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.
Highlights
Methylmercury (MeHg+) is one of the mercury chemical forms of highest toxicity for humans among mercury compounds [1]
The template ion MeHg+ in the Imprinted Polymer (IIP) was removed with a mixture of tiourea 2.5% w/v and HCl 1 mol L−1 solution until mercury could no longer be detected in the solution by thermal decomposition amalgamation atomic absorption spectrometry (TDA–AAS), following a previously proposed method [10]
The adsorption value increased with the increase in the concentration of MeHg+ in all materials, and it revealed that IIP–MBI–acrylic acid (AA) (161 μg g−1) has higher adsorption capacity than that of non-imprinted polymers NIP–MBI (135 μg g−1) and NIP–AA (68 μg g−1)
Summary
Methylmercury (MeHg+) is one of the mercury chemical forms of highest toxicity for humans among mercury compounds [1]. In the synthesis of IIPs, ligands containing electron-rich heteroatoms, such as nitrogen, phosphorus, sulfur and oxygen, are normally used to promote the formation of chelate with the targeted metal [23] This three-step synthesis normally involves: (1) formation of a pre-polymerization complex with interaction of the metal ion, ligand and functional monomer (FM); (2) polymerization of the complex monomer with the addition of a cross-linker and initiator; (3) removal of the template to produce the imprinted polymer [24]. The template ion MeHg+ in the IIPs was removed with a mixture of tiourea 2.5% w/v and HCl 1 mol L−1 solution until mercury could no longer be detected in the solution by thermal decomposition amalgamation atomic absorption spectrometry (TDA–AAS), following a previously proposed method [10]. The synthesized materials were IIP–MBI–AA and IIP–MBT–AA (CH3Hg+ imprinted polymers), NIP–MBI–AA and NIP–MBT–AA (non-imprinted polymers with ligand) and NIP–AA (non-imprinted polymers without ligand)
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