Heavy metal ions removal by nano-sized spherical polymer brushes

Nano-sized spherical polymer brushes (SPBs) consisting of both a polystyrene (PS) core and a brush shell of poly(acrylic acid) (PAA), poly(N-acrylcysteamine) (PSH), or poly(N-acrylcysteamine-co-acrylic acid) (P(SH-co-AA)), were prepared by photo-emulsion polymerization. The core-shell structure was observed by dynamic light scattering and transmission electron microscopy. Due to the strengthened Donnan effect, the PAA brush can adsorb heavy metal ions. Effects of the contact time, thickness of PAA brush and pH value on the adsorption results were investigated. Due to the coordination between the mercapto groups and heavy metal ions as well as the electrostatic interactions, SPBs with mercapto groups are capable to remove heavy metal ions selectively from aqueous solutions. The order of adsorption capacity of the heavy metal ions by SPBs with mercapto groups is: Hg²⁺ ≈ Au³⁺ > Pb²⁺ > Cu²⁺ > Ni²⁺. The adsorbed heavy metal ions can be eluted from SPB by aqueous HCl solution, and the SPBs can be recovered. After three regenerations the recovered SPBs still maintain their adsorption capacity.