Cadmium ion-imprinted polymers for adsorption and detection of cadmium ions

Cadmium is a typical heavy metal ion. Long-term exposure to cadmium can lead to diseases like renal tubular dysfunction and bone degeneration. Therefore, it is necessary to develop efficient separation methods and detection techniques for cadmium ions. In this paper, adsorption enrichment was combined with detection to rapidly detect cadmium ions in water. Cadmium ion imprinted polymers (Cd(II)-IIPs) were prepared by bulk polymerization using Cd(II) as template ion, itaconic acid (IA) as functional monomer, ethylene dimethacrylate (EGDMA) as cross-linker, 4-(2-pyridylazo)-resorcinol (PAR) as chromogenic ligand, and azobisisobutyronitrile (AIBN) as initiator. The preparation conditions were optimized and the prepared Cd(II)-IIPs were characterized by Fourier transform infrared spectroscopy (FT-IR), solid-state 13C nuclear magnetic resonance (13C NMR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and X-ray photoelectron spectroscopy (XPS). In the adsorption experiment, the adsorption equilibrium was reached within 10 min in a solution of pH 7.0, and the saturation adsorption capacity of IIPs and NIPs were 50.542 mg·g−1 and 33.762 mg·g−1, respectively. The Cd(II)–IIPs exhibited selectivity for Cd(II) ions in the presence of Ni(II), Fe(II), Co(II), Cu(II), and Pb(II) ions; and after eight adsorption–desorption cycles, the adsorption capacity of Cd(II)-IIPs retained > 90%. In addition, the detection performance of the Cd(II)-IIPs was investigated by digital image colorimetric (DIC) and ultraviolet spectrophotometric methods; the detection limits were 1.46 and 1.74 μg·L−1, respectively, and the quantitative detection range was 8–100 μg·L−1. The Cd(II)-IIPs exhibited excellent adsorption properties and an obvious color gradient variation, which could be used for quantitative colorimetric detection over a range of concentrations.