Synthesis of multi-ion imprinted polymers based on dithizone chelation for simultaneous removal of Hg2+, Cd2+, Ni2+ and Cu2+ from aqueous solutions

Abstract

Simultaneous analysis and removal of various heavy metal ions has received increasing concerns because they are usually co-existent with different toxicological effects. Ion imprinted polymers (IIPs) can effectively identify water-soluble ions especially heavy metal ions, however, multi-ion imprinting is rarely performed owing to possible cross-reactivity and matrix interferences. In this work, a novel and generally applicable IIPs strategy was proposed for simultaneous preconcentration and removal of four heavy metal ions based on dithizone chelation. Multi-ion imprinted polymers (MIIPs) embedded in a sol–gel matrix were prepared by using Hg²⁺, Cd²⁺, Ni²⁺ and Cu²⁺ as templates and 3-aminopropyltriethoxysilane as a functional monomer, and the possible synergy mechanism was explored between dithizone coordination chemistry and multi-ion imprinting. The structures, morphologies and thermostability of MIIPs were well characterized by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and thermogravimetry analysis (TGA). The resultant MIIPs showed high binding capacity and fast dynamics, and the adsorption processes obeyed Langmuir isotherm and pseudo-second-order dynamic models. The MIIPs displayed excellent selectivity toward the four target ions particularly over Pb²⁺, Zn²⁺ and Co²⁺ with selective coefficients of 6.8–16.9, as well as high anti-interference ability when confronted with common co-present various ions. Moreover, a high preparation yield of 41% and good reusability over 90% desorption efficiency were obtained. Consequently, the MIIPs were used as solid-phase extraction sorbents for preconcentration of trace Hg²⁺, Cd²⁺, Ni²⁺ and Cu²⁺, presenting high detectability up to 6.0–22.5 ng L⁻¹ and satisfactory recoveries ranging from 94.7–110.2% in seawater samples. The developed MIIPs-based method proved to be a practically feasible method in heavy metal removal and water pretreatment.