By adjusting the stretch state of a triethylenetetramine (TETA) chain in an amine-functionalized porous organic polymer (POP), two adsorbents were designed to study the rational microenvironment for heavy metal ion removal. The quantum calculation elucidated that the hooped amino chains in FC-POP-CH2TETA-H exhibited stronger interactions with Pb(II) than the extended one in FC-POP-CH2TETA-E, not only through metal-ligand chelation but also metal coordination. The high binding energy of -2624 kJ mol-1 as well as the constructed microenvironment by the hooped amino chains ensured an extremely high Pb(II) capacity of 1134 mg g-1 on FC-POP-CH2TETA-H. Meanwhile, no more than 5 min to approach adsorption equilibrium revealed its ultrafast adsorption rate. It also showed excellent broad removal capability for multiple metal ions and nonsensitivity to pH. Therefore, by controlling the microenvironmental structures with suitable porosity, functional group stretching states, and coordination modes, the removal efficiency of heavy metal ions would be significantly enhanced, which further provided a promising strategy for designing a rational microenvironment to improve the task-specific separation properties.
Keywords: amino-chain stretching state; coordination mode; heavy metal ion removal; porous organic polymer; rational microenvironment.