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The increasing use of Gd-based contrast agents for magnetic resonance imaging at hospitals and research centers has led to the rapidly growing demand for Gd and Gd anomalies in surface waters. Recycling Gd from hospital effluents could simultaneously address Gd demand and severe concerns about Gd contamination. Here, we present a study relevant to the extraction and preconcentration of Gd from hospital effluents that contain parts per billion-level Gd via the ligand-assisted electrochemical aerosol formation (LEAF) process. We demonstrate that the LEAF process extracts ∼75% GdIII from 50 ppb Gd-spiked water samples, including diluted artificial urine samples while preconcentrating Gd by up to 390-fold. Mechanistic studies confirm that the surface activity of the Gd-binding ligand is essential for successful LEAF extraction. The ligands are recyclable by performing electrophoretic separation in an origami paper device, followed by water extraction. The steep pH gradient and strong electric field in the origami paper device enabled the dissociation of Gd-ligand complexes, spatial separation of Gd and ligand, and precipitation of GdIII as Gd(OH)3. Approximately 80% of the ligands were recovered from the paper device by water extraction and reused in subsequent extraction cycles. This straightforward and green method could also be adapted to other aqueous rare earth metal wastes in the future. 

Abstract Atmospheric NO₂is of great concern due to its adverse effects on human health and the environment, motivating research on NO₂detection and remediation. Existing low-cost room-temperature NO₂sensors often suffer from low sensitivity at the ppb level or long recovery times, reflecting the trade-off between sensor response and recovery time. Here, we report an atomically dispersed metal ion strategy to address it. We discover that bimetallic PbCdSe quantum dot (QD) gels containing atomically dispersed Pb ionic sites achieve the optimal combination of strong sensor response and fast recovery, leading to a high-performance room-temperature p-type semiconductor NO₂sensor as characterized by a combination of ultra–low limit of detection, high sensitivity and stability, fast response and recovery. With the help of theoretical calculations, we reveal the high performance of the PbCdSe QD gel arises from the unique tuning effects of Pb ionic sites on NO₂binding at their neighboring Cd sites.