Rational Design of an Ion-Imprinted Polymer for Aqueous Methylmercury Sorption

Abstract

Methylmercury (MeHg⁺) is a mercury species that is very toxic for humans, and its monitoring and sorption from environmental samples of water are a public health concern. In this work, a combination of theory and experiment was used to rationally synthesize an ion-imprinted polymer (IIP) with the aim of the extraction of MeHg⁺ from samples of water. Interactions among MeHg⁺ and possible reaction components in the pre-polymerization stage were studied by computational simulation using density functional theory. Accordingly, 2-mercaptobenzimidazole (MBI) and 2-mercaptobenzothiazole (MBT), acrylic acid (AA) and ethanol were predicted as excellent sulfhydryl ligands, a functional monomer and porogenic solvent, respectively. Characterization studies by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) revealed the obtention of porous materials with specific surface areas of 11 m² g^-1 (IIP-MBI-AA) and 5.3 m² g^-1 (IIP-MBT-AA). Under optimized conditions, the maximum adsorption capacities were 157 µg g^-1 (for IIP-MBI-AA) and 457 µg g^-1 (for IIP-MBT-AA). The IIP-MBT-AA was selected for further experiments and application, and the selectivity coefficients were MeHg⁺/Hg²⁺ (0.86), MeHg⁺/Cd²⁺ (260), MeHg⁺/Pb²⁺ (288) and MeHg⁺/Zn²⁺ (1510), highlighting the material's high affinity for MeHg⁺. The IIP was successfully applied to the sorption of MeHg⁺ in river and tap water samples at environmentally relevant concentrations.

Keywords: bulk polymerization; computational modelling; environmental analysis; imprinting technology; ion recognition; ionic imprinting polymers; mercury detection and removal; sample preparation; separation science; water analysis.

Figure 1

Schematic illustration of the synthesis of ion-imprinted polymers (IIPs) (A); pre-polymerization complex with the 2-mercaptobenzimidazole (MBI) ligand (B).

Figure 2

Geometry optimization of methylmercury (MeHg⁺)–MBI (A) and MeHg⁺–2-mercaptobenzothiazole (MBT) (B) in ethanol (EtOH), and optimized geometries of the pre-polymerization step of MeHg⁺–MBI (C) and MeHg⁺–MBT (D) complexes with acrylic acid (AA) as the functional monomer (FM).

Figure 3

SEM images of (A) IIP–MBI–AA, (B) non-imprinted polymer (NIP)–MBI–AA, (C) IIP–MBT–AA, (D) NIP–MBT–AA, and (E) NIP–AA; the scale bar is 1 µm in all figures.

Figure 4

(A) Effect of pH on sorption of MeHg⁺ on IIP–MBI–AA, NIP–MBI–AA, IIP–MBT–AA, NIP–MBT–AA, and NIP–AA; 3 mg of polymeric material, [MeHg⁺] = 100 µg L⁻¹, volume = 2.0 mL, shaking time = 2 h, room temperature. (B) The effect of MeHg⁺ initial concentration on the adsorption of MeHg⁺ on IIP–MBI–AA, NIP–MBI–AA, IIP–MBT–AA NIP–MBT–AA, and NIP–AA; 3 mg of polymeric material, [MeHg⁺] = 25–800 µg L⁻¹, pH = 8, volume = 2.0 mL, shaking time = 2 h, room temperature. (C) Kinetics of MeHg⁺ adsorption on IIP–MBI–AA, NIP–MBI–AA, IIP–MBT–AA NIP–MBT–AA, and NIP–AA; 3 mg of polymeric material, [MeHg⁺] = 100 µg L⁻¹, pH = 8, shaking time = 5–300 min, volume = 2.0 mL, room temperature. (D) The selectivity profiles of the IIPs and NIPs for binary mixtures containing MeHg⁺ and potential interferents. In all experiments n = 3.