, Volume 55, Issue 12, pp 2554-2561
Date: 09 Nov 2012

Novel smart supramolecular metallo-hydrogel that could selectively recognize and effectively remove Pb2+ in aqueous solution

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Abstract

A series of novel and simple ligands based on a biscarboxyl-functionalized benzimidazole derivative were synthesized. The experiments showed that the ligand L2 as a low molecular weight (LMW) hydrogelator could form stable metallo-hydrogels in the presence of up to 0.3 equiv. of lead ions. The metallo-hydrogels were characterized using powder X-ray diffraction, scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopic techniques. When the molar ratio of L2:Pb2+ was in the range of 1:0.3 to 1:0.5 a translucent gel was produced. When the L2:Pb2+ molar ratio was higher than 1:0.5 the resulting gel tended to be opaque. The morphologies of these metallo-hydrogels were L2/Pb ratio dependent, ranging from worm-like to rod-shaped and nanofibrous. The FT-IR and X-ray diffraction (XRD) studies revealed that L2-Pb complexation was the main driving force for the formation of the metallo-hydrogels. In addition, these metallo-hydrogels exhibited outstanding thermostability and thermoreversibility, and displayed a reversible sol-gel transition induced by changes in pH and EDTA concentration. Importantly, ligand L2 showed an excellent capacity for the removal of Pb2+ in aqueous solution through the formation of metallo-hydrogels. At a L2:Pb molar ratio of 1:0.5 and below, the concentration of residual Pb2+ was as low as 7.6 × 10−5 mol/L in aqueous solution, and the removal ratio was as high as 95.4%. These results demonstrate that multi-channel responsive smart metallo-hydrogels have the potential to be widely applied in materials science, and might provide the basis for lead pollution capture and removal.