Ultralow loaded waste polystyrene derived hyper-cross-linked polymer for incineration flue gas demercuration: Synergistic effect of transition metal and halogen species

•Hyper-cross-linked polymer based Hg0 adsorbent was synthesized from waste plastic under mild conditions.•Ultralow loading active species can be achieved over HCPs surface for efficient Hg0 capture.•The interaction between active species and HCP substrate can be described as physical-bridging, chemical-complexation and organic-bonding.•The activity of Fe site can be regulated by surrounding halogen sites.