All-in-one Janus-type SERS membrane enables simultaneous ultrasensitive detecting and efficient removing heavy metal ions in complex aquatic environments

Heavy metal ion pollution in aquatic environments poses a serious threat to public health, yet current methods struggle to achieve both highly sensitive detection and efficient removal. Herein, we propose a new Janus-type filter membrane featuring an Ag nanoparticles/ZnAl-layered double hydroxide/polyvinylidene fluoride/nickel foam (Ag/ZnAl-LDH/PVDF/NF) composite architecture as a versatile platform integrating filtration, enrichment, surface-enhanced Raman scattering (SERS) detection, and removal of heavy metal ions. The unique top-down gradient pore structure enables pretreatment-free filtration, effectively eliminating matrix interferences. The synergistic coupling in the Ag/ZnAl-LDH functional layer enhances SERS performance via molecular resonance, charge transfer resonance, and electromagnetic resonance, with theoretical simulations further corroborating this synergistic mechanism. Leveraging the enhanced SERS effect with 4-mercaptophenylboronic acid (4-MPBA) as the recognition probe, this platform enables ultrasensitive discrimination and detection of methylmercury (CH₃Hg⁺) with a detection limit as low as 10⁻¹¹ м. Moreover, the designed hierarchical micro/nano structure and tunable wettability of the Ag/ZnAl-LDH/PVDF/NF membrane enable the rapid extraction of CH₃Hg⁺ from real water samples, achieving fast detection (<5 min) and near-complete removal. Our study shows a novel, practical and versatile platform for on-site water quality monitoring and purification.