Magnetically Recoverable Fe3O4/Cu2O-Ag Plasmonic Nanocomposites for Integrated Photocatalytic Degradation and Ultrasensitive SERS Detection of Tetracycline

The persistent accumulation of tetracycline (TC) antibiotics in aquatic environments poses severe ecological and public health risks, necessitating the development of multifunctional platforms capable of simultaneous detection and degradation. Herein, we report magnetically recoverable plasmonic Fe3O4/Cu2O-Ag nanocomposites (NCs) that integrate visible-light-driven photocatalysis with ultrasensitive surface-enhanced Raman scattering (SERS) detection. Hierarchical flower-like Fe3O4 nanocrystals were employed as magnetic supports, followed by in situ growth of Cu2O nanocrystals and controlled deposition of Ag nanocrystals. The optimized composite (FCA-2) exhibited enhanced visible-light absorption (Eg = 1.86 eV), suppressed electron–hole recombination, and improved photocurrent response, which were attributed to Schottky barrier formation at the Cu2O-Ag interface and localized surface plasmon resonance (LSPR) effects. Under simulated solar irradiation, FCA-2 NCs achieved 91.79% degradation of TC within 60 min, following pseudo-first-order kinetics (k = 20.37 × 10−3 min−1). Finite-difference time-domain (FDTD) simulations revealed that optimal Ag loading maximized plasmonic “hot spot” density, thereby enhancing electromagnetic field intensity and SERS performance. The FCA-2 substrate enabled ultrasensitive TC detection with a limit of detection of as low as 10−10 M. Moreover, the superparamagnetic Fe3O4 core allowed for rapid magnetic separation and sustained performance over multiple SERS–photocatalysis cycles, with negligible signal attenuation after 30 days. This work presents a rational strategy for constructing plasmonic magnetic NCs that synergistically couple photocatalytic remediation, ultrasensitive sensing, and magnetic recyclability, offering significant potential for integrated environmental monitoring and sustainable water treatment applications.