water. The remarkable SERS performance is attributed to the porous MOF structure, which enriches Cr(VI) via Zr–O coordination, electrostatic interactions, and pore-filling effects. Importantly, under simulated sunlight, Ag@FUN effectively reduced Cr(VI) within 70 minutes. The composites also demonstrated outstanding recyclability, retaining their SERS sensitivity and photocatalytic efficiency through five consecutive "detection–reduction" cycles. Overall, the Ag@FUN composites developed in this work exhibit high SERS sensitivity and robust photocatalytic activity, offering significant potential for environmental monitoring and ecological remediation.