Novel magnetic coordination polymer gel facilitates high efficiency dual-mode trace Cd(II) detection and cleanup from real samples

Abstract

Cadmium (Cd(II)) is highly toxic to humans and the environment. Therefore, efficient monitoring and control of Cd(II) is required for environmental protection and human security. Over the years, impressive advances have been made, however, majority of the research focuses on either detection or removal. Herein, a novel magnetic coordination polymer gel, CoFe₂O₄@Zrtdpa, is explored for the twin objectives of dual mode trace Cd(II) determination and removal from real samples. Box-Behnken design combined genetic algorithm and Taguchi L₃₂ (4⁶ 2¹) design optimized the removal and extraction process variables, respectively. The experimental adsorption capacity at saturation was 179.07 mg g⁻¹ at 298 K. The uptake of Cd(II) was multimolecular (n > 1), endothermic and spontaneous. XPS revealed that two active sites were oxygen and sulphur. The adsorption energies ($E_1$ = 41.79–46.00 kJ mol⁻¹, $E_2$ = 29.85–32.19 kJ mol⁻¹) indicated that complexation at the first and electrostatic interaction through ion exchange at the second active site are at play. Density functional theory (DFT) calculations verified the same asserting that the uptake was more favorable onto the first active site (sulphur). The best fit fractal like pseudo second order model and site energy distribution analysis established energetic heterogeneity. The limits of detection (LODs) and limits of quantifications (LOQs) for the enrichment-spectrophotometric and ICP-AES methods were 1.36 μg L⁻¹, 4.11 μg L⁻¹, and 0.019 μg L⁻¹, 0.062 μg L⁻¹ respectively. The developed adsorption, enrichment-spectrophotometric and ICP-AES methods were successfully employed for the removal and trace Cd(II) determination in real samples with good reusability.