Highly selective removal of Hg(II) ions from aqueous solution using thiol-modified porous polyaminal-networked polymer

An efficient porous organic polymer (POP)-based adsorbent (4AS-MBP), synthesized from melamine, 4-allyloxy benzaldehyde and ethanedithiol (EDT) via a Schiff-base reaction and thiol-ene addition in a straightforward strategy, was prepared to remove Hg(II) ions from water. The chemical structure and morphology of 4AS-MBP were investigated by FT-IR, solid-state C-13 NMR, EA, SEM, TEM and BET analysis. Adsorption experiments were conducted by varying the Hg(II) concentration, contact time and pH to study the adsorption kinetics and equilibrium. Mesoporous 4AS-MBP exhibited a maximum adsorption capacity of 312 mg g(-1). The results indicated that Hg(II) adsorbed onto the adsorbent through monolayer chemisorption. Interestingly, 4AS-MBP was highly stable, even in the presence of 2 M NaOH or HCl, and displayed similar adsorption capacities over a wide pH range. Furthermore, the adsorbents could be reused at least five times without a loss of adsorption capacity. More importantly, the relative selectivity coefficients of 4AS-MBP for Hg()/Pb(II), Hg(II)/Cd(II), Hg(II)/Cu(II), Hg(II)/Zn(II) and Hg(II)/Mg(II) were 54.3, 221, 243, 468 and 823, respectively.