Magnetic Covalent Organic Framework for Efficient Solid-Phase Extraction of Uranium for on-Site Determination by Portable X-ray Fluorescence Spectrometry

Uranium plays a pivotal role in the nuclear industry; however, its inadvertent release has raised concerns regarding health and environmental implications. It is crucial for a prompt warning and accurate tracing of uranium contamination in emergency scenarios. In this study, a novel and simple method was proposed that combines magnetic dispersive solid-phase extraction (MDSPE) with portable X-ray fluorescence spectrometry (XRF) for the on-site sampling and determination of trace uranium in real samples. A magnetic covalent organic framework (Fe₃O₄@COF) composite with excellent chemical stability and a large adsorption capacity of 311 mg/g was synthesized and employed as an efficient adsorbent for the solid-phase extraction of trace uranium. Without the need for a centrifuge or filter requirement, the established method by benchtop wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) exhibits an exceptionally low limit of detection (LOD) of 0.008 μg/L with a sample volume of 50 mL and a fast adsorption time of 15 min, rendering it suitable for environmental monitoring of UO₂²⁺. Consequently, this approach, in combination with a hand-held portable XRF instrument with an LOD of 0.1 μg/L, was successfully implemented for the on-site extraction and quality assessment of real water samples, yielding accurate results and satisfactory spike recoveries.