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

•The porous organic polymer, 4AS-MBP, was prepared via a simple Schiff-base reaction.•The absorbent, 4AS-MBP, has excellent tolerance to harsh acidic and basic conditions.•4AS-MBP displayed similar adsorption capacities over a wide pH range.•The relative selectivity coefficients of 4AS-MBP for Hg(II)/Metal(II) were in a range of 54.3–823.