Study on the synthesis of poly(pyrrole methane)s with the hydroxyl in different substituent position and their selective adsorption for Pb²⁺

Two poly(pyrrole methane)s (PPD2HBA and PPD3HBA) were successfully synthesized, with focusing on the effect of steric hindrance on the selective adsorption of heavy metal ions. The structure and morphology of PPD2HBA and PPD3HBA were characterized by FT-IR, UV–Vis, ¹H NMR, BET, SEM, XPS and Zeta potential. The influencing factors of the Pb²⁺-adsorption onto the two adsorbents were systematically studied, including various solution conditions and co-existing metal ions effect. These results demonstrated that the two adsorbents showed slightly different adsorption behaviors. The maximum adsorption capacities of Pb²⁺ onto PPD2HBA and PPD3HBA were 41.35 and 32.10 mg·g⁻¹ at pH = 6.0 and 318 K, respectively. The crucial steric hindrance verified by FT-IR and XPS before and after Pb²⁺ adsorption, showed better consistence in PPD2HBA with the size and shape of the hydrated Pb²⁺ than that in PPD3HBA, which can be further supported by the adsorption property of PPD4HBA. In addition, the effect of the co-existing metal ions of Pb²⁺ onto PPD2HBA and PPD3HBA could be testified by the HSBA theory. The proposed adsorption mechanism in this paper was of remarkable potential for the design of new adsorbent to selectively adsorb heavy metal ions from wastewater.