Surface Ion-imprinted Magnetic Halloysite Nano Clay Composite with Double Specific Binding Sites for Selective Extraction and Preconcentration of Cadmium and Lead in Water

A dual-template magnetic ion-imprinted polymer based on halloysite (Fe₃O₄@HNT-DIIP) was synthesised via surface imprinting and co-precipitation. This material was utilised in magnetic solid-phase extraction (MSPE) to selectively and simultaneously concentrate cadmium (Cd 2+ ) and lead (Pb 2+ ) from both aqueous samples and environmental water sources. The morphological structure, crystallinity, and surface characteristics were analysed using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and a zetasizer. The maximum adsorption capacities of Fe 3 O 4 @HNT-DIIP for Cd 2+ and Pb 2+ ions were 44.4 and 58.5 mg/g. The adsorption kinetics exhibited a strong correlation with the pseudo-second-order model, and the Langmuir isotherm suggested that the Fe 3 O 4 @HNT-DIIP adsorbent facilitates monolayer sorption on uniform sites. The Fe 3 O 4 @HNT-DIIP adsorbent proved selective towards Cd 2+ and Pb 2+ ions in the presence of Co 2+ and Zn 2+ . Under optimum conditions, the Fe 3 O 4 @HNT-DIIP-MSPE coupled with inductively coupled plasma optical emission spectrometry (ICP-OES) exhibited wide linear ranges (0.712-100), acceptable limits of quantification (LOQs = 0.712–1.45 µg/L) and limit of detection (LODs = 0.214–0.440 µg/L) for Cd 2+ and Pb 2+ ions. The proposed method demonstrated excellent performance in preconcentrating and detecting trace metals in surface and groundwater samples, yielding recoveries of 95.5–102%.