Thioether-functionalized porphyrin-based polymers for Hg2+ efficient removal in aqueous solution

In this paper, thioether-functionalized porphyrin-based polymers (TPPs) were constructed according to two different "bottom-up" and "top-down" strategies and they were applied for Hg2+ capture in aqueous solution. TPP1, which was constructed by one-step polycondensation of 2,5-bis(methylthio) terephthalaldehyde (BMTA) with pyrrole according to the "bottom-up" strategy, owned high Brunauer-Emmett-Teller (BET) surface area (SBET, 554 m2/g), pore volume (Vtotal, 0.32 cm3/g), and S content (16.8%), resulting in high Hg2+ capture (913 mg/g) with high removal efficiency (> 99%). The adsorption mechanism clarified that the strong coordination between the S species and Hg2+ was the main driving force. In comparison, TPP2 and TPP3 were fabricated by the thioether functionalization of the porphyrin-based polymers according to the "top-down" strategy. They showed much lower SBET, Vtotal, and S content for the reason that the post-functionalization process greatly blocked the pores and the functional sites were hardly fully post-functionalized, resulting in much lower Hg2+ capture (555 mg/g and 609 mg/g, respectively). This work reveals the advantage of the "bottom-up" strategy for the construction of the thioether-functionalized polymers and it offers the guidance for the construction of some other thioether-functionalized polymers.