Efficient mercury(II) capture by functionalized poly(pyrrole methane)s: The role of chloro and imino groups

Efficient mercury ion removal from water is a primary challenge for ecosystem protection and public health. This study improves the effect of functional groups on mercury removal by functionalizing and tuning the molecular structure of poly(pyrrole ethene) (PPyE) with chloro, i.e. poly[pyrrole-2,5-bis(2-chloroethane)] (PPyCE), and imino groups, i.e. poly[pyrrole-2,5-bis(2-ethylamino ethane)] (PPyEE). The resultant functionalized poly(pyrrole methane)s can efficiently remove mercury (Hg(II)) from water with uptake capacities of 684.59 mg/g (chloro functionalized) and 389.57 mg/g (imino functionalized) at room temperature, which was much higher than that of unfunctionalized poly(pyrrole ethane) (only 122.74 mg/g). The functionalized poly(pyrrole methane)s had additional benefits of low usage, excellent selectivity for mercury ions and anti-coexisting ion interference performance. Furthermore, the chloro functionalized poly(pyrrole methane)s also exhibited exceptional recyclability for the adsorption capacity remaining above 80% of the original after 5 regeneration cycles. These results were largely attributed to the functional groups of chloro and imino in the material backbone as chelating sites to bind with mercury, which was confirmed by Fourier Transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) before and after mercury capture. This study provides a potential strategy for designing and tuning the adsorbents to efficiently remove mercury and other heavy metal ions from aqueous solutions for environmental remediation.